Pioglitazone Induces Vascular Smooth Muscle Cell Apoptosis Through a Peroxisome Proliferator-Activated Receptor-γ, Transforming Growth Factor-β1, and a Smad2-Dependent Mechanism

Abstract

Thiazolidinediones, such as pioglitazone, seem to exert direct antiatherosclerotic and antirestenotic effects on type 2 diabetes, in part due to an induction of vascular smooth muscle cell (VSMC) apoptosis. We aimed to study the role of transforming growth factor (TGF)-␤ in rat aortic VSMC. Pioglitazone at 100 mol/l increased apoptosis without affecting DNA synthesis, and this effect was reversed by an anti-TGF-␤1 antibody. Extracellular TGF-␤1 levels were rapidly increased after treatment with pioglitazone in a peroxisome proliferator-activated receptor (PPAR)-␥-dependent mechanism because this secretion was blocked by the PPAR-␥ inhibitor GW9662. Pioglitazone subsequently increased the nuclear recruitment of phospho-Smad2, without any effect on protein expression. According to our results, we propose that the apoptotic effect of pioglitazone on VSMC depends on the following sequence: PPAR-␥ activation, TGF-␤1 release, and selective phospho-Smad2 nuclear recruitment. Management of Smad signaling on VSMC might provide future clinical benefits in vascular diseases. Diabetes 54: [811][812][813][814][815][816][817] 2005 T ype 2 diabetes is a major risk factor for atherosclerosis, the leading cause of morbidity and mortality in developed countries (1). In addition, diabetic patients show an increased risk for suffering postangioplasty restenosis (2). Vascular wall size depends on a relative balance between proliferation and apoptosis (3). When the ratio of proliferation to apoptosis increases, an early atherosclerotic plaque or a postangioplasty restenosis is faced.Thiazolidinediones (TZDs) are an emerging class of antidiabetic drugs that enhance insulin sensitivity in a peroxisome proliferator-activated receptor (PPAR)-␥-dependent fashion (4). However, they have also been demonstrated to exert some direct effects in decreasing neointimal growth after balloon injury (5) and angioplasty (6), two situations with an increased ratio for vascular smooth muscle cell (VSMC) proliferation to apoptosis. Many of the studies concerning the cellular effects of TZD have focused on cell cycle and DNA synthesis regulation. Surprisingly, these effects seem to be PPAR-␥ independent (7). On the other hand, at higher doses, TZDs have been proven to induce apoptosis in VSMCs by involving PPAR-␥ (8).Transforming growth factor (TGF)-␤1 is an essential cytokine involved in the control of the balance between proliferation and apoptosis in VSMCs. TZDs and TGF-␤1 share the induction of apoptosis by similar mechanisms, such as GADD45 (9,10). In addition, some crosstalk between TGF-␤1 and PPAR-␥ has been described; thus, in the long term, TGF-␤1 inhibits PPAR-␥ expression (11), whereas PPAR-␥ agonists and PPAR-␥ itself interact with the TGF-␤1 signaling pathway by inhibiting Smad3 (12). Therefore, Smad2 appears as a likely target for TGF-␤ in TZD-treated VSMCs.In the present study, we show that the apoptotic effect of the TZD pioglitazone in VSMC depends on the following sequence: PPAR-␥ agonism, rapid TGF-␤1 autocrine secretion, and select...

Pioglitazone Induces Apoptosis in Human Vascular Smooth Muscle Cells from Diabetic Patients Involving the Transforming Growth Factor-β/Activin Receptor-Like Kinase-4/5/7/Smad2 Signaling Pathway

“…The canonical pathway of TGF-␤1 in VSMC involves activation of ALK-4/ 5/7 receptor-related kinases, which phosphorylates Smad2 (Ten Dijke et al, 2002). Interestingly, the importance of the TGF-␤1/Smad2 pathway in PIO-mediated rat VSMC apoptosis has been demonstrated by our group (Redondo et al, 2005). We found that PIO increased TGF-␤1 release in rat VSMC and that this cytokine mediated the apoptosis of PIO through the Smad2 pathway.…”

“…Because TGF-␤1 seems to be involved in the apoptotic effect of PIO, we studied whether this drug was able to increase the release of TGF-␤1 from cultured human VSMC obtained from nondiabetic and diabetic patients pretreated with 15 mM glucose for 48 h before PIO treatment. Figure 4A shows a rapid and transient increase in the release of total TGF-␤1 induced by 100 M pioglitazone as early as 30 min after treatment in VSMC from nondiabetic patients, as reported in rat VSMC (Redondo et al, 2005). However, VSMC from diabetic patients showed a different pattern of TGF-␤1 release.…”

Peroxisome Proliferator-Activated Receptor-γ–Mediated Effects in the Vasculature

“…Pioglitazone increases transforming growth factor ␤1 secretion and phosphorylation of Smad2 in cultured VSMCs. 77,78 PPAR-␥ agonists increase IRF-1 gene expression while inducing VSMC apoptosis, and conversely inhibition of IRF-1 by antisense oligonucleotide decreases the VSMC apoptosis in vitro. 79 However, VSMC apoptosis can decrease the stability of atherosclerotic plaques and predispose them to rupture.…”

“…[75][76][77][78][79] The mechanisms include upregulation of growth arrest and DNA damageinducible gene 45 expression, 75,76 as well as p53 expression (Figure 2). 76 The transforming growth factor ␤1/Smad2 pathway 77,78 and IFN regulatory factor (IRF)-1 79 are also involved ( Figure 2). Pioglitazone increases transforming growth factor ␤1 secretion and phosphorylation of Smad2 in cultured VSMCs.…”

Transforming Growth Factor-β Type I Receptor Inhibitor Induces Functional and Morphologic Recovery in a Rat Model of Erectile Dysfunction and Cavernous Fibrosis

“…22,23 Furthermore, the TGF-β1-Smad2 pathway is involved in apoptosis of vascular smooth muscle cells induced by pioglitazone, a peroxisome proliferatoractivated receptor γ ligand. 24 TGF-β is also known to inhibit endothelial cell proliferation via the ALK5-Smad2/3 pathway, [25][26][27] whereas inhibition of ALK5 facilitates endothelial cell proliferation. 26,27 We also investigated whether ALK5 inhibitor can induce regression of cavernous fibrosis.…”