title: Actin cytoskeleton dynamics promotes leptin-induced vascular smooth muscle hypertrophy via RhoA/ROCK- and phosphatidylinositol 3-kinase/protein kinase B-dependent pathways.
abstract: Obesity is associated with increased leptin production that may contribute to cardiovascular pathology through a multiplicity of effects. Leptin has been shown to contribute to vascular remodeling through various mechanisms, including production of vascular smooth muscle (VSMC) hypertrophy; however, the mechanisms underlying the vascular hypertrophic effect of leptin remain unknown. In the present study, we investigated the contributions of the RhoA/Rho kinase (ROCK) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathways, actin dynamics, and the expression of serum-response factor (SRF) in the hypertrophic effects of leptin on vascular tissue. Strips of rat portal vein (RPV) were cultured with or without leptin at 3.1 nM for 1 to 3 days. Leptin significantly increased RhoA activity by 163 +/- 20%, whereas phosphorylation of downstream factors, including LIM kinase 1 and cofilin-2, was increased by 160 +/- 25 and 290 +/- 25%, respectively. Leptin also significantly phosphorylated Akt by 130 +/- 30%, which was inhibited by the PI3K inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). RhoA/ROCK and PI3K/Akt activation was associated with a significant increase in RPV wet weight (11 +/- 1%), protein synthesis (45 +/- 7%), SRF expression (136 +/- 11%), and polymerization of actin, as reflected by an increase in the F-/G-actin ratio, effects that were significantly attenuated by a leptin receptor (leptin obese receptor) antibody, the ROCK inhibitor (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) (Y-27632) as well as the PI3K inhibitor LY294002. Our results indicate that the activation of RhoA/ROCK and PI3K/Akt plays a pivotal role in leptin signaling, leading to the development of VSMC hypertrophy through a mechanism involving altered actin dynamics.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada.
authors.forename: Asad
authors.initials: A
authors.lastname: Zeidan
authors.forename: Ben
authors.initials: B
authors.lastname: Paylor
authors.forename: Karly J
authors.initials: KJ
authors.lastname: Steinhoff
authors.forename: Sabzali
authors.initials: S
authors.lastname: Javadov
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Rajapurohitam
authors.forename: Subrata
authors.initials: S
authors.lastname: Chakrabarti
authors.forename: Morris
authors.initials: M
authors.lastname: Karmazyn
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D003599:Cytoskeleton / Q000378:metabolism; D006984:Hypertrophy / Q000209:etiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D020738:Leptin / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000473:pathology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000199:Actins; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein