The coronavirus disease 2019 (COVID-19) pandemic represents a public health emergency
of international proportions, which is having catastrophic consequences throughout
the world . To date, around 6 million confirmed cases have been diagnosed worldwide
and over 370,000 people perished because of COVID-19 . The clinical disease called
COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),
a novel betacoronavirus sharing 79% sequence identity with SARS-CoV, the agent which
provoked the 2003 SARS outbreak .
Recent evidence suggested that SARS-CoV-2 uses the ACE2 receptor for cell entry, in
synergy with the host’s TMPRSS2 . More specifically, the viral S glycoprotein is
cleaved by TMPRSS2, thus facilitating viral activation and representing one of the
essential host factors for SARS-CoV-2 pathogenicity (Figure 1) . This process is
similar to viral activation and cell entry of other coronaviruses, including SARS-CoV,
as well as influenza virus such as influenza H1N1 . Despite several studies reported
that in vitro activation of viral spikes could be mediated by other proteases such
as TMPRSS4, TMPRSS11A, TMPRSS11D and TMPRSS11E1, TMPRSS2 activity is currently considered
the sole crucial for cell entry and viral pathogenesis .
Regulation of TMPRSS2 gene transcription and process of severe acute respiratory syndrome
coronavirus 2 entry into target cells.
Androgen receptor gene and ACE2 gene are located on Xq12 and Xp22.2, respectively.
Testosterone and dihydrotestosterone stimulate androgen receptor activity. Activated
androgen receptor regulates transcription of TMPRSS2 gene. TMPRSS2:ERG gene fusion
is associated with prostate cancer development. SARS-CoV-2 engages ACE2 as the entry
receptor and uses TMPRSS2 for spike protein priming. Serine protease inhibitors, like
camostat mesylate, can inhibit TMPRSS2 and partially block SARS-CoV-2 spike protein-driven
SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2.
From the early days of coronavirus outbreak in China, significant differences in terms
of severe cases and deaths have been reported between adult males and females (around
58 and 42%, respectively) . Moreover, this pattern seems to be largely repeating
itself, albeit with slightly different proportions, as indicated by recent epidemiological
data across distinct continents and countries . The international scientific community
is investigating the reasons behind these gender differences, with biological and
behavioral features (e.g., cigarette smoking) which have been called into question,
including TMPRSS2 .
Interestingly, TMPRSS2 gene has a pivotal role also in prostate cancer development
and progression. TMPRSS2 is expressed on the luminal side of the normal prostatic
epithelium and it is increased in malignant prostatic tissue. In particular, the TMPRSS2:v-ets
avian erythroblastosis virus E26 oncogene homolog (ERG) gene fusion is present in
about 50% of prostate tumors in Caucasian men and is frequently an early event in
prostate carcinogenesis [5,6]. TMPRS22 and ERG genes are located tandemly on chromosome
21q22 and expression of TMPRSS2 is androgen-regulated and prostate-specific . The
fusion results from intrachromosomal deletion of ~3-Mb of the interstitial region
between the TMPRSS2 and ERG loci or from an insertion of the interstitial region causing
a chromosomal rearrangement . The role of this gene fusion is crucial in the development
of prostate cancer because it leads to the activation of ERG transcription factor.
In fact, in the presence of this gene fusion androgen-responsive elements within the
TMPRSS2 promoter drive the overexpression of ERG. ERG is a member of the E-twenty-six
family members (ETS), master transcription factors that have a key role in differentiation,
apoptosis, cell proliferation and inflammation. TMPRSS2:ERG fusion can cause cancer
progression by disrupting the androgen receptor (AR) lineage-specific differentiation
program of the prostate and favoring EZH2-mediated cellular de-differentiation .
The gene fusion can produce a repression of the AR signaling, thus creating a selective
pressure that leads to the development of recurrent tumors with AR amplification and
resistance to hormone deprivation therapies. ERG can directly induce epigenetic silencing
of developmental regulators and tumor suppressor genes via direct activation of the
polycomb group protein EZH2, thus favoring EZH2-mediated stem cell-like de-differentiation
. Moreover, this gene fusion often coexists with phosphatase tensin homolog (PTEN)
loss, thus promoting the development of invasive carcinoma . TMPRSS2:ERG fusion
positive prostate tumors have also been associated with activation of the NOTCH pathway
that promotes proliferation and maintenance of progenitor cells in the developing
prostate. This finding could have therapeutic implication since NOTCH1 inhibition
can reduce cell growth and invasion . The prognostic and predictive role of TMPRSS2:ERG
fusion has been widely investigated. The presence of this fusion has been associated
with poor survival outcomes, aggressive disease and biochemical recurrence . Furthermore,
TMPRSS2:ERG fusion was not found to be predictive of response to abiraterone acetate
in metastatic castration resistant prostate cancer patients .
It is recognized that SARS-CoV-2 infection, similarly to SARS-CoV, is transmitted
through respiratory droplets which penetrate in the upper respiratory tract .
As stated above, TMPRSS2 seems to play a crucial role in SARS-CoV and SARS-CoV-2 pathogenesis;
moreover, despite TMPRSS2 expression is several times higher in prostate epithelium
compared with any other tissue, TMPRSS2 has been found also in the aerodigestive tract
. Interestingly, differences in TMPRSS2 expression in lung cells may vary across
different populations, an element which could be implied in susceptibility to coronavirus
and influenza virus infections. Thus, revealing how the expression of TMPRSS2 protein
in the lung could vary between men and women has been indicated as an important element
in understanding differential susceptibility to SARS-CoV-2 infection. Nonetheless,
several studies have reported controversial results, most of them suggesting that
constitutive expression of TMPRSS2 in lung cells do not seem to differ according to
Here, we investigate ACE2 and TMPRSS2 expression levels and their distribution across
cell types in lung tissue (12 donors, 39,778 cells) and in cells derived from subsegmental
bronchi al branches (four donors, 17,521 cells) by single nuclei and single cell RNA
sequencing, respectively. While TMPRSS2 is strongly expressed in both tissues, in
the subsegmental bronchial branches ACE2 is predominantly expressed in a transient
secretory cell type. Interestingly, these transiently differentiating cells show an
enrichment for pathways related to RHO GTPase function and viral processes suggesting
increased vulnerability for SARS-CoV-2 infection. Our data provide a rich resource
for future investigations of COVID-19 infection and pathogenesis
A report by Bertram et al. suggested that TMPRSS2 is less expressed in Type II alveolar
cells and alveolar macrophages than in bronchial epithelial cells ; moreover,
this study found no expression of TMPRSS2 protein in Type I alveolar cells of the
respiratory surface. In this context, another key element to consider could lie in
the modifications of lung TMPRSS2 expression caused by viral infections, as suggested
by previous findings on SARS-CoV and ACE2 receptor . Moreover, single nucleotide
polymorphisms (SNPs) have been linked to higher expression of TMPRSS2 protein, something
which has been associated with an increased susceptibility to influenza virus infection
A recent study by Song et al. analyzed gene co-expression of ACE2 and TMPRSS2 in 24,519
human prostate cells, finding that the 0.61% of club cells and the 0.40% of hillock
cells co-expressed TMPRSS2 and ACE2 . The authors conducted the same analysis
in human lung club cells, human lung secretory cells and murine lung club cells; the
report found that higher TMPRSS2 and ACE2 co-expression was detected in males pneumocytes
I/II compared with female cells, representing an interesting evidence which could
play a role in gender ‘pattern’ of COVID-19.
Another recent study by Lukassen et al. investigated ACE2 and TMPRSS2 expression levels
across 39,778 lung cells and in 17,521 cells derived from subsegmental bronchial branches
. Although TMPRSS2 expression resulted high in both tissues, subsegmental bronchial
branches cells showed higher ACE2 expression, especially in transient secretory cells;
more specifically, transient secretory cell types presented an enrichment of RHO GTPases
with their relative pathways. Most notably, RHO GTPases have been associated, according
to previous studies, with membrane remodeling and viral cycle, especially in terms
of entry, replication and viral spread [20,21]; thus, transient secretory pulmonary
cells could be particularly vulnerable to SARS-CoV-2 infection.
Since COVID-19 is a disease previously unknown to human beings, no proven treatments
exist at present and the most important public health solution would be an effective
vaccine . However, the male preference of SARS-CoV-2 and the androgen-dependent
expression of TMPRSS2 indicate that targeting TMPRSS2 could emerge as a novel option
to treat COVID-19, as in the case of SARS-CoV and influenza virus .
A recent study by Montopoli et al. analyzed data on 9280 SARS-CoV-2 positive patients,
of which 4532 (44%) males and 118 (1.3%) with prostate cancer . Males developed
more severe complications, were more frequently hospitalized (men 60% and women 40%),
and accounted for more deaths (men 62% and women 38%). Prostate cancer patients receiving
androgen deprivation therapy (ADT) had a significantly lower risk of SARS-CoV-2 infection
compared with patients who did not receive ADT (odds ratio: 4.05; 95% CI: 1.55–10.59).
This study sets the scenario for further studies assessing the role of antiandrogens
commonly used for prostate cancer patients to prevent or treat COVID-19.
Another recent study in 19 high-volume medical oncology departments in Italy examined
the frequency of COVID-19 in prostate cancer patients undergoing ADT, either alone
or in combination with another agent . A concomitant confirmed diagnosis of SARS-CoV-2
infection was found in 1.8% (36 out of 1949 total patients) of the examined population.
ADT did not seem to have a protective effect considering the higher lethality of SARS-CoV-2
in patients <70 years (25% in prostate cancer patients compared with 13% in infected
Italian males). The findings of these two analyses on prostate cancer patients seem
conflicting [22,23], supporting the need for further retrospective or prospective
evidence on the role of antiandrogen agents in patients with COVID-19.
Expression levels and variants in ACE2 and TMPRSS2 genes have been investigated for
their possible role in affecting COVID-19 severity in a large Italian cohort .
Italians resulted to have a significant decrease in the burden of deleterious variants
compared with Europeans. One the four SNPs with significant different frequency in
Italians compared with East Asians and Europeans is the missense substitution p.Val160Met,
that is associated with genomic rearrangements involving TMPRSS2 associated with higher
risk of prostate cancer . Moreover, in the analysis by Asselta et al. two haplotypes
(the first composed at least of SNPs rs463727, rs34624090, rs55964536, rs734056, rs4290734,
rs34783969, rs11702475, rs35899679 and rs35041537; the second composed of three SNPs,
rs2070788, rs9974589 and rs7364083) associated with upregulation of TMPRSS2 gene expression
resulted to be more frequent in Italians than in the East Asian population .
These findings are of particular interest considering the putative role of TMPRSS2
in SARS-CoV-2 infection. Considering that the expression of TMPRSS2 gene is modulated
by estrogens and androgens, hormone receptors signaling antagonists could be explored
as treatments strategies against COVID-19 for their role in downregulating TMPRSS2.
In this line, men with prostate cancer presenting TMPRSS2:ERG fusion and receiving
androgens receptor signaling inhibitors could represent a subset of patients with
reduced risk of SARS-CoV-2 infection or severity .
Regarding treatment implications, further data are needed to assess androgen targeting
agents in the management of COVID-19. Evaluating TMPRSS2 gene expression in lung tissue
in patients with prostate cancer undergoing antiandrogen agents could provide preliminary
data to elaborate clinical trials assessing these agents in COVID-19 patients.
In a recent in vitro study by Hoffmann et al., the TMPRSS2 inhibitor camostat mesylate
blocked the SARS-CoV-2 entry into primary lung cells, suggesting that TMPRSS2 could
represent a potential target in SARS-CoV-2 treatment . Nonetheless, previous studies
have suggested no gender differences in TMPRSS2 mRNA expression levels in pulmonary
tissue ; moreover, some authors reported that normal female androgen levels could
be able to regulate TMPRSS2 transcription, and similarly, TMPRSS2 also seems to respond
to estrogenic stimulation .
Since serine proteases inhibitors such as camostat mesylate and nafamostat are able
to block TMPRSS2, these antiandrogens could help in developing novel measures to inhibit
viral entry and pathogenesis in an in vivo setting . Studies are required with
the aim to investigate the association between the severity of COVID-19 disease and
androgenic activity, a connection which could represent the source of novel potential
treatments for COVID-19 infection.