Abstract 911: Lacking SOCS3 Gene in Macrophages Prevents the Development of Atherosclerosis in ApoE Deficient Mice
Background: Atherosclerosis is now generally accepted as a chronic inflammatory disease characterized by accumulation of blood-derived macrophages in the arterial wall. It has been shown that suppressor of cytokine signaling 3 (SOCS3) is an intrinsic negative regulator of interleukin-6 (IL-6)-STAT3 signaling that plays an essential role in inflammatory response. In the present study, we determined whether STAT3-mediated IL-6 signaling and SOCS3 within the macrophages would play an important role in the development of atherosclerosis.
Methods and Results: We examined the activation of STAT3 and expressions of IL-6 family cytokines and SOCS3 in the aorta of apolipoprotein E knockout mice (ApoE-KO) and control mice by western blot, immunohistochemical staining and RT-PCR. Western blot revealed that STAT3 is phosphorylated in the atherosclerotic lesions from ApoE-KO mice but not in those from control mice. Dual immunohistochemical staining revealed that phosphorylated STAT3 and macrophage marker, MOMA2, were co-expressed in the atherosclerotic plaque in ApoE-KO deficient mice, suggesting that the STAT3 signaling pathway within the macrophages was activated in atherosclerosis. Next, to investigate the role of STAT3-mediated IL-6 signaling and SOCS3 in macrophages during atherogenesis, we created ApoE-KO mice with a macrophage-restricted deletion of SOCS3 gene (ApoE/SOCS3-KO). We found that atherosclerotic lesion area by oil-red O staining was significantly reduced in ApoE/SOCS3-KO (n=17) compared with control ApoE-KO mice (n=13) (4.63±0.43 vs. 8.29±0.50 %, p<0.01). In in vitro analyses, enzyme-linked immunosorbent assay revealed that LPS-induced TNF-alpha production were significantly smaller in SOCS3 deficient macrophages compared with wild type macrophages (n=8, 2238±155 vs. 992±83 pg/ml, p<0.01). Also we found that IL-6-induced oxidized-LDL uptake was 42% reduced in SOCS3 deficient macrophages compared with wild type macrophages (p<0.01).
Conclusion: Our data show that the deletion of SOCS3 in macrophages prevents the development of atherosclerosis in mice, possibly by inhibiting the inflammatory cytokine production and oxidized-LDL uptake in macrophages.