PI Bar Ilan University, Faculty of Life Science Jerusalem, United States
Abstract: Variants in the WDR19 gene, encoding IFT144 - a critical component of the intraflagellar transport (IFT) complex A - are associated with renal cystic ciliopathies, a prevalent genetic cause of chronic kidney disease (CKD). In the Arab Druze population, a newly identified hypomorphic WDR19 homozygous missense variant (c.878G>A; p.Cys293Tyr) is the most common genetic mutation associated with kidney failure. To validate the pathogenicity of this hypomorphic variant and explore the molecular mechanisms underlying its effects, we investigated the impact of this mutation on the kidney using kidney organoids derived from CRISPR-Cas9-edited human embryonic stem cells and patient-derived induced pluripotent stem cells (iPSCs). Our findings demonstrate that the WDR19 mutation impairs nephron differentiation from early developmental stages, leading to delayed renal vesicle formation and cystogenesis. At the molecular level, the hypomorphic mutation results in increased activation of the Sonic Hedgehog (Shh) pathway. Notably, elevated Shh signaling was observed even in cells harboring severe nonsense mutations with near-total ciliation absence. This activation correlated with significant downregulation of Fibroblast Growth Factor 8 (FGF8) and transcriptomic alterations in associated pathways, suggesting a potential inverse relationship between these signaling pathways during kidney organoid development. In contrast to the kidney organoids, cerebral organoids derived from the same hPSC lines exhibited no abnormalities, indicating tissue-specific effects of the mutation. Our study validates the pathogenic role of the WDR19 hypomorphic mutation in adult-onset, non-syndromic renal failure and highlights how hypomorphic pathogenic variants disrupt kidney development. These findings emphasize the essential role of cilia in renal development and provide deeper insights into the mechanisms underlying renal ciliopathies. From a broader perspective, our results demonstrate the utility of hPSC-derived kidney organoids as a robust platform for validating the effects of novel candidate pathogenic variants and for investigating adult-onset kidney disorders.
