Insight on the loading-mediated regulation of Runx1 in skeletal muscle

Skeletal muscle adaptation during conditions of dynamic muscle loading such as resistance-type exercise occurs in conjunction with pronounced changes in gene expression. The objective of this study was to comprehensively evaluate gene expression at the onset of rapid muscle hypertrophy in mice. We analyzed the global, nascent, stable, and myonuclear transcriptome utilizing RNA-sequencing. C57BL6/J mice were treated with 5-ethenyl uridine at the end of 72 hours of synergist ablation mechanical overload of the plantaris muscle to assess transcriptional dynamics; sham mice served as controls. Mice with in vivo fluorescent myonuclear labeling were used to obtain RNA-sequencing in exclusively myonuclei from overloaded and sham mice. In these analyses, RUNX family transcription factor 1 ( Runx1, or Aml1) was significantly elevated in all conditions (adj. p<0.05x10-15) and was among the most induced genes across datasets. These findings allude to Runx1 as a highly regulated mediator of muscle hypertrophy that is enriched specifically in muscle fibers during loading. Myonucleus-specific global DNA methylome analysis also report exon and intron CpG hypomethylation in the Runx1 gene after overload. As gene body methylation can mediate alternative splicing, we subsequently hypothesized Runx1 may be subject to alternative splicing and conducted preliminary analyses of RNA splice isoforms present after acute overload. We found that a non-canonical isoform of Runx1 ( Runx1-202, coding for a 387 amino acid protein) was relatively more induced than the Runx1-201 transcript that codes for the full-length 465 amino acid protein (30- versus 17-fold induction, respectively), while Runx1 is essentially not expressed in sham muscle. Ongoing analysis will validate Runx1 splice variant expression during overload in muscle, the potential influence of DNA methylation, and the impact of the Runx1 short isoform on muscle hypertrophy. This work is supported by the National Institutes of Health under grant R00 AG063994 to Kevin A. Murach. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.