Vascular apolipoprotein e expression and recruitment from circulation to modulate smooth muscle cell response to endothelial denudation

Apolipoprotein E (apoE) has been shown previously to have anti-proliferative and anti-migratory effects on smooth muscle cells in culture. In addition, overexpression of the apoE gene also reduces neointimal hyperplasia in mice after endothelial denudation. In this investigation, immunohistochemical techniques were used to demonstrate that apoE was present in the medial smooth muscle layers of the carotid artery between 1 and 28 days after endothelial cell denudation. Analysis of transgenic mice overexpressing human apoE in the liver revealed that apoE was recruited from the circulation to the injured site of the vessel wall. In situ hybridization using a mouse-specific apoE mRNA probe confirmed that apoE was also synthesized in the carotid artery after endothelial denudation. Interestingly, apoE accumulation in apoE transgenic mice followed a layer-specific pattern, and was inversely associated with smooth muscle alpha-actin expression. The vascular accumulation of apoE after endothelial denudation, and its association with alpha-actin-depleted smooth muscle cells, suggest that apoE inhibition of injury-induced neointimal hyperplasia is not due to the inhibition of injury-induced smooth muscle cell de-differentiation, but is likely a direct effect of apoE on smooth muscle cell migration and proliferation.