Atherosclerotic plaque rupture is a leading cause of acute coronary syndromes, such as unstable angina and myocardial infarction ( 1 ). Infl ammatory cells are regarded as key players in the pathogenesis of plaque rupture ( 2, 3 ), and the mast cell, a potent infl ammatory cell, has been shown to accumulate in the rupture-prone shoulder region of human atheromas ( 4 ). Activated mast cells have been identifi ed in the adventitia of vulnerable and ruptured lesions in patients with myocardial infarction, and more importantly, their numbers and degree of activation were found to correlate with the incidence of plaque rupture and erosion ( 5 ). We previously demonstrated that systemic mast cell activation during atherogenesis leads to increased plaque progression in apoE defi cient mice ( 6 ), while others show that the absence of mast cells, and in particular mast cell-derived interleukin (IL)-6 and interferon (IFN)-␥ , attenuated atherosclerotic lesion development in low-density lipoprotein receptor-deficient (LDLr Ϫ / Ϫ ) mice ( 7 ). Moreover, focal activation of mast cells in the adventitia of advanced carotid artery plaques promoted macrophage apoptosis, microvascular leakage, de novo leukocyte infl ux, and the incidence of intraplaque hemorrhage. Mast cell stabilization by cromolyn was seen to prevent these pathophysiological events ( 6 ).Various pathways of mast cell activation have been demonstrated such as cross-linking of the high-affi nity Abstract Lysophosphatidic acid (LPA), a bioactive lysophospholipid, accumulates in the atherosclerotic plaque. It has the capacity to activate mast cells, which potentially exacerbates plaque progression. In this study, we thus aimed to investigate whether LPA contributes to plaque destabilization by modulating mast cell function. We here show by an imaging mass spectrometry approach that several LPA species are present in atherosclerotic plaques. Subsequently, we demonstrate that LPA is a potent mast cell activator which, unlike other triggers, favors release of tryptase. Local perivascular administration of LPA to an atherosclerotic carotid artery segment increases the activation status of perivascular mast cells and promotes intraplaque hemorrhage and macrophage recruitment without impacting plaque cell apoptosis. The mast cell stabilizer cromolyn could prevent intraplaque hemorrhage elicited by LPAmediated mast cell activation. Finally, the involvement of mast cells in these events was further emphasized by the lack of effect of perivascular LPA administration in mast cell defi cient animals. We demonstrate that increased accumulation of LPA in plaques induces perivascular mast cell activation and in this way contributes to plaque destabilization in vivo. This study points to local LPA availability as an important factor in atherosclerotic plaque stability. Press, February 10, 2013 DOI 10.1194 Lysophosphatidic acid triggers mast cell-driven atherosclerotic plaque destabilization by increasing vascular infl ammation Abbreviations: apoE Ϫ / Ϫ , apolipoprotein E-defi...
