Molecular mechanisms of sex difference in COVID-19 enabling novel therapeutics

ABSTRACT The central focus of this Administrative Supplement application to is to identify detailed molecular mechanisms of estrogen-dependent sex difference in COVID-19 to enable development of novel therapeutics that are in urgent need to control the pandemic. The outbreak of coronavirus disease 2019 (COVID-19) has become a worldwide pandemic that has remained uncontained. We have previously published a classical article to recognize sex difference of COVID-19 for the first time, documenting that males are more susceptible to COVID-19 than females, and more often to develop more severe disease with higher mortality (Cai H, Lancet Respiratory Medicine, April 2020, Citation: 549 by 01/22/22). This important observation has been further confirmed by additional literatures. The gender difference observed in COVID-19 patients is potentially linked to higher prevalence of cigarette smoking in men that was shown to be associated with higher viral receptor ACE2 levels. However, we found that protein levels of ACE2 and TMPRSS2 were not changed in endothelial cells exposed to cigarette smoking extract (CSE). The otherwise observed worse outcomes in COVID-19 patients who are smokers, is likely linked to baseline respiratory diseases associated with chronic smoking. Instead, we hypothesize that estrogen mediated protection might however underlie less severe disease in females, and that short term estrogen administration might be used as a robust therapeutic option for the treatment of COVID-19, especially in men and postmenopausal women. This is supported by strong preliminary data and our latest publication indicating that SARS-CoV-2 spike protein (S protein) and interleukin-6 (IL-6) stimulated endothelial cell NADPH oxidase isoform 2 (NOX2) activation and oxidative stress, as well as upregulation of viral receptor ACE2 and inflammatory protein MCP-1, were all substantially attenuated by estrogen treatment (Redox Biology, Aug 2021). The upregulation in NOX2 and MCP-1 by S protein is mediated by activation of ACE2 since blockage of ACE2 with neutralizing antibody was able to abrogate the responses. These data indicate that oxidative stress and endothelial dysfunction triggered by initial viral infection (S protein), and by cytokine storm (IL-6) at later stage, which represent major pathological features of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS)/multi-organ failure, can all be remarkably alleviated by estrogen to effectively reduce disease severity and mortality. The current project aims to address two specific aims: 1) To examine whether estrogen treatment alleviates SARS-CoV-2 S protein induced ALI/ARDS and multi-organ injuries in vivo via abrogation of p22phox and p47phox- dependent activation of NOX2 and activation of netrin-1 signaling. 2) To identify and validate novel genes and gene pathways/networks regulated by S protein and estrogen with a special focus on netrin-1 signaling, enabling discoveries of novel therapeutic targets. Overall, accomplishments of both of highly mechanistic and well-integrated aims will no doubt reveal novel sex difference related molecular mechanisms of COVID-19, targeting of which would facilitate development of innovative therapies urgently in need to control the devastating pandemic.