PKCδ Impaired Vessel Formation and Angiogenic Factor Expression in Diabetic Ischemic Limbs

Decreased collateral vessel formation in diabetic peripheral limbs is characterized by abnormalities of the angiogenic response to ischemia. Hyperglycemia is known to activate protein kinase C (PKC), affecting the expression and activity of growth factors such as vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF). The current study investigates the role of PKCδ in diabetes-induced poor collateral vessel formation and inhibition of angiogenic factors expression and actions. Ischemic adductor muscles of diabetic Prkcd(+/+) mice exhibited reduced blood reperfusion, vascular density, and number of small vessels compared with nondiabetic Prkcd(+/+) mice. By contrast, diabetic Prkcd(−/−) mice showed significant increased blood flow, capillary density, and number of capillaries. Although expression of various PKC isoforms was unchanged, activation of PKCδ was increased in diabetic Prkcd(+/+) mice. VEGF and PDGF mRNA and protein expression were decreased in the muscles of diabetic Prkcd(+/+) mice and were normalized in diabetic Prkcd(−/−) mice. Furthermore, phosphorylation of VEGF receptor 2 (VEGFR2) and PDGF receptor-β (PDGFR-β) were blunted in diabetic Prkcd(+/+) mice but elevated in diabetic Prkcd(−/−) mice. The inhibition of VEGFR2 and PDGFR-β activity was associated with increased SHP-1 expression. In conclusion, our data have uncovered the mechanisms by which PKCδ activation induced poor collateral vessel formation, offering potential novel targets to regulate angiogenesis therapeutically in diabetic patients.