TLR5 Signaling Ameliorates Liver Fibrosis by Inducing Interferon β-Interleukin-1 Receptor Antagonist in Mice

Abstract

Background: Bacterial flagellin, recognized by cell surface of toll-like receptor (TLR) 5, is a potent activator of many types of cells, leading to the activation of innate or adaptive immunity, which are pivotal in regulating fibrotic process. However, the exact role of TLR5 signaling in liver fibrosis is still unclear. Methods: Hepatotoxin- and cholestasis-induced liver fibrosis models were used in this study. Real-time PCR, Western blotting, and histopathologic analysis were performed to elucidate the underlying mechanism of TLR5 signaling in the pathogenesis of liver fibrosis. Findings: Flagellin-induced TLR5 activation significantly decreased the severity of liver fibrosis. Notably, hepatic expression of interleukin-1 receptor antagonist (IL-1ra) and interferon (IFN) β was markedly increased in fibrotic livers upon flagellin treatment. Consistently, in vivo activation of TLR5 signaling significantly increased IFNβ and IL-1ra expression in the livers. Interestingly, flagellin injection significantly exacerbated the severity of liver fibrosis in IFN-α/β receptor-1 (IFNAR1)-deficient mice. Furthermore, hepatic expression of IL-1ra in the fibrotic livers of IFNAR1-deficient mice was significantly lower than those of WT mice. In support of these findings, flagellin-mediated IL-1ra production is not sufficient to alleviate the severity of hepatic fibro-inflammatory responses in IFNAR1-deficient milieu. Finally, hepatic stellate cells treated with IL-1ra showed significantly decreased cellular activation and its associated fibrogenic responses. Interpretation: Collectively, manipulation of TLR5 signaling may be a promising therapeutic strategy for the treatment of liver fibrosis. Funding Statement: This research was supported by grant (NRF-2017R1D1A3B03030521, 2017R1A6A3A11032024) of the Basic Science Research Program through the National Research Foundation (NRF), funded by the Ministry of Education, Republic of Korea Declaration of Interests: The authors declare that there are no conflicts of interests. Ethics Approval Statement: Experimental procedures and animal management procedures were undertaken in accordance with the requirements of the Animal Care and Ethics Committees of Chonbuk National University. The animal facility of Chonbuk National University is fully accredited by the National Association of Laboratory Animal Care.