The Role And Mechanism Of Sema7A In Coxsackievirus B3 Induced Myocarditis

Viral myocarditis(viral myocarditis, VMC) is a common clinical disease of the cardiovascular system caused by myocardial cell necrosis and interstitial inflammatory cell infiltration.VMC can further progress to dilated cardiomyopathy, and even heart failure. In recent years, the incidence of VMC is increasing. Children and infants take up the majority of VMC patient. A variety of viruses can induce myocarditis, including coxsackie virus, cytomegalovirus, echo virus, HIV, polio virus, adenovirus, etc. Among them coxsackievirus B3(CVB3)), a single positive strand picrornavirus, is the most common.So far, the pathogenesis of VMC is not completely clear and there is no effective treatment. Previous studies demonstrate that both the virus-induced early direct damage and the following host immune inflammatory responses are the reasons of VMC and the overwhelming immune response takes a key role. Therefore, anti-viral treatments and controlling inflammation have been made in the clinical to relieve VMC at present. An increasing number of studies suggest that Semaphorin7A(Sema7A) not only plays an important role in nerve axons growth, tumor suppressing, tissue remodeling, but also regulates inflammations in multiple disease, such as viral infection, skin inflammation, the cornea inflammation, pulmonary fibrosis, liver fibrosis, nerve damage, and sclerosis inflammation. For instance, Sema7 A derived from intestinal epithelial cell(IEC) can negatively regulate the process of colitis through IL-10 in dextran sulfate sodium induced colitis model. In vitro studies demonstrate that Sema7 A acts as chemotaxis for monocytes and can induce the expression of proinflammatory factors such as IL-8, TNF-α and IL–6. The over-expression of Sema7 A can activate monocytes to secret inflammatory IL-8 through α1β1 integrin. When α1β1 integrin was blocked, the pro-inflammatory effects decreased significantly. In corneal inflammation models, Sema7 A expressed on T cells interacts with α1β1 integrin on the surface of macrophage, promoting the recruitment of macrophage to the sites of inflammation. However some studies reported that Sema7 A expressed on intestinal epithelial cells and induces anti-inflammatory cytokines production through interacting with α1β1 integrin on intestinal macrophages. These studies indicate that Sema7 A may take different roles in regulating inflammation depending on the receptors. In this study, we successfully established a VMC mice model and then detected the expression of Sema7 A from day 0 to day 7. We found a gradually increase of Sema7 A expression during the progress of disease, which suggests that Sema7 A may participate in the process of VMC. Next, we generated the down-expression plasmid shRNA-Sema7 A and request over-expression plasmid Sema7 A from Professor Kumanogoh Atsushi at Osaka University. We manipulated the in vivo Sema7 A expression by orbital injection of PEI packaged above plasmids. Results showed that the symptoms of viral myocarditis in shRNA-Sema7 A group were significantly alleviated evidenced by improved heart function and decreased death rate, indicating that Sema7 A plays an important role in viral myocarditis. By determining the secretion of inflammatory cytokines in heart, we found that the down-regulation of Sema7 A can effectively inhibit the inflammatory response. Finally, we explore the potential mechanism of Sema7 A in CVB3 induced myocarditis. Two types of macrophage cells(α1β1 integrin and αvβ1 integrin) exist in CVB3 induced myocarditis. In our previous studies we find that macrophages play an important role in the process of the pathogenesis of viral myocarditis. We then examined the inflammatory cytokines secretion by these two cells and found that compared with αvβ1 integrin macrophages, α1β1 integrin macrophages can secrete large amounts of pro-inflammatory factors. In the experiment of Sema7 A neutralization antibody treatment, we found that the notable number change of α1β1 integrin macrophages comparing to αvβ1 integrin macrophages. Moreover, we found the increase of α1β1 integrin macrophages when co-culture with CVB3-stimulated myocardial cells on which the Sema7 A expression was up-regulated. It indicated that Sema7 A may promote the pro-inflammatory response through activating of α1β1 integrin macrophages.Taken together, we conclude that Sema7 A is up-regulated in heart of CVB3 induced VMC mice. Sema7 A can activate infiltrated α1β1 integrin macrophages to produce pro-inflammatory cytokines by interacting with α1β1 integrin on cell surface. The increased inflammation may accelerate the development of VMC. Our study implies the role of Sema7 A in the process of CVB3-induced myocarditis and provides new insights to the pathogenesis and treatments of VMC.