Foxn1, short for Forkhead box N1, belongs to a large family of transcription factors that bind DNA and switch other genes on or off. The gene first earned scientific fame because mutations in it cause nude mice to be hairless and immune-deficient, a phenotype traced to failed development of the thymus and hair follicles. In humans, mutations in FOXN1 produce a rare form of severe combined immunodeficiency accompanied by alopecia and nail dystrophy. What the new study adds is a systematic portrait of what happens when Foxn1 dosage is halved in otherwise healthy animals and how that half-dose interacts with aging itself.

The researchers worked with three groups of animals: young mice at twenty days of age, middle-aged mice at one year, and old mice at two years. At each time point they compared wild-type animals, carrying two normal copies of Foxn1, with heterozygous knockout animals carrying only one. Because no live-animal procedures were involved, the team collected tissue post-mortem, in accordance with European Directive 2010/63/EU. They then applied a battery of techniques ranging from histology and immunofluorescence to western blotting and quantitative PCR, supplemented by liquid chromatography with tandem mass spectrometry, to build a layered picture of gene expression, protein abundance, and tissue structure.

The morphological differences were striking. Skin from the heterozygous animals had a thinner epidermis and a thicker dermis than that of their wild-type counterparts. Within the epidermis, keratinocyte differentiation was disrupted, with an enlarged spinous layer dominating the tissue. The spinous layer is the thick middle stratum of the epidermis where differentiating keratinocytes are held together by numerous desmosomes, giving the cells their spiny appearance under the microscope. Its expansion in Foxn1 haploinsufficient mice points to a shift in how basal cells exit the proliferative compartment and mature into the protective barrier layers above, a process governed by a finely tuned sequence of lineage-specific keratins and terminal differentiation markers such as keratin 10, loricrin, and filaggrin.

Collagen composition told an equally intriguing story. Wild-type skin accumulated more collagen I, the stiff, rope-like fiber that provides tensile strength and is characteristic of mature, repair-oriented extracellular matrix. Heterozygous skin, by contrast, maintained elevated levels of collagen III, the thinner, more pliable fiber that dominates embryonic and regenerative tissue and is normally replaced by collagen I during scar maturation. This shift hints that reduced Foxn1 dosage preserves a more regeneration-friendly matrix profile, a property of considerable interest for wound-healing and anti-aging research, where the goal is often to coax adult skin back toward a fetal-like repair mode rather than a scarring one.

Perhaps the most consequential finding concerned cellular senescence, the state of stable cell-cycle arrest that accumulates in aging tissues and drives inflammation through the molecules senescent cells secrete. The team measured expression of p21, encoded by the Cdkn1a gene, a canonical readout of senescence signaling. In wild-type mice, p21 expression climbed steadily with age, exactly as expected for tissue progressively filling with senescent cells. In the heterozygous mice, however, p21 remained low even in aged animals, suggesting that halving Foxn1 dosage fundamentally alters the senescence pathway in skin. The authors are careful to frame this as an altered trajectory rather than proven rejuvenation, but the implication is provocative: a transcription factor could reprogram how skin cells respond to the molecular damage of time.

Foxn1 also emerged as a modulator of the hypoxia response and of redox homeostasis, the biochemical balancing act between reactive oxygen species and the antioxidant systems that neutralize them. Reactive oxygen species are unavoidable byproducts of mitochondrial metabolism and, when unchecked, damage lipids, proteins, and DNA, making redox balance a cornerstone of aging biology. The researchers examined HIF-1α, the hypoxia-inducible factor that coordinates cellular responses to low oxygen, along with factor inhibiting HIF-1, the oxygen-dependent hydroxylase that switches HIF signaling off. They also profiled the thioredoxin system, including thioredoxins 1 and 2 and their reductases Txnrd1 through Txnrd3, plus sulfiredoxin 1, all central components of the cellular antioxidant arsenal. Differences in these pathways between the genotypes were most pronounced in young and middle-aged animals, and notably faded in the oldest group.

That age-dependent fading is itself an important message. The regulatory influence of Foxn1 on hypoxia signaling, oxidative stress, and cellular protection appears strongest when the skin is still youthful and wanes as animals reach advanced age. In other words, Foxn1 behaves like an age-sensitive governor: in early and mid-life it helps hold skin homeostasis in check, but by two years of age its grip loosens, and the aging phenotype proceeds regardless of genotype. This dynamic complicates any simple therapeutic narrative, because simply knowing that a gene matters is not enough; the timing of its activity defines when an intervention might work.

The study also documented Foxn1 protein inside epidermal keratinocytes and hair follicles in both genotypes and at all three ages, using immunofluorescence and transgenic FOXN1::eGFP reporter mice generously provided by Professor Thomas Boehm of the Max Planck Institute of Immunobiology and Epigenetics. The nuclear localization of the protein within keratinocytes is consistent with its established function as a DNA-binding transcription factor and supports the idea that Foxn1 acts directly within the epidermal lineage rather than merely indirectly through immune or dermal effects. Hair follicle counts in the dermis and in the dermal white adipose tissue, the fat layer under the skin that hosts follicle bulges, further mapped how structural changes distribute across skin compartments with age and genotype.

For a broad audience, the takeaway is that skin aging is not a one-way slide but a genetically choreographed process with named conductors. Foxn1 now joins the short list of genes whose dosage measurably reshapes tissue structure, extracellular matrix composition, senescence signaling, and stress responses in an intact aging organism. Because the work was performed in mice, translating it to human skin will require caution; human and murine skin differ in thickness, follicle density, and immune composition. Still, the identification of a single transcription factor whose partial loss keeps p21 low and preserves a regenerative collagen profile gives aging researchers a concrete molecular handle. Whether pharmacologically tuning Foxn1 activity could one day slow skin aging or improve wound repair remains an open question, but this study transforms it from speculation into a testable hypothesis, and it does so with the kind of multi-system, age-resolved evidence that the field has long demanded.

Subject of Research: The role of the Foxn1 transcription factor in skin structure, redox balance, and aging

Article Title: Foxn1 regulates epidermal structure, redox balance, and age related changes

Article References: Machcinska-Zielinska, S., Kopcewicz, M., Wisniewska, J., Valdivieso, K., Ogrodnik, M., Walendzik, K., & Gawronska-Kozak, B. (2026). Foxn1 regulates epidermal structure, redox balance, and age related changes. BMC Biology. https://doi.org/10.1186/s12915-026-02737-x

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02737-x

Keywords: Foxn1, skin aging, epidermis, keratinocytes, collagen, redox homeostasis, reactive oxygen species, senescence, p21, HIF-1 alpha, thioredoxin, mice

The formula, known as gu-ben-hua-shi, or AESS, was developed by Professor Dacan Chen and descends from the san-shu formula first recorded in a Qing dynasty materia medica from 1767. It combines Atractylodes rhizomes, zedoary, honeysuckle flower, sophora flower, coix seed, fangfeng root and rehmannia root in proportions designed, in traditional terms, to invigorate the spleen and eliminate dampness. In modern terms, the study published in the Journal of Cellular and Molecular Medicine set out to determine whether this centuries-old prescription works through the Hippo-YAP signalling pathway, a master regulator of keratinocyte growth and differentiation, and through autophagy, the cellular recycling process that keeps the epidermis functional.

The evidence came from three complementary lines of investigation. First, a prospective single-arm clinical trial enrolled 34 adults with moderate-to-severe atopic dermatitis, 97 percent of whom fell into the moderate or severe category. Participants drank the AESS decoction twice daily for eight weeks while using standardized moisturizers, with no steroids or other topical anti-inflammatory drugs permitted. Second, the team ran network pharmacology and animal studies in dust-mite-induced atopic dermatitis mice. Third, they tested AESS-containing serum on human keratinocytes grown under inflammatory conditions mimicking the disease.

The clinical results were striking. After eight weeks, the mean SCORAD score fell from 44.8 to 11.6, the EASI score dropped from 9.2 to 1.1, and the Investigator’s Global Assessment fell from 2.9 to 0.6, all highly significant changes. Nearly a quarter of patients achieved a 90 percent improvement in SCORAD, and almost three-quarters achieved at least a 50 percent improvement. Itching and sleep scores improved substantially, as did quality-of-life measures. On instrumental testing, transepidermal water loss, a gold-standard marker of barrier leakiness, fell significantly in lesional skin, while stratum corneum hydration rose significantly in non-lesional skin. Blood tests showed eosinophil counts dropping sharply and the Th1/Th2 and Treg/Th17 immune ratios shifting toward balance. Only two adverse events were recorded, both common colds judged unrelated to treatment.

To understand how a mixture of plant extracts could produce such effects, the researchers first used ultra-high-performance liquid chromatography coupled with tandem mass spectrometry to catalogue the chemistry. They detected 91 compounds and identified 76, including organic acids, terpenoids, flavonoids and diarylheptanoids. Ten of the most abundant compounds surviving into the bloodstream, among them chlorogenic acid, rutin and narcissoside, were then fed into network pharmacology databases to map their likely protein targets against known atopic dermatitis genes. The analysis converged on 326 overlapping targets and highlighted 30 core candidates, including TNF, TP53, SRC, IL-6 and mTOR, with enriched pathways pointing squarely at autophagy, mTOR signalling and immune regulation.

The animal experiments then delivered the causal evidence. In mice whose dermatitis was induced by repeated application of house dust mite extract, oral AESS reduced dermatitis scores, ear thickness and lesion thickness, lowered transepidermal water loss and raised skin hydration in a dose-dependent manner. Crucially, when the researchers silenced YAP, the key downstream effector of the Hippo pathway, using lentiviral shRNA injected into the lesions, the benefits of AESS largely evaporated: dermatitis scores climbed back, barrier proteins fell and inflammation returned. Dexamethasone, the positive control, suppressed inflammation but actually damaged the barrier, increasing water loss and reducing hydration while cutting levels of the barrier proteins filaggrin, involucrin and loricrin.

The mechanistic story centres on the Hippo kinase cascade. In atopic dermatitis, whether in mouse skin or in human keratinocytes stimulated with interferon-gamma and tumour necrosis factor-alpha, YAP expression drops while its inhibitory phosphorylation rises, driven by activated MST1/2 and LATS1/2 kinases that trap YAP in the cytoplasm. AESS treatment reversed this pattern, reducing phosphorylation of the cascade and allowing YAP to accumulate in the nucleus, where it can switch on genes for keratinocyte proliferation and differentiation. Barrier proteins filaggrin, involucrin and loricrin, which build the structural scaffolding of the stratum corneum, rose in step with YAP restoration and fell again when YAP was knocked down, in both mice and cell cultures.

Autophagy emerged as the second arm of the mechanism. Reduced autophagy is increasingly recognized as a feature of atopic dermatitis, impairing keratinocyte differentiation and defence against pathogens such as Staphylococcus aureus. In the diseased mice and cells, the researchers observed fewer autophagosomes and autolysosomes under the electron microscope, reduced LC3 lipidation and elevated p62, together with heightened mTOR activity, mTOR being a known brake on autophagy. AESS restored autophagic flux in a dose-dependent manner, boosting LC3, lowering p62 and dampening p-mTOR, and tandem mRFP-GFP-LC3 assays confirmed that the flux through autolysosomes genuinely accelerated rather than merely stalled. Immunofluorescence showed YAP and LC3 co-localizing after treatment, and YAP knockdown abolished the autophagy boost, placing YAP upstream of the autophagy programme.

The cell experiments rounded out the picture. AESS-containing serum, tested at 5, 10 and 15 percent concentrations, increased the proliferation of inflamed keratinocytes and reduced their apoptosis, effects again reversed by YAP silencing. The authors suggest this dual action, simultaneously rebuilding the physical barrier through YAP-driven differentiation and autophagy while calming the Th2- and Th17-skewed immune storm, addresses the two principal drivers of atopic dermatitis in one intervention, something no single conventional drug currently achieves without barrier side effects.

The researchers are careful about the limits of the work. The clinical arm was a small, uncontrolled, single-arm pilot without a placebo group, so expectation effects cannot be excluded, and the eight-week follow-up cannot speak to long-term safety or relapse. A placebo-controlled randomized trial is now under way. The network pharmacology, while suggestive, relies on prediction databases, and the precise compound or compounds within the 76 identified constituents that activate the Hippo-YAP axis remain unidentified. Still, the convergence of clinical improvement, dose-dependent animal efficacy, genetic loss-of-function confirmation and cellular mechanism is unusual rigor for a traditional medicine study, and it offers a template for how classical formulas might be validated and mechanistically dissected. If the ongoing randomized trial confirms these findings, an eight-herb decoction first described in 1767 could earn a place in the modern eczema arsenal, not as folklore but as a multi-target therapy that teaches damaged skin to repair itself.

Subject of Research: Mechanism of a traditional Chinese herbal formula regulating autophagy via the Hippo-YAP pathway to restore the skin barrier in atopic dermatitis

Article Title: Mechanism of Gu‐Ben‐Hua‐Shi (AESS) Formula Regulating Autophagy Through Hippo‐YAP Pathway in Restoring the Skin Barrier in Atopic Dermatitis

Article References: Ma, X., Huang, Y., Lv, X., Mo, X., Liu, J., Yan, F., Ye, S., Zhang, Y., Chen, D., & Jia, J. (2026). Mechanism of Gu‐Ben‐Hua‐Shi ( AESS ) Formula Regulating Autophagy Through Hippo‐ YAP Pathway in Restoring the Skin Barrier in Atopic Dermatitis. Journal of Cellular and Molecular Medicine, 30(17), Article e71361. https://doi.org/10.1111/jcmm.71361

Image Credits: AI Generated

DOI: 10.1111/jcmm.71361

Keywords: atopic dermatitis, traditional Chinese medicine, Hippo-YAP pathway, autophagy, skin barrier, filaggrin, transepidermal water loss, keratinocytes, mTOR, clinical trial, network pharmacology, eczema

The research team, led by Zhe Gao and Xin Zhang, set out to explore a question that has remained surprisingly open: what role, if any, does TRIM28 play in regulating the behavior of macrophages and the keratinocytes they communicate with? TRIM28, short for tripartite motif-containing 28, is a multifunctional protein best known for its involvement in transcriptional regulation and epigenetic modification. It can influence protein stability through ubiquitination and SUMOylation, two post-translational modifications that attach small protein tags to targets and alter their behavior. Despite growing interest in TRIM family proteins across immunology and cancer biology, TRIM28’s role in macrophage polarization had not been clearly defined.

To probe this question, the researchers used a well-established laboratory model. They cultured human THP-1 monocytic cells and differentiated them into macrophage-like cells using a chemical called phorbol 12-myristate 13-acetate. Separately, they maintained HaCaT keratinocytes, an immortalized human skin cell line. Using small interfering RNAs, they silenced TRIM28 expression in the macrophages, and in complementary experiments they boosted TRIM28 levels using an overexpression plasmid. These two approaches, gene knockdown and gene overexpression, allowed the team to observe what happens when TRIM28 is removed or amplified within the same cellular environment.

The results were striking. When TRIM28 was silenced, flow cytometry analysis revealed a marked shift in macrophage phenotype: the proportion of CD68-positive CD206-positive cells, associated with an M2-like or anti-inflammatory profile, increased to 25 percent from lower baseline levels. Conversely, the proportion of CD68-positive CD86-positive cells, associated with an M1-like or pro-inflammatory profile, dropped to just 5 percent. Enzyme-linked immunosorbent assays confirmed the functional consequences: silencing TRIM28 reduced secretion of the pro-inflammatory cytokines IL-6 and TNF-α while increasing the anti-inflammatory cytokine IL-10. Western blotting reinforced these findings, showing decreased expression of the M1-associated marker iNOS and increased expression of the M2-associated marker Arg1. When TRIM28 was overexpressed, every one of these trends reversed, pushing macrophages toward the pro-inflammatory state.

The team then traced the molecular pathway underlying this effect. Prior research had suggested that TRIM28 can stabilize NLRP3, a key component of the inflammasome, a multiprotein complex that triggers inflammatory signaling. NLRP3, in turn, is known to activate its downstream partner SGT1. In the current study, TRIM28 knockdown reduced the expression of both NLRP3 and SGT1, while overexpression raised their levels. Crucially, the researchers also examined functional readouts of inflammasome activation. TRIM28 knockdown decreased levels of cleaved caspase-1 and mature IL-1β, both hallmarks of inflammasome activity, and reduced secretion of IL-1β into the culture medium. Overexpression produced the opposite pattern. Co-immunoprecipitation experiments further revealed that TRIM28 physically interacts with NLRP3 and that TRIM28 overexpression significantly increased the SUMOylation of NLRP3, a modification previously linked to inflammasome stabilization.

With the macrophage-side mechanism established, the investigators turned to the keratinocyte side of the equation. They placed modified macrophages in the upper chamber of a Transwell system, separated by a porous membrane from HaCaT keratinocytes below, allowing soluble factors to pass but preventing direct cell contact. After 24 hours of co-culture, they measured keratinocyte viability and invasive capacity. The differences were dramatic. Co-culture with TRIM28-silenced macrophages reduced HaCaT cell viability to 60 percent of control levels, while co-culture with TRIM28-overexpressing macrophages raised viability to 140 percent. Invasion assays showed a similar pattern: silencing TRIM28 in macrophages reduced keratinocyte invasion to 60 percent of baseline, whereas overexpression increased it to 180 percent. These cellular behaviors, hyperproliferation and invasion, are relevant to inflammatory skin responses, although the authors are careful to note that they do not by themselves demonstrate a role for TRIM28 in psoriasis in living organisms.

To confirm that the NLRP3/SGT1 axis and SUMOylation were genuinely required for these effects rather than incidental, the researchers performed a series of rescue experiments. They knocked down NLRP3 or SGT1 in macrophages overexpressing TRIM28, or treated the cells with 2-D08, a chemical inhibitor of SUMOylation. Each intervention partially reversed the TRIM28-driven shift toward the pro-inflammatory macrophage phenotype, restoring the balance of CD86-positive and CD206-positive populations. The interventions also normalized cytokine secretion patterns, reduced cleaved caspase-1 and mature IL-1β levels, and attenuated the enhanced NLRP3 SUMOylation. Most importantly, these same interventions partially reversed the proliferative and invasive changes observed in co-cultured keratinocytes, confirming that the NLRP3/SGT1 pathway and SUMOylation are functionally required for the macrophage-mediated effects on skin cells.

The study places TRIM28 within a growing family of TRIM proteins implicated in inflammatory skin biology. Previous work has shown that TRIM14 promotes psoriasis-like inflammation by activating NF-κB signaling, and that TRIM27 amplifies IL-6/STAT3 signaling in keratinocytes. The current research extends this picture by suggesting that TRIM28 operates through a distinct mechanism, one involving post-translational modification of the NLRP3 inflammasome rather than transcriptional regulation alone. This positions TRIM28 as a potential bridging molecule between the epigenetic machinery of the cell and the innate immune response, a role that has parallels in other inflammatory conditions. The researchers draw comparisons to the HSP90β-SGT1 complex, which stabilizes NLRP3 in autoinflammatory syndromes, and to studies in fatty liver disease where HSP90 inhibition suppresses NLRP3 activation.

Nevertheless, the authors are emphatic about the limitations of their work. All experiments were performed in simplified in vitro systems using immortalized cell lines, which cannot fully replicate the cellular diversity, tissue architecture, and immune microenvironment of human psoriatic skin. The team did not examine TRIM28 expression in actual psoriatic lesions, did not analyze patient-derived samples, and did not correlate TRIM28 levels with disease severity. Macrophage polarization was assessed using a limited marker panel, and the authors acknowledge that the M1/M2 framework is a simplified operational model rather than a definitive classification of macrophage states. More comprehensive approaches, including single-cell RNA sequencing and multiplex flow cytometry, would be needed to fully characterize the macrophage phenotypes regulated by TRIM28. Additionally, the specific enzyme responsible for NLRP3 SUMOylation in this context remains unknown, as TRIM28 itself lacks SUMO ligase activity, suggesting intermediary proteins may be involved.

Looking forward, the researchers outline several priorities for future investigation. They propose examining TRIM28 expression and localization in human psoriatic tissue alongside clinical markers, validating the TRIM28–NLRP3/SGT1 axis in patient-derived cells and three-dimensional organotypic skin cultures, and testing whether modulating TRIM28 alters inflammation in animal models of psoriasis-like dermatitis. They also call for a more precise mapping of the molecular interactions between TRIM28, NLRP3, and SGT1, including identification of the relevant SUMO E3 ligase and assessment of downstream inflammasome assembly events. Until such work is completed, the current study stands as a rigorous piece of mechanistic cell biology, defining a TRIM28-dependent inflammatory pathway in a controlled laboratory setting. Its contribution is foundational rather than translational: it illuminates how a single regulatory protein can reshape the inflammatory conversation between two cell types central to skin immunity, while leaving open the critical question of whether that conversation drives human disease.

Subject of Research: TRIM28 regulation of macrophage polarization and keratinocyte behavior via the NLRP3/SGT1 axis in vitro

Article Title: TRIM28 Promotes Keratinocyte Proliferation and Invasion by Activating NLRP3/SGT1 Axis‐Mediated Macrophage Pro‐Inflammatory Polarization in an In Vitro Macrophage–Keratinocyte Co‐Culture Model

Article References: Gao, Z., Zhang, X., Wang, J., & Yang, N. (2026). TRIM28 Promotes Keratinocyte Proliferation and Invasion by Activating NLRP3/SGT1 Axis‐Mediated Macrophage Pro‐Inflammatory Polarization in an In Vitro Macrophage–Keratinocyte Co‐Culture Model. Immunity, Inflammation and Disease, 14(9), Article e70522. https://doi.org/10.1002/iid3.70522

Image Credits: AI Generated

DOI: 10.1002/iid3.70522

Keywords: TRIM28, macrophage polarization, NLRP3 inflammasome, SGT1, SUMOylation, keratinocytes, psoriasis, inflammation, IL-1β, co-culture, innate immunity, skin biology

The therapeutic material, known as a secretome, is the complete collection of bioactive molecules that stem cells release into their surroundings, including growth factors, cytokines, nucleic acids such as microRNAs, lipid metabolites, and extracellular vesicles like exosomes. Mounting evidence suggests that the clinical benefits of mesenchymal stem cells come not from the cells themselves engrafting and replacing worn-out tissue, but from these paracrine signals. That insight has fueled interest in secretome-based therapies as safer, more controllable alternatives to live-cell transplantation, eliminating risks of rejection, uncontrolled proliferation, or tumorigenicity. Human umbilical cord-derived mesenchymal stem cells are especially attractive sources because they are readily available, ethically uncontroversial, non-invasive to procure, and expand vigorously in culture. Prior work by the same team showed that this secretome could stimulate hair growth through the PI3K/AKT/mTOR pathway, but its role in photoaging had remained poorly defined.

To test the secretome’s anti-aging potential, researchers at Southern Medical University in Guangzhou, China, built a chronic photoaging model in mice. Over 40 days, depilated dorsal skin was irradiated with a carefully calibrated mixture of UVA and UVB whose intensity ratio of roughly 6.7 to 1 mirrors the spectral balance of natural sunlight reaching Earth’s surface. Doses escalated gradually from 10 to 30 minutes per day, avoiding the acute burns that plague many UV experiments and instead mimicking the cumulative, sub-erythemal sun exposure that ages human skin in real life. The mice developed the expected phenotype: leathery thickening, erythema, scaling, and a measurable collapse in skin elasticity, hydration, and barrier function as water loss through the epidermis climbed. Topical application of the secretome, delivered as 200 microliters daily for 30 days beginning after an adaptation period, visibly and statistically reversed nearly all of it.

Histology told the same story at the tissue level. Hematoxylin and eosin staining revealed that UV-driven epidermal hyperplasia and dermal thickening were substantially attenuated by the treatment. Masson’s trichrome staining showed that chronic irradiation had fragmented and depleted the dermal collagen network, the structural scaffold that keeps skin firm, while secretome-treated skin retained intact collagen fibers and significantly greater total collagen content. Immunohistochemistry and Western blotting traced the molecular basis: UV exposure suppressed the structural collagens COL1 and COL3 while ramping up the matrix-degrading enzymes MMP1, MMP3, and MMP9, and the secretome normalized all of these shifts. Senescence markers responded in parallel. The nuclear envelope protein Lamin B1, which declines as cells age, was restored to near-normal levels, while the cell-cycle inhibitors p16 and p21, elevated by UV stress, were pushed back down.

Notably, the treatment showed a reassuring safety profile. In mice that received the secretome without any UV exposure, modest improvements in hydration and water-loss parameters were observed, indicating support for barrier function under normal conditions, but there was no epidermal or dermal thickening and no alteration of collagen turnover. In other words, the therapy behaves differently depending on context: gentle maintenance when skin is healthy, active repair when skin is damaged. That stress-responsive selectivity matters for any candidate cosmetic or clinical intervention, because it suggests the secretome is not forcing skin into an abnormal proliferative state but rather helping stressed tissue recover its equilibrium.

The mechanistic heart of the study lies in mitochondria, the energy-producing organelles that are both a primary source of reactive oxygen species and particularly vulnerable to UV damage. Chronic irradiation mutates mitochondrial DNA, breaks respiratory chain function, and floods cells with oxidative stress, creating a vicious cycle that drives senescence. Cells normally dispose of dysfunctional mitochondria through mitophagy, a selective autophagy process that tags damaged organelles and delivers them to lysosomes for destruction. The classical PINK1/Parkin pathway orchestrates much of this quality control. Using transmission electron microscopy, the team documented severe mitochondrial injury in UV-exposed skin, including matrix swelling and fragmented cristae, alongside accumulation of mitochondrial proteins TOM20, TIM23, and HSP60 and the autophagy adaptor p62, all signs of clogged disposal machinery. The secretome reversed every one of these defects, restored PINK1 and Parkin levels, and boosted the fusion of mitochondria with lysosomes, confirmed by confocal imaging and colocalization statistics.

Why does clearing broken mitochondria matter so much for aging? The answer lies in a second pathway: cGAS-STING, the innate immune circuit that senses misplaced DNA. When damaged mitochondria leak their DNA into the cytoplasm, the sensor protein cGAS mistakes this self-DNA for a viral invader and synthesizes the messenger cGAMP, which activates STING and triggers a phosphorylation cascade through TBK1, IRF3, and IKK. The result is a flood of type I interferons and inflammatory cytokines, including IL-6, IL-8, and IFN-beta, a chronic low-grade inflammation researchers call inflammaging. The study showed this pathway roaring to life in UV-irradiated mouse skin and UVB-exposed human keratinocytes, with cytosolic double-stranded DNA accumulating visibly under the microscope. Secretome treatment shut the whole cascade down, from cGAS expression through cytokine secretion, both in tissue and in serum.

The causal architecture was tested with an elegant pharmacological epistasis design. The mitophagy inhibitor Mdivi-1, which blocks the fission protein Drp1, abolished the secretome’s protective effect and reactivated cGAS-STING signaling, elevating inflammatory cytokines and restoring senescence markers. Conversely, the mitophagy agonist CCCP mimicked the secretome’s benefits on its own, while the STING inhibitor H151 enhanced protection further. Most tellingly, when Mdivi-1 and H151 were combined, H151 bypassed the mitophagy blockade entirely and restored full protection, demonstrating that STING sits downstream of mitophagy in a strict hierarchy: the secretome protects skin primarily by reactivating mitochondrial housekeeping, which prevents DNA leakage and thereby disarms the inflammatory driver of senescence.

The implications reach well beyond dermatology. The mitophagy-cGAS-STING axis has been implicated in neurodegeneration and cardiac hypertrophy, and this study provides direct in vivo evidence that the same cascade operates in skin aging and can be therapeutically targeted by a cell-free biologic. A standardized secretome, harvested from a single validated donor batch, sterile-filtered, and frozen in aliquots, could sidestep many regulatory and safety hurdles of live-cell therapy while remaining simple to apply topically. The authors caution that murine skin and immortalized keratinocyte lines cannot fully recapitulate human biology, and clinical validation will be essential before any anti-aging product reaches the clinic. Still, the demonstration that boosting a cellular waste-disposal system can quiet an inflammatory aging program offers a compelling mechanistic template, not just for smoother skin, but potentially for a broad class of mitochondrial-driven age-related disorders.

Subject of Research: Cell-free mesenchymal stem cell secretome therapy for skin photoaging via the mitophagy-cGAS-STING axis

Article Title: The Secretome Derived From Human Umbilical Cord Mesenchymal Stem Cells Improves Skin Photoaging by Enhancing Mitophagy to Inhibit the cGAS‐STING Pathway

Article References: Tang, T., Lin, M., Yang, J., Yang, X., Xu, X., Wang, X., Zhang, Y., Chen, Q., Zhao, S., Guo, C., Zhang, H., Zhang, M., Zhang, L., & Wang, X. (2026). The Secretome Derived From Human Umbilical Cord Mesenchymal Stem Cells Improves Skin Photoaging by Enhancing Mitophagy to Inhibit the cGAS ‐ STING Pathway. Aging Cell, 25(9), Article e70701. https://doi.org/10.1111/acel.70701

Image Credits: AI Generated

DOI: 10.1111/acel.70701

Keywords: skin photoaging, mesenchymal stem cells, secretome, mitophagy, cGAS-STING, inflammaging, UV radiation, keratinocytes, cell-free therapy, collagen degradation, senescence, regenerative dermatology

The research team, led by Qingqing He and Junlin Liu, set out to map the molecular targets through which calcitriol exerts its anti-psoriatic effects. Calcitriol is best known for its role in calcium homeostasis and bone mineralization, but it also regulates cell proliferation, differentiation, oxidative stress, angiogenesis, immune modulation and antimicrobial peptide production. When calcitriol binds the vitamin D receptor, it dampens excessive T cell activation, particularly of Th17 cells, reducing interleukin-17 secretion, and it suppresses pro-inflammatory cytokines such as interleukin-6 and tumour necrosis factor-alpha. The enzyme CYP24A1 then hydroxylates calcitriol at the C-23 or C-24 position, converting it into less active metabolites that are eventually excreted, a safeguard against hypercalcaemia. What remained unclear was which downstream genes calcitriol might regulate to produce its therapeutic benefit in skin.

The researchers focused on CHI3L2, also known as YKL-39, a member of the chitinase-like protein family. Unlike its better-known relative CHI3L1, or YKL-40, CHI3L2 has been comparatively neglected in inflammatory disease research, although it is expressed in macrophages, chondrocytes and epithelial cells and can be induced by interleukin-6 and tumour necrosis factor-alpha. The protein displays chemotactic activity, growth factor activity, the ability to induce cytokine secretion and the capacity to stimulate angiogenesis. Previous work had connected CHI3L2 to the ERK1/2 signalling pathway in glioblastoma, and to STAT3 phosphorylation in invasive ductal carcinoma, where its role appears to depend on the molecular subtype of breast cancer. Because STAT3 is a critical transcription factor downstream of interleukin-6, interleukin-17, interleukin-22 and epidermal growth factor, and because persistent STAT3 activation in psoriatic keratinocytes and immune cells drives hyperproliferation, anti-apoptosis and inflammatory cytokine production, the team hypothesized that calcitriol might relieve psoriatic inflammation by suppressing CHI3L2 through inhibition of STAT3 signalling.

To test this idea in living animals, the researchers used the imiquimod-induced mouse model of psoriasis, in which topical application of the toll-like receptor 7/8 agonist activates the interleukin-23/interleukin-17 inflammatory axis that closely mirrors human disease pathogenesis. In a unilateral ear model, BALB/c mice received daily topical calcitriol solution before imiquimod cream for seven consecutive days. The treatment significantly reduced the clinical hallmarks of erythema, scaling and thickening, and histological examination showed markedly attenuated epidermal hyperplasia. Real-time quantitative PCR of ear tissue revealed substantially reduced expression of the pro-inflammatory cytokines interleukin-1alpha, interleukin-6, interleukin-17A and interleukin-23A. Importantly, serum calcium levels rose only to 2.500 millimoles per litre, comfortably within the normal physiological range of 2.0 to 2.6, and body weight, haematological parameters and organ histopathology remained unremarkable, indicating an excellent safety profile at the dose used.

The most striking finding emerged from a bilateral ear model designed to test whether local treatment could influence distant lesions. After seven days of calcitriol and imiquimod application to the right ear, the untreated left ears of the same mice were challenged with imiquimod alone for five days. Remarkably, even though only the right ear had ever received calcitriol, the left ears showed only mild psoriasiform changes compared with controls, with attenuated epidermal hyperplasia and reduced cytokine expression. Serum calcium returned to normal within five days of stopping treatment. This systemic effect suggests that calcitriol or its downstream mediators may enter the circulation and act at distal sites, although the precise circulating factors responsible remain to be identified. The observation raises intriguing questions about whether topical vitamin D therapy could benefit psoriatic lesions beyond the site of application in patients.

To dissect the cellular mechanisms, the team turned to HaCaT human keratinocytes stimulated with a five-cytokine cocktail, abbreviated M5, comprising interleukin-17A, interleukin-22, interleukin-1alpha, oncostatin M and tumour necrosis factor-alpha, which mimics the psoriatic inflammatory milieu. In psoriasis, the intermediate filament protein KRT1 is downregulated, marking impaired differentiation, while KRT6 is upregulated, indicating excessive proliferation and inflammatory activation. Calcitriol reversed both changes, restoring KRT1 and suppressing KRT6. CCK-8 and colony-formation assays showed that calcitriol counteracted the abnormal proliferation induced by M5, wound-healing assays demonstrated reduced aberrant migration, and quantitative PCR confirmed downregulation of interleukin-1alpha, interleukin-6, interleukin-17A and interleukin-23A messenger RNA.

The pivotal clue came from RNA sequencing of M5-stimulated cells treated with or without calcitriol. The analysis identified 537 differentially expressed genes, 344 upregulated and 193 downregulated. As expected, CYP24A1, the canonical calcitriol-metabolizing enzyme, was the most significantly upregulated gene, confirming that the vitamin D pathway was engaged. But the most significantly downregulated gene was CHI3L2, a result the researchers validated by quantitative PCR. When the team silenced CHI3L2 using short hairpin RNA, the effects phenocopied calcitriol treatment: KRT1 and KRT6 levels normalized, cell viability and colony formation declined, migratory capacity was impaired, and pro-inflammatory cytokine expression dropped. These loss-of-function experiments position CHI3L2 as a pro-inflammatory and pro-proliferative factor in psoriatic keratinocytes and a critical downstream effector of calcitriol.

Next, the researchers asked which signalling pathway mediates the CHI3L2 effect. KEGG pathway enrichment analysis of the downregulated genes pointed strongly to the STAT pathway, with no significant enrichment of the ERK pathway. Western blotting confirmed this: silencing CHI3L2 reduced phosphorylated STAT3 at both Tyr705 and Ser727 as well as total STAT3 protein, while phosphorylated and total ERK1/2 remained unchanged. Comparing the two STAT3 phosphorylation sites revealed that Tyr705 was the dominant regulatory node, with Ser727 showing a smaller, less pronounced change. Tyr705 phosphorylation is essential for STAT3 dimerization, nuclear translocation and transcriptional activity, so CHI3L2 appears primarily to facilitate STAT3 activation at this residue. The reduction in total STAT3 protein upon CHI3L2 knockdown also raises the possibility that CHI3L2 stabilizes STAT3 or enhances its expression, a hypothesis the authors flag for future investigation.

The authors are careful to acknowledge the limitations of their work. The imiquimod model, while widely accepted, does not fully capture the chronic, relapsing nature of human psoriasis and involves TLR7/8-driven inflammation that may not perfectly mirror the human disease. The in vitro experiments relied on HaCaT cells, an immortalized keratinocyte line, and validation in primary human keratinocytes or organotypic skin models would strengthen physiological relevance. Crucially, the study does not establish whether STAT3 or the vitamin D receptor directly binds the CHI3L2 promoter; chromatin immunoprecipitation and luciferase reporter assays would be needed to determine whether the regulation is direct or mediated through secondary transcription factors. It also remains unknown whether CHI3L2 interacts with STAT3 directly or acts through upstream receptor-mediated signalling. The systemic improvement seen in the bilateral ear model demands further exploration of circulating factors such as calcium, vitamin D metabolites or soluble inflammatory mediators.

Nevertheless, the study delivers a compelling new framework for understanding how vitamin D-based therapies work in psoriasis. By identifying CHI3L2 as a previously unrecognized downstream effector of calcitriol and demonstrating that its suppression depends on inhibiting STAT3 phosphorylation at Tyr705, the research links vitamin D signalling to chitinase-like protein regulation for the first time in cutaneous inflammation. The findings suggest that CHI3L2 could serve as a biomarker predicting response to vitamin D treatment, and that combining CHI3L2 inhibition with calcitriol administration might yield additive or synergistic benefits. With psoriasis prevalence rising worldwide and no cure in sight, uncovering a druggable node in the STAT3/CHI3L2 axis offers both mechanistic insight and a tangible target for the next generation of anti-psoriatic therapies.

Subject of Research: The mechanism by which calcitriol suppresses psoriatic inflammation and keratinocyte hyperproliferation through downregulation of CHI3L2 via the STAT3 pathway

Article Title: Downregulating CHI3L2 via the STAT3 Pathway: The Mechanism of Calcitriol in Suppressing Psoriatic Inflammation and Keratinocyte Hyperproliferation

Article References: He, Q., & Liu, J. (2026). Downregulating CHI3L2 via the STAT3 Pathway: The Mechanism of Calcitriol in Suppressing Psoriatic Inflammation and Keratinocyte Hyperproliferation. Journal of Cellular and Molecular Medicine, 30(18), Article e71367. https://doi.org/10.1111/jcmm.71367

Image Credits: AI Generated

DOI: 10.1111/jcmm.71367

Keywords: psoriasis, calcitriol, vitamin D, CHI3L2, STAT3, keratinocytes, imiquimod model, inflammation, HaCaT cells, CYP24A1, interleukin-17, drug mechanism

The core innovation is deceptively simple. Rather than relying on invasive skin biopsies, blood draws or urine collection, the protocol uses hairs plucked with intact follicles, ideally in the anagen or growth phase, when the follicle is rich in proliferative keratinocytes. Once plucked, the hairs are placed in a kit and can be mailed over long distances without refrigeration. In the laboratory, keratinocytes are released from the follicles by trypsinization, an enzymatic digestion that separates the cells from the hair shaft, and are then cultured under conditions that preserve their proliferative capacity. The authors report that samples remain stable for days at ambient temperature, provided standard biosafety precautions are observed, which makes ordinary postal and courier services viable conduits for human biological material.

Why does the choice of starting cell matter so much? Induced pluripotent stem cells, first generated by Shinya Yamanaka and colleagues in 2007 through the forced expression of defined transcription factors, can differentiate into all three embryonic lineages, including the neural lineage that gives rise to neurons and glia. But the quality and efficiency of reprogramming depend heavily on the source cell. Dermal fibroblasts require a punch biopsy, an uncomfortable procedure that typically must be performed by a clinician. Peripheral blood mononuclear cells require venipuncture and careful handling, and although blood held at room temperature has been used successfully, the window is limited. Renal epithelial cells from urine are noninvasive but yield variable numbers of cells and are not suitable for every donor. Keratinocytes, by contrast, reprogram efficiently, and hair plucking is essentially painless.

The Yale team’s protocol lowers the technical barrier even further by requiring fewer follicles than previous hair-based approaches. Earlier methods for isolating keratinocytes from plucked hair existed, including protocols published by Aasen and colleagues in 2008 and 2010, but they generally demanded either fresh local collection or specialized handling. The new kit-based workflow explicitly anticipates the realities of remote participation: a donor, a family member or a healthcare provider can perform the collection after watching a short instructional video that accompanies the protocol, and the resulting sample tolerates the delays of long-distance shipping. This matters enormously for rare disease research, where patients are geographically dispersed and where systematic reviews have documented substantial inequities in access to clinical genetic services.

Once the keratinocytes arrive in the laboratory, the workflow follows a well-trodden but carefully optimized path. The cells are expanded in culture, with the Rho kinase inhibitor Y-27632 playing a supporting role in improving survival, a trick borrowed from the keratinocyte literature where ROCK inhibition prolongs the lifespan of adult cells in vitro. Reprogramming then converts the keratinocytes into iPS cells, a process the protocol completes within roughly two months of receiving the hair samples. Notably, the authors emphasize that the procedure requires only basic familiarity with mammalian cell culture techniques and no specialized equipment beyond what a standard cell biology laboratory already possesses. That accessibility is a deliberate design choice: the protocol is written to be executable by labs that have never worked with human iPS cells before.

Quality control is built into the workflow. The published protocol includes characterization steps confirming that the resulting iPS cells express canonical pluripotency markers, retain a normal karyotype, and can differentiate into all three germ layers, including neural lineages. The authors demonstrate the full pipeline by generating cerebral organoids, three-dimensional self-organizing cultures that recapitulate key features of early human brain development. Organoid generation from the iPS cells takes 30 to 40 days and requires one piece of specialized equipment, an orbital shaker, which keeps the growing organoids suspended and nourished in culture. Whole-mount imaging and immunostaining confirm that the organoids contain the expected neural cell populations, establishing that hair-derived iPS cells are fully competent for demanding three-dimensional differentiation protocols.

The protocol did not emerge in a vacuum. It was developed and refined in the course of a primary research study, published in Nature in 2025, in which Zhang and colleagues showed that dysregulation of mTOR signalling is a converging mechanism in lissencephaly, a severe malformation of cortical development. For that study, the team needed iPS cells and brain organoids from patients with rare neurogenetic conditions, many of whom lived far from any research center. The kit-based hair collection method proved to be the practical answer, and the new Nature Protocols article distills that hard-won experience into a form other laboratories can adopt directly. The authors acknowledge the patients and families who contributed samples, underscoring that the method was shaped by the needs of the very people it is meant to serve.

The broader implications reach into drug development, disease modeling and eventually cell therapy. Human iPS cell-derived models allow researchers to study cellular and molecular mechanisms of disease in genuinely human tissue, something animal models often fail to capture, and cerebral organoids in particular have transformed the study of neurodevelopmental disorders since Lancaster and colleagues first described them in 2013. By making the front end of that pipeline, patient sample acquisition, dramatically easier, the Yale protocol could expand the diversity of genetic backgrounds represented in organoid studies, a long-standing concern in a field where most cell lines derive from patients already connected to major academic medical centers. Populations in low-resource settings, pediatric patients for whom blood draws are difficult, and elderly donors with fragile veins all stand to benefit from a collection method that requires nothing more than a pair of tweezers and a mailing envelope.

There are, of course, practical considerations. The protocol specifies that hairs must be plucked with follicles intact, since the follicle bulb contains the keratinocyte population of interest, and the accompanying video walks collectors through identifying suitable anagen-phase hairs. Shipping times must remain within the window during which the keratinocytes stay viable at ambient temperature, and laboratories must handle all human material under appropriate biosafety procedures. Reprogramming efficiency, while generally high for keratinocytes, still varies between donors, as it does for all somatic cell sources. Yet the authors argue that the advantages outweigh these constraints: the method is noninvasive, the samples are robust, the timeline is competitive, and the equipment requirements are minimal. As personalized medicine pushes toward models built from each patient’s own genome, protocols like this one may determine who gets to participate. A technology that turns a handful of plucked hairs into a patient-specific mini brain, mailed across continents in an ordinary package, is a striking reminder that sometimes the most transformative tools in biomedicine are also the most humble.

Subject of Research: A kit-based protocol for remote collection of hair follicle keratinocytes and their reprogramming into induced pluripotent stem cells for cerebral organoid generation

Article Title: Kit-based remote collection and isolation of human reprogrammable somatic cells for generation of induced pluripotent stem cells and cerebral organoids

Article References: Cheng, I. Q., Ruiz, J. F., Casalino, E. K., Zhang, C., & Louvi, A. (2026). Kit-based remote collection and isolation of human reprogrammable somatic cells for generation of induced pluripotent stem cells and cerebral organoids. Nature Protocols. https://doi.org/10.1038/s41596-026-01440-z

Image Credits: AI Generated

DOI: 10.1038/s41596-026-01440-z

Keywords: induced pluripotent stem cells, keratinocytes, hair follicles, cerebral organoids, reprogramming, remote sample collection, disease modeling, personalized medicine, neurodevelopmental disorders, Nature Protocols, cell culture, lissencephaly

The research team, led by Andrés Caicedo of Universidad San Francisco de Quito in Ecuador together with a broad international consortium, set out to answer a deceptively simple question: do skin cells share mitochondria with one another under normal conditions, and does that sharing change when the skin is under assault from sunlight? Horizontal mitochondrial transfer, or HMT, is an emerging form of intercellular communication that has been documented in other tissues, where stressed or damaged cells can receive functioning mitochondria from healthier neighbors, restoring their energy supply and improving their survival. But whether the cells of the epidermis and dermis engage in this exchange, and how it might relate to regenerative strategies built around mitochondria, remained poorly understood.

To find out, the investigators used a coculture system in which donor cells were labeled with MitoTracker Red, a fluorescent dye that stains active mitochondria, while recipient cells carried a green tag. When red-labeled organelles appeared inside green recipient cells, transfer had occurred, and fluorescence microscopy allowed the team to quantify how often it happened. The experiments were run in two configurations: direct two-dimensional coculture, in which donor and recipient cells physically touch, and transwell systems, in which a porous membrane separates the two populations while still allowing soluble factors to diffuse through. This design allowed the researchers to distinguish contact-dependent transfer from contact-independent mechanisms.

The results were unambiguous. Under basal conditions, transfer from melanocytes to keratinocytes was already the dominant route of exchange, and when the cells were exposed to ultraviolet radiation the transfer rate climbed dramatically, reaching approximately 39 percent of recipient keratinocytes in direct coculture. In transwell assays, where cells could not touch, the same donor–recipient pair transferred at less than 9 percent, indicating that the exchange relies overwhelmingly on direct cell-to-cell contact rather than on mitochondria or mitochondrial fragments drifting through the culture medium. Every other donor–recipient combination among the three skin cell types remained below 4 percent, and some pairs—melanocyte to melanocyte, keratinocyte to keratinocyte, melanocyte to fibroblast, and keratinocyte to melanocyte—showed no detectable transfer at all. Fibroblasts, notably, took up very few mitochondria from any source, whether from their own kind or from other skin cells, even after ultraviolet exposure.

That last observation may carry the most physiological weight. Keratinocytes, which form the outermost barrier of the skin and absorb much of the ultraviolet dose, appear to receive mitochondrial help precisely when they need it most, drawing functional organelles from melanocytes, the pigment-producing cells that sit alongside them in the basal epidermis. Fibroblasts, by contrast, live deeper in the dermis where ultraviolet penetration is weaker, but their apparent inability to import mitochondria suggests they may lack a stress-adaptation pathway available to their epidermal neighbors. The authors propose that this contact-dependent, cell-type-specific exchange represents a built-in resilience mechanism for the skin’s protective barrier, one that has gone unnoticed because it only operates at meaningful levels between particular cell pairs and under particular kinds of stress.

Having established that skin cells naturally share mitochondria, the team turned to the therapeutic question: can this process be exploited deliberately? The answer came in two stages. The first was artificial mitochondrial transfer, or AMT, performed in the laboratory. The researchers isolated mitochondria from three sources—human dermal fibroblasts, human Wharton’s jelly mesenchymal stem/stromal cells (WJ-MSCs) derived from umbilical cord tissue, and mouse bone marrow mesenchymal stem cells (BM-MSCs)—and delivered them to recipient fibroblasts. Before use, the isolated organelles were rigorously quality-controlled: scanning electron microscopy confirmed their structural integrity, tetramethylrhodamine methyl ester staining demonstrated that they retained an active membrane potential, and oxygraph measurements confirmed that they consumed oxygen and respired on substrates such as glutamate, pyruvate, and malate. These were not cellular debris but functioning bioenergetic machines.

When these stem-cell-derived mitochondria were delivered to fibroblasts, two clinically relevant effects emerged. First, WJ-MSC-derived mitochondria reduced the burst of reactive oxygen species, or ROS, that ultraviolet radiation normally triggers in skin cells, pointing to a direct antioxidant and protective function. Second, mitochondria from both human WJ-MSCs and mouse BM-MSCs significantly increased fibroblast proliferation, though the magnitude of the effect depended on the dose of mitochondria delivered, underscoring that dosing will be a critical parameter in any future clinical protocol. Fibroblasts are the workhorses of wound repair, producing collagen and rebuilding the dermal matrix, so a cell-free treatment that simultaneously lowers oxidative damage and boosts their proliferation could be valuable for burns, chronic wounds, and radiation-injured skin.

The second stage moved from the dish to living animals. In a murine model of primary-intention wound healing, the researchers applied mitochondria isolated from mouse BM-MSCs directly to the wounds. Histological analysis showed enhanced early tissue repair, and the effects were comparable to those achieved by administering the intact stem cells themselves—a remarkable result, because it suggests that at least part of the regenerative benefit of mesenchymal stem cell therapy can be reproduced by their mitochondria alone, without the cells. This has profound implications. Live stem cell therapies face hurdles of manufacturing complexity, immune compatibility, tumorigenicity concerns, and regulatory scrutiny; mitochondria are simpler, cannot replicate on their own, and could in principle be standardized, stored, and dosed like a conventional biologic.

To confirm the findings in a species whose skin more closely resembles our own, the team repeated the experiment in pigs, applying mitochondria derived from human Wharton’s jelly MSCs to primary-intention wounds. The outcomes were measured with a wound healing index, histological assessment of tissue organization, and spatial quantification of Ki67, a protein marker of actively dividing cells. Treated wounds showed a higher wound healing index, improved organization of collagen-containing tissue, and increased Ki67 positivity in both the epidermal and dermal regions directly involved in repair. In other words, the transplanted mitochondria appeared to wake up the local proliferative response on both sides of the skin’s architecture, driving new cell generation precisely where the healing front was advancing.

Taken together, the study draws a translational line between a naturally occurring behavior of skin cells and a new class of cell-free regenerative medicine. On one end, melanocytes appear to act as mitochondrial donors to keratinocytes under ultraviolet stress, a contact-dependent rescue mechanism that may help explain how skin tolerates lifelong sun exposure. On the other end, mitochondria isolated from mesenchymal stromal cells can be manufactured, applied to wounded tissue, and shown to accelerate healing across two mammalian species. The authors argue that this establishes a coherent biological rationale for mitochondria-based therapies in dermatology and wound care. Much work remains—optimal dosing, delivery vehicles, immunological considerations, and eventual human trials—but the conceptual advance is clear: the mitochondria that power our cells may one day be prescribed like medicine, harvested from stem cells and delivered to the skin to quench oxidative damage and rebuild what injury has destroyed.

Subject of Research: Horizontal mitochondrial transfer and mitochondrial transplantation for protection against ultraviolet radiation-induced damage and enhancement of skin wound healing

Article Title: Horizontal mitochondrial transfer and mitochondrial transplantation in skin: protection against UVR-induced ROS damage and enhancement of cell proliferation and wound healing

Article References: Horizontal mitochondrial transfer and mitochondrial transplantation in skin: protection against UVR-induced ROS damage and enhancement of cell proliferation and wound healing. (n.d.). https://doi.org/10.1186/s12967-026-08801-y

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08801-y

Keywords: mitochondria, horizontal mitochondrial transfer, mitochondrial transplantation, skin, ultraviolet radiation, reactive oxygen species, mesenchymal stem cells, wound healing, keratinocytes, melanocytes, fibroblasts, regenerative medicine

TMEM232 is not an arbitrary suspect. It is a known susceptibility gene for atopic dermatitis, meaning genetic variants in or near the gene are statistically linked to the disease in human populations. What has remained murky until now is what the protein actually does inside skin cells and how that activity could translate into the leaky, irritated skin that defines the condition. The research team set out to close that gap by combining patient tissue samples, primary human keratinocytes, laboratory-grown human adult low-calcium cutaneous keratinocytes, and mouse models of the disease.

The first clue came from expression analysis. TMEM232 levels were significantly elevated in lesional skin from atopic dermatitis patients, and the degree of upregulation tracked with the severity of tight junction dysfunction. Tight junctions are protein assemblies — including the claudins, occludin and zonula occludens proteins — that zip adjacent keratinocytes together and seal the paracellular route through which water, allergens and microbes would otherwise pass. When the researchers measured transepithelial electrical resistance, a standard readout of barrier tightness, and ran permeability assays using fluorescent tracers, keratinocytes with excess TMEM232 showed weakened resistance and increased leakage, while reducing the protein restored junctional integrity.

To find the mechanism, the team mapped where TMEM232 resides inside the cell. Immunofluorescence revealed that the protein accumulates in the perinuclear region and is selectively enriched at mitochondria-associated endoplasmic reticulum membranes, or MAMs — the specialized lipid and protein platforms where the reticulum and mitochondria come within nanometers of each other. MAMs are the cells’ principal conduits for calcium transfer: calcium released from the endoplasmic reticulum crosses into mitochondria through a well-characterized channel trio consisting of the inositol 1,4,5-trisphosphate receptor 3 on the reticular side, glucose-regulated protein 75 as the cytosolic linker, and voltage-dependent anion channel 1 on the mitochondrial outer membrane.

Using co-immunoprecipitation, proximity ligation assays and colocalization microscopy, the researchers showed that TMEM232 physically associates with this IP3R3-GRP75-VDAC1 complex and, critically, promotes its assembly. The functional consequence was measured directly with calcium-sensitive fluorescent dyes: Mag-Fluo-4 reported a drop in calcium stored within the endoplasmic reticulum, while Rhod-2 recorded a corresponding surge of calcium accumulating inside mitochondria. In other words, when TMEM232 is abundant, the calcium bridge between the two organelles runs wide open, draining the reticulum and flooding the mitochondria.

That calcium imbalance triggered a damaging cascade. Depletion of reticular calcium is a canonical activator of endoplasmic reticulum stress, and the team documented activation of the classic unfolded protein response sensors, including PERK and its downstream phosphorylation of eukaryotic translation initiation factor 2α, alongside other ER stress markers. Meanwhile, mitochondrial calcium overload stoked the electron transport chain into leaking electrons, which the researchers detected as elevated mitochondrial superoxide and increased total intracellular reactive oxygen species using mitochondrial superoxide indicators and H2DCFDA-based assays. Oxidative stress of this kind is well known to destabilize junctional proteins and disrupt cytoskeletal anchoring, providing a plausible route from organelle stress to broken tight junctions.

The causal chain was tested by interrupting it at multiple points. When the researchers disrupted the IP3R3-GRP75-VDAC1 complex, or when they relieved endoplasmic reticulum stress with the chemical chaperone 4-phenylbutyric acid, the tight junction damage caused by TMEM232 overexpression was effectively rescued. These rescue experiments matter because they show that the calcium-transfer complex and the resulting ER stress are not incidental byproducts but necessary links between TMEM232 and barrier failure. The team also employed tools such as thapsigargin and 2-aminoethoxydiphenyl borate to manipulate calcium handling, reinforcing the picture of a TMEM232-driven calcium leak as the upstream event.

The in vivo evidence strengthened the case further. In a mouse model of atopic dermatitis induced by the contact sensitizer 2,4-dinitrochlorobenzene, animals genetically engineered to lack Tmem232 developed milder dermatitis than wild-type controls. Importantly, a more translationally oriented approach — applying small interfering RNA topically to knock down Tmem232 in the skin — also ameliorated the AD-like disease. Together with the cell-based findings, these results position TMEM232 as a genuine driver of barrier pathology rather than a passive biomarker, and they suggest that silencing it at the skin surface could have therapeutic value.

The study reframes atopic dermatitis barrier dysfunction as an organelle-level disease. Rather than viewing the leaky epidermis purely as a consequence of failed structural proteins or inflammatory damage, the work inserts MAMs — and the calcium flux they regulate — into the causal pathway, connecting a genetic risk factor to ER stress, mitochondrial oxidative damage, and ultimately the disintegration of tight junctions. It also raises questions for future research: whether TMEM232 variants differ in their calcium-regulating activity between individuals, whether MAM-targeted interventions could complement existing biologics and barrier repair therapies, and whether similar mechanisms operate in other barrier tissues such as the gut and airways, where tight junction failure underlies distinct chronic diseases.

For patients, the practical hope is a new class of targets. Current atopic dermatitis treatments broadly suppress inflammation or repair lipids in the stratum corneum, but a therapy aimed at TMEM232 or its calcium-channel partners would intervene at a more fundamental point in the disease mechanism. Topical siRNA delivery, as validated in the mouse model, offers a plausible development route, and small molecules that stabilize ER calcium stores or dampen mitochondrial oxidative stress represent alternative strategies. The researchers conclude that targeting TMEM232 represents a potential therapeutic strategy for atopic dermatitis, and their demonstration that the pathway is rescueable in both cells and living animals provides the proof-of-concept needed to pursue it.

Subject of Research: The role of TMEM232 in ER-mitochondrial calcium transfer and tight junction dysfunction in atopic dermatitis

Article Title: TMEM232 associates with the IP3R3-GRP75-VDAC1 complex to enhance ER-Mitochondrial calcium transfer and impair tight junctions in atopic dermatitis

Article References: Chen, L., Wang, Y., He, Z., Xu, J., Zhang, Y., Wang, Z., Wang, M., Li, C., Cai, X., & Xiao, F. (2026). TMEM232 associates with the IP3R3-GRP75-VDAC1 complex to enhance ER-Mitochondrial calcium transfer and impair tight junctions in atopic dermatitis. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08932-2

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08932-2

Keywords: atopic dermatitis, TMEM232, tight junctions, mitochondria-associated ER membranes, calcium signaling, endoplasmic reticulum stress, IP3R3-GRP75-VDAC1 complex, skin barrier, keratinocytes, oxidative stress, siRNA, Journal of Translational Medicine

The delivery strategy is disarmingly simple. Preformed high-fidelity Cas9-ribonucleoproteins are mixed with a molar excess of the peptide in a buffer containing the crowding reagent PEG-PVA, which encourages complexation. The cationic peptide electrostatically binds the negatively charged guide RNA within the RNP, forming nanoparticles that cells take up through a route involving class A scavenger receptors. Ornithine residues built into the peptide’s sequence shield it from degradation by serum proteases. Gel shift assays confirmed that even the lowest peptide ratios immobilized the RNPs, and transmission electron microscopy revealed substantially enlarged nanoparticles at a 1:100 molar ratio compared with RNPs alone. Confocal microscopy using red-fluorescent Cas9 showed punctate intracellular signal within one hour, consistent with endosomal entrapment, followed by diffuse cytoplasmic and nuclear fluorescence by 24 hours.

Optimization began with a titration of Cas9-RNP concentrations, from 10 to 17 nanomolar, against peptide molar ratios spanning 1:50 to 1:200. Higher doses drove editing rates up to roughly 75 percent in fibroblasts and 70 percent in keratinocytes but devastated viability, dropping to as low as 9 percent at the most aggressive condition in keratinocytes. The sweet spot emerged at 10 nanomolar Cas9-RNP with a 1:100 peptide ratio, which preserved about 90 percent viability in fibroblasts and 86 percent in keratinocytes, compared with 74 and 66 percent respectively for electroporation. Although electroporation edited a larger fraction of surviving cells, the superior survival of peptide-treated cultures yielded comparable total numbers of edited cells.

Gene expression profiling added a biological argument for gentleness. Using droplet digital PCR 24 hours after editing, the team found that electroporation upregulated CDKN1A, a marker of cell cycle arrest, while suppressing BUB1, a master regulator of mitotic spindle assembly, in fibroblasts. Most strikingly, electroporated fibroblasts showed elevated TGFB1 expression, a hallmark of fibroblast activation and differentiation into myofibroblasts. Because TGF-beta1 is a major driver of fibrosis and squamous cell carcinoma progression in recessive dystrophic epidermolysis bullosa, seeding engineered skin grafts with electrically stressed, myofibroblast-prone cells could undermine clinical outcomes. Peptide delivery perturbed these pathways to a noticeably smaller extent.

A single amino acid proved consequential. Adding one C-terminal lysine to PepFect14 produced PF14-K, which delivered a consistent, roughly 10 percent improvement in editing across three guide RNAs compared with the parent peptide. Structural analysis offered a possible explanation: circular dichroism spectroscopy showed slightly elevated alpha-helical content in PF14-K, and dynamic light scattering revealed larger RNP-peptide particles, around 130 nanometers versus 90 nanometers for the original peptide, with similar polydispersity. The longer, positively charged lysine side chain may strengthen interaction with the RNP’s negatively charged surface. By contrast, a variant in which the N-terminal stearic acid was replaced by oleic acid lost activity across all tested guides, consistent with the idea that the saturated fatty acid’s straight tail promotes tight hydrophobic packing that stabilizes the nanoparticles, while oleic acid’s double-bond kink disrupts it.

Solvent and serum conditions also mattered. Dissolving the peptide in 90 percent ethanol with 10 percent DMSO, rather than water, yielded subtle but reproducible editing gains, echoing prior observations that this solvent combination better solubilizes both the charged and hydrophobic faces of amphipathic peptides and discourages formation of large micellar aggregates. Despite the peptide’s ornithine-stabilized serum resistance, transfection in serum-free medium improved editing by 15 to 20 percent, with two of three guide RNAs reaching statistical significance. Under fully optimized conditions, PF14-K routinely achieved 70 to 75 percent editing in primary fibroblasts and 50 to 60 percent in keratinocytes, at viability exceeding 80 to 90 percent, versus roughly 70 percent for electroporated cultures.

The therapeutic applications were tested directly in patient-derived cells. For recessive dystrophic epidermolysis bullosa, which stems from COL7A1 mutations, the team used dual Cas9-RNPs to excise mutation-bearing exons and restore the reading frame. In patient keratinocytes carrying a heterozygous single-base deletion within exon 31, PF14-K achieved deletion efficiencies up to 58.4 percent by Nanopore amplicon sequencing, and up to 67.8 percent in patient fibroblasts. Electroporation reached 85 to 90 percent but at the cost of viability averaging just 50.7 percent in patient fibroblasts and 63.3 percent in patient keratinocytes, cells already fragile and slow-growing. Flow cytometry confirmed restoration of COL7 protein in up to 61 percent of peptide-edited keratinocytes. Because 20 to 35 percent editing is considered sufficient for therapeutic benefit in epidermolysis bullosa, the peptide-edited cell populations, being both sufficiently corrected and substantially healthier, could represent a superior graft product.

The most technically demanding result was precise homology-directed repair. Using short single-stranded repair templates co-delivered with the RNPs, the researchers corrected a prevalent nonsense mutation in LAMB3, c.1903C>T, which underlies junctional epidermolysis bullosa. In primary patient keratinocytes, the baseline 3:1:100 molar ratio of template to RNP to peptide achieved 14 percent mutation correction. Raising the peptide ratio to 3:1:150 lifted silent marker incorporation to 48 percent, and adding small-molecule inhibitors of the DNA repair enzymes polymerase theta and DNA-PK pushed precise correction to 37 percent by CRISPResso2 analysis, with electroporation reaching up to 51 percent, or 65 percent with inhibitors, but again with lower viability. Notably, the authors state this is the first demonstration of HDR-mediated repair of a pathogenic mutation, or exon skipping, in primary human cells using a non-viral cell-penetrating peptide strategy; earlier peptide HDR efforts were confined to transfection-permissible cell lines, reporter constructs, or safe-harbor loci.

Caveats remain. The AZD7648 DNA-PK inhibitor used in the dual-inhibition scheme has been linked to large-scale genomic alterations in other contexts, so genome-wide off-target assessment will be essential, even though pairing it with a polymerase theta inhibitor has been shown to mitigate genotoxicity. The gene expression analysis covered only a small panel of markers, and three-dimensional skin models will be needed to test whether PF14-K can deliver editors into intact tissue; prior work showed the parent peptide can deliver miRNA via subcutaneous injection in mice, an encouraging precedent. Still, the mix-and-incubate approach requires nothing more exotic than a commercially synthesized peptide and preformed RNPs, sidestepping the packaging limits and insertional risks of viral vectors, the specialized hardware and cytotoxicity of electroporation, and the microfluidics and mRNA-manufacturing burden of lipid nanoparticles. With base and prime editors increasingly bypassing the need for DNA templates altogether, the researchers argue that PF14-K and its successors could extend non-viral genome editing to a broad range of hard-to-transfect primary cells, and perhaps one day, directly to the skin itself.

Subject of Research: Non-viral CRISPR/Cas9 delivery into primary human skin cells using a PepFect14 cell-penetrating peptide analog for genome editing and repair of epidermolysis bullosa mutations

Article Title: A PepFect14 analog improves non‐viral CRISPR delivery in primary human cells to facilitate genome editing and repair

Article References: du Rand, A., Masterson, C., Verdon, D., Siow, A., Loef, E., Dunbar, R., Kingston, R., Harris, P., & Sheppard, H. (2026). A PepFect14 analog improves non‐viral CRISPR delivery in primary human cells to facilitate genome editing and repair. Bioengineering & Translational Medicine, Article e70172. https://doi.org/10.1002/btm2.70172

Image Credits: AI Generated

DOI: 10.1002/btm2.70172

Keywords: CRISPR, Cas9 ribonucleoproteins, cell-penetrating peptides, PepFect14, PF14-K, epidermolysis bullosa, COL7A1, LAMB3, homology-directed repair, gene therapy, keratinocytes, non-viral delivery