Functional insights into P4-ATPases in liver cells in vivo and in vitro

P4-ATPases are essential membrane proteins that establish and maintain phospholipid asymmetry in cellular membranes, a process critical for membrane integrity, signal transduction, vesicle trafficking, and the clearance of apoptotic cells. Disruption of this asymmetry compromises membrane function and contributes to various pathological conditions, including bleeding disorders, autoimmune diseases, and neurological dysfunctions. This thesis presents a comprehensive investigation into the expression patterns and physiological roles of multiple P4-ATPases in human and mouse tissues.
Expression profiling of fourteen P4-ATPases revealed that ATP8B1, ATP9A, ATP9B, ATP11A, and ATP11C exhibit moderate-to-high expression in the liver of both species, supporting the use of mice as relevant models for functional studies. Additionally, ATP8A1 and ATP8A2 were predominantly expressed in the brain, correlating with the neurological deficits seen in ATP8A2-deficient mice. These patterns suggest tissue-specific roles for P4-ATPases in maintaining cellular function.
Functional studies in ATP11C-deficient mice showed impaired hepatic uptake of unconjugated bile salts due to mislocalization of key transporters such as OATP1B2, while conjugated bile salt transport remained intact. Loss of CDC50A, likely due to proteasomal degradation, was partially rescued by proteasome inhibition. Comparisons with ATP8B1-deficient mice revealed both shared and unique liver phenotypes.
Furthermore, ATP9A knockdown in HepG2, THP-1, and MCF-7 cells led to increased exosome release and changes in actin-regulating proteins, implicating ATP9A in vesicle biogenesis and cytoskeletal dynamics.
These findings emphasize the diverse and critical roles of P4-ATPases in organ-specific functions and their broader significance in liver physiology, immune regulation, and cellular communication.