Cell Cycle Progression of Vascular Smooth Muscle cell Through Modulation of p38 MAPK and GSK-3beta Activities Under High Glucose Condition

Kang, Yang Ho; Kim, In Ju; Kim, Yong Ki; Son, Seok Man

Abstract

BACKGOUND: Macroangiopathy, with atherosclerosis, is the leading cause of mortality and morbidity in diabetic patients. Vascular smooth muscle cells play a crucial role in atherosclerosis, as they proliferate, migrate and express genes that encode inducible growth factors. However, the mechanisms induced by hyperglycemia that accelerate the proliferative change of vascular smooth muscle cells in diabetes remain unclear. This study was aimed at clarifying the respective roles of hyperglycemia in the acceleration of vascular complications in diabetes, examine the effects of hyperglycemia on vascular smooth muscle cell proliferation and the possible underlying mechanisms, including cell cycle progression.
METHODS
Primary cultured rat aortic RASMs were exposed to normal glucose(5 mmol/L D-glucose), high glucose(30 mmol/L D-glucose) or an osmotic control (5mmol/L D-glucose plus 24.5 mmol/L mannitol) for 72 hours. The effect of high glucose on cell proliferation was determined by assessing the cell count and BrdU incorporation. Proteins involved in the cell proliferation pathway (PDK1, Akt/PKB, p42/44 MAPK, p38 MAPK, GSK-3beta) and those in cell cycle progression (cdk4, cyclin D, cdk2, cyclin E and ppRb phosphorylation) were determined by Western blot analysis. cdk4 kinase and PKC activity assays were also performed.
RESULTS
A high level of glucose increased both the cell count(P<0.01) and BrdU incorporation(P<0.01). The PDK1, Akt/PKB and p42/44 MAPK activities were not significantly increased. A high level of glucose significantly increased the activities of p38 MAPK (P<0.01) and GSK-3beta(P<0.05) and the expressions of cdk4, cyclin D and ppRb phosphorylation. The cdk4 (P<0.01) and PKC (P<0.05) activities were also significantly increased. The inhibition of protein kinase C with GF109203X markedly reduced the phosphorylations of p38 MAPK and GSK-3betaand the expressions of cdk4 and cyclin D. In addition, pretreatment with GF109203X decreased the cell number in response to a high glucose level.
CONCLUSION
These findings suggest that a high level of glucose increases vascular smooth muscle cell proliferation, with the possible mechanism further increases the G1 to S phase cell cycle progression via the activation of PKC, p38 MAPK and GSK-3beta.