The metabolic syndrome induces early changes in the swine renal medullary mitochondria

Abstract

The metabolic syndrome (MetS) is associated with nutrient surplus and kidney hyperfiltration, accelerating chronic renal failure. Mitochondria can be overwhelmed by substrate excess, leading to inefficient energy production and thereby tissue hypoxia. Mitochondrial dysfunction is emerging as an important determinant of renal damage, but whether it contributes to MetS-induced renal injury remains unknown. We hypothesized that early MetS induces kidney mitochondrial abnormalities and dysfunction, which would be notable in the vulnerable renal medulla. Pigs were studied after 16 weeks of diet-induced MetS, MetS treated for the last 4 weeks with the mitochondria-targeted peptide elamipretide (0.1 mg/kg SC q.d), and Lean controls (n = 7 each). Single-kidney renal blood flow, glomerular filtration rate, and oxygenation were measured in-vivo, whereas cortical and medullary mitochondrial structure and function and renal injurious pathways were studied ex-vivo. Blood pressure was slightly elevated in MetS pigs, and their renal blood flow and glomerular filtration rate were elevated. Blood oxygen level-dependent magnetic resonance imaging demonstrated that this was associated with medullary hypoxia, whereas cortical oxygenation remained intact. MetS decreased renal content of the inner mitochondrial membrane cardiolipin, particularly the tetra-linoleoyl (C18:2) cardiolipin species, and altered mitochondrial morphology and function, particularly in the medullary thick ascending limb. MetS also increased renal cytochrome-c-induced apoptosis, oxidative stress, and tubular injury. Chronic mitoprotection restored mitochondrial structure, ATP synthesis, and antioxidant defenses and decreased mitochondrial oxidative stress, medullary hypoxia, and renal injury. These findings implicate medullary mitochondrial damage in renal injury in experimental MetS, and position the mitochondria as a therapeutic target.