A Mouse Model of SARS-CoV-2 Infection and Pathogenesis

Exploring the biological mechanisms of severe COVID-19 in the elderly: Insights from an aged mouse model

The elderly population, who have increased susceptibility to severe outcomes, have been particularly impacted by the coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), leading to a global health crisis. However, definitive parameters or mechanisms underlying the severity of COVID-19 in elderly people remain unclear. Thus, this study seeks to elucidate the mechanism behind the increased vulnerability of elderly individuals to severe COVID-19. We employed an aged mouse model with a mouse-adapted SARS-CoV-2 strain to mimic the severe symptoms observed in elderly patients with COVID-19. Comprehensive analyses of the whole lung were performed using transcriptome and proteome sequencing, comparing data from aged and young mice. For transcriptome analysis, bulk RNA sequencing was conducted using an Illumina sequencing platform. Proteomic analysis was performed using mass spectrometry following protein extraction, digestion, and peptide labelling. We analysed the transcriptome and proteome profiles of young and aged mice and discovered that aged mice exhibited elevated baseline levels of inflammation and tissue damage repair. After SARS-CoV-2 infection, aged mice showed increased antiviral and inflammatory responses; however, these responses were weaker than those in young mice, with significant complement and coagulation cascade responses. In summary, our study demonstrates that the increased vulnerability of the elderly to severe COVID-19 may be attributed to an attenuated antiviral response and the overactivation of complement and coagulation cascades. Future research on antiviral and inflammatory responses is likely to yield treatments that reduce the severity of viral respiratory diseases in the elderly.

A human-ACE2 knock-in mouse model for SARS-CoV-2 infection recapitulates respiratory disorders but avoids neurological disease associated with the transgenic K18-hACE2 model

Animal models have been instrumental in elucidating the pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and in testing coronavirus disease 2019 (COVID-19) vaccines and therapeutics. Wild-type (WT) mice are not susceptible to many SARS-CoV-2 variants, and therefore, transgenic K18-hACE2 mice have emerged as a standard model system. However, this model is characterized by a severe disease, particularly associated with neuroinfection, which leads to early humane endpoint euthanasia. Here, we established a novel knock-in (KI) mouse model by inserting the original K18-hACE2 transgene into the collagen type I alpha chain (COL1A1) locus using a recombinase-mediated cassette exchange (RMCE) system. Once the Col1a1-K18-hACE2 mouse colony was established, animals were challenged with a B.1 SARS-CoV-2 (D614G) isolate and were monitored for up to 14 days. Col1a1-K18-hACE2 mice exhibited an initial weight loss similar to the K18-hACE2 transgenic model but did not develop evident neurologic clinical signs. The majority of Col1a1-K18-hACE2 mice did not reach the pre-established humane endpoint, showing a progressive weight gain 9 days postinfection (dpi). Importantly, despite this apparent milder pathogenicity of the virus in this mouse model compared to the K18-hACE2 transgenic model, high levels of viral RNA were detected in the lungs, oropharyngeal swab, and nasal turbinates. Moreover, the remaining lesions and inflammation in the lungs were still observed 14 dpi. In contrast, although low-level viral RNA could be detected in a minority of Col1a1-K18-hACE2 animals, no brain lesions were observed at any timepoint. Overall, Col1a1-K18-hACE2 mice constitute a new model for investigating SARS-CoV-2 pathogenesis and treatments, with potential implications for studying long-term COVID-19 sequelae.IMPORTANCEK18-hACE2 mice express high levels of the human protein angiotensin-converting enzyme 2 (ACE2), the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and are therefore susceptible to infection by this virus. These animals have been crucial to understanding viral pathogenesis and to testing coronavirus disease 2019 (COVID-19) vaccines and antiviral drugs. However, K18-hACE2 often dies after infection with initial SARS-CoV-2 variants, likely due to a massive brain infection that does not occur in humans. Here, we used a technology known as knock-in (KI) that allows for the targeted insertion of a gene into a mouse, and we have generated a new human ACE2 (hACE2) mouse. We have characterized this new animal model demonstrating that, upon challenge with SARS-CoV-2, the virus replicates in the respiratory tract, damaging lung tissue and causing inflammation. In contrast to K18-hACE2 mice, only limited or no brain infection could be detected in this new model. After 14 days, most animals recovered from the infection, although lung tissue lesions were still observed. This new model could be instrumental for the study of specific disease aspects such as post-COVID-19 condition, sequelae, and susceptibility to reinfection.

SIRT2 suppresses aging-associated cGAS activation and protects aged mice from severe COVID-19

Aging-associated vulnerability to coronavirus disease 2019 (COVID-19) remains poorly understood. Here, we show that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected aged mice lacking SIRT2, a cytosolic NAD+-dependent deacetylase, develop more severe disease and show increased mortality, while treatment with an NAD+ booster, 78c, protects aged mice from lethal infection. Mechanistically, we demonstrate that SIRT2 modulates the acetylation of cyclic GMP-AMP synthase (cGAS), an immune sensor for cytosolic DNA, and suppresses aging-associated cGAS activation and inflammation. Furthermore, we show that SARS-CoV-2 infection-induced inflammation is mediated at least in part by ORF3a, which triggers mtDNA release and cGAS activation. Collectively, our study reveals a molecular basis for aging-associated susceptibility to COVID-19 and suggests therapeutic approaches to protect aged populations from severe SARS-CoV-2 infection.

Engineering Mice to Study Human Immunity

Humanized mice, which carry a human hematopoietic and immune system, have greatly advanced our understanding of human immune responses and immunological diseases. These mice are created via the transplantation of human hematopoietic stem and progenitor cells into immunocompromised murine hosts further engineered to support human hematopoiesis and immune cell growth. This article explores genetic modifications in mice that enhance xeno-tolerance, promote human hematopoiesis and immunity, and enable xenotransplantation of human tissues with resident immune cells. We also discuss genetic editing of the human immune system, provide examples of how humanized mice with humanized organs model diseases for mechanistic studies, and highlight the roles of these models in advancing knowledge of organ biology, immune responses to pathogens, and preclinical drugs tested for cancer treatment. The integration of multi-omics and state-of-the art approaches with humanized mouse models is crucial for bridging existing human data with causality and promises to significantly advance mechanistic studies.

Impedance-based method for the quantification of infectious SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiologic agent involved in the coronavirus disease 2019 (COVID-19) pandemic. The development of infectious titration methods is crucial to provide data for a better understanding of transmission routes, as well as to validate the efficacy of inactivation treatments. Nevertheless, the low-throughput analytical capacity of traditional methods may be a limiting factor for a large screening of samples. The aim of the study was to develop a Real-Time Cell Analysis (RTCA) assay based on the measurement of cell impedance to quantify infectious SARS-CoV-2. The kinetics of cell impedance showed a virus-specific Cell Index (CI) drop. This enabled the correlation between viral concentrations and time at which a 50 % drop in CI values was observed (tCI50), with establishment of a standard curve. In parallel, the improved Spearman and Kärber method was used to quantify infectious titer since the virus-induced CI drop is correlated to the Cytopathic Effect. The estimated uncertainty was respectively 0.57, 0.36, and 0.26 log10 with 4, 8, and 16 wells per dilution. Thus, the RTCA assay is a powerful tool with a greatly simplified workflow for effective risk assessment in the field of food and environmental virology.

New mouse model for inducible hACE2 expression enables to dissect SARS-CoV-2 pathology beyond the respiratory system

The Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection is not limited to the respiratory tract as receptors, including the angiotensin-converting enzyme 2 (ACE2), are expressed across many tissues. This study employed a new conditional mouse model, Rosa26creERT2/chACE2, which expresses human ACE2 (hACE2) across multiple organs, to investigate the effects of SARS-CoV-2 infection beyond the respiratory system. This strain demonstrated susceptibility to SARS-CoV-2 infection in a dose and sex-dependent manner, showing that infected male mice exhibited more severe disease outcomes, including significant weight loss, pronounced lung pathology and dysfunction, and increased mortality, compared to females. In contrast to intratracheal infection, intranasal virus administration facilitated viral spread to the brain, thereby underscoring the nasal route's role in the pathogenesis of neurological manifestations. Intranasal infection also led to increased innate immune system activation as compared to intratracheal virus administration, even though both routes activated the adaptive immune response. This model provides a valuable tool to study SARS-CoV-2 in individual tissues or use a multisystemic approach, and it also advances possibilities for preclinical evaluation of antiviral therapies and vaccine strategies.

Enhancing human ACE2 expression in mouse models to improve COVID-19 research

Mice are one of the most common biological models for laboratory use. However, wild-type mice are not susceptible to COVID-19 infection due to the low affinity of mouse ACE2, the entry protein for SARS-CoV-2. Although mice with human ACE2 (hACE2) driven by Ace2 promoter reflect its tissue specificity, these animals exhibit low ACE2 expression, potentially limiting their fidelity in mimicking COVID-19 manifestations and their utility in viral studies. Here, we created and compared hACE2 mouse models generated with different strategies. Our findings show that distinct β-globin insertion within hACE2 cassette significantly influences its expression, with downstream placement enhancing transcription. Moreover, optimizing hACE2 codons (opt-hACE2) improves translation efficiency in multiple tissues. Notably, opt-hACE2 mice displayed more active immune responses and severe COVID-19 phenotypes following SARS-CoV-2 challenge compared to other models. Our study demonstrates the dual regulatory role of β-globin element in transgene transcription and suggests that opt-hACE2 mice might serve as valuable tools for SARS-CoV-2 research.

Animal Models for Long COVID: Current Advances, Limitations, and Future Directions

Long COVID (LC) represents a chronic, systemic, and often disabling condition that poses a significant ongoing threat to public health. Foundational scientific studies are needed to unravel the underlying mechanisms, with the ultimate goal of developing effective preventative and therapeutic strategies. Therefore, there is an urgent demand for animal models that can accurately replicate the clinical features of LC. This review integrates clinical epidemiological data to summarize the pathological changes in extrapulmonary systems involved in LC. Additionally, it critically examines the capacity of existing animal models, including nonhuman primates, genetically modified mice, and Syrian hamsters, to exhibit enduring postinfection symptoms that align with human clinical manifestations, and identifies key areas requiring further development. The objective is to offer insights that will aid in the development of next-generation animal models, thereby accelerating our understanding of how acute respiratory viral infections transition into chronic conditions, and ensuring preparedness for future pandemics.

Animal Models of Non-Respiratory, Post-Acute Sequelae of COVID-19

Post-acute sequelae of COVID-19 (PASC) are a diverse set of symptoms and syndromes driven by dysfunction of multiple organ systems that can persist for years and negatively impact the quality of life for millions of individuals. We currently lack specific therapeutics for patients with PASC, due in part to an incomplete understanding of its pathogenesis, especially for non-pulmonary sequelae. Here, we discuss three animal models that have been utilized to investigate PASC: non-human primates (NHPs), hamsters, and mice. We focus on neurological, gastrointestinal, and cardiovascular PASC and highlight advances in mechanistic insight that have been made using these animal models, as well as discussing the sequelae that warrant continued and intensive research.

Animal Models for Human-Pathogenic Coronavirus and Animal Coronavirus Research

Coronavirus epidemics have posed a serious threat to both human and animal health. To combat emerging infectious diseases caused by coronaviruses, various animal infection models have been developed and applied in research, including non-human primate models, ferret models, hamster models, mouse models, and others. Moreover, new approaches have been utilized to develop animal models that are more susceptible to infection. These approaches include using viral delivery methods to induce the expression of viral receptors in mouse tissues and employing gene-editing techniques to create genetically modified mice. This has led to the successful establishment of infection models for multiple coronaviruses, significantly advancing related research. In contrast, livestock and pets that can be infected by animal coronaviruses provide valuable insights when used as infection models, enabling the collection of accurate clinical data through the analysis of post-infection pathological features. However, despite the potential insights, there is a paucity of research data pertaining to these infection models. In this review, we provide a detailed overview of recent progress in the development of animal models for coronaviruses that cause diseases in both humans and animals and suggest ways in which animal models can be adapted to further enhance their value in research.

Placental SARS-CoV-2 Infection and Its Implications for Increased Risk of Adverse Pregnancy Outcomes

OBJECTIVE

 Pregnant women are at increased risk of coronavirus disease 2019 (COVID-19). This could be explained through the prism of physiologic and immunologic changes in pregnancy. In addition, certain immunological reactions originate in the placenta in response to viral infections.This study aimed to investigate whether severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) can infect the human placenta and discuss its implications in the pathogenesis of adverse pregnancy outcomes.

STUDY DESIGN

 We conducted a retrospective cohort study in which we collected placental specimens from pregnant women who had a laboratory-confirmed SARS-CoV-2 infection. We performed RNA in situ hybridization assay on formalin-fixed paraffin-embedded tissues to establish the in vivo evidence for placental infectivity by this corona virus. In addition, we infected trophoblast isolated from uninfected term human placenta with SARS-CoV-2 variants to further provide in vitro evidence for such an infectivity.

RESULTS

 There was a total of 21 cases enrolled, which included 5 cases of spontaneous preterm birth (SPTB) and 2 intrauterine fetal demises (IUFDs). Positive staining of positive-sense strand of SARS-CoV-2 virions was detected in 15 placentas including 4 SPTB and both IUFDs. In vitro infection assay demonstrated that SARS-CoV-2 virions were highly capable of infecting both cytotrophoblast and syncytiotrophoblast.

CONCLUSION

 This study implies that placental SARS-CoV-2 infection may be associated with an increased risk of adverse obstetrical outcomes.

KEY POINTS

· SARS-CoV-2 can effectively infect human placenta.. · Such infectivity is confirmed by in vitro experiments.. · Placental SARS-CoV-2 corelates with adverse obstetrical outcomes..

Chinese Medicine for Treatment of COVID-19: A Review of Potential Pharmacological Components and Mechanisms

Coronavirus disease 2019 (COVID-19) is an acute infectious respiratory disease that has been prevalent since December 2019. Chinese medicine (CM) has demonstrated its unique advantages in the fight against COVID-19 in the areas of disease prevention, improvement of clinical symptoms, and control of disease progression. This review summarized the relevant material components of CM in the treatment of COVID-19 by searching the relevant literature and reports on CM in the treatment of COVID-19 and combining with the physiological and pathological characteristics of the novel coronavirus. On the basis of sorting out experimental methods in vivo and in vitro, the mechanism of herb action was further clarified in terms of inhibiting virus invasion and replication and improving related complications. The aim of the article is to explore the strengths and characteristics of CM in the treatment of COVID-19, and to provide a basis for the research and scientific, standardized treatment of COVID-19 with CM.

Generation of a SARS-CoV-2-susceptible mouse model using adenovirus vector expressing human angiotensin-converting enzyme 2 driven by an elongation factor 1α promoter with leftward orientation

Introduction

To analyze the molecular pathogenesis of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a small animal model such as mice is needed: human angiotensin converting enzyme 2 (hACE2), the receptor of SARS-CoV-2, needs to be expressed in the respiratory tract of mice.

Methods

We conferred SARS-CoV-2 susceptibility in mice by using an adenoviral vector expressing hACE2 driven by an elongation factor 1α (EF1α) promoter with a leftward orientation.

Results

In this model, severe pneumonia like human COVID-19 was observed in SARS-CoV-2-infected mice, which was confirmed by dramatic infiltration of inflammatory cells in the lung with efficient viral replication. An early circulating strain of SARS-CoV-2 caused the most severe weight loss when compared to SARS-CoV-2 variants such as Alpha, Beta and Gamma, although histopathological findings, viral replication, and cytokine expression characteristics were comparable.

Discussion

We found that a distinct proteome of an early circulating strain infected lung characterized by elevated complement activation and blood coagulation, which were mild in other variants, can contribute to disease severity. Unraveling the specificity of early circulating SARS-CoV-2 strains is important in elucidating the origin of the pandemic.

Pathogenesis and virulence of coronavirus disease: Comparative pathology of animal models for COVID-19

Animal models that can replicate clinical and pathologic features of severe human coronavirus infections have been instrumental in the development of novel vaccines and therapeutics. The goal of this review is to summarize our current understanding of the pathogenesis of coronavirus disease 2019 (COVID-19) and the pathologic features that can be observed in several currently available animal models. Knowledge gained from studying these animal models of SARS-CoV-2 infection can help inform appropriate model selection for disease modelling as well as for vaccine and therapeutic developments.

The lethal K18-hACE2 knock-in mouse model mimicking the severe pneumonia of COVID-19 is practicable for antiviral development

Animal models of COVID-19 facilitate the development of vaccines and antivirals against SARS-CoV-2. The efficacy of antivirals or vaccines may differ in different animal models with varied degrees of disease. Here, we introduce a mouse model expressing human angiotensin-converting enzyme 2 (ACE2). In this model, ACE2 with the human cytokeratin 18 promoter was knocked into the Hipp11 locus of C57BL/6J mouse by CRISPR - Cas9 (K18-hACE2 KI). Upon intranasal inoculation with high (3 × 105 PFU) or low (2.5 × 102 PFU) dose of SARS-CoV-2 wildtype (WT), Delta, Omicron BA.1, or Omicron BA.2 variants, all mice showed obvious infection symptoms, including weight loss, high viral loads in the lung, and interstitial pneumonia. 100% lethality was observed in K18-hACE2 KI mice infected by variants with a delay of endpoint for Delta and BA.1, and a significantly attenuated pathogenicity was observed for BA.2. The pneumonia of infected mice was accompanied by the infiltration of neutrophils and pulmonary fibrosis in the lung. Compared with K18-hACE2 Tg mice and HFH4-hACE2 Tg mice, K18-hACE2 KI mice are more susceptible to SARS-CoV-2. In the antivirals test, REGN10933 and Remdesivir had limited antiviral efficacies in K18-hACE2 KI mice upon the challenge of SARS-CoV-2 infections, while Nirmatrelvir, monoclonal antibody 4G4, and mRNA vaccines potently protected the mice from death. Our results suggest that the K18-hACE2 KI mouse model is lethal and stable for SARS-CoV-2 infection, and is practicable and stringent to antiviral development.

Tight junction protein LSR is a host defense factor against SARS-CoV-2 infection in the small intestine

The identification of host factors with antiviral potential is important for developing effective prevention and therapeutic strategies against SARS-CoV-2 infection. Here, by using immortalized cell lines, intestinal organoids, ex vivo intestinal tissues and humanized ACE2 mouse model as proof-of-principle systems, we have identified lipolysis-stimulated lipoprotein receptor (LSR) as a crucial host defense factor against SARS-CoV-2 infection in the small intestine. Loss of endogenous LSR enhances ACE2-dependent infection by SARS-CoV-2 Spike (S) protein-pseudotyped virus and authentic SARS-CoV-2 virus, and exogenous administration of LSR protects against viral infection. Mechanistically, LSR interacts with ACE2 both in cis and in trans, preventing its binding to S protein, and thus inhibiting viral entry and S protein-mediated cell-cell fusion. Finally, a small LSR-derived peptide blocks S protein binding to the ACE2 receptor in vitro. These results identify both a previously unknown function for LSR in antiviral host defense against SARS-CoV-2, with potential implications for peptide-based pan-variant therapeutic interventions.

Liang-Ge-San protects against viral infection-induced acute lung injury through inhibiting α7nAChR-mediated mitophagy

BACKGROUND

Acute lung injury (ALI) is the main cause of death in clinical respiratory virus infection. Liang-Ge-San (LGS), a famous traditional Chinese formula, has been proved to be effective in treating ALI caused by lipopolysaccharide. However, the effects of LGS on ALI induced by viral infections remain uncertain.

PURPOSE

To investigate the effect and mechanism of action of LGS on viral infection-induced ALI.

METHODS

The inhibitory effects of LGS on virus-induced inflammation in vitro were evaluated by qRT-PCR and ELISA. The protein expression of α7nAChR was examined by Western blotting. α7nAChR was inhibited by the transfection of siRNA or methyllycaconitine citrate (MLA, an α7nAChR inhibitor) to investigate the role of α7nAChR in the anti-inflammatory effect of LGS. Adoptive culture and co-culture systems of macrophages RAW264.7 and alveolar epithelial cells MLE-12 were established to mimic their interaction. Western blotting, immunofluorescence, flow cytometry and transmission electron microscopy were used to examine the effects of LGS on mitophagy inhibition. In vivo, ALI mouse models induced by SARS-CoV-2, H1N1 or Poly(I:C) infection were established to explore the therapeutic effect and mechanism of LGS.

RESULTS

LGS reduced the release of IL-6, TNF-α and IL-1β and increased the expression of α7nAChR in virus-infected RAW264.7 cells. The blockage of α7nAChR counteracted the anti-inflammatory effect of LGS. Moreover, LGS significantly inhibited autophagy in MLE-12 cells induced by Poly(I:C) in adoptive culture and co-culture systems of RAW264.7 and MLE-12 cells, which could be attenuated after the inhibition of α7nAChR in RAW264.7 cells by decreasing the secretion of IL-6, TNF-α and IL-1β. Further study showed that LGS suppressed TNF-α-induced mitochondrial damage and mitophagy by inhibiting the generation of ROS in MLE-12 cells. In vivo, LGS significantly prolonged the survival time, alleviated pathological injury and acute inflammation of ALI mice induced by SARS-CoV-2, H1N1 or Poly(I:C) infection which were associated with the inhibition of α7nAChR-mediated mitophagy.

CONCLUSION

This study first demonstrates that LGS inhibits virus infection-induced inflammation in RAW246.7 cells by increasing the expression of α7nAChR, thereby inhibiting mitophagy induction in MLE-12 cells to alleviate ALI. This work indicates that LGS may serve as a candidate drug for treating ALI/ARDS caused by viral infection.

Progress and challenges in development of animal models for dengue virus infection

ABSTRACTThe severity of the dengue epidemic is on the rise, with its geographic range had expanded to southern Europe by 2024. In this August, the WHO updated the pathogens that could spark the next pandemic, dengue virus was on the list. Vaccines and drugs serve as powerful tools for both preventing dengue infections and treating patients. Animal models play a pivotal role in vaccine development and drug screening. Available potential susceptible animals, including non-human primates, rodents, pigs, and tree shrews, have been extensively explored to establish animal models of dengue disease. Despite significant advancements, there are still notable limitations. Different animal models exhibit distinct constraining factors such as viraemia, host susceptibility, immune function of the host, clinical symptoms, ADE (antibody-dependent enhancement) phenomena, cytokine storm response to various serotypes and strain variations. Furthermore, despite extensive research on the dengue virus receptor in recent years, genetically modified animal models immunocompetent harbouring dengue virus susceptibility receptors have not yet been available. This work reviewed the research progress of dengue virus receptors and dengue animal models, suggesting that the development of genetically modified murine models expressing dengue virus functional receptors may hold a promise for future dengue disease research, especially for its vaccine development.

Oro-faecal transmission of SARS-CoV-2: A systematic review of studies employing viral culture from gastrointestinal and other potential oro-faecal sources and evidence for transmission to humans

The extent to which the oro-faecal route contributes to the transmission of SARS-CoV-2 is not established.We systematically reviewed the evidence on the presence of infectious SARS-CoV-2 in faeces and other gastrointestinal sources by examining studies that used viral culture to investigate the presence of replication-competent virus in these samples. We conducted searches in the WHO COVID-19 Database, LitCovid, medRxiv, and Google Scholar for SARS-CoV-2 using keywords and associated synonyms, with a search date up to 28 November 2023.We included 13 studies involving 229 COVID-19 subjects - providing 308 faecal or rectal swab SARS-CoV2 reverse transcription-polymerase chain reaction (RT-PCR)-positive samples tested with viral culture. The methods used for viral culture across the studies were heterogeneous. Three studies (two cohorts and one case series) reported observing replication-competent SARS-CoV-2 confirmed by quantitative RT-PCR (qPCR) and whole-genome sequencing, and qPCR including appropriate cycle threshold changes. Overall, six (1.9%) of 308 faecal samples subjected to cell culture showed replication-competent virus. One study found replication-competent samples from one immunocompromised patient. No studies were identified demonstrating direct evidence of oro-faecal transmission to humans.Our review found a relatively low frequency of replication-competent SARS-CoV-2 in faecal and other gastrointestinal sources. Although it is biologically plausible, more research is needed using standardized cell culture methods, control groups, adequate follow-up, and robust epidemiologic methods, including whether secondary infections occurred, to determine the role of the oro-faecal route in the transmission of SARS-CoV-2.

Neuroinflammation in Post COVID-19 Sequelae: Neuroinvasion and Neuroimmune Crosstalk

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019 triggered a swift global spread, leading to a devastating pandemic. Alarmingly, approximately one in four individuals diagnosed with coronavirus disease 2019 (COVID-19) experience varying degrees of cognitive impairment, raising concerns about a potential increase in neurological sequelae cases. Neuroinflammation seems to be the key pathophysiological hallmark linking mild respiratory COVID-19 to cognitive impairment, fatigue, and neurological sequelae in COVID-19 patients, highlighting the interaction between the nervous and immune systems following SARS-CoV-2 infection. Several hypotheses have been proposed to explain how the virus disrupts physiological pathways to trigger inflammation within the CNS, potentially leading to neuronal damage. These include neuroinvasion, systemic inflammation, disruption of the lung and gut-brain axes, and reactivation of latent viruses. This review explores the potential origins of neuroinflammation and the underlying neuroimmune cross-talk, highlighting important unanswered questions in the field. Addressing these fundamental issues could enhance our understanding of the virus's impact on the CNS and inform strategies to mitigate its detrimental effects.

Advancing CRISPR-Based Solutions for COVID-19 Diagnosis and Therapeutics

Since the onset of the COVID-19 pandemic, a variety of diagnostic approaches, including RT-qPCR, RAPID, and LFA, have been adopted, with RT-qPCR emerging as the gold standard. However, a significant challenge in COVID-19 diagnostics is the wide range of symptoms presented by patients, necessitating early and accurate diagnosis for effective management. Although RT-qPCR is a precise molecular technique, it is not immune to false-negative results. In contrast, CRISPR-based detection methods for SARS-CoV-2 offer several advantages: they are cost-effective, time-efficient, highly sensitive, and specific, and they do not require sophisticated instruments. These methods also show promise for scalability, enabling diagnostic tests. CRISPR technology can be customized to target any genomic region of interest, making it a versatile tool with applications beyond diagnostics, including therapeutic development. The CRISPR/Cas systems provide precise gene targeting with immense potential for creating next-generation diagnostics and therapeutics. One of the key advantages of CRISPR/Cas-based therapeutics is the ability to perform multiplexing, where different sgRNAs or crRNAs can target multiple sites within the same gene, reducing the likelihood of viral escape mutants. Among the various CRISPR systems, CRISPR/Cas13 and CARVER (Cas13-assisted restriction of viral expression and readout) are particularly promising. These systems can target a broad range of single-stranded RNA viruses, making them suitable for the diagnosis and treatment of various viral diseases, including SARS-CoV-2. However, the efficacy and safety of CRISPR-based therapeutics must be thoroughly evaluated in pre-clinical and clinical settings. While CRISPR biotechnologies have not yet been fully harnessed to control the current COVID-19 pandemic, there is an optimism that the limitations of the CRISPR/Cas system can be overcome soon. This review discusses how CRISPR-based strategies can revolutionize disease diagnosis and therapeutic development, better preparing us for future viral threats.

Characterization of Collaborative Cross mouse founder strain CAST/EiJ as a novel model for lethal COVID-19

Mutations in SARS-CoV-2 variants of concern (VOCs) have expanded the viral host range beyond primates, and a few other mammals, to mice, affording the opportunity to exploit genetically diverse mouse panels to model the broad spectrum of responses to infection in patient populations. Here we surveyed responses to VOC infection in genetically diverse Collaborative Cross (CC) founder strains. Infection of wild-derived CC founder strains produced a broad range of viral burden, disease susceptibility and survival, whereas most other strains were resistant to disease despite measurable lung viral titers. In particular, CAST/EiJ, a wild-derived strain, developed high lung viral burdens, more severe lung pathology than seen in other CC strains, and a dysregulated cytokine profile resulting in morbidity and mortality. These inbred mouse strains may serve as a valuable platform to evaluate therapeutic countermeasures against severe COVID-19 and other coronavirus pandemics in the future.

Characterizing a lethal CAG-ACE2 transgenic mouse model for SARS-CoV-2 infection using Cas9-enhanced nanopore sequencing

The SARS-CoV-2 pandemic has underscored the necessity for functional transgenic animal models for testing. Mouse lines with overexpression of the human receptor ACE2 serve as the common animal model to study COVID-19 infection. Overexpression of ACE2 under a strong ubiquitous promoter facilitates convenient and sensitive testing of COVID-19 pathology. We performed pronuclear microinjections using a 5 kb CAG-ACE2 linear transgene construct and identified three founder lines with 140, 72, and 73 copies, respectively. Two of these lines were further analyzed for ACE2 expression profiles and sensitivity to SARS-CoV-2 infection. Both lines expressed ACE2 in all organs analyzed. Embryonic fibroblast cell lines derived from transgenic embryos demonstrated severe cytopathic effects following infection, even at low doses of SARS-CoV-2 (0,1-1.0 TCID50). Infected mice from the two lines began to show COVID-19 clinical signs three days post-infection and succumbed between days 4 and 7. Histological examination of lung tissues from terminally ill mice revealed severe pathological alterations. To further characterize the integration site in one of the lines, we applied nanopore sequencing combined with Cas9 enrichment to examine the internal transgene concatemer structure. Oxford Nanopore sequencing (ONT) is becoming the gold standard for transgene insert characterization, but it is relatively inefficient without targeted region enrichment. We digested genomic DNA with Cas9 and gRNA against the ACE2 transgene to create ends suitable for ONT adapter ligation. ONT data analysis revealed that most of the transgene copies were arranged in a head-to-tail configuration, with palindromic junctions being rare. We also detected occasional plasmid backbone fragments within the concatemer, likely co-purified during transgene gel extraction, which is a common occurrence in pronuclear microinjections.

SARS-CoV-2 Delta and Omicron variants resist spike cleavage by human airway trypsin-like protease

Soluble host factors in the upper respiratory tract can serve as the first line of defense against SARS-CoV-2 infection. In this study, we described the identification and function of a human airway trypsin-like protease (HAT), capable of reducing the infectivity of ancestral SARS-CoV-2. Further, in mouse models, HAT analogue expression was upregulated by SARS-CoV-2 infection. The antiviral activity of HAT functioned through the cleavage of the SARS-CoV-2 spike glycoprotein at R682. This cleavage resulted in inhibition of the attachment of ancestral spike proteins to host cells, which inhibited the cell-cell membrane fusion process. Importantly, exogenous addition of HAT notably reduced the infectivity of ancestral SARS-CoV-2 in vivo. However, HAT was ineffective against the Delta variant and most circulating Omicron variants, including the BQ.1.1 and XBB.1.5 subvariants. We demonstrate that the P681R mutation in Delta and P681H mutation in the Omicron variants, adjacent to the R682 cleavage site, contributed to HAT resistance. Our study reports what we believe to be a novel soluble defense factor against SARS-CoV-2 and resistance of its actions in the Delta and Omicron variants.

Emerging and reemerging infectious diseases: global trends and new strategies for their prevention and control

To adequately prepare for potential hazards caused by emerging and reemerging infectious diseases, the WHO has issued a list of high-priority pathogens that are likely to cause future outbreaks and for which research and development (R&D) efforts are dedicated, known as paramount R&D blueprints. Within R&D efforts, the goal is to obtain effective prophylactic and therapeutic approaches, which depends on a comprehensive knowledge of the etiology, epidemiology, and pathogenesis of these diseases. In this process, the accessibility of animal models is a priority bottleneck because it plays a key role in bridging the gap between in-depth understanding and control efforts for infectious diseases. Here, we reviewed preclinical animal models for high priority disease in terms of their ability to simulate human infections, including both natural susceptibility models, artificially engineered models, and surrogate models. In addition, we have thoroughly reviewed the current landscape of vaccines, antibodies, and small molecule drugs, particularly hopeful candidates in the advanced stages of these infectious diseases. More importantly, focusing on global trends and novel technologies, several aspects of the prevention and control of infectious disease were discussed in detail, including but not limited to gaps in currently available animal models and medical responses, better immune correlates of protection established in animal models and humans, further understanding of disease mechanisms, and the role of artificial intelligence in guiding or supplementing the development of animal models, vaccines, and drugs. Overall, this review described pioneering approaches and sophisticated techniques involved in the study of the epidemiology, pathogenesis, prevention, and clinical theatment of WHO high-priority pathogens and proposed potential directions. Technological advances in these aspects would consolidate the line of defense, thus ensuring a timely response to WHO high priority pathogens.

The effects of iron deficient and high iron diets on SARS-CoV-2 lung infection and disease

Introduction

The severity of Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is often dictated by a range of comorbidities. A considerable literature suggests iron deficiency and iron overload may contribute to increased infection, inflammation and disease severity, although direct causal relationships have been difficult to establish.

Methods

Here we generate iron deficient and iron loaded C57BL/6 J mice by feeding standard low and high iron diets, with mice on a normal iron diet representing controls. All mice were infected with a primary SARS-CoV-2 omicron XBB isolate and lung inflammatory responses were analyzed by histology, immunohistochemistry and RNA-Seq.

Results

Compared with controls, iron deficient mice showed no significant changes in lung viral loads or histopathology, whereas, iron loaded mice showed slightly, but significantly, reduced lung viral loads and histopathology. Transcriptional changes were modest, but illustrated widespread dysregulation of inflammation signatures for both iron deficient vs. controls, and iron loaded vs. controls. Some of these changes could be associated with detrimental outcomes, whereas others would be viewed as beneficial.

Discussion

Diet-associated iron deficiency or overload thus induced modest modulations of inflammatory signatures, but no significant histopathologically detectable disease exacerbations.

Ex vivo challenge models for infectious diseases

Traditionally, molecular mechanisms of pathogenesis for infectious agents were studied in cell culture or animal models but have limitations on the extent to which the resulting data reflect natural infection in humans. The COVID-19 pandemic has highlighted the urgent need to rapidly develop laboratory models that enable the study of host-pathogen interactions, particularly the relative efficacy of preventive measures. Recently, human and animal ex vivo tissue challenge models have emerged as a promising avenue to study immune responses, screen potential therapies and triage vaccine candidates. This approach offers the opportunity to closely approximate human disease from the perspective of pathology and immune response. It has advantages compared to animal models which are expensive, lengthy and often require containment facilities. Herein, we summarize some recent advances in the development of ex vivo tissue challenge models for COVID-19, HIV-1 and other pathogens. We focus on the contribution of these models to enhancing knowledge of host-pathogen interactions, immune modulation, and their value in testing therapeutic agents. We further highlight the advantages and limitations of using ex vivo challenge models and briefly summarize how the use of organoids provides a useful advancement over current approaches. Collectively, these developments have enormous potential for the study of infectious diseases.

Association Between COVID-19 and Neurological Diseases: Evidence from Large-Scale Mendelian Randomization Analysis and Single-Cell RNA Sequencing Analysis

Observational studies have suggested that SARS-CoV-2 infection increases the risk of neurological diseases, but it remains unclear whether the association is causal. The present study aims to evaluate the causal relationships between SARS-CoV-2 infections and neurological diseases and analyzes the potential routes of SARS-CoV-2 entry at the cellular level. We performed Mendelian randomization (MR) analysis with CAUSE method to investigate causal relationship of SARS-CoV-2 infections with neurological diseases. Then, we conducted single-cell RNA sequencing (scRNA-seq) analysis to obtain evidence of potential neuroinvasion routes by measuring SARS-CoV-2 receptor expression in specific cell subtypes. Fast gene set enrichment analysis (fGSEA) was further performed to assess the pathogenesis of related diseases. The results showed that the COVID-19 is causally associated with manic (delta_elpd, - 0.1300, Z-score: - 2.4; P = 0.0082) and epilepsy (delta_elpd: - 2.20, Z-score: - 1.80; P = 0.038). However, no significant effects were observed for COVID-19 on other traits. Moreover, there are 23 cell subtypes identified through the scRNA-seq transcriptomics data of epilepsy, and SARS-CoV-2 receptor TTYH2 was found to be specifically expressed in oligodendrocyte and astrocyte cell subtypes. Furthermore, fGSEA analysis showed that the cell subtypes with receptor-specific expression was related to methylation of lysine 27 on histone H3 (H3K27ME3), neuronal system, aging brain, neurogenesis, and neuron projection. In summary, this study shows causal links between SARS-CoV-2 infections and neurological disorders such as epilepsy and manic, supported by MR and scRNA-seq analysis. These results should be considered in further studies and public health measures on COVID-19 and neurological diseases.

Antiviral effect of cannabidiol on K18-hACE2 transgenic mice infected with SARS-CoV-2

The aim of this study was to determine the antiviral activity of cannabidiol (CBD) against SARS-CoV-2 infection. CBD is the second most studied cannabinoid obtained from Cannabis plants. We investigated the potential use of CBD, which has so far proven to have a positive effect on different diseases, in the SARS-CoV-2 infection. To test this, in vivo studies were carried out using K18-hACE2 transgenic mice. To reveal the potential therapeutic effect of the CBD at the histopathological and molecular level challenge experiments were performed. The study was designed with two groups (n = 10) and in the treatment group animals were infected with SARS-CoV-2 virus strain B.1.1.7 alpha before the administration of CBD. While the disease progressed and resulted in death in the control group that was infected by the virus alone, it was observed that the infection slowed down and the survival rate increased in the mice treated with CBD along with the virus. In this study, K18-hACE2 transgenic mice infected with the wild SARS-CoV-2 virus were used to investigate and prove the antiviral activity of CBD.

MVA-based vaccine candidates expressing SARS-CoV-2 prefusion-stabilized spike proteins of the Wuhan, Beta or Omicron BA.1 variants protect transgenic K18-hACE2 mice against Omicron infection and elicit robust and broad specific humoral and cellular immune responses

Despite the decrease in mortality and morbidity due to SARS-CoV-2 infection, the incidence of infections due to Omicron subvariants of SARS-CoV-2 remains high. The mutations acquired by these subvariants, mainly concentrated in the receptor-binding domain (RBD), have caused a shift in infectivity and transmissibility, leading to a loss of effectiveness of the first authorized COVID-19 vaccines, among other reasons, by neutralizing antibody evasion. Hence, the generation of new vaccine candidates adapted to Omicron subvariants is of special interest in an effort to overcome this immune evasion. Here, an optimized COVID-19 vaccine candidate, termed MVA-S(3P_BA.1), was developed using a modified vaccinia virus Ankara (MVA) vector expressing a full-length prefusion-stabilized SARS-CoV-2 spike (S) protein from the Omicron BA.1 variant. The immunogenicity and efficacy induced by MVA-S(3P_BA.1) were evaluated in mice in a head-to-head comparison with the previously generated vaccine candidates MVA-S(3P) and MVA-S(3Pbeta), which express prefusion-stabilized S proteins from Wuhan strain and Beta variant, respectively, and with a bivalent vaccine candidate composed of a combination of MVA-S(3P) and MVA-S(3P_BA.1). The results showed that all four vaccine candidates elicited, after a single intramuscular dose, protection of transgenic K18-hACE2 mice challenged with SARS-CoV-2 Omicron BA.1, reducing viral loads, histopathological lesions, and levels of proinflammatory cytokines in the lungs. They also elicited anti-S IgG and neutralizing antibodies against various Omicron subvariants, with MVA-S(3P_BA.1) and the bivalent vaccine candidate inducing higher titers. Additionally, an intranasal immunization in C57BL/6 mice with all four vaccine candidates induced systemic and mucosal S-specific CD4+ and CD8+ T-cell and humoral immune responses, and the bivalent vaccine candidate induced broader immune responses, eliciting antibodies against the ancestral Wuhan strain and different Omicron subvariants. These results highlight the use of MVA as a potent and adaptable vaccine vector against new emerging SARS-CoV-2 variants, as well as the promising feature of combining multivalent MVA vaccine candidates.

Endurance Exercise Does Not Exacerbate Cardiac Inflammation in BALB/c Mice Following mRNA COVID-19 Vaccination

The mechanism underlying myopericarditis associated with mRNA COVID-19 vaccination, including increased susceptibility in young males, remains poorly understood. This study aims to explore the hypothesis that engaging in physical exercise at the time of mRNA COVID-19 vaccination may promote a cardiac inflammatory response, leading to the development of myopericarditis. Male BALB/c mice underwent treadmill running or remained sedentary for five weeks. Subsequently, two doses of the Pfizer/BioNTech vaccine or vehicle were administered with a 14-day interval, while the exercise regimen continued. The animals were euthanized days after the second vaccination. Vaccination was followed by body weight loss, increased hepatic inflammation, and an antigen-specific T cell response. Small foci of fibrovascular inflammation and focal cell loss were observed in the right ventricle, irrespective of vaccination and/or exercise. Vaccination did not elevate cardiac troponin levels. Cardiac tissue from the vaccinated mice showed upregulated mRNA expression of the genes IFNγ and IL-1β, but not IL-6 or TNFα. This pro-inflammatory signature in the heart was not exacerbated by endurance exercise. Ex vivo vascular reactivity remained unaffected by vaccination. Our data provide evidence for the cardiac safety of mRNA COVID-19 vaccination. The role of exercise in the development of pro-inflammatory cardiac changes post mRNA vaccination could not be established.

CD4+ and CD8+ T cells are required to prevent SARS-CoV-2 persistence in the nasal compartment

SARS-CoV-2 infection induces the generation of virus-specific CD4+ and CD8+ effector and memory T cells. However, the contribution of T cells in controlling SARS-CoV-2 during infection is not well understood. Following infection of C57BL/6 mice, SARS-CoV-2-specific CD4+ and CD8+ T cells are recruited to the respiratory tract, and a vast proportion secrete the cytotoxic molecule granzyme B. Using depleting antibodies, we found that T cells within the lungs play a minimal role in viral control, and viral clearance occurs in the absence of both CD4+ and CD8+ T cells through 28 days postinfection. In the nasal compartment, depletion of both CD4+ and CD8+ T cells, but not individually, results in persistent, culturable virus replicating in the nasal epithelial layer through 28 days postinfection. Viral sequencing analysis revealed adapted mutations across the SARS-CoV-2 genome, including a large deletion in ORF6. Overall, our findings highlight the importance of T cells in controlling virus replication within the respiratory tract during SARS-CoV-2 infection.

Characterization of Collaborative Cross mouse founder strain CAST/EiJ as a novel model for lethal COVID-19

Mutations in SARS-CoV-2 variants of concern (VOCs) have expanded the viral host range beyond primates, and a limited range of other mammals, to mice, affording the opportunity to exploit genetically diverse mouse panels to model the broad range of responses to infection in patient populations. Here we surveyed responses to VOC infection in genetically diverse Collaborative Cross (CC) founder strains. Infection of wild-derived CC founder strains produced a broad range of viral burden, disease susceptibility and survival, whereas most other strains were resistant to disease despite measurable lung viral titers. In particular, CAST/EiJ, a wild-derived strain, developed high lung viral burdens, more severe lung pathology than seen in other CC strains, and a dysregulated cytokine profile resulting in morbidity and mortality. These inbred mouse strains may serve as a valuable platform to evaluate therapeutic countermeasures against severe COVID-19 and other coronavirus pandemics in the future.

A BSL-2 compliant mouse model of SARS-CoV-2 infection for efficient and convenient antiviral evaluation

Animal models of authentic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection require operation in biosafety level 3 (BSL-3) containment. In the present study, we established a mouse model employing a single-cycle infectious virus replicon particle (VRP) system of SARS-CoV-2 that can be safely handled in BSL-2 laboratories. The VRP [ΔS-VRP(G)-Luc] contains a SARS-CoV-2 genome in which the spike gene was replaced by a firefly luciferase (Fluc) reporter gene (Rep-Luci), and incorporates the vesicular stomatitis virus glycoprotein on the surface. Intranasal inoculation of ΔS-VRP(G)-Luc can successfully transduce the Rep-Luci genome into mouse lungs, initiating self-replication of Rep-Luci and, accordingly, inducing acute lung injury mimicking the authentic SARS-CoV-2 pathology. In addition, the reporter Fluc expression can be monitored using a bioluminescence imaging approach, allowing a rapid and convenient determination of viral replication in ΔS-VRP(G)-Luc-infected mouse lungs. Upon treatment with an approved anti-SARS-CoV-2 drug, VV116, the viral replication in infected mouse lungs was significantly reduced, suggesting that the animal model is feasible for antiviral evaluation. In summary, we have developed a BSL-2-compliant mouse model of SARS-CoV-2 infection, providing an advanced approach to study aspects of the viral pathogenesis, viral-host interactions, as well as the efficacy of antiviral therapeutics in the future.IMPORTANCESevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly contagious and pathogenic in humans; thus, research on authentic SARS-CoV-2 has been restricted to biosafety level 3 (BSL-3) laboratories. However, due to the scarcity of BSL-3 facilities and trained personnel, the participation of a broad scientific community in SARS-CoV-2 research had been greatly limited, hindering the advancement of our understanding on the basic virology as well as the urgently necessitated drug development. Previously, our colleagues Jin et al. had generated a SARS-CoV-2 replicon by replacing the essential spike gene in the viral genome with a Fluc reporter (Rep-Luci), which can be safely operated under BSL-2 conditions. By incorporating the Rep-Luci into viral replicon particles carrying vesicular stomatitis virus glycoprotein on their surface, and via intranasal inoculation, we successfully transduced the Rep-Luci into mouse lungs, developing a mouse model mimicking SARS-CoV-2 infection. Our model can serve as a useful platform for SARS-CoV-2 pathological studies and antiviral evaluation under BSL2 containment.

Impact of age and sex on neuroinflammation following SARS-CoV-2 infection in a murine model

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the etiological agent of COVID-19, is known to infect people of all ages and both sexes. Senior populations have the greatest risk of severe COVID-19, and sexual dimorphism in clinical outcomes has been reported. Neurological symptoms are widely observed in COVID-19 patients, with many survivors exhibiting persistent neurological and cognitive impairment. The present study aims to investigate the impact of age and sex on the neuroinflammatory response to SARS-CoV-2 infection using a mouse model. Wild-type C57BL/6J mice were intranasally inoculated with SARS-CoV-2 lineage B.1.351, a variant known to infect mice. Older male mice exhibited a significantly greater weight loss and higher viral loads in the lung at 3 days post infection. Notably, no viral RNA was detected in the brains of infected mice. Nevertheless, expression of IL-6, TNF-α, and CCL-2 in the lung and brain increased with viral infection. RNA-seq transcriptomic analysis of brains showed that SARS-CoV-2 infection caused significant changes in gene expression profiles, implicating innate immunity, defense response to virus, and cerebrovascular and neuronal functions. These findings demonstrate that SARS-CoV-2 infection triggers a neuroinflammatory response, despite the lack of detectable virus in the brain. Aberrant activation of innate immune response, disruption of blood-brain barrier and endothelial cell integrity, and suppression of neuronal activity and axonogenesis underlie the impact of SARS-CoV-2 infection on the brain. Understanding the role of these affected pathways in SARS-CoV-2 pathogenesis helps identify appropriate points of therapeutic interventions to alleviate neurological dysfunction observed during COVID-19.

Protection of K18-hACE2 Mice against SARS-CoV-2 Challenge by a Capsid Virus-like Particle-Based Vaccine

The SARS-CoV-2 pandemic and the emergence of novel virus variants have had a dramatic impact on public health and the world economy, underscoring the need for detailed studies that explore the high efficacy of additional vaccines in animal models. In this study, we confirm the pathogenicity of the SARS-CoV-2/Leiden_008 isolate (GenBank accession number MT705206.1) in K18-hACE2 transgenic mice. Using this isolate, we show that a vaccine consisting of capsid virus-like particles (cVLPs) displaying the receptor-binding domain (RBD) of SARS-CoV-2 (Wuhan strain) induces strong neutralizing antibody responses and sterilizing immunity in K18-hACE2 mice. Furthermore, we demonstrate that vaccination with the RBD-cVLP vaccine protects mice from both a lethal infection and symptomatic disease. Our data also indicate that immunization significantly reduces inflammation and lung pathology associated with severe disease in mice. Additionally, we show that the survival of naïve animals significantly increases when sera from animals vaccinated with RBD-cVLP are passively transferred, prior to a lethal virus dose. Finally, the RBD-cVLP vaccine has a similar antigen composition to the clinical ABNCOV2 vaccine, which has shown non-inferiority to the Comirnaty mRNA vaccine in phase I-III trials. Therefore, our study provides evidence that this vaccine design is highly immunogenic and confers full protection against severe disease in mice.

Establishment and characterization of an hACE2/hTMPRSS2 knock-in mouse model to study SARS-CoV-2

Despite a substantial body of research, we lack fundamental understanding of the pathophysiology of COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) including pulmonary and cardiovascular outcomes, in part due to limitations of murine models. Most models use transgenic mice (K18) that express the human (h) angiotensin converting enzyme 2 (ACE2), ACE2 knock-in (KI) mice, or mouse-adapted strains of SARS-CoV-2. Further, many SARS-CoV-2 variants produce fatal neurologic disease in K18 mice and most murine studies focus only on acute disease in the first 14 days post inoculation (dpi). To better enable understanding of both acute (<14 dpi) and post-acute (>14 dpi) infection phases, we describe the development and characterization of a novel non-lethal KI mouse that expresses both the ACE2 and transmembrane serine protease 2 (TMPRSS2) genes (hACE2/hTMPRSS2). The human genes were engineered to replace the orthologous mouse gene loci but remain under control of their respective murine promoters, resulting in expression of ACE2 and TMPRSS2 instead of their murine counterparts. After intranasal inoculation with an omicron strain of SARS-CoV-2, hACE2/hTMPRSS2 KI mice transiently lost weight but recovered by 7 dpi. Infectious SARS-CoV-2 was detected in nasopharyngeal swabs 1-2 dpi and in lung tissues 2-6 dpi, peaking 4 dpi. These outcomes were similar to those in K18 mice that were inoculated in parallel. To determine the extent to which hACE2/hTMPRSS2 KI mice are suitable to model pulmonary and cardiovascular outcomes, physiological assessments measuring locomotion, behavior and reflexes, biomonitoring to measure cardiac activity and respiration, and micro computed tomography to assess lung function were conducted frequently to 6 months post inoculation. Male but not female SARS-CoV-2 inoculated hACE2/hTMPRSS2 KI mice showed a transient reduction in locomotion compared to control saline treated mice. No significant changes in respiration, oxygen saturation, heart rate variability, or conductivity were detected in SARS-CoV-2 inoculated mice of either sex. When re-inoculated 6 months after the first inoculation, hACE2/hTMPRSS2 KI became re-infected with disease signs similar to after the first inoculation. Together these data show that a newly generated hACE2/hTMPRSS2 KI mouse can be used to study mild COVID-19.

Immune reactivity of two biological models to vaccination with inactivated vaccine QazVac against coronavirus infection COVID-19

INTRODUCTION

Specific prevention of a number of infectious diseases has been introduced into the vaccination schedule. The production of immunoprophylactic drugs, in order to establish standard properties, including safety and specific effectiveness, requires strict adherence to manufacturing regulations, and the reliability of the results obtained requires monitoring of these parameters. The specific effectiveness of vaccine preparations is standardized according to the indicators of stimulation of specific antibody response formed in the body of vaccinated model biological objects.

OBJECTIVE

Determination of the immune reactivity of white mice to vaccination with the QazVac vaccine to establish the possibility of using them as a biological model in assessing the immunogenicity of the vaccine instead of Syrian hamsters.

MATERIALS AND METHODS

The immune reactivity of model animals was assessed by the seroconversion rate, dynamics of antibody titers to the SARS-CoV-2 virus formed in the body after vaccination with the test vaccine. In the case of seropositivity of animals before administration of vaccine or placebo, the level of immune reactivity was calculated by the difference in antibody titers between control and vaccinated animals or by the difference in antibody titers before and after immunization. Specific antibodies were detected and their titer was determined using a neutralization reaction.

RESULTS

The research results showed that the tested biological models had approximately the same immune reactivity to the administration of the QazVac vaccine, confirmed by the level and dynamics of antibody titers. When analyzing the fold increase in antibody titers in comparison to those of control animals, Syrian hamsters were more reactive compared to mice. But SPF white mice were standardized in their lack of the immune reactivity to SARS-CoV-2 virus before the immunization.

CONCLUSION

The data obtained indicate that the immune reactivity of white mice to the administration of the QazVac vaccine in terms of the rate and dynamics of the formation of virus-neutralizing antibodies is approximately equivalent to the immune reactivity of Syrian hamsters. Before immunization with the vaccine, SPF white mice, in contrast to Syrian hamsters, do not have humoral immunity specific to the SARS-CoV-2 virus. The immune reactivity equivalent to that observed of Syrian hamsters and the absence of antibodies to the SARS-CoV-2 virus at a baseline indicate the superiority of the use of white mice in assessing the immunogenicity of vaccines against COVID-19 and/or obtaining specific factors of humoral immunity.

A murine model of DC-SIGN humanization exhibits increased susceptibility against SARS-CoV-2

To generate a new murine model for virus, DC-SIGN gene in murine was humanized. In this study, we successfully generated a humanized C57BL/6N mouse model expressing human DC-SIGN (hDC-SIGN) using CRISPR/Cas9 technology, and evaluated its characters and susceptibility to virus. The humanized mice could survival as usual, and with normal physiological index just like the wild-type mice. Whereas, we found significant differences in the intestinal flora and metabolic profiles between wild-type mice and humanized mice. Following intranasal infection with SARS-CoV-2, hDC-SIGN mice exhibited significantly increased viral loads in the lungs and nasal turbinates, along with more severe lung damage. This phenomenon may be associated with differential lipid metabolism and Fcγ receptor-mediated phagocytosis in two mouse models. This study provides a useful tool for investigating the mechanisms of coronavirus infection and potential drug therapies against novel coronavirus.

Characterization of a pangolin SARS-CoV-2-related virus isolate that uses the human ACE2 receptor

Various SARS-CoV-2-related coronaviruses have been increasingly identified in pangolins, showing a potential threat to humans. Here we report the infectivity and pathogenicity of the SARS-CoV-2-related virus, PCoV-GX/P2V, which was isolated from a Malayan pangolin (Manis javanica). PCoV-GX/P2V could grow in human hepatoma, colorectal adenocarcinoma cells, and human primary nasal epithelial cells. It replicated more efficiently in cells expressing human angiotensin-converting enzyme 2 (hACE2) as SARS-CoV-2 did. After intranasal inoculation to the hACE2-transgenic mice, PCoV-GX/P2V not only replicated in nasal turbinate and lungs, but also caused interstitial pneumonia, characterized by infiltration of mixed inflammatory cells and multifocal alveolar hemorrhage. Existing population immunity established by SARS-CoV-2 infection and vaccination may not protect people from PCoV-GX/P2V infection. These findings further verify the hACE2 utility of PCoV-GX/P2V by in vivo experiments using authentic viruses and highlight the importance for intensive surveillance to prevent possible cross-species transmission.

Interstitial macrophages are a focus of viral takeover and inflammation in COVID-19 initiation in human lung

Early stages of deadly respiratory diseases including COVID-19 are challenging to elucidate in humans. Here, we define cellular tropism and transcriptomic effects of SARS-CoV-2 virus by productively infecting healthy human lung tissue and using scRNA-seq to reconstruct the transcriptional program in "infection pseudotime" for individual lung cell types. SARS-CoV-2 predominantly infected activated interstitial macrophages (IMs), which can accumulate thousands of viral RNA molecules, taking over 60% of the cell transcriptome and forming dense viral RNA bodies while inducing host profibrotic (TGFB1, SPP1) and inflammatory (early interferon response, CCL2/7/8/13, CXCL10, and IL6/10) programs and destroying host cell architecture. Infected alveolar macrophages (AMs) showed none of these extreme responses. Spike-dependent viral entry into AMs used ACE2 and Sialoadhesin/CD169, whereas IM entry used DC-SIGN/CD209. These results identify activated IMs as a prominent site of viral takeover, the focus of inflammation and fibrosis, and suggest targeting CD209 to prevent early pathology in COVID-19 pneumonia. This approach can be generalized to any human lung infection and to evaluate therapeutics.

Susceptibility and transmissibility of SARS-CoV-2 variants in transgenic mice expressing the cat angiotensin-converting enzyme 2 (ACE-2) receptor

The emergence of SARS-CoV-2 in 2019 and its rapid spread throughout the world has caused the largest pandemic of our modern era. The zoonotic origin of this pathogen highlights the importance of the One Health concept and the need for a coordinated response to this kind of threats. Since its emergence, the virus has caused >7 million deaths worldwide. However, the animal source for human outbreaks remains unknown. The ability of the virus to jump between hosts is facilitated by the presence of the virus receptor, the highly conserved angiotensin-converting enzyme 2 (ACE2), found in various mammals. Positivity for SARS-CoV-2 has been reported in various species, including domestic animals and livestock, but their potential role in bridging viral transmission to humans is still unknown. Additionally, the virus has evolved over the pandemic, resulting in variants with different impacts on human health. Therefore, suitable animal models are crucial to evaluate the susceptibility of different mammalian species to this pathogen and the adaptability of different variants. In this work, we established a transgenic mouse model that expresses the feline ACE2 protein receptor (cACE2) under the human cytokeratin 18 (K18) gene promoter's control, enabling high expression in epithelial cells, which the virus targets. Using this model, we assessed the susceptibility, pathogenicity, and transmission of SARS-CoV-2 variants. Our results show that the sole expression of the cACE2 receptor in these mice makes them susceptible to SARS-CoV-2 variants from the initial pandemic wave but does not enhance susceptibility to omicron variants. Furthermore, we demonstrated efficient contact transmission of SARS-CoV-2 between transgenic mice that express either the feline or the human ACE2 receptor.

Generation of a humanized mAce2 and a conditional hACE2 mouse models permissive to SARS-COV-2 infection

The Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) remains a public health concern and a subject of active research effort. Development of pre-clinical animal models is critical to study viral-host interaction, tissue tropism, disease mechanisms, therapeutic approaches, and long-term sequelae of infection. Here, we report two mouse models for studying SARS-CoV-2: A knock-in mAce2F83Y,H353K mouse that expresses a mouse-human hybrid form of the angiotensin-converting enzyme 2 (ACE2) receptor under the endogenous mouse Ace2 promoter, and a Rosa26 conditional knock-in mouse carrying the human ACE2 allele (Rosa26hACE2). Although the mAce2F83Y,H353K mice were susceptible to intranasal inoculation with SARS-CoV-2, they did not show gross phenotypic abnormalities. Next, we generated a Rosa26hACE2;CMV-Cre mouse line that ubiquitously expresses the human ACE2 receptor. By day 3 post infection with SARS-CoV-2, Rosa26hACE2;CMV-Cre mice showed significant weight loss, a variable degree of alveolar wall thickening and reduced survival rates. Viral load measurements confirmed inoculation in lung and brain tissues of infected Rosa26hACE2;CMV-Cre mice. The phenotypic spectrum displayed by our different mouse models translates to the broad range of clinical symptoms seen in the human patients and can serve as a resource for the community to model and explore both treatment strategies and long-term consequences of SARS-CoV-2 infection.

SARS-CoV-2 aberrantly elevates mitochondrial bioenergetics to induce robust virus propagation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a 'highly transmissible respiratory pathogen, leading to severe multi-organ damage. However, knowledge regarding SARS-CoV-2-induced cellular alterations is limited. In this study, we report that SARS-CoV-2 aberrantly elevates mitochondrial bioenergetics and activates the EGFR-mediated cell survival signal cascade during the early stage of viral infection. SARS-CoV-2 causes an increase in mitochondrial transmembrane potential via the SARS-CoV-2 RNA-nucleocapsid cluster, thereby abnormally promoting mitochondrial elongation and the OXPHOS process, followed by enhancing ATP production. Furthermore, SARS-CoV-2 activates the EGFR signal cascade and subsequently induces mitochondrial EGFR trafficking, contributing to abnormal OXPHOS process and viral propagation. Approved EGFR inhibitors remarkably reduce SARS-CoV-2 propagation, among which vandetanib exhibits the highest antiviral efficacy. Treatment of SARS-CoV-2-infected cells with vandetanib decreases SARS-CoV-2-induced EGFR trafficking to the mitochondria and restores SARS-CoV-2-induced aberrant elevation in OXPHOS process and ATP generation, thereby resulting in the reduction of SARS-CoV-2 propagation. Furthermore, oral administration of vandetanib to SARS-CoV-2-infected hACE2 transgenic mice reduces SARS-CoV-2 propagation in lung tissue and mitigates SARS-CoV-2-induced lung inflammation. Vandetanib also exhibits potent antiviral activity against various SARS-CoV-2 variants of concern, including alpha, beta, delta and omicron, in in vitro cell culture experiments. Taken together, our findings provide novel insight into SARS-CoV-2-induced alterations in mitochondrial dynamics and EGFR trafficking during the early stage of viral infection and their roles in robust SARS-CoV-2 propagation, suggesting that EGFR is an attractive host target for combating COVID-19.

ISG15 blocks cardiac glycolysis and ensures sufficient mitochondrial energy production during Coxsackievirus B3 infection

AIMS

Virus infection triggers inflammation and, may impose nutrient shortage to the heart. Supported by type I interferon (IFN) signalling, cardiomyocytes counteract infection by various effector processes, with the IFN-stimulated gene of 15 kDa (ISG15) system being intensively regulated and protein modification with ISG15 protecting mice Coxsackievirus B3 (CVB3) infection. The underlying molecular aspects how the ISG15 system affects the functional properties of respective protein substrates in the heart are unknown.

METHODS AND RESULTS

Based on the protective properties due to protein ISGylation, we set out a study investigating CVB3-infected mice in depth and found cardiac atrophy with lower cardiac output in ISG15-/- mice. By mass spectrometry, we identified the protein targets of the ISG15 conjugation machinery in heart tissue and explored how ISGylation affects their function. The cardiac ISGylome showed a strong enrichment of ISGylation substrates within glycolytic metabolic processes. Two control enzymes of the glycolytic pathway, hexokinase 2 (HK2) and phosphofructokinase muscle form (PFK1), were identified as bona fide ISGylation targets during infection. In an integrative approach complemented with enzymatic functional testing and structural modelling, we demonstrate that protein ISGylation obstructs the activity of HK2 and PFK1. Seahorse-based investigation of glycolysis in cardiomyocytes revealed that, by conjugating proteins, the ISG15 system prevents the infection-/IFN-induced up-regulation of glycolysis. We complemented our analysis with proteomics-based advanced computational modelling of cardiac energy metabolism. Our calculations revealed an ISG15-dependent preservation of the metabolic capacity in cardiac tissue during CVB3 infection. Functional profiling of mitochondrial respiration in cardiomyocytes and mouse heart tissue by Seahorse technology showed an enhanced oxidative activity in cells with a competent ISG15 system.

CONCLUSION

Our study demonstrates that ISG15 controls critical nodes in cardiac metabolism. ISG15 reduces the glucose demand, supports higher ATP production capacity in the heart, despite nutrient shortage in infection, and counteracts cardiac atrophy and dysfunction.

SARS-CoV-2 induces blood-brain barrier and choroid plexus barrier impairments and vascular inflammation in mice

The coronavirus disease of 2019 (COVID-19) pandemic has led to more than 700 million confirmed cases and nearly 7 million deaths. Although severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus mainly infects the respiratory system, neurological complications are widely reported in both acute infection and long-COVID cases. Despite the success of vaccines and antiviral treatments, neuroinvasiveness of SARS-CoV-2 remains an important question, which is also centered on the mystery of whether the virus is capable of breaching the barriers into the central nervous system. By studying the K18-hACE2 infection model, we observed clear evidence of microvascular damage and breakdown of the blood-brain barrier (BBB). Mechanistically, SARS-CoV-2 infection caused pericyte damage, tight junction loss, endothelial activation and vascular inflammation, which together drive microvascular injury and BBB impairment. In addition, the blood-cerebrospinal fluid barrier at the choroid plexus was also impaired after infection. Therefore, cerebrovascular and choroid plexus dysfunctions are important aspects of COVID-19 and may contribute to neurological complications both acutely and in long COVID.

SARS-CoV-2 strains bearing Omicron BA.1 spike replicate in C57BL/6 mice

Introduction

SARS-CoV-2, the cause of the COVID pandemic, is an RNA virus with a high propensity to mutate. Successive virus variants, including variants of concern (VOC), have emerged with increased transmission or immune escape. The original pandemic virus and early variants replicated poorly, if at all, in mice at least partly due to a mismatch between the receptor binding domain on the viral spike protein and the murine angiotensin converting enzyme 2 (ACE2). Omicron VOC emerged in late 2021 harboring > 50 new mutations, 35 of them in the spike protein. This variant resulted in a very large wave of infections, even in the face of prior immunity, albeit being inherently less severe than earlier variants. Reflecting the lower severity reported in humans, Omicron displayed attenuated infection in hamsters and also in the K18-hACE2 mouse model. K18-hACE2 mice express both the human ACE2 as well as the endogenous mouse ACE2.

Methods

Here we infected hACE2 knock-in mice that express only human ACE2 and no murine ACE2, or C57BL/6 wildtype mice with SARS-CoV-2 D614G (first-wave isolate), Delta or Omicron BA.1 variants and assessed infectivity and downstream innate immune responses.

Results

While replication of SARS-CoV-2 Omicron was lower in the lungs of hACE2 knock-in mice compared with SARS-CoV-2 D614G and VOC Delta, it replicated more efficiently than the earlier variants in C57BL/6 wildtype mice. This opens the opportunity to test the effect of host genetics on SARS-CoV-2 infections in wildtype mice. As a proof of principle, we tested Omicron infection in mice lacking expression of the interferon-alpha receptor-1 (IFNAR1). In these mice we found that loss of type I IFN receptor signaling resulted in higher viral loads in the lungs were detected. Finally, using a chimeric virus of first wave SARS-CoV-2 harboring the Omicron spike protein, we show that Omicron spike increase infection of C57BL/6 wildtype mice, but non-spike genes of Omicron confer attenuation of viral replication.

Discussion

Since this chimeric virus efficiently infected C57BL/6 wildtype mice, and replicated in their lungs, our findings illustrate a pathway for genetic mapping of virushost interactions during SARS-CoV-2 infection.

SARS-CoV-2 infection activates inflammatory macrophages in vascular immune organoids

SARS-CoV-2 provokes devastating tissue damage by cytokine release syndrome and leads to multi-organ failure. Modeling the process of immune cell activation and subsequent tissue damage is a significant task. Organoids from human tissues advanced our understanding of SARS-CoV-2 infection mechanisms though, they are missing crucial components: immune cells and endothelial cells. This study aims to generate organoids with these components. We established vascular immune organoids from human pluripotent stem cells and examined the effect of SARS-CoV-2 infection. We demonstrated that infections activated inflammatory macrophages. Notably, the upregulation of interferon signaling supports macrophages' role in cytokine release syndrome. We propose vascular immune organoids are a useful platform to model and discover factors that ameliorate SARS-CoV-2-mediated cytokine release syndrome.

Lung repair and regeneration: Advanced models and insights into human disease

The respiratory system acts as both the primary site of gas exchange and an important sensor and barrier to the external environment. The increase in incidences of respiratory disease over the past decades has highlighted the importance of developing improved therapeutic approaches. This review will summarize recent research on the cellular complexity of the mammalian respiratory system with a focus on gas exchange and immunological defense functions of the lung. Different models of repair and regeneration will be discussed to help interpret human and animal data and spur the investigation of models and assays for future drug development.