Protease-activated receptors (PARs) are a unique group of four G-protein coupled receptors. They are
widely expressed within the cardiovascular system and the heart. PARs are activated via cleavage by serine proteases.
In vitro and in vivo studies showed that the activation of PAR1 and PAR2 plays a crucial role in virus induced
inflammatory diseases. The receptors enable cells to recognize pathogen-derived changes in the extracellular environment.
An infection with Coxsackie-virus B3 (CVB3) can cause myocarditis. Recent studies have been shown
that PAR1 signaling enhanced the antiviral innate immune response via interferon β (IFNβ) and thus limited the virus
replication and cardiac damage. In contrast, PAR2 signaling decreased the antiviral innate immune response via
IFNβ und thus increased the virus replication, which caused severe myocarditis. Along with CVB3 other viruses
such as influenza A virus (IAV) and herpes simplex virus (HSV) can induce myocarditis. The role of PAR signaling
in IAV infections is contrarily discussed. During HSV infections PARs facilitate the virus infection of the host
cell. These studies show that PARs might be interesting drug targets for the treatment of virus infections and inflammatory heart diseases.
First studies with PAR agonists, antagonists, and serine protease inhibitors have been conducted in mice. The inhibition of thrombin the
main PAR1 activating protease decreased the IFNβ response and increased the virus replication in CVB3-induced myocarditis. This indicates
that further studies with direct PAR agonists and antagonists are needed to determine whether PARs are useful drug targets for the
therapy of virus-induced heart diseases.
Keywords: Protease-activated receptor, myocarditis, virus infection, innate immune system, tissue factor, coagulation, interferon beta,
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