A metabolic sensor–driven metabolite repair system maintains muscle stem cell homeostasis - PROJECT SUMMARY Loss of skeletal muscle stem cell (satellite cell, SC) function is a central driver of impaired regeneration, progressive muscle wasting, and frailty in aging, muscular dystrophies, and metabolic diseases. These conditions represent a rapidly growing public health burden, contributing to loss of mobility and independence, diminished quality of life and increased healthcare costs worldwide, yet no effective therapies exist to preserve SC function or resilience. SCs are normally poised to remain quiescent until activated by injury or stress, at which point they expand, differentiate to repair damaged fibers, or self-renew to replenish the stem cell pool. With age and disease, this balance of fate decisions is disrupted, leading to stem cell depletion and impaired regenerative capacity. Although metabolism is recognized as a critical regulator of SC fate transitions, the mechanisms that preserve mitochondrial function and metabolic fidelity across the lifespan remain poorly defined. Our preliminary studies identify the CREB-regulated transcriptional coactivators (CRTCs) as essential, previously unexplored metabolic sensors in SCs. We discovered that CRTCs preserve mitochondrial respiration not by regulating canonical PGC1α–driven biogenesis, but through controlling the mitochondrial metabolite repair enzyme FAHD2A. FAHD2A prevents buildup of toxic enol-oxaloacetate, a by-product that inhibits succinate dehydrogenase, thereby safeguarding oxidative phosphorylation and SC proliferation. Importantly, FAHD2A levels decline with age in both mouse and human SCs, linking disruption of this pathway to SC attrition and regenerative failure. These findings uncover a CRTC–driven metabolite repair system as a critical safeguard of SC metabolism and function. The overall goal of this proposal is to establish the CRTC- FAHD2A axis as a novel metabolic sensor–driven metabolite repair pathway that protects mitochondrial metabolism, preserves stem cell competence, and sustains regeneration during injury and aging. Aim 1 will define the function of CRTCs in SC mitochondrial homeostasis using SC-specific CRTC mutant mice, high- resolution imaging, and mitochondrial diagnostics to test how CRTCs preserve respiration efficiency independent of biogenesis. Aim 2 will dissect the mechanism by which CRTCs regulate FAHD2A, and test whether FAHD2A restoration rescues mitochondrial and regenerative defects in CRTC-deficient SCs. Aim 3 will establish the role of the CRTC-FAHD2A axis in aging, assessing how this pathway is altered in aged mouse and human SCs, whether its loss exacerbates mitochondrial dysfunction and regenerative failure, and whether reactivation rejuvenates aged SCs in vivo and in primary human myoblasts across the aging spectrum. Completion of these studies will establish a new paradigm in stem cell biology by identifying metabolite repair as a fundamental safeguard of mitochondrial integrity and regenerative capacity. This work reframes stem cell decline during aging as a breakdown of metabolite quality control and positioning CRTCs and FAHD2A as therapeutic targets to preserve muscle health and combat muscle-wasting diseases.
