Glucose-Induced Phosphatidylinositol 3-Kinase and Mitogen-Activated Protein Kinase-Dependent Upregulation of the Platelet-Derived Growth Factor-β Receptor Potentiates Vascular Smooth Muscle Cell Chemotaxis

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Abstract
The aim of this study was to investigate the effects of elevated d-glucose concentrations on vascular smooth muscle cell (VSMC) expression of the platelet-derived growth factor (PDGF)β receptor and VSMC migratory behavior. Immunoprecipitation, immunofluorescent staining, and RT-PCR of human VSMCs showed that elevated d-glucose induced an increase in the PDGFβ receptor that was inhibited by phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathway inhibitors. Exposure to 25 mmol/l d-glucose (HG) induced increased phosphorylation of protein kinase B (PKB) and extracellular-regulated kinase (ERK). All HG chemotaxis assays (with either 10 days’ preincubation in HG or no preincubation) in a FCS or PDGF-BB gradient showed positive chemotaxis, whereas those in 5 mmol/l d-glucose did not. Assays were also run with concentrations ranging from 5 to 25 mmol/l d-glucose. Chemotaxis was induced at concentrations ≥9 mmol/l d-glucose. An anti-PDGFβ receptor antibody inhibited glucose-potentiated VSMC chemotaxis, as did the inhibitors for the PI3K and MAPK pathways. This study has shown that small increases in d-glucose concentration, for a short period, increase VSMC expression of the PDGFβ receptor and VSMC sensitivity to chemotactic factors in serum, leading to altered migratory behavior in vitro. It is probable that similar processes occur in vivo with glucose-enhanced chemotaxis of VSMCs, operating through PDGFβ receptor-operated pathways, contributing to the accelerated formation of atheroma in diabetes.