Cholesterol loading rescues OxLDL‐induced activation of endothelial Rho/ROCK/Akt/p27kip1 cascade

Abstract

Oxidized modifications of LDL (oxLDL) are known to activate multiple signaling pathways that lead to impairment and disbalance of endothelial function impairment of the barrier function and including abnormal proliferation. It is generally believed that oxLDL exerts its effects on endothelial function via enhanced loading of cholesterol. Our studies, however, show that this is not the case. In contrast, we show that oxLDL and cholesterol loading have opposite effects on several key signaling events in human aortic endothelial cells (HAECs). Moreover, we show that cholesterol loading may rescue oxLDL‐induced effects on EC signaling. We also we provide comparative analysis of the effects of two major types of oxLDL, copper oxidized LDL (Cu‐oxLDL) and Lipoxygenase oxidized LDL (LPO‐oxLDL). Specifically, we show that both, Cu‐oxLDL or LPO‐oxLDL significantly increase Akt phosphorylation whereas inhibiting Akt with a specific inhibitor MK2206 blocks oxLDL‐induced increase in the proliferation of HAECs. Furthermore, blocking Rho with C3 or its downstream target ROCK with Y27632 significantly inhibits oxLDL‐induced Akt phosphorylation and cell proliferation induced by both Cu‐ and LPO‐oxLDL. In contrast, blocking Rac1 with MSC inhibitor has no effect neither on oxLDL‐induced Akt phosphorylation or cell proliferation of HAECs. Further evidence shows that oxLDL‐induced Rho/Akt pathway leads to downregulation of p27kip1, a well‐known negative regulator of cell proliferation. Most importantly, we also show that preloading cells with cholesterol prevents oxLDL‐induced activation of RhoA and oxLDL‐induced Akt phosphorylation. Furthermore, cholesterol pre‐loading also rescues oxLDL‐induced loss of p27kip1 expression. We propose that oxLDL impairs endothelial function by increasing the cellular content of oxysterols which disrupt the structure of endothelial membrane, an effect that can be repaired by an increase in cellular cholesterol.Support or Funding InformationNIH grants HL‐073965 and HL‐083298 to I.L.