Abstract 22: Absence of Circadian Gene Bmal in Macrophage Enhances Atherosclerosis

Abstract

Backgrounds: Peripheral cell-intrinsic clock is present in all types of cells and is important for synchronization of physiological function in response to changes of environment. Bmal (encoded by Arntl gene) is a transcription factor that forms complex with Clock and induces rhythmic transcription. Peripheral clock has been demonstrated in monocyte to regulate inflammatory responses. In this regards, we hypothesize that disruption of circadian rhythm in myeloid cells enhances atherosclerosis in Apoe -/- mice. Methods and Results: Apoe -/- mice housed under weekly switch between regular (ZT12-ZT0: dark) and inverted (ZT12-ZT0: light) ligh/dark cycle developed more atherosclerotic lesion than Apoe-/- mice housed under regular L/D cycle. Myeloid cell-specific Bmal knockout mice ( Arntl LoxP/LoxP Lyz2 Cre ) as Bmal MKO and Bmal wild type ( Arntl LoxP/ LoxP ) as Bmal MWT were crossbred with Apoe-/- to generate Apoe-Bmal MKO and Apoe-Bmal MWT mice. Mice with disruption of myeloid circadian rhythm (Apoe-Bmal MKO ) on Western diet showed enhanced atherosclerotic plaque formation by en face oil red o staining, compared with their WT control. Flow cytometry showed more infiltrating macrophages within the plaque of Apoe-Bmal MKO mice, accompanied with upregulation of proinflammatory genes Tnf, Il1b, Nos2, S100a8; chemokines and adhesion molecules Vcam1, Icam1, Sele, Ccl2, Ccl8; and downregulation of anti-inflammatory genes. Aortic root staining showed more macrophages by CD68 staining, more CD11c + pro-inflammatory macrophages, and more Ly6c + infiltrating monocyte-derived macrophages in Apoe-Bmal MKO mice. In vitro culture of bone marrow derived macrophage from Apoe-Bmal MKO and Apoe-Bmal MWT mice demonstrated that deletion of myeloid Bmal impaired rhythmic transcription of Ccl2 and Ccl8, causing higher expressions. Meanwhile, lipid profile and endothelial function were unaltered in Apoe-Bmal MKO compared with Apoe-Bmal MWT mice. Conclusions: Our data showed disruption of myeloid circadian rhythm increased inflammation and enhanced atherosclerosis