Expression and function of RIG-I in oral keratinocytes and fibroblasts

ACE2 expression and spike S1 protein-mediated immune responses in oral mucosal cells

OBJECTIVES

ACE2, known as a host receptor involved with SARS-CoV-2 infection, binds to viral spike proteins for host cell entry. However, details regarding its induction and function in oral mucosal cells remain unknown.

MATERIALS AND METHODS

We examined ACE2 expression and its induction by transfected mimic nucleotides and pro-inflammatory cytokines in oral keratinocytes (RT7) and fibroblasts (GT1). Subsequently, the effects of viral spike S1 protein via ACE2 on CXCL10 expression induced by pro-inflammatory cytokines in both cells were examined.

RESULTS

ACE2 was constitutively expressed in RT7 and GT1. Transfected Poly(I:C) and Poly(dA:dT) increased ACE2 expression in those cells, while knockdown of RIG-I decreased ACE2 expression induced by those transfected ds nucleotides. IFN-γ and TNF-α enhanced transfected ds nucleotides-induced ACE2 expression in RT7 but not GT1. S1 protein alone did not affect CXCL10 expression in either cell type, whereas it enhanced IFN-β-induced CXCL10 in both, while immune responses of IFN-γ- and TNF-α-induced CXCL10 enhanced by S1 protein were different between RT7 and GT1. Finally, knockdown of ACE2 decreased cytokines and S1 protein mediated-CXCL10 levels in both cells.

CONCLUSIONS

ACE2 in oral mucosal cells may contribute to development of infection and inflammation in cooperation with pro-inflammatory cytokines following SARS-CoV-2 invasion.

Mechanisms of mesothelial cell response to viral infections: HDAC1-3 inhibition blocks poly(I:C)-induced type I interferon response and modulates the mesenchymal/inflammatory phenotype

Infectious peritonitis is a leading cause of peritoneal functional impairment and a primary factor for therapy discontinuation in peritoneal dialysis (PD) patients. Although bacterial infections are a common cause of peritonitis episodes, emerging evidence suggests a role for viral pathogens. Toll-like receptors (TLRs) specifically recognize conserved pathogen-associated molecular patterns (PAMPs) from bacteria, viruses, and fungi, thereby orchestrating the ensuing inflammatory/immune responses. Among TLRs, TLR3 recognizes viral dsRNA and triggers antiviral response cascades upon activation. Epigenetic regulation, mediated by histone deacetylase (HDAC), has been demonstrated to control several cellular functions in response to various extracellular stimuli. Employing epigenetic target modulators, such as epidrugs, is a current therapeutic option in several cancers and holds promise in treating viral diseases. This study aims to elucidate the impact of TLR3 stimulation on the plasticity of human mesothelial cells (MCs) in PD patients and to investigate the effects of HDAC1-3 inhibition. Treatment of MCs from PD patients with the TLR3 agonist polyinosinic:polycytidylic acid (Poly(I:C)), led to the acquisition of a bona fide mesothelial-to-mesenchymal transition (MMT) characterized by the upregulation of mesenchymal genes and loss of epithelial-like features. Moreover, Poly(I:C) modulated the expression of several inflammatory cytokines and chemokines. A quantitative proteomic analysis of MCs treated with MS-275, an HDAC1-3 inhibitor, unveiled altered expression of several proteins, including inflammatory cytokines/chemokines and interferon-stimulated genes (ISGs). Treatment with MS-275 facilitated MMT reversal and inhibited the interferon signature, which was associated with reduced STAT1 phosphorylation. However, the modulation of inflammatory cytokine/chemokine production was not univocal, as IL-6 and CXCL8 were augmented while TNF-α and CXCL10 were decreased. Collectively, our findings underline the significance of viral infections in acquiring a mesenchymal-like phenotype by MCs and the potential consequences of virus-associated peritonitis episodes for PD patients. The observed promotion of MMT reversal and interferon response inhibition by an HDAC1-3 inhibitor, albeit without a general impact on inflammatory cytokine production, has translational implications deserving further analysis.

LL-37-dsRNA Complexes Modulate Immune Response via RIG-I in Oral Keratinocytes

Recognition of nucleic acids as pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) promotes an inflammatory response. On the other hand, LL-37, an antimicrobial peptide, is a multifunctional modulator of immune response, though whether it modulates inflammatory responses induced by nucleic acids in oral keratinocytes is unknown. In this study, we firstly investigated the effect of LL-37 on CXCL10 induced by DAMPs and PAMPs in immortalized oral keratinocytes, RT7. Furthermore, the effects of LL-37 on translocation of exogenous nucleic acids into cytoplasm as well as cytosolic receptor, RIG-I on immune responses mediated by LL-37-nucleic acid complexes were examined. From these results, LL-37 enhanced necrotic cell supernatant (NCS)-induced CXCL10 expression in RT7, while the response was decreased by RNase. Complexes of LL-37 and double-stranded (ds) RNA, Poly(I:C) enhanced CXCL10 expression in comparison with each alone, which were associated with NF-κB activation. Furthermore, LL-37 was shown to bind with ds nucleotides and translocate into cytoplasm. Knockdown of RIG-I decreased expression of CXCL10 induced by LL-37-Poly(I:C) complexes, and RIG-I were co-localized with Poly(I:C) entered by LL-37 in cytoplasm. LL-37 modulates dsRNA-mediated inflammatory response via RIG-I in oral keratinocytes, which may play an important role in the pathogenesis of oral inflammatory diseases.

The Priming Potential of Interferon Lambda-1 for Antiviral Defense in the Oral Mucosa

The oral mucosa is one of the first lines of the innate host defense system against microbial invasion. Interferon (IFN) lambda-1 (IFN-λ1), a type III IFN, exhibits type I IFN-like antiviral activity. In contrast to ubiquitously expressed type I IFN receptors, IFN-λ receptor 1 (IFN-λR1), which has higher affinity for type III IFNs than low-affinity interleukin (IL)-10 receptor 2, is mainly expressed on epithelial cells. Although IFN-λ1 has been shown to exert antiviral effects in the respiratory tract, gastrointestinal tract, and skin, the regulation of type III IFN receptor expression and its functions in the oral mucosa remain unclear. We herein showed the expression of IFN-λR1 in human gingival keratinocytes. The expression of IL-6, angiotensin-converting enzyme 2 (a critical molecule for severe acute respiratory syndrome coronavirus 2 infection), and IL-8 in human primary gingival keratinocytes (HGK) were significantly higher following treatments with either type I IFN (IFN-β) or type II IFN (IFN-γ) than with IFN-λ1. However, the IFN-λ1 treatment strongly induced toll-like receptor (TLR) 3 and retinoic acid-inducible gene I (RIG-I), which mainly recognize viral nucleic acids, via the STAT1-mediated pathway. Furthermore, a stimulation with a RIG-I or TLR3 agonist promoted the production of IL-6, IL-8, and IFN-λ in HGK, which was significantly enhanced by a pretreatment with IFN-λ1. These results suggest that IFN-λ1 may contribute to the activation of innate immune responses to oral viral infections by up-regulating the expression of RIG-I and TLR3 and priming their functions in keratinocytes.

Keratinocyte Response to Infection with Sporothrix schenckii

Sporotrichosis is a subacute, or chronic mycosis caused by traumatic inoculation of material contaminated with the fungus Sporothrix schenckii which is part of the Sporothrix spp. complex. The infection is limited to the skin, although its progression to more severe systemic or disseminated forms remains possible. Skin is the tissue that comes into contact with Sporothrix first, and the role of various cell lines has been described with regard to infection control. However, there is little information on the response of keratinocytes. In this study, we used the human keratinocyte cell line (HaCaT) and evaluated different aspects of infection from modifications in the cytoskeleton to the expression of molecules of the innate response during infection with conidia and yeast cells of Sporothrix schenckii. We found that during infection with both phases of the fungus, alterations of the actin cytoskeleton, formation of membrane protuberances, and loss of stress fibers were induced. We also observed an overexpression of the surface receptors MR, TLR6, CR3 and TLR2. Cytokine analysis showed that both phases of the fungus induced the production of elevated levels of the chemokines MCP-1 and IL-8, and proinflammatory cytokines IFN-α, IFN-γ and IL-6. In contrast, TNF-α production was significant only with conidial infection. In late post-infection, cytokine production was observed with immunoregulatory activity, IL-10, and growth factors, G-CSF and GM-CSF. In conclusion, infection of keratinocytes with conidia and yeast cells of Sporothrix schenckii induces an inflammatory response and rearrangements of the cytoskeleton.

Two PARP13 isoforms are associated with induction of antiviral factors in oral mucosal cells

Innate immune systems in the oral cavity have important roles in the host defense against viral invasion of oral mucosa. Poly(ADP‑ribose) polymerase 13 (PARP13), which has a strong antiviral ability, has been reported to possess two isoforms; a full‑length protein, zinc‑finger antiviral protein long (ZAPL), and a shorter protein (ZAPS). However, the expression and function of these two isoforms in oral mucosa remain unknown. In the present study, the expression levels of ZAPL and ZAPS induced by transfected double‑stranded (ds) RNA, Poly(I:C), and dsDNA, Poly(dA:dT), in immortalized oral keratinocytes and fibroblasts (RT7 and GT1 cell lines, respectively) were investigated. Subsequently, the effects of the knockdown of ZAPL and ZAPS on transfected nucleotide‑induced antiviral factors were examined. The results demonstrated constitutive expression of ZAPL and ZAPS in RT7 and GT1 cells, and their expression in both cell types was notably increased by transfection of Poly(I:C) and Poly(dA:dT) when compared with no transfection. Specific knockdown of ZAPL and ZAPS in RT7 cells decreased IFN‑β and C‑X‑C motif chemokine ligand 10 (CXCL10) expression induced by transfected Poly(I:C) and Poly(dA:dT). On the other hand, knockdown of ZAPL and ZAPS in GT1 cells decreased the expression of CXCL10 induced by the transfected nucleotides, whereas that had no effect on IFN‑β expression induced by Poly(dA:dT). Their knockdown was also associated with transfected nucleotides‑induced IFN regulatory factor 3 phosphorylation in both cell types. Taken together, these results indicate that ZAPL and ZAPS, isoforms of PARP13, in oral mucosal cells participate in host defense against viral infection of oral mucosa.

The parapoxvirus Orf virus inhibits IFN-β expression induced by dsRNA

Orf virus (ORFV) is the type species of the Parapoxvirus genus that belongs to the Poxviridae family. Type I interferons (IFN) are critical in the host defence against viruses. They induce hundreds of interferon stimulated genes (ISGs) many of which have an antiviral role. The ability of ORFV to modulate type I IFN production was undertaken to investigate whether ORFV could inhibit IFN-β expression via dsRNA dependant signalling pathways. HEK293 cells are known to lack DNA pattern-recognition receptors and Toll-like receptors however, they do express the cytosolic dsRNA receptors RIG-I and MDA5. HEK293 cells were shown to produce high levels of IFN-β when cells were stimulated with poly(I:C) and this was shown to be predominantly via RIG-I-dependant signalling as confirmed by siRNA knock-down of RIG-I. Further we showed that HEK293 cells are permissive for ORFV and caused potent inhibition of IFN-β transcription when cells were stimulated with poly(I:C) post-viral infection. Studies using heat inactivated ORFV suggested that de novo synthesis of early genes was required. In addition our findings showed that the ORFV encoded factor ORF020, that is known to bind dsRNA, is involved in antagonising IFN expression. Overall, this study has shown for first time the ability of ORFV to counteract type I IFN expression by antagonising dsRNA-activated RIG-I signalling.

Effects of CEACAM1 in oral keratinocytes on HO-1 expression induced by Candida β-glucan particles

Objective

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a member of the carcinoembryonic antigen family. Although its expression has been found in chronic oral inflammatory epithelium, this study aimed to know whether CEACAM1 in oral keratinocytes participates in host immune response against Candida albicans .

Methodology

We investigated CEACAM1 expression in oral keratinocytes induced by C. albicans as well as by Candida cell wall component β-glucan particles (β-GPs). Furthermore, the effects of CEACAM1 on β-GPs-induced heme oxygenase-1 (HO-1) expression and its related signals were examined.

Results

Fluorescence staining showed CEACAM1 expression in oral keratinocytes (RT7) cells, whereas quantitative reverse transcription (RT)-PCR indicated that both live and heat-killed C. albicans increased CEACAM1 mRNA expression in RT7 cells. Examinations using quantitative RT-PCR and western blotting indicated that CEACAM1 expression was also increased by β-GPs derived from C. albicans . Specific siRNA for CEACAM1 decreased HO-1 expression induced by β-GPs from C. albicans as well as the budding yeast microorganism Saccharomyces cerevisiae . Moreover, knockdown of CEACAM1 decreased β-GPs-induced ROS activity in the early phase and translocation of Nrf2 into the nucleus.

Conclusion

CEACAM1 in oral keratinocytes may have a critical role in regulation of HO-1 for host immune defense during Candida infection.

The Role of Cutaneous Type I IFNs in Autoimmune and Autoinflammatory Diseases

IFNs are well known as mediators of the antimicrobial response but also serve as important immunomodulatory cytokines in autoimmune and autoinflammatory diseases. An increasingly critical role for IFNs in evolution of skin inflammation in these patients has been recognized. IFNs are produced not only by infiltrating immune but also resident skin cells, with increased baseline IFN production priming for inflammatory cell activation, immune response amplification, and development of skin lesions. The IFN response differs by cell type and host factors and may be modified by other inflammatory pathway activation specific to individual diseases, leading to differing clinical phenotypes. Understanding the contribution of IFNs to skin and systemic disease pathogenesis is key to development of new therapeutics and improved patient outcomes. In this review, we summarize the immunomodulatory role of IFNs in skin, with a focus on type I, and provide insight into IFN dysregulation in autoimmune and autoinflammatory diseases.

Participation of Endosomes in Toll-Like Receptor 3 Transportation Pathway in Murine Astrocytes

TLR3 provides immediate type I IFN response following entry of stimulatory PAMPs into the CNS, as it is in HSV infection. The receptor plays a vital role in astrocytes, contributing to rapid infection sensing and suppression of viral replication, precluding the spread of virus beyond neurons. The route of TLR3 mobilization culminating in the receptor activation remains unexplained. In this research, we investigated the involvement of various types of endosomes in the regulation of the TLR3 mobility in C8-D1A murine astrocyte cell line. TLR3 was transported rapidly to early EEA1-positive endosomes as well as LAMP1-lysosomes following stimulation with the poly(I:C). Later, TLR3 largely associated with late Rab7-positive endosomes. Twenty-four hours after stimulation, TLR3 co-localized with LAMP1 abundantly in lysosomes of astrocytes. TLR3 interacted with poly(I:C) intracellularly from 1 min to 8 h following cell stimulation. We detected TLR3 on the surface of astrocytes indicating constitutive expression, which increased after poly(I:C) stimulation. Our findings contribute to the understanding of cellular modulation of TLR3 trafficking. Detailed analysis of the TLR3 transportation pathway is an important component in disclosing the fate of the receptor in HSV-infected CNS and may help in the search for rationale therapeutics to control the replication of neuropathic viruses.

Immune response to cytosolic DNA via intercellular receptor modulation in oral keratinocytes and fibroblasts

OBJECTIVE

Double-strand (ds) DNA-enveloped viruses can cause oral infection. Our aim is to investigate whether oral mucosal cells participate in immune response against cytosolic dsDNA invasion.

METHODS

We examined the response to transfected herpes simplex virus (HSV) dsDNA via intracellular receptors in oral keratinocytes (RT7) and fibroblasts (GT1), and the effect of TNF-α on those responses.

RESULTS

Transfected dsDNA increased CXCL10 expression via NF-κB activation in both cell types, while those responses were inhibited by knockdown of RIG-I, an RNA sensor. Although IFI16, a DNA sensor, was expressed in the nuclei of both types, its knockdown decreased transfected dsDNA-induced CXCL10 expression in GT1 but not RT7 cells. IFI16 in GT1 cells was translocated into cytoplasm from nuclei, which was attributed to immune response to cytosolic dsDNA. TNF-α enhanced transfected dsDNA-induced CXCL10, and knockdown of IFI16 decreased TNF-α and dsDNA-driven CXCL10 expression in both RT7 and GT1 cells. Finally, the combination of TNF-α and transfected dsDNA resulted in translocation of IFI16 from nuclei to cytoplasm in RT7 cells.

CONCLUSION

RIG-I and IFI16 in oral mucosal cells may play important roles in host immune response against DNA viral infection, while TNF-α contributes to development of an antiviral system via those intracellular receptors.

The influence of interferon on healthy and diseased skin

Type I interferons (IFNs) are an immunomodulatory class of cytokines that serve to protect against viral and bacterial infection. In addition, mounting evidence suggests IFNs, particularly type I but also IFNγ, are important to the pathogenesis of autoimmune and inflammatory skin diseases, such as cutaneous lupus erythematosus (CLE). Understanding the role of IFNs is relevant to anti-viral responses in the skin, skin biology, and therapeutics for these IFN-related conditions. Type I IFNs (α and β) are produced by recruited inflammatory cells and by the epidermis itself (IFNκ) and have important roles in autoimmune and inflammatory skin disease. Here, we review the current literature utilizing a PubMed database search using terms [interferon/IFN/type I IFN AND lupus/ cutaneous lupus/CLE/dermatomyositis/Sjogrens/psoriasis/lichen planus/morphea/alopecia areata/vitiligo] with a focus on the role of IFNs in basic keratinocyte biology and their implications in the cutaneous autoimmune and inflammatory diseases: cutaneous lupus erythematosus, dermatomyositis, Sjogren's syndrome, psoriasis, lichen planus, alopecia areata and vitiligo. We provide information about genes and proteins induced by IFNs and how downstream mechanisms relate to clinical disease.

Keratinocyte infection by Actinomadura madurae triggers an inflammatory response

BACKGROUND

Actinomycetoma is a syndrome of the skin characterized by chronic inflammation and lesions with nodular grain-like structures. The most common aetiological agents are Nocardia brasiliensis and Actinomadura madurae. In response to infection with these organisms the body produces an inflammatory immune response in the skin. The aim of the present study was to determine the production of chemokines, pro-inflammatory cytokines, antimicrobial peptides and the expression of Toll-like receptors (TLRs) in keratinocytes infected by A. madurae.

METHODS

A cell line of HaCaT keratinocytes was infected with A. madurae at a multiplicity of infection of 20:1 for 2 h and the samples were collected from 2 to 72 h post-infection. Intracellular replication of the bacterium was evaluated by counting of colony-forming units, the TLR expression and antimicrobial peptide production were assayed by confocal microscopy and chemokine and pro-inflammatory cytokine levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Early in the infection, A. madurae was able to achieve intracellular replication in keratinocytes, however, the cells eventually controlled the infection. In response to the infection, keratinocytes overexpressed TLR2 and TLR6, produced high concentrations of cytokines monocyte chemoattractant protein-1, interleukin 8, human β-defensin-1, human β-defensin-2 and LL37 and low levels of tumour necrosis factor α.

CONCLUSIONS

The human keratinocytes contribute to the inflammatory process in response to A. madurae infection by overexpressing TLRs and producing chemokines, pro-inflammatory cytokines and antimicrobial peptides.

Candida albicans β-Glucan-Containing Particles Increase HO-1 Expression in Oral Keratinocytes via a Reactive Oxygen Species/p38 Mitogen-Activated Protein Kinase/Nrf2 Pathway

Oral keratinocytes provide the first line of host defense against oral candidiasis. We speculated that interactions of fungal cell wall components with oral keratinocytes regulate the stress response against Candida infection and examined the expression of genes induced by heat-killed Candida albicans in oral immortalized keratinocytes using a cDNA microarray technique. Of 24,000 genes revealed by that analysis, we focused on HO-1, a stress-inducible gene, as its expression was increased by both heat-killed and live C. albicans In histological findings, HO-1 expression in the superficial layers of the oral epithelium following Candida infection was elevated compared to that in healthy epithelium. We then investigated fungal cell wall components involved in induction of HO-1 expression and found that β-glucan-containing particles (β-GPs) increased its expression. Furthermore, β-glucan was observed on the surface of both heat-killed C. albicans and Candida cells that had invaded the oral epithelium. Fungal β-GPs also promoted induction of intracellular reactive oxygen species (ROS), NADPH oxidase activation, and p38 mitogen-activated protein kinase (MAPK) phosphorylation, while those specific inhibitors inhibited the HO-1 expression induced by fungal β-GPs. Moreover, fungal β-GPs induced Nrf2 translocation into nuclei via p38 MAPK signaling, while the HO-1 expression induced by fungal β-GPs was inhibited by Nrf2-specific small interfering RNA (siRNA). Finally, knockdown of cells by HO-1- and Nrf2-specific siRNAs resulted in increased β-GP-mediated ROS production compared to that in the control cells. Our results show that the HO-1 induced by fungal β-GPs via ROS/p38 MAPK/Nrf2 from oral keratinocytes may have important roles in host defense against the stress caused by Candida infection in the oral epithelium.

Oncostatin M induces RIG-I and MDA5 expression and enhances the double-stranded RNA response in fibroblasts

Interleukin (IL)-6-type cytokines have no direct antiviral activity; nevertheless, they display immune-modulatory functions. Oncostatin M (OSM), a member of the IL-6 family, has recently been shown to induce a distinct number of classical interferon stimulated genes (ISG). Most of them are involved in antigen processing and presentation. However, induction of retinoic acid-inducible gene (RIG)-I-like receptors (RLR) has not been investigated. Here we report that OSM has the capability to induce the expression of the DExD/H-Box RNA helicases RIG-I and melanoma differentiation antigen 5 (MDA5) as well as of the transcription factors interferon regulatory factor (IRF)1, IRF7 and IRF9 in primary fibroblasts. Induction of the helicases depends on tyrosine as well as serine phosphorylation of STAT1. Moreover, we could show that the OSM-induced STAT1 phosphorylation is predominantly counter-regulated by a strong STAT3-dependent SOCS3 induction, as Stat3 as well as Socs3 knock-down results in an enhanced and prolonged helicase and IRF expression. Other factors involved in regulation of STAT1 or IRF1 activity, like protein tyrosine phosphatase, non-receptor type 2 (PTPN2), promyelocytic leukaemia protein (PML) or small ubiquitin-related modifier 1 (SUMO1), play a minor role in OSM-mediated induction of RLR. Remarkably, OSM and interferon-γ (IFN-γ) synergize to mediate transcription of RLR and pre-treatment of fibroblasts with OSM fosters the type I interferon production in response to a subsequent encounter with double-stranded RNA. Together, these findings suggest that the OSM-induced JAK/STAT1 signalling is implicated in virus protection of non-professional immune cells and may cooperate with interferons to enhance RLR expression in these cells.