The researchers traced part of the mechanism to interactions between astrocytes and neurons. The experimental evidence is causal within the tested mouse and cell systems, although the postmortem observations alone cannot establish when or why ABCA1 expression becomes elevated in human disease. Mechanistic experiments located ABCA1 in neuronal lysosomes, where it facilitated cholesterol import.

The researchers further reported that ABCA1-mediated lysosomal cholesterol accumulation impeded autophagy by activating the lysosomal cholesterol sensor GPR155. These results link a specific route of intracellular cholesterol handling to the accumulation of pathological α-synuclein and cell death, rather than associating elevated ABCA1 merely with already damaged tissue. The protective effects were then tested in the PFF mouse model of Parkinson’s disease.

Genetic silencing of Abca1 in dopaminergic neurons attenuated neurodegeneration and disease-related pathology, while silencing Abca1 in astrocytes reduced excessive cholesterol efflux and lessened neurodegeneration and behavioral deficits. The researchers also identified magnesium citrate as an ABCA1 inhibitor and reported that treatment reduced dopaminergic neuronal loss in PFF mice. These findings support ABCA1 inhibition as a possible disease-modifying strategy, but the evidence comes from experimental models.

Subject of Research: ABCA1-dependent cholesterol trafficking as a mechanism of neurodegeneration in Parkinson’s disease

Article Title: Dysregulated cholesterol trafficking through ABCA1 drives neurodegeneration in Parkinson’s disease

Article References: Ma, F.-X., Zhao, X.-X., Wang, X.-X., Fang, S.-Y., Xu, S.-H., Wang, M., Liu, Y.-X., Wang, C., Wang, Q.-L., Lu, M., & Cao, L. (2026). Dysregulated cholesterol trafficking through ABCA1 drives neurodegeneration in Parkinson’s disease. Nature Neuroscience. https://doi.org/10.1038/s41593-026-02487-7

Image Credits: AI Generated

DOI: 10.1038/s41593-026-02487-7

Keywords: ABCA1, Parkinson’s disease, cholesterol trafficking, astrocytes, dopaminergic neurons, lysosomes, autophagy, α-synuclein, magnesium citrate, mouse models, Dysregulated, cholesterol

Chronic kidney disease becomes steadily more common with age, and one of its quiet drivers is the accumulation of senescent cells, particularly in the proximal tubular epithelial cells, or TECs. These cells perform the demanding job of reabsorbing filtered substances and are essential to kidney function. Senescence can initially serve a protective purpose, halting cells that have suffered DNA damage before they turn cancerous. But when senescent cells linger, they secrete inflammatory and profibrotic signaling molecules that injure surrounding tissue, promote scarring and gradually erode organ performance. Understanding what tips a stressed TEC into persistent senescence has therefore become a central question in kidney aging research.

The Amsterdam team focused their attention on lysosomes, the cellular compartments that break down and recycle biological material. Lysosomal function depends on a specialized set of membrane phospholipids, most notably bis(monoacylglycerol)phosphate, or BMP, a lipid that helps organize the internal architecture of the lysosome and supports its digestive activity. Earlier studies had reported that BMP abundance rises during aging and in kidney disease, but the lipid’s exact contribution to senescence remained murky. That gap led the researchers to PLA2G15, a phospholipase enzyme resident in the lysosome that participates in BMP breakdown and broader lipid metabolism.

The first evidence came from a comparison of young and aged mouse kidneys. In older animals, the researchers observed greater accumulation of BMP lipids alongside increased expression of the Pla2g15 gene, together with molecular signatures of cellular senescence. While these observations were associative rather than causal, they established that lysosomal lipid metabolism shifts in parallel with kidney aging, setting the stage for a more direct experimental test of whether the enzyme actually influences the senescence program.

To probe that relationship, the team used CRISPR/Cas9 gene editing to disrupt Pla2g15 in immortalized mouse proximal tubular epithelial cells. Two independently generated knockout lines showed sharply reduced PLA2G15 protein levels and enzyme activity, giving the researchers a clean system in which to examine the consequences of losing the enzyme. Lipidomic profiling of these cells revealed widespread remodeling of phospholipid metabolism. Total BMP abundance rose, as did levels of its precursor, lysophosphatidylglycerol, but the composition of the BMP pool changed in a more telling way: several long-chain unsaturated BMP species were actually reduced. In other words, PLA2G15 does not simply control how much BMP is present; it shapes which specific molecular species of the lipid dominate the lysosomal membrane.

The decisive experiment came when the researchers exposed both normal and Pla2g15-deficient kidney cells to doxorubicin, a chemotherapy drug that is widely used in the laboratory to inflict DNA damage and trigger senescence. In ordinary cells, doxorubicin raised levels of the senescence-associated protein P21 and forced cells into a pronounced arrest at the G2/M checkpoint of the cell cycle. Cells lacking Pla2g15 responded very differently: P21 expression was significantly lower and G2/M arrest was reduced, indicating that the senescence response had been substantially attenuated. The knockout cells also showed improved mitochondrial and lysosomal health compared with their normal counterparts under the same stress.

Follow-up lipidomics sharpened the picture. Doxorubicin-treated normal cells accumulated several long-chain polyunsaturated BMP species, including BMP42:6, BMP42:8 and BMP44:8, while Pla2g15-deficient cells shifted toward shorter BMP species and away from the long-chain unsaturated forms. This species-specific pattern suggests that the buildup of particular long-chain BMP lipids is not merely a byproduct of senescence but may be mechanistically tied to its development. As the authors state in the paper, “Here, we identify a critical role for lysosomal phospholipid metabolism in senescent TECs,” framing the lipid remodeling as an active participant in the senescent state rather than passive chemistry.

To understand how a lysosomal enzyme could reach into other cellular compartments, the researchers performed proteomic analysis, quantifying more than 3,400 proteins. The knockout cells showed increased abundance of proteins tied to mitochondrial metabolic pathways, including components of NAD+ metabolism and fatty acid oxidation. Among the upregulated proteins were NAMPT and NMNAT3, both involved in generating and recycling NAD+, a molecule central to cellular energy metabolism, and CPT2, an enzyme that shuttles fatty acids into mitochondrial oxidation. The proteomic data also revealed reduced levels of proteins driving cell-cycle progression and ribosomal processes, along with increased expression of LAMP1, a lysosomal membrane protein. “Our findings point to PLA2G15 as a critical regulator of senescence through its role in lysosomal lipid remodelling and mitochondrial metabolism,” the authors conclude. The team is careful to note, however, that direct measurements of mitochondrial metabolic function and lysosomal activity were not performed, so the proposed functional benefits still require confirmation.

The implications for chronic kidney disease are potentially significant, because impaired lipid metabolism, mitochondrial dysfunction and persistent senescence all converge in the damaged aging kidney. By naming PLA2G15 as a regulator of BMP composition and senescence-related changes, the study offers a concrete molecular handle for future interventions aimed at preserving kidney-cell health during aging. Yet the work remains firmly preclinical. The observations in aged mouse kidneys were associative, and the protective effects of Pla2g15 disruption were demonstrated only in cultured mouse cells exposed to doxorubicin, a model that does not fully reproduce natural kidney aging or chronic kidney disease in a living organism. The researchers also emphasize that pharmacological inhibition of PLA2G15 has not been tested, and it is unknown whether a drug-based approach would reproduce the effects seen with genetic deletion.

Several questions will shape the next phase of research. Genetically modified animals, alternative senescence models and direct functional measurements of mitochondria and lysosomes will be needed to establish the biological mechanisms and therapeutic relevance of targeting PLA2G15. Because the mouse experiments involved only males, future studies must also determine whether the same lipid-senescence relationship holds in females. Even with those caveats, the study adds an intriguing new dimension to the biology of aging: the idea that the molecular species of lipids lining the lysosome, not just their total amount, help determine whether a stressed kidney cell quietly exits the cell cycle or locks itself into a damaging senescent state. If that relationship holds up in living animals, selectively modifying BMP metabolism could open a new route to slowing the cellular decline that underlies age-related kidney disease.

Subject of Research: The role of the lysosomal enzyme PLA2G15 and BMP phospholipid metabolism in cellular senescence of kidney tubular cells

Article Title: Targeting PLA2G15 reduces senescence and alters lipid metabolism in kidney cells

Article References: Targeting PLA2G15 reduces senescence and alters lipid metabolism in kidney cells. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: PLA2G15, cellular senescence, kidney aging, lysosomes, BMP phospholipids, chronic kidney disease, mitochondria, lipid metabolism, tubular epithelial cells, CRISPR, NAD+ metabolism, doxorubicin

Writing in Frontiers in Aging, Kayo Moreira Bagri, Morgana Teixeira Lima Castelo-Branco, and Claudia Mermelstein describe a primary cell culture model in which skeletal muscle senescence can be induced, measured, and—crucially—partially reversed. The system relies on embryonic chick muscle cells, a classic preparation in developmental biology that has fallen somewhat out of fashion in the era of immortalized mouse cell lines. The authors argue that this old workhorse still outperforms its modern rivals in one decisive respect: the chick myogenic program is highly autonomous, differentiating robustly without serum withdrawal, and chick myotubes can form with hundreds of nuclei, whereas myotubes from commonly used lines such as C2C12 typically contain only about a dozen. That sheer cellular scale makes the chick system uniquely informative for studying multinucleated muscle fibers under stress.

The cultures also contain roughly 20 percent fibroblasts alongside the 80 percent myoblast population, a ratio the team verified by triple-labeling cells with DAPI, the muscle-specific marker desmin, and the fibroblast marker flotillin-2. This mixed composition is not a nuisance but a feature. Fibroblasts secrete collagen, laminin, fibronectin, and a host of growth factors and cytokines, so their presence mimics the connective tissue environment of real muscle. In effect, the dish recapitulates the two principal cell types of living muscle tissue, giving the model a physiological realism that pure myoblast lines cannot match.

To trigger senescence, the researchers turned to cytosine arabinoside, or Ara-C, a synthetic antimetabolite and structural analogue of cytidine. Ara-C is an S-phase-specific drug that inhibits DNA synthesis and blocks cell proliferation, and at low doses it has been shown to interfere with differentiation. The protocol is elegantly simple: primary cultures grown for 96 hours are treated with just 150 nanomolar Ara-C for 72 hours, then trypsinized and replated, washed, and maintained in drug-free medium over a total of roughly 15 days. An MTT viability assay confirmed that this low concentration did not significantly compromise cell survival, meaning the phenotype the team observed reflects genuine senescence rather than simple toxicity.

The evidence that senescence was actually induced is extensive. Treated cultures showed a more than fourfold increase in beta-galactosidase expression, the gold-standard marker of cellular senescence, with staining appearing in mononucleated myoblasts, fibroblasts, and multinucleated myotubes alike—indicating the phenotype penetrates all three major cell types in the dish. Western blot analysis revealed increased expression of p53 and p21, the canonical cell-cycle-arrest proteins, while immunolabeling for phospho-histone H3, a marker of active cell division, dropped prominently. Live-cell imaging with the fluorescent probe H2DCFDA documented a remarkable surge in reactive oxygen species production, and staining with acridine orange and LysoTracker revealed a striking expansion of acidic organelles and lysosomal compartments, with intense labeling in senescent myotubes. Sudan Black B staining, which detects lipofuscin accumulation, confirmed the phenotype under both bright-field and far-red fluorescence microscopy.

Morphology told its own story. Senescent cultures showed shrunken myotubes with reduced diameter and fewer nuclei, a decreased myoblast fusion index, and a drop in desmin protein expression—all signatures of impaired muscle differentiation and fiber atrophy that echo earlier findings that muscle atrophy accelerates during senescence. Meanwhile, fibroblasts swelled into giant cells with increased size, elevated numbers of nuclei including binucleated forms, and a rise in actin-containing stress fibers visible with phalloidin and anti-alpha-tubulin labeling. The team quantified these changes across fifty randomly chosen microscopic fields from three independent experiments, applying false discovery rate correction to the image-based counts.

Perhaps the most consequential finding concerns the senescence-associated secretory phenotype, or SASP—the inflammatory cocktail that senescent cells release into their surroundings. Using ELISA on conditioned media, normalized to total cell number per well, the researchers measured increased secretion of interleukin-6, tumor necrosis factor alpha, and transforming growth factor beta. Each of these molecules carries weight in muscle biology: TGF-beta1 is a major regulator of senescence capable of activating the p53 pathway through oxidative stress, and IL-6 has been shown to induce skeletal muscle atrophy. Notably, IL-6 can amplify senescence in the very cells that produce it through an autocrine loop, suggesting the secretory phenotype may actively entrench the senescent state once established.

The authors are candid about a conceptual wrinkle their data expose: the difficulty of distinguishing cellular senescence from cellular stress. The Ara-C-induced phenotype included increased ROS, SASP factors, and heightened lysosomal activity—all markers of stress—yet Ara-C is also a well-known inducer of cell cycle arrest, the hallmark of senescence. This convergence supports the view, increasingly voiced in the field, that senescence should be understood as a general cellular stress response program rather than strictly as a barrier to unlimited rounds of cell division. In muscle cells, the two programs appear deeply intertwined, and the new model provides a controlled setting in which to disentangle them.

The mechanistic payoff came when the team probed the fibroblast growth factor signaling pathway, selected for its previously described roles in regulating senescence and aging in skeletal muscle—and for the suggestive appearance of giant fibroblasts in their senescent cultures. Treating cells with SU-5402, an inhibitor of the fibroblast growth factor receptor, partially recovered the Ara-C-induced senescent phenotype, as judged by increased muscle fiber formation. The result implies that FGF signaling participates in establishing the senescent state in chick muscle cells and that blocking it can, at least in part, prevent muscle cell senescence. Further work will be needed to dissect the molecular mechanisms of FGFR signaling during the process, but the finding immediately nominates a druggable target.

The model’s advantages are practical as well as biological: it requires only a single drug to achieve muscle senescence within 15 days, and it preserves the muscle-plus-fibroblast composition of living tissue. Its main limitation, the authors acknowledge, is the absence of a head-to-head comparison with other known senescence inducers such as ionizing radiation, doxorubicin, or hydrogen peroxide—experiments they plan to pursue. Even so, the system stands ready as a tool for investigating the molecules and signaling pathways behind muscle degeneration in aging, sarcopenia, disuse, and muscular dystrophies, and for screening new therapeutic interventions aimed at ameliorating senescence-associated conditions. For a problem that has long been studied in fragments, the dish now holds the whole picture.

Subject of Research: A new in vitro chick muscle cell culture model induces skeletal muscle cell senescence with low-dose cytosine arabinoside and shows that FGFR inhibition partially recovers the senescent phenotype.

Article Title: Unraveling skeletal muscle senescence in an in vitro cell culture model

Article References: Bagri, K. M., Lima Castelo-Branco, M. T., & Mermelstein, C. (2026). Unraveling skeletal muscle senescence in an in vitro cell culture model. Frontiers in Aging, 7, Article 1866906. https://doi.org/10.3389/fragi.2026.1866906

Image Credits: AI Generated

DOI: 10.3389/fragi.2026.1866906

Keywords: cellular senescence, skeletal muscle, sarcopenia, cytosine arabinoside, p53, p21, SASP, reactive oxygen species, lysosomes, fibroblast growth factor receptor, desmin, chick embryo culture

The research, published in Frontiers in Aging, analyzed autophagy flux in primary skin fibroblasts from apparently healthy male donors aged 20, 38, 74, and 96 years. Fibroblasts are a widely adopted aging cell system because they retain the cellular and molecular signatures of their donors: the skin is directly exposed to ultraviolet radiation, pollutants, and genotoxic agents over a lifetime, so fibroblasts from older individuals carry the in vivo wear of their chronological age into a controlled culture dish. By comparing cells across this age range, the team could trace how each phase of autophagy changes as human cells grow old.

Autophagy is a multi-step assembly line. Under starvation signaling, inhibition of mTOR activates the ULK1/2 kinase complex, which nucleates a phagophore. Two ubiquitin-like conjugation systems, ATG12/ATG5/ATG16L and LC3, elongate and seal the membrane into an autophagosome. The SNARE protein syntaxin 17 is then recruited to mature autophagosomes, licensing their fusion with lysosomes to form autolysosomes, where hydrolases degrade the luminal content. Because each step can fail independently, measuring flux across the whole pathway is essential for designing therapies that reactivate the specific phase that is actually broken.

The master switch of this pathway is transcription factor EB, or TFEB, which controls the expression of autophagy and lysosomal genes. Under nutrient-rich conditions, phosphorylated TFEB sits inert in the cytoplasm; during stress, calcineurin-mediated dephosphorylation drives it into the nucleus. When the researchers examined fibroblasts by confocal microscopy, TFEB activation looked surprisingly intact, even enhanced, in aging. Starvation pushed TFEB into the nuclei of cells from all donors, and the 96-year-old fibroblasts showed the strongest nuclear signal, even accumulating TFEB in the nucleus under normal, non-starved conditions.

That nuclear buildup translated into transcription. Quantitative RT-PCR showed that the TFEB target genes LAMP1, SQSTM1, and MAP1LC3B responded to starvation in cells from all ages, with SQSTM1 and MAP1LC3B transcripts rising markedly higher in the 96-year-old fibroblasts than in the 20-year-old controls. The authors interpret this premature nuclear accumulation of TFEB in old cells as a compensatory alarm: a signaling mechanism mobilized to counteract the impaired flux and lysosomal dysfunction discovered downstream. Alternative explanations, such as altered mTORC1- or ERK-mediated phosphorylation trapping TFEB in the nucleus, or an age-dependent decline in CRM1-mediated nuclear export, remain to be tested.

Autophagosome formation also held up. Treating cells with chloroquine, which blocks autophagosome-lysosome fusion, revealed LC3-positive puncta in fibroblasts from all donors, and Western blotting of the LC3-I to LC3-II conversion showed that autophagosomes formed with similar efficiency across the age spectrum. Flow cytometry with Cyto-ID dye even found a greater accumulation of autophagic vacuoles in the older cultures, implying that the early machinery operates at least as vigorously in old cells, likely as an active coping mechanism against age-related cellular stress.

The picture changed when the team probed the end of the line. The selective autophagy receptor p62, which is itself degraded in autolysosomes, normally accumulates when flux is blocked. Yet when fibroblasts were starved and treated with the lysosomal inhibitors E64D and pepstatin A, young and middle-aged cells accumulated LC3-II and p62 robustly, while cells from the 74- and 96-year-old donors showed no significant accumulation at all. The lysosome-dependent turnover of the canonical autophagy markers had decayed with age, a result the authors confirmed with bafilomycin A1, an inhibitor of the V-ATPase pump that arrests autophagosome-lysosome fusion.

Confocal colocalization assays pinpointed where the assembly line jams. In young fibroblasts, starvation significantly increased the overlap between LC3 and syntaxin 17, indicating enhanced autophagosome maturation, with Pearson correlation coefficients rising from 0.35 to 0.63. In old fibroblasts, starvation produced no such increase, with coefficients of 0.42 versus 0.39. Similarly, the colocalization of LC3 with the lysosomal membrane protein LAMP1, an indicator of autophagosome-lysosome fusion, rose sharply in young cells under starvation but only marginally in aged cells. The final two steps of autophagy, maturation and fusion, had quietly failed.

The culprit appears to be the lysosome itself. LysoBrite staining revealed that fibroblasts from the oldest donor carried a significantly increased abundance of lysosomes, and starvation enlarged lysosomes in all cultures, with the most expanded organelles in the 74- and 96-year-old cells. These enlarged lysosomes were unresponsive to autophagy induction: the 96-year-old fibroblasts showed the greatest basal lysosomal activity but failed to activate it further under starvation, unlike cells from younger donors. Consistent with overloaded, dysfunctional organelles, lipofuscin, the non-degradable autofluorescent pigment formed by incomplete lysosomal digestion, accumulated heavily in the oldest fibroblasts, and starvation could clear it in young cells but not in old ones.

The findings carry a clear therapeutic message. Rather than simply switching autophagy on, interventions in aging may need to target the final steps of the pathway: TFEB activators to stimulate lysosomal biogenesis through the CLEAR gene network, mTOR inhibitors such as rapamycin to restore flux, and lysosomal acidification enhancers, from small molecules to acidic nanoparticles, to boost enzymatic activity. The authors acknowledge that a single donor per age group limits generalizability, and future studies with additional donors will be needed to confirm whether late-stage autophagy impairment is a universal hallmark of fibroblast aging. But the core conclusion stands: in old human cells, the recycling plant’s opening hours are fine; it is the crusher at the end of the line that has broken down.

Subject of Research: Impaired autophagy flux and lysosome dysfunction in aged human fibroblasts

Article Title: Impaired autophagy and lysosome function in human fibroblast aging

Article References: Unzueta-Mendoza, J. J., García-Aguirre, I., Königsberg, M., Arrieta-Cruz, I., Lizcano-Meneses, S., Magaña, J. J., Alarcón-Aguilar, A., & Cisneros, B. (2026). Impaired autophagy and lysosome function in human fibroblast aging. Frontiers in Aging, 7, Article 1971981. https://doi.org/10.3389/fragi.2026.1971981

Image Credits: AI Generated

DOI: 10.3389/fragi.2026.1971981

Keywords: autophagy, lysosomes, TFEB, fibroblast aging, lipofuscin, autophagosome-lysosome fusion, LC3, p62, cellular recycling, aging biology, Impaired, lysosome

The authors frame the problem as a fundamental dialectic. Synthetic probes deliver sensitivity, molecular specificity, and compatibility with advanced microscopy, allowing ions, metabolites, and reactive species to be visualized in real time with subcellular resolution. Yet the very features that make probes bright and targetable, including high-affinity binding, lipophilic partitioning, organelle trapping, and excited-state reactivity, constitute measurement back-action. Label-free imaging, which draws contrast from intrinsic properties such as autofluorescence, refractive index, and molecular vibrations, emerged partly as a response to this paradox, but it carries its own burden of spectral congestion and mechanistic ambiguity.

Endogenous fluorophores occupy a conceptually privileged position in this debate. Aromatic amino acids such as tryptophan and tyrosine absorb in the ultraviolet and emit fluorescence whose properties are modulated by protein folding, binding interactions, and local polarity. Metabolites of the kynurenine pathway extend this landscape into the near-visible UV-A range, while the redox cofactors NAD(P)H and flavins provide spatially resolved metabolic readouts whose optical redox ratio and fluorescence lifetime report on cellular state. Because these molecules are constitutive components of biochemistry, their optical properties are a consequence of function rather than a precondition for it, placing native fluorescence at a lower bound on perturbation against which every exogenous labeling strategy must be benchmarked.

That benchmark is not a gold standard. NAD(P)H autofluorescence cannot distinguish NADH from NADPH contributions, and fluorescence lifetimes shift with pH, binding partners, and local dielectric properties, so the same sensitivity that encodes microenvironmental information also produces non-specificity. Kynurenine pathway activity varies with inflammation, immune activation, aging, and disease, meaning changes in fluorescence may reflect metabolite concentrations rather than the biological process under investigation. The authors conclude that label-free imaging is not a replacement for probes but a diagnostic, defining a lower bound on perturbation and an upper bound on interpretability challenges.

Nowhere is probe back-action more transparent than in calcium imaging. Classical indicators such as quin-2, fura-2, and indo-1 are derivatives of high-affinity chelator chemistry that can reach millimolar intracellular concentrations, directly competing with every endogenous calcium-binding protein for the same pool of free ions. To sense calcium with sufficient signal-to-noise, the indicator must bind it; to bind it competitively, it must buffer it. There is no regime in which a high-affinity chelator reports calcium without reshaping the calcium landscape it reports on, making the indicator both the ruler and a force applied to the object being measured.

Experiments in Xenopus oocytes demonstrated that buffer kinetics, not merely affinity, reshape signaling patterns. The slow buffer EGTA accelerated calcium signals and fragmented propagating waves into localized puff-like events, while the fast buffer BAPTA slowed responses and promoted spatially uniform signals. These differential effects arose through modulation of calcium-induced calcium release feedback rather than generic calcium clearance, and signals evoked by influx through voltage-gated channels were substantially less affected. The implication is profound: the probe actively participates in the decision-making machinery of calcium signaling, and spatial microdomains encoding biological decisions can be reclassified by the presence of the indicator itself.

Organelle-targeted dyes present a different but equally fundamental problem. Lipophilic cations accumulate in mitochondria because the negative inner membrane potential pulls them in, yet at imaging concentrations those same cations can depolarize the membrane, impair electron transport, and stimulate uncoupled respiration. Weak-base amines accumulate in lysosomes because acidic compartments protonate and trap them, but in doing so they titrate the very proton gradient that defines lysosomal identity, raising intralysosomal pH and altering organelle morphology and enzymatic activity. The concept of dark toxicity extends this further: penetrating cations can facilitate proton transport, react with respiratory-chain redox centers, and inhibit metabolic enzymes entirely in the absence of light, meaning their biological footprint precedes any imaging session. The authors propose that the boundary between imaging agent and pharmacological effector should be defined empirically, through organelle morphology, functional parameters, and viability assessed over the full experimental duration, not by chemical structure alone.

Phototoxicity, meanwhile, is not merely a dosimetry problem but a mechanistically predictable consequence of excited-state chemistry. Every fluorophore that undergoes intersystem crossing to a triplet state is transiently a photosensitizer, and every triplet state that encounters molecular oxygen is a potential source of singlet oxygen and downstream reactive oxygen species. Quantitatively, singlet oxygen quantum yields span orders of magnitude, from less than 0.01 for silicon-rhodamine dyes in their cell-permeable form to roughly 0.76 for rhodamine B in organic solvents, and halogenation can push BODIPY derivatives above 0.5, the regime of photodynamic therapy agents. Molecular rotor BODIPYs engineered for intramolecular motion suppress triplet formation and reduce phototoxicity three- to ten-fold, offering a template for next-generation probes. Yet the boundary between safe intrinsic contrast and reactive exogenous labeling is one of degree rather than kind: endogenous kynurenine metabolites are bona fide photosensitizers, and in the aging eye lens they can shift from photoprotective UV filters to mediators of protein crosslinking and cataract formation.

Middle-ground strategies redistribute rather than resolve the paradox. Chemigenetic tags such as HaloTag and SNAP-tag replace thermodynamic partitioning with covalent, genetically encoded specificity, and fluorogenic polymethine dyes deliver turn-on responses exceeding one hundred-fold with no-wash imaging. But self-labeling tags are large fusion proteins that can alter target localization, activity, and interactions, translocating the observer effect from dye chemistry to fusion biology. Bioorthogonal fluorogenic chemistry, including tetrazine-trans-cyclooctene cycloadditions, reduces the concentration of unbound non-specifically localized dye, but metabolic handle incorporation competes with endogenous biosynthetic pathways and can trigger stress responses. Stimulated Raman scattering microscopy pushes further toward minimal perturbation by detecting isotope-enriched amino acids and alkynyl vibrational tags that preserve native biochemical behavior, though it remains constrained by instrumental complexity, moderate sensitivity, and the photothermal effects of high-intensity near-infrared irradiation.

On the quantitative side, ratiometric imaging and fluorescence lifetime imaging microscopy each correct specific confounds while introducing new ones. FLIM is largely independent of fluorophore concentration and can separate free from protein-bound NADH and FAD, but it replaces concentration artifacts with photon-statistics artifacts, instrument response distortions, and pile-up effects that can bias lifetime estimates in ways mimicking genuine biological signals. The authors propose six design principles for zero-perturbation probes: tune affinity to the minimum required for signal fidelity, minimize the intrinsic biological activity of targeting motifs, engineer away from triplet-state formation, exploit fluorogenicity to lower effective probe dose, favor covalent over non-covalent localization, and co-optimize photophysics and biological activity in the same synthetic iteration. Their central conclusion is that measurement is never separable from intervention, and that the next frontier in biological imaging is not optical but epistemological, demanding perturbation assessment as a first-class experimental variable so that imaging data are interpreted not as a picture of the cell, but as a picture of the cell as perturbed by the act of looking at it.

Subject of Research: Perturbations caused by small-molecule fluorescent probes in live-cell imaging and label-free alternatives

Article Title: To label or not to label? The paradox of small-molecule probes in biological characterization

Article References: Cuevas-Galindo, M. E., & Jiménez-Sánchez, A. (2026). To label or not to label? The paradox of small-molecule probes in biological characterization. Frontiers in Photonics, 7, Article 1858154. https://doi.org/10.3389/fphot.2026.1858154

Image Credits: AI Generated

DOI: 10.3389/fphot.2026.1858154

Keywords: fluorescent probes, observer effect, calcium imaging, autofluorescence, FLIM, phototoxicity, reactive oxygen species, mitochondria, lysosomes, bioorthogonal chemistry, HaloTag, stimulated Raman scattering

The team’s starting point was a simple epidemiological observation with profound implications. Mining a published microarray dataset of 41 human frontal cortex samples spanning ages 24 to 106, they found that CHCHD2 gene expression declines steadily and significantly across the human lifespan, with a Pearson correlation coefficient of −0.63. The drop was present in both sexes but was steeper and statistically stronger in women. Because CHCHD2 levels were already known to be reduced in the brains and even the red blood cells of Parkinson’s patients, the finding suggested that the gradual erosion of this mitochondrial protein could be one of the quiet preconditions that makes an aging brain vulnerable to Lewy body pathology in the first place.

To test whether boosting CHCHD2 could counteract aging, the researchers engineered transgenic mice expressing the human wild-type protein specifically in neurons, using the same prion protein promoter strategy they had previously used to create mice carrying the Parkinson’s-linked T61I mutation. The resulting CHCHD2-WT animals expressed roughly 2.3-fold more CHCHD2 transcript than normal littermates, and the extra protein correctly localized to the mitochondrial intermembrane space, the compartment where the endogenous protein resides. Crucially, the mice appeared entirely normal: their body weights, brain morphology, synaptic protein levels, and hippocampal electrophysiology, including long-term potentiation at the CA3-CA1 synapse, were indistinguishable from wild-type controls. Whatever the extra CHCHD2 was doing, it was not disturbing normal neuronal function.

The protective effects emerged only with age, and they were striking. At 12 months of age, the CHCHD2-WT mice had significantly more tyrosine hydroxylase-positive dopaminergic neurons in the substantia nigra than wild-type littermates, the very cell population that dies in Parkinson’s disease. By 18 months, when ordinary mice show mounting neuroinflammation, the transgenic animals displayed markedly reduced immunoreactivity for Iba1 and GFAP, the standard markers of activated microglia and astrocytes. Silver staining of the substantia nigra revealed nearly twice as many degenerating axons in age-matched mice carrying the T61I mutation compared with both wild-type and CHCHD2-WT animals, and the mutant mice also accumulated conspicuous CHCHD2-positive aggregates in the midbrain that were absent from the protected animals.

Proteomics told a similar story at the level of the entire protein complement of the cortex. In 12-month-old CHCHD2-WT mice, unbiased mass spectrometry of soluble and insoluble cortical fractions showed that the vast majority of altered proteins shifted in the direction of solubility: 169 of 240 significantly changed soluble proteins were elevated, while most of the 145 altered insoluble proteins were reduced. A contingency analysis confirmed that the ratio of insoluble to soluble proteins fell significantly, with an odds ratio of 0.381. That stands in dramatic contrast to the T61I mutant brains, which the same group had previously shown to skew in the opposite direction with an odds ratio of 23.4. In other words, wild-type CHCHD2 keeps the proteome fluid and degradable, while the mutant pushes it toward the aggregated, detergent-resistant state that defines proteinopathies.

The mechanistic heart of the paper lies in what happened when the researchers compared the two variants head to head. Pathway analysis of the cortical proteome revealed that the T61I mutation broadly suppresses the CLEAR signaling network, the transcriptional program that coordinates lysosomal biogenesis and function, alongside disruptions of mTOR and integrated stress response pathways. Lysosomal hydrolases, including cathepsin B, cathepsin L, and hexosaminidase A, were markedly depleted in mutant brains. Using a proximity-labeling interactome screen in which CHCHD2 variants were targeted to the mitochondrial intermembrane space fused to the BirA biotin ligase, the team discovered that T61I preferentially associates with cathepsins B and L. Proximity ligation assays and co-immunoprecipitation confirmed the interaction, and fluorometric enzyme assays showed that cathepsin B and L activities were significantly reduced in the forebrains of mutant mice, while cathepsin D was untouched.

Why does this matter for Parkinson’s disease? Cathepsin B and cathepsin L are the principal lysosomal enzymes that cleave alpha-synuclein within its amyloid-forming region, and genetic evidence links cathepsin B levels to Parkinson’s risk. When the researchers exposed cultured hippocampal neurons to sonicated alpha-synuclein pre-formed fibrils, cells expressing wild-type CHCHD2 cleared the pathological protein efficiently over 45 hours, whereas T61I-expressing cells retained significantly more of it. The mutant protein also accumulated in an insoluble form within isolated lysosomal fractions from mouse cortex, permeabilized lysosomal membranes as measured by galectin-3 puncta, and induced a greater than fourfold increase in swollen LAMP1-positive vacuoles. Recombinant T61I protein, unlike the wild-type protein, aggregated spontaneously at body temperature and resisted degradation after uptake into cells, suggesting that the misfolded mutant physically clogs and damages the very disposal machinery it is supposed to support.

Transmission electron microscopy provided the visual proof of the mitochondria-lysosome axis in action. In young wild-type mice, more than 86 percent of cortical mitochondria were classified as healthy, with elongated shapes and dense cristae, and every lysosome fell into the healthiest category. By 12 to 13 months of age, ordinary mice showed the expected deterioration: rounded mitochondria with sparse cristae and lysosomes stuffed with lipofuscin and lipid droplets. The CHCHD2-WT mice retained significantly healthier organelles on both counts, while the T61I animals fared worst of all, with no lysosomes classified as healthy and mitochondria showing severe ultrastructural abnormalities. The findings align with the human data: in postmortem frontal cortex from nine cortical Lewy body disease patients, soluble CHCHD2 was reduced by about 65 percent and cathepsin B by about 45 percent relative to controls, with the two proteins correlating significantly across all samples.

What emerges is a coherent model of how the aging brain loses its grip on protein quality control. CHCHD2, a mitochondrial intermembrane space protein, appears to sustain lysosomal health, possibly through the vesicular trafficking routes that shuttle material from mitochondria to lysosomes, and the T61I mutation corrupts this relationship by misfolding, aggregating, sequestering cathepsins, and rupturing lysosomal membranes. The authors are careful to note that the causal direction between mitochondrial and lysosomal abnormalities remains to be fully established, and the precise basis for the selectivity toward cathepsins B and L is still unclear. But the therapeutic implication is hard to miss: strategies that stabilize CHCHD2 expression, prevent its misfolding, or block the pathological interaction between mutant CHCHD2 and lysosomal cathepsins could simultaneously protect both organelles, addressing a root cause of the proteostatic failure that underlies Parkinson’s disease and perhaps brain aging more broadly. Preventing the age-associated decline of a single small mitochondrial protein, the study suggests, may be one of the most economical ways to keep an aging brain clean, functional, and resilient.

Subject of Research: Role of CHCHD2 in maintaining mitochondria-lysosome homeostasis during brain aging and Lewy body disease

Article Title: CHCHD2 mitigates age-associated proteostatic collapse by maintaining homeostasis of the mitochondria-lysosome axis

Article References: Kee, T. R., Masters, B. M., Tran, K. D., Jeon, H., Long, M., Xu, G., Khan, S. A., Vázquez-Rosa, E., Sridharan, P. S., Koh, Y., Fujioka, H., Chaput, D., Wang, X., Zhao, X., Pieper, A. A., Kang, D. E., & Woo, J.-A. A. (2026). CHCHD2 mitigates age-associated proteostatic collapse by maintaining homeostasis of the mitochondria-lysosome axis. Acta Neuropathologica, 152(1), Article 54. https://doi.org/10.1007/s00401-026-03093-4

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03093-4

Keywords: CHCHD2, Parkinson's disease, Lewy body disorders, mitochondria-lysosome axis, lysosomes, cathepsin B, cathepsin L, alpha-synuclein, proteostasis, neurodegeneration, brain aging, neuroinflammation

The epidermis of C. elegans depends on a collagen-rich extracellular matrix, the cuticle, to serve as its first line of defense against environmental threats, including pathogenic bacteria. This structure is not static. Like bone in vertebrates, the cuticle undergoes continuous turnover, with collagen components being deposited, organized, and degraded in a carefully balanced cycle. At the heart of that degradation process sit lysosomes, the membrane-bound organelles that act as the cell’s digestive compartments. Lysosomes must maintain an acidic internal environment, achieved by proton pumps embedded in their membranes, to activate the enzymes that break down cellular cargo. When lysosomal acidification falters, maturation stalls, degradation slows, and the turnover of structural proteins such as collagen becomes erratic, undermining the precise architecture that gives the cuticle its strength.

What has remained murky is how the nervous system, which constantly monitors the environment and coordinates the animal’s behavioral and physiological responses, might influence this lysosomal housekeeping in the skin. Neurons are known to send signals that modulate immunity and stress responses across tissues, but whether pathogens could weaponize such neuro-epidermal communication to compromise the extracellular matrix had not been demonstrated. The new study set out to answer that question using the well-established infection model in which C. elegans nematodes are exposed to Pseudomonas aeruginosa strain PA14, a virulent isolate that rapidly kills the worms and has long served as a workhorse for dissecting host-pathogen interactions.

The researchers found that when worms were exposed to PA14, their neurons responded by secreting a signaling molecule the team named NSIF-1, for Neuronal Secreted Immune Factor 1. Rather than acting locally within the nervous system, NSIF-1 left the neurons and traveled to the epidermis, where it set off a cascade of damaging effects. Genetic experiments established the neuronal origin of this factor with precision: when the researchers knocked down nsif-1 expression specifically in neurons, the downstream damage to epidermal lysosomes was prevented, confirming that the signal originates in the nervous system and acts at a distance on the skin.

Inside the epidermal cells, the consequences of NSIF-1’s arrival were striking. The infected worms showed impaired lysosomal acidification, meaning the organelles failed to acidify their interiors properly. Lysosomal maturation, the process by which these compartments acquire the full complement of degradative machinery, was disrupted, and the degradation of cargo slowed accordingly. Because lysosomes govern the turnover of cuticle collagen, this failure rippled outward: the collagen structure of the cuticle became disorganized, its density dropped, and the barrier integrity of the epidermis was compromised. In practical terms, the animal’s protective armor deteriorated at precisely the moment it faced a bacterial assault, and the worms became less resistant to infection.

The molecular linchpin of this sabotage turned out to be a transcription factor called ELT-3. Transcription factors are proteins that bind to specific DNA sequences and switch target genes on or off, and ELT-3 normally plays a constructive role in the epidermis, promoting the lysosomal activity required for extracellular matrix repair. The study demonstrated that NSIF-1 interferes with ELT-3 by inhibiting its nuclear localization, that is, by preventing the protein from entering the nucleus where it would otherwise bind DNA and activate its target genes. With ELT-3 locked out of the nucleus, the transcriptional program that supports lysosomal function and collagen homeostasis went quiet, leaving the epidermis unable to maintain or repair its collagen framework.

The evidence for this mechanism came from a series of complementary genetic approaches. Worms carrying mutations in the nsif-1 gene retained healthy lysosomal function during PA14 exposure, showed enhanced collagen density in their cuticles, and survived infection at significantly higher rates than wild-type animals. These gains were not merely correlational; the restoration of lysosomal acidification and maturation in the mutants, together with the preserved organization of collagen fibers, traced a coherent causal chain from neuronal secretion to epidermal breakdown. The convergence of survival data, imaging of cuticle architecture, and molecular readouts of lysosomal state gives the pathway a level of internal consistency that strengthens the authors’ interpretation considerably.

From an evolutionary standpoint, the strategy makes grim sense for the pathogen. Pseudomonas aeruginosa is a formidable opportunistic pathogen in humans, notorious for infections of wounds, lungs in cystic fibrosis patients, and immunocompromised individuals, and it is renowned for its arsenal of virulence tactics. Subverting host signaling rather than simply mounting a brute-force assault on tissue allows the bacterium to weaken defenses with economy. Although C. elegans is a microscopic nematode, the cellular logic at play, neurons communicating with barrier tissues, lysosomes managing extracellular matrix turnover, and transcription factors coordinating repair, has deep parallels in mammalian biology. Neuro-immune crosstalk and lysosomal regulation of the extracellular matrix are active frontiers in human research, touching on fields from wound healing to fibrosis and neurodegeneration.

The identification of NSIF-1 and ELT-3 as opposing nodes in this pathway opens concrete therapeutic possibilities. If a comparable neuronal signal can be shown to act on epidermal or epithelial barriers in mammalian systems, blocking that signal, or stabilizing the activity of an ELT-3-like transcription factor, might help preserve matrix integrity during infection. Conversely, the study offers a caution: interventions that boost lysosomal activity without accounting for upstream neuronal signals may be undermined by the very pathways pathogens exploit. The authors suggest that NSIF-1 and ELT-3 represent potential targets to counteract infection-driven extracellular matrix dysregulation, a framing that invites screening for small molecules capable of restoring lysosomal acidification or protecting transcription factor localization in infected tissue.

For the broader scientific community, the work adds a vivid example to a growing catalog of pathogen strategies that operate through the host’s own regulatory circuits rather than against them. It also underscores how much a simple worm can teach. The C. elegans cuticle, with its tractable genetics and optically transparent body, allowed the team to connect a neuronal secretion, a transcription factor, an organelle, and a whole-animal outcome, survival, within a single experimental system. That end-to-end clarity is rare, and it transforms a subtle molecular observation into a complete biological narrative: a bacterium whispers to the nervous system, the nervous system unwittingly betrays the skin, and the skin’s recycling machinery grinds to a halt just when the animal needs it most. As researchers now search for echoes of this neuro-epidermal axis in higher organisms, the humble nematode has once again proven that the shortest path to understanding a complex infection may run through a millimeter-long worm.

Subject of Research: Pathogen-induced neuronal signaling that disrupts epidermal lysosomal function and collagen homeostasis in C. elegans

Article Title: Pathogen subversion of neuro-epidermal signaling impairs lysosomal function to disrupt collagen homeostasis in Caenorhabditis elegans

Article References: Li, Q., Liu, Y., Chen, H., Xiao, W., & Qi, B. (2026). Pathogen subversion of neuro-epidermal signaling impairs lysosomal function to disrupt collagen homeostasis in Caenorhabditis elegans. PLOS Biology, 24(9), e3004016. https://doi.org/10.1371/journal.pbio.3004016

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004016

Keywords: Caenorhabditis elegans, Pseudomonas aeruginosa, NSIF-1, ELT-3, lysosomes, collagen, extracellular matrix, neuro-epidermal signaling, cuticle integrity, host-pathogen interaction, innate immunity, PLOS Biology

CMA works with remarkable precision. The cytosolic chaperone HSC70 patrols the cell interior, binding proteins that carry a KFERQ-like amino acid motif and delivering them to LAMP2A, a receptor embedded in the lysosomal membrane. When substrates arrive, LAMP2A molecules multimerize into a translocation complex that unfolds and threads each protein into the lysosomal lumen for degradation. This process is not merely housekeeping. CMA regulates the cell cycle, metabolism, cellular differentiation, immune activation and even circadian rhythms. It also declines with age in most tissues, and its malfunction has been linked to neurodegenerative disease, metabolic syndrome and atherosclerosis. What remained unknown until now was how this decline shapes the fate of senescent cells, the growth-arrested cells that accumulate in aging organs and drive inflammation and tissue dysfunction.

The team began with mouse ear fibroblasts, a reliable primary model for studying aging outside the confounding effects of replicative senescence. Using fibroblasts from transgenic KFERQ-Dendra reporter mice, in which a fluorescent CMA substrate lights up as puncta inside lysosomes, the researchers tracked CMA activity as cells entered senescence. In fibroblasts from young, four-month-old mice, senescence induction with the CDK4/6 inhibitor palbociclib triggered a robust upregulation of CMA, consistent with earlier work showing that the pathway is activated when cells remodel their proteome. Fibroblasts from twenty-three-month-old mice, however, told a different story. They displayed lower basal CMA activity and completely failed to boost the pathway in response to the senescence stimulus. The deficit was not due to reduced reporter expression but to impaired delivery and internalization of substrates into lysosomes, confirming that aged cells lose the ability to engage CMA precisely when they need it most.

To dissect the consequences, the researchers stably knocked down Lamp2a, the rate-limiting component of CMA, in untransformed NIH3T3 fibroblasts. Strikingly, these CMA-deficient cells acquired several senescence-like features even before any senescence stimulus: elevated senescence-associated beta-galactosidase staining, nuclear accumulation of the chromatin protein HMGB1, partial increases in p21 and the DNA damage marker gamma-H2A.X, and nuclear indentations. Yet they kept proliferating normally and arrested only after palbociclib treatment, indicating that CMA loss alone does not drive full conventional senescence. Principal component analysis of multiple readouts placed the knockdown cells in an intermediate cluster between healthy controls and senescent cells. The message was clear: CMA is dispensable for initiating senescence, but its loss warps the senescence program itself, producing cells with properties that resemble those of aged senescent cells.

Quantitative proteomics revealed just how deep that resemblance runs. Blocking CMA in young cells reproduced nearly half of the proteome changes seen in aged cells, with shared alterations concentrated in lipid metabolism, oxidative phosphorylation, protein translation, vesicular trafficking and extracellular matrix remodeling. When young control, young CMA-deficient and aged fibroblasts were all pushed into senescence, the CMA-deficient and aged groups showed forty-five percent concordance in their proteome remodeling, with close to four hundred proteins changing in parallel and only about two hundred differing between them despite their twenty-month age gap. By inhibiting lysosomal proteolysis and comparing degradation profiles, the team identified sixty-four proteins that are no longer degraded in lysosomes in aged cells, more than half of them bona fide CMA substrates. In other words, a substantial fraction of the aging proteome is simply a backlog of proteins that the failing CMA machinery can no longer clear.

Metabolomics added a second layer of evidence. Under basal conditions, CMA-deficient fibroblasts phenocopied many metabolic features of aged cells, including changes in energy production, carbohydrate and glycosylation pathways, lipid and membrane biosynthesis, and amino acid and methylation pathways. Upon senescence induction, young control cells mounted a characteristic metabolic shift, engaging fatty acid beta-oxidation, while CMA-deficient and aged cells failed to make that transition and instead showed unique changes in the tricarboxylic acid cycle, aromatic amino acid metabolism and nucleotide metabolism. An integrative analysis combining proteomic and metabolomic datasets confirmed that proteins normally degraded by CMA during senescence accounted for a large share of these metabolic differences, particularly the failure to engage fatty acid and one-carbon metabolism. Because the senescence-associated secretory phenotype, or SASP, depends on this metabolic reprogramming, the stage was set for a dramatic effect on what senescent cells secrete.

That effect materialized in the secretome. Using an ER-TurboID system that biotinylates proteins inside the endoplasmic reticulum, the researchers separated conventionally secreted proteins from those released through unconventional routes such as exosomes and lysosomal docking. CMA-deficient cells showed a deregulated basal secretome and a profoundly altered response to senescence: rather than completing a normal SASP, they failed to downregulate thirty-nine conventionally secreted proteins and upregulated forty-seven others involved in cell migration, protein folding and lysosomal enzymes, with pronounced enrichment of immune-related factors. Unconventionally secreted nuclear proteins appeared in the medium, a selective release not attributable to cell death. Functionally, the medium from CMA-deficient cells, even before senescence induction, drove paracrine senescence in healthy neighboring fibroblasts, raising SA-beta-gal positivity, p21 levels and nuclear HMGB1 loss to degrees comparable to medium from senescent control cells. The secreted metabolites were similarly skewed toward proinflammatory signaling and known regulators of macrophage function.

The most consequential discovery concerned macrophages, the professional scavengers that clear senescent cells through phagocytosis and efferocytosis. Bone marrow-derived macrophages from aged mice showed significantly reduced CMA activity, and exposure to the secretome of senescent fibroblasts suppressed CMA in young macrophages, with the strongest inhibition from CMA-deficient senescent cells. Macrophages engineered to lack LAMP2A displayed reduced phagocytosis and impaired efferocytosis of dying cells, and co-culture experiments showed senescent fibroblasts persisting in their presence. The mechanism traced to SIRPalpha, a phagocytosis-inhibitory receptor that is normally degraded via CMA after endocytic internalization. Without CMA, SIRPalpha accumulates on the macrophage surface, recruits the phosphatase SHP-1, and amplifies the CD47-SIRPalpha ‘do not eat me’ signal, suppressing the actin remodeling that engulfment requires. Aged macrophages showed the same elevated SIRPalpha and SHP-1 levels. In mice lacking LAMP2A specifically in macrophages, senescent cell burden rose in adipose tissue, liver, lung and brain, and full-thickness wounds healed more slowly, with lingering p21-positive cells despite abundant macrophages at the injury site.

The therapeutic implications were tested with CA77.1, a small-molecule CMA activator. Oral administration to eighteen-month-old mice for five months prevented the age-related rise in senescent cells across adipose tissue, liver and lung, dampened inflammatory and senescence gene expression, reduced fibrosis, and restored the phagocytic activity of aged macrophages to levels comparable to those of young animals. In a bleomycin model of pulmonary fibrosis, early CMA activation preserved body weight, cut lung fibrosis, lowered collagen and p16 expression, and normalized the expansion of lung macrophages, while late treatment was far less effective. Human data lent clinical weight: a transcriptional CMA score declined with age in lung cells and was significantly reduced in patients with idiopathic pulmonary fibrosis, whose isolated lysosomes showed unstable LAMP2 and reduced substrate uptake. Together, the results reframe senescent cell accumulation not as a failure of senescence itself but as a failure of its resolution, and they position CMA upregulation as a dual-action strategy, simultaneously improving the health of senescent cells’ secretions and re-arming the immune cells that must dispose of them.

Subject of Research: How age-related decline of chaperone-mediated autophagy alters senescent cells and impairs macrophage-mediated immune clearance

Article Title: Decline of chaperone-mediated autophagy in aging impairs macrophage clearance of senescent cells

Article References: Sereda, R., Lindenau, K., Diaz, A., Liu, Z., Santiago-Fernández, O., Khawaja, R. R., Cutler, R., Calyeca, J., McCabe, M., Durand, S., Aprahamian, F., Vanegas, N. D. P., Chen, H., Vilicich, F., Chavda, B., Botbol, Y., Kroemer, G., Finkel, T., Gavathiotis, E., … Cuervo, A. M. (2026). Decline of chaperone-mediated autophagy in aging impairs macrophage clearance of senescent cells. Nature Aging. https://doi.org/10.1038/s43587-026-01240-w

Image Credits: AI Generated

DOI: 10.1038/s43587-026-01240-w

Keywords: chaperone-mediated autophagy, cellular senescence, macrophages, aging, LAMP2A, SASP, efferocytosis, proteomics, metabolomics, pulmonary fibrosis, CA77.1, lysosomes

The research, led by Ana Cristina Reguera and Rosalía Rodríguez-Rodríguez at the Universitat Internacional de Catalunya, together with colleagues in Spain, Austria, and the United Kingdom, focuses on an unusual phospholipid known as bis(monoacylglycero)phosphate, or BMP. Unlike most cellular lipids, BMP is not scattered across membranes; it is almost exclusively found in late endosomes, the acidic compartments where cellular cargo is sorted, degraded, and recycled. BMP is required for the formation of intraluminal vesicles, the small bubbles that carry cargo into the interior of these compartments, and it plays a central role in cholesterol handling and lysosomal function. Without adequate BMP, the late endosomal system essentially loses its operating fluid.

What has puzzled researchers is how neurons maintain the right amount of this specialized lipid. BMP is chemically unusual, resistant to many common phospholipases, but it does have one known executioner: an enzyme called ABHD6, alpha-beta hydrolase domain containing 6. ABHD6 can hydrolyze BMP, breaking it down. The new work shows that the activity of this hydrolase is not constant; it is tuned by the metabolic state of the cell, and the tuning knob is CPT1C, a brain-specific member of the carnitine palmitoyltransferase family that sits in the endoplasmic reticulum and is known to respond to nutrient and energy cues.

CPT1C is an intriguing protein in its own right. Unlike its relatives CPT1A and CPT1B, which drive fatty acid import into mitochondria, CPT1C has negligible transferase activity. Instead, it behaves as a lipid and energy sensor, accumulating in neurons during fasting and low-energy states and helping neurons adapt their metabolism accordingly. The new study reveals an unexpected downstream target for this sensor: by restraining ABHD6, CPT1C protects the BMP pool that late endosomes depend on. In other words, a protein long studied for its role in energy sensing turns out to be a critical regulator of the lipid composition of the degradative compartments themselves.

The experimental logic of the study is straightforward and compelling. When the researchers removed CPT1C from neurons, ABHD6 activity rose, intracellular BMP levels fell, and the endolysosomal system began to falter. The consequences were measurable at several points along the pathway. Endosomal maturation was impaired, meaning early endosomes failed to progress properly into functional late compartments. The release of extracellular vesicles, including exosomes, which bud from late endosomes and depend on intraluminal vesicle formation, was reduced. Lysosomes lost their normal acidity, and their proteolytic activity, the enzymatic digestion of cargo, declined. Each of these defects is consistent with a shortage of the BMP that late endosomes and lysosomes need to build and maintain their internal architecture.

Crucially, the team showed that the problem was not a failure to synthesize BMP but an acceleration of its destruction. When they acutely inhibited ABHD6 in CPT1C-deficient neurons, BMP levels recovered, and the endolysosomal defects were rescued. This pharmacological rescue is one of the strongest signals in the paper, because it establishes a clear causal chain: CPT1C loss elevates ABHD6 activity, elevated ABHD6 depletes BMP, and BMP depletion undermines endolysosomal function. Blocking the hydrolase reverses the cascade at its source.

The nutrient dimension of the story emerged when the researchers exposed cells and animals to lipid overload. In wild-type neurons and in the hypothalamus of mice fed excess fat, ABHD6 activity increased and BMP levels dropped, mirroring the phenotype seen in CPT1C-deficient cells. But there was a telling difference: CPT1C-deficient neurons and mice already displayed constitutively elevated ABHD6 activity, and when faced with additional lipid excess, they failed to adapt further. Their regulatory range was exhausted. This suggests that CPT1C does not merely set a baseline for BMP homeostasis; it provides the adaptive capacity that neurons need when the lipid environment changes, as it does in high-fat diets and obesity.

Why does this matter for whole-body metabolism? The hypothalamus is the command center that integrates hormonal and nutrient signals to regulate food intake, energy expenditure, and glucose homeostasis. If lipid overload degrades the endolysosomal health of hypothalamic neurons, it could compromise the very cells responsible for sensing metabolic state and orchestrating the response. Defective lysosomal acidification and proteolysis would impair the degradation of proteins and organelles, including through autophagy, while reduced exosome release could alter intercellular communication within hypothalamic circuits. The study does not claim to have demonstrated these downstream physiological effects, but it establishes the molecular lesion, BMP depletion through unrestrained ABHD6, that could plausibly feed into hypothalamic dysfunction in metabolic disease.

The findings also connect to a broader and rapidly growing literature on lysosomal lipids in neurobiology. BMP has attracted intense interest because it is the receptor for a family of DNAJ proteins that stimulate lysosomal activity, and because altered BMP metabolism has been implicated in neurodegenerative conditions in which lysosomal failure is a hallmark. Neurons are particularly vulnerable to lysosomal dysfunction because they are long-lived and cannot dilute accumulated damage by cell division. A pathway in which a nutrient sensor controls the abundance of the signature lipid of the degradative pathway therefore offers a direct mechanistic bridge between diet, neuronal metabolism, and cellular housekeeping.

Therapeutically, the study points to ABHD6 as a druggable node. Pharmacological ABHD6 inhibition restored BMP levels in CPT1C-deficient neurons, raising the possibility that modulating this hydrolase could protect endolysosomal function in settings of chronic lipid excess. ABHD6 inhibitors have already been explored in other contexts, including endocannabinoid signaling, which gives medicinal chemists a starting point. The authors caution, implicitly, that much remains to be worked out: how CPT1C physically restrains ABHD6, whether the axis operates in other neuronal populations, and whether restoring BMP in vivo can correct hypothalamic dysfunction in obesity models. But the identification of a nutrient-sensitive CPT1C-ABHD6 axis governing BMP homeostasis gives researchers a concrete molecular handle on a process that had been almost entirely opaque. It reframes CPT1C not just as a metabolic sensor at the endoplasmic reticulum but as a custodian of the neuronal recycling system, and it suggests that the road from a fatty diet to faulty cellular waste disposal in the brain may run through a single, targetable enzyme.

Subject of Research: Nutrient-sensitive regulation of BMP lipid homeostasis and endolysosomal function in hypothalamic neurons via the CPT1C-ABHD6 axis

Article Title: A nutrient-sensitive CPT1C-ABHD6 axis regulates BMP homeostasis and endolysosomal function in hypothalamic neurons

Article References: Reguera, A. C., Miralpeix, C., Bernard, M., Zagmutt, S., Bolaños-Hurtado, M., Palacín, C., Fuentes, A., Rodríguez-García, M., Fosch, A., Garcia-Chica, J., Barnadas-Rodríguez, R., Fawzy, N., Zimmermann, R., Eden, E., Casals, N., & Rodríguez-Rodríguez, R. (2026). A nutrient-sensitive CPT1C-ABHD6 axis regulates BMP homeostasis and endolysosomal function in hypothalamic neurons. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06451-3

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06451-3

Keywords: CPT1C, ABHD6, BMP, endolysosomal system, hypothalamus, neurons, lipid metabolism, lysosomes, nutrient sensing, exosomes, obesity, endosomes

The promise of TFEB has never been in doubt. The transcription factor controls the expression of hundreds of genes involved in lysosomal biogenesis and autophagy, the twin processes by which cells build new recycling machinery and degrade damaged components. When TFEB is active, it migrates into the nucleus and switches on the genetic program that keeps cellular clearance running. Boosting TFEB activity, researchers reasoned, could help cells cope with the buildup of toxic material that characterizes many diseases. The idea has attracted enormous attention: nearly 3,000 scientific publications now focus on TFEB, more than 90 percent of them appearing in the last decade alone. Experimental studies have explored TFEB activation as a strategy in lysosomal storage disorders, Parkinson’s disease, obesity and cancer, and the protein ranks among the priority targets of the Michael J. Fox Foundation’s Targets to Therapies initiative for Parkinson’s disease.

Yet a stubborn obstacle has kept TFEB from the clinic. Transcription factors as a class are notoriously difficult to target with drugs. They operate inside the nucleus, lack the well-defined enzymatic pockets that medicinal chemists prefer to bind, and are embedded in dense regulatory networks that are hard to manipulate selectively. No therapy specifically designed to activate TFEB has reached patients, despite years of effort. What was missing, essentially, was a handle: an upstream control point that could be pharmacologically tuned to dial TFEB activity up or down. The new study, coordinated by Gennaro Napolitano at TIGEM, provides exactly that. Rather than attacking TFEB itself, the researchers mapped the molecular machinery that senses lysosomal stress and switches TFEB on, revealing several proteins along the way that are far more amenable to drug development.

The scientific lineage of the work runs through Andrea Ballabio, former scientific director of TIGEM, whose research in 2009 first established TFEB as the master regulator of lysosomal function and cellular clearance. That discovery transformed lysosomal biology, recasting the lysosome from a static waste bin into a dynamically regulated system with its own genetic control hub. But one fundamental question remained open: how do cells actually detect that their lysosomes are malfunctioning, and how do they translate that signal into TFEB activation? The sensing step, the molecular bridge between lysosomal perturbation and the nuclear response, had never been fully described. Closing that gap was the central achievement of the new research, which involved collaborators at the University of Fribourg in Switzerland, UC Berkeley in the United States, the University of Rome Tor Vergata in Italy and the German Cancer Research Center (DKFZ) in Germany, with primary support from Fondazione Telethon and Fondazione AIRC.

The answer the team uncovered is a signaling cascade that begins at the lysosome itself. When lysosomal function is disturbed, the lysosomal proton pump known as v-ATPase, a molecular machine that acidifies the organelle’s interior, initiates the response. The stress signal is then transmitted through the adaptor protein TAX1BP1 to two enzymes, TBK1 and ULK1, which become activated. Once switched on, these kinases modify a protein called FNIP1, and this modification sets off a chain of events that releases TFEB to move from the cytoplasm into the nucleus. There, TFEB activates the genes that drive cellular recycling and lysosomal biogenesis. In effect, the cell possesses a dedicated alarm system for lysosomal trouble, wired through TBK1 and ULK1, and TFEB is the responder that answers the call.

“Researchers have known for years that TFEB plays a fundamental role in helping cells maintain their recycling machinery and adapt to stress,” says Alessandra Esposito, first author of the study. “What remained unclear was how cells sense lysosomal dysfunction and translate that signal into TFEB activation. Our work identifies the molecular players involved in this process and reveals a signaling pathway that had never been described before.” The identification of this axis, running from v-ATPase through TAX1BP1 and the TBK1 and ULK1 kinases to FNIP1 and finally TFEB, gives researchers a complete wiring diagram of the lysosomal stress response, and every component in that diagram is a potential point of pharmacological intervention.

The discovery is not only about boosting cellular recycling. The researchers also examined the pathway in the context of follicular lymphoma, a blood cancer in which mutations affecting ATP6V1B2, a component of the v-ATPase proton pump, are relatively common. They showed that these mutations cause persistent activation of TFEB, which in turn helps tumor cells survive and proliferate in nutrient-poor environments, a hallmark of the tumor microenvironment in lymphoma. In this setting, the newly mapped pathway works against the patient: cancer cells exploit the lysosomal stress response to adapt to scarcity and keep growing. That finding suggests a second therapeutic strategy, one of inhibition rather than activation. Drugs that block the TBK1-ULK1 signaling axis might deprive such tumors of their survival advantage, opening a potential avenue for treating follicular lymphoma and possibly other malignancies that depend on lysosomal reprogramming.

“Rather than targeting TFEB itself, our study identifies molecular regulators that control its activation,” Esposito explains. “This provides new entry points for the development of therapeutic strategies aimed at harnessing TFEB activity in disease.” The distinction matters enormously for drug development. Kinases such as TBK1 and ULK1 are enzymes with well-characterized active sites, and potent inhibitors of both already exist in the chemical biology toolkit. A pathway made of kinases and adaptor proteins is, from a medicinal chemistry standpoint, a far more tractable target than a transcription factor. By identifying the regulators upstream of TFEB, the study converts an aspirational goal, pharmacological control of the cell’s recycling master switch, into a concrete set of engineering problems that pharmaceutical researchers know how to approach.

“The identification of the TBK1/ULK1 pathway expands the therapeutic opportunities for modulating TFEB,” says Napolitano, the study’s lead investigator. “Because this mechanism acts upstream of TFEB, it could offer new opportunities not only in TFEB-dependent cancers but also in a broader spectrum of diseases where improving lysosomal function may be beneficial.” That broader spectrum is large. Lysosomal dysfunction lies at the heart of dozens of rare genetic diseases, collectively affecting a substantial number of patients worldwide, and has been implicated in common neurodegenerative disorders, metabolic conditions and aging itself. A single druggable pathway that modulates lysosomal clearance could therefore have applications that span from ultra-rare pediatric storage diseases to some of the most prevalent illnesses of old age.

The study, published under the title describing a TBK1-ULK1 signaling axis that couples lysosomal stress to TFEB activation, marks a turning point in a research story that began in 2009. For fifteen years, the field has known what TFEB does; now it knows how cells control it, and the control points are druggable. Translating that knowledge into medicines will take years of further work, from developing selective modulators of the pathway to testing them in disease models and, eventually, patients. But the direction is clear. By uncovering the molecular sensors and kinases that stand between lysosomal stress and the master regulator of cellular recycling, the TIGEM-led team has brought researchers a decisive step closer to turning one of lysosomal biology’s most celebrated discoveries into real therapies for rare genetic diseases, cancer and beyond.

Subject of Research: The TBK1-ULK1 signaling pathway that regulates TFEB activation in response to lysosomal stress

Article Title: Newly discovered pathway unlocks the therapeutic potential of TFEB

Article References: Newly discovered pathway unlocks the therapeutic potential of TFEB. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: TFEB, lysosomes, TBK1, ULK1, FNIP1, autophagy, lysosomal storage diseases, follicular lymphoma, v-ATPase, TAX1BP1, drug targets, TIGEM