A Tryptophan-derived Uremic Metabolite-Ahr-Pdk4 Axis Promotes Skeletal Muscle Mitochondriopathy in Chronic Kidney Disease
Authors: Thome Trace , Vugman Nicholas , Stone Lauren , Wimberly Keon , Scali Salvatore , Ryan Terence 
Published: May 2024

Introduction: Chronic kidney disease (CKD) and the subsequent accumulation of tryptophan-derived uremic metabolites (UMs) in circulation negatively impact skeletal muscle (SkM) health and function. Specifically, indoles and kynurenines are strongly associated with SkM atrophy, weakness, and fatigue found in CKD patients. Notably, these tryptophan-derived UMs are known agonist to the ubiquitously expressed aryl hydrocarbon receptor (AHR), a ligand activated transcription factor, which has been shown to be activated in the blood of CKD patients and whose chronic activation has been proven toxic to multiple tissue types. Purpose: The purpose of this study was to determine whether chronic activation of the AHR by tryptophan-derived UMs contributes to CKD associated SkM atrophy and metabolic dysfunction. Methods: Muscle biopsies from CKD patients and adult controls with normal renal function were used to examine AHR signaling and mitochondrial function. The mechanistic role of the AHR was explored using SkM-specific AHR knockout mice (AHRmKO) and SkM-specific AHR knockdown via adeno-associated virus in mice with adenine-induced CKD, as well as ectopic expression of a constitutively active AHR (CAAHR) in mice with normal kidney function. Additional mechanistic experiments were carried out in cultured muscle cells. Outcome measures included gene and protein expression, mitochondrial bioenergetic testing, and robust muscle functional phenotyping. Results: Compared to controls with normal kidney function, AHR-dependent gene expression ( CYP1A1 and CYP1B1) was significantly upregulated in gastrocnemius SkM of CKD patients ( P=0.032) and the magnitude of AHR activation was inversely correlated with mitochondrial respiration ( P<0.001). In mice with CKD, SkM mitochondrial oxidative phosphorylation (OXPHOS) was significantly impaired and strongly correlated with both the level of tryptophan-derived UMs and AHR activation. AHRmKO significantly improved mitochondrial OXPHOS in mice with CKD (~28% increase, P=0.045) and abolished the relationship between UMs and OXPHOS. The uremic metabolite-AHR-mitochondrial axis in SkM was further confirmed using SkM-specific AHR knockdown in C57BL6J that express a high-affnity AHR allele, as well as ectopic viral expression of CAAHR in mice with normal renal function. AHR activation led to impairments in pyruvate dehydrogenase (PDH) enzyme function (~29% decrease, P<0.05), significant increases in Pdk4 expression ( P<0.05) and phosphorylation of PDH enzyme ( P<0.05), mechanistically contributing to impaired pyruvate-supported OXPHOS function. Conclusion: These findings establish a uremic metabolite-AHR-Pdk4 axis in SkM that governs mitochondrial deficits in CKD. Supported by grants from the National Institutes of Health R01-HL149704 (TER) and F31-DK128920 (TT). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.