Induction of pro-inflammatory cytokines by 29-kDa FN-f via cGAS/STING pathway

Unravelling the interplay between ER stress, UPR and the cGAS-STING pathway: Implications for osteoarthritis pathogenesis and treatment strategy

Osteoarthritis (OA) is a debilitating chronic degenerative disease affecting the whole joint organ leading to pain and disability. Cellular stress and injuries trigger inflammation and the onset of pathophysiological changes ensue after irreparable damage and inability to resolve inflammation, impeding the completion of the healing process. Extracellular matrix (ECM) degradation leads to dysregulated joint tissue metabolism. The reparative effort induces the proliferation of hypertrophic chondrocytes and matrix protein synthesis. Aberrant protein synthesis leads to endoplasmic reticulum (ER) stress and chondrocyte apoptosis with consequent cartilage matrix loss. These events in a vicious cycle perpetuate inflammation, hindering the restoration of normal tissue homeostasis. Recent evidence suggests that inflammatory responses and chondrocyte apoptosis could be caused by the activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling axis in response to DNA damage. It has been reported that there is a crosstalk between ER stress and cGAS-STING signalling in cellular senescence and other diseases. Based on recent evidence, this review discusses the role of ER stress, Unfolded Protein Response (UPR) and cGAS-STING pathway in mediating inflammatory responses in OA.

TBK1 pharmacological inhibition mitigates osteoarthritis through attenuating inflammation and cellular senescence in chondrocytes

Objectives

TANK-binding kinase 1 (TBK1) is pivotal in autoimmune and inflammatory diseases, yet its role in osteoarthritis (OA) remains elusive. This study sought to elucidate the effect of the TBK1 inhibitor BX795 on OA and to delineate the underlying mechanism by which it mitigates OA.

Methods

Interleukin-1 Beta (IL-1β) was utilized to simulate inflammatory responses and extracellular matrix degradation in vitro. In vivo, OA was induced in 8-week-old mice through destabilization of the medial meniscus surgery. The impact of BX795 on OA was evaluated using histological analysis, X-ray, micro-CT, and the von Frey test. Additionally, Western blot, RT-qPCR, and immunofluorescence assays were conducted to investigate the underlying mechanisms of BX795.

Results

Phosphorylated TBK1 (P-TBK1) levels were found to be elevated in OA knee cartilage of both human and mice. Furthermore, intra-articular injection of BX795 ameliorated cartilage degeneration and alleviated OA-associated pain. BX795 also counteracted the suppression of anabolic processes and the augmentation of catabolic activity, inflammation, and senescence observed in the OA mice. In vitro studies revealed that BX795 reduced P-TBK1 levels and reversed the effects of anabolism inhibition, catabolism promotion, and senescence induction triggered by IL-1β. Mechanistically, BX795 inhibited the IL-1β-induced activation of the cGAS-STING and TLR3-TRIF signaling pathways in chondrocytes.

Conclusions

Pharmacological inhibition of TBK1 with BX795 protects articular cartilage by inhibiting the activation of the cGAS-STING and TLR3-TRIF signaling pathways. This action attenuates inflammatory responses and cellular senescence, positioning BX795 as a promising therapeutic candidate for OA treatment.

The translational potential of this article

This study furnishes experimental evidence and offers a potential mechanistic explanation supporting the efficacy of BX795 as a promising candidate for OA treatment.

Synoviocytes assist in modulating the effect of Ross River virus infection in micromass-cultured primary human chondrocytes

Introduction. Ross River virus (RRV) is a mosquito-borne virus prevalent in Australia and the islands of the South Pacific, where it causes an arthritogenic illness with a hallmark feature of severe joint pain. The joint space is a unique microenvironment that contains cartilage and synovial fluid. Chondrocytes and synoviocytes are crucial components of the joint space and are known targets of RRV infection.Hypothesis/Gap statement. Understanding the relationship between synoviocytes and chondrocytes during RRV infection will provide further insights into RRV-induced joint pathology.Methodology. To better understand the unique dynamics of these cells during RRV infection, we used primary chondrocytes cultured in physiologically relevant micromasses. We then directly infected micromass chondrocytes or infected primary fibroblast-like synoviocytes (FLS), co-cultured with micromass chondrocytes. Micromass cultures and supernatants were collected and analysed for viral load with a PCR array of target genes known to play a role in arthritis.Results. We show that RRV through direct or secondary infection in micromass chondrocytes modulates the expression of cellular factors that likely contribute to joint inflammation and disease pathology, as well as symptoms such as pain. More importantly, while we show that RRV can infect micromass-cultured chondrocytes via FLS infection, FLS themselves affect the regulation of cellular genes known to contribute to arthritis.Conclusion. Single-cell culture systems lack the complexity of in vivo systems, and understanding the interaction between cell populations is crucial for deciphering disease pathology, including for the development of effective therapeutic strategies.

CDC7 inhibition drives an inflammatory response and a p53-dependent senescent-like state in breast epithelial cells

Drugs that block DNA replication prevent cell proliferation, which may result in anticancer activity. The latter is dependent on the drug's mode of action as well as on cell type-dependent responses to treatment. The inhibition of Cell division cycle 7-related protein kinase (CDC7), a key regulator of DNA replication, decreases the efficiency of origin firing and hampers the restarting of paused replication forks. Here, we show that upon prolonged CDC7 inhibition, breast-derived MCF10A cells progressively withdraw from the cell cycle and enter a reversible senescent-like state. This is characterised by the rewiring of the transcriptional programme with the induction of cytokine and chemokine expression and correlates with the accumulation of Cyclic GMP-AMP synthase (cGAS)-positive micronuclei. Importantly, cell fate depends on Cellular tumour antigen p53 (p53) function as cells no longer enter senescence but are funnelled into apoptosis upon p53 knockout. This work uncovers key features of the secondary response to CDC7 inhibitors, which could aid the development of these compounds as anticancer drugs.

cGAS-STING pathway in pathogenesis and treatment of osteoarthritis and rheumatoid arthritis

Osteoarthritis (OA) and Rheumatoid Arthritis (RA) are significant health concerns with notable prevalence and economic impact. RA, affecting 0.5% to 1.0% of the global population, leads to chronic joint damage and comorbidities. OA, primarily afflicting the elderly, results in joint degradation and severe pain. Both conditions incur substantial healthcare expenses and productivity losses. The cGAS-STING pathway, consisting of cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING), is a crucial component of mammalian immunity. This pathway is responsible for detecting foreign DNA, particularly double-stranded DNA (dsDNA), triggering innate immune defense responses. When cGAS recognizes dsDNA, it catalyzes the synthesis of cyclic GMP-AMP (cGAMP), which then binds to and activates STING. Activated STING, in turn, initiates downstream signaling events leading to the production of interferons and other immune mediators. The cGAS-STING pathway is essential for defending against viral infections and maintaining cellular balance. Dysregulation of this pathway has been implicated in various inflammatory diseases, including arthritis, making it a target for potential therapeutic interventions. Understanding the intricate molecular signaling network of cGAS-STING in these arthritis forms offers potential avenues for targeted therapies. Addressing these challenges through improved early detection, comprehensive management, and interventions targeting the cGAS-STING pathway is crucial for alleviating the impact of OA and RA on individuals and healthcare systems. This review offers an up-to-date comprehension of the cGAS-STING pathway's role in the development and therapeutic approaches for these arthritis types.

A conserved methyltransferase active site residue of Zika virus NS5 is required for the restriction of STING activation and interferon expression

Zika virus (ZIKV) is a re-emerging RNA virus and causes major public health events due to its link to severe neurological complications in foetuses and neonates. The cGAS-STING signalling pathway regulates innate immunity and plays an important role in the invasion of DNA and RNA viruses. This study reveals a distinct mechanism by which ZIKV restricts the cGAS-STING signalling to repress IFN-β expression. ZIKV attenuates IFN-β expression induced by DNA viruses (herpes simplex virus type 1, HSV-1) or two double-stranded DNAs (dsDNA90 and HSV120) in mouse embryonic fibroblasts (MEFs). Notably, ZIKV NS5, the viral RNA-dependent RNA polymerase, was responsible for the repression of IFN-β. NS5 interacts with STING in the cytoplasm, suppresses IRF3 phosphorylation and nucleus localization and promotes the cleavage of STING K48-linked polyubiquitination. Furthermore, the NS5 methyltransferase (MTase) domain interacts with STING to restrict STING-induced IFN-β expression. Interestingly, point mutation analyses of conserved methyltransferase active site residue D146 indicate that it is critical for repressing IFN-β expression induced by STING stimulation in cGAS-STING signalling.

Cartilage extracellular matrix-derived matrikines in osteoarthritis

Osteoarthritis (OA) is among the most frequent diseases of the musculoskeletal system. Degradation of cartilage extracellular matrix (ECM) is a hallmark of OA. During the degradation process, intact/full-length proteins and proteolytic fragments are released which then might induce different downstream responses via diverse receptors, therefore leading to different biological consequences. Collagen type II and the proteoglycan aggrecan are the most abundant components of the cartilage ECM. However, over the last decades, a large number of minor components have been identified and for some of those, a role in the manifold processes associated with OA has already been demonstrated. To date, there is still no therapy able to halt or cure OA. A better understanding of the matrikine landscape occurring with or even preceding obvious degenerative changes in joint tissues is needed and might help to identify molecules that could serve as biomarkers, druggable targets, or even be blueprints for disease modifying drug OA drugs. For this narrative review, we screened PubMed for relevant literature in the English language and summarized the current knowledge regarding the function of selected ECM molecules and the derived matrikines in the context of cartilage and OA.

Potential health risks of mRNA-based vaccine therapy: A hypothesis

Therapeutic applications of synthetic mRNA were proposed more than 30 years ago, and are currently the basis of one of the vaccine platforms used at a massive scale as part of the public health strategy to get COVID-19 under control. To date, there are no published studies on the biodistribution, cellular uptake, endosomal escape, translation rates, functional half-life and inactivation kinetics of synthetic mRNA, rates and duration of vaccine-induced antigen expression in different cell types. Furthermore, despite the assumption that there is no possibility of genomic integration of therapeutic synthetic mRNA, only one recent study has examined interactions between vaccine mRNA and the genome of transfected cells, and reported that an endogenous retrotransposon, LINE-1 is unsilenced following mRNA entry to the cell, leading to reverse transcription of full length vaccine mRNA sequences, and nuclear entry. This finding should be a major safety concern, given the possibility of synthetic mRNA-driven epigenetic and genomic modifications arising. We propose that in susceptible individuals, cytosolic clearance of nucleotide modified synthetic (nms-mRNAs) is impeded. Sustained presence of nms-mRNA in the cytoplasm deregulates and activates endogenous transposable elements (TEs), causing some of the mRNA copies to be reverse transcribed. The cytosolic accumulation of the nms-mRNA and the reverse transcribed cDNA molecules activates RNA and DNA sensory pathways. Their concurrent activation initiates a synchronized innate response against non-self nucleic acids, prompting type-I interferon and pro-inflammatory cytokine production which, if unregulated, leads to autoinflammatory and autoimmune conditions, while activated TEs increase the risk of insertional mutagenesis of the reverse transcribed molecules, which can disrupt coding regions, enhance the risk of mutations in tumour suppressor genes, and lead to sustained DNA damage. Susceptible individuals would then expectedly have an increased risk of DNA damage, chronic autoinflammation, autoimmunity and cancer. In light of the current mass administration of nms-mRNA vaccines, it is essential and urgent to fully understand the intracellular cascades initiated by cellular uptake of synthetic mRNA and the consequences of these molecular events.

Pathways Activated by Infected and Bystander Chondrocytes in Response to Ross River Virus Infection

Old world alphaviruses, such as Ross River virus (RRV), cause debilitating arthralgia during acute and chronic stages of the disease. RRV-induced cartilage degradation has been implicated as a cause of joint pain felt by RRV patients. Chondrocytes are a major cell type of cartilage and are involved in the production and maintenance of the cartilage matrix. It is thought that these cells may play a vital role in RRV disease pathogenesis. In this study, we used RNA-sequencing (RNA-Seq) to examine the transcriptomes of RRV-infected and bystander chondrocytes in the same environment. RRV containing green fluorescent protein (GFP) allowed for the separation of RRV-infected (GFP+) and bystander uninfected cells (GFP-). We found that whereas GFP+ and GFP- populations commonly presented similar gene expression profiles during infection, there were also unique signatures. For example, RIMS2 and FOXJ1 were unique to GFP+ cells, whilst Aim2 and CCL8 were only found in bystander chondrocytes. This indicates that careful selection of potential therapeutic targets is important to minimise adverse effects to the neighbouring uninfected cell populations. Our study serves as a resource to provide more information about the pathways and responses elicited by RRV in cells which are both infected and stimulated because of neighbouring infected cells.

Identification in synovial fluid of a new potential pathogenic player in arthropathies

STING (stimulator of interferon genes) has been recognized as an important signaling molecule in the innate immune response to cytosolic nucleic acids. Although it has been proposed that STING signaling pathway may play a pathogenic role in developing autoimmune and autoinflammatory diseases, its involvement in rheumatic disease processes remains to be elucidated. Here, we evaluated STING protein levels, expression and relationship with inflammatory parameters in synovial fluid (SF) of patients with psoriatic arthritis (PsA), rheumatoid arthritis (RA), gout, calcium pyrophosphate crystal-induced arthritis (CPP-IA), osteoarthritis (OA), and OA with CPP crystals (OA + CPP). The correlation with its negative regulator, nuclear factor erythroid 2-related factor 2 (Nrf2), was also investigated. SFs from 72 patients were analyzed for white blood cell (WBC) count, polymorphonuclear cell percentage (PMN%), and IL-1β, IL-6, IL-8, extra- and intracellular STING levels. STING and Nrf2 expression was also determined. WBC count and PMN% were greater in SF from inflammatory arthritis, while they were lower in OA groups. RA and gouty SFs have the highest levels of IL-1β, IL-8, and IL-6; while OA and OA + CPP showed the lowest concentrations. Gout and RA had the highest intracellular STING levels, while extracellular STING was greater in CPP-IA and OA SFs. STING was not detectable in PsA. STING mRNA was lower in PsA than other arthritides. Nrf2 mRNA was not detectable in OA. This study determines the presence of STING in SF of different arthritides, except for PsA, and suggests that it may be involved in pathogenesis and progression of arthropathies.

Gelsevirine improves age-related and surgically induced osteoarthritis in mice by reducing STING availability and local inflammation

Low-grade and chronic inflammation is recognized as an important mediator of the pathogenesis of osteoarthritis (OA). The aim of current work was to test the therapeutic effects of gelsevirine on age-related and surgically induced OA in mice and elucidate the underlying mechanism. The in vitro studies revealed that gelsevirine treatment mitigated IL-1β-induced inflammatory response and degeneration in cultured chondrocytes, evidenced by reduced apoptosis and expression of MMP3, MMP9, MMP13, IFNβ, TNFɑ, and Il6, and increased expression of Col2A and Il10. Furthermore, gelsevirine treatment in IL-1β-stimulated chondrocytes reduced the protein expression of stimulator of IFN genes (STING, also referred to Tmem173) and p-TBK1. Importantly, gelsevirine treatment did not provide further protection in STING-deficient chondrocytes against IL-1β stimulation. The in vivo studies revealed that gelsevirine treatment mitigated articular cartilage destruction in age-related and destabilization of the medial meniscus (DMM)-induced OA. Similarly, gelsevirine treatment did not provide further beneficial effects against OA in STING deficient mice. Mechanistically, gelsevirine promoted STING K48-linked poly-ubiquitination and MG-132 (a proteasome inhibitor) reversed the inhibitive effects of gelsevirine on IL-1β-induced activation of STING/TBK1 pathway in chondrocytes. Collectively, we identify that gelsevirine targets STING for K48 ubiquitination and degradation and improves age-related and surgically induced OA in mice.

Discovery of Non-Nucleotide Small-Molecule STING Agonists via Chemotype Hybridization

The identification of agonists of the stimulator of interferon genes (STING) pathway has been an area of intense research due to their potential to enhance innate immune response and tumor immunogenicity in the context of immuno-oncology therapy. Initial efforts to identify STING agonists focused on the modification of 2',3'-cGAMP (1) (an endogenous STING activator ligand) and other closely related cyclic dinucleotides (CDNs). While these efforts have successfully identified novel CDNs that have progressed into the clinic, their utility is currently limited to patients with solid tumors that STING agonists can be delivered to intratumorally. Herein, we report the discovery of a unique class of non-nucleotide small-molecule STING agonists that demonstrate antitumor activity when dosed intratumorally in a syngeneic mouse model.

Proteins from the DNA Damage Response: Regulation, Dysfunction, and Anticancer Strategies

Cells respond to genotoxic stress through a series of complex protein pathways called DNA damage response (DDR). These monitoring mechanisms ensure the maintenance and the transfer of a correct genome to daughter cells through a selection of DNA repair, cell cycle regulation, and programmed cell death processes. Canonical or non-canonical DDRs are highly organized and controlled to play crucial roles in genome stability and diversity. When altered or mutated, the proteins in these complex networks lead to many diseases that share common features, and to tumor formation. In recent years, technological advances have made it possible to benefit from the principles and mechanisms of DDR to target and eliminate cancer cells. These new types of treatments are adapted to the different types of tumor sensitivity and could benefit from a combination of therapies to ensure maximal efficiency.

The TLR-2/TonEBP signaling pathway regulates 29-kDa fibronectin fragment-dependent expression of matrix metalloproteinases

Tonicity-responsive enhancer-binding protein (TonEBP; nuclear factor of activated T cells 5) is a transcription factor that responds to changes in osmolality. However, recent studies have shown that it also modulates immune responses under inflammatory conditions independently of hyperosmolality. Fibronectin fragments (FN-fs), which are abundant in the synovial fluid of patients with osteoarthritis (OA), induce expression of matrix metalloproteinases (MMPs) via the toll-like receptor-2 (TLR-2) signaling pathway. In this study we examined whether TonEBP is involved in 29-kDa FN-f-induced expression of MMPs. The expression of TonEBP was significantly higher in human osteoarthritis compared with normal cartilage samples. 29-kDa FN-f affected the expression of MMPs 1, 3, and 13 via TonEBP, and expression and nuclear accumulation of TonEBP were induced by activation of the phospholipase C/NF-κB/MAPK signaling pathway and, in particular, modulated by TLR-2. In addition, 29-kDa FN-f induced the expression of osmoregulatory genes, including Tau-T, SMIT, and AR, as well as voltage-dependent calcium channels via the TonEBP/TLR-2 signaling pathway. These results show that 29-kDa FN-f upregulates MMPs in chondrocytes via the TLR-2/TonEBP signaling pathway.

Evaluation of biomarkers in liver following Solanum melongena green calyx administration in diabetic rats

Background

Solanum melongena green calyx (SMGC) has antioxidant properties. Diabetes mellitus (DM) increases oxidative stress and causes cellular damages in liver. This study attempts to show the protective effects of SMGC against morphometric, inflammatory, oxidative, and apoptotic changes in liver following DM induction.

Methods

For DM induction, the streptozotocin (60 mg/kg) was injected intraperitoneally. After the preparation of the SMGC extract, phytochemical content was analyzed. Sixty-four rats were categorized into 8 groups (n = 8); control, diabetic, SMGC, and diabetic + SMGC. SMGC administration was applied orally with doses of 100, 300, 500 mg/kg for 4 weeks. The assays of nitrite oxide, lipid peroxidation (LP), and Ferric Reducing Ability of Plasma (FRAP) were conducted for sample analysis. P53, Bcl2, and Bax genes expression, inflammatory cytokines, enzymes, and morphological features were measured. Apoptotic cell index, body weight, and levels of glucose and insulin were also analyzed. A one-way ANOVA test was used for statistical analysis.

Result

According to the phytochemical analysis, the SMGC is rich in Tannins and Saponins. Antioxidant values, p53 and Bax genes expression, inflammatory cytokines, enzymes, body weight, serum glucose, and morphometrical features were increased significantly (except insulin and FRAP levels and Bcl2 gene expression which were decreased) in diabetic group compared to the control group (P < 0.05). Also, evaluated parameters were reduced significantly (except insulin and FRAP levels and Bcl2 gene expression which were increased) in SMGC and diabetic + SMGC groups in comparison with the diabetic group (P < 0.05).

Conclusion

These findings revealed that the SMGC attenuates blood glucose levels in diabetic animals and also eliminates destructive effects of DM on liver through antioxidant features.

Cyclic GMP-AMP synthase promotes the inflammatory and autophagy responses in Huntington disease

Huntington disease (HD) is a genetic disorder caused by glutamine-expansion in the huntingtin (mHTT) protein, which affects motor, psychiatric, and cognitive function, but the mechanisms remain unclear. mHTT is known to induce DNA damage and affect autophagy, both associated with inflammatory responses, but what mediates all these were unknown. Here we report that cGAS, a DNA damage sensor, is highly upregulated in the striatum of a mouse model and HD human patient’s tissue. We found ribosomes, which make proteins, are robustly accumulated on the cGAS mRNA in HD cells. cGAS depletion decreases—and cGAS expression increases—both inflammatory and autophagy responses in HD striatal cells. Thus, cGAS is a therapeutic target for HD. Blocking cGAS will prevent/slow down HD symptoms.

Huntington disease (HD) is caused by an expansion mutation of the N-terminal polyglutamine of huntingtin (mHTT). mHTT is ubiquitously present, but it induces noticeable damage to the brain’s striatum, thereby affecting motor, psychiatric, and cognitive functions. The striatal damage and progression of HD are associated with the inflammatory response; however, the underlying molecular mechanisms remain unclear. Here, we report that cGMP-AMP synthase (cGAS), a DNA sensor, is a critical regulator of inflammatory and autophagy responses in HD. Ribosome profiling revealed that the cGAS mRNA has high ribosome occupancy at exon 1 and codon-specific pauses at positions 171 (CCG) and 172 (CGT) in HD striatal cells. Moreover, the protein levels and activity of cGAS (based on the phosphorylated STING and phosphorylated TBK1 levels), and the expression and ribosome occupancy of cGAS-dependent inflammatory genes (Ccl5 and Cxcl10) are increased in HD striatum. Depletion of cGAS diminishes cGAS activity and decreases the expression of inflammatory genes while suppressing the up-regulation of autophagy in HD cells. In contrast, reinstating cGAS in cGAS-depleted HD cells activates cGAS activity and promotes inflammatory and autophagy responses. Ribosome profiling also revealed that LC3A and LC3B, the two major autophagy initiators, show altered ribosome occupancy in HD cells. We also detected the presence of numerous micronuclei, which are known to induce cGAS, in the cytoplasm of neurons derived from human HD embryonic stem cells. Collectively, our results indicate that cGAS is up-regulated in HD and mediates inflammatory and autophagy responses. Thus, targeting the cGAS pathway may offer therapeutic benefits in HD.

Airway Epithelial cGAS Is Critical for Induction of Experimental Allergic Airway Inflammation

DNA damage could lead to the accumulation of cytosolic DNA, and the cytosolic DNA-sensing pathway has been implicated in multiple inflammatory diseases. However, the role of cytosolic DNA-sensing pathway in asthma pathogenesis is still unclear. This article explored the role of airway epithelial cyclic GMP-AMP synthase (cGAS), the major sensor of cytosolic dsDNA, in asthma pathogenesis. Cytosolic dsDNA accumulation in airway epithelial cells (ECs) was detected in the setting of allergic inflammation both in vitro and in vivo. Mice with cGAS deletion in airway ECs were used for OVA- or house dust mite (HDM)-induced allergic airway inflammation. Additionally, the effects of cGAS knockdown on IL-33-induced GM-CSF production and the mechanisms by which IL-33 induced cytosolic dsDNA accumulation in human bronchial epithelial (HBE) cells were explored. Increased accumulation of cytosolic dsDNA was observed in airway epithelium of OVA- or HDM-challenged mice and in HBE cells treated with IL-33. Deletion of cGAS in the airway ECs of mice significantly attenuated the allergic airway inflammation induced by OVA or HDM. Mechanistically, cGAS participates in promoting T_H2 immunity likely via regulating the production of airway epithelial GM-CSF. Furthermore, Mito-TEMPO could reduce IL-33-induced cytoplasmic dsDNA accumulation in HBE cells possibly through suppressing the release of mitochondrial DNA into the cytosol. In conclusion, airway epithelial cGAS plays an important role via sensing the cytosolic dsDNA in asthma pathogenesis and could serve as a promising therapeutic target against allergic airway inflammation.