As we grow older, a torn or injured muscle simply does not bounce back the way it once did. What was once a swift, almost invisible repair process becomes slow, incomplete, and prone to scarring. A new study published in the journal GeroScience offers a striking explanation for why this happens, and a potential way to fix it. Researchers at the University of Ottawa report that a single lipid molecule called Resolvin E1, or RvE1, can jump-start the failing repair machinery of aged mouse muscle by simultaneously calming chronic inflammation and directly stimulating the stem cells that rebuild muscle fibers. The findings, drawn from a combination of cell culture experiments and a mouse model of muscle injury, position RvE1 as a serious therapeutic candidate for age-related muscle dysfunction.
The story begins with the biology of muscle repair itself. Skeletal muscle has a remarkable capacity to regenerate, and the workhorses of this process are muscle stem cells, known as MuSCs, which sit quietly beside muscle fibers until injury wakes them. Once activated, they proliferate, differentiate into myoblasts, and fuse to replace damaged tissue. But the stem cells do not act alone. They are embedded in a niche populated by immune cells, and the quality of repair depends on a precisely choreographed conversation between the two. Neutrophils flood the wound first, followed by pro-inflammatory macrophages that clear dead debris and release signals such as interleukin-6 and prostaglandin E2, which push MuSCs into their activation and expansion phase.
In a young, healthy muscle, this fiery opening act gives way to a calmer second act. Macrophages shift toward an anti-inflammatory profile, and the tissue begins producing a family of bioactive fats called specialized pro-resolving mediators, or SPMs. These molecules, which include resolvins, protectins, and maresins and are derived mainly from omega-3 polyunsaturated fatty acids, do not simply suppress inflammation the way a steroid might. Instead, they actively drive the resolution program: they help clear neutrophils, encourage macrophages to adopt repair-oriented states, and preserve the host defenses needed to fight infection. Crucially, this lipid-mediated class switch is what allows the regenerative environment to mature so that myoblasts can differentiate, fuse, and complete the repair.
Aging scrambles this choreography. Previous work has shown that old skeletal muscle is deficient in endogenous SPMs while remaining awash in pro-inflammatory eicosanoids such as prostaglandins and leukotrienes. The result is a niche stuck in first gear: macrophages and neutrophils linger far longer than they should, chronic inflammatory signaling persists, fibrosis accumulates, and MuSCs receive contradictory instructions that blunt their regenerative output. The Ottawa team, led by senior author Junio Dort, wanted to know whether supplying one key SPM from outside could compensate for this age-related deficit. They chose RvE1, the principal member of the E-series resolvins, which is derived from eicosapentaenoic acid and had been well characterized in other tissues but largely unexplored in skeletal muscle, where its D-series cousins had received most of the attention.
The first experiments were conducted in a dish. The researchers isolated bone marrow monocytes from mice older than twenty months, which corresponds to advanced age in the mouse lifespan, and differentiated them into macrophages. When these aged macrophages were stimulated with bacterial lipopolysaccharide and interferon-gamma to mimic an inflammatory assault, treatment with 200 nanomolar RvE1 produced a clear shift. The proportion of macrophages expressing CD206, a canonical anti-inflammatory marker, rose by roughly one and a half fold, while the fraction expressing CD163, another resolution-associated receptor, increased fourfold. Western blotting confirmed elevated CD206 protein. At the same time, quantitative PCR revealed that RvE1 significantly suppressed the expression of pro-inflammatory genes including tumor necrosis factor-alpha and transforming growth factor-beta, with downward trends in the neutrophil-recruiting chemokine CXCL1 and the inflammatory enzyme Ptgs2.
Interestingly, the molecule’s effects on classical anti-inflammatory genes such as interleukin-10 were modest. The authors interpret this selectivity through the lens of receptor biology. RvE1 signals primarily through ChemR23, a receptor enriched on inflammatory neutrophils and macrophages, where its activation dampens NF-kappaB signaling and cytokine production. In other words, RvE1 does not install a brand-new anti-inflammatory program; it switches off the persistent pro-inflammatory hum, and that silencing itself feeds back to promote pro-resolving macrophage polarization. This distinction matters therapeutically, because it suggests the molecule fine-tunes rather than blanket-suppresses immunity, preserving the early inflammatory cues that muscle stem cells actually need to begin repairing tissue.
The in vivo experiments then tested whether these cellular effects translate into better healing. The team injured the tibialis anterior muscle of aged mice with cardiotoxin and, beginning twenty-four hours after injury, gave the animals twice-weekly subcutaneous injections of RvE1 at five micrograms per kilogram for two weeks. Fourteen days later, the treated muscles looked meaningfully different from the vehicle controls. Total macrophage infiltration trended downward, the proportion of anti-inflammatory F4/80-positive CD206-positive macrophages rose significantly, and neutrophil accumulation, measured by Ly6G staining, dropped markedly. The regenerating tissue also contained more PAX7-positive muscle stem cells and more MYOG-positive differentiating myoblasts, indicating an expanded and more advanced myogenic cell pool.
Some structural measures told a subtler story. RvE1 did not change the number of newly formed embryonic myosin heavy chain-positive fibers or the average fiber cross-sectional area at the day-14 endpoint, but it significantly reduced the percentage of centrally nucleated fibers, a hallmark of repeated cycles of degeneration and regeneration, and showed a downward trend in collagen-rich fibrotic areas. Force testing with a dual-mode lever system revealed a general trend toward improved contractile function in the treated muscles, although the authors are careful to note that the relatively small sample size of three animals per group limited statistical power for some histological and functional outcomes. The picture that emerges is one of accelerated regenerative kinetics rather than a finished product: RvE1 appears to move the whole repair process forward in time.
The team also asked whether RvE1 acts directly on the muscle stem cells themselves, not just on their immune environment. When primary myoblasts isolated from aged mice were treated with RvE1 for sixteen hours in proliferation medium, levels of the myogenic transcription factor MYOD rose significantly, accompanied by increased Ki67 staining, a marker of active cell division. After four days in differentiation conditions, however, the molecule had minimal effect on myotube diameter or fusion index, suggesting that its direct myogenic action is concentrated in the early expansion phase. The authors propose that RvE1 may engage the BLT1 receptor expressed on myoblasts, and that in living muscle, RvE1-polarized anti-inflammatory macrophages likely add a paracrine boost by secreting myogenic growth factors such as insulin-like growth factor-1 and interleukin-4.
The study has limitations the authors acknowledge candidly. Macrophage polarization was assessed mainly through CD206 and CD163, whereas macrophage activation is now understood as a continuum of states rather than a binary M1/M2 switch; single-cell transcriptomics would paint a richer picture. The single day-14 endpoint cannot capture whether early cellular gains mature into lasting architectural and functional improvements, and the trends in fibrosis and muscle force await confirmation in larger cohorts. Native RvE1 is also hampered by a short biological half-life, though metabolically stable analogs and orally active SPM mimetics are in development, and early clinical studies of SPM-enriched supplements have shown encouraging effects on inflammatory biomarkers in conditions such as knee osteoarthritis. Even with those caveats, the convergence of evidence is compelling: a single omega-3-derived lipid can reprogram the aged muscle niche, clearing out lingering neutrophils, steering macrophages toward repair, expanding the stem cell pool, and nudging old muscle toward the regenerative behavior of its younger self. For a population whose falls, frailty, and lost independence trace back to muscles that no longer heal, that is a molecule worth watching.
Subject of Research: The role of the specialized pro-resolving mediator Resolvin E1 in inflammation resolution and skeletal muscle regeneration during aging
Article Title: Resolvin E1 promotes the resolution of inflammation and enhances myogenic responses during aged skeletal muscle regeneration
Article References: Arsenault, R., Ziadeh, A., Assebbane, A., Yezihalem, H., Green, A., & Dort, J. (2026). Resolvin E1 promotes the resolution of inflammation and enhances myogenic responses during aged skeletal muscle regeneration. GeroScience. https://doi.org/10.1007/s11357-026-02566-4
Image Credits: AI Generated
DOI: 10.1007/s11357-026-02566-4
Keywords: Resolvin E1, specialized pro-resolving mediators, skeletal muscle regeneration, muscle stem cells, macrophage polarization, inflammation resolution, aging, omega-3 fatty acids, myogenesis, neutrophil clearance, fibrosis, GeroScience
