Cystic Development in Ift140 Knockout Mice Depends on Knockout Timing

Background: Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease, causing kidney failure, and is primarily caused by mutations in PKD1 (~81%) or PKD2 (~13%), however, >8 minor genes, including IFT140, have been identified. The ADPKD-IFT140 phenotype is distinct, featuring a lower number of large cysts. IFT140, an intraflagellar transport protein, is critical for the generation and function of primary cilia, but the monoallelic cystic disease pathomechanisms are unclear. Methods: We employed an inducible conditional mouse model (Ift140flox/flox;Pax8-rtTA;(tetO)7-Cre) to achieve kidney tubule-specific Ift140 knockout (KO) at different stages. Doxycycline treatment (Ift140 KO) via food was introduced to pregnant or nursing dams at embryonic day (E) 14.5 and 16.5, or postnatal day (P) 1, and 7. To monitor PKD severity/progression, MRI and total kidney volume (TKV) were assessed at 1, 3, and 6 months (m) in living animals, and histological and kidney function analyses performed post-sacrifice. Results: TKV was significantly increased at 1m in E14.5 and E16.5-induced mice (Fig. 1), but P1 and P7-induced mice were unaffected. The degree of cystic severity at 1m differed greatly between the E14.5 and E16.5 groups, showing a steep decline from E14.5 to E16.5. Furthermore, P1 and P7-induced mice did not develop cysts up to 6m. However, E14.5-induced mice had severe disease, with lethality by 1m, whereas E16.5 mice, with milder disease, survived beyond 3m in some cases. Conclusion: The timing of Ift140 removal greatly influenced the rate of cyst development in mice between E14.5 and E16.5, while no cysts formed at or after P1. This dramatically contrasts with the later kidney development switch point between severe and mild PKD for Pkd1 (~P13). This raises questions about when embryonic reduction of IFT140 in ADPKD-IFT140 may be critical for cyst development and how this contrasts with ADPKD-PKD1. To further elucidate IFT140 pathomechanisms, we will analyze ciliary protein trafficking and structure at different time points. Funding: NIDDK Support