Marked Up-Regulation of ACE2 in Hearts of Patients With Obstructive Hypertrophic Cardiomyopathy: Implications for SARS-CoV-2-Mediated COVID-19

Abstract

Objective: To explore the transcriptomic differences between patients with hypertrophic cardiomyopathy (HCM) and controls.

Patients and methods: RNA was extracted from cardiac tissue flash frozen at therapeutic surgical septal myectomy for 106 patients with HCM and 39 healthy donor hearts. Expression profiling of 37,846 genes was performed using the Illumina Human HT-12v3 Expression BeadChip. All patients with HCM were genotyped for pathogenic variants causing HCM. Technical validation was performed using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. This study was started on January 1, 1999, and final analysis was completed on April 20, 2020.

Results: Overall, 22% of the transcriptome (8443 of 37,846 genes) was expressed differentially between HCM and control tissues. Analysis by genotype revealed that gene expression changes were similar among genotypic subgroups of HCM, with only 4% (1502 of 37,846) to 6% (2336 of 37,846) of the transcriptome exhibiting differential expression between genotypic subgroups. The qRT-PCR confirmed differential expression in 92% (11 of 12 genes) of tested transcripts. Notably, in the context of coronavirus disease 2019 (COVID-19), the transcript for angiotensin I converting enzyme 2 (ACE2), a negative regulator of the angiotensin system, was the single most up-regulated gene in HCM (fold-change, 3.53; q-value =1.30×10^-23), which was confirmed by qRT-PCR in triplicate (fold change, 3.78; P=5.22×10^-4), and Western blot confirmed greater than 5-fold overexpression of ACE2 protein (fold change, 5.34; P=1.66×10^-6).

Conclusion: More than 20% of the transcriptome is expressed differentially between HCM and control tissues. Importantly, ACE2 was the most up-regulated gene in HCM, indicating perhaps the heart's compensatory effort to mount an antihypertrophic, antifibrotic response. However, given that the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses ACE2 for viral entry, this 5-fold increase in ACE2 protein may confer increased risk for COVID-19 manifestations and outcomes in patients with increased ACE2 transcript expression and protein levels in the heart.

Figure 1

Top up-regulated and down-regulated genes in hypertrophic cardiomyopathy (HCM). Bar diagram shows the top 10 up-regulated (left) and down-regulated (right) genes in tissues of patients with obstructive HCM compared with controls.

Figure 2

Technical validation of the microarray technique. Microarray fold change and quantitative real-time polymerase chain reaction (qRT-PCR) fold change are plotted side by side for the 12 genes tested. The qRT-PCR data validated the microarray data for 11 of 12 genes (92%).

Figure 3

Marked accentuation of angiotensin-converting enzyme type 2 (ACE2) in hypertrophic cardiomyopathy (HCM). Bar diagram shows: (A) 5.3-fold increase in ACE2 protein in HCM patients compared with controls by Western blot analysis and (B) significant staining of ACE2 antibody in the myectomy specimen from a patient with obstructive HCM. Flow chart shows (C) the role of ACE2 in converting angiotensin (ang) I to ang (1-9) and angiotensin II to ang (1-7) to counter the effects of angiotensin II. SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.

Figure 4

Angiotensin-converting enzyme type 2 (ACE2) overexpression and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Central illustration shows possible mechanism behind ACE2 overexpression and SARS-CoV-2 infection picturing normal ACE2 expression (left) and ACE2 protein overexpression in obstructive hypertrophic cardiomyopathy (HCM; right). The SARS-CoV-2 virus hijacks membrane-bound ACE2 for cellular entry. Aside from allowing cellular invasion and viral replication, internalization of the SARS-CoV-2–ACE2 complex causes a decrease in surface ACE2. Loss of surface ACE2: (1) increases the angiotensin II to ang (1-7) ratio and (2) increases angiotensin type 1 receptor (AT1R) activity with a resultant increase in damaging angiotensin II activity. Shown are potential therapeutic targets (and clinical trials) using either angiotensin receptor blockers (ARBs; losartan specifically) or human recombinant soluble ACE2 (hrsACE2). For patients with ACE2-accentuating heart diseases such as obstructive HCM, the speculated increase in viral infectivity of the heart muscle remains to be proven. (Portion of figure adapted from: Simmons G, Zmora P, Gierer S, Heurich A, Pöhlman S. Proteolytic activation of the SARS-coronavirus spike protein: Cutting enzymes at the cutting edge of antiviral research. Antivir Res. 2013;100(3):605-614 with permission from Elsevier, license number 4814880904484).