The myeloid heat shock transcription factor 1/β-catenin axis regulates NLR family, pyrin domain-containing 3 inflammasome activation in mouse liver ischemia/reperfusion injury

Macrophage Dvl2 deficiency promotes NOD1-Driven pyroptosis and exacerbates inflammatory liver injury

Dishevelled 2 (Dvl2) is a key mediator of the Wingless/Wnt signaling pathway that regulates cell proliferation, migration, and immune function. However, little is known about the role of macrophage Dvl2 in modulating NOD1-mediated pyroptosis and hepatocyte death in oxidative stress-induced inflammatory liver injury. In a mouse model of oxidative stress-induced liver inflammation, mice with myeloid-specific Dvl2 knockout (Dvl2M-KO) displayed exacerbated ischemia/reperfusion (IR) stress-induced hepatocellular damage with increased serum ALT levels, oxidative stress, and proinflammatory mediators. Unlike in Dvl2FL/FL controls, Dvl2M-KO enhanced NOD1, caspase-1, GSDMD, and NF-κB activation in liver macrophages after IR. Interestingly, IR stress enhanced YAP colocalized with HSF1 in Dvl2FL/FL macrophages, while macrophage Dvl2 deficiency reduced YAP and HSF1 colocalization in the nucleus under inflammatory conditions. Importantly, Dvl2 deletion diminished nuclear YAP interacted with HSF1 and augmented NOD1/caspase-1 and GSDMD activation in response to inflammatory stimulation. However, Dvl2 activation increased YAP interaction with HSF1 and activated HSF1 target gene eEF2, inhibiting NOD1/caspase-1, GSDMD, and NF-κB activity. Moreover, macrophage eEF2 deletion increased the NOD1-caspase-1 interaction, GSDMD activation, HMGB1 release, and hepatocyte LDH release after macrophage/hepatocyte co-culture. Adoptive transfer of eEF2-expressing macrophages in Dvl2M-KO mice alleviated IR-triggered liver inflammation and hepatocellular damage. Therefore, macrophage Dvl2 deficiency promotes NOD1-mediated pyroptosis and exacerbates IR-induced hepatocellular death by disrupting the YAP-HSF1 axis. eEF2 is crucial for modulating NOD1-driven pyroptosis, inflammatory response, and hepatocyte death. Our findings underscore a novel role of macrophage Dvl2 in modulating liver inflammatory injury and imply the therapeutic potential in organ IRI and transplant recipients.

β-Catenin disruption decreases macrophage exosomal α-SNAP and impedes Treg differentiation in acute liver injury

Hepatic macrophages and regulatory T cells (Tregs) play an important role in the maintenance of liver immune homeostasis, but the mechanism by which hepatic macrophages regulate Tregs in acute liver injury remains largely unknown. Here, we found that the hepatic Treg proportion and β-catenin expression in hepatic macrophages were associated with acetaminophen- and d-galactosamine/LPS-induced acute liver injury. Interestingly, β-catenin was markedly upregulated only in infiltrating macrophages but not in resident Kupffer cells. Myeloid-specific β-catenin-knockout mice showed an increased inflammatory cell infiltration and hepatocyte apoptosis. Moreover, myeloid β-catenin deficiency decreased the hepatic Treg proportion in the injured liver. Mechanistically, in vitro coculture experiments revealed that macrophage β-catenin modulated its exosome composition and influenced Treg differentiation. Using mass spectrometry-based proteomics, we identified that macrophage β-catenin activation increased the level of exosomal alpha soluble NSF attachment protein (α-SNAP), which in turn promoted Treg differentiation. Overall, our findings demonstrated a molecular mechanism that macrophage β-catenin regulated the Treg proportion in the liver by enhancing the expression of exosomal α-SNAP, providing insights into the pathophysiology of acute liver injury.

Age-dependent heat shock hormesis to HSF-1 deficiency suggests a compensatory mechanism mediated by the unfolded protein response and innate immunity in young Caenorhabditis elegans

The transcription factor HSF-1 (heat shock factor 1) acts as a master regulator of heat shock response in eukaryotic cells to maintain cellular proteostasis. The protein has a protective role in preventing cells from undergoing ageing, and neurodegeneration, and also mediates tumorigenesis. Thus, modulating HSF-1 activity in humans has a promising therapeutic potential for treating these pathologies. Loss of HSF-1 function is usually associated with impaired stress tolerance. Contrary to this conventional knowledge, we show here that inactivation of HSF-1 in the nematode Caenorhabditis elegans results in increased thermotolerance at young adult stages, whereas HSF-1 deficiency in animals passing early adult stages indeed leads to decreased thermotolerance, as compared to wild-type. Furthermore, a gene expression analysis supports that in young adults, distinct cellular stress response and immunity-related signaling pathways become induced upon HSF-1 deficiency. We also demonstrate that increased tolerance to proteotoxic stress in HSF-1-depleted young worms requires the activity of the unfolded protein response of the endoplasmic reticulum and the SKN-1/Nrf2-mediated oxidative stress response pathway, as well as an innate immunity-related pathway, suggesting a mutual compensatory interaction between HSF-1 and these conserved stress response systems. A similar compensatory molecular network is likely to also operate in higher animal taxa, raising the possibility of an unexpected outcome when HSF-1 activity is manipulated in humans.

Blockade of the mitochondrial DNA release ameliorates hepatic ischemia-reperfusion injury through avoiding the activation of cGAS-Sting pathway

BACKGROUND

Liver surgery during the perioperative period often leads to a significant complication known as hepatic ischemia-reperfusion (I/R) injury. Hepatic I/R injury is linked to the innate immune response. The cGAS-STING pathway triggers the activation of innate immune through the detection of DNA within cells. Nevertheless, the precise mechanism and significance of the cGAS-STING pathway in hepatic I/R injury are yet to be investigated.

METHODS

Mouse model of hepatic I/R injury was used in the C57BL/6 WT mice and the STING knockout (STING-KO) mice. In addition, purified primary hepatocytes were used to construct oxygen-glucose deprivation reperfusion (OGD-Rep) treatment models.

RESULTS

Our research revealed a notable increase in mRNA and protein levels of cGAS and STING in liver during I/R injury. Interestingly, the lack of STING exhibited a safeguarding impact on hepatic I/R injury by suppressing the elevation of liver enzymes, liver cell death, and inflammation. Furthermore, pharmacological cGAS and STING inhibition recapitulated these phenomena. Macrophages play a crucial role in the activation of the cGAS-STING pathway during hepatic I/R injury. The cGAS-STING pathway experiences a significant decrease in activity and hepatic I/R injury is greatly diminished following the elimination of macrophages. Significantly, we demonstrate that the activation of the cGAS-STING pathway is primarily caused by the liberation of mitochondrial DNA (mtDNA) rather than nuclear DNA (nDNA). Moreover, the safeguarding of the liver against I/R injury is also attributed to the hindrance of mtDNA release through the utilization of inhibitors targeting mPTP and VDAC oligomerization.

CONCLUSIONS

The results of our study suggest that the release of mtDNA plays a significant role in causing damage to liver by activating the cGAS-STING pathway during I/R injury. Furthermore, inhibiting the release of mtDNA can provide effective protection against hepatic I/R injury.

NLRP3 Inflammasome in Acute and Chronic Liver Diseases

NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) is an intracellular complex that upon external stimuli or contact with specific ligands, recruits other components, forming the NLRP3 inflammasome. The NLRP3 inflammasome mainly mediates pyroptosis, a highly inflammatory mode of regulated cell death, as well as IL-18 and IL-1β production. Acute and chronic liver diseases are characterized by a massive influx of pro-inflammatory stimuli enriched in reactive oxygen species (ROS) and damage-associated molecular patterns (DAMPs) that promote the assemblage and activation of the NLRP3 inflammasome. As the major cause of inflammatory cytokine storm, the NLRP3 inflammasome exacerbates liver diseases, even though it might exert protective effects in regards to hepatitis C and B virus infection (HCV and HBV). Here, we summarize the current knowledge concerning NLRP3 inflammasome function in both acute and chronic liver disease and in the post liver transplant setting, focusing on the molecular mechanisms involved in NLRP3 activity.

Identification and validation of potential diagnostic signature and immune cell infiltration for HIRI based on cuproptosis-related genes through bioinformatics analysis and machine learning

Background and aims

Cuproptosis has emerged as a significant contributor in the progression of various diseases. This study aimed to assess the potential impact of cuproptosis-related genes (CRGs) on the development of hepatic ischemia and reperfusion injury (HIRI).

Methods

The datasets related to HIRI were sourced from the Gene Expression Omnibus database. The comparative analysis of differential gene expression involving CRGs was performed between HIRI and normal liver samples. Correlation analysis, function enrichment analyses, and protein-protein interactions were employed to understand the interactions and roles of these genes. Machine learning techniques were used to identify hub genes. Additionally, differences in immune cell infiltration between HIRI patients and controls were analyzed. Quantitative real-time PCR and western blotting were used to verify the expression of the hub genes.

Results

Seventy-five HIRI and 80 control samples from three databases were included in the bioinformatics analysis. Three hub CRGs (NLRP3, ATP7B and NFE2L2) were identified using three machine learning models. Diagnostic accuracy was assessed using a receiver operating characteristic (ROC) curve for the hub genes, which yielded an area under the ROC curve (AUC) of 0.832. Remarkably, in the validation datasets GSE15480 and GSE228782, the three hub genes had AUC reached 0.904. Additional analyses, including nomograms, decision curves, and calibration curves, supported their predictive power for diagnosis. Enrichment analyses indicated the involvement of these genes in multiple pathways associated with HIRI progression. Comparative assessments using CIBERSORT and gene set enrichment analysis suggested elevated expression of these hub genes in activated dendritic cells, neutrophils, activated CD4 memory T cells, and activated mast cells in HIRI samples versus controls. A ceRNA network underscored a complex regulatory interplay among genes. The genes mRNA and protein levels were also verified in HIRI-affected mouse liver tissues.

Conclusion

Our findings have provided a comprehensive understanding of the association between cuproptosis and HIRI, establishing a promising diagnostic pattern and identifying latent therapeutic targets for HIRI treatment. Additionally, our study offers novel insights to delve deeper into the underlying mechanisms of HIRI.

Social defeat stress induces liver injury by modulating endoplasmic reticulum stress in C57BL/6J mice

Social defeat stress is associated with endoplasmic reticulum (ER) stress, inflammation and apoptosis. ER stress is thought to contribute to many lifestyle diseases such as liver injury, cardiovascular dysfunction and depression. We investigated the expression of the ER stress markers RNA-dependent protein kinase-like ER kinase (PERK), eukaryotic translation initiation factor 2α (eIF2α) and C/EBP homologous protein (CHOP), as well as inflammatory and apoptotic factors, to assess how social defeat stress induces liver injury. Furthermore, we evaluated the effects of the ER stress inhibitor phenylbutyric acid (PBA) and ER stress inducer thapsigargin (TG) on liver injury. Adult mice were divided into the control, social defeat, social defeat + PBA, TG, PBA and TG + PBA groups. The social defeat and social defeat + PBA groups were simultaneously exposed to social defeat stress for 10 days. The social defeat + PBA, TG, PBA and TG + PBA groups were treated with PBA or TG via intraperitoneal injections. PBA was injected 1 h before the TG injection into the TG + PBA group. Liver samples from six groups of mice were analyzed by histological analysis and western blotting. Social defeat stress promoted ER stress, increased the expression of inflammatory factors and induced apoptosis in the liver of socially defeated mice, which was reversed by PBA. Moreover, ER stress induces TG-induced liver injury by initiating ER stress. Social defeat stress initiates ER stress, promotes the expression of inflammatory and apoptotic factors, and induces liver injury. PBA suppresses liver injury caused by social defeat stress and TG treatment.

Biomimetic Lung-Targeting Nanoparticles with Antioxidative and Nrf2 Activating Properties for Treating Ischemia/Reperfusion-Induced Acute Lung Injury

Ischemia/reperfusion (IR)-induced acute lung injury (ALI) has a high mortality rate. Reactive oxygen species (ROS) play a crucial role in causing cellular damage and death in IR-induced ALI. In this work, we developed a biomimetic lung-targeting nanoparticle (PC@MB) as an antioxidative lung protector for treating IR-induced ALI. PC@MBs showed excellent ROS scavenging and Nrf2 activation properties, along with a lung-targeting function through autologous cell membrane coating. The PC@MBs exhibited an impressive antioxidative and pulmonary protective role via redox homeostasis recovery through Nrf2 and heme oxygenase-1 activation. PC@MBs could maintain cell viability by effectively scavenging the intracellular ROS and restoring the redox equilibrium in the lesion. In the IR mouse model, the PC@MBs preferentially accumulated in the lung and distinctly repaired the pneumonic damage. Our strategy has the potential to offer a promising therapeutic paradigm for treating IR-induced ALI through the incorporation of different therapeutic mechanisms.

Loss of macrophage TSC1 exacerbates sterile inflammatory liver injury through inhibiting the AKT/MST1/NRF2 signaling pathway

Tuberous sclerosis complex 1 (TSC1) plays important roles in regulating innate immunity. However, the precise role of TSC1 in macrophages in the regulation of oxidative stress response and hepatic inflammation in liver ischemia/reperfusion injury (I/R) remains unknown. In a mouse model of liver I/R injury, deletion of myeloid-specific TSC1 inhibited AKT and MST1 phosphorylation, and decreased NRF2 accumulation, whereas activated TLR4/NF-κB pathway, leading to increased hepatic inflammation. Adoptive transfer of AKT- or MST1-overexpressing macrophages, or Keap1 disruption in myeloid-specific TSC1-knockout mice promoted NRF2 activation but reduced TLR4 activity and mitigated I/R-induced liver inflammation. Mechanistically, TSC1 in macrophages promoted AKT and MST1 phosphorylation, and protected NRF2 from Keap1-mediated ubiquitination. Furthermore, overexpression AKT or MST1 in TSC1-knockout macrophages upregulated NRF2 expression, downregulated TLR4/NF-κB, resulting in reduced inflammatory factors, ROS and inflammatory cytokine-mediated hepatocyte apoptosis. Strikingly, TSC1 induction in NRF2-deficient macrophages failed to reverse the TLR4/NF-κB activity and production of pro-inflammatory factors. Conclusions: Macrophage TSC1 promoted the activation of the AKT/MST1 signaling pathway, increased NRF2 levels via reducing Keap1-mediated ubiquitination, and modulated oxidative stress-driven inflammatory responses in liver I/R injury. Our findings underscore the critical role of macrophage TSC1 as a novel regulator of innate immunity and imply the therapeutic potential for the treatment of sterile liver inflammation in transplant recipients. Schematic illustration of macrophage TSC1-mediated AKT/MST1/NRF2 signaling pathway in I/R-triggered liver inflammation. Macrophage TSC1 can be activated in I/R-stressed livers. TSC1 activation promotes phosphorylation of AKT and MST1, which in turn increases NRF2 expression and inhibits ROS production and TLR4/NF-κB activation, resulting in reduced hepatocellular apoptosis in I/R-triggered liver injury.

Non-Canonical Inflammasome Pathway: The Role of Cell Death and Inflammation in Ehrlichiosis

Activating inflammatory caspases and releasing pro-inflammatory mediators are two essential functions of inflammasomes which are triggered in response to pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs). The canonical inflammasome pathway involves the activation of inflammasome and its downstream pathway via the adaptor ASC protein, which causes caspase 1 activation and, eventually, the cleavage of pro-IL-1b and pro-IL-18. The non-canonical inflammasome pathway is induced upon detecting cytosolic lipopolysaccharide (LPS) by NLRP3 inflammasome in Gram-negative bacteria. The activation of NLRP3 triggers the cleavage of murine caspase 11 (human caspase 4 or caspase 5), which results in the formation of pores (via gasdermin) to cause pyroptosis. Ehrlichia is an obligately intracellular bacterium which is responsible for causing human monocytic ehrlichiosis (HME), a potentially lethal disease similar to toxic shock syndrome and septic shock syndrome. Several studies have indicated that canonical and non-canonical inflammasome activation is a crucial pathogenic mechanism that induces dysregulated inflammation and host cellular death in the pathophysiology of HME. Mechanistically, the activation of canonical and non-canonical inflammasome pathways affected by virulent Ehrlichia infection is due to a block in autophagy. This review aims to explore the significance of non-canonical inflammasomes in ehrlichiosis, and how the pathways involving caspases (with the exception of caspase 1) contribute to the pathophysiology of severe and fatal ehrlichiosis. Improving our understanding of the non-canonical inflammatory pathway that cause cell death and inflammation in ehrlichiosis will help the advancement of innovative therapeutic, preventative, and diagnostic approaches to the treatment of ehrlichiosis.

Macrophage RIPK3 triggers inflammation and cell death via the XBP1-Foxo1 axis in liver ischaemia-reperfusion injury

Background & Aims

Receptor-interacting serine/threonine-protein kinase 3 (RIPK3) is a central player in triggering necroptotic cell death. However, whether macrophage RIPK3 may regulate NOD1-dependent inflammation and calcineurin/transient receptor potential cation channel subfamily M member 7 (TRPM7)-induced hepatocyte death in oxidative stress-induced liver inflammatory injury remains elusive.

Methods

A mouse model of hepatic ischaemia-reperfusion (IR) injury, the primary hepatocytes, and bone marrow-derived macrophages were used in the myeloid-specific RIPK3 knockout (RIPK3M-KO) and RIPK3-proficient (RIPK3FL/FL) mice.

Results

RIPK3M-KO diminished IR stress-induced liver damage with reduced serum alanine aminotransferase/aspartate aminotransferase levels, macrophage/neutrophil infiltration, and pro-inflammatory mediators compared with the RIPK3FL/FL controls. IR stress activated RIPK3, inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α), x-box binding protein 1 (XBP1), nucleotide-binding oligomerisation domain-containing protein 1 (NOD1), NF-κB, forkhead box O1 (Foxo1), calcineurin A, and TRPM7 in ischaemic livers. Conversely, RIPK3M-KO depressed IRE1α, XBP1, NOD1, calcineurin A, and TRPM7 activation with reduced serum tumour necrosis factor α (TNF-α) levels. Moreover, Foxo1M-KO alleviated IR-induced liver injury with reduced NOD1 and TRPM7 expression. Interestingly, chromatin immunoprecipitation coupled with massively parallel sequencing revealed that macrophage Foxo1 colocalised with XBP1 and activated its target gene Zc3h15 (zinc finger CCCH domain-containing protein 15). Activating macrophage XBP1 enhanced Zc3h15, NOD1, and NF-κB activity. However, disruption of macrophage Zc3h15 inhibited NOD1 and hepatocyte calcineurin/TRPM7 activation, with reduced reactive oxygen species production and lactate dehydrogenase release after macrophage/hepatocyte coculture. Furthermore, adoptive transfer of Zc3h15-expressing macrophages in RIPK3M-KO mice augmented IR-triggered liver inflammation and cell death.

Conclusions

Macrophage RIPK3 activates the IRE1α-XBP1 pathway and Foxo1 signalling in IR-stress livers. The XBP1-Foxo1 interaction is essential for modulating target gene Zc3h15 function, which is crucial for the control of NOD1 and calcineurin-mediated TRPM7 activation. XBP1 functions as a transcriptional coactivator of Foxo1 in regulating NOD1-driven liver inflammation and calcineurin/TRPM7-induced cell death. Our findings underscore a novel role of macrophage RIPK3 in stress-induced liver inflammation and cell death, implying the potential therapeutic targets in liver inflammatory diseases.

Impact and implications

Macrophage RIPK3 promotes NOD1-dependent inflammation and calcineurin/TRPM7-induced cell death cascade by triggering the XBP1-Foxo1 axis and its target gene Zc3h15, which is crucial for activating NOD1 and calcineurin/TRPM7 function, implying the potential therapeutic targets in stress-induced liver inflammatory injury.

Macrophage PTEN controls STING-induced inflammation and necroptosis through NICD/NRF2 signaling in APAP-induced liver injury

BACKGROUND

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling has been known to play a critical role in maintaining cellular and tissue homeostasis, which also has an essential role in the inflammatory response. However, it remains unidentified whether and how the macrophage PTEN may govern the innate immune signaling stimulator of interferon genes (STING) mediated inflammation and hepatocyte necroptosis in APAP-induced liver injury (AILI).

METHODS

Myeloid-specific PTEN knockout (PTEN^M-KO) and floxed PTEN (PTEN^FL/FL) mice were treated with APAP (400 mg/kg) or PBS. In a parallel in vitro study, bone marrow-derived macrophages (BMMs) were isolated from these conditional knockout mice and transfected with CRISPR/Cas9-mediated Notch1 knockout (KO) or CRISPR/Cas9-mediated STING activation vector followed by LPS (100 ng/ml) stimulation.

RESULTS

Here, we report that myeloid-specific PTEN knockout (PTEN^M-KO) mice were resistant to oxidative stress-induced hepatocellular injury with reduced macrophage/neutrophil accumulation and proinflammatory mediators in AILI. PTEN^M-KO increased the interaction of nuclear Notch intracellular domain (NICD) and nuclear factor (erythroid-derived 2)-like 2 (NRF2) in the macrophage nucleus, reducing reactive oxygen species (ROS) generation. Mechanistically, it is worth noting that macrophage NICD and NRF2 co-localize within the nucleus under inflammatory conditions. Additionally, Notch1 promotes the interaction of immunoglobulin kappa J region (RBPjκ) with NRF2. Disruption of the Notch1 signal in PTEN deletion macrophages, reduced RBPjκ and NRF2 binding, and activated STING signaling. Moreover, PTEN^M-KO macrophages with STING activated led to ROS generation and TNF-α release, resulting in hepatocyte necroptosis upon co-culture with primary hepatocytes.

CONCLUSIONS

Our findings demonstrate that the macrophage PTEN-NICD/NRF2-STING axis is critical to regulating oxidative stress-induced liver inflammation and necroptosis in AILI and implies the therapeutic potential for managing sterile liver inflammation. Video Abstract.

The Potential of Cylindromatosis (CYLD) as a Therapeutic Target in Oxidative Stress-Associated Pathologies: A Comprehensive Evaluation

Oxidative stress (OS) arises as a consequence of an imbalance between the formation of reactive oxygen species (ROS) and the capacity of antioxidant defense mechanisms to neutralize them. Excessive ROS production can lead to the damage of critical biomolecules, such as lipids, proteins, and DNA, ultimately contributing to the onset and progression of a multitude of diseases, including atherosclerosis, chronic obstructive pulmonary disease, Alzheimer's disease, and cancer. Cylindromatosis (CYLD), initially identified as a gene linked to familial cylindromatosis, has a well-established and increasingly well-characterized function in tumor inhibition and anti-inflammatory processes. Nevertheless, burgeoning evidence suggests that CYLD, as a conserved deubiquitination enzyme, also plays a pivotal role in various key signaling pathways and is implicated in the pathogenesis of numerous diseases driven by oxidative stress. In this review, we systematically examine the current research on the function and pathogenesis of CYLD in diseases instigated by oxidative stress. Therapeutic interventions targeting CYLD may hold significant promise for the treatment and management of oxidative stress-induced human diseases.

Hyperhomocysteinemia activates NLRP3 inflammasome to cause hepatic steatosis and insulin resistance via MDM2-mediated ubiquitination of HSF1

Hyperhomocysteinemia (HHcy) is associated with nonalcoholic fatty liver disease (NAFLD) and insulin resistance (IR). However, the underlying mechanism is still unknown. Recent studies have demonstrated that NLRP3 inflammasome activation plays a vital role in NAFLD and IR. Our study aimed to explore whether NLRP3 inflammasome contributed to HHcy-induced NAFLD and IR as well as dissected the underlying mechanism. C57BL/6 mice were fed a high-methionine diet (HMD) for 8 weeks to establish the HHcy mouse model. Compared with a chow diet, HMD induced hepatic steatosis (HS) and IR as well as activation of hepatic NLRP3 inflammasome. Moreover, HHcy-induced NAFLD and IR characterization disclosed that NLRP3 inflammasome activation occurred in liver tissue of HMD-fed mice, but was very marginal in either NLRP3^-/- or Caspase-1^-/- mice. Mechanistically, high levels of homocysteine (Hcy) up-regulated the expression of mouse double minute 2 homolog (MDM2), which directly ubiquitinates heat shock transcription factor 1 (HSF1) and consequently activated hepatic NLRP3 inflammasome in vivo and in vitro. In addition, in vitro experiments showed P300-mediated HSF1 acetylation at K298 hindered MDM2-mediated ubiquitination of HSF1 at K372, which plays important role in determining the HSF1 level. Importantly, either inhibition of MDM2 by JNJ-165 or activation of HSF1 by HSF1A reversed HMD-induced hepatic NLRP3 inflammasome, and consequently alleviated HS and IR in mice. This study demonstrates that NLRP3 inflammasome activation contributes to HHcy-induced NAFLD and IR, and further identified that HSF1 as a new substrate of MDM2 and its decrease on MDM2-mediated ubiquitination at K372 modulates NLRP3 inflammasome activation. These findings may provide novel therapeutic strategies aimed at halting HS or IR.

XBP1 modulates endoplasmic reticulum and mitochondria crosstalk via regulating NLRP3 in renal ischemia/reperfusion injury

The functional status of mitochondria and the endoplasmic reticulum are central to renal ischemia/reperfusion injury (IRI). X-box binding protein 1 (XBP1) is an important transcription factor in endoplasmic reticulum stress. NLR family pyrin domain containing-3 (NLRP3) inflammatory bodies are closely related to renal IRI. In vivo and in vitro, we examined the molecular mechanisms and functions of XBP1-NLRP3 signaling in renal IRI, which influences ER-mitochondrial crosstalk. In this study, mice were subjected to 45 min of unilateral renal warm ischemia, the other kidney resected, and reperfusion was performed for 24 h in vivo. In vitro, murine renal tubular epithelial cells (TCMK-1) were exposed to hypoxia for 24 h and reoxygenation for 2 h. Tissue or cell damage was evaluated by measuring blood urea nitrogen and creatinine levels, histological staining, flow cytometry, terminal deoxynucleotidyl transferase-mediated nick-end labeling, diethylene glycol staining, and transmission electron microscopy (TEM). Western blotting, immunofluorescence staining, and ELISA were used to analyze protein expression. Whether XBP1 regulates the NLRP3 promoter was evaluated using a luciferase reporter assay. Kidney damage was reduced with decreasing blood urea nitrogen, creatinine, interleukin-1β, and interleukin-18 levels. XBP1 deficiency reduced tissue damage and cell apoptosis, protecting the mitochondria. Disruption of XBP1 was associated with reduced NLRP3 and cleaved caspase-1 levels and markedly improved survival. In vitro in TCMK-1 cells, XBP1 interference inhibited caspase-1-dependent mitochondrial damage and reduced the production of mitochondrial reactive oxygen species. The luciferase assay showed that spliced XBP1 isoforms enhanced the activity of the NLRP3 promoter. These findings reveal that XBP1 downregulation suppresses the expression of NLRP3, a potential regulator of endoplasmic reticulum mitochondrial crosstalk in nephritic injury and a potential therapeutic target in XBP1-mediated aseptic nephritis.

HSF1 Alleviates Brain Injury by Inhibiting NLRP3-Induced Pyroptosis in a Sepsis Model

BACKGROUND

Sepsis, which could cause a systemic inflammatory response, is a life-threatening disease with a high morbidity and mortality rate. There is evidence that brain injury may be related to severe systemic infection induced by sepsis. The brain injury caused by sepsis could increase the risk of mortality in septic patients, which seriously affects the septic patient's prognosis of survival. Although there remains a focus on sepsis research, clinical measures to prevent and treat brain injury in sepsis are not yet available, and the high mortality rate is still a big health burden. Therefore, it is necessary to investigate the new molecules or regulated pathways that can effectively inhibit the progress of sepsis.

OBJECTIVE

NLR family pyrin domain-containing 3 (NLRP3) increased in the procession of sepsis and functioned as the key regulator of pyroptosis. Heat shock factor 1 (HSF1) can protect organs from multiorgan dysfunction syndrome induced by lipopolysaccharides in mice, and NLRP3 could be inhibited by HSF1 in many organs. However, whether HSF1 regulated NLRP3 in sepsis-induced brain injury, as well as the detailed mechanism of HSF1 in brain injury, remains unknown in the sepsis model. In this research, we try to explore the relationship between HSF1 and NLRP3 in a sepsis model and try to reveal the mechanism of HSF1 inhibiting the process of brain injury.

METHODS

In this study, we used wild-type mice and hsf1 -/- mice for in vivo research and PC12 cells for in vitro research. Real-time PCR and Western blot were used to analyze the expression of HSF1, NLRP3, cytokines, and pyrolytic proteins. EthD-III staining was chosen to detect the pyroptosis of the hippocampus and PC12 cells.

RESULTS

The results showed that HSF1 is negatively related to pyroptosis. The pyroptosis in cells of brain tissue was significantly increased in the hsf1 -/- mouse model compared to hsf1 +/+ mice. In PC12 cells, hsf1 siRNA can upregulate pyroptosis while HSF1-transfected plasmid could inhibit the pyroptosis. HSF1 could negatively regulate the NLRP3 pathway in PC12 cells, while hsf1 siRNA enhanced the pyroptosis in PC12 cells, which could be reversed by nlrp3 siRNA.

CONCLUSION

These results imply that HSF1 could alleviate sepsis-induced brain injury by inhibiting pyroptosis through the NLRP3-dependent pathway in brain tissue and PC12 cells, suggesting HSF1 as a potential molecular target for treating brain injury in sepsis clinical studies.

Decreased ZO1 expression causes loss of time-dependent tight junction function in the liver of ob/ob mice

Diabetes patients are at a high risk of developing complications related to angiopathy and disruption of the signal transduction system. The liver is one of the multiple organs damaged during diabetes. Few studies have evaluated the morphological effects of adhesion factors in diabetic liver. The influence of diurnal variation has been observed in the expression and functioning of adhesion molecules to maintain tissue homeostasis associated with nutrient uptake. The present study demonstrated that the rhythm-influenced functioning of tight junction was impaired in the liver of ob/ob mice. The tight junctions of hepatocytes were loosened during the dark period in control mice compared to those in ob/ob mice, where the hepatocyte gaps remained open throughout the day. The time-dependent expression of zonula occludens 1 (ZO1, encoded by Tjp1 gene) in the liver plays a vital role in the functioning of the tight junction. The time-dependent expression of ZO1 was nullified and its expression was attenuated in the liver of ob/ob mice. ZO1 expression was inhibited at the mRNA and protein levels. The expression rhythm of ZO1 was found to be regulated by heat shock factor (HSF)1/2, the expression of which was reduced in the liver of ob/ob mice. The DNA-binding ability of HSF1/2 was decreased in the liver of ob/ob mice compared to that in control mice. These findings suggest the involvement of impaired expression and functioning of adhesion factors in diabetic liver complications.

Expression of STING Is Increased in Monocyte-Derived Macrophages and Contributes to Liver Inflammation in Hepatic Ischemia-Reperfusion Injury

Ischemia/reperfusion (I/R) injury, aggravated by innate immune cell-mediated inflammatory response, is a major problem in liver transplantation. Stimulator of interferon gene (STING) is a crucial regulatory signaling molecule in the DNA-sensing pathway, and its activation can produce strong innate immunity. However, the STING-mediated innate immune pathway in hepatic I/R injury has not been fully elucidated. In this study, we first examined the STING expression changes in the liver tissues of mice after hepatic I/R injury by using quantitative polymerase chain reaction and Western blot assays. We then investigated the role of STING in I/R injury by using a murine hepatic I/R model. STING up-regulation in mouse liver tissues in response to I/R injury and STING deficiency in myeloid cells was found to significantly ameliorate I/R-induced liver injury and inflammatory responses. STING inhibitors were also able to ameliorate hepatic I/R injury. Mechanically, STING may have a protective effect on hepatic I/R injury by the inhibition of hypoxia-inducible factor-1 alpha and enhancement of phosphorylated AMP-activated protein kinase to reduce macrophage activation. These findings show the potential regulatory effects of STING in hepatic I/R and suggest a new method for clinical protection of hepatic I/R injury.

Endoplasmic Reticulum Stress in Chronic Obstructive Pulmonary Disease: Mechanisms and Future Perspectives

The endoplasmic reticulum (ER) is an integral organelle for maintaining protein homeostasis. Multiple factors can disrupt protein folding in the lumen of the ER, triggering ER stress and activating the unfolded protein response (UPR), which interrelates with various damage mechanisms, such as inflammation, apoptosis, and autophagy. Numerous studies have linked ER stress and UPR to the progression of chronic obstructive pulmonary disease (COPD). This review focuses on the mechanisms of other cellular processes triggered by UPR and summarizes drug intervention strategies targeting the UPR pathway in COPD to explore new therapeutic approaches and preventive measures for COPD.

XBP1-mediated activation of the STING signalling pathway in macrophages contributes to liver fibrosis progression

Background & Aims

XBP1 modulates the macrophage proinflammatory response, but its function in macrophage stimulator of interferon genes (STING) activation and liver fibrosis is unknown. X-box binding protein 1 (XBP1) has been shown to promote macrophage nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) activation in steatohepatitis. Herein, we aimed to explore the underlying mechanism of XBP1 in the regulation of STING signalling and the subsequent NLRP3 activation during liver fibrosis.

Methods

XBP1 expression was measured in the human fibrotic liver tissue samples. Liver fibrosis was induced in myeloid-specific Xbp1-, STING-, and Nlrp3-deficient mice by carbon tetrachloride injection, bile duct ligation, or a methionine/choline-deficient diet.

Results

Although increased XBP1 expression was observed in the fibrotic liver macrophages of mice and clinical patients, myeloid-specific Xbp1 deficiency or pharmacological inhibition of XBP1 protected the liver against fibrosis. Furthermore, it inhibited macrophage NLPR3 activation in a STING/IRF3-dependent manner. Oxidative mitochondrial injury facilitated cytosolic leakage of macrophage self-mtDNA and cGAS/STING/NLRP3 signalling activation to promote liver fibrosis. Mechanistically, RNA sequencing analysis indicated a decreased mtDNA expression and an increased BCL2/adenovirus E1B interacting protein 3 (BNIP3)-mediated mitophagy activation in Xbp1-deficient macrophages. Chromatin immunoprecipitation (ChIP) assays further suggested that spliced XBP1 bound directly to the Bnip3 promoter and inhibited the transcription of Bnip3 in macrophages. Xbp1 deficiency decreased the mtDNA cytosolic release and STING/NLRP3 activation by promoting BNIP3-mediated mitophagy activation in macrophages, which was abrogated by Bnip3 knockdown. Moreover, macrophage XBP1/STING signalling contributed to the activation of hepatic stellate cells.

Conclusions

Our findings demonstrate that XBP1 controls macrophage cGAS/STING/NLRP3 activation by regulating macrophage self-mtDNA cytosolic leakage via BNIP3-mediated mitophagy modulation, thus providing a novel target against liver fibrosis.

Lay summary

Liver fibrosis is a typical progressive process of chronic liver disease, driven by inflammatory and immune responses, and is characterised by an excess of extracellular matrix in the liver. Currently, there is no effective therapeutic strategy for the treatment of liver fibrosis, resulting in high mortality worldwide. In this study, we found that myeloid-specific Xbp1 deficiency protected the liver against fibrosis in mice, while XBP1 inhibition ameliorated liver fibrosis in mice. This study concluded that targeting XBP1 signalling in macrophages may provide a novel strategy for protecting the liver against fibrosis.

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Macrophage STING signalling can be activated by mtDNA cytosolic leakage from macrophages themselves.

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Xbp1 depletion suppresses cGAS/STING/NLRP3 activation by restoring BNIP3-mediated mitophagy activation in macrophages.

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XBP1 targets and inhibits the transcription of Bnip3 directly in macrophages.

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Myeloid-specific Xbp1 deficiency, or STING deficiency, or Nlrp3 depletion protect livers against fibrosis in mice.

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Pharmacological inhibition of XBP1 ameliorates liver fibrosis in mice.

USP15 regulates p66Shc stability associated with Drp1 activation in liver ischemia/reperfusion

Liver ischemia/reperfusion (I/R) injury is a major clinical concern of liver transplantation, which accounts for organ rejection and liver dysfunction. The adaptor protein p66Shc acts as a crucial redox enzyme and is implicated in liver I/R. Elevated p66Shc expression is associated with hepatocellular apoptosis in liver I/R, but the molecular mechanisms of p66Shc responsible for its aberrant expression and function remain unknown. In the present study, hepatocyte-specific p66Shc-knockdown mice exhibited clear inhibition in hepatocellular apoptosis and oxidative stress under liver I/R, while hepatocyte-specific p66Shc overexpression mice displayed the deteriorative impairment. Mechanistically, p66Shc-triggered mitochondrial fission and apoptosis in liver I/R by mediating ROS-driven Drp1 activation. Furthermore, a screening for p66Shc-interacting proteins identified ubiquitin-specific protease 15 (USP15) as a mediator critical for abnormal p66Shc expression. Specifically, USP15 interacted with the SH2 domain of p66Shc and maintained its stabilization by removing ubiquitin. In vivo, p66Shc knockdown abrogated USP15-driven hepatocellular apoptosis, whereas p66Shc overexpression counteracted the antiapoptotic effect of USP15 silencing in response to liver I/R. There was clinical evidence for the positive association between p66Shc and USP15 in patients undergoing liver transplantation. In summary, p66Shc contributes to mitochondrial fission and apoptosis associated with Drp1 activation, and abnormal p66Shc expression relies on the activity of USP15 deubiquitination under liver I/R. The current study sheds new light on the molecular mechanism of p66Shc, and identifies USP15 as a novel mediator of p66Shc to facilitate better therapeutics against liver I/R.

TREM2/β-catenin attenuates NLRP3 inflammasome-mediated macrophage pyroptosis to promote bacterial clearance of pyogenic bacteria

Triggering receptors expressed on myeloid cells 2 (TREM2) is considered a protective factor to protect host from bacterial infection, while how it elicits this role is unclear. In the present study, we demonstrate that deficiency of triggering receptors expressed on myeloid cells 2 (TREM2) significantly enhanced macrophage pyroptosis induced by four common pyogenic bacteria including Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Escherichia coli. TREM2 deficiency also decreased bacterial killing ratio of macrophage, while Caspase-1 or GSDMD inhibition promoted macrophage-mediated clearance to these bacteria. Further study demonstrated that the effect of TREM2 on macrophage pyroptosis and bacterial eradication mainly dependents on the activated status of NLRP3 inflammasome. Moreover, as the key downstream of TREM2, β-catenin phosphorylated at Ser675 by TREM2 signal and accumulated in nucleus and cytoplasm. β-catenin mediated the effect of TREM2 on NLRP3 inflammasome and macrophage pyroptosis by reducing NLRP3 expression, and inhibiting inflammasome complex assembly by interacting with ASC. Collectively, TREM2/β-catenin inhibits NLRP3 inflammasome to regulate macrophage pyroptosis, and enhances macrophage-mediated pyogenic bacterial clearance.

Ubiquitin ligase E3 HUWE1/MULE targets transferrin receptor for degradation and suppresses ferroptosis in acute liver injury

Hepatic ischemia followed by reperfusion (I/R), a major clinical problem during liver surgical procedures, can induce liver injury with severe cell death including ferroptosis which is characterized by iron-dependent accumulation of lipid peroxidation. The HECT domain-containing ubiquitin E3 ligase HUWE1 (also known as MULE) was initially shown to promote apoptosis. However, our preliminary study demonstrates that high expression of HUWE1 in the liver donors corelates with less injury and better hepatic function after liver transplantation in patients. Thus, we investigate the role of HUWE1 in acute liver injury, and identify HUWE1 as a negative ferroptosis modulator through transferrin receptor 1(TfR1). Deficiency of Huwe1 in mice hepatocytes (HKO) exacerbated I/R and CCl4-induced liver injury with more ferroptosis occurrence. Moreover, Suppression of Huwe1 remarkably enhances cellular sensitivity to ferroptosis in primary hepatocytes and mouse embryonic fibroblasts. Mechanistically, HUWE1 specifically targets TfR1 for ubiquitination and proteasomal degradation, thereby regulates iron metabolism. Importantly, chemical and genetic inhibition of TfR1 dramatically diminishes the ferroptotic cell death in Huwe1 KO cells and Huwe1 HKO mice. Therefore, HUWE1 is a potential protective factor to antagonize both aberrant iron accumulation and ferroptosis thereby mitigating acute liver injury. These findings may provide clinical implications for patients with the high-expression Huwe1 alleles.

Novel role of macrophage TXNIP-mediated CYLD-NRF2-OASL1 axis in stress-induced liver inflammation and cell death

Background & Aims

The stimulator of interferon genes (STING)/TANK-binding kinase 1 (TBK1) pathway is vital in mediating innate immune and inflammatory responses during oxidative/endoplasmic reticulum (ER) stress. However, it remains unknown whether macrophage thioredoxin-interacting protein (TXNIP) may regulate TBK1 function and cell death pathways during oxidative/ER stress.

Methods

A mouse model of hepatic ischaemia/reperfusion injury (IRI), the primary hepatocytes, and bone marrow-derived macrophages were used in the myeloid-specific TXNIP knockout (TXNIPM-KO) and TXNIP-proficient (TXNIPFL/FL) mice.

Results

The TXNIPM-KO mice were resistant to ischaemia/reperfusion (IR) stress-induced liver damage with reduced serum alanine aminotransferase (ALT)/aspartate aminotransferase (AST) levels, macrophage/neutrophil infiltration, and pro-inflammatory mediators compared with the TXNIPFL/FL controls. IR stress increased TXNIP, p-STING, and p-TBK1 expression in ischaemic livers. However, TXNIPM-KO inhibited STING, TBK1, interferon regulatory factor 3 (IRF3), and NF-κB activation with interferon-β (IFN-β) expression. Interestingly, TXNIPM-KO augmented nuclear factor (erythroid-derived 2)-like 2 (NRF2) activity, increased antioxidant gene expression, and reduced macrophage reactive oxygen species (ROS) production and hepatic apoptosis/necroptosis in IR-stressed livers. Mechanistically, macrophage TXNIP deficiency promoted cylindromatosis (CYLD), which colocalised and interacted with NADPH oxidase 4 (NOX4) to enhance NRF2 activity by deubiquitinating NOX4. Disruption of macrophage NRF2 or its target gene 2',5' oligoadenylate synthetase-like 1 (OASL1) enhanced Ras GTPase-activating protein-binding protein 1 (G3BP1) and TBK1-mediated inflammatory response. Notably, macrophage OASL1 deficiency induced hepatocyte apoptotic peptidase activating factor 1 (APAF1), cytochrome c, and caspase-9 activation, leading to increased caspase-3-initiated apoptosis and receptor-interacting serine/threonine-protein kinase 3 (RIPK3)-mediated necroptosis.

Conclusions

Macrophage TXNIP deficiency enhances CYLD activity and activates the NRF2-OASL1 signalling, controlling IR stress-induced liver injury. The target gene OASL1 regulated by NRF2 is crucial for modulating STING-mediated TBK1 activation and Apaf1/cytochrome c/caspase-9-triggered apoptotic/necroptotic cell death pathway. Our findings underscore a novel role of macrophage TXNIP-mediated CYLD-NRF2-OASL1 axis in stress-induced liver inflammation and cell death, implying the potential therapeutic targets in liver inflammatory diseases.

Lay summary

Liver inflammation and injury induced by ischaemia and reperfusion (the absence of blood flow to the liver tissue followed by the resupply of blood) is a significant cause of hepatic dysfunction and failure following liver transplantation, resection, and haemorrhagic shock. Herein, we uncover an underlying mechanism that contributes to liver inflammation and cell death in this setting and could be a therapeutic target in stress-induced liver inflammatory injury.

Role of XBP1 in regulating the progression of non-alcoholic steatohepatitis

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is associated with the dysregulation of lipid metabolism and hepatic inflammation, though the underlying mechanisms remain unclear. We aimed to investigate the role of X-box binding protein-1 (XBP1) in the progression of NASH.

METHODS

Human liver tissues obtained from patients with NASH and controls were used to assess XBP1 expression. NASH models were developed in hepatocyte-specific Xbp1 knockout (Xbp1ΔHep), macrophage-specific Xbp1 knockout (Xbp1ΔMf), macrophage-specific Nlrp3 knockout, and wild-type (Xbp1FL/FL or Nlrp3FL/FL) mice fed with a high-fat diet for 26 weeks or a methionine/choline-deficient diet for 6 weeks.

RESULTS

The expression of XBP1 was significantly upregulated in liver samples from patients with NASH. Hepatocyte-specific Xbp1 deficiency inhibited the development of steatohepatitis in mice fed the high-fat or methionine/choline-deficient diets. Meanwhile, macrophage-specific Xbp1 knockout mice developed less severe steatohepatitis and fibrosis than wild-type Xbp1FL/FL mice in response to the high-fat or methionine/choline-deficient diets. Macrophage-specific Xbp1 knockout mice showed M2 anti-inflammatory polarization. Xbp1-deleted macrophages reduced steatohepatitis by decreasing the expression of NLRP3 and secretion of pro-inflammatory cytokines, which mediate M2 macrophage polarization in macrophage-specific Xbp1 knockout mice. Steatohepatitis was less severe in macrophage-specific Nlrp3 knockout mice than in wild-type Nlrp3FL/FL mice. Xbp1-deleted macrophages prevented hepatic stellate cell activation by decreasing expression of TGF-β1. Less fibrotic changes were observed in macrophage-specific Xbp1 knockout mice than in wild-type Xbp1FL/FL mice. Inhibition of XBP1 suppressed the development of NASH.

CONCLUSION

XBP1 regulates the development of NASH. XBP1 inhibitors protect against steatohepatitis. Thus, XBP1 is a potential target for the treatment of NASH.

LAY SUMMARY

XBP1 is a transcription factor that is upregulated in liver tissues of patients with non-alcoholic steatohepatitis (NASH). Conditional knockout of Xbp1 in hepatocytes resulted in decreased lipid accumulation in mice, while genetic deletion of Xbp1 in macrophages ameliorated nutritional steatohepatitis and fibrosis in mice. Pharmacological inhibition of XBP1 protects against steatohepatitis and fibrosis, highlighting a promising therapeutic strategy for NASH.

Notch-activated mesenchymal stromal/stem cells enhance the protective effect against acetaminophen-induced acute liver injury by activating AMPK/SIRT1 pathway

Background

Notch signaling plays important roles in regulating innate immunity. However, little is known about the role of Notch in mesenchymal stromal/stem cell (MSC)-mediated immunomodulation during liver inflammatory response.

Methods

Notch activation in human umbilical cord-derived MSCs was performed by a tissue culture plate coated with Notch ligand, recombinant human Jagged1 (JAG1). Mice were given intravenous injection of Notch-activated MSCs after acetaminophen (APAP)-induced acute liver injury. Liver tissues were collected and analyzed by histology and immunohistochemistry.

Results

MSC administration reduced APAP-induced hepatocellular damage, as manifested by decreased serum ALT levels, intrahepatic macrophage/neutrophil infiltration, hepatocellular apoptosis and proinflammatory mediators. The anti-inflammatory activity and therapeutic effects of MSCs were greatly enhanced by Notch activation via its ligand JAG1. However, Notch2 disruption in MSCs markedly diminished the protective effect of MSCs against APAP-induced acute liver injury, even in the presence of JAG1 pretreatment. Strikingly, Notch-activated MSCs promoted AMP-activated protein kinase (AMPKα) phosphorylation, increased the sirtuins 1 (SIRT1) deacetylase expression, but downregulated spliced X-box-binding protein 1 (XBP1s) expression and consequently reduced NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation. Furthermore, SIRT1 disruption or XBP1s overexpression in macrophages exacerbated APAP-triggered liver inflammation and augmented NLRP3/caspase-1 activity in MSC-administrated mice. Mechanistic studies further demonstrated that JAG1-pretreated MSCs activated Notch2/COX2/PGE2 signaling, which in turn induced macrophage AMPK/SIRT1 activation, leading to XBP1s deacetylation and inhibition of NLRP3 activity.

Conclusions

Activation of Notch2 is required for the ability of MSCs to reduce the severity of APAP-induced liver damage in mice. Our findings underscore a novel molecular insights into MSCs-mediated immunomodulation by activating Notch2/COX2/AMPK/SIRT1 pathway and thus provide a new strategy for the treatment of liver inflammatory diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02999-6.

The Role of NLRP3 Inflammasome Activation Pathway of Hepatic Macrophages in Liver Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is considered an inherent component involved in liver transplantation, which induce early organ dysfunction and failure. And the accumulating evidences indicate that the activation of host innate immune system, especially hepatic macrophages, play a pivotal role in the progression of LIRI. Inflammasomes is a kind of intracellular multimolecular complexes that actively participate in the innate immune responses and proinflammatory signaling pathways. Among them, NLRP3 inflammasome is the best characterized and correspond to regulate caspase-1 activation and the secretion of proinflammatory cytokines in response to various pathogen-derived as well as danger-associated signals. Additionally, NLRP3 is highly expressed in hepatic macrophages, and the assembly of NLRP3 inflammasome could lead to LIRI, which makes it a promising therapeutic target. However, detailed mechanisms about NLRP3 inflammasome involving in the hepatic macrophages-related LIRI is rarely summarized. Here, we review the potential role of the NLRP3 inflammasome pathway of hepatic macrophages in LIRI, with highlights on currently available therapeutic options.

Macrophage nuclear factor erythroid 2-related factor 2 deficiency promotes innate immune activation by tissue inhibitor of metalloproteinase 3-mediated RhoA/ROCK pathway in the ischemic liver

BACKGROUND AND AIMS

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of reactive oxygen species (ROS) and inflammation and has been implicated in both human and murine inflammatory disease models. We aimed to characterize the roles of macrophage-specific Nrf2 in liver ischemia/reperfusion injury (IRI).

APPROACH AND RESULTS

First, macrophage Nrf2 expression and liver injury in patients undergoing OLT or ischemia-related hepatectomy were analyzed. Subsequently, we created a myeloid-specific Nrf2-knockout (Nrf2M-KO ) strain to study the function and mechanism of macrophage Nrf2 in a murine liver IRI model. In human specimens, macrophage Nrf2 expression was significantly increased in liver tissues after transplantation or hepatectomy. Interestingly, lower Nrf2 expressions correlated with more severe liver injury postoperatively. In a mouse model, we found Nrf2M-KO mice showed worse hepatocellular damage than Nrf2-proficient controls based on serum biochemistry, pathology, ROS, and inflammation. In vitro, Nrf2 deficiency promoted innate immune activation and migration in macrophages on toll-like receptor (TLR) 4 stimulation. Microarray profiling showed Nrf2 deletion caused markedly lower transcriptional levels of tissue inhibitor of metalloproteinase 3 (Timp3). ChIP-seq, PCR, and luciferase reporter assay further demonstrated Nrf2 bound to the promoter region of Timp3. Moreover, a disintegrin and metalloproteinase (ADAM) 10/ROCK1 was specifically increased in Nrf2-deficient macrophages. Increasing Timp3 expression effectively inhibited ADAM10/ROCK1 expression and rescued the Nrf2M-KO -mediated inflammatory response on TLR4 stimulation in vitro. Importantly, Timp3 overexpression, recombinant Timp3 protein, or ROCK1 knockdown rescued Nrf2M-KO -related liver IRI by inhibiting macrophage activation.

CONCLUSIONS

In conclusion, macrophage Nrf2 mediates innate proinflammatory responses, attenuates liver IRI by binding to Timp3, and inhibits the RhoA/ROCK pathway, which provides a therapeutic target for clinical organ IRI.

Endoplasmic Reticulum Stress and the Unfolded Protein Response in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an acute cerebrovascular disease characterized by sudden interruption of blood flow in a certain part of the brain, leading to serious disability and death. At present, treatment methods for ischemic stroke are limited to thrombolysis or thrombus removal, but the treatment window is very narrow. However, recovery of cerebral blood circulation further causes cerebral ischemia/reperfusion injury (CIRI). The endoplasmic reticulum (ER) plays an important role in protein secretion, membrane protein folding, transportation, and maintenance of intracellular calcium homeostasis. Endoplasmic reticulum stress (ERS) plays a crucial role in cerebral ischemia pathophysiology. Mild ERS helps improve cell tolerance and restore cell homeostasis; however, excessive or long-term ERS causes apoptotic pathway activation. Specifically, the protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways are significantly activated following initiation of the unfolded protein response (UPR). CIRI-induced apoptosis leads to nerve cell death, which ultimately aggravates neurological deficits in patients. Therefore, it is necessary and important to comprehensively explore the mechanism of ERS in CIRI to identify methods for preserving brain cells and neuronal function after ischemia.

Icariin attenuates ischemic stroke through suppressing inflammation mediated by endoplasmic reticulum stress signaling pathway in rats

Ischemic stroke possesses the characteristics of high incidence, high disability, and high mortality. Icariin (ICA) is a flavonoid extracted from the traditional Chinese medicine Epimedium. The protective effect of ICA on ischemic stroke is worthy to be further studied. In this study, male Sprague-Dawley rats were randomly divided into the following seven groups: sham, model, ICA low-dose (10 mg/kg), ICA medium-dose (20 mg/kg), ICA high-dose (40 mg/kg), positive control drug (12 mg/kg nimodipine) and endoplasmic reticulum stress induction (0.16 mg/kg tunicamycin) groups. The model of cerebral ischemia-reperfusion injury in the rats, including 2 h ischemia and 24 h reperfusion, was accomplished by applying the method of transient middle cerebral artery occlusion (MCAO). At 24 h reperfusion, neurological deficits, brain water content, pathological damage of brain tissues, the expression of inflammation-related targets, and the signal pathway-related proteins were explored. Compared with the model group, ICA significantly improved neurological deficits, brain edema and pathological damage after MCAO. In addition, ICA increased neuron survival, reduced microglial activation and expression of IL-1β, alleviating the inflammatory damage caused by ischemic stroke. Moreover, ICA suppressed the expressions of glucose-regulated protein 78 (GRP78), inositol requiring enzyme-1 α (IRE1α), phospho-IRE1α (p-IRE1α), protein kinase RNA-like ER kinase (PERK), phospho-PERK (p-PERK), spliced XBP1 (XBP1s), unspliced XBP1 (XBP1u), thioredoxin-interacting protein (TXNIP), NLRP3, and caspase-1. These results suggested that ICA offers neuroprotection against ischemic stroke by inhibiting ER stress-mediated inflammation. This article is protected by copyright. All rights reserved.

Hyperglycemia-triggered ATF6-CHOP pathway aggravates acute inflammatory liver injury by β-catenin signaling

Although hyperglycemia has been documented as an unfavorable element that can further induce liver ischemia–reperfusion injury (IRI), the related molecular mechanisms remain to be clearly elaborated. This study investigated the effective manner of endoplasmic reticulum (ER) stress signaling in hyperglycemia-exacerbated liver IRI. Here we demonstrated that in the liver tissues and Kupffer cells (KCs) of DM patients and STZ-induced hyperglycemic mice, the ER stress-ATF6-CHOP signaling pathway is activated. TLR4-mediated pro-inflammatory activation was greatly attenuated by the addition of 4-phenylbutyrate (PBA), one common ER stress inhibitor. The liver IRI in hyperglycemic mice was also significantly reduced after PBA treatment. In addition, deficiency of CHOP (CHOP^−/−) obviously alleviates the hepatic IRI, and pro-inflammatory effects deteriorated by hyperglycemia. In hyperglycemic mice, β-catenin expression was suppressed while the ATF6-CHOP signal was activated. In the liver tissues of PBA-treated or CHOP^−/− hyperglycemic mice, the expression of β-catenin was restored. Furthermore, CHOP deficiency can induce protection against hyperglycemia-related liver IRI, which was disrupted by the knockdown of β-catenin will cause this protection to disappear. High glucose (HG) treatment stimulated ATF6-CHOP signaling, reduced cellular β-catenin accumulation, and promoted the TLR4-related inflammation of BMDMs. But the above effects were partially rescued in BMDMs with CHOP deficiency or by PBA treatment. In BMDMs cultured in HG conditions, the anti-inflammatory functions of CHOP^−/− were destroyed by the knockdown of β-catenin. Finally, chimeric mice carrying WT or CHOP^−/− BMDMs by bone marrow transplantation were adopted to verify the above conclusion. The current study suggested that hyperglycemia could trigger ER stress-ATF6-CHOP axis, inhibit β-catenin activation, accelerate inflammation, and deteriorate liver IRI, thus providing the treatment potential for management of sterile liver inflammation in DM patients.

Causal Biological Network Model for Inflammasome Signaling Applied for Interpreting Transcriptomic Changes in Various Inflammatory States

Virtually any stressor that alters the cellular homeostatic state may result in an inflammatory response. As a critical component of innate immunity, inflammasomes play a prominent role in the inflammatory response. The information on inflammasome biology is rapidly growing, thus creating the need for structuring it into a model that can help visualize and enhance the understanding of underlying biological processes. Causal biological network (CBN) models provide predictive power for novel disease mechanisms and treatment outcomes. We assembled the available literature information on inflammasome activation into the CBN model and scored it with publicly available transcriptomic datasets that address viral infection of the lungs, osteo- and rheumatoid arthritis, psoriasis, and aging. The scoring inferred pathway activation leading to NLRP3 inflammasome activation in these diverse conditions, demonstrating that the CBN model provides a platform for interpreting transcriptomic data in the context of inflammasome activation.

The gut microbial metabolite, 3,4-dihydroxyphenylpropionic acid, alleviates hepatic ischemia/reperfusion injury via mitigation of macrophage pro-inflammatory activity in mice

Hepatic ischemia/reperfusion injury (HIRI) is a serious complication that occurs following shock and/or liver surgery. Gut microbiota and their metabolites are key upstream modulators of development of liver injury. Herein, we investigated the potential contribution of gut microbes to HIRI. Ischemia/reperfusion surgery was performed to establish a murine model of HIRI. 16S rRNA gene sequencing and metabolomics were used for microbial analysis. Transcriptomics and proteomics analysis were employed to study the host cell responses. Our results establish HIRI was significantly increased when surgery occurred in the evening (ZT12, 20:00) when compared with the morning (ZT0, 08:00); however, antibiotic pretreatment reduced this diurnal variation. The abundance of a microbial metabolite 3,4-dihydroxyphenylpropionic acid was significantly higher in ZT0 when compared with ZT12 in the gut and this compound significantly protected mice against HIRI. Furthermore, 3,4-dihydroxyphenylpropionic acid suppressed the macrophage pro-inflammatory response in vivo and in vitro. This metabolite inhibits histone deacetylase activity by reducing its phosphorylation. Histone deacetylase inhibition suppressed macrophage pro-inflammatory activation and diminished the diurnal variation of HIRI. Our findings revealed a novel protective microbial metabolite against HIRI in mice. The potential underlying mechanism was at least in part, via 3,4-dihydroxyphenylpropionic acid-dependent immune regulation and histone deacetylase (HDAC) inhibition in macrophages.

The ER stress sensor inositol-requiring enzyme 1α in Kupffer cells promotes hepatic ischemia-reperfusion injury

Hepatic ischemia/reperfusion (I/R) injury is an inflammation-mediated process arising from ischemia/reperfusion-elicited stress in multiple cell types, causing liver damage during surgical procedures and often resulting in liver failure. Endoplasmic reticulum (ER) stress triggers the activation of the unfolded protein response (UPR) and is implicated in tissue injuries, including hepatic I/R injury. However, the cellular mechanism that links the UPR signaling to local inflammatory responses during hepatic I/R injury remains largely obscure. Here, we report that IRE1α, a critical ER-resident transmembrane signal transducer of the UPR, plays an important role in promoting Kupffer-cell-mediated liver inflammation and hepatic I/R injury. Utilizing a mouse model in which IRE1α is specifically ablated in myeloid cells, we found that abrogation of IRE1α markedly attenuated necrosis and cell death in the liver, accompanied by reduced neutrophil infiltration and liver inflammation following hepatic I/R injury. Mechanistic investigations in mice as well as in primary Kupffer cells revealed that loss of IRE1α in Kupffer cells not only blunted the activation of the NLRP3 inflammasome and IL-1β production, but also suppressed the expression of the inducible nitric oxide synthase (iNos) and proinflammatory cytokines. Moreover, pharmacological inhibition of IRE1α′s RNase activity was able to attenuate inflammasome activation and iNos expression in Kupffer cells, leading to alleviation of hepatic I/R injury. Collectively, these results demonstrate that Kupffer cell IRE1α mediates local inflammatory damage during hepatic I/R injury. Our findings suggest that IRE1α RNase activity may serve as a promising target for therapeutic treatment of ischemia/reperfusion-associated liver inflammation and dysfunction.

Icariin inhibits the expression of IL-1β, IL-6 and TNF-α induced by OGD/R through the IRE1/XBP1s pathway in microglia

CONTEXT

Icariin (ICA), a flavonol glycoside extracted from Epimedium brevicornum Maxim (Berberidaceae), has been proven to inhibit inflammatory response in ischaemic rats in our laboratory's previous work. However, its underlying mechanism is still unclear.

OBJECTIVE

This study investigates the effects of ICA on endoplasmic reticulum (ER) stress mediated inflammation induced by cerebral ischaemia-reperfusion (I/R) injury in vitro.

MATERIALS AND METHODS

The primary cultured microglia were treated with oxygen-glucose deprivation (OGD) for 2 h followed by a 24 h reoxygenation. ICA (0.37, 0.74 and 1.48 μmol/L) administration was performed 1 h prior OGD and acting through 2 h OGD. The control group was cultured in normal conditions. At 24 h after reoxygenation, the expression of IRE1α, XBP1u, XBP1s, NLRP3 and caspase-1 was detected by western blotting (WB) and quantitative real-time (qRT) PCR; the expression of p-IRE1α was examined by WB; the expression of IL-1β, IL-6 and TNF-α was measured by WB and enzyme-linked immunosorbent assay (ELISA).

RESULTS

ICA (0.37, 0.74 and 1.48 μmol/L) reduced the ratio of p-IRE1α/IRE1α, the mRNA level of IRE1α, the expression of XBP1u, XBP1s, NLRP3, caspase-1 at both the mRNA and protein level expression of IL-1β, IL-6 and TNF-α in OGD/R injured microglia. Overexpression of IRE1 significantly reversed the effects of ICA.

DISCUSSION AND CONCLUSIONS

These results suggested that ICA might decrease the expression of IL-1β, IL-6 and TNF-α by inhibiting IRE1/XBP1s pathway. The anti-inflammatory effect of ICA may provide a potential therapeutic strategy for the treatment of brain injury after stroke.

CMPK2 accelerates liver ischemia/reperfusion injury via the NLRP3 signaling pathway

Cytidine monophosphate kinase 2 (CMPK2) is a mitochondrial nucleotide monophosphate kinase which is important for the substrates of mitochondrial DNA synthesis and has been reported to participate in macrophage activation and the inflammatory response. The purpose of the present research was to determine the potential role of CMPK2 in hepatic ischemia/reperfusion (I/R) injury and to elucidate the underlying molecular mechanisms. The present study investigated the role of CMPK2 in regulating the NLRP3 pathway and liver dysfunction induced by hepatic I/R both in vivo and in vitro. It was revealed that hypoxia/reoxygenation (H/R) treatment enhanced the mRNA expression levels of CMPK2, NLRP3, IL-18, IL-1β and TNF-α in RAW 264.7 cells. The protein expression levels of IL-18, IL-1β and cleaved-caspase-1 were decreased following CMPK2 knockdown. Furthermore, the inhibition of AIM2 downregulated the expression level of IL-1β, IL-18 and cleaved-caspase-1 in the CMPK2 knockdown group followed by H/R treatment, while the inhibition of NLRP3 did not. CMPK2 deficiency also decreased alanine aminotransferase and aspartate aminotransferase expression in mice serum, as well as the pathological changes in the liver. Similarly, the release of IL-18 and IL-1β in mouse serum was also restrained with the decline of CMPK2. In conclusion, the results of the present study demonstrate that CMPK2 is indispensable for NLRP3 inflammasome activation, making CMPK2 an effective target to relieve the liver from I/R injury. In addition, the function of CMPK2 is closely associated with NLRP3 inflammasome activation, instead of AIM2.

Inhibition of microRNA-297 alleviates THLE-2 cell injury induced by hypoxia/reoxygenation by inhibiting NLRP3 inflammasome activation via SIRT3

It has been acknowledged that microRNAs (miRNAs/miRs) assume a critical role in hypoxia/reoxygenation (H/R)-induced hepatocyte injury. Therefore, cell experiments were performed in this study to investigate the mechanism of miR-297 in H/R-induced hepatocyte injury with the involvement of Sirtuin 3 (SIRT3) and NLRP3. Initially, THLE-2 cells were utilized for H/R challenge. After miR-297 antagomir and NLRP3 adenovirus vector delivery, THLE-2 cell proliferation and apoptosis were measured by MTT, EdU and TUNEL assays, respectively. Enzyme-linked immunosorbent assay was conducted to evaluate the levels of apoptosis-related indicators (Bax and Bcl-2) and inflammation-related indicators (IL-6 and IL-10), western blot analysis to detect NLRP3 and Cleaved Caspase-1 expression. The binding relation between miR-297 and SIRT3 was examined using dual-luciferase assay. The results showed that miR-297 antagomir repressed the apoptosis and inflammation induced by H/R treatment in THLE-2 cells. Mechanistically, miR-297 antagomir diminished the extent of IκBα and NF-κB phosphorylation and NLRP3 activation in H/R-induced THLE-2 cells by targeting SIRT3. Furthermore, NLRP3 overexpression normalized the promoting effects of miR-297 antagomir on proliferation and its inhibitory effects on apoptosis and inflammation in H/R-induced THLE-2 cells. In summary, our results elucidated that miR-297 antagomir repressed H/R-induced THLE-2 cell injury via SIRT3 promotion and NLRP3 inactivation.

Integrative Analysis of the Roles of lncRNAs and mRNAs in Itaconate-Mediated Protection Against Liver Ischemia-Reperfusion Injury in Mice

Purpose

Itaconate is well known for its strong anti-inflammatory and antioxidant effect, but little is known about the potential role of long non-coding RNAs (lncRNAs) in the underlying mechanisms of hepatic ischemia-reperfusion (IR) injury. The aim of our study is to identify lncRNAs related to IR injury and itaconate-mediated protection and to demonstrate the mechanism by which itaconate acts in liver IR injury from the new perspective of lncRNAs.

Methods

4-Octyl itaconate (OI), a membrane-permeable derivative of itaconate, was used as a substitute for itaconate in our study. By using a mouse model of hepatic IR injury, serum and liver samples were collected to measure indexes of liver injury. Then, the liver samples of the mice were subjected to RNA sequencing (RNA-seq) and subsequent bioinformatics analysis.

Results

Itaconate attenuated liver IR injury. A total of 138 lncRNAs and 156 messenger RNAs (mRNAs) were markedly differentially expressed in the IR-damaged liver tissues pretreated with OI compared with the matched liver tissues treated with vehicle. Functional analysis indicated that lncRNAs may indirectly participate in the effects of itaconate. Furthermore, 41 mRNAs were examined for the protein-protein interaction (PPI) network analysis, and a key gene cluster was defined. Then, combined the coexpression analysis and the cis and trans regulatory function prediction of lncRNAs, some "candidate" lncRNA-mRNA pairs which might relate to itaconate-mediated liver protection were identified, while the relationship requires future validation.

Conclusion

Our study revealed that itaconate could protect the liver against IR injury and that lncRNAs might play a role in this process. Our study provides a novel way to investigate the mechanism by which itaconate affects hepatic IR injury and exerts its anti-inflammatory and antioxidative stress effects.

HSF1 is involved in suppressing A1 phenotype conversion of astrocytes following spinal cord injury in rats

Background

Two activation states of reactive astrocytes termed A1 and A2 subtypes emerge at the lesion sites following spinal cord injury (SCI). A1 astrocytes are known to be neurotoxic that participate in neuropathogenesis, whereas A2 astrocytes have been assigned the neuroprotective activity. Heat shock transcription factor 1 (HSF1) plays roles in protecting cells from stress-induced apoptosis and in controlling inflammatory activation. It is unknown whether HSF1 is involved in suppressing the conversion of A1 astrocytes following SCI.

Methods

A contusion model of the rat spinal cord was established, and the correlations between HSF1 expression and onset of A1 and A2 astrocytes were assayed by Western blot and immunohistochemistry. 17-AAG, the agonist of HSF1, was employed to treat the primary cultured astrocytes following a challenge by an A1-astrocyte-conditioned medium (ACM) containing 3 ng/ml of IL-1α, 30 ng/ml of TNF-α, and 400 ng/ml of C1q for induction of the A1 subtype. The effects of 17-AAG on the phenotype conversion of astrocytes, as well as underlying signal pathways, were examined by Western blot or immunohistochemistry.

Results

The protein levels of HSF1 were significantly increased at 4 days and 7 days following rat SCI, showing colocalization with astrocytes. Meanwhile, C3-positive A1 astrocytes were observed to accumulate at lesion sites with a peak at 1 day and 4 days. Distinctively, the S100A10-positive A2 subtype reached its peak at 4 days and 7 days. Incubation of the primary astrocytes with ACM markedly induced the conversion of the A1 phenotype, whereas an addition of 17-AAG significantly suppressed such inducible effects without conversion of the A2 subtype. Activation of HSF1 remarkably inhibited the activities of MAPKs and NFκB, which was responsible for the regulation of C3 expression. Administration of 17-AAG at the lesion sites of rats was able to reduce the accumulation of A1 astrocytes.

Conclusion

Collectively, these data reveal a novel mechanism of astrocyte phenotype conversion following SCI, and HSF1 plays key roles in suppressing excessive increase of neurotoxic A1 astrocytes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02271-3.

CD47-Mediated Hedgehog/SMO/GLI1 Signaling Promotes Mesenchymal Stem Cell Immunomodulation in Mouse Liver Inflammation

BACKGROUND AND AIMS

The cluster of differentiation 47 (CD47)-signal regulatory protein alpha (SIRPα) signaling pathway plays important roles in immune homeostasis and tissue inflammatory response. Activation of the Hedgehog/smoothened (SMO)/GLI family zinc finger 1 (Gli1) pathway regulates cell growth, differentiation, and immune function. However, it remains unknown whether and how the CD47-SIRPα interaction may regulate Hedgehog/SMO/Gli1 signaling in mesenchymal stem cell (MSC)-mediated immune regulation during sterile inflammatory liver injury.

APPROACH AND RESULTS

In a mouse model of ischemia/reperfusion (IR)-induced sterile inflammatory liver injury, we found that adoptive transfer of MSCs increased CD47 expression and ameliorated liver IR injury. However, deletion of CD47 in MSCs exacerbated IR-induced liver damage, with increased serum ALT levels, macrophage/neutrophil infiltration, and pro-inflammatory mediators. MSC treatment augmented SIRPα, Hedgehog/SMO/Gli1, and Notch1 intracellular domain (NICD), whereas CD47-deficient MSC treatment reduced these gene expressions in IR-stressed livers. Moreover, disruption of myeloid SMO or Notch1 increased IR-triggered liver inflammation with diminished Gli1 and NICD, but enhanced NIMA related kinase 7 (NEK7) and NLR family pyrin domain containing 3 (NLRP3) activation in MSC-transferred mice. Using a MSC/macrophage co-culture system, we found that MSC CD47 and macrophage SIRPα expression were increased after LPS stimulation. The CD47-SIRPα interaction increased macrophage Gli1 and NICD nuclear translocation, whereby NICD interacted with Gli1 and regulated its target gene Dvl2 (dishevelled segment polarity protein 2), which in turn inhibited NEK7/NLRP3 activity.

CONCLUSIONS

The CD47-SIRPα signaling activates the Hedgehog/SMO/Gli1 pathway, which controls NEK7/NLRP3 activity through a direct interaction between Gli1 and NICD. NICD is a coactivator of Gli1, and the target gene Dvl2 regulated by the NICD-Gli1 complex is crucial for the modulation of NLRP3-driven inflammatory response in MSC-mediated immune regulation. Our findings provide potential therapeutic targets in MSC-mediated immunotherapy of sterile inflammatory liver injury.

The Role of Melatonin on NLRP3 Inflammasome Activation in Diseases

NLRP3 inflammasome is a part of the innate immune system and responsible for the rapid identification and eradication of pathogenic microbes, metabolic stress products, reactive oxygen species, and other exogenous agents. NLRP3 inflammasome is overactivated in several neurodegenerative, cardiac, pulmonary, and metabolic diseases. Therefore, suppression of inflammasome activation is of utmost clinical importance. Melatonin is a ubiquitous hormone mainly produced in the pineal gland with circadian rhythm regulatory, antioxidant, and immunomodulatory functions. Melatonin is a natural product and safer than most chemicals to use for medicinal purposes. Many in vitro and in vivo studies have proved that melatonin alleviates NLRP3 inflammasome activity via various intracellular signaling pathways. In this review, the effect of melatonin on the NLRP3 inflammasome in the context of diseases will be discussed.

Progress in research on the roles of TGR5 receptor in liver diseases

TGR5 (G protein-coupled bile acid receptor 1, GPBAR-1) is a G protein-coupled receptor with seven transmembrane domains and is widely distributed in various organs and tissues. As an important bile acid receptor, TGR5 can be activated by primary and secondary bile acids. Increased expression of TGR5 is a risk factor for polycystic liver disease and hepatobiliary cancer. However, there is evidence that the anti-inflammatory effect of the TGR5 receptor and its regulatory effect on hydrophobic bile acid confer protective effects against most liver diseases. Recent studies have shown that TGR5 receptor activation can alleviate the development of diabetic liver fibrosis, regulate the differentiation of natural killer T cells into NKT10 cells, increase the secretion of anti-inflammatory factors, inhibit the invasion of hepatitis B virus, promote white adipose tissue browning, improve arterial vascular dynamics, maintain tight junctions between bile duct cells, and protect against apoptosis. In portal hypertension, TGR5 receptor activation can inhibit the contraction of hepatic stellate cells and improve intrahepatic microcirculation. In addition, the discovery of the regulatory relationship between the TGR5 receptor and miRNA-26a provides a new direction for further studies of the molecular mechanism underlying the effects of TGR5. In this review, we describe recent findings linking TGR5 to various liver diseases, with a focus on the mechanisms underlying its effects and potential therapeutic implications.

Heat shock preconditioning mesenchymal stem cells attenuate acute lung injury via reducing NLRP3 inflammasome activation in macrophages

OBJECTIVES

Acute lung injury (ALI) remains a common cause of morbidity and mortality worldwide, and to date, there is no effective treatment for ALI. Previous studies have revealed that topical administration of mesenchymal stem cells (MSCs) can attenuate the pathological changes in experimental acute lung injury. Heat shock (HS) pretreatment has been identified as a method to enhance the survival and function of cells. The present study aimed to assess whether HS-pretreated MSCs could enhance immunomodulation and recovery from ALI.

MATERIALS AND METHODS

HS pretreatment was performed at 42 °C for 1 h, and changes in biological characteristics and secretion functions were detected. In an in vivo mouse model of ALI, we intranasally administered pretreated umbilical cord-derived MSCs (UC-MSCs), confirmed their therapeutic effects, and detected the phenotypes of the macrophages in bronchoalveolar lavage fluid (BALF). To elucidate the underlying mechanisms, we cocultured pretreated UC-MSCs with macrophages in vitro, and the expression levels of inflammasome-related proteins in the macrophages were assessed.

RESULTS

The data showed that UC-MSCs did not exhibit significant changes in viability or biological characteristics after HS pretreatment. The administration of HS-pretreated UC-MSCs to the ALI model improved the pathological changes and lung damage-related indexes, reduced the proinflammatory cytokine levels, and modulated the M1/M2 macrophage balance. Mechanistically, both the in vivo and in vitro studies demonstrated that HS pretreatment enhanced the protein level of HSP70 in UC-MSCs, which negatively modulated NLR family pyrin domain containing 3 (NLRP3) inflammasome activation in alveolar macrophages. These effects were partially reversed by knocking down HSP70 expression.

CONCLUSION

HS pretreatment can enhance the beneficial effects of UC-MSCs in inhibiting NLRP3 inflammasome activation in macrophages during ALI. The mechanism may be related to the upregulated expression of HSP70.

The cGAS-STING Pathway: Novel Perspectives in Liver Diseases

Liver diseases represent a major global health burden accounting for approximately 2 million deaths per year worldwide. The liver functions as a primary immune organ that is largely enriched with various innate immune cells, including macrophages, dendritic cells, neutrophils, NK cells, and NKT cells. Activation of these cells orchestrates the innate immune response and initiates liver inflammation in response to the danger signal from pathogens or injured cells and tissues. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a crucial signaling cascade of the innate immune system activated by cytosol DNA. Recognizing DNA as an immune-stimulatory molecule is an evolutionarily preserved mechanism in initiating rapid innate immune responses against microbial pathogens. The cGAS is a cytosolic DNA sensor eliciting robust immunity via the production of cyclic GMP-AMPs that bind and activate STING. Although the cGAS-STING pathway has been previously considered to have essential roles in innate immunity and host defense, recent advances have extended the role of the cGAS-STING pathway to liver diseases. Emerging evidence indicates that overactivation of cGAS-STING may contribute to the development of liver disorders, implying that the cGAS-STING pathway is a promising therapeutic target. Here, we review and discuss the role of the cGAS-STING DNA-sensing signaling pathway in a variety of liver diseases, including viral hepatitis, nonalcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), primary hepatocellular cancer (HCC), and hepatic ischemia-reperfusion injury (IRI), with highlights on currently available therapeutic options.

Liver kinase B1 attenuates liver ischemia/reperfusion injury via inhibiting the NLRP3 inflammasome

Liver ischemia/reperfusion injury (IRI), a serious inflammatory response driven by innate immunity, occurs in liver surgeries such as liver resection and liver transplantation, leading to liver dysfunction, liver failure, and even rejection after transplantation. Liver kinase B1 (LKB1) plays a pivotal anti-inflammatory role in IRI. One of the most important factors involved in liver IRI is the aberrant activation of the nucleotide binding oligomerization domain like receptor (NLR) family, pyrin domain-containing 3 (NLRP3) inflammasome in Kupffer cells. However, the mechanisms underlying the effect of LKB1 on the NLRP3 inflammasome in liver IRI remain elusive. In this study, we found that the expression of LKB1 was decreased in liver IRI, while the NLRP3 inflammasome level was increased as shown, as revealed by RT-qPCR and western blot analysis. Furthermore, upregulation of LKB1 abrogated the expression of the NLRP3 inflammasome, which improved liver function and liver pathology in the liver IRI model in vivo. In vitro, overexpression of LKB1 inhibited the activation of NLRP3 inflammasome and nuclear factor-κB, while the inhibitory effect was reversed by silencing the expression of the forkhead box protein O1 in the RAW264.7 macrophage hypoxia/reoxygenation model. In conclusion, our results suggest that LKB1 exerts a protective effect against liver IRI by downregulating the NLRP3 inflammasome.

Lycopene alleviates hepatic ischemia reperfusion injury via the Nrf2/HO-1 pathway mediated NLRP3 inflammasome inhibition in Kupffer cells

Background

Lycopene is a naturally occurring carotenoid found in many fruits and vegetables, which has antioxidant effects. Although lycopene’s protective effect has been observed on ischemia reperfusion (IR) injury in different organs, the effect of lycopene on Kupffer cells (KCs) has not been clearly elucidated in IR-induced acute hepatic inflammatory injury.

Methods

Mice were administered with either olive oil (10 mL/kg body weight) as the control or lycopene (20 mg/kg body weight) by gavage for 2 weeks before undergoing hepatic IR injury.

Results

In this study, we observed that the levels of aspartate aminotransferases (AST), alanine aminotransferase (ALT), and the percentages of hepatocellular apoptosis in mice pretreated with lycopene were significantly lower than control mice. Lycopene inhibited F4/80+ macrophage and Ly6G+ neutrophil accumulation, which further decreased the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin 6 (IL-6). Interestingly, lycopene induced increased autophagy in KCs, which was evidenced by elevated autophagosomes and the increased protein level of LC3B. In these KCs, lycopene-induced upregulation of autophagy inhibited NOD-like receptor family pyrin domain-containing 3 protein (NLRP3) inflammasome activation, which was demonstrated by the reduced mRNA and protein levels of NLRP3, cleaved caspase-1, an apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and IL-1β. Furthermore, 3-methyladenine, an autophagy inhibitor, abolished lycopene’s inhibitory effect on the NLRP3 inflammasome in KCs, which led to increased hepatic IR injury. Intriguingly, we identified that the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) were elevated in KCs isolated from IR-stressed mice pretreated with lycopene. Nrf2-siRNA or HO-1-siRNA could block the autophagy activation enhanced by lycopene in KCs, resulting in the activation of the NLRP3 inflammasome and aggravated hepatic IR injury.

Conclusions

Our findings demonstrated that lycopene promoted Nrf2/HO-1 pathway activation and further suppressed the NLRP3 inflammasome via enhancing KC autophagy, which alleviated hepatic IR injury.

Chronic intermittent hypoxia-induced mitochondrial dysfunction mediates endothelial injury via the TXNIP/NLRP3/IL-1β signaling pathway

Oxidative stress and inflammation induced by chronic intermittent hypoxia (CIH) are trigger factors of cardiovascular diseases in patients with obstructive sleep apnea (OSA). This study aimed to investigate the role of CIH-induced mitochondrial dysfunction in vascular endothelial injury both in vivo and in vitro. Human umbilical vein endothelial cells and Sprague Dawley rats were exposed to CIH. CIH promoted the production of intracellular reactive oxygen species, caused mitochondrial dysfunction, and induced cell apoptosis in human umbilical vein endothelial cells. RNA-Seq analysis revealed that the NOD-like receptor signaling pathway was involved in endothelial injury induced by CIH. TXNIP/NLRP3/IL-1β pathway was found to be upregulated by CIH. Knock-down of TNXIP rescued the endothelial cells from CIH-induced apoptosis, indicating that activation of the TXNIP/NLRP3/IL-1β pathway mediated the CIH-induced endothelial apoptosis. Administration of the mitochondria-targeted antioxidant mito-TEMPO improved mitochondrial function and suppressed upregulation of the TXNIP/NLRP3/IL-1β pathway, thereby alleviating CIH-induced endothelial apoptosis. In vivo experiments confirmed the results, where mito-TEMPO was found to ameliorate endothelial injury in rat aortas exposed to CIH. The results imply that CIH-induced mitochondrial dysfunction mediates endothelial injury implication of TXNIP/NLRP3/IL-1β signaling pathway.

Deficiency of TGR5 exacerbates immune-mediated cholestatic hepatic injury by stabilizing the β-catenin destruction complex

Intrahepatic cholestasis induced by drug toxicity may cause cholestatic hepatic injury (CHI) leading to liver fibrosis and cirrhosis. The G protein-coupled bile acid receptor 1 (TGR5) is a membrane receptor with well-known roles in the regulation of glucose metabolism and energy homeostasis. However, the role and mechanism of TGR5 in the context of inflammation during CHI remains unclear. Wild-type (WT) and TGR5 knockout (TGR5^−/−) mice with CHI induced by bile duct ligation (BDL) were involved in vivo, and WT and TGR5^−/− bone marrow-derived macrophages (BMDMs) were used in vitro. TGR5 deficiency significantly exacerbated BDL-induced liver injury, inflammatory responses and hepatic fibrosis compared with WT mice in vivo. TGR5^−/− macrophages were more susceptible to lipopolysaccharide (LPS) stimulation than WT macrophages. TGR5 activation by its ligand suppressed LPS-induced pro-inflammatory responses in WT but not TGR5^−/− BMDMs. Notably, expression of β-catenin was effectively inhibited by TGR5 deficiency. Furthermore, TGR5 directly interacted with Gsk3β to repress the interaction between Gsk3β and β-catenin, thus disrupting the β-catenin destruction complex. The pro-inflammatory nature of TGR5-knockout was almost abolished by lentivirus-mediated β-catenin overexpression in BMDMs. BMDM migration in vitro was accelerated under TGR5-deficient conditions or supernatant from LPS-stimulated TGR5^−/− BMDMs. From a therapeutic perspective, TGR5^−/− BMDM administration aggravated BDL-induced CHI, which was effectively rescued by β-catenin overexpression. Our findings reveal that TGR5 plays a crucial role as a novel regulator of immune-mediated CHI by destabilizing the β-catenin destruction complex, with therapeutic implications for the management of human CHI.

Can the hyperthermia-mediated heat shock factor/heat shock protein 70 pathway dampen the cytokine storm during SARS-CoV-2 infection?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major global public health problem. Infection by this virus involves many pathophysiological processes, such as a "cytokine storm," that is, very aggressive inflammatory response that offers new perspectives for the management and treatment of patients. Here, we analyse relevant mechanism involved in the hyperthermia-mediated heat shock factors (HSFs)/heat shock proteins (HSP)70 pathway which may provide a possible treatment tool.