Genetic reduction of cilium length by targeting intraflagellar transport 88 protein impedes kidney and liver cyst formation in mouse models of autosomal polycystic kidney disease.

Polycystin-1 (PC1) and -2 (PC2), products of the PKD1 and PKD2 genes, are mutated in autosomal dominant polycystic kidney disease (ADPKD). They localize to the primary cilia; however, their ciliary function is in dispute. Loss of either the primary cilia or PC1 or PC2 causes cyst formation. However, loss of both cilia and PC1 or PC2 inhibits cyst growth via an unknown pathway. To help define a pathway, we studied cilium length in human and mouse kidneys. We found cilia are elongated in kidneys from patients with ADPKD and from both Pkd1 and Pkd2 knockout mice. Cilia elongate following polycystin inactivation. The role of intraflagellar transport proteins in Pkd1-deficient mice is also unknown. We found that inactivation of Ift88 (a gene expressing a core component of intraflagellar transport) in Pkd1 knockout mice, as well as in a new Pkd2 knockout mouse, shortened the elongated cilia, impeded kidney and liver cystogenesis, and reduced cell proliferation. Multi-stage in vivo analysis of signaling pathways revealed ß-catenin activation as a prominent, early, and sustained event in disease onset and progression in Pkd2 single knockout but not in Pkd2.Ift88 double knockout mouse kidneys. Additionally, AMPK, mTOR and ERK pathways were altered in Pkd2 single knockout mice but only AMPK and mTOR pathway alteration were rescued in Pkd2.Ift88 double knockout mice. Thus, our findings advocate an essential role of polycystins in the structure and function of the primary cilia and implicate ß-catenin as a key inducer of cystogenesis downstream of the primary cilia. Our data suggest that modulating cilium length and/or its associated signaling events may offer novel therapeutic approaches for ADPKD.

TGF-ß-activated kinase 1 is crucial in podocyte differentiation and glomerular capillary formation.

TGF-ß-activated kinase 1 (TAK1) is a key intermediate in signal transduction induced by TGF-ß or inflammatory cytokines, such as TNF-α and IL-1, which are potent inducers of podocyte injury responses that lead to proteinuria and glomerulosclerosis. Nevertheless, little is known about the physiologic and pathologic roles of TAK1 in podocytes. To examine the in vivo role of TAK1, we generated podocyte-specific Tak1 knockout mice (Nphs2-Cre(+):Tak1(fx/fx); Tak1(∆/∆)). Targeted deletion of Tak1 in podocytes resulted in perinatal lethality, with approximately 50% of animals dying soon after birth and 90% of animals dying within 1 week of birth. Tak1(∆/∆) mice developed proteinuria from P1 and exhibited delayed glomerulogenesis and reduced expression of Wilms' tumor suppressor 1 and nephrin in podocytes. Compared with Tak1(fx/fx) mice, Tak1(∆/∆) mice exhibited impaired formation of podocyte foot processes that caused disruption of the podocyte architecture with prominent foot process effacement. Intriguingly, Tak1(∆/∆) mice displayed increased expression of vascular endothelial growth factor within the glomerulus and abnormally enlarged glomerular capillaries. Furthermore, 4- and 7-week-old Tak1(∆/∆) mice with proteinuria had increased collagen deposition in the mesangium and the adjacent tubulointerstitial area. Thus, loss of Tak1 in podocytes is associated with the development of proteinuria and glomerulosclerosis. Taken together, our data show that TAK1 regulates the expression of Wilms' tumor suppressor 1, nephrin, and vascular endothelial growth factor and that TAK1 signaling has a crucial role in podocyte differentiation and attainment of normal glomerular microvasculature during kidney development and glomerular filtration barrier homeostasis.

Pyrimethamine inhibits adult polycystic kidney disease by modulating STAT signaling pathways.

Autosomal dominant polycystic kidney disease (ADPKD) is a commonly inherited disorder mostly caused by mutations in PKD1, encoding polycystin-1 (PC1). The disease is characterized by development and growth of epithelium-lined cyst in both kidneys, often leading to renal failure. There is no specific treatment for this disease. Here, we report a sustained activation of the transcription factor signal transducer and activator of transcription 3 (STAT3) in ischemic injured and uninjured Pkd1 knockout polycystic kidneys and in human ADPKD kidneys. Through a chemical library screen, we identified the anti-parasitic compound pyrimethamine as an inhibitor of STAT3 function. Treatment with pyrimethamine decreases cell proliferation in human ADPKD cells and blocks renal cyst formation in an adult and a neonatal PKD mouse model. Moreover, we demonstrated that a specific STAT3 inhibitor, S3I-201, reduces cyst formation and growth in a neonatal PKD mouse model. Our results suggest that PC1 acts as a negative regulator of STAT3 and that blocking STAT3 signaling with pyrimethamine or similar drugs may be an attractive therapy for human ADPKD.

SK2 channels are required for function and long-term survival of efferent synapses on mammalian outer hair cells.

Cochlear hair cells use SK2 currents to shape responses to cholinergic efferent feedback from the brain. Using SK2(-/-) mice, we demonstrate that, in addition to their previously defined role in modulating hair cell membrane potentials, SK2 channels are necessary for long-term survival of olivocochlear fibers and synapses. Loss of the SK2 gene also results in loss of electrically driven olivocochlear effects in vivo, and down regulation of ryanodine receptors involved in calcium-induced calcium release, the main inducer of nAChR evoked SK2 activity. Generation of double-null mice lacking both the alpha10 nAChR gene, loss of which results in hypertrophied olivocochlear terminals, and the SK2 gene, recapitulates the SK2(-/-) synaptic phenotype and gene expression, and also leads to down regulation of alpha9 nAChR gene expression. The data suggest a hierarchy of activity necessary to maintain early olivocochlear synapses at their targets, with SK2 serving an epistatic, upstream, role to the nAChRs.