| Summary: | Vascular endothelial cell loss initiates directional migration of medial smooth muscle cells into the arterial intima contributing to in-stent restenosis, atherosclerosis and coronary arterial by-pass graft failure. N-cadherin is a cell-cell adhesion molecule that mediates the interaction between vascular endothelial cells and the innermost smooth muscle cells to stabilize the arterial wall. Upon injury, I reasoned that relocalization of N-cadherin on the inner most smooth muscle cells to the posterior-lateral borders stimulates cell polarization to enable directional migration. Using an in vitro scratch-wound model to stimulate cell polarity and locally remove cell-cell contacts at one pole of smooth muscle cells, I found that N-cadherin localization provides signaling cues via a Cdc42/GSK pathway that promote polarized reorganization of the cytoskeleton and directional cell migration. I also found that N-cadherin was important to functions of lamellipodia at the anterior of migrating cells. In lamellipodia, actin polymerization drives protrusion of the leading edge and coincident, but more posterior, actin depolymerization results in retrograde flow of actin and associated plasma membrane structures. Using live cell imaging, I found that clusters of N-cadherin-GFP repeatedly accumulated at the leading edge specifically at the neck of large pinocytotic vesicles called macropinosomes that were internalized and transported away from the leading edge. This localization is consistent with a role for N-cadherin in closure and scission of vesicles during macropinocytosis.
These are the first studies to examine polarity in migrating vascular smooth muscle cells, and advance our understanding concerning cell-cell adhesions in controlling directional cell migration. My results suggest that N-cadherin may serve as a viable target for the treatment of arterial stenosis that would limit smooth muscle cell migration and stabilize the arterial wall. Furthermore, I report on a novel localization and function of N-cadherin in the biogenesis of macropinosomes in the lamellipodia that contribute to cell protrusion.
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