Protein arginine methyltransferase biology in humans during acute and chronic skeletal muscle plasticity

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, carm1 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, carm1 mKO led to increased mitochondrial PRKN/parkin accumulation, which suggests that CARM1 is required for basal mitochondrial turnover and autophagic clearance. carm1 deletion also elicited PPARGC1A (PPARG coactivator 1 alpha) activity and a slower, more oxidative muscle phenotype. As such, these carm1 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.Abbreviation: 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; H2O2: 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.

Characterization of the skeletal muscle arginine methylome in health and disease reveals remodeling in amyotrophic lateral sclerosis

Arginine methylation is a protein posttranslational modification important for the development of skeletal muscle mass and function. Despite this, our understanding of the regulation of arginine methylation under settings of health and disease remains largely undefined. Here, we investigated the regulation of arginine methylation in skeletal muscles in response to exercise and hypertrophic growth, and in diseases involving metabolic dysfunction and atrophy. We report a limited regulation of arginine methylation under physiological settings that promote muscle health, such as during growth and acute exercise, nor in disease models of insulin resistance. In contrast, we saw a significant remodeling of asymmetric dimethylation in models of atrophy characterized by the loss of innervation, including in muscle biopsies from patients with myotrophic lateral sclerosis (ALS). Mass spectrometry-based quantification of the proteome and asymmetric arginine dimethylome of skeletal muscle from individuals with ALS revealed the largest compendium of protein changes with the identification of 793 regulated proteins, and novel site-specific changes in asymmetric dimethyl arginine (aDMA) of key sarcomeric and cytoskeletal proteins. Finally, we show that in vivo overexpression of PRMT1 and aDMA resulted in increased fatigue resistance and functional recovery in mice. Our study provides evidence for asymmetric dimethylation as a regulator of muscle pathophysiology and presents a valuable proteomics resource and rationale for numerous methylated and nonmethylated proteins, including PRMT1, to be pursued for therapeutic development in ALS.

Sex-Specific Effect of CARM1 in Skeletal Muscle Adaptations to Exercise

PURPOSE

The purpose of this study was to determine how the intersection of coactivator-associated arginine methyltransferase 1 (CARM1) and biological sex affects skeletal muscle adaptations to chronic physical activity.

METHODS

Twelve-week-old female (F) and male (M) wild-type (WT) and CARM1 skeletal muscle-specific knockout (mKO) mice were randomly assigned to sedentary (SED) or voluntary wheel running (VWR) experimental groups. For 8 wk, the animals in the VWR cohort had volitional access to running wheels. Subsequently, we performed whole-body functional tests, and 48 h later muscles were harvested for molecular analysis. Western blotting, enzyme activity assays, as well as confocal and transmission electron microscopy were used to examine skeletal muscle biology.

RESULTS

Our data reveal a sex-dependent reduction in VWR volume caused by muscle-specific ablation of CARM1, as F CARM1 mKO mice performed less chronic, volitional exercise than their WT counterparts. Regardless of VWR output, exercise-induced adaptations in physiological function were similar between experimental groups. A broad panel of protein arginine methyltransferase (PRMT) biology measurements, including markers of arginine methyltransferase expression and activity, were unaffected by VWR, except for CARM1 and PRMT7 protein levels, which decreased and increased with VWR, respectively. Changes in myofiber morphology and mitochondrial protein content showed similar trends among animals. However, a closer examination of transmission electron microscopy images revealed contrasting responses to VWR in CARM1 mKO mice compared with WT littermates, particularly in mitochondrial size and fractional area.

CONCLUSIONS

The present findings demonstrate that CARM1 mKO reduces daily running volume in F mice, as well as exercise-evoked skeletal muscle mitochondrial plasticity, which indicates that this enzyme plays an essential role in sex-dependent differences in exercise performance and mitochondrial health.

Impact of short-term, pharmacological CARM1 inhibition on skeletal muscle mass, function, and atrophy in mice

Coactivator-associated arginine methyltransferase 1 (CARM1) catalyzes the methylation of arginine residues on target proteins critical for health and disease. The purpose of this study was to characterize the effects of short-term, pharmacological CARM1 inhibition on skeletal muscle size, function, and atrophy. Adult mice (n = 10 or 11/sex) were treated with either a CARM1 inhibitor (150 mg/kg EZM2302; EZM) or vehicle (Veh) via oral gavage for 11-13 days and muscle mass, function, and exercise capacity were assessed. In addition, we investigated the effect of CARM1 suppression on unilateral hindlimb denervation (DEN)-induced muscle atrophy (n = 8/sex). We report that CARM1 inhibition caused significant reductions in the asymmetric dimethylation of known CARM1 substrates but no change in CARM1 protein or mRNA content in skeletal muscle. Reduced CARM1 activity did not affect body or muscle mass, however, we observed a decrease in exercise capacity and muscular endurance in male mice. CARM1 methyltransferase activity increased in the muscle of Veh-treated mice following 7 days of DEN, and this response was blunted in EZM-dosed mice. Skeletal muscle mass and myofiber cross-sectional area were significantly reduced in DEN compared with contralateral, non-DEN limbs to a similar degree in both treatment groups. Furthermore, skeletal muscle atrophy and autophagy gene expression programs were elevated in response to DEN independent of CARM1 suppression. Collectively, these results suggest that short-term, pharmacological CARM1 inhibition in adult animals affects muscle performance in a sex-specific manner but does not impact the maintenance and remodeling of skeletal muscle mass during conditions of neurogenic muscle atrophy.NEW & NOTEWORTHY Short-term pharmacological inhibition of coactivator-associated arginine methyltransferase 1 (CARM1) was effective at significantly reducing CARM1 methyltransferase function in skeletal muscle. CARM1 inhibition did not impact muscle mass, but exercise capacity was impaired, particularly in male mice, whereas morphological and molecular signatures of denervation-induced muscle atrophy were largely maintained in animals administered the inhibitor. Altogether, the role of CARM1 in neuromuscular biology remains complex and requires further investigation of its therapeutic potential in muscle-wasting conditions.

PRMT5 links lipid metabolism to contractile function of skeletal muscles

Skeletal muscle plays a key role in systemic energy homeostasis besides its contractile function, but what links these functions is poorly defined. Protein Arginine Methyl Transferase 5 (PRMT5) is a well-known oncoprotein but also expressed in healthy tissues with unclear physiological functions. As adult muscles express high levels of Prmt5, we generated skeletal muscle-specific Prmt5 knockout (Prmt5MKO ) mice. We observe reduced muscle mass, oxidative capacity, force production, and exercise performance in Prmt5MKO mice. The motor deficiency is associated with scarce lipid droplets in myofibers due to defects in lipid biosynthesis and accelerated degradation. Specifically, PRMT5 deletion reduces dimethylation and stability of Sterol Regulatory Element-Binding Transcription Factor 1a (SREBP1a), a master regulator of de novo lipogenesis. Moreover, Prmt5MKO impairs the repressive H4R3 symmetric dimethylation at the Pnpla2 promoter, elevating the level of its encoded protein ATGL, the rate-limiting enzyme catalyzing lipolysis. Accordingly, skeletal muscle-specific double knockout of Pnpla2 and Prmt5 normalizes muscle mass and function. Together, our findings delineate a physiological function of PRMT5 in linking lipid metabolism to contractile function of myofibers.

The role of exercise-induced myokines in promoting angiogenesis

Ischemic diseases are a major cause of mortality or disability in the clinic. Surgical or medical treatment often has poor effect on patients with tissue and organ ischemia caused by diffuse stenoses. Promoting angiogenesis is undoubtedly an effective method to improve perfusion in ischemic tissues and organs. Although many animal or clinical studies tried to use stem cell transplantation, gene therapy, or cytokines to promote angiogenesis, these methods could not be widely applied in the clinic due to their inconsistent experimental results. However, exercise rehabilitation has been written into many authoritative guidelines in the treatment of ischemic diseases. The function of exercise in promoting angiogenesis relies on the regulation of blood glucose and lipids, as well as cytokines that secreted by skeletal muscle, which are termed as myokines, during exercise. Myokines, such as interleukin-6 (IL-6), chemokine ligand (CXCL) family proteins, irisin, follistatin-like protein 1 (FSTL1), and insulin-like growth factor-1 (IGF-1), have been found to be closely related to the expression and function of angiogenesis-related factors and angiogenesis in both animal and clinical experiments, suggesting that myokines may become a new molecular target to promote angiogenesis and treat ischemic diseases. The aim of this review is to show current research progress regarding the mechanism how exercise and exercise-induced myokines promote angiogenesis. In addition, the limitation and prospect of researches on the roles of exercise-induced myokines in angiogenesis are also discussed. We hope this review could provide theoretical basis for the future mechanism studies and the development of new strategies for treating ischemic diseases.

The CARM1 transcriptome and arginine methylproteome mediate skeletal muscle integrative biology

OBJECTIVE

Coactivator-associated arginine methyltransferase 1 (CARM1) catalyzes the methylation of arginine residues on target proteins to regulate critical processes in health and disease. A mechanistic understanding of the role(s) of CARM1 in skeletal muscle biology is only gradually emerging. The purpose of this study was to elucidate the function of CARM1 in regulating the maintenance and plasticity of skeletal muscle.

METHODS

We used transcriptomic, methylproteomic, molecular, functional, and integrative physiological approaches to determine the specific impact of CARM1 in muscle homeostasis.

RESULTS

Our data defines the occurrence of arginine methylation in skeletal muscle and demonstrates that this mark occurs on par with phosphorylation and ubiquitination. CARM1 skeletal muscle-specific knockout (mKO) mice displayed altered transcriptomic and arginine methylproteomic signatures with molecular and functional outcomes confirming remodeled skeletal muscle contractile and neuromuscular junction characteristics, which presaged decreased exercise tolerance. Moreover, CARM1 regulates AMPK-PGC-1α signalling during acute conditions of activity-induced muscle plasticity.

CONCLUSIONS

This study uncovers the broad impact of CARM1 in the maintenance and remodelling of skeletal muscle biology.

PRMT7: A Pivotal Arginine Methyltransferase in Stem Cells and Development

Protein arginine methylation is a posttranslational modification catalyzed by protein arginine methyltransferases (PRMTs), which play critical roles in many biological processes. To date, nine PRMT family members, namely, PRMT1, 2, 3, 4, 5, 6, 7, 8, and 9, have been identified in mammals. Among them, PRMT7 is a type III PRMT that can only catalyze the formation of monomethylarginine and plays pivotal roles in several kinds of stem cells. It has been reported that PRMT7 is closely associated with embryonic stem cells, induced pluripotent stem cells, muscle stem cells, and human cancer stem cells. PRMT7 deficiency or mutation led to severe developmental delay in mice and humans, which is possibly due to its crucial functions in stem cells. Here, we surveyed and summarized the studies on PRMT7 in stem cells and development in mice and humans and herein provide a discussion of the underlying molecular mechanisms. Furthermore, we also discuss the roles of PRMT7 in cancer, adipogenesis, male reproduction, cellular stress, and cellular senescence, as well as the future perspectives of PRMT7-related studies. Overall, PRMT7 mediates the proliferation and differentiation of stem cells. Deficiency or mutation of PRMT7 causes developmental delay, including defects in skeletal muscle, bone, adipose tissues, neuron, and male reproduction. A better understanding of the roles of PRMT7 in stem cells and development as well as the underlying mechanisms will provide information for the development of strategies for in-depth research of PRMT7 and stem cells as well as their applications in life sciences and medicine.

Role of Protein Arginine Methyltransferases and Inflammation in Muscle Pathophysiology

Arginine methylation mediated by protein arginine methyltransferases (PRMTs) is a post-translational modification of both histone and non-histone substrates related to diverse biological processes. PRMTs appear to be critical regulators in skeletal muscle physiology, including regeneration, metabolic homeostasis, and plasticity. Chronic inflammation is commonly associated with the decline of skeletal muscle mass and strength related to aging or chronic diseases, defined as sarcopenia. In turn, declined skeletal muscle mass and strength can exacerbate chronic inflammation. Thus, understanding the molecular regulatory pathway underlying the crosstalk between skeletal muscle function and inflammation might be essential for the intervention of muscle pathophysiology. In this review, we will address the current knowledge on the role of PRMTs in skeletal muscle physiology and pathophysiology with a specific emphasis on its relationship with inflammation.

CARM1 Regulates AMPK Signaling in Skeletal Muscle

Coactivator-associated arginine methyltransferase 1 (CARM1) is an emerging mediator of skeletal muscle plasticity. We employed genetic, physiologic, and pharmacologic approaches to determine whether CARM1 regulates the master neuromuscular phenotypic modifier AMP-activated protein kinase (AMPK). CARM1 skeletal muscle-specific knockout (mKO) mice displayed reduced muscle mass and dysregulated autophagic and atrophic processes downstream of AMPK. We observed altered interactions between CARM1 and AMPK and its network, including forkhead box protein O1, during muscle disuse. CARM1 methylated AMPK during the early stages of muscle inactivity, whereas CARM1 mKO mitigated progression of denervation-induced atrophy and was accompanied by attenuated phosphorylation of AMPK targets such as unc-51 like autophagy-activating kinase 1^Ser555. Lower acetyl-coenzyme A corboxylase^Ser79 phosphorylation, as well as reduced peroxisome proliferator-activated receptor-γ coactivator-1α, was also observed in mKO animals following acute administration of the direct AMPK activator MK-8722. Our study suggests that targeting CARM1-AMPK interplay may have broad impacts on neuromuscular health and disease.

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Role of the arginine methyltransferase CARM1 in muscle biology remains undefined

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Skeletal muscle-specific removal of CARM1 alters autophagic and atrophic processes

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CARM1 methylates AMPK and mediates AMPK signaling during neurogenic muscle disuse

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Targeted pharmacological AMPK stimulation is impacted by CARM1 in skeletal muscle

The emergence of protein arginine methyltransferases in skeletal muscle and metabolic disease

Protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyze the methylation of arginine residues on target proteins and thus alter the stability, localization, or activity of the substrate. In doing so, PRMTs mediate a variety of intracellular functions that are essential for survival. Additionally, PRMT dysregulation is involved in a number of the most prevalent health disorders, including cancer and neurodegenerative and cardiovascular diseases, as well as in the aging process. Investigations of PRMT biology in skeletal muscle cells began in 2002, and since then these enzymes have emerged as regulators of skeletal muscle phenotype determination, maintenance, and remodeling. Specifically, more recent in vivo studies have revealed that PRMTs impact multiple aspects of skeletal muscle biology, including satellite cell function and phenotypic plasticity in response to exercise and disuse. Skeletal muscle plays critically important roles in regulating whole body metabolism, and recent investigations have also begun elucidating PRMT expression and function under conditions of metabolic dysfunction. The goals of this review are to 1) summarize the literature on PRMT biology in skeletal muscle with a particular emphasis on the in vivo evidence and 2) survey PRMTs in metabolic disorders, namely, obesity and type 2 diabetes mellitus. We also identify notable knowledge gaps therein and present opportunities to further expand our understanding of these enzymes so critical to health and disease.