Role of Jak3 in cross talk between Intestinal and biliary epithelial cells
Authors: Kumar Narendra , Alpini Gianfranco , Mishra Jayshree 
Published: May 2022

Background

Primary biliary cholangitis (PBC) is one of the most common chronic inflammatory condition of the liver affecting 1 in 1000 women over the age of 40. The exact etiology and pathogenetic mechanisms of PBC is unknown and currently, there is no cure to it. PBC progressively affects the intrahepatic and extrahepatic biliary tree leading to bile duct strictures, cholestasis, and hepatic fibrosis. A better understanding of the initial pathologic events is essential to develop appropriate intervention. Recent studies suggest gut‐liver communication has greater implications in hepatic health where the gut microbiome and the gut barrier functions are implicated in bacterial translocation and bile acid metabolism. However, the mechanistic role of intestinal mucosal epithelial cells in gut‐dysbiosis‐mediated PBC are less understood. Janus kinase 3 (Jak3) is a non‐receptor protein kinase that plays essential role in hematopoietic and intestinal epithelial (IEC) differentiation. Previously, we reported that loss of Jak3 exacerbates symptoms in murine model of DSS‐induced colitis through compromised intestinal differentiation. In this work, we investigated the tissue‐specific role of Jak3 in hepatic canalicular remodeling and cholestasis during intestinal chronic low‐grade inflammation (CLGI).

Methods

We used a biliary epithelial cell model and global and IEC Jak3 KO (Jak3−/−) mice and their littermate control and compared the effects of Jak3 on gut dysbiosis and hepatic canalicular remodeling and cholangitis. We also investigated the status of hepatic TLR signaling and TGFb1 pathways using a combination of flow cytometry, confocal microscopy, and western analysis techniques.

Results

Our results show that Jak3 regulates both mucosal epithelial and biliary epithelial (BEC) tolerance through the regulation of TLR where Jak3 impacted BEC remodeling and canalicular structure formation. Studies using hematoxylin and eosin‐stained liver sections demonstrated marked infiltration of lympho‐plasmacytic cells in portal tracts surrounding interlobular bile ducts. An interlobular bile duct showed distorted lumen, and cellular detachment from the basement membrane with infiltration of several lymphoid cells into the cellular layer in both global Jak3‐KO and IEC‐Jak3‐KO mice. Immunohistochemical (IHC) analysis of liver of Jak3−/− and IEC‐Jak3−/−and their littermate control mice using monoclonal antibodies to CD4 and CD8 showed that CD8‐positive cells were predominant along with CD4‐positive cells that were distributed mainly at the peribiliary areas of the portal veins with some CD8 cells in the sinusoidal spaces. CD8 T‐cells and mononuclear cell were also seen attached to bile duct epithelium indicating invasion of these cells into the biliary epithelial layer. A differential flowcytometric assay showed an increased influx of monocytes in Jak3 KO mice compared to control. Moreover, KO mice showed an increased hepatic expression of TLR‐2 and TLR‐4 and a higher IL‐6, IL‐17 and Tnf‐α as compared to the control mice. Together, these results showed that loss of Jak3 expression leads to compromise biliary tolerance coupled with increased extravasation of the circulating monocytes into the liver. In addition, we also found an increased Th17 effector function and simultaneous suppression of Treg cell proliferation in the absence of Jak3, when compared to its control mice. Collectively, these results indicate that Jak3 plays a major role in hepatic canalicular remodeling and cholestasis during intestinal CLGI.