ACE2 expression refers to the level at which the angiotensin-converting enzyme 2 (ACE2) protein is produced in a particular tissue or cell type. ACE2 is a key enzyme involved in regulating blood pressure and is also the receptor that the SARS-CoV-2 virus uses to enter host cells during infection. Research on ACE2 expression is important for understanding the pathophysiology of diseases such as hypertension, cardiovascular disease, and COVID-19, and for developing potential therapeutic strategies targeting ACE2. Studies on ACE2 expression often involve analyzing gene expression levels, protein levels, and localization in different tissues and cell types.