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Abstract: FR-PO268

The Polycystin-1 C-Terminal Tail (CTT) Suppresses Cystic Disease: Elucidating the Underlying Mechanisms

Session Information

Category: Genetic Diseases of the Kidneys

  • 1101 Genetic Diseases of the Kidneys: Cystic

Authors

  • Onuchic, Laura, Yale School of Medicine, New Haven, Connecticut, United States
  • Padovano, Valeria, Yale School of Medicine, New Haven, Connecticut, United States
  • Schena, Giorgia, Yale School of Medicine, New Haven, Connecticut, United States
  • Rajendran, Vanathy, Yale School of Medicine, New Haven, Connecticut, United States
  • Shi, Xiaojian, Yale School of Medicine, New Haven, Connecticut, United States
  • Dong, Ke, Yale School of Medicine, New Haven, Connecticut, United States
  • Gresko, Nikolay P., Yale School of Medicine, New Haven, Connecticut, United States
  • Shen, Hongying, Yale School of Medicine, New Haven, Connecticut, United States
  • Somlo, Stefan, Yale School of Medicine, New Haven, Connecticut, United States
  • Caplan, Michael J., Yale School of Medicine, New Haven, Connecticut, United States
Background

Mutations in PKD1, which encodes polycystin-1, account for ~78% of autosomal dominant polycystic kidney disease (ADPKD) cases. We have previously shown that transgenic CTT expression in the Pkd1fl/fl;Pax8rtTA;TetO-Cre ADPKD mouse model suppresses cystic phenotype and preserves renal function. We have also shown that this suppression is dependent on an interaction between CTT and Nicotinamide Nucleotide Transhydrogenase (NNT). NNT is a mitochondrial enzyme that modulates NAD(P)(H) levels. In the present study, we assessed CTT-dependent changes in both redox modulation and NNT enzymatic activity. Furthermore, we expressed CTT in a non-inducible, early and rapidly progressing ADPKD mouse model.

Methods

Mice were generated on C57BL/6N ("N"; NNT-competent) and C57BL/6J ("J"; NNT-deficient) backgrounds.
Kidney NAD(P)(H) levels were determined by targeted LC-MS.
NNT enzymatic activity was measured with a spectrophotometric assay.
ADPKD mice +/- CTT, in which Cre expression is driven by the Pkhd1 promoter, were generated by crossing "J"-Pkd1fl/fl;Pkhd1-Cre with "N"- and "J"-CTT-expressing Pkd1fl/fl;Pax8rtTA;TetO-Cre mice.

Results

"N" cystic CTT-expressing mice exhibited an ~3-fold increase in NADPH/NADP+ and an ~2.5-fold increase in NADH/NAD+ ratios when compared to CTT-negative littermates. CTT expression on the "J" background did not affect either ratio. We detected a 20% decrease in NNT enzymatic activity in "N" cystic mice compared to “N” WT controls. Interestingly, CTT expression in "N" cystic mice rescued enzymatic activity to the same level observed in “N” WT controls. Finally, CTT expression in the Nnt-heterozygous F1 progeny (J-Pkd1fl/fl;Pkhd1-Cre x N-Pkd1fl/fl;Pax8rtTA;TetO-Cre+CTT) led to a 25% decrease in kidney-to-body weight ratio. As expected, CTT expression in the "J" Nnt-deficient F1 progeny did not suppress cystic disease.

Conclusion

While the directionality of the reaction catalyzed by NNT in the context of ADPKD remains to be determined, it is likely that CTT-dependent modulation of mitochondrial redox and NNT activity contributes to disease suppression. Furthermore, we confirmed CTT-dependent disease suppression in a second Pkd1-KO model, which supports the idea that this small fragment may open the doors to the exploration of gene therapy approaches.

Funding

  • NIDDK Support