Impact of Age and Sex on neuroinflammation due to SARS-CoV2 infection in a murine model.
Objectives: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) causes the worldwide COVID-19 pandemic. While SARS-CoV-2 can infect people of all ages and both sexes, senior populations are at greatest risk of severe disease and worse outcomes, and sexual dimorphism has been reported in COVID-19. COVID-19 causes damage to multiple organ systems, including the brain. Neurological symptoms are widely observed in patients with Covid-19, with many survivors suffering from persistent neurological impairment, potentially accelerating Alzheimer's disease (AD). This study aims to investigate the mechanisms underlying the impact of age, and sex on neuroinflammation due to SARS-CoV-2 infection using mouse models. Methods: Wild-type C57BL/6 mice were subjected to intranasal inoculation of SARS-CoV-2 lineage B.1.351, followed by daily body weight monitoring. At 7 dpi, viral burden and inflammatory cytokine/chemokine responses in the lung and brain were determined by quantitative RT-PCR, followed by immunohistochemical and transcriptomic analyses. Results: Older age, male sex, showed increased lung viral loads and severity of SARS-CoV-2 infection in mice. No viral RNA was detected in the brains of infected mice; however, IL-6 and CCL2 mRNA increased significantly, particularly in brains of old and APOE4 mice. Unbiased brain RNA-seq/transcriptomic analysis showed that SARS-CoV-2 infection caused significant changes in gene expression profiles, and pathway analysis identified innate immunity and defense response to virus and other organisms as the major molecular networks affected in the brain by SARS-CoV-2 infection. Conclusions: Our findings demonstrate that age, and sex, modify the progression and outcome of SARS-CoV-2 infection. SARS-CoV-2 infection triggers neuroinflammatory responses despite the lack of detectable virus in the brain. Changes in molecular networks of innate immunity and defense response to microorganisms underlie the impact of SARS-CoV-2 infection in the brain. These findings in mice mimic epidemiological and clinical observations in humans with Covid-19. Overall design: We performed bulk mRNA-seq to examine the transcriptomic changes associated with SARS-CoV-2 infection in wild-type mice. RNA-Seq data was collected from 12 mice (6 males & 6 female)  at 10 months of age at 7 days post-infection. Sequencing was performed using Illumina NovaSeq 6000 platform, generating 20 million reads per sample on a 150-bp paired-end run.