TGF-β through Smad3 signaling stimulates vascular smooth muscle cell proliferation and neointimal formation

Abstract

The objective of this study was to better understand the role of transforming growth factor-beta (TGF-beta) and its primary signaling protein Smad3 in the development of intimal hyperplasia. Male Sprague-Dawley rats underwent left carotid balloon injury followed by intra-arterial infection with adenovirus-expressing Smad3 (AdSmad3). In uninfected injured arteries, endogenous Smad3 was upregulated with the expression peaking at 14 days. Moreover, in arteries infected with AdSmad3, we observed an enhancement of intimal hyperplasia and increased vascular smooth muscle cell (VSMC) proliferation. The novel finding, that TGF-beta/Smad3 stimulated rather than inhibited VSMC proliferation, was confirmed in cultured VSMCs infected with AdSmad3 and treated with TGF-beta. To identify the mechanism underlying TGF-beta/Smad3-mediated VSMC proliferation, we studied the cyclin-dependent kinase inhibitor p27. Although the upregulation of Smad3 in VSMCs had no significant effect on total p27 levels, Smad3 did stimulate the phosphorylation of p27 at serine-10 as well as the nuclear export of p27, events associated with cell proliferation. Furthermore, serine-10-phosphorylated p27 was also increased in AdSmad3-infected injured rat carotid arteries, demonstrating the existence of this same mechanism in vivo. In conclusion, our findings identify a novel mechanism for the effect of TGF-beta on intimal hyperplasia. In the presence of elevated levels of Smad3 that develop in response to injury, TGF-beta stimulates smooth muscle cell proliferation through a mechanism involving the phosphorylation and nuclear export of p27.

Crosstalk between p38 and Smad3 through TGF-β1 in JEG-3 choriocarcinoma cells

“…Our result reveals that TGF-β1 not only activates Smad3, but also induces smad3 translocation into nucleus in JEG-3 cell line. The translocation induced by TGF-β1 is almost complete in 6 h and the nuclear expression of phospho-smad3 is strong positive compared with the control group, whereas, there is still a small amount of phospho-smad3 expressed in the cytoplasm of untreated cells, which indicates that TGF-β autocrine mechanism may exist in JEG-3 cells (31).…”

AMP-activated protein kinase inhibits transforming growth factor-β-mediated vascular smooth muscle cell growth: implications for a Smad-3-dependent mechanism

“…In VSMCs, TGF-␤ has historically been considered antiproliferative (2, 14 -16); however, other findings suggest that TGF-␤ and its downstream Smads stimulate growth in primary VSMCs (9,18,19,(25)(26)(27). Adding to this uncertainty, in cultured cells TGF-␤1 is suggested to switch between growth stimulation and growth suppression depending on concentration (3,18) and cell density (9).…”

“…Another component of this signal transduction pathway is inhibitory Smad7 that suppresses TGF-␤ signaling by interfering with activation of the R-Smads (18,21,28). The growthstimulating capacity of TGF-␤ in VSMCs has recently been suggested to involve Smad3-mediated phosphorylation and nuclear export of p27, a cyclin-dependent kinase inhibitor (27). The many uncertain aspects of TGF-␤/Smad signaling, particularly in VSM, justify continued study and present an attractive target for future therapeutic interests.…”

ADAMTS-7 promotes vascular smooth muscle cells proliferation in vitro and in vivo

“…Excessive proliferation of VSMCs in response to injury has been related to activation of a variety of growth factors and cytokine such as basic fibroblast growth factor (bFGF) [30], platelet-derived growth factor (PDGF) [31], transforming growth factor-β (TGF-β) [32], angiotensin II [33], and/or insulin like growth factor-1 (IGF) [34]. Growth factors and cytokines share a final proliferative signaling pathway, namely the cell cycle [35].…”