Mycobacterium bovis Induces Endoplasmic Reticulum Stress Mediated-Apoptosis by Activating IRF3 in a Murine Macrophage Cell Line

ER-transiting bacterial toxins amplify STING innate immune responses and elicit ER stress

The cGAS/STING sensor system drives innate immune responses to intracellular microbial double-stranded DNA (dsDNA) and bacterial cyclic nucleotide second messengers (e.g., c-di-AMP). STING-dependent cell-intrinsic responses can increase resistance to microbial infection and speed pathogen clearance. Correspondingly, STING activation and signaling are known to be targeted for suppression by effectors from several bacterial pathogens. Whether STING responses are also positively regulated through sensing of specific bacterial effectors is less clear. We find that STING activation through dsDNA, by its canonical ligand 2'-3' cGAMP, or the small molecule DMXAA is potentiated following intracellular delivery of the AB5 toxin family member pertussis toxin from Bordetella pertussis or the B subunit of cholera toxin from Vibrio cholerae. Entry of pertussis toxin or cholera toxin B into mouse macrophages triggers markers of endoplasmic reticulum (ER) stress and enhances ligand-dependent STING responses at the level of STING receptor activation in a manner that is independent of toxin enzymatic activity. Our results provide an example in which STING responses integrate information about the presence of relevant ER-transiting bacterial toxins into the innate inflammatory response and may help to explain the in vivo adjuvant effects of catalytically inactive toxins.

Multiple unfolded protein response pathways cooperate to link cytosolic dsDNA release to stimulator of interferon gene activation

The double-stranded DNA (dsDNA) sensor STING has been increasingly implicated in responses to "sterile" endogenous threats and pathogens without nominal DNA or cyclic di-nucleotide stimuli. Previous work showed an endoplasmic reticulum (ER) stress response, known as the unfolded protein response (UPR), activates STING. Herein, we sought to determine if ER stress generated a STING ligand, and to identify the UPR pathways involved. Induction of IFN-β expression following stimulation with the UPR inducer thapsigargin (TPG) or oxygen glucose deprivation required both STING and the dsDNA-sensing cyclic GMP-AMP synthase (cGAS). Furthermore, TPG increased cytosolic mitochondrial DNA, and immunofluorescence visualized dsDNA punctae in murine and human cells, providing a cGAS stimulus. N-acetylcysteine decreased IFN-β induction by TPG, implicating reactive oxygen species (ROS). However, mitoTEMPO, a mitochondrial oxidative stress inhibitor did not impact TPG-induced IFN. On the other hand, inhibiting the inositol requiring enzyme 1 (IRE1) ER stress sensor and its target transcription factor XBP1 decreased the generation of cytosolic dsDNA. iNOS upregulation was XBP1-dependent, and an iNOS inhibitor decreased cytosolic dsDNA and IFN-β, implicating ROS downstream of the IRE1-XBP1 pathway. Inhibition of the PKR-like ER kinase (PERK) pathway also attenuated cytoplasmic dsDNA release. The PERK-regulated apoptotic factor Bim was required for both dsDNA release and IFN-β mRNA induction. Finally, XBP1 and PERK pathways contributed to cytosolic dsDNA release and IFN-induction by the RNA virus, Vesicular Stomatitis Virus (VSV). Together, our findings suggest that ER stressors, including viral pathogens without nominal STING or cGAS ligands such as RNA viruses, trigger multiple canonical UPR pathways that cooperate to activate STING and downstream IFN-β via mitochondrial dsDNA release.

Lovastatin-Induced Mitochondrial Oxidative Stress Leads to the Release of mtDNA to Promote Apoptosis by Activating cGAS-STING Pathway in Human Colorectal Cancer Cells

Statins are 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase inhibitors widely used in the treatment of hyperlipidemia. The inhibition of HMG-CoA reductase in the mevalonate pathway leads to the suppression of cell proliferation and induction of apoptosis. The cyclic GMP-AMP synthase (cGAS) stimulator of the interferon genes (STING) signaling pathway has been suggested to not only facilitate inflammatory responses and the production of type I interferons (IFN), but also activate other cellular processes, such as apoptosis. It has not been studied, however, whether cGAS-STING activation is involved in the apoptosis induced by statin treatment in human colorectal cancer cells. In this study, we reported that lovastatin impaired mitochondrial function, including the depolarization of mitochondrial membrane potential, reduction of oxygen consumption, mitochondrial DNA (mtDNA) integrity, and mtDNA abundance in human colorectal cancer HCT116 cells. The mitochondrial dysfunction markedly induced ROS production in mitochondria, whereas the defect in mitochondria respiration or depletion of mitochondria eliminated reactive oxygen species (ROS) production. The ROS-induced oxidative DNA damage by lovastatin treatment was attenuated by mitochondrial-targeted antioxidant mitoquinone (mitoQ). Upon DNA damage, mtDNA was released into the cytosol and bound to DNA sensor cGAS, thus activating the cGAS-STING signaling pathway to trigger a type I interferon response. This effect was not activated by nuclear DNA (nuDNA) or mitochondrial RNA, as the depletion of mitochondria compromised this effect, but not the knockdown of retinoic acid-inducible gene-1/melanoma differentiation-associated protein 5 (RIG-I/MDA5) adaptor or mitochondrial antiviral signaling protein (MAVS). Moreover, lovastatin-induced apoptosis was partly dependent on the cGAS-STING signaling pathway in HCT116 cells as the knockdown of cGAS or STING expression rescued cell viability and mitigated apoptosis. Similarly, the knockdown of cGAS or STING also attenuated the antitumor effect of lovastatin in the HCT116 xenograft model in vivo. Our findings suggest that lovastatin-induced apoptosis is at least partly mediated through the cGAS-STING signaling pathway by triggering mtDNA accumulation in the cytosol in human colorectal cancer HCT116 cells.

Multiple Unfolded Protein Response pathways cooperate to link cytosolic dsDNA release to Stimulator of Interferon Gene (STING) activation

The double-stranded DNA (dsDNA) sensor STING has been increasingly implicated in responses to "sterile" endogenous threats and pathogens without nominal DNA or cyclic di-nucleotide stimuli. Previous work showed an endoplasmic reticulum (ER) stress response, known as the unfolded protein response (UPR), activates STING. Herein, we sought to determine if ER stress generated a STING ligand, and to identify the UPR pathways involved. Induction of IFN-β expression following stimulation with the UPR inducer thapsigargin (TPG) or oxygen glucose deprivation required both STING and the dsDNA-sensing cyclic GMP-AMP synthase (cGAS). Furthermore, TPG increased cytosolic mitochondrial DNA, and immunofluorescence visualized dsDNA punctae in murine and human cells, providing a cGAS stimulus. N-acetylcysteine decreased IFN-β induction by TPG, implicating reactive oxygen species (ROS). However, mitoTEMPO, a mitochondrial oxidative stress inhibitor did not impact TPG-induced IFN. On the other hand, inhibiting the inositol requiring enzyme 1 (IRE1) ER stress sensor and its target transcription factor XBP1 decreased the generation of cytosolic dsDNA. iNOS upregulation was XBP1-dependent, and an iNOS inhibitor decreased cytosolic dsDNA and IFN-β, implicating ROS downstream of the IRE1-XBP1 pathway. Inhibition of the PKR-like ER kinase (PERK) pathway also attenuated cytoplasmic dsDNA release. The PERK-regulated apoptotic factor Bim was required for both dsDNA release and IFN-β mRNA induction. Finally, XBP1 and PERK pathways contributed to cytosolic dsDNA release and IFN-induction by the RNA virus, Vesicular Stomatitis Virus (VSV). Together, our findings suggest that ER stressors, including viral pathogens without nominal STING or cGAS ligands such as RNA viruses, trigger multiple canonical UPR pathways that cooperate to activate STING and downstream IFN-β via mitochondrial dsDNA release.

STING dependent BAX-IRF3 signaling results in apoptosis during late-stage Coxiella burnetii infection

STING (STimulator of Interferon Genes) is a cytosolic sensor for cyclic dinucleotides (CDNs) and initiates an innate immune response upon binding to CDNs. Coxiella burnetii is a Gram-negative obligate intracellular bacterium and the causative agent of the zoonotic disease Q fever. The ability of C. burnetii to inhibit host cell death is a critical factor in disease development. Previous studies have shown that C. burnetii inhibits host cell apoptosis at early stages of infection. However, during the late-stages of infection, there is host cell lysis resulting in the release of bacteria to infect bystander cells. Thus, we investigated the role of STING during late-stages of C. burnetii infection and examined STING's impact on host cell death. We show that the loss of STING results in higher bacterial loads and abrogates IFNβ and IL6 induction at 12 days post-infection. The absence of STING during C. burnetii infection significantly reduces apoptosis through decreased caspase-8 and -3 activation. During infection, STING activates IRF3 which interacts with BAX. BAX then translocates to the mitochondria, which is followed by mitochondrial membrane depolarization. This results in increased cytosolic mtDNA in a STING-dependent manner. The presence of increased cytosolic mtDNA results in greater cytosolic 2'-3' cGAMP, creating a positive feedback loop and leading to further increases in STING activation and its downstream signaling. Taken together, we show that STING signaling is critical for BAX-IRF3-mediated mitochondria-induced apoptosis during late-stage C. burnetii infection.

cGAS-STING, inflammasomes and pyroptosis: an overview of crosstalk mechanism of activation and regulation

BACKGROUND

Intracellular DNA-sensing pathway cGAS-STING, inflammasomes and pyroptosis act as critical natural immune signaling axes for microbial infection, chronic inflammation, cancer progression and organ degeneration, but the mechanism and regulation of the crosstalk network remain unclear. Cellular stress disrupts mitochondrial homeostasis, facilitates the opening of mitochondrial permeability transition pore and the leakage of mitochondrial DNA to cell membrane, triggers inflammatory responses by activating cGAS-STING signaling, and subsequently induces inflammasomes activation and the onset of pyroptosis. Meanwhile, the inflammasome-associated protein caspase-1, Gasdermin D, the CARD domain of ASC and the potassium channel are involved in regulating cGAS-STING pathway. Importantly, this crosstalk network has a cascade amplification effect that exacerbates the immuno-inflammatory response, worsening the pathological process of inflammatory and autoimmune diseases. Given the importance of this crosstalk network of cGAS-STING, inflammasomes and pyroptosis in the regulation of innate immunity, it is emerging as a new avenue to explore the mechanisms of multiple disease pathogenesis. Therefore, efforts to define strategies to selectively modulate cGAS-STING, inflammasomes and pyroptosis in different disease settings have been or are ongoing. In this review, we will describe how this mechanistic understanding is driving possible therapeutics targeting this crosstalk network, focusing on the interacting or regulatory proteins, pathways, and a regulatory mitochondrial hub between cGAS-STING, inflammasomes, and pyroptosis.

SHORT CONCLUSION

This review aims to provide insight into the critical roles and regulatory mechanisms of the crosstalk network of cGAS-STING, inflammasomes and pyroptosis, and to highlight some promising directions for future research and intervention.

cGAS-STING at the crossroads in cancer therapy

DNA is highly immunogenic, both exogenous and endogenous DNA can activate the pathogen-associated molecular pattern (PAMP) and danger-associated molecular pattern (DAMP), respectively, and hence activate the evolutionarily conserved cGAS-STING pathway for inflammatory responses. The cGAS-STING signaling pathway plays a very important role in the pathogenesis and progression of neoplastic diseases. For cancer therapy, there are some discrepancies on whether cGAS-STING should be inhibited or activated. Deregulated cGAS-STING signaling pathway might be the origin and pathogenesis of tumor, understanding and modulating cGAS-STING signaling holds great promise for cancer therapy. In this review article, we discuss the molecular mechanisms underlying cGAS-STING deregulation, highlighting the tumor inhibiting and promoting roles and challenges with cGAS-STING agonists in the context of cancer therapies.

STING promotes ferroptosis through NCOA4-dependent ferritinophagy in acute kidney injury

Ferroptosis in tubules has been implicated in the pathogenesis of acute kidney injury (AKI), whereas the regulatory mechanism remains unclear. The stimulator of interferon genes (STING) is previously recognized as a critical mediator of innate immunity via a DNA-sensing pathway and has been increasingly linked to lipid peroxidation, a hallmark of ferroptosis. Herein we investigated the role and the underlying mechanism of STING in AKI models established by ischemia/reperfusion (IR) in C57BL mice. The expression level of STING was predominantly increased in tubules of kidney after IR treatment. Besides, STING deficiency markedly alleviated IR-induced lipid peroxidation, tissue damage and renal dysfunction. Consistently, in vitro experiments demonstrated that the increase in ferroptotic cell death, lipid ROS production and the decrease in GSH peroxidase 4 (GPX4) expression in renal tubular cells subjected to ferroptosis agonist or hypoxia/reoxygenation intervention were all mitigated by genetic deficiency or pharmacological inhibition of STING, while all exacerbated by STING overexpression. Further, these detrimental effects of STING overexpression relied on the induction of ferritinophagy, i.e. autophagic degradation of ferritin, leading to iron overload. Mechanistically, STING mediated the initiation of ferritinophagy through interacting with nuclear receptor coactivator 4 (NCOA4), a fundamental receptor for the transfer of ferritin into lysosome. Collectively, STING contributes to ferroptosis during ischemic AKI through facilitating NCOA4-mediated ferritinophagy and shows the potential as a promising therapeutic choice for AKI.

Novel insight into cGAS-STING pathway in ischemic stroke: from pre- to post-disease

Ischemic stroke, a primary cause of disability and the second leading cause of mortality, has emerged as an urgent public health issue. Growing evidence suggests that the Cyclic GMP-AMP synthase (cGAS)- Stimulator of interferon genes (STING) pathway, a component of innate immunity, is closely associated with microglia activation, neuroinflammation, and regulated cell death in ischemic stroke. However, the mechanisms underlying this pathway remain inadequately understood. This article comprehensively reviews the existing literature on the cGAS-STING pathway and its multifaceted relationship with ischemic stroke. Initially, it examines how various risk factors and pre-disease mechanisms such as metabolic dysfunction and senescence (e.g., hypertension, hyperglycemia, hyperlipidemia) affect the cGAS-STING pathway in relation to ischemic stroke. Subsequently, we explore in depth the potential pathophysiological relationship between this pathway and oxidative stress, endoplasmic reticulum stress, neuroinflammation as well as regulated cell death including ferroptosis and PANoptosis following cerebral ischemia injury. Finally, it suggests that intervention targeting the cGAS-STING pathway may serve as promising therapeutic strategies for addressing neuroinflammation associated with ischemic stroke. Taken together, this review concludes that targeting the microglia cGAS-STING pathway may shed light on the exploration of new therapeutic strategies against ischemic stroke.

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Significance of the cGAS-STING Pathway in Health and Disease

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway plays a significant role in health and disease. In this pathway, cGAS, one of the major cytosolic DNA sensors in mammalian cells, regulates innate immunity and the STING-dependent production of pro-inflammatory cytokines, including type-I interferon. Moreover, the cGAS-STING pathway is integral to other cellular processes, such as cell death, cell senescence, and autophagy. Activation of the cGAS-STING pathway by "self" DNA is also attributed to various infectious diseases and autoimmune or inflammatory conditions. In addition, the cGAS-STING pathway activation functions as a link between innate and adaptive immunity, leading to the inhibition or facilitation of tumorigenesis; therefore, research targeting this pathway can provide novel clues for clinical applications to treat infectious, inflammatory, and autoimmune diseases and even cancer. In this review, we focus on the cGAS-STING pathway and its corresponding cellular and molecular mechanisms in health and disease.

The Chicken cGAS-STING Pathway Exerts Interferon-Independent Antiviral Function via Cell Apoptosis

It has been recently recognized that the DNA sensing innate immune cGAS-STING pathway exerts an IFN-independent antiviral function; however, whether and how chicken STING (chSTING) exerts such an IFN-independent antiviral activity is still unknown. Here, we showed that chSTING exerts an antiviral activity in HEK293 cells and chicken cells, independent of IFN production. chSTING was able to trigger cell apoptosis and autophagy independently of IFN, and the apoptosis inhibitors, rather than autophagy inhibitors, could antagonize the antiviral function of chSTING, suggesting the involvement of apoptosis in IFN-independent antiviral function. In addition, chSTING lost its antiviral function in IRF7-knockout chicken macrophages, indicating that IRF7 is not only essential for the production of IFN, but also participates in the other activities of chSTING, such as the apoptosis. Collectively, our results showed that chSTING exerts an antiviral function independent of IFN, likely via apoptosis.

Activation of cDCs and iNKT cells contributes to triptolide-induced hepatotoxicity via STING signaling pathway and endoplasmic reticulum stress

Triptolide (TP) exhibits therapeutic potential against multiple diseases. However, its application in clinics is limited by TP-induced hepatoxicity. TP can activate invariant natural killer T (iNKT) cells in the liver, shifting Th1 cytokine bias to Th2 cytokine bias. The damaging role of iNKT cells in TP-induced hepatoxicity has been established, and iNKT cell deficiency can mitigate hepatotoxicity. However, the activation of iNKT cells in vitro by TP requires the presence of antigen-presenting cells. Therefore, we hypothesized that TP could induce dendritic cells (DCs) to activate iNKT cells, thereby leading to hepatotoxicity. The hepatic conventional DCs (cDCs) exhibited immunogenic activities after TP administration, upregulating the expression of CD1d, co-stimulatory molecules, and IL-12. Neutralization with IL-12p40 antibody extenuated TP-induced hepatotoxicity and reduced iNKT cell activation, suggesting that IL-12 could cause liver injury by activating iNKT cells. TP triggered the activation and upregulation of STING signaling pathway and increased endoplasmic reticulum (ER) stress. Downregulation of STING reduced cDC immunogenicity, inhibiting the activation of iNKT cells and hepatic damage. These indicated the regulatory effects of STING pathway on cDCs and iNKT cells, and the important roles it plays in hepatoxicity. ER stress inhibitor, 4-phenylbutyrate (4-PBA), also suppressed iNKT cell activation and liver injury, which might be regulated by the STING signaling pathway. Our results demonstrated the possible mechanisms underlying TP-induced hepatoxicity, where the activation of cDCs and iNKT cells was stimulated by upregulated STING signaling and increased ER stress as a result of TP administration.

Gut microbiota and transcriptome dynamics in every-other-day fasting are associated with neuroprotection in rats with spinal cord injury

Introduction

Every-other-day fasting (EODF) is a classical intermittent fasting (IF) mode with neuroprotective effects that promotes motor function recovery after spinal cord injury (SCI) in rats. However, its dynamic effects on the gut microbiota and spinal cord transcriptome remain unknown.

Methods

In this study, 16S rRNA sequencing and RNA-seq analysis were used to investigate the effects of ad libitum (AL) and EODF dietary modes on the structural characteristics of rat gut microbiota in rats and the spinal cord transcriptome at various time points after SCI induction.

Results

Our results showed that both dietary modes affected the bacterial community composition in SCI rats, with EODF treatment inducing and suppressing dynamic changes in the abundances of potentially anti-inflammatory and pro-inflammatory bacteria. Furthermore, the differentially expressed genes (DEGs) enriched after EODF intervention in SCI rats were associated with various biological events, including immune inflammatory response, cell differentiation, protein modification, neural growth, and apoptosis. In particular, significant spatiotemporal differences were apparent in the DEGs associated with neuroprotection between the EODF and AL interventions. These DGEs were mainly focused on days 1, 3, and 7 after SCI. The relative abundance of certain genera was significantly correlated with DEGs associated with neuroprotective effects in the EODF-SCI group.

Discussion

Our results showed that EODF treatment may exert neuroprotective effects by modulating the transcriptome expression profile following SCI in rats. Furthermore, gut microbiota may be partially involved in mediating these effects.

PI3K/AKT/mTOR, NF-κB and ERS pathway participated in the attenuation of H2O2-induced IPEC-J2 cell injury by koumine

ETHNOPHARMACOLOGICAL RELEVANCE

Koumine, an indole alkaloid extracted from Gelsemium elegans Benth, exerts anti-inflammation and antioxidant activities. However, the effects of koumine on intestinal injury induced by H₂O₂ and its potential molecular mechanisms need larger studies.

AIM OF THE STUDY

We established an IPEC-J2 cell damage model induced by H₂O₂ to explore the protective mechanism of koumine on intestinal injury.

MATERIALS AND METHODS

In the experiment, cell damage models were made with hydrogen peroxide. To assess the protective effect of koumine on H₂O₂-induced IPEC-J2 cell injury, CCK-8, the release of LDH and ROS, transmission electron microscopy and Annexin V-FITC/PI were employed. Western Blot and Quantitative Real-time PCR were used to determine the potential alleviated mechanism of koumine on H₂O₂-trigged IPEC-J2 cell damage.

RESULTS

The results of CCK-8 and LDH implied that koumine has a mitigative effect on H₂O₂-induced cell damage via upregulating cell viability and suppressing cell membrane fragmentation. Simultaneously, koumine notably inhibited the level of pro-inflammatory factors (IL-1β, IL-6, IL-8, TNF-α and TGF-β), the over-production of ROS along with decreasing the injury of mitochondrion, endoplasmic reticulum and lysosome induced by H₂O₂. Moreover, koumine dramatically attenuated H₂O₂-triggered IPEC-J2 cell apoptosis and autophagy. Subsequently, Western blot analysis identified NF-ΚB, PI3K and ERS as possible pathway responsible for the protective effect of koumine on H₂O₂-stimulated IPEC-J2 cell inflammation.

CONCLUSIONS

This in vitro experimental study suggests that koumine suppresses the H₂O₂-induced activation of inflammatory pathways, oxidative injury, ER stress, apoptosis and autophagy, which provide a rationale for therapeutically use in major intestinal diseases.

How the Innate Immune DNA Sensing cGAS-STING Pathway Is Involved in Apoptosis

The cGAS-STING signaling axis can be activated by cytosolic DNA, including both non-self DNA and self DNA. This axis is used by the innate immune system to monitor invading pathogens and/or damage. Increasing evidence has suggested that the cGAS-STING pathway not only facilitates inflammatory responses and the production of type I interferons (IFN), but also activates other cellular processes, such as apoptosis. Recently, many studies have focused on analyzing the mechanisms of apoptosis induced by the cGAS-STING pathway and their consequences. This review gives a detailed account of the interplay between the cGAS-STING pathway and apoptosis. The cGAS-STING pathway can induce apoptosis through ER stress, NLRP3, NF-κB, IRF3, and IFN signals. Conversely, apoptosis can feed back to regulate the cGAS-STING pathway, suppressing it via the activation of caspases or promoting it via mitochondrial DNA (mtDNA) release. Apoptosis mediated by the cGAS-STING pathway plays crucial roles in balancing innate immune responses, resisting infections, and limiting tumor growth.

Constitutively active STING causes neuroinflammation and degeneration of dopaminergic neurons in mice

Stimulator of interferon genes (STING) is activated after detection of cytoplasmic dsDNA by cGAS (cyclic GMP-AMP synthase) as part of the innate immunity defence against viral pathogens. STING binds TANK-binding kinase 1 (TBK1). TBK1 mutations are associated with familial amyotrophic lateral sclerosis, and the STING pathway has been implicated in the pathogenesis of further neurodegenerative diseases. To test whether STING activation is sufficient to induce neurodegeneration, we analysed a mouse model that expresses the constitutively active STING variant N153S. In this model, we focused on dopaminergic neurons, which are particularly sensitive to stress and represent a circumscribed population that can be precisely quantified. In adult mice expressing N153S STING, the number of dopaminergic neurons was smaller than in controls, as was the density of dopaminergic axon terminals and the concentration of dopamine in the striatum. We also observed alpha-synuclein pathology and a lower density of synaptic puncta. Neuroinflammation was quantified by staining astroglia and microglia, by measuring mRNAs, proteins and nuclear translocation of transcription factors. These neuroinflammatory markers were already elevated in juvenile mice although at this age the number of dopaminergic neurons was still unaffected, thus preceding the degeneration of dopaminergic neurons. More neuroinflammatory markers were blunted in mice deficient for inflammasomes than in mice deficient for signalling by type I interferons. Neurodegeneration, however, was blunted in both mice. Collectively, these findings demonstrate that chronic activation of the STING pathway is sufficient to cause degeneration of dopaminergic neurons. Targeting the STING pathway could therefore be beneficial in Parkinson's disease and further neurodegenerative diseases.

Porcine cGAS-STING signaling induced autophagy inhibits STING downstream IFN and apoptosis

The innate immune DNA sensing cGAS-STING signaling pathway has been widely recognized for inducing interferons (IFNs) and subsequent antiviral state. In addition to IFN, the cGAS-STING pathway also elicits other cell autonomous immunity events including autophagy and apoptosis. However, the downstream signaling events of this DNA sensing pathway in livestock have not been well defined. Here, we systematically analyzed the porcine STING (pSTING) induced IFN, autophagy and apoptosis, revealed the distinct dynamics of three STING downstream events, and established the IFN independent inductions of autophagy and apoptosis. Further, we investigated the regulation of autophagy on pSTING induced IFN and apoptosis. Following TBK1-IRF3-IFN activation, STING induced Atg5/Atg16L1 dependent autophagy through LIR motifs. In turn, the autophagy likely promoted the pSTING degradation, inhibited both IFN production and apoptosis, and thus restored the cell homeostasis. Therefore, this study sheds lights on the molecular mechanisms of innate immunity in pigs.

Inhibition of the cGAS-STING Pathway Attenuates Lung Ischemia/Reperfusion Injury via Regulating Endoplasmic Reticulum Stress in Alveolar Epithelial Type II Cells of Rats

Purpose

Endoplasmic reticulum stress (ERS) plays an important role in the pathogenesis of lung ischemia/reperfusion (I/R) injury. Cyclic GMP-AMP synthase (cGAS) is a cytosol dsDNA sensor, coupling with downstream stimulator of interferon genes (STING) located in the ER, which involves innate immune responses. The aim of our present study was to investigate the effects of cGAS on lung I/R injury via regulating ERS.

Methods

We used Sprague-Dawley rats to make the lung I/R model by performing left hilum occlusion-reperfusion surgery. cGAS-specific inhibitor RU.521, STING agonist SR-717, and 4-phenylbutyric acid (4-PBA), the ERS inhibitor, were intraperitoneally administered in rats. Double immunofluorescent staining was applied to detect the colocalization of cGAS or BiP, an ERS protein, with alveolar epithelial type II cells (AECIIs) marker. We used transmission electron microscopy to examine the ultrastructure of ER and mitochondria. Apoptosis and oxidative stress in the lungs were assessed, respectively. The profiles of pulmonary edema and lung tissue injury were evaluated. And the pulmonary ventilation function was measured using a spirometer system.

Results

In lung I/R rats, the cGAS-STING pathway was upregulated, which implied they were activated. After cGAS-STING pathway was inhibited or activated in lung I/R rats, the ERS was alleviated after cGAS was inhibited, while when STING was activated after lung I/R, ERS was aggravated in the AECIIs, these results suggested that cGAS-STING pathway might trigger ERS responses. Furthermore, activation of cGAS-STING pathway induced increased apoptosis, inflammation, and oxidative stress via regulating ERS and therefore resulted in pulmonary edema and pathological injury in the lungs of I/R rats. Inhibition of cGAS-STING pathway attenuated ERS, therefore attenuated lung injury and promoted pulmonary ventilation function in I/R rats.

Conclusion

Inhibition of the cGAS-STING pathway attenuates lung ischemia/reperfusion injury via alleviating endoplasmic reticulum stress in alveolar epithelial type II cells of rats.

Gut dysbacteriosis attenuates resistance to Mycobacterium bovis infection by decreasing Cyclooxygenase 2 to inhibit endoplasmic reticulum stress

AbstractThe role of gut microbiota has been described as an important influencer of the immune system. Gut-lung axis is critical in the prevention of mycobacterium infection, but the specific mechanism by which dysbiosis affects tuberculosis have not been reported. In this study, we attempted to provide more information on how the gut-lung axis contributes to Mycobacterium bovis (M. bovis) infection. Mice pre-treated with broad-spectrum antibiotics cocktail (Abx) to induce gut dysbiosis. Interestingly, dysbiosis of microbes showed a significant increase in the bacterial burden in lungs, and inhibited the level of COX-2. After fecal transplantation, cyclooxygenase 2（COX-2） expression was restored and the inflammatory lesion in the lung was reduced. Further research found that the deficiency of COX-2 inhibited endoplasmic reticulum stress (ER-stress). This mechanism was completed by COX-2 interaction with BIP. Moreover, we found a positive feedback mechanism by which blocking ER-stress could reduce COX-2 levels via the NF-κB pathway. Taken together, we reveal for the first time gut dysbacteriosis exacerbates M. bovis disease by limiting COX-2 /ER-stress pathway. The finding strengthens the foundation of gut microbiota-targeted therapy for tuberculosis treatment.

Induction of Endoplasmic Reticulum Stress by CdhM Mediates Apoptosis of Macrophage During Mycobacterium tuberculosis Infection

The normal operation of the endoplasmic reticulum (ER) is critical for cells and organisms. However, ER stress, caused by imbalanced protein folding, occurs frequently, which perturbs the function of the ER and even results in cell apoptosis eventually. Many insults can induce ER stress; pathogen infection is one of them. Most of the genes involved in ER stress have been reported to be upregulated in Mycobacterium tuberculosis (Mtb) granulomas of humans and mice, implicating that infection with Mtb can induce ER stress. However, little is known about the molecular mechanism of Mtb induction of ER stress. Here, we reveal that Mycobacterium protein CDP-diglyceride hydrolase of Mycobacteriumn (CdhM) could target the ER and cause abnormal ER morphology and cell death. RNA-seq analysis suggests that most of the ER stress-involved genes were modulated by CdhM. Further assessed by biochemical experiments, the transcription and protein levels of ER stress markers BiP and CHOP, as well as the levels of XBP1 splicing and eIF2α phosphorylation, were significantly increased by CdhM, confirming that CdhM could induce ER stress alone or during infection. A single conserved amino acid mutant of CdhM, including L44A, G96A, H150A, and W175A, was incapable of inducing ER stress, which indicates that induction of ER stress by CdhM is specific and functional. Furthermore, CdhM-induced ER stress could also promote apoptosis of macrophages during Mtb infection. Overexpression of CdhM conferred a significant benefit for Mtb replication by releasing Mtb into extracellular during infection of macrophage in vitro, as presented in CFU assays. Overall, our study identified a novel Mtb effector protein CdhM which may promote Mtb dissemination and proliferation by induction of ER stress and apoptosis and provided new insight into the physiological significance of induction of ER stress in tuberculosis (TB) granulomas.

Impact of STING Inflammatory Signaling during Intracellular Bacterial Infections

The early detection of bacterial pathogens through immune sensors is an essential step in innate immunity. STING (Stimulator of Interferon Genes) has emerged as a key mediator of inflammation in the setting of infection by connecting pathogen cytosolic recognition with immune responses. STING detects bacteria by directly recognizing cyclic dinucleotides or indirectly by bacterial genomic DNA sensing through the cyclic GMP-AMP synthase (cGAS). Upon activation, STING triggers a plethora of powerful signaling pathways, including the production of type I interferons and proinflammatory cytokines. STING activation has also been associated with the induction of endoplasmic reticulum (ER) stress and the associated inflammatory responses. Recent reports indicate that STING-dependent pathways participate in the metabolic reprogramming of macrophages and contribute to the establishment and maintenance of a robust inflammatory profile. The induction of this inflammatory state is typically antimicrobial and related to pathogen clearance. However, depending on the infection, STING-mediated immune responses can be detrimental to the host, facilitating bacterial survival, indicating an intricate balance between immune signaling and inflammation during bacterial infections. In this paper, we review recent insights regarding the role of STING in inducing an inflammatory profile upon intracellular bacterial entry in host cells and discuss the impact of STING signaling on the outcome of infection. Unraveling the STING-mediated inflammatory responses can enable a better understanding of the pathogenesis of certain bacterial diseases and reveal the potential of new antimicrobial therapy.

From pyroptosis, apoptosis and necroptosis to PANoptosis: A mechanistic compendium of programmed cell death pathways

Pyroptosis, apoptosis and necroptosis are the most genetically well-defined programmed cell death (PCD) pathways, and they are intricately involved in both homeostasis and disease. Although the identification of key initiators, effectors and executioners in each of these three PCD pathways has historically delineated them as distinct, growing evidence has highlighted extensive crosstalk among them. These observations have led to the establishment of the concept of PANoptosis, defined as an inflammatory PCD pathway regulated by the PANoptosome complex with key features of pyroptosis, apoptosis and/or necroptosis that cannot be accounted for by any of these PCD pathways alone. In this review, we provide a brief overview of the research history of pyroptosis, apoptosis and necroptosis. We then examine the intricate crosstalk among these PCD pathways to discuss the current evidence for PANoptosis. We also detail the molecular evidence for the assembly of the PANoptosome complex, a molecular scaffold for contemporaneous engagement of key molecules from pyroptosis, apoptosis, and/or necroptosis. PANoptosis is now known to be critically involved in many diseases, including infection, sterile inflammation and cancer, and future discovery of novel PANoptotic components will continue to broaden our understanding of the fundamental processes of cell death and inform the development of new therapeutics.

cGAS-STING Signaling Pathway and Liver Disease: From Basic Research to Clinical Practice

The cGAS-STING signaling pathway is an autoimmune inflammatory pathway that can trigger the expression of a series of inflammatory factors represented by type 1 interferon. Recent studies have found that the cGAS-STING signaling pathway played a significant role in liver physiology and was closely related to the progress of liver diseases. For example, activating the cGAS-STING signaling pathway could significantly inhibit hepatitis B virus (HBV) replication in vivo. Moreover, the cGAS-STING signaling pathway was also closely associated with tumor immunity in hepatocellular carcinoma (HCC). This review summarized the role of the cGAS-STING signaling pathway in several common liver diseases, especially the current application of the cGAS-STING signaling pathway in liver disease treatment, and prospected its future research, which provided a new idea for understanding and treating liver diseases.

The Advancing of Selenium Nanoparticles Against Infectious Diseases

Infectious diseases, caused by the direct exposure of cellular or acellular pathogens, are found to be closely associated with multiple inflammation and immune responses, keeping one of the top threats to human health. As an indispensable trace element, Selenium (Se) plays important roles in antioxidant defence and redox state regulation along with a variety of specific metabolic pathways. In recent decades, with the development of novel nanotechnology, Selenium nanoparticles (Se NPs) emerged as a promising agent for biomedical uses due to their low toxicity, degradability and high bioavailability. Taking the advantages of the strong ability to trigger apoptosis or autophagy by regulating reactive oxygen species (ROS), Se NPs have been widely used for direct anticancer treatments and pathogen killing/clearance in host cells. With excellent stability and drug encapsulation capacity, Se NPs are now serving as a kind of powerful nano-carriers for anti-cancer, anti-inflammation and anti-infection treatments. Notably, Se NPs are also found to play critical roles in immunity regulations, such as macrophage and T effector cell activation, which thus provides new possibilities to achieve novel nano-immune synergetic strategy for anti-cancer and anti-infection therapies. In this review, we summarized the progress of preparation methods for Se NPs, followed by the advances of their biological functions and mechanisms for biomedical uses, especially in the field of anti-infection treatments. Moreover, we further provide some prospects of Se NPs in anti-infectious diseases, which would be helpful for facilitating their future research progress for anti-infection therapy.

The STING1 network regulates autophagy and cell death

Cell death and immune response are at the core of life. In past decades, the endoplasmic reticulum (ER) protein STING1 (also known as STING or TMEM173) was found to play a fundamental role in the production of type I interferons (IFNs) and pro-inflammatory cytokines in response to DNA derived from invading microbial pathogens or damaged hosts by activating multiple transcription factors. In addition to this well-known function in infection, inflammation, and immunity, emerging evidence suggests that the STING1-dependent signaling network is implicated in health and disease by regulating autophagic degradation or various cell death modalities (e.g., apoptosis, necroptosis, pyroptosis, ferroptosis, mitotic cell death, and immunogenic cell death [ICD]). Here, we outline the latest advances in our understanding of the regulating mechanisms and signaling pathways of STING1 in autophagy and cell death, which may shed light on new targets for therapeutic interventions.

Caspase-1 inhibits IFN-β production via cleavage of cGAS during M. bovis infection

Mycobacterium bovis (M. bovis) infection triggers cytokine production via pattern recognition receptors. These cytokines include type I interferons (IFNs) and interleukin-1β (IL-1β). Excessive type I IFN levels impair host resistance to M. bovis infection. Therefore, strict control of type I IFN production is helpful to reduce pathological damage and bacterial burden. Here, we found that a deficiency in caspase-1, which is the critical component of the inflammasome responsible for IL-1β production, resulted in increased IFN-β production upon M. bovis infection. Subsequent experiments demonstrated that caspase-1 activation reduced cyclic GMP-AMP synthase (cGAS) expression, thereby inhibiting downstream TANK-binding kinase 1 (TBK1)- interferon regulatory factor 3 (IRF3) signaling and ultimately reducing IFN production. A deficiency in caspase-1 activation enhanced the bacterial burden during M. bovis infection in vitro and in vivo and aggravated pathological lesion formation. Thus, caspase-1 activation reduced IFN-β production upon M. bovis infection by dampening cGAS-TBK1-IRF3 signaling, suggesting that the inflammasome protects hosts by negatively regulating harmful cytokines.

DNA damage-triggered activation of cGAS-STING pathway induces apoptosis in human keratinocyte HaCaT cells

Exposure to ultraviolet B (UVB) from sunlight causes DNA damage, serious cellular inflammation and aging, and even cell death in the skin, commonly known as sunburn, leading to cutaneous tissue disorders. DNA damage can be sensed as a danger-associated molecular pattern (DAMP) by the innate immune system. It has not been studied, however, whether cGAS-STING activation is involved in the apoptosis induced by UVB irradiation or by cisplatin treatment. Here we report the findings that within hours of DNA damages keratinocytes show an innate immune response, which involves the activation of cGAS-STING; a cytosolic DNA receptor, cGAS (cyclic guanosine monophosphate-adenosine monophosphate synthase), cyclic GMP-AMP (cGAMP) synthase, and DNA sensing adaptor, STING (protein stimulator of interferon genes). Either UVB irradiation or cisplatin treatment can cause DNA damages, releasing fragmented DNA from nucleus and/or mitochondria. Roles of cGAS-STING were examined in the HaCaT cells with DNA damages caused by UVB irradiation or cisplatin treatment. Silencing STING by siRNA rescued HaCaT cells from UVB or cisplatin-induced apoptosis. NF-κB, one of the major downstream components of STING pathway, which usually regulates the classical STING apoptotic pathway, was translocated to nucleus in the HaCaT cells irradiated with UVB. This translocation was attenuated by STING silencing. Treatment with BAY, an inhibitor of NF-κB pathway, blocked UVB-induced apoptosis. cGAS-STING-mediated production of IFNβ was induced by nuclear translocation of interferon regulatory factor 3 (IRF3). UVB irradiation inceased the nuclear translocation of IRF3, accompanied by enhanced expression level of IFNβ mRNA. The nuclear translocation of IRF3 and expression of IFNβ mRNA were attenuated by STING silencing. Treatment with MRT67307, an inhibitor of TBK1-IRF3-IFNβ pathway, blocked UVB-induced apoptosis. Therefore, we conclude that NF-κB pathway and IFNβ pathway residing in the downstream of STING are resposible for apoptosis of UVB-irradiated or cisplatin-treated HaCaT cells.

STING, the Endoplasmic Reticulum, and Mitochondria: Is Three a Crowd or a Conversation?

The anti-viral pattern recognition receptor STING and its partnering cytosolic DNA sensor cGAS have been increasingly recognized to respond to self DNA in multiple pathologic settings including cancer and autoimmune disease. Endogenous DNA sources that trigger STING include damaged nuclear DNA in micronuclei and mitochondrial DNA (mtDNA). STING resides in the endoplasmic reticulum (ER), and particularly in the ER-mitochondria associated membranes. This unique location renders STING well poised to respond to intracellular organelle stress. Whereas the pathways linking mtDNA and STING have been addressed recently, the mechanisms governing ER stress and STING interaction remain more opaque. The ER and mitochondria share a close anatomic and functional relationship, with mutual production of, and inter-organelle communication via calcium and reactive oxygen species (ROS). This interdependent relationship has potential to both generate the essential ligands for STING activation and to regulate its activity. Herein, we review the interactions between STING and mitochondria, STING and ER, ER and mitochondria (vis-à-vis calcium and ROS), and the evidence for 3-way communication.

STING, a promising target for small molecular immune modulator: A review

Stimulator of interferon genes (STING) plays a crucial role in human innate immune system, which is gradually concerned following the emerging immunotherapy. Activated STING induces the production of type I interferons (IFNs) and proinflammatory cytokines through STING-TBK1-IRF3/NF-κB pathway, which could be applied into the treatment of infection, inflammation, and tumorigenesis. Here, we provided a detailed summary of STING from its structure, function and regulation. Especially, we illustrated the canonical or noncanonical cyclic dinucleotides (CDNs) and synthetic small molecules for STING activation or inhibition and their efficacy in related diseases. Importantly, we particularly emphasized the discovery, development and modification of STING agonist or antagonist, attempting to enlighten reader's mind for enriching small molecular modulator of STING. In addition, we summarized biological evaluation methods for the assessment of small molecules activity.

Crosstalk between cGAS-STING signaling and cell death

Cytosolic nucleic acid sensors have a critical role in detecting endogenous nucleic acids to initiate innate immune responses during microbial infections and/or cell death. Several seminal studies over the past decade have delineated the conserved mechanism of cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) and the downstream signaling adapter stimulator of interferon genes (STING) in mediating innate immune signaling pathways as a host defense mechanism. Besides the predominant role in microbial infections and inflammatory diseases, there is an increased attention on alternative functional responses of cGAS-STING-mediated signaling. Here we review the complexity of interactions between the cGAS-STING signaling and cell death pathways. A better understanding of molecular mechanisms of this interplay is important with regard to the development of new therapeutics targeting cGAS-STING signaling in cancer, infectious, and chronic inflammatory diseases.

STING or Sting: cGAS-STING-Mediated Immune Response to Protozoan Parasites

Emerging evidence suggests that the DNA-sensing pathway plays a crucial role in innate immunity against multiple diseases, especially infectious diseases. Cyclic GMP-AMP synthase (cGAS), as a DNA sensor, and stimulator of interferon (IFN) genes (STING), as an adaptor protein, are the central components that link DNA sensing to immunologic functions - including, but not limited to, the type I IFN response. Recently, a series of studies have revealed that genomic DNA from protozoan parasites triggers the cGAS-STING pathway, and these studies identified the positive and negative regulators that modulate the signaling in parasite infection. Here, we summarize current understanding of the critical functions and potential applications of the cGAS-STING axis in parasitic diseases, specifically those caused by malaria parasites.

Diet-Induced Obesity Mice Execute Pulmonary Cell Apoptosis via Death Receptor and ER-Stress Pathways after E. coli Infection

Obesity has developed into a considerable health problem in the whole world. Escherichia coli (E. coli) can cause nosocomial pneumonia and induce cell apoptosis during injury and infection. Normal (lean) and diet-induced obesity mice (DIO, fed with high-fat diet) were chosen to perform nasal instillation with E. coli to establish a nonfatal acute pneumonia model. At 0 h, 12 h, 24 h, and 72 h postinfection, lung tissues were obtained to measure cell apoptosis. As shown in this study, both lean and DIO mice exhibited histopathological lesions of acute pneumonia and increased cell apoptosis in the lung infected with E. coli. Interestingly, the relative mRNA and protein expressions associated with either endoplasmic reticulum stress or death receptor apoptotic pathway were all dramatically increased in the DIO mice after infection, while only significant upregulation of death receptor apoptotic pathway in the lean mice at 72 h. These results indicated that the DIO mice executed excess cell apoptosis in the nonfatal acute pneumonia induced by E. coli infection through endoplasmic reticulum stress and death receptor apoptotic pathway.

The emerging role of STING-dependent signaling on cell death

STING is a newly identified adaptor protein for sensing cytosolic nucleic acid. It is well established that STING plays a crucial role in innate immune response via inducing production of type I IFN. Emerging evidence suggests that the activation of STING-dependent signaling is also implicated in the process of cell death, such as apoptosis, pyroptosis, necroptosis, and autophagy. Of note, the pro-death outcome is even predominant in certain cell types, like lymphocytes, myeloid cells, and hepatocytes. Given that STING agonists are being tested for enhancing antitumor immune responses, it is necessary to fully understand the outcome of STING activation. The anti-microorganism response mediated by STING has been well described; therefore, we focus on the role of STING-dependent signaling on cell death in this review.

Aberrant ER Stress Induced Neuronal-IFNβ Elicits White Matter Injury Due to Microglial Activation and T-Cell Infiltration after TBI

Persistent endoplasmic reticulum (ER) stress in neurons is associated with activation of inflammatory cells and subsequent neuroinflammation following traumatic brain injury (TBI); however, the underlying mechanism remains elusive. We found that induction of neuronal-ER stress, which was mostly characterized by an increase in phosphorylation of a protein kinase R-like ER kinase (PERK) leads to release of excess interferon (IFN)β due to atypical activation of the neuronal-STING signaling pathway. IFNβ enforced activation and polarization of the primary microglial cells to inflammatory M1 phenotype with the secretion of a proinflammatory chemokine CXCL10 due to activation of STAT1 signaling. The secreted CXCL10, in turn, stimulated the T-cell infiltration by serving as the ligand and chemoattractant for CXCR3⁺ T-helper 1 (Th1) cells. The activation of microglial cells and infiltration of Th1 cells resulted in white matter injury, characterized by impaired myelin basic protein and neurofilament NF200, the reduced thickness of corpus callosum and external capsule, and decline of mature oligodendrocytes and oligodendrocyte precursor cells. Intranasal delivery of CXCL10 siRNA blocked Th1 infiltration but did not fully rescue microglial activation and white matter injury after TBI. However, impeding PERK-phosphorylation through the administration of GSK2656157 abrogated neuronal induction of IFNβ, switched microglial polarization to M2 phenotype, prevented Th1 infiltration, and increased Th2 and Treg levels. These events ultimately attenuated the white matter injury and improved anxiety and depressive-like behavior following TBI.SIGNIFICANCE STATEMENT A recent clinical study showed that human brain trauma patients had enhanced expression of type-1 IFN; suggests that type-1 IFN signaling may potentially influence clinical outcome in TBI patients. However, it was not understood how TBI leads to an increase in IFNβ and whether induction of IFNβ has any influence on neuroinflammation, which is the primary reason for morbidity and mortality in TBI. Our study suggests that induction of PERK phosphorylation, a characteristic feature of ER stress is responsible for an increase in neuronal IFNβ, which, in turn, activates microglial cells and subsequently manifests the infiltration of T cells to induce neuroinflammation and subsequently white matter injury. Blocking PERK phosphorylation using GSK2656157 (or PERK knockdown) the whole cascade of neuroinflammation was attenuated and improved cognitive function after TBI.

Reactive oxygen species-mediated endoplasmic reticulum stress response induces apoptosis of Mycobacterium avium-infected macrophages by activating regulated IRE1-dependent decay pathway

Mycobacterium avium, a slow‐growing nontuberculous mycobacterium, causes fever, diarrhoea, loss of appetite, and weight loss in immunocompromised people. We have proposed that endoplasmic reticulum (ER) stress‐mediated apoptosis plays a critical role in removing intracellular mycobacteria. In the present study, we investigated the role of the regulated IRE1‐dependent decay (RIDD) pathway in macrophages during M. avium infection based on its role in the regulation of gene expression. The inositol‐requiring enzyme 1 (IRE1)/apoptosis signal‐regulating kinase 1 (ASK1)/c‐Jun N‐terminal kinase (JNK) signalling pathway was activated in macrophages after infection with M. avium. The expression of RIDD‐associated genes, such as Bloc1s1 and St3gal5, was decreased in M. avium‐infected macrophages. Interestingly, M. avium‐induced apoptosis was significantly suppressed by pretreatment with irestatin (inhibitor of IRE1α) and 4μ8c (RIDD blocker). Macrophages pretreated with N‐acetyl cysteine (NAC) showed decreased levels of reactive oxygen species (ROS), IRE1α, and apoptosis after M. avium infection. The expression of Bloc1s1 and St3gal5 was increased in NAC‐pretreated macrophages following infection with M. avium. Growth of M. avium was significantly increased in irestatin‐, 4μ8c‐, and NAC‐treated macrophages compared with the control. The data indicate that the ROS‐mediated ER stress response induces apoptosis of M. avium‐infected macrophages by activating IRE1α‐RIDD. Thus, activation of IRE1α suppresses the intracellular survival of M. avium in macrophages.

Kallikrein 12 Regulates Innate Resistance of Murine Macrophages against Mycobacterium bovis Infection by Modulating Autophagy and Apoptosis

Mycobacterium bovis (M. bovis) is a member of the Mycobacterium tuberculosis (Mtb) complex causing bovine tuberculosis (TB) and imposing a high zoonotic threat to human health. Kallikreins (KLKs) belong to a subgroup of secreted serine proteases. As their role is established in various physiological and pathological processes, it is likely that KLKs expression may mediate a host immune response against the M. bovis infection. In the current study, we report in vivo and in vitro upregulation of KLK12 in the M. bovis infection. To define the role of KLK12 in immune response regulation of murine macrophages, we produced KLK12 knockdown bone marrow derived macrophages (BMDMs) by using siRNA transfection. Interestingly, the knockdown of KLK12 resulted in a significant downregulation of autophagy and apoptosis in M. bovis infected BMDMs. Furthermore, we demonstrated that this KLK12 mediated regulation of autophagy and apoptosis involves mTOR/AMPK/TSC2 and BAX/Bcl-2/Cytochrome c/Caspase 3 pathways, respectively. Similarly, inflammatory cytokines IL-1β, IL-6, IL-12 and TNF-α were significantly downregulated in KLK12 knockdown macrophages but the difference in IL-10 and IFN-β expression was non-significant. Taken together, these findings suggest that upregulation of KLK12 in M. bovis infected murine macrophages plays a substantial role in the protective immune response regulation by modulating autophagy, apoptosis and pro-inflammatory pathways. To our knowledge, this is the first report on expression and the role of KLK12 in the M. bovis infection and the data may contribute to a new paradigm for diagnosis and treatment of bovine TB.

The emerging role of stimulator of interferons genes signaling in sepsis: Inflammation, autophagy, and cell death

Stimulator of interferons genes (STING) is an adaptor protein that plays a critical role in the secretion of type I interferons and pro-inflammatory cytokines in response to cytosolic nucleic acid. Recent research indicates the involvement of the STING pathway in uncontrolled inflammation, sepsis, and shock. STING signaling is significantly up-regulated in human sepsis, and STING agonists are suggested to contribute to the pathogenesis of sepsis and shock. Nevertheless, little is known about the consequences of activated STING-mediated signaling during sepsis. It has been shown that aberrant activation of the STING-dependent way can result in increased inflammation, type I interferons responses, and cell death (including apoptosis, necroptosis, and pyroptosis). In addition, autophagy modulation has been demonstrated to protect against multiple organs injuries in animal sepsis model. However, impaired autophagy may contribute to the aberrant activation of STING signaling, leading to uncontrolled inflammation and cell death. Here we present a comprehensive review of recent advances in the understanding of STING signaling, focusing on the regulatory mechanisms and the roles of this pathway in sepsis.

DNA-stimulated cell death: implications for host defence, inflammatory diseases and cancer

The immune system detects disturbances in homeostasis that occur during infection, sterile tissue damage and cancer. This initiates immune responses that seek to eliminate the trigger of immune activation and to re-establish homeostasis. At the same time, these mechanisms can also play a crucial role in the progression of disease. The occurrence of DNA in the cytosol constitutes a potent trigger for the innate immune system, governing the production of key inflammatory cytokines such as type I interferons and IL-1β. More recently, it has become clear that cytosolic DNA also triggers other biological responses, including various forms of programmed cell death. In this article, we review the emerging literature on the pathways governing DNA-stimulated cell death and the current knowledge on how these processes shape immune responses to exogenous and endogenous challenges.

Endoplasmic Reticulum Stress Induces Macrophages to Produce IL-1β During Mycobacterium bovis Infection via a Positive Feedback Loop Between Mitochondrial Damage and Inflammasome Activation

Mycobacterium bovis, the causative agent of tuberculosis in cattle and humans, infects host macrophages and induces endoplasmic reticulum stress (ERS), mitochondrial damage, and interleukin (IL)-1β production. The relationship between these phenotypes is yet to be elucidated. In this study, we investigated the role of ERS in mitochondrial damage and IL-1β production in macrophages during infection with a virulent M. bovis strain. We found that ERS activates the inflammasome via NOD-like receptor family, pyrin domain-containing 3 (NLRP3)-caspase-8 and that IFN-inducible protein absent in melanoma 2 (AIM2) triggered mitochondrial damage. ERS increased reactive oxygen species (ROS), which promoted translocation of the inflammasome to the mitochondria. NLRP3, but not AIM2, was involved in the ERS-induced cleavage of caspase-8 and Bid, leading to mitochondrial damage, which was required for the production of mature IL-1β. Our data suggest that ERS induces macrophages to produce mature IL-1β during infection with virulent M. bovis through a positive feedback loop between mitochondrial damage and inflammasome activation. To the best of our knowledge, this is the first evidence of the involvement of ERS and mitochondrial damage in inflammasome activation during M. bovis infection.

Rv3033, as an Emerging Anti-apoptosis Factor, Facilitates Mycobacteria Survival via Inhibiting Macrophage Intrinsic Apoptosis

Apoptosis inhibition is a critical strategy of mycobacteria facilitating its survival in macrophages, but the underlying mechanism is not completely understood. In this study, we found that Rv3033, a secreted virulence factor of mycobacteria, played an important role in bacillary survival within macrophages. Forced over-expressed of Rv3033 in macrophages could efficiently resist mycobacteria-induced early and late apoptosis, accompanied with the obvious increased cellular bacterial burden. By exploring the underlying mechanism, we found that Rv3033 efficiently repressed the intrinsic (caspase-9 meditated), but not the extrinsic (caspase-8 mediated) apoptotic pathway in mycobacteria-infected macrophages. And this repression relied on the orchestrating blockade of both mitochondrial cytochrome c release and endoplasmic reticulum (ER) stress PERK branch activation. Our study uncovered a novel function of mycobacterial virulence factor Rv3033 as an anti-apoptotic protein, which may provide a new target for tuberculosis (TB) treatment.

Alleviation of endoplasmic reticulum stress protects against cisplatin-induced ovarian damage

BACKGROUND

Cisplatin (CDDP), a widely used chemotherapeutic agent, can induce excessive granulosa cell apoptosis, follicle loss and even premature ovarian insufficiency (POI). However, the mechanism remains elusive, although some studies have indicated the involvement of endoplasmic reticulum stress (ERS). The aim of our study was to investigate the possible mechanism ERS in CDDP-induced granulosa cell apoptosis and follicle loss.

METHODS

A POI mouse model was generated by CDDP. The ovaries samples were collected and processed for isobaric tags for relative and absolute quantification analysis (iTRAQ) to screen out our interested proteins of HSPA5 and HSP90AB1, and the decline in their expression were verified by a real-time quantitative PCR and a western blotting assay. In vitro, human granulosa cells, KGN and COV434 cells were transfected with siRNA targeting HSPA5 and HSP90AB1 and then treated with CDDP, or treated with CDDP with/without CDDP+ 4-phenylbutyric acid (4-PBA) and 3-methyladenine (3-MA). The levels of ERS, autophagy and apoptosis were evaluated by western blotting, DALGreen staining and flow cytometry. In vivo, ovaries from mice that received intraperitoneal injections of saline, CDDP, CDDP+ 4-PBA and CDDP+ 3-MA were assayed by immunofluorescence, hematoxylin and eosin (H&E) staining for follicle counting, and terminal-deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) staining for cell apoptosis assay. The plasma hormone levels were measured by an enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

We have clarified the relationships between ERS, autophagy, and apoptosis in CDDP-induced granulosa cell apoptosis, both in vitro and in vivo. Alleviating ERS by inhibiting HSPA5 and HSP90AB1 attenuated CDDP-induced autophagy and apoptosis. 4-PBA treatment significantly attenuated CDDP-induced cell autophagy and apoptosis in cultured KGN and COV434 cells. However, inhibiting cell autophagy with 3-MA negligibly restored the CDDP-induced changes in ERS and apoptosis. In vivo experiments also demonstrated that treatment with 4-PBA, but not 3-MA, prevented CDDP-induced ovarian damage and hormone dysregulation.

CONCLUSIONS

CDDP-induced ERS could promote autophagy and apoptosis in granulosa cells, causing excessive follicle loss and endocrine disorders. Alleviation of ERS with 4-PBA, but not of autophagy with 3-MA, protect against CDDP-induced granulosa cell apoptosis and ovarian damage. Thus, 4-PBA can be used to protect the ovary during chemotherapy in women.

Mycobacterium fortuitum-induced ER-Mitochondrial calcium dynamics promotes calpain/caspase-12/caspase-9 mediated apoptosis in fish macrophages

Mycobacterium fortuitum is a natural fish pathogen. It induces apoptosis in headkidney macrophages (HKM) of catfish, Clarias sp though the mechanism remains largely unknown. We observed M. fortuitum triggers calcium (Ca²⁺) insult in the sub-cellular compartments which elicits pro-apototic ER-stress factor CHOP. Alleviating ER-stress inhibited CHOP and attenuated HKM apoptosis implicating ER-stress in the pathogenesis of M. fortuitum. ER-stress promoted calpain activation and silencing the protease inhibited caspase-12 activation. The study documents the primal role of calpain/caspase-12 axis on caspase-9 activation in M. fortuitum-pathogenesis. Mobilization of Ca²⁺ from ER to mitochondria led to increased mitochondrial Ca²⁺ (Ca²⁺)_m load,_, mitochondrial permeability transition (MPT) pore opening, altered mitochondrial membrane potential (ΔΨm) and cytochrome c release eventually activating the caspase-9/-3 cascade. Ultra-structural studies revealed close apposition of ER and mitochondria and pre-treatment with (Ca²⁺)_m-uniporter (MUP) blocker ruthenium red, reduced Ca²⁺ overload suggesting (Ca²⁺)_m fluxes are MUP-driven and the ER-mitochondria tethering orchestrates the process. This is the first report implicating role of sub-cellular Ca²⁺ in the pathogenesis of M. fortuitum. We summarize, the dynamics of Ca²⁺ in sub-cellular compartments incites ER-stress and mitochondrial dysfunction, leading to activation of pro-apoptotic calpain/caspase-12/caspase-9 axis in M. fortuitum-infected HKM.