What Causes Atherosclerotic Plaques to Rupture?
The reasons for thinning and rupture of the fibrous cap are not known. Two main hypotheses have been proposed. The first is that rupture is a result of loss of smooth muscle cells, thought to be the main producers of cap-stabilizing collagen. This is caused by the loss of cells from apoptosis. Bennett and others 16,17 have suggested that such apoptosis may be mediated by the interaction between smooth muscle cells and monocyte/macrophages. Apoptosis of smooth muscle cells has also been shown to be promoted by chymase produced by mast cells, which are present in the plaque in significant numbers. 18–21 It may even be the case that smooth muscle cells in the atherosclerotic plaque undergo apoptosis by default unless their viability is maintained, for example, by the presence of insulin-like growth factor 1 in the interstitial milieu. 22 In addition to undergoing apoptosis, smooth muscle cells within the plaque are very slow to divide 23–25 and stop proliferating altogether after 2 to 5 p
