Histone methyltransferase MLL4 controls myofiber identity and muscle performance through MEF2 interaction
Lin Liu, Chenyun Ding, Tingting Fu, Zhenhua Feng, Ji-Eun Lee, Liwei Xiao, Zhisheng Xu, Yujing Yin, Qiqi Guo, Zongchao Sun, Wanping Sun, Yan Mao, Likun Yang, Zheng Zhou, Danxia Zhou, Leilei Xu, Zezhang Zhu, Yong Qiu, Kai Ge, Zhenji Gan
Lin Liu, Chenyun Ding, Tingting Fu, Zhenhua Feng, Ji-Eun Lee, Liwei Xiao, Zhisheng Xu, Yujing Yin, Qiqi Guo, Zongchao Sun, Wanping Sun, Yan Mao, Likun Yang, Zheng Zhou, Danxia Zhou, Leilei Xu, Zezhang Zhu, Yong Qiu, Kai Ge, Zhenji Gan
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Research Article Metabolism Muscle biology

Histone methyltransferase MLL4 controls myofiber identity and muscle performance through MEF2 interaction

Abstract

Skeletal muscle depends on the precise orchestration of contractile and metabolic gene expression programs to direct fiber-type specification and to ensure muscle performance. Exactly how such fiber type–specific patterns of gene expression are established and maintained remains unclear, however. Here, we demonstrate that histone monomethyl transferase MLL4 (KMT2D), an enhancer regulator enriched in slow myofibers, plays a critical role in controlling muscle fiber identity as well as muscle performance. Skeletal muscle–specific ablation of MLL4 in mice resulted in downregulation of the slow oxidative myofiber gene program, decreased numbers of type I myofibers, and diminished mitochondrial respiration, which caused reductions in muscle fatty acid utilization and endurance capacity during exercise. Genome-wide ChIP-Seq and mRNA-Seq analyses revealed that MLL4 directly binds to enhancers and functions as a coactivator of the myocyte enhancer factor 2 (MEF2) to activate transcription of slow oxidative myofiber genes. Importantly, we also found that the MLL4 regulatory circuit is associated with muscle fiber–type remodeling in humans. Thus, our results uncover a pivotal role for MLL4 in specifying structural and metabolic identities of myofibers that govern muscle performance. These findings provide therapeutic opportunities for enhancing muscle fitness to combat a variety of metabolic and muscular diseases.

Authors

Lin Liu, Chenyun Ding, Tingting Fu, Zhenhua Feng, Ji-Eun Lee, Liwei Xiao, Zhisheng Xu, Yujing Yin, Qiqi Guo, Zongchao Sun, Wanping Sun, Yan Mao, Likun Yang, Zheng Zhou, Danxia Zhou, Leilei Xu, Zezhang Zhu, Yong Qiu, Kai Ge, Zhenji Gan

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Figure 3

MLL4 coordinately regulates gene programs controlling muscle contraction and energy metabolism.

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MLL4 coordinately regulates gene programs controlling muscle contraction...
(A) Volcano plot showing fold changes versus P values for analyzed RNA-Seq data generated from the GC muscle of 8-week-old male Mll4SET-mKO mice compared with littermate controls (WT). Significantly upregulated genes are represented by red dots, whereas downregulated genes are represented by blue dots. (B) GO enrichment analysis of gene transcripts regulated in Mll4SET-mKO muscle. (C) Heatmap analysis of contraction-related genes regulated in Mll4SET-mKO muscle compared with WT controls. n = 3 independent samples per group. Color scheme for fold change is provided. (D) Expression of genes (qRT-PCR) involved in muscle contraction, calcium handling, and metabolism in GC muscle from the indicated genotypes. n = 5–6 mice per group. (E) Left: LDH isoenzymes were separated by polyacrylamide gel electrophoresis using whole-cell extracts from heart (Ht, control) and GC muscle from indicated mice. A representative gel showing 4 independent mice per group is shown. Right: quantification of LDH isoenzyme activity gel electrophoresis shown on the left. (F) Mitochondrial respiration rates were determined from the EDL muscle of the indicated genotypes using pyruvate or palmitoylcarnitine as a substrate. Pyruvate/malate (Py/M) or palmitoylcarnitine/malate (PC/M) stimulated, ADP-dependent respiration, and oligomycin induced (oligo) are shown. n = 6–7 mice per group. (G) OCRs in skeletal myotubes harvested from Mll4SETfl/fl mice subjected to adenovirus-based overexpression of Cre compared with control virus. Basal OCR was first measured, followed by administration of 10 mM sodium pyruvate, and 2 μM oligomycin (to inhibit ATP synthase), uncoupler FCCP (2 μM), or rotenone/antimycin (Rot/A; 1 μM), as indicated. n = 6 separate experiments done with 5 biological replicates. Values are represented as mean ± SEM. *P < 0.05 vs. corresponding controls, 2-tailed unpaired Student’s t test.