STING-mediated intestinal barrier dysfunction contributes to lethal sepsis

circFLNA promotes intestinal injury during abdominal sepsis through Fas-mediated apoptosis pathway by sponging miR-766-3p

BACKGROUND

Intra-abdominal infections are the second most common cause of sepsis in the intensive care unit. Intestinal epithelial injury due to abdominal sepsis results in a variety of pathological changes, such as intestinal bacteria and toxins entering the blood, leading to persistent systemic inflammation and multiple organ dysfunction. The increased apoptosis of intestinal epithelial cells induced by sepsis further exacerbates the progression of sepsis. Although several studies have revealed that circRNAs are involved in intestinal epithelial injury in sepsis, few studies have identified the roles of circRNAs in intestinal epithelial apoptosis.

METHODS

We used laser capture microdissection to obtain purified epithelial cells located in intestinal crypts from four patients with abdominal sepsis induced by intestinal perforation and four samples from age and sex-matched non-septic patients. Microarray analysis of circRNAs was conducted to assess differentially expressed circRNAs between patients with and without sepsis. Lastly, in vitro and in vivo assays were performed to study the mechanism of circFLNA in intestinal epithelial apoptosis during sepsis.

RESULTS

circFLNA was upregulated in the intestinal epithelium after abdominal sepsis induced by intestinal perforation. Inhibition of miR-766-3p impaired si-circFLNA-mediated inhibition of apoptosis and inflammation factor levels in lipopolysaccharide (LPS)-treated HIEC-6 cells. circFLNA aggravated apoptosis and inflammation through the Fas-mediated apoptosis pathway in both LPS-treated HIEC-6 cells and a mouse cecal ligation and puncture model.

CONCLUSION

Our findings showed that circFLNA promotes intestinal injury in abdominal sepsis through the Fas-mediated apoptosis pathway by sponging miR-766-3p. The circFLNA/miR-766-3p/Fas axis has potential as a novel therapeutic target for treating intestinal injury in sepsis.

ATG2B upregulated in LPS-stimulated BMSCs-derived exosomes attenuates septic liver injury by inhibiting macrophage STING signaling

Pretreated mesenchymal stem cells (MSCs)-derived exosomes have shown great potential in the treatment of various inflammatory diseases. Recent evidence suggests that macrophage stimulator of interferon genes (STING) signal activation plays a critical role in sepsis and septic liver injury. Here, we aimed to investigate the role and effects of lipopolysaccharide (LPS)-pretreated bone marrow mesenchymal stem cells (BMSCs)-derived exosomes (L-Exo) on macrophage STING signaling in septic liver injury. Exosomes were collected from the BMSCs medium via ultracentrifugation. Liver injury, intrahepatic inflammation, and the activation of macrophage STING signaling were analyzed. Mitophagy and the release of mitochondrial DNA (mtDNA) into the cytosol were investigated. Through in vivo and in vitro experiments, L-Exo could markedly attenuate cecal ligation and puncture-induced septic liver injury and inhibit macrophage STING signaling. Mechanistically, L-Exo inhibited macrophage STING signaling by enhancing mitophagy and inhibiting the release of mtDNA into the cytosol. Furthermore, autophagy-related protein 2 homolog B (ATG2B) may be a major factor involved in this effect of L-Exo. These findings reveal that macrophage STING signaling plays an important role in septic liver injury and may be a therapeutic target. In addition, LPS pretreatment is an effective and promising approach for optimizing the therapeutic efficacy of MSCs-derived exosomes in septic liver injury, providing new strategies for treatment.

Glucomannan from Aloe vera gel maintains intestinal barrier integrity via mitigating anoikis mediated by Nrf2-mitochondria axis

Impairment of intestinal epithelium barrier is a hallmark of gut pathology. Cell death can compromise barrier function and impair epithelial restitution directly or indirectly in inflammatory bowel disease (IBD). Our previous work demonstrated that glucomannan from Aloe vera gel (AGP) protected mice from DSS-induced colitis, with unclear mechanism of AGP-intestinal barrier interactions. Here, AGP maintained the integrity of intestinal barrier in colitis mice. RNA-Sequencing results indicated that pathways related to anoikis (apoptosis induced by loss of cell-matrix interaction), mitochondrial function and oxidative stress were significantly altered in the process of AGP-intestinal barrier interaction. Further experiments confirmed that AGP activated Nrf2, decreased ROS levels, mitigated mitochondrial dysfunction and anoikis of colonic epithelial cells in mice. Intriguingly, AGP reversed oxidative stress and mitochondrial dysfunction induced by knockdown or inhibitor (ML385) of Nrf2 in IEC-6 cells, which indicated the essential role of Nrf2-mitochondrial axis in the intestinal protective function of AGP. In addition, AGP alleviated anoikis caused by impaired mitochondrial function. Hence, this current work indicated that AGP might maintain intestinal barrier integrity by mitigating anoikis mediated by Nrf2-mitochondria axis. These findings provide new evidence into the effect of polysaccharides maintaining intestinal barrier integrity.

Nano Parthenolide Improves Intestinal Barrier Function of Sepsis by Inhibiting Apoptosis and ROS via 5-HTR2A

Background

Intestinal barrier dysfunction is an important complication of sepsis, while the treatment is limited. Recently, parthenolide (PTL) has attracted much attention as a strategy of sepsis, but whether nano parthenolide (Nano PTL) is therapeutic in sepsis-induced intestinal barrier dysfunction is obscured.

Methods

In this study, cecal ligation and puncture (CLP)-induced sepsis rats and lipopolysaccharide (LPS)-stimulated intestinal epithelial cells (IECs) were used to investigate the effect of PTL on intestinal barrier dysfunction. Meanwhile, we synthesized Nano PTL and compared the protective effect of Nano PTL with ordinary PTL on intestinal barrier function in septic rats and IECs. Network pharmacology and serotonin 2A (5-HTR2A) inhibitor were used to explore the mechanism of PTL on the intestinal barrier function of sepsis.

Results

The encapsulation rate of Nano PTL was 95±1.5%, the drug loading rate was 11±0.5%, and the average uptake rate of intestinal epithelial cells was 94%. Ordinary PTL and Nano PTL improved the survival rate and survival time of septic rats, reduced the mean arterial pressure and the serum level of inflammatory cytokines, and protected the liver and kidney functions in vivo, and increased the value of transmembrane resistance (TEER) reduced the reactive oxygen species (ROS) and apoptosis in IECs in vitro through 5-HTR2A. Nano PTL had better effect than ordinary PTL.

Conclusion

Ordinary PTL and Nano PTL can protect the intestinal barrier function of septic rats by inhibiting apoptosis and ROS through up-regulating 5-HTR2A, Nano PTL is better than ordinary PTL.

Salidroside protects against intestinal barrier dysfunction in septic mice by regulating IL‑17 to block the NF‑κB and p38 MAPK signaling pathways

Sepsis is a systemic inflammatory response syndrome, mainly caused by infection or suspected infectious factors. The intestine is not only one of the most easily involved organs in the course of sepsis, but also the dynamic organ for the course of sepsis. The present study investigated the protective effect and mechanism of salidroside on intestinal barrier dysfunction of septic mice. Briefly, C57BL/6 mice were used to establish a septic model and then administered with salidroside. The ileum tissues of mice were examined by histopathological examination. Fluorescein isothiocyanate-dextran concentration was measured. IL-17, IL-6, IL-13 and TNF-α levels in ileum tissues and NF-κB and p38 MAPK activations were detected by ELISA and the expressions of NF-κB p65 and p38 MAPK protein with their phosphorylation and intestinal tight junction proteins were gauged by western blotting. The above assays were performed again to investigate the effect of anti-IL-17A and salidroside (160 mg/kg) alone or in combination. The septic model induced the ileum tissue injury, increased intestinal permeability and TNF-α, IL-17 and IL-6 levels, activated NF-κB and p38 MAPK pathways, promoted the expressions of NF-κB p65 and p38 MAPK and their phosphorylation, while suppressing the levels of IL-13 and intestinal tight junction proteins. Salidroside and anti-IL-17A partially reversed the above effects of septic model, which in combination further strengthened the reversing effect. Collectively, salidroside protected against intestinal barrier dysfunction in septic mice by downregulating IL-17 level to inhibit NF-κB and p38 MAPK signaling pathways, thus providing a new treatment direction.

Ag85a-S2 Activates cGAS-STING Signaling Pathway in Intestinal Mucosal Cells

Brucellosis is a zoonotic disease caused by Gram-negative bacteria. Most of the brucellosis vaccines in the application are whole-bacteria vaccines. Live-attenuated vaccines are widely used for brucellosis prevention in sheep, goats, pigs, and cattle. Thus, there is also a need for an adjuvanted vaccine for human brucellosis, because the attenuated Brucella vaccines now utilized in animals cause human illness. Here, we developed a live-attenuated Brucella suis strain 2 vaccine (S2) adjuvanted with Ag85a (Ag85a-S2). We found that Ag85a-S2 activated cGAS-STING pathways both in intestinal mucosal cells in vivo and in the BMDM and U937 cell line in vitro. We demonstrated that the cGAS knockout significantly downregulated the abundance of interferon and other cytokines induced by Ag85a-S2. Moreover, Ag85a-S2 triggered a stronger cellular immune response compared to S2 alone. In sum, Ag85a-S2-mediated enhancement of immune responses was at least partially dependent on the cGAS-STING pathway. Our results provide a new candidate for preventing Brucella pathogens from livestock, which might reduce the dosage and potential toxicity compared to S2.

MFG-E8 has guiding significance for the prognosis and treatment of sepsis

Sepsis remains a significant clinical challenge. Ferroptosis is involved in the pathogenesis of sepsis. Ferroptosis is associated with oxidative stress, and excessive oxidative stress is suppressed by milk fat globule epidermal growth factor 8 (MFG-E8) under various conditions. However, the role of MFG-E8 in sepsis-induced ferroptosis and oxidative stress is still unclear. First, we collected blood samples from patients with sepsis and detected the expression of serum MFG-E8. Then, the relationship between serum concentrations of MFG-E8 and disease severity was detected. Finally, the effects of MFG-E8 treatment on ferroptosis and oxidative stress in the livers of septic mice were determined. The expression of serum MFG-E8 in healthy subjects was notably higher than that in septic patients. In addition, when nonsurvivors and survivors of sepsis were compared, MFG-E8 levels were considerably lower in the former. The ROC curve for MFG-E8 was also generated. The area under the curve for MFG-E8 was 0.768 (95% confidence interval [CI] 0.627-0.909, p = 0.003). The patients were separated into two groups based on the MFG-E8 cut-off value of 3.86 ng/mL. According to the Kaplan‒Meier survival analysis, patients with low MFG-E8 levels had a significantly decreased 28-day survival rate compared with patients with high MFG-E8 levels. High MFG-E8 levels were substantially related to a decreased risk of death, as demonstrated by the Cox proportional hazard model that we utilized. In addition, compared with sham mice, septic mice exhibited liver and kidney damage, and MFG-E8 may have protective effects. The survival study indicated that MFG-E8 could effectively improve the survival rate of septic mice. Treatment with MFG-E8 suppresses oxidative stress and ferroptosis in the livers of septic mice. Serum MFG-E8 levels are lower in septic patients and are negatively related to disease severity. Treatment with MFG-E8 suppresses oxidative stress and ferroptosis in the livers of septic mice, contributing to significantly improved survival in septic mice. These findings showed that MFG-E8 could be a new sepsis predictive biomarker. MFG-E8 may have therapeutic potential in the treatment of sepsis.

Inhibition of platelet activation suppresses reactive enteric glia and mitigates intestinal barrier dysfunction during sepsis

Background

Intestinal barrier dysfunction, which is associated with reactive enteric glia cells (EGCs), is not only a result of early sepsis but also a cause of multiple organ dysfunction syndrome. Inhibition of platelet activation has been proposed as a potential treatment for septic patients because of its efficacy in ameliorating the organ damage and barrier dysfunction. During platelet activation, CD40L is translocated from α granules to the platelet surface, serving as a biomarker of platelet activation a reliable predictor of sepsis prognosis. Given that more than 95% of the circulating CD40L originate from activated platelets, the present study aimed to investigate if inhibiting platelet activation mitigates intestinal barrier dysfunction is associated with suppressing reactive EGCs and its underlying mechanism.

Methods

Cecal ligation and puncture (CLP) was performed to establish the sepsis model. 24 h after CLP, the proportion of activated platelets, the level of sCD40L, the expression of tight-junction proteins, the intestinal barrier function and histological damage of septic mice were analyzed. In vitro, primary cultured EGCs were stimulated by CD40L and LPS for 24 h and EGCs-conditioned medium were collected for Caco-2 cells treatment. The expression of tight-junction proteins and transepithelial electrical resistance of Caco-2 cell were evaluated.

Results

In vivo, inhibiting platelet activation with cilostazol mitigated the intestinal barrier dysfunction, increased the expression of ZO-1 and occludin and improved the survival rate of septic mice. The efficacy was associated with reduced CD40L⁺ platelets proportion, decreased sCD40L concentration, and suppressed the activation of EGCs. Comparable results were observed upon treatment with compound 6877002, a blocker of CD40L-CD40-TRAF6 signaling pathway. Also, S-nitrosoglutathione supplement reduced intestinal damage both in vivo and in vitro. In addition, CD40L increased release of TNF-α and IL-1β while suppressed the release of S-nitrosoglutathione from EGCs. These EGCs-conditioned medium reduced the expression of ZO-1 and occludin on Caco-2 cells and their transepithelial electrical resistance, which could be reversed by CD40-siRNA and TRAF6-siRNA transfection on EGCs.

Conclusions

The inhibition of platelet activation is related to the suppression of CD40L-CD40-TRAF6 signaling pathway and the reduction of EGCs activation, which promotes intestinal barrier function and survival in sepsis mice. These results might provide a potential therapeutic strategy and a promising target for sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00562-w.

Low-dose ganciclovir ameliorates dextran sulfate sodium-induced ulcerative colitis through inhibiting macrophage STING activation in mice

Ganciclovir (GCV) is a prodrug nucleoside analogue and is clinically used as antiviral drug for the treatment of cytomegalovirus (CMV) and other infections. Based on the potential anti-inflammatory activity of GCV, this study aimed to investigate the therapeutic effects of ganciclovir on dextran sulfate sodium (DSS)-induced ulcerative colitis (UC), which may involve cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathways. Our results demonstrated that incubation of GCV (50 μM) inhibited cGAS-STING pathway in macrophage RAW264.7 cells. Then, it was found that intestinal cGAS-STING pathways were upregulated in UC patients, Crohn's disease colitis (CD) patients, and DSS-induced colitis mice. Intraperitoneal injection of low-dose GCV (10 mg/kg/day) attenuated DSS-induced colitis and abdominal pain in mice. GCV treatment significantly inhibited the upregulation of cGAS-STING pathway in DSS-induced colitis mice. Moreover, DSS-induced colitis and gut dysbiosis was markedly attenuated in STING deficient mice compared with that of wild-type (WT) mice. Finally, there was lacking therapeutic effect of GCV on DSS-induced colitis in STING deficient mice. Together, our results indicated that low-dose GCV ameliorated DSS-induced UC in mice, possibly through inhibiting STING signaling in colonic macrophages, indicating that GCV may be useful for the treatment of UC.

Activating transcription factor 4 protects mice against sepsis-induced intestinal injury by regulating gut-resident macrophages differentiation

BACKGROUND

Gut-resident macrophages (gMacs) supplemented by monocytes-to-gMacs differentiation play a critical role in maintaining intestinal homeostasis. Activating transcription factor 4 (ATF4) is involved in immune cell differentiation. We therefore set out to investigate the role of ATF4-regulated monocytes-to-gMacs differentiation in sepsis-induced intestinal injury.

METHODS

Sepsis was induced in C57BL/6 wild type (WT) mice and Atf4- knockdown ( Atf4+/ - ) mice by cecal ligation and puncture or administration of lipopolysaccharide (LPS). Colon, peripheral blood mononuclear cells, sera, lung, liver, and mesenteric lymph nodes were collected for flow cytometry, hematoxylin and eosin staining, immunohistochemistry, quantitative reverse transcription polymerase chain reaction, and enzyme-linked immunosorbent assay, respectively.

RESULTS

CD64, CD11b, Ly6C, major histocompatibility complex-II (MHC-II), CX3CR1, Ly6G, and SSC were identified as optimal primary markers for detecting the process of monocytes-to-gMacs differentiation in the colon of WT mice. Monocytes-to-gMacs differentiation was impaired in the colon during sepsis and was associated with decreased expression of ATF4 in P1 (Ly6C hi monocytes), the precursor cells of gMacs. Atf4 knockdown exacerbated the impairment of monocytes-to-gMacs differentiation in response to LPS, resulting in a significant reduction of gMacs in the colon. Furthermore, compared with WT mice, Atf4+/- mice exhibited higher pathology scores, increased expression of inflammatory factor genes ( TNF-α, IL-1β ), suppressed expression of CD31 and vascular endothelial-cadherin in the colon, and increased translocation of intestinal bacteria to lymph nodes and lungs following exposure to LPS. However, the aggravation of sepsis-induced intestinal injury resulting from Atf4 knockdown was not caused by the enhanced inflammatory effect of Ly6C hi monocytes and gMacs.

CONCLUSION

ATF4, as a novel regulator of monocytes-to-gMacs differentiation, plays a critical role in protecting mice against sepsis-induced intestinal injury, suggesting that ATF4 might be a potential therapeutic target for sepsis treatment.

Inhibition of platelet activation suppresses reactive enteric glia and mitigates intestinal barrier dysfunction during sepsis

Background

Intestinal barrier dysfunction, which is associated with reactive enteric glia cells (EGCs), is not only a result of early sepsis but also a cause of multiple organ dysfunction syndrome. Inhibition of platelet activation has been proposed as a potential treatment for septic patients because of its efficacy in ameliorating the organ damage and barrier dysfunction. During platelet activation, CD40L is translocated from α granules to the platelet surface, serving as a biomarker of platelet activation a reliable predictor of sepsis prognosis. Given that more than 95% of the circulating CD40L originate from activated platelets, the present study aimed to investigate if inhibiting platelet activation mitigates intestinal barrier dysfunction is associated with suppressing reactive EGCs and its underlying mechanism.

Methods

Cecal ligation and puncture (CLP) was performed to establish the sepsis model. 24 h after CLP, the proportion of activated platelets, the level of sCD40L, the expression of tight-junction proteins, the intestinal barrier function and histological damage of septic mice were analyzed. In vitro, primary cultured EGCs were stimulated by CD40L and LPS for 24 h and EGCs-conditioned medium were collected for Caco-2 cells treatment. The expression of tight-junction proteins and transepithelial electrical resistance of Caco-2 cell were evaluated.

Results

In vivo, inhibiting platelet activation with cilostazol mitigated the intestinal barrier dysfunction, increased the expression of ZO-1 and occludin and improved the survival rate of septic mice. The efficacy was associated with reduced CD40L⁺ platelets proportion, decreased sCD40L concentration, and suppressed the activation of EGCs. Comparable results were observed upon treatment with compound 6,877,002, a blocker of CD40L–CD40–TRAF6 signaling pathway. Also, S-nitrosoglutathione supplement reduced intestinal damage both in vivo and in vitro. In addition, CD40L increased release of TNF-α and IL-1β while suppressed the release of S-nitrosoglutathione from EGCs. These EGCs-conditioned medium reduced the expression of ZO-1 and occludin on Caco-2 cells and their transepithelial electrical resistance, which could be reversed by CD40-siRNA and TRAF6-siRNA transfection on EGCs.

Conclusions

The inhibition of platelet activation is related to the suppression of CD40L-CD40-TRAF6 signaling pathway and the reduction of EGCs activation, which promotes intestinal barrier function and survival in sepsis mice. These results might provide a potential therapeutic strategy and a promising target for sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00556-8.

Methanolic Moringa oleifera leaf extract protects against epithelial barrier damage and enteric bacterial translocation in intestinal I/R: Possible role of caspase 3

Background: Activation of caspase 3 has been implicated in the pathogenesis of I/R injury in various organs, but there is a paucity of data on its role in IIRI. Also, no reports were found on the beneficial role of methanolic Moringa oleifera leaf extract (MMOLE) in IIRI. This study investigated the involvement of caspase 3 in IIRI, and the impact of MMOLE in IIRI.

Methods: Male Wistar rats were randomized into five groups; the sham-operated group that was sham-operated and received 0.5 ml of distilled water for 7 days prior to sham surgery, and the IIRI, febuxostat (FEB) +IIRI, low dose MMOLE (LDMO)+IIRI, and high dose MMOLE (HDMO)+IIRI groups that underwent I/R and also received 0.5 ml of distilled water, 10 mg/kg of febuxostat, 200 mg/kg of MMOLE, and 400 mg/kg of MMOLE respectively for 7 days prior to I/R. Markers of hepatic function, oxidative stress, and inflammation as well as enteric bacterial translocation and histoarchitecture integrity of intestinal and hepatic tissues were evaluated. The bioactive components of MMOLE were also determined by GC-MS.

Results: As revealed by GC-MS, the active bioactive components of MMOLE were thiosemicarbazone, hydrazine, 1,3-dioxolane, octanoic acid, 1,3-benzenediamine, 9-octadecenoic acid, oleic acid, nonadecanoic acid, 3-undecanone, phosphonic acid, and cyclopentanecarboxylic acid. MMOLE alleviated IIRI-induced rise in intestinal and hepatic injury markers, malondialdehyde, TNF-α, IL-6, and myeloperoxidase activities. MMOLE improved IIRI-induced suppression of reduced glutathione, thiol and non-thiol proteins, and superoxide dismutase, catalase and glutathione peroxidase activities. These were associated with suppression of IIRI-induced caspase 3 activity and bacterial translocation. Histopathological evaluation revealed that MMOLE attenuated IIRI-induced alterations in intestinal and hepatic histoarchitecture integrity. MMOLE also militated against increased absolute and relative intestinal and hepatic weight, intestinal and hepatic injuries, epithelial mucosal barrier dysfunction, and enteric bacterial translocation associated with IIRI by downregulating oxidative stress-mediated activation of caspase 3.

Conclusion: IIRI is associated with a rise in caspase 3 activity. Also, MMOLE confers protection against IIRI, possibly due to its constituent bioactive molecules, especially hydrazine, 9-octadecenoic acid, 1,3-dioxolane, oleic acid, and nonadecanoic acid.

Sestrin2 suppresses ferroptosis to alleviate septic intestinal inflammation and barrier dysfunction

OBJECTIVE

Alterations in intestinal function play a crucial role in the pathogenesis of sepsis, and the repair of the intestinal barrier is a potential strategy for the treatment of sepsis. Sestrin2 (SESN2), a highly conserved stress-responsive protein, can be induced in response to stress.

AIM

This paper aimed to explore the role and mechanism of SESN2 in septic intestinal dysfunction. Methods: Blood samples were collected from patients with septic intestinal dysfunction, and Caco-2 cells were subjected to lipopolysaccharide (LPS) to construct in vitro models. The expression level of SESN2 was determined in the blood samples and cells. The impacts of SESN2 overexpression on cell inflammation, oxidative stress, barrier integrity, and MAPK/Nrf2 signaling were evaluated. To determine the mediated role of MAPK signaling and ferroptosis, AMPK inhibitor (Compound C) and ferroptosis inducer (erastin) were separately used to treat cells, and the influences on the above aspects in cells were assessed.

RESULTS

The expression level of SESN2 was down-regulated in patients with septic intestinal dysfunction and LPS-induced cells. SESN2 overexpression was found to suppress cell inflammation and oxidative stress, maintain barrier integrity and activate AMPK/Nrf2 signaling. Following the AMPK signaling was inhibited or the ferroptosis was triggered, the effects of SESN2 overexpression on the cells were both reversed.

CONCLUSION

Reduced SESN2 contributed to inflammatory response and barrier dysfunction in septic intestinal dysfunction by promoting ferroptosis via activating the AMPK/Nrf2 signaling pathway.

NAT10 regulates neutrophil pyroptosis in sepsis via acetylating ULK1 RNA and activating STING pathway

Emerging evidence suggests that pyroptosis is involved in sepsis. However, the role of neutrophil pyroptosis in sepsis and the mechanisms remains elusive. We find that N-acetyltransferase 10 (NAT10), an acetyltransferase responsible for the N⁴-acetylation of Cytidine (ac⁴C) in mRNA, is significantly downregulated in neutrophils from septic mice. Neutrophil-specific over-expression of NAT10 improves the survival and ameliorates lung injury in septic mice by inhibiting neutrophil pyroptosis. Notably, UNC-52-like kinase 1 (ULK1) is identified as the target of NAT10 in neutrophils. The decreased expression of NAT10 resultes in the decay of ULK1 transcripts and therefore the reduced expression of ULK1. As a regulator of STING phosphorylation, the loss of ULK1 enhances the activation of STING-IRF3 signaling and subsequently the elevated pyroptosis-inducing NLRP3 inflammasome in neutrophils. While over-expression of NAT10 restrains pyroptosis in neutrophils as well as septic lethality in mice by reversing the ULK1-STING-NLRP3 axis. The decreased expression of NAT10 are also observed in sepsis patients and its correlation with clinical severity is found. Collectively, our findings disclose that NAT10 is a negative regulator of neutrophil pyroptosis and its downregulation contributes to the progress of sepsis by exacerbating pyroptosis via the ULK1-STING-NLRP3 axis, therefore revealing a potential therapeutic target for sepsis.

The enzyme N-acetyltransferase NAT10 is a negative regulator of neutrophil pyroptosis and its downregulation contributes to the progress of sepsis by exacerbating pyroptosis via the ULK1-STING-NLRP3 pathway.

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

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

The β-catenin/CBP signaling axis participates in sepsis-induced inflammatory lung injury

Sepsis-induced inflammatory lung injury is a key factor causing failure of the lungs and other organs, as well as death, during sepsis. In the present study, a caecal ligation and puncture (CLP)-induced sepsis model was established to investigate the effect of β-catenin on sepsis-induced inflammatory lung injury and the corresponding underlying mechanisms. C57BL/6 mice were randomly divided into five groups, namely, the sham, CLP, β-catenin knockout (KO) + CLP, XAV-939 + CLP, and ICG-001 + CLP groups; the XAV-939 + CLP and ICG-001 + CLP groups were separately subjected to intraperitoneal injections of the β-catenin inhibitors XAV-939 and ICG-001 for 1 week preoperatively and 2 days postoperatively, respectively. Forty-eight hours after CLP, we measured β-catenin expression in lung tissues and evaluated mouse mortality, histopathological characteristics of hematoxylin and eosin (H&E)-stained lung tissues, serum cytokine (tumor necrosis factor [TNF]-α, interleukin [IL]-10, and IL-1β) levels, lung myeloperoxidase (MPO) activity, and the number of apoptotic cells in the lung tissues. Our results indicated that both the inhibition of β-catenin expression and blockage of β-catenin/CREB-binding protein (CBP) interactions by ICG-001 effectively decreased mouse mortality, alleviated pathological lung injury, and reduced the serum TNF-α, IL-10, and IL-1β levels, in addition to reducing the lung MPO activity and the number of apoptotic cells in lung tissues of the sepsis model mice. Therefore, it can be deduced that the β-catenin/CBP signaling axis participates in regulating sepsis-induced inflammatory lung injury.

COVID-19 and the Pancreas: A Narrative Review

The outbreak of COVID-19, initially developed in China in early December 2019, has rapidly spread to other countries and represents a public health emergency of international concern. COVID-19 has caused great concern about respiratory symptoms, but it is worth noting that it can also affect the gastrointestinal tract. However, the data on pancreatic involvement during SARS-CoV-2 infection are limited. The prevalence and severity of pancreatic damage and acute pancreatitis, as well as its pathophysiology, are still under debate. Moreover, the possible implication of pancreatic damage as an apparent adverse effect of COVID-19 therapies or vaccines are issues that need to be addressed. Finally, the COVID-19 pandemic has generated delays and organizational consequences for pancreatic surgery, an element that represent indirect damage from COVID-19. This narrative review aims to summarize and analyze all the aspects of pancreatic involvement in COVID-19 patients, trying to establish the possible underlying mechanisms and scientific evidence supporting the association between COVID-19 and pancreatic disease.

Role of released mitochondrial DNA in acute lung injury

Acute lung injury(ALI)/acute respiratory distress syndrome(ARDS) is a form of acute-onset hypoxemic respiratory failure characterised by an acute, diffuse, inflammatory lung injury, and increased alveolar-capillary permeability, which is caused by a variety of pulmonary or nonpulmonary insults. Recently, aberrant mitochondria and mitochondrial DNA(mtDNA) level are associated with the development of ALI/ARDS, and plasma mtDNA level shows the potential to be a promising biomarker for clinical diagnosis and evaluation of lung injury severity. In mechanism, the mtDNA and its oxidised form, which are released from impaired mitochondria, play a crucial role in the inflammatory response and histopathological changes in the lung. In this review, we discuss mitochondrial outer membrane permeabilisation (MOMP), mitochondrial permeability transition pore(mPTP), extracellular vesicles (EVs), extracellular traps (ETs), and passive release as the principal mechanisms for the release of mitochondrial DNA into the cytoplasm and extracellular compartments respectively. Further, we explain how the released mtDNA and its oxidised form can induce inflammatory cytokine production and aggravate lung injury through the Toll-like receptor 9(TLR9) signalling, cytosolic cGAS-stimulator of interferon genes (STING) signalling (cGAS-STING) pathway, and inflammasomes activation. Additionally, we propose targeting mtDNA-mediated inflammatory pathways as a novel therapeutic approach for treating ALI/ARDS.

STING signaling sensing of DRP1-dependent mtDNA release in kupffer cells contributes to lipopolysaccharide-induced liver injury in mice

Aberrant pro-inflammatory activation of Kupffer cells (KCs) is strongly involved in the pathogenesis of septic liver injury. Recent evidence indicates the crucial roles of excessive stimulator of interferon genes (STING) signaling activation during sepsis. However, the role of STING signaling in septic liver injury remains unclear. In this study, we demonstrated that STING signaling was markedly activated in KCs isolated from wild type mice after lipopolysaccharide (LPS) treatment. STING deficiency effectively protected liver function, attenuated systemic inflammatory response and decreased mortality in LPS-treated mice, which were aggravated by STING agonist (DMXAA). Importantly, STING signaling activation in KCs contributed to LPS-induced liver injury through promoting hepatocyte death. Mechanistically, STING signaling could be activated by release of mitochondrial DNA (mtDNA) through dynamin-related protein 1 (DRP1)-dependent mitochondrial fission in LPS-treated KCs. Additionally, LPS stimulation enhanced DRP1-dependent mitochondrial ROS production, which promoted the leak of mtDNA into the cytosol and subsequent STING signaling activation in KCs. The in vivo experiments showed that pharmacological inhibition of DRP1 with Mdivi-1 partially prevented the activation of STING signaling in KCs isolated from LPS-challenged mice, as well as alleviated liver injury and inhibited systemic inflammatory response. In summary, our study comprehensively confirmed that STING signaling senses the DRP1-dependent release of mtDNA in KCs and its activation might play a key role in LPS-induced liver injury, which offers new sights and therapeutic targets for management of septic liver injury.

The STING1-MYD88 complex drives ACOD1/IRG1 expression and function in lethal innate immunity

ACOD1 (also known as IRG1) has emerged as a regulator of immunometabolism that operates by producing metabolite itaconate. Here, we report a key role of STING1 (also known as STING and TMEM173) in mediating ACOD1 expression in myeloid cells in response to toll-like receptor (TLR) signaling. The activation of STING1 through exogenous cyclic dinucleotides (e.g., 3'3'-cGAMP) or endogenous gain-of-function mutation (e.g., V155M) enhances lipopolysaccharide-induced ACOD1 expression and itaconate production in macrophages and monocytes, whereas the deletion of STING1 blocks this process. The adaptor protein MYD88, instead of DNA sensor cyclic GMP-AMP synthase (CGAS), favors STING1-dependent ACOD1 expression. Mechanistically, MYD88 directly blocks autophagic degradation of STING1 and causes subsequent IRF3/JUN-mediated ACOD1 gene transcription. Consequently, the conditional deletion of STING1 in myeloid cells fails to produce ACOD1 and itaconate, thereby protecting mice against endotoxemia and polymicrobial sepsis. Our results, therefore, establish a direct link between TLR4 signaling and ACOD1 expression through the STING1-MYD88 complex during septic shock.

Curcumin Improved Intestinal Epithelial Barrier Integrity by Up-Regulating ZO-1/Occludin/Claudin-1 in Septic Rats

Objective

To investigate the protective effect and mechanism of curcumin on intestinal barrier function in rats with enterogenic sepsis.

Methods

Rats were divided into Sham group (Sham), Model group (Model), low-dose curcumin group (100 mg/kg), and high-dose curcumin group (200 mg/kg), with 10 rats in each group. Sepsis model was established in model group, low-dose curcumin group, and high-dose curcumin group. After drug intervention, hematoxylin-eosin (HE) staining was used to observe the histopathological changes of small intestine in each group. The levels of TNF-α, IL-1β, and IL-6 in serum and intestinal tissues of rats were determined by ELISA. The expression of ZO-1, occludin, and claudin-1 in ileum was detected by QRT-PCR and Western blot. Western blotting was used to detect the expression of ERK/JNK signaling pathway, NF-κB p65, apoptosis-related proteins Caspase-3, and TNF-α in rat intestinal tissues.

Results

HE staining showed that curcumin treatment reduced epithelial cell shedding, interstitial edema, and apoptosis. Compared with model group, DAO activity, serum intestinal fatty acid binding protein (I-FABP), TNF-α, IL-6, and IL-1β expression in curcumin group were decreased in a dose-dependent manner. Curcumin can upregulate the mRNA and protein expression levels of ZO-1, occludin, and claudin-1 in ileum of CLP-induced rats. In addition, curcumin inhibits NF-κB p65 activation and apoptosis by regulating ERK/JNK signaling pathway.

Conclusion

Curcumin can reduce inflammatory response and upregulate the expression of intestinal tight junction proteins ZO-1, occludin, and claudin-1 in rats with enterogenic sepsis, and protect intestinal barrier function.

1,25(OH)2 D3 blocks IFNβ production through regulating STING in epithelial layer of oral lichen planus

Stimulator of interferon genes (STING) is reported to exert vital functions in inflammatory responses and autoimmune diseases. Nevertheless, the status and roles of STING in oral lichen planus (OLP) remain elusive. Here, we state that STING and its downstream cytokine interferon‐β (IFNβ) expression is boosted in the oral keratinocytes from patients suffering OLP in comparison with those from healthy participants. Mechanistically, transcription factor GATA‐binding protein 1 (GATA1) which is highly increased in diseased samples specifically interacts with its element in the promoter of STING to enhance STING transcripts. 1,25(OH)₂D₃, the active form of vitamin D, is capable of restricting STING and IFNβ increases in oral keratinocyte models resembling OLP in vitro. Moreover, there is a negative correlation between vitamin D receptor (VDR) and STING or IFNβ in human samples. Using plasmids and small interfering RNA transfection technologies, we find 1,25(OH)₂D₃ regulates STING and IFNβ through a mechanism controlled by the hypoxia‐inducible factor‐1α (HIF‐1α)‐GATA1 axis. Collectively, our findings unveil that 1,25(OH)₂D₃ lowers STING and IFNβ overexpression in the context of OLP.

Emodin Ameliorates Intestinal Dysfunction by Maintaining Intestinal Barrier Integrity and Modulating the Microbiota in Septic Mice

Sepsis-induced inflammatory response leads to intestinal damage and secondary bacterial translocation, causing systemic infections and eventually death. Emodin is a natural anthraquinone derivative in many plants with promising bioactivities. However, the effects and mechanisms of emodin on sepsis-induced intestinal dysfunctions have not been well clarified yet. We found that emodin treatment suppressed the inflammatory response in the intestines of septic mice. Intestinal barrier function was also improved by emodin through enhancing ZO-1 and occludin expression, which prevented the secondary translocation of Escherichia coli. By proteome microarray investigation, JNK2 was identified as a direct target of emodin. In vitro study also showed that emodin inhibited LPS-induced inflammatory response in intestinal epithelial cells. Nuclear factors including NF-κB and AP-1 were further identified as downstream effectors of JNK2. Bioinformatic analysis based on 16s rRNA gene sequencing illustrated that emodin treatment significantly increased the alpha- and beta-diversity of gut microbiota in septic mice. Moreover, data according to functional prediction showed that emodin decreased the abundance of potential pathogenic bacteria in gut. Our findings have shown that emodin treatment prevented inflammatory induced barrier dysfunction and decreased the potential pathogenicity of lumen bacteria, reducing the hazard of lumen bacterial translocation during sepsis.

Card9 protects sepsis by regulating Ripk2-mediated activation of NLRP3 inflammasome in macrophages

Sepsis is characterized by systemic inflammation, it's caused by primary infection of pathogenic microorganisms or secondary infection of damaged tissue. In this study, we focus on sepsis-induced intestine barrier functional disturbalice, presenting as increased permeability of intestinal epithelium. We observed that the phenotype of LPS-induced sepsis was exacerbated in Card9^-/- mice, especially displaying more serious intestinal inflammation and gut barrier dysfunction. Next, we found the hyperactivation of NLRP3 inflammasome in the intestinal macrophages of Card9^-/--sepsis mice. Moreover, Card9 over-expression decreased NLRP3 inflammasome activation in macrophages. Furthermore, we found that Card9 inhibited NLRP3 inflammasome activation by recruiting Ripk2. The competitive binding between Ripk2 with Caspase-1, instead of ASC with Caspase-1, inhibited the NLRP3 inflammasome activation. Over-expression of Ripk2 alleviated septic intestinal injury caused by Card9 deficiency. Taken together, we suggested Card9 acts as a negative regulation factor of NLRP3 inflammasome activation, which protects against intestinal damage during sepsis. Therefore, maintaining Card9-Ripk2 signaling homeostasis may provide a novel therapy of septic intestinal damage.

The protective effects of HIF-1α activation on sepsis induced intestinal mucosal barrier injury in rats model of sepsis

The integrity of the intestinal barrier is critical for protecting the host against the pathogen. The role of hypoxia-inducible factor-1α (HIF-1α) in the intestinal barrier disfunction related to sepsis remained unclear. The purpose of the present study is to investigate the role of HIF-1α on oxidative damage, the intestinal mucosal permeability, structural and morphological changes during sepsis. Twenty-four Sprague Dawley (SD) rats were randomly divided into four groups of 6 rats each: the sham group (sham), sepsis group (subjected to cecal ligation and perforation, CLP), sepsis + DMOG group (40 mg/kg of DMOG by intraperitoneal injection for 7 consecutive days before CLP), and sepsis + BAY 87–2243 group (9 mg/kg of BAY 87–2243 orally administered for 3 consecutive days before CLP). Sepsis increased plasma levels of inflammatory mediators, oxidative stress markers and HIF-1α expression; caused pathological damage; increased permeability (P < 0.05); and decreased TJ protein expression in the intestinal mucosa of rats with sepsis (P < 0.05). The addition of DMOG up-regulated HIF-1α, then decreased the plasma levels of inflammatory mediators, oxidative stress markers, alleviated pathological damage to the intestinal mucosa and decreased intestinal permeability (P < 0.05); while BAY 87–2243 treatment had the opposite effects. Our findings showed that HIF-1α protects the intestinal barrier function of septic rats by inhibiting intestinal inflammation and oxidative damage, our results provide a novel insight for developing sepsis treatment.

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

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

Mitochondrial DNA Release Contributes to Intestinal Ischemia/Reperfusion Injury

Mitochondria release many damage-associated molecular patterns (DAMPs) when cells are damaged or stressed, with mitochondrial DNA (mtDNA) being. MtDNA activates innate immune responses and induces inflammation through the TLR-9, NLRP3 inflammasome, and cGAS-STING signaling pathways. Released inflammatory factors cause damage to intestinal barrier function. Many bacteria and endotoxins migrate to the circulatory system and lymphatic system, leading to systemic inflammatory response syndrome (SIRS) and even damaging the function of multiple organs throughout the body. This process may ultimately lead to multiple organ dysfunction syndrome (MODS). Recent studies have shown that various factors, such as the release of mtDNA and the massive infiltration of inflammatory factors, can cause intestinal ischemia/reperfusion (I/R) injury. This destroys intestinal barrier function, induces an inflammatory storm, leads to SIRS, increases the vulnerability of organs, and develops into MODS. Mitophagy eliminates dysfunctional mitochondria to maintain cellular homeostasis. This review discusses mtDNA release during the pathogenesis of intestinal I/R and summarizes methods for the prevention or treatment of intestinal I/R. We also discuss the effects of inflammation and increased intestinal barrier permeability on drugs.

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

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

Systemic inflammatory response syndrome is triggered by mitochondrial damage (Review)

Mitochondria are key organelles of cellular energy metabolism; both mitochondrial function and metabolism determine the physiological function of cells and serve an essential role in immune responses. Key damage-associated molecular patterns (DAMPs), such as mitochondrial DNA and N-formyl peptides, released following severe trauma-induced mitochondrial damage may affect the respiratory chain, enhance oxidative stress and activate systemic inflammatory responses via a variety of inflammation-associated signaling pathways. Severe trauma can lead to sepsis, multiple organ dysfunction syndrome and death. The present review aimed to summarize the pathophysiological mechanisms underlying the effects of human mitochondrial injury-released DAMPs on triggering systemic inflammatory responses and to determine their potential future clinical applications in preventing and treating sepsis.

GRP75 Regulates Mitochondrial-Supercomplex Turnover to Modulate Insulin Sensitivity

GRP75 (75-kDA glucose-regulated protein), defined as a major component of both the mitochondrial quality control system and mitochondria-associated membrane, plays a key role in mitochondrial homeostasis. In this study, we assessed the roles of GRP75, other than as a component, in insulin action in both in vitro and in vivo models with insulin resistance. We found that GRP75 was downregulated in mice fed a high-fat diet (HFD) and that induction of Grp75 in mice could prevent HFD-induced obesity and insulin resistance. Mechanistically, GRP75 influenced insulin sensitivity by regulating mitochondrial function through its modulation of mitochondrial-supercomplex turnover rather than mitochondria-associated membrane communication: GRP75 was negatively associated with respiratory chain complex activity and was essential for mitochondrial-supercomplex assembly and stabilization. Moreover, mitochondrial dysfunction in Grp75-knockdown cells might further increase mitochondrial fragmentation, thus triggering cytosolic mtDNA release and activating the cGAS/STING-dependent proinflammatory response. Therefore, GRP75 can serve as a potential therapeutic target of insulin resistant-related diabetes or other metabolic diseases.

The cGAS-STING signaling in cardiovascular and metabolic diseases: Future novel target option for pharmacotherapy

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling exert essential regulatory function in microbial-and onco-immunology through the induction of cytokines, primarily type I interferons. Recently, the aberrant and deranged signaling of the cGAS-STING axis is closely implicated in multiple sterile inflammatory diseases, including heart failure, myocardial infarction, cardiac hypertrophy, nonalcoholic fatty liver diseases, aortic aneurysm and dissection, obesity, etc. This is because of the massive loads of damage-associated molecular patterns (mitochondrial DNA, DNA in extracellular vesicles) liberated from recurrent injury to metabolic cellular organelles and tissues, which are sensed by the pathway. Also, the cGAS-STING pathway crosstalk with essential intracellular homeostasis processes like apoptosis, autophagy, and regulate cellular metabolism. Targeting derailed STING signaling has become necessary for chronic inflammatory diseases. Meanwhile, excessive type I interferons signaling impact on cardiovascular and metabolic health remain entirely elusive. In this review, we summarize the intimate connection between the cGAS-STING pathway and cardiovascular and metabolic disorders. We also discuss some potential small molecule inhibitors for the pathway. This review provides insight to stimulate interest in and support future research into understanding this signaling axis in cardiovascular and metabolic tissues and diseases.

STING1 in sepsis: Mechanisms, functions, and implications

Sepsis is a life-threatening clinical syndrome and one of the most challenging health problems in the world. Pathologically, sepsis and septic shock are caused by a dysregulated host immune response to infection, which can eventually lead to multiple organ failure and even death. As an adaptor transporter between the endoplasmic reticulum and Golgi apparatus, stimulator of interferon response cGAMP interactor 1 (STING1, also known as STING or TMEM173) has been found to play a vital role at the intersection of innate immunity, inflammation, autophagy, and cell death in response to invading microbial pathogens or endogenous host damage. There is ample evidence that impaired STING1, through its immune and non-immune functions, is involved in the pathological process of sepsis. In this review, we discuss the regulation and function of the STING1 pathway in sepsis and highlight it as a suitable drug target for the treatment of lethal infection.

Sinomenine ameliorates septic acute lung injury in mice by modulating gut homeostasis via aryl hydrocarbon receptor/Nrf2 pathway

Sepsis is a systemic inflammatory response syndrome caused by a host's immune response to infection. Acute lung injury (ALI) is one of the most common complications of sepsis with high mortality and morbidity. Recent evidence demonstrated that the 'gut-lung axis' was related to the progression of septic acute lung injury, which regarded gut microbiota and intestinal barrier as two critical factors correlated with acute lung injury. Sinomenine is an isoquinoline alkaloid component extracted from Sinomenium acutum Rehd，et Wils, which has been already reported to have significant anti-inflammatory, immunosuppressive, and anti-arthritis properties. In this research, we observed that sinomenine could repair the lung injury and alleviate inflammatory response induced by cecum ligation and puncture (CLP). Illumine sequencing of 16S rDNA revealed that sinomenine could improve the richness of gut microbiota and modulate the composition of intestinal flora in cecum ligation and puncture mice. Meanwhile, sinomenine could reduce the colon pathological damage and improve the intestine barrier integrity in cecum ligation and puncture mice. We also found that the molecular mechanism of sinomenine's protective effect on intestinal tract was related to the activation of aryl hydrocarbon receptor/nuclear factor erythroid-2 related factor 2（Nrf2）pathway both in vivo and vitro experiments. Collectively, the prevention of septic acute lung injury by sinomenine might be mediated by modulating gut microbiota and restoring intestinal barrier via aryl hydrocarbon receptor/Nrf2-dependent pathway.

Signaling pathways and intervention therapies in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by dysregulated host systemic inflammatory and immune response to infection. Over decades, advanced understanding of host-microorganism interaction has gradually unmasked the genuine nature of sepsis, guiding toward new definition and novel therapeutic approaches. Diverse clinical manifestations and outcomes among infectious patients have suggested the heterogeneity of immunopathology, while systemic inflammatory responses and deteriorating organ function observed in critically ill patients imply the extensively hyperactivated cascades by the host defense system. From focusing on microorganism pathogenicity, research interests have turned toward the molecular basis of host responses. Though progress has been made regarding recognition and management of clinical sepsis, incidence and mortality rate remain high. Furthermore, clinical trials of therapeutics have failed to obtain promising results. As far as we know, there was no systematic review addressing sepsis-related molecular signaling pathways and intervention therapy in literature. Increasing studies have succeeded to confirm novel functions of involved signaling pathways and comment on efficacy of intervention therapies amid sepsis. However, few of these studies attempt to elucidate the underlining mechanism in progression of sepsis, while other failed to integrate preliminary findings and describe in a broader view. This review focuses on the important signaling pathways, potential molecular mechanism, and pathway-associated therapy in sepsis. Host-derived molecules interacting with activated cells possess pivotal role for sepsis pathogenesis by dynamic regulation of signaling pathways. Cross-talk and functions of these molecules are also discussed in detail. Lastly, potential novel therapeutic strategies precisely targeting on signaling pathways and molecules are mentioned.

Interference on Cytosolic DNA Activation Attenuates Sepsis Severity: Experiments on Cyclic GMP-AMP Synthase (cGAS) Deficient Mice

Although the enhanced responses against serum cell-free DNA (cfDNA) in cases of sepsis—a life-threatening organ dysfunction due to systemic infection—are understood, the influence of the cytosolic DNA receptor cGAS (cyclic guanosine monophosphate–adenosine monophosphate (GMP–AMP) synthase) on sepsis is still unclear. Here, experiments on cGAS deficient (cGAS^-/-) mice were conducted using cecal ligation and puncture (CLP) and lipopolysaccharide (LPS) injection sepsis models and macrophages. Severity of CLP in cGAS^-/- mice was less severe than in wildtype (WT) mice, as indicated by mortality, serum LPS, cfDNA, leukopenia, cytokines (TNF-α, IL-6 and IL-10), organ histology (lung, liver and kidney) and spleen apoptosis. With the LPS injection model, serum cytokines in cGAS^-/- mice were lower than in WT mice, despite the similar serum cfDNA level. Likewise, in LPS-activated WT macrophages, the expression of several mitochondria-associated genes (as revealed by RNA sequencing analysis) and a profound reduction in mitochondrial parameters, including maximal respiration (determined by extracellular flux analysis), DNA (mtDNA) and mitochondrial abundance (revealed by fluorescent staining), were demonstrated. These data implied the impact of cfDNA resulting from LPS-induced cell injury. In parallel, an additive effect of bacterial DNA on LPS, seen in comparison with LPS alone, was demonstrated in WT macrophages, but not in cGAS^-/- cells, as indicated by supernatant cytokines (TNF-α and IL-6), M1 proinflammatory polarization (iNOS and IL-1β), cGAS, IFN-γ and supernatant cyclic GMP–AMP (cGAMP). In conclusion, cGAS activation by cfDNA from hosts (especially mtDNA) and bacteria was found to induce an additive proinflammatory effect on LPS-activated macrophages which was perhaps responsible for the more pronounced sepsis hyperinflammation observed in WT mice compared with the cGAS^-/- group.

The immunostimulatory RNA RN7SL1 enables CAR-T cells to enhance autonomous and endogenous immune function

Poor tumor infiltration, development of exhaustion, and antigen insufficiency are common mechanisms that limit chimeric antigen receptor (CAR)-T cell efficacy. Delivery of pattern recognition receptor agonists is one strategy to improve immune function; however, targeting these agonists to immune cells is challenging, and off-target signaling in cancer cells can be detrimental. Here, we engineer CAR-T cells to deliver RN7SL1, an endogenous RNA that activates RIG-I/MDA5 signaling. RN7SL1 promotes expansion and effector-memory differentiation of CAR-T cells. Moreover, RN7SL1 is deployed in extracellular vesicles and selectively transferred to immune cells. Unlike other RNA agonists, transferred RN7SL1 restricts myeloid-derived suppressor cell (MDSC) development, decreases TGFB in myeloid cells, and fosters dendritic cell (DC) subsets with costimulatory features. Consequently, endogenous effector-memory and tumor-specific T cells also expand, allowing rejection of solid tumors with CAR antigen loss. Supported by improved endogenous immunity, CAR-T cells can now co-deploy peptide antigens with RN7SL1 to enhance efficacy, even when heterogenous CAR antigen tumors lack adequate neoantigens.

Gold nanoparticles alleviates the lipopolysaccharide-induced intestinal epithelial barrier dysfunction

Nanotechnology is used in the immune response manipulation to treat various human diseases. In the present study, we explored the effects of Au nanoparticles (AuNPs) on the lipopolysaccharide (LPS)-induced epithelial barrier dysfunction and inflammatory response of colonic epithelial NCM460 cells. According to the results of cell counting kit-8 and flow cytometry analysis, the viability of NCM460 cells was inhibited, and the apoptosis was increased after LPS treatment, and AuNPs reversed these changes in a dose-dependent way. The permeability was evaluated by detecting the flux of fluorescein isothiocyanate-dextran and transepithelial electrical resistance. LPS enhanced the permeability and promoted barrier dysfunction of NCM460 cells. Enzyme-linked immunosorbent sorbent assay results revealed that the concentrations of pro-inflammatory factors and nitric oxide were elevated by LPS treatment and decreased by the AuNPs. LPS aggravated the inflammatory response, which was rescued by the AuNPs. Moreover, LPS promoted the activation of the nuclear factor kappa-B and extracellular signal-regulated kinase/c-Jun NH-terminal kinase signaling pathways, which were inhibited by AuNPs.

cGAS-STING pathway: post-translational modifications and functions in sterile inflammatory diseases

Cytoplasmic microbial and host aberrant DNAs act as danger signals and trigger host immune responses. Upon recognition, the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) catalyzes the production of a second messenger 2'3'-cGAMP, which activates endoplasmic reticulum (ER)-associated stimulator of interferon (IFN) genes (STING) and ultimately leads to the induction of type I IFNs and inflammatory genes that collectively initiate host immune defense against microbial invasion. Inappropriate activation or suppression of this signaling pathway has been implicated in the development of some autoimmune diseases, sterile inflammation, and cancers. In this review, we describe how the activity of cGAS and STING is regulated by host post-translational modifications and summarize the recent advances of cell-specific cGAS-STING activation and its association in sterile inflammatory diseases. We also discuss key outstanding questions in the field, including how our knowledge of cGAS-STING pathway could be translated into clinical applications.

Sepsis induces variation of intestinal barrier function in different phase through nuclear factor kappa B signaling

The intestinal barrier function disrupted in sepsis, while little is known about the variation in different phases of sepsis. In this study, mouse models of sepsis were established by caecal ligation and puncture (CLP). The H&E staining of sections and serum diamine oxidase concentration were evaluated at different timepoint after CLP. TUNEL assay and EdU staining were performed to evaluate the apoptosis and proliferation of intestinal epithelium. Relative protein expression was assessed by Western blotting and serum concentrations of pro-inflammatory cytokines was measured by ELISA. The disruption of intestinal barrier worsened in the first 24 h after the onset of sepsis and gradually recovered over the next 24 h. The percentage of apoptotic cell increased in the first 24 h and dropped at 48 h, accompanied with the proliferative rate of intestinal epithelium inhibited in the first 6 h and regained in the later period. Furthermore, the activity of nuclear factor kappa B (NF-κB) presented similar trend with the intestinal barrier function, shared positive correction with apoptosis of intestinal epithelium. These findings reveal the conversion process of intestinal barrier function in sepsis and this process is closely correlated with the activity of NF-κB signaling.

Circulating Mitochondrial DNA Stimulates Innate Immune Signaling Pathways to Mediate Acute Kidney Injury

Mitochondrial dysfunction is increasingly considered as a critical contributor to the occurrence and progression of acute kidney injury (AKI). However, the mechanisms by which damaged mitochondria mediate AKI progression are multifactorial and complicated. Mitochondrial DNA (mtDNA) released from damaged mitochondria could serve as a danger-associated molecular pattern (DAMP) and activate the innate immune system through STING, TLR9, NLRP3, and some other adaptors, and further mediate tubular cell inflammation and apoptosis. Accumulating evidence has demonstrated the important role of circulating mtDNA and its related pathways in the progression of AKI, and regulating the proteins involved in these pathways may be an effective strategy to reduce renal tubular injury and alleviate AKI. Here, we aim to provide a comprehensive overview of recent studies on mtDNA-mediated renal pathological events to provide new insights in the setting of AKI.

Dysbiosis exacerbates colitis by promoting ubiquitination and accumulation of the innate immune adaptor STING in myeloid cells

Alterations in the cGAS-STING DNA-sensing pathway affect intestinal homeostasis. We sought to delineate the functional role of STING in intestinal inflammation. Increased STING expression was a feature of intestinal inflammation in mice with colitis and in humans afflicted with inflammatory bowel disease. Mice bearing an allele rendering STING constitutively active exhibited spontaneous colitis and dysbiosis, as well as progressive chronic intestinal inflammation and fibrosis. Bone marrow chimera experiments revealed STING accumulation in intestinal macrophages and monocytes as the initial driver of inflammation. Depletion of Gram-negative bacteria prevented STING accumulation in these cells and alleviated intestinal inflammation. STING accumulation occurred at the protein rather than transcript level, suggesting post-translational stabilization. We found that STING was ubiquitinated in myeloid cells, and this K63-linked ubiquitination could be elicited by bacterial products, including cyclic di-GMP. Our findings suggest a positive feedback loop wherein dysbiosis foments the accumulation of STING in intestinal myeloid cells, driving intestinal inflammation.

The STING1 network regulates autophagy and cell death

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

Zizyphus jujuba cv. Muzao polysaccharides enhance intestinal barrier function and improve the survival of septic mice

This study aimed to examine the role of Zizyphus jujuba cv. Muzao polysaccharides (ZJPs) in protecting intestinal barrier function and the survival of septic mice. The sepsis mouse model was generated through cecal ligation and puncture (CLP) to observe the effect of ZJPs on the function of the intestinal barrier in the context of sepsis. We observed the clinical symptoms and survival time of the mice and evaluated serum inflammatory cytokines, intestinal pathological changes and intestinal permeability. Moreover, tight junction (TJ) proteins and apoptosis-associated proteins in intestinal tissue were examined. Finally, TLR4/NF-κB pathway-related proteins were measured in all groups. The results showed that pretreatment with ZJPs improved clinical and histological scores and reduced intestinal barrier permeability, and the levels of proinflammatory factors were decreased. Pretreatment with ZJPs also upregulated the levels of TJ proteins and downregulated the expression of proapoptotic proteins. Moreover, the activation of TLR4/NF-κB signaling was partly inhibited in septic mice by ZJPs pretreatment. The current study provides evidence that ZJPs have the potential to protect intestinal barrier function and improve the survival of septic mice via the attenuation of TLR4/NF-κB inflammatory signaling. PRACTICAL APPLICATIONS: This study reports the potential protective effect of ZJPs against cecal ligation and puncture (CLP)-induced sepsis. Our data reveal that CLP induced damage to the gut mucosal barrier, inflammation, and apoptosis in intestinal tissues. However, pretreatment with ZJPs improved clinical and histological scores, reduced intestinal barrier permeability, and decreased the levels of proinflammatory factors in mice. Pretreatment with ZJPs also upregulated the levels of TJ proteins and downregulated the expression of proapoptotic proteins. Moreover, the activation of TLR4/NF-κB signaling was partly inhibited in septic mice after ZJPs pretreatment. These findings provide evidence that pretreatment with ZJPs has the potential to attenuate CLP-induced gut damage in mice by restraining inflammation and apoptosis via the attenuation of NF-κB signaling. It provides a basis for further study of ZJPs in sepsis.

Cyclic GMP-AMP promotes the acute phase response and protects against Escherichia coli infection in mice

The acute phase response, as a component of the innate immune system, is part of the first line of defense against invading pathogens. The Stimulator of Interferon Genes (STING) pathway initiates innate immune responses upon recognition of exogenous bacterial and viral DNA. However, whether STING signaling pathway plays any roles in regulating acute phase response during bacterial infection remains unknown. In this study, we used STING-deficient (Tmem173^gt) and wildtype mice to investigate acute phase responses to bacterial infection (Escherichia coli, E. coli) and test the effect of exogenous cyclic GMP-AMP (cGAMP, a STING agonist) treatment. Bacterial infection of STING-deficient mice resulted in an increase in mortality and bacterial dissemination. Also, inflammation-induced acute phase response was drastically reduced in STING-deficient mice, showing significant reduction in expression of cytokine TNF-α and acute phase proteins. In contrast, exogenous cGAMP treatment enhanced inflammation-induced acute phase response by increasing the expression of TNF-α and acute phase proteins. Also, cGAMP accelerated bacterial clearance and improved survival rate of wildtype mice, but not STING-deficient mice. Interestingly, cGAMP treatment mitigated bacterial infection induced liver injury in both wildtype and STING-deficient mice. Further in vitro evidence showed that cGAMP treatment retarded TNF-α-mediated hepatocyte apoptosis, potentially accelerating autophagy. Taken together, our results indicated that cGAMP/STING signaling pathway is critical for organism to initiate blood-borne innate immune-responses to defend bacterial infection, and cGAMP is envisaged as a drug candidate for further clinical trial.

Intestinal microbiota and antibiotic-associated acute gastrointestinal injury in sepsis mice

BACKGROUND

To investigate the changes of intestinal microbiota and metabolites in sepsis mice with acute gastrointestinal injury before and after the use of antibiotics, and to explore the possible effects of these changes on the body.

METHODS

Twenty-four 6-8-w-old SPF-grade C57BL/6J male mice were selected, and the mice were randomly divided into three groups. The mice were treated by tail vein injection for 3 days. The intestinal motility of mice after administration was detected. The mice feces were collected for 16S rRNA and Untargeted metabonomics detection.

RESULTS

The use of antibiotics in sepsis mice can change the composition of intestinal microbiota and metabolites. LD3, AD3 and LAD3 samples had significant differences in bacterial species. Desulfovibrio was the species with a significant difference in LAD3. In addition, we found that the composition of those intestinal microbiota were correlated with changes in intestinal motility. The untargeted metabolomics analysis showed that the fecal metabolites of LD3 and LAD3 samples were significantly different. In addition to the basic metabolites, Benzoic acid and 4-Hydroxybenzoic acid were also found, and Desulfovibrio was associated with them.

CONCLUSIONS

The use of antibiotics in sepsis mice can lead to changes in the intestinal microbiota and metabolite levels, which may be related to the severity of acute gastrointestinal injury in sepsis mice. Inhibiting Desulfovibrio in the intestine and using Benzoic acid and 4-Hydroxybenzoic acid as a marker for the production of Desulfovibrio may reduce the inflammatory degree of acute gastrointestinal injury in sepsis.

The role of cGAS/STING in intestinal immunity

The gastrointestinal tract is a highly complex microenvironment under constant interaction with potentially harmful pathogens. Inflammatory bowel disease (IBD) is an archetypical inflammatory disease, in which the intestinal epithelium, defective autophagy, endoplasmic reticulum stress and dysbiosis play a key role. Although no risk-mediating gene variants of STING (TMEM173) have been identified so far, several seminal findings have elucidated a novel understanding of STING in the context of acute and chronic inflammation. STING, an endoplasmic reticulum resident adaptor protein binding cyclic dinucleotides, is a main inducer of type I interferons and canonically involved in antiviral and antibacterial immunity. Recent research has shed light on additional features of STING signaling involved in regulating the microbiota, facilitating autophagy, cell death or ER stress. Importantly, an increasing amount of studies suggests a considerable overlap of IBD pathophysiology and features of STING signaling. Since compelling evidence shows dysregulated type I IFNs in IBD, it is prompting to speculate on the hypothetical role of cGAS/STING/type I IFN signaling in IBD. Here, we summarize recent findings about the origin and function of STING signaling in the gastrointestinal tract and evolve the hypothesis that disturbed STING signaling might be profoundly interconnected with the pathophysiology of IBD.

EZH2 inhibitor GSK343 inhibits sepsis-induced intestinal disorders

Enhancer of zeste homolog 2 (EZH2) is positively associated with poor clinical outcomes in a number of aggressive tumors. Recent studies have demonstrated that inhibition of EZH2 also suppressed the inflammatory response during sepsis. The present study aimed to investigate whether an inhibitor of EZH2, GSK343, could protect the intestine against sepsis-induced injury in vivo. Mice underwent cecal ligation and perforation (CLP) to induce sepsis and were assigned into three groups: Sham, CLP and CLP + GSK343. For GSK343 treatment, the septic mice were intravenously injected with GSK343 at 6 h post-CLP. The results indicated that EZH2 was highly expressed while tight junction (TJ) proteins ZO-1, occludin and claudin-1 expression was reduced in the intestinal tissue of mice subjected to CLP compared with the sham group. CLP operation also caused intestinal pathological injury and the production of inflammatory cytokines including TNF-α, IL-1β and IL-6 in both serum and intestinal tissues. Meanwhile, CLP induced cell apoptosis of intestinal tissue based on the increased number of apoptotic cells, reduced expression of Bcl-2 and higher expression of caspase-3 and Bax. However, the presence of GSK343 partially rescued intestinal pathological injury, reduced the level of inflammatory cytokines, repressed cell apoptosis and promoted TJ protein expression. Finally, the decreased number of Paneth cells caused by CLP operation was reversed by GSK343 treatment. In conclusion, the results of the present study demonstrated that GSK343 could protect the intestine against sepsis-induced injury in vivo. Inhibition of EZH2 may provide a therapeutic approach for intestinal dysfunction during sepsis.

Cyclic Guanosine Monophosphate-Adenosine Monophosphate Synthase (cGAS), a Multifaceted Platform of Intracellular DNA Sensing

Innate immune pathways are the first line of cellular defense against pathogen infections ranging from bacteria to Metazoa. These pathways are activated following the recognition of pathogen associated molecular patterns (PAMPs) by membrane and cytosolic pattern recognition receptors. In addition, some of these cellular sensors can also recognize endogenous danger-associated molecular patterns (DAMPs) arising from damaged or dying cells and triggering innate immune responses. Among the cytosolic nucleic acid sensors, the cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) synthase (cGAS) plays an essential role in the activation of the type I interferon (IFNs) response and the production of pro-inflammatory cytokines. Indeed, upon nucleic acid binding, cGAS synthesizes cGAMP, a second messenger mediating the activation of the STING signaling pathway. The functional conservation of the cGAS-STING pathway during evolution highlights its importance in host cellular surveillance against pathogen infections. Apart from their functions in immunity, cGAS and STING also play major roles in nuclear functions and tumor development. Therefore, cGAS-STING is now considered as an attractive target to identify novel biomarkers and design therapeutics for auto-inflammatory and autoimmune disorders as well as infectious diseases and cancer. Here, we review the current knowledge about the structure of cGAS and the evolution from bacteria to Metazoa and present its main functions in defense against pathogens and cancer, in connection with STING. The advantages and limitations of in vivo models relevant for studying the cGAS-STING pathway will be discussed for the notion of species specificity and in the context of their integration into therapeutic screening assays targeting cGAG and/or STING.