Enigmatic functions of ATP8B1: cholestasis, inflammation, phosphoinositide flipping, and cellular homeostasis.

Mutations in ATP8B1 cause a spectrum of cholestatic liver disease, ranging from Progressive-Familial-Intrahepatic-Cholestasis type-1 (PFIC1) to Benign-Recurrent-Intrahepatic-Cholestasis type-1 (BRIC1). Manifestations of PFIC1 include severe pruritus, jaundice, and liver damage. Extrahepatic features sometimes observed in PFIC1 include sensorineural hearing loss, diarrhea, pancreatitis, and short stature. ATP8B1 was shown to translocate phospholipids across the plasma membrane; however, expression of ATP8B1 in many tissues and the range of pathological manifestations in ATP8B1 deficiency suggest diverse physiological functions of ATP8B1, and pleiotropic mechanisms regulating its activity. Recent studies suggest that phosphoinositides, including PIP2 and PIP3, can function as regulators, substrates, and binding partners of ATP8B1. New research shows that ATP8B1 modulates host immune system by regulating cleavage of pyroptotic-executioner Gasdermin D (GSDMD), and inflammation-resolution pathways such as phagocytosis/efferocytosis. Further mechanistic insights can accelerate development of new therapies for restoring membrane integrity, reducing inflammasome activity, and correcting metabolic imbalances caused by ATP8B1 dysfunction.