Objective—Activated mast cells (MCs) induce endothelial cell (EC) apoptosis in vitro and are present at sites of plaque erosions in vivo. To further elucidate the role of MCs in endothelial apoptosis and consequently in plaque erosion, we have studied the molecular mechanisms involved in MC-induced EC apoptosis.

Methods and Results—Primary cultures of rat cardiac microvascular ECs (RCMECs) and human coronary artery ECs (HCAECs) were treated either with rat MC releasate (ie, mediators released on MC activation), rat chymase and TNF (TNF-), or with human chymase and TNF-, respectively. MC releasate induced RCMEC apoptosis by inactivating the focal adhesion kinase (FAK) and Akt-dependent survival signaling pathway, and apoptosis was partially inhibited by chymase and TNF- inhibitors. Chymase avidly degraded both vitronectin (VN) and fibronectin (FN) produced by the cultured RCMECs. In addition, MC releasate inhibited the activation of NF-B (p65) and activated caspase-8 and -9. Moreover, in HCAECs, human chymase and TNF- induced additive levels of apoptosis.

Conclusions—Activated MCs induce EC apoptosis by multiple mechanisms: chymase inactivates the FAK-mediated cell survival signaling, and TNF- triggers apoptosis. Thus, by inducing EC apoptosis, MCs may contribute to plaque erosion and complications of atherosclerosis.