GLUD1 dictates muscle stem cell differentiation by controlling mitochondrial glutamate levels

Muscle stem cells (MuSCs) enable muscle growth and regeneration after exercise or injury. Upon activation MuSCs metabolically rewire to meet the changing demands of proliferation. Here we describe that primary changes in metabolism itself can dictate MuSC fate decisions to control differentiation and fusion. We found that glutamine anaplerosis into the TCA cycle decreases during MuSC differentiation and coincides with decreased expression of the mitochondrial glutamate deaminase GLUD1. Genetic deletion of Glud1 in proliferating MuSCs resulted in precocious differentiation and imbalanced fusion combined with loss of self-renewal in vitro and in vivo. Mechanistically, deleting Glud1 caused mitochondrial glutamate accumulation in proliferating MuSCs and inhibited the malate-aspartate shuttle (MAS). Restoring MAS activity by supplementation of alanine normalized differentiation. In conclusion, high GLUD1 activity in proliferating MuSCs prevents deleterious mitochondrial glutamate accumulation and inactivation of the MAS. It thereby acts as a compartment specific metabolic brake on MuSC differentiation. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=194 SRC="FIGDIR/small/560525v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@e3585dorg.highwire.dtl.DTLVardef@1be4a54org.highwire.dtl.DTLVardef@1f077org.highwire.dtl.DTLVardef@15220f1_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIGlutamine is the major TCA cycle substrate in MuSCs with decreasing contribution upon differentiation. C_LIO_LILoss of Glud1 impairs MuSC self-renewal capacity and causes imbalanced fusion in vitro and in vivo. C_LIO_LIGlud1 deletion leads to mitochondrial glutamate trapping and malate-aspartate shuttle (MAS) dysfunction. C_LIO_LIRestoration of MAS activity in Glud1 deficient MuSCs reverses precocious differentiation and imbalanced fusion. C_LI