Diabetic nephropathy (DN) is the leading cause of renal failure in the US. Hyperglycemia (HG) has been identified as the primary risk factor for DN, but therapies targeting the known pathways of HG-induced renal damage have not shown significant benefits. We proposed endogenous protective mechanisms exist which mitigate the adverse effects of HG that contribute to DN development. Examination of a unique cohort of type 1 diabetic (T1D) patients (Joslin Medalist Study; n=1007) who have had the disease for 50?87 years, of whom only 13.2% have significant renal disease independent of HbA1c support this conclusion. Proteomic analysis of Medalists' post-mortem renal glomeruli, comparing DN class 0-I to IIB ?III identified multiple enzymes in the glycolytic, aldose reductase, methylglyoxal (MG) and mitochondrial pathways as higher in those protected from DN. Additionally, metabolomic analyses comparing those with DN (eGFR <45 ml/min/1.73 m2) and those without (eGFR >90 ml/min/1.73 m2) showed many glycolytic intermediates, sorbitol, MG and DAG to be decreased. This suggests an ability to metabolize intracellular glucose via glycolysis, the aldose reductase pathway, MG degradation and mitochondrial oxidative phosphorylation. A subset comparison of metabolites from Medalists' without DN to younger individuals who progressed rapidly to DN supports PKM2's protective nature. Plasma PKM2 levels from the Medalists correlated with eGFR, MG and DN class. Therefore, activating the key regulatory allosteric glycolytic enzyme, pyruvate kinase (PK), especially the M2 isoform, may increase flux via glycolysis and the mitochondrial oxidative phosphorylation pathways and prevent the onset or stop DN progression. We have documented PKM2 activation reversed HG-induced elevations of diacylglycerol, protein kinase C, sorbitol, MG, and mitochondrial dysfunction, as well as apoptosis in podocytes. Further, knockdown of PKM2 exaggerated the toxic effects of HG. In vivo studies using a small molecule activator of PKM2 and PKM2 podocyte specific knock-outs support the importance of PKM2 to normalize mitochondrial biogenesis and function, and prevent pathology of DN in the presence of HG. These data indicate increases in glycolysis and mitochondrial function, possibly by PKM2 activation, can prevent renal damage due to HG.
Specific Aim 1 : Validate and reproduce the association of glomeruli PKM2 protein levels with renal cortex and serum metabolite levels in post-mortem glomerular specimens from Medalists to establish a relationship with PKM2 plasma levels and clinical markers of renal function.
Specific Aim 2 : Compare plasma PKM2 levels, serum metabolite profiles and clinical renal markers in samples from the Medalist population and in a shorter duration population, and establish a longitudinal relationship with PKM2 levels and the progression of renal disease.
Specific Aim 3 : Characterize the mechanism that causes the decreased expression or activities of PKM2 by HG and the effect of its activation to restore mitochondria and cellular function, and survival of podocytes in HG conditions.
We propose PKM2 is an endogenous protective protein, identified by proteomic and metabolomics analyses from human renal tissue which mitigates the adverse effects of hyperglycemia preventing diabetic nephropathy by decreasing the toxic metabolites of high glucose levels and inducing mitochondrial biogenesis. Importantly, this was identified using pre- mortem clinical data and post-mortem specimens from an extraordinary cohort with type 1 diabetes for 50 or more years, of whom only 13.2% had significant nephropathy with no association to glycemic control. In this proposal we link the organ specific activity of the protein with systemic markers and demonstrate the effect of activating PKM2 to prevent or reverse the effects of high glucose indicating the presence of a mechanism for the prevention of diabetic nephropathy.
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