Uremic metabolites impair skeletal muscle mitochondrial energetics through disruption of the electron transport system and matrix dehydrogenase activity

Abstract

Chronic kidney disease (CKD) impacts more than 25 million Americans and is associated with higher risk of all‐cause and cardiovascular mortality. Impaired kidney function leads to retention of metabolic waste products, termed uremic toxins, that negatively impact skeletal muscle resulting in increased fatigue, weakness, and muscle atrophy. Previous evidence has implicated mitochondria within the skeletal muscle as a primary mediator of muscle dysfunction in CKD, yet the underlying mechanisms are unknown. Therefore, the purpose of this study was to define the impact of uremic toxins on mitochondrial energetics. Skeletal muscle mitochondria were isolated from healthy C57BL/6N mice and exposed to vehicle (DMSO) or varying doses of the following uremic toxins: indoxyl sulfate, indole‐3‐acetic‐acid, L‐kynurenine, kynurenic acid, and methylguanidine. We employed a comprehensive mitochondrial phenotyping platform that included assessments of mitochondrial OXPHOS conductance across several levels of energy demand, hydrogen peroxide production (JH2O2), and dehydrogenase flux (using NADH autofluorescence). Exposure to uremic toxins resulted in a dose‐dependent decrease in OXPHOS conductance for all toxins, with 100nM exposure resulting in an average decrease of ~22% supported by pyruvate/malate (all P<0.05, n= 5–6/group). Uremic toxins did not decrease pyruvate dehydrogenase activity even at millimolar concentrations (all P>0.64), suggesting the decreased OXPHOS conductance occurs downstream of matrix dehydrogenases. Consistent with decreased OXPHOS conductance, uremic toxins dose‐dependently increased JH2O2 by 2–5‐fold (all P<0.01, n=4/group). These findings provide direct evidence that uremic toxins negatively impact skeletal muscle mitochondrial energetics, resulting in decreased energy transfer. Impaired mitochondrial energetics appears to be mediated downstream of matrix dehydrogenases, through either direct interaction within the electron transport system or ATP synthase. Support or Funding Information Partially supported by AHA Grant 18CDA34110044 to TER This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Impaired skeletal muscle mitochondrial bioenergetics and physical performance in chronic kidney disease

“…CKD is a catabolic and proinflammatory condition that may disrupt mitochondrial energy metabolism via several biochemical pathways (3). Uremic toxins, such as indoxyl sulfate, L-kynurenine, kynurenic acid, indole-3-acetic acid, and p-Cresol sulfate, adversely affect mitochondrial metabolism (12,13) and insulin resistance (14). Exposure of isolated skeletal muscle mitochondria from the C57BL/6N mice to uremic toxins leads to deficits in the electron transport system characterized by decreased complex III and IV activity in addition to increased H 2 O 2 production (13).…”

“…Uremic toxins, such as indoxyl sulfate, L-kynurenine, kynurenic acid, indole-3-acetic acid, and p-Cresol sulfate, adversely affect mitochondrial metabolism (12,13) and insulin resistance (14). Exposure of isolated skeletal muscle mitochondria from the C57BL/6N mice to uremic toxins leads to deficits in the electron transport system characterized by decreased complex III and IV activity in addition to increased H 2 O 2 production (13). Uremic toxins can also impair UDP-glucuronosyltransferases critical for the metabolism of drugs and toxins, the buildup of which can lead to impaired mitochondrial oxidative phosphorylation (15).…”

Gut-Derived Protein-Bound Uremic Toxins

“…Kynurenine, kynurenic acid, IAA, and IS also impact skeletal muscle mitochondrial energetics by disrupting the electron transport chain and associated dehydrogenases. This impairs mitochondrial oxidative phosphorylation and respiratory capacity, and leads to muscle weakness, atrophy, and fatigue [ 60 ]. Quinolinic acid acts as an N-methyl-D-aspartate (NMDA) receptor agonist to induce neuronal excitotoxicity [ 50 ], and also causes neurotoxicity through inducing excessive glutamate release and lipid peroxidation [ 61 ].…”

Mitochondrial Dysfunction in Kidney Disease and Uremic Sarcopenia

“…Several experiments indicate mitochondrial dysfunction in the skeletal muscle of patients with CKD ( Gamboa et al, 2016 ; Sato et al, 2016 ; Kikuchi et al, 2019 ; Thome et al, 2019 ; Xu et al, 2020 ). Both mitochondrial volume density and mtDNA copy numbers were decreased in skeletal biopsy specimens sampled from kidney failure patients who underwent HD ( Gamboa et al, 2016 ) or PD ( Xu et al, 2020 ) ( Figures 1B , 2 ).…”

“…Several studies have recognized the impaired role of the PDHC at a molecular level in the mitochondria of skeletal muscle in CKD sarcopenia ( Sato et al, 2016 ; Thome et al, 2019 ; Xu et al, 2020 ). The PDHC is essential to energy production under anaerobic condition, as the enzyme converts pyruvate to acetyl-CoA for the TCA cycle.…”