Cholesterol oxidation products, named oxysterols, may derive from the diet or originate endogenously by autoxidative nonenzymatic modification of cholesterol as well as through enxymatic pathways involved in lipid metabolism and maintenance of cholesterol homeostasis. Oxysterols have been shown to exert several in vitro and in vivo biochemical activities of both physiologic and pathologic relevance and they appear to be implicated in the pathogenesis of various age-related chronic diseases, including atherosclerosis and Alzheimer's disease (AD), where hypercholesterolemia represents a primary risk factor, and a redox state impairment and inflammation seem to play a central role. Our recent studies show that, in cells of the macrophage lineage or in human neuronal cells (differentiated or not), respectively in the contest of atherosclerosis or AD, oxysterols can initiate specific signal transduction pathways that are relevant to the development of these diseases. Regarding atherosclerosis, we have observed that oxysterols can contribute to plaque instability and rupture by enhancing inflammatory responses and matrix turnover through an unbalanced up-regulation of MMP-9. Concerning AD, we have demonstrated that oxysterols may promote neuroinflammatory changes and accelerate APP processing toward β-amyloid production by up-regulating APP and BACE1 protein levels. In addition, TLR4, a key player of immune and inflammatory signaling responses, seems to have an important role in the pathogenesis of both atherosclerosis and AD.
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