Bile acid metabolism and T cell responses in cholangiopathy: Not one-way traffic

BAAT away liver cancer: conjugated bile acids impair T cell function in hepatocellular carcinoma immunotherapy

In this renaissance era of gene therapy, a new study published by the Susan Kaech lab in Science demonstrates the use of CRISPR-Cas9 technology to selectively deplete conjugated bile acids in the liver by targeting the bile acid-CoA:amino acid N-acyltransferase (Baat) gene to improve responsiveness to immunotherapy. This study highlights the role of conjugated bile acids in impairing intratumoral T cell function by directly accumulating in resident liver T cells and driving mitochondrial dysfunction. Knockout of Baat reduced hepatic conjugated bile acid production, thus improving immunotherapy potency and reducing tumor burden. Subsequently, Baat liver knockout reduced levels of microbially produced secondary bile acids such as lithocholic acid, a known carcinogen and T cell toxin. This study mechanistically links bile acids to liver cancer immunotherapy success, setting the stage for bile acid-based screening approaches and pharmacologic manipulations for improved patient outcomes.

Liver-restricted deletion of the biliary atresia candidate gene Pkd1l1 causes bile duct dysmorphogenesis and ciliopathy

BACKGROUND AND AIMS

A recent multicenter genetic exploration of the biliary atresia splenic malformation syndrome identified mutations in the ciliary gene PKD1L1 as candidate etiologic contributors. We hypothesized that deletion of Pkd1l1 in developing hepatoblasts would lead to cholangiopathy in mice.

APPROACH AND RESULTS

CRISPR-based genome editing inserted loxP sites flanking exon 8 of the murine Pkd1l1 gene. Pkd1l1Fl/Fl cross-bred with alpha-fetoprotein-Cre expressing mice to generate a liver-specific intrahepatic Pkd1l1 -deficient model (LKO). From embryonic day 18 through week 30, control ( Fl/Fl ) and LKO mice were evaluated with standard serum chemistries and liver histology. At select ages, tissues were analyzed using RNA sequencing, immunofluorescence, and electron microscopy with a focus on biliary structures, peribiliary inflammation, and fibrosis. Bile duct ligation for 5 days of Fl/Fl and LKO mice was followed by standard serum and liver analytics. Histological analyses from perinatal ages revealed delayed biliary maturation and reduced primary cilia, with progressive cholangiocyte proliferation, peribiliary fibroinflammation, and arterial hypertrophy evident in 7- to 16-week-old LKO versus Fl/Fl livers. Following bile duct ligation, cholangiocyte proliferation, peribiliary fibroinflammation, and necrosis were increased in LKO compared with Fl/Fl livers.

CONCLUSIONS

Bile duct ligation of the Pkd1l1 -deficient mouse model mirrors several aspects of the intrahepatic pathophysiology of biliary atresia in humans including bile duct dysmorphogenesis, peribiliary fibroinflammation, hepatic arteriopathy, and ciliopathy. This first genetically linked model of biliary atresia, the Pkd1l1 LKO mouse, may allow researchers a means to develop a deeper understanding of the pathophysiology of this serious and perplexing disorder, including the opportunity to identify rational therapeutic targets.