5B). These findings support the possibility that PBGs and the epithelial network may serve as a reservoir of epithelial cells either to differentiate into or repopulate the mucosa during the regenerative response of the bile duct unit after an injury. To directly examine the proliferative

potential of PBGs, we quantified cellular proliferation by BrdU uptake in two models of cholestasis. First, we counted the number of BrdU+/CK19+ cells after IP administration of RRV into newborn mice. Infection of RRV soon after birth is a well-established injury model of the biliary epithelium and shares phenotypic features of human biliary atresia, the most common cause of chronic cholestatic liver disease in children.[19] selleck inhibitor We found an unexpectedly high baseline number of BrdU+ cells in age-matched controls (receiving

saline rather than RRV), both in CK-19+ cells of PBGs and the peribiliary epithelium and in CK-negative cells in the submucosal compartment of the duct along the entire length of EHBDs (Fig. 7). After RRV, the percentage of BrdU+/CK19+ epithelial cells did not change from controls (12% ± 3% versus 12% ± 2%; P = 0.8), neither did PBG cells (7% ± 3% versus 10% ± 5%; P = 0.25) at day 3, but increased in both the epithelium (18% ± 6% versus 8% ± 3%; P = 0.009) and PBGs (20% ± 8% versus 7% ± 6%; P = 0.01) Angiogenesis inhibitor at day 4. These findings are also reproduced when the results of BrdU+ cells are expressed for all epithelial cells together (mucosa plus PBGs; Fig. 7). We were unable to quantify BrdU+/CK19+ cells reproducibly beyond day 4 because of the widespread epithelial loss that typically begins on day 5 after RRV (data not shown). To investigate whether the high baseline BrdU uptake in control newborn

mice was the result of a normal growth phase of postnatal development, we compared the BrdU uptake by CK19+ cells in ducts of unchallenged neonatal and adult mice. We found that baseline BrdU uptake decreased in adult Low-density-lipoprotein receptor kinase mice in both epithelial cells (10% ± 3% neonate versus 1% ± 1% adult; P < 0.0001) and PBG cells (9% ± 6% neonate versus 1% ± 1% adult; P = 0.0004; Supporting Fig. 3). To assess cellular proliferation in adult mice, we quantified BrdU+/CK19+ cells after surgical ligation of the CBD. Though the percentage of BrdU+/CK19+ cells remained low at baseline levels at 6 and 12 hours after BDL, BrdU+/CK19+ cells of PBGs and the epithelium underwent a dramatic surge to 39% in PBGs and 33% in the epithelium at 24 hours (P = 0.002 and P < 0.001, respectively, when compared to sham operation) or 39% for ligation and 1% for sham when analyzing all cell types collectively for the entire duct (P < 0.001; Fig 8).