Characterization of Glycolytic Enzymes and Pyruvate Kinase M2 in Type 1 and 2 Diabetic Nephropathy

Abstract

Elevated glycolytic enzymes in renal glomeruli correlated with preservation of renal function in the Medalist Study, individuals with ‡50 years of type 1 diabetes. Specifically, pyruvate kinase M2 (PKM2) activation protected insulin-deficient diabetic mice from hyperglycemia-induced glomerular pathology. This study aims to extend these findings in a separate cohort of individuals with type 1 and type 2 diabetes and discover new circulatory biomarkers for renal protection through proteomics and metabolomics of Medalists' plasma. We hypothesize that increased glycolytic flux and improved mitochondrial biogenesis will halt the progression of diabetic nephropathy. RESEARCH DESIGN AND METHODS Immunoblots analyzed selected glycolytic and mitochondrial enzymes in postmortem glomeruli of non-Medalists with type 1 diabetes (n = 15), type 2 diabetes (n = 19), and no diabetes (n = 5). Plasma proteomic (SOMAscan) (n = 180) and metabolomic screens (n = 214) of Medalists with and without stage 3b chronic kidney disease (CKD) were conducted and significant markers validated by ELISA. RESULTS Glycolytic (PKM1, PKM2, and ENO1) and mitochondrial (MTCO2) enzymes were significantly elevated in glomeruli of CKD2 versus CKD+ individuals with type 2 diabetes. Medalists' plasma PKM2 correlated with estimated glomerular filtration rate (r 2 = 0.077; P = 0.0002). Several glucose and mitochondrial enzymes in circulation were upregulated with corresponding downregulation of toxic metabolites in CKD-protected Medalists. Amyloid precursor protein was also significantly upregulated, tumor necrosis factor receptors downregulated, and both confirmed by ELISA. CONCLUSIONS Elevation of enzymes involved in the metabolism of intracellular free glucose and its metabolites in renal glomeruli is connected to preserving kidney function in both type 1 and type 2 diabetes. The renal profile of elevated glycolytic enzymes and reduced toxic glucose metabolites is reflected in the circulation, supporting their use as biomarkers for endogenous renal protective factors in people with diabetes.

Gene Regulatory Effect of Pyruvate Kinase M2 is Involved in Renal Inflammation in Type 2 Diabetic Nephropathy

“…We found that the plasma PKM2 levels increased in patients with diabetes, which was consistent with the findings of previous studies showing elevated serum PKM2 level in some inflammatory diseases [31][32][33]. Plasma PKM2 level is associated with type 1 and type 2 diabetic nephropathy; thus, the assessment of serum PKM2 level is important [34]. Th17 differentiation is involved in the pathological progression of DN [35].…”

Pyruvate-Enriched Oral Rehydration Solution Improves Glucometabolic Disorders in the Kidneys of Diabetic db/db Mice

“…Accumulating studies demonstrated that disturbances of glucose metabolic pathways, particularly, pyruvate kinase (PK M2) depression and the Warburg phenomenon, glomerular microvascular endothelial mitochondrial dysfunction, and endoplasmic reticulum stress in renal proximal tubular epithelial cells all stimulated by hyperglycemia (HG) play crucial roles in DN onset and progression in diabetic rodent models and patients [ 3 – 7 ]. Specifically, renal hypoxia, oxidative stress, inflammation, and advanced glycation end products (AGEs) are simultaneously participated in the process, leading to a vicious circle in DN exacerbation [ 7 – 10 ].…”

Protective factors as biomarkers and targets for prevention and treatment of diabetic nephropathy: From current human evidence to future possibilities

“…The circulating levels of 120 proteins were increased in diabetes patients who were protected from CKD compared with those with CKD stage 3b, which shows potential protective factors against DN. The results of integrated network analysis identified enhancement/upregulation of several novel (pyruvate kinase M2, amyloid precursor protein), as well as previously known pathways (EGFR) in CKD-protected Medalists 48 . Subsequently, the presence of plasma pyruvate kinase M2 has been confirmed in a general population of patients with type 1 and type 2 diabetes.…”

“…The study used kidney biopsies and proteomic as well as metabolomic approaches to identify markers whose expression patterns might explain the profound protection in this cohort. To screen for markers underlying protection from DN, the authors utilized untargeted metabolomics, as well as an aptamer-based array that measures 1123 proteins in plasma 47,48 . The circulating levels of 120 proteins were increased in diabetes patients who were protected from CKD compared with those with CKD stage 3b, which shows potential protective factors against DN.…”