Investigation of common disease mechanisms in nonsyndromic and syndromic PKD

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Polycystic kidney diseases (PKD) are a group of disorders associated with defects in primary cilia and often causing end stage kidney disease. They can be divided into disorders mainly involving just kidney and liver, nonsyndromic PKDs (NS-PKDs), and ones involving other organ systems, including the brain, skeleton, and sensory organs, syndromic PKDs (S-PKDs). Autosomal recessive PKD (ARPKD; PKHD1) is the main recessively inherited NS-PKD, whereas S-PKDs are a group of diverse, mainly recessive diseases, including: Meckel [MKS], Joubert syndrome [JBTS]; and short rib thoracic dysplasia (SRTD), with up to 80 different genes involved. S-PKDs have marked genetic complexity, for instance the gene, TMEM67, is associated with several different disorders, and although the underlying reason for the varied phenotypes is not well understood, allelic effects may be important. In addition, it is becoming clear that heterozygous carriers of recessive PKHD1 alleles can have a mild cystic kidney/liver phenotype, similar to very mild autosomal dominant PKD (ADPKD). We have recently found that IFT140, an S-PKD gene encoding an intraflagella transport protein (IFT140) that is required to generate a fully functional cilium, also has a heterozygous phenotype of mild kidney cyst development. The goal of this grant is to better understand the genetic complexity associated with recessive (and sometimes dominant) PKD, with the premise that understanding the effects of gene loss and reduction (gene dosage), including the role of allelic effects, will improve our understanding of the etiology and pathogenesis of PKDs. Aim 1, Mutation screen a PKD positive and PKD unknown population to identify the role of “recessive” PKD alleles to the etiology of S-PKD and NS-PKD, will conduct mutation screening using next generation sequencing methods. A PKD cohort and a population of individuals not known to have PKD (Mayo Clinic Biobank; n=53,220) will be screened to determine the etiology of the PKD population and evaluate the role of single “recessive” PKD alleles to manifest as mild cystic disease. Aim 2, Develop cell-based assays to evaluate NS-PKD (PKHD1) and S-PKD (TMEM67) alleles, will establish in vitro systems to determine the pathogenicity of variants of unknown significance (VUS) in an NS-PKD gene, PKHD1, and an S-PKD gene, TMEM67. Trafficking, maturation, and ciliary localization of products of these genes will be determined. Aim 3, Explore the disease mechanism of IFT140 pathogenic alleles, will generate animal models to better understand disease pathogenesis. Both conditional and hypomorphic allele approaches will be employed to generate viable models and characterize the renal and extrarenal phenotypes. Aim 4, Determine ciliary defects and genetic interactions associated with NS-PKD and S-PKD genes, will monitor ciliary trafficking and composition in cells from NS-PKD and S-PKD models, and explore genetic interactions between these genes. Overall, these studies will provide diagnosis, prognostic and mechanistic data, important steps toward developing novel therapeutics for this group of devastating diseases.