title: TGF-β/Smad3 inhibit vascular smooth muscle cell apoptosis through an autocrine signaling mechanism involving VEGF-A.
abstract: We have previously shown that in the presence of elevated Smad3, transforming growth factor-β (TGF-β) transforms from an inhibitor to a stimulant of vascular smooth muscle cell (SMC) proliferation and intimal hyperplasia (IH). Here we identify a novel mechanism through which TGF-β/Smad3 also exacerbates IH by inhibiting SMC apoptosis. We found that TGF-β treatment led to inhibition of apoptosis in rat SMCs following viral expression of Smad3. Conditioned media from these cells when applied to naive SMCs recapitulated this effect, suggesting an autocrine pathway through a secreted factor. Gene array of TGF-β/Smad3-treated cells revealed enhanced expression of vascular endothelial growth factor (VEGF), a known inhibitor of endothelial cell apoptosis. We then evaluated whether VEGF is the secreted mediator responsible for TGF-β/Smad3 inhibition of SMC apoptosis. In TGF-β/Smad3-treated cells, VEGF mRNA and protein as well as VEGF secretion were increased. Moreover, recombinant VEGF-A inhibited SMC apoptosis and a VEGF-A-neutralizing antibody reversed the inhibitory effect of conditioned media on SMC apoptosis. Stimulation of SMCs with TGF-β led to the formation of a complex of Smad3 and hypoxia-inducible factor-1α (HIF-1α) that in turn activated the VEGF-A promoter and transcription. In rat carotid arteries following arterial injury, Smad3 and VEGF-A expression were upregulated. Moreover, Smad3 gene transfer further enhanced VEGF expression as well as inhibited SMC apoptosis. Finally, blocking either the VEGF receptor or Smad3 signaling in injured carotid arteries abrogated the inhibitory effect of Smad3 on vascular SMC apoptosis. Taken together, our study reveals that following angioplasty, elevation of both TGF-β and Smad3 leads to SMC secretion of VEGF-A that functions as an autocrine inhibitor of SMC apoptosis. This novel pathway provides further insights into the role of TGF-β in the development of IH.
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: X
authors.initials: X
authors.lastname: Shi
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: L-W
authors.initials: LW
authors.lastname: Guo
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Seedial
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Si
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: B
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: T
authors.initials: T
authors.lastname: Takayama
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Suwanabol
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: D
authors.initials: D
authors.lastname: DiRenzo
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: B
authors.initials: B
authors.lastname: Liu
authors.affiliation: Department of Surgery, University of Wisconsin, 1111 Highland Avenue, WIMR Building, Madison, WI 53705, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Kent
mesh_terms: D000818:Animals; D017209:Apoptosis; D019898:Autocrine Communication; D002478:Cells, Cultured; D006801:Humans; D006965:Hyperplasia / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D032389:Myocytes, Smooth Muscle / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D017539:Tunica Intima / Q000166:cytology / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*
chemical_list: D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D042461:Vascular Endothelial Growth Factor A