Abstract 15333: An Intermediary for Sirpα/Skap2-dependent Integrin-Stimulated Cytoskeletal Rearrangement in Macrophages, and the Implications for Atherosclerosis
Background: Integrins mediate macrophage behaviors that are critical for atherogenesis. The macrophage membrane protein Sirpα cooperates with the adaptor protein Skap2 to control integrin-induced actin reorganization and migration. We hypothesized that CD47 interacts with these proteins to control actin polymerization and that, through their roles in macrophage function, these signaling elements modulate atherosclerosis.
Results: Because Sirpα cooperates with Skap2 in an integrin-dependent manner, and because Sirpα is a known receptor for CD47, we tested integrin-induced actin polymerization in CD47-/- bone marrow-derived macrophages (BMMs). Similar to Skap2- and Sirpα-deficient cells, CD47-/- BMMs have impaired local integrin-induced actin polymerization compared to wild-type BMMs (1.1 ± 0.4 units vs. 7.9 ± 1.7 units, n = 20, p < 10-4). Furthermore, we find enhanced recruitment of CD47 to sites of antibody-mediated integrin ligation (3.1 ± 0.7 units vs. 1.0 ± 0.4 units for control antibody, n = 20, p < 5 x 10-3), and this CD47 recruitment correlates with the upregulated actin polymerization. Through direct engagement of CD47 with antibody-coated microbeads, we show that CD47 is involved in Sirpα recruitment to sites of integrin activation. We have previously found that Skap2 deficiency in apoE-knockout mice results in increased atherosclerotic plaque in the aortic root. Macrophage content of atheromata is intact in these mice, proportional to the size of the plaque, and there are no detected differences in T cell, B cell, or endothelial cell distribution in Skap2-deficient atheromata. We also find no difference in CD47-inhibited cell phagocytosis by Skap2-deficient macrophages, suggesting that Skap2-mediated actin polymerization, while acting through Sirpα and CD47, may be unrelated to the Sirpα-CD47 anti-phagocytic mechanism.
Conclusions: Overall, we detail a pathway by which Skap2 and Sirpα direct integrin-mediated actin reorganization in macrophages, with an apparent requirement for CD47 that is independent from the Sirpα-CD47 mechanism of anti-phagocytosis in these cells. The findings provide new insight into an integrin-mediated signaling pathway that may contribute to the inflammatory component of atherosclerosis.
Author Disclosures: F.J. Alenghat: None. D. Hyatt: None. K.D. Swanson: None. D.E. Golan: None.
This research has received full or partial funding support from the American Heart Association
- © 2014 by American Heart Association, Inc.