Transcriptome analysis of skeletal muscle tissue from Hras G12V mutant mice

Costello syndrome (CS) is a congenital disorder caused by heterozygous activating germline HRAS mutations in the canonical Ras/mitogen-activated protein kinase (Ras/MAPK) pathway. CS is one of the RASopathies, a large group of syndromes due to mutations within various components of the Ras/MAPK pathway. An important part of the phenotype that greatly impacts quality of life is hypotonia. To gain a better understanding of the mechanisms underlying hypotonia in CS, a mouse model with an activating HrasG12V allele was utilized. We identified a skeletal myopathy that was due in part to an inhibition of embryonic myogenesis and myofiber formation, resulting in a reduction of myofiber size and number that led to reduced muscle mass and strength. In addition to hyperactivation of the Ras/MAPK and PI3K/AKT pathways, there was a significant reduction of p38 signaling, as well as global transcriptional alterations consistent with the myopathic phenotype. Inhibition of Ras/MAPK pathway signaling using a MEK inhibitor rescued the HrasG12V myopathy phenotype both in vitro and in vivo, demonstrating that increased MAPK signaling is the main cause of the muscle phenotype in CS. Overall design: The study consisted of 2 groups of mice with triplicate samples per group. The experimental group consisted of mice that were heterozygous (HrasG12V/+) for the HrasG35T (p.G12V) mutation. Control mice were homozygous (Hras+/+) for wild type Hras. Gastrocnemius muscle tissue was harvested from 21-day-old mice and snap-frozen for subsequent RNA extraction and transcriptome profiling with RNA-Sequencing (RNA-Seq) analysis.