Abstract 1038: Map Kinase Phosphatase-5 Deficiency Impairs Macrophage Efferocytosis And Exacerbates Late-stage Atherosclerosis

Objective: Atherosclerosis is a vascular inflammatory disease that is a major cause of death in Westernized society. Late-stage atherosclerosis is characterized by a vulnerable plaque, which consists of a thin fibrous cap and a large necrotic core that is prone to rupture. Efferocytosis is a repair mechanism that clears apoptotic cells within the plaque, contributing to plaque stability. In late-stage atherosclerotic conditions efferocytosis is impaired and promotes rupture. MAPK phosphatase-5 (MKP5) regulates various processes such as immune diseases and cardiac fibrosis. The goal of this project is to identify the role of MKP5 in late-stage atherosclerotic plaque stability. Approach/Results: To induce late-stage atherosclerosis, male and female LDLR -/- and LDLR -/- MKP5 -/- mice were subjected to transverse aortic constriction (TAC) surgery and fed on a highfat diet (western diet with 1.25% cholesterol) for 12 weeks. Our data show that MKP5 deficiency exacerbates plaque instability, through decreased cap thickness, decreased collagen content, increased lesion size and necrosis in the plaque, and severe coronary lesions. Furthermore, there are higher instances of intraplaque hemorrhage in the right carotids of the LDLR -/- MKP5 -/- mice. Mechanistically, TUNEL staining of the aortic roots was performed to determine efferocytotic capabilities in vivo. Results showed fewer macrophage-associated TUNEL-positive cells in LDLR -/- MKP5 -/- aortic roots. To further investigate this mechanism, bone-marrow-derived macrophages (BMDMs) isolated from WT and MKP5 -/- mice were incubated with apoptotic Jurkat cells and then analyzed to determine the engulfment of apoptotic cells by the macrophages via confocal microscopy and flow cytometry. Results showed that efferocytosis was significantly inhibited in MKP5 -/- BMDMs. Bulk-RNA sequencing analysis revealed that the expression of efferocytotic genes in MKP5 -/- BMDMs was decreased at basal and oxLDL stimulated conditions. Conclusion: Results suggest that MKP5 deficiency impairs efferocytosis, exacerbates atherosclerosis, and causes late-stage plaque to move toward unstable phenotypes.