PROJECT SUMMARY/ABSTRACT Peripheral artery disease (PAD) is caused by atherosclerosis in the lower extremities which leads to a spectrum of life-altering symptomatology, including claudication, ischemic rest pain, and gangrene requiring limb amputation. Complicating the etiology of PAD, patients typically present with comorbid conditions or risk factors that accelerate disease evolution and substantially worsen pathology contributing to increased mortality risk. Among these, chronic kidney disease (CKD) accelerates the development of atherosclerosis, decreases functional capacity, and increases risk of amputation or death, however the underlying biologic mechanism(s) are poorly understood and vastly understudied compared with other comorbidities (i.e. smoking and diabetes). We have uncovered a novel molecular pathway that may link CKD and PAD pathobiology. We find that many uremic metabolites, which accumulate in CKD, cause chronic activation of the aryl hydrocarbon receptor (AHR) which leads to disruption of the mitochondrial electron transport system that exacerbates ischemic muscle injury and impairs angiogenesis. Preliminary experiments demonstrate that genetic knockdown of the AHR is protective against uremic toxicity, whereas expression of a constitutively active AHR causes mitochondrial dysfunction. Thus, we propose to test the novel hypothesis that the chronic activation of the AHR pathway results in ischemic muscle injury and impaired angiogenesis, thereby linking CKD and PAD pathobiology. This hypothesis will be tested using muscle- and vascular-specific inducible knockout of the AHR as well as adeno- associated virus-mediated expression of the a constitutively active AHR in pre-clinical models of CKD/PAD. Finally, our recent human data indicate elevated AHR signaling in PAD patients with CKD. We propose to extend these findings to establish a clinical link between muscle health/function, mitochondrial energetics, and AHR signaling in human PAD patients. Success in these studies will provide mechanistic insight into the impact of CKD on PAD pathobiology, and would provide a novel target for therapeutic development aimed to treat a patient population that currently has few available options.