Glucose-Induced TGF-β1 and TGF-β Receptor-1 Expression in Vascular Smooth Muscle Cells Is Mediated by Protein Kinase C-α

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Abstract
Sclerosis and increased matrix expression in diabetes are mediated by glucose-induced transforming growth factor (TGF)-β1 expression. The intracellular effects of high glucose occur at least in part by way of protein kinase C (PKC). We previously described a role for PKC-α in glucose-induced permeability. We now investigated the hypothesis that glucose-induced expression of TGF-β1 and its receptors (TGF-β-R1 and -R2) are mediated by activation of this PKC isoform. TGF-β1 and TGF-β-R expressions were determined in vascular smooth muscle cells (VSMCs) by immunocytochemistry and Western blotting. PKC isoforms were assessed by confocal microscopy. PKC isoforms were inhibited with antisense oligodeoxynucleotides. PKC-α was upregulated by overexpression or microinjection. High glucose (20 mmol/L) increased VSMC TGF-β1 and TGF-β-R1 expression but not TGF-β-R2 expression. PKC inhibitors and specific PKC-α downregulation by antisense treatment prevented this effect, whereas antisense treatment against PKC-β, -ε, and -ζ had no influence. PKC-α overexpression increased TGF-β1 and TGF-β-R1 expression but not TGF-β-R2 expression. PKC-α microinjection into individual VSMCs also increased TGF-β1 and TGF-β-R immunofluorescence. Last, VSMCs from PKC-α-deficient mice did not respond to high glucose compared with VSMCs from wild-type mice. We propose that high glucose-induced TGF-β1 and TGF-β-R1 expression is mediated by PKC-α. Our findings suggest an autocrine feedback mechanism and a possible role for PKC-α in diabetic vascular disease.