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Abstract: PO1661

Segmental Expression of Nephrin in the Slit Diaphragm of a Patient with a Nonsense Mutation in NPHS1

Session Information

Category: Genetic Diseases of the Kidneys

  • 1002 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Unnersjö-Jess, David, Department II of Internal Medicine and Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Nordrhein-Westfalen, Germany
  • Butt, Linus, Department II of Internal Medicine and Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Nordrhein-Westfalen, Germany
  • Hieronymi, Lina, Department II of Internal Medicine and Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Nordrhein-Westfalen, Germany
  • Höhne, Martin, Department II of Internal Medicine and Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Nordrhein-Westfalen, Germany
  • Blom, Hans, Science for life Laboratory, Dept. of Applied Physics, Royal Institute of Technology, Solna, Stockholm, Sweden
  • Hoyer, Peter, Pediatric Nephrology, Pediatrics II, Univeristy of Duisburg-Essen, Cologne, Nordrhein-Westfalen, Germany
  • Schermer, Bernhard, Department II of Internal Medicine and Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Nordrhein-Westfalen, Germany
  • Benzing, Thomas, Department II of Internal Medicine and Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Nordrhein-Westfalen, Germany
Background

Nephrotic syndrome due to nonsense mutations in the NPHS1 gene typically presents with a severe congenital proteinuria. However, patients harboring nonsense mutations close to the carboxyl terminus of the NPHS1 encoded nephrin protein can present with a milder phenotype. In this study, we use high-resolution microscopy to investigate the expression pattern of nephrin p.1160X in a patient with such a mutation.

Methods

We used confocal and stimulated emission depletion (STED) microscopy to visualize the distribution of nephrin p.1160X at the glomerular filtration barrier and to study the correlation between nephrin expression and foot process morphology.

Results

Confocal microscopy revealed a highly heterogeneous expression pattern of nephrin p.1160X. While most glomerular capillaries showed absence of nephrin, there were sharply defined patches with almost normal levels (see figure). To clarify whether this unexpected pattern was due to sporadic re-expression of a wild-type nephrin, we used antibodies raised against the carboxyl terminus of nephrin which is lacking in the mutant protein. These data confirmed expression of nephrin p.1160X. Moreover, qPCR and cell culture experiments indicated normal levels of nephrin mRNA, but a decreased stability of p.1160X nephrin which could partly be rescued by inhibition of proteasomes.

Conclusion

We here show, that mutations in NPHS1 may result in heterogeneous expression patterns of the truncated protein. We also found a directly observable link between insertion of nephrin in the slit diaphragm and normal foot process morphology. Taken together, these data suggest potential therapeutic interventions targeting proteasomal degradation of nephrin as a novel treatment strategy in selected patients with congenital nephrotic syndrome.

Micrographs showing patches of nephrin p.1160X in glomerular capillaries. Severe foot process effacement is only present outside of these patches.

Funding

  • Government Support - Non-U.S.