Activation Of The Renin-Angiotensin System Drives Renal Metabolic Abnormalities In Diabetic Nephropathy.

Activation of the renin-angiotensin system (RAS) is a major contributor to the pathogenesis of diabetic nephroathy (DN). However, the precise mechanisms of renoprotection associated with RAS blockade in DN are not entirely clear. The aim of this study is to examine whether metabolic effects of RAS blockade might contribute to renoprotection. We utilized a mouse model of DN combining severe type I diabetes (the Akita mutation) with a single-copy renin transgene (ReninTG) driven by the albumin promoter. Akita-ReninTG mice on a 129/Sv background (DN-susceptible mice) develop clinical features of human DN including high-grade albuminuria, renal interstitial inflammation and glomerulosclerosis, while Akita-ReninTG mice on a C57BL/6 background (DN-resistant mice) do not develop significant kidney disease. These two experimental groups were treated with the angiotensin receptor blocker (ARB) losartan 10 mg/kg/day for 12 weeks, and metabolic profiles in kidney tissues were examined using a targeted metabolomics assay. The DN-susceptible mice exhibited high-grade albuminuria that was significantly attenuated by ARB (Vehicle vs ARB: 1480±562 vs 193±42 μg/day, p =0.045), while DN-resistant mice had minimal albuminuria that was not affected by ARB (Vehicle vs ARB: 80±14 vs 75±14 μg/day, p =0.801). The metabolomics profiles of the DN-resistant mice were similar to C57BL/6 wild-type controls. By contrast, DN-susceptible mice exhibited broad reductions in even-chain acyl-carnitines and an abnormal profile of TCA cycle intermediates compared to 129/Sv wild-type controls, suggesting substantial impairments of renal mitochondrial fuel oxidation including altered fatty acid metabolism. RAS blockade had broad effects to correct this profile by increasing acetyl-carnitines generated from acetyl-CoA and concomitantly normalizing expression of genes associated with mitochondrial fatty acid metabolism including PPAR-α, PGC-1α, CPT1 and CPT2. ARB treatment restored TCA cycle activity to normal. These findings suggest that effects of RAS blockade re-establish normal fuel metabolism and mitochondrial fatty acid oxidation in kidney and may contribute to renoprotection.