key: cord-1013368-r0buami3
authors: Robinson, Emma L.; Alkass, Kanar; Bergmann, Olaf; Maguire, Janet J.; Roderick, H. Llewelyn; Davenport, Anthony P.
title: Genes encoding ACE2, TMPRSS2 and related proteins mediating SARS-CoV-2 viral entry are upregulated with age in human cardiomyocytes
date: 2020-08-18
journal: J Mol Cell Cardiol
DOI: 10.1016/j.yjmcc.2020.08.009
sha: 624d3e1f02009b2833f7359e12e468b8517d5aba
doc_id: 1013368
cord_uid: r0buami3

[Figure: see text]

Age (>70 years), case fatality rate (CFR,10.2%) and coexisting conditions, particularly cardiovascular disease (CFR,10.5%) and hypertension (CFR,6.0%), are independent predictors of adverse outcome for 45,000 COVID-19 patients in China [1] . A consensus has emerged that SARS-CoV-2 uses the same 'receptor' as SARS-CoV, the angiotensin converting enzyme 2 (ACE2), for initial binding to the host cell.

This must be co-expressed with the serine protease TMPRSS2, that primes the spike protein S1 for endocytosis-mediated internalization of virus, employing the S2 domain for fusion to the host membrane ( Figure [1A] ) [2] [3] [4] . A key difference in SARS-CoV-2 is a spike protein second site (S2'), proposed to be cleaved by the proteinase furin 2 . Once inside the cell cysteine proteases, cathepsin L and B, are thought critical for endosomal processing in certain cells [3] [4] .

In the cardiovascular system, ACE2 protein [5] and mRNA [6] are present in cardiomyocytes. ACE2 normally functions as a carboxypeptidase cleaving single Cterminal amino acids thus hydrolysing Pro-Phe in Ang-II to Ang 1-7 , [Pyr 1 ]-apelin-13 to [Pyr 1 ]-apelin (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) and des-Arg 9 -bradykinin to inactive bradykinin (1) (2) (3) (4) (5) (6) (7) (8) [4] . Internalization of ACE2 by virus potentially reduces the beneficial counter regulatory function of these peptide products to the RAAS pathway [2, 4] . Conversely, the serine protease ADAM17 cleaves ACE2 to release its ectodomain and this is stimulated by Ang-II and, potentially, apelin acting via their respective G-protein coupled receptors [7] .

Shed ACE2 binds SARS-CoV-2, a complex predicted not to internalize, and therefore circulating ACE2 could be exploited as a beneficial viral decoy substrate.

Intriguingly, ACE2 is highly expressed in the GI tract where it is associated with B 0 AT1 (SLC6A19) that actively transports most neutral amino acids across the apical membrane of epithelial cells [4, 8] . It is not yet known if B 0 AT1 and ACE2 are coexpressed in cardiomyocytes and represent an important mechanism of viral entry, but they can form a heterodimer, with the ACE2 capable of binding the spike protein S1 [8] . Interleukin 6 (IL-6), normally transiently produced, is elevated in serum and positively correlated with disease severity in COVID-19 patients [9] . We hypothesised that differential expression of genes encoding proteins in these See recent review [4] for a comprehensive list of references supporting the concepts outlined in this letter.

[A] Schematic diagram of the key proteins predicted from RNASeq data to be expressed by human cardiomyocytes. We propose SARS-CoV-2 binds initially to ACE2 (with the ACE2/B 0 AT1 complex as a potential second entry site). TMPRSS2

priming of the spike protein S1, together with further protease activation by cathepsins B and L, facilitates viral cell entry and internalization by endocytosis.

Furin may also have a role in this process. Internalization of the virus with ACE2 inhibits ACE2 carboxypeptidase activity that normally hydrolyses Ang-II, apelin and des-Arg 9 -bradykinin. ADAM17, present on the cell surface, cleaves ACE2 to a soluble form that circulates in the plasma and could act as a decoy substrate for the virus. Levels of ADAM17 may be regulated by Ang-II and apelin acting via their respective G protein-coupled receptors [4] . ↑ -indicates genes with increased expression in aged cardiomyocytes vs young.

[B] Log 2 fold change for expressed genes encoding SARS-CoV-2 entry proteins, peptide receptors in ACE/ACE2 pathway and IL-6 and interferon receptors in aged cardiomyocytes. A Chi Squared analysis for the selected gene panel shown in [B] showed significant enrichment for differentially expressed genes compared with the RNASeq data set as an entirety (P < .05, 95 % confidence level). 

Preventing a covid-19 pandemic: ACE inhibitors as a potential risk factor for fatal Covid-19

The Science Underlying COVID-19: Implications for the Cardiovascular System

SARS-CoV-2 Cell Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a Clinically Proven Protease Inhibitor

A rational roadmap for SARS-CoV-2/COVID-19 pharmacotherapeutic research and development. IUPHAR Review 29

The protein expression profile of ACE2 in human tissues bioRxiv

Myocyte Specific Upregulation of ACE2 in Cardiovascular Disease: Implications for SARS-CoV-2 mediated myocarditis

Clinical Relevance and Role of Neuronal AT1 Receptors in ADAM17-Mediated ACE2 Shedding in Neurogenic Hypertension

Structural basis for the recognition of SARS-CoV-2 by full-length human ACE2