Abstract 4344466: Nobiletin inhibits atherosclerosis by regulating macrophage Bmal1 and Hif1α

Abstract

Dysfunction of macrophage cholesterol homeostasis is a risk factor for atherosclerosis and metabolic disorders. We have shown that macrophage-specific Bmal1 (Brain and Muscle Arnt-like protein-1) deficiency increases atherosclerosis by enhancing oxidized low-density lipoprotein (oxLDL) uptake via Cd36, diminishing cellular cholesterol efflux by reducing Abca1/Abcg1, and inhibiting cholesterol egress from lysosomes by reducing Npc1/Noc2. Nobiletin (NOB) has been shown to activate Bmal1 expression. Here, we studied the effect of NOB on atherosclerosis in macrophage-specific Bmal1-deficient (M- Bmal1 -/- Apoe -/- ) and control Bmal1 fl/fl Apoe -/- mice. We observed that NOB significantly decreases atherosclerosis in Bmal1 fl/fl Apoe -/- mice, but it is less effective in M- Bmal1 -/- Apoe -/- mice in reducing atherosclerosis lesions, indicating that NOB requires macrophage Bmal1 to exert its anti-atherosclerotic effects. Mechanistic studies in isolated macrophages showed that NOB increases cholesterol efflux by enhancing Abca1 (ATP-binding cassette transporter A1), Abcg1 (ATP binding cassette subfamily G member 1), and intracellular trafficking by augmenting Npc1/Npc2 (Niemann-Pick disease type C 1/2) in Bmal1 fl/fl Apoe -/- macrophages but not in Bmal1 deficient macrophages. These studies suggested that NOB regulates Abca1/Abcg1 and Npc1/Npc2 by augmenting Bmal1 expression. Surprisingly, we observed that NOB reduced oxLDL uptake and Cd36 (cluster of differentiation 36) expression in both control and macrophage-specific Bmal1-deficient macrophages. Mechanistic studies revealed that NOB reduced Hif1α (Hypoxia-inducible factor 1-alpha) in Bmal1 fl/fl Apoe -/- as well as M- Bmal1 -/- Apoe -/- mice. Therefore, NOB reduces oxLDL and Cd36 expression by enhancing Hif1α activity. These studies showed that NOB regulates Hif1α and Baml1 to regulate cholesterol metabolism in macrophages and could be useful in treating atherosclerosis.