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-/-/Casp8Δhepa 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-/-/Casp8Δhepa 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.
