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

Abstract

Abstract-Sclerosis and increased matrix expression in diabetes are mediated by glucose-induced transforming growth factor (TGF)-␤1 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-␣ in glucose-induced permeability. We now investigated the hypothesis that glucose-induced expression of TGF-␤1 and its receptors (TGF-␤-R1 and -R2) are mediated by activation of this PKC isoform. TGF-␤1 and TGF-␤-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-␣ was upregulated by overexpression or microinjection. High glucose (20 mmol/L) increased VSMC TGF-␤1 and TGF-␤-R1 expression but not TGF-␤-R2 expression. PKC inhibitors and specific PKC-␣ downregulation by antisense treatment prevented this effect, whereas antisense treatment against PKC-␤, -⑀, and -had no influence. PKC-␣ overexpression increased TGF-␤1 and TGF-␤-R1 expression but not TGF-␤-R2 expression. PKC-␣ microinjection into individual VSMCs also increased TGF-␤1 and TGF-␤-R immunofluorescence. Last, VSMCs from PKC-␣-deficient mice did not respond to high glucose compared with VSMCs from wild-type mice. We propose that high glucose-induced TGF-␤1 and TGF-␤-R1 expression is mediated by PKC-␣. Our findings suggest an autocrine feedback mechanism and a possible role for PKC-␣ in diabetic vascular disease. Key Words: glucose Ⅲ growth substances Ⅲ protein kinases Ⅲ diabetes Ⅲ muscle, vascular, smooth Ⅲ atherosclerosis R enal hypertrophy, basement membrane thickening, and extracellular matrix accumulation characterize diabetic nephropathy. 1 Several cytokines with fibrogenic potential contribute to this, particularly transforming growth factor (TGF)-␤1. 2 TGF-␤1 increases matrix synthesis, inhibits matrix degradation, upregulates adhesion molecules, and enhances chemoattraction. 3,4 The possible importance of TGF-␤1 in diabetic nephropathy has been demonstrated in vitro by glucose-induced upregulation of this cytokine in different cell types. 5-13 Increased TGF-␤1 expression has also been demonstrated in diabetic animal models and human patients. 14,15 TGF-␤ binds specific serine/threonine kinase type I and type II receptors. The receptors form heteromeric cell surface complexes with TGF-␤. 16,17 The type II receptor determines ligand specificity, whereas the type I receptor interacts with the type II receptor and might not have a specific ligand. The type II receptor, likely in conjunction with the type I receptor, is probably required for the antiproliferative effect, whereas the type I receptor is the probable mediator of extracellular gene expression. 16,17 High glucose upregulates TGF-␤1 receptors in vitro and in vivo. 18,19 Hyperglycemia might mediate the effect of protein kinase C (PKC) activation. 20 -24 PKC consists of several isoforms with distinct cellular functions and different ex...

Diminished Loss of Proteoglycans and Lack of Albuminuria in Protein Kinase C-α—Deficient Diabetic Mice

“…TGF-␤ 1 plays a key role in the development of renal hypertrophy and accumulation of extracellular matrix in diabetic nephropathy (43). We have recently shown that high glucose leads to a PKC-␣-dependent expression of TGF-␤ 1 in vascular smooth muscle cells under in vitro conditions (11). Surprisingly, our present findings do not support a role for PKC-␣ in the regulation of TGF-␤ 1 expression in vivo.…”

“…Other isoforms were less distinctly affected (10). Recently, we showed that glucose-induced activation of PKC-␣ in vitro leads to an increased expression of transforming growth factor-␤1 (TGF-␤ 1 ) (11). We tested the hypothesis that high-glucose-induced PKC-␣ activation in vivo is a mediator of functional and structural alterations in experimental diabetic nephropathy.…”

Fibromodulin, an extracellular matrix protein: characterization of its unique gene and protein expression in B-cell chronic lymphocytic leukemia and mantle cell lymphoma

“…Glucose and iron have been reported to induce TGF-␤ production. 49,50 Iron is important for the expression of cell-cycle and apoptosis-related genes, 51 and it may inhibit the proliferation of Burkitt lymphoma cells. 52 Iron is also required for PMA-induced expression of certain genes 53 and is necessary for protein kinase C activity.…”

Effect of telmisartan on expression of protein kinase C-? in kidneys of diabetic mice

“…The enhanced expressions of TGF-β 1 and VEGF stimulated by high glucose have proven to be regulated via a PKCdependent pathway [14][15][16] . A recent study showed that PKC-α lead to an increased expression of TGF-β 1 [17] , but other studies have reported that PKC-α is only involved in the regulation of VEGF and its receptor rather than TGF-β 1 under high glucose conditions [18] . Therefore, the relations of PKC-α to TGF β 1 and VEGF need further clarification.…”