Membrane-anchored serine proteases in health and disease

TMPRSS13 promotes the cell entry of swine acute diarrhea syndrome coronavirus

Swine acute diarrhea syndrome coronavirus (SADS-CoV) has caused severe intestinal diseases in pigs. It originates from bat coronaviruses HKU2 and has a potential risk of cross-species transmission, raising concerns about its zoonotic potential. Viral entry-related host factors are critical determinants of susceptibility to cells, tissues, or species, and remain to be elucidated for SADS-CoV. Type II transmembrane serine proteases (TTSPs) family is involved in many coronavirus infections and has trypsin-like catalytic activity. Here we examine all 18 members of the TTSPs family through CRISPR-based activation of endogenous protein expression in cells, and find that, in addition to TMPRSS2 and TMPRSS4, TMPRSS13 significantly facilitates SADS-CoV infection. This is confirmed by ectopic expression of TMPRSS13, and specific to trypsin-dependent SADS-CoV. Infection with pseudovirus bearing SADS-CoV spike protein indicates that TMPRSS13 acts at the entry step and is sensitive to serine protease inhibitor Camostat. Moreover, both human and pig TMPRSS13 are able to enhance the cell-cell membrane fusion and cleavage of spike protein. Overall, we demonstrate that TMPRSS13 is another host serine protease promoting the membrane-fusion entry of SADS-CoV, which may expand its host tropism by using diverse TTSPs.

Pigs lacking TMPRSS2 displayed fewer lung lesions and reduced inflammatory response when infected with influenza A virus

Influenza A virus (IAV) infection is initiated by hemagglutinin (HA), a glycoprotein exposed on the virion's lipid envelope that undergoes cleavage by host cell proteases to ensure membrane fusion, entry into the host cells, and completion of the viral cycle. Transmembrane protease serine S1 member 2 (TMPRSS2) is a host transmembrane protease expressed throughout the porcine airway epithelium and is purported to play a major role in the HA cleavage process, thereby influencing viral pathogenicity and tissue tropism. Pigs are natural hosts of IAV and IAV disease causes substantial economic impact on the pork industry worldwide. Previous studies in mice demonstrated that knocking out expression of TMPRSS2 gene was safe and inhibited the spread of IAV after experimental challenge. Therefore, we hypothesized that knockout of TMPRSS2 will prevent IAV infectivity in the swine model. We investigated this hypothesis by comparing pathogenesis of an H1N1pdm09 virus challenge in wildtype (WT) control and in TMPRSS2 knockout (TMPRSS2 -/-) pigs. We demonstrated that TMPRSS2 was expressed in the respiratory tract in WT pigs with and without IAV infection. No differences in nasal viral shedding and lung lavage viral titers were observed between WT and TMPRSS2 -/- pigs. However, the TMPRSS2 -/- pig group had significantly less lung lesions and significant reductions in antiviral and proinflammatory cytokines in the lung. The virus titer results in our direct challenge model contradict prior studies in the murine animal model, but the reduced lung lesions and cytokine profile suggest a possible role for TMPRSS2 in the proinflammatory antiviral response. Further research is warranted to investigate the role of TMPRSS2 in swine IAV infection and disease.

Precision nutrition to reset virus-induced human metabolic reprogramming and dysregulation (HMRD) in long-COVID

SARS-CoV-2, the etiological agent of COVID-19, is devoid of any metabolic capacity; therefore, it is critical for the viral pathogen to hijack host cellular metabolic machinery for its replication and propagation. This single-stranded RNA virus with a 29.9 kb genome encodes 14 open reading frames (ORFs) and initiates a plethora of virus-host protein-protein interactions in the human body. These extensive viral protein interactions with host-specific cellular targets could trigger severe human metabolic reprogramming/dysregulation (HMRD), a rewiring of sugar-, amino acid-, lipid-, and nucleotide-metabolism(s), as well as altered or impaired bioenergetics, immune dysfunction, and redox imbalance in the body. In the infectious process, the viral pathogen hijacks two major human receptors, angiotensin-converting enzyme (ACE)-2 and/or neuropilin (NRP)-1, for initial adhesion to cell surface; then utilizes two major host proteases, TMPRSS2 and/or furin, to gain cellular entry; and finally employs an endosomal enzyme, cathepsin L (CTSL) for fusogenic release of its viral genome. The virus-induced HMRD results in 5 possible infectious outcomes: asymptomatic, mild, moderate, severe to fatal episodes; while the symptomatic acute COVID-19 condition could manifest into 3 clinical phases: (i) hypoxia and hypoxemia (Warburg effect), (ii) hyperferritinemia ('cytokine storm'), and (iii) thrombocytosis (coagulopathy). The mean incubation period for COVID-19 onset was estimated to be 5.1 days, and most cases develop symptoms after 14 days. The mean viral clearance times were 24, 30, and 39 days for acute, severe, and ICU-admitted COVID-19 patients, respectively. However, about 25-70% of virus-free COVID-19 survivors continue to sustain virus-induced HMRD and exhibit a wide range of symptoms that are persistent, exacerbated, or new 'onset' clinical incidents, collectively termed as post-acute sequelae of COVID-19 (PASC) or long COVID. PASC patients experience several debilitating clinical condition(s) with >200 different and overlapping symptoms that may last for weeks to months. Chronic PASC is a cumulative outcome of at least 10 different HMRD-related pathophysiological mechanisms involving both virus-derived virulence factors and a multitude of innate host responses. Based on HMRD and virus-free clinical impairments of different human organs/systems, PASC patients can be categorized into 4 different clusters or sub-phenotypes: sub-phenotype-1 (33.8%) with cardiac and renal manifestations; sub-phenotype-2 (32.8%) with respiratory, sleep and anxiety disorders; sub-phenotype-3 (23.4%) with skeleto-muscular and nervous disorders; and sub-phenotype-4 (10.1%) with digestive and pulmonary dysfunctions. This narrative review elucidates the effects of viral hijack on host cellular machinery during SARS-CoV-2 infection, ensuing detrimental effect(s) of virus-induced HMRD on human metabolism, consequential symptomatic clinical implications, and damage to multiple organ systems; as well as chronic pathophysiological sequelae in virus-free PASC patients. We have also provided a few evidence-based, human randomized controlled trial (RCT)-tested, precision nutrients to reset HMRD for health recovery of PASC patients.

ACE2 and TMPRSS2 expression in patients before, during, and after SARS-CoV-2 infection

During the SARS-CoV-2 pandemic angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) were constantly under the scientific spotlight, but most studies evaluated ACE2 and TMPRSS2 expression levels in patients infected by SARS-CoV-2. Thus, this study aimed to evaluate the expression levels of both proteins before, during, and after-infection. For that, nasopharyngeal samples from 26 patients were used to measure ACE2/TMPRSS2 ex-pression via qPCR. Symptomatic patients presented lower ACE2 expression levels before and after the infection than those in asymptomatic patients; however, these levels increased during SARS-CoV-2 infection. In addition, symptomatic patients presented higher expression levels of TMPRSS2 pre-infection, which decreased in the following periods. In summary, ACE2 and TMPRSS2 expression levels are potential risk factors for the development of symptomatic COVID-19, and the presence of SARS-CoV-2 potentially modulates those levels.

Matriptase as a potential biomarker and therapeutic target in newly diagnosed type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder that affects the processing of carbohydrates, proteins, and lipids. In T2DM, metabolic dysregulation occurs through various pathways caused by increased levels of many adipokines and inflammatory chemokines. Impaired insulin-glucose metabolism occurs in tissues. The proteolytic enzyme matriptase is thought to be closely related to glucose metabolism due to its glycolization sites.

AIM

Our study aimed to evaluate the correlation between matriptase, a proteolytic enzyme, and metabolic parameters in individuals recently diagnosed with T2DM. We also sought to investigate the potential involvement of matriptase in the development of diabetes.

METHODS

We measured all participants' metabolic laboratory parameters, including basic biochemical tests, hemograms, high-sensitivity C-reactive protein (hsCRP), and matriptase levels.

RESULTS

Our results showed a significant increase in circulating matriptase levels in individuals with T2DM compared to the control group. Furthermore, individuals with metabolic syndrome had significantly higher matriptase levels than those without in the T2DM and control groups. We also observed that T2DM patients had elevated levels of Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), hsCRP, and matriptase, which displayed a positive correlation.

CONCLUSION

Our study is the first to report elevated levels of matriptase in individuals with newly diagnosed T2DM and/or metabolic syndrome. Additionally, we found a significant positive correlation between matriptase levels and metabolic and inflammatory parameters, indicating a potential role for matriptase in the pathogenesis of T2DM and glucose metabolism. Further research on matriptase could lead to its recognition as a novel target for investigation.

Spatial position is a key determinant of N-glycan functionality of the scavenger receptor cysteine-rich domain of human hepsin

The scavenger receptor cysteine-rich (SRCR) domain is a key constituent in diverse proteins. N-glycosylation is important in protein expression and function. In the SRCR domain of different proteins, N-glycosylation sites and functionality vary substantially. In this study, we examined the importance of N-glycosylation site positions in the SRCR domain of hepsin, a type II transmembrane serine protease involved in many pathophysiological processes. We analysed hepsin mutants with alternative N-glycosylation sites in the SRCR and protease domains using three-dimensional modelling, site-directed mutagenesis, HepG2 cell expression, immunostaining, and western blotting. We found that the N-glycan function in the SRCR domain in promoting hepsin expression and activation on the cell surface cannot be replaced by alternatively created N-glycans in the protease domain. Within the SRCR domain, the presence of an N-glycan in a confined surface area was essential for calnexin-assisted protein folding, endoplasmic reticulum (ER) exiting, and zymogen activation of hepsin on the cell surface. Hepsin mutants with alternative N-glycosylation sites on the opposite side of the SRCR domain were trapped by ER chaperones, resulting in the activation of the unfolded protein response in HepG2 cells. These results indicate that the spatial N-glycan positioning in the SRCR domain is a key determinant in the interaction with calnexin and subsequent cell surface expression of hepsin. These findings may help to understand the conservation and functionality of N-glycosylation sites in the SRCR domains of different proteins.

Copy Number Variation Regions Differing in Segregation Patterns Span Different Sets of Genes

Copy number variations regions (CNVRs) can be classified either as segregating, when found in both parents, and offspring, or non-segregating. A total of 65 segregating and 31 non-segregating CNVRs identified in at least 10 individuals within a dense pedigree of the Gochu Asturcelta pig breed was subjected to enrichment and functional annotation analyses to ascertain their functional independence and importance. Enrichment analyses allowed us to annotate 1018 and 351 candidate genes within the bounds of the segregating and non-segregating CNVRs, respectively. The information retrieved suggested that the candidate genes spanned by segregating and non-segregating CNVRs were functionally independent. Functional annotation analyses allowed us to identify nine different significantly enriched functional annotation clusters (ACs) in segregating CNVR candidate genes mainly involved in immunity and regulation of the cell cycle. Up to five significantly enriched ACs, mainly involved in reproduction and meat quality, were identified in non-segregating CNVRs. The current analysis fits with previous reports suggesting that segregating CNVRs would explain performance at the population level, whereas non-segregating CNVRs could explain between-individuals differences in performance.

Intersection of Coagulation and Fibrinolysis by the Glycosylphosphatidylinositol (GPI)-Anchored Serine Protease Testisin

Hemostasis is a delicate balance between coagulation and fibrinolysis that regulates the formation and removal of fibrin, respectively. Positive and negative feedback loops and crosstalk between coagulation and fibrinolytic serine proteases maintain the hemostatic balance to prevent both excessive bleeding and thrombosis. Here, we identify a novel role for the glycosylphosphatidylinositol (GPI)-anchored serine protease testisin in the regulation of pericellular hemostasis. Using in vitro cell-based fibrin generation assays, we found that the expression of catalytically active testisin on the cell surface accelerates thrombin-dependent fibrin polymerization, and intriguingly, that it subsequently promotes accelerated fibrinolysis. We find that the testisin-dependent fibrin formation is inhibited by rivaroxaban, a specific inhibitor of the central prothrombin-activating serine protease factor Xa (FXa), demonstrating that cell-surface testisin acts upstream of factor X (FX) to promote fibrin formation at the cell surface. Unexpectedly, testisin was also found to accelerate fibrinolysis by stimulating the plasmin-dependent degradation of fibrin and enhancing plasmin-dependent cell invasion through polymerized fibrin. Testisin was not a direct activator of plasminogen, but it is able to induce zymogen cleavage and the activation of pro-urokinase plasminogen activator (pro-uPA), which converts plasminogen to plasmin. These data identify a new proteolytic component that can regulate pericellular hemostatic cascades at the cell surface, which has implications for angiogenesis, cancer biology, and male fertility.

Structural analysis of pathogenic TMPRSS3 variants and their cochlear implantation outcomes of sensorineural hearing loss

TMPRSS3, a type II transmembrane serine protease, is involved in various biological processes including the development and maintenance of the inner ear. Biallelic variants in TMPRSS3 typically result in altered protease activity, causing autosomal recessive non-syndromic hearing loss (ARNSHL). Structural modeling has been conducted to predict the pathogenicity of TMPRSS3 variants and to gain a better understanding of their prognostic correlation. The mutant-driven changes in TMPRSS3 had substantial impacts on neighboring residues, and the pathogenicity of variants was predicted based on their distance from the active site. However, a more in-depth analysis of other factors, such as intramolecular interactions and protein stability, which affect proteolytic activities is yet to be conducted for TMPRSS3 variants. Among 620 probands who provided genomic DNA for molecular genetic testing, eight families with biallelic TMPRSS3 variants that were segregated in a trans configuration were included. Seven different mutant alleles, either homozygous or compound heterozygous, contributed to TMPRSS3-associated ARNSHL, expanding the genotypic spectrum of disease-causing TMPRSS3 variants. Through three-dimensional modeling and structural analysis, TMPRSS3 variants compromise protein stability by altering intramolecular interactions, and each mutant differently interacts with the serine protease active site. Furthermore, the changes in intramolecular interactions leading to regional instability correlate with the results of functional assay and residual hearing function, but overall stability predictions do not. Our findings also build on previous evidence indicating that most recipients with TMPRSS3 variants have favorable cochlear implantation (CI) outcomes. We found that age at CI was significantly correlated with speech performance outcomes; genotype was not correlated with these outcomes. Collectively, the results of this study contribute to a more structural understanding of the underlying mechanisms of ARNSHL caused by TMPRSS3 variants.

Plant derived active compounds as potential anti SARS-CoV-2 agents: an in-silico study

Plants are a valued potential source of drugs for a variety of diseases and are often considered less toxic to humans. We investigated antiviral compounds that may potentially target SARS-CoV-2 antigenic spike (S) and host proteins; angiotensin-converting enzyme2 (ACE2), and transmembrane serine protease2 (TMPRSS2). We scrutinized 36 phytochemicals from 15 Indian medicinal plants known to be effective against RNA viruses via molecular docking. Besides, the TMPRSS2 structure was modeled and validated using the SWISS-MODEL. Docking was performed using Autodock Vina and 4.2 followed by visualization of the docking poses on Pymol version 2.4.0 and Discovery Studio Visualizer. Molecular docking showed that 12 out of 36 active compounds interacted efficiently with S, ACE2, and TMPRSS2 proteins. The ADMET profile generated using the swissADME and pkCSM server revealed that these compounds were possessed druggable properties. The Amber 12 simulation package was used to carry out energy minimizations and molecular dynamics (MD) simulations. The total simulation time for both S protein: WFA and S protein: WND complexes was 300 ns (100 ns per replica). A total of 120 structures were extracted from the last 60 ns of each MD simulation for further analysis. MM-PBSA and MM-GBSA were employed to assess the binding energy of each ligand and the receptor-binding domain of the viral S-protein. The methods suggested that WND and WFA showed thermodynamically favorable binding energies, and the S protein had a higher affinity with WND. Interestingly, Leu455 hotspot residue in the S protein, also predicted to participate in binding with ACE2, was engaged by WND and WFA. HighlightsPlants' natural active compounds may aid in the development of COVID-19 therapeutics.MD simulation study revealed stable binding of withanolide D and withaferin A with spike proteinWithanolide D and withaferin A could be effective against SARS-CoV-2 spike protein.Discovery of druggable agents that have less or lack of binding affinity with ACE2 to avoid the organs associated with comorbidities.According to ADMET selected phytochemicals may be used as druggable compounds.Communicated by Ramaswamy H. Sarma.

Uncovering a Subtype of Microviridins via the Biosynthesis Study of FR901451

Microviridins are a class of ribosomally synthesized and post-translationally modified peptides originally discovered from cyanobacteria, featured by intramolecular ω-ester and ω-amide bonds catalyzed by two ATP-grasp ligases. In this study, 104 biosynthetic gene clusters of microviridins from Bacteroidetes were bioinformatically analyzed, which unveiled unique features of precursor peptides. The analysis of core peptides revealed a microviridin-like biosynthetic gene cluster from Chitinophagia japonensis DSM13484 consisting of two potential precursors ChiA1 and ChiA2. Unexpectedly, the core peptide sequence of ChiA1 is consistent with the backbone of the elastase-inhibiting peptide FR901451, while ChiA2 is likely to be a precursor of an unknown product. However, an unusual C-terminal follower cleavage compared to the previously known microviridin pathways was observed and found to be dispensable for other modifications. To confirm the biosynthetic origin of FR901451, ATP-grasp ligases ChiC and ChiB were biochemically characterized to be responsible for the intramolecular ester and amide bond formation, respectively. In vitro reconstitution of the pathway showed the three-fold dehydrations of ChiA1 while unusual four-fold dehydrations were observed for ChiA2. Furthermore, in vivo gene coexpression facilitated the production of chitinoviridin A1 (FR901451) and two novel microviridin-class compounds chitinoviridin A2A and chitinoviridin A2B, with an extra macrolactone ring. All of these peptides showed potent inhibitory effects against elastase and chymotrypsin independently.

Identification of a rare Gli1+ progenitor cell population contributing to liver regeneration during chronic injury

In adults, hepatocytes are mainly replenished from the existing progenitor pools of hepatocytes and cholangiocytes during chronic liver injury. However, it is unclear whether other cell types in addition to classical hepatocytes and cholangiocytes contribute to hepatocyte regeneration after chronic liver injuries. Here, we identified a new biphenotypic cell population that contributes to hepatocyte regeneration during chronic liver injuries. We found that a cell population expressed Gli1 and EpCAM (EpCAM⁺Gli1⁺), which was further characterized with both epithelial and mesenchymal identities by single-cell RNA sequencing. Genetic lineage tracing using dual recombinases revealed that Gli1⁺ nonhepatocyte cell population could generate hepatocytes after chronic liver injury. EpCAM⁺Gli1⁺ cells exhibited a greater capacity for organoid formation with functional hepatocytes in vitro and liver regeneration upon transplantation in vivo. Collectively, these findings demonstrate that EpCAM⁺Gli1⁺ cells can serve as a new source of liver progenitor cells and contribute to liver repair and regeneration.

Transmembrane serine protease TMPRSS2 implicated in SARS-CoV-2 infection is autoactivated intracellularly and requires N-glycosylation for regulation

Transmembrane protease serine 2 (TMPRSS2) is a membrane-bound protease expressed in many human epithelial tissues, including the airway and lung. TMPRSS2-mediated cleavage of viral spike protein is a key mechanism in severe acute respiratory syndrome coronavirus 2 activation and host cell entry. To date, the cellular mechanisms that regulate TMPRSS2 activity and cell surface expression are not fully characterized. In this study, we examined two major post-translational events, zymogen activation and N-glycosylation, in human TMPRSS2. In experiments with human embryonic kidney 293, bronchial epithelial 16HBE, and lung alveolar epithelial A549 cells, we found that TMPRSS2 was activated via intracellular autocatalysis and that this process was blocked in the presence of hepatocyte growth factor activator inhibitors 1 and 2. By glycosidase digestion and site-directed mutagenesis, we showed that human TMPRSS2 was N-glycosylated. N-glycosylation at an evolutionarily conserved site in the scavenger receptor cysteine-rich domain was required for calnexin-assisted protein folding in the endoplasmic reticulum and subsequent intracellular trafficking, zymogen activation, and cell surface expression. Moreover, we showed that TMPRSS2 cleaved severe acute respiratory syndrome coronavirus 2 spike protein intracellularly in human embryonic kidney 293 cells. These results provide new insights into the cellular mechanism in regulating TMPRSS2 biosynthesis and function. Our findings should help to understand the role of TMPRSS2 in major respiratory viral diseases.

TMPRSS13 zymogen activation, surface localization, and shedding is regulated by proteolytic cleavage within the non-catalytic stem region

TMPRSS13 is a member of the type II transmembrane serine protease (TTSP) family. Here we characterize a novel post-translational mechanism important for TMPRSS13 function: proteolytic cleavage within the extracellular TMPRSS13 stem region located between the transmembrane domain and the first site of N-linked glycosylation at asparagine (N)-250 in the scavenger receptor cysteine rich (SRCR) domain. Importantly, the catalytic competence of TMPRSS13 is essential for stem region cleavage, suggesting an autonomous mechanism of action. Site-directed mutagenesis of the 10 basic amino acids (four arginine and six lysine residues) in this region abrogated zymogen activation and catalytic activity of TMPRSS13, as well as phosphorylation, cell surface expression, and shedding. Mutation analysis of individual arginine residues identified R223, a residue located between the low-density lipoprotein receptor class A domain and the SRCR domain, as important for stem region cleavage. Mutation of R223 causes a reduction in the aforementioned functional processing steps of TMPRSS13. These data provide further insight into the roles of different post-translational modifications as regulators of the function and localization of TMPRSS13. Additionally, the data suggest the presence of complex interconnected regulatory mechanisms that may serve to ensure the proper levels of cell-surface and pericellular TMPRSS13-mediated proteolysis under homeostatic conditions.

Functionally impaired isoforms regulate TMPRSS6 proteolytic activity

TMPRSS6 is a type II transmembrane serine protease involved in iron homeostasis expressed as 4 isoforms in humans. TMPRSS6 isoform 2 downregulates hepcidin production by cleaving hemojuvelin and other surface proteins of hepatocytes. The functions of catalytically impaired isoforms 3 and 4 are still unknown. Here we demonstrate that TMPRSS6 isoforms 3 and 4 reduce the proteolytic activity of isoform 2 and uncover the ability of isoforms to interact. Moreover, we identified 49 potential protein partners common to TMPRSS6 isoforms, including TfR1, known to be involved in iron regulation. By co-expressing TMPRSS6 and TfR1, we show that TfR1 is cleaved and shed from the cell surface. Further, we demonstrate that TMPRSS6 isoforms 3 and 4 behave as dominant negative.

SARS-CoV-2 and Emerging Variants: Unmasking Structure, Function, Infection, and Immune Escape Mechanisms

As of April 1, 2022, over 468 million COVID-19 cases and over 6 million deaths have been confirmed globally. Unlike the common coronavirus, SARS-CoV-2 has highly contagious and attracted a high level of concern worldwide. Through the analysis of SARS-CoV-2 structural, non-structural, and accessory proteins, we can gain a deeper understanding of structure-function relationships, viral infection mechanisms, and viable strategies for antiviral therapy. Angiotensin-converting enzyme 2 (ACE2) is the first widely acknowledged SARS-CoV-2 receptor, but researches have shown that there are additional co-receptors that can facilitate the entry of SARS-CoV-2 to infect humans. We have performed an in-depth review of published papers, searching for co-receptors or other auxiliary membrane proteins that enhance viral infection, and analyzing pertinent pathogenic mechanisms. The genome, and especially the spike gene, undergoes mutations at an abnormally high frequency during virus replication and/or when it is transmitted from one individual to another. We summarized the main mutant strains currently circulating global, and elaborated the structural feature for increased infectivity and immune evasion of variants. Meanwhile, the principal purpose of the review is to update information on the COVID-19 outbreak. Many countries have novel findings on the early stage of the epidemic, and accruing evidence has rewritten the timeline of the outbreak, triggering new thinking about the origin and spread of COVID-19. It is anticipated that this can provide further insights for future research and global epidemic prevention and control.

Transmembrane serine protease 2 (TMPRSS2) proteolytically activates the epithelial sodium channel (ENaC) by cleaving the channel's γ-subunit

The epithelial sodium channel (ENaC) is a heterotrimer consisting of α-, β-, and γ-subunits. Channel activation requires proteolytic release of inhibitory tracts from the extracellular domains of α-ENaC and γ-ENaC; however, the proteases involved in the removal of the γ-inhibitory tract remain unclear. In several epithelial tissues, ENaC is coexpressed with the transmembrane serine protease 2 (TMPRSS2). Here, we explored the effect of human TMPRSS2 on human αβγ-ENaC heterologously expressed in Xenopus laevis oocytes. We found that coexpression of TMPRSS2 stimulated ENaC-mediated whole-cell currents by approximately threefold, likely because of an increase in average channel open probability. Furthermore, TMPRSS2-dependent ENaC stimulation was not observed using a catalytically inactive TMPRSS2 mutant and was associated with fully cleaved γ-ENaC in the intracellular and cell surface protein fractions. This stimulatory effect of TMPRSS2 on ENaC was partially preserved when inhibiting its proteolytic activity at the cell surface using aprotinin but was abolished when the γ-inhibitory tract remained attached to its binding site following introduction of two cysteine residues (S155C–Q426C) to form a disulfide bridge. In addition, computer simulations and site-directed mutagenesis experiments indicated that TMPRSS2 can cleave γ-ENaC at sites both proximal and distal to the γ-inhibitory tract. This suggests a dual role of TMPRSS2 in the proteolytic release of the γ-inhibitory tract. Finally, we demonstrated that TMPRSS2 knockdown in cultured human airway epithelial cells (H441) reduced baseline proteolytic activation of endogenously expressed ENaC. Thus, we conclude that TMPRSS2 is likely to contribute to proteolytic ENaC activation in epithelial tissues in vivo.

TMPRSS12 Functions in Meiosis and Spermiogenesis and Is Required for Male Fertility in Mice

Serine proteases are involved in many physiological activities as initiators of proteolytic cascades, and some members have been reported to play roles in male reproduction. Transmembrane serine protease 12 (TMPRSS12) has been shown to regulate sperm motility and uterotubal junction migration in mice, but its role in the testis remains unknown. In this study, we verified that TMPRSS12 was expressed in the spermatocytes and spermatids of testis and the acrosome of sperm. Mice deficient in Tmprss12 exhibited male sterility. In meiosis, TMPRSS12 was demonstrated to regulate synapsis and double-strand break repair; spermatocytes of Tmprss12^−/− mice underwent impaired meiosis and subsequent apoptosis, resulting in reduced sperm counts. During spermiogenesis, TMPRSS12 was found to function in the development of mitochondria; abnormal mitochondrial structure in Tmprss12^−/− sperm led to reduced availability of ATP, impacting sperm motility. The differential protein expression profiles of testes in Tmprss12^−/− and wild-type mice and further molecule identification revealed potential targets of TMPRSS12 related to meiosis and mitochondrial function. Besides, TMPRSS12 was also found to be involved in a series of sperm functions, including capacitation, acrosome reaction and sperm-egg interaction. These data imply that TMPRSS12 plays a role in multiple aspects of male reproduction.

Anti-Protease Activity Deficient Secretory Leukocyte Protease Inhibitor (SLPI) Exerts Cardioprotective Effect against Myocardial Ischaemia/Reperfusion

Inhibition of proteases shows therapeutic potential. Our previous studies demonstrated the cardioprotection by the Secretory Leukocyte Protease Inhibitor (SLPI) against myocardial ischaemia/reperfusion (I/R) injury. However, it is unclear whether the cardioprotective effect of SLPI seen in our previous works is due to the inhibition of protease enzymes. Several studies demonstrate that the anti-protease independent activity of SLPI could provide therapeutic benefits. Here, we show for the first time that recombinant protein of anti-protease deficient mutant SLPI (L72K, M73G, L74G) (mt-SLPI) could significantly reduce cell death and intracellular reactive oxygen species (ROS) production against an in vitro simulated I/R injury. Furthermore, post-ischaemic treatment of mt-SLPI is found to significantly reduce infarct size and cardiac biomarkers lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) activity, improve cardiac functions, attenuate I/R induced-p38 MAPK phosphorylation, and reduce apoptotic regulatory protein levels, including Bax, cleaved-Caspase-3 and total Capase-8, in rats subjected to an in vivo I/R injury. Additionally, the beneficial effect of mt-SLPI was not significantly different from the wildtype (wt-SLPI). In summary, SLPI could provide cardioprotection without anti-protease activity, which could be more clinically beneficial in terms of providing cardioprotection without interfering with basal serine protease activity.

Distinctive Roles of Furin and TMPRSS2 in SARS-CoV-2 Infectivity

The spike protein (S) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) directs infection of the lungs and other tissues following its binding to the angiotensin-converting enzyme 2 (ACE2) receptor. For effective infection, the S protein is cleaved at two sites: S1/S2 and S2′. The “priming” of the surface S protein at S1/S2 (PRRAR₆₈₅↓) [the underlined basic amino acids refer to critical residues needed for the furin recognition] by furin has been shown to be important for SARS-CoV-2 infectivity in cells and small-animal models. In this study, for the first time we unambiguously identified by proteomics the fusion activation site S2′ as KPSKR₈₁₅↓ (the underlined basic amino acids refer to critical residues needed for the furin recognition) and demonstrated that this cleavage was strongly enhanced by ACE2 engagement with the S protein. Novel pharmacological furin inhibitors (BOS inhibitors) effectively blocked endogenous S protein processing at both sites in HeLa cells, and SARS-CoV-2 infection of lung-derived Calu-3 cells was completely prevented by combined inhibitors of furin (BOS) and type II transmembrane serine protease 2 (TMPRSS2) (camostat). Quantitative analyses of cell-to-cell fusion and S protein processing revealed that ACE2 shedding by TMPRSS2 was required for TMPRSS2-mediated enhancement of fusion in the absence of S1/S2 priming. We further demonstrated that the collectrin dimerization domain of ACE2 was essential for the effect of TMPRSS2 on cell-to-cell fusion. Overall, our results indicate that furin and TMPRSS2 act synergistically in viral entry and infectivity, supporting the combination of furin and TMPRSS2 inhibitors as potent antivirals against SARS-CoV-2.

IMPORTANCE SARS-CoV-2, the etiological agent of COVID-19, has so far resulted in >6.1 million deaths worldwide. The spike protein (S) of the virus directs infection of the lungs and other tissues by binding the angiotensin-converting enzyme 2 (ACE2) receptor. For effective infection, the S protein is cleaved at two sites: S1/S2 and S2′. Cleavage at S1/S2 induces a conformational change favoring the S protein recognition by ACE2. The S2′ cleavage is critical for triggering membrane fusion and virus entry into host cells. Our study highlights the complex dynamics of interaction between the S protein, ACE2, and the host proteases furin and TMPRSS2 during SARS-CoV-2 entry and suggests that the combination of a nontoxic furin inhibitor with a TMPRSS2 inhibitor significantly reduces viral entry in lung cells, as evidenced by an average synergistic ∼95% reduction of viral infection. This represents a powerful novel antiviral approach to reduce viral spread in individuals infected by SARS-CoV-2 or future related coronaviruses.

The discovery and development of transmembrane serine protease 2 (TMPRSS2) inhibitors as candidate drugs for the treatment of COVID-19

INTRODUCTION

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has caused the devastating pandemic named coronavirus disease 2019 (COVID-19). Unfortunately, the discovery of antiviral agents to combat COVID-19 is still an unmet need. Transmembrane serine protease 2 (TMPRSS2) is an important mediator in viral infection and thus, TMPRRS2 inhibitors may be attractive agents for COVID-19 treatment.

AREAS COVERED

This review article discusses the role of TMPRSS2 in SARS-CoV-2 cell entry and summarizes the inhibitors of TMPRSS2 and their potential anti-SARS activity. Two known TMPRSS2 inhibitors, namely camostat and nafamostat, approved drugs for the treatment of pancreatitis, are under clinical trials as potential drugs against COVID-19.

EXPERT OPINION

Due to the lack of the crystal structure of TMPRSS2, homology models have been developed to study the interactions of known inhibitors, including repurposed drugs, with the enzyme. However, novel TMPRSS2 inhibitors have been identified through high-throughput screening, and appropriate assays studying their in vitro activity have been set up. The discovery of TMPRSS2's crystal structure will facilitate the rational design of novel inhibitors and in vivo studies and clinical trials will give a clear answer if TMPRSS2 inhibitors could be a new weapon against COVID-19.

In vitro interaction of potential antiviral TMPRSS2 inhibitors with human serum albumin and cytochrome P 450 isoenzymes

The interactions of four sulfonylated Phe(3-Am)-derived inhibitors (MI-432, MI-463, MI-482 and MI-1900) of type II transmembrane serine proteases (TTSP) such as transmembrane protease serine 2 (TMPRSS2) were examined with serum albumin and cytochrome P450 (CYP) isoenzymes. Complex formation with albumin was investigated using fluorescence spectroscopy. Furthermore, microsomal hepatic CYP1A2, 2C9, 2C19 and 3A4 activities in presence of these inhibitors were determined using fluorometric assays. The inhibitory effects of these compounds on human recombinant CYP3A4 enzyme were also examined. In addition, microsomal stability assays (60-min long) were performed using an UPLC-MS/MS method to determine depletion percentage values of each compound. The inhibitors showed no or only weak interactions with albumin, and did not inhibit CYP1A2, 2C9 and 2C19. However, the compounds tested proved to be potent inhibitors of CYP3A4 in both assays performed. Within one hour, 20%, 12%, 14% and 25% of inhibitors MI-432, MI-463, MI-482 and MI-1900, respectively, were degraded. As essential host cell factor for the replication of the pandemic SARS-CoV-2, the TTSP TMPRSS2 emerged as an important target in drug design. Our study provides further preclinical data on the characterization of this type of inhibitors for numerous trypsin-like serine proteases.

A Review of Special Considerations on Insulin Resistance Induced Hyperandrogenemia in Women with Polycystic Ovary Syndrome: A Prominent COVID-19 Risk Factor

Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) infecting mechanism depends on hosting angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) as essential components and androgens as regulators for inducing the expression of these components. Therefore, hyperandrogenism-related disease such as polycystic ovary syndrome (PCOS) in insulin resistant women in reproductive-age is a high-risk factor for SARS-CoV-2 infection. Here, we describe the signaling pathways that might increase the susceptibility and severity of this new pandemic in PCOS women with insulin resistance (IR). Luteinizing hormone and insulin increase the risk of SARS-CoV-2 infection in these patients via the induction of steroidogenic enzymes expression through cAMP-response element binding protein and Forkhead box protein O1 (FOXO1), respectively. TMPRSS2 expression is activated through phosphorylation of FOXO1 in ovaries. In other words, SARS-CoV-2 infection is associated with temporary IR by affecting ACE2 and disturbing β-pancreatic function. Therefore, PCOS, IR, and SARS-CoV-2 infection are three corners of the triangle that have complicated relations, and their association might increase the risk of SARS-CoV-2 infection and severity.

Secretases Related to Amyloid Precursor Protein Processing

Alzheimer’s disease (AD) is a common neurodegenerative disease whose prevalence increases with age. An increasing number of findings suggest that abnormalities in the metabolism of amyloid precursor protein (APP), a single transmembrane aspartic protein that is cleaved by β- and γ-secretases to produce β-amyloid protein (Aβ), are a major pathological feature of AD. In recent years, a large number of studies have been conducted on the APP processing pathways and the role of secretion. This paper provides a summary of the involvement of secretases in the processing of APP and the potential drug targets that could provide new directions for AD therapy.

SARS-CoV-2 and helminth co-infections, and environmental pollution exposure: An epidemiological and immunological perspective

Soil-transmitted helminths infect billions of people globally, particularly those residing in low- and middle-income regions with poor environmental sanitation and high levels of air and water pollution. Helminths display potent immunomodulatory activity by activating T helper type 2 (Th2) anti-inflammatory and Th3 regulatory immune responses. The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus that causes Coronavirus disease 2019 (COVID-19), can exacerbate Th1/Th17 pro-inflammatory cytokine production in humans, leading to a cytokine storm. Air pollutants (particulate matter, oxygen radicals, hydrocarbons and volatile organic compounds) and water pollutants (metals and organic chemicals) can also intensify Th1/Th17 immune response and could exacerbate SARS-CoV-2 related respiratory distress and failure. The present review focused on the epidemiology of SARS-CoV-2, helminths and fine particulate matter 2.5 µm or less in diameter (PM2.5) air pollution exposure in helminth endemic regions, the possible immunomodulatory activity of helminths against SARS-CoV-2 hyper-inflammatory immune response, and whether air and water pollutants can further exacerbate SARS-CoV-2 related cytokine storm and in the process hinder helminths immunomodulatory functionality. Helminth Th2/Th3 immune response is associated with reductions in lung inflammation and damage, and decreased expression levels of angiotensin-converting enzyme 2 (ACE2) receptors (SARS-CoV-2 uses the ACE2 receptors to infect cells and associated with extensive lung damage). However, air pollutants are associated with overexpression of ACE2 receptors in the epithelial cell surface of the respiratory tract and exhaustion of Th2 immune response. Helminth-induced immunosuppression activity reduces vaccination efficacy, and diminishes vital Th1 cytokine production immune responses that are crucial for combating early stage infections. This could be reversed by continuous air pollution exposure which is known to intensify Th1 pro-inflammatory cytokine production to a point where the immunosuppressive activities of helminths could be hindered. Again, suppressed activities of helminths can also be disadvantageous against SARS-CoV-2 inflammatory response. This "yin and yang" approach seems complex and requires more understanding. Further studies are warranted in a cohort of SARS-CoV-2 infected individuals residing in helminths and air pollution endemic regions to offer more insights, and to impact mass periodic deworming programmes and environmental health policies.

Computational and in vitro experimental analyses of the anti-COVID-19 potential of Mortaparib and MortaparibPlus

Coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has become a global health emergency. Although new vaccines have been generated and being implicated, discovery and application of novel preventive and control measures are warranted. We aimed to identify compounds that may possess the potential to either block the entry of virus to host cells or attenuate its replication upon infection. Using host cell surface receptor expression (angiotensin-converting enzyme 2 (ACE2) and Transmembrane protease serine 2 (TMPRSS2)) analysis as an assay, we earlier screened several synthetic and natural compounds and identified candidates that showed ability to down-regulate their expression. Here, we report experimental and computational analyses of two small molecules, Mortaparib and MortaparibPlus that were initially identified as dual novel inhibitors of mortalin and PARP-1, for their activity against SARS-CoV-2. In silico analyses showed that MortaparibPlus, but not Mortaparib, stably binds into the catalytic pocket of TMPRSS2. In vitro analysis of control and treated cells revealed that MortaparibPlus caused down-regulation of ACE2 and TMPRSS2; Mortaparib did not show any effect. Furthermore, computational analysis on SARS-CoV-2 main protease (Mpro) that also predicted the inhibitory activity of MortaparibPlus. However, cell-based antiviral drug screening assay showed 30-60% viral inhibition in cells treated with non-toxic doses of either MortaparibPlus or Mortaparib. The data suggest that these two closely related compounds possess multimodal anti-COVID-19 activities. Whereas MortaparibPlus works through direct interactions/effects on the host cell surface receptors (ACE2 and TMPRSS2) and the virus protein (Mpro), Mortaparib involves independent mechanisms, elucidation of which warrants further studies.

Identification of novel TMPRSS2 inhibitors for COVID-19 using e-pharmacophore modelling, molecular docking, molecular dynamics and quantum mechanics studies

SARS coronavirus 2 (SARS-CoV-2) has spread rapidly around the world and continues to have a massive global health effect, contributing to an infectious respiratory illness called coronavirus infection-19 (COVID-19). TMPRSS2 is an emerging molecular target that plays a role in the early stages of SARS-CoV-2 infection; hence, inhibiting its activity might be a target for COVID-19. This study aims to use many computational approaches to provide compounds that could be optimized into clinical candidates. As there is no experimentally derived protein information, initially we develop the TMPRSS2 model. Then, we generate a pharmacophore model from TMPRSS2 active site consequently, and the developed models were employed for the screening of one million molecules from the Enamine database. The created model was then screened using e-pharmacophore-based screening, molecular docking, free energy estimation and molecular dynamic simulation. Also, ADMET prediction and density functional theory calculations were performed. Three potential molecules (Z126202570, Z46489368, and Z422255982) exhibited promising stable binding interactions with the target. In conclusion, these findings empower further in vitro and clinical assessment for these compounds as novel anti-COVID19 agents.

Computational Analysis of Missense Variants in the Human Transmembrane Protease Serine 2 (TMPRSS2) and SARS-CoV-2

The human transmembrane protease serine 2 (TMPRSS2) protein plays an important role in prostate cancer progression. It also facilitates viral entry into target cells by proteolytically cleaving and activating the S protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In the current study, we used different available tools like SIFT, PolyPhen2.0, PROVEAN, SNAP2, PMut, MutPred2, I-Mutant Suite, MUpro, iStable, ConSurf, ModPred, SwissModel, PROCHECK, Verify3D, and TM-align to identify the most deleterious variants and to explore possible effects on the TMPRSS2 stability, structure, and function. The six missense variants tested were evaluated to have deleterious effects on the protein by SIFT, PolyPhen2.0, PROVEAN, SNAP2, and PMut. Additionally, V160M, G181R, R240C, P335L, G432A, and D435Y variants showed a decrease in stability by at least 2 servers; G181R, G432A, and D435Y are highly conserved and identified posttranslational modifications sites (PTMs) for proteolytic cleavage and ADP-ribosylation using ConSurf and ModPred servers. The 3D structure of TMPRSS2 native and mutants was generated using 7 meq as a template from the SwissModeller group, refined by ModRefiner, and validated using the Ramachandran plot. Hence, this paper can be advantageous to understand the association between these missense variants rs12329760, rs781089181, rs762108701, rs1185182900, rs570454392, and rs867186402 and susceptibility to SARS-CoV-2.

Posttranslational modifications of serine protease TMPRSS13 regulate zymogen activation, proteolytic activity, and cell surface localization

TMPRSS13, a member of the type II transmembrane serine protease (TTSP) family, harbors four N-linked glycosylation sites in its extracellular domain. Two of the glycosylated residues are located in the scavenger receptor cysteine-rich (SRCR) protein domain, while the remaining two sites are in the catalytic serine protease (SP) domain. In this study, we examined the role of N-linked glycosylation in the proteolytic activity, autoactivation, and cellular localization of TMPRSS13. Individual and combinatory site-directed mutagenesis of the glycosylated asparagine residues indicated that glycosylation of the SP domain is critical for TMPRSS13 autoactivation and catalytic activity toward one of its protein substrates, the prostasin zymogen. Additionally, SP domain glycosylation-deficient TMPRSS13 displayed impaired trafficking of TMPRSS13 to the cell surface, which correlated with increased retention in the endoplasmic reticulum. Importantly, we showed that N-linked glycosylation was a critical determinant for subsequent phosphorylation of endogenous TMPRSS13. Taken together, we conclude that glycosylation plays an important role in regulating TMPRSS13 activation and activity, phosphorylation, and cell surface localization.

Host variations in SARS-CoV-2 infection

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the zoonotic pathogen that causes the "Coronavirus Disease of 2019 (COVID-19)", and COVID-19 itself is yet to be thoroughly understood. Both the disease as well as the mechanisms by which the host interacts with the SARS-CoV-2 have not been fully enlightened. The epidemiological factors -e.g. age, sex, race-, the polymorphisms of the host proteins, the blood types and individual differences have all been in discussions about affecting the progression and the course of COVID-19 both individually and collectively, as their effects are mostly interwoven. We focused mainly on the effect of polymorphic variants of the host proteins that have been shown to take part in and/or affect the pathogenesis of COVID-19. Additionally, how the procedures of diagnosing and treating COVID-19 are affected by these variants and what possible changes can be implemented are the other questions, which are sought to be answered.

Host Serine Proteases: A Potential Targeted Therapy for COVID-19 and Influenza

The ongoing pandemic illustrates limited therapeutic options for controlling SARS-CoV-2 infections, calling a need for additional therapeutic targets. The viral spike S glycoprotein binds to the human receptor angiotensin-converting enzyme 2 (ACE2) and then is activated by the host proteases. Based on the accessibility of the cellular proteases needed for SARS-S activation, SARS-CoV-2 entrance and activation can be mediated by endosomal (such as cathepsin L) and non-endosomal pathways. Evidence indicates that in the non-endosomal pathway, the viral S protein is cleaved by the furin enzyme in infected host cells. To help the virus enter efficiently, the S protein is further activated by the serine protease 2 (TMPRSS2), provided that the S has been cleaved by furin previously. In this review, important roles for host proteases within host cells will be outlined in SARS-CoV-2 infection and antiviral therapeutic strategies will be highlighted. Although there are at least five highly effective vaccines at this time, the appearance of the new viral mutations demands the development of therapeutic agents. Targeted inhibition of host proteases can be used as a therapeutic approach for viral infection.

Molecular Modeling Targeting Transmembrane Serine Protease 2 (TMPRSS2) as an Alternative Drug Target Against Coronaviruses

Since November 2019, the new Coronavirus disease (COVID-19) caused by the etiological agent SARS-CoV-2 has been responsible for several cases worldwide, becoming pandemic in March 2020. Pharmaceutical industries and academics have joined their efforts to discover new therapies to control the disease, since there are no specific drugs to combat this emerging virus. Thus, several targets have been explored, among them the transmembrane protease serine 2 (TMPRSS2) has gained greater interest in the scientific community. In this context, this review will describe the importance of TMPRSS2 protease and the significant advances in virtual screening focused on discovering new inhibitors. In this review, it was observed that molecular modeling methods could be powerful tools in identifying new molecules against SARS-CoV-2. Thus, this review could be used to guide researchers worldwide to explore the biological and clinical potential of compounds that could be promising drug candidates against SARS-CoV-2, acting by inhibition of TMPRSS2 protein.

A Review on Expression, Pathological Roles, and Inhibition of TMPRSS2, the Serine Protease Responsible for SARS-CoV-2 Spike Protein Activation

SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, uses the host cell membrane receptor angiotensin-converting enzyme 2 (ACE2) for anchoring its spike protein, and the subsequent membrane fusion process is facilitated by host membrane proteases. Recent studies have shown that transmembrane serine protease 2 (TMPRSS2), a protease known for similar role in previous coronavirus infections, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS), is responsible for the proteolytic cleavage of the SARS-CoV-2 spike protein, enabling host cell fusion of the virus. TMPRSS2 is known to be expressed in the epithelial cells of different sites including gastrointestinal, respiratory, and genitourinary system. The infection site of the SARS-CoV-2 correlates with the coexpression sites of ACE2 and TMPRSS2. Besides, age-, sex-, and comorbidity-associated variation in infection rate correlates with the expression rate of TMPRSS2 in those groups. These findings provide valid reasons for the assumption that inhibiting TMPRSS2 can have a beneficial effect in reducing the cellular entry of the virus, ultimately affecting the infection rate and case severity. Several drug development studies are going on to develop potential inhibitors of the protease, using both conventional and computational approaches. Complete understanding of the biological roles of TMPRSS2 is necessary before such therapies are applied.

Harnessing the non-specific immunogenic effects of available vaccines to combat COVID-19

No proven remedy is identified for COVID-19 yet. SARS-CoV-2, the viral agent, is recognized by some endosomal and cytosolic receptors following cell entry, entailing innate and adaptive immunity stimulation, notably through interferon induction. Impairment in immunity activation in some patients, mostly elderlies, leads to high mortalities; thus, promoting immune responses may help. BCG vaccine is under investigation to prevent COVID-19 due to its non-specific effects on the immune system. However, other complementary immune-induction methods at early stages of the disease may be needed. Here, the potentially preventive immunologic effects of BCG and influenza vaccination are compared with the immune response defects caused by aging and COVID-19. BCG co-administration with interferon-α/-β, or influenza vaccine is suggested to overcome its shortcomings in interferon signaling against COVID-19. However, further studies are highly recommended to assess the outcomes of such interventions considering their probable adverse effects especially augmented innate immune responses and overproduction of proinflammatory mediators.

Pathogenesis and Management of COVID-19

COVID-19, occurring due to SARS-COV-2 infection, is the most recent pandemic disease that has led to three million deaths at the time of writing. A great deal of effort has been directed towards altering the virus trajectory and/or managing the interactions of the virus with its subsequent targets in the human body; these interactions can lead to a chain reaction-like state manifested by a cytokine storm and progress to multiple organ failure. During cytokine storms the ratio of pro-inflammatory to anti-inflammatory mediators is generally increased, which contributes to the instigation of hyper-inflammation and confers advantages to the virus. Because cytokine expression patterns fluctuate from one person to another and even within the same person from one time to another, we suggest a road map of COVID-19 management using an individual approach instead of focusing on the blockbuster process (one treatment for most people, if not all). Here, we highlight the biology of the virus, study the interaction between the virus and humans, and present potential pharmacological and non-pharmacological modulators that might contribute to the global war against SARS-COV-2. We suggest an algorithmic roadmap to manage COVID-19.

Crystal structure of inhibitor-bound human MSPL that can activate high pathogenic avian influenza

The structure of extracellular domain of MSPL and inhibitor complex helps to understand the TTSP functions, including TMPRSS2, and provides the insights of the infection of influenza and SARS-CoV.

Infection of certain influenza viruses is triggered when its HA is cleaved by host cell proteases such as proprotein convertases and type II transmembrane serine proteases (TTSP). HA with a monobasic motif is cleaved by trypsin-like proteases, including TMPRSS2 and HAT, whereas the multibasic motif found in high pathogenicity avian influenza HA is cleaved by furin, PC5/6, or MSPL. MSPL belongs to the TMPRSS family and preferentially cleaves [R/K]-K-K-R↓ sequences. Here, we solved the crystal structure of the extracellular region of human MSPL in complex with an irreversible substrate-analog inhibitor. The structure revealed three domains clustered around the C-terminal α-helix of the SPD. The inhibitor structure and its putative model show that the P1-Arg inserts into the S1 pocket, whereas the P2-Lys and P4-Arg interacts with the Asp/Glu-rich 99-loop that is unique to MSPL. Based on the structure of MSPL, we also constructed a homology model of TMPRSS2, which is essential for the activation of the SARS-CoV-2 spike protein and infection. The model may provide the structural insight for the drug development for COVID-19.

Association between ABO blood types and coronavirus disease 2019 (COVID-19), genetic associations, and underlying molecular mechanisms: a literature review of 23 studies

An association of various blood types and the 2019 novel coronavirus disease (COVID-19) has been found in a number of publications. The aim of this literature review is to summarize key findings related to ABO blood types and COVID-19 infection rate, symptom presentation, and outcome. Summarized findings include associations between ABO blood type and higher infection susceptibility, intubation duration, and severe outcomes, including death. The literature suggests that blood type O may serve as a protective factor, as individuals with blood type O are found COVID-19 positive at far lower rates. This could suggest that blood type O individuals are less susceptible to infection, or that they are asymptomatic at higher rates and therefore do not seek out testing. We also discuss genetic associations and potential molecular mechanisms that drive the relationship between blood type and COVID-19. Studies have found a strong association between a locus on a specific gene cluster on chromosome three (chr3p21.31) and outcome severity, such as respiratory failure. Cellular models have suggested an explanation for blood type modulation of infection, evidencing that spike protein/Angiotensin-converting enzyme 2 (ACE2)-dependent adhesion to ACE2-expressing cell lines was specifically inhibited by monoclonal or natural human anti-A antibodies, so individuals with non-A blood types, specifically O, or B blood types, which produce anti-A antibodies, may be less susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection due to the inhibitory effects of anti-A antibodies.

TMPRSS11D and TMPRSS13 Activate the SARS-CoV-2 Spike Protein

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) utilizes host proteases, including a plasma membrane-associated transmembrane protease, serine 2 (TMPRSS2) to cleave and activate the virus spike protein to facilitate cellular entry. Although TMPRSS2 is a well-characterized type II transmembrane serine protease (TTSP), the role of other TTSPs on the replication of SARS-CoV-2 remains to be elucidated. Here, we have screened 12 TTSPs using human angiotensin-converting enzyme 2-expressing HEK293T (293T-ACE2) cells and Vero E6 cells and demonstrated that exogenous expression of TMPRSS11D and TMPRSS13 enhanced cellular uptake and subsequent replication of SARS-CoV-2. In addition, SARS-CoV-1 and SARS-CoV-2 share the same TTSPs in the viral entry process. Our study demonstrates the impact of host TTSPs on infection of SARS-CoV-2, which may have implications for cell and tissue tropism, for pathogenicity, and potentially for vaccine development.

COVID-19, Angiotensin-Converting Enzyme 2 and Renin-Angiotensin System Inhibition: Implications for Practice

BACKGROUND

Recent studies suggested that patients with coronavirus disease 2019 (COVID-19) who use renin-angiotensin system (RAS) inhibitors have an increased risk of respiratory failure and death. The hypothesis was that angiotensin-converting enzyme inhibitor (ACEIs) or angiotensin receptor blocker (ARBs) may up-regulate ACE2 expression that is used as receptor for viral entry into cells.

OBJECTIVE

The purpose of this review is to discuss the existing evidence on the interaction between COVID-19 infection, ACE2 and ACEIs or ARBs and to examine the main implications for clinical practice. In addition, novel therapeutic strategies for blocking ACE2-mediated COVID-19 infection will be displayed.

METHODS

We performed a comprehensive review of the literature to identify data from clinical and experimental studies for the association between COVID-19 infection, ACE2 and RAS inhibition.

RESULTS

The current clinical and experimental evidence for ACEIs or ARBs to facilitate severe acute respiratory distress syndrome-coronavirus-2 (SARS-CoV-2) is insufficient to suggest discontinuing these drugs. Several observational studies arrive at the conclusion that the continued use of RAS inhibitors is unlike to be harmful in COVID-19-positive patients.

CONCLUSIONS

Further randomized trials are needed to answer definitely the question of whether RAS inhibitors are harmful or beneficial to patients with COVID-19.

A review on possible mechanistic insights of Nitazoxanide for repurposing in COVID-19

The global pandemic of Coronavirus Disease 2019 (COVID-19) has brought the world to a grinding halt. A major cause of concern is the respiratory distress associated mortality attributed to the cytokine storm. Despite myriad rapidly approved clinical trials with repurposed drugs, and time needed to develop a vaccine, accelerated search for repurposed therapeutics is still ongoing. In this review, we present Nitazoxanide a US-FDA approved antiprotozoal drug, as one such promising candidate. Nitazoxanide which is reported to exert broad-spectrum antiviral activity against various viral infections, revealed good in vitro activity against SARS-CoV-2 in cell culture assays, suggesting potential for repurposing in COVID-19. Furthermore, nitazoxanide displays the potential to boost host innate immune responses and thereby tackle the life-threatening cytokine storm. Possibilities of improving lung, as well as multiple organ damage and providing value addition to COVID-19 patients with comorbidities, are other important facets of the drug. The review juxtaposes the role of nitazoxanide in fighting COVID-19 pathogenesis at multiple levels highlighting the great promise the drug exhibits. The in silico data and in vitro efficacy in cell lines confirms the promise of nitazoxanide. Several approved clinical trials world over further substantiate leveraging nitazoxanide for COVID-19 therapy.

A comparative analysis of remdesivir and other repurposed antivirals against SARS-CoV-2

The ongoing SARS-CoV-2 pandemic stresses the need for effective antiviral drugs that can quickly be applied in order to reduce morbidity, mortality, and ideally viral transmission. By repurposing of broadly active antiviral drugs and compounds that are known to inhibit viral replication of related viruses, several advances could be made in the development of treatment strategies against COVID-19. The nucleoside analog remdesivir, which is known for its potent in vitro activity against Ebolavirus and other RNA viruses, was recently shown to reduce the time to recovery in patients with severe COVID-19. It is to date the only approved antiviral for treating COVID-19. Here, we provide a mechanism and evidence-based comparative review of remdesivir and other repurposed drugs with proven in vitro activity against SARS-CoV-2.

Hepsin: a multifunctional transmembrane serine protease in pathobiology

Cell membrane-bound serine proteases are important in the maintenance of physiological homeostasis. Hepsin is a type II transmembrane serine protease highly expressed in the liver. Recent studies indicate that hepsin activates prohepatocyte growth factor in the liver to enhance Met signaling, thereby regulating glucose, lipid, and protein metabolism. In addition, hepsin functions in nonhepatic tissues, including the adipose tissue, kidney, and inner ear, to regulate adipocyte differentiation, urinary protein processing, and auditory function, respectively. In mouse models, hepsin deficiency lowers blood glucose, lipid, and protein levels, impairs uromodulin assembly in renal epithelial cells, and causes hearing loss. Elevated hepsin expression has also been found in many cancers. As a type II transmembrane protease, cell surface expression and zymogen activation are essential for hepsin activity. In this review, we discuss the current knowledge regarding hepsin biosynthesis, activation, and functions in pathobiology.

Role of proteolytic enzymes in the COVID-19 infection and promising therapeutic approaches

In the Fall of 2019 a sudden and dramatic outbreak of a pulmonary disease (Coronavirus Disease COVID-19), due to a new Coronavirus strain (i.e., SARS-CoV-2), emerged in the continental Chinese area of Wuhan and quickly diffused throughout the world, causing up to now several hundreds of thousand deaths. As for common viral infections, the crucial event for the viral life cycle is the entry of genetic material inside the host cell, realized by the spike protein of the virus through its binding to host receptors and its activation by host proteases; this is followed by translation of the viral RNA into a polyprotein, exploiting the host cell machinery. The production of individual mature viral proteins is pivotal for replication and release of new virions. Several proteolytic enzymes either of the host and of the virus act in a concerted fashion to regulate and coordinate specific steps of the viral replication and assembly, such as (i) the entry of the virus, (ii) the maturation of the polyprotein and (iii) the assembly of the secreted virions for further diffusion. Therefore, proteases involved in these three steps are important targets, envisaging that molecules which interfere with their activity are promising therapeutic compounds. In this review, we will survey what is known up to now on the role of specific proteolytic enzymes in these three steps and of most promising compounds designed to impair this vicious cycle.

Identification of Candidate Genes and Pathways Associated with Obesity-Related Traits in Canines via Gene-Set Enrichment and Pathway-Based GWAS Analysis

The present study aimed to identify causative loci and genes enriched in pathways associated with canine obesity using a genome-wide association study (GWAS). The GWAS was first performed to identify candidate single-nucleotide polymorphisms (SNPs) associated with obesity and obesity-related traits including body weight and blood sugar in 18 different breeds of 153 dogs. A total of 10 and 2 SNPs were found to be significantly (p < 3.74 × 10^-7) associated with body weight and blood sugar, respectively. None of the SNPs were identified to be significantly associated with obesity trait. We subsequently followed up the GWAS analysis with gene-set enrichment and pathway analyses. A gene-set with 1057, 1409, and 1243 SNPs annotated to 449, 933 and 820 genes for obesity, body weight, and blood sugar, respectively was created by sub-setting the GWAS result at a threshold of p < 0.01 for the gene-set enrichment analysis. In total, 84 GO and 21 KEGG pathways for obesity, 114 GO and 44 KEGG pathways for blood sugar, 120 GO and 24 KEGG pathways for body weight were found to be enriched. Among the pathways and GO terms, we highlighted five enriched pathways (Wnt signaling pathway, adherens junction, pathways in cancer, axon guidance, and insulin secretion) and seven GO terms (fat cell differentiation, calcium ion binding, cytoplasm, nucleus, phospholipid transport, central nervous system development, and cell surface) that were found to be shared among all the traits. Our data provide insights into the genes and pathways associated with obesity and obesity-related traits.

A conserved LDL-receptor motif regulates corin and CD320 membrane targeting in polarized renal epithelial cells

Selective protein distribution on distinct plasma membranes is important for epithelial cell function. To date, how proteins are directed to specific epithelial cell surface is not fully understood. Here we report a conserved DSSDE motif in LDL-receptor (LDLR) modules of corin (a transmembrane serine protease) and CD320 (a receptor for vitamin B12 uptake), which regulates apical membrane targeting in renal epithelial cells. Altering this motif prevents specific apical corin and CD320 expression in polarized Madin-Darby canine kidney (MDCK) cells. Mechanistic studies indicate that this DSSDE motif participates in a Rab11a-dependent mechanism that specifies apical sorting. In MDCK cells, inhibition of Rab11a, but not Rab11b, expression leads to corin and CD320 expression on both apical and basolateral membranes. Together, our results reveal a novel molecular recognition mechanism that regulates LDLR module-containing proteins in their specific apical expression in polarized renal epithelial cells.

Variability in genes related to SARS-CoV-2 entry into host cells (ACE2, TMPRSS2, TMPRSS11A, ELANE, and CTSL) and its potential use in association studies

BACKGROUND

The prevalence and mortality of the outbreak of the COVID-19 pandemic show marked geographic variation. The presence of several subtypes of the coronavirus and the genetic differences in the populations could condition that variation. Thus, the objective of this study was to propose variants in genes that encode proteins related to the SARS-CoV-2 entry into the host cells as possible targets for genetic associations studies.

METHODS

The allelic frequencies of the polymorphisms in the ACE2, TMPRSS2, TMPRSS11A, cathepsin L (CTSL), and elastase (ELANE) genes were obtained in four populations from the American, African, European, and Asian continents reported in the 1000 Genome Project. Moreover, we evaluated the potential biological effect of these variants using different web-based tools.

RESULTS

In the coding sequences of these genes, we detected one probably-damaging polymorphism located in the TMPRSS2 gene (rs12329760) that produces a change of amino acid. Furthermore, forty-eight polymorphisms with possible functional consequences were detected in the non-coding sequences of the following genes: three in ACE2, seventeen in TMPRSS2, ten in TMPRSS11A, twelve in ELANE, and six in CTSL. These polymorphisms produce binding sites for transcription factors and microRNAs. The minor allele frequencies of these polymorphisms vary in each community; indeed, some of them are high in specific populations.

CONCLUSION

In summary, using data of the 1000 Genome Project and web-based tools, we propose some polymorphisms, which, depending on the population, could be used for genetic association studies.

Inhibitors of type II transmembrane serine proteases in the treatment of diseases of the respiratory tract - A review of patent literature

INTRODUCTION

Type II transmembrane serine proteases (TTSPs) of the human respiratory tract generate high interest owing to their ability, among other roles, to cleave surface proteins of respiratory viruses. This step is critical in the viral invasion of coronaviruses, including SARS-CoV-2 responsible for COVID-19, but also influenza viruses and reoviruses. Accordingly, these cell surface enzymes constitute appealing therapeutic targets to develop host-based therapeutics against respiratory viral diseases. Additionally, their deregulated levels or activity has been described in non-viral diseases such as fibrosis, cancer, and osteoarthritis, making them potential targets in these indications.

AREAS COVERED

Areas covered: This review includes WIPO-listed patents reporting small molecules and peptide-based inhibitors of type II transmembrane serine proteases of the respiratory tract.

EXPERT OPINION

Expert opinion: Several TTSPs of the respiratory tract represent attractive pharmacological targets in the treatment of respiratory infectious diseases (notably COVID-19 and influenza), but also against idiopathic pulmonary fibrosis and lung cancer. The current emphasis is primarily on TMPRSS2, matriptase, and hepsin, yet other TTSPs await validation. Compounds listed herein are predominantly peptidomimetic inhibitors, some with covalent reversible mechanisms of action and high potencies. Their selectivity profile, however, are often only partially characterized. Preclinical data are promising and warrant further advancement in the above diseases.

Why COVID-19 Transmission Is More Efficient and Aggressive Than Viral Transmission in Previous Coronavirus Epidemics?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing a pandemic of coronavirus disease 2019 (COVID-19). The worldwide transmission of COVID-19 from human to human is spreading like wildfire, affecting almost every country in the world. In the past 100 years, the globe did not face a microbial pandemic similar in scale to COVID-19. Taken together, both previous outbreaks of other members of the coronavirus family (severe acute respiratory syndrome (SARS-CoV) and middle east respiratory syndrome (MERS-CoV)) did not produce even 1% of the global harm already inflicted by COVID-19. There are also four other CoVs capable of infecting humans (HCoVs), which circulate continuously in the human population, but their phenotypes are generally mild, and these HCoVs received relatively little attention. These dramatic differences between infection with HCoVs, SARS-CoV, MERS-CoV, and SARS-CoV-2 raise many questions, such as: Why is COVID-19 transmitted so quickly? Is it due to some specific features of the viral structure? Are there some specific human (host) factors? Are there some environmental factors? The aim of this review is to collect and concisely summarize the possible and logical answers to these questions.