Abstract 5107: Notch3 Signaling in Macrophages Promotes Obesity and Atherosclerosis in Hypercholesterolemic Mice
Background: Macrophage activation participates in the pathogenesis of atherosclerosis and obesity, major components of the cardiometabolic syndrome. The Notch signaling pathway involves four receptors (Notch1– 4) and regulates various biological processes during development. We previously demonstrated that Notch signaling induces proinflammatory responses in macrophages in vitro. However, the role of each receptor in macrophage activation remains unclear. The present study has determined the reality in vivo of our in vitro findings by exploring whether Notch3 expression in macrophages promotes cardiometabolic disorders.
Methods and Results: We established macrophage-selective transgenic mice for the Notch3 intercellular domain (a constitutively active form) under control of the scavenger receptor A promoter/enhancer (Notch3tg). In vitro studies demonstrated that peritoneal macrophages of Notch3tg mice expressed higher levels of various molecules associated with inflammation (e.g., IL-1β, iNOS) and arterial remodeling and calcification (MMP-8/collagenase-2, MMP-13/collagenase-3, BMP-4 and BMP-7) than wild-type macrophages (p<0.05). To assess the in vivo role of macrophage activation via Notch3 in visceral obesity and atherosclerosis, we generated compound mutant mice by crossing Notch3tg with Ldlr−/− mice, a model of atherosclerosis and the metabolic syndrome. After high fat feeding for 24 weeks, the weight of epididymal fat in Notch3tg:Ldlr−/− mice (n=10) was greater than that of Ldlr−/− littermates (n=10, p<0.05). Notch3tg:Ldlr−/− epididymal fat expressed higher RNA levels of leptin and lower levels of hormone sensitive lipase, a key regulator of lipolysis in fat tissue, consistent with visceral fat accumulation. In addition, N3tg:Ldlr−/− mice showed increased plaque size in atherosclerotic aortas (p<0.05). The aorta of N3tg:Ldlr−/− mice further exhibited more advanced calcification than Ldlr−/− mice (p<0.05) in association with higher levels of the osteogenesis inducer BMP-7 (p<0.01).
Conclusion: These data indicate that macrophage activation through Notch3 signaling promotes obesity and atherosclerosis and provide new insight into the pathogenesis of chronic inflammatory diseases.