Nontypeable Haemophilus influenzae DNA stimulates type I interferon expression via STING signaling pathway

cGAS-STING targeting offers therapy choice in lung diseases

Cyclic GMP/AMP (cGAMP) synthase (cGAS), along with the endoplasmic reticulum (ER)-associated stimulator of interferon genes (STING), are crucial elements of the type 1 interferon response. cGAS senses microbial DNA and self-DNA, labeling cGAS-STING as a crucial mechanism in autoimmunity, sterile inflammatory responses, and cellular senescence. However, chronic and aberrant activation of the cGAS-STING axis results in inflammatory and autoimmune diseases. cGAS-STING has emerged as a vital mechanism driving inflammation-related diseases, including lung diseases. Insights into the biology of the cGAS-STING pathway have enabled the discovery of small-molecule agents which have the potential to inhibit the cGAS-STING axis in lung diseases. In this review, we first outline the principal components of the cGAS-STING signaling cascade. Then, we discuss recent research that highlights general mechanisms by which cGAS-STING contributes to lung diseases. Then, we focus on summarizing a list of bioactive small-molecule compounds which inhibit the cGAS-STING pathway, reviewing their potential mechanisms.These review highlights a novel groundbreaking therapeutic possibilities through targeting cGAS-STING in lung diseases.

Microbiome-host interactions in the pathogenesis of acute exacerbation of chronic obstructive pulmonary disease

Objective

To explore the underlying mechanisms the airway microbiome contributes to Acute Exacerbation of Chronic Obstructive Pulmonary Disease(AECOPD).

Methods

We enrolled 31 AECOPD patients and 26 stable COPD patients, their sputum samples were collected for metagenomic and RNA sequencing, and then subjected to bioinformatic analyses. The expression of host genes was validated by Quantitative Real-time PCR(qPCR) using the same batch of specimens.

Results

Our results indicated a higher expression of Rothia mucilaginosa(p=0.015) in the AECOPD group and Haemophilus influenzae(p=0.005) in the COPD group. The Different expressed genes(DEGs) detected were significantly enriched in "type I interferon signaling pathway"(p<0.001, q=0.001) in gene function annotation, and "Cytosolic DNA-sensing pathway"(p=0.002, q=0.024), "Toll-like receptor signaling pathway"(p=0.006, q=0.045), and "TNF signaling pathway"(p=0.006, q=0.045) in KEGG enrichment analysis. qPCR amplification experiment verified that the expression of OASL and IL6 increased significantly in the AECOPD group.

Conclusion

Pulmonary bacteria dysbiosis may regulate the pathogenesis of AECOPD through innate immune system pathways like type I interferon signaling pathway and Toll-like receptor signaling pathway.

Nucleic acid sensor STING drives remodeling and its inhibition enhances steroid responsiveness in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is progressive and irreversible chronic lung inflammatory disease. Cigarette smoke, the main cause of COPD, is often associated with double-stranded DNA release which potentially activates DNA-sensing pathways, such as STING. This study, therefore, analyzed the role of STING pathway in inducing pulmonary inflammation, steroid resistance, and remodeling in COPD.

METHODS

Primary cultured lung fibroblasts were isolated from healthy non-smoker, healthy smoker, and smoker COPD individuals. The expression of STING pathway, remodeling, and steroid resistance signatures were investigated in these fibroblasts upon LPS stimulation and treatment with dexamethasone and/or STING inhibitor, at both mRNA and protein levels using qRT-PCR, western blot, and ELISA.

RESULTS

At baseline, STING was elevated in healthy smoker fibroblasts and to a higher extent in smoker COPD fibroblasts when compared to healthy non-smoker fibroblasts. Upon using dexamethasone as monotherapy, STING activity was significantly inhibited in healthy non-smoker fibroblasts but showed resistance in COPD fibroblasts. Treating both healthy and COPD fibroblasts with STING inhibitor in combination with dexamethasone additively inhibited STING pathway in both groups. Moreover, STING stimulation triggered a significant increase in remodeling markers and a reduction in HDAC2 expression. Interestingly, treating COPD fibroblasts with the combination of STING inhibitor and dexamethasone alleviated remodeling and reversed steroid hyporesponsiveness through an upregulation of HDAC2.

CONCLUSION

These findings support that STING pathway plays an important role in COPD pathogenesis, via inducing pulmonary inflammation, steroid resistance, and remodeling. This raises the possibility of using STING inhibitor as a potential therapeutic adjuvant in combination with common steroid treatment.

Santos R, Brito CB, Ferrero MC, Ortiz Wilczyñski JM, Silva EAC, C. Oliveira S, Baldi PC. Role of the cGAS/STING pathway in the control of Brucella abortus infection acquired through the respiratory route

Despite the importance of the respiratory route for Brucella transmission, the lung immune response to this pathogen is scarcely characterized. We investigated the role of the cGAS/STING pathway of microbial DNA recognition in the control of respiratory Brucella infection. After in vitro B. abortus infection, CFU numbers were significantly higher in alveolar macrophages (AM) and lung explants from STING KO mice than in samples from wild type (WT) mice, but no difference was observed for cGAS KO samples. CFU were also increased in WT AM and lung epithelial cells preincubated with the STING inhibitor H151. Several proinflammatory cytokines (TNF-α, IL-1β, IL-6, IP-10/CXCL10) were diminished in Brucella-infected lung explants and/or AM from STING KO mice and cGAS KO mice. These cytokines were also reduced in infected AM and lung epithelial cells pretreated with H151. After intratracheal infection with B. abortus, STING KO mice exhibited increased CFU in lungs, spleen and liver, a reduced expression of IFN-β mRNA in lungs and spleen, and reduced levels of proinflammatory cytokines and chemokines in bronchoalveolar lavage fluid (BALF) and lung homogenates. Increased lung CFU and reduced BALF cytokines were also observed in cGAS KO mice. In summary, the cGAS/STING pathway induces the production of proinflammatory cytokines after respiratory Brucella infection, which may contribute to the STING-dependent control of airborne brucellosis.

STING Targeting in Lung Diseases

The cGAS-STING pathway displays important functions in the regulation of innate and adaptive immunity following the detection of microbial and host-derived DNA. Here, we briefly summarize biological functions of STING and review recent literature highlighting its important contribution in the context of respiratory diseases. Over the last years, tremendous progress has been made in our understanding of STING activation, which has favored the development of STING agonists or antagonists with potential therapeutic benefits. Antagonists might alleviate STING-associated chronic inflammation and autoimmunity. Furthermore, pharmacological activation of STING displays strong antiviral properties, as recently shown in the context of SARS-CoV-2 infection. STING agonists also elicit potent stimulatory activities when used as an adjuvant promoting antitumor responses and vaccines efficacy.

Advances in cGAS-STING Signaling Pathway and Diseases

Pathogens can produce conserved pathogen-associated molecular patterns (PAMPs) after invading the body, which can be specifically recognized by host pattern recognition receptors (PRRs). In recent years, it has been found that cytoplasmic DNA receptors recognize exogenous DNA inducing activation of interferon 1 (IFN1), which is a rapid advance in various research areas. The cyclic GMP–AMP synthase (cGAS) stimulator of interferon gene (STING) signaling pathway is a critical natural immune pathway in cells. Early studies revealed that it plays a crucial regulatory role in pathogen infection and tumor, and it is associated with various human autoimmune diseases. Recently studies have found that activation of cGAS-STING signaling pathway is related to different organ injuries. The present review elaborates on the regulation of the cGAS-STING signaling pathway and its role in various diseases, aiming to provide a theoretical basis for immunotherapy targeting this pathway.

Nod-like Receptors: Critical Intracellular Sensors for Host Protection and Cell Death in Microbial and Parasitic Infections

Cell death is an essential immunological apparatus of host defense, but dysregulation of mutually inclusive cell deaths poses severe threats during microbial and parasitic infections leading to deleterious consequences in the pathological progression of infectious diseases. Nucleotide-binding oligomerization domain (NOD)-Leucine-rich repeats (LRR)-containing receptors (NLRs), also called nucleotide-binding oligomerization (NOD)-like receptors (NLRs), are major cytosolic pattern recognition receptors (PRRs), their involvement in the orchestration of innate immunity and host defense against bacteria, viruses, fungi and parasites, often results in the cleavage of gasdermin and the release of IL-1β and IL-18, should be tightly regulated. NLRs are functionally diverse and tissue-specific PRRs expressed by both immune and non-immune cells. Beyond the inflammasome activation, NLRs are also involved in NF-κB and MAPK activation signaling, the regulation of type I IFN (IFN-I) production and the inflammatory cell death during microbial infections. Recent advancements of NLRs biology revealed its possible interplay with pyroptotic cell death and inflammatory mediators, such as caspase 1, caspase 11, IFN-I and GSDMD. This review provides the most updated information that caspase 8 skews the NLRP3 inflammasome activation in PANoptosis during pathogen infection. We also update multidimensional roles of NLRP12 in regulating innate immunity in a content-dependent manner: novel interference of NLRP12 on TLRs and NOD derived-signaling cascade, and the recently unveiled regulatory property of NLRP12 in production of type I IFN. Future prospects of exploring NLRs in controlling cell death during parasitic and microbial infection were highlighted.

Value of refined care in patients with acute exacerbation of chronic obstructive pulmonary disease

BACKGROUND

Under physiological conditions, sputum produced during acute exacerbation of chronic obstructive pulmonary disease (AECOPD) can move passively with the cilia in the airway; the sputum is gradually excreted from the depth of the airways through the stimulation of the coughing reflex on the sensory nerve on the surface of the airway. However, when the sputum is thick, the cough is weak, or the tracheal cilia are abnormal, sputum accumulation may occur and affect the exchange of oxygen and carbon dioxide in the lung. Furthermore, the presence of pathogenic microorganisms in sputum may cause or aggravate the symptoms of pulmonary infection in patients, which is the main factor leading to AECOPD. Therefore, promoting effective drainage of sputum and maintaining airway opening are key points requiring clinical attention.

AIM

To explore the effect of refined nursing strategies in patients with AECOPD and dysphagia.

METHODS

We selected 126 patients with AECOPD and difficulty of expectoration at our hospital, and divided them into a refined care group and a routine care group, with 63 cases each, using a random number table. The two groups of patients were treated with expectorant, anti-infection, oxygen inhalation, and other basic treatment measures; patients in the refined care group were given refined nursing intervention during hospitalization, and the routine care group received conventional nursing intervention. The differences in sputum expectoration, negative pressure suction rate, blood gas parameters, dyspnea score measured through the tool developed by the Medical Research Council (MRC), and quality of life were compared between the two groups.

RESULTS

After 7 d of intervention, the sputum expectoration effect of the refined care group was 62.30%, the effective rate was 31.15%, and the inefficiency rate was 6.56%. The sputum expectoration effect of the routine care group was 44.07%, the effective rate was 42.37%, and the inefficiency rate was 13.56%. The refined care group had better sputum expectoration than the routine care group (P < 0.05). The negative pressure suction rate in the refined care group was significantly lower than that of the routine care group during the treatment (22.95% vs 44.07%, P < 0.05). Before the intervention, the arterial oxygen saturation (PaO₂) and arterial carbon dioxide saturation (PaCO₂) values were not significantly different between the two groups (P > 0.05); the PaO₂ and PaCO₂ values in the refined care group were comparable to those in the routine care group after 7 d of intervention (P > 0.05). Before the intervention, there was no significant difference in the MRC score between the two groups (P > 0.05); the MRC score of the refined care group was lower than that of the routine care group after 7 d of intervention, but the difference was not statistically significant (P > 0.05). Before intervention, there was no significant difference in the symptoms, activities, disease impact, or St. George’s Respiratory questionnaire (SGRQ) total scores between the two groups (P> 0.05). After 7 days of intervention, the symptoms, activities, and total score of SGRQ of the refined care group were higher than those of the routine care group, but the difference was not statistically significant (P > 0.05).

CONCLUSION

AECOPD with thick sputum, weak coughing reflex, and abnormal tracheal cilia function will lead to sputum accumulation and affect the exchange of oxygen and carbon dioxide in the lung. Patients with AECOPD who have difficulty expectorating sputum may undergo refined nursing strategies that will promote expectoration, alleviate clinical symptoms, and improve the quality of life.

Evaluation of immunological responses against outer membrane vesicles (OMV) of nontypeable Haemophilus influenzae using MPLA-CpG adjuvant as a vaccine candidate

Background and Objectives

Nontypeable Haemophilus influenzae (NTHi) are major causes of non-invasive infections, including otitis media and sinusitis and it can also contribute to respiratory infections of all ages. Currently, there is no licensed vaccine against NTHi commercially available. Many studies have been conducted on the use of OMV as a vaccine against NTHi. The purpose of this study is to achieve an immunogenic vaccine against NTHi.

Materials and Methods

In this study, standard OMV Haemophilus (ATCC49766) with adjuncts CpG and MPLA was used and after infusion into BALB/c mice, the levels of antibodies and cytokines were measured on serum of immunized mice.

Results

The results showed that total IgG antibody and IgG1 and IgG2a isotypes in OMV immunized mice with mixture of CpG-MPLA adjuvant had a significant increase. Also, the results of cytokines (IL-10, IL-4 and IFN-γ) showed that IL-4 had the highest rate.

Conclusion

These findings indicate that OMVs derived from NTHi strains have a high potential to act as a vaccine against NTHi infections.

Impact of Type I Interferons on Susceptibility to Bacterial Pathogens

Interferons (IFNs) are a broad class of cytokines that have multifaceted roles. Type I IFNs have variable effects when it comes to host susceptibility to bacterial infections, that is, the resulting outcomes can be either protective or deleterious. The mechanisms identified to date have been wide and varied between pathogens. In this review, we discuss recent literature that provides new insights into the mechanisms of how type I IFN signaling exerts its effects on the outcome of infection from the host's point of view.

Lipopolysaccharide enhances DNA-induced IFN-β expression and autophagy by upregulating cGAS expression in A549 cells

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is a newly identified cytosolic DNA sensor, but its function in lung epithelial cells is relatively unknown. In the present study, the effects of lipopolysaccharide (LPS) on the expression and function of cGAS in the A549 lung epithelial cell line was investigated. The cells were treated with LPS at different concentrations (e.g., 100, 200, 400 and 800 ng/ml), and the cGAS expression levels were examined via western blot analysis and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The cells were pretreated with LPS, followed by E. coli DNA transfection using Lipofectamine^® 3000. After 24 h, interferon (IFN)-β production was measured using ELISA and the expression of the autophagic markers, microtubule-associated proteins 1A/1B light chain 3 and sequestosome-1, were determined using western blot analysis. The cells were also pretreated with either a toll-like receptor (TLR) 4 inhibitor, a serine/threonine-protein kinase TBK1 (TBK1) inhibitor or an nuclear factor (NF)-κB inhibitor, followed by LPS treatment, and the cGAS expression levels were examined via western blot analysis and RT-qPCR. The result showed that LPS treatment upregulated cGAS expression in a dose-dependent manner. E. coli DNA treatment could induce IFN-β production and autophagy via cGAS, which was enhanced by LPS pretreatment. The effect of LPS on cGAS expression was suppressed by treatment with a TLR4 inhibitor, a TBK1 inhibitor and an NF-κB inhibitor. In conclusion, LPS enhances DNA-induced IFN-β production and autophagy by upregulating cGAS expression through the myeloid differentiation primary response protein MyD88-independent TLR4 signaling pathway in A549 cells.

Diminished stimulator of interferon genes production with cigarette smoke-exposure contributes to weakened anti-adenovirus vectors response and destruction of lung in chronic obstructive pulmonary disease model

Cigarette smoke (CS) is the primary risk factor for chronic obstructive pulmonary disease (COPD) and dampens antiviral response, which increases viral infections and leads to COPD acute exacerbation (AECOPD). Adenovirus, a nonenveloped DNA virus, is linked with AECOPD, whose DNAs trigger innate immune response via interacting with pattern recognition receptors (PRRs). Stimulator of interferon genes (STING), as a cytosolic DNA sensor, participates in adenovirus-induced interferon β (IFNβ)-dependent antiviral response. STING is involved in various pulmonary diseases, but role of STING in pathogenesis of AECOPD is not well documented. In the present study, we explored relationship between STING and AECOPD induced by recombinant adenovirus vectors (rAdVs) and CS in wild type (WT) and STING-/- mice; and also characterized the inhibition of STING- IFNβ pathway in pulmonary epithelium exposed to cigarette smoke extract (CSE). We found that CS or CSE exposure alone dramatically inhibited STING expression, but not significantly effected IFNβ production. Moreover, CS or CSE-exposed significantly suppressed activation of STING-IFNβ pathway induced by rAdVs and suppressed clearance of rAdVs DNA. Inflammation, fibrosis and emphysema of lung tissues were exaggerated when treated with CS plus rAdVs, which further deteriorate in absences of STING. In A549 cells with knockdown of STING, we also observed enhancing apoptosis related to emphysema, especially CSE and adenovirus vectors in combination. Therefore, STING may play a protective role in preventing the progress of COPD.

Type I interferon induced by DNA of nontypeable Haemophilus influenza modulates inflammatory cytokine profile to promote susceptibility to this bacterium

Type I interferon (IFN) is indispensable for antiviral immunity, but its role in bacterial infections is controversial and not fully described. Nontypeable Haemophilus influenzae (NTHi) is one of the most common bacterial pathogens in patients with chronic obstructive pulmonary disease (COPD). NTHi-DNA activates type I IFN production in macrophages, but the function of type I IFN in host-pathogen interactions, in the context of NTHi infection, is still unclear. Here, we showed that type I IFN, induced by NTHi-DNA, restrained bacterial killing in vitro and promoted COPD development in vivo in response to NTHi. Mice deficient for type I IFN receptor (IFNAR) exhibited improved resistance to NTHi infection. Moreover, similar to exogenous IFN-β, NTHi-DNA-induced type I IFN increased the production of IL-6, IL-1β, IL-12 and CXCL10 via p38 MAPK activation. Our findings demonstrated that NTHi-DNA-induced type I IFN signaling played a negative role in host defense against NTHi infection and identified potential targets for future therapeutic management of COPD.

Mitochondrial DNA Leakage Caused by Streptococcus pneumoniae Hydrogen Peroxide Promotes Type I IFN Expression in Lung Cells

Streptococcus pneumoniae (S. pn), the bacterial pathogen responsible for invasive pneumococcal diseases, is capable of producing substantial amounts of hydrogen peroxide. However, the impact of S. pn-secreted hydrogen peroxide (H₂O₂) on the host immune processes is not completely understood. Here, we demonstrated that S. pn-secreted H₂O₂ caused mitochondrial damage and severe histopathological damage in mouse lung tissue. Additionally, S. pn-secreted H₂O₂ caused not only oxidative damage to mitochondrial deoxyribonucleic acid (mtDNA), but also a reduction in the mtDNA content in alveolar epithelia cells. This resulted in the release of mtDNA into the cytoplasm, which subsequently induced type I interferons (IFN-I) expression. We also determined that stimulator of interferon genes (STING) signaling was probably involved in S. pn H₂O₂-inducing IFN-I expression in response to mtDNA damaged by S. pn-secreted H₂O₂. In conclusion, our study demonstrated that H₂O₂ produced by S. pn resulted in mtDNA leakage from damaged mitochondria and IFN-I production in alveolar epithelia cells, and STING may be required in this process, and this is a novel mitochondrial damage mechanism by which S. pn potentiates the IFN-I cascade in S. pn infection.

The Interplay Between Immune Response and Bacterial Infection in COPD: Focus Upon Non-typeable Haemophilus influenzae

Chronic obstructive pulmonary disease (COPD) is a debilitating respiratory disease and one of the leading causes of morbidity and mortality worldwide. It is characterized by persistent respiratory symptoms and airflow limitation due to abnormalities in the lower airway following consistent exposure to noxious particles or gases. Acute exacerbations of COPD (AECOPD) are characterized by increased cough, purulent sputum production, and dyspnea. The AECOPD is mostly associated with infection caused by common cold viruses or bacteria, or co-infections. Chronic and persistent infection by non-typeable Haemophilus influenzae (NTHi), a Gram-negative coccobacillus, contributes to almost half of the infective exacerbations caused by bacteria. This is supported by reports that NTHi is commonly isolated in the sputum from COPD patients during exacerbations. Persistent colonization of NTHi in the lower airway requires a plethora of phenotypic adaptation and virulent mechanisms that are developed over time to cope with changing environmental pressures in the airway such as host immuno-inflammatory response. Chronic inhalation of noxious irritants in COPD causes a changed balance in the lung microbiome, abnormal inflammatory response, and an impaired airway immune system. These conditions significantly provide an opportunistic platform for NTHi colonization and infection resulting in a "vicious circle." Episodes of large inflammation as the consequences of multiple interactions between airway immune cells and NTHi, accumulatively contribute to COPD exacerbations and may result in worsening of the clinical status. In this review, we discuss in detail the interplay and crosstalk between airway immune residents and NTHi, and their effect in AECOPD for better understanding of NTHi pathogenesis in COPD patients.