High glucose attenuates insulin-induced mitogen-activated protein kinase phosphatase-1 (MKP-1) expression in vascular smooth muscle cells

The mechanisms for the effect of hyperglycemia on insulin-induced mitogenes is were investigated using rat vascular smooth muscle cells (VSMC). VSMC we re preincubated in serum-free medium with low (5 mM) glucose (LG condition) or high (25 mM) glucose (HG condition), and examined for DNA synthesis usi ng bromodeoxyuridine (BrdUrd) incorporation. Mitogen-activated protein kina se (MAPK) activity and MAPK phosphatase (MKP-1) protein expression were det ected by Western blot analysis. Phosphatidylinositol 3-kinase (PI-3K) activ ity was detected by thin layer chromatography. Insulin induced a dose-depen dent increase in BrdUrd incorporation (123.3 +/- 2.6% over basal level with 1 mu M insulin) in the LG group and this effect was significantly enhanced (161.6 +/- 10.4% over basal level) in the PIG group. Tn the LG group, MAPK activity was transient with a peak activation (137.4 +/- 11.2% over basal level) after 10 min exposure to 100 nM insulin. In the HG group, the MAPK a ctivity was significantly potentiated (two-fold compared to the LG group) a nd was sustained even after 60 min. Insulin also induced PI-3K activity and MKP-1 expression, both of which were blocked by the PI-3K inhibitor wortma nnin. In the HG group, insulin-induced PI-3K and MKP-1 expression was almos t abolished. In conclusion, high glucose enhances insulin-induced mitogenes is associated with the potentiation of insulin-stimulated MAPK activity in VSMC. These effects of glucose might in part be due to the attenuation of M KP-1 expression through the blockage of the insulin-PI-3K signal pathway. ( C) 2000 Elsevier Science B.V. All rights reserved.