Targeting an anchored phosphatase-deacetylase unit restores renal ciliary homeostasis

Abstract

In the kidney, primary cilia projecting into the lumen of cells lining the inner medullary-collecting duct bend with urine flow to initiate intracellular signaling events. This mechano-sensory apparatus is defective in Polycystic Kidney Disease (PKD), inherited disorders that are characterized by the progressive formation of fluid-filled cysts in the kidney and end stage renal disease. Molecular defects include aberrant cAMP and calcium signaling, changes in apical actin, altered AQP2 trafficking and impaired formation of primary cilia. My studies as a rotation student in the Scott lab led to an intriguing discovery, that loss of the A-Kinase Anchoring protein AKAP220, correlates with increased cilia formation and altered cilia morphology. Using CRISPR-Cas9 gene editing to modify AKAP220 such that it does not anchor protein-phosphatase 1 (PP1), I found that this phosphatase plays an important role in cilia formation through its interaction with histone deacetylase 6 (HDAC6), the depolymerizer of primary cilia. Loss of AKAP220-anchored PP1 inactivates HDAC6 and this led to hyper ciliation. Further, proximity ligation assays showed that HDAC6 also interacts with AKAP220 and cycloheximide-chase degradation assays show that the anchoring protein dictates the stability of the deacetylase. Thus, drug-induced inactivation of HDAC6 restores control over ciliogenesis. Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder associated with abnormal cytoskeletal dynamics in the kidney collecting ducts and perturbed calcium and cAMP signaling in the ciliary compartment. Pharmacological blocking of local HDAC6 activity alters cilia development and reduces cystogenesis in kidney-on-chip and organoid models of ADPKD. These findings identify the AKAP220-PPI-HDAC6 pathway as a therapeutic target for ADPKD.