Effects of cigarette smoking on SARS-CoV-2 receptor ACE2 expression in the respiratory epithelium

Due to the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic, the world is currently facing high morbidity and mortality rates as well as severe disruption to normal societal and social structures. SARS-CoV-2 uses the ACE2 receptor for cellular entry. In a recent publication of The Journal of Pathology, Liu and coworkers highlight the effects of cigarette smoking on ACE2 expression in the respiratory epithelium. The authors studied the effects of acute cigarette smoke exposure in a murine model and confirmed their findings in human lung tissues and gene expression datasets. Their findings demonstrate that cigarette smoking increases ACE2 expression specifically at the apical surface of the airway epithelium. Smoking cessation resulted in lower ACE2 expression, with implications for attenuating the risk of transmission of the virus. The role of ACE2 expression in the development of COVID-19 symptoms is still under investigation, with conflicting results from experimental models on the role of ACE2 expression in SARS-CoV-2-induced lung injury. In this commentary, we highlight the implications and limitations of the study of Liu et al as well as future therapeutic strategies directed towards ACE2. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.