Biochemical mechanisms of hyperglycaemic injury are potential targets for novel therapeutic intervention aimed at reducing glucose toxicity, which is decreased but not completely prevented by current glucose-lowering treatment strategies. The glycolytic side product methylglyoxal (MGO) is a major mediator of glucose toxicity. Trapping MGO with ¿-carnosine (CAR), a selective scavenger of carbonyl species, was shown effective in protecting against diabetic vascular complications, an effect that was associated with suppressed Hypoxia-inducible factor 1-alpha (HIF-1¿) upregulation in the vasculature of diabetic mice. As part of a project financed by funds from the Sapienza University of Rome ( Bando Ricerca 2017), we investigated the role of MGO in driving high glucose (HG)-mediated HIF-1alfa induction and the associated Warburg effect and found that 1) CAR is able to reverse HIF-1¿ induction and related metabolic changes induced by HG; 2) MGO mimics the effect of HG on cellular bioenergetics. From a mechanistic view, we observed that glucose-derived MGO activates HIF-1¿ and leads to accumulation of toxic glucose metabolites (i.e., sorbitol and advanced glycation end-products). The aim of this project is twofold: 1) to assess the role of HIF-1¿, pyruvate kinase M2 (PKM2) and their interplay in renal cell dysfunction induced by HG; 2) to investigate the reciprocal modulating effects of HIF-1alfa and PKM2 expression and activity in HG conditions, resulting in a Warburg-like effect and glucose toxicity. PKM2 is a glycolytic enzyme that catalyzes the last step within glycolysis and has been recently involved in the pathogenesis of diabetic nephropathy in both humans and preclinical models. Though PKM2 is a well-known transcriptional target of HIF-1¿ and its pharmacological activation has been shown to reverse HG-induced mitochondrial dysfunction, the relationship between HIF-1¿ and PKM2 activity in cellular bioenergetics changes induced by HG has not yet been investigated
Biochemical mechanisms of hyperglycaemic injury are potential targets for novel therapeutic intervention aimed at reducing glucose toxicity, which is decreased but not completely prevented by current glucose-lowering treatment strategies. Since the role of superoxide as initial instigator of diabetic complications was questioned [1], an alternative mechanism underlying the shift of glucose metabolism towards extra-mitochondrial glycolysis and alternative pathological glycolytic pathways is needed. This research project investigates a novel mechanistic link between HG, the toxic by-product of glycolysis MGO and the instigation of a HIF-1alfa/PKM2-mediated Warburg effect, providing new explanation for the changes in glucose energy metabolism and consequent biochemical abnormalities responsible for podocyte and endothelial cell dysfunction and injury, i.e., two major glomerular cells involved in the pathogenesis of diabetic nephropathy. We also postulate that CAR, the MGO-scavenger shown to be highly effective in preventing diabetic vascular complications and HIF-1¿ upregulation [2], and TEPP-46, the PKM2 inducer shown to protect renal cells from the toxic effects of glucose [3,4], might help to reverse the HG-induced biochemical changes by inhibiting HIF-1¿ induction, the raising of PKM2 levels and consequent changes in cell energetics. We are confident that, apart from filling a cognitive gap in the molecular mechanisms underlying glucose toxicity, the findings from this proposal have the potential to introduce a paradigm shift for the prevention and treatment of diabetic nephropathy by identifying new molecular players and, thus, new therapeutic opportunities. Development of therapeutic strategies capable of protecting renal cells from abnormalities in cell glucose metabolism caused by hyperglycemia may abate residual long-term glucose toxicity resulting from insufficient glycaemic control. What is more, since a randomized controlled trial investigating the effects of CAR on cardiovascular health in type 2 diabetic patients has been already started [5], we think that our mechanistic study may be of potential help for the interpretation of the clinical findings.
References
1.Dugan LL et al. J Clin Invest. 2013; 123:4888-4899
2. Menini S et al. Diabetologia 2015; 58:845-853
3.Qi W et al. Nat. Med. 2017; 23:753-762
4. Li L et al. Exp Clin Endocrinol Diabetes. 2020; Jan 20 [Epub ahead of print]
5. Baye E et al. BMJ Open. 2017;7:e01769