Acute glucose-induced downregulation of PKC-beta II accelerates cultured VSMC proliferation

Accelerated vascular smooth muscle cell (VSMC) proliferation contributes to the formation of atherosclerotic lesions. To investigate protein kinase C (PKC)-beta II functions with regard to glucose-induced VSMC proliferation, human VSMC from aorta (AoSMC), a clonal VSMC line of rat aorta (A10), and A 10 cells overexpressing PKC-beta I (beta I-A10) and PKC-beta II (beta II-A1 0) were studied with the use of three techniques to evaluate glucose effect s on aspects affecting proliferation. High glucose (25 mM) increased DNA sy nthesis and accelerated cell proliferation compared with normal glucose (5. 5 mM) in AoSMC and A10 cells, but not in beta I-A10 and beta II-A10 cells. The PKC-beta II specific inhibitor CGP-53353 inhibited glucose-induced cell proliferation and DNA synthesis in AoSMC and A10 cells. In flow cytometry analysis, high glucose increased the percentage of A10 cells at 12 h after cell cycle initiation but did not increase the percentage of beta I-A10 or beta II-A10 cells entering S phase. PKC-beta II protein levels decreased be fore the peak of DNA synthesis, and high glucose further decreased PKC-beta II mRNA and protein levels in AoSMC and A10 cells. These results suggest t hat high glucose downregulates endogenous PKC-beta II, which then alters th e normal inhibitory role of PKC-beta II in cell cycle progression, resultin g in the stimulation of VSMC proliferation through acceleration of the cell cycle.