Cutting edge: Endoplasmic reticulum stress licenses macrophages to produce mature IL-1β in response to TLR4 stimulation through a caspase-8- and TRIF-dependent pathway

cFLIP in the molecular regulation of astroglia-driven neuroinflammation in experimental glaucoma

BACKGROUND

Recent experimental studies of neuroinflammation in glaucoma pointed to cFLIP as a molecular switch for cell fate decisions, mainly regulating cell type-specific caspase-8 functions in cell death and inflammation. This study aimed to determine the importance of cFLIP for regulating astroglia-driven neuroinflammation in experimental glaucoma by analyzing the outcomes of astroglia-targeted transgenic deletion of cFLIP or cFLIPL.

METHODS

Glaucoma was modeled by anterior chamber microbead injections to induce ocular hypertension in mouse lines with or without conditional deletion of cFLIP or cFLIPL in astroglia. Morphological analysis of astroglia responses assessed quantitative parameters in retinal whole mounts immunolabeled for GFAP and inflammatory molecules or assayed for TUNEL. The molecular analysis included 36-plexed immunoassays of the retina and optic nerve cytokines and chemokines, NanoString-based profiling of inflammation-related gene expression, and Western blot analysis of selected proteins in freshly isolated samples of astroglia.

RESULTS

Immunoassays and immunolabeling of retina and optic nerve tissues presented reduced production of various proinflammatory cytokines, including TNFα, in GFAP/cFLIP and GFAP/cFLIPL relative to controls at 12 weeks of ocular hypertension with no detectable alteration in TUNEL. Besides presenting a similar trend of the proinflammatory versus anti-inflammatory molecules displayed by immunoassays, NanoString-based molecular profiling detected downregulated NF-κB/RelA and upregulated RelB expression of astroglia in ocular hypertensive samples of GFAP/cFLIP compared to ocular hypertensive controls. Analysis of protein expression also revealed decreased phospho-RelA and increased phospho-RelB in parallel with an increase in caspase-8 cleavage products.

CONCLUSIONS

A prominent response limiting neuroinflammation in ocular hypertensive eyes with cFLIP-deletion in astroglia values the role of cFLIP in the molecular regulation of glia-driven neuroinflammation during glaucomatous neurodegeneration. The molecular responses accompanying the lessening of neurodegenerative inflammation also seem to maintain astroglia survival despite increased caspase-8 cleavage with cFLIP deletion. A transcriptional autoregulatory response, dampening RelA but boosting RelB for selective expression of NF-κB target genes, might reinforce cell survival in cFLIP-deleted astroglia.

Adipose tissue IL-18 production is independent of caspase-1 and caspase-11

BACKGROUND

Inflammation in adipose tissue, resulting from imbalanced caloric intake and energy expenditure, contributes to the metabolic dysregulation observed in obesity. The production of inflammatory cytokines, such as IL-1β and IL-18, plays a key role in this process. While IL-1β promotes insulin resistance and diabetes, IL-18 regulates energy expenditure and food intake. Previous studies have suggested that caspase-1, activated by the Nlrp3 inflammasome in response to lipid excess, mediates IL-1β production, whereas activated by the Nlrp1b inflammasome in response to energy excess, mediates IL-18 production. However, this has not been formally tested.

METHODS

Wild-type and caspase-1-deficient Balb/c mice, carrying the Nlrp1b1 allele, were fed with regular chow or a high-fat diet for twelve weeks. Food intake and mass gain were recorded weekly. At the end of the twelve weeks, glucose tolerance and insulin resistance were evaluated. Mature IL-18 protein levels and the inflammatory process in the adipose tissue were determined. Fasting lipid and cytokine levels were quantified in the sera of the different experimental groups.

RESULTS

We found that IL-18 production in adipose tissue is independent of caspase-1 activity, regardless of the metabolic state, while Nlrp3-mediated IL-1β production remains caspase-1 dependent. Additionally, caspase-1 null Balb/c mice did not develop metabolic abnormalities in response to energy excess from the high-fat diet.

CONCLUSION

Our findings suggest that IL-18 production in the adipose tissue is independent of Nlrp3 inflammasome and caspase-1 activation, regardless of caloric food intake. In contrast, Nlrp3-mediated IL-1β production is caspase-1 dependent. These results provide new insights into the mechanisms underlying cytokine production in the adipose tissue during both homeostatic conditions and metabolic stress, highlighting the distinct roles of caspase-1 and the Nlrp inflammasomes in regulating inflammatory responses.

Protective Effects of Inulin on Stress-Recurrent Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the digestive tract and is closely associated with the homeostasis of the gut microbiota. Inulin, as a natural prebiotic, displays anti-inflammatory activity and maintains equilibrium of the intestinal microbiota. In this study, our research aimed to explore the potential of inulin in enhancing intestinal immunity and reducing inflammation in stress-recurrent IBD. In this study, a co-culture intestinal epithelium model and a stress-recurrent IBD mouse model was used to examine the protective effects of inulin. It was observed that inulin digesta significantly reduced pro-inflammatory cytokine expression (CXCL8/IL8 and TNFA) and increased MUC2 expression in intestinal epithelial cells. In vivo, our findings showed that Inulin intake significantly prevented IBD symptoms. This was substantiated by a decrease in serum inflammatory markers (IL-6, CALP) and a downregulation of inflammatory cytokine (Il6) in colon samples. Additionally, inulin intake led to an increase in short-chain fatty acids (SCFAs) in cecal contents and a reduction in the expression of endoplasmic reticulum (ER) stress markers (CHOP, BiP). Our results highlight that inulin can improve stress-recurrent IBD symptoms by modulating microbiota composition, reducing inflammation, and alleviating ER stress. These findings suggested the therapeutic potential of inulin as a dietary intervention for ameliorating stress-recurrent IBD.

Current Views about the Inflammatory Damage Triggered by Bacterial Superantigens and Experimental Attempts to Neutralize Superantigen-Mediated Toxic Effects with Natural and Biological Products

Superantigens, i.e., staphylococcal enterotoxins and toxic shock syndrome toxin-1, interact with T cells in a different manner in comparison to conventional antigens. In fact, they activate a larger contingent of T lymphocytes, binding outside the peptide-binding groove of the major histocompatibility complex class II. Involvement of many T cells by superantigens leads to a massive release of pro-inflammatory cytokines, such as interleukin (IL)-1, IL-2, IL-6, tumor necrosis factor-alpha and interferon-gamma. Such a storm of mediators has been shown to account for tissue damage, multiorgan failure and shock. Besides conventional drugs and biotherapeutics, experiments with natural and biological products have been undertaken to attenuate the toxic effects exerted by superantigens. In this review, emphasis will be placed on polyphenols, probiotics, beta-glucans and antimicrobial peptides. In fact, these substances share a common functional denominator, since they skew the immune response toward an anti-inflammatory profile, thus mitigating the cytokine wave evoked by superantigens. However, clinical applications of these products are still scarce, and more trials are needed to validate their usefulness in humans.

Myeloid OTULIN deficiency couples RIPK3-dependent cell death to Nlrp3 inflammasome activation and IL-1β secretion

Loss-of-function mutations in the deubiquitinase OTULIN result in an inflammatory pathology termed "OTULIN-related autoinflammatory syndrome" (ORAS). Genetic mouse models revealed essential roles for OTULIN in inflammatory and cell death signaling, but the mechanisms by which OTULIN deficiency connects cell death to inflammation remain unclear. Here, we identify OTULIN deficiency as a cellular condition that licenses RIPK3-mediated cell death in murine macrophages, leading to Nlrp3 inflammasome activation and subsequent IL-1β secretion. OTULIN deficiency uncoupled Nlrp3 inflammasome activation from gasdermin D-mediated pyroptosis, instead allowing RIPK3-dependent cell death to act as an Nlrp3 inflammasome activator and mechanism for IL-1β release. Accordingly, elevated serum IL-1β levels in myeloid-specific OTULIN-deficient mice were diminished by deleting either Ripk3 or Nlrp3. These findings identify OTULIN as an inhibitor of RIPK3-mediated IL-1β release in mice.

Toll-like Receptors as Pro-Thrombotic Drivers in Viral Infections: A Narrative Review

Toll-like receptors (TLRs) have a critical role in the pathogenesis and disease course of viral infections. The induced pro-inflammatory responses result in the disturbance of the endovascular surface layer and impair vascular homeostasis. The injury of the vessel wall further promotes pro-thrombotic and pro-coagulatory processes, eventually leading to micro-vessel plugging and tissue necrosis. Moreover, TLRs have a direct role in the sensing of viruses and platelet activation. TLR-mediated upregulation of von Willebrand factor release and neutrophil, as well as macrophage extra-cellular trap formation, further contribute to (micro-) thrombotic processes during inflammation. The following review focuses on TLR signaling pathways of TLRs expressed in humans provoking pro-thrombotic responses, which determine patient outcome during viral infections, especially in those with cardiovascular diseases.

Genetic diversity and thermotolerance in Holstein cows: Pathway analysis and marker development using whole-genome sequencing

Heat stress causes extensive losses in the dairy sector, due to negative effects on milk production and reproduction. Cows have evolved a series of protective mechanisms, (physiological, biochemical, behavioural) to cope with the thermostressing environments, which have allowed the preservation of productive and reproductive potential of specific animals during summer; these animals are considered thermotolerant and could be used to design programs of selective breeding. These programs, targeting the generations of a population of heat-resistant animals, would increase the frequency of the desired phenotypes, tackling the financial losses on one hand and reducing the carbon footprints of the dairy sector on the other. The development of genomics techniques has enabled genome wide variant calling, to detect SNPs associated with the desired phenotypes. In this study, we used a comparative genomics approach to detect genetic variation associated with thermotolerance and to design molecular markers for characterizing the animals as tolerant/sensitive. A total of 40 cows from each group were split in four sequencing pools and a whole-genome sequencing approach was used. Results and conclusion: Genome-wide genetic variation between groups was characterized and enrichment analysis revealed specific pathways which participate in the adaptive mechanisms of thermotolerance, implicated into systemic and cellular responses, including the immune system functionality, Heat Stress and Unfolded Protein Response. The markers made a promising set of results, as specific SNPs in five genes encoding for Heat Shock Proteins were significantly associated with thermotolerance.

Refractory adult-onset Still's disease complicated with monoclonal gammopathy of undetermined significance: A case report

RATIONALE

Adult-onset Still's disease (AOSD) is a rare inflammatory disease characterized by a classic triad of daily spike fever, arthritis, and a typical salmon-pink rash. The involvement of inflammatory cytokines by various factors such as infection, drug, or neoplasm causes refractory AOSD.

PATIENT CONCERNS

We report a 63-year-old man with a high fever, rash, hyperferritinemia, and M proteinemia. His serum levels of interleukin-6 and interleukin-18 were remarkably high at 192 and 114,250 pg/mL, respectively.

DIAGNOSIS

AOSD complicated with monoclonal gammopathy of undetermined significance was diagnosed.

INTERVENTIONS

After steroid pulse therapy followed by oral prednisolone, cyclosporin, methotrexate, and colchicine, serum ferritin levels temporarily declined, but secondary cytomegalovirus infections exacerbated AOSD's activity.

OUTCOMES

Finally, after tocilizumab induction, AOSD activity was gradually suppressed over a long period.

LESSONS

The disease activity of AOSD is exacerbated by multiple factors, including comorbidities or infections. Clinicians need to consider that monoclonal gammopathy of undetermined significance complications might become AOSD refractory by an elevation of the inflammatory cytokines. Moreover, further prospective studies are required to confirm this result.

Caspase-8 but not caspase-7 influences inflammasome activation to act in control of Brucella abortus infection

Programmed cell death (PCD) is an important mechanism of innate immunity against bacterial pathogens. The innate immune PCD pathway involves the molecules caspase-7 and caspase-8, among others. Brucella abortus is a gram-negative bacterium that causes a zoonotic disease termed brucellosis. The innate immune response against this pathogen involves activation of inflammasome components and induction of pyroptosis. However, no studies so far have revealed the role of caspase-7 or caspase-8 during this bacterial infection. Herein, we demonstrate that caspase-7 is dispensable for caspase-1 processing, IL-1β secretion and cell death in macrophages. Additionally, caspase-7 deficient animals control B. abortus infection as well as the wild type mice. Furthermore, we addressed the role of caspase-8 in inflammasome activation and pyroptosis during this bacterial infection. Macrophages deficient in caspase-8 secreted reduced amounts of IL-1β that parallels with diminished caspase-1 activity when compared to wild type cells. Additionally, caspase-8 KO macrophages showed reduced LDH release when compared to wild type, suggesting that caspase-8 may play an important role in pyroptosis in response to B. abortus. Finally, caspase-8 KO animals were more susceptible to Brucella infection when compared to wild type mice. Overall, this study contributes to a better understanding of the involvement of caspase-7 and caspase-8 in innate immunity against B. abortus infection.

Innate immune mechanisms of mRNA vaccines

The lipid nanoparticle (LNP)-encapsulated, nucleoside-modified mRNA platform has been used to generate safe and effective vaccines in record time against COVID-19. Here, we review the current understanding of the manner whereby mRNA vaccines induce innate immune activation and how this contributes to protective immunity. We discuss innate immune sensing of mRNA vaccines at the cellular and intracellular levels and consider the contribution of both the mRNA and the LNP components to their immunogenicity. A key message that is emerging from recent observations is that the LNP carrier acts as a powerful adjuvant for this novel vaccine platform. In this context, we highlight important gaps in understanding and discuss how new insight into the mechanisms underlying the effectiveness of mRNA-LNP vaccines may enable tailoring mRNA and carrier molecules to develop vaccines with greater effectiveness and milder adverse events in the future.

Biting the hand that feeds: Metabolic determinants of cell fate during infection

Metabolic shifts can occur in cells of the innate immune system in response to microbial infection. Whether these metabolic shifts benefit host defense and propagation of an immune response appears to be context dependent. In an arms race, host-adapted microbes and mammalian cells vie for control of biosynthetic machinery, organelles, and metabolites. Herein, we discuss the intersection of host metabolism and cell-intrinsic immunity with implications for cell fate during infection. Sensation of microbial ligands in isolation results in host metabolic shifts that imbues normal innate immune function, such as cytokine secretion. However, living microbes have an arsenal of effectors and strategies to subvert cell-intrinsic immune responses by manipulating host metabolism. Consequently, host metabolism is monitored as an indicator of invasion or manipulation by a pathogen, primarily through the actions of guard proteins and inflammasome pathways. In this review, we frame initiation of cell-intrinsic immunity in the context of host metabolism to include a physiologic “Goldilocks zone” of allowable shifts with guard circuits monitoring wide perturbations away from this zone for the initiation of innate immune responses. Through comparison of studies with purified microbial ligands, dead microbes, and live pathogens we may begin to understand how shifts in metabolism determine the outcome of host-pathogen interactions.

No longer married to inflammasome signaling: the diverse interacting pathways leading to pyroptotic cell death

For over 15 years the lytic cell death termed pyroptosis was defined by its dependency on the inflammatory caspase, caspase-1, which, upon pathogen sensing, is activated by innate immune cytoplasmic protein complexes known as inflammasomes. However, this definition of pyroptosis changed when the pore-forming protein gasdermin D (GSDMD) was identified as the caspase-1 (and caspase-11) substrate required to mediate pyroptotic cell death. Consequently, pyroptosis has been redefined as a gasdermin-dependent cell death. Studies now show that, upon liberation of the N-terminal domain, five gasdermin family members, GSDMA, GSDMB, GSDMC, GSDMD and GSDME can all form plasma membrane pores to induce pyroptosis. Here, we review recent research into the diverse stimuli and cell death signaling pathways involved in the activation of gasdermins; death and toll-like receptor triggered caspase-8 activation of GSDMD or GSMDC, apoptotic caspase-3 activation of GSDME, perforin-granzyme A activation of GSDMB, and bacterial protease activation of GSDMA. We highlight findings that have begun to unravel the physiological situations and disease states that result from gasdermin signaling downstream of inflammasome activation, death receptor and mitochondrial apoptosis, and necroptosis. This new era in cell death research therefore holds significant promise in identifying how distinct, yet often networked, pyroptotic cell death pathways might be manipulated for therapeutic benefit to treat a range of malignant conditions associated with inflammation, infection and cancer.

Exosomes from Human Placenta Choriodecidual Membrane-Derived Mesenchymal Stem Cells Mitigate Endoplasmic Reticulum Stress, Inflammation, and Lung Injury in Lipopolysaccharide-Treated Obese Mice

Endoplasmic reticulum (ER) stress mediates the effects of obesity on aggravating sepsis-induced lung injury. We investigated whether exosomes from human placenta choriodecidual membrane-derived mesenchymal stem cells (pcMSCs) can mitigate pulmonary ER stress, lung injury, and the mechanisms of inflammation, oxidation, and apoptosis in lipopolysaccharide-treated obese mice. Diet-induced obese (DIO) mice (adult male C57BL/6J mice fed with a 12-week high-fat diet) received lipopolysaccharide (10 mg/kg, i.p.; DIOLPS group) or lipopolysaccharide plus exosomes (1 × 108 particles/mouse, i.p.; DIOLPSExo group). Our data demonstrated lower levels of ER stress (upregulation of glucose-regulated protein 78, phosphorylated eukaryotic initiation factor 2α, and C/EBP homologous protein; p = 0.038, <0.001, and <0.001, respectively), inflammation (activation of nuclear factor-kB, hypoxia-inducible factor-1α, macrophages, and NLR family pyrin domain containing 3; upregulation of tumor necrosis factor-α, interleukin-1β, and interleukin-6; p = 0.03, <0.001, <0.001, <0.001, <0.001, <0.001, and <0.001, respectively), lipid peroxidation (p < 0.001), and apoptosis (DNA fragmentation, p = 0.003) in lung tissues, as well as lower lung injury level (decreases in tidal volume, peak inspiratory flow, and end expiratory volume; increases in resistance, injury score, and tissue water content; p < 0.001, <0.001, <0.001, <0.001, <0.001, and =0.002, respectively) in the DIOLPSExo group than in the DIOLPS group. In conclusion, exosomes from human pcMSCs mitigate pulmonary ER stress, inflammation, oxidation, apoptosis, and lung injury in lipopolysaccharide-treated obese mice.

Inflammasome Contribution to the Activation of Th1, Th2, and Th17 Immune Responses

Inflammasomes are cytosolic polyprotein complexes formed in response to various external and internal stimuli, including viral and bacterial antigens. The main product of the inflammasome is active caspase 1 which proteolytically cleaves, releasing functional interleukin-1 beta (IL-1β) and interleukin-18 (IL-18). These cytokines play a central role in shaping immune response to pathogens. In this review, we will focus on the mechanisms of inflammasome activation, as well as their role in development of Th1, Th2, and Th17 lymphocytes. The contribution of cytokines IL-1β, IL-18, and IL-33, products of activated inflammasomes, are summarized. Additionally, the role of cytokines released from tissue cells in promoting differentiation of lymphocyte populations is discussed.

ERAP1 is a critical regulator of inflammasome-mediated proinflammatory and ER stress responses

Background

In addition to its role in antigen presentation, recent reports establish a new role for endoplasmic reticulum aminopeptidase 1 (ERAP1) in innate immunity; however, the mechanisms underlying these functions are not fully defined. We previously confirmed that loss of ERAP1 functions resulted in exaggerated innate immune responses in a murine in vivo model. Here, we investigated the role of ERAP1 in suppressing inflammasome pathways and their dependence on ER stress responses.

Results

Using bone marrow-derived macrophages (BMDMs), we found that loss of ERAP1 in macrophages resulted in exaggerated production of IL-1β and IL-18 and augmented caspase-1 activity, relative to wild type macrophages. Moreover, an in vivo colitis model utilizing dextran sodium sulfate (DSS) confirmed increased levels of proinflammatory cytokines and chemokines in the colon of DSS treated ERAP1^−/− mice as compared to identically stimulated WT mice. Interestingly, stimulated ERAP1^−/− BMDMs and CD4⁺ T cells simultaneously demonstrated exaggerated ER stress, assessed by increased expression of ER stress-associated genes, a state that could be reverted to WT levels with use of the ER stress inhibitor Tauroursodeoxycholic acid (TUDCA).

Conclusions

Together, these results not only suggest that ERAP1 is important for regulating inflammasome dependent innate immune response pathways in vivo, but also propose a mechanism that underlies these changes, that may be associated with increased ER stress due to lack of normal ERAP1 functions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-022-00481-9.

Molecular regulation of neuroinflammation in glaucoma: Current knowledge and the ongoing search for new treatment targets

Neuroinflammation relying on the inflammatory responses of glial cells has emerged as an impactful component of the multifactorial etiology of neurodegeneration in glaucoma. It has become increasingly evident that despite early adaptive and reparative features of glial responses, prolonged reactivity of the resident glia, along with the peripheral immune cells, create widespread toxicity to retinal ganglion cell (RGC) axons, somas, and synapses. As much as the synchronized responses of astrocytes and microglia to glaucoma-related stress or neuron injury, their bi-directional interactions are critical to build and amplify neuroinflammation and to dictate the neurodegenerative outcome. Although distinct molecular programs regulate somatic and axonal degeneration in glaucoma, inhibition of neurodegenerative inflammation can provide a broadly beneficial treatment strategy to rescue RGC integrity and function. Since inflammatory toxicity and mitochondrial dysfunction are converging etiological paths that can boost each other and feed into a vicious cycle, anti-inflammatory treatments may also offer a multi-target potential. This review presents an overview of the current knowledge on neuroinflammation in glaucoma with particular emphasis on the cell-intrinsic and cell-extrinsic factors involved in the reciprocal regulation of glial responses, the interdependence between inflammatory and mitochondrial routes of neurodegeneration, and the research aspects inspiring for prospective immunomodulatory treatments. With the advent of powerful technologies, ongoing research on molecular and functional characteristics of glial responses is expected to accumulate more comprehensive and complementary information and to rapidly move the field forward to safe and effective modulation of the glial pro-inflammatory activities, while restoring or augmenting the glial immune-regulatory and neurosupport functions.

Jianpi Qingchang Decoction Ameliorates Chronic Colitis in Piroxicam-Induced IL-10 Knockout Mice by Inhibiting Endoplasmic Reticulum Stress

Background

Excessive endoplasmic reticulum (ER) stress in intestinal epithelial cells (IEC) may lead to impaired intestinal mucosal barrier function and then participate in the pathogenesis of ulcerative colitis (UC). Jianpi Qingchang decoction (JPQCD) has been shown to have protective effects on UC. However, further studies are needed to determine whether JPQCD regulates PERK/eIF2α/ATF4/CHOP pathways to play a role in treating UC.

Methods

IL-10^−/− mice were randomly assigned into five groups: control, model, low-dose JPQCD (JPQCD L), middle-dose JPQCD (JPQCD M), and high-dose JPQCD (JPQCD H). All groups except for the control group were given model feed containing 200 ppm piroxicam for 10 d to induce colitis. As a comparison, we used wild-type mice that were the progeny of IL-10^+/− matings, bred in the same facility. The control group and wild-type mice were fed with common feed. At the same time, mice in each group were given corresponding drugs by gavage for 14 d. The disease activity index of mice in each group was evaluated daily. Colon tissues of mice were collected, colon length was measured, and pathological changes and ultrastructure of colon epithelial cells were observed. The effects of JPQCD on the PERK/eIF2α/ATF4/CHOP pathways were evaluated by western blotting and reverse transcription-polymerase chain reaction (RT-PCR). The expression of CHOP in colon tissue was detected by tissue immunofluorescence assay. The expression of NF-κB, p-NF-κB p65 protein was analyzed by western blotting; the level of IL-17 in colon tissue was detected by enzyme-linked immunosorbent assay (ELISA) and verified by examining NF-κB and IL-17 mRNA levels by RT-PCR.

Results

Compared with the control group, the model group showed significant colitis symptoms and severe colonic tissue damage. The results showed that JPQCD significantly reduced body weight loss, ameliorated disease activity index, and restored colon length in IL-10^−/− mice with piroxicam-induced colitis. Western blotting and RT-PCR showed that the PERK/eIF2α/ATF4/CHOP pathway was activated in colon tissue of model mice, suggesting that the pathway is involved in the pathogenesis of ulcerative colitis (UC) and could become a potential therapeutic target. The JPQCD treatment inhibited the activation of the PERK/eIF2α/ATF4/CHOP pathway, alleviated the ER stress, and played a role in preventing and treating UC. In addition, JPQCD can also downregulate the protein of NF-κB, p-NF-κB p65, downregulate the mRNA expression of NF-κB, and reduce the content of IL-17 and its mRNA expression in colon tissues.

Conclusion

JPQCD may play a protective role in UC by regulating the PERK/eIF2α/ATF4/CHOP signaling pathway and relieving endoplasmic reticulum stress.

Interaction of Mycobacteria With Host Cell Inflammasomes

The inflammasome complex is important for host defense against intracellular bacterial infections. Mycobacterium tuberculosis (Mtb) is a facultative intracellular bacterium which is able to survive in infected macrophages. Here we discuss how the host cell inflammasomes sense Mtb and other related mycobacterial species. Furthermore, we describe the molecular mechanisms of NLRP3 inflammasome sensing of Mtb which involve the type VII secretion system ESX-1, cell surface lipids (TDM/TDB), secreted effector proteins (LpqH, PPE13, EST12, EsxA) and double-stranded RNA acting on the priming and/or activation steps of inflammasome activation. In contrast, Mtb also mediates inhibition of the NLRP3 inflammasome by limiting exposure of cell surface ligands via its hydrolase, Hip1, by inhibiting the host cell cathepsin G protease via the secreted Mtb effector Rv3364c and finally, by limiting intracellular triggers (K+ and Cl- efflux and cytosolic reactive oxygen species production) via its serine/threonine kinase PknF. In addition, Mtb inhibits the AIM2 inflammasome activation via an unknown mechanism. Overall, there is good evidence for a tug-of-war between Mtb trying to limit inflammasome activation and the host cell trying to sense Mtb and activate the inflammasome. The detailed molecular mechanisms and the importance of inflammasome activation for virulence of Mtb or host susceptibility have not been fully investigated.

Genomic organization, evolution and functional characterization of caspase-2 and caspase-8 in miiuy croaker (Miichthys miiuy)

As the central link and executor of cell apoptosis, the caspase protease family has received extensive attention in recent years. However, the genetic characteristics and immune functions of some caspases are still unknown in fish. In our study, we cloned the full-length caspase-2 (mmCasp2) and caspase-8 (mmCasp2) of miiuy croaker, then we analyzed characteristics and functions of these two genes which are upstream of the apoptosis cascade reaction. Mmcasp2 and mmCasp8 exhibited a conserved domain (CASc), and the different part is that the mmCasp2 has a CARD domain, while mmCasp8 have two DED domains. Sequence and evolution analysis results showed that caspase-2 is more conservative than caspae-8 in the process of evolution. Cellular localization analysis showed that the distribution of mmCasp2 and mmCasp2 was in cytoplasm. The real-time PCR analysis showed that these two caspases are constitutively expressed in different tissues, and the expression of mmCasp2 and mmCasp8 were up-regulated in the liver, spleen, and kidney after infection with V. anguillarum. Lastly, qRT-PCR and Luciferase assays analysis showed that mmCasp2 and mmCasp8 can inhibit the NF-кB pathway. In general, we systematically analyzed the structure, evolution and related functional experiments of the caspase-2 and caspase-8 in miiuy croaker, which will help further understand the role caspase family plays in the apoptosis and immune response.

Crosstalk Between ER Stress, Autophagy and Inflammation

The endoplasmic reticulum (ER) is not only responsible for protein synthesis and folding but also plays a critical role in sensing cellular stress and maintaining cellular homeostasis. Upon sensing the accumulation of unfolded proteins due to perturbation in protein synthesis or folding, specific intracellular signaling pathways are activated, which are collectively termed as unfolded protein response (UPR). UPR expands the capacity of the protein folding machinery, decreases protein synthesis and enhances ER-associated protein degradation (ERAD) which degrades misfolded proteins through the proteasomes. More recent evidences suggest that UPR also amplifies cytokines-mediated inflammatory responses leading to pathogenesis of inflammatory diseases. UPR signaling also activates autophagy; a lysosome-dependent degradative pathwaythat has an extended capacity to degrade misfolded proteins and damaged ER. Thus, activation of autophagy limits inflammatory response and provides cyto-protection by attenuating ER-stress. Here we review the mechanisms that couple UPR, autophagy and cytokine-induced inflammation that can facilitate the development of novel therapeutic strategies to mitigate cellular stress and inflammation associated with various pathologies.

The Interplay between the Unfolded Protein Response, Inflammation and Infection in Cystic Fibrosis

In cystic fibrosis (CF), p.Phe508del is the most frequent mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The p.Phe508del-CFTR protein is retained in the ER and rapidly degraded. This retention likely triggers an atypical Unfolded Protein Response (UPR) involving ATF6, which reduces the expression of p.Phe508del-CFTR. There are still some debates on the role of the UPR in CF: could it be triggered by the accumulation of misfolded CFTR proteins in the endoplasmic reticulum as was proposed for the most common CFTR mutation p.Phe508del? Or, is it the consequence of inflammation and infection that occur in the disease? In this review, we summarize recent findings on UPR in CF and show how infection, inflammation and UPR act together in CF. We propose to rethink their respective role in CF and to consider them as a whole.

Novel insights into RIPK1 as a promising target for future Alzheimer's disease treatment

Alzheimer's disease (AD) is an intractable neurodegenerative disease showing a clinical manifestation with memory loss, cognitive impairment and behavioral dysfunction. The predominant pathological characteristics of AD include neuronal loss, β-amyloid (Aβ) deposition and hyperphosphorylated Tau induced neurofibrillary tangles (NFTs), while considerable studies proved these could be triggered by neuronal death and neuroinflammation. Receptor-interacting protein kinase 1 (RIPK1) is a serine/threonine kinase existed at the cross-point of cell death and inflammatory signaling pathways. Emerging investigations have shed light on RIPK1 for its potential role in AD progression. The present review makes a bird's eye view on the functions of RIPK1 and mainly focus on the underlying linkages between RIPK1 and AD from comprehensive aspects including neuronal death, Aβ and Tau, inflammasome activation, BBB rupture, AMPK/mTOR, mitochondrial dysfunction and O-glcNAcylation. Moreover, the discovery of RIPK1 inhibitors, ongoing clinical trials along with future RIPK1-targeted therapeutics are also reviewed.

Species-Specific Endotoxin Stimulus Determines Toll-Like Receptor 4- and Caspase 11-Mediated Pathway Activation Characteristics

The innate immune system is the body’s first line of defense against pathogens and its protection against infectious diseases. On the surface of host myeloid cells, Toll-like receptor 4 (TLR4) senses lipopolysaccharide (LPS), the major outer membrane component of Gram-negative bacteria. Intracellularly, LPS is recognized by caspase 11 through the noncanonical inflammasome to induce pyroptosis—an inflammatory form of lytic cell death. While TLR4-mediated signaling perturbations result in secretion of cytokines and chemokines that help clear infection and facilitate adaptive immunity, caspase 11-mediated pyroptosis leads to the release of damage-associated molecular patterns and inflammatory mediators. Although the core signaling events and many associated proteins in the TLR4 signaling pathway are known, the complex signaling events and protein networks within the noncanonical inflammasome pathway remain obscure. Moreover, there is mounting evidence for pathogen-specific innate immune tuning. We characterized the major LPS structures from two different pathogens, modeled their binding to the surface receptors, systematically examined macrophage inflammatory responses to these LPS molecules, and surveyed the temporal differences in global protein secretion resulting from TLR4 and caspase 11 activation in macrophages using mass spectrometry (MS)-based quantitative proteomics. This integrated strategy, spanning functional activity assays, top-down structural elucidation of endotoxins, and secretome analysis of stimulated macrophages, allowed us to identify crucial differences in TLR4- and caspase 11-mediated protein secretion in response to two Gram-negative bacterial endotoxins.

IMPORTANCE Macrophages and monocytes are innate immune cells playing an important role in orchestrating the initial innate immune response to bacterial infection and the tissue damage. This response is facilitated by specific receptors on the cell surface and intracellularly. One of the bacterial molecules recognized is a Gram-negative bacteria cell wall component, lipopolysaccharide (LPS). The structure of LPS differs between different species. We have characterized the innate immune responses to the LPS molecules from two bacteria, Escherichia coli and Bordetella pertussis, administered either extracellularly or intracellularly, whose structures we first determined. We observed marked differences in the temporal dynamics and amounts of proteins secreted by the innate immune cells stimulated by any of these molecules and routes. This suggests that there is specificity in the first line of response to different Gram-negative bacteria that can be explored to tailor specific therapeutic interventions.

The Unfolded Protein Response in Immune Cells as an Emerging Regulator of Neuroinflammation

Immune surveillance is an essential process that safeguards the homeostasis of a healthy brain. Among the increasing diversity of immune cells present in the central nervous system (CNS), microglia have emerged as a prominent leukocyte subset with key roles in the support of brain function and in the control of neuroinflammation. In fact, impaired microglial function is associated with the development of neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD). Interestingly, these pathologies are also typified by protein aggregation and proteostasis dysfunction at the level of the endoplasmic reticulum (ER). These processes trigger activation of the unfolded protein response (UPR), which is a conserved signaling network that maintains the fidelity of the cellular proteome. Remarkably, beyond its role in protein folding, the UPR has also emerged as a key regulator of the development and function of immune cells. However, despite this evidence, the contribution of the UPR to immune cell homeostasis, immune surveillance, and neuro-inflammatory processes remains largely unexplored. In this review, we discuss the potential contribution of the UPR in brain-associated immune cells in the context of neurodegenerative diseases.

Multifactorial Pathogenic Processes of Retinal Ganglion Cell Degeneration in Glaucoma towards Multi-Target Strategies for Broader Treatment Effects

Glaucoma is a chronic neurodegenerative disease characterized by apoptosis of retinal ganglion cell (RGC) somas, degeneration of axons, and loss of synapses at dendrites and axon terminals. Glaucomatous neurodegeneration encompasses multiple triggers, multiple cell types, and multiple molecular pathways through the etiological paths with biomechanical, vascular, metabolic, oxidative, and inflammatory components. As much as intrinsic responses of RGCs themselves, divergent responses and intricate interactions of the surrounding glia also play decisive roles for the cell fate. Seen from a broad perspective, multitarget treatment strategies have a compelling pathophysiological basis to more efficiently manipulate multiple pathogenic processes at multiple injury sites in such a multifactorial neurodegenerative disease. Despite distinct molecular programs for somatic and axonal degeneration, mitochondrial dysfunction and glia-driven neuroinflammation present interdependent processes with widespread impacts in the glaucomatous retina and optic nerve. Since dysfunctional mitochondria stimulate inflammatory responses and proinflammatory mediators impair mitochondria, mitochondrial restoration may be immunomodulatory, while anti-inflammatory treatments protect mitochondria. Manipulation of these converging routes may thus allow a unified treatment strategy to protect RGC axons, somas, and synapses. This review presents an overview of recent research advancements with emphasis on potential treatment targets to achieve the best treatment efficacy to preserve visual function in glaucoma.

Potential therapeutic compounds from traditional Chinese medicine targeting endoplasmic reticulum stress to alleviate rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease which affects about 0.5-1% of people with symptoms that significantly impact a sufferer's lifestyle. The cells involved in propagating RA tend to display pro-inflammatory and cancer-like characteristics. Medical drug treatment is currently the main avenue of RA therapy. However, drug options are limited due to severe side effects, high costs, insufficient disease retardation in a majority of patients, and therapeutic effects possibly subsiding over time. Thus there is a need for new drug therapies. Endoplasmic reticulum (ER) stress, a condition due to accumulation of misfolded proteins in the ER, and subsequent cellular responses have been found to be involved in cancer and inflammatory pathologies, including RA. ER stress protein markers and their modulation have therefore been suggested as therapeutic targets, such as GRP78 and CHOP, among others. Some current RA therapeutic drugs have been found to have ER stress-modulating properties. Traditional Chinese Medicines (TCMs) frequently use natural products that affect multiple body and cellular targets, and several medicines and/or their isolated compounds have been found to also have ER stress-modulating capabilities, including TCMs used in RA treatment by Chinese Medicine practitioners. This review encourages, in light of the available information, the study of these RA-treating, ER stress-modulating TCMs as potential new pharmaceutical drugs for use in clinical RA therapy, along with providing a list of other ER stress-modulating TCMs utilized in treatment of cancers, inflammatory diseases and other diseases, that have potential use in RA treatment given similar ER stress-modulating capacity.

BTK Promotes Atherosclerosis by Regulating Oxidative Stress, Mitochondrial Injury, and ER Stress of Macrophages

Atherosclerosis (AS) is a chronic metabolic disease in arterial walls, characterized by lipid deposition and persistent aseptic inflammation. AS is regarded as the basis of a variety of cardiovascular and cerebrovascular diseases. It is widely acknowledged that macrophages would become foam cells after internalizing lipoprotein particles, which is an initial factor in atherogenesis. Here, we showed the influences of Bruton's tyrosine kinase (BTK) in macrophage-mediated AS and how BTK regulates the inflammatory responses of macrophages in AS. Our bioinformatic results suggested that BTK was a potential hub gene, which is closely related to oxidative stress, ER stress, and inflammation in macrophage-induced AS. Moreover, we found that BTK knockdown could restrain ox-LDL-induced NK-κB signaling activation in macrophages and repressed M1 polarization. The mechanistic studies revealed that oxidative stress, mitochondrial injury, and ER stress in macrophages were also suppressed by BTK knockdown. Furthermore, we found that sh-BTK adenovirus injection could alleviate the severity of AS in ApoE^−/− mice induced by a high-fat diet in vivo. Our study suggested that BTK promoted ox-LDL-induced ER stress, oxidative stress, and inflammatory responses in macrophages, and it may be a potential therapeutic target in AS.

Hallmarks of Aging in Macrophages: Consequences to Skin Inflammaging

The skin is our largest organ and the outermost protective barrier. Its aging reflects both intrinsic and extrinsic processes resulting from the constant insults it is exposed to. Aging in the skin is accompanied by specific epigenetic modifications, accumulation of senescent cells, reduced cellular proliferation/tissue renewal, altered extracellular matrix, and a proinflammatory environment favoring undesirable conditions, including disease onset. Macrophages (Mφ) are the most abundant immune cell type in the skin and comprise a group of heterogeneous and plastic cells that are key for skin homeostasis and host defense. However, they have also been implicated in orchestrating chronic inflammation during aging. Since Mφ are related to innate and adaptive immunity, it is possible that age-modified skin Mφ promote adaptive immunity exacerbation and exhaustion, favoring the emergence of proinflammatory pathologies, such as skin cancer. In this review, we will highlight recent findings pertaining to the effects of aging hallmarks over Mφ, supporting the recognition of such cell types as a driving force in skin inflammaging and age-related diseases. We will also present recent research targeting Mφ as potential therapeutic interventions in inflammatory skin disorders and cancer.

IFNs Reset the Differential Capacity of Human Monocyte Subsets to Produce IL-12 in Response to Microbial Stimulation

Human primary monocytes are composed of a minor, more mature CD16+(CD14low/neg) population and a major CD16neg(CD14+) subset. The specific functions of CD16+ versus CD16neg monocytes in steady state or inflammation remain poorly understood. In previous work, we found that IL-12 is selectively produced by the CD16+ subset in response to the protozoan pathogen, Toxoplasma gondii In this study, we demonstrated that this differential responsiveness correlates with the presence of an IFN-induced transcriptional signature in CD16+ monocytes already at baseline. Consistent with this observation, we found that in vitro IFN-γ priming overcomes the defect in the IL-12 response of the CD16neg subset. In contrast, pretreatment with IFN-γ had only a minor effect on IL-12p40 secretion by the CD16+ population. Moreover, inhibition of the mTOR pathway also selectively increased the IL-12 response in CD16neg but not in CD16+ monocytes. We further demonstrate that in contrast to IFN-γ, IFN-α fails to promote IL-12 production by the CD16neg subset and blocks the effect of IFN-γ priming. Based on these observations, we propose that the acquisition of IL-12 responsiveness by peripheral blood monocyte subsets depends on extrinsic signals experienced during their developmental progression in vivo. This process can be overridden during inflammation by the opposing regulatory effects of type I and II IFN as well as the mTOR inhibition.

In vitro Evaluation of Programmed Cell Death in the Immune System of Pacific Oyster Crassostrea gigas by the Effect of Marine Toxins

Programmed cell death (PCD) is an essential process for the immune system's development and homeostasis, enabling the remotion of infected or unnecessary cells. There are several PCD's types, depending on the molecular mechanisms, such as non-inflammatory or pro-inflammatory. Hemocytes are the main component of cellular immunity in bivalve mollusks. Numerous infectious microorganisms produce toxins that impair hemocytes functions, but there is little knowledge on the role of PCD in these cells. This study aims to evaluate in vitro whether marine toxins induce a particular type of PCD in hemocytes of the bivalve mollusk Crassostrea gigas during 4 h at 25°C. Hemocytes were incubated with two types of marine toxins: non-proteinaceous toxins from microalgae (saxitoxin, STX; gonyautoxins 2 and 3, GTX2/3; okadaic acid/dynophysistoxin-1, OA/DTX-1; brevetoxins 2 and 3, PbTx-2,-3; brevetoxin 2, PbTx-2), and proteinaceous extracts from bacteria (Vibrio parahaemolyticus, Vp; V. campbellii, Vc). Also, we used the apoptosis inducers, staurosporine (STP), and camptothecin (CPT). STP, CPT, STX, and GTX 2/3, provoked high hemocyte mortality characterized by apoptosis hallmarks such as phosphatidylserine translocation into the outer leaflet of the cell membrane, exacerbated chromatin condensation, DNA oligonucleosomal fragments, and variation in gene expression levels of apoptotic caspases 2, 3, 7, and 8. The mixture of PbTx-2,-3 also showed many apoptosis features; however, they did not show apoptotic DNA oligonucleosomal fragments. Likewise, PbTx-2, OA/DTX-1, and proteinaceous extracts from bacteria Vp, and Vc, induced a minor degree of cell death with high gene expression of the pro-inflammatory initiator caspase-1, which could indicate a process of pyroptosis-like PCD. Hemocytes could carry out both PCD types simultaneously. Therefore, marine toxins trigger PCD's signaling pathways in C. gigas hemocytes, depending on the toxin's nature, which appears to be highly conserved both structurally and functionally.

Regulation of Caspase-8 Activity at the Crossroads of Pro-Inflammation and Anti-Inflammation

Caspase-8 has been classified as an apoptotic caspase, and its initial definition was an initiator of extrinsic cell death. During the past decade, the concept of caspase-8 functioning has been changed by findings of its additional roles in diverse biological processes. Although caspase-8 was not originally thought to be involved in the inflammation process, many recent works have determined that caspase-8 plays an important role in the regulatory functions of inflammatory processes. In this review, we describe the recent advances in knowledge regarding the manner in which caspase-8 modulates the inflammatory responses concerning inflammasome activation, cell death, and cytokine induction.

Inhibition of Endoplasmic Reticulum Stress by 4-Phenyl Butyric Acid Presents Therapeutic Effects on Periodontitis: Experimental Studies In Vitro and in Rats

This study investigated the probable mechanisms of endoplasmic reticulum (ER) stress involved in periodontitis in vitro and in vivo. We isolated periodontal ligament stem cells from periodontitis patients and healthy controls (P-PDLSCs and H-PDLSCs). To further simulate the periodontal microenvironment in patients, lipopolysaccharide (LPS) was used to treat H-PDLSCs. The results showed that periodontitis-related inflammation gave rise to the upregulated expression levels of ER stress representative genes including GRP78, PERK, ATF4, and CHOP. In contrast, the treatment of 4-phenyl butyric acid (4-PBA) remarkably suppressed ER stress and supported cell viability. The increased secretion of proinflammatory factors like TNF-α, IL-1β, and IL-6 and the activation of NF-κB pathway were also attenuated by 4-PBA treatment. Moreover, 4-PBA treatment restored the impaired osteogenic differentiation ability of PDLSCs, as demonstrated by the upregulated expression levels of Runx2 and OCN as well as the enhanced Alizarin red staining. Local administration of 4-PBA could rescue alveolar bone resorption of LPS-induced periodontitis rats. Thus, our findings suggested ER stress might act as a promising therapeutic target against periodontitis.

Structure, Activation and Regulation of NLRP3 and AIM2 Inflammasomes

The inflammasome is a three-component (sensor, adaptor, and effector) filamentous signaling platform that shields from multiple pathogenic infections by stimulating the proteolytical maturation of proinflammatory cytokines and pyroptotic cell death. The signaling process initiates with the detection of endogenous and/or external danger signals by specific sensors, followed by the nucleation and polymerization from sensor to downstream adaptor and then to the effector, caspase-1. Aberrant activation of inflammasomes promotes autoinflammatory diseases, cancer, neurodegeneration, and cardiometabolic disorders. Therefore, an equitable level of regulation is required to maintain the equilibrium between inflammasome activation and inhibition. Recent advancement in the structural and mechanistic understanding of inflammasome assembly potentiates the emergence of novel therapeutics against inflammasome-regulated diseases. In this review, we have comprehensively discussed the recent and updated insights into the structure of inflammasome components, their activation, interaction, mechanism of regulation, and finally, the formation of densely packed filamentous inflammasome complex that exists as micron-sized punctum in the cells and mediates the immune responses.

Gasdermin D restricts Burkholderia cenocepacia infection in vitro and in vivo

Burkholderia cenocepacia (B. cenocepacia) is an opportunistic bacterium; causing severe life threatening systemic infections in immunocompromised individuals including cystic fibrosis patients. The lack of gasdermin D (GSDMD) protects mice against endotoxin lipopolysaccharide (LPS) shock. On the other hand, GSDMD promotes mice survival in response to certain bacterial infections. However, the role of GSDMD during B. cenocepacia infection is not yet determined. Our in vitro study shows that GSDMD restricts B. cenocepacia replication within macrophages independent of its role in cell death through promoting mitochondrial reactive oxygen species (mROS) production. mROS is known to stimulate autophagy, hence, the inhibition of mROS or the absence of GSDMD during B. cenocepacia infections reduces autophagy which plays a critical role in the restriction of the pathogen. GSDMD promotes inflammation in response to B. cenocepacia through mediating the release of inflammasome dependent cytokine (IL-1β) and an independent one (CXCL1) (KC). Additionally, different B. cenocepacia secretory systems (T3SS, T4SS, and T6SS) contribute to inflammasome activation together with bacterial survival within macrophages. In vivo study confirmed the in vitro findings and showed that GSDMD restricts B. cenocepacia infection and dissemination and stimulates autophagy in response to B. cenocepacia. Nevertheless, GSDMD promotes lung inflammation and necrosis in response to B. cenocepacia without altering mice survival. This study describes the double-edged functions of GSDMD in response to B. cenocepacia infection and shows the importance of GSDMD-mediated mROS in restriction of B. cenocepacia.

Regulation of distinct caspase-8 functions in retinal ganglion cells and astroglia in experimental glaucoma

Retinal ganglion cells (RGCs) expanding from the retina to the brain are primary victims of neurodegeneration in glaucoma, a leading cause of blindness; however, the neighboring astroglia survive the glaucoma-related stress and promote neuroinflammation. In light of diverse functions of caspase-8 in apoptosis, cell survival, and inflammation, this study investigated the importance of caspase-8 in different fates of glaucomatous RGCs and astroglia using two experimental approaches in parallel. In the first approach, cell type-specific responses of RGCs and astroglia to a caspase-8 cleavage-inhibiting pharmacological treatment were studied in rat eyes with or without experimentally induced glaucoma. The second approach utilized an experimental model of glaucoma in mice in which astroglial caspase-8 was conditionally deleted by cre/lox. Findings of these experiments revealed cell type-specific distinct processes that regulate caspase-8 functions in experimental glaucoma, which are involved in inducing the apoptosis of RGCs and promoting the survival and inflammatory responses of astroglia. Deletion of caspase-8 in astroglia protected RGCs against glia-driven inflammatory injury, while the inhibition of caspase-8 cleavage inhibited apoptosis in RGCs themselves. Various caspase-8 functions impacting both RGC apoptosis and astroglia-driven neuroinflammation may suggest the multi-target potential of caspase-8 regulation to provide neuroprotection and immunomodulation in glaucoma.

Crosstalk between endoplasmic reticulum stress and oxidative stress: Focus on protein disulfide isomerase and endoplasmic reticulum oxidase 1

Cellular stress and inflammation, establishing as disease pathology, have reached great heights in the last few decades. Stress conditions such as hyperglycemia, hyperlipidemia and lipoproteins are known to disturb proteostasis resulting in the accumulation of unfolded or misfolded proteins, alteration in calcium homeostasis culminating in unfolded protein response. Protein disulfide isomerase and endoplasmic reticulum oxidase-1 are the key players in protein folding. The protein folding process assisted by endoplasmic reticulum oxidase-1 results in the production of reactive oxygen species in the lumen of the endoplasmic reticulum. Production of reactive oxygen species beyond the quenching capacity of the antioxidant systems perturbs ER homeostasis. Endoplasmic reticulum stress also induces the production of cytokines leading to inflammatory responses. This has been proven to be the major causative factor for various pathophysiological states compared to other cellular triggers in diseases, which further manifests to increased oxidative stress, mitochondrial dysfunction, and altered inflammatory responses, deleterious to cellular physiology and homeostasis. Numerous studies have drawn correlations between the progression of several diseases in association with endoplasmic reticulum stress, redox protein folding, oxidative stress and inflammatory responses. This review aims to provide an insight into the role of protein disulfide isomerase and endoplasmic reticulum oxidase-1 in endoplasmic reticulum stress, unfolded protein response, mitochondrial dysfunction, and inflammatory responses, which exacerbate the progression of various diseases.

Roles of Interactions Between Toll-Like Receptors and Their Endogenous Ligands in the Pathogenesis of Systemic Juvenile Idiopathic Arthritis and Adult-Onset Still's Disease

Systemic juvenile idiopathic arthritis (JIA) and adult-onset Still’s disease (AOSD) are systemic inflammatory disorders that manifest as high-spiking fever, joint pain, evanescent skin rash, and organomegaly. Their pathogenesis is unclear, but inflammation is triggered by activation of the innate immune system with aberrant production of proinflammatory cytokines. Along with extrinsic factors, intrinsic pathways can trigger an unexpected immune response. Damage-associated molecular patterns (DAMPs) induce the activation of innate immune cells, leading to sterile inflammation in systemic JIA and AOSD. These endogenous proteins interact with Toll-like receptors (TLRs), which are pattern recognition receptors, and mediate immune signaling following stimulation by pathogen-associated molecular patterns and DAMPs. Several DAMPs, such as S100 proteins, play a role in the development or severity of systemic JIA and AOSD, in which their interactions with TLRs are altered. Also, the expression levels of genes encoding DAMPs contribute to the susceptibility to systemic JIA and AOSD. Herein, we review reports that TLR and DAMP signaling initiates and/or maintains the inflammatory response in systemic JIA and AOSD, and their correlations with the clinical characteristics of those diseases. In addition, we assess their utility as biomarkers or therapeutics for systemic JIA and AOSD.

Does intestinal dysbiosis contribute to an aberrant inflammatory response to severe acute respiratory syndrome coronavirus 2 in frail patients?

In a few months, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has become the main health problem worldwide. Epidemiologic studies revealed that populations have different vulnerabilities to SARS-CoV-2. Severe outcomes of the coronavirus disease 2019 (COVID-19) with an increased risk of death are observed in patients with metabolic syndrome, as well as diabetic and heart conditions (frail population). Excessive proinflammatory cytokine storm could be the main cause of increased vulnerability in this frail population. In patients with diabetes and/or heart disease, a low inflammatory state is often associated with gut dysbiosis. The increase amount of microbial metabolites (i.e., trimethylamine N-oxide and lipopolysaccharide), which generate an inflammatory microenvironment, is probably associated with an improved risk of severe illness from COVID-19. Nutritional interventions aimed at restoring the gut microbial balance could represent preventive strategies to protect the frail population from COVID-19. This narrative review presents the possible molecular mechanisms by which intestinal dysbiosis that enhances the inflammatory state could promote the spread of SARS-CoV-2 infection. Some nutritional strategies to counteract inflammation in frail patients are also analyzed.

Si-Wu-Tang Alleviates Nonalcoholic Fatty Liver Disease via Blocking TLR4-JNK and Caspase-8-GSDMD Signaling Pathways

Background

Nonalcoholic fatty liver disease (NAFLD) has high global prevalence; however, the treatments of NAFLD are limited due to lack of approved drugs.

Methods

Mice were randomly assigned into three groups: Control group, NAFLD group, NAFLD plus Si-Wu-Tang group. A NAFLD mice model was established by feeding with a methionine- and choline-deficient (MCD) diet for four weeks. Si-Wu-Tang was given orally by gastric gavage at the beginning of 3rd week, and it lasted for two weeks. The treatment effects of Si-Wu-Tang were confirmed by examining the change of body weight, serum alanine aminotransferase (ALT) and aspartate transaminase (AST) levels, Oil Red O staining, and hematoxylin and eosin (H&E) staining of the liver samples and accompanied by steatosis grade scores. The expression and activation of the possible signaling proteins involved in the pathogenesis of NAFLD were determined by western blotting.

Results

Mice fed with four weeks of MCD diet displayed elevated serum levels of ALT and AST, while there was decreased body weight. The hepatic Oil Red O staining and H&E staining showed severe liver steatosis with high steatosis grade scores. All these can be improved by treating with Si-Wu-Tang for two weeks. Mechanistically, the increased hepatic TLR4 expression and its downstream JNK phosphorylation induced by MCD diet were suppressed by Si-Wu-Tang. Moreover, the upregulations of Caspase-8, gasdermin D (GSDMD), and cleaved-GSDMD in liver mediated by MCD diet were all inhibited by Si-Wu-Tang.

Conclusions

Treatment with Si-Wu-Tang improves MCD diet-induced NAFLD in part via blocking TLR4-JNK and Caspase-8-GSDMD signaling pathways, suggesting that Si-Wu-Tang has potential for clinical application in treating NAFLD.

Inflammasome signaling and regulation of interleukin-1 family cytokines

Specific IL-1 family cytokines are initially expressed as inactive, cytosolic pro-forms. Chan and Schroder review inflammasome signaling and cell death decisions, mechanisms underpinning IL-1α, IL-1β, IL-18, and IL-37 maturation and release, and the functions of these cytokines in protective and pathological inflammation.

Specific IL-1 family cytokines are expressed by cells as cytosolic pro-forms that require cleavage for their activity and cellular release. IL-1β, IL-18, and IL-37 maturation and secretion is governed by inflammatory caspases within signaling platforms called inflammasomes. By inducing pyroptosis, inflammasomes can also drive the release of the alarmin IL-1α. Recent advances have transformed our mechanistic understanding of inflammasome signaling, cell death decisions, and cytokine activation and secretion. Here, we provide an updated view of inflammasome signaling; mechanisms underpinning IL-1α, IL-1β, IL-18, and IL-37 maturation and release; and the functions of these cytokines in protective and pathological inflammation.

Caspase-8-Dependent Inflammatory Responses Are Controlled by Its Adaptor, FADD, and Necroptosis

Cell death pathways regulate various homeostatic processes. Autoimmune lymphoproliferative syndrome (ALPS) in humans and lymphoproliferative (LPR) disease in mice result from abrogated CD95-induced apoptosis. Because caspase-8 mediates CD95 signaling, we applied genetic approaches to dissect the roles of caspase-8 in cell death and inflammation. Here, we describe oligomerization-deficient Caspase-8^{F122GL123G/F122GL123G} and non-cleavable Caspase-8^D387A/D387A mutant mice with defective caspase-8-mediated apoptosis. Although neither mouse developed LPR disease, removal of the necroptosis effector Mlkl from Caspase-8^D387A/D387A mice revealed an inflammatory role of caspase-8. Ablation of one allele of Fasl, Fadd, or Ripk1 prevented the pathology of Casp8^D387A/D387AMlkl^-/- animals. Removing both Fadd alleles from these mice resulted in early lethality prior to post-natal day 15 (P15), which was prevented by co-ablation of either Ripk1 or Caspase-1. Our results suggest an in vivo role of the inflammatory RIPK1-caspase-8-FADD (FADDosome) complex and reveal a FADD-independent inflammatory role of caspase-8 that involves activation of an inflammasome.

The first evidence of four transcripts from two Interleukin 18 genes in animal and their involvement in immune responses in the largest amphibian Andrias davidianus

Interleukin 18 (IL-18), a member of IL-1 cytokine superfamily, is an important proinflammatory cytokine with multiple functions in both innate immunity and acquired immunity. However, the characteristics and functional roles of IL-18 remain largely unknown in amphibians, which were classed as major group of vertebrates. In the present study, two IL-18 genes (AdIL-18A and AdIL-18B) and four transcripts (AdIL-18A1, AdIL-18A2, AdIL-18B1 and AdIL-18B2) were firstly identified and characterized from Chinese giant salamander (Andrias davidianus). To the best of our knowledge, this is the first report on the presence of more than one gene copy or two transcripts of IL-18 in one species. The complete open reading frames of AdIL-18A1, AdIL-18A2, AdIL-18B1 and AdIL-18B2 were 588 bp, 603 bp, 591 bp and 606 bp, respectively. The putative AdIL-18 proteins possessed the typical IL-1 domains and phylogenetic analysis indicated that AdIL-18s grouped together with other vertebrate IL-18 proteins. The expression profiles of AdIL-18s were investigated under the challenges of Aeromonas hydrophila, Staphylococcus ureae and Poly (I:C) respectively, and the results suggested that AdIL-18s were involved in the immune responses against both bacterial and viral infections. Moreover, the expression levels of two NF-κBs (P100 and P105) and four proinflammatory cytokines (IL-1β, IL-6, TNF-α and IFN-γ) were inhibited in AdIL-18A1/A2-silenced cells when treated with bacteria and viral RNA analog. Additionally, the transcription levels of these immune-related cytokine genes were markedly induced when the lymphocytes were treated with recombinant AdIL-18A1 or AdIL-18A2 proteins, implying the involvement of AdIL-18s in triggering NF-κB signaling and proinflammatory responses. These results might provide new insights into the origin or evolution of IL-18 in amphibians and even in vertebrates.

The Emerging Roles of Endoplasmic Reticulum Stress in Balancing Immunity and Tolerance in Health and Diseases: Mechanisms and Opportunities

The endoplasmic reticulum (ER) is an organelle equipped with mechanisms for proper protein folding, trafficking, and degradation to maintain protein homeostasis in the secretory pathway. As a defense mechanism, perturbation of ER proteostasis by ER stress agents activates a cascade of signaling pathways from the ER to the nucleus known as unfolded protein response (UPR). The primary goal of UPR is to induce transcriptional and translational programs to restore ER homeostasis for cell survival. As such, defects in UPR signaling have been implicated as a key contributor to multiple diseases including metabolic diseases, degenerative diseases, inflammatory disorders, and cancer. Growing evidence support the critical role of ER stress in regulating the fate as well as the magnitude of the immune response. Moreover, the availability of multiple UPR pharmacological inhibitors raises the hope that targeting UPR can be a new strategy for immune modulation and immunotherapy of diseases. This paper reviews the principal mechanisms by which ER stress affects immune cell biology and function, with a focus of discussion on UPR-associated immunopathology and the development of potential ER stress-targeted therapeutics.

Molecular Signatures of Neuroinflammation Induced by αSynuclein Aggregates in Microglial Cells

Alpha-synuclein (αSyn_Agg) are pathological hallmarks of Parkinson's disease (PD) and other synucleinopathies that induce microglial activation and immune-mediated neurotoxicity, but the molecular mechanisms of αSyn_Agg-induced immune activation are poorly defined. We performed quantitative proteomics by mass spectrometry coupled with PCR, immunohistochemical and functional validations studies to define the molecular characteristics of alpha synuclein mediated microglial activation. In mouse microglia, αSyn_Agg induced robust pro-inflammatory activation (increased expression of 864 genes including Irg1, Ifit1, and Pyhin) and increased nuclear proteins involved in RNA synthesis, splicing, and anti-viral defense mechanisms. Conversely, αSyn_Agg decreased expression several proteins (including Cdc123, Sod1, and Grn), which were predominantly cytosolic and involved in metabolic, proteasomal and lysosomal mechanisms. Pathway analyses and confirmatory in vitro studies suggested that αSyn_Agg partly mediates its effects via Stat3 activation. As predicted by our proteomic findings, we verified that αSyn_Agg induces mitochondrial dysfunction in microglia. Twenty-six proteins differentially expressed by αSyn_Agg were also identified as PD risk genes in genome-wide association studies (upregulated: Brd2, Clk1, Siglec1; down-regulated: Memo1, Arhgap18, Fyn, and Pgrn/Grn). We validated progranulin (PGRN) as a lysosomal PD-associated protein that is downregulated by αSyn_Agg in microglia in-vivo and is expressed by microglia in post-mortem PD brain, congruent with our in vitro findings. Conclusion: Together, proteomics approach both reveals novel molecular insights into αSyn-mediated neuroinflammation in PD and other synucleinopathies.

Pharmacological Inhibition of Caspase-8 Suppresses Inflammation-Induced Angiogenesis in the Cornea

Inflammation-induced angiogenesis is closely related to many diseases and has been regarded as a therapeutic target. Caspase-8 has attracted increasing attention for its immune properties and therapeutic potential in inflammatory disorders. The aim of our study is to investigate the clinical application of pharmacological inhibition of caspase-8 and the underlying molecular mechanisms in inflammation-induced angiogenesis in the cornea. A model of alkali burn (AB)-induced corneal neovascularization (CNV) in C57BL/6 wild-type (WT) mice and toll-like receptor 4 knockout (Tlr4^-/-) mice was used. We found that AB increased caspase-8 activity and the pharmacological inhibition of caspase-8 exerted substantial inhibitory effects on CNV, with consistent decreases in caspase-8 activity, inflammatory cell infiltration, macrophage recruitment and activation, VEGF-A, TNF-α, IL-1β, MIP-1, and MCP-1 expression in the cornea. In vitro, caspase-8 mediated TLR4–dependent chemokines and VEGF-A production by macrophages. The TLR4 knockout significantly alleviated CNV, suppressed caspase-8 activity and downregulated expression of inflammatory cytokines and chemokines after AB. Taken together, these findings provide the first demonstration that the pharmacological inhibition of caspase-8 suppresses inflammation-induced angiogenesis and support the use of a pharmacological caspase-8 inhibitor as a novel clinical treatment for CNV and other angiogenic disorders.

The role of IL-1β in aortic aneurysm

Interleukin-1β (IL-1β) is a vital cytokine that plays an important role in regulating immune responses to infectious challenges and sterile insults. In addition, two endogenous inhibitors of functional receptor binding, IL-1 receptor antagonist (IL-1Ra), complete the family. To gain biological activity, IL-1β requires processing by the protease caspase-1 and activation of inflammasomes. Numerous clinical association studies and experimental approaches have implicated members of the IL-1 family, their receptors, or components of the processing machinery in the underlying processes of cardiovascular diseases. Here, we summarize the current state of knowledge regarding the pro-inflammatory and disease-modulating role of the IL-1 family in aneurysm. We discuss clinical evidence, signalling pathway, and mechanism of action and last, lend a perspective on currently developing therapeutic strategies involving IL-1β in aneurysm.

Cigarette smoke inhibits the NLRP3 inflammasome and leads to caspase-1 activation via the TLR4-TRIF-caspase-8 axis in human macrophages

The NLRP3 inflammasome is formed by the sensor NLRP3, the adaptor ASC, and pro-caspase-1. Assembly and activation of the inflammasome trigger caspase-1-dependent cleavage of pro-IL-1β and pro-IL-18 into their secreted forms. Cigarette smoke is a risk factor for chronic inflammatory diseases and is associated with macrophage dysfunction. The impact of cigarette smoke on NLRP3-dependent responses in macrophages is largely unknown. Herein, we investigated the effects of cigarette smoke extract (CSE) on the NLRP3 inflammasome in human monocyte-derived macrophages (MDMs) and THP-1 cells stimulated with lipopolysaccharide (LPS) and LPS plus the NLRP3 inflammasome activator ATP. We found that CSE inhibited the release of IL-1β and IL-18 as well as the expression of NLRP3 acting mainly at the transcriptional level. Interestingly, we found that CSE increased the caspase-1 activity via an NLRP3-independent and TLR4-TRIF-caspase-8-dependent pathway. Activation of caspase-1 by CSE led to a reduction of the basal glycolytic flux and impaired glycolytic burst in response to LPS. Overall, our findings unveil novel pathways leading to immune-metabolic alterations in human macrophages exposed to cigarette smoke. These mechanisms may contribute to macrophage dysfunction and increased risk of infection in smokers.

InP/ZnS Quantum Dots Cause Inflammatory Response in Macrophages Through Endoplasmic Reticulum Stress and Oxidative stress

Purpose

Quantum dots (QDs) are widely used semiconductor nanomaterials. Indium phosphide/zinc sulfide (InP/ZnS) QDs are becoming potential alternatives to toxic heavy metal-containing QDs. However, the potential toxicity and, in particular, the immunotoxicity of InP/ZnS QDs are unknown. This study aimed to investigate the impacts of InP/ZnS QDs on inflammatory responses both in vivo and in vitro.

Methods

Mice and mouse bone marrow-derived macrophages (BMMs) were exposed to polyethylene glycol (PEG) coated InP/ZnS QDs. The infiltration of neutrophils and the release of interleukin-6 (IL-6) were measured using a hematology analyzer and an enzyme-linked immunosorbent assay (ELISA) for the in vivo test. Cytotoxicity, IL-6 secretion, oxidative stress and endoplasmic reticulum (ER) stress were studied in the BMMs, and then, inhibitors of oxidative stress and ER stress were used to explore the mechanism of the InP/ZnS QDs.

Results

We found that 20 mg/kg PEG-InP/ZnS QDs increased the number of neutrophils and the levels of IL-6 in both peritoneal lavage fluids and blood, which indicated acute phase inflammation in the mice. PEG-InP/ZnS QDs also activated the BMMs and increased the production of IL-6. In addition, PEG-InP/ZnS QDs triggered oxidative stress and the ER stress-related PERK-ATF4 pathway in the BMMs. Moreover, the inflammatory response caused by the PEG-InP/ZnS QDs could be attenuated in the macrophages by blocking the oxidative stress or the ER stress with inhibitors.

Conclusion

InP/ZnS QDs can activate macrophages and induce acute phase inflammation both in vivo and in vitro, which may be regulated by oxidative stress and ER stress. Our present work is expected to help clarify the biosafety of InP/ZnS QDs and promote their safe application in biomedical and engineering fields.