Complications are associated to a higher risk of developing severe forms of COVID-19, requiring consequent mechanical ventilation and leading to increased mortality. Periodontitis has become a potential risk factor among the complications affecting the prognosis of COVID-19 patients12, 14. This may be partly related to the binding of SARS-CoV-2 to ACE2, which is expressed in oral tissues, especially in the epithelial cells of the tongue, buccal mucosa and gingiva17. Furthermore, periodontal pathogens promote the increased expression of ACE2 in the oral tissues and may increase the infection rate of SARS-CoV-225. Interestingly, cytokine storm and expression profile in severe COVID-19 infection are similar to that in periodontitis, suggesting a possible link between periodontitis and COVID-19 and its related complications18. Therefore, elucidating the key genes and pathways of periodontitis and COVID-19 is crucial to deciphering the molecular associations and mechanisms of these diseases.elucidating the key genes and pathways in periodontitis and COVID-19 is crucial to decipher the molecular association and mechanisms shared by these pathologies. Here, based on the GEO database, we studied gene expression patterns in two RNA-seq datasets from patients with periodontitis and COVID-19, and established a potential molecular association between the two diseases through systematic bioinformatics analysis. We found that TFs and immune response-related pathways play an important role in the pathogenesis of these two disease, which may provide new therapeutic targets for patients with co-morbidity COVID-19 and periodontitis.
The nine co-upregulated TFs in both diseases were found by analyzing the datasets. NFE2(nuclear factor erythroid 2) is a key TF regulating antioxidant expression26. NFE2 plays a critical role in protecting the host from periodontitis tissue damage. It can up-regulate NFE2-associated antioxidant and detoxification enzymes to enhance the protective effect on cells, and finally decreased inflammatory signal transduction and oxidative damage in tissues26, 27. Similarly, in clinical trial, NFE2 activator reduced lung alveolar cells damage in COVID-19 positive patients28. Accordingly, we believe that NFE2 activation may be a feasible adjuvant treatment for preventing periodontitis and COVID-19. With regard to POU2AF, researchers observed expression of POU domain class 2–associating factor 1 (POU2AF1) in a genome-wide RNA-seq analysis of human airway epithelium gene expression29. And it was identified as a novel host defense regulator in the human airway epithelium30. This gene was previously thought to be specifically expressed in lymphocytes. POU2AF1 encodes OCA-B protein(coactivator of OCT2, as a B cell specific TF), plays a pivotal role in the regulation of normal and neoplastic germinal center B cells31. Thus, we think that POU2AF1 might be therapeutic targets for COVID-19-related airway diseases. XBP1, as a crucial TF, plays a key role in the endoplasmic reticulum (ER) stress response32. Studies have shown that XBP1 regulates the transcription of many genes related lipid (hepatic lipogenesis and adipocyte differentiation)33, glucose metabolism34 and immune responses. It also participates in the development and differentiation of various immune cells35. XBP1 has been proved to be the necessary TF for mature B lymphocytes to eventually differentiate into plasma cells22. Therefore, XBP1 can be an important target for studying various diseases. As a member of the interferon regulatory family of TFs, IRF4, like XBP1, also participates in immune response, cell development and differentiation, growth regulation and metabolism36. For example, IRF4 can regulate the development of germinal center B cells and plasma cells23, and IRF4 is necessary for receptor editing in immunoglobulin gene rearrangement, which is important stage for B cell self-tolerance36. Although the specific role of IRF4 in the pathogenesis of periodontitis is poorly defined, however, our analysis found that TRF4 was co-upregulated in both periodontitis and COVID-19, and was involved in the immune response process of the two diseases. Moreover, IRF4 participates in autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis37. STAT3 is a critical pathway for regulating the immune and inflammatory responses, and it also has important roles in cell proliferation, survival and apoptosis38. A recent study indicated that activated STAT3 signaling pathway may contribute to neuroinflammation and cognitive impairment in ligature-induced periodontitis rats39. For COVID-19, due to the occurrence of cytokine storm, the over-activation of STAT-3 can play a critical role in the COVID-19 pathogenesis. The IL-6/JAK/STAT-3 axis potently potentiates inflammatory responses40 and may cause the decrease of lymphocytes in COVID-1941. Thus STAT-3 may be considered as a possible therapeutic target for severe COVID-19. EPAS1, located on chromosome 2, is transcribed into two protein-coding transcripts whose expresion is enhanced in the lungs. EPAS1, also known as Hypoxia inducible factor 2 alpha (HIF2α), play an important role in the transcription of many hypoxia-responsive genes42. In addition, EPAS1 has associated with various diseases, such as non-small cell lung cancer43, paraganglioma and pheochromocytoma44, and chronic mountain sickness, which can regulate proliferation of erythroblasts45. In general, consistent with previous findings, these TFs play an extremely important role in immune inflammatory response. In addition, we discovered TFs, E2F3, ELL and ARID3A are up-regulated in periodontitis tissues compared with the healthy control, however, there was no statistical significance, there may be shortcomings of small sample size. These three TFs have not been reported in other studies and need to be further explored in the future.
Our results also show that lymphocyte activation in immune response is a common biological process of periodontitis and COVID-19. Exactly, which lymphocytes are involved in the development of the disease, we concluded that both diseases cause increased levels of plasma cells through analysis. Some studies have also reported the same results. A high-dimensional single-cell analysis showed that CD4+ T cell depletion, T cell differentiation, plasma cell amplification, and the reduced antigen presentation capacity of innate immunity in COVID-1920. In all immune cell clusters, the percentage of plasma cells increased significantly among all five COVID-19 patients compared with healthy controls, which in line with previous research results46. A study showed that the risk of death in severe COVID-19 patients with plasma cells detected in peripheral blood was reduced, indicating that plasma cells may play a critical role in the immune response to COVID-1947. Antibody mediated immune response produced by plasma cells plays an important role in SARS-COV-2 infection. The main target of SARS-COV-2 neutralizing antibody is S protein, which binds to the receptor binding domain (RBD) to block the binding of virus with ACE2. The timing of antibodies is regular at different times of viral infection, with one study showing that positive IgA diagnoses are highest (88.2%) in 4–10 days after symptoms appear, which proved that IgA had a good diagnostic effect in the early stage48. For periodontitis, previous data analysis also showed plasma cells was elevated in periodontitis tissues49. Plasma cells in periodontal tissue mainly secreted IgA and IgG specific for periodontal pathogens to protect the tissue from damage50. Moreover, plasma cells potentially participated in and regulated the bone loss through IL-35 and IL-3719. Some cytokines are involved in plasma cell proliferation, differentiation and survival. Apart from cytokine, some TFs, such as PRDM1, XBP1 and IRF4, can regulate plasma cell properties and functions51, 52. Our analysis also showed that XBP1 and IRF4 are up-regulated in COVID-19 patients.
While the data supporting an association between periodontitis and COVID-19 is unclear, there is a potential biological link between the two diseases in terms of immunity and inflammation perspective. Based on our findings, we believe TFs can be used as potential therapeutic targets, and immunotherapy and can make major breakthroughs in the future for COVID-19 and periodontitis. Previous studies have found that plasma cells in periodontitis and COVID-19 play an immunomodulatory role by producing IgA48, 50. SARS-COV-2 invades human body mainly through respiratory tract, oral mucosa and conjunctival epithelium17, so it is speculated that mucosal IgA has a protective effect on these physical barriers to a certain extent. Studies have shown that oral and nasal administration of mucosal vaccine targeting SARS-COV-2 RBD can induce the secretion of IgA in mucosa, which could prevent the development of COVID-1953, 54. Therefore, we speculate that the mucosal vaccine can prevent the progression of periodontitis. On the other hand, periodontal health may prevent COVID-19 exacerbations and complications, and can reduce the host's susceptibility to COVID-19.