Probes for INS

The development of mouse models for COVID-19 has enabled testing of vaccines and therapeutics and defining aspects of SARS-CoV-2 pathogenesis. SARS-CoV-2 disease is severe in K18 transgenic mice (K18-hACE2-Tg) expressing human ACE2 (hACE2), the SARS-CoV-2 receptor, under an ectopic cytokeratin promoter, with high levels of infection measured in the lung and brain. Here, we evaluated SARS-CoV-2 infection in hACE2 KI mice that express hACE2 under an endogenous promoter in place of murine ACE2 (mACE2). Intranasal inoculation of hACE2 KI mice with SARS-CoV-2 WA1/2020 resulted in substantial viral replication within the upper and lower respiratory tracts with limited spread to extra-pulmonary organs. However, SARS-CoV-2-infected hACE2 KI mice did not lose weight and developed limited pathology. Moreover, no significant differences in viral burden were observed in hACE2 KI mice infected with B.1.1.7 or B.1.351 variants compared to WA1/2020 strain. Because the entry mechanisms of SARS-CoV-2 in mice remains uncertain, we evaluated the impact of the naturally-occurring, mouse-adapting N501Y mutation by comparing infection of hACE2 KI, K18-hACE2-Tg, ACE2-deficient, and wild-type C57BL/6 mice. The N501Y mutation minimally affected SARS-CoV-2 infection in hACE2 KI mice but was required for viral replication in wild-type C57BL/6 mice in a mACE2-dependent manner and augmented pathogenesis in the K18-hACE2 Tg mice. Thus, the N501Y mutation likely enhances interactions with mACE2 or hACE2 in vivo. Overall, our study highlights the hACE2 KI mice as a model of mild SARS-CoV-2 infection and disease and clarifies the requirement of the N501Y mutation in mice. IMPORTANCE Mouse models of SARS-CoV-2 pathogenesis have facilitated the rapid evaluation of countermeasures. While the first generation of models developed pneumonia and severe disease after SARS-CoV-2 infection, they relied on ectopic expression of supraphysiological levels of human ACE2 (hACE2). This has raised issues with their relevance to humans as the hACE2 receptor shows a more restricted expression pattern in the respiratory tract. Here we evaluated SARS-CoV-2 infection and disease with viruses containing or lacking a key mouse-adapting mutation in the spike gene in hACE2 KI mice, which express hACE2 under an endogenous promoter in place of murine ACE2. While infection of hACE2 KI mice with multiple strains of SARS-CoV-2 including variants of concern resulted in viral replication within the upper and lower respiratory tracts, the animals did not sustain severe lung injury. Thus, hACE2 KI mice serve as a model of mild infection with both ancestral and emerging SARS-CoV-2 variant strains.

Introduction. During the COVID-19 pandemic, the question regarding an effect of related infection on the body of pregnant women and the fetoplacental complex has emerged, with many aspects of this issue still being unknown. At the moment, it has been proven that in some cases the course of COVID-19 can be accompanied by severe systemic inflammatory reaction leading to hypercoagulable state.Aim: to search for evidence of a direct and/or indirect effect of SARS-CoV-2 infection on human placenta structure.Materials and Methods. Taking into account the goal, this review was compiled according to the type of a narrative review of publications on a topic of interest. A search for English-language publications dated of 01.12.2019 till 01.12.2021 in PubMed/MEDLINE, Cochrane, Web of Science databases was made. The search queries included the following keywords: combinations of «coronavirus» and «infection during pregnancy», «placental structure» and «2019-nCoV», «COVID-19 and pregnancy», «SARSCoV-2 and pregnancy». In the process of writing the article, in order to improve the reader's understanding of the essence of debated issue, there was a need to discuss some of the results with literary sources published earlier 2019 that were not directly related to the topic of the new coronavirus infection (there are 6 such sources). We analyzed full-text publications, both reports on original research and meta-analyses on relevant topics. In total, 351 full-text publications met the query criteria, of which 54 were selected as meeting the objectives of the study. The select reports were discussed by the co-authors, duplicates were excluded and 34 of them were included in this review. In those that were excluded from the review, information about the clinical course of pregnancy and its outcome during novel coronavirus infection prevailed, or isolated cases of studying insignificant placental structural changes were discussed. Studies with a small number of observations were selected only in the case of the uniqueness of the published data, the absence of scientific papers where similar studies would have been conducted in larger sample.Results. Pregnancy complicated by COVID-19 may be accompanied by placental structural changes, which represent both a manifestation of compensatory-adaptive reactions and a consequence of the damaging effect to the placenta due to infectious process. In case of late (in the III trimester) disease in pregnant woman with mild COVID-19, placental disorders are predominantly of compensatory-adaptive nature, specific cytological signs of viral cell damage are uncharacteristic. During COVID-19 infection, chronic histiocytic intervillositis and syncytiotrophoblast necrosis occur more often than in average population, and adverse fetal outcomes are characterized by additional marked increase in intervillous fibrinoid deposition. Before COVID-19 pandemic, chronic histiocytic intervillositis was described in about 6 out of 10,000 placentas (0.6 %) in II and III trimesters.Conclusion. The high frequency of chronic histiocytic intervillositis, both in the placenta of paired women with live-born infants infected prenatally due to maternal virus transmission, and in the placentas of stillborn infected infants, allows us to cautiously assume that such placental structural changes are more characteristic for damage by SARS-CoV-2 rather than other infectious agents. It is necessary to study a relationship between placental structural changes occurred at different gestation ages, as well as clinical course and outcome of pregnancy during COVID-19.

Animal models recapitulating COVID-19 are critical to enhance our understanding of SARS-CoV-2 pathogenesis. Intranasally inoculated transgenic mice expressing human angiotensin-converting enzyme 2 under the cytokeratin 18 promoter (K18-hACE2) represent a lethal model of SARS-CoV-2 infection. We evaluated the clinical and virological dynamics of SARS-CoV-2 using two intranasal doses (104 and 106 PFUs), with a detailed spatiotemporal pathologic analysis of the 106 dose cohort. Despite generally mild-to-moderate pneumonia, clinical decline resulting in euthanasia or death was commonly associated with hypothermia and viral neurodissemination independent of inoculation dose. Neuroinvasion was first observed at 4 days post-infection, initially restricted to the olfactory bulb suggesting axonal transport via the olfactory neuroepithelium as the earliest portal of entry. Absence of viremia suggests neuroinvasion occurs independently of transport across the blood-brain barrier. SARS-CoV-2 tropism was neither restricted to ACE2-expressing cells (e.g., AT1 pneumocytes), nor inclusive of some ACE2-positive cell lineages (e.g., bronchiolar epithelium and brain vasculature). Absence of detectable ACE2 protein expression in neurons but overexpression in neuroepithelium suggest this as the most likely portal of neuroinvasion, with subsequent ACE2 independent lethal neurodissemination. A paucity of epidemiological data and contradicting evidence for neuroinvasion and neurodissemination in humans call into question the translational relevance of this model.

Significance Gaining insights into severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) high transmissibility and the role played by inflammatory mediators in viral proliferation are critical to investigating new therapeutic targets against COVID-19. Electron microscopy reveals important SARS-CoV-2 features, including the combination of large, rapidly released viral clusters and the massive shedding of epithelial cells packed with virions. Interleukin-13 (IL-13), a Th2 cytokine up-regulated in allergic asthma and associated with less severe COVID-19, protects against SARS-CoV-2 viral and cell shedding. Using gene expression analyses and biochemical assays, IL-13 is shown to affect viral entry, replication, and cell-to-cell transmission. Given the broad spectrum of COVID-19 clinical symptoms, it is important to elucidate intrinsic factors that modulate viral load and spreading mechanisms.

The emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) variants has altered the trajectory of the COVID-19 pandemic and raised some uncertainty on the long-term efficiency of vaccine strategy. The development of new therapeutics against a wide range of SARS-CoV-2 variants is imperative. We, here, have designed an inhalable siRNA, C6G25S, which covers 99.8% of current SARS-CoV-2 variants and is capable of inhibiting dominant strains, including Alpha, Delta, Gamma, and Epsilon, at picomolar ranges of IC50 in vitro. Moreover, C6G25S could completely inhibit the production of infectious virions in lungs by prophylactic treatment, and decrease 96.2% of virions by cotreatment in K18-hACE2-transgenic mice, accompanied by a significant prevention of virus-associated extensive pulmonary alveolar damage, vascular thrombi, and immune cell infiltrations. Our data suggest that C6G25S provides an alternative and effective approach to combating the COVID-19 pandemic.