Molecular Mechanism of Milk Fat Globule Epidermal Growth Factor VIII (Mfge8) on Regulation of Contraction in Vascular Smooth Muscle

Vascular smooth muscle cells (VSMCs) are the main constitutive stromal cells of the vascular wall, whose major function is contraction and maintaining vascular tone and blood pressure. These contractile VSMCs express a large number of contractile proteins, which are present in controlled concentrations for contraction to occur precisely. There are two overlapping pathways which regulate VSMC contraction; 1) actin-­‐myosin cross bridge formation and 2) formation of subcortical filamentous actin that link the actin-­‐myosin cross bridges to the extracellular matrix (ECM) through integrins. Vascular hypercontractility, featured with increased response to contractile stimulants and enhanced VSMC contractility, contributes to the excessive vascular tone involved in the pathogenesis of various cardiovascular diseases, such as hypertension, atherosclerosis, coronary vasospasm, diabetes-­‐associated vasculopathy and arterial aging. However, the molecular pathways that regulate the vascular hypercontractility are incompletely understood. Inflammatory cytokines produced by macrophages, T-­‐cells, monocytes, endothelial and vascular smooth muscle cells are elevated in the vascular system during the pathological processes. Growing body of evidence has revealed that inflammatory cytokines induce vascular hypercontractility by upregulating RhoA/Rho-­‐kinase signaling, which in turn results in sustained actomyosin interaction, leading to the development of excessive vascular tone. Milk fat globule epidermal growth factor VIII (Mfge8), a secreted glycoprotein with multiple functional domains, has emerged as a novel mediator in the complicated networks of cardiovascular system. Our preliminary data demonstrated that Mfge8 enhanced the cytokine-­‐induced hypercontractility in common carotid arteries (CCAs). Our in vitro studies revealed that Mfge8 promoted the expression of SMC differentiation promotor, TGF-­‐β and serum response factor (SRF), as well as increased the level of contractile proteins. Additionally, our data also indicated that Mfge8 significantly increased the integrin-­‐mediated focal adhesion kinase (FAK) phosphorylation and the subsequent formation of subcortical actin filament. Therefore, in this application, we will test the global hypothesis that Mfge8 enhances cytokine-­‐induced vascular hypercontractility by increasing the expression of contractile proteins and subcortical actin cytoskeleton remodeling. The specific aims to support our hypothesis are: 1) To ascertain whether Mfge8 promotes cytokine-­‐induced VSMC contraction by initiating TGF-­‐β-­‐SRF signaling axis, leading to the elevated expression of contractile proteins. 2) To determine whether Mfge8 increases cytokine-­‐induced VSMC contractile force by promoting integrin-­‐dependent subcortical actin polymerization. 3) To determine the roles of the EGF and discoidin domains of Mfge8 in regulating VSMC contraction. These results will help us to understand the cellular and molecular mechanisms underlying the regulation of Mfge8 on vascular hypercontractility, and could lead to the development of a novel treatment strategy in the future.

Project ID:PC10507-0416
External Project ID:MOST105-2320-B182-022