Signal transduction in atherosclerosis: integration of cytokines and the eicosanoid network

Abstract

Atherosclerosis can be defined in broad terms as a vascular disease accompanied by dysregulation of cholesterol metabolism and the accumulation of smooth muscle cells and macrophages within the vessel wall. At the interface of the blood and the vessel wall is the endothelium, which actively participates in a plethora of critical homeostatic functions in addition to affecting cholesterol trafficking in the underlying smooth muscle cell and macrophage. These events include: 1) inflammation resulting in release of cytokines, 2) changes in vascular reactivity causing release of endothelial cell derived relaxing factor (EDRF) and PGI2, and 3) control of vascular smooth cell proliferation via release of growth factors and growth suppressor molecules. Each process has been linked to the regulation of cholesterol accretion in the arterial cell. Furthermore, each homeostatic process is regulated by transmembrane signaling mechanisms at the lipid-protein interface of the membrane. Data have emerged recently indicating that biological response modifiers that trigger transmembrane signaling work in a sequential manner to control cell function. We review studies of the regulatory mechanisms of transmembrane signal transduction that advance the concept that phosphorylation of the specific protein components of the receptor machinery may result in a cooperative cellular response to ligands that will ultimately affect cholesterol delivery and trafficking within cells. We review recent data demonstrating that eicosanoids and cytokines released from one cell activate their receptors on neighboring cells, and interact with each other during this "cross-talk phenomenon." Cross-talking among phosphorylation reactions involving, for example, protein kinases A and C and tyrosine protein kinase, coupled with the highly regulated eicosanoid pathways and the diacylglycerol-phosphatidyl inositol (DG-PI) system, are discussed in terms of their metabolic impact on cholesterol delivery, intracellular processing, and efflux.