Seth, A.; Brancale, J.; Dashti-Gibson, N.; Florentino, R. M.; Faccioli, L. A. P.; Liu, Z.; Konkwo, C.; Hong, H.; Soto-Gutierrez, A.; Vilarinho, S.

Pathogenic variants in kinesin family member 12 (KIF12) cause pediatric liver disease, yet the cellular mechanisms underlying this phenotype remain unknown. Here we show that KIF12 expression in the healthy human liver is primarily detected in biliary epithelial cells, as revealed by single cell RNA-sequencing data. To investigate its role in biliary pathology, we introduced a homozygous KIF12 p.Arg219* mutation into induced pluripotent stem cells (iPSCs), which were differentiated into 2D cholangiocyte-like cells (iCCs) and 3D biliary organoids. Pioneering single-molecule fluorescence microscopy in live iCCs, we observed wildtype KIF12 co-localizing with microtubules, consistent with its predicted role as a microtubule-associated motor protein. Our data reveals that KIF12 dysfunction causes abnormal perinuclear clustering of mitochondria and lysosomes, and mislocalization of primary cilia in cholangiocytes. Restoration of wildtype KIF12 expression in mutant KIF12 iCCs rescued organelle positioning and normalized GGT activity. This study uncovers a novel link between KIF12 dysfunction and organelle dynamics in human cholangiocytes, extending our understanding of kinesin roles beyond their established functions in neuronal systems. Our findings provide new insights into the pathogenesis of KIF12-related cholestatic liver disease and lay the groundwork for developing targeted genetic therapies.