A liver-specific mouse model for MYO5B-associated cholestasis reveals a toxic gain-of-function as underlying disease mechanism.

Myosin Vb (MYO5B) deficiency, referring to the loss of protein expression or function, causes microvillus inclusion disease (MVID) and/or progressive familial intrahepatic cholestasis-type 10 (PFIC10) in humans. MYO5B plays a role in intracellular trafficking, but the mechanisms by which it contributes to cholestasis are not understood. The aim of this study was to generate a liver-specific mouse model and investigate the mechanism of MYO5B-associated cholestasis. In this study, we generated a liver-specific Myo5b cKO mice via CRISPR/Cas9 genome editing in conjunction with albumin-cre recombinase. Cholestatic stress was induced by dietary-administration of cholic acid (CA) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). To investigate the frequently recurring MYO5B variant (c.2470C > T/p.(Arg824Cys)), adenoviral vectors encoding either the missense variant or blank control sequence were delivered to wild-type and Myo5b cKO mice through tail-vein injection. Serum and liver tissues were harvested from all mice for biochemical and histological analysis. Our findings indicated that loss of Myo5b expression did not cause cholestatic liver disease and did not augment CA or DDC feeding-induced cholestatic stress. By contrast, expression of the MYO5B c.2470C > T/p. (Arg824Cys) variant induced cholestasis, evidenced by elevated levels of serum alanine aminotransferase, alkaline phosphatase and bilirubin, mild hepatocellular injury, and altered bile salt export pump (Bsep) localization, resembling that observed in human PFIC10. In summary, we have developed a mouse model of MYO5B-associated cholestasis. The expression of the MYO5B-p. (Arg824Cys) variant but not the loss of Myo5b expression caused cholestasis, indicating a toxic gain-of-function as underlying disease mechanism.