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Kidney Week

Abstract: PO0206

Changes in NAD and Lipid Metabolism Drive Acidosis-Induced AKI

Session Information

  • AKI Mechanisms - 2
    October 22, 2020 | Location: On-Demand
    Abstract Time: 10:00 AM - 12:00 PM

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Bugarski, Milica, Institute of Anatomy, University of Zurich, Zurich, Switzerland
  • Ghazi, Susan, Institute of Anatomy, University of Zurich, Zurich, Switzerland
  • Polesel, Marcello, Institute of Anatomy, University of Zurich, Zurich, Switzerland
  • Martins, Joana Raquel Delgado, Institute of Anatomy, University of Zurich, Zurich, Switzerland
  • Hall, Andrew, Institute of Anatomy, University of Zurich, Zurich, Switzerland
Background

The kidney has an important role in maintaining normal blood pH. Mitochondria in the proximal tubule (PT) produce ammonia and bicarbonate from glutamine, and during metabolic acidosis (MA) this pathway (ammoniagenesis) is acutely upregulated. MA is frequently associated with acute kidney injury (AKI); however, to what extent the former causes the latter was unclear.

Methods

Multiphoton imaging of mitochondrial function in mouse kidney cortical slices and in vivo; oxygen consumption rate (OCR) in isolated PTs; histological analysis and electron microscopy (EM) in fixed tissue. MA was induced using an established protocol (gavage with 0.8 g/kg NH4Cl).

Results

Acutely lowering extracellular pH to 6.5 decreased mitochondrial NADH fluorescence signal specifically in PTs, without changing total NADH content, baseline OCR or mitochondrial membrane potential. However, maximal OCR was decreased and response to rotenone was exaggerated, suggesting a switch to complex I and increased oxidation of NADH to NAD+, which is required for ammoniagenesis. PTs in acidotic animals displayed intense Oil Red O staining and large multi-lamellar bodies (MLBs), consistent with a major decrease in lipid metabolism. Supplementing or reducing NAD (with lactate) and increasing pH back to 7.4 inhibited/reversed the appearance of MLBs, implying that changes in NAD and lipid metabolism are linked.
Histological analysis of acidotic animals showed thinning of PTs and shedding of debris, indicative of AKI. Intravital imaging revealed that mitochondria remained energized, but endocytosis of fluorescently labeled dextrans was markedly decreased, confirming a severe functional defect in solute transport. Partially reversing MA with intravenous injection of bicarbonate (0.42 g/kg) or supplementing NAD with nicotinamide (0.4 g/kg, prior to MA induction) both substantially improved dextran uptake.

Conclusion

MA induces major changes in PT NAD and lipid metabolism that result in a functional AKI state, which can be reversed or prevented. These findings might also help to explain why MA accelerates decline in function in chronic kidney disease.