Enhancing human ACE2 expression in mouse models to improve COVID-19 research.

Mice are one of the most common biological models for laboratory use. However, wild-type mice are not susceptible to COVID-19 infection due to the low affinity of mouse ACE2, the entry protein for SARS-CoV-2. Although mice with human ACE2 (hACE2) driven by Ace2 promoter reflect its tissue specificity, these animals exhibit low ACE2 expression, potentially limiting their fidelity in mimicking COVID-19 manifestations and their utility in viral studies. Here, we created and compared hACE2 mouse models generated with different strategies. Our findings show that distinct β-globin insertion within hACE2 cassette significantly influences its expression, with downstream placement enhancing transcription. Moreover, optimizing hACE2 codons (opt-hACE2) improves translation efficiency in multiple tissues. Notably, opt-hACE2 mice displayed more active immune responses and severe COVID-19 phenotypes following SARS-CoV-2 challenge compared to other models. Our study demonstrates the dual regulatory role of β-globin element in transgene transcription and suggests that opt-hACE2 mice might serve as valuable tools for SARS-CoV-2 research.