Molecular mechanism of ATF6 in unfolded protein response and its role in disease

Irisin: muscle's novel player in endoplasmic reticulum stress and disease

Irisin, an exercise-induced myokine, exhibits elevated levels during physical activity, yet its role in modulating the unfolded protein response (UPR) remains poorly understood. This comprehensive review pioneers an in-depth examination of irisin-mediated endoplasmic reticulum (ER) stress mitigation across various diseases. We provide a nuanced characterization of irisin's molecular profile, biological activity, and significance as a skeletal muscle-derived cytokine analogue. Our discussion elucidates the complex interplay between exercise, irisin signalling, and metabolic outcomes, highlighting key molecular interactions driving salutary effects. Moreover, we delineate the UPR's role as a critical ER stress countermeasure and underscore irisin's pivotal function in alleviating this stress, revealing potential therapeutic avenues for disease management. Exercise-induced release of irisin ameliorates ER stress through AMPK phosphorylation during various diseases (Icon image source: www.flaticon.com ).

Targeting Endoplasmic Reticulum Stress by Natural and Chemical Compounds Ameliorates Cisplatin-Induced Nephrotoxicity: A Review

Cisplatin is a chemotherapeutic that dose-dependently causes renal complications such as decreased kidney function and acute kidney injury. The endoplasmic reticulum (ER) is responsible for calcium homeostasis and protein folding and plays a major part in cisplatin's nephrotoxicity. The current article reviews how chemical and natural compounds modulate cisplatin-induced apoptosis, autophagy, and inflammation by inhibiting ER stress signaling pathways. The available evidence indicates that natural compounds (Achyranthes aspera water-soluble extract, morin hydrate, fucoidan, isoliquiritigenin, leonurine, epigallocatechin-3-gallate, grape seed proanthocyanidin, and ginseng polysaccharide) and chemicals (Sal003, NSC228155, TUG891, dorsomorphin (compound C), HC-030031, dexmedetomidine, and recombinant human erythropoietin (rHuEpo)) can alleviate cisplatin nephrotoxicity by suppression of ER stress signaling pathways including IRE1α/ASK1/JNK, PERK-eIF2α-ATF4, and ATF6, as well as PI3K/AKT signaling pathway. Since ER and related signaling pathways are important in cisplatin nephrotoxicity, agents that can inhibit the abovementioned signaling pathways may hold promise in alleviating this untoward adverse effect.

Embelin improves alcoholic steatohepatitis in alcohol-associated liver disease via ATF6-mediated P2X7r-NLRP3 signaling pathway

BACKGROUND

Alcohol-associated liver disease (ALD) manifests with impaired lipid metabolism and inflammation within the liver. Embelin (EB), a natural para-benzoquinone compound derived from the Embelia ribes Burm.f. has several pharmacological properties.

OBJECTIVE

This research examines how EB influences the inflammatory milieu of the liver in ALD.

METHODS

In vivo, we created an ALD model by subjecting mice to the Lieber-DeCarli diet for ten days, supplemented by a solitary binge, and subsequent ATF6 silencing. We employed RNA sequencing to analyze the ALD-related signaling pathways. In vitro experiments involved treating AML12 with EB and ethanol, and administering a siRNA-ATF6 to HepG2 cells. We investigated the ATF6 and P2 × 7r promoter interaction through a dual-luciferase assay. Mouse bone marrow-derived macrophages (BMDMs) were also treated with lipopolysaccharide/adenosine triphosphate (LPS/ATP) and EB to produce a conditioned medium.

RESULTS

EB effectively mitigated lipid synthesis and the formation of neutrophil extracellular traps (NETs) during ALD. RNA sequencing revealed significant alterations in the ATF6/NOD-like receptor pathway in alcohol-induced mice. EB up-regulated ATF6 while down-regulating P2 × 7r-NLRP3 and its target genes. shRNA-mediated ATF6 knockdown markedly increased P2 × 7r protein and mRNA levels in mouse livers and exacerbated lipid accumulation. The absence of ATF6 in hepatocytes impaired the inhibitory effect of EB on the P2 × 7r-NLRP3 pathway. It was demonstrated that ATF6 directly binds to the P2 × 7r promoter. Moreover, EB reduced pyroptosis in BMDMs, thereby diminishing the inflammatory response.

CONCLUSIONS

These findings suggest that EB ameliorates alcoholic steatohepatitis (ASH) by modulating the ATF6-P2 × 7r/NLRP3 signaling pathway in ALD. EB might be a prospective therapeutic candidate, and its mechanism would be a new direction or strategy for alcoholic liver disease.

Molecular mechanisms of pyroptosis in non-alcoholic steatohepatitis and feasible diagnosis and treatment strategies

Pyroptosis is a distinct form of cell death that plays a critical role in intensifying inflammatory responses. It primarily occurs via the classical pathway, non-classical pathway, caspase-3/6/7/8/9-mediated pathways, and granzyme-mediated pathways. Key effector proteins involved in the pyroptosis process include gasdermin family proteins and pannexin-1 protein. Pyroptosis is intricately linked to the onset and progression of non-alcoholic steatohepatitis (NASH). During the development of NASH, factors such as pyroptosis, innate immunity, lipotoxicity, endoplasmic reticulum stress, and gut microbiota imbalance interact and interweave, collectively driving disease progression. This review analyzes the molecular mechanisms of pyroptosis and its role in the pathogenesis of NASH. Furthermore, it explores potential diagnostic and therapeutic strategies targeting pyroptosis, offering new avenues for improving the diagnosis and treatment of NASH.

Parkinson's Disease: The Neurodegenerative Enigma Under the "Undercurrent" of Endoplasmic Reticulum Stress

Parkinson's disease (PD), a prevalent neurodegenerative disorder, demonstrates the critical involvement of endoplasmic reticulum stress (ERS) in its pathogenesis. This review comprehensively examines the role and molecular mechanisms of ERS in PD. ERS represents a cellular stress response triggered by imbalances in endoplasmic reticulum (ER) homeostasis, induced by factors such as hypoxia and misfolded protein aggregation, which activate the unfolded protein response (UPR) through the inositol-requiring enzyme 1 (IRE1), protein kinase R-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6) pathways. Clinical, animal model, and cellular studies have consistently demonstrated a strong association between PD and ERS. Abnormal expression of ERS-related molecules in PD patients' brains and cerebrospinal fluid (CSF) correlates with disease progression. In animal models (e.g., Drosophila and mice), ERS inhibition alleviates dopaminergic neuronal damage. Cellular experiments reveal that PD-mimicking pathological conditions induce ERS, while interactions between ERS and mitochondrial dysfunction promote neuronal apoptosis. Mechanistically, (1) pathological aggregation of α-synuclein (α-syn) and ERS mutually reinforce dopaminergic neuron damage; (2) leucine-rich repeat kinase 2 (LRRK2) gene mutations induce ERS through thrombospondin-1 (THBS1)/transforming growth factor beta 1 (TGF-β1) interactions; (3) molecules such as Parkin and PTEN-induced kinase 1 (PINK1) regulate ERS in PD. Furthermore, ERS interacts with mitochondrial dysfunction, oxidative stress, and neuroinflammation to exacerbate neuronal injury. Emerging therapeutic strategies show significant potential, including artificial intelligence (AI)-assisted drug design targeting ERS pathways and precision medicine approaches exploring non-pharmacological interventions such as personalized electroacupuncture. Future research should focus on elucidating ERS-related mechanisms and identifying novel therapeutic targets to develop more effective treatments for PD patients, ultimately improving their quality of life.

ETS1 promotes cisplatin resistance of NSCLC cells by promoting GRP78 transcription

Non-small cell lung cancer (NSCLC) is a common malignant tumor characterized by rapid growth and invasive power. Glucose regulatory protein 78 (GRP78) is important in cancer cell progression. Here, this study aimed to explore the effect and mechanism of GRP78 on cisplatin (DDP) resistance of NSCLC cells. qRT-PCR and Western blot detected the expression of genes and proteins. Flow cytometry was used to analyze endoplasmic reticulum stress (ERS) induced by DDP in NSCLC. Cell proliferation and apoptosis were examined using cell counting kit-8 (CCK8), cell cloning, and flow cytometry, respectively. Chromatin immunoprecipitation assay (CHIP) and dual-luciferase reporter assays were performed to determine the binding of ETS1 and GRP78 promoter. Mouse xenograft models were constructed for in vivo analysis. ERS was induced by DDP in NSCLC cells. GRP78 were upregulated in DDP-resistant NSCLC tissues, and knockdown of GRP78 suppressed DDP resistance, clone formation, promoted apoptosis, and inhibited ERS in DDP-resistant NSCLC cells. ETS1 knockdown repressed GRP78 expression and NSCLC tumor growth. Interestingly, ETS1 played a role in DDP-resistant NSCLC via GRP78. ETS1 inhibits cisplatin sensitivity of NSCLC cells by promoting GRP78 transcription.

Fisetin may protect early porcine embryos from oxidative stress by down-regulating GRP78 levels

Fisetin is a natural flavonol with a variety of biological activities, including anti-inflammatory and antitumor activities. However, the effect of fisetin on mammalian oocyte and embryo development is unknown, so in this study, we used porcine oocytes as an experimental model, and added optimal concentrations of fisetin to the in vitro culture medium after parthenogenetic activated to investigate the effect of fisetin on porcine embryo development. It was found that 0.1 µM fisetin significantly increased the cleavage rate and blastocyst formation rate, and the quality of blastocysts was also improved. Staining results showed that the levels of reactive oxygen species (ROS), autophagy, endoplasmic reticulum stress and apoptosis were significantly reduced, while glutathione levels and mitochondrial function were significantly increased in the 0.1 µM fisetin-treated group of early porcine embryos compared with the control group. Meanwhile, fisetin decreased the expression level of the endoplasmic reticulum stress marker protein GRP78 (0.71 ± 0.19). In addition, fisetin decreased the expression of genes related to pro-apoptosis, autophagy and endoplasmic reticulum stress and increased the expression of genes related to antioxidant, pluripotency and mitochondrial. According to our results, fisetin promotes early embryonic development in porcine, and this effect may be realized by down-regulating the expression level of GRP78.

Indole-3-acetic acid and chenodeoxycholic acid attenuate TLR4/NF-κB signaling and endoplasmic reticulum stress in valproic acid-induced neurotoxicity

Valproic acid (VA) is a commonly prescribed medication for epilepsy and other neurological conditions. Although effective, VA use can lead to neurotoxicity, especially with chronic use. This study aimed to investigate the potential neuroprotective properties of indole-3-acetic acid (IAA) and chenodeoxycholic acid (CDCA) in an animal model of VA-induced brain injury. Rats received intraperitoneal injections of VA at a dose of 500 mg/kg/day for 3 weeks. Concurrently, they were orally treated with IAA (40 mg/kg/day) and/or CDCA (90 mg/kg/day). The results showed significantly increased oxidative stress and inflammation markers in the VA-exposed group indicated by the reduced levels of glutathione (GSH, P < 0.0001) and superoxide dismutase (SOD, P < 0.01) and the elevated inflammatory cytokines Interleukin-6 (IL-6, P < 0.0001) and tumor necrosis factor-alpha (TNFα, P < 0.01). VA also induced nuclear factor kappa B (NF-κB, P < 0.01), toll-like receptor 4 (TLR4, P < 0.05), and endoplasmic reticulum (ER) stress markers, as evidenced by increased immunoreactivity of GRP78 (glucose-regulated protein 78, P < 0.0001), transcription factor 6 (ATF-6, P < 0.05) and CHOP (C/EBP homologous protein, P < 0.0001). Treatment with IAA or CDCA attenuated VA-induced neurotoxicity, to a variable extent, by improving oxidative, inflammatory, and ER stress markers. This study demonstrates that IAA and CDCA exert protective effects against VA-induced neurotoxicity by mitigating oxidative stress, inflammation, and ER stress. Further investigations are recommended to validate these findings in other neurotoxicity models.

Corticosterone effects induced by stress and immunity and inflammation: mechanisms of communication

The body instinctively responds to external stimuli by increasing energy metabolism and initiating immune responses upon receiving stress signals. Corticosterone (CORT), a glucocorticoid (GC) that regulates secretion along the hypothalamic-pituitary-adrenal (HPA) axis, mediates neurotransmission and humoral regulation. Due to the widespread expression of glucocorticoid receptors (GR), the effects of CORT are almost ubiquitous in various tissue cells. Therefore, on the one hand, CORT is a molecular signal that activates the body's immune system during stress and on the other hand, due to the chemical properties of GCs, the anti-inflammatory properties of CORT act as stabilizers to control the body's response to stress. Inflammation is a manifestation of immune activation. CORT plays dual roles in this process by both promoting inflammation and exerting anti-inflammatory effects in immune regulation. As a stress hormone, CORT levels fluctuate with the degree and duration of stress, determining its effects and the immune changes it induces. The immune system is essential for the body to resist diseases and maintain homeostasis, with immune imbalance being a key factor in the development of various diseases. Therefore, understanding the role of CORT and its mechanisms of action on immunity is crucial. This review addresses this important issue and summarizes the interactions between CORT and the immune system.

PERK-Olating Through Cancer: A Brew of Cellular Decisions

The type I protein kinase PERK is an endoplasmic reticulum (ER) transmembrane protein that plays a multifaceted role in cancer development and progression, influencing tumor growth, metastasis, and cellular stress responses. The activation of PERK represents one of the three signaling pathways induced during the unfolded protein response (UPR), which is triggered, in particular, in tumor cells that constitutively experience various intracellular and extracellular stresses that impair protein folding within the ER. PERK activation can lead to both pro-survival and proapoptotic outcomes, depending on the cellular context and the extent of ER stress. It helps the reprogramming of the gene expression in cancer cells, thereby ensuring survival in the face of oncogenic stress, such as replicative stress and DNA damage, and also microenvironmental challenges, including hypoxia, angiogenesis, and metastasis. Consequently, PERK contributes to tumor initiation, transformation, adaptation to the microenvironment, and chemoresistance. However, sustained PERK activation in cells can also impair cell proliferation and promote apoptotic death by various interconnected processes, including mitochondrial dysfunction, translational inhibition, the accumulation of various cellular stresses, and the specific induction of multifunctional proapoptotic factors, such as CHOP. The dual role of PERK in promoting both tumor progression and suppression makes it a complex target for therapeutic interventions. A comprehensive understanding of the intricacies of PERK pathway activation and their impact is essential for the development of effective therapeutic strategies, particularly in diseases like cancer, where the ER stress response is deregulated in most, if not all, of the solid and liquid tumors. This article provides an overview of the knowledge acquired from the study of animal models of cancer and tumor cell lines cultured in vitro on PERK's intracellular functions and their impact on cancer cells and their microenvironment, thus highlighting potential new therapeutic avenues that could target this protein.

A deafness-blindness syndrome results from ATF6-based disruption of the unfolded protein response

Sensorineural hearing loss (SNHL) is the most prevalent form of permanent hearing impairment, arising from factors such as aging, exposure to loud noise, disease, ototoxic medications, and genetic mutations. Despite extensive research, effective treatments or cures for SNHL remain elusive. In this issue of the JCI, Lee et al. reveal a link between mutations in ATF6 and SNHL in patients with achromatopsia. The study also shows that Atf6-deficient (Atf6-/-) mice exhibit disorganized stereocilia and age-related loss of outer hair cells. Additionally, the researchers show that Atf6 is critical for cochlear hair cell function. Mice lacking Atf6 expression experienced ER stress, which ultimately led to SNHL. Collectively, these findings enhance our understanding of the emerging role of protein homeostasis and ER stress in the pathogenesis of SNHL.

Ceapin-A7 suppresses the protective effects of Octreotide in human and bovine lung endothelial cells

Endothelial injury can be the cause and consequence of severe inflammation and injury. Synthetic somatostatin analogs-which suppress Growth Hormone-are clinically-approved drugs associated with anti-inflammatory activities. In the present study, we suggest that the protective activities of Octreotide in human and bovine endothelial cells are mitigated by Ceapin-A7, which is an activating transcription factor 6 inhibitor. To study endothelial function, we assessed protein expression levels of key cytoskeletal proteins, as well as paracellular permeability. To evaluate inflammation, we measured factors that promote vascular leak, as well as reactive oxygen species generation. Collectively, our study supports the involvement of activating transcription factor 6 in the protective effects of Octreotide in endothelial barrier function.

Noncanonical UPR factor CREB3L2 drives immune evasion of triple-negative breast cancer through Hedgehog pathway modulation in T cells

The unfolded protein response (UPR) pathway is crucial for tumorigenesis, mainly by regulating cancer cell stress responses and survival. However, whether UPR factors facilitate cell-cell communication between cancer cells and immune cells to drive cancer progression remains unclear. We found that adenosine 3',5'-monophosphate response element-binding protein 3-like protein 2 (CREB3L2), a noncanonical UPR factor, is overexpressed and activated in triple-negative breast cancer, where its cleavage releases a C-terminal fragment that activates the Hedgehog pathway in neighboring CD8+ T cells. The enhanced Hedgehog pathway represses CD8+ T cell activation and inhibits its cytotoxic effects. Consequently, overexpression of CREB3L2 not only promotes tumor growth but also causes resistance to immune checkpoint blockade (ICB). Inhibition of the Hedgehog pathway impedes the growth of CREB3L2-overexpressed tumors and sensitizes them to ICB therapy. In summary, we identified a previously unidentified mechanism by which the UPR pathway dictates cross-talk between cancer cells and immune cells, providing important anticancer therapeutic opportunities.

ATF6 enables pathogen infection in ticks by inducing stomatin and altering cholesterol dynamics

How tick-borne pathogens interact with their hosts has been primarily studied in vertebrates where disease is observed. Comparatively less is known about pathogen interactions within the tick. Here, we report that Ixodes scapularis ticks infected with either Anaplasma phagocytophilum (causative agent of anaplasmosis) or Borrelia burgdorferi (causative agent of Lyme disease) show activation of the ATF6 branch of the unfolded protein response (UPR). Disabling ATF6 functionally restricts pathogen survival in ticks. When stimulated, ATF6 functions as a transcription factor, but is the least understood out of the three UPR pathways. To interrogate the Ixodes ATF6 transcriptional network, we developed a custom R script to query tick promoter sequences. This revealed stomatin as a potential gene target, which has roles in lipid homeostasis and vesical transport. Ixodes stomatin was experimentally validated as a bona fide ATF6-regulated gene through luciferase reporter assays, pharmacological activators, and RNAi transcriptional repression. Silencing stomatin decreased A. phagocytophilum colonization in Ixodes and disrupted cholesterol dynamics in tick cells. Furthermore, blocking stomatin restricted cholesterol availability to the bacterium, thereby inhibiting growth and survival. Taken together, we have identified the Ixodes ATF6 pathway as a novel contributor to vector competence through Stomatin-regulated cholesterol homeostasis. Moreover, our custom, web-based transcription factor binding site search tool "ArthroQuest" revealed that the ATF6-regulated nature of stomatin is unique to blood-feeding arthropods. Collectively, these findings highlight the importance of studying fundamental processes in non-model organisms.

A stress paradox: the dual role of the unfolded protein response in the placenta

The placenta is a temporary organ that forms during pregnancy and is essential for fetal development and maternal health. As an endocrine organ, proper placental function requires continual production, folding, and transport of proteins and lipids. Central to these processes is the endoplasmic reticulum (ER), a dynamic organelle responsible for maintaining cellular protein and lipid synthesis and processing. ER stress occurs when there is an accumulation of unfolded or misfolded proteins, which triggers the activation of cellular pathways collectively called the unfolded protein response. Unfolded protein response pathways act to alleviate the misfolded protein burden and restore ER homeostasis, or if unresolved, initiate cell death. While prolonged ER stress has been linked to deficient placental function and adverse pregnancy outcomes, basal activation of unfolded protein response pathways is required for placental development and function. This review explores the importance of ER homeostasis in placental development and function, examining how disruptions in ER stress responses may contribute to adverse pregnancy outcomes.

Understanding the impact of ER stress on lung physiology

Human lungs consist of a distinctive array of cell types, which are subjected to persistent challenges from chemical, mechanical, biological, immunological, and xenobiotic stress throughout life. The disruption of endoplasmic reticulum (ER) homeostatic function, triggered by various factors, can induce ER stress. To overcome the elevated ER stress, an adaptive mechanism known as the unfolded protein response (UPR) is activated in cells. However, persistent ER stress and maladaptive UPR can lead to defects in proteostasis at the cellular level and are typical features of the lung aging. The aging lung and associated lung diseases exhibit signs of ER stress-related disruption in cellular homeostasis. Dysfunction resulting from ER stress and maladaptive UPR can compromise various cellular and molecular processes associated with aging. Hence, comprehending the mechanisms of ER stress and UPR components implicated in aging and associated lung diseases could enable to develop appropriate therapeutic strategies for the vulnerable population.

Circulating MicroRNAs in Idiopathic Pulmonary Fibrosis: A Narrative Review

Idiopathic pulmonary fibrosis (IPF) is a chronic, deathly disease with no recognized effective cure as yet. Furthermore, its diagnosis and differentiation from other diffuse interstitial diseases remain a challenge. Circulating miRNAs have been measured in IPF and have proven to be an adequate option as biomarkers for this disease. These miRNAs, released into the circulation outside the cell through exosomes and proteins, play a crucial role in the pathogenic pathways and mechanisms involved in IPF development. This review focuses on the serum/plasma miRNAs reported in IPF that have been validated by real-time PCR and the published evidence regarding the fibrotic process. First, we describe the mechanisms by which miRNAs travel through the circulation (contained in exosomes and bound to proteins), as well as the mechanism by which miRNAs perform their function within the cell. Subsequently, we summarize the evidence concerning miRNAs reported in serum/plasma, where we find contradictory functions in some miRNAs (dual functions in IPF) when comparing the findings in vitro vs. in vivo. The most relevant finding, for instance, the levels of miRNAs let-7d and miR-21 reported in the serum/plasma in IPF, correspond to those found in studies in lung fibroblasts and the murine bleomycin model, reinforcing the usefulness of these miRNAs as future biomarkers in IPF.

Cysteinyl Leukotriene Receptor Antagonism by Montelukast to Treat Visual Deficits

Montelukast, a Food and Drug Administration-approved drug for asthma and allergic rhinitis modulates leukotriene (LT) receptors and serves as a critical anti-inflammatory agent. Recent research suggests that the LT signaling pathway targeted by montelukast has broader implications for diseases such as fibrosis, cardiovascular diseases, cancer, cerebrovascular disease, and immune defense. This expanded understanding highlights montelukast's potential for repurposing in conditions involving aberrant stress mechanisms, including ocular diseases marked by inflammation, oxidative stress, ER stress, and apoptosis, among several others. This review delves into montelukast's therapeutic mechanisms across various diseases, draws parallels to ocular conditions, and examines clinical trials and associated adverse effects to underscore the unmet need for cysteinyl LT receptor antagonism by montelukast as an effective therapy for visual deficits.

Endothelial Unfolded Protein Response-Mediated Cytoskeletal Effects

The endothelial semipermeable monolayers ensure tissue homeostasis, are subjected to a plethora of stimuli, and their function depends on cytoskeletal integrity and remodeling. The permeability of those membranes can fluctuate to maintain organ homeostasis. In cases of severe injury, inflammation or disease, barrier hyperpermeability can cause irreparable damage of endothelium-dependent issues, and eventually death. Elucidation of the signaling regulating cytoskeletal structure and barrier integrity promotes the development of targeted pharmacotherapies towards disorders related to the impaired endothelium (e.g., acute respiratory distress syndrome, sepsis). Recent reports investigate the role of unfolded protein response in barrier function. Herein we review the cytoskeletal components, the unfolded protein response function; and their interrelations on health and disorder. Moreover, we emphasize on unfolded protein response modulators, since they ameliorate illness related to endothelial leak.

Research Progress of Endoplasmic Reticulum Targeting Metal Complexes in Cancer Therapy

The development of anticancer drugs that target different organelles has received extensive attention due to the characteristics of cancer recurrence, metastasis, and drug resistance. The endoplasmic reticulum (ER) is an important structure within the cell that is primarily responsible for protein synthesis, folding, modification, and transport and plays a crucial role in cell function and health. ER stress activation induces cancer cell apoptosis. New anticancer drugs with different anticancer mechanisms and selectivity can be designed because of redox activity, composition diversity, and metal complexes structure regulation. Over the past few decades, dozens of metal complexes have killed cancer cells through ER stress, showing powerful tumor-suppressive effects. This review summarizes the progress of research on anticancer metallic drugs that induce ER stress over the past few years, which is expected to bring more breakthroughs in the field of medicine and life science.

CTGF regulated by ATF6 inhibits vascular endothelial inflammation and reduces hepatic ischemia-reperfusion injury

Vascular endothelial inflammation is crucial in hepatic ischemia-reperfusion injury (IRI). Our previous research has shown that connective tissue growth factor (CTGF), secreted by endothelial cells, protects against acute liver injury, but its upstream mechanism is unclear. We aimed to clarify the protective role of CTGF in endothelial cell inflammation during IRI and reveal the regulation between endoplasmic reticulum stress-induced activating transcription factor 6 (ATF6) and CTGF. Hypoxia/reoxygenation in endothelial cells, hepatic IRI in mice and clinical specimens were used to examine the relationships between CTGF and inflammatory factors and determine how ATF6 regulates CTGF and reduces damage. We found that activating ATF6 promoted CTGF expression and reduced liver damage in hepatic IRI. In vitro, activated ATF6 upregulated CTGF and downregulated inflammation, while ATF6 inhibition had the opposite effect. Dual-luciferase assays and chromatin immunoprecipitation confirmed that activated ATF6 binds to the CTGF promoter, enhancing its expression. Activated ATF6 increases CTGF and reduces extracellular regulated protein kinase 1/2 (ERK1/2) phosphorylation, decreasing inflammatory factors. Conversely, inhibiting ATF6 decreases CTGF and increases the phosphorylation of ERK1/2, increasing inflammatory factor levels. ERK1/2 inhibition reverses this effect. Clinical samples have shown that CTGF increases after IRI, inversely correlating with inflammatory cytokines. Therefore, ATF6 activation during liver IRI enhances CTGF expression and reduces endothelial inflammation via ERK1/2 inhibition, providing a novel target for diagnosing and treating liver IRI.

Icariin alleviates cellular injury induced by cardiac ischemia-reperfusion injury by inhibiting IRE1/JNK-induced ferroptosis

BACKGROUND

Ischemia-induced cellular damage and stress responses significantly impact cellular viability and function. Icariin (ICA), known for its protective effects, has been studied to understand its role in mitigating oxygen-glucose deprivation/reperfusion (OGD/R)-induced endoplasmic reticulum (ER) stress and ferroptosis in H9C2 cardiomyoblast cells.

METHODS

We employed an in vitro OGD/R model using H9C2 cells. ICA's effects were analyzed across multiple concentrations. Key indicators of ER stress, autophagy, and ferroptosis-including markers like Bip, PERK, IRE1, ATF6, P62, FTH1, LC3II/LC3I, and NCOA4-were assessed using Western blotting, electron microscopy, and biochemical assays. Additionally, the role of the IRE1/JNK pathway in mitochondrial dynamics and its influence on mitochondrial dynamics protein was explored through specific inhibition and activation experiments.

RESULTS

ICA significantly reduced the activation of UPR pathways, decreased autophagic vacuole formation, and maintained cell viability in response to OGD/R and Erastin-induced ferroptosis. These protective effects were associated with modulated autophagic processes, reduced lipid peroxidation, and decreased ferrous ion accumulation. Inhibition of the IRE1/JNK pathway and subsequent Drp1 activity demonstrated reduced mitochondrial recruitment and mitophagy, correlating with decreased ferroptosis markers and improved cell survival.

CONCLUSION

Our findings highlight ICA's potential in modulating IRE1/JNK pathway, autophagy, providing a therapeutic avenue for mitigating ferroptosis in myocardial ischemia-reperfusion injury (MIRI).

Activating Transcription Factor 6 Mediates Inflammation in Experimental Varicocele-Induced Epididymal Epithelial Cells

Introduction

Varicocele is a dilatation of the internal spermatic vein and it is generally recognized as one cause of male infertility. This study aimed to analyze the roles of activating transcription factor 6 (ATF-6) in experimental varicocele-induced epididymal epithelial cells.

Methods

Experimental left varicocele was established in rats through partial left renal vein ligation. At 8 weeks after surgery, the left epididymal damage was observed using H&E and TUNEL staining. The expressions of neutral α-glucosidase (NAG), ATF-6, tumor necrosis factor (TNF)-α, and phospho-nuclear factor (p-NF)-κB p65 (S536) in the left epididymis were measured by immunohistochemistry. ATF-6 silence in rat epididymal epithelial cells was established by ATF-6 siRNA transfection. The cells were treated with hypoxia for 24 h, and cell viability was measured by CCK-8, levels of NAG, TNF-α, and interleukin (IL)-8 in cells were measured by ELISA, levels of p-NF-κB p65 (S536)/NF-κB p65 protein in cells were measured by Western blotting.

Results

The results showed that the experimental left varicocele induced hypertrophy and apoptosis of epididymal epithelial cells (p<0.05), and decreased the expressions of NAG in the epididymal epithelial cells compared with the sham-operated control rats (p<0.01). Meanwhile, the expressions of ATF-6, TNF-α, and p-NF-κB p65 (S536) were increased in the epididymal epithelial cells after the experimental left varicocele compared with the sham-operated control rats (p<0.05). In the hypoxia-treated cells, ATF-6 silence increased the cell viability and decreased the levels of TNF-α, IL-8, and p-NF-κB p65 (S536) compared with the control cells (p<0.05).

Discussion

The ATF-6 pathway was activated in a rat's left varicocele-induced epididymal damage. Inhibition of the ATF-6 pathway might be a possible novel therapeutic approach for left varicocele-induced epididymal damage.

The Involvement of Endoplasmic Reticulum Stress during the Interaction between Calcium Oxalate Crystals and Renal Tubular Epithelial Cells

Our study aimed to elucidate the mechanisms behind the interaction between calcium oxalate (CaOx) crystals and renal tubular epithelial cells through transcriptome sequencing analysis. HK-2 cells were stimulated with or without CaOx monohydrate crystals and subjected to RNA-seq to assess the effects of CaOx crystals on gene expression changes, key pathways, and molecular players during this interaction. A total of 629 differentially expressed genes (DEGs) were identified between the control group and experimental group, with 491 genes up-regulated and 138 down-regulated. Functional enrichment analysis indicated that the DEGs were significantly associated with endoplasmic reticulum stress (ERS) and unfolded protein response. To validate our findings, we compared our results with the public dataset GSE73680 and confirmed the increased expression of two ERS-related DEGs, CHAC1 and FGF21, in renal papillary tissues from patients with CaOx stones. Collectively, these findings suggest that ERS plays a crucial role in the crystal-cell interaction and highlight the potential for developing therapeutic strategies aimed at reducing CaOx stone formation by targeting ERS-related molecules and pathways.

A new perspective on liver diseases: Focusing on the mitochondria-associated endoplasmic reticulum membranes

The pathogenesis of liver diseases is multifaceted and intricate, posing a persistent global public health challenge with limited therapeutic options. Therefore, further research into liver diseases is imperative for better comprehension and advancement in treatment strategies. Numerous studies have confirmed the endoplasmic reticulum (ER) and mitochondria as key organelles driving liver diseases. Notably, the mitochondrial-associated ER membranes (MAMs) establish a physical and functional connection between the ER and mitochondria, highlighting the importance of inter-organelle communication in maintaining their functional homeostasis. This review delves into the intricate architecture and regulative mechanism of the integrated MAM that facilitate the physiological transfer of signals and substances between organelles. Additionally, we also provide a detailed overview regarding the varied pathogenic roles of malfunctioning MAM in liver diseases, focusing on its involvement in the progression of ER stress and mitochondrial dysfunction, the regulation of mitochondrial dynamics and Ca2+ transfer, as well as the disruption of lipid and glucose homeostasis. Furthermore, the current challenges and prospects associated with MAM in liver disease research are thoroughly discussed. In conclusion, elucidating the specific structure and function of MAM in different liver diseases may pave the way for novel therapeutic strategies.

Endoplasmic reticulum stress in the pathogenesis of chemotherapy-induced mucositis: Physiological mechanisms and therapeutic implications

Chemotherapy is a common and effective treatment for cancer, but these drugs are also associated with significant side effects affecting patients' well-being. One such debilitating side effect is mucositis, characterized by inflammation, ulcerations, and altered physiological functions of the gastrointestinal (GI) tract's mucosal lining. Understanding the mechanisms of chemotherapy-induced intestinal mucositis (CIM) is crucial for developing effective preventive measures and supportive care. Chemotherapeutics not only target cancer cells but also rapidly dividing cells in the GI tract. These drugs disrupt endoplasmic reticulum (ER) homeostasis, leading to ER-stress and activation of the unfolded protein response (UPR) in various intestinal epithelial cell types. The UPR triggers signaling pathways that exacerbate tissue inflammation and damage, influence the differentiation and fate of intestinal epithelial cells, and compromise the integrity of the intestinal mucosal barrier. These factors contribute significantly to mucositis development and progression. In this review, we aim to give an in-depth overview of the role of ER-stress in mucositis and its impact on GI function. This will provide valuable insights into the underlying mechanisms and highlighting potential therapeutic interventions that could improve treatment-outcomes and the quality of life of cancer patients.

Tamoxifen modulates nutrition deprivation-induced ER stress through AMPK-mediated ER-phagy in breast cancer cells

PURPOSE

Rapid proliferation and nutrition starvation in the tumor microenvironment pose significant challenges to cellular protein homeostasis. The accumulation of misfolded proteins in the endoplasmic reticulum lumen induces stress on cells and causes irreversible damage to cells if unresolved. Emerging reports emphasize the influence of the tumor microenvironment on therapeutic molecule efficacy and treatment outcomes. Hence, we aimed to understand the influence of tamoxifen on the cellular adaptation to endoplasmic reticulum stress during metabolic stress in breast cancer cells.

METHODS

Nutrition deprivation induces endoplasmic reticulum stress (ER stress), and the unfolded protein response (UPR) in breast cancer cells was confirmed by a Thioflavin B assay and western blotting. Tamoxifen-indued ER-phagy was studied using an MCD assay, confocal microscopy, and western blotting.

RESULTS

Nutrition deprivation induces ER stress in breast cancer cells. Interestingly, tamoxifen modulates the nutrition deprivation-induced endoplasmic reticulum stress through enhancing the selective ER-phagy, a specialized autophagy. The tamoxifen-induced ER-phagy is mediated by AMPK activation. The pharmacological inhibition of AMPK blocks tamoxifen-induced ER-phagy and tamoxifen modulatory effect on ER stress during nutrition deprivation.

CONCLUSION

Tamoxifen modulates ER stress by inducing ER-phagy through AMPK, thereby, may support breast cancer cell survival during nutrition deprivation conditions.

Insights into the Activation of Unfolded Protein Response Mechanism during Coronavirus Infection

Coronaviruses represent a significant class of viruses that affect both animals and humans. Their replication cycle is strongly associated with the endoplasmic reticulum (ER), which, upon virus invasion, triggers ER stress responses. The activation of the unfolded protein response (UPR) within infected cells is performed from three transmembrane receptors, IRE1, PERK, and ATF6, and results in a reduction in protein production, a boost in the ER's ability to fold proteins properly, and the initiation of ER-associated degradation (ERAD) to remove misfolded or unfolded proteins. However, in cases of prolonged and severe ER stress, the UPR can also instigate apoptotic cell death and inflammation. Herein, we discuss the ER-triggered host responses after coronavirus infection, as well as the pharmaceutical targeting of the UPR as a potential antiviral strategy.