Anatomical and histological characteristics of the hepatobiliary system in adult Sox17 heterozygote mice

Versatile application of fast green FCF as a visible cholangiogram in adult mice to medium-sized mammals

An aqueous solution of a common food dye, Fast Green FCF (FG), mimics cholyl-lysyl-fluorescein to visualize embryonic bile flow via single peritoneal injection into intrauterine mouse embryos. Despite its efficacy in embryos, its suitability for adult mice and small to medium-sized mammals remained uncertain. In this study, we investigated FG cholangiography in adult mice, dogs, and goats. The results demonstrate that FG injection enables progressive cholangiography in these species, highlighting its versatility across different animal models without necessitating specialized equipment. To further evaluate diagnostic utility, FG cholangiography was performed in various mouse models of bile flow disorders. FG successfully visualized dilated lumina in the extrahepatic bile duct of BDL mice and revealed aberrant luminal structures in the gallbladder walls of Sox17+/- or Shh-cre; Sox17flox/- mice. In Mab21l1-/- mice with contracted gallbladders, FG influx was limited to the gallbladder neck. Moreover, stereomicroscopic video analysis of FG influx into the gallbladder post-fasting revealed differences in gallbladder wall state and its bile composition between Sox17+/- and wild-type mice, suggesting the potential for detecting variations in gallbladder stored bile properties. These findings underscore the efficacy of FG in facilitating progressive cholangiography across mammalian species.

Identification of Gallbladder-Specific Distal Regulatory Sequence of Murine Sox17

Sox17 is a key transcriptional regulator of endoderm formation and function in the gallbladder, blood vessels and reproductive organs. Although multiple transcript variants of Sox17 have been suggested, the precise mechanisms underlying their time- and tissue-specific expression remain unclear. In this study, we discovered two putative regulatory sequences (R1 and R2) adjacent to different transcription start sites of mouse Sox17 exon 1 and generated deletion mice for these regions (Sox17Δdr/Δdr). Sox17Δdr/Δdr mice were alive and fertile, and they possessed a normal-sized gallbladder. However, semiquantitative analysis of immunostaining showed that the expression levels of SOX17 in Sox17Δdr/Δdr embryos were reduced to less than 50% of the wild-type in the gallbladder epithelium. Furthermore, the bile ductal epithelium marker SOX9 was abnormally upregulated, and PAS/DBA-positive mucin secretion-like epithelial cells were induced in the Sox17Δdr/Δdr gallbladder. Our results demonstrate that the distal sequence of Sox17, including R1 and R2, is important for the regulation of Sox17 gene expression in the embryonic gallbladder and is crucial for normal gallbladder epithelial development.

Impact of gallbladder hypoplasia on hilar hepatic ducts in biliary atresia

BACKGROUND

Biliary atresia (BA) is an intractable disease of unknown cause that develops in the neonatal period. It causes jaundice and liver damage due to the destruction of extrahepatic biliary tracts,. We have found that heterozygous knockout mice of the SRY related HMG-box 17 (Sox17) gene, a master regulator of stem/progenitor cells in the gallbladder wall, exhibit a condition like BA. However, the precise contribution of hypoplastic gallbladder wall to the pathogenesis of hepatobiliary disease in Sox17 heterozygous embryos and human BA remains unclear.

METHODS

We employed cholangiography and histological analyses in the mouse BA model. Furthermore, we conducted a retrospective analysis of human BA.

RESULTS

We show that gallbladder wall hypoplasia causes abnormal multiple connections between the hilar hepatic bile ducts and the gallbladder-cystic duct in Sox17 heterozygous embryos. These multiple hilar extrahepatic ducts fuse with the developing intrahepatic duct walls and pull them out of the liver parenchyma, resulting in abnormal intrahepatic duct network and severe cholestasis. In human BA with gallbladder wall hypoplasia (i.e., abnormally reduced expression of SOX17), we also identify a strong association between reduced gallbladder width (a morphometric parameter indicating gallbladder wall hypoplasia) and severe liver injury at the time of the Kasai surgery, like the Sox17-mutant mouse model.

CONCLUSIONS

Together with the close correlation between gallbladder wall hypoplasia and liver damage in both mouse and human cases, these findings provide an insight into the critical role of SOX17-positive gallbladder walls in establishing functional bile duct networks in the hepatic hilus of neonates.

Generation of in vivo-like multicellular liver organoids by mimicking developmental processes: A review

Liver is involved in metabolic reactions, ammonia detoxification, and immunity. Multicellular liver tissue cultures are more desirable for drug screening, disease modeling, and researching transplantation therapy, than hepatocytes monocultures. Hepatocytes monocultures are not stable for long. Further, hepatocyte-like cells induced from pluripotent stem cells and in vivo hepatocytes are functionally dissimilar. Organoid technology circumvents these issues by generating functional ex vivo liver tissue from intrinsic liver progenitor cells and extrinsic stem cells, including pluripotent stem cells. To function as in vivo liver tissue, the liver organoid cells must be arranged precisely in the 3-dimensional space, closely mimicking in vivo liver tissue. Moreover, for long term functioning, liver organoids must be appropriately vascularized and in contact with neighboring epithelial tissues (e.g., bile canaliculi and intrahepatic bile duct, or intrahepatic and extrahepatic bile ducts). Recent discoveries in liver developmental biology allows one to successfully induce liver component cells and generate organoids. Thus, here, in this review, we summarize the current state of knowledge on liver development with a focus on its application in generating different liver organoids. We also cover the future prospects in creating (functionally and structurally) in vivo-like liver organoids using the current knowledge on liver development.

Biliary Atresia Animal Models: Is the Needle in a Haystack?

Biliary atresia (BA) is a progressive fibro-obliterative process with a variable degree of inflammation involving the hepatobiliary system. Its consequences are incalculable for the patients, the affected families, relatives, and the healthcare system. Scientific communities have identified a rate of about 1 case per 10,000-20,000 live births, but the percentage may be higher, considering the late diagnoses. The etiology is heterogeneous. BA, which is considered in half of the causes leading to orthotopic liver transplantation, occurs in primates and non-primates. To consolidate any model, (1) more transport and cell membrane studies are needed to identify the exact mechanism of noxa-related hepatotoxicity; (2) an online platform may be key to share data from pilot projects and new techniques; and (3) the introduction of differentially expressed genes may be useful in investigating the liver metabolism to target the most intricate bilio-toxic effects of pharmaceutical drugs and toxins. As a challenge, such methodologies are still limited to very few centers, making the identification of highly functional animal models like finding a "needle in a haystack". This review compiles models from the haystack and hopes that a combinatorial search will eventually be the root for a successful pathway.