Alterations in the gene expression of SARS-COV-2 entry receptors and enzymes in lungs and hearts of controlled and uncontrolled diabetic mice

BACKGROUND

The entry of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into the host cell is carried out by specific receptors and enzymes, including human angiotensin-converting enzyme 2 receptor (ACE2), transmembrane serine protease 2 (TMPRSS2), and cathepsin-L (CTSL). COVID-19 patients with comorbidities, such as diabetes mellitus (DM), are more prone to severe symptoms and have a higher risk of mortality.

AIMS

The present study aimed to investigate the impact of controlled and uncontrolled type 1 DM (T1DM) on the gene expression of mouse Ace2, Tmprss2, and Ctsl and correlate it with the pathological alterations in the lungs and the heart of DM mice.

METHODS

Balb/c mice were administered a single dose of 240 mg/kg streptozocin to induce T1DM. The blood glucose level was measured to confirm the induction of DM. Normalization of blood glucose levels in T1DM mice was achieved using 0.1 mL/kg Mixtard® insulin therapy. The mice's lungs and hearts were harvested, and the mRNA was extracted and converted to cDNA. The gene expression of Ace2, Tmprss2, Ctsl, Cyp4a11, and Adrb1 genes, which play a role in the homeostasis of lungs and hearts, were measured using quantitative real-time polymerase chain reaction (RT-PCR). The pathological alterations in the hearts and lungs induced by T1DM were evaluated using the relative heart and lung weights, in addition to the pathohistological examination.

RESULTS

After inducing T1DM for 14 days, we observed a significant reduction in the total weight of uncontrolled DM (UDM) mice (P < 0.05). Pathohistological examination of UDM lung tissues revealed thickening of the alveolar walls with narrowing of the surface of the alveolar sacs. Additionally, we found that UDM mice exhibited downregulation of Ace2 gene expression (P < 0.05) in their lungs, while both UDM and control DM (CDM) mice showed upregulation of Ctsl gene expression in their hearts (P < 0.05). Notably, Cyp4a12 gene expression was significantly downregulated (P < 0.05) in UDM mice but returned to normal levels in CDM mice.

CONCLUSIONS

We conclude from this study that T1DM downregulates Ace2 receptor and Cyp4a12 gene expression, which is correlated with the thickening of alveolar walls and narrowing of the surface of alveolar sacs in the lungs. Insulin administration for controlling T1DM ameliorated these pathological alterations. These results can help increase our understanding of the impact of controlled and uncontrolled T1DM on the lungs and may explain, at least in part, why DM patients with COVID-19 experience exacerbation of symptoms.

Ancestral, Delta, and Omicron (BA.1) SARS-CoV-2 strains are dependent on serine proteases for entry throughout the human respiratory tract

BACKGROUND

The SARS-CoV-2 Omicron BA.1 variant emerged in late 2021 and became the globally dominant variant by January 2022. Authentic virus and pseudovirus systems have shown Omicron spike has an increased dependence on the endosomal pathway for entry.

METHODS

We investigated the entry mechanisms of Omicron, Delta, and ancestral viruses in cell models that represent different parts of the human respiratory tract, including nasal epithelial cells (hNECs), large-airway epithelial cells (LAECs), small-airway epithelial cells, and embryonic stem cell-derived type II alveolar cells.

FINDINGS

Omicron had an early replication advantage in LAECs, while Delta grew to higher titers in all cells. Omicron maintained dependence on serine proteases for entry in all culture systems. While serine protease inhibition with camostat was less robust for Omicron in hNECs, endosomal entry was not enhanced.

CONCLUSIONS

Our findings demonstrate that entry of Omicron BA.1 SARS-CoV-2 is dependent on serine proteases for entry throughout the respiratory tract.

FUNDING

This work was supported by The Medical Research Future Fund (MRF9200007; K.S., J.M.P.) and the DHHS Victorian State Government grant (Victorian State Government; DJPR/COVID-19; K.S, J.M.P.). K.S. is supported by a National Health and Medical Research Council of Australia Investigator grant (APP1177174).

Computational Analysis of CD46 Protein Interaction with SARS-CoV-2 Structural Proteins: Elucidating a Putative Viral Entry Mechanism into Human Cells

This study examines an unexplored aspect of SARS-CoV-2 entry into host cells, which is widely understood to occur via the viral spike (S) protein's interaction with human ACE2-associated proteins. While vaccines and inhibitors targeting this mechanism are in use, they may not offer complete protection against reinfection. Hence, we investigate putative receptors and their cofactors. Specifically, we propose CD46, a human membrane cofactor protein, as a potential putative receptor and explore its role in cellular invasion, acting possibly as a cofactor with other viral structural proteins. Employing computational techniques, we created full-size 3D models of human CD46 and four key SARS-CoV-2 structural proteins-EP, MP, NP, and SP. We further developed 3D models of CD46 complexes interacting with these proteins. The primary aim is to pinpoint the likely interaction domains between CD46 and these structural proteins to facilitate the identification of molecules that can block these interactions, thus offering a foundation for novel pharmacological treatments for SARS-CoV-2 infection.

The Transmembrane Protease Serine 2 (TMPRSS2) Non-Protease Domains Regulating Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Spike-Mediated Virus Entry

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters cells by binding to the angiotensin-converting enzyme 2 (hACE2) receptor. This process is aided by the transmembrane protease serine 2 (TMPRSS2), which enhances entry efficiency and infectiousness by cleaving the SARS-CoV-2 surface glycoprotein (Spike). The cleavage primes the Spike protein, promoting membrane fusion instead of receptor-mediated endocytosis. Despite the pivotal role played by TMPRSS2, our understanding of its non-protease distinct domains remains limited. In this report, we present evidence indicating the potential phosphorylation of a minimum of six tyrosine residues within the cytosolic tail (CT) of TMPRSS2. Via the use of TMPRSS2 CT phospho-mimetic mutants, we observed a reduction in TMPRSS2 protease activity, accompanied by a decrease in SARS-CoV-2 pseudovirus transduction, which was found to occur mainly via the endosomal pathway. We expanded our investigation beyond TMPRSS2 CT and discovered the involvement of other non-protease domains in regulating infection. Our co-immunoprecipitation experiments demonstrated a strong interaction between TMPRSS2 and Spike. We revealed a 21 amino acid long TMPRSS2-Spike-binding region (TSBR) within the TMPRSS2 scavenger receptor cysteine-rich (SRCR) domain that contributes to this interaction. Our study sheds light on novel functionalities associated with TMPRSS2's cytosolic tail and SRCR region. Both of these regions have the capability to regulate SARS-CoV-2 entry pathways. These findings contribute to a deeper understanding of the complex interplay between viral entry and host factors, opening new avenues for potential therapeutic interventions.

Human Immunodeficiency Viruses Pseudotyped with SARS-CoV-2 Spike Proteins Infect a Broad Spectrum of Human Cell Lines through Multiple Entry Mechanisms

Severe acute respiratory syndrome-related coronavirus (SARS-CoV-2), the causative agent of coronavirus disease 19 (COVID-19), enters cells through attachment to the human angiotensin converting enzyme 2 (hACE2) via the receptor-binding domain (RBD) in the surface/spike (S) protein. Several pseudotyped viruses expressing SARS-CoV-2 S proteins are available, but many of these can only infect hACE2-overexpressing cell lines. Here, we report the use of a simple, two-plasmid, pseudotyped virus system comprising a SARS-CoV-2 spike-expressing plasmid and an HIV vector with or without vpr to investigate the SARS-CoV-2 entry event in various cell lines. When an HIV vector without vpr was used, pseudotyped SARS-CoV-2 viruses produced in the presence of fetal bovine serum (FBS) were able to infect only engineered hACE2-overexpressing cell lines, whereas viruses produced under serum-free conditions were able to infect a broader range of cells, including cells without hACE2 overexpression. When an HIV vector containing vpr was used, pseudotyped viruses were able to infect a broad spectrum of cell types regardless of whether viruses were produced in the presence or absence of FBS. Infection sensitivities of various cell types did not correlate with mRNA abundance of hACE2, TMPRSS2, or TMPRSS4. Pseudotyped SARS-CoV-2 viruses and replication-competent SARS-CoV-2 virus were equally sensitive to neutralization by an anti-spike RBD antibody in cells with high abundance of hACE2. However, the anti-spike RBD antibody did not block pseudotyped viral entry into cell lines with low abundance of hACE2. We further found that CD147 was involved in viral entry in A549 cells with low abundance of hACE2. Thus, our assay is useful for drug and antibody screening as well as for investigating cellular receptors, including hACE2, CD147, and tyrosine-protein kinase receptor UFO (AXL), for the SARS-CoV-2 entry event in various cell lines.

Potential detrimental role of soluble ACE2 in severe COVID-19 comorbid patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters the host cell by binding to angiotensin-converting enzyme 2 (ACE2) receptor. Other important proteins involved in this process include disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) also known as tumour necrosis factor-α-converting enzyme and transmembrane serine protease 2. ACE2 converts angiotensin II (Ang II) to angiotensin (1-7), to balance the renin angiotensin system. Membrane-bound ACE2 ectodomain shedding is mediated by ADAM17 upon viral spike binding, Ang II overproduction and in several diseases. The shed soluble ACE2 (sACE2) retains its catalytic activity, but its precise role in viral entry is still unclear. Therapeutic sACE2 is claimed to exert dual effects; reduction of excess Ang II and blocking viral entry by masking the spike protein. Nevertheless, the paradox is why SARS-CoV-2 comorbid patients struggle to attain such benefit in viral infection despite having a high amount of sACE2. In this review, we discuss the possible detrimental role of sACE2 and speculate on a series of events where protease primed or non-primed virus-sACE2 complex might enter the host cell. As extracellular virus can bind many sACE2 molecules, sACE2 level could be reduced drastically upon endocytosis by the host cell. A consequential rapid rise in Ang II level could potentially aggravate disease severity through Ang II-angiotensin II receptor type 1 (AT1R) axis in comorbid patients. Hence, monitoring sACE2 and Ang II level in coronavirus disease 2019 comorbid patients are crucial to ensure safe and efficient intervention using therapeutic sACE2 and vaccines.