Background Dissection of the regulatory pathways that control skeletal muscle development and atrophy is important for the treatment of muscle wasting. Long noncoding RNA (lncRNA) play important roles in various stages of muscle development. We previously reported that Synaptopodin‐2 (SYNPO2) intron sense‐overlapping lncRNA (SYISL) regulates myogenesis through an interaction with enhancer of zeste homologue 2 (EZH2). However, it remains unclear whether SYISL homologues exist in humans and pigs, and whether the functions and mechanisms of these homologues are conserved among species. Methods Bioinformatics, cell fractionation, and quantitative real‐time polymerase chain reaction (qRT‐PCR) analyses were used for the identification and molecular characterization of SYISL homologues in humans and pigs. Effects on myogenesis and muscle atrophy were determined via loss‐of‐function or gain‐of‐function experiments using C2C12 myoblasts, myogenic progenitor cells, dexamethasone (DEX), and aging‐induced muscle atrophy models. RNA pulldown, RNA immunoprecipitation, dual luciferase reporting, and co‐transfection experiments were used to explore the mechanisms of SYISL interactions with proteins and miRNAs. Results We identified SYISL homologues in humans (designated hSYISL) and pigs (designated pSYISL). Functional experiments demonstrated that hSYISL and pSYISL regulate myogenesis through interactions with EZH2. Interestingly, we showed that SYISL functions to regulate muscle atrophy and sarcopenia through comparative analysis. SYISL is significantly up‐regulated after muscle atrophy (P < 0.01); it significantly promotes muscle atrophy in DEX‐induced muscle atrophy models (P < 0.01). SYISL knockdown or knockout alleviates muscle atrophy and sarcopenia in DEX‐induced and aged mice. The tibialis anterior (TA) muscle weight of 3‐month‐old wild‐type (WT) mice decreased by 33.24% after DEX treatment (P < 0.001), while the muscle weight loss of 3‐month‐old SYISL knockout mice was only 18.20% after DEX treatment (P < 0.001). SYISL knockout in 18‐month‐old WT mice significantly increased the weights of quadriceps (Qu), gastrocnemius (Gas), and TA muscles by 10.45% (P < 0.05), 13.95% (P < 0.01), and 24.82% (P < 0.05), respectively. Mechanistically, SYISL increases the expression levels of the muscle atrophy genes forkhead box protein O3a (FoxO3a), muscle ring finger 1 (MuRF1), and muscle atrophy‐related F‐box (Atrogin‐1) via sponging of miR‐23a‐3p/miR‐103‐3p/miR‐205‐5p and thus promotes muscle atrophy. Additionally, we verified that human SYISL overexpression in muscles of 18‐month‐old WT mice significantly decreased the weights of Gas, Qu, and TA muscles by 7.76% (P < 0.01), 12.26% (P < 0.05), and 13.44% (P < 0.01), respectively, and accelerates muscle atrophy through conserved mechanisms. Conclusions Our results identify SYISL as a conserved lncRNA that modulates myogenesis in mice, pigs, and humans. We also demonstrated its previously unknown ability to promote muscle atrophy.
The proportions of the various muscle ber types are important in the regulation of skeletal muscle metabolism, as well as animal meat production. Four-and-a-half LIM domain protein 3 (FHL3) is highly expressed in fast glycolytic muscle bers and differentially regulates the expression of myosin heavy chain (MyHC) isoforms at the cellular level. Whether FHL3 regulates the transformation of muscle ber types in vivo and the regulatory mechanism are unclear. In this study, muscle-speci c FHL3 transgenic mice were generated by random integration, and lentivirus-mediated gene knockdown or overexpression in muscles of mice or pigs was conducted. Functional analysis showed that overexpression of FHL3 in muscles signi cantly increased the proportion of fast-twitch myo bers and muscle mass but decreased muscle succinate dehydrogenase (SDH) activity and whole-body oxygen consumption. Lentivirusmediated FHL3 knockdown in muscles signi cantly decreased muscle mass and the proportion of fasttwitch myo bers. Mechanistically, FHL3 directly interacted with the Yin yang 1(YY1) DNA-binding domain, repressed the binding of YY1 to the fast glycolytic MyHC2b gene 5' regulatory region, and thereby decreased MyHC2b expression. FHL3 also competed with EZH2 to bind the repression domain of YY1 and reduced H3K27me3 enrichment in the MyHC2b regulatory region. Moreover, FHL3 overexpression reduced glucose tolerance by affecting muscle glycolytic metabolism, and its mRNA expression in muscle was positively associated with hemoglobin A1c (HbA1c) in patients with type 2 diabetes. Therefore, FHL3 is a novel potential target gene for the treatment of muscle metabolism-related diseases and improvement of animal meat production.
The proportions of the various muscle fiber types are important in the regulation of skeletal muscle metabolism, as well as animal meat production. Four-and-a-half LIM domain protein 3 (FHL3) is highly expressed in fast glycolytic muscle fibers and differentially regulates the expression of myosin heavy chain (MyHC) isoforms at the cellular level. Whether FHL3 regulates the transformation of muscle fiber types in vivo and the regulatory mechanism are unclear. In this study, muscle-specific FHL3 transgenic mice were generated by random integration, and lentivirus-mediated gene knockdown or overexpression in muscles of mice or pigs was conducted. Functional analysis showed that overexpression of FHL3 in muscles significantly increased the proportion of fast-twitch myofibers and muscle mass but decreased muscle succinate dehydrogenase (SDH) activity and whole-body oxygen consumption. Lentivirus-mediated FHL3 knockdown in muscles significantly decreased muscle mass and the proportion of fast-twitch myofibers. Mechanistically, FHL3 directly interacted with the Yin yang 1(YY1) DNA-binding domain, repressed the binding of YY1 to the fast glycolytic MyHC2b gene 5' regulatory region, and thereby decreased MyHC2b expression. FHL3 also competed with EZH2 to bind the repression domain of YY1 and reduced H3K27me3 enrichment in the MyHC2b regulatory region. Moreover, FHL3 overexpression reduced glucose tolerance by affecting muscle glycolytic metabolism, and its mRNA expression in muscle was positively associated with hemoglobin A1c (HbA1c) in patients with type 2 diabetes. Therefore, FHL3 is a novel potential target gene for the treatment of muscle metabolism-related diseases and improvement of animal meat production.
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