Role of Tumor necrosis factor receptor 1 in a mouse model of chronic liver inflammation

Abstract

Tumor necrosis factor receptor 1 (TNFR1) is a ubiquitously expressed pro-inflammatory cytokine receptor. It is known to promote disease progression of chronic liver disease (CLD) through the induction of cell death as well as the release of pro-inflammatory and pro-fibrotic mediators. In contrast, it is also involved in mediating pro survival signaling and regeneration. This work analyzed how the absence of TNFR1 affects disease progression in Mdr2-/- mice, a mouse model of chronic liver inflammation and inflammation-induced HCC. For that purpose, Tnfr1−/− mice were crossed with Mdr2−/− mice, creating Tnfr1−/−/Mdr2−/− mice. TNFR1 deficient Mdr2−/− mice displayed a more severe phenotype indicated by increased plasma levels of the liver enzymes alanine aminotransferase (ALT) and alkaline phosphatase. Increased plasma levels of bilirubin with concomitant reduction cholesterol indicated impaired biliary excretion of livers of TNFR1 deficient Mdr2−/−. TNFR1 deficiency in the chronically inflamed liver did not abrogate apoptotic cell as seen in western blot analysis of an active subunit of caspase 3 (Casp3), nor did it appear to affect the induction of regenerative proliferation indicated by increased gene expression of proliferation markers (Pcna, Ccna2, Cdk1). Compared to Mdr2−/− mice, Tnfr1−/−/Mdr2−/− mice displayed a more pronounced fibrotic response seen in significantly higher collagen content, and gene expression of fibrotic markers including α-smooth muscle actin (α-sma), matrix metalloproteinases (MMPs), and their tissue inhibitors (TIMPs). The absence of TNFR1 influenced the gene expression of inflammatory cytokines (Il1b, Il23, Tgfb1, Il17a), chemokines (Ccl2, Cxcl1, Cx3cl1) and chemokine receptors (Ccr6, Cxcr6, Cx3cr1) in livers of Tnfr1−/−/Mdr2−/− mice, which in combination created a microenvironment favoring TH17 cell activation. Flow cytometric analysis showed that the hepatic immune cell compartment of Tnfr1−/−/Mdr2−/− mice was enriched in IL-17 producing TH17 cells as well as neutrophils. The aggravated tissue injury in Tnfr1−/−/Mdr2−/− mice positively correlated with enhanced IL-17 production in the injured liver. Additionally, western blot analysis of liver lysates revealed that Tnfr1−/−/Mdr2−/− mice displayed increased hepatic activation of receptor interacting protein Serine/Threonine kinase 3 (RIPK3), which was not related to necroptotic cell death. Instead, frequencies of infiltrating CX3CR1+ monocytes increased over time in livers of Tnfr1−/−/Mdr2−/− mice, which expressed significantly higher levels of Ripk3 expression than those of Mdr2−/− mice. Overall, it can be concluded that the ablation of TNFR1 exacerbated disease progression of chronic liver inflammation in the Mdr2−/−. This work adds to the extensive research aimed to delineate underlying mechanisms of CLD disease progression, to improve treatment options and consequently disease outcomes. Future research should be aimed at identifying the underlying mechanism by which TNFR1 deficiency promotes pathogenic TH17 cell responses during chronic liver disease.