Endocrine Abstracts

Primary cilia are microtubule-based organelles that protrude from cell membranes to mediate diverse developmental signalling pathways and senses extracellular stimuli to maintain tissue homeostasis. We show that glucocorticoid (GC) signalling via the glucocorticoid receptor (GR) regulates normal primary cilia formation in the renal tubule. RNA sequencing of E18.5 fetal kidney from GR-null mice compared to wild-type controls identified reduced mRNA levels of key ciliogenesis-associated genes. Real-time-qPCR analysis confirmed reduced mRNA levels for the cilia-associated proteins Ccp110 (fold -2.18), Cep97 (fold -1.78), Cep290 (fold -2.91), Kif3a (fold -1.82) and Rpgr (fold -1.90). Confocal microscopy showed abnormal, stunted primary cilia in renal proximal tubules, collecting ducts and podocytes in GR-null or in renal tubule conditional GR-deleted mice, created using the HoxB7 Cre-driver allele. Primary cilia length was decreased in kidney proximal tubule cells in GR-null mice (5.01 ± 0.11μm) compared with wildtype controls (6.20 ± 0.15μm). Scanning electron microscopy of E18.5 GR-null kidney showed aberrant primary cilia morphology in the proximal renal tubules. Activation of GR signalling with dexamethasone in cultured mouse IMCD3 and human HK2 kidney proximal tubule cells increased primary cilia length (IMCD3; 2.89 ± 0.04μm) compared to controls (2.46 ± 0.28μm), an effect blocked by the GR antagonist RU486 (vehicle + RU486: 2.06 ± 0.02μm, dexamethasone + RU486: 2.00 ± 0.02μm). Aurora kinase A (AURKA) is a known regulator of primary ciliogenesis in-part via the AKT cell signalling pathway. AURKA protein levels were downregulated in GR-null kidney and in DEX-treated IMCD3 cells which suggest the GR both positively and negatively regulates AURKA levels to control the assembly and disassembly of primary cilia. Together, these results demonstrate that GC signalling via the GR is required for normal primary ciliogenesis in the developing kidney and suggests that synthetic GR agonists may provide a novel therapy for human ciliopathies such as those observed in polycystic kidney disease.