Mechanisms of mechanical stretch-induced vascular smooth muscle remodeling :role of leptin -

Abstract

Background and aims: Hypertension and obesity are key risk factors for cardiovascular disease. Obesity is associated with increased leptin production that may contribute to cardiovascular pathology through a multiplicity of effects. Hypertension and leptin have been shown to contribute to vascular remodeling through various mechanisms, including production of vascular smooth muscle cell (VSMC) hypertrophy; however, the mechanisms underlying the vascular hypertrophic effect of leptin are not clearly known. The aim of this study was to take a closer look at these mechanisms and link them to reactive oxygen species (ROS) production.Methods: Rat portal vein (RPV) organ culture was used to investigate the effect of mechanical stretch (mimicking hypertension) or exogenous leptin (3.1 nM) on VSMCs. The wet weight and dry-wet changes were calculated as hypertrophic markers. Leptin and leptin receptor b (OBRb) mRNA expressions were quantified using qPCR analysis. Western blot analysis was done to detect proteins such as leptin, p-ERK 1-2, p-p38, p-AKT, and p-Cofilin. Electrophoretic Mobility Shift Assay (EMSA) was performed to detect of serum response factor (GATA-4)-DNA complex levels. Moreover, we used laser confocal microscopy on frozen RPV sections to detect leptin, F-actin, G-actin, and ROS levels. We investigated the contributions of ROS formation, RhoA, MAP kinase, PI3K pathways on RPV remodeling. The actin depolymerization agent cytochalasin D was also used to investigate the involvement of intact actin cytoskeleton on mechanical stretch or leptin-induced VSMC remodeling.Results: Both mechanical stretch and leptin induce RPV hypertrophy, as elicited by changes in wet weight and dry-wet. Mechanisms that lead to VSMC remodeling were the RhoA pathway, actin cytoskeleton dynamics, PI3K-AKT pathway, MAP kinase pathway and ROS production. All were studied and activated by either mechanical stretch or leptin. Mechanical stretch increases the expression of leptin and OBRb mRNA, while preincubation of the RPV with the ROC