Sarcopenia is one of the quiet epidemics of an aging world. It is diagnosed when both muscle strength and muscle quantity fall below defined thresholds, and it predicts falls, fractures, hospitalization, and death. Yet the biology behind it remains only partly understood. Most research has focused on neuromuscular decline, protein metabolism, chronic inflammation, and inactivity. The new study turns attention to a less obvious suspect: the network of tiny blood vessels that feeds muscle tissue, and the molecular signals that build and maintain that network.

Angiogenesis — the sprouting of new capillaries from existing vessels — is essential to muscle health. Every muscle fiber depends on a dense microcirculation to deliver oxygen, glucose, amino acids, and hormones, and to clear metabolic waste. When a muscle is injured, new vessel formation is one of the earliest events in repair, preceding the regeneration of the muscle fibers themselves. As people age, capillary density in skeletal muscle falls, a process called capillary rarefaction, and the decline is most pronounced around the fast-twitch type II fibers that sarcopenia strips away first. Human biopsy studies have linked this vascular thinning directly to weaker grip, smaller appendicular muscle mass, and poorer physical performance.

The research team, led by Hui Li and Feng Jia of Nanyang Central Hospital together with colleagues at the Seventh People’s Hospital of Zhengzhou, measured three serum angiogenesis markers using enzyme-linked immunosorbent assays: VEGF, the master driver of new vessel growth; ANGPT1, which stabilizes and matures vessels; and ANGPT2, which antagonizes ANGPT1 and promotes vessel remodeling. Fasting blood samples were drawn the morning after admission, processed under standardized conditions, stored at minus 80 degrees Celsius, and assayed in duplicate by laboratory staff blinded to each patient’s clinical status. Quality controls kept measurement variability below 10 percent within assays and below 15 percent between batches spread across five years.

Sarcopenia was defined according to the Asian Working Group for Sarcopenia criteria, requiring both reduced hand grip strength and reduced appendicular skeletal muscle mass. Grip was tested with a calibrated dynamometer in a standardized seated posture, three trials per hand, with the best value recorded. Muscle mass was estimated by multi-frequency bioimpedance analysis using an eight-frequency device that measured each limb separately, performed after an overnight fast with strict controls for hydration status. Of the 471 participants, 68 — or 14.44 percent — met the criteria for sarcopenia.

The results were striking in their consistency. Patients with sarcopenia had significantly lower VEGF — an average of 116.95 picograms per milliliter versus 138.60 in those without the condition — and dramatically lower ANGPT1, at 23.68 nanograms per milliliter versus 34.15. ANGPT2, by contrast, showed no meaningful difference. In regression models adjusted first for age, sex, and body mass index, and then further for comorbidity burden, hemoglobin, albumin, smoking, alcohol use, and hypertension, VEGF remained positively correlated with both grip strength and muscle mass, while ANGPT1 held its association with muscle mass and, in the fully adjusted model, with grip strength as well.

The risk statistics are the headline numbers. Using receiver operating characteristic analysis, the team derived cutoff values — VEGF at or below 102.55 picograms per milliliter and ANGPT1 at or below 19.47 nanograms per milliliter — and validated them with ten-fold cross-validation to guard against overestimation. In fully adjusted logistic models, low VEGF was associated with roughly a threefold higher odds of sarcopenia (odds ratio 3.360), and low ANGPT1 with even greater odds (3.709, p < 0.001). Among patients with low ANGPT1, more than a quarter — 25.55 percent — had sarcopenia, compared with fewer than 10 percent of those with normal levels. Adding either marker to a base clinical model built from age, sex, BMI, comorbidities, and routine labs significantly improved the model’s statistical fit, with ANGPT1 delivering the largest gain.

Why would vessel-building signals track so closely with failing muscle? The authors propose a dual-hit mechanism rooted in the aging muscle’s microenvironment. Endothelial cells and satellite cells — the stem cells that rebuild muscle — sit side by side and exchange chemical messages. VEGF acts directly on satellite cell receptors to trigger their activation, proliferation, and migration after injury; ANGPT1 then supports their survival and coordinates their differentiation and fusion into mature, multinucleated muscle fibers. When circulating VEGF and ANGPT1 both fall, the regenerative sequence is disrupted at both ends: the vascular supply shrinks and the stem cell pipeline stalls, leaving chronic micro-injuries to heal poorly — the hallmark of sarcopenic muscle. Animal work supports the plausibility: VEGF gene delivery improves muscle ischemia and repair in rodents, and ANGPT1 enhances regeneration in mice, while exercise and even massage raise VEGF expression in skeletal muscle.

The study’s limitations deserve equal billing. It is cross-sectional, so it cannot say whether low angiogenic markers cause muscle loss or simply reflect it — reverse causation remains a real possibility. Serum VEGF and ANGPT1 are systemic signals, not direct measurements of the muscle microenvironment, and their blood levels can be swayed by subclinical disease, inflammation, nutrition, and activity. The cohort was drawn from a single hospital’s gastroenterology and general surgery service rather than the community, and physical performance testing was unavailable, preventing severity grading. The diagnostic discrimination of the markers alone was modest — area under the curve of 0.641 for VEGF and 0.668 for ANGPT1 — meaning they add incremental value to clinical assessment rather than replacing it. ANGPT2, notably, contributed nothing once confounders were accounted for.

Even with those caveats, the findings open an intriguing therapeutic window. If the vascular niche truly governs the regenerative failure of aging muscle, then interventions that boost angiogenesis — exercise training being the most proven, with hypoxic training, pneumatic compression, and gene therapy as research frontiers — might slow or partially reverse sarcopenia. And if larger, longitudinal, community-based studies confirm that a routine blood draw can flag failing muscle years before a fall, sarcopenia screening could shift from the grip dynamometer to the phlebotomy tray. For now, the message is measured but provocative: the health of aging muscles may be written, in part, in the chemistry of their blood supply.

Subject of Research: Associations between serum angiogenesis markers VEGF and ANGPT1 and sarcopenia in older adults

Article Title: Relationships between serum angiogenesis markers and sarcopenia: a cross-sectional study

Article References: Li, H., Liu, H., Liu, Y., Shi, W., Shi, L., & Jia, F. (2026). Relationships between serum angiogenesis markers and sarcopenia: a cross-sectional study. Frontiers in Medicine, 13, Article 1922045. https://doi.org/10.3389/fmed.2026.1922045

Image Credits: AI Generated

DOI: 10.3389/fmed.2026.1922045

Keywords: sarcopenia, angiogenesis, VEGF, ANGPT1, aging, muscle loss, blood vessels, biomarkers, geriatric medicine, cross-sectional study, hand grip strength, muscle regeneration

The research team, led by Cristina Antinozzi and Luigi Di Luigi, set out to address a gap in what is known about PDE5 inhibitors and muscle. Skeletal muscle regeneration depends on the activation, proliferation and eventual differentiation of myogenic progenitor cells, the satellite cells that sit dormant along muscle fibers until injury or exercise wakes them up. Nitric oxide signaling is known to be a key player in this process, and because PDE5 inhibitors prolong cGMP signaling downstream of nitric oxide, scientists have long suspected the drugs could influence how muscle repairs itself. What remained unclear was what happens when cells are exposed to tadalafil not for hours, but for days.

To find out, the researchers used C2C12 cells, a mouse myoblast cell line that is one of the workhorses of muscle biology research. When switched to low-serum conditions, these cells reliably exit the cell cycle, fuse together and form multinucleated myotubes, allowing scientists to track every stage of myogenesis in a dish. In the study, the cells were treated with 1 micromolar tadalafil for up to seven days, a prolonged exposure designed to mimic sustained pharmacological use rather than a single transient dose. The team then measured proliferation, cell viability, the activation of myogenic marker genes and the release of myokines, the signaling molecules that muscle cells secrete.

The first striking result was survival and growth. Tadalafil significantly increased cell proliferation and survival across all time points, reducing cell death throughout the treatment period. In practical terms, the drug appeared to keep the myoblast population expanding robustly instead of losing cells to apoptosis or stress. For a field where muscle-wasting disorders such as Duchenne muscular dystrophy and age-related sarcopenia are driven partly by the exhaustion and death of regenerative cells, any compound that keeps progenitor pools alive and dividing is of obvious therapeutic interest.

The myogenic program itself, however, showed a more nuanced response. Tadalafil enhanced the expression of early myogenic factors, the transcriptional switches that mark the beginning of the muscle-building program. Yet at the same time, it delayed terminal differentiation. Cells exposed to the drug for seven days produced fewer myosin heavy chain-positive multinucleated myotubes, the mature structures that represent the end point of myogenesis, and they maintained higher expression levels of Pax7 and Myf6, two markers associated with a less differentiated, more stem-like phenotype. In other words, tadalafil did not simply accelerate muscle formation; it appeared to keep the cells poised in an earlier, more regenerative state.

That combination, more proliferation plus delayed differentiation, is exactly the profile one would want from a drug intended to boost the regenerative capacity of muscle. Satellite cells that differentiate too quickly may rebuild a damaged fiber but fail to replenish the stem cell pool, whereas cells that self-renew can sustain repair over repeated rounds of injury. The Pax7 protein in particular is a master regulator of muscle stem cell self-renewal, and Myf6 has been implicated in maintaining the satellite cell niche. By sustaining expression of these factors, tadalafil seems to preserve the regenerative reserve rather than spend it, a mechanism the authors describe as promoting a highly proliferative state while preventing premature differentiation.

The molecular signature behind this shift offers further clues. The treated cells showed upregulation of Sirt3, the mitochondrial sirtuin deacetylase that governs mitochondrial fitness, oxidative stress resistance and metabolic adaptation, alongside increased IL6, an interleukin with well-documented roles as a muscle-derived myokine that can support regeneration. At the same time, the cells downregulated myostatin and TGF-beta, two of the most powerful brakes on muscle growth in the body. Myostatin inhibition is already a major strategy in the development of drugs for muscular dystrophy and other atrophic conditions, so its suppression under tadalafil treatment is a particularly meaningful signal. Reduced TGF-beta signaling likewise removes a barrier that normally restrains progenitor cell activation and progression through the myogenic program.

These results build on a body of earlier work by the same group and others. Previous studies had shown that tadalafil regulates lipid homeostasis in human skeletal muscle cells, improves lean mass and endothelial function in certain patients, and that nitric oxide and cGMP signaling sustain long-term muscle regeneration by controlling the fate of satellite cells. Clinical observations in boys with Duchenne muscular dystrophy have suggested that PDE5 inhibition can alleviate functional muscle ischemia, and recent epidemiological work has even associated PDE5 inhibitor use with reduced mortality and lower rates of cardiovascular disease and dementia. The new study adds a direct cellular mechanism: prolonged cGMP signaling appears to reprogram myogenic progenitors toward expansion and self-renewal while dialing down the anti-growth factors that would otherwise push them to mature and stop.

The therapeutic implications are considerable. If the same biology holds in human tissue, tadalafil or related compounds could serve as adjuvant pharmacological therapy for muscle-wasting disorders, helping patients with dystrophies, sarcopenia or disuse atrophy maintain a larger, healthier pool of regenerative cells. The drug is already widely prescribed, has a well-characterized safety profile and acts on a pathway that is naturally engaged by exercise itself, since muscle contraction increases nitric oxide production. A licensed medicine that amplifies an endogenous repair pathway is an attractive candidate for repurposing, and the authors explicitly point to this potential in their conclusions.

But the same mechanism that excites clinicians also alarms anti-doping authorities. A drug that increases progenitor cell proliferation, suppresses myostatin and TGF-beta, and keeps muscle in a regeneration-primed state is, on paper, a potential performance enhancer, capable of accelerating recovery from training damage and possibly supporting hypertrophy. The researchers themselves highlight this concern, noting that the potent improvement of the muscle regenerative machinery raises critical questions about misuse in sport and calling for evaluation by anti-doping agencies. As with any cell-culture study, important caveats remain: the work was done in a mouse cell line at a specific dose, and whether prolonged tadalafil exposure produces the same progenitor-sparing effect in living human muscle is not yet known. Still, the study marks a notable step in understanding how a familiar cardiovascular drug talks to the stem cells of the musculoskeletal system, and it ensures that both regenerative medicine specialists and sports regulators will be watching the next round of experiments closely.

Subject of Research: Effects of prolonged tadalafil exposure on myogenesis and myogenic marker activation in C2C12 skeletal muscle cells

Article Title: Prolonged tadalafil exposure promotes skeletal muscle myogenesis and regulates early myogenic markers activation in C2C12 cell lines

Article References: Antinozzi, C., & Di Luigi, L. (2026). Prolonged tadalafil exposure promotes skeletal muscle myogenesis and regulates early myogenic markers activation in C2C12 cell lines. Molecular Biology Reports, 53(1), Article 1701. https://doi.org/10.1007/s11033-026-12929-x

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12929-x

Keywords: tadalafil, PDE5 inhibitors, myogenesis, C2C12 cells, satellite cells, muscle regeneration, myostatin, Pax7, Sirt3, interleukin-6, muscle-wasting disorders, doping

The research began with a question that has lingered in the muscle biology literature for years. Calcium dysregulation is a well-documented feature of diseased and aging muscle. Patients with systemic hypercalcemia, defined by serum calcium exceeding 3.0 millimolar, frequently complain of fatigue and proximal muscle weakness. Duchenne muscular dystrophy drives chronic cytosolic calcium overload through loss of the structural protein dystrophin. Aging muscle, meanwhile, shows increased resting intracellular calcium, leaky ryanodine receptors, and inefficient calcium reuptake by SERCA pumps. Yet most research had focused on how calcium controls contraction in mature fibers, leaving the impact on regenerating muscle largely unexplored.

To connect those dots, the team, led by Kee K. Kim of Chungnam National University, first turned to human data. Analyzing transcriptomes from 679 individuals in the GTEx v8 dataset, they compared gastrocnemius muscle from people aged 50 and older with samples from those under 40. Gene set enrichment analysis revealed that aged muscle showed coordinated activation of calcium signaling pathways and muscle cell proliferation programs, alongside upregulation of the quiescence regulator SPRY1, the early myogenic factor PAX3, and the proliferation marker CCND1. Crucially, the signature appeared in both men and women, suggesting that a proliferative bias tied to calcium signaling is a general feature of aging muscle rather than a sex-specific phenomenon.

The researchers then moved into the laboratory to test whether calcium excess directly alters myoblast behavior. When C2C12 mouse myoblasts and primary myoblasts isolated from hindlimb muscle were exposed to elevated calcium chloride under normal growth conditions, nothing dramatic happened. But when the same cells were pushed to differentiate while bathed in 3 or 6 millimolar calcium chloride, a striking picture emerged: total cell numbers rose significantly, the proliferative marker PAX7 climbed at both the protein and mRNA levels, and the cells failed to exit the cell cycle. Calcium imaging with the Fluo-4 AM indicator confirmed that intracellular calcium remained persistently elevated throughout the differentiation window, rising in a dose-dependent manner in primary myoblasts.

That persistent proliferative state came at a direct cost to myogenesis. Myotube formation declined dose-dependently in calcium-exposed C2C12 cultures, and levels of the myogenic markers MYH3 and myogenin dropped alongside their messenger RNAs. Primary mouse myoblasts showed the same defects, and, importantly, the phenomenon crossed the species line: human embryonic stem cell-derived myoblasts differentiated for two weeks in 3 millimolar calcium chloride formed fewer myotubes and produced less total myosin heavy chain. Notably, prolonged exposure to lower concentrations sufficed to impair differentiation, indicating that the duration of calcium elevation, rather than its absolute peak, is the critical determinant of pathology.

RNA sequencing of calcium-exposed primary myoblasts identified 2,776 differentially expressed genes and revealed the underlying transcriptional logic. Genes upregulated by calcium exposure were enriched for cell division and chromosome segregation, while downregulated genes clustered around muscle contraction and sarcomere organization. Gene set enrichment analysis flagged activation of the calcium-dependent NFAT pathway. Mechanistic experiments followed: NFATc1, tagged with green fluorescent protein, translocated into the nucleus of calcium-exposed myoblasts; the NFAT target gene Ccnd1, encoding cyclin D1, was upregulated; and chromatin immunoprecipitation showed that NFATc1 binding to the Ccnd1 promoter was significantly enhanced under calcium excess. In short, calcium was hijacking a pathway that normally helps orchestrate differentiation and repurposing it to keep the cell-cycle engine running.

To confirm the mechanism in living animals, the team used two complementary models. The first was the ovariectomized mouse, in which estrogen deficiency destabilizes calcium handling by hyperphosphorylating the ryanodine receptor 1, provoking spontaneous calcium release from the sarcoplasmic reticulum. These mice lost bone density, performed worse on treadmill endurance tests, and developed gastrocnemius atrophy. Their muscle transcriptomes mirrored the in vitro signature: enrichment of calcium signaling and proliferation programs, downregulation of developing and mature myosin heavy chain genes, upregulation of Pax7 and MyoD, shrunken myofiber cross-sectional areas, and clear nuclear translocation of NFATc1. The second model was human calcific tendinitis. In supraspinatus muscle samples taken from patients during calcific deposit removal, tissue adjacent to the calcium deposits showed downregulation of SPRY1, PAX3, and MYH3 together with upregulation of CCND1 compared with remote regions, demonstrating that even localized calcium overload in human tissue produces the same proliferative, anti-myogenic fingerprint.

The most translational part of the study came from pharmacological rescue. Using VIVIT, a selective peptide inhibitor of NFAT, the researchers blocked calcium-induced nuclear accumulation of NFATc1 in both C2C12 cells and primary myoblasts. VIVIT restored MYH3 expression and reversed the myotube formation defect under calcium overload. A complementary experiment using caffeine to induce sarcoplasmic reticulum calcium leak recapitulated the suppression of myoblast fusion, and VIVIT rescued that too, confirming the effect arises from intracellular calcium dysregulation rather than nonspecific stress. In vivo, the team injured tibialis anterior muscles with barium chloride, which triggers calcium-dependent proteolysis and robust regeneration, and injected VIVIT locally on days 0 and 2. Treated muscles showed improved regenerative morphology, larger myofiber cross-sectional areas, and a dramatic reduction in the proportion of immature myogenin-positive fibers, all without measurable changes in inflammatory markers such as Il6, Tnfa, and Inos.

One conceptual takeaway is that NFAT plays a duration-dependent dual role in muscle. Transient calcium-dependent NFAT activation has classically been viewed as a positive regulator of myogenesis, supporting fiber-type specification and hypertrophy. The new data show that when calcium elevation persists, the same pathway flips into an anti-myogenic mode, sustaining cyclin D1 expression and preventing the cell-cycle exit that myoblasts must undergo to fuse into contractile fibers. The authors also suggest this framework may help explain osteosarcopenia, the poorly understood co-occurrence of osteoporosis and muscle loss, since both tissues depend on well-regulated calcium handling, although they caution that this connection remains inferential and requires direct testing.

Limitations remain, and the researchers are candid about them. The therapeutic benefit of VIVIT was demonstrated in an acute injury model, not in the chronic ovariectomy setting, because repeated intramuscular injections over a six-week protocol would introduce local tissue damage and inflammation that could confound the results. Future work with long-term pharmacological approaches or genetic models will be needed to validate NFAT as a drug target for chronic calcium-associated myopathies. Still, by tracing a single molecular thread from aged human muscle through mouse myoblasts, ovariectomized mice, calcific tendinitis patients, and a rescued injury model, the study establishes chronic calcium-NFAT signaling as a credible mechanism linking calcium dysregulation to failed muscle repair, and it offers a concrete starting point for therapies aimed at restoring the regenerative capacity of weakened muscle.

Subject of Research: Mechanism by which pathological calcium overload impairs skeletal muscle regeneration through sustained NFAT-dependent proliferative signaling

Article Title: Pathological calcium overload impairs skeletal muscle regeneration through sustained NFAT-dependent proliferative signaling

Article References: Lee, S., Cho, N., Jo, S., Ji, J.-H., Kim, J. O., Park, C., Choi, S., Kim, E.-M., & Kim, K. K. (2026). Pathological calcium overload impairs skeletal muscle regeneration through sustained NFAT-dependent proliferative signaling. Experimental &amp; Molecular Medicine. https://doi.org/10.1038/s12276-026-01856-3

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01856-3

Keywords: skeletal muscle, muscle regeneration, calcium signaling, NFATc1, myogenesis, satellite cells, cyclin D1, sarcopenia, calcific tendinitis, VIVIT, aging muscle, ovariectomy

The protein in question is CD37, a member of the tetraspanin family. Tetraspanins are small four-pass transmembrane proteins that do not act as classical receptors themselves. Instead, they function as molecular organizers, clustering immune receptors into microdomains on the cell surface and fine-tuning the signals those receptors deliver. On leukocytes, CD37 has been implicated in B cell signaling, phagocytosis, and inflammatory regulation, but its role in ischemic tissue injury had remained largely unexplored. The NYU team began with a simple observation drawn from human tissue: in gastrocnemius muscle samples from patients with PAD, CD37 expression was markedly elevated, hinting that this immune organizer might be part of the disease process rather than a bystander.

To understand what that elevation meant, the researchers applied deconvolution-based immune profiling to transcriptomic data from human PAD muscle. This computational approach infers the composition of immune cell populations within bulk tissue gene expression data, allowing the team to link CD37 levels to specific immune programs. The results were striking. CD37 expression correlated strongly with overall immune infiltration, with a correlation coefficient of 0.51 and a p-value of 0.0002. More tellingly, its strongest relationship was with inflammatory macrophage programs, showing a correlation of 0.48 with a p-value of 0.0003. Macrophages, the tissue-resident scavenger cells capable of both fueling and resolving inflammation, appeared to be the cell type most tightly linked to CD37 abundance in failing human muscle.

Correlation alone cannot establish causation, so the team turned to an experimental system. They used the murine hindlimb ischemia model, a standard technique in which blood flow to a mouse’s hind leg is surgically interrupted, mimicking the ischemic injury of severe PAD. They then compared wild-type mice with genetically engineered mice lacking CD37 entirely, known as Cd37 knockout mice. Over the following weeks, the researchers measured perfusion recovery using laser-based blood flow imaging, examined skeletal muscle histology under the microscope, and profiled gene expression in the recovering tissue. The differences between the two groups were immediate and substantial.

The knockout mice revascularized far faster than their normal counterparts. By the key recovery timepoint, Cd37-deficient animals had achieved 87.6 percent reperfusion on average, compared with only 62.9 percent in wild-type mice, a difference that reached statistical significance at p less than 0.04. Blood flow, however, was only part of the story. When the researchers examined the muscle itself, they found that the knockout mice had rebuilt far more of their damaged tissue. Mature muscle fibers made up 77.9 percent of the recovered tissue in CD37-deficient animals versus just 46.7 percent in wild-type controls, with a p-value below 0.02. In other words, removing CD37 did not merely restore circulation; it allowed the muscle to genuinely regenerate rather than degenerate into scar tissue and fat.

To dissect the molecular mechanisms behind this accelerated healing, the team performed RNA sequencing on post-ischemic muscle from both groups. The analysis identified 594 differentially expressed genes at an adjusted p-value threshold of less than 0.05, a substantial transcriptional rewiring driven by the absence of a single surface protein. Pathway analysis revealed a coherent pattern. In the knockout muscle, genes related to muscle mass maintenance and collagen degradation were upregulated, suggesting active tissue rebuilding and clearance of fibrotic deposits. Conversely, pathways governing mitochondrial oxidative metabolism and proinflammatory signaling were downregulated. That the metabolic machinery of the muscle shifted away from oxidative programs may seem counterintuitive, but it likely reflects a reduced burden of inflammatory stress, which is known to distort mitochondrial function in ischemic tissue.

The most compelling findings emerged when the researchers integrated their RNA module scoring with immunohistochemistry, staining tissue sections to identify specific immune cell populations. This combined approach revealed that CD37 deficiency was associated with a fundamental reprogramming of macrophages toward a resolution phenotype. The knockout muscle contained macrophages with higher proresolving signatures and lower inflammatory signatures, and it harbored increased numbers of CD163-positive macrophages, a marker classically associated with anti-inflammatory, tissue-repairing macrophage states. In essence, the immune environment of the healing muscle had flipped from one that attacks damaged tissue to one that cleans up and rebuilds it.

To confirm that this shift originated in the macrophages themselves rather than being a secondary effect of the healthier tissue environment, the team isolated bone marrow-derived macrophages from both mouse groups and stimulated them ex vivo. Macrophages lacking CD37 secreted significantly lower levels of inflammatory cytokines and chemokines, the chemical messengers that recruit and activate additional immune cells and amplify tissue-damaging inflammation. This cell-autonomous result strengthens the causal chain: CD37 on macrophages directly promotes their inflammatory behavior, and that behavior, in turn, impairs the revascularization and regeneration of ischemic muscle.

The translational implications are considerable. Current therapies for chronic limb-threatening ischemia, including surgical bypass, angioplasty, and drug-eluting stents, address the plumbing of the disease but often leave the inflammatory biology untouched. Anti-inflammatory approaches to cardiovascular disease have gained momentum in recent years, but targeting inflammation broadly carries infection risks. CD37 offers something more precise: a surface molecule on immune cells whose removal shifts macrophages toward resolution without eliminating them. Notably, CD37 is already a validated target in oncology, with anti-CD37 antibody therapies in clinical development for B cell malignancies, which means the immunomodulatory toolkit for this protein is further along than for most novel targets. Repurposing or adapting those strategies for vascular medicine is a plausible next step, though the authors and outside observers alike would caution that a genetically engineered mouse is a long way from a diabetic patient with a non-healing foot ulcer.

There are also important caveats embedded in the data. The human findings are associative, drawn from transcriptomic correlations rather than direct functional experiments in patients. The mouse studies used complete knockout animals, so the effects of partial or transient CD37 inhibition remain unknown, as do potential consequences for the immune functions CD37 serves elsewhere, including B cell development and antitumor surveillance. The study was funded by the National Institutes of Health under grant R01HL167917 and by an American Heart Association postdoctoral fellowship, and the authors report no competing interests. Still, the convergence of human association, mouse genetics, transcriptomics, histology, and ex vivo cell biology makes a unusually coherent case. If future work confirms that blocking CD37 in patients with critical limb-threatening ischemia can tip their macrophages toward resolution, a protein once studied mainly by immunologists could become an unexpected lever for saving limbs, and the millions of people living with the silent narrowing of their leg arteries may finally gain a therapy that heals muscle, not just vessels.

Subject of Research: The role of the leukocyte tetraspanin CD37 in inflammation, revascularization, and skeletal muscle recovery in peripheral artery disease

Article Title: CD37 impairs revascularization and muscle recovery in peripheral artery disease

Article References: Dai, M., Gindri Dos Santos, B., Wu, J., Ferreira, E., Li, Z., Biswas, B., Schlamp, F., Boothman, I., & Barrett, T. J. (2026). CD37 impairs revascularization and muscle recovery in peripheral artery disease. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08799-3

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08799-3

Keywords: peripheral artery disease, CD37, tetraspanin, macrophages, inflammation, hindlimb ischemia, revascularization, muscle regeneration, critical limb-threatening ischemia, immune reprogramming, translational medicine, cytokines

The clinical backdrop is significant. Sarcopenia, the progressive loss of muscle mass, strength and function that accompanies ageing, is now formally recognized by the World Health Organization as a disease in its own right. Its prevalence climbs steeply with age, reaching up to 29 percent of older adults in community settings and between 11 and 50 percent of people aged 80 and above. Beyond ageing itself, risk factors include low protein intake, malabsorption, physical inactivity, metabolic and endocrine disorders, and hospitalization. Crucially, no drug has been approved to treat the condition. Current management relies on exercise, caloric control and nutritional supplementation, while experimental pharmacological approaches such as selective androgen receptor modulators and myostatin inhibitors have focused mainly on increasing muscle mass rather than restoring strength. That gap has pushed researchers toward dietary compounds that might support muscle function at the cellular level, and urolithins have emerged as leading candidates.

Urolithin A already has a track record in muscle research. Previous preclinical and clinical studies have shown that it promotes mitophagy, the cellular housekeeping process that clears damaged mitochondria, thereby improving mitochondrial quality and muscle function. Urolithin B has attracted less attention, though recent work identified it as a regulator of skeletal muscle mass that promotes the differentiation and hypertrophy of myotubes, the multinucleated fibers that form in culture when muscle stem cells mature. Some studies also suggest urolithin B exerts testosterone-like effects that tip muscle protein balance toward growth. What remained unknown was how the two molecules compare when applied to genuine human muscle cells under identical conditions, and whether their effects converge on shared pathways or diverge into entirely different biology.

To find out, the researchers isolated satellite cells, the resident stem cells of skeletal muscle, from biopsies of the vastus lateralis muscle taken post-mortem from nine donors aged between 55 and 96, with ethical approval from the University of Liège. The cells were purified using immunomagnetic sorting for the satellite cell marker CD56, expanded in culture, and then differentiated for 48 hours into myotubes, a transition confirmed by measuring myogenic markers such as myosin. The mature myotubes were treated for 24 hours with either urolithin A or urolithin B at a concentration of 5 micromolar, a dose chosen to balance biological activity with physiological plausibility, since pharmacokinetic studies indicate that urolithin A can reach low micromolar levels in human plasma after supplementation. The team then sequenced the entire transcriptome of each sample, generating roughly 20 million reads per sample and analyzing differential gene expression with a paired statistical design that accounted for donor-to-donor baseline differences.

The scale of the response differed dramatically between the two compounds. Urolithin A significantly altered the expression of 1,918 genes, whereas urolithin B affected only 339. Despite this imbalance, 180 genes were regulated by both molecules, with 162 commonly down-regulated and 18 commonly up-regulated, pointing to shared effects that likely stem from their well-documented antioxidant and anti-inflammatory properties. More intriguing were the nine genes that moved in opposite directions. Eight genes, including EPB41L1, JPH1, GOT1, IL-17B, ESYT1, BEAN1, PCSK9 and SLCO4C1, were pushed up by urolithin B and pulled down by urolithin A, while a single gene, NQO1, was up-regulated by urolithin A and down-regulated by urolithin B. This pattern of discordant regulation suggests the two metabolites are not interchangeable, and that the net effect of a polyphenol-rich diet could depend on the relative abundance of each compound in an individual’s circulation.

Two of the oppositely regulated genes carry particular weight. IL-17B, an inflammatory signaling molecule, was decreased by roughly 49 percent under urolithin A but increased by about 45 percent under urolithin B. Recent work on dystrophinopathies has identified IL-17B as a biomarker of active muscle regeneration, enriched in regenerating fibers rather than in quiescent tissue. The authors interpret the opposing regulation not as a simple pro- versus anti-inflammatory split, but as evidence that the two compounds tune different inflammatory and regenerative programs: urolithin A may dampen the chronic low-grade inflammation implicated in sarcopenia, while urolithin B may nudge cells toward a remodeling state in which a controlled inflammatory component is part of repair. NQO1, meanwhile, encodes an enzyme that defends cells against oxidative stress by reducing quinones and preventing reactive oxygen species from forming. Its induction by urolithin A fits neatly with that compound’s established role in mitochondrial maintenance, whereas its suppression by urolithin B raises open questions about how anabolic signaling and oxidative defense are balanced under the second metabolite.

Pathway analysis sharpened the contrast. In urolithin A-treated cells, the most affected canonical pathways included inositol phosphate metabolism, calcium signaling and protein glycosylation routes, with most showing predicted inhibition. The authors propose that moderate inhibition of the inositol phosphate pathway, which is tightly linked to mitochondrial function through signaling molecules such as IP3, could trigger a compensatory boost in mitophagy and mitochondrial biogenesis, consistent with urolithin A’s known benefits. The glycosylation findings matter too, because protein glycosylation is now recognized as essential for maintaining normal muscle structure, and glycosylation defects are linked to muscle disease. Urolithin B told a different story: it strongly activated cholesterol biosynthesis and the mevalonate pathway, moderately activated adipogenesis, suppressed eicosanoid signaling in a way that could reduce inflammatory lipid mediators, and up-regulated CXCR4 signaling, a pathway recently shown to be critical for satellite cell activation, proliferation and self-renewal during muscle regeneration.

Validation experiments in cells from a subset of four donors confirmed several of these signals. Quantitative PCR showed that urolithin A increased expression of NOTCH1, a master regulator of muscle cell fate, as well as MYMX, a muscle-specific membrane protein involved in myogenic fusion, and PANX1, a newly identified regulator of myoblast proliferation and differentiation, while dose-dependently reducing FGF9 and ICAM5. Urolithin B was ineffective on these particular genes. Both compounds, however, dose-dependently reduced production of TGFBI, a protein associated with skeletal muscle remodeling, measured by ELISA in the culture supernatant. Live-cell imaging with label-free microscopy added a phenotypic dimension: fusion-like events appeared as early as six hours after treatment with either compound, and after 24 hours both treated conditions showed fewer isolated mononucleated cells than controls, consistent with enhanced incorporation of myoblasts into multinucleated myotubes.

The authors are careful to frame the work as mechanistic and exploratory rather than definitive. The myotubes were derived from post-mortem tissue, which may not fully mirror living muscle, although the use of expanded CD56-positive satellite cells, excellent RNA integrity and prior evidence that such cells retain functional competence mitigate that concern. The anonymized tissue source also meant detailed clinical phenotyping was unavailable, and the small, sex-unbalanced sample of six men and three women precluded formal analysis of age- or sex-specific responses. The short-term transcriptional data likewise cannot predict whether urolithin B’s activation of lipid-related pathways would be beneficial or, if chronically sustained in muscle, would contribute to the fatty infiltration associated with declining muscle quality. Still, the study sketches a compelling division of labor: urolithin A as a candidate for combating mitochondrial dysfunction and chronic inflammation in ageing muscle, and urolithin B as a potential ally for regeneration and repair after injury or surgery. The distinct yet complementary profiles raise the possibility of combination strategies targeting both the degenerative and regenerative faces of muscle decline, and they add a new layer to the growing science of the gut-muscle axis, in which the microbes of the colon may quietly shape how our muscles age.

Subject of Research: Transcriptomic effects of the gut microbial metabolites urolithin A and urolithin B on human skeletal muscle cells in relation to sarcopenia

Article Title: Exploring the Impact of Urolithins A and B on Muscle Health: A Transcriptomic Analysis in Human Myotubes

Article References: Henrotin, Y., Florin, A., Sanchez, C., Centonze, P., Coelho, T. P., Bekisz, S., Dubuc, J.-E., Galand, O., & Lambert, C. (2026). Exploring the Impact of Urolithins A and B on Muscle Health: A Transcriptomic Analysis in Human Myotubes. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70385. https://doi.org/10.1002/jcsm.70385

Image Credits: AI Generated

DOI: 10.1002/jcsm.70385

Keywords: urolithin A, urolithin B, sarcopenia, skeletal muscle, gut microbiota, ellagitannins, mitophagy, transcriptomics, myotubes, muscle regeneration, pomegranate polyphenols, inflammation

The research team, led by Jing Pan and Tzu-Shao Yeh of the Department of Nutrition and Food Hygiene at Nantong University in China, together with Luthfia Dewi of Universitas Muhammadiyah Semarang in Indonesia, focused their experiments on C2C12 cells, a widely used mouse skeletal muscle cell line that recapitulates key stages of muscle formation. These cells can be induced to behave like satellite cells, the resident stem cells of skeletal muscle, and to progress through the full differentiation program that turns undifferentiated myoblasts into mature, multinucleated myotubes, the cellular equivalent of muscle fibers. By treating these cells with boswellic acid and measuring changes at both the RNA and protein levels, the investigators were able to map the compound’s effects across the entire myogenic cascade.

The results were striking at multiple points along this cascade. Boswellic acid treatment produced a 17 percent increase in the number of Pax7-positive cells. Pax7 is the canonical marker of satellite cell identity and quiescent muscle stemness, and an expanded Pax7-positive population suggests that the compound preserves or expands the pool of cells capable of regenerating damaged or aging muscle tissue. This is a critical finding for the muscle aging field, because one hallmark of aged muscle is the depletion and dysfunction of its satellite cell reserve, leaving old muscles increasingly unable to repair themselves after injury, disuse, or disease.

Beyond stemness, the compound appeared to push cells more rapidly through the commitment and differentiation stages of muscle formation. The researchers quantified the relative messenger RNA levels of four master regulators of myogenesis: Pax7, Myf5, MyoD, and MyoG. These myogenic regulatory factors act in a choreographed sequence, with Pax7 maintaining the stem cell state, Myf5 and MyoD committing cells to the muscle lineage, and myogenin driving terminal differentiation and fusion into myotubes. Following boswellic acid treatment, the mRNA and protein levels of Myf5, MyoD, and MyoG were all significantly upregulated, indicating that the treated cells were accelerating through the myogenic differentiation program. The study also documented a two to four hour advancement in the myoblast renewal cycle, suggesting that the compound speeds the temporal rhythm by which muscle precursor cells proliferate and renew themselves before differentiating.

Protein-level confirmation came from Western blotting, a technique that separates proteins by molecular weight and detects them with specific antibodies. The team measured protein expression of Pax7, Myf5, MyoD, and MyoG, alongside loading controls such as beta-actin and GAPDH, and found the upregulation observed at the RNA level faithfully mirrored at the protein level. Immunofluorescence staining was used to visualize Pax7 and MyoD expression within individual cells, providing spatial confirmation that the molecular changes translated into shifts in the cellular populations themselves. Cell viability was assessed with the XTT assay, ensuring that the observed pro-myogenic effects were not simply an artifact of compound toxicity or stress-induced changes in cell behavior.

Perhaps the most translationally intriguing results concern hypertrophy, the enlargement of existing muscle fibers. Boswellic acid treatment significantly enhanced myotube hypertrophy through activation of the canonical hypertrophic signaling axis: the Akt-mTOR-p70S6K pathway. This pathway is the central growth-control circuit of skeletal muscle, integrating signals from insulin-like growth factor 1, mechanical loading, and nutrient availability to drive protein synthesis. Akt, or protein kinase B, phosphorylates and regulates downstream targets including mTOR, the mammalian target of rapamycin, which in turn activates p70S6K, a ribosomal protein S6 kinase that promotes ribosomal biogenesis and translation of muscle proteins. The researchers observed increased phosphorylation of all three nodes, indicating that boswellic acid switches on the same anabolic program engaged by resistance exercise and IGF-1 signaling.

The convergence of two effects, expanded stem cell activity and heightened anabolic signaling, is what distinguishes this study from many single-mechanism nutraceutical investigations. Aging muscle fails on both fronts: satellite cells become less numerous and less responsive, and the Akt-mTOR axis becomes progressively resistant to the anabolic stimuli of food intake and exercise, a phenomenon sometimes called anabolic resistance. A compound that simultaneously supports the regenerative stem cell compartment and re-energizes protein synthesis signaling could, in principle, address both dimensions of sarcopenia. The authors suggest that boswellic acid warrants consideration as a nutraceutical agent to enhance muscle differentiation and hypertrophy, and as a potential novel therapeutic strategy for mitigating muscle aging.

Boswellic acid itself has a long pharmacological history. It is the principal bioactive component of frankincense, the resin of Boswellia serrata and related species, and has been studied extensively for its anti-inflammatory properties, particularly its inhibition of 5-lipoxygenase and its effects on inflammatory pathways relevant to arthritis and inflammatory bowel disease. This new study extends its potential repertoire into muscle biology, a domain more commonly occupied by compounds such as creatine, leucine, and other branched-chain amino acids, and by pharmaceutical agents under development for sarcopenia. The triterpenoid structure of boswellic acid allows it to interact with multiple signaling proteins, which may explain its pleiotropic effects across the myogenic program and the growth-factor cascade.

The authors are careful to frame the work within its in vitro limits. All experiments were conducted in murine cell cultures, and the physiological concentration, absorption, and tissue distribution of boswellic acid in living organisms remain open questions. Satellite cell behavior in aged muscle is shaped by a complex niche of inflammatory signals, extracellular matrix changes, and vascular decline that a simplified cell culture cannot fully reproduce. The researchers explicitly state that additional in vivo and clinical investigations are warranted before any therapeutic relevance can be established. Human trials would need to establish safe dosing, bioavailability, and whether oral supplementation can achieve tissue concentrations capable of activating the pathways observed in culture.

Even so, the study adds to a growing scientific effort to identify accessible dietary compounds that can bias the balance between muscle loss and muscle regeneration in favor of renewal. With sarcopenia estimated to affect a substantial share of adults over sixty and to drive frailty, falls, and loss of independence, the search for safe, well-tolerated interventions is intensifying. If future animal and human studies confirm the mechanisms reported here, boswellic acid, a molecule that humans have consumed for millennia in the form of frankincense, could emerge as an unusually well-characterized candidate for supporting muscle health across the lifespan. For now, the finding stands as a compelling proof of concept: an ancient resin component, examined with modern molecular tools, appears capable of speaking the native language of regenerating muscle.

Subject of Research: Effects of boswellic acid on myogenic and hypertrophic signaling in skeletal muscle cells as a potential strategy against muscle aging

Article Title: Boswellic acid modulates myogenic and hypertrophic signaling in vitro: implications for muscle aging

Article References: Pan, J., Dewi, L., & Yeh, T.-S. (2026). Boswellic acid modulates myogenic and hypertrophic signaling in vitro: implications for muscle aging. BMC Complementary Medicine and Therapies. https://doi.org/10.1186/s12906-026-05596-9

Image Credits: AI Generated

DOI: 10.1186/s12906-026-05596-9

Keywords: boswellic acid, satellite cells, sarcopenia, muscle aging, myogenesis, skeletal muscle hypertrophy, Akt-mTOR-p70S6K, myogenic regulatory factors, nutraceutical, C2C12 cells, muscle regeneration, frankincense