Myeloid HMG-CoA (3-Hydroxy-3-Methylglutaryl-Coenzyme A) Reductase Determines Atherosclerosis by Modulating Migration of Macrophages

Objective— Inhibition of HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase) is atheroprotective primarily by decreasing plasma LDL (low-density lipoprotein)-cholesterol. However, it is unknown whether inhibition of HMGCR in myeloid cells contributes to this atheroprotection. We sought to determine the role of myeloid HMGCR in the development of atherosclerosis. Approach and Results— We generated mice with genetically reduced Hmgcr in myeloid cells ( Hmgcr m− /m − ) using LysM (Cre) and compared various functions of their macrophages to those of Hmgcr fl/fl control mice. We further compared the extent of atherosclerosis in Hmgcr m −/ m − and Hmgcr fl/fl mice in the absence of Ldlr (LDL receptor). Hmgcr m −/ m − macrophages and granulocytes had significantly lower Hmgcr mRNA expression and cholesterol biosynthesis than Hmgcr fl/fl cells. In vitro, Hmgcr m −/ m − monocytes/macrophages had reduced ability to migrate, proliferate, and survive compared with Hmgcr fl/fl monocytes/macrophages. However, there was no difference in ability to adhere, phagocytose, store lipids, or polarize to M1 macrophages between the 2 types of macrophages. The amounts of plasma membrane–associated small GTPase proteins, such as RhoA (RAS homolog family member A), were increased in Hmgcr m −/ m − macrophages. In the setting of Ldlr deficiency, Hmgcr m −/ m − mice developed significantly smaller atherosclerotic lesions than Hmgcr fl/fl mice. However, there were no differences between the 2 types of mice either in plasma lipoprotein profiles or in the numbers of proliferating or apoptotic cells in the lesions in vivo. The in vivo migration of Hmgcr m −/ m − macrophages to the lesions was reduced compared with Hmgcr fl/fl macrophages. Conclusions— Genetic reduction of HMGCR in myeloid cells may exert atheroprotective effects primarily by decreasing the migratory activity of monocytes/macrophages to the lesions.