Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida.
Center for Exercise Science, University of Florida, Gainesville, Florida.
Am J Physiol Cell Physiol. 2019 Oct 1;317(4):C701-C713. doi: 10.1152/ajpcell.00098.2019. Epub 2019 Jul 10.
Chronic kidney disease (CKD) leads to increased skeletal muscle fatigue, weakness, and atrophy. Previous work has implicated mitochondria within the skeletal muscle as a mediator of muscle dysfunction in CKD; however, the mechanisms underlying mitochondrial dysfunction in CKD are not entirely known. The purpose of this study was to define the impact of uremic metabolites on mitochondrial energetics. Skeletal muscle mitochondria were isolated from C57BL/6N mice and exposed to vehicle (DMSO) or varying concentrations of uremic metabolites: indoxyl sulfate, indole-3-acetic-acid, l-kynurenine, and kynurenic acid. A comprehensive mitochondrial phenotyping platform that included assessments of mitochondrial oxidative phosphorylation (OXPHOS) conductance and respiratory capacity, hydrogen peroxide production (HO), matrix dehydrogenase activity, electron transport system enzyme activity, and ATP synthase activity was employed. Uremic metabolite exposure resulted in a ~25-40% decrease in OXPHOS conductance across multiple substrate conditions ( < 0.05, = 5-6/condition), as well as decreased ADP-stimulated and uncoupled respiratory capacity. ATP synthase activity was not impacted by uremic metabolites; however, a screen of matrix dehydrogenases indicated that malate and glutamate dehydrogenases were impaired by some, but not all, uremic metabolites. Assessments of electron transport system enzymes indicated that uremic metabolites significantly impair complex III and IV. Uremic metabolites resulted in increased HO under glutamate/malate, pyruvate/malate, and succinate conditions across multiple levels of energy demand (all < 0.05, = 4/group). Disruption of mitochondrial OXPHOS was confirmed by decreased respiratory capacity and elevated superoxide production in cultured myotubes. These findings provide direct evidence that uremic metabolites negatively impact skeletal muscle mitochondrial energetics, resulting in decreased energy transfer, impaired complex III and IV enzyme activity, and elevated oxidant production.
慢性肾脏病(CKD)导致骨骼肌疲劳、无力和萎缩增加。先前的研究表明,CKD 中的骨骼肌线粒体是肌肉功能障碍的介导物;然而,CKD 中线粒体功能障碍的机制尚不完全清楚。本研究旨在定义尿毒症代谢物对线粒体能量学的影响。从小鼠的 C57BL/6N 骨骼肌中分离出线粒体,并将其暴露于载体(DMSO)或不同浓度的尿毒症代谢物:吲哚硫酸、吲哚-3-乙酸、L-犬尿氨酸和犬尿氨酸中。采用综合线粒体表型平台,包括评估线粒体氧化磷酸化(OXPHOS)电导和呼吸能力、过氧化氢产生(HO)、基质脱氢酶活性、电子传递系统酶活性和 ATP 合酶活性。尿毒症代谢物暴露导致多种底物条件下的 OXPHOS 电导下降约 25-40%(<0.05,=5-6/条件),以及 ADP 刺激和去耦呼吸能力下降。ATP 合酶活性不受尿毒症代谢物影响;然而,基质脱氢酶的筛选表明,一些但不是所有尿毒症代谢物都会损害苹果酸脱氢酶和谷氨酸脱氢酶。电子传递系统酶的评估表明,尿毒症代谢物显著损害复合物 III 和 IV。在多种能量需求水平下,谷氨酸/苹果酸、丙酮酸/苹果酸和琥珀酸条件下,尿毒症代谢物导致 HO 增加(所有<0.05,=4/组)。在培养的肌管中,呼吸能力下降和超氧化物产生增加证实了线粒体 OXPHOS 的破坏。这些发现提供了直接证据,表明尿毒症代谢物对骨骼肌线粒体能量学产生负面影响,导致能量传递减少、复合物 III 和 IV 酶活性受损以及氧化应激产物增加。