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Abstract: TH-PO804

Podocyte Development/Function Depends on Primary Cilia and the Exocyst

Session Information

Category: Glomerular Diseases

  • 1201 Glomerular Diseases: Fibrosis and Extracellular Matrix

Authors

  • Solanki, Ashish K., Medical University of South Carolina, Charleston, South Carolina, United States
  • Arif, Ehtesham, Medical University of South Carolina, Charleston, South Carolina, United States
  • Sampson, Matt G., University of Michigan, Ann Arbor, Michigan, United States
  • Nihalani, Deepak, Medical University of South Carolina, Charleston, South Carolina, United States
  • Lipschutz, Joshua H., Medical University of South Carolina, Charleston, South Carolina, United States
Background

Diseases affecting podocytes are leading causes of ESRD. Until recently, podocytes were thought not to have primary cilia, as cilia are not seen on adult podocytes; however, primary cilia were reported on developing podocytes in 2010. In 2014, a mutation in ciliary protein IFT139 was found in patients with FSGS, suggesting cilia involvement in GN. Our mRNA profiling of injured podocytes showed downregulation of the highly-conserved 8 protein exocyst trafficking complex. We previously showed that the exocyst is necessary for ciliogenesis in kidney tubule cells, zebrafish, and mice. Exocyst members were also mutated in families with ciliopathies affecting the kidney. Thus, we hypothesized that the exocyst is critical for podocyte development/function.

Methods

We generated podocyte-specific Exoc5 knockout (KO) mice, by crossing Podocin-Cre and Exoc5 fl/fl mice, and studied patients in the Nephrotic Syndrome Study Network (NEPTUNE).

Results

Podocyte-specific Exoc5 KO mice showed massive proteinuria and died within 5 weeks of birth. Importantly, isolated glomeruli stained with acetylated alpha tubulin showed primary cilia in wild-type, but not Exoc5 KO, mouse glomeruli. Histological analysis showed severe defects with increased fibrosis, proteinaceous casts, effaced podocytes, and slit diaphragm loss in Exoc5 KO mice; while IF showed significant mislocalization of slit diaphragm proteins Neph1 and Nephrin. Podocyte-specific Exoc5 KO mice phenocopied Cdc42, an exocyst regulator, KO mice reported by others. Mapping and Western blot analyses showed upregulation of canonical and non-canonical arms of the TGFβ pathway, including ERK and SMAD3 activation, in Exoc5 knockdown podocytes, and Exoc5 KO glomeruli. We next examined copy number variation (CNV) data derived from genome-wide SNP arrays from 256 patients with nephrotic syndrome enrolled in NEPTUNE. This dataset identified CNV that were greater than 100kb, overlapped a gene, and were ultra-rare or absent in control populations. Within, we identified two patients with qualifying CNV affecting exocyst component, EXOC4: a male toddler of Asian ancestry with steroid resistant minimal change, and an African-American female in her third decade with collapsing FSGS.

Conclusion

Our data implicate exocyst-based ciliogenic mechanisms in podocyte development/function, and suggest a novel target for intervention.

Funding

  • NIDDK Support