# Lack of ANKMY2 suppresses kidney cystogenesis in embryonic- and adult-onset polycystic kidney disease

## TL;DR

This study shows that the protein ANKMY2 promotes kidney cyst formation in polycystic kidney disease by controlling ciliary cAMP signaling, offering new therapeutic insights.

## Contribution

The study identifies ANKMY2 as a novel regulator of ciliary adenylyl cyclase trafficking and cyst initiation in polycystic kidney disease.

## Key findings

- ANKMY2 deficiency suppresses cyst formation in both embryonic- and adult-onset mouse models of PKD.
- ANKMY2 controls ciliary trafficking of adenylyl cyclases without disrupting cilia structure.
- Ciliary elongation during cyst progression is ANKMY2-dependent, suggesting a role in early cystogenesis.

## Abstract

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive bilateral cyst formation. Multiple cellular pathways including second messenger cAMP signaling are dysregulated in ADPKD, but mechanisms initiating cysts are unknown. ADPKD is caused by mutations in PKD1/PKD2 genes encoding for polycystins that localize to primary cilia—nonmotile, microtubule-based dynamic compartments sensing extracellular chemical/mechanical signals. The compact cylindrical structure of cilia enables tunable signaling amplification regulatable by ciliary length. Severe cystogenesis from polycystin loss is cilia dependent and ciliary elongation is common in cystic epithelia. However, uncoupling the cilium-specific signals repressed by polycystins from downstream cystogenic pathways has proven challenging. Here we aim to understand roles of compartmentalized cAMP signaling in cystogenesis and ciliary length control. We investigated ANKMY2, an Ankyrin repeat MYND domain protein involved in maturation and ciliary localization of membrane adenylyl cyclases—enzymes generating cAMP. In kidney-specific Ankmy2/Pkd1 knockout mice, loss of ANKMY2 suppressed early postnatal cystogenesis and significantly extended survival in an embryonic-onset Pkd1 deletion model. Similarly, in an adult inducible Pkd1 knockout model, ANKMY2 deficiency reduced cyst burden. Mechanistically, ANKMY2 controlled the ciliary trafficking of multiple adenylyl cyclases in mouse and human kidney epithelial cells without disrupting cilia while retaining cellular pools. Ciliary elongation began in dilatated tubules of adult onset ADPKD mice and further increased in cystic kidneys. Both initial and progressive phases of cilia lengthening were ANKMY2-dependent. Our findings indicate that ciliary adenylyl cyclase signaling likely promotes cilia-dependent cyst initiation distinct from cyst progression involving cellular cAMP. Importantly, kidneys lacking ANKMY2 did not show ciliary elongation despite elevated cAMP, suggesting that cilia lengthening during cyst progression could be contingent upon pre-cystic ciliary regulation. These results suggest a critical role for compartmentalized adenylyl cyclase signaling in ADPKD pathogenesis and a framework for identifying ciliary effectors and early subcellular events in cystogenesis.

Abnormal formation of fluid sacs called cysts occurs in kidney nephrons in polycystic kidney disease (PKD). Increased cellular levels of the second messenger cAMP occurs in cysts. Current therapies are primarily designed to antagonize cAMP increase in cysts but are not fully effective in reducing cyst burden, highlighting the need to better understand the mechanisms underlying cyst initiation and progression. Polycystin channels, the major gene products affected in PKD, localize to primary cilia. Cilia are minute cellular compartments that effectively regulate cellular signaling. Cyst formation occurring from polycystin loss requires cilia, suggesting that polycystins normally inhibit cyst promoting signals within cilia. Identifying these cilia localized signals could reveal effective therapeutic targets. Here we studied an Ankyrin repeat and MYND domain protein, ANKMY2 that determines maturation and ciliary localization of adenylyl cyclases—enzymes generating cAMP. We found that loss of ANKMY2 suppresses cyst formation in both early postnatal and adult mouse models of PKD. Our results suggest that ANKMY2-dependent trafficking of adenylyl cyclases to cilia likely promotes compartmentalized ciliary adenylyl cyclase signaling, initiating cyst formation through a mechanism distinct from later cyst progression involving cellular cAMP levels. Targeting ciliary-specific adenylyl cyclase function could improve current therapies that reduce cellular cAMP levels.