Inositol-Requiring Enzyme 1 Alpha Endoribonuclease Specific Inhibitor STF-083010 Alleviates Carbon Tetrachloride Induced Liver Injury and Liver Fibrosis in Mice

Biomimetic mesenchymal stem cell membrane-coated nanoparticle delivery of MKP5 inhibits hepatic fibrosis through the IRE/XBP1 pathway

Hepatic fibrosis is a common disease with high morbidity and mortality rates. The complex and poorly understood mechanisms underlying hepatic fibrosis represent a significant challenge for the development of more effective therapeutic strategies. MKP5 is a potential regulator of multiple fibrotic diseases. However, its precise role and mechanism of action in hepatic fibrosis remains unclear. This study identified a reduction in MKP5 expression in fibrotic liver tissues of mice treated with CCl4 and observed that MKP5 knockout mice exhibited a more pronounced development of hepatic fibrosis. In addition, RNA-seq data indicated activation of protein processing in the endoplasmic reticulum signalling pathway in fibrotic liver tissues of mice lacking MKP5. Mechanistically, MKP5 inhibits the activation of hepatic stellate cells (HSCs) and hepatocyte apoptosis through the regulation of the IRE/XBP1 pathway. Based on these findings, we developed PLGA-MKP5 nanoparticles coated with a mesenchymal stem cell membrane (MSCM). Our results demonstrated that MSCM-PLGA-MKP5 was most effective in attenuating hepatic inflammation and fibrosis in murine models by modulating the IRE/XBP1 axis. This study contributes to the current understanding of the pathogenesis of hepatic fibrosis, suggesting that the targeted delivery of MKP5 via a nano-delivery system may represent a promising therapeutic approach to treat hepatic fibrosis.

Regulation mechanism of endoplasmic reticulum stress on metabolic enzymes in liver diseases

The endoplasmic reticulum (ER) plays a pivotal role in protein folding and secretion, Ca2+ storage, and lipid synthesis in eukaryotic cells. When the burden of protein synthesis and folding required to be handled exceeds the processing capacity of the ER, the accumulation of misfolded/unfolded proteins triggers ER stress. In response to short-term ER stress, the unfolded protein response (UPR) is activated to allow cells to survive. When ER stress is severe and sustained, it typically provokes cell death through multiple approaches. It is well documented that ER stress and metabolic deregulation are functionally intertwined, both are considered contributing factors to the pathogenesis of liver diseases, including non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), ischemia/reperfusion (I/R) injury, viral hepatitis, liver fibrosis, and hepatocellular carcinoma (HCC). Hepatocytes are rich in smooth and rough ER, which harbor metabolic enzymes that are capable of sensing alterations in various nutritional status and external stimuli. Extensive research has focused on the molecular mechanism linking ER stress with metabolic enzymes. The purpose of this review is to summarize the current knowledge regarding the effects of ER stress on metabolic enzymes in various liver diseases and to provide potential therapeutic strategies for chronic liver diseases via targeting UPR.

STF-083010 an inhibitor of IRE1α endonuclease activity affects mitochondrial respiration and generation of mitochondrial membrane potential

STF-083010 is an inhibitor of endonuclease activity of inositol requiring-enzyme 1α (IRE1α) that is involved in activation of IRE1α-XBP1 axis of the unfolded protein response after ER stress. STF-083010 was tested as a possible antitumor agent in some previous studies exhibiting the ability either to induce death of tumour cells or to increase sensitivity of tumours cells to other neoplastic agents. STF-083010 exhibits also hepatoprotective effects in different models of liver injury and hepatic steatohepatitis. We have shown that STF-083010 has significant impact on mitochondrial functions that is not dependent on the way of STF-083010 application. We have observed that STF-083010 decrease of both maximal respiration (representing maximal electron transfer capacity of mitochondrial respiratory chain) and spare respiratory capacity after either incubation of the SH-SY5Y cells with STF-083010 or direct addition of STF-083010 to the respiration medium. In addition, we have documented impact of STF-083010 on generation of mitochondrial membrane potential (ΔΨm) that could be a result of decreased mitochondrial substrate level phosphorylation. Finally, increased sensitivity of ΔΨm to uncoupler in the presence of STF-083010 was documented. Our results indicate that STF-083010 has important impact on mitochondrial functions independently of its ability to inhibit endonuclease activity of IRE1α that is involved in activation of IRE1α-XBP1 axis of the unfolded protein response after ER stress. The impact of STF-083010 on mitochondrial functions could be associated with its possible off-target effect.

Unfolded protein response is involved in resistance to Neospora caninum infection via IRE1α-XBP1s-NOD2 Axis

Neospora caninum, an intracellular protozoan parasite, causes neosporosis resulting in major losses in the livestock industry worldwide. However, no effective drugs or vaccines have been developed to control neosporosis. An in-depth study on the immune response against N. caninum could help to search for effective approaches to prevent and treat neosporosis. The host unfolded protein response (UPR) functions as a double-edged sword in several protozoan parasite infections, either to initiate immune responses or to help parasite survival. In this study, the roles of the UPR in N. caninum infection in vitro and in vivo were explored, and the mechanism of the UPR in resistance to N. caninum infection was analyzed. The results revealed that N. caninum triggered the UPR in mouse macrophages, such as the activation of the IRE1 and PERK branches, but not the ATF6 branch. Inhibition of the IRE1α-XBP1s branch increased the N. caninum number both in vitro and in vivo, while inhibition of the PERK branch did not affect the parasite number. Furthermore, inhibition of the IRE1α-XBP1s branch reduced the production of cytokines by inhibiting NOD2 signalling and its downstream NF-κB and MAPK pathways. Taken together, the results of this study suggest that the UPR is involved in the resistance of N. caninum infection via the IRE1α-XBP1s branch by regulating NOD2 and its downstream NF-κB and MAPK pathways to induce the production of inflammatory cytokines, which provides a new perspective for the research and development of anti-N. caninum drugs.

Cellular battle against endoplasmic reticulum stress and its adverse effect on health

The endoplasmic reticulum (ER) is a dynamic organelle and a reliable performer for precisely folded proteins. To maintain its function and integrity, arrays of sensory and quality control systems enhance protein folding fidelity and resolve the highest error-prone areas. Yet numerous internal and external factors disrupt its homeostasis and trigger ER stress responses. Cells try to reduce the number of misfolded proteins via the UPR mechanism, and ER-related garbage disposals systems like ER-associated degradation (ERAD), ER-lysosome-associated degradation (ERLAD), ER-Associated RNA Silencing (ERAS), extracellular chaperoning, and autophagy systems, which activates and increase the cell survival rate by degrading misfolded proteins, prevent the aggregated proteins and remove the dysfunctional organelles. Throughout life, organisms must confront environmental stress to survive and develop. Communication between the ER & other organelles, signaling events mediated by calcium, reactive oxygen species, and inflammation are linked to diverse stress signaling pathways and regulate cell survival or cell death mechanisms. Unresolved cellular damages can cross the threshold limit of their survival, resulting in cell death or driving for various diseases. The multifaceted ability of unfolded protein response facilitates the therapeutic target and a biomarker for various diseases, helping with early diagnosis and detecting the severity of diseases.

Genetic and pharmacological inhibition of XBP1 protects against APAP hepatotoxicity through the activation of autophagy

Acetaminophen (APAP) hepatotoxicity induces endoplasmic reticulum (ER) stress which triggers the unfolded protein response (UPR) in hepatocytes. However, the mechanisms underlying ER stress remain poorly understood, thus reducing the options for exploring new pharmacological therapies for patients with hyperacute liver injury. Eight-to-twelve-week-old C57BL/6J Xbp1-floxed (Xbp1f/f) and hepatocyte-specific knockout Xbp1 mice (Xbp1∆hepa) were challenged with either high dose APAP [500 mg/kg] and sacrificed at early (1-2 h) and late (24 h) stages of hepatotoxicity. Histopathological examination of livers, immunofluorescence and immunohistochemistry, Western blot, real time (RT)-qPCR studies and transmission electron microscopy (TEM) were performed. Pharmacological inhibition of XBP1 using pre-treatment with STF-083010 [STF, 75 mg/kg] and autophagy induction with Rapamycin [RAPA, 8 mg/kg] or blockade with Chloroquine [CQ, 60 mg/kg] was also undertaken in vivo. Cytoplasmic expression of XBP1 coincided with severity of human and murine hyperacute liver injury. Transcriptional and translational activation of the UPR and sustained activation of JNK1/2 were major events in APAP hepatotoxicity, both in a human hepatocytic cell line and in a preclinical model. Xbp1∆hepa livers showed decreased UPR and JNK1/2 activation but enhanced autophagy in response to high dose APAP. Additionally, blockade of XBP1 splicing by STF, mitigated APAP-induced liver injury and without non-specific off-target effects (e.g., CYP2E1 activity). Furthermore, enhanced autophagy might be responsible for modulating CYP2E1 activity in Xbp1∆hepa animals. Genetic and pharmacological inhibition of Xbp1 specifically in hepatocytes ameliorated APAP-induced liver injury by enhancing autophagy and decreasing CYP2E1 expression. These findings provide the basis for the therapeutic restoration of ER stress and/or induction of autophagy in patients with hyperacute liver injury.

Autophagic Organelles in DNA Damage Response

Autophagy is an important subcellular event engaged in the maintenance of cellular homeostasis via the degradation of cargo proteins and malfunctioning organelles. In response to cellular stresses, like nutrient deprivation, infection, and DNA damaging agents, autophagy is activated to reduce the damage and restore cellular homeostasis. One of the responses to cellular stresses is the DNA damage response (DDR), the intracellular pathway that senses and repairs damaged DNA. Proper regulation of these pathways is crucial for preventing diseases. The involvement of autophagy in the repair and elimination of DNA aberrations is essential for cell survival and recovery to normal conditions, highlighting the importance of autophagy in the resolution of cell fate. In this review, we summarized the latest information about autophagic recycling of mitochondria, endoplasmic reticulum (ER), and ribosomes (called mitophagy, ER-phagy, and ribophagy, respectively) in response to DNA damage. In addition, we have described the key events necessary for a comprehensive understanding of autophagy signaling networks. Finally, we have highlighted the importance of the autophagy activated by DDR and appropriate regulation of autophagic organelles, suggesting insights for future studies. Especially, DDR from DNA damaging agents including ionizing radiation (IR) or anti-cancer drugs, induces damage to subcellular organelles and autophagy is the key mechanism for removing impaired organelles.

Targeting unfolded protein response: a new horizon for disease control

Unfolded protein response (UPR) is an evolutionarily conserved pathway triggered during perturbation of endoplasmic reticulum (ER) homeostasis in response to the accumulation of unfolded/misfolded proteins under various stress conditions like viral infection, diseased states etc. It is an adaptive signalling cascade with the main purpose of relieving the stress from the ER, which may otherwise lead to the initiation of cell death via apoptosis. ER stress if prolonged, contribute to the aetiology of various diseases like cancer, type II diabetes, neurodegenerative diseases, viral infections etc. Understanding the role of UPR in disease progression will help design pharmacological drugs targeting the sensors of signalling cascade acting as potential therapeutic agents against various diseases. The current review aims at highlighting the relevance of different pathways of UPR in disease progression and control, including the available pharmaceutical interventions responsible for ameliorating diseased state via modulating UPR pathways.

Chemokine CXCL14 acts as a potential genetic target for liver fibrosis

There are multiple causes of liver fibrosis, common ones include ethanol, toxins, and cholestasis. However, whether these different etiologies lead to the same pathological outcomes contain common genetic targets or signaling pathways, the current research has not attracted widespread attention. GSE40041 and GSE55747 were downloaded from the Gene Expression Omnibus (GEO) database. GSE40041 and GSE55747 represent the differential expression profiles in the liver of mice with bile duct ligation (BDL) and carbon tetrachloride (CCl4) induced liver fibrosis models, respectively. By using GEO2R, 701 differential expression genes (DEGs) in GSE40041 and 6540 DEGs in GSE55747 were identified. 260 co-DEGs were shared and extracted for gene ontology (GO) analysis. Through GO analysis, it was found that the regulation of cell migration in biological processes (BPs) was closely related to the pathogenesis of liver fibrosis, and the genes involved in this process include a key gene, chemokine (C-X-C motif) ligand 14 (CXCL14). Subsequently, further bioinformatic analysis showed that CXCL14 may be regulated by miR-122 to participate in the progression of liver fibrosis. Then real-time PCR and western blotting were performed to validate the expression of CXCL14 in liver tissue after liver fibrosis caused by different etiologies (ethanol, CCl4). The expression of CXCL4 in liver fibrosis induced by BDL was verified in another GEO dataset. Basically consistent with our bioinformatics results, our experimental results showed that the expression of CXCL14 was most significantly increased in alcoholic liver fibrosis model, followed by CCl4-induced liver fibrosis, which was also significantly increased in the BDL-induced model. Thus, CXCL14 can act as a common potential genetic target for different liver fibrosis diseases.

Endoplasmic reticulum stress and protein degradation in chronic liver disease

Endoplasmic reticulum (ER) stress is easily observed in chronic liver disease, which often causes accumulation of unfolded or misfolded proteins in the ER, leading to unfolded protein response (UPR). Regulating protein degradation is an integral part of UPR to relieve ER stress. The major protein degradation system includes the ubiquitin-proteasome system (UPS) and autophagy. All three arms of UPR triggered in response to ER stress can regulate UPS and autophagy. Accumulated misfolded proteins could activate these arms, and then generate various transcription factors to regulate the expression of UPS-related and autophagy-related genes. The protein degradation process regulated by UPR has great significance in many chronic liver diseases, including non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), viral hepatitis, liver fibrosis, and hepatocellular carcinoma(HCC). In most instances, the degradation of excessive proteins protects cells with ER stress survival from apoptosis. According to the specific functions of protein degradation in chronic liver disease, choosing to promote or inhibit this process is promising as a potential method for treating chronic liver disease.

Inhibition of Endoplasmic Reticulum Stress Attenuated Ethanol-Induced Exosomal miR-122 and Acute Liver Injury in Mice

AIMS

In acute alcoholic liver injury, alcohol can directly or indirectly induce endoplasmic reticulum stress (ERS) to participate in liver injury, and it is found that the expression of serum exosomal miR-122 is significantly affected. Therefore, the present study investigated the effects of endoplasmic reticulum stress inhibition on the expression of serum exosomal miR-122 and acute liver injury.

METHODS

The acute alcoholic liver injury models were established by the intragastric administration of ethanol (5 g/kg) in ICR mice. Intervention group received 4-phenylbutyric acid (PBA, endoplasmic reticulum stress inhibitor; 75 mg/kg and 150 mg/kg, intraperitoneal) 12 and 24 hours before intragastric administration. Mice treated with saline were used as controls.

RESULTS

The ethanol treated mice exhibited significantly elevated hepatosomatic index (liver weight/body weight) and alanine aminotransferase (ALT), compared with those in the control group (P < 0.05). The ERS inhibitor 4-phenylbutyric acid protected against ethanol induced acute liver injury and hepatocyte necrosis, and PBA 150 mg/kg significantly attenuated ethanol induced hepatic ER stress-related proteins (GRP78, pIRE1α and pIF2α) (P < 0.05). Moreover, PBA 150 mg/kg markedly alleviated ethanol induced elevation of hepatic and serum exosomal miR-122 and pri-miR-122 (P < 0.05).

CONCLUSIONS

These findings suggest that ER stress inhibitor PBA attenuated ethanol induced acute liver injury and serum exosomal miR-122, and provides a potential therapy strategy for acute alcoholic liver injury.

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

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

Inositol-requiring enzyme 1 alpha endoribonuclease specific inhibitor STF-083010 protects the liver from thioacetamide-induced oxidative stress, inflammation and injury by triggering hepatocyte autophagy

Acute liver injury caused by toxins or drugs is a common condition that threatens patients' lives. Inositol-requiring enzyme 1 alpha (IRE1α), the most conserved endoplasmic reticulum (ER) stress sensor, has been implicated in the pathophysiology of liver injury. Activated IRE1α endoribonuclease (RNase) can splice X-box binding protein 1 (XBP1) mRNA to produce the sXBP1 transcription factor. STF-083010, a specific inhibitor of IRE1α RNase, has recently been suggested to exhibit anti-oxidant and anti-inflammatory properties in multiple injury models. However, it remains unknown whether STF-083010 has a protective effect against thioacetamide (TAA)-induced acute liver injury. Here, we demonstrated that IRE1α-sXBP1 signaling is involved in the development of TAA-induced acute liver injury and correlates with the severity of liver damage. STF-083010 protected against TAA-induced liver injury, as evidenced by higher survival rates in response to a lethal dose of TAA and less severe liver injury in response to a toxic dose of TAA. Mechanistic exploration showed that STF-083010 triggered hepatocyte autophagy in response to TAA stimulation both in vivo and in vitro, leading to reduced reactive oxygen species (ROS) production and attenuated hepatic inflammation. We also found that Beclin-1 played a critical role in STF-083010-mediated autophagy in response to TAA stimulation. Autophagy inhibition by chloroquine (CQ) in vivo and Beclin-1 knockdown in vitro markedly abrogated the protective role of STF-083010 against TAA-induced oxidative stress, inflammation and hepatotoxicity. Our results suggested STF-083010 as a potential therapeutic application to prevent TAA-induced acute liver injury.