Bacterial translocation and inflammasome activation trigger chronic liver disease in the Mdr2-/- mouse model

Background & Aims:

Recent data highlight the role of intestinal dysbiosis and gut-liver interaction for progression of alcoholic and non-alcoholic fatty liver disease. However, the functional implications of intestinal microbiota and inflammasome mediated innate immune response for cholestatic liver disease is unclear. Here, we investigated gut-liver crosstalk and NLRP3 inflammasome activation in the murine Mdr2 knockout (Mdr2^-/-) model resembling primary sclerosing cholangitis (PSC).

Methods:

Male Mdr2^-/-, Mdr2^-/-/Casp8^Δhepa and WT control mice were housed for 8w or 52w. The relevance of Mdr2 deletion on liver injury as well as bile acid profile were studied. A comprehensive analysis of NLRP3 inflammasome and caspase activation in the gut-liver axis was performed. Caspase activation was blocked using a pan-caspase inhibitor (IDN-7314).

Results:

Mdr2^-/- mice displayed significantly increased serum transaminases compared to WT mice. Mdr2^-/- liver was characteristic presenting a strong chronic periductular inflammatory response with a strong induction of apoptotic cell death, progressive bile duct proliferation and periportal fibrosis development over time (52 weeks). The abnormal bile acid composition in Mdr2^-/- mice was associated with an altered intestinal microbiota composition. This was linked to an impaired intestinal barrier, including colonic mucus layers, reduction of tight junction expression and increased permeability evidenced by an in-vivo FITC-dextran assay. Intestinal dysbiosis in Mdr2^-/- mice urged increased translocation of endotoxin and augmented the hepatic innate immune response. Mechanistically, enhanced hepatic NLRP3 inflammasome activation via caspase-1 triggered macrophage and neutrophil infiltration and caspase-3, -8 and -9 mediated apoptotic cell death. However, by introducing Mdr2^-/-/Casp8^Δhepa animals the Mdr2^-/- phenotype could not be rescued indicating that hepatocytic caspase-8 activation is a downstream consequence and dispensable for the inflammatory response. Strikingly, pan-caspase inhibition using the inhibitor IDN-7314 dampened inflammasome activation and ameliorated liver injury as evidenced by significantly improved liver function tests, periportal inflammation as well as bile duct proliferation and serum bile acid profile.

Conclusions:

Mdr2 associated cholestasis triggers intestinal dysbiosis leading to translocation of endotoxin and bacterial DNA in the portal vein and subsequent NLRP3 inflammasome activation, which contributes to higher liver injury. This process can be blocked by Caspase-1/-8, but not hepatocytic caspase-8 inhibition.