Scientists Catch Muscle Aging in a Dish: A New Lab Model of Skeletal Muscle Senescence

Skeletal muscle does far more than move our limbs. It stabilizes joints, powers breathing, holds posture, and underpins quality of life throughout the human lifespan. When muscle function declines—whether through aging, sarcopenia, cancer, immobilization, or disease—cellular senescence is often lurking in the background. Yet how muscle cells actually enter and maintain the senescent state has remained stubbornly opaque, largely because researchers have lacked a faithful experimental system in which to watch the process unfold. Now, a team at the Federal University of Rio de Janeiro has built one, and their new model is already revealing molecular details that could reshape how we think about muscle wasting.

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