Nuclear translocation of pyruvate kinase M2 drives high glucose-induced angiogenesis in retinal endothelial cells via the HIF-1α axis

AIM: To investigate the role of pyruvate kinase M2 (PKM2) in high glucose (HG)-stimulated retinal endothelial cells and its underlying molecular mechanisms and signaling pathways in retinal angiogenesis. METHODS: Human retinal microvascular endothelial cells (HRMECs) were cultured and divided into the following groups: normal glucose (NG, 5.5 mmol/L), HG (30 mmol/L), HG with PKM2 knockdown (HG+shPKM2), and HG treated with the pharmacological activator TEPP-46 (HG+TEPP-46). Cellular viability, proliferation, migration, and tube-forming ability were assessed using CCK-8, EdU, wound healing/Transwell, and Matrigel assays, respectively. The expression levels of PKM2, phosphorylated PKM2 (p-PKM2, Y105), hypoxia-inducible factor-1α (HIF-1α), and vascular endothelial growth factor A (VEGFA) were detected by Western blotting. The oligomerization status of PKM2 was analyzed via native gel electrophoresis. The subcellular localization of PKM2 was examined by immunofluorescence and nuclear-cytoplasmic fractionation. RESULTS: Under HG stimulation, the expression level of PKM2 was significantly increased (P0.05). Knockdown of PKM2 was found to markedly suppress cell viability, proliferation, migration, and tube formation in HRMECs (P0.05). Mechanistic studies revealed that phosphorylation of PKM2 at the Y105 site was promoted by HG treatment, which induced its dissociation from a tetramer to a dimer, thereby driving its nuclear translocation. Upon entering the nucleus, PKM2 was shown to exert critical non-metabolic functions; it was physically bound to HIF-1α and acted as its co-activator, leading to significant upregulation of VEGFA expression (P0.05). In contrast, the PKM2 activator TEPP-46 effectively prevented dimerization and nuclear translocation of PKM2 by promoting its tetramerization. Consequently, the PKM2/HIF-1α axis-mediated upregulation of VEGFA was blocked, ultimately resulting in the reversal of HG-induced angiogenesis. CONCLUSION: HG influences retinal endothelial cell function by inducing PKM2 phosphorylation, dimerization, and nuclear translocation. The shift in PKM2 phosphorylation and oligomerization status represents a key mechanism through which TEPP-46 reverses HG-induced angiogenesis.