Bile acids engage the SIPR-STAT3 signaling axis to modulate regulatory T cell responses in fibrosing cholangiopathies.

BACKGROUND & AIM: Regulatory T cells (Tregs), a subset of CD4 lymphocytes, protect from inflammatory tissue injury. How retention of bile acids (BA) in fibrosing cholangiopathies like biliary atresia or primary sclerosing cholangitis shape hepatic Treg responses is unknown.

METHODS

Mice were fed a diet containing 0.1% of 3,5-diethoxycarbonyl-1,4-dihydrocollidine for 14 days to induce sclerosing cholangitis (SC) followed by 28 days on regular chow to study repair. Serial hepatic cell and nuclear preparations from these mice were subjected to single-cell RNA- and ATAC-seq, respectively, to describe gene regulatory networks controlling Tregs under cholestatic conditions. Candidate molecules mediating the effects of Tauro-/Chenodeoxycholic Acids (T/CDCA) on Tregs were validated in vitro, in three murine models of SC, and in liver tissue samples from 130 infants with biliary atresia.

RESULTS

Single cell genomics revealed induction of a Th17 transcriptional program in Tregs during cholestasis and upregulation of amphiregulin (Areg) during repair. S1P receptors were nominated to mediate effects of T/CDCA on Tregs which was validated in vitro and in the Abcb4 model of SC. Deletion of the transcription factor STAT3 in CD4 cells augmented hepatic Treg responses following bile duct ligation. IBAT inhibitor mediated reduction of hepatic BA concentration promoted hepatic Treg surge leading to diminished liver injury and fibrosis in Abcb4 mice which was abrogated upon depletion of Tregs or neutralization of Areg. Lastly, a liver transcriptional profile of Treg activation and upregulation of AREG in infants with biliary atresia at diagnosis was associated with improved 2-year native liver survival.

CONCLUSION

BAs repress Treg suppressor function, polarize Tregs towards a Th17 phenotype, and thus constrain their capacity to protect from immune mediated cholangiocyte injury.

IMPACT AND IMPLICATIONS

This research examines the role of CD4 lymphocytes in controlling bile duct epithelial injury in fibrosing cholangiopathies, with potential implications for developing targeted therapies for biliary atresia and primary sclerosing cholangitis. Using single cell genomics, functional assays, and complementary mouse models of sclerosing cholangitis, mechanisms by which chenodeoxycholic acid derived bile acids determine polarization and suppressor functions of CD4 lymphocytes were investigated. Reduction of hepatic bile acid concentration with IBAT inhibitor, antagonizing STAT3 in CD4 lymphocytes, or blocking of S1P receptors boost hepatic regulator T cells in experimental sclerosing cholangitis and protect from cholestatic liver injury. The preclinical studies will inform future clinical trials in affected patients.