Nature and nurture: Environmental toxins and biliary atresia

In Utero Extrahepatic Bile Duct Damage and Repair: Implications for Biliary Atresia

Biliary atresia (BA) is a cholangiopathy affecting the extrahepatic bile duct (EHBD) of newborns. The etiology and pathophysiology of BA are not fully understood; however, multiple causes of damage and obstruction of the neonatal EHBD have been identified. Initial damage to the EHBD likely occurs before birth. We discuss how different developmental stages in utero and birth itself could influence the susceptibility of the fetal EHBD to damage and a damaging wound-healing response. We propose that a damage-repair response of the fetal and neonatal EHBD involving redox stress and a program of fetal wound healing could-regardless of the cause of the initial damage-lead to either obstruction and BA or repair of the duct and recovery. This overarching concept should guide future research targeted toward identification of factors that contribute to recovery as opposed to progression of injury and fibrosis. Viewing BA through the lens of an in utero damage-repair response could open up new avenues for research and suggests exciting new therapeutic targets.

Rotavirus Infection and Cytopathogenesis in Human Biliary Organoids Potentially Recapitulate Biliary Atresia Development

There is substantial evidence indicating the possible involvement of rotavirus in biliary atresia (BA) development, at least in a subset of patients, but concrete proof remains lacking. In a mouse model, it has been well demonstrated that rotavirus can infect the biliary epithelium to cause biliary inflammation and obstruction, representing the pathogenesis of BA in humans. By using recently developed organoids technology, we now have demonstrated that human biliary organoids are susceptible to rotavirus infection, and this provokes active virus-host interactions and causes severe cytopathogenesis. Thus, our model recapitulates some essential aspects of BA development. Furthermore, we have demonstrated that antiviral drugs and neutralizing antibodies are capable of counteracting the infection and BA-like morphological changes, suggesting their potential for mitigating BA in patients.

Biliary atresia (BA) is a neonatal liver disease characterized by progressive fibroinflammatory obliteration of both intrahepatic and extrahepatic bile ducts. The etiologies of BA remain largely unknown, but rotavirus infection has been implicated at least for a subset of patients, and this causal relation has been well demonstrated in mouse models. In this study, we aim to further consolidate this evidence in human biliary organoids. We obtained seven batches of human biliary organoids cultured from fetal liver, adult liver, and bile duct tissues. We found that these organoids are highly susceptible and support the full life cycle of rotavirus infection in three-dimensional culture. The robust infection triggers active virus-host interactions, including interferon-based host defense mechanisms and injury responses. We have observed direct cytopathogenesis in organoids upon rotavirus infection, which may partially recapitulate the development of BA. Importantly, we have demonstrated the efficacy of mycophenolic acid and interferon alpha but not ribavirin in inhibiting rotavirus in biliary organoids. Furthermore, neutralizing antibody targeting rotavirus VP7 protein effectively inhibits infection in organoids. Thus, we have substantiated the causal evidence of rotavirus inducing BA in humans and provided potential strategies to combat the disease.

Th17-associated cytokines multiplex testing indicates the potential of macrophage inflammatory protein-3 alpha in the diagnosis of biliary atresia

BACKGROUND & AIMS

Biliary atresia (BA) is a neonatal obliterative cholangiopathy with high prevalence in south China. Accurate identification of BA among infants with obstructive jaundice is still difficult by noninvasive diagnostic tools. Th17 cells have been reported closely related with the development of BA, which suggest that Th17-associated cytokines were potential biomarkers for the diagnosis of BA patients.

METHODS

In the training study, 76 infants who were divided into 2 groups, including BA group (n = 31) and non-BA jaundice group (n = 45). Clinical and routine laboratory data were collected from all subjects. Totally 25 Th17-associated cytokines were tested and compared between groups. The diagnostic value of each differential cytokine was evaluated by the area under the receiver operating characteristic curve (AUC). The best potential diagnostic biomarker was further validated in a cohort including 68 jaundice infants from our partnering institution in a blinded fashion.

RESULTS

Data from the training study showed that gamma-glutamyl transferase (GGT) and clay stool would be helpful in the identification of BA patients in jaundice subjects. Th17-associated cytokines assay indicated that IL-17F, IL-10, macrophage inflammatory protein-3alpha (MIP3a), IL-22, IL-13, IL-33, IL-6, IL-17E, IL-27, IL-31, TNF-a and TNF-b were differentially expressed in BA patients, and the AUC of MIP3a was higher than other markers. MIP3a alone or combined with other laboratory data would significantly increase the diagnostic accuracy of BA. The diagnostic value of MIP3a was further confirmed in our validation study.

CONCLUSION

MIP3a alone or combined with other laboratory data would significantly increase the diagnostic accuracy of BA.

Gene expression profile of TLR7 signaling pathway in the liver of rhesus rotavirus-induced murine biliary atresia

PURPOSE

To identify genes potentially involved in the pathogenesis of bile duct obstruction in biliary atresia (BA).

METHODS

We used rhesus rotavirus (RRV) Balb/c mouse BA model to study BA. Liver and serum samples were harvested from BA and normal control (NC) groups at 1, 3, 5, 7, 10 and 14 days postinoculation. Serum total bilirubin (STB) and conjugated bilirubin (CB) were measured. Livers of each group at day 7 were used for a genome-wide expression analysis. Expression of TLR7 signaling pathway in liver was measured by immunohistochemical staining and western blotting, including expression of TLR7, activation of phosphorylated IRF7 and secretion of IFN-β, IL-1α and IL-6. Cell viability and survival rate after RRV infection were measured by using TLR7 knockdown human cholangiocarcinoma cell RBE.

RESULTS

STB was significantly elevated from day 5 postinoculation and CB was from day 7 postinoculation, while CK19 (the biomarker of biliary epithelial cells) expression by western blotting was decreased. By microarray analysis of liver tissues at day 7 postinoculation, TLR7 signaling pathway was up-regulated in BA mice. Based on the results of microarray analysis, the protein expression of TLR7 in the liver tissues of BA groups were found to be up-regulated from day 5 comparing to respective NC groups, although it was increased as pups aged in NC groups. And the level of p-IRF7 and secretion of cytokines were also statistically significant in BA groups. In vitro, TLR7 knockdown cell line showed less cellular proliferation and more susceptible to RRV infection.

CONCLUSION

By in vivo study, TLR7 signal pathway was up-regulated in BA group; by additional in vitro study, intact TLR7 signal pathway might have some protective abilities in BA pathogenesis.