Cardiovascular disease (CVD) is the leading cause of death in the U.S., with the annual total cost of care estimated at $351 billion. Vascular calcification is a nontraditional CVD risk factor associated with a significant increase in morbidity and mortality in the general population. Unlike other established risk factors, it is not yet regarded as a modifiable factor. However, there is emerging evidence that it may drive the pathogenesis of atherosclerosis and play an important role in the regression of atherosclerotic plaques. Our data demonstrated that overexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelial cells accelerated coronary atherosclerosis in hyperlipidemic mice, while the TNAP inhibitor SBI-425 reduced manifestations of coronary artery disease in this model. Subendothelial microcalcification was frequently observed in the internal elastic lamina in mice and in human arteries and was predicted by computational fluid structure interaction (FSI) modeling to redistribute wall shear stress on the endothelium. The idea that calcification can promote atherosclerosis was further supported by an observation of increased low density lipoprotein (LDL) uptake by endothelial cells cultured on surfaces textured with hydroxyapatite particles. More evidence from mouse models showed that TNAP activity in macrophages was sufficient to increase calcification during progression of atherosclerosis and interfere with plaque regression, leading to maladaptive dilation of the aortic root. We hypothesize that calcification is a modifiable factor in atherosclerosis and that inhibiting TNAP-mediated vascular calcification may have therapeutic value. The overarching goal of this project is to gain a better understanding of the role of calcification during atherosclerotic lesion initiation, progression, and resolution, and to determine whether calcification is an active pathogenic factor in atherosclerosis or a mere, likely benign, secondary response. The project will use computational and in vivo models to delineate hemodynamic mechanism by which subendothelial microcalcifications increases retention of LDL in the arterial wall. The effects of the conditional genetic ablation of TNAP in macrophages or an increase of TNAP activity in plasma will then be tested in a mouse model of familial hypercholesterolemia. Because regression of calcified plaques can lead to eccentric aortic root remodeling during lipid lowering, we will interrogate whether inhibition of TNAP with SBI-425 could suppress calcification and alleviate maladaptive remodeling of the aortic root in a mouse model during reversal of atherosclerosis. In testing TNAP inhibition for its therapeutic utility for atherosclerotic calcification, we will keep close attention on potential bone side effects by monitoring bone microarchitecture using micro-computed tomography. The results of this project will establish whether calcification is a modifiable risk factor in CVD and determine whether systemic TNAP inhibition or elimination of osteogenic TNAP-expressing macrophages is a viable therapeutic approach in atherosclerosis. The results of this study will help guide future development of novel therapeutics for this prevalent disease.
Heart disease causes one in four deaths in the United States. Since vascular calcification is a strong predictor of future heart disease and/or death from heart disease, this project will determine whether calcification is not only a risk factor for atherosclerosis, but also involved in the pathogenesis and propagation of this disease. The proposed study will benefit public health by providing potential new therapeutic avenues that complement lipid-lowering approaches to improve outcomes for millions of Americans.