Muscle repair gene CSRP3 works in pigs but not mice, study finds

A single gene, CSRP3, turns out to be indispensable for muscle stem cell differentiation in pigs yet almost entirely dispensable in mice, according to a study published on 7 August 2026 in the journal Cell Regeneration. The finding, reported by Li Zhang, Wenya Li, Mingli Zhu and colleagues led by Yiming Xing, reveals a striking species-specific wiring of the molecular machinery that governs how satellite cells—the body’s resident muscle stem cells—mature into new muscle fibers. Because pigs resemble humans far more closely than rodents do in musculoskeletal structure and regeneration dynamics, the result carries practical weight for anyone hoping to turn satellite cell transplantation into a dependable therapy for damaged muscle.

Satellite cells sit quietly beneath the basal lamina that sheathes each muscle fiber until injury wakes them. Once activated, they proliferate, switch on myogenic determinants such as MyoD and Myf5, and then, under the influence of myogenin (MyoG), commit to differentiation and fuse into multinucleated myotubes. Clinical trials of satellite cell transplantation for muscular dystrophies have established the approach’s safety, but its effectiveness has remained stubbornly limited, partly because the cells differentiate suboptimally and large numbers of injections are needed. Understanding what controls the differentiation step is therefore a central problem in regenerative muscle biology, and it is the problem the team set out to attack.

The researchers focused on CSRP3, also known as muscle LIM protein, a highly conserved LIM-domain protein enriched in striated muscle and dynamically expressed during muscle development and repair. Its two LIM domains mediate protein–protein interactions, allowing the protein to shuttle between nucleus and cytoplasm. In humans, CSRP3 mutations are associated with cardiomyopathies, and mouse studies have linked the gene to cardiac and skeletal muscle integrity. But its role in pig skeletal muscle was poorly defined, so the team first mapped its expression during repair. Using a barium chloride-induced injury model in the longissimus dorsi muscle of pigs, they documented severe damage by day 2 and robust regeneration by day 6. PAX7-positive proliferating satellite cells peaked at day 6 and then declined sharply at day 9 as differentiation progressed, while CSRP3-positive cells surged at days 6 and 9—suggesting the protein acts late in the regenerative program, during myotube formation and maturation, rather than during early stem cell activation.

In vitro experiments with primary satellite cells from newborn piglets confirmed the pattern: CSRP3 expression rose steadily as myotubes formed over three days of differentiation. To test whether the protein was merely a bystander or a driver, the researchers generated knockdown (CSRP3KD) and overexpressing (CSRP3OE) satellite cells using lentiviral shRNA and overexpression vectors. Three days after differentiation was induced, knockdown cut the fusion index—the proportion of nuclei residing inside multinucleated myosin heavy chain-positive myotubes—by nearly half, from 48.4 percent in controls to 25.6 percent. Knockdown myotubes were also smaller, mostly containing 2 to 30 nuclei, whereas control cultures built larger myotubes with more than 30 nuclei. Overexpression did the opposite, raising the fusion index at day 2 from 16.0 to 33.3 percent and pushing myotubes into the 20-to-50-nucleus range. Because the fusion index measures nuclei inside multinucleated myotubes, it primarily reflects myoblast fusion efficiency rather than early lineage commitment, pointing to a role for CSRP3 in fusion and myotube maturation.

The mechanism ran through MYOG protein stability. Knockdown did not change MYOD expression or MYOG mRNA levels, but it destabilized the MYOG protein itself: a cycloheximide chase assay showed the MYOG half-life shrank from 4 hours in control cells to 1 hour in CSRP3-deficient cells. Downstream fusogenic genes MYMK and MYMX dropped accordingly. Quantitative proteomics of knockdown versus control cells at day 2 of differentiation flagged alterations in AKT signaling and in the activity of SERCA, the sarco/endoplasmic reticulum calcium ATPase pump. Western blotting confirmed that knockdown cells had reduced phosphorylated AKT and SERCA2, while overexpression boosted both. Treating differentiating cells with the AKT inhibitor AZD5363 (capivasertib) reproduced the knockdown phenotype in a dose-dependent fashion—at 4 micromolar the drug shortened the MYOG half-life from 4 hours to just 40 minutes and severely impaired myotube formation, although the authors note they could not fully exclude cytotoxic effects at that high concentration, even though overall cell numbers looked comparable. Conversely, the AKT agonist SC79 rescued the differentiation defect in CSRP3-knockdown cells, restoring both myotube formation and SERCA2 expression.

Downstream of SERCA2, the consequences cascaded into calcium and mitochondrial chaos. SERCA2 pumps cytoplasmic calcium back into the endoplasmic reticulum, and its dysfunction is a known route to calcium overload and mitochondrial damage. Knockdown cells showed markedly elevated intracellular calcium, total cellular reactive oxygen species, and mitochondrial-specific superoxide by day 2 of differentiation, alongside reduced expression of the mitochondrial genes CYCS, MCAD and COX5B. Transmission electron microscopy revealed the damage directly: where control cells maintained normal elliptical mitochondria with well-organized cristae, CSRP3-deficient cells carried elongated, irregular mitochondria with sparse, shortened cristae. Pharmacological inhibition of SERCA2 with thapsigargin phenocopied the knockdown, lowering MYOG protein, shrinking the fusion index and shortening MYOG half-life. Encouragingly, the mitochondria-targeted antioxidant MitoTEMPO restored differentiation capacity, MYOG protein levels and mitochondrial gene expression in knockdown cells, tying the pathology back to oxidative mitochondrial injury.

The surprise came when the same questions were asked of mice. The team generated Csrp3-null mice, which were born without apparent skeletal muscle defects. Although injury induced Csrp3 expression in wild-type muscle, 8-week-old knockout mice regenerated normally after barium chloride injury of the tibialis anterior, and their isolated satellite cells differentiated in vitro into myotubes indistinguishable from controls by day 3, with similar proliferation rates and unchanged MyoD and MyoG expression at both protein and mRNA levels. Phosphorylated AKT and SERCA2 levels were comparable between knockout and control muscle, even though both rose on post-injury days 5 and 7 in wild-type mice, mirroring the pig. The decisive difference appeared to be location: quantitative nuclear-to-cytoplasmic fluorescence ratios showed that in pigs CSRP3 accumulates in the cytoplasm after injury, whereas in mice it is predominantly nuclear. Protein–protein interaction analysis nominated CALML4, CANX and CALR as potential connectors between CSRP3 and the AKT-SERCA2 axis, and a reduction in calnexin (CANX) mRNA and protein emerged specifically in porcine knockdown cells but not in knockout mouse satellite cells—hinting at a pig-specific, CANX-mediated regulatory route.

The therapeutic payoff came from transplantation experiments. The team injected roughly one million porcine satellite cells into barium chloride-injured tibialis anterior muscles of immunodeficient NOD-PrkdcscidIL2rgtm1/Bcgen mice and harvested the muscles two weeks later. Grafts of CSRP3-overexpressing cells outperformed controls, with improved muscle mass-to-weight ratios, increased fiber diameter, and larger regenerated myofibers exceeding 2400 square micrometers compared with 1000 to 2200 square micrometers in controls. Knockdown grafts did the opposite, producing smaller muscles with fibers of only 200 to 1200 square micrometers. Critically, activating AKT with SC79 in knockdown cells before transplantation restored regenerative capacity to control levels, normalizing muscle mass, diameter and fiber size—confirming that CSRP3’s benefit operates through AKT-dependent mechanisms.

The authors are careful about the limits of their work. Whether cytoplasmically stabilized MYOG is efficiently translocated into the nucleus to exert its transcriptional activity remains unresolved, and the precise mechanism by which cytoplasmic CSRP3 stabilizes MYOG—possibly through the ubiquitin–proteasome system or molecular chaperones—remains to be elucidated, with no experimental evidence yet of direct binding between the two proteins. How CSRP3, which lacks intrinsic kinase activity, promotes AKT phosphorylation is also open; the authors speculate it may act as a scaffold for signaling complexes or indirectly through calcium homeostasis. Long-term questions linger too: the transplantation study captured acute regeneration at two weeks, but self-renewal of the PAX7-positive stem cell pool and durable engraftment were not assessed. Most importantly, the team cautions against extrapolating pig results to humans, since CSRP3’s localization, function and interacting partners may differ substantially in human cells, and validation in human satellite cells or humanized models is still needed. Within those bounds, the study delivers a clear message: a gene once assumed to work the same way across mammals orchestrates muscle stem cell differentiation in a species-specific fashion, and strategically engineering porcine satellite cells through CSRP3 modulation could sharpen the effectiveness of xenotransplantation-based approaches to muscle repair.

Subject of Research: Species-specific role of the CSRP3 gene in satellite cell-mediated muscle regeneration in pigs and mice

Article Title: Species-specific functions of CSRP3 in satellite cell-driven muscle regeneration and relevance to porcine stem cell therapy

Article References: Zhang, L., Li, W., Zhu, M., Yang, H., Bai, Y., Sun, B., & Xing, Y. (2026). Species-specific functions of CSRP3 in satellite cell-driven muscle regeneration and relevance to porcine stem cell therapy. Cell Regeneration, 15(1), Article 25. https://doi.org/10.1186/s13619-026-00294-w

Image Credits: AI Generated

DOI: 10.1186/s13619-026-00294-w

Keywords: CSRP3, satellite cells, muscle regeneration, myogenin, AKT-SERCA2 pathway, mitochondrial dysfunction, calcium homeostasis, porcine stem cells, xenotransplantation, MYOG stability, species-specific gene function, Cell Regeneration