title: Effects of PPAR-gamma knock-down and hyperglycemia on insulin signaling in vascular smooth muscle cells from hypertensive rats.
abstract: Peroxisome proliferator-activated receptor (PPAR)-gamma, a target in the treatment of diabetes, improves insulin sensitivity and exerts cardiovascular protective effects by mechanisms that are not completely elucidated. To investigate underlying molecular mechanisms responsible for PPAR-gamma-associated vascular insulin signaling in hypertension, we tested whether PPAR-gamma downregulation in vascular smooth muscle cells (VSMC) from WKY and SHRSP rats would decrease insulin signaling and glucose uptake and whether this response would be worsened by hyperglycemia to a greater extent in VSMC of hypertensive origin. Passaged mesenteric artery VSMC grown in euglycemic (5.5 mmol/L) or hyperglycemic media (25.0 mmol/L) were treated with PPAR-gamma-siRNA (5 nmol/L), PPAR-gamma antagonist (GW-9662, 10 micromol/L), or PPAR-gamma activator (rosiglitazone, 10 micromol/L) in the presence or absence of insulin (100 nmol/L). Immunoblotting revealed that hyperglycemia and PPAR-gamma inhibition significantly (P < 0.001) decreased insulin-stimulated insulin receptor (IR)-beta, Akt, and glycogen synthase kinase (GSK)-3beta phosphorylation, whereas phosphotyrosine phosphatase (PTP)-1B expression was increased in VSMC from both strains. These effects were more pronounced in SHRSP under hyperglycemia. Rosiglitazone tended to increase insulin-mediated IR-beta, Akt, and GSK-3beta phosphorylation in VSMC from both strains, whereas insulin-induced PTP-1B expression was reduced by hyperglycemia. Insulin-stimulated GLUT-4 expression and glucose transport were attenuated by hyperglycemia in both VSMC. These data suggest that PPAR-gamma inhibition results in decreased insulin signaling, particularly in SHR, in an IR-beta phosphorylation-dependent manner.
authors.affiliation: Hypertension and Vascular Research Unit, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec, Canada.
authors.forename: Nihar R
authors.initials: NR
authors.lastname: Pandey
authors.forename: Karim
authors.initials: K
authors.lastname: Benkirane
authors.forename: Farhad
authors.initials: F
authors.lastname: Amiri
authors.forename: Ernesto L
authors.initials: EL
authors.lastname: Schiffrin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D015536:Down-Regulation; D024202:Electrophoretic Mobility Shift Assay; D005434:Flow Cytometry; D020868:Gene Silencing; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D047495:PPAR gamma / Q000037:antagonists & inhibitors* / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D014162:Transfection
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D047495:PPAR gamma; D034741:RNA, Small Interfering; C495694:Slc2a4 protein, rat; D005947:Glucose