A Novel Humanized ACE2 Mouse Model For Evaluating COVID-19 Infection In Cardiovascular Disease

The COVID-19 pandemic has resulted in over 6.7 million deaths worldwide. Patients with cardiovascular disease are at increased risk for severe illness and mortality with COVID-19. Increased systemic inflammation driven by macrophages, a key cellular source of inflammatory cytokine IL-1β, may play a role in the mechanism of SARS-CoV-2 pathogenesis. We seek to understand the mechanisms whereby inflammation associated with vascular disease may drive severity of COVID-19. Under culture conditions that mimic atherosclerotic plaque cholesterol exposure, we found that macrophage IL-1β signaling may promote expression of ACE2, the established receptor for SARS-CoV-2, through NF-κB-mediated transcription. We generated a novel, “humanized” ACE2 mouse strain ( hACE2 ) by using CRISPR-Cas9 technology to insert the human ACE2 cDNA sequence into the native mouse ACE2 locus under regulation of the native promoter. Using lung tissue, presence of hACE2 mRNA was verified by RT-qPCR and protein expression was verified by immunofluorescence staining. Overall, SARS-CoV-2 intranasal inoculation of hACE2 mice revealed milder infection when compared to the K18 promoter driven hACE2 ( K18-hACE2 ) overexpression strain, which exhibits severe infection with high morality. hACE2 mice had 100% survival after infection with stable body weight despite detectable viral burden in the lung fields. Histological analysis of the lungs revealed inflammatory infiltrate and pulmonary consolidation with alveolar hemorrhage that were comparable to the K18-hACE2 mice, and immunohistochemistry confirmed detection of viral nucleocapsid in the lung consolidations. Infected hACE2 mice also demonstrated a unique plasma cytokine signature relative to K18-hACE2 mice, including elevated levels of IL-1β, IL-1α, and VEGF-A, but decreased IL-6 and TNF-α. In summary, we have established a novel model of COVID-19 that survives infection and may facilitate comparative studies involving experimental vascular disease. The ability to model COVID-19 in the context of experimental atherosclerosis may help to define new mechanisms driving severity of SARS-CoV-2 infection.