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Abstract: SA-PO300

Inactivation of the Mitochondrial Structural Protein Opa1 in Distal Tubules and Collecting Ducts in the Mouse Causes Nephrogenic Diabetes Insipidus

Session Information

Category: Fluid and Electrolytes

  • 901 Fluid and Electrolytes: Basic

Authors

  • Cassina, Laura, San Raffaele Scientific Institute, Milan, Italy
  • Chiaravalli, Marco, San Raffaele Scientific Institute, Milan, Italy
  • Maserati, Martina, San Raffaele Scientific Institute, Milan, Italy
  • Mannella, Valeria, IRCSS Policlinico San Donato, Milano, Italy
  • Musco, Giovanna, San Raffaele Scientific Institute, Milan, Italy
  • Boletta, Alessandra, San Raffaele Scientific Institute, Milan, Italy
Background

Optic Atrophy-1 protein (OPA1) is a nuclear-encoded mitochondrial protein localizing in the inner mitochondrial membrane, where it participates to mitochondria fusion and supports cristae folding. Mitochondria in the kidney provide energy to the Na,K-ATPase that generates ion gradients for nutrient reabsorption, electrolyte and fluid balance (Bhargava 2017). Given their essential function in aerobic metabolism, mitochondria are of interest to the pathophysiology of diabetes. To study how mitochondria fitness contributes to kidney physiology, we inactivated Opa1 gene expression in the kidney epithelium.

Methods

We generated a kidney-specific Opa1fl/fl mouse model expressing the Cre recombinase under the kidney-specific cadherin 16 promoter (Opa1 KO, for short). Mitochondria ultrastructure was analyzed by transmission electron microscopy (TEM), metabolomics analysis by NMR spectroscopy.

Results

Opa1 KO mice die within the first three months of age. Mice were housed in metabolic cages and showed progressive polydipsia and polyuria, low urinary pH, decreased urinary electrolyte concentration but no gross alteration of total electrolyte excretion. We observed kidney enlargement from P30 onwards, which results from enhanced proliferation of Opa1 KO epithelial cells of distal tubules and collecting ducts, where Opa1 is inactivated, by Ki67 staining. Expression of markers of distal tubule subsegments is preserved indicating maintenance of cell identity, with the exception of aquaporin 2 that is reduced in Opa1 KO collecting ducts, causing polyuria. We detected the expected alterations in mitochondria structure by TEM and decreased mitochondrial cytochrome c oxidase activity in Opa1 KO epithelial cells. Metabolomics showed that these alterations result in a massive switch to glycolysis that sustains cell proliferation, ultimately resulting in renal dysfunction.

Conclusion

Inactivation of Opa1 induces kidney enlargement and a gross impairment of renal water reabsorption, thus recapitulating the key features of nephrogenic diabetes insipidus. Further investigations will clarify the molecular mechanisms that link mitochondria dysfunction to epithelial cell proliferation, a response that seems to be unique of the kidney.

Funding

  • Private Foundation Support