Kidney Week

Abstract: FR-PO625

Loss of ARL13B's Guanine Nucleotide Exchange Factor Activity for ARL3 in Cilia Suppresses Cystogenesis in Adult Mouse Models of Polycystic Kidney Disease

Session Information

• Cystic Kidney Diseases: Mechanisms and Models
  October 25, 2024 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Genetic Diseases of the Kidneys

• 1201 Genetic Diseases of the Kidneys: Cystic

Authors

• Van Sciver, Robert E., Emory University School of Medicine, Atlanta, Georgia, United States

Robert E. Van Sciver, PhD

• Forster, Avery, Emory University School of Medicine, Atlanta, Georgia, United States

Avery Forster

• Caspary, Tamara, Emory University School of Medicine, Atlanta, Georgia, United States

Tamara Caspary, PhD

Background

Polycystic kidney disease (PKD) is largely driven by mutations in PKD1 or PKD2, which encode for ciliary polycystin proteins. Mouse models predict the presence of a cilia-dependent cyst activating (CDCA) pathway that functions in cilia to drive PKD cystogenesis. This CDCA pathway is normally inhibited by the polycystin proteins, yet the identity of this pro-cystic pathway remains unknown. ARL13B is an atypical ciliary GTPase which also possesses guanine nucleotide exchange factor (GEF) activity for another ARL family GTPase, ARL3. Recent work revealed a central role of ARL13B’s cilia localization in cystogenesis, yet its role in the CDCA pathway is unknown.

Methods

To directly test ARL13B’s role in the CDCA pathway, we engineered two distinct Arl13b mutant alleles at the endogenous locus in mice: (1) Arl13b^V358A, which mutates a single amino acid in ARL13B’s cilia-localization motif; and (2) Arl13b^R79Q, which prevents its GEF activity for ARL3. ARL13B^V358A retains all known ARL13B biochemical functions, is stably expressed yet is undetectable in cilia. ARL13B^R79Q localizes to cilia, retains its GTPase activity, yet cannot activate ARL3. Combining these alleles with the kidney-specific loss Pkd1 allowed us to directly test ARL13B’s ciliary and enzymatic roles in kidney cystogenesis in vivo.

Results

At 18-weeks, control mouse kidneys had a kidney weight to body weight ratio (KW:BW) of 1.39±0.04. In adult induction models, loss of Pkd1 alone led to severe cystic kidneys with KW:BW of 11.98±0.99. Ciliary exclusion of ARL13B (V358A), total loss of its GEF activity for ARL3 (R79Q), or loss of its GEF activity, specifically in cilia (V358A/R79Q) suppressed the cystic phenotype caused by loss of Pkd1 alone with KW:BW of 2.47±0.36 and 4.09±0.78, 3.75±0.70, respectively.

Conclusion

In PKD mouse models, loss of ARL13B from cilia, its GEF activity for ARL3 everywhere, or its GEF activity specifically in cilia suppressed the severe cystic kidney phenotype caused by loss of Pkd1 alone. These results suggest that the ARL13B–ARL3 axis are major components of the CDCA pathway. Our findings indicate that ARL13B activates a pro-cystogenic pathway via its GEF activity for ARL3 in cilia, providing a mechanism that could be targeted therapeutically.

Funding

• NIDDK Support