Global deletion of BCATm increases expression of skeletal muscle genes associated with protein turnover

Lynch CJ, Kimball SR, Xu Y, Salzberg AC, Kawasawa YI. Global deletion of BCATm increases expression of skeletal muscle genes associated with protein turnover. Physiol Genomics 47: 569-580, 2015. First published September 8, 2015; doi:10.1152/physiolgenomics.00055.2015.-Consumption of a protein-containing meal by a fasted animal promotes protein accretion in skeletal muscle, in part through leucine stimulation of protein synthesis and indirectly through repression of protein degradation mediated by its metabolite, alpha-ketoisocaproate. Mice lacking the mitochondrial branched-chain aminotransferase (BCATm/Bcat2), which interconverts leucine and alpha-ketoisocaproate, exhibit elevated protein turnover. Here, the transcriptomes of gastrocnemius muscle from BCATm knockout (KO) and wildtype mice were compared by next-generation RNA sequencing (RNA-Seq) to identify potential adaptations associated with their persistently altered nutrient signaling. Statistically significant changes in the abundance of 1,486/similar to 39,010 genes were identified. Bioinformatics analysis of the RNA-Seq data indicated that pathways involved in protein synthesis [eukaryotic initiation factor (eIF)-2, mammalian target of rapamycin, eIF4, and p70S6K pathways including 40S and 60S ribosomal proteins], protein breakdown (e.g., ubiquitin mediated), and muscle degeneration (apoptosis, atrophy, myopathy, and cell death) were upregulated. Also in agreement with our previous observations, the abundance of mRNAs associated with reduced body size, glycemia, plasma insulin, and lipid signaling pathways was altered in BCATm KO mice. Consistently, genes encoding anaerobic and/or oxidative metabolism of carbohydrate, fatty acids, and branched chain amino acids were modestly but systematically reduced. Although there was no indication that muscle fiber type was different between KO and wild-type mice, a difference in the abundance of mRNAs associated with a muscular dystrophy phenotype was observed, consistent with the published exercise intolerance of these mice. The results suggest transcriptional adaptations occur in BCATm KO mice that along with altered nutrient signaling may contribute to their previously reported protein turnover, metabolic and exercise phenotypes.