title: Sulforaphane inhibits platelet-derived growth factor-induced vascular smooth muscle cell proliferation by targeting mTOR/p70S6kinase signaling independent of Nrf2 activation.
abstract: Activation of nuclear factor erythroid 2-related factor 2 (Nrf2, a transcription factor) and/or inhibition of mammalian target of rapamycin (mTOR) are implicated in the suppression of vascular smooth muscle cell (VSMC) proliferation. The present study has examined the likely regulatory effects of sulforaphane (SFN, an antioxidant) on Nrf2 activation and platelet-derived growth factor (PDGF)-induced mTOR signaling in VSMCs. Using human aortic VSMCs, nuclear extraction and siRNA-mediated downregulation studies were performed to determine the role of Nrf2 on SFN regulation of PDGF-induced proliferative signaling. Immunoprecipitation and/or immunoblot studies were carried out to determine how SFN regulates PDGF-induced mTOR/p70S6K/S6 versus ERK and Akt signaling. Immunohistochemical analysis was performed to determine SFN regulation of S6 phosphorylation in the injured mouse femoral artery. SFN (5μM) inhibits PDGF-induced activation of mTOR without affecting mTOR association with raptor in VSMCs. While SFN inhibits PDGF-induced phosphorylation of p70S6K and 4E-BP1 (downstream targets of mTOR), it does not affect ERK or Akt phosphorylation. In addition, SFN diminishes exaggerated phosphorylation of S6 ribosomal protein (a downstream target of p70S6K) in VSMCs in vitro and in the neointimal layer of injured artery in vivo. Although SFN promotes Nrf2 accumulation to upregulate cytoprotective genes (e.g., heme oxygenase-1 and thioredoxin-1), downregulation of endogenous Nrf2 by target-specific siRNA reveals an Nrf2-independent effect for SFN-mediated inhibition of mTOR/p70S6K/S6 signaling and suppression of VSMC proliferation. Strategies that utilize local delivery of SFN at the lesion site may limit restenosis after angioplasty by targeting mTOR/p70S6K/S6 axis in VSMCs independent of Nrf2 activation.
authors.affiliation: Center for Pharmacy and Experimental Therapeutics, University of Georgia College of Pharmacy, Augusta, GA, USA; Charlie Norwood VA Medical Center, Augusta, GA, USA; Department of Pharmacology and Toxicology, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt.
authors.forename: Noha M
authors.initials: NM
authors.lastname: Shawky
authors.affiliation: Center for Pharmacy and Experimental Therapeutics, University of Georgia College of Pharmacy, Augusta, GA, USA; Charlie Norwood VA Medical Center, Augusta, GA, USA; Vascular Biology Center, Department of Pharmacology and Toxicology, Georgia Regents University, Augusta, GA, USA; Department of Medicine, Pennsylvania State University College of Medicine, Hershey, PA, USA. Electronic address: lsegar@augusta.edu.
authors.forename: Lakshman
authors.initials: L
authors.lastname: Segar
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000378:metabolism; D006801:Humans; D017879:Isothiocyanates / Q000494:pharmacology*; D008297:Male; D008810:Mice, Inbred C57BL; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013454:Sulfoxides; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D017879:Isothiocyanates; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D010982:Platelet-Derived Growth Factor; D013454:Sulfoxides; D019938:Cyclin D1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C016766:sulforaphane
keywords: Dimethyl Sulfoxide (PubChem CID: 679); Nrf2; PDGF; Sulforaphane; Sulforaphane (PubChem CID: 5350); Vascular smooth muscle cells; mTOR