Abstract
BACKGROUND: Hereditary intrahepatic cholestasis is caused by variants of various genes involved in enterohepatic bile circulation, metabolization, and conjugation. Originally classified into 3 groups, the number of contributing genes is still increasing, underlining the need for a deeper understanding of the molecular interaction during intrahepatic cholestasis. METHODS: In the present study, we investigate the interplay of heterozygous variants in 3 cholestasis-associated genes (ABCB11, ABCB4, and MYO5B) by exploiting iPSC-based hepatic organoids from a patient suffering from recurrent intrahepatic cholestasis. RESULTS: Functional characterization of MRP2-mediated cholyl-lysyl-fluorescein (CLF) and BSEP-mediated Tauro-nor-THCA-24-DBD transport demonstrated a marked reduction of transport in MYO5B-deficient organoids, in comparison to unaffected control organoids. Moreover, iPSC-based organoids derived from the patient carrying 3 heterozygous variants in ABCB11, ABCB4, and MYO5B also exhibited absence of BSEP-mediated Tauro-nor-THCA-24-DBD transport, but functional MRP2-mediated CLF-transport. Interestingly, CRISPR/Cas9-mediated correction of the mutated ABCB11 allele could not restore the impaired BSEP function, suggesting the heterozygous MYO5B variant as the main driver of the transport deficiency. In fact, CRISPR/Cas-mediated correction of the MYO5B variant finally resulted in a restoration of the BSEP-mediated Tauro-nor-THCA-24-DBD transport. CONCLUSIONS: iPSC-based organoids serve as an authentic model for functional assessment of the hepatobiliary transport with fluorescent substrates. This allows the characterization of variants of uncertain significance and other variants in cholestasis-associated genes and revealed that a heterozygous MYO5B variant increases the susceptibility to defective hepatobiliary BSEP-mediated transport.