Glucosamine enhances platelet-derived growth factor-induced DNA synthesis via phosphatidylinositol 3-kinase pathway in rat aortic smooth muscle cells

Vascular smooth muscle cells play a key role in the development of atherosclerosis. Culture of vascular smooth muscle A10 cells with high glucose for 4 weeks enhanced platelet-derived growth factor (PDGF)-induced BrdU incorporation. Since a long period of high glucose incubation was required for the effect, and it was inhibited by co-incubation with azaserine, the role of hexosamine biosynthesis in the development of atherosclerosis in diabetes was studied in A10 cells. Addition of glucosamine to the culture media enhanced PDGF-stimulated BrdU incorporation, and PDGF-induced tyrosine phosphorylation of the PDGF beta-receptor was increased by glucosamine treatment. Of the subsequent intracellular signaling pathways, PDGF-induced PDGF beta-receptor association with PLC gamma was not affected, whereas tyrosine phosphorylation of Shc, subsequent association of Shc with Grb2, and MAP kinase activation were relatively decreased. In contrast, PDGF-induced PDGF beta-receptor association with the p85 regulatory subunit of PI3-kinase and PI3-kinase activation were increased by 20% (P<0.01) and 36% (P<0.01), respectively. The intracellular signaling molecules responsible for the glucosamine effect were further examined using pharmacological inhibitors. Pretreatment with PLC inhibitor (U73122) had negligible effects, and MEK1 inhibitor (PD98059) showed only a slight inhibitory effect on the PDGF-induced BrdU incorporation. In contrast, pretreatment with PI3-kinase inhibitor (LY294002) significantly inhibited glucosamine enhancement of PDGF-induced BrdU incorporation. These findings suggest that glucosamine is involved in the development of atherosclerosis by enhancing PDGF-induced mitogenesis specifically via the PI3-kinase pathway.