Roles of IFT-A paralogs, Thm1 and Thm2, in the pathogenesis of ciliopathies

Abstract

Primary cilia are antenna-like sensory organelles that extend from the apical surface of most vertebrate cells. Mutation of ciliary genes results in ciliopathies, which commonly manifest renal and hepatic cystic diseases, via mechanisms that remain unclear. To address this knowledge gap, I investigated the role of the intraflagellar transport-A (IFT-A) gene, Thm1, in the polycystic kidney disease (PKD) and polycystic liver disease (PLD) of juvenile and adult Autosomal Dominant PKD (ADPKD) mouse models, caused by conditional deletion of Pkd2. Thm1 deletion in juvenile Pkd2 conditional knock-out (cko) mice both ameliorated and exacerbated different aspects of PKD in a renal tubular-specific manner, while Thm1 deletion in an adult Pkd2 cko mouse, markedly attenuated virtually all facets of PKD renal cystogenesis. Further, while perinatal deletion of Thm1 alone caused a non-cystic liver phenotype – a ductular reaction, characterized by abnormal proliferation of cholangiocytes and biliary fibrosis, Thm1 deletion in juvenile Pkd2 cko mice exacerbated liver enlargement and necrosis of the PLD. In contrast, Thm1 deletion in adult Pkd2 cko mice attenuated liver enlargement of the PLD in male mice. These data suggest that differential factors between cell types and between developing versus mature renal and hepatic microenvironments influence cilia dysfunction and ADPKD pathobiology. Additionally, using mouse embryonic fibroblasts (MEF), I explored the roles of Thm1 and its paralog, Thm2, in cilia homeostatic processes and signaling. Analyses of Thm1, Thm2, and Thm1;Thm2-mutant MEF and embryos reveal that Thm1 and Thm2 interact to regulate serum-induced cilia loss, ciliary import of membrane-associated proteins, Hedgehog signaling, and embryogenesis. Taken together, this dissertation reveals novel physiological and mechanistic roles for IFT-A in healthy and diseased states, laying groundwork for the design of future therapeutic strategies against ciliopathies, such as ADPKD.