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

Chang'an decoction alleviates endoplasmic reticulum stress by regulating mitofusin 2 to improve colitis

OBJECTIVE

To evaluate the protective effects of Chang'an decoction (, CAD) on colitis, and investigate the potential mechanisms underlying these effects from the perspectives of endoplasmic reticulum (ER) stress induced by mitofusin 2 (MFN2).

METHODS

The composition of CAD was identified by liquid chromatography-mass spectrometry technology. A mice model of dextran sulfate sodium (DSS) induced colitis was established and therapeutic effects of CAD were determined by detecting body weight, disease activity index, colon length and histopathological changes. Then, the expression levels of MFN2, ER stress markers and Nucleotide-binding domain and leucine-rich repeat protein3 (NLRP3) relevant proteins were detected by polymerase chain reaction (PCR), Western blot, immunohistochemistry and immunofluorescence staining. Subsequently, knockdown and overexpression cell model were constructed to further investigate the underlying mechanism of MFN2 mediating ER stress and energy metabolism by PCR, Western blot, electron microscopy and reactive oxygen species (ROS) staining. Finally, inflammatory indicator and tight junction proteins were measured by PCR and immunofluorescence staining to evaluate the protective effects of CAD.

RESULTS

Results showed that the indispensable regulatory role of MFN2 in mediating ER stress and mitochondrial damage was involved in the protective effects of CAD on colitis in mice fed with DSS. Network pharmacology analysis also revealed CAD may play a protective effect on colitis by affecting mitochondrial function. In addition, our data also suggested a causative role for MFN2 in the development of inflammatory responses and energy metabolic alterations by constructing a knockdown and overexpression cell model whereby alter proper ER-mitochondria interaction in Caco-2 cells. Furthermore, relative expression analyses of ER stress markers and NLRP3 inflammasome showed the onset of ER stress and activation of NLRP3 inflammasome, which is consistent with the above findings. In contrast, intervention of CAD could improve the mucosal barrier integrity and colonic inflammatory response effectively through inhibiting ER stress response mediated by MFN2.

CONCLUSION

CAD could alleviate ER stress by regulating MFN2 to exert therapeutic effects on DSS-induced colitis, which might provide an effective natural therapeutic approach for the treatment of ulcerative colitis.

Host and microbial regulation of mitochondrial reactive oxygen species during mycobacterial infections

Mycobacteria, including Mycobacterium tuberculosis (Mtb) and non-tuberculous mycobacteria (NTM), pose challenges in treatment due to their increased resistance to antibiotics. Following infection, mycobacteria and their components trigger robust innate and inflammatory immune responses intricately associated with the modulation of mitochondrial functions, including oxidative phosphorylation (OXPHOS) and metabolism. Certainly, mitochondrial reactive oxygen species (mtROS) are an inevitable by-product of OXPHOS and function as a bactericidal weapon; however, an excessive accumulation of mtROS are linked to pathological inflammation and necroptotic cell death during mycobacterial infection. Despite previous studies outlining various host pathways involved in regulating mtROS levels during antimicrobial responses in mycobacterial infection, our understanding of the precise mechanisms orchestrating the fine regulation of this response remains limited. Emerging evidence suggests that mycobacterial proteins play a role in targeting the mitochondria of the host, indicating the potential influence of microbial factors on mitochondrial functions within host cells. In this review, we provide an overview of how both host and Mtb factors influence mtROS generation during infection. A comprehensive study of host and microbial factors that target mtROS will shed light on innovative approaches for effectively managing drug-resistant mycobacterial infections.

Reactive oxygen species trigger inflammasome activation after intracellular microbial interaction

The intracellular production of reactive oxygen species (ROS), composed of oxygen-reduced molecules, is important not only because of their lethal effects on microorganisms but also due to their potential inflammatory and metabolic regulation properties. The ROS pro-inflammatory properties are associated with the second signal to inflammasome activation, leading to cleaving pro-IL-1β and pro-IL18 before their secretion, as well as gasdermin-D, leading to pyroptosis. Some microorganisms can modulate NLRP3 and AIM-2 inflammasomes through ROS production: whilst Mycobacterium bovis, Mycobacterium kansasii, Francisella novicida, Brucella abortus, Listeria monocytogenes, Influenza virus, Syncytial respiratory virus, Porcine reproductive and respiratory syndrome virus, SARS-CoV, Mayaro virus, Leishmania amazonensis and Plasmodium sp. enhance inflammasome assembly, Hepatitis B virus, Mycobacterium marinum, Mycobacterium tuberculosis, Francisella tularensis and Leishmania sp. disrupt it. This process represents a recent cornerstone in our knowledge of the immunology of intracellular pathogens, which is reviewed in this mini-review.

Endoplasmic Reticulum Stress Mediated NLRP3 Inflammasome Activation and Pyroptosis in THP-1 Macrophages Infected with Bacillus Calmette-Guérin

Tuberculosis (TB) is a zoonotic infectious disease caused by Mycobacterium tuberculosis (Mtb). Mtb is a typical intracellular parasite, and macrophages are its main host cells. NLRP3 inflammasome-mediated pyroptosis is a form of programmed cell death implicated in the clearance of pathogenic infections. The bidirectional regulatory effect of endoplasmic reticulum stress (ERS) plays a crucial role in determining cell survival and death. Whether ERS is involved in macrophage pyroptosis with Mtb infection remains unclear. This article aims to explore the regulation of the NLRP3 inflammasome and pyroptosis by ERS in THP-1 macrophages infected with Mycobacterium bovis Bacillus Calmette-Guérin (BCG). The results showed that BCG infection induced THP-1 macrophage ERS, NLRP3 inflammasome activation and pyroptosis, which was inhibited by ERS inhibitor TUDCA. NLRP3 inhibitor MCC950 inhibited THP-1 macrophage NLRP3 inflammasome activation and pyroptosis caused by BCG infection. Compared with specific Caspase-1 inhibitor VX-765, pan-Caspase inhibitor Z-VAD-FMK showed a more significant inhibitory effect on BCG infection-induced pyroptosis of THP-1 macrophages. Taken together, this study demonstrates that ERS mediated NLRP3 inflammasome activation and pyroptosis after BCG infection of THP-1 macrophages, and that BCG infection of THP-1 macrophages induces pyroptosis through canonical and noncanonical pathways.

SIRT1 ameliorated septic associated-lung injury and macrophages apoptosis via inhibiting endoplasmic reticulum stress

BACKGROUND

The inappropriate apoptosis of macrophages plays an important role in the pathogenesis of sepsis-induced acute lung injury, however, the detailed regulatory mechanisms remain largely unknown. As an endogenous apoptosis pathway, endoplasmic reticulum (ER) stress plays an important role in cell damage in patients with sepsis. Clarifying the ER stress response and its effect on macrophages during the development of sepsis is helpful to explore new strategies for the prevention and treatment of ALI in sepsis.

METHODS

The mouse model and the RAW264.7 inflammation model were stimulated with LPS to establish in vivo and in vitro. We explored the effects of different expression levels of silent information regulator factor 2-related enzyme 1 (SIRT1) on the ER stress response and apoptosis of macrophages in the sepsis-related injury model.

RESULTS

Our studies found that the increased expression of SIRT1 can significantly improve sepsis-related lung injury and relieve lung inflammation. SRT1720, a SIRT1 activator, can significantly inhibit the ER stress response of lung tissue and macrophages, inhibit the expression of pro-apoptotic proteins, promote the expression of anti-apoptotic proteins, and reduce macrophages of apoptosis. While the EX527, an inhibitor of SIRT1, had the opposite effect.

CONCLUSION

SIRT1 can significantly improve sepsis-associated lung injury and LPS-induced macrophage apoptosis. This protective effect is closely related to its inhibition of the ER stress response via the PERK/eIF2-α/ATF4/CHOP pathway.

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.

Leptin Induces Apoptotic and Pyroptotic Cell Death via NLRP3 Inflammasome Activation in Rat Hepatocytes

Leptin, a hormone that is predominantly produced by adipose tissue, is closely associated with various liver diseases. However, there is a lack of understanding as to whether leptin directly induces cytotoxic effects in hepatocytes as well as the mechanisms that are involved. Inflammasomes, which are critical components in the innate immune system, have been recently shown to modulate cell death. In this study, we examined the effect of leptin on the viability of rat hepatocytes and the underlying mechanisms, with a particular focus on the role of inflammasomes activation. Leptin treatment induced cytotoxicity in rat hepatocytes, as determined by decreased cell viability, increased caspase-3 activity, and the enhanced release of lactate dehydrogenase. NLRP3 inflammasomes were activated by leptin both in vitro and in vivo, as determined by the maturation of interleukin-1β and caspase-1, and the increased expression of inflammasome components, including NLRP3 and ASC. Mechanistically, leptin-induced inflammasome activation is mediated via the axis of ROS production, ER stress, and autophagy. Notably, the inhibition of inflammasomes by treatment with the NLRP3 inhibitor or the IL-1 receptor antagonist protected the hepatocytes from leptin-induced cell death. Together, these results indicate that leptin exerts cytotoxic effects in hepatocytes, at least in part, via the activation of NLRP3 inflammasomes.

Mycobacterium bovis induces mitophagy to suppress host xenophagy for its intracellular survival

Mitophagy is a selective autophagy mechanism for eliminating damaged mitochondria and plays a crucial role in the immune evasion of some viruses and bacteria. Here, we report that Mycobacterium bovis (M. bovis) utilizes host mitophagy to suppress host xenophagy to enhance its intracellular survival. M. bovis is the causative agent of animal tuberculosis and human tuberculosis. In the current study, we show that M. bovis induces mitophagy in macrophages, and the induction of mitophagy is impaired by PINK1 knockdown, indicating the PINK1-PRKN/Parkin pathway is involved in the mitophagy induced by M. bovis. Moreover, the survival of M. bovis in macrophages and the lung bacterial burden of mice are restricted by the inhibition of mitophagy and are enhanced by the induction of mitophagy. Confocal microscopy analysis reveals that induction of mitophagy suppresses host xenophagy by competitive utilization of p-TBK1. Overall, our results suggest that induction of mitophagy enhances M. bovis growth while inhibition of mitophagy improves growth restriction. The findings provide a new insight for understanding the intracellular survival mechanism of M. bovis in the host.

Abbreviations: BMDM: mouse bone marrow-derived macrophage; BNIP3: BCL2/adenovirus E1B interacting protein 3; BNIP3L/NIX: BCL2/adenovirus E1B interacting protein 3-like; BCL2L13: BCL2-like 13 (apoptosis facilitator); CCCP: carbonyl cyanide m-cholorophenyl hydrazone; FUNDC1: FUN14 domain-containing 1; FKBP8: FKBP506 binding protein 8; HCV: hepatitis C virus; HBV: hepatitis B virus; IFN: interferon; L. monocytogenes: Listeria monocytogenes; M. bovis: Mycobacterium bovis; Mtb: Mycobacterium tuberculosis; Mdivi-1: mitochondrial division inhibitor 1; PINK1: PTEN-induced putative kinase 1; TBK1: TANK-binding kinase 1; TUFM: Tu translation elongation factor, mitochondrial; TEM: transmission electron microscopy

Koumiss promotes Mycobacterium bovis infection by disturbing intestinal flora and inhibiting endoplasmic reticulum stress

Mycobacterium bovis is the causative agent of bovine tuberculosis and also responsible for serious threat to public health. Koumiss is a fermented mare's milk product, used as traditional drink. Here, we explored the effect of koumiss on gut microbiota and the host immune response against M bovis infection. Therefore, mice were treated with koumiss and fresh mare milk for 14 days before M bovis infection and continue for 5 weeks after infection. The results showed a clear change in the intestinal flora of mice treated with koumiss, and the lungs of mice treated with koumiss showed severe edema, inflammatory infiltration, and pulmonary nodules in M bovis-infected mice. Notably, we found that the content of short-chain fatty acids was significantly lower in the koumiss-treated group compared with the control group. However, the expression of endoplasmic reticulum stress and apoptosis-related proteins in the lungs of koumiss-treated mice were significantly decreased. Collectively, these findings suggest that koumiss treatment disturb the intestinal flora of, which is associated with disease severity and the possible mechanism that induces lungs pathology. Our current findings can be exploited further to establish the "gut-lung" axis which might be a novel strategy for the control of tuberculosis.

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.

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.

Apoptotic caspases suppress Mycobacterium bovis-induced IFN-β production in murine macrophage

Caspases are classified as inflammatory or apoptotic category. Inflammatory caspases participate in inflammasome activation, while apoptotic caspases mediate apoptotic activation. Previous studies have shown that apoptotic caspases prevent the production of IFN-β during apoptosis or virus infection. However, the relationship between apoptotic caspases and IFN-β production during intracellular bacterial infection is still unclear. Here, we investigated the role of apoptotic caspases in IFN-β production induced by Mycobacterium bovis (M. bovis) infection. M. bovis is an intracellular bacterium and belongs to the Mycobacterium tuberculosis complex. M. bovis infection can cause tuberculosis in animals and human beings. In the current study, we found that M. bovis infection triggered mitochondrial stress, which caused the leakage of cytochrome c into the cytoplasm, and in turn, activated the downstream caspase-9 and-3. Furthermore, our results showed that activation of apoptotic caspases reduced IFN-β production during M. bovis infection and vice versa. Confocal microscopy analysis revealed that apoptotic caspases prevented IFN-β production by decreasing p-IRF3 nuclear translocation. Our findings demonstrate that apoptotic caspases negatively regulate the production of IFN-β induced by an intracellular bacterial infection.

Downregulation of XBP1 protects kidney against ischemia-reperfusion injury via suppressing HRD1-mediated NRF2 ubiquitylation

Ischemia-reperfusion (IR) injury to the renal epithelia is associated with endoplasmic reticulum stress (ERS) and mitochondria dysfunction, which lead to oxidative stress-induced acute kidney injury (AKI). X-box binding protein 1 (XBP1), an ERS response protein, could play a prominent role in IR-induced AKI. In this study, we revealed that XBP1 and its downstream target HRD1 participated in the crosstalk between ERS and mitochondrial dysfunction via regulation of NRF2/HO-1-mediated reactive oxidative stress (ROS) signaling. Mice with reduced expression of XBP1 (heterozygous Xbp1±) were resistant to IR-induced AKI due to the enhanced expression of NRF2/HO-1 and diminished ROS in the kidney. Downregulation of XBP1 in renal epithelial cells resulted in reduced HRD1 expression and increased NRF2/HO-1 function, accompanied with enhanced antioxidant response. Furthermore, HRD1 served as an E3-ligase to facilitate the downregulation of NRF2 through ubiquitination-degradation pathway, and the QSLVPDI motif on NRF2 constituted an active site for its interaction with HRD1. Thus, our findings unveil an important physiological role for XBP1/HRD1 in modulating the antioxidant function of NRF2/HO-1 in the kidney under stress conditions. Molecular therapeutic approaches that target XBP1-HRD1-NRF2 pathway may represent potential effective means to treat renal IR injury.

The complex interplay between endoplasmic reticulum stress and the NLRP3 inflammasome: a potential therapeutic target for inflammatory disorders

Inflammation is the result of a complex network of cellular and molecular interactions and mechanisms that facilitate immune protection against intrinsic and extrinsic stimuli, particularly pathogens, to maintain homeostasis and promote tissue healing. However, dysregulation in the immune system elicits excess/abnormal inflammation resulting in unintended tissue damage and causes major inflammatory diseases including asthma, chronic obstructive pulmonary disease, atherosclerosis, inflammatory bowel diseases, sarcoidosis and rheumatoid arthritis. It is now widely accepted that both endoplasmic reticulum (ER) stress and inflammasomes play critical roles in activating inflammatory signalling cascades. Notably, evidence is mounting for the involvement of ER stress in exacerbating inflammasome-induced inflammatory cascades, which may provide a new axis for therapeutic targeting in a range of inflammatory disorders. Here, we comprehensively review the roles, mechanisms and interactions of both ER stress and inflammasomes, as well as their interconnected relationships in inflammatory signalling cascades. We also discuss novel therapeutic strategies that are being developed to treat ER stress- and inflammasome-related inflammatory disorders.

Therapeutic Potential of Pharmacological Targeting NLRP3 Inflammasome Complex in Cancer

Introduction

Dysregulation of NLRP3 inflammasome complex formation can promote chronic inflammation by increased release of IL-1β. However, the effect of NLRP3 complex formation on tumor progression remains controversial. Therefore, we sought to determine the effect of NLRP3 modulation on the growth of the different types of cancer cells, derived from lung, breast, and prostate cancers as well as neuroblastoma and glioblastoma in-vitro.

Method

The effect of Caspase 1 inhibitor (VX765) and combination of LPS/Nigericin on NLRP3 inflammasome activity was analyzed in A549 (lung cancer), MCF-7 (breast cancer), PC3 (prostate cancer), SH-SY5Y (neuroblastoma), and U138MG (glioblastoma) cells. Human fibroblasts were used as control cells. The effect of VX765 and LPS/Nigericin on NLRP3 expression was analyzed using western blot, while IL-1β and IL-18 secretion was detected by ELISA. Tumor cell viability and progression were determined using Annexin V, cell proliferation assay, LDH assay, sphere formation assay, transmission electron microscopy, and a multiplex cytokine assay. Also, angiogenesis was investigated by a tube formation assay. VEGF and MMPs secretion were detected by ELISA and a multiplex assay, respectively. Statistical analysis was done using one-way ANOVA with Tukey’s analyses and Kruskal–Wallis one-way analysis of variance.

Results

LPS/Nigericin increased NRLP3 protein expression as well as IL-1β and IL-18 secretion in PC3 and U138MG cells compared to A549, MCF7, SH-SY5Y cells, and fibroblasts. In contrast, MIF expression was commonly found upregulated in A549, PC3, SH-SY5Y, and U138MG cells and fibroblasts after Nigericin treatment. Nigericin and a combination of LPS/Nigericin decreased the cell viability and proliferation. Also, LPS/Nigericin significantly increased tumorsphere size in PC3 and U138MG cells. In contrast, the sphere size was reduced in MCF7 and SH-SY5Y cells treated with LPS/Nigericin, while no effect was detected in A549 cells. VX765 increased secretion of CCL24 in A549, MCF7, PC3, and fibroblasts as well as CCL11 and CCL26 in SH-SY5Y cells. Also, VX765 significantly increased the production of VEGF and MMPs and stimulated angiogenesis in all tumor cell lines.

Discussion

Our data suggest that NLRP3 activation using Nigericin could be a novel therapeutic approach to control the growth of tumors producing a low level of IL-1β and IL-18.

Emerging roles of absent in melanoma 2 in cardiovascular diseases

Absent in melanoma 2 (AIM2) is a member of the PYHIN (pyrin and HIN domain-containing protein) family with important roles in sensing double-stranded DNA (dsDNA) and assembling the AIM2 inflammasome, which has wide-ranging, pro-inflammatory and pro-pyroptotic properties. The AIM2 inflammasome can become activated in atherosclerotic plaque, abdominal aortic aneurysm wall and injured myocardium, and its activation is tightly regulated by a variety of atherogenic factors. Activation of the AIM2 inflammasome has close links to the progression of several cardiovascular diseases. This review will summarize the current knowledge of AIM2 biology, providing the latest insights into the mechanisms and contributions of atherogenic factors to AIM2 inflammasome activation. In addition, we will also explore crosstalk between AIM2 and the pathologies of atherosclerosis, abdominal aortic aneurysm, myocardial infarction and heart failure. A better understanding of the pathological roles of AIM2 in these disorders will be helpful in developing novel therapeutic approaches.

Knockdown of fatty acid binding protein 4 exacerbates Bacillus Calmette-Guerin infection-induced RAW264.7 cell apoptosis via the endoplasmic reticulum stress pathway

Mycobacterial infection can induce alveolar macrophage apoptosis, which plays a vital role in the pathogenesis of tuberculosis. Accumulating evidence has demonstrated that fatty acid oxidation is involved in apoptosis during various pathological processes, including bacterial infection. However, whether fatty acid oxidation regulates mycobacterial infection-induced macrophage apoptosis remains unclear. Hence, the present study aimed to investigate the role of fatty acid binding protein 4 (FABP4) which is a carrier protein for fatty acids, in regulating apoptosis in RAW264.7 cells infected with Bacillus Calmette-Guerin (BCG). In our study, the impact of BCG infection on apoptosis and fatty acid oxidation in RAW264.7 cells was examined. Notably, we found that FABP4 was overexpressed during this process. Furthermore, small interfering RNAs targeting FABP4 were used to investigate the role of FABP4 in regulating apoptosis and fatty acid oxidation in BCG-infected RAW264.7 cells. The results indicated that mycobacterial infection promoted apoptosis and enhanced fatty acid oxidation in RAW264.7 cells. Moreover, FABP4 knockdown exacerbated BCG-induced apoptosis and upregulated the expression of p-PERK, p-eIF2α and chop, which are endoplasmic reticulum (ER) stress markers. In addition, FABP4 knockdown promoted fatty acid oxidation and ROS production, which result in the activation of ER stress. Our data suggested that FABP4 knockdown exacerbated BCG-induced apoptosis in RAW264.7 cells via the ER stress pathway.

Exosomes Secreted From Bone Marrow Mesenchymal Stem Cells Attenuate Oxygen-Glucose Deprivation/Reoxygenation-Induced Pyroptosis in PC12 Cells by Promoting AMPK-Dependent Autophagic Flux

Background: Cerebral ischemia–reperfusion (I/R) injury can lead to severe dysfunction, and its treatment is difficult. It is reported that nucleotide-binding domain and leucine-rich repeat family protein 3 (NLRP3) inflammasome-mediated cell pyroptosis is an important part of cerebral I/R injury and the activation of autophagy can inhibit pyroptosis in some tissue injury. Our previous study found that the protective effects of bone marrow mesenchymal stem cells (BMSCs) in cerebral I/R injury may be associated with the regulation of autophagy. Recent studies have demonstrated that exosomes secreted from BMSCs (BMSC-Exos) may play an essential role in the effective biological performance of BMSCs and the protective mechanism of BMSC-Exos is associated with the activation of autophagy and the remission of inflammation, but it has not been reported in studies of cerebral I/R injury. We aimed to investigate the effects of BMSC-Exos on cerebral I/R injury and determine if the mechanism is associated with the regulation of pyroptosis and autophagic flux.

Method: PC12 cells were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) to induce cerebral I/R in vitro and were cocultured with BMSC-Exos. Cell viability was determined with CCK-8 and lactate dehydrogenase (LDH) detection kits. Scanning electron microscopy (SEM), Hoechst 33342/propidium iodide (PI) double staining, 2′,7′-dichlorodihydrofluorescein diacetate assay, immunofluorescence, Western blot, and Enzyme-linked immunosorbent assay (ELISA) were used to detect cell pyroptosis. Furthermore, transmission electron microscopy (TEM), GFP-RFP-LC3 adenovirus transfection, and Western blot were used to detect autophagic flux and its influence on pyroptosis. Finally, coimmunoprecipitation was used to detect the binding interaction between NLRP3 and LC3.

Results: BMSC-Exos increased cell viability in OGD/R. The inhibitory effect of BMSC-Exos on pyroptosis was comparable to the NLRP3 inhibitor MCC950 and was reversed by NLRP3 overexpression. Furthermore, BMSC-Exos promoted autophagic flux through the AMP-activated kinase (AMPK)/mammalian target of the rapamycin pathway, whereas chloroquine, AMPK silencing, and compound C blocked the inhibitory effect on pyroptosis.

Conclusions: BMSC-Exos can protect PC12 cells against OGD/R injury via attenuation of NLRP3 inflammasome-mediated pyroptosis by promoting AMPK-dependent autophagic flux.

Topical Application of the Antimicrobial Agent Triclosan Induces NLRP3 Inflammasome Activation and Mitochondrial Dysfunction

5-Chloro-2-(2,4-dichlorophenoxy)phenol (triclosan) is an antimicrobial chemical widely used in consumer household and clinical healthcare products. Human and animal studies have associated triclosan exposure with allergic disease. Mechanistic studies have identified triclosan as a mitochondrial uncoupler; recent studies suggest that mitochondria play an important role in immune cell function and are involved in activation of the NLRP3 inflammasome. In this study, early immunological effects were evaluated via NLRP3 activation following dermal triclosan application in a BALB/c murine model. These investigations revealed rapid caspase-1 activation and mature IL-1β secretion in the skin and draining lymph nodes (dLNs) after 1.5% and 3% triclosan exposure. Correspondingly, pro-Il-1b and S100a8 gene expression increased along with extracellular ATP in the skin. Peak gene expression of chemokines associated with caspase-1 activation occurred after 2 days of exposure in both skin tissue and dLNs. Phenotypic analysis showed an increase in neutrophils and macrophages in the dLN and myeloid and inflammatory monocytes in the skin tissue. Triclosan also caused mitochondrial dysfunction shown through effects on mitochondrial reactive oxygen species, mass, mitochondrial membrane potential, and mitochondrial morphology. These results indicate that following triclosan exposure, activation of the NLRP3 inflammasome occurs in both the skin tissue and dLNs, providing a possible mechanism for triclosan's effects on allergic disease and further support a connection between mitochondrial involvements in immunological responses.

Sodium Butyrate Abrogates the Growth and Pathogenesis of Mycobacterium bovis via Regulation of Cathelicidin (LL37) Expression and NF-κB Signaling

Mycobacterium bovis is the causative agent of bovine tuberculosis, has been identified a serious threat to human population. It has been found that sodium butyrate (NaB), the inhibitor of histone deacetylase, can promote the expression of cathelicidin (LL37) and help the body to resist a variety of injuries. In the current study, we investigate the therapeutic effect of NaB on the regulation of host defense mechanism against M. bovis infection. We found an increased expression of LL37 in M. bovis infected THP-1 cells after NaB treatment. In contrast, NaB treatment significantly down-regulated the expression of Class I HDAC in THP-1 cells infected with M. bovis. Additionally, NaB reduced the expression of phosphorylated P65 (p-P65) and p-IκBα, indicating the inhibition of nuclear factor-κB (NF-κB) signaling. Furthermore, we found that NaB treatment reduced the production of inflammatory cytokines (IL-1β, TNF-α, and IL-10) and a key anti-apoptotic marker protein Bcl-2 in THP-1 cell infected with M. bovis. Notably, mice showed high resistance to M. bovis infection after NaB treatment. The reduction of viable M. bovis bacilli indicates that NaB-induced inhibition of M. bovis infection mediated by upregulation of LL37 and inhibition of NF-κB signaling pathway. These observations illustrate that NaB mediate protective immune responses against M. bovis infection. Overall, these results suggest that NaB can be exploited as a therapeutic strategy for the control of M. bovis in animals and human beings.

Endoplasmic Reticulum Targeting Ratiometric Fluorescent Probe for Carboxylesterase 2 Detection in Drug-Induced Acute Liver Injury

Carboxylesterase 2 (CES2), an endoplasmic reticulum (ER) located phase I enzyme, plays a vital role in the metabolism of various endogenous and exogenous substances, and is regarded as an important target for the design of prodrugs. Unfortunately, superior highly selective ER targeting fluorescent probes for monitoring of CES2 are not currently available. Herein, we report an ER targeting CES2 selective and sensitive ratiometric fluorescent probe ERNB based on the ER localizing group p-toluenesulfonamide. ERNB possessed high specificity, sensitivity, and exhibited excellent subcellular localization when compared to commercial ER tracker, and was used to image CES2 in the ER of living cells. Additionally, using ERNB we evaluated the CES2 regulation under d,l-dithiothreitol and tunicamycin-induced ER stress. Furthermore, we determined the down regulation of CES2 activity and expression in the acetaminophen-induced acute liver injury model. On the basis of these results, we conclude that ERNB is a promising tool for highlighting the role of CES2 in the ER and in exploring the role of CES2 in the development of diseases associated with ER stress.