SARS-CoV-2 causes infection primarily by binding to the human angiotensin-converting enzyme 2 (ACE2) receptor in the upper respiratory epithelium and lungs. However, nearly 20% of all COVID-19-associated deaths are from cardiac complications. There is much debate about how such complications arise, how to treat them, and whether patients already taking angiotensin converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARB) should continue with them.
To help answer these questions, researchers from Masonic Medical Research Institute (MMRI) and collaborators have applied state-of-the-art single nucleus sequencing to human heart samples.
Their study suggests the amount of the viral receptor is increased in patients with pre-existing cardiac conditions, but only in the beating cells of the heart, termed cardiomyocytes. Additionally, they found that the effect of anti-hypertension medications, or ACE inhibitors, do not appreciably affect the levels of ACE2 in a way that requires any change in clinical use of these medications. The group’s report was published this week in Circulation.
“This is but an early step in our understanding of cardiac pathology in people who contract COVID-19,” said Nathan Tucker, assistant professor at MMRI and first author of the manuscript. “There’s much more work to do. As an example, we are already working to establish direct evidence of cardiac infection, while also examining receptor distributions in other populations and through other approaches. We hope to provide more information as soon as we are able.” The research was a collaboration between MMRI, the Broad Institute, the University of Pennsylvania, and Bayer US.
Evidence about the effects of the novel severe coronavirus on the heart is growing. In one recent single-center report of 416 patients hospitalized with COVID-19, 19.7% had evidence of cardiac injury. Moreover, the presence of cardiac injury was associated with a 5-fold increase in mechanical ventilation and a 51.2% mortality rate.
Currently more than a dozen clinical trials of ACE Inhibitors in COVID-19 patients are ongoing. ACE is involved in the renin-angiotensin-aldosterone system and stimulates the conversion of angiotensin I to angiotensin II. ACE inhibitors are competitive inhibitors of ACE, which prevents the conversion of angiotensin I to angiotensin II. Angiotensin II is a potent vasoconstrictor. When inhibited, it can reduce blood pressure by dilating vessels and decreasing aldosterone secretion
In their study, Tucker and his collaborators assessed ACE2 expression by performing bulk and single nucleus RNAseq on the left ventricles of 11 individuals with dilated cardiomyopathy (DCM), 15 individuals with hypertrophic cardiomyopathy (HCM), and 16 non- failing controls from the Penn Human Heart Tissue Biobank. Data generated by the 10X Genomics 3’ solution v3 were processed with the CellRanger 3.1.0 toolkit followed by strict quality control for transcriptional complexity, mitochondrial read counts, proportion of spliced reads, and entropy. Differential gene expression was performed by summing gene counts across all nuclei in each cell type and applying a limma-voom testing pipeline, adjusting for age and sex.
Consistent with other recent reports, cardiac ACE2 expression was strongest in pericytes, which line the microvasculature, but it was also found in vascular smooth muscle cells, fibroblasts, and cardiomyocytes.
“We also evaluated the expression of the proteases encoded by TMPRSS2 and CTSL, which facilitate membrane fusion and viral uptake during SARS-CoV-2 infection,” the authors write in their paper. “TMPRSS2 was minimally expressed across all cell types, while CTSL displayed low levels of expression in all cell types with strongest expression in fibroblasts (18.1% and 56.7% of cells in the two populations found in non-failing controls), macrophages (39.1%), adipocytes (41.5%), and cardiomyocytes (11.4%),” they added.
The authors suggest their study offers a potential explanation as to why patients with pre-existing heart disease are more likely to suffer severe cardiac symptoms from COVID-19 infection. it also provides data on the effects of anti-hypertensive medications, supporting the the American Heart Association, American College of Cardiology, and European Society of Cardiology’s current position which urges continued use of ACE inhibitors in these patients.