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Al‑Benna ﻿Afr J Urol
https://doi.org/10.1186/s12301-021-00192-4

ORIGINAL RESEARCH

African Journal of Urology
Open AccessAngiotensin‑converting enzyme 2 gene
expression in human male urological tissues:
implications for pathogenesis and virustransmission pathways
Sammy Al‑Benna*

Abstract
Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection occurs through binding andinternalization of the viral spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor on the host cell
membrane. Pathological changes are caused by damage and failure of vital organs that express high levels of ACE2,
including the lungs, the heart and the kidneys. The aim of this study was to investigate ACE2 gene expression in thehuman male urogenital tract using a public database.
Methods: A search of transcriptomic datasets from a database to investigate ACE2 gene expression in human uro‑
genital tract tissue.
Results: The gene expression profile demonstrated that ACE2 gene expression was higher in human kidney cor‑tex and testis than human lung tissue. The gene expression profile demonstrated that ACE2 gene expression in thehuman bladder and prostate was comparable to human lung tissue.
Conclusions: Male urogenital tissues are directly susceptible to SARS-CoV-2 infection through the expression of
ACE2. Moreover, the SARS-Cov-2/ACE2 interaction may disturb the male genital and reproductive functions.
Keywords: Urology, Genitalia, Male, Angiotensin-converting enzyme 2 receptor, Coronavirus, Severe acuterespiratory syndrome coronavirus 2, COVID-19, Fertility
1 Background
Severe acute respiratory syndrome coronavirus 2 (SARSCoV-2) is an enveloped, positive-sense, single-strandedribonucleic acid β-coronavirus [1]. SARS-CoV-2 causes
the disease called coronavirus disease 2019 (COVID-19)[1–3]. It was first identified in late 2019 in Wuhan, China,
and quickly spread to become a worldwide pandemic andpublic health emergency [1–3]. As of 15 October 2020,
a total of 38,789,613 accumulated cases and 1,097,567*Correspondence: albenna@sun.ac.za
Department of Surgical Sciences, Faculty of Medicine and Health
Sciences, Stellenbosch University and Tygerberg Academic Hospital,
Francie van Zijl Drive, PO Box 241, Cape Town 8000, South Africa

deaths are reported worldwide, with an overall mortality
rate of about 1% [3]. With this evolving pathology, the fastdeveloping evidence base must be constantly integrated
into the present understanding of the disease [4–6].
Epidemiologically, the genome of SARS-CoV-2 consistsof 29,891 nucleotides, with an 89% identity to humansevere acute respiratory syndrome coronavirus (SARSCoV) [10, 11]. SARS-CoV-2 infects the human cells byattaching to angiotensin-converting enzyme 2 (ACE2),
through its exterior spike (S) protein, modulates theexpression of ACE2 and initiates tissue damage [10, 11].
ACE2 is a zinc metalloprotease which shares 42% aminoacid homology with angiotensin-converting enzyme(ACE) in its catalytic domain, and consists of 805 amino© The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) andthe source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material
in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material
is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds thepermitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://​creat​iveco​
mmons.​org/​licen​ses/​by/4.​0/.

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acids including a C-terminal membrane binding domain
and a 17-amino acid N-terminal signal sequence [10, 11].
ACE2 contains one HEXXH zinc-binding motif and isable to hydrolyze angiotensin I (AT1) to produce angiotensin-(1–9) and also has a high affinity for angiotensin
II (AT2) to generate angiotensin (1–7) [AT(1–7)] [7].
AT2, the major component of the ACE/AT2/AT1 (AT2
type 1) pathway, facilitates vasoconstriction, promotes
cell proliferation and maintains fluid homeostasis [12].
AT(1–7) is an important component of the human reninangiotensin system (RAS) [12]. It is an endogenous ligand
for the G protein-coupled receptor Mas and specificallyinhibits AT2 by AT1 receptor antagonism [12]. Furthermore, AT(1–7), the major component of the ACE2/
AT(1–7)/Mas pathway is an anti-growth pathway inhibits
inflammation, induces vasodilation and is cardioprotective [12].
Tissues that express ACE2 are direct targets of SARSCoV-2 infection, which can lead to significant pathological changes, tissue organ failure and even mortality in
critical cases [14]. Evidence has been accumulating thatbesides respiratory injury, SARS-CoV-2 also damages
other systems, such as the cardiovascular and hepatic[15]. The immune privileged environment of testicles routinely allows immunogenic sperm cells (spermatocytes; spermatids; spermatozoa) to elude the hostimmune system. However, certain viruses are able tocross between the Sertoli cells of the seminiferous tubules
into this immune privileged testicular environment andstimulate an immune response [16]. Systemic viral infections, such as mumps orchitis, can involve the male urogenital system [16]. The seeding and entry of viruses intomale reproductive tract cells after SARS-CoV-2 infection
is poorly understood and requires further investigation[16]. The aim of this article was to search a gene expression database to find ACE2 expression in tissues of thehuman urological system.

2 Methods
This section presents a search of a public gene expression
database (https://​www.​gtexp​ortal.​org/​home/) for ACE2
expression in various normal human urogenital tract tissues [17]. The resource database from Genotype-Tissue
Expression (Version 8 data release) integrates the expression data of 11,688 normal tissue samples covering 54
tissue types to comprehensively annotate the expression
patterns of each gene. Human samples are aligned against
the GRCh38 human reference genome. The search provided public RNA sequencing (RNA-seq) data of ACE2
expression. A differential expression analysis was appliedon the selected ACE2 dataset to dynamically obtain differentially expressed genes in ­log2(TPM + 1) transformed
expression data. The transformed expression data fromPage 2 of 5

all tissue samples available were plotted using the box
plots available from the GTExPortal website with plots
shown as median and 25th and 75th percentiles and dots
displayed as outliers if they are above or below 1.5 times
the interquartile range. All data are publically available
online.

3 Results
The gene expression database included ACE2 expression profile. The gene expression profile demonstrated
that ACE2 gene expression was present in human urogenital tract tissues (Fig. 1). The gene expression profile

Fig. 1 ACE2 gene expression in human urogenital system tissues andhuman lung tissue

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demonstrated that ACE2 gene expression was higher inhuman kidney cortex and testis than in human lung tissue (Fig. 1). In addition, the gene expression profile demonstrated that ACE2 gene expression was in the human
bladder and prostate was comparable to human lungtissue.

4 Discussion
The ACE2 receptor is perceived as the receptor for thepassage of SARS-CoV-2 into host cells [10, 11]. SARSCoV-2 has high proclivity for the ACE2 receptor [10,11]. SARS-CoV-2 infection is vigorous in cells expressing
ACE2 receptor, a type I integral membrane protein that
controls cardiovascular and renal functions by negatively
modulating the RAS [10, 11]. During virus ingress, thecoronavirus S protein requires priming and cleavage at
the S1/S2 site of the protein by transmembrane proteaseserine 2 [11]. The S1 site contains a receptor-binding
domain, which then binds to the ACE2 to facilitate virus
entry into the cell [1].
This study establishes that ACE2 gene expression in
the male urogenital system is greater than or comparable
to human lung tissue, the principal corpus tissue whosecells are affected by SARS-CoV-2 infection. ElevatedACE2 expression amplifies virus infection in COVID-19
patients and has been shown to play a role in COVID19 morbidity and mortality trends, but research on othertissues has not been conducted [13, 18, 19]. Moreover, ACE2 receptor gene expression is upregulated in
COVID-19 [18]. ACE2 gene expression level was highest
in human male testes, suggesting that they may be more
susceptible to the effects of the SARS-CoV-2 virus. The
majority of COVID-19 patients present with respiratory
symptoms, but little is known about urogenital-related
manifestations of the infection [14, 15].
The RAS plays a key role in the modulation of many
functions in the body, including the widely known cardiovascular homeostatic mechanisms [12]. The latest
developments in tumour pathobiology indicate that local
RAS importantly configures the cancer microenvironment and induces angiogenesis, proliferation of tumour
cells and metastatic behaviour [20, 21]. Meanwhile, theACE2/AT(1–7)/Mas axis is associated with anti-proliferative, vasodilatory, antifibrotic and anti-metastatic properties [20]. In addition, the RAS plays a critical role in thetesticular function in humans [22, 23]. In Leydig cells, thebiological roles of ACE2 involve regulation of productionof testosterone and regulation of local vascular systems tobalance interstitial fluid volume via modulating conversion of AT2 to AT1 [24–26]. SARS-CoV-2 infection andpathogenesis is predominantly determined by receptor
recognition [9]. SARS-CoV-2 has higher binding affinity in cells with higher ACE2 expression, which supports

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more efficient cell entry [9, 26]. Intervention strategies
can only be improved by understanding SARS-CoV-2 cell
entry mechanisms.
There are two critical observations with regard tohuman male urological tissues and the COVID-19 pandemic: (1) adult males have a higher prevalence of severe
COVID-19 complications; and (2) children have lesssevere symptoms with a relative immunity [27, 28]. Previous studies have shown that a variety of viruses may affectmen’s testicles such as hepatitis B and C viruses, Epstein–Barr virus, human immunodeficiency virus, human papilloma viruses and mumps virus [23]. Some viruses cause
orchitis indirectly through an immune response, whileother viruses directly attack the testes [23]. The resultant
viral orchitis from either direct or indirect attack can leadto male infertility and testicular tumours [23].
Although SARS-CoV virus has never been detected in
SARS patients’ testis tissues, orchitis and spermatogenic
cell damage have been demonstrated in these SARS-positive patients [22]. Orchitis with scarce or nil spermatozoa
in the seminiferous epithelium, sperm cell destruction,
spermatogenic cell apoptosis, thickened basement membrane and leukocyte infiltration were found in all testes
acquired at autopsy from individuals who died of SARSCoV [23].
The Sertoli cells of the seminiferous tubules do notshield against SARS-CoV-2 infection, resulting in compromised gonadal function and aberrant expression ofmale sex hormones [9]. Significant seminiferous tubular injury, decreased Leydig cells, and mild lymphocytic
inflammation have been demonstrated in testes fromCOVID-19 patients [29]. It is proposed that during peakviraemia, SARS-CoV-2 reaches testicular interstitium,
where ACE2 expression is high, via the vascular circulation and Leydig cells may be one of the first targets inthe testes, impacting testicular function. Male reproductive systems are susceptible to SARS-CoV-2 infection and significant changes in sex hormones in patientswith COVID-19 have been observed, suggesting gonadal
function impairment [29, 30]. COVID-19 patients havesignificantly raised luteinizing hormone serum levels,
intimating that SARS-CoV-2 infection may instigate male
hypogonadism [30].
Furthermore, when 81 COVID-19-positive malepatients were compared to 100 age-matched healthy
counterparts, the testosterone-to-luteinizing hormone
ratio was dramatically and significantly lower [30]. The
serum testosterone-to-luteinizing hormone ratio (asan indicator of male gonadal function) was also suggested as a possible marker of reproductive deficiency
caused by SARS-CoV-2 [30]. Changes in the steroidogenic pathways that result from SARS-CoV-2 testicular
infection may account for the malfunction of Leydig

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cells that produce hormone and the lower serum testosterone-to-luteinizing hormone ratio [30]. Furthermore, Sertoli cells in the seminiferous tubules also
express ACE2 and may similarly be infected by SARSCoV-2 [30]. Chemokines and cytokines generated by
SARS-CoV-2 infection of Leydig cells and Sertoli cells
may attract pro-inflammatory peripheral immune
cells such as macrophages, monocytes and virusspecific T cells, which may exacerbate inflammationand orchitis, as recorded by up to one in five COVID19-positive males crossexamined [30], but could also
aid viral elimination. COVID-19-positive males rarely
report orchitis; it is hypothesized as the immunosuppressive properties of Sertoli cells of the seminiferous
tubules and macrophages in the testes, quash inflammation, and in contrast to other organs constraining virus-related injury of the testes. Nevertheless,
COVID-19-associated inflammation may temporarily
disturb the cohesion of Sertoli cells of the seminiferous tubules that may impact spermatogenesis [29].
As a result, urogenital symptoms and signs should beassessed and investigated in COVID-19 male patients.
Further research using both in vitro and in vivo models is necessary to elucidate the effect of SARS-CoV-2
infection on testes function including hormone manufacture, cohesion and organization of the Sertoli cellsof the seminiferous tubules, and germ cell decreases
to advance the knowledge of the effect of SARS-CoV-2
and COVID-19 on male reproductive ability.
Two studies have reported the absence of SARSCoV-2 in the semen of males recovering from COVID19, while two other studies demonstrated its presencein the semen of active and recovering patients [9, 28,
31, 32]. In contrast to a recent study that demonstrated
sparse gene expression of ACE2 in the testis, this study
found high ACE2 gene expression in the testis [33].
The ramifications of recoverable SARS-CoV-2 ribonucleic acid in semen stay indeterminate, concerningwhether this means animate virus or damaged remaining nucleic acid. Future study, including histopathological diagnosis, tissue culture, electron microscopy,
nucleic acid detection and immunofluorescence, candecide whether SARS-CoV-2 can be spread throughsemen and determine the concerned processes [34].
Post-recovery from COVID-19, recovered malepatients who are interested in having children should
receive a consultation regarding their fertility to monitor and evaluate their male reproductive function,
including sperm analysis and sperm cryopreservationin the early stage of disease, and follow-up of reproductive function in the following months.

Page 4 of 5

5 Conclusion
ACE2 gene expression is higher in certain parts of theurogenital system than in the respiratory system, andurogenital system pathologies may ensue. The testes,
bladder, and prostate, as well as the respiratory system,
may be impacted by SARS-CoV-2 infection, both directly
and indirectly via the ACE2 receptor. Adult Leydig cells
selectively express ACE2 and play a crucial role in steroidogenesis regulation. ACE2 expression variations
between males and females can influence not only potential disease sites and viral reservoirs, but also increased
prevalence of severe COVID-19 disease in males. Moreresearch into ACE2 gene expression and modulation in
the male urogenital tract, as well as other related cell
types that may influence ACE2 and SARS-CoV-2 pathogenesis, is needed.
Abbreviations
ACE: Angiotensin-converting enzyme; ACE2: Angiotensin-converting enzyme
2; AT1: Angiotensin I; AT2: Angiotensin II; AT(1–7): Angiotensin (1–7); S: Spike.
Acknowledgements
None.
Authors’ contributions
SAB contributed to the conception, design, analysis and interpretation of data;drafting of the article or revising it for critically important intellectual content;
and the final approval of the version to be published.
Funding
None.
Availability of data and materials
All data are publically available.

Declarations
Ethics approval and consent to participate
Ethics approval and consent to participate were not required. The study exclu‑
sively used publically available data.
Consent for publication
Not applicable.
Competing interests
None.
Received: 20 August 2020 Accepted: 6 December 2020

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