Abstract 14154: Macrophage Notch1 Accelerates Lesion Formation In Mechanically-injured Mouse Femoral Arteries
Background: We previously demonstrated that the Notch ligand Delta-like 4 (Dll4) promotes macrophage activation. However, the role of each Notch receptor expressed by macrophages remains unknown. We hypothesized that macrophage Notch1 induces macrophage activation and accelerates the development of vascular disease.
Method and results: Overexpression of the Notch1 intracellular domain (a constitutively active form, Notch1-ICD) in the macrophage cell line RAW264.7 induced various pro-inflammatory genes typical of “M1” polarization (e.g., IL-1 beta, IL-6, MCP-1, iNOS). To explore the role of macrophage Notch1 in vivo, we established macrophage-selective genetically-altered mice that lack Notch1 (Notch1-/- mice) or overexpress the constitutively active Notch1 (Notch1-ICD mice) using the Cre/LoxP technology. We used the wire injury model in femoral arteries of these strains. Macrophage selective deletion of Notch1 reduced neointima formation 28 days after injury as compared to Control mice (Intima/madia (I/M) ratio: Control, 2.5±0.3; Notch1-/-, 1.2±0.3; N=7 each; p<0.01). However, Notch1-ICD overexpression failed to significantly increase the lesion development (I/M ratio: Control, 2.5±0.3; Notch1-ICD, 3.4±0.3; N=7 and 5, N.S.). To further address the underlying mechanism, we analyzed earlier arterial lesions 7 days after injury. In Notch1-/- mice, macrophage accumulation in injured arteries was lower than Control mice (Mac3 stain; N=5 each; p<0.05). Peritoneal macrophages from Notch1-/- mice showed lower expression of the chemokine receptor CCR2 (qPCR, p<0.01) and decreased chemotaxis to MCP-1 (modified Boyden chamber method, p<0.01) as compared to Control mice. Cell proliferation at 7 days after arterial injury was lower in Notch1-/- mice (PCNA, p<0.05). Conditioned media (CM) of macrophages from Control mice induced growth and migration of cultured smooth muscle cells (SMC), both of which were suppressed by CM from Notch1-/- macrophages.
Conclusion: These data indicate that macrophage Notch1 signaling promotes activation of these pro-inflammatory phagocytes and their crosstalk with SMC, offering a new therapeutic target for vascular diseases.
- © 2013 by American Heart Association, Inc.