The Initiatory Mechanism Of Semaphrin7A Participate In The Development Of Atherosclerosis Of Mice

Atherosclerosis is the major cause of cardiovascular diseases. Currently, atherosclerosis is regarded as a systematic inflammatory disease in which both innate immunity and adaptive immunity are involved. The earliest morphologically visible lesion of arterial atherosclerosis, the fatty streak, already is an advanced metabolic and immunologic locus that manifests as abnormalities of vascular tone, inflammation, cellular growth, and endothelial cell dysfunction. After years to decades, the lesions advance to form plaques that grow and eventually either impinge on the arterial lumen or rupture. Plaque rupture leads to acute coronary syndrome(ACS), myocardial infarction or stroke, which threat to human health. The mechanisms are only poorly understood so that searching the potential drugs to improve outcomes in atherosclerosis is the main task to scientists.Semaphorins are a large family of proteins that were initially implicated in axonal guidance but have since been shown to contribute to organogenesis, vasculogenesis, angiogenesis. Sema7 A is a membrane-associated glycosylphosphatidylinositol(GPI)-linked cell-surface glycoprotein that belongs to the class VII semaphorin subfamily. Binding of β1 integrin to Sema7 A can transduce Sema7 A signaling to promote axon outgrowth and to initiate T-cell-mediated inflammatory responses.Sema7 A stimulates the production of proinflammatory cytokines, such as IL-8, IL-6, IL-1βand tumor necrosis factor TNF-α from monocytes. Recently, Sema7 A has also been found to participate in several pathophysiological conditions including liver fibrosis, neuronal injury, pulmonary fibrosis, skin inflammation, corneal inflammation, and multiple sclerosis.Although much was known about the role of Sema7 A in pathophysiological processes, whether Sema7 A participates in the progress of atherosclerosis is unclear. The presence of Sema7 A or its receptors on T cells, monocytes, dendritic cells(DCs), endothelial cells, and platelets, puts this molecule in locations that are intimately involved in atherosclerosis. The line of evidence that endothelial Sema7 A promotes leukocyte transmigration during hypoxia further implies its role in facilitating the migration of inflammatory cells into the vascular wall during atherosclerosis. Thus, we initiated the studies asking whether Sema7 A participates in the development of atherosclerosis and showed that deletion of Sema7 A decreased plaque formation in Apo E-/- mice.Objective:Here we test the hypothesis that Sema7 A will attenuate the size of atherosclerotic plaques and confer protection against the development of atherosclerosis.Methods:1. By feeding HFD for 1 week, 4 weeks, 12 weeks, compare the expression of Sema7 A to find out the relationship between Sema7 A and atherosclerosis.2. Establishment of Sema7A-/-Apo E-/- mice.3. Using Apo E deficient mice on a high-fat diet(HFD), we established the mouse model of hyperlipidemia and atherosclerosis.4. We measured the weight of mice and the plasma lipid contents through obtaining the venous blood of hyperlipidemia mice and compared the mice with or without 12 weeks HFD.5. By feeding on HFD for 12 weeks, Apo E-deficient mice can generate plaque. The thoracic aorta plaque size was calculated through Sudan IV staining and inflammatory cells infiltration into plaques were compared between the Sema7A-/-Apo E-/- mice and Sema7A+/+Apo E-/- mice.6. Obtaining atherosclerotic aorta tissue, detect the RNA expression level of macrophage subtypes through RT-QPCR in order to measure the macrophage polarity.7. After atherosclerotic model established, T cell related inflammatory cytokine level was calculated to indicate the T cell activation and differentiation during atherosclerosis development.Results:1. During HFD, Sema7 A expression has a stable pattern and comparing to chow diet, HFD leads to Sema7 A expression up-regulation and reaches the maximal level at 1 week.2. Successfully establish the mice-cross-method and obtain the Sema7A-/-Apo E-/- mice.3. After 12 weeks on HFD, Apo E-/- mice showed large area of plaques formed in the aorta and results showed that atherosclerotic lesion size in the entire aorta was decreased by 51.18%(P=0.0024) in Sema7A-/-Apo E-/- mice(5.01±1.04%, n=13) compared to Sema7A+/+Apo E-/- control mice(10.26±1.15%, n=13).4. After atherosclerosis model established, comparing to Sema7A+/+Apo E-/-control mice, Sema7A-/-Apo E-/- mice showed significant decrease in inflammatory cell infiltration including macrophages, dendritic cells and T lymphocytes, which contributing to the attenuating atherosclerosis.5. Sema7A-/-Apo E-/- mice showed obvious increase in collagen content of the atherosclerotic plaque comparing to Sema7A+/+Apo E-/- control mice, which contributing to the stabilize atherosclerotic lesions.6. By HFD for 12 weeks, Sema7A-/-Apo E-/- mice showed obvious decrease in M1 subtype polarity of macrophage and slight increase in M1 comparing to Sema7A+/+Apo E-/- control mice.7. Detecting the T cell inflammatory cytokine of the plasma revealed that, comparing to Sema7A+/+Apo E-/- control mice, Sema7A-/-Apo E-/- mice has impaired immunity response to inflammation under HFD so that protect mice from atherosclerosis.Conclusions:These results demonstrate that genetic deletion of systemic Sema7 A slows down atherosclerosis by decreasing inflammatory and immune response,which reducing inflammatory cells(macrophage, dendritic cell and T-cell) accumulation and impairing T-cell priming in secondary lymphoid organs, which are crucially involved in atherosclerotic plaque development. Therefore Sema7 A may represent a novel agent for treatment of atherosclerosis disease.