Project description:The on-going COVID-19 pandemic has given rise to SARS-CoV-2 clades and variants with differing levels of symptoms and severity. To this end, we aim to systematically elucidate the changes in the pathogenesis as SARS-CoV-2 evolved from ancestral to the recent Omicron VOC, on their mechanisms (e.g. cytokine storm) resulting in tissue damage, using the established K18-hACE2 murine model. We reported that among the SARS-CoV-2 viruses tested, infection profiles were initially similar between viruses from early clades but started to differ greatly starting from VOC Delta, where the trend continues in Omicron. VOCs Delta and Omicron both accumulated a significant number of mutations, and when compared to VOCs Alpha, Beta, and earlier predecessors, showed reduced neurotropism and less apparent gene expression in cytokine storm associated pathways. They were shown to leverage on other pathways to cause tissue damage (or lack of in the case of Omicron). Our study highlighted the importance of elucidating the response profiles of individual SARS-CoV-2 iterations, as their propensity of severe infection via pathways like cytokine storm changes as more variant evolves. This will then affect the overall threat assessment of each variant as well as the use of immunomodulatory treatments as management of severe infections of each variant.
Project description:Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiological agent of COVID-19, causes life-threatening disease. This novel coronavirus enters host cells via the respiratory tract, promoting the formation of severe pulmonary lesions and systemic disease. Few animal models can simulate the clinical signs and pathology of COVID-19 patients. Diverse preclinical studies using K18-hACE2 mice and Syrian golden hamsters, which are highly permissive to SARS-CoV-2 in the respiratory tract, are emerging; however, the systemic pathogenesis and cellular tropism of these models remain obscure. We intranasally infected K18-hACE2 mice and Syrian golden hamsters with SARS-CoV-2, and compared the clinical features, pathogenesis, cellular tropism and infiltrated immune-cell subsets. In K18-hACE2 mice, SARS-CoV-2 persistently replicated in alveolar cells and caused pulmonary and extrapulmonary disease, resulting in fatal outcomes. Conversely, in Syrian golden hamsters, transient SARS-CoV-2 infection in bronchial cells caused reversible pulmonary disease, without mortality. Our findings provide comprehensive insights into the pathogenic spectrum of COVID-19 using preclinical models.
Project description:To explore the effects of SARS-CoV-2 proteins on expression of host genes in lung of infected mice, 4 groups of K18-hACE2 mice (4 mice per group) were mock-infected or infected cells with SARS-CoV-2 WT or its NPS1, or NSP15 mutants respectively.The mice were euthanized at 4 days post-infection to collect the lungs to isolate RNA for RNA sequencing.
Project description:The emerging SARS-CoV-2 variants of concern (VOCs) may display enhanced transmissibility, more severity and/or immune evasion; however, the pathogenesis of these new VOCs in experimental SARS-CoV-2 models or the potential infection of other animal species is not completely understood. Here we infected K18-hACE2 transgenic mice with B.1, B.1.351/Beta, B.1.617.2/Delta and BA.1.1/Omicron isolates and demonstrated heterogeneous infectivity and pathogenesis. B.1.351/Beta variant was the most pathogenic, while BA.1.1/Omicron led to lower viral RNA in the absence of major visible clinical signs. In parallel, we infected wildtype (WT) mice and confirmed that, contrary to B.1 and B.1.617.2/Delta, B.1.351/Beta and BA.1.1/Omicron can infect them. Infection in WT mice coursed without major clinical signs and viral RNA was transient and undetectable in the lungs by day 7 post-infection. In silico modeling supported these findings by predicting B.1.351/Beta receptor binding domain (RBD) mutations result in an increased affinity for both human and murine ACE2 receptors, while BA.1/Omicron RBD mutations only show increased affinity for murine ACE2.
Project description:Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) not only affects the respiratory tract but also causes neurological symptoms such as loss of smell and taste, headache, fatigue or severe cerebrovascular complications. Using transgenic mice expressing human angiotensin-converting enzyme 2 (hACE2), we investigated the spatiotemporal distribution and pathomorphological features in the CNS following intranasal infection with SARS-CoV-2 variants, as well as after prior influenza A virus infection. Apart from Omicron, we found all variants to frequently spread to and within the CNS. Infection was restricted to neurons and appeared to spread from the olfactory bulb mainly in basally oriented regions in the brain and into the spinal cord, independent of ACE2 expression and without evidence of neuronal cell death, axonal damage or demyelination. However, microglial activation, microgliosis and a mild macrophage and T cell dominated inflammatory response was consistently observed, accompanied by apoptotic death of endothelial, microglial and immune cells, without their apparent infection. Microgliosis and immune cell apoptosis indicate a potential role of microglia for pathogenesis and viral effect in COVID-19 and the possible impairment of neurological functions, especially in long COVID. These data may also be informative for the selection of therapeutic candidates and broadly support the investigation of agents with adequate penetration into relevant regions of the CNS.
Project description: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.
Project description:Longevity of the immune response following viral exposure is an essential aspect of SARS-CoV-2 infection. Mild SARS-CoV-2 infection of K18-hACE2 mice was implemented for evaluating the mounting and longevity of a specific memory immune response. We show that the infection of K18-hACE2 mice induced robust humoral and cellular immunity (systemic and local), which persisted for at least six months. Virus-specific T cells and neutralizing antibody titers decreased over time, yet their levels were sufficient to provide sterile immunity against lethal rechallenge six months post-primary infection. The study substantiates the role of naturally induced immunity against SARS-CoV-2 infection for preventing recurring morbidity.
Project description: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.
Project description:Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection can cause neurological disease in humans, but little is known about the pathogenesis of SARS-CoV-2 infection in the central nervous system (CNS). Herein, using K18-hACE2 mice, we demonstrate that SARS-CoV-2 neuroinvasion and encephalitis is associated with mortality in these mice. Intranasal infection of K18-hACE2 mice with 105 plaque-forming units of SARS-CoV-2 resulted in 100% mortality by day 6 after infection. The highest virus titers in the lungs were observed on day 3 and declined on days 5 and 6 after infection. By contrast, very high levels of infectious virus were uniformly detected in the brains of all the animals on days 5 and 6. Onset of severe disease in infected mice correlated with peak viral levels in the brain. SARS-CoV-2-infected mice exhibited encephalitis hallmarks characterized by production of cytokines and chemokines, leukocyte infiltration, hemorrhage and neuronal cell death. SARS-CoV-2 was also found to productively infect cells within the nasal turbinate, eye and olfactory bulb, suggesting SARS-CoV-2 entry into the brain by this route after intranasal infection. Our data indicate that direct infection of CNS cells together with the induced inflammatory response in the brain resulted in the severe disease observed in SARS-CoV-2-infected K18-hACE2 mice.