Absence of BSEP (ABCB11) protects MDR2 (ABCB4) KO mice from cholestatic liver and bile duct injury through anti-inflammatory bile acid composition and signaling

Background:

BsepKO mice are protected from acquired cholestatic injury by metabolic preconditioning with a hydrophilic bile acid (BA) pool with formation of tetrahydroxylated bile acids (THBAs). We aimed to explore whether increased BA-detoxification alters inflammatory signaling, thereby improving liver injury in the Mdr2KO mouse.

Methods:

Cholestatic liver injury, hepatic inflammation and fibrosis in Mdr2/Bsep DKO and Mdr2KO mice was studied for comparison. BDL WT and Mdr2KO mice were treated with THBA. RORγt+ and FOXP3+ T cells from liver were quantified by FACS. The impact of THBA on CDCA induced inflammation in IHH cells and RORγt as well as NFκB signaling in Jurcat cells were analyzed.

Results:

Mdr2KO but not DKO mice displayed increased BA-hydroxylation and lacked histological features of sclerosing cholangitis. 67% of serum BAs in DKO mice were polyhydroxylated, (THBAs most prominent), while Mdr2KO mice had no such BAs. In contrast to profoundly increased gene expression of inflammatory/fibrotic markers in Mdr2KO, no increases were seen in DKO. Increased levels of PHBAs were associated with reduced RORγt+ cells but increased FOXP3+ cell within the CD4+CD3+ T cell population (50% RORγt+; 5% FOXP3+ in Mdr2KO vs. 10% RORγt+; 30% FOXP3+ cells in DKO). THBA feeding reduced inflammation (by 50%) and fibrosis (by 80%) in Mdr2KO. In WT BDL mice, bile infarct size and inflammatory gene expression were also profoundly reduced by THBA. In IHH, THBA reduced CDCA induced inflammation and attenuated CDCA-induced NFκB activation in GFP-NFκB transfected Jurcat cells. Also in Jurcat cells, THBA attenuated RORγt signaling at mRNA levels (IL23 – 55%, TGFβ-25%; TH17 related cytokines).

Conclusion:

Increased formation of THBA or THBA administration represses key pro-inflammatory signals such as NFκB and RORγt in hepatocytes and immune cells, protecting Mdr2KO mice from cholestasis-associated inflammation and fibrosis. Therefore, THBA and their downstream targets may be a new potential treatment strategy for cholestatic liver diseases.