Role of primary cilia-mediated signaling in human and mouse models of Autosomal Dominant Polycystic Kidney Disease

Abstract

Primary cilia are non-motile microtubule-based organelles that extend from the apical plasma membrane of most vertebrate cells and mediate signaling pathways. Mutations in ciliary genes often result in renal cyst formation, yet, the mechanisms connecting primary cilia dysfunction to renal cystogenesis are unclear. To address this gap, I have examined the role of ciliary-mediated Hedgehog (Hh) signaling in human and mouse models of the most common renal cystic disease, Autosomal Dominant Polycystic Kidney Disease (ADPKD), and have investigated initiating mechanisms of renal cystogenesis in a ciliary mouse model, Thm1 conditional knock-out (cko) mice. Here, I show that human ADPKD renal tissue has increased Hh activator, GLI1, in the nuclei of interstitial and cyst-lining epithelial cells, indicating increased paracrine and autocrine Hh activity, respectively. Further, Hh inhibitors reduced cell proliferation and microcyst formation of ADPKD primary cells, suggesting a functional role for increased Hh signaling in human ADPKD. To extend these investigations to mouse models, I downregulated Hh signaling genetically in jck, Pkd1 and Pkd2 cko mice on mixed strain backgrounds and found a trend toward reduced kidney weight/body weight ratios in jck and Pkd1 cko mice, suggesting increased Hh signaling has a role in renal cystogenesis in vivo. Finally, to investigate initiating mechanisms of renal cystogenesis in Thm1 cko mice, RNA sequencing was performed on whole kidney extracts, which revealed approximately 10 genes that are upregulated in both pre-cystic and cystic kidneys. Collectively, these genes are typically expressed by renal epithelial cells, endothelial cells and immune cells, suggesting misregulation of genes and pathways in all three compartments may potentiate Thm1 cko renal cystogenesis. Of these 10 molecules, STAT3 appears most prominently activated and present in epithelia of non-dilated, dilated and cystic tubules and in the interstitium. Interestingly, IL6 cytokine-treated THM1 knock-down 293T human renal cells showed a more robust second wave of STAT3 activation that is preceded by enhanced ERK activation, suggesting that THM1 regulates STAT3 and ERK signaling. Together, these data are the first to suggest increased Hh signaling has a role in ADPKD disease progression and increased STAT3 signaling has a role in disease initiation in a ciliary mouse model. Hh and STAT3 inhibitors are FDA-approved, and therefore, these pharmaceutical therapies may potentially be repurposed to treat ADPKD