Enhancing Human ACE2 Expression in Mouse Models for Improved COVID-19 Research

Several humanized ACE2 (hACE2) mouse models have been developed for COVID-19 studies. Insertion of hACE2 at mouse Ace2 locus enables the utilization of endogenous promoter to drive its expression, better reflecting ACE2 abundance in various cell types and tissues. However, the relatively low expression of hACE2 in these mice may limit their fidelity in mimicking COVID-19 manifestations in humans and hinder their application in viral studies. In this study, we generated four hACE2 mouse models using different strategies for hACE2 expression. We found that the position of the β-globin intron within hACE2 cassette could have contrasting effects on hACE2 expression, with its placement downstream of hACE2 significantly increasing its transcription. Western blot analysis demonstrated that optimizing hACE2 codon usage further enhanced translation efficiency from all tested tissue. Consistent with elevated hACE2 expression, opt-hACE2 mice displayed more active immune response and severe COVID-19 phenotypes following SARS-CoV-2 challenging compared to other hACE2 mouse models. Thus, our study has elucidated the dual role of β-globin element in transgene expression, and highlighted that mice with optimized hACE2 codon preference could serve as a better model for SARS-CoV-2 studies.