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Kidney Week

Abstract: TH-PO020

Spatiotemporal ATP Dynamics In Podocytes During Ischemic Reperfusion Injury Predicts Later Foot Process Effacement

Session Information

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Takahashi, Masahiro, Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan
  • Yamamoto, Shigenori, Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan
  • Yamamoto, Masamichi, Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan
  • Yanagita, Motoko, Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan
Background

Mitochondrial dysfunction, genetic or postnatal, is closely related to podocyte injury, suggesting the possibility that hypoxia or oxidative stress during ischemic AKI causes podocyte injury. Indeed, some studies report proteinuria after kidney transplantation, however, little is investigated regarding pathophysiological changes of podocytes during AKI. Here we investigated the dynamics of adenosine 5’ triphosphate (ATP) in podocytes during ischemic AKI, because ATP is essential for stabilization of foot process.

Methods

To enable spatiotemporal ATP imaging, we utilized ATeam mice, which expressed the FRET-based ATP biosensor systemically, and monitored ATP changes of podocytes during IRI by multi-photon microscopy. Furthermore, we performed microstructural analysis of podocytes two weeks after IRI, and assessed the correlation between the ATP recovery in acute phase and morphological change in chronic phase.

Results

While the ATP levels of podocytes gradually decreased to the plateau level in twenty minutes after ischemia induction, they recovered rapidly in less than five minutes after reperfusion. The % ATP recoveries after 15, 30, 37, 45 and 60 minute-ischemia were 95%, 93%, 87%, 84% and 80% respectively, and were dependent on the length of ischemia. Electron microscopy two weeks after IRI revealed significant foot process effacement and mitochondrial fragmentation in mice subjected to severer IRI. Foot process widths were 367, 361, 381, 450 and 480 nm, and mitochondrial circularities, an indicator of mitochondria fragmentation, were 0.80, 0.80, 0.83, 0.86 and 0.88 after 15, 30, 37, 45 and 60 minute-ischemia, respectively. Mitochondrial circularities were strongly correlated with foot process widths, supporting the importance of energy metabolism in the maintenance of foot processes. Notably, the % ATP recoveries in acute phase were well correlated with the foot process widths and mitochondrial circularities in chronic phase.

Conclusion

We, for the first time, succeeded in visualizing ATP dynamics of podocytes during IRI. Our results show the close link between podocyte energy metabolism and ultrastructural changes during and after AKI, and provide the basis for understanding the mechanism of proteinuria after AKI or kidney transplantation.