Cardiovascular and Cerebrovascular aging. Aging is associated with the development of atherosclerosis resulting from the deposition of cholesterol in the artery wall and the induction of oxidative events that sustain vascular inflammation. Apolipoprotein (apo) A-I, the major plasma apolipoprotein, is equipped to combat atherosclerosis by mediating the efflux of cholesterol from macrophage foam-cells. The process of cellular cholesterol efflux constitutes the rate-limiting step in the anti-atherogenic reverse cholesterol transport (RCT) pathway. It is not known whether stimulation of RCT is sufficient to attenuate the chronic induction of key mediators that sustain vascular inflammation and atherosclerosis during aging. This issue is important for devising new strategies for the treatment of cardiovascular disease. The development of new therapeutic strategies requires the identification of the helical segments of apoA-I that initiate RCT by mediating cellular cholesterol efflux. Cellular cholesterol efflux mediated by apoA-I is dependent on the ATP-binding cassette transporter A1 (ABCA1) which is down regulated via a degradation pathway. One goal of the proposed studies is to identify the helical structural elements of apoA-I that prevent ABCA1 degradation and mediate cholesterol efflux in an ABCA1-dependent manner. This will be achieved using synthetic peptides based on apoA-I amphipathic or alpha-helices. Recently, a cysteine-bearing variant of apoA-I, i.e. apoA-I(Milano), was found to be a potent inhibitor of lipid peroxidation; thus, the cysteine mutation endows the cholesterol efflux mediating apoA-I with antioxidant capability. The mechanistic basis for the antioxidant activity of apoA-I(Milano) will be elucidated in proposed studies. It is hypothesized that apoA-I(Milano) possesses chain-breaking antioxidant on phospholipid surfaces due to the presence of a free thiol located at the lipid-water interface of an amphipathic alpha-helix. Synthetic peptides that mediate cholesterol efflux and stabilize ABCA1 will be developed with and without apoA-I(Milano)-like antioxidant activity. In vivo studies will be conducted to test whether a peptide with antioxidant activity plus cholesterol efflux-mediating properties is more effective than a peptide that mediates cholesterol efflux alone in preventing the induction of key mediators that sustain vascular inflammation and atherosclemsis in aging mice. These studies are relevant for devising novel strategies to combat cardiovascular aging.
| Vedhachalam, Charulatha; Narayanaswami, Vasanthy; Neto, Nicole et al. (2007) The C-terminal lipid-binding domain of apolipoprotein E is a highly efficient mediator of ABCA1-dependent cholesterol efflux that promotes the assembly of high-density lipoproteins. Biochemistry 46:2583-93 |
