Angiotensin-converting enzyme 2 (ACE2) is a member of the angiotensin-converting enzyme (ACE) family of dipeptidyl carboxypeptidases. ACE2 is expressed in a variety of human tissues and has a high affinity for angiotensin I (Ang I) and angiotensin II (Ang II) receptors. ACE2 catalyzes the cleavage of Ang I to angiotensin 1-9 (Ang 1-9) and Ang II to angiotensin 1-7 (Ang 1-7), which have vasodilatory and hypotensive effects ^[1]. ACE2 plays a role in regulating blood pressure, fluid balance, inflammation, cell proliferation, hypertrophy, and fibrosis, as well as in the regulation of cardiovascular and renal function and fertility ^[2]. ACE2 is also the common functional receptor for the spike protein of human coronaviruses HCoV-NL63, SARS-CoV, and SARS-CoV-2 ^[3]. However, due to species differences, the SARS-CoV-2 virus cannot bind to the ACE2 receptor of wild-type rodents ^[4-5]. Replacement of mouse Ace2 with human ACE2 by gene editing techniques resulted in humanized ACE2 mice (hACE2) that stably express human ACE2 receptors for COVID-19 studies. In this strain, the mouse endogenous Ace2 gene sequence was replaced with the coding sequence (CDS) of the human ACE2 gene, while retaining the sequence encoding the mouse ACE2 protein signal peptide. This resulted in the expression of the hACE2 protein under the control of the endogenous mouse Ace2 regulatory elements. In addition, an enhanced green fluorescent protein (EGFP) expression cassette was inserted into the model to allow tracking of hACE2 expression. The integration site of the hACE2 is located on the mouse chromosome X. Homozygous female and hemizygous male hACE2-EGFP mice are viable and fertile.

Angiotensin-converting enzyme 2 (ACE2) is a member of the angiotensin-converting enzyme (ACE) family of dipeptidyl carboxypeptidases. ACE2 is expressed in a variety of human tissues and has a high affinity for angiotensin I (Ang I) and angiotensin II (Ang II) receptors. ACE2 catalyzes the cleavage of Ang I to angiotensin 1-9 (Ang 1-9) and Ang II to angiotensin 1-7 (Ang 1-7), which have vasodilatory and hypotensive effects ^[1]. ACE2 plays a role in regulating blood pressure, fluid balance, inflammation, cell proliferation, hypertrophy, and fibrosis, as well as in the regulation of cardiovascular and renal function and fertility ^[2]. ACE2 is also the common functional receptor for the spike protein of human coronaviruses HCoV-NL63, SARS-CoV, and SARS-CoV-2 ^[3]. However, due to species differences, the SARS-CoV-2 virus cannot bind to the ACE2 receptor of wild-type rodents ^[4-5]. Replacement of mouse Ace2 with human ACE2 by gene editing techniques resulted in humanized ACE2 mice (hACE2) that stably express human ACE2 receptors for COVID-19 studies. This strain is a human ACE2 (hACE2) conditional overexpression model generated by integrating the hACE2 gene expression element into the mouse ROSA26 safe harbor site. Under normal conditions, the expression of hACE2 is blocked by the upstream loxP-Stop-loxP expression stop cassette. Upon mating with Cre mice, the Cre recombinase mediates the deletion of the sequence between the loxP sites, including the stop cassette, thereby enabling the expression of hACE2. When bred with tissue-specific Cre mice, overexpression of the hACE2 gene and protein can be achieved in specific tissues of the offspring mice. Homozygous ROSA26-LSL-hACE2 mice are viable and fertile.

Angiotensin-converting enzyme 2 (ACE2) is a member of the angiotensin-converting enzyme (ACE) family of dipeptidyl carboxypeptidases. ACE2 is expressed in a variety of human tissues and has a high affinity for angiotensin I (Ang I) and angiotensin II (Ang II) receptors. ACE2 catalyzes the cleavage of Ang I to angiotensin 1-9 (Ang 1-9) and Ang II to angiotensin 1-7 (Ang 1-7), which have vasodilatory and hypotensive effects ^[1]. ACE2 plays a role in regulating blood pressure, fluid balance, inflammation, cell proliferation, hypertrophy, and fibrosis, as well as in the regulation of cardiovascular and renal function and fertility ^[2]. ACE2 is also the common functional receptor for the spike protein of human coronaviruses HCoV-NL63, SARS-CoV, and SARS-CoV-2 ^[3]. However, due to species differences, the SARS-CoV-2 virus cannot bind to the ACE2 receptor of wild-type rodents ^[4-5]. Replacement of mouse Ace2 with human ACE2 by gene editing techniques resulted in humanized ACE2 mice (hACE2) that stably express human ACE2 receptors for COVID-19 studies. This strain contains a loxP-hACE2 CDS-loxP gene expression cassette inserted at the endogenous mouse Ace2 gene locus, which enables the regulation of human ACE2 gene (hACE2) expression by the mouse endogenous Ace2 regulatory element. When bred with relevant tissue-specific Cre mouse mating, knockout of the hACE2 gene can be achieved in specific tissues of the offspring mice. Homozygous LoxP-hACE2-CDS^tm mice are viable and fertile.

Angiotensin-converting enzyme 2 (ACE2) is the predominant cell surface receptor for SARS-CoV-2 virus infection in humans, but due to interspecies differences, the SARS-CoV-2 virus is unable to bind to ACE2 receptors in most wild-type rodents, including mice. Replacement of mouse Ace2 with human ACE2 by gene editing techniques resulted in humanized ACE2 mice (hACE2) that stably express human ACE2 receptors for COVID-19 studies. This strain is a mouse Ace2 gene humanization model that uses gene editing technology to replace the endogenous mouse Ace2 gene sequence with human ACE2 CDS, preserving the mouse signal peptide sequence and achieving hACE2 expression directed by the endogenous mouse Ace2 regulatory element. This gene is located on the mouse chromosome X, and homozygous females and heterozygous males are viable and fertile.

Angiotensin-converting enzyme 2 (ACE2) is the predominant cell surface receptor for SARS-CoV-2 virus infection in humans, but due to interspecies differences, the SARS-CoV-2 virus is unable to bind to ACE2 receptors in most wild-type rodents, including mice. Replacement of mouse Ace2 with human ACE2 by gene editing techniques resulted in humanized ACE2 mice (hACE2) that stably express human ACE2 receptors for COVID-19 studies. This strain is a mouse Ace2 gene humanization model that uses gene editing technology to replace the endogenous mouse Ace2 gene sequence with human ACE2 CDS, preserving the mouse signal peptide sequence and achieving hACE2 expression directed by the endogenous mouse Ace2 regulatory element. This gene is located on the mouse chromosome X. Homozygous females and heterozygous males are viable and fertile.

Angiotensin-converting enzyme 2 (ACE2) is the predominant cell surface receptor for SARS-CoV-2 virus infection in humans, but due to species differences, the SARS-CoV-2 virus is unable to bind to the ACE2 receptor in most wild-type rodents. By inserting the "K18 promoter-human ACE2 CDS-P2A-CreERT2-rBGpA" sequence into the safety harbor of the mouse genome through gene editing technology, humanized ACE2 mice (K18-hACE2) that stably express the human ACE2 receptor can be obtained. This mouse model expresses human ACE2 protein in epithelial cells under the regulation of the human keratin K18 promoter, including the most initially infected airway epithelial cells. This model also carries the CreERT2 element, which can be induced by tamoxifen to express the Cre recombinase, so this strain can be used either alone for COVID-19 and related studies or in combination with flox mice for studying the role of specific host genes in response to SARS-CoV-2 virus infection. K18-hACE2 mice can be infected with the SARS-CoV-2 virus, resulting in severe disease characterized by weight loss, rapid respiration, hunched posture, and immobility. This strain responds to viral attack in a dose-dependent manner, thus allowing the study of severe acute respiratory disease in mice heavily infected by high doses of the virus, as well as the long-term effects of low doses of mild infection. The model should be handled in strict accordance with the guidelines for the prevention of SARS-CoV-2 virus infection in humans as specified by CDC, ABSA, and WHO, and appropriate personal protective equipment (PPE) and handling methods should always be used when using these mice for research.