A Good Helper for SARS-CoV-2 & COVID-19 Research: Selection and Application of Mouse Models

Animal models have assisted researchers’ understanding of COVID-19 pathogenesis and host immune response to SARS-CoV-2 infection, and are of great significance in helping the rapid development of disease preventatives, vaccines, and treatments.

The physiological characteristics and immune regulation of non-human primates are the most conserved with humans, and they are the animal models of choice for the study of SARS-CoV-2 infection. However, given the increasing demand for research and rising economic and time costs, gene-edited mice with targeted genetic modification and stable inheritance are becoming a highly used animal research model.

Angiotensin-converting enzyme-2 (ACE2) is the most important cell surface receptor for the SARS-CoV-2 virus to invade the human body, but due to differences between species, the receptor-binding domain (RBD) of the SARS-CoV-2 Spike (S) protein cannot bind to the ACE2 receptor of wild-type rodents under natural conditions, but by replacing mouse Ace2 with human ACE2 through gene editing technology, humanized ACE2 mice (hACE2) stably expressing human ACE2 receptors can be obtained. Related studies have proved that hACE2 mice are susceptible to SARS-CoV-2 infection and play a role in different research directions.

Recommended SARS-CoV-2 Mouse Models

Cyagen has generated strains of hACE2 mice across three genetic backgrounds (BALB/c, C57BL/6J, and C57BL/6N) using our proprietary TurboKnockout and optimized CRISPR-Pro technologies, and designed a variety of gene targeting designs to meet the animal model needs of customers in basic research and new drug development.

Current SARS-CoV-2/COVID-19 Animal Models for Research

Among these, the most popular animal models, hACE2-All CDS-B6J and K18-hACE2-2A-CreERT2 mouse strains, can be ordered immediately and can be shipped in as little as one week!

▶ hACE2-All CDS-B6J live mice

This mouse model uses the human ACE2 CDS to replace the mouse endogenous Ace2 sequence (retaining the mouse Ace2 signal peptide sequence) so that the expression of hACE2 is directed by the mouse endogenous Ace2 regulatory elements. The gene is located on the X chromosome, and homozygous females and hemizygous males are viable and fertile.

▶ K18-hACE2-2A-CreERT2 live mice

This mouse model expresses human ACE2 in epithelial cells, including initially infected airway epithelial cells, driven by the human keratin K18 promoter. The mouse model contains the CreERT2 element, which can be time-specifically regulated and expressed using Tamoxifen-inducible Cre mice.

K18-hACE2 mice can be infected with the SARS-CoV-2 virus, causing a severe disease characterized by weight loss, rapid breathing, hunched posture, and inactivity. These mice responded to virus challenge in a dose-dependent manner, allowing the study of severe acute respiratory disease in mice challenged with high viral titers as well as the long-term effects of mild infection at low doses.

Featured Application Cases

Cyagen’s hACE2 mouse model has helped researchers make breakthroughs in SARS-CoV-2-related studies, and its application directions include research on virus infection mechanisms, vaccine development and evaluation, preventive drug screening, postviral complications, antibody drug development and verification, and more.

▶ Research on the infection mechanisms of SARS-CoV-2

Current studies have proved that the Spike (S) protein of the SARS-CoV-2 virus is the binding site to the ACE2 receptor present in human cells , but the molecular and cellular mechanisms of the combination of the two remain unclear. The researchers used K18-hACE2-2A-CreERT2 mice driven by the epithelial cell-specific promoter K18 (product number: C001244) and finally revealed that the S2' fragment generated by spike hydrolysis during SARS-CoV-2 virus infection is one of the indispensable molecular events in the process of coronavirus infection, and the role of specific fragments in the recognition between viruses and receptors, membrane fusion and other processes.^[1]

▶ Evaluation of SARS-CoV-2 vaccine development

Vaccination is the preferred method to control and prevent the COVID-19 pandemic, and there remains an urgent need to develop a long-acting SARS-CoV-2 vaccine against infection. Researchers validated a newly developed vaccine using hACE2-All CDS-BALBC mice (product number: C001227) and demonstrated that a vaccine based on mSM virus-like particles and Al/CpG adjuvant is an effective and promising vaccine against COVID-19.^[2]

▶ Preventive drug screening of SARS-CoV-2

Studies have shown that reducing the level of ACE2 protein by half can significantly reduce the infection severity of SARS-CoV-2, suggesting that partially reducing the level of ACE2 protein may be one of the new strategies to prevent SARS-CoV-2 infection. The researchers used hACE2-All CDS-B6J mice (product number: C001191) for drug screening and found that the natural compound vitamin C (VitC) can reduce the level of ACE2 protein to prevent SARS-CoV-2 infection, and its mechanism of action was further studied.^[3]

▶ Research on SARS-CoV-2 postviral complications

SARS-CoV-2 mainly causes clinical symptoms such as lung inflammation and fever through respiratory tract infection but also has various complications such as anosmia, catatonic schizophrenia, digestive diseases, thrombocytopenia, and testicular damage. Learning about the pathogenesis of different complications is also very important for the treatment of the patient's disease. Using hACE2-All CDS-B6J mice (product number: C001191) as a validation model, the researchers determined the molecular mechanism of VEGF overproduction in the gut following SARS-CoV-2 S protein stimulation, proving that ERK/VEGF is a key axis of COVID-19 potential biomarkers and therapeutic targets for intestinal inflammation and disease progression.^[4]

▶ Antibody drug development and verification

The  SARS-CoV-2 virus has constantly mutated throughout the epidemic, and the emergence of multiple pathogenic or transmissible mutant strains such as Delta and Omicron has brought considerable challenges to the prevention and treatment of the disease. Given this, more effective prevention and treatment strategies are urgently needed, and broad-spectrum neutralizing antibodies are one of the strategies to deal with it. Researchers used hACE2-All CDS-B6J mice (product number: C001191) to evaluate the in vivo protective effect of the R1-32 antibody and confirmed that R1-32 has protective activity against SARS-CoV-2 infection.^[5]

References:

[1] Yu, Shi., Yu, Shi., Zheng, Xu., Zheng, Xu., and Zhou, Bingjie.. "SARS-CoV-2 spike engagement of ACE2 primes S2' site cleavage and fusion initiation." Proceedings of the National Academy of Sciences of the United States of America 119.1(2022).

[2] Chen, Jing., Chen, Jing., Xu, Wang., Li, Letian., and Yi, Lichao.. "Immunogenicity and protective potential of chimeric virus-like particles containing SARS-CoV-2 spike and H5N1 matrix 1 proteins." Frontiers in cellular and infection microbiology.

[3] Yibo Zuo, Zhijin Zheng, Yingkang Huang, Jiuyi He, Lichao Zang, and Tengfei Ren.. "Vitamin C is an efficient natural product for prevention of SARS-CoV-2 infection by targeting ACE2 in both cell and in vivo mouse models." bioRxiv.

[4] Zeng, Fa-Min., Zeng, Fa-Min., Li, Ying-Wen., Deng, Zhao-Hua., and He, Jian-Zhong.. "SARS-CoV-2 spike spurs intestinal inflammation via VEGF production in enterocytes." EMBO molecular medicine 14.5(2022):e14844.

[5] Ping He, Banghui Liu, Xijie Gao, Qihong Yan,Rongjuan Pei, Sun Jing, and Chen Qiuluan.. "SARS-CoV-2 Delta and Omicron variants evade population antibody response by mutations in a single spike epitope." Nature Microbiology.