Proteomic and metabolomic profiling nominates druggable targets and biomarkers for pulmonary arterial hypertension–associated myopathy and exercise intolerance in male monocrotaline rats

Background: Pulmonary arterial hypertension (PAH) is a rare but debilitating condition that causes exercise intolerance and ultimately death. Skeletal muscle derangements contribute to depressed exercise capacity in PAH, but the mechanisms underlying muscle dysfunction, including the changes in muscle biology based on fiber type, are understudied. Methods: We evaluated exercise capacity, muscle histopathology, mitochondrial density, mitochondrial proteomics, and metabolomics/lipidomics of quadriceps (predominately fast fibers) and soleus (predominately slow fibers) muscles in the monocrotaline (MCT) rat model of PAH. Results: MCT rats exhibited impaired exercise capacity. Surprisingly, there were divergent atrophic and metabolic remodeling in the quadriceps and soleus muscles of MCT rats. In the quadriceps, there was a mild atrophic response only in type II fibers. In contrast, both type I and II fibers atrophied in the soleus. Both muscles exhibited fibrotic infiltration, but mitochondrial density was reduced in the quadriceps only. Mitochondrial proteomics and tissue metabolomics/lipidomics profiling demonstrated that the 2 muscles exhibited distinct responses, as the quadriceps had impairments in oxidative phosphorylation/fat metabolism and storage of triacylglycerides. However, the soleus showed signs of proteasome deficiencies and alterations in phosphatidylcholine/phosphatidylethanolamine homeostasis. Finally, profiling of metabolites/lipids in the serum identified potential novel biomarkers of exercise intolerance in PAH, including the dimethylarginine pathway, cysteine, and triacylglycerides. Conclusions: Our data suggest differential cachectic and metabolic responses occur in PAH-induced myopathy. We nominate mitochondrial biogenesis and proteasome activation as potential druggable targets for PAH myopathy.