Identification of intramural epithelial networks linked to peribiliary glands that express progenitor cell markers and proliferate after injury in mice

Abstract

Peribiliary glands (PBGs) are clusters of epithelial cells residing in the submucosal compartment of extrahepatic bile ducts (EHBDs). While their function is largely undefined, they may represent a stem cell niche. Here, we hypothesized that PBGs are populated by mature and undifferentiated cells capable of proliferation in pathological states. To address this hypothesis, we developed a novel whole-mount immunostaining assay that preserves the anatomical integrity of EHBDs coupled with confocal microscopy, and found that PBGs populate the entire length of the extrahepatic biliary tract, except the gallbladder. Notably, in addition to the typical position of PBGs adjacent to the duct mucosa, PBGs elongate and form intricate intramural epithelial networks that communicate between different segments of the bile duct mucosa. Network formation begins where the cystic duct combines with hepatic ducts to form the common bile duct, and continues along the common bile duct. The cells of PBGs and the peribiliary network stain positively for α-tubulin, mucins, and chromogranin A, as well as for endoderm transcription factors Sox17 and Pdx1, and proliferate robustly following duct injury induced by virus infection and bile duct ligation. Conclusion PBGs form elaborate epithelial networks within the walls of EHBDs, contain cells of mature and immature phenotypes, and proliferate in response to bile duct injury. The anatomical organization of the epithelial network in tubules and the link with PBGs support an expanded cellular reservoir with the potential to restore the integrity and function of the bile duct mucosa in diseased states.

Peribiliary Glands Are Key in Regeneration of the Human Biliary Epithelium After Severe Bile Duct Injury

“…In our ex vivo model of human precision‐cut bile duct slices, patches of newly formed epithelial cell layers appeared in the proximity of PBG collections, yet at both the basolateral and luminal side of the slices. The formation of new epithelium at the basolateral sides may, at first glance, seem contradictory to the peribiliary anatomical design in which PBG cells can replenish the luminal epithelium through small connecting tubules that run transversely through the mural stroma . However, in our model of cultured, ultrathin bile duct slices of approximately 300 µm, connecting tubules between PBG and the central lumen may be transected, resulting in a lack of mechanical guidance for migrating PBG cells.…”

“…In a model of mechanically induced bile duct injury in guinea pigs, PBG have been described as crypts and glands in which all stages of mitoses can be observed 24 hours after the injury, resulting in small patches of newly formed epithelial layers . In addition, pronounced PBG cell proliferation has been described 24 hours after bile duct ligation in mice …”

Hypothermic oxygenated machine perfusion reduces bile duct reperfusion injury after transplantation of donation after circulatory death livers

“…The DHOPE‐preserved livers in the present study demonstrated significantly less severe injury of the deep and periluminal PBG after reperfusion compared with the control livers that did not undergo DHOPE. This histological finding is clinically relevant because the PBG have been identified as a local niche of biliary progenitor cells that contribute to the regeneration of biliary epithelium after injury . Severe injury of the deep PBG at the time of transplantation is a significant risk factor for the development of NAS .…”

Activation of biliary tree stem cells within peribiliary glands in primary sclerosing cholangitis

“…The involvement of PBGs in biliary tract pathologies has only recently been investigated in experimental models [20] and humans [21]. In ischemic biliary lesions, an increased number of proliferating progenitor cells has been demonstrated in PBGs [22].…”