The natural history of platelet-rich mural thrombi in systemic arteries of hypercholesterolaemic monkeys: light- and electron-microscope observations

P66Shc mediates increased platelet activation and aggregation in hypercholesterolemia

BACKGROUND AND HYPOTHESIS

Hypercholesterolemia leads to a prothrombotic phenotype. Platelet hyperactivity associated with hypercholesterolemia has been attributed, in part, to oxidative stress. P66Shc is a well-known determinant of cellular and organismal oxidative stress. However, its role in platelet biology is not known. We hypothesized that p66Shc mediates platelet hyperactivation and hyperaggregation in hypercholesterolemia.

METHODS AND RESULTS

P66Shc was expressed in both human and mouse platelets, as determined by qRT-PCR and immunoblotting. Mouse platelet p66Shc expression was upregulated by hypercholesterolemia induced by high-fat diet feeding. Compared to wild-type mice, high-fat diet-induced p66Shc expression in platelets was suppressed in transgenic mice expressing a short hairpin RNA targeting p66Shc (p66ShcRNAi). High-fat diet feeding of wild-type mice amplified surface P-selectin expression on platelets stimulated by the thrombin receptor agonist protease-activated receptor-4 (PAR4), and increased aggregation of platelets induced by thrombin. These exaggerated platelet responses induced by high-fat diet feeding were significantly blunted in p66ShcRNAi mice. Finally, thrombin-stimulated platelet reactive oxygen species were suppressed in p66ShcRNAi mice.

CONCLUSIONS

Hypercholesterolemia stimulates p66Shc expression in platelets, promoting platelet oxidative stress, hyperreactivity and hyperaggregation via p66Shc.

Role of the vascular endothelial cell antigen system in the etiology of atherosclerosis

An autoantibody directed against an antigen system that is expressed on the vascular endothelial cell (VEC) was recently identified in random patients with peripheral vascular disease. This VEC antigen system is also present on the peripheral blood monocyte but not on any other cell type studied to date. In a randomized study of 112 patients with peripheral vascular disease at the Albany Medical College, 46% demonstrated an autoantibody against their autologous monocytes and VEC. This autoantibody is a highly cytotoxic, complement-fixing antibody directed against VEC antigens. It does not crossreact with autologous T or B lymphocytes and appears to be highly polymorphic. It is present in only nine per cent of the age-matched controls and was never detected in young controls. This preliminary investigation suggests that immunological injury may be the initiating factor in the development of atherosclerotic lesions more frequently than currently appreciated. Whether this autoantibody to VEC is the result of or the cause of endothelial cell damage in these patients is still under study.

Diet-induced aortic atherosclerosis in Malaysian long-tailed monkeys (Macaca irus)

Moderate hypercholesterolaemia has been produced in eight adult male M. irus monkeys by feeding an egg-toast preparation containing butter and 0.14 per cent. total cholesterol. At autopsy, after two to four years of persistent hypercholesterolaemia, there was massive fatty streaking of the aorta involving 21 to 78 per cent. of the intimal surface. The distribution and morphology of the fatty streaks was similar to that in man. In addition, there were fibrous plaques including "soft" lipid-rich atherosclerotic plaques identical to their human counterpart. There was no grossly detectable thromobosis, haemorrhage or ulceration. Atherosclerotic lesions were also present in the coronary, carotid, subclavian, iliac and femoral arteries. In a control group of monkeys fed a low-fat, cholesterol-free diet, arterial lesions were identical in type and extent to those in freshly captured wild monkeys.