Background: The novel coronavirus SARS-CoV-2, responsible for the COVID-19 outbreak, has become a pandemic, threatening millions of lives worldwide. Despite the plethora of studies that have advanced our understanding of the SARS-CoV-2 infection many mechanisms remain to be better understood in order to control the virus's spread and treat COVID-19 clinical cases. Peptidyl-arginine deiminases (PADs) are a family of cellular enzymes which dysregulation leads to an aberrant citrullination (a post translational modification) which is a biomarker of several inflammatory conditions. Based on some similarities between the clinical outcome observed in autoinflammatory disease and COVID-19, including lung involvement and abnormal cytokine release, this study aimed to evaluate the antiviral activity of PAD inhibitors in vitro and in vivo, as well as their ability to mitigate pro-inflammatory reactions.
Methods: Using different SARS-CoV-2 strains, we tested the antiviral and anti-inflammatory activity of PAD inhibitors in human cell lines and in K18-hACE2 transgenic mice. We used qPCR to quantify viral genomes, Western blot analysis to evaluate the expression of viral proteins, plaque assay to evaluate the production of new virions, and ELISA to evaluate cytokines production. Furthermore, we assessed PAD4 expression and the pattern of protein citrullination upon infection.
Results: SARS-CoV-2 infections were significantly associated with PAD-mediated citrullination in vitro and with a specific increase in PAD4 expression. Moreover, the pharmacological inhibition of the PAD4 enzyme led to a significant reduction of viral replication and pro-inflammatory mediators.
Conclusions: Our results suggested that SARS-CoV-2 induces an increase in citrullination and that this increase plays a key role in COVID-19 pathology. All in all, the ability to modulate both of these features would make PAD-inhibitors promising candidates for the control of the COVID-19 disease.