Disrupted Cystine Transport Via xCT Induces Serine Metabolic Reprogramming and Enhances Differentiation in Skeletal Muscle Cells

Abstract

Skeletal muscle (SKM) is a remarkable tissue that exerts many important functions such as maintaining posture and mobility, but also plays a major role in metabolism. SKM health is affected by redox homeostasis, which involves electron transfer between molecules driven by redox pairs that interconvert between oxidized and reduced states. The antioxidant glutathione (GSH) and its oxidized disulfide form (GSSG) is one such redox pair that is very abundant in cells, including muscle stem cells (MuSCs), and therefore generally determines cellular redox state. The synthesis of GSH is limited by the availability of cyst(e)ine, which mostly enters cells through the cystine/glutamate plasma membrane antiporter xCT. The goal of this work was to assess the impact of disrupted cystine import on MuSC health and SKM regeneration (myogenesis). Specifically, the understanding of the specific metabolic implications induced by xCT dysfunction, and their consequence on mitochondrial function and myogenesis was sought. MuSCs from mice harboring a mutation in the Slc7a11 gene encoding xCT (Slc7a11ˢᵘᵗᐟˢᵘᵗ) were investigated and findings demonstrated perturbed GSH homeostasis and higher H₂O₂ production compared to WT. Moreover, Slc7a11ˢᵘᵗᐟˢᵘᵗ MuSCs had lower mitochondrial oxidative function and higher Drp1-mediated mitochondrial fission. Metabolomics analyses and [U-¹³C]-glucose stable isotope tracing showed profound metabolic reprogramming in Slc7a11ˢᵘᵗᐟˢᵘᵗ MuSCs, characterized by lower TCA cycle activity and increased glucose flux towards de novo serine and cysteine synthesis. Finally, Slc7a11ˢᵘᵗᐟˢᵘᵗ MuSCs demonstrated higher differentiation and regeneration rates as evidenced by a higher fusion index of myotubes at day 2 of differentiation and increased tissue myofiber cross-sectional area at 21 days post-cardiotoxin injury. Therefore, beyond its established function in redox homeostasis, this work unravels a critical metabolic function of xCT in muscle cells, providing insights that may inform therapeutic strategies for muscular pathologies.