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Abstract: SA-PO192

Loss of Tubular Angiotensin-Converting Enzyme 2 (ACE2) into the Urine with ACE2 Casts: A Key Pathophysiologic and Diagnostic Alteration in AKI?

Session Information

  • AKI: Mechanisms - III
    November 04, 2023 | Location: Exhibit Hall, Pennsylvania Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Cianfarini, Cosimo L., Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Shirazi, Mina, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Wysocki, Jan, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Wang, Jiao-Jing, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Ye, Minghao, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Zhang, Zheng Jenny, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
  • Batlle, Daniel, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States
Background

In acute kidney injury (AKI) the renin angiotensin system (RAS) is overactive. ACE2 is a tissue RAS enzyme that is highly expressed in the apical tubular border in kidney cortex and corticomedullary region where it controls Angiotensin II degradation to form Angiotensin 1-7. We hypothesize that in AKI there is a loss of apical tubular ACE2 that amplifies RAS overactivity and results in worsening of proximal tubular injury.

Methods

We used the mouse model of AKI by ischemia-reperfusion-injury (IRI) in male C57BL/6 mice by clamping of the left renal pedicle for 30min followed by removal of the right kidney (unilateral IRI). Kidneys were harvested 48hrs after the surgery and stained for ACE2 by immunohistochemistry (IHC) and immunofluorescence (IF). Kidney ACE2 protein was assessed in membrane protein lysates and enzymatic activity measured using a fluorogenic substrate. ACE2 protein by western blot and enzymatic activity were assessed in mouse urine collected 48hrs post IRI.

Results

IHC and IF revealed a striking maldistribution of tubular ACE2 (Fig. A, B) compared to healthy control kidneys including spillage into the tubular lumen and presence of ACE2 positive luminal casts in the medulla (C) where ACE2 is usually absent. ACE2 protein in membrane lysates and enzymatic activity were reduced (37±3.5 vs. 100±5.6 ACE2/ß-Actin, p=0.0004 and 96±14 vs. 152±5.6 RFU/μg total protein/h, p=0.006). In the urine the full-length membrane bound ACE2 protein was increased (2606±1764 vs. 100±47 ACE2/µl urine, p=0.04) and activity in the urine sediment was increased as well (7.7±1.9 vs. 2±0.2 RFU/µg Cr, p=0.01). Moreover, ACE2 containing casts were recovered in the urine sediment.

Conclusion

In a mouse model of AKI caused by IRI there is a marked loss of ACE2 from the apical tubular border with deposition of ACE2 positive material in the medulla and increased urinary excretion of the full length membrane-bound ACE2. The deficiency of apical ACE2 not only results in the loss of its kidney protective effects but may also serve as a diagnostic marker of AKI.

Funding

  • Other NIH Support