Abstract 227: Inhibition Of Protein Tyrosine Phosphatase Improves Hyperglycemic Impaired Angiogenesis

Abstract

Our previous study shows that hyperglycemia impairs myocardial angiogenesis via impairment of angiopoietin-1(Ang-1)/Akt/eNOS phosphorylation. Protein tyrosine phosphatase (PTP) plays an essential role in intracellular signal transduction by regulating tyrosine phosphorylation. PTP inhibitor has been shown to modulate Akt/eNOS phosphorylation, but little is known about the inhibition of PTP on angiogenesis under hyperglycemic conditions. We investigated the role of inhibition of PTP on hyperglycemia-induced impairment of angiogenic signaling pathways and angiogenesis. Our data demonstrate that exposure of mouse heart microvascular endothelial cells (MHMECs) to hyperglycemia leads to an increase in caspase-3 activity. Pretreatment of cells with the protein tyrosine phosphatase inhibitor, sodium orthovanadate (OV, 5 μM), significantly enhances the Ang-1-inhibitory effect on caspase-3 activity both under normal or hyperglycemic conditions. Pretreatment of MHMEC with the PTP inhibitor OV (0.5–20 μM) significantly enhances cell survival in a dose dependent manner under hyperglycemic conditions as measured by MTT assay. Pretreatment of MHMEC with OV (5 μM) enhances the effect of Ang-1 on endothelial cell survival under hyperglycemic conditions. As expected, Ang-1-induced Akt and eNOS phosphorylation is minimal under hyperglycemic conditions. Pretreatment of MHMEC with OV (5 μM) for 30 minutes leads to an increase in Akt phosphorylation at baseline and augments Ang-1-induced Akt and eNOS phosphorylation under hyperglycemic conditions. Additionally, systemic administration of bis(maltolato) oxovanadium(IV) (BMOV, 0.2g/L) in db/db mice results in a dramatic decrease in plasma glucose levels and an increase in vessel outgrowth in response to Ang-1 (250 ng/ml) stimulation. Treatment of db/db mice with BMOV significantly increases myocardial ischemia-induced HIF expression. Furthermore, bone marrow differentiation into endothelial cell progenitor cell is also significantly improved in the BMOV treated db/db mice. Our data implicate that upregulation of Ang-1/Akt/eNOS phosphorylation by PTP inhibitors should be considered as a new therapeutic strategy for the treatment or prevention of diabetic impaired angiogenesis.