CARM1 drives mitophagy and autophagy flux during fasting-induced skeletal muscle atrophy.

CARM1 (coactivator associated arginine methyltransferase 1) has recently emerged as a powerful regulator of skeletal muscle biology. However, the molecular mechanisms by which the methyltransferase remodels muscle remain to be fully understood. In this study, skeletal muscle-specific knockout (mKO) mice exhibited lower muscle mass with dysregulated macroautophagic/autophagic and atrophic signaling, including depressed AMP-activated protein kinase (AMPK) site-specific phosphorylation of ULK1 (unc-51 like autophagy activating kinase 1; Ser555) and FOXO3 (forkhead box O3; Ser588), as well as MTOR (mechanistic target of rapamycin kinase)-induced inhibition of ULK1 (Ser757), along with AKT/protein kinase B site-specific suppression of FOXO1 (Ser256) and FOXO3 (Ser253). In addition to lower mitophagy and autophagy flux in skeletal muscle, mKO led to increased mitochondrial PRKN/parkin accumulation, which suggests that CARM1 is required for basal mitochondrial turnover and autophagic clearance. deletion also elicited PPARGC1A (PPARG coactivator 1 alpha) activity and a slower, more oxidative muscle phenotype. As such, these mKO-evoked adaptations disrupted mitophagy and autophagy induction during food deprivation and collectively served to mitigate fasting-induced muscle atrophy. Furthermore, at the threshold of muscle atrophy during food deprivation experiments in humans, skeletal muscle CARM1 activity decreased similarly to our observations in mice, and was accompanied by site-specific activation of ULK1 (Ser757), highlighting the translational impact of the methyltransferase in human skeletal muscle. Taken together, our results indicate that CARM1 governs mitophagic, autophagic, and atrophic processes fundamental to the maintenance and remodeling of muscle mass. Targeting the enzyme may provide new therapeutic approaches for mitigating skeletal muscle atrophy.: ADMA: asymmetric dimethylarginine; AKT/protein kinase B: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ATG: autophagy related; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; CARM1: coactivator associated arginine methyltransferase 1; Col: colchicine; CSA: cross-sectional area; CTNS: cystinosin, lysosomal cystine transporter; EDL: extensor digitorum longus; FBXO32/MAFbx: F-box protein 32; FOXO: forkhead box O; GAST: gastrocnemius; HO: hydrogen peroxide; IMF: intermyofibrillar; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; mKO: skeletal muscle-specific knockout; MMA: monomethylarginine; MTOR: mechanistic target of rapamycin kinase; MYH: myosin heavy chain; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; OXPHOS: oxidative phosphorylation; PABPC1/PABP1: poly(A) binding protein cytoplasmic 1; PPARGC1A/PGC-1α: PPARG coactivator 1 alpha; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; PRMT: protein arginine methyltransferase; Sal: saline; SDMA: symmetric dimethylarginine; SIRT1: sirtuin 1; SKP2: S-phase kinase associated protein 2; SMARCC1/BAF155: SWI/SNF related, matrix associated, actin dependent regulator of chromatin subfamily c member 1; SOL: soleus; SQSTM1/p62: sequestosome 1; SS: subsarcolemmal; TA: tibialis anterior; TFAM: transcription factor A, mitochondrial; TFEB: transcription factor EB; TOMM20: translocase of outer mitochondrial membrane 20; TRIM63/MuRF1: tripartite motif containing 63; ULK1: unc-51 like autophagy activating kinase 1; VPS11: VPS11 core subunit of CORVET and HOPS complexes; WT: wild-type.