Abstract 18680: Skap2 Regulates the Inflammatory Macrophage Response in Atherogenesis
Background: Macrophages are central to atherosclerosis. A macrophage-specific, integrin-stimulated signaling pathway acts through the adaptor protein Skap2 to drive actin reorganization and migration. Absence of this pathway yields accelerated atherosclerosis, but the manner in which Skap2 governs macrophage behavior in atherogenesis is undefined.
Results: We have previously shown that Skap2-/-;apoE-/- mice have increased atherosclerotic plaque in their aortic roots compared to their Skap2+/+;apoE-/- counterparts on a standard diet, and there is no difference in weight, lipid profile, development, or other organ pathology. Here, we find that despite in vitro defects in chemotaxis and migration, Skap2-deficient apoE-/- mice have intact macrophage content (F4/80 stain) in their atheromata. M1 and M2 polarized bone marrow-derived macrophages express canonical mRNA markers: Tnfa and Nos2 for M1 and Ym1 and Arg1 for M2. In this system, compared to polarized wild-type (WT) cells, Skap2-/- M1s express higher levels of inflammatory M1 markers [Nos2: 1.0 +/- 0.005 a.u. for Skap2-/- vs. 0.22 +/- 0.02 a.u. for WT; p < 0.05], and Skap2-/- M2s express lower levels of M2 markers [Arg1: 0.66 +/- 0.15 a.u. for Skap2-/- vs. 1.0 +/- 0.02 a.u. for WT; Nos2: 0.38 +/- 0.04 a.u for Skap2-/- vs. 1.0 +/- 0.006 a.u. for WT; p < 0.05]. Compared to WT M2s, Skap2-/- M2s also express lower levels of the M2 marker CD206 by Western blot analysis. There is also higher Skap2 protein expression in wild-type M2s compared to wild-type M1s by Western analysis and immunofluorescence staining. In apoE-/- mice, Skap2+ atheromata have commingled CD86 and CD206 expression, whereas Skap2-/- lesions predominantly express the M1 marker CD86 such that the ratio of CD86:CD206 is skewed away from M2 in Skap2-deficient lesions. In an in vitro system of efferocytosis, Skap2-/- macrophages show impaired uptake of apoptotic foam cells.
Conclusions: Overall, we find that a Skap2-dependent pathway contributes to regulation of atherogenesis through maintenance of normal lesional macrophage homeostasis. Taken together, our findings support a model in which Skap2 does this by driving macrophages toward a regulatory, efferocytic phenotype.
Author Disclosures: D. Hyatt: None. F.J. Alenghat: None.
- © 2015 by American Heart Association, Inc.