Chronic aryl hydrocarbon receptor activation and skeletal myopathy in chronic kidney disease

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Abstract Chronic Kidney Disease (CKD) is accompanied by a progressively debilitating myopathy characterized by muscle wasting, weakness, and fatigue. Activation of proteolytic pathways including the ubiquitin proteasome system, caspases/calpains, myostatin, and dysregulation of autophagy have been implicated as causal factors for muscle wasting and reduced quality of life in patients. Despite this body of literature, the systemic molecular mechanism(s) linking impaired kidney function to activation of these pathways in muscle remains unknown. A major function of the kidneys is to rid the body of waste materials that are ingested or produced endogenously by normal metabolism. However, CKD results in the retention and accumulation of metabolites, termed uremia. A number of these metabolites are derived from tryptophan catabolism through indolic and kynurenine pathways including; indoxyl sulfate, L-kynurenine, kynurenic acid, and indole-3-acetic acid which are ligands for the aryl hydrocarbon receptor (AHR), a transcriptional regulator of xenobiotic metabolism. The AHR usually upregulates detoxifying pathways such as cytochrome P450 enzymes, however chronic activation of the AHR can be toxic. My preliminary data reveals robust AHR activation in skeletal muscle of both mice and humans with CKD. Furthermore, treatment of muscle cells with tryptophan-derived AHR ligands results in mitochondrial dysfunction, which was prevented by genetic knockdown of the AHR with short hairpin RNA. Lastly, expression of a constitutively active AHR receptor in muscle cells mimicked uremic metabolite exposure causing atrophy and mitochondrial dysfunction. Based on these preliminary data, I propose to test my hypothesis that chronic activation of the AHR plays a causal role in CKD-associated myopathy. Aim 1 will determine if muscle-specific knockout of the AHR protects against muscle atrophy and mitochondrial dysfunction in mice with CKD using a Cre-lox system and delivery of tamoxifen to induce muscle specific knockout of the AHR at the onset of CKD. Aim 2 will test whether constitutive AHR activation via AAV delivery is sufficient to cause muscle atrophy and mitochondrial dysfunction in mice with normal kidney function. A detailed training program with a mixture of junior/senior faculty that involves specific research skill enhancement in molecular biology, muscle mechanics, mitochondrial energetics, and renal physiology has been developed. The application will receive additional career mentoring involving grant/manuscript writing, presentation skills, and professional development including participation in national and international scientific conferences. Completion of the aims and training plan will result in excellent training in mitochondrial functional analysis, muscle biology and contractile function, renal physiology, protein synthesis and degradation, and proteomics which will provide a strong foundation for my career goals.