Dottorato in SCIENZE ENDOCRINOLOGICHE

Titolo della tesi: HIF-1α, PKM2 AND THEIR INTERPLAY IN GLUCOSE TOXICITY: METABOLIC REWIRING IN DIABETIC COMPLICATIONS

Intracellular metabolism of excess glucose induces mitochondrial dysfunction and diversion of glycolytic intermediates into branch pathways, leading to cell injury and inflammation. Hyperglycemia-driven overproduction of mitochondrial superoxide was thought to be the initiator of these biochemical changes, but this hypothesis has recently been put into question. In this project we tested the hypothesis that hypoxia inducible factor (HIF)-1α and pyruvate kinase M2 (PKM2), two master regulators of energetic metabolism involved in the reprogramming of glucose metabolism towards glycolysis (Warburg effect), play an initiating role in glucotoxicity. By using human endothelial cells and macrophages, we demonstrated that high glucose (HG) induces HIF-1α activity and a switch from oxidative metabolism to glycolysis and its principal branches. We identified in methylglyoxal (MGO), a glycolysis side product, the non-hypoxic stimulus to HIF-1α activation in HG by inhibiting its degradation via post-translational modification of the prolyl hydroxylase D2 enzyme. Given the known interplay that exists between HIF-1α and PKM2 in inducing glucose metabolic reprogramming and the recent evidence indicating a key role for PKM2 in diabetic complications, we also tested the hypothesis that HIF-1α and PKM2 are components of a molecular network that regulates Warburg effect in HG and that this interplay is implicated in HG-induced renal cells dysfunction. We demonstrated that HG induces a HIF-1α-mediated shift of the physiological balance between PKM1 and PKM2, with reduction of the enzymatically active tetrameric form. Dimeric PKM2 interacts at nuclear level with HIF-1α and together these two factors induce an energetic reprogramming leading to the accumulation of toxic glucose metabolite and, thus, to cell damage. We also demonstrated the protective effect provided by Carnosine by inhibiting this molecular network via its anti-carbonyl activity. This project provides new insights on the changes of cellular glucose metabolism associated with DM complications and the role of HIF-1α and PKM2 as components of a molecular network that regulates metabolic reprograming towards the Warburg effect in glucose toxicity.