Putative Roles for Peptidylarginine Deiminases in COVID-19

Abstract

<jats:p>Peptidylarginine deiminases (PADs) are a family of calcium-regulated enzymes that are phylogenetically conserved and cause post-translational deimination/citrullination, contributing to protein moonlighting in health and disease. PADs are implicated in a range of inflammatory and autoimmune conditions, in the regulation of extracellular vesicle (EV) release, and their roles in infection and immunomodulation are known to some extent, including in viral infections. In the current study we describe putative roles for PADs in COVID-19, based on in silico analysis of BioProject transcriptome data (PRJNA615032 BioProject), including lung biopsies from healthy volunteers and SARS-CoV-2-infected patients, as well as SARS-CoV-2-infected, and mock human bronchial epithelial NHBE and adenocarcinoma alveolar basal epithelial A549 cell lines. In addition, BioProject Data PRJNA631753, analysing patients tissue biopsy data (n = 5), was utilised. We report a high individual variation observed for all PADI isozymes in the patients’ tissue biopsies, including lung, in response to SARS-CoV-2 infection, while PADI2 and PADI4 mRNA showed most variability in lung tissue specifically. The other tissues assessed were heart, kidney, marrow, bowel, jejunum, skin and fat, which all varied with respect to mRNA levels for the different PADI isozymes. In vitro lung epithelial and adenocarcinoma alveolar cell models revealed that PADI1, PADI2 and PADI4 mRNA levels were elevated, but PADI3 and PADI6 mRNA levels were reduced in SARS-CoV-2-infected NHBE cells. In A549 cells, PADI2 mRNA was elevated, PADI3 and PADI6 mRNA was downregulated, and no effect was observed on the PADI4 or PADI6 mRNA levels in infected cells, compared with control mock cells. Our findings indicate a link between PADI expression changes, including modulation of PADI2 and PADI4, particularly in lung tissue, in response to SARS-CoV-2 infection. PADI isozyme 1–6 expression in other organ biopsies also reveals putative links to COVID-19 symptoms, including vascular, cardiac and cutaneous responses, kidney injury and stroke. KEGG and GO pathway analysis furthermore identified links between PADs and inflammatory pathways, in particular between PAD4 and viral infections, as well as identifying links for PADs with a range of comorbidities. The analysis presented here highlights roles for PADs in-host responses to SARS-CoV-2, and their potential as therapeutic targets in COVID-19.</jats:p>

COVID-19 as a mediator of interferon deficiency and hyperinflammation: Rationale for the use of JAK1/2 inhibitors in combination with interferon

“…The efficacy of ruxolitinib in calming the cytokine storm has been thoroughly investigated in animal models of HLS [ [118] , [119] , [120] , [121] , [122] , [123] ], showing that the mechanisms of action involve inhibition of among others CD8 + T cells and important inflammatory cytokines, including IFN gamma [ [148] , [149] , [150] , [151] , [152] ], being of utmost importance for the development of HLS [ 122 , 123 ]. Most lately, NETosis has attracted great interest in the pathogenesis of organ damage in COVID-19 afflicted patients [ [95] , [96] , [97] , [98] , [99] , [100] , [101] ], with NETs contributing both to ARDS and immunothrombosis in COVID-19 [ 101 ]. Accordingly, it has been argued that NETs might be a potential target in COVID-19 [ 95 ].…”

“…8. As alluded to above, most recent studies have shown that NETosis is deeply involved in thrombogenesis and organ damage in COVID-19 afflicted patients [ [95] , [96] , [97] , [98] , [99] , [100] , [101] ]. Ruxolitinib inhibits NET formation in patients with MPN [ 104 ] and may likely do so in patients with COVID-19 as well.…”

“…Therefore, targeting the cytokine storm by potent JAK1/2 inhibition [ [7] , [8] , [9] , 26 , [55] , [56] , [57] , [58] , [59] , [60] , [61] , [62] ] may likely also reduce the risk of life-threatening thromboembolic disease burden by dampening inflammation-mediated in vivo leukocyte, platelet and endothelial activation and activation of the coagulation system as well. Furthermore, since not only platelets and endothelial cells are involved in COVID-19 induced thrombogenesis and the diffuse thrombotic microangiopathy, but also neutrophils and neutrophil extracellular trap formation (NETosis) are of paramount importance as well [ [95] , [96] , [97] , [98] , [99] , [100] , [101] ], targeting the myeloid compartment and NETosis might be equally important. In this context, IFN-alpha2 (IFN-alpha2) or IFN-beta (IFN-beta) might be highly efficacious, dampening the inflammasome [ 102 ] and NETosis [ 103 ] together with a JAK1/2 inhibitor, which also impairs NET formation [ 104 ], and at the same time IFN potently inhibiting virus replication [ [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] , [52] , [53] , [54] ].…”

Inter-proteomic posttranslational modifications of the SARS-CoV-2 and the host proteins ‒ A new frontier

“…An in silico analysis of SARS-CoV-2-infected lung tissues and cell lines has identified that SARS-CoV-2-infection modulates the expression of PADs, predominantly PAD-2 and PAD-4, with link to inflammatory pathways. 33 Other studies have lent strong support to this notion by demonstrating that SARS-CoV-2 leads to activation of neutrophils and triggers the release of neutrophil extracellular traps (NETs) in the circulation 34,35 and organ tissues. 34 NETs are extracellular webs of DNA, proteins and histones, and their release was found to be dependent on ACE2, serine protease, virus replication, and PAD-4 activation.…”

“…Recent studies have proposed a role for posttranslational deimination by peptidylarginine deiminases (PADs) in SARS-CoV-2-infection. 33–35 Deimination converts arginine residue in a protein into citrulline, and allows the modified protein to carry out multifaceted functions, a phenomenon termed “protein moonlighting.” There are five PADs in humans, with different tissue expressions and deimination activities, and they are involved in multiple diseases, including autoimmune diseases and viral infections. An in silico analysis of SARS-CoV-2-infected lung tissues and cell lines has identified that SARS-CoV-2-infection modulates the expression of PADs, predominantly PAD-2 and PAD-4, with link to inflammatory pathways.…”