GLUD1 determines murine muscle stem cell fate by controlling mitochondrial glutamate levels

Muscle stem cells (MuSCs) enable muscle growth and regeneration after exercise or injury, but how metabolism controls their regenerative potential is poorly understood. We describe that primary metabolic changes can determine murine MuSC fate decisions. We found that glutamine anaplerosis into the TCA cycle decreases during MuSC differentiation and coincides with decreased expression of the mitochondrial glutamate deaminase GLUD1. Deletion of Glud1 in proliferating MuSCs resulted in precocious differentiation and fusion combined with loss of self-renewal in vitro and in vivo. Mechanistically, deleting Glud1 caused mitochondrial glutamate accumulation and inhibited the malate-aspartate shuttle (MAS). The resulting defect in transporting NADH reducing equivalents into the mitochondria induced compartment-specific NAD+/NADH ratio shifts. MAS activity restoration or directly altering NAD+/NADH ratios normalised myogenesis. In conclusion, GLUD1 prevents deleterious mitochondrial glutamate accumulation and inactivation of the MAS in proliferating MuSCs. It thereby acts as a compartment specific metabolic brake on MuSC differentiation. Overall design: Sample type and origin: Primary myoblasts isolated from mouse hind-limb mucles were used. Experimental conditions: The data set includes 3 experimental conditions corresponding to 3 different time points during myogenic differentiation in vitro: myoblasts cultured in growth media for 24h (proliferating myoblasts), differentiated myotubes for 48h (end of differentiation step) and fused myotubes (end of fusion step) (see methods for details). Genotypes: myoblasts with 2 different genotypes were used: wild type (used as control) and Glud1 deficient myoblasts. Replicates: at least 3 experimental replicates per condition were included. Except for Glud1-deficient differentiated myoblasts where only 2 replicates were included.