Atp8b1, encoding FIC1, is a P4-ATPase phospholipid flippase. It's crucial for maintaining phospholipid asymmetry in biological membranes, which is essential for membrane protein targeting, vesicle biogenesis, and barrier function [3,5]. It's involved in multiple pathways such as lysosomal fusion in macrophages, and has potential connections to diseases like cholestasis [4,5]. Genetic models, like knockout mice, have been valuable in studying its functions.

In intestinal epithelial cell-specific Atp8b1-knockout (Atp8b1IEC-KO) mice, loss of Atp8b1 leads to malabsorption of lysophosphatidylcholine (LPC), causing hepatic choline deficiency and progression to steatohepatitis by 4 weeks. However, choline-supplemented diets can reverse this condition, indicating Atp8b1 regulates hepatic choline levels via intestinal LPC absorption [1]. In pancreatic acinar cells, during chronic pancreatitis development in PRSS1 transgenic mice, decreased Atp8b1 expression was observed. Atp8b1 complementation increased LPC concentration and improved disease outcomes, suggesting the acinar Atp8b1/LPC pathway has a protective role [2].

In conclusion, Atp8b1 plays essential roles in maintaining membrane phospholipid asymmetry and is involved in processes like lysosomal fusion, and regulation of hepatic choline levels. Gene-knockout mouse models have revealed its significance in diseases such as steatohepatitis and chronic pancreatitis, providing insights into potential therapeutic strategies for these conditions.

References:

1. Tamura, Ryutaro, Sabu, Yusuke, Mizuno, Tadahaya, Ando, Tomohiro, Hayashi, Hisamitsu. 2023. Intestinal Atp8b1 dysfunction causes hepatic choline deficiency and steatohepatitis. In Nature communications, 14, 6763. doi:10.1038/s41467-023-42424-x. https://pubmed.ncbi.nlm.nih.gov/37990006/

2. Yang, Wan-Jun, Cao, Rong-Chang, Xiao, Wang, Jin, Jin, Zhang, Guo-Wei. 2022. Acinar ATP8b1/LPC pathway promotes macrophage efferocytosis and clearance of inflammation during chronic pancreatitis development. In Cell death & disease, 13, 893. doi:10.1038/s41419-022-05322-6. https://pubmed.ncbi.nlm.nih.gov/36273194/

3. Dieudonné, Thibaud, Kümmerer, Felix, Laursen, Michelle Juknaviciute, Lindorff-Larsen, Kresten, Nissen, Poul. 2023. Activation and substrate specificity of the human P4-ATPase ATP8B1. In Nature communications, 14, 7492. doi:10.1038/s41467-023-42828-9. https://pubmed.ncbi.nlm.nih.gov/37980352/

4. Bull, Laura N, Thompson, Richard J. 2018. Progressive Familial Intrahepatic Cholestasis. In Clinics in liver disease, 22, 657-669. doi:10.1016/j.cld.2018.06.003. https://pubmed.ncbi.nlm.nih.gov/30266155/

5. Gómez-Mellado, Valentina E, Ho-Mok, Kam S, van der Mark, Vincent A, Elferink, Ronald P J Oude, Paulusma, Coen C. 2022. The phospholipid flippase ATP8B1 is required for lysosomal fusion in macrophages. In Cell biochemistry and function, 40, 914-925. doi:10.1002/cbf.3752. https://pubmed.ncbi.nlm.nih.gov/36169099/