Abstract 5573: Critical Role of Notch1 in Bone Marrow-derived Macrophages in Mediating Atherosclerosis
Background: Notch receptors regulate binary cell fate determination and are critical for embryonic development. However, the role of Notch signaling in the postnatal period remains to be determined. Although Notch receptors and ligands are expressed in atherosclerotic lesions, its functional role in macrophages in mediating atherosclerosis is unknown.
Methods: To determine the role of macrophage Notch receptors in atherosclerosis, we transplanted bone marrow (BM) from wild-type (WT), Notch1+/− and Notch3−/− mice into irradiated recipient LDLr−/− mice. Atherosclerosis was induced with a 16-week diet containing 15.8% wt/wt fat and 1.25% cholesterol. The degree of atherosclerosis in the en face aorta and subaortic sinus was evaluated using Oil Red O staining. Macrophage recruitment and chemotaxis were evaluated by thioglycollate-induced peritonitis and in a modified Boyden chamber, respectively. Statistical analysis was performed using Mann-Whitney U-test. A p value <0.05 was considered significant.
Results: Physiological parameters after BM transplantation (BMT) and following atherogenic diet were not different between the 3 groups. Compared to WT BMT mice, Notch1+/− BMT mice showed substantially less atherosclerotic lesions in the aorta (9.7% vs. 13.6%, p<0.05) and subaortic sinus (515 ×103 μm2 vs. 696 ×103 μm2, p<0.05). In contrast, Notch3−/− BMT mice developed similar degree of atherosclerosis compared to WT BMT mice (aortic lesion: 14.7%; subaortic sinus lesion: 670 ×103 μm2; p<0.05 for both compared to WT BMT mice). This correlated with decreased recruitment of macrophages in response to thioglycollate-induced peritonitis in Notch1+/− BMT mice, but not in Notch3−/− or WT BMT mice. Indeed, Notch1+/− macrophage exhibited decreased chemotaxis to monocyte chemotactic protein (MCP)-1. The decreased chemotaxis in Notch1+/− macrophages was associated with decreased extracellular regulated kinase (ERK) phosphorylation.
Conclusions: Our findings indicate that Notch1 in BM-derived macrophages contributes to atherosclerosis by mediating macrophage chemotaxis, in part, through the ERK signaling pathway and suggest that inhibition of Notch1 signaling in macrophages may have therapeutic benefits in preventing atherosclerosis.