Targeting Smooth Muscle Cell BMAL1 as a New Therapeutic Strategy Against Restenosis

Project Summary/Abstract Coronary heart disease (CHD) is the single leading cause of death in the United States. Coronary revascularization, including coronary artery bypass graft and percutaneous coronary intervention, is the most common modality in patients with CHD. However, it is often associated with a high incidence of restenosis. Although the rate of restenosis is reduced significantly by using bare-metal stent (BMS) and particularly with drug-eluting stent (DES), a persistently high rate of restenosis after BMS and an increased risk of in-stent thrombosis with DES has been encountered as a major significant gap in the field. The current application proposes to bridge this gap and specifically investigates the role of the smooth muscle cell (SMC) BMAL1 in neointimal hyperplasia in mouse models of arterial injury. BMAL1 is a core molecular component of the circadian clock. It has long been believed that loss of function of BMAL1 is detrimental to well-being. However, this dogma was challenged by our recent report that genetic deletion of Bmal1 in SMCs (SM-Bmal1-KO) protects mice from aldosterone or angiotensin II-induced abdominal aortic aneurysm. Consistent with this finding, our preliminary demonstrate that SMC-specific Bmal1 deletion also protects mice femoral artery wire injury- or carotid artery ligation-induced neointimal hyperplasia. While the underlying mechanism remains elusive, our preliminary data reveal arachidonic acid metabolism is most significantly affected by SMC-specific Bmal1 deletion. Interestingly, among enzymes implicated in arachidonic acid metabolism, cytosolic phospholipase A2 alpha (cPLA2α) is most downregulated by SMC-specific Bmal1 deletion. Mechanistically, our preliminary data illustrate that BMAL1 binds to the mouse cPLA2α promoter, and SMC BMAL1 is required for vascular injury-induced cPLA2α upregulation in neointima. Given the potential role of cPLA2α in VSMC proliferation and neointimal hyperplasia, we hypothesize that upregulation of BMAL1 in SMCs by vascular injury promotes cPLA2α expression, thus mediating the initiation and progression of neointimal hyperplasia and significantly contributing to the development of restenosis after coronary revascularization. Aim 1 will test the hypothesis that upregulation of SMC BMAL1 by vascular injury is critical for the onset and progression of neointimal hyperplasia. Aim 2 will define the mechanism by which SMC BMAL1 regulates cPLA2α and thereby mediates vascular injury-induced neointimal hyperplasia. To achieve the goals, SM-Bmal1-KO, SM-cPLA2α- KO, and SM-Bmal1/cPLA2α-KO mice will be subjected to femoral artery wire injury or carotid artery ligation to induce neointimal hyperplasia and to determine the mechanism by which SMC BMAL1 and cPLA2α mediate vascular injury-induced neointimal hyperplasia. Results from the proposed studies will provide new mechanistic insight on how SMC BMAL1 mediates vascular injury-induced neointimal hyperplasia via cPLA2α. Moreover, results from the proposed studies will provide preclinical evidence that inhibiting the BMAL1/cPLA2α signaling at the lesion site is a new therapeutic strategy against restenosis after coronary revascularization.