title: Pioglitazone, a PPARγ agonist, attenuates PDGF-induced vascular smooth muscle cell proliferation through AMPK-dependent and AMPK-independent inhibition of mTOR/p70S6K and ERK signaling.
abstract: Pioglitazone (PIO), a PPARγ agonist that improves glycemic control in type 2 diabetes through its insulin-sensitizing action, has been shown to exhibit beneficial effects in the vessel wall. For instance, it inhibits vascular smooth muscle cell (VSMC) proliferation, a major event in atherosclerosis and restenosis after angioplasty. Although PPARγ-dependent and PPARγ-independent mechanisms have been attributed to its vasoprotective effects, the signaling events associated with PIO action in VSMCs are not fully understood. To date, the likely intermediary role of AMP-activated protein kinase (AMPK) toward PIO inhibition of VSMC proliferation has not been examined. Using human aortic VSMCs, the present study demonstrates that PIO activates AMPK in a sustained manner thereby contributing in part to inhibition of key proliferative signaling events. In particular, PIO at 30μM concentration activates AMPK to induce raptor phosphorylation, which diminishes PDGF-induced mTOR activity as evidenced by decreased phosphorylation of p70S6K, 4E-BP1, and S6 and increased accumulation of p27(kip1), a cell cycle inhibitor. In addition, PIO inhibits the basal phosphorylation of ERK in VSMCs. Downregulation of endogenous AMPK by target-specific siRNA reveals an AMPK-independent effect for PIO inhibition of ERK, which contributes in part to diminutions in cyclin D1 expression and Rb phosphorylation and the suppression of VSMC proliferation. Furthermore, AMPK-dependent inhibition of mTOR/p70S6K and AMPK-independent inhibition of ERK signaling occur regardless of PPARγ expression/activation in VSMCs as evidenced by gene silencing and pharmacological inhibition of PPARγ. Strategies that utilize nanoparticle-mediated PIO delivery at the lesion site may limit restenosis after angioplasty without inducing PPARγ-mediated systemic adverse effects.
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.
authors.forename: Islam
authors.initials: I
authors.lastname: Osman
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@gru.edu.
authors.forename: Lakshman
authors.initials: L
authors.lastname: Segar
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000077214:Becaplermin; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D047495:PPAR gamma / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D000077205:Pioglitazone; D010982:Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D020574:Proto-Oncogene Proteins c-sis / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D045162:Thiazolidinediones / Q000494:pharmacology*
chemical_list: D007004:Hypoglycemic Agents; D047495:PPAR gamma; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D011994:Recombinant Proteins; D045162:Thiazolidinediones; D000077214:Becaplermin; C546842:MTOR protein, human; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D055372:AMP-Activated Protein Kinases; C000588423:ACACA protein, human; D000103:Acetyl-CoA Carboxylase; D000077205:Pioglitazone
keywords: AMPK; ERK; Pioglitazone; Vascular smooth muscle cells; p70S6K