RANKL Elevation Contributes to Skeletal Muscle Myopathy in Aging: Unveiling of Novel Mechanisms

Age-related muscle wasting, or sarcopenia, is characterized by oxidative stress, inflammaging, and disruption of scaffolding (e.g., dystrophin, a-syntrophin) and signaling (e.g., neuronal nitric oxide synthase: nNOS) proteins of the sarcolemmal dystrophin-glycoprotein complex (DGC). nNOS regulates skeletal muscle mass, blood flow, and mitochondrial function, and the loss of nNOS with spaceflight and Duchenne muscular dystrophy leads to myopathy. Receptor Activator of Nuclear factor Kappa-Β Ligand (RANKL) has been historically deemed causal in elevated osteoclast activity and osteoporosis, but has recently been linked to skeletal muscle wasting, including sarcopenia. We hypothesized that elevated RANKL in aging skeletal muscle would be linked to loss of sarcolemmal DGC, impaired mitochondrial function, immune cell invasion, and thus Ca2+ overload. To test our hypothesis, we used osteoprotegerin fusion protein (OPG-Fc), a physiological RANKL inhibitor, as a short-term intervention (28 days) in aged mice. RANKL protein levels were significantly elevated in skeletal muscle from old (24-month) mice compared with adult (6-month) mice. Treatment with OPG-Fc (1 mg/kg every 3 days) reduced RANKL levels in aged muscle by 30% (p=0.0525), with levels no different than adult controls. OPG-Fc conferred improvement in mitochondrial coupling, as evidenced by reduced mitochondrial leak. In addition, OPG-Fc reduced calpain activity, a marker of Ca 2+ overload, by over 50%. Importantly, OPG-Fc also mitigated aging-associated sarcolemmal loss of nNOS. Similarly, OPG-Fc treatment ameliorated aging-related disruption of sarcolemmal dystrophin and a-syntrophin. In addition, RANKL inhibition also reduced age-associated elevation of cytotoxic T-cells (CD8+), and myeloid cells (CD68+) using immunoblot and immunofluorescence staining. Our data reveal a novel site of RANKL-induced disruption of skeletal muscle function: DGC and nNOS disruption, contributing to mitochondrial dysfunction, immune cell invasion, and Ca 2+ dyshomeostasis. The above findings will lead to future studies that will further elucidate novel mechanisms by which RANKL-elicited disruption of the DGC and mitochondrial function contributes to the sarcopenic process. Supported by NASA (80NSSC19K0432, NNX80NSSC17K0118, NNX13AE45G), NSBRI, and Huffines Institute, FightDMD. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.