Compensatory mechanisms in non-muscle organs in myotubular myopathy
X-Linked myotubular myopathy (XLMTM), is associated with very severe muscle weakness and reduced life expectancy. Liver dysfunction was also reported. The pathomechanism and the impact of non-muscular defects affecting survival are barely known. Here, we investigated organ-specific effects of XLMTM in the faithful Mtm1-/y mouse model. We performed RNA-sequencing to identify a shared mechanism in several skeletal muscles, and to investigate potential phenotypes and/or compensation in heart and liver. The cardiac and hepatic function and structural integrity were also studied in vivo and in vitro. There was no defect in liver function and morphology. A disease signature shared across several skeletal muscles including diaphragm highlighted dysregulations of muscle development, inflammation, cell adhesion and oxidative phosphorylation as main pathomechanisms. Heart displayed only slight functional alterations without obvious structural defects. An opposite dysregulation of specific pathways in cardiac compared to skeletal muscles was revealed at the transcriptome level. More specifically, biochemical and cellular experiments demonstrated that OXPHOS mitochondrial function, cell adhesion and beta integrin trafficking were strongly affected in skeletal muscle and normal in cardiac muscle. Moreover, biomarkers reflecting the molecular activity of MTM1, such as PtdIns3P and dynamin 2 levels, were increased in the skeletal muscles but not in cardiac muscle. Overall, these data identified a compensatory mechanism preserving cardiac function, indicating therapeutic targets to cure the severe skeletal muscle defects in XLMTM. Overall design: To assess the impact of XLCNM on gene expression in different muscle and non-muscle tissues, we performed RNA-seq in Mtm1-/y mice and their wild-type (WT) littermates at 5 weeks in the heart, the liver, the gastrocnemius and the diaphragm.