C GRANATA1, V THALLAS-BONKE1, N CARUANA3, K HUYNH2, C XUE QIN2, M SNELSON1, A LASKOWSKI1, J ANTHONISZ1, E JAP2, G RAMM4, M COOPER1, P MEIKLE2, D STROUD3, R RITCHIE5, M COUGHLAN1
1Department of Diabetes, Central Clinical School, Monash University, Melbourne, Australia, 2Baker Heart & Diabetes Institute, Melbourne, Australia, 3Department of Biochemistry and Molecular Biology and The Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, Australia, 4Membrane Biology Group, Department of Biochemistry and Molecular Biology, Monash University, Clayton, Australia, 5Monash Institute of Pharmaceutical Science, Monash University , Parkville, Australia
Background: Changes in mitochondrial function and signaling thought to be central to the development of diabetic kidney disease (DKD); however, whether this response is explicitly driven by systemic glucose concentrations remains unknown.
Aim: Here, we investigated the effects of titrating blood glucose in a rodent model of diabetes on the metabolome, lipidome and mitoproteome landscape in the kidney.
Methods: Sprague dawley rats were administered either vehicle (citrate buffer) or streptozotocin (STZ), a pancreatic beta cell toxin, in order to induce insulin deficiency and result in hyperglycemia. Hyperglycemic rats were treated with either 7-8 units of insulin/day to achieve moderate blood glucose levels (MHG, ~20mmol/l glucose) or 1-2 units of insulin/day to achieve severe blood glucose levels (SHG, ~30mmol/l) and rats were followed for eight weeks. Urinary albumin, Kim-1 and cystatin c were determined by ELISA. Mitochondria were isolated from renal cortices. Mass spectrometry was used to determine metabolites, lipids and proteins.
Results: Intensive insulin therapy (MHG) afforded renoprotection, leading to improved glomerular hyperfiltration and decreased albuminuria, glomerular injury and fibrosis. Quantitative mitochondrial proteomics revealed a clear change in the mitochondrial signature induced by SHG with an upregulation of fatty acid metabolism and downregulation of a cluster of mitochondrial carrier family proteins (SLC25). Lipidomic analysis revealed that mitochondrial cardiolipin remodeling was robustly induced with hyperglycemia and positively correlated with renal injury. Lowering blood glucose normalized the Cardiolipin lipidome and improved renal injury. Hyperglycemia induced lipid catabolism in the kidney through upregulation of β-oxidation of odd and branched chain fatty acids. Metabolomics indicated enrichment of TCA cycle metabolites.
Conclusions: These results have implications for therapeutic strategies aiming at the reinvigoration of mitochondrial function and signaling in diabetes.
Associate Professor Melinda Coughlan is Head of the Glycation, Nutrition & Metabolism Laboratory within the Department of Diabetes, Central Clinical School, Monash University, Alfred Health, Melbourne, Australia. She studied Biology and Nutrition before obtaining a PhD from the University of Melbourne after which time she began research into diabetic nephropathy. A/Prof Coughlan has already made a number of exciting observations in the preclinical space with respect to drug target identification and has now extended her research to translational studies. She holds funding from NHMRC and a Career Development Fellowship from the JDRF for her work into diabetes and its complications.