Metabolic and proteomic characterization of stress susceptibility in the mdx mouse model of Duchenne muscular dystrophy

Abstract

Duchenne muscular dystrophy (DMD) is a lethal neuromuscular disease caused by dystrophin protein loss due to mutations in the DMD gene and does not currently have a cure. The DMD disease course often involves secondary neurocognitive and behavioral disorders. The mdx mouse model of DMD displays mild disease progression in comparison to the human DMD population, but is uniquely susceptible to graded forms of psychological stress exposure that result in prolonged tonic immobility, hypotension, and lethality. Pathological stress phenotypes in the mdx mouse are rescued by skeletal muscle-specific restoration of dystrophin or its fetal homolog, utrophin. Stress-induced inactivity and peripheral hypotension implicate the central nervous system and cardiovascular system in the aberrant mdx stress response and suggest an underexamined dystrophin-dependent stress intolerance in DMD patients that impairs quality of life. While mdx stress response phenotypes have been well-characterized, it is not understood how dystrophin expression in skeletal muscle regulates the central stress response in DMD.In this thesis, I investigated multiple coordinated metabolic pathways and the skeletal muscle secretome at the transcript, protein, and metabolite level to identify stress-dependent metabolic and proteomic alterations in mdx skeletal muscle that orchestrate pathological inter-organ crosstalk. Metabolic dysregulation along the kynurenine pathway of tryptophan degradation and the cluster of differentiation 38 (CD38) route of nicotinamide adenine dinucleotide (NAD+) catabolism were previously implicated in chronic stress susceptibility and mdx cardiovascular pathology. Kynurenine and CD38 metabolic dysfunction is evident in mdx skeletal muscle; however, genetic amelioration of these pathway alterations did not rescue aberrant mdx stress phenotypes. Metabolomics and extracellular fluid proteomics analyses revealed circulating metabolite and skeletal muscle-secreted proteins as novel candidates for inter-organ signaling molecules that influence systemic mdx stress pathology. The work presented in this thesis contributes to an improved understanding of the mechanisms underlying DMD stress vulnerability and the critical role of skeletal muscle in regulating whole-body physiology.