Cardiovascular ACE2 receptor expression in patients undergoing heart transplantation

Abstract

Aims: Membrane-bound angiotensin-converting enzyme (ACE)2 is the main cellular access point for SARS-CoV-2, but its expression and the effect of ACE inhibition have not been assessed quantitatively in patients with heart failure. The aim of this study was to characterize membrane-bound ACE2 expression in the myocardium and myocardial vasculature in patients undergoing heart transplantation and to assess the effect of pharmacological ACE inhibition.

Methods and results: Left ventricular (LV) tissue was obtained from 36 explanted human hearts from patients undergoing heart transplantation. Immunohistochemical staining with antibodies directed against ACE2 co-registered with cardiac troponin T (cTnT) and α-smooth muscle cell actin (SMA) was performed across the entire cohort. ACE2 receptor expression was quantitatively assessed throughout the myocardium and vasculature. ACE2 was consistently expressed throughout the LV myocardium (28.3% ± 22.2% of cardiomyocytes). ACE2 expression was also detected in small calibre blood vessels (range, 2-9 μm), albeit at quantitatively much lower levels (5% ± 9% of blood vessels). There was no significant difference in ACE2 expression between patients receiving ACE inhibitors prior to transplantation and ACE inhibitor-negative controls (P > 0.05). ACE2 expression did not differ significantly between the different diagnostic groups as the underlying reason for heart transplantation (ANOVA > 0.05). N-terminal pro-brain natriuretic peptide (NT-proBNP) (R² = 0.37, P = 0.0006) and pulmonary capillary wedge pressure (PCWP) (R² = 0.13, P = 0.043) assessed by right heart catheterization were significantly correlated with greater ACE2 expression in cardiomyocytes.

Conclusions: These data provide a comprehensive characterization of membrane-bound cardiac ACE2 expression in patients with heart failure with no demonstrable effect exerted by ACE inhibitors.

Keywords: COVID-19; SARS-CoV-2; Heart failure; Heart transplantation; ACE inhibitor.

Figure 1

Visualization of Covid19 binding sites by ACE2 receptor expression. (A) Schematic of study design. Heart explant sections were obtained from 36 patients undergoing heart transplantation. Paraffin‐embedded sections were stained for cTnT/ACE2 and SMA/ACE2 across the entire cohort. The results were subsequently correlated with pretransplant characteristics. (B) Validation of ACE2 antibodies. Expression of ACE2 in human left ventricular myocardium. Scale bars: 25 and 10 μm, respectively. (C) IgG Isotype control for ACE2, demonstrating specificity of staining. Scale bar, 25 μm. (D) Expression of the accessory protease TMPRSS2 and ACE2, demonstrating co‐expression in a subset of cardiomyocytes. Scale bars: 25 and 10 μm, respectively. (E) IgG Isotype control for TMPRSS2, demonstrating specificity of staining. Scale bar: 25 μm.Abbreviations: LV, left ventricular; ACE2, angiotensin‐converting enzyme 2; cTnT, cardiac muscle troponin T; IgG, immunoglobulin G.

Figure 2

Quantification of myocardial ACE2 expression in explanted human hearts.(A) ACE2 expression in human cardiomyocytes in explanted hearts. Scale bar: 25 μm. (B) Quantification of ACE2 expression expressed as % of ACE2‐positive cardiomyocytes of all cardiomyocytes. Bottom pie chart shows group stratification. (C) ACE2 expression in patients according to underlying reason for heart transplantation. HCM, hypertrophic cardiomyopathy; ICM, ischaemic cardiomyopathy; ACM, arrhythmogenic cardiomyopathy; DCM, dilated cardiomyopathy. (D) Effect of ACE inhibitor administration on ACE2 expression. (E) Baseline clinical variables significantly correlated with myocardial ACE2 expression. Shown is NT‐proBNP. (F) Correlation of PCWP (mmHg) with myocardial ACE2 expression.Abbreviations: ACE2, angiotensin‐converting enzyme 2; cTnT, cardiac muscle troponin T; IgG, immunoglobulin G.

Figure 3

Quantification of vascular ACE2 expression in explanted human hearts.(A) ACE2 and SMA co‐expression in blood vasculature of explanted human hearts. White arrows indicate co‐expression. Scale bars: 25 and 10 μm, respectively. (B) Quantification of ACE2 expression expressed as % of ACE2‐positive blood vessels of all blood vessels. Bottom pie chart shows group stratification. (C) Average vessel diameter in μm in ACE2+/SMA+ patients. (D) ACE2 and CD31 co‐expression in blood vasculature of explanted human hearts. White arrow indicates co‐expression. (E) Vascular ACE2 expression in patients according to underlying reason for heart transplantation. HCM, hypertrophic cardiomyopathy; ICM, ischaemic cardiomyopathy; ACM, arrhythmogenic cardiomyopathy; DCM, dilated cardiomyopathy. (F) Effect of ACE inhibitor administration on ACE2 expression in blood vasculature.Abbreviations: SMA, alpha smooth muscle actin; ACE2, angiotensin‐converting enzyme 2; CD31, cluster of differentiation 31; ACEi, angiotensin‐converting enzyme inhibitor.