Transferrable protection by gut microbes against STING-associated lung disease

Microbial dysbiosis fuels STING-driven autoinflammation through cyclic dinucleotides

Aberrant activation of the stimulator of interferon genes (STING) pathway is a hallmark of autoinflammatory disorders such as STING-associated vasculopathy with onset in infancy (SAVI), characterized by systemic inflammation affecting blood vessels, skin, and lungs. Despite its clinical significance, the mechanisms linking STING activation to disease pathology remain poorly defined. In this study, we demonstrated that SAVI mice harboring the N153S STING mutation exhibit diverse disease phenotypes, with a subset developing severe colitis and diarrhea alongside exacerbated systemic inflammation. These diarrheal SAVI mice showed pronounced dysbiosis, marked by reduced short-chain fatty acid-producing bacteria and an enrichment of segmented filamentous bacteria. This microbial imbalance was accompanied by elevated levels of both microbial and host-derived cyclic dinucleotides (CDNs), potent activators of the STING pathway. Notably, antibiotic treatment ameliorated inflammation, underscoring the role of dysbiosis in driving STING-mediated autoinflammation. Furthermore, in SAVI patients, elevated systemic microbial and host-derived CDNs were observed. In conditions such as systemic lupus erythematosus (SLE)-a heterogeneous autoimmune disease with potential STING involvement-systemic microbial CDNs were significantly correlated with disease biomarkers, including type I interferon scores and anti-dsDNA antibodies. In contrast, no such correlations were observed in STING-independent conditions like rheumatoid arthritis (RA). Importantly, this study highlights that both microbial and host-derived CDNs are key drivers of STING activation, suggesting that personalized treatment strategies could target cGAS or the microbiome based on a patient's specific CDN profile. These findings position systemic CDNs as valuable biomarkers and therapeutic targets for STING-driven diseases.

Exploring the Probiotic Potential of Bacteroides spp. Within One Health Paradigm

Probiotics are pivotal in maintaining or restoring the balance of human intestinal microbiota, a crucial factor in mitigating diseases and preserving the host's health. Exploration into Bacteroides spp. reveals substantial promise in their development as next-generation probiotics due to their profound interaction with host immune cells and capability to regulate the microbiome's metabolism by significantly impacting metabolite production. These beneficial bacteria exhibit potential in ameliorating various health issues such as intestinal disorders, cardiovascular diseases, behavioral disorders, and even cancer. Though it's important to note that a high percentage of them are as well opportunistic pathogens, posing risks under certain conditions. Studies highlight their role in modifying immune responses and improving health conditions by regulating lymphocytes, controlling metabolism, and preventing inflammation and cancer. The safety and efficacy of Bacteroides strains are currently under scrutiny by the European Commission for authorization in food processing, marking a significant step towards their commercialization. The recent advancements in bacterial isolation and sequencing methodologies, coupled with the integration of Metagenome-Assembled Genomes (MAGs) binning from metagenomics data, continue to unveil the potential of Bacteroides spp., aiding in the broader understanding and application of these novel probiotics in health and disease management.

ArfGAP2 promotes STING proton channel activity, cytokine transit, and autoinflammation

Stimulator of interferon genes (STING) transmits signals downstream of the cytosolic DNA sensor cyclic guanosine monophosphate-AMP synthase (cGAS), leading to transcriptional upregulation of cytokines. However, components of the STING signaling pathway, such as IRF3 and IFNAR1, are not essential for autoinflammatory disease in STING gain-of-function (STING-associated vasculopathy with onset in infancy [SAVI]) mice. Recent discoveries revealed that STING also functions as a proton channel that deacidifies the Golgi apparatus. Because pH impacts Golgi enzyme activity, protein maturation, and trafficking, we hypothesized that STING proton channel activity influences multiple Golgi functions. Here, we show that STING-mediated proton efflux non-transcriptionally regulates Golgi trafficking of protein cargos. This process requires the Golgi-associated protein ArfGAP2, a cell-type-specific dual regulator of STING-mediated proton efflux and signaling. Deletion of ArfGAP2 in hematopoietic and endothelial cells markedly reduces STING-mediated cytokine and chemokine secretion, immune cell activation, and autoinflammatory pathology in SAVI mice. Thus, ArfGAP2 facilitates STING-mediated signaling and cytokine release in hematopoietic cells, significantly contributing to autoinflammatory disease pathogenesis.

Tissue inflammation induced by constitutively active STING is mediated by enhanced TNF signaling

Constitutive activation of STING by gain-of-function mutations triggers manifestation of the systemic autoinflammatory disease STING-associated vasculopathy with onset in infancy (SAVI). In order to investigate the role of signaling by tumor necrosis factor (TNF) in SAVI, we used genetic inactivation of TNF receptors 1 and 2 in murine SAVI, which is characterized by T cell lymphopenia, inflammatory lung disease, and neurodegeneration. Genetic inactivation of TNFR1 and TNFR2, however, rescued the loss of thymocytes, reduced interstitial lung disease, and neurodegeneration. Furthermore, genetic inactivation of TNFR1 and TNFR2 blunted transcription of cytokines, chemokines, and adhesions proteins, which result from chronic STING activation in SAVI mice. In addition, increased transendothelial migration of neutrophils was ameliorated. Taken together, our results demonstrate a pivotal role of TNFR signaling in the pathogenesis of SAVI in mice and suggest that available TNFR antagonists could ameliorate SAVI in patients.

Involvement of gut microbiota in chlorpyrifos-induced subchronic toxicity in mice

Chlorpyrifos (CPF) is one of the most widely used organophosphorus pesticides all over the world. Unfortunately, long-term exposure to CPF may cause considerable toxicity to organisms. Some evidence suggests that the intestinal microbial community may be involved in regulating the toxicity of CPF. In this study, we explored if the intestinal microbial community is involved in regulating the toxicity of CPF. Adult mice were continuously exposed to CPF (4 mg/kg body weight /day) for 10 weeks with or without a 2-week pretreatment of antibiotics to change the ecological structure of intestinal microorganisms in advance. Pathological changes in the liver and kidneys were examined and the biochemical parameters in serum for liver and kidney functions were detected, and changes in the intestinal microbial community of the mice were measured. The results showed that subchronic exposure to low-dose CPF caused an ecological imbalance in the intestinal flora and caused pathological damage to the liver and kidneys. Serum biochemical indicators for liver function such as alanine aminotransferase and total bile acids contents and renal biochemical indicators such as urea nitrogen and creatinine were disrupted. Changes in intestinal microbial community structure by using antibiotics in advance can effectively alleviate the pathological and functional damage to the liver and kidneys caused by CPF exposure. Further analysis showed that intestinal microorganisms such as Saccharibacteria (TM7), Odoribacter, Enterococcus and AF12 genera may be involved in managing the toxicity of CPF. Together, our results indicated that long-term low-dose CPF exposure could induce hepatotoxicity and nephrotoxicity, and liver and kidney damage may be mitigated by altering the ecology of intestinal microorganisms.

The microbiome: an integral player in immune homeostasis and inflammation in the respiratory tract

The last decade of microbiome research has highlighted its fundamental role in systemic immune and metabolic homeostasis. The microbiome plays a prominent role during gestation and into early life, when maternal lifestyle factors shape immune development of the newborn. Breast milk further shapes gut colonization, supporting the development of tolerance to commensal bacteria and harmless antigens while preventing outgrowth of pathogens. Environmental microbial and lifestyle factors that disrupt this process can dysregulate immune homeostasis, predisposing infants to atopic disease and childhood asthma. In health, the low-biomass lung microbiome, together with inhaled environmental microbial constituents, establishes the immunological set point that is necessary to maintain pulmonary immune defense. However, in disease perturbations to immunological and physiological processes allow the upper respiratory tract to act as a reservoir of pathogenic bacteria, which can colonize the diseased lung and cause severe inflammation. Studying these host-microbe interactions in respiratory diseases holds great promise to stratify patients for suitable treatment regimens and biomarker discovery to predict disease progression. Preclinical studies show that commensal gut microbes are in a constant flux of cell division and death, releasing microbial constituents, metabolic by-products, and vesicles that shape the immune system and can protect against respiratory diseases. The next major advances may come from testing and utilizing these microbial factors for clinical benefit and exploiting the predictive power of the microbiome by employing multiomics analysis approaches.

What we need to know about the germ-free animal models

The gut microbiota (GM), as a forgotten organ, refers to the microbial community that resides in the gastrointestinal tract and plays a critical role in a variety of physiological activities in different body organs. The GM affects its targets through neurological, metabolic, immune, and endocrine pathways. The GM is a dynamic system for which exogenous and endogenous factors have negative or positive effects on its density and composition. Since the mid-twentieth century, laboratory animals are known as the major tools for preclinical research; however, each model has its own limitations. So far, two main models have been used to explore the effects of the GM under normal and abnormal conditions: the isolated germ-free and antibiotic-treated models. Both methods have strengths and weaknesses. In many fields of host-microbe interactions, research on these animal models are known as appropriate experimental subjects that enable investigators to directly assess the role of the microbiota on all features of physiology. These animal models present biological model systems to either study outcomes of the absence of microbes, or to verify the effects of colonization with specific and known microbial species. This paper reviews these current approaches and gives advantages and disadvantages of both models.

Regulation of cGAS and STING signaling during inflammation and infection

Stimulator of interferon genes (STING) is a sensor of cyclic dinucleotides including cyclic GMP-AMP, which is produced by cyclic GMP-AMP synthase (cGAS) in response to cytosolic DNA. The cGAS-STING signaling pathway regulates both innate and adaptive immune responses, as well as fundamental cellular functions such as autophagy, senescence, and apoptosis. Mutations leading to constitutive activation of STING cause devastating human diseases. Thus, the cGAS-STING pathway is of great interest because of its role in diverse cellular processes and because of the potential therapeutic implications of targeting cGAS and STING. Here, we review molecular and cellular mechanisms of STING signaling, and we propose a framework for understanding the immunological and other cellular functions of STING in the context of disease.

Elucidating gut microbiota and metabolite patterns shaped by goat milk-based infant formula feeding in mice colonized by healthy infant feces

The gut microbiota plays an evolutionarily conserved role in host metabolism, which is influenced by diet. Here, we investigated differences in shaping the gut microbiota and regulating metabolism in cow milk-based infant formula, goat milk-based infant formula, and mix milk-based infant formula compared with pasteurized human milk. 16S rRNA results showed that goat milk-based infant formula selectively increased the relative abundance of Blautia, Roseburia, Alistites and Muribaculum in the gut compared to other infant formulas. Metabolomics identification indicated that goat milk-based infant formula mainly emphasized bile acid biosynthesis, arachidonic acid metabolism and steroid biosynthesis metabolic pathways. Metabolites associated with these metabolic pathways were positively associated with increased microorganisms in goat milk-based infant formula, particularly Alistipes. Furthermore, we found a deficiency of Akkermansia abundance in three infant formula-fed compared to pasteurizedhuman milk-fed. This study presents new insights into the improvement and application of goat milk-based infant formulas in terms of intestinal microecology.

Vascular traffic control of neutrophil recruitment to the liver by microbiota-endothelium crosstalk

During bloodstream infections, neutrophils home to the liver as part of an intravascular immune response to eradicate blood-borne pathogens, but the mechanisms regulating this crucial response are unknown. Using in vivo imaging of neutrophil trafficking in germ-free and gnotobiotic mice, we demonstrate that the intestinal microbiota guides neutrophil homing to the liver in response to infection mediated by the microbial metabolite D-lactate. Commensal-derived D-lactate augments neutrophil adhesion in the liver independent of granulopoiesis in bone marrow or neutrophil maturation and activation in blood. Instead, gut-to-liver D-lactate signaling primes liver endothelial cells to upregulate adhesion molecule expression in response to infection and promote neutrophil adherence. Targeted correction of microbiota D-lactate production in a model of antibiotic-induced dysbiosis restores neutrophil homing to the liver and reduces bacteremia in a model of Staphylococcus aureus infection. These findings reveal long-distance traffic control of neutrophil recruitment to the liver by microbiota-endothelium crosstalk.

Type-1 interferon-dependent and -independent mechanisms in cyclic GMP-AMP synthase-stimulator of interferon genes-driven auto-inflammation

The cyclic cyclic gaunosine monophosphate adenosine monophosphate (GMP-AMP) synthase-stimulator of interferon genes (cGAS-STING) pathway senses cytosolic dsDNA and initiates immune responses against pathogens. It is also implicated in several auto-inflammatory diseases known as monogenic interferonopathies, specifically Three prime repair exonuclease 1 (Trex1) loss-of-function (LOF), Dnase2 LOF, and stimulator of interferon genes-associated-vasculopathy-with-onset-in-infancy (SAVI). Although monogenic interferonopathies have diverse clinical presentations, they are distinguished by the elevation of type-1 interferons (T1IFNs). However, animal models have demonstrated that T1IFNs contribute to only some disease outcomes and that cGAS-STING activation also promotes T1IFN-independent pathology. For example, while T1IFNs drive the immunopathology associated with Trex1 LOF, disease in Dnase2 LOF is partially independent of T1IFNs, while disease in SAVI appears to occur entirely independent of T1IFNs. Additionally, while the cGAS-STING pathway is well characterized in hematopoietic cells, these animal models point to important roles for STING activity in nonhematopoietic cells in disease. Together, these models illustrate the complex role that cGAS-STING-driven responses play in the pathogenesis of inflammatory diseases across tissues.

Fucosylated Chondroitin Sulfate against Parkinson's Disease through Inhibiting Inflammation Induced by Gut Dysbiosis

Growing evidence for the importance of the gut-brain axis in Parkinson's disease (PD) has attracted researchers' interest in the possible application of microbiota-based treatment approaches. Using a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model, we looked into the prospect of treating PD with fucosylated chondroitin sulfate obtained from sea cucumbers Isostichopus badionotus (fCS-Ib). We showed that giving fCS-Ib polysaccharide orally greatly reduced the motor deficits, dopamine depletion, and alpha-synuclein increase caused by MPTP in the substantia nigra (SN). It appears that the anti-PD action of fCS-Ib polysaccharide could be attained by squelching inflammation. Glial cell hyperactivation in SN and overproduction of proinflammatory substances in serum could both be suppressed by fCS-Ib polysaccharide injection. The bacterial DNA in fresh colonic feces was submitted to 16S rRNA and untargeted metabolic analyses to confirm the participation of the microbiota-gut-brain axis in the aforementioned interpretation. The findings showed that the MPTP treatment-induced decrease in norank_f_Muribaculaceae and the increase in Staphylococcus were reversed by the administration of fCS-Ib polysaccharide. The NF-κB signaling pathway was shown to be involved in the fCS-Ib polysaccharide-induced anti-inflammation. In conclusion, our research demonstrated for the first time how fCS-Ib polysaccharide combats PD by reducing inflammation caused by gut microbial dysbiosis.

The IFN-γ receptor promotes immune dysregulation and disease in STING gain-of-function mice

STING gain-of-function mutations cause STING-associated vasculopathy with onset in infancy (SAVI) in humans, a disease characterized by spontaneous lung inflammation and fibrosis. Mice with STING gain-of-function mutations (SAVI mice) develop αβ T cell–dependent lung disease and also lack lymph nodes. Although SAVI has been regarded as a type I interferonopathy, the relative contributions of the three interferon receptors are incompletely understood. Here, we show that STING gain of function led to upregulation of IFN-γ–induced chemokines in the lungs of SAVI mice and that deletion of the type II IFN receptor (IFNGR1), but not the type I IFN receptor (IFNAR1) or type III IFN receptor (IFNλR1), ameliorated lung disease and restored lymph node development in SAVI mice. Furthermore, deletion of IFNGR1, but not IFNAR1 or IFNλR1, corrected the ratio of effector to Tregs in SAVI mice and in mixed bone marrow chimeric mice. Finally, cultured SAVI mouse macrophages were hyperresponsive to IFN-γ, but not IFN-β, in terms of Cxcl9 upregulation and cell activation. These results demonstrate that IFNGR1 plays a major role in autoinflammation and immune dysregulation mediated by STING gain of function.

Role of the cGAS-STING pathway in systemic and organ-specific diseases

Cells are equipped with numerous sensors that recognize nucleic acids, which probably evolved for defence against viruses. Once triggered, these sensors stimulate the production of type I interferons and other cytokines that activate immune cells and promote an antiviral state. The evolutionary conserved enzyme cyclic GMP-AMP synthase (cGAS) is one of the most recently identified DNA sensors. Upon ligand engagement, cGAS dimerizes and synthesizes the dinucleotide second messenger 2',3'-cyclic GMP-AMP (cGAMP), which binds to the endoplasmic reticulum protein stimulator of interferon genes (STING) with high affinity, thereby unleashing an inflammatory response. cGAS-binding DNA is not restricted by sequence and must only be >45 nucleotides in length; therefore, cGAS can also be stimulated by self genomic or mitochondrial DNA. This broad specificity probably explains why the cGAS-STING pathway has been implicated in a number of autoinflammatory, autoimmune and neurodegenerative diseases; this pathway might also be activated during acute and chronic kidney injury. Therapeutic manipulation of the cGAS-STING pathway, using synthetic cyclic dinucleotides or inhibitors of cGAMP metabolism, promises to enhance immune responses in cancer or viral infections. By contrast, inhibitors of cGAS or STING might be useful in diseases in which this pro-inflammatory pathway is chronically activated.

Gut Microbiota Ecosystem Governance of Host Inflammation, Mitochondrial Respiration and Skeletal Homeostasis

Osteoporosis and osteoarthritis account for the leading causes of musculoskeletal dysfunction in older adults. Senescent chondrocyte overburden, inflammation, oxidative stress, subcellular organelle dysfunction, and genomic instability are prominent features of these age-mediated skeletal diseases. Age-related intestinal disorders and gut dysbiosis contribute to host tissue inflammation and oxidative stress by affecting host immune responses and cell metabolism. Dysregulation of gut microflora correlates with development of osteoarthritis and osteoporosis in humans and rodents. Intestinal microorganisms produce metabolites, including short-chain fatty acids, bile acids, trimethylamine N-oxide, and liposaccharides, affecting mitochondrial function, metabolism, biogenesis, autophagy, and redox reactions in chondrocytes and bone cells to regulate joint and bone tissue homeostasis. Modulating the abundance of Lactobacillus and Bifidobacterium, or the ratio of Firmicutes and Bacteroidetes, in the gut microenvironment by probiotics or fecal microbiota transplantation is advantageous to suppress age-induced chronic inflammation and oxidative damage in musculoskeletal tissue. Supplementation with gut microbiota-derived metabolites potentially slows down development of osteoarthritis and osteoporosis. This review provides latest molecular and cellular insights into the biological significance of gut microorganisms and primary and secondary metabolites important to cartilage and bone integrity. It further highlights treatment options with probiotics or metabolites for modulating the progression of these two common skeletal disorders.

STING Agonists/Antagonists: Their Potential as Therapeutics and Future Developments

The cGAS STING pathway has received much attention in recent years, and it has been recognized as an important component of the innate immune response. Since the discovery of STING and that of cGAS, many observations based on preclinical models suggest that the faulty regulation of this pathway is involved in many type I IFN autoinflammatory disorders. Evidence has been accumulating that cGAS/STING might play an important role in pathologies beyond classical immune diseases, as in, for example, cardiac failure. Human genetic mutations that result in the activation of STING or that affect the activity of cGAS have been demonstrated as the drivers of rare interferonopathies affecting young children and young adults. Nevertheless, no data is available in the clinics demonstrating the therapeutic benefit in modulating the cGAS/STING pathway. This is due to the lack of STING/cGAS-specific low molecular weight modulators that would be qualified for clinical exploration. The early hopes to learn from STING agonists, which have reached the clinics in recent years for selected oncology indications, have not yet materialized since the initial trials are progressing very slowly. In addition, transforming STING agonists into potent selective antagonists has turned out to be more challenging than expected. Nevertheless, there has been progress in identifying novel low molecular weight compounds, in some cases with unexpected mode of action, that might soon move to clinical trials. This study gives an overview of some of the potential indications that might profit from modulation of the cGAS/STING pathway and a short overview of the efforts in identifying STING modulators (agonists and antagonists) suitable for clinical research and describing their potential as a "drug".