Expression and Functional Effect of ACE2 in Heme Protein-Mediated AKI (HP-AKI) in Rodents

Background: Our prior study demonstrated that ACE2 expression is markedly reduced following acute renal ischemia (IRI-AKI) [Kidney360 2(7):p 1095-1106, 2021]. As ACE2 has previously been shown to be protective in IRI, we now investigate whether a similar expression profile exists in HP-AKI, and the functional significance of ACE2 in this model. Methods: The glycerol model of HP-AKI was induced in Sprague Dawley rats and C57BL/6J mice by intramuscular injection (6 and 5 mL/kg, respectively). ACE2+/+ and ACE2-/- mice were also subjected to HP-AKI (6 mL/kg). Assessments of ACE2 mRNA and protein expression were performed, as well as measurements of renal ACE2 activity. Assessments of renal functional markers (serum creatinine and BUN) were also undertaken. Results: In the rat, ACE2 mRNA and protein were both reduced significantly at 1 day after induction of HP-AKI. At 2 days after HP-AKI, ACE2 protein expression and activity were both markedly reduced (by approximately 50% and 36%, respectively). In the mouse, ACE2 mRNA expression was reduced at 1 day post HP-AKI induction (8.4±1.0 vs 4.2±0.4, P=0.0013), but was not significantly altered at 8 hours after HP-AKI induction. Serum creatinine following HP-AKI was significantly lower in ACE2-/- mice, compared with ACE2+/+ mice (2.2±0.1 vs 2.7±0.1 mg/dL, P=0.0096). BUN levels, however, were not significantly different between ACE2+/+ and ACE2-/- mice subjected to HP-AKI at this time point. Conclusion: As in our previous IRI-AKI studies, the present rat and mouse studies show that ACE2 mRNA, protein, and activity levels are all significantly reduced after HP-AKI induction (as early as 1 day and through at least 2 days). In contrast to prior studies showing that ACE2 deficiency exacerbates the IRI-AKI model, our studies failed to show a similar exacerbation in ACE2-/- mice subjected to HP-AKI. Indeed, as assessed by 1 of 2 functional markers (serum creatinine), we observe a mild protective effect of ACE2 deficiency. These findings point to significant differences between IRI-AKI and HP-AKI as regards the functional roles of ACE2. Further study is required to delineate the basis for the reduced expression of ACE2 in HP-AKI and the functional significance of ACE2 in this model. Funding: NIDDK Support