Cytokines and Lipid Mediators of Inflammation in Lungs of SARS-CoV-2 Infected Mice

Abstract

Coronavirus disease 19 (COVID-19) is the clinical manifestation of severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) infection. A hallmark of COVID-19 is a lung inflammation characterized by an abundant leukocyte infiltrate, elevated levels of cytokines/chemokines, lipid mediators of inflammation (LMI) and microthrombotic events. Animal models are useful for understanding the pathophysiological events leading to COVID-19. One such animal model is the K18-ACE2 transgenic mice. Despite their importance in inflammation, the study of LMI in lung of SARS-CoV-2 infected K18-ACE2 mice has yet to be studied to our knowledge. Using tandem mass spectrometry, the lung lipidome at different time points of infection was analyzed. Significantly increased LMI included N-oleoyl-serine, N-linoleoyl-glycine, N-oleoyl-alanine, 1/2-linoleoyl-glycerol, 1/2-docosahexaenoyl-glycerol and 12-hydroxy-eicosapenatenoic acid. The levels of prostaglandin (PG) E1, PGF2α, stearoyl-ethanolamide and linoleoyl-ethanolamide were found to be significantly reduced relative to mock-infected mice. Other LMI were present at similar levels (or undetected) in both uninfected and infected mouse lungs. In parallel to LMI measures, transcriptomic and cytokine/chemokine profiling were performed. Viral replication was robust with maximal lung viral loads detected on days 2-3 post-infection. Lung histology revealed leukocyte infiltration starting on day 3 post-infection, which correlated with the presence of high concentrations of several chemokines/cytokines. At early times post-infection, the plasma of infected mice contained highly elevated concentration of D-dimers suggestive of blood clot formation/dissolution. In support, the presence of blood clots in the lung vasculature was observed during infection. RNA-Seq analysis of lung tissues indicate that SARS-CoV-2 infection results in the progressive modulation of several hundred genes, including several inflammatory mediators and genes related to the interferons. Analysis of the lung lipidome indicated modest, yet significant modulation of a minority of lipids. In summary, our study suggests that SARS-CoV-2 infection in humans and mice share common features, such as elevated levels of chemokines in lungs, leukocyte infiltration and increased levels of circulating D-dimers. However, the K18-ACE2 mouse model highlight major differences in terms of LMI being produced in response to SARS-CoV-2 infection. The potential reasons and impact of these differences on the pathology and therapeutic strategies to be employed to treat severe COVID-19 are discussed.

Early alveolar epithelial cell necrosis is a potential driver of COVID-19-induced acute respiratory distress syndrome

“…Although the pathogenicity of SARS-CoV-2 is complex, stimulation of pathogen-associated pattern recognition receptors including toll-like receptors 26,27 and retinoic acid-inducible gene-I receptors 28 by viral components is the principal driver of lung inflammation, and subsequent alveolar tissue damage. In the present study, the bioinformatic analysis of lung tissue transcriptomes demonstrated that the COVID-19 mimicking animal model with SARS-CoV-2 spike protein and poly (I:C) recapitulated key biological responses in inflammatory and cell death pathways induced by SARS-CoV-2 [32][33][34][35][36][37] . Moreover, alveolar cell death patterns in our COVID-19 animal model were similar to those 16 observed in human COVID-19 29,30 .…”

“…4A). We found 6 publicly available lung tissue RNA-seq datasets of mice infected with SARS-CoV-2 from the NCBI Gene Expression Omnibus database (Table S3) [32][33][34][35][36][37] and performed comparative analysis for all the datasets including the data obtained from this study. Comparison of differentially expressed genes (DEGs) showed only small overlaps, even when comparisons were performed among the infection models (Table S4).…”

SARS-CoV-2 type I Interferon modulation by nonstructural proteins 1 and 2

“…Three days postinfection, cytokine load and antiviral related genes were measured in mouse lungs. No change in body weight or temperature was observed at this time (30). As shown in Fig.…”

SARS-CoV-2 Nsp2 Contributes to Inflammation by Activating NF-κB

“…Three days post-infection, the mice were euthanized and their lungs used for further analyses. No change in body weight or temperature was observed during this time [ 36 ]. As shown in Figure 1 A,B, all the infected mice had significant pulmonary infectious viral loads and expressed abundant SARS-CoV-2 E gene copy numbers.…”