Role of the Thrombin-PAR-1 Pathway in Coxsackievirus Induced Hepatitis

Objective: Coxsackievirus B3 (CVB3) can infect different tissues including the heart and liver. Recently, we found that activation of the coagulation cascade and protease-activated receptor 1 (PAR-1) enhances toll-like receptor-3 (TLR3) mediated interferon-β (IFN-β) expression and protects mice from CVB3-induced myocarditis. Here, we investigated the role of PAR-1 in early anti-viral responses in mice and isolated hepatocytes.

Methods: Wild-type (WT) and PAR-1 deficient (PAR-1^-/-) mice were infected with CVB3 intraperitoneally. The innate immune response, viral load, liver enzyme plasma levels, and inflammation levels were analyzed. Bone-marrow transplantation experiments with the combination of WT mice PAR-1^-/- mice were performed to identify the cellular source of PAR-1 contributing to the innate immune response to CVB3. We also analyzed the effect of the direct thrombin inhibition with dabigatran etexilate on CVB3 hepatitis. In addition, we analyzed the effect of PAR-1 activation on TLR3-dependent interferon (IFN)-β expression in primary mouse hepatocytes and the human hepatocyte cell line PH5CH8 in vitro.

Results: PAR-1^-/- mice exhibited a reduced early innate immune response in the liver at day 4 after infection, which was associated at later times (day 8) to higher viral titers in the liver, increased alanine transaminase plasma levels and more remarkable inflammation compared to control WT mice. Bone marrow transplantation experiments demonstrated that PAR-1 on non-hematopoietic played the major role in the innate immune response of CVB3 hepatitis. Stimulation of PAR-1 with either thrombin or agonist peptide on primary mouse hepatocytes and human PH5CH8 cells in vitro enhanced the antiviral response to dsRNA by increasing IFN-β and C-X-C motif chemokine 10 (CXCL10) expressions, supporting the results of in vivo experiments.

Conclusion: Our results suggest that activation of PAR-1 on hepatocytes enhances the innate immune response to CVB3 in the liver.