IRE1 signaling affects cell fate during the unfolded protein response

Protein disulphide isomerase A4 as a potential biomarker for coronavirus disease 2019: Correlation with cytokine profiles and disease progression

This study investigated the role of protein disulphide isomerase A4 (PDIA4) in the pathogenesis of coronavirus disease 2019 (COVID-19), focusing on its relationship with disease severity and potential as a biomarker. We analysed a cohort of adult COVID-19 patients with varying disease severity, grouped by vaccination status. Serum levels of PDIA4 and cytokines (interleukin [IL]-6, interferon gamma inducible protein-10 [IP-10], IL-16, monocyte chemoattractant protein-1 [MCP-1], and platelet-derived growth factor-BB [PDGF-BB]) were measured using enzyme-linked immunosorbent assay and compared among patients with different disease severities. Statistical analyses were performed to assess the correlation between PDIA4 levels, disease severity, and inflammatory markers. Unvaccinated COVID-19 patients with pneumonia had significantly higher PDIA4 levels than those without pneumonia (517.94 ± 264 vs. 284.86 ± 2.24; p = 0.0022). Although unvaccinated patients requiring oxygen support exhibited higher PDIA4 levels than those not requiring oxygen (519.30 ± 269.67 vs. 420.89 ± 240.49; p = 0.4825), the difference was not statistically significant. No significant difference was observed in the PDIA4 levels between unvaccinated patients with and without respiratory failure. Levels of PDIA4 were positively correlated with the levels of IL-16, MCP-1, IP-10, and IL-6 (correlation coefficients: 0.28-0.62), although this correlation was weaker or absent in vaccinated patients. Our findings suggest that PDIA4 is associated with COVID-19 severity and may serve as a potential biomarker of disease progression. Further studies are needed to elucidate the mechanisms by which PDIA4 influences the immune response and assess its potential for therapeutic exploration in COVID-19.

NOXA exacerbates endoplasmic-reticulum-stress-induced intervertebral disc degeneration by activating apoptosis and ECM degradation

Intervertebral disc degeneration (IVDD) is a prevalent condition leading to low back pain. Endoplasmic reticulum stress (ERS) is strongly linked to IVDD progression, although the underlying mechanisms remain unclear. In this study, we investigated the effects of NOXA on ERS-induced IVDD. Primary nucleus pulposus cells (NPCs) were stimulated with Thapsigargin to mimic the ERS microenvironment in IVDD. Western blot analysis, PCR, immunofluorescence, and immunohistochemistry assay were performed to measure the expression levels of PERK, NOXA, and cell apoptosis- and extracellular-matrix-degradation-relevant proteins. JC-1 fluorescent probes, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, and flow cytometry were used to measure mitochondrial function and apoptosis in NPCs under ERS conditions. Magnetic resonance imaging, Safranin O staining, alcian blue staining, and immunohistochemistry were performed to estimate the effects of NOXA knockdown on acupuncture-mediated IVDD in rats at both imaging and histological levels. The results showed that ERS induced and activated the PERK pathway during IVDD development. Mechanically, ERS induced NPC apoptosis and ECM degradation by upregulating PERK expression and activating NOXA expression. The genetic overexpression of NOXA inhibited cell proliferation and increased apoptosis, whereas its knockdown decreased MCL-1 expression and alleviated IVDD degeneration in human NPCs and rat models. NOXA plays a crucial role in the PERK/NOXA/MCL-1 axis, mediating the link between ERS and IVDD. Targeting NOXA expression may be an effective method for treating IVDD, laying the foundation for future research on molecular mechanisms and the development of new therapies.

Global research trends on endoplasmic reticulum stress in retinal diseases from 2000 to 2024

PURPOSE

To comprehensively explore global research trends on endoplasmic reticulum stress (ERS) in retinal diseases over the past 24 years.

METHODS

An analysis of 917 publications from the Web of Science Core Collection, spanning from 1 January 2000 to 15 April 2024, was conducted to explore ERS research in retinal diseases. Bibliometric and visualisation software was employed to identify key contributors and research trends.

RESULTS

Hideaki Hara and Sarah X. Zhang were identified as the most published and most cited authors, respectively. The United States led in both publications and citations. Sun Yat-sen University ranked highest in publications, while the University of Oklahoma received the most citations. Investigative Ophthalmology & Visual Science was the leading journal in both publications and citations. A total of 108 of the 1385 author keywords, each occurring five or more times, clustered into four major themes: retinal photoreceptor degeneration, glaucoma and optic nerve damage, diabetic retinopathy and age-related macular degeneration. Keywords such as "in vivo", "dominant retinitis pigmentosa", "endothelial growth factor", "molecular", and "quality control" displayed the strongest citation bursts. ERS research (2000 ~ 2024) has evolved from retinal neuroprotection to include specific cell types and diseases, explored signalling pathways and therapeutic mechanisms, and more recently has focused on molecular insights and gene therapy applications.

CONCLUSION

This bibliometric analysis highlighted significant growth in publications on ERS in retinal diseases, reflecting an increasing scholarly focus. ERS represents a potential target for exploring pathological changes in retinal neuro-microvascular and related disorders, warranting further investigation.

Ceramide mediates cell-to-cell ER stress transmission by modulating membrane fluidity

Under endoplasmic reticulum (ER) stress (ERS), cells initiate the unfolded protein response (UPR) to maintain ER homeostasis. Recent studies revealed ERS transmission between cells and tissues, by activating the cell-nonautonomous UPR in cells that do not experience ERS directly. Here, we report that ERS triggers a rapid release of ceramide independent of the UPR, but requiring the acid sphingomyelinase activity. Carried by lipoproteins, ceramide is delivered to receiving cells to induce the UPR and regulate cell functions at multiple aspects, including lipid accumulation, cell death, and cytokine production. Mechanistically, extracellular ceramide stimulates ceramide synthesis at the transcription level in receiving cells, leading to ceramide accumulation in the ER so as to reduce membrane fluidity to disrupt ER calcium homeostasis, thus activating the UPR. Sphingomyelin counterbalanced the effect of ceramide. UPR induction is the frontline response to protect cells from ceramide insult. Our study suggests ceramide-mediated ERS transmission as a universal cell-cell communication model regulating a wide range of physiological events.

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.

Decoding ischemic stroke: Perspectives on the endoplasmic reticulum, mitochondria, and their crosstalk

Stroke is known for its high disability and mortality rates. Ischemic stroke (IS), the most prevalent form, imposes a considerable burden on affected individuals. Nevertheless, existing treatment modalities are hindered by limitations, including narrow therapeutic windows, substantial adverse effects, and suboptimal neurological recovery. Clarifying the pathological mechanism of IS is a prerequisite for developing new therapeutic strategies. In this context, the functional disruption of mitochondria, the endoplasmic reticulum (ER), and the crosstalk mechanisms between them have garnered increasing attention for their contributory roles in the progression of IS. Therefore, this review provides a comprehensive summary of the current pathomechanisms associated with the involvement of the ER and mitochondria in IS, emphasising Ca2+ destabilization homeostasis, ER stress, oxidative stress, disordered mitochondrial quality control, and mitochondrial transfer. Additionally, this article highlights the functional interaction between the ER and mitochondria, as well as the mitochondrial-ER contacts (MERCs) that structurally connect mitochondria and the ER, aiming to provide ideas and references for the research and treatment of IS.

Autophagy disruption and mitochondrial stress precede photoreceptor necroptosis in multiple mouse models of inherited retinal disorders

Inherited retinal diseases (IRDs) are a leading cause of blindness worldwide. One of the greatest barriers to developing treatments for IRDs is the heterogeneity of these disorders, with causative mutations identified in over 280 genes. It is therefore a priority to find therapies applicable to a broad range of genetic causes. To do so requires a greater understanding of the common or overlapping molecular pathways that lead to photoreceptor death in IRDs and the molecular processes through which they converge. Here, we characterise the contribution of different cell death mechanisms to photoreceptor degeneration and loss throughout disease progression in humanised mouse models of IRDs. Using single-cell transcriptomics, we identify common transcriptional signatures in degenerating photoreceptors. Further, we show that in genetically and functionally distinct IRD models, common early defects in autophagy and mitochondrial damage exist, triggering photoreceptor cell death by necroptosis in later disease stages. These results suggest that, regardless of the underlying genetic cause, these pathways likely contribute to cell death in IRDs. These insights provide potential therapeutic targets for novel, gene-agnostic treatments for IRDs applicable to the majority of patients.

Expression of CREB3L1 blocks key cancer pathways and suppresses metastasis of lung squamous cell carcinoma cells

Lung cancer is the leading cause of death due to cancer, with higher mortality rates than cancers of the colon, breast and prostate combined. About one quarter of lung cancers are lung squamous cell carcinomas (LUSC), with a five-year survival rate of only 16 %. We discovered that the majority of LUSCs have reduced expression of a key transcription factor CREB3L1 (cAMP responsive element binding protein 3 like 1), known to function as a metastasis suppressor in breast, bladder and ovarian cancers. In this report, we set out to determine if CREB3L1 functions as a metastasis suppressor in LUSCs. A differential gene expression analysis showed that ectopic expression of CREB3L1 in NCI-H2170 and NCI-1703 cells caused significant reductions in many signaling pathway genes involved in promoting cell viability, survival, migration and angiogenesis. Expression of CREB3L1 was able to reduce cell migration and anchorage-independent growth in soft agar in NCI-H2170, NCI-H1703 and NCI-H226 LUSC cells. Expression of CREB3L1 had less impact on the growth of primary xenograft tumors for NCI-H2170 and NCI-H1703 cells, the latter of which formed atypical masses filled with blood. In contrast, xenografts of NCI-H226 expressing CREB3L1 showed significant reductions in primary tumor growth. Finally, in a mouse metastasis assay, expression of CREB3L1 in NCI-H2170 cells significantly reduced the formation of liver metastases and in NCI-H226 cells, lung metastases, as compared to their respective CREB3L1-deficient parental LUSC cells. Taken together, these results strongly support a role for CREB3L1 as a metastasis suppressor in lung squamous cell carcinoma cells.

IRE1α-mediated UPR activation in gastrointestinal cancers: Adaptive mechanisms and therapeutic potential

The endoplasmic reticulum (ER) plays a crucial role in protein synthesis, folding and quality control. Disruptions in these processes lead to ER stress (ERS) and activate the unfolded protein response (UPR) to restore cellular homeostasis. In gastrointestinal cancers, inositol-requiring enzyme 1α (IRE1α) is a key regulator of the UPR, enabling cancer cells to adapt to hostile conditions such as hypoxia, oxidative stress and chemotherapy. Elevated IRE1α activity supports tumor survival, progression and metastasis by mitigating ERS-induced apoptosis. However, targeting IRE1α signaling presents a promising therapeutic strategy by impairing cancer cell adaptation to stress, offering promising therapeutic opportunities for gastrointestinal cancers.

A comprehensive map of missense trafficking variants in rhodopsin and their response to pharmacologic correction

Rhodopsin (RHO) missense variants are a leading cause of autosomal dominant retinitis pigmentosa (adRP), a progressive retinal degeneration with no currently approved therapies. Interpreting the pathogenicity of the growing number of identified RHO variants is a major clinical challenge, and understanding their disease mechanisms is essential for developing effective therapies. Here, we present a high-resolution map of RHO missense variant trafficking using two complementary deep mutational scanning (DMS) approaches based on a surface abundance immunoassay and a membrane proximity assay. We generated a comprehensive dataset encompassing all 6,612 possible single-residue missense variants, revealing a strong correlation between the two methods. Over 700 variants were identified with pathogenic trafficking scores, significantly expanding the number of RHO variants with functional evidence supporting pathogenicity. We demonstrate a high concordance between the trafficking scores and ClinVar pathogenicity classifications, highlighting this approach's utility in resolving variants of uncertain significance (VUS). The data also identified structurally clustered trafficking-deficient variants, predominantly within the N-terminal region and second extracellular loop, in and above the extracellular/intradiscal beta-plug region. Furthermore, we evaluated the efficacy of the non-retinoid pharmacological chaperone YC-001, observing significant rescue of trafficking defects in a majority of mistrafficking variants. This comprehensive functional map of RHO missense variants provides a valuable resource for pathogenicity assessment, genotype-phenotype correlations, and the development of targeted therapeutic strategies for RHO-adRP, paving the way for improved diagnosis and treatment for patients.

Endoplasmic reticulum stress in liver fibrosis: Mechanisms and therapeutic potential

This paper reviews the important role of endoplasmic reticulum stress in the patho mechanism of liver fibrosis and its potential as a potential target for the treatment of liver fibrosis. Liver fibrosis is the result of sustained inflammation and injury to the liver due to a variety of factors, triggering excessive deposition of extracellular matrix and fibrous scar formation, which in turn leads to loss of liver function and a variety of related complications. Endoplasmic reticulum stress is one of the characteristics of chronic liver disease and is closely related to the pathological process of chronic liver disease, including alcohol-related liver disease, viral hepatitis, and liver fibrosis. The unfolded protein response is one of the important response mechanisms to endoplasmic reticulum stress. It is associated with several pathological aspects of liver fibrosis and the maintenance of endoplasmic reticulum homeostasis. Interventions targeting endoplasmic reticulum stress for the treatment of liver fibrosis have potential research and application value. An in-depth understanding of the biological basis of endoplasmic reticulum stress is also needed in the treatment of liver fibrosis, as well as the development of more effective drugs and interventions to accurately regulate the endoplasmic reticulum signaling network, to achieve the restoration and maintenance of endoplasmic reticulum homeostasis at the cellular and organ levels, and to further promote the reversal of the pathological process of liver fibrosis.

Endoplasmic reticulum stress and rhodopsin accumulation in an organoid model of Retinitis Pigmentosa carrying a RHO pathogenic variant

BACKGROUND

Retinitis Pigmentosa (RP) is the most prevalent inherited retinal dystrophy, with more than 120 causative genes. Among them, RHO was the first photoreceptor gene described to harbor mutations responsible for RP. RHO pathogenic variants usually induce a dominant negative effect in which the accumulation of misfolded rhodopsin protein leads to ER stress, autophagy and lastly rod photoreceptor death.

METHODS

We differentiated photoreceptor precursors and retinal organoids from an iPSC line of a patient carrying the Pro215Leu mutation in RHO gene. Both cell models were analyzed to determine their maturation, the expression and localization of RHO mRNA and the rhodopsin protein and the activation of autophagy or ER pathways.

RESULTS

The Pro215Leu mutation causes rhodopsin accumulation in the soma of rod photoreceptor precursors along with a faster recycling by the proteasome. In both precursors and retinal organoids, we observed autophagy defects and late endoplasmic reticulum stress through CHOP increase.

CONCLUSIONS

Unraveling the molecular pathophysiology of these mutations is key for understanding the basis of the disease and design proper gene and cell therapies for its treatment.

In Vitro Inhibition of Endoplasmic Reticulum Stress: A Promising Therapeutic Strategy for Patients with Crohn's Disease

BACKGROUND

Crohn's disease (CD) is an inflammatory bowel disease marked by an abnormal immune response and excessive pro-inflammatory cytokines, leading to impaired protein processing and endoplasmic reticulum (ER) stress. This stress, caused by the accumulation of misfolded proteins, triggers the unfolded protein response (UPR) through IRE1/Xbp-1, PERK/eIF2α, and ATF6 pathways, which are linked to intestinal inflammation. This study aimed to investigate ER stress in CD patients' intestinal mucosa and evaluate phenylbutyrate (PBA) as an ER stress inhibitor.

METHODS

Colon biopsies from CD patients and controls were cultured under five conditions, including 4-PBA treatments. Real-time PCR, cytokine level, and immunohistochemistry were performed.

RESULTS

Immunohistochemistry revealed that ER stress was activated in CD patients' intestinal epithelial cells and lamina propria cells. PERK/eIF2α, but not IRE1/Xbp-1 or ATF6, was upregulated in CD patients compared to controls. UPR-related genes (STC2, CALR, HSPA5, HSP90B1) were also elevated in CD patients. PBA treatment significantly reduced ER stress and UPR markers while decreasing apoptotic markers like DDIT3. Pro-inflammatory cytokines, such as IL-1β, IL-6, IL-17, TNF- α, and sCD40L, were significantly reduced after PBA treatment.

CONCLUSION

ER stress and UPR pathways are activated in CD colonic mucosa, and PBA reduces these markers, suggesting potential therapeutic benefits for CD-related inflammation.

RNA exosome-driven RNA processing instructs the duration of the unfolded protein response

Upon stresses, cellular compartments initiate adaptive programs meant to restore homeostasis. Dedicated to the resolution of transient perturbations, these pathways are typically maintained at a basal level, activated upon stress, and critically downregulated upon reestablishment of cellular homeostasis. As such, prolonged activation of the unfolded protein response (UPR), a conserved adaptive transcriptional response to defective endoplasmic reticulum (ER) proteostasis, leads to cell death. Here, we elucidate an unanticipated role for the nuclear RNA exosome, an evolutionarily conserved ribonuclease complex that processes multiple classes of RNAs, in the control of UPR duration. Remarkably, the inactivation of Rrp6, an exclusively nuclear catalytic subunit of the RNA exosome, curtails UPR signaling, which is sufficient to promote the cell's resistance to ER stress. Mechanistically, accumulation of unprocessed RNA species diverts the processing machinery that maturates the messenger RNA encoding the master UPR regulator Hac1, thus restricting the UPR. Significantly, Rrp6 expression is naturally dampened upon ER stress, thereby participating in homeostatic UPR deactivation.

Transmission of unfolded protein response-a regulator of disease progression, severity, and spread in virus infections

The unfolded protein response (UPR) is a cell-autonomous stress response aimed at restoring homeostasis due to the accumulation of misfolded proteins in the endoplasmic reticulum (ER). Viruses often hijack the host cell machinery, leading to an accumulation of misfolded proteins in the ER. The cell-autonomous UPR is the immediate response of an infected cell to this stress, aiming to restore normal function by halting protein translation, degrading misfolded proteins, and activating signaling pathways that increase the production of molecular chaperones. The cell-non-autonomous UPR involves the spreading of UPR signals from initially stressed cells to neighboring unstressed cells that lack the stressor. Though viruses are known modulators of cell-autonomous UPR, recent advancements have highlighted that cell-non-autonomous UPR plays a critical role in elucidating how local infections cause systemic effects, thereby contributing to disease symptoms and progression. Additionally, by utilizing cell-non-autonomous UPR, viruses have devised novel strategies to establish a pro-viral state, promoting virus spread. This review discusses examples that have broadened the understanding of the role of UPR in virus infections and disease progression by looking beyond cell-autonomous to non-autonomous processes and mechanistic details of the inducers, spreaders, and receivers of UPR signals.

Mutations in unfolded protein response regulator ATF6 cause hearing and vision loss syndrome

Activating transcription factor 6 (ATF6) is a key regulator of the unfolded protein response (UPR) and is important for ER function and protein homeostasis in metazoan cells. Patients carrying loss-of-function ATF6 disease alleles develop the cone dysfunction disorder achromatopsia. The effect of loss of ATF6 function on other cell types, organs, and diseases in people remains unclear. Here, we report that progressive sensorineural hearing loss was a notable complaint in some patients carrying ATF6 disease alleles and that Atf6-/- mice also showed progressive auditory deficits affecting both sexes. In mice with hearing deficits, we found disorganized stereocilia on hair cells and focal loss of outer hair cells. Transcriptomics analysis of Atf6-/- cochleae revealed a marked induction of the UPR, especially through the protein kinase RNA-like endoplasmic reticulum kinase (PERK) arm. These findings identify ATF6 as an essential regulator of cochlear health and function. Furthermore, they support the idea that ATF6 inactivation in people causes progressive sensorineural hearing loss as part of a blindness-deafness genetic syndrome targeting hair cells and cone photoreceptors. Last, our genetic findings indicate that ER stress is an important pathomechanism underlying cochlear damage and hearing loss, with clinical implications for patient lifestyle modifications that minimize environmental and physiological sources of ER stress to the ear.

Effect of Dync1h1 on Phototransduction Protein Transport and the Development and Maintenance of Photoreceptor Cells in Zebrafish

Purpose

Retinitis pigmentosa (RP) is a hereditary retinal disease characterized by progressive degeneration of photoreceptor cells (PRCs). Identifying potential pathogenic genes and understanding the mechanisms of PRC degeneration are essential for improving diagnosis and treatment. Cytoplasmic dynein 1, responsible for retrograde axonal transport along microtubules, plays critical roles in neuronal function. This study utilized dync1h1-deficient zebrafish to investigate its roles in PRC morphogenesis and degeneration.

Methods

Heterozygous and homozygous dync1h1-deficient zebrafish were confirmed through Sanger sequencing. Morphological changes and retinal phenotypes were assessed through histological analysis. RNA sequencing and bioinformatics were used to explore molecular mechanisms in dync1h1-/- zebrafish, with endoplasmic reticulum (ER) stress and apoptosis pathways validated in vivo.

Results

Dync1h1-/- zebrafish exhibit severe developmental defects, including microphthalmia, disorganized retinal lamination, and PRC apoptosis. In dync1h1+/-, mild but progressive growth retardation and PRC defects were observed. Dync1h1 loss impaired retrograde axonal transport, leading to defects in cilium biogenesis and transport disorder of phototransduction proteins in PRCs. This triggered ER stress, activating BiP-ATF4-CHOP signaling pathway and leading to PRC degeneration.

Conclusions

Dync1h1 is essential for maintaining retrograde axonal transport and proper trafficking of phototransduction proteins in PRCs. Non-resolving ER stress-induced PRC apoptosis is a key factor in DYNC1H1-associated retinal degeneration. This study provides important insights into the precise diagnosis and may help in the development of targeted therapies for retinal degenerative diseases.

Endoplasmic reticulum membrane remodeling by targeting reticulon-4 induces pyroptosis to facilitate antitumor immune

Pyroptosis is an identified programmed cell death that has been highly linked to endoplasmic reticulum (ER) dynamics. However, the crucial proteins for modulating dynamic ER membrane curvature change that trigger pyroptosis are currently not well understood. In this study, a biotin-labeled chemical probe of potent pyroptosis inducer α-mangostin (α-MG) was synthesized. Through protein microarray analysis, reticulon-4 (RTN4/Nogo), a crucial regulator of ER membrane curvature, was identified as a target of α-MG. We observed that chemically induced proteasome degradation of RTN4 by α-MG through recruiting E3 ligase UBR5 significantly enhances the pyroptosis phenotype in cancer cells. Interestingly, the downregulation of RTN4 expression significantly facilitated a dynamic remodeling of ER membrane curvature through a transition from tubules to sheets, consequently leading to rapid fusion of the ER with the cell plasma membrane. In particular, the ER-to-plasma membrane fusion process is supported by the observed translocation of several crucial ER markers to the "bubble" structures of pyroptotic cells. Furthermore, α-MG-induced RTN4 knockdown leads to pyruvate kinase M2 (PKM2)-dependent conventional caspase-3/gasdermin E (GSDME) cleavages for pyroptosis progression. In vivo, we observed that chemical or genetic RTN4 knockdown significantly inhibited cancer cells growth, which further exhibited an antitumor immune response with anti-programmed death-1 (anti-PD-1). In translational research, RTN4 high expression was closely correlated with the tumor metastasis and death of patients. Taken together, RTN4 plays a fundamental role in inducing pyroptosis through the modulation of ER membrane curvature remodeling, thus representing a prospective druggable target for anticancer immunotherapy.

4-Phenylbutyric acid mitigates ER stress-induced neurodegeneration in the spinal cords of a GM2 gangliosidosis mouse model

Sandhoff disease (SD), a fatal and rare lysosomal storage disorder (LSD), is caused by a deficiency of the enzyme β-hexosaminidase B and leads to severe accumulation of GM2 gangliosides in lysosomes, primarily within the central nervous system (CNS). This accumulation results in severe neurological impairment, lower motor neuron disease, and death. Currently, there are no effective therapies available for SD. Here, we explored the role of endoplasmic reticulum (ER) stress in the spinal cord during disease progression in an established mouse model of SD and revealed the beneficial outcome of off-label treatment with the FDA-approved drug, 4-phenylbutyric acid (4-PBA). We analyzed the expression and localization of ER stress and cellular apoptosis markers, which revealed significant upregulation of these factors within motor neurons. Additionally, we observed a > 50% reduction in neuronal numbers throughout all spinal cord regions. Our studies also tested the impact of the chemical chaperone 4-PBA on ER stress in mice, and following administration, we observed significant improvements in motor neuromuscular function and life span throughout disease progression. 4-PBA treatment significantly reduced apoptosis in spinal cord neurons and increased the number of choline acetyltransferase (ChAT)-positive neurons, with little effect on astrogliosis or sensory interneurons. Overall, this study provides strong evidence for the role of chronic ER stress in the pathophysiology of SD and highlights 4-PBA as a promising therapeutic treatment for SD and potentially other related LSDs.

Hypertensive disorders of pregnancy affected thyroid hormone synthesis via endoplasmic reticulum stress in preterm infant rats

Background

Maternal hypertensive disorders of pregnancy (HDP) was associated with increased risk of congenital hypothyroidism in preterm infants, but its underlying mechanisms remain unclear.

Objective

To investigate the possible mechanisms by which intrauterine exposure to HDP affects thyroid hormone synthesis in preterm infant rats.

Methods

preterm infant rats were obtained by Caesarean section delivery from the L-NAME group and Control groups which was induced by L-NAME and saline, respectively. Thyroid hormone levels of preterm infant rats were detected by ELISA, and morphology structure were observed by H&E staining and electron microscopy, and the expression of key factors of thyroid hormone synthesis and endoplasmic reticulum stress indicators were analyzed by RT-qPCR and Western blotting.

Results

Compared with the Control group, significantly higher serum TSH concentration was observed in the L-NAME group (p < 0.05), while T3 and T4 levels showed no noticeable change. The L-NAME group revealed a reduction in the size and number of thyroid follicles, with the emergence of thyroid follicular epithelial hyperplasia. While electron microscopy revealed that the endoplasmic reticulum of thyroid follicular epithelial cells was marked swollen within L-NAME group. Additionally, the mRNA expression of Ttf1, Pax8 and Tshr was down-regulated in thyroid tissues of L-NAME group. Furthermore, the protein levels of Tg, NIS and TSHR were reduced, while the protein level of p-IRE1α, ATF6α, XBP1s and Bip were increased in the L-NAME group.

Conclusion

The results indicated that HDP may reduce the expression of key molecules involved in thyroid synthesis through endoplasmic reticulum stress which could ultimately result in the development of congenital hypothyroidism.

Mechanisms of Rhodopsin-Related Inherited Retinal Degeneration and Pharmacological Treatment Strategies

Retinitis pigmentosa (RP) is a hereditary disease characterized by progressive vision loss ultimately leading to blindness. This condition is initiated by mutations in genes expressed in retinal cells, resulting in the degeneration of rod photoreceptors, which is subsequently followed by the loss of cone photoreceptors. Mutations in various genes expressed in the retina are associated with RP. Among them, mutations in the rhodopsin gene (RHO) are the most common cause of this condition. Due to the involvement of numerous genes and multiple mutations in a single gene, RP is a highly heterogeneous disease making the development of effective treatments particularly challenging. The progression of this disease involves complex cellular responses to restore cellular homeostasis, including the unfolded protein response (UPR) signaling, autophagy, and various cell death pathways. These mechanisms, however, often fail to prevent photoreceptor cell degradation and instead contribute to cell death under certain conditions. Current research focuses on the pharmacological modulation of the components of these pathways and the direct stabilization of mutated receptors as potential treatment strategies. Despite these efforts, the intricate interplay between these mechanisms and the diverse causative mutations involved has hindered the development of effective treatments. Advancing our understanding of the interactions between photoreceptor cell death mechanisms and the specific genetic mutations driving RP is critical to accelerate the discovery and development of therapeutic strategies for this currently incurable disease.

MMP-2 inhibition attenuates ER stress-mediated cell death during myocardial ischemia-reperfusion injury by preserving IRE1α

Endoplasmic reticulum (ER) stress is one of the major events accompanying myocardial ischemia-reperfusion (IR) injury, as hypoxia and oxidative stress disrupt protein folding in the ER. As a result, the unfolded protein response (UPR) is activated through different sensors including inositol-requiring enzyme 1α (IRE1α) and protein kinase R-like ER kinase (PERK). Failure of the UPR to reduce ER stress induces cellular dysfunction. Matrix metalloproteinase-2 (MMP-2) is a ubiquitous protease that is activated intracellularly in response to oxidative stress and partially localizes near the ER. However, its role in ER homeostasis is unknown. We hypothesized that MMP-2 is involved in the regulation of the UPR and ER stress-mediated apoptosis during IR injury. Isolated mouse hearts subjected to IR injury showed impaired recovery of post-ischemic contractile function compared to aerobically perfused controls. Ventricular extracts from IR hearts had higher levels of glucose-regulated protein-78 and protein disulfide isomerase and lower levels of IRE1α and PERK compared to aerobic controls. MMP-2 inhibitors, ARP-100 or ONO-4817, given 10 min before ischemia, improved cardiac post-ischemic recovery and preserved IRE1α level in hearts subjected to 30 min ischemia/40 min reperfusion. IR also increased the levels of CHOP and mitochondrial Bax and caspase-3 and -9 activities, indicating induction of apoptosis, all of which were attenuated by MMP-2 inhibitors, regardless of the reperfusion time. Immunoprecipitation showed an association between MMP-2 and IRE1α in aerobic and IR hearts. During myocardial IR injury MMP-2 may impair the UPR and induce apoptosis by proteolysis of IRE1α. Inhibition of MMP-2 activity protects against cardiac contractile dysfunction in part by preserving IRE1α and preventing the progression to myocardial cell death.

Wild-Type and rtA181T/sW172* Mutant Strains of Hepatitis B Virus Drive Hepatocarcinogenesis via Distinct GRP78-Mediated ER Stress Pathways

Glucose-regulated protein 78 kDa (GRP78), a key marker of endoplasmic reticulum stress (ERS), is upregulated in hepatocellular carcinoma (HCC) tissues, but its role in hepatitis B virus (HBV)-induced tumorigenesis remains unclear. This study aimed to investigate the contribution of GRP78 to HBV-associated tumor development and explore the ERS pathways involved. The results showed that increased GRP78 expression in patients with HBV-related HCC was associated with a poor prognosis within the first 2 years following diagnosis. Furthermore, using wild-type HBV strain and the oncogenic HBV rtA181T/sW172* mutant, this study demonstrated that the HBV-induced GRP78 expression correlated with elevated reactive oxygen species (ROS) levels. Moreover, GRP78 expression enhanced hepatocyte proliferation and resistance to apoptosis. In wild-type HBV-infected hepatocytes, GRP78 suppressed apoptosis by inhibiting the PERK/p38 pathway. In contrast, the HBV rtA181T/sW172* mutation led to increased GRP78 expression and inhibition of cell apoptosis through activation of the IRE-1α/XBP1/BCL-2 pathway. In conclusion, GRP78 plays a pivotal role in HBV-induced hepatocarcinogenesis by modulating distinct ERS pathways. Targeting these pathways may aid in the therapeutic management of HBV-associated hepatocarcinogenesis.

Roles of X-box binding protein 1 in liver pathogenesis

The prevalence of drug-induced liver injury (DILI) and viral liver infections presents significant challenges in modern healthcare and contributes to considerable morbidity and mortality worldwide. Concurrently, metabolic dysfunctionassociated steatotic liver disease (MASLD) has emerged as a major public health concern, reflecting the increasing rates of obesity and leading to more severe complications such as fibrosis and hepatocellular carcinoma. X-box binding protein 1 (XBP1) is a distinct transcription factor with a basic-region leucine zipper structure, whose activity is regulated by alternative splicing in response to disruptions in endoplasmic reticulum (ER) homeostasis and the unfolded protein response (UPR) activation. XBP1 interacts with a key signaling component of the highly conserved UPR and is critical in determining cell fate when responding to ER stress in liver diseases. This review aims to elucidate the emerging roles and molecular mechanisms of XBP1 in liver pathogenesis, focusing on its involvement in DILI, viral liver infections, MASLD, fibrosis/cirrhosis, and liver cancer. Understanding the multifaceted functions of XBP1 in these liver diseases offers insights into potential therapeutic strategies to restore ER homeostasis and mitigate liver damage.

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.

NLRX1 attenuates endoplasmic reticulum stress via STING in cardiac hypertrophy

Endoplasmic reticulum stress-induced cell apoptosis is a pivotal mechanism underlying the progression of cardiac hypertrophy. NLRX1, a member of the NOD-like receptor family, modulates various cellular processes, including STING, NF-κB, MAPK pathways, reactive oxygen species production, essential metabolic pathways, autophagy and cell death. Emerging evidence suggests that NLRX1 may offer protection against diverse cardiac diseases. However, the impacts and mechanisms of NLRX1 on endoplasmic reticulum stress in cardiac hypertrophy remains largely unexplored. In our study, we observed that the NLRX1 and phosphorylated STING (p-STING) were highly expressed in both hypertrophic mouse heart and cellular model of cardiac hypertrophy. Whereas over-expression of NLRX1 mitigated the expression levels of p-STING, as well as the endoplasmic reticulum stress markers, including transcription activating factor 4 (ATF4), C/EBP homologous protein (CHOP) and the ratios of phosphorylated PERK to PERK, phosphorylated IRE1 to IRE1 and phosphorylated eIF2α to eIF2α in an Angiotensin II (Ang II)-induced cellular model of cardiac hypertrophy. Importantly, the protective effects of NLRX1 were attenuated upon pretreatment with the STING agonist, DMXAA. Our findings provide the evidence that NLRX1 attenuates the PERK-eIF2α-ATF4-CHOP axis of endoplasmic reticulum stress response via inhibition of p-STING in Ang II-treated cardiomyocytes, thereby ameliorating the development of cardiac hypertrophy.

Induction of LARP1B under endoplasmic reticulum stress and its regulatory role in proliferation of esophageal squamous cell carcinoma

Endoplasmic Reticulum Stress (ER stress) is a series of cellular responses activated in response to misfolded and unfolded protein accumulation and calcium imbalance in the ER lumen. Cumulating evidence emphasized the crucial involvement of ER stress in cell survival, death, and proliferation. However, the precise process remained obscure, especially in esophageal squamous cell carcinoma (ESCC). In the present study, LARP1B was detected to be one of the genes with significant differential expression in the ER stress ESCC cell model by RNA sequencing. ESCC cells exposed to ER stress stimulants (thapsigargin and tunicamycin) showed increased expression levels of LARP1B. ER stress initiated the expression of LARP1B through activation of the ERN1-XBP1 pathway, with XBP1 acting as a transcription factor to boost LARP1B transcription. Up-regulation of LARP1B was detected in ESCC tissues and cell lines. Suppression of LARP1B effectively curtailed the growth of cells and hindered the progression of the cell cycle. By detecting the expression of some genes closely related to proliferation and cell cycle regulation, CCND1 was identified as the main contributor to the cell proliferation induced by LARP1B. As an RNA-binding protein, LARP1B has the capability to attach to CCND1 mRNA, thereby increasing its stability. Inhibiting CCND1 might partially counterbalance the proliferation-promoting impact of LARP1B overexpression on ESCC cells. These findings indicate that, upon ER stress, up-regulation of LARP1B, triggered by ERN1-XBP1 pathway, facilitates proliferation of ESCC cells through enhancing the mRNA stability of CCND1, and LARP1B may be used as a potential therapeutic target of ESCC.

ATM facilitates autophagy and protects against oxidative stress and apoptosis in response to ER stress in vitro

The endoplasmic reticulum (ER) responds to cellular stress by initiating an unfolded protein response (UPR) that mitigates misfolded protein accumulation by promoting protein degradation pathways. Chronic ER stress leads to UPR-mediated apoptosis and is a common underlying feature of various diseases, highlighting the modulators of the UPR as attractive targets for therapeutic intervention. Ataxia-telangiectasia mutated protein kinase (ATM) is a stress-responsive kinase that initiates autophagy in response to reactive oxygen species (ROS), and ATM deficiency is associated with increased ER stress markers in vitro. However, whether ATM participates in the UPR remains unclear. In this in vitro study, a novel role for ATM in the ER stress response is described using the well-characterized HEK293 cells treated with the common ER stress-inducing agent, tunicamycin, with and without the potent ATM inhibitor, KU-60019. We show for the first time that ATM is activated in a time-dependent manner downstream of UPR initiation in response to tunicamycin treatment. Furthermore, we demonstrate that ATM is required for p62-bound protein cargo degradation through the autophagy pathway in response to ER stress. Lastly, our data suggest a protective role for ATM in ER stress-mediated oxidative stress and mitochondrial apoptosis. Taken together, we highlight ATM as a potential novel drug target in ER stress-related diseases.

Endoplasmic reticulum stress: The underlying mechanism of chronic pain

Chronic pain (CP) affects over 30 % of the global population, imposing significant financial burdens on individuals and society. However, existing treatments for CP offer limited efficacy and troublesome side effects, primarily owing to a lack of knowledge of its precise underlying mechanism. Pathological stimuli disrupt the intricate process of protein folding and endoplasmic reticulum (ER) homeostasis. This disruption leads to the accumulation of misfolded or unfolded proteins in the ER, generating a condition termed ER stress. Emerging data have indicated that ER stress, occurring in the peripheral and central nervous systems, contributes to the development and maintenance of CP. This review aimed to comprehensively explore the intersection of ER stress and CP within the lower and upper nervous systems and highlight the cell-specific contributions of the unfolded protein response in different CP types. We provide a comprehensive synthesis of evidence from animal models, examining neuronal and non-neuronal mechanisms and discuss the damaging ER stress-linked inflammation, autophagy, oxidative stress, and apoptosis, which collectively drive disease progression and contribute to a neurotoxic environment. However, the mechanisms through which ER stress influences the most advanced centre-of-pain projections in the brain remain unclear. Further investigation in this area is crucial to elucidate the relationship between ER stress and CP and facilitate the development of novel therapeutic drugs for this intractable dilemma.

Tumour suppressor protein sMEK1 links to IRE1 signalling pathway to modulate its activity during ER stress

The Endoplasmic Reticulum is a pervasive, dynamic cellular organelle that performs a wide range of functions in the eukaryotic cell, including protein folding and maturation. Upon stress, ER activates an adaptive cellular pathway, namely Unfolded Protein Response, that transduces information from ER to nucleus, restoring homeostasis in the ER milieu. UPR consists of three membrane-tethered sensors; IRE1, PERK and ATF6. Among all the UPR sensors, the IRE1 branch acts as a central pathway that orchestrates several pathways to determine cell fate. However, the detailed knowledge underlying the whole process is not understood yet. Previously, we determined the sMEK1 as one of the interacting partners of IRE1. sMEK1 is a protein phosphatase, which has been indicated in a number of critical cellular functions like apoptosis, cell proliferation, and tumour suppression. In this study, we evaluated the role of sMEK1 on the IRE1 signalling pathway. Our data indicate that sMEK1 can inhibit IRE1 phosphorylation under ER stress. This inhibitory effect of sMEK1 could be reflected in its downstream effectors, Xbp1 and RIDD, which are downregulated in the presence of sMEK1. We also found that the repressing effect of sMEK1 was specific to the IRE1 signalling pathway and could be preserved even under prolonged ER stress. Our findings also indicate that sMEK1 can inhibit IRE1 and its downstream molecules under ER stress irrespective of other UPR sensors. These results help to draw the mechanistic details giving insights into different molecular connections of UPR with other pathways.

Arsenic trioxide and p97 inhibitor synergize against acute myeloid leukemia by targeting nascent polypeptides and activating the ZAKα-JNK pathway

Arsenic trioxide (ATO) has exhibited remarkable efficacy in treating acute promyelocytic leukemia (APL), primarily through promoting the degradation of the PML-RARα fusion protein. However, ATO alone fails to confer any survival benefit to non-APL acute myeloid leukemia (AML) patients and exhibits limited efficacy when used in combination with other agents. Here, we explored the general toxicity mechanisms of ATO in APL and potential drugs that could be combined with ATO to exhibit synergistic lethal effects on other AML. We demonstrated that PML-RARα degradation and ROS upregulation were insufficient to cause APL cell death. Based on the protein synthesis of different AML cells and their sensitivity to ATO, we established a correlation between ATO-induced cell death and protein synthesis. Our findings indicated that ATO induced cell death by damaging nascent polypeptides and causing ribosome stalling, accompanied by the activation of the ZAKα-JNK pathway. Furthermore, ATO-induced stress activated the GCN2-ATF4 pathway, and ribosome-associated quality control cleared damaged proteins with the assistance of p97. Importantly, our data revealed that inhibiting p97 enhanced the effectiveness of ATO in killing AML cells. These explorations paved the way for identifying optimal synthetic lethal drugs to enhance ATO treatment on non-APL AML.

IRE1 is implicated in protein synthesis regulation under ER stress conditions in plants

The unfolded protein response (UPR) is a crucial cellular mechanism for maintaining protein folding homeostasis during endoplasmic reticulum (ER) stress. In this study, the role of IRE1, a key component of the UPR, was investigated in protein translation regulation under ER stress conditions in Arabidopsis. We discovered that the loss of IRE1A and IRE1B leads to diminished protein translation, indicating a significant role for IRE1 in this process. However, this regulation was not solely dependent on the interaction with bZIP60, a key transcription factor in the UPR. Interestingly, while chemical chaperones TUDCA and PBA effectively alleviated the translation inhibition observed in ire1a ire1b mutants, this effect was more pronounced than the mitigation observed from suppressing GCN2 expression or introducing a non-phosphorylatable eIF2α variant. Additionally, the kinase and ribonuclease activities of IRE1B were demonstrated to be crucial for plant adaptation and protein synthesis regulation under ER stress conditions. Overall, this study not only highlights the complex regulatory mechanisms of IRE1 in plant ER stress responses but also provides insights into its multifaceted roles in protein translation regulation.

Toll-like receptor 4 damages the intestinal epithelial cells by activating endoplasmic reticulum stress in septic rats

Background

The severity of acute gastrointestinal injury (AGI) is a critical determinant of survival in sepsis. However, there is no specifically interventional management for gastrointestinal dysfunction. Toll-like Receptor 4 (TLR4) is an important contributor to sepsis-induced multiple organ dysfunction syndrome. So, we investigated the effect of TLR4 on leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) + cells and goblet cells and its potential mechanism.

Methods

A cecal ligation and puncture (CLP) model reflecting the development of clinical sepsis was developed. Tak-242, a TLR4 inhibitor, was administered to septic rats at a dose of 3 mg/kg via intraperitoneal injection. Immunohistochemistry was performed to detect TLR4 and Lgr5+ cells. AB-PAS staining was performed to detect goblet cells. MUC1 and MUC2 secreted by goblet cells, biomarkers of endoplasmic reticulum (ER) stress and inflammatory cytokines in the intestine were detected by western blotting and real-time PCR.

Results

We found that the upregulation of the TLR4/NF-κB signaling pathway activated intestinal inflammatory response in sepsis. Meanwhile, the structure of intestinal mucosa was destroyed, Lgr5+ cells and goblet cells count were significantly reduced, and the secretory function of goblet cells also decreased. Further studies have found that TLR4 increased the levels of activating transcription factor-6 (ATF6), XBP1, ER chaperone (Bip) and CHOP, but did not activate the protein kinase RNA (PKR)-like ER kinase (P-PERK).

Conclusion

We concluded that the inhibition of TLR4/NF-κB signaling pathway can reduce intestinal inflammatory response, protect intestinal mucosa, protect Lgr5+ cells, goblet cells and relieve ER stress. Our findings suggest that Tak-242 protects Lgr5+ cells and goblet cells after sepsis, partly may be through the suppression of ER stress. Thus, inhibition of TLR4-mediated ER stress may be a promising therapy of septic AGI.

Krüppel-like factor 6 involvement in the endoplasmic reticulum homeostasis of extravillous trophoblasts

INTRODUCTION

Trophoblast homeostasis and differentiation require a proper endoplasmic reticulum (ER) function. The Krüppel-like factor-6 (KLF6) transcription factor modulates trophoblast migration, differentiation, and reactive oxygen species (ROS) production. Since ROS may impact on ER homeostasis, we assessed whether downregulation of KLF6 altered the unfolded protein response (UPR) and cellular process associated with ER homeostasis.

MATERIALS AND METHODS

Protein and RNA expression were analyzed by Western blot and qRT-PCR, respectively, in extravillous trophoblast HTR-8/SVneo cells silenced for KLF6. Apoptosis was detected by flow cell cytometry using Annexin V Apoptosis Detection Kit. Protein trafficking was assessed by confocal microscopy of a reporter fluorescent protein whose release from the ER was synchronized.

RESULTS

KLF6 downregulation reduced the expression of BiP, the master regulator of the UPR, at protein, mRNA, and pre-mRNA levels. Ire1α protein, XBP1 splicing, and DNAJB9 mRNA levels were also reduced in KLF6-silenced cells. Instead, PDI, Ero1α, and the p-eIF2α/eIF2α ratio as well as autophagy and proteasome dependent protein degradation remained unchanged while intracellular trafficking was increased. Under thapsigargin-induced stress, KLF6 silencing impaired BiP protein and mRNA expression increase, as well as the activation of the Ire1α pathway, but it raised the p-eIF2α/eIF2α ratio and CHOP protein levels. Nevertheless, apoptosis was not increased.

DISCUSSION

Results provide the first evidence of KLF6 as a modulator of the UPR components. The increase in protein trafficking and protection from apoptosis, observed in KLF6-silenced cells, are consistent with its role in extravillous trophoblast migration and differentiation.

Hyperactivation of ATF4/TGF-β1 signaling contributes to the progressive cardiac fibrosis in Arrhythmogenic cardiomyopathy caused by DSG2 Variant

BACKGROUND

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy characterized with progressive cardiac fibrosis and heart failure. However, the exact mechanism driving the progression of cardiac fibrosis and heart failure in ACM remains elusive. This study aims to investigate the underlying mechanisms of progressive cardiac fibrosis in ACM caused by newly identified Desmoglein-2 (DSG2) variation.

METHODS

We identified homozygous DSG2F531C variant in a family with 8 ACM patients using whole-exome sequencing and generated Dsg2F536C knock-in mice. Neonatal and adult mouse ventricular myocytes isolated from Dsg2F536C knock-in mice were used. We performed functional, transcriptomic and mass spectrometry analyses to evaluate the mechanisms of ACM caused by DSG2F531C variant.

RESULTS

All eight patients with ACM were homozygous for DSG2F531C variant. Dsg2F536C/F536C mice displayed cardiac enlargement, dysfunction, and progressive cardiac fibrosis in both ventricles. Mechanistic investigations revealed that the variant DSG2-F536C protein underwent misfolding, leading to its recognition by BiP within the endoplasmic reticulum, which triggered endoplasmic reticulum stress, activated the PERK-ATF4 signaling pathway and increased ATF4 levels in cardiomyocytes. Increased ATF4 facilitated the expression of TGF-β1 in cardiomyocytes, thereby activating cardiac fibroblasts through paracrine signaling and ultimately promoting cardiac fibrosis in Dsg2F536C/F536C mice. Notably, inhibition of the PERK-ATF4 signaling attenuated progressive cardiac fibrosis and cardiac systolic dysfunction in Dsg2F536C/F536C mice.

CONCLUSIONS

Hyperactivation of the ATF4/TGF-β1 signaling in cardiomyocytes emerges as a novel mechanism underlying progressive cardiac fibrosis in ACM. Targeting the ATF4/TGF-β1 signaling may be a novel therapeutic target for managing ACM.

Caffeine: The Story beyond Oxygen-Induced Lung and Brain Injury in Neonatal Animal Models-A Narrative Review

Caffeine is one of the most commonly used drugs in intensive care to stimulate the respiratory control mechanisms of very preterm infants. Respiratory instability, due to the degree of immaturity at birth, results in apnea of prematurity (AOP), hyperoxic, hypoxic, and intermittent hypoxic episodes. Oxidative stress cannot be avoided as a direct reaction and leads to neurological developmental deficits and even a higher prevalence of respiratory diseases in the further development of premature infants. Due to the proven antioxidant effect of caffeine in early use, largely protective effects on clinical outcomes can be observed. This is also impressively observed in experimental studies of caffeine application in oxidative stress-adapted rodent models of damage to the developing brain and lungs. However, caffeine shows undesirable effects outside these oxygen toxicity injury models. This review shows the effects of caffeine in hyperoxic, hypoxic/hypoxic-ischemic, and intermittent hypoxic rodent injury models, but also the negative effects on the rodent organism when caffeine is administered without exogenous oxidative stress. The narrative analysis of caffeine benefits in cerebral and pulmonary preterm infant models supports protective caffeine use but should be given critical consideration when considering caffeine treatment beyond the recommended corrected gestational age.

Endoplasmic reticulum stress in diseases

The endoplasmic reticulum (ER) is a key organelle in eukaryotic cells, responsible for a wide range of vital functions, including the modification, folding, and trafficking of proteins, as well as the biosynthesis of lipids and the maintenance of intracellular calcium homeostasis. A variety of factors can disrupt the function of the ER, leading to the aggregation of unfolded and misfolded proteins within its confines and the induction of ER stress. A conserved cascade of signaling events known as the unfolded protein response (UPR) has evolved to relieve the burden within the ER and restore ER homeostasis. However, these processes can culminate in cell death while ER stress is sustained over an extended period and at elevated levels. This review summarizes the potential role of ER stress and the UPR in determining cell fate and function in various diseases, including cardiovascular diseases, neurodegenerative diseases, metabolic diseases, autoimmune diseases, fibrotic diseases, viral infections, and cancer. It also puts forward that the manipulation of this intricate signaling pathway may represent a novel target for drug discovery and innovative therapeutic strategies in the context of human diseases.

Pivotal role of the endoplasmic reticulum stress-related XBP1s/miR-22/SIRT1 axis in acute myeloid leukemia apoptosis and response to chemotherapy

Malignant growth relies on rapid protein synthesis frequently leading to endoplasmic reticulum (ER) overload and accumulation of unfolded or misfolded protein in this cellular compartment. In the ER, protein homeostasis is finely regulated by a mechanism called the unfolded protein response (UPR), involving the activation of signalization pathways mediated by three transmembrane proteins, namely PERK, IRE1 and ATF6. IRE1 endoribonuclease activation leads in particular to the splicing of the cytosolic mRNA encoding the key UPR-specific transcription factor XBP1s. Our study shows that sustained activation of XBP1s expression in acute myeloid leukemia (AML) cells induces apoptosis in vitro and in vivo, whereas a moderate XBP1s expression sensitizes cells to chemotherapeutic treatments. ChIP-seq experiments identified specific XBP1s target genes including the MIR22HG lncRNA, the precursor transcript of microRNA-22-3p. miR-22-3p upregulation by XBP1s or forced expression of miR-22 significantly decreases cell's viability and sensitizes leukemic cells to chemotherapy. We found that miR-22-3p intracellular effects result at least partially from the targeting of the mRNA encoding the deacetylase sirtuin-1 (SIRT1), a well-established pro-survival factor. Therefore, this novel XBP1s/miR-22/SIRT1 axis identified could play a pivotal role in the proliferation and chemotherapeutic response of leukemic cells.

ATF4-mediated different mode of interaction between autophagy and mTOR determines cell fate dependent on the level of ER stress induced by Cr(VI)

Hexavalent chromium [Cr(VI)] exists widely in occupational environments. The mechanistic target of rapamycin (mTOR) has been well-documented to regulate autophagy negatively. However, we found that low concentration of Cr(VI) (0.2 μM) elevated both mTOR and autophagy and promote cell survival. Conversely, high concentration of Cr(VI) (6 μM) caused cell death by inhibiting mTOR and subsequently inducing autophagy. Tunicamycin (Tm), as an Endoplasmic reticulum (ER) stress activator was used to induce mild ER stress at 0.1 μg/ml and it activated both autophagy and mTOR, which also caused cell migration in a similar manner to that observed with low concentration of Cr(VI). Severe ER stress caused by Tm (2 μg/ml) decreased mTOR, increased autophagy and then inhibited cell migration, which was the same as 6 μM Cr(VI) treatment, although Cr(VI) in high concentration inhibited ER stress. Activating transcription factor 4 (ATF4), a downstream target of ER stress, only increased under mild ER stress but decreased under severe ER stress and 6 μM Cr(VI) treatment. Chromatin immunoprecipitation (ChIP) experiment indicated that ATF4 could bind to the promoter of ATG4B and AKT1. To sum up, our data revealed that mild ER stress induced by low concentration of Cr(VI) could enhance transcriptional regulation of ATG4B and AKT1 by ATF4, which induced both autophagy and mTOR to promote cell viability.

Toxicological effects of solvent-extracted organic matter associated with PM2.5 on human bronchial epithelial cell line NL-20

The heterogeneity and complexity of solvent-extracted organic matter associated with PM2.5 (SEOM-PM2.5) is well known; however, there is scarce information on its biological effects in human cells. This work aimed to evaluate the effect of SEOM-PM2.5 collected in northern Mexico City during the cold-dry season (November 2017) on NL-20 cells, a human bronchial epithelial cell line. The SEOM obtained accounted for 15.5% of the PM2.5 mass and contained 21 polycyclic aromatic hydrocarbons (PAHs). The cell viability decreased following exposure to SEOM-PM2.5, and there were noticeable morphological changes such as increased cell size and the presence of cytoplasmic vesicles in cells treated with 5-40 μg/mL SEOM-PM2.5. Exposure to 5 μg/mL SEOM-PM2.5 led to several alterations compared with the control cells, including the induction of double-stranded DNA breaks based (p < 0.001); nuclear fragmentation and an increased mitotic index (p < 0.05); 53BP1 staining, a marker of DNA repair by non-homologous end-joining (p < 0.001); increased BiP protein expression; and reduced ATF6, IRE1α, and PERK gene expression. Conversely, when exposed to 40 μg/mL SEOM-PM2.5, the cells showed an increase in reactive oxygen species formation (p < 0.001), BiP protein expression (p < 0.05), and PERK gene expression (p < 0.05), indicating endoplasmic reticulum stress. Our data suggest concentration-dependent toxicological effects of SEOM-PM2.5 on NL-20 cells, including genotoxicity, genomic instability, and endoplasmic reticulum stress.

Sex-specific and cell-specific regulation of ER stress and neuroinflammation after traumatic brain injury in juvenile mice

Endoplasmic reticulum (ER) stress and neuroinflammation play an important role in secondary brain damage after traumatic brain injury (TBI). Due to the complex brain cytoarchitecture, multiple cell types are affected by TBI. However, cell type-specific and sex-specific responses to ER stress and neuroinflammation remain unclear. Here we investigated differential regulation of ER stress and neuroinflammatory pathways in neurons and microglia during the acute phase post-injury in a mouse model of impact acceleration TBI in both males and females. We found that TBI resulted in significant weight loss only in males, and sensorimotor impairment and depressive-like behaviors in both males and females at the acute phase post-injury. By concurrently isolating neurons and microglia from the same brain sample of the same animal, we were able to evaluate the simultaneous responses in neurons and microglia towards ER stress and neuroinflammation in both males and females. We discovered that the ER stress and anti-inflammatory responses were significantly stronger in microglia, especially in female microglia, compared with the male and female neurons. Whereas the degree of phosphorylated-tau (pTau) accumulation was significantly higher in neurons, compared with the microglia. In conclusion, TBI resulted in behavioral deficits and cell type-specific and sex-specific responses to ER stress and neuroinflammation, and abnormal protein accumulation at the acute phase after TBI in immature mice.

TXNDC5 Plays a Crucial Role in Regulating Endoplasmic Reticulum Activity through Different ER Stress Signaling Pathways in Hepatic Cells

The pathogenesis of non-alcoholic fatty liver disease (NAFLD) is influenced by a number of variables, including endoplasmic reticulum stress (ER). Thioredoxin domain-containing 5 (TXNDC5) is a member of the protein disulfide isomerase family and acts as an endoplasmic reticulum (ER) chaperone. Nevertheless, the function of TXNDC5 in hepatocytes under ER stress remains largely uncharacterized. In order to identify the role of TXNDC5 in hepatic wild-type (WT) and TXNDC5-deficient (KO) AML12 cell lines, tunicamycin, palmitic acid, and thapsigargin were employed as stressors. Cell viability, mRNA, protein levels, and mRNA splicing were then assayed. The protein expression results of prominent ER stress markers indicated that the ERN1 and EIF2AK3 proteins were downregulated, while the HSPA5 protein was upregulated. Furthermore, the ATF6 protein demonstrated no significant alterations in the absence of TXNDC5 at the protein level. The knockout of TXNDC5 has been demonstrated to increase cellular ROS production and its activity is required to maintain normal mitochondrial function during tunicamycin-induced ER stress. Tunicamycin has been observed to disrupt the protein levels of HSPA5, ERN1, and EIF2AK3 in TXNDC5-deficient cells. However, palmitic acid has been observed to disrupt the protein levels of ATF6, HSPA5, and EIF2AK3. In conclusion, TXNDC5 can selectively activate distinct ER stress pathways via HSPA5, contingent on the origin of ER stress. Conversely, the absence of TXNDC5 can disrupt the EIF2AK3 cascade.

Deciphering ER stress-unfolded protein response relationship by visualizing unfolded proteins in the ER

Despite the consensus that accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen, i.e. ER stress, activates the unfolded protein response (UPR), studies under physiological and pathophysiological conditions suggest that ER stress may not always trigger the UPR, and the UPR can be activated in an ER stress-independent way. To better understand how the UPR is regulated and its relationship with ER stress requires direct detection of unfolded proteins in the ER, a method that is still lacking. Here, we report a strategy of visualizing unfolded protein accumulation in the ER lumen in living cells by employing an engineered ER stress sensor, PERK, which forms fluorescence puncta upon unfolded protein binding, in a fast and reversible way. Our reporter enables us to clarify the involvement of unfolded proteins in UPR activation under several physiological conditions and suggests that persistent unfolded protein accumulation in the ER despite UPR attenuation predicts cell death.

Membralin is required for maize development and defines a branch of the endoplasmic reticulum-associated degradation pathway in plants

Endoplasmic reticulum (ER)-associated degradation (ERAD) plays key roles in controlling protein levels and quality in eukaryotes. The Ring Finger Protein 185 (RNF185)/membralin ubiquitin ligase complex was recently identified as a branch in mammals and is essential for neuronal function, but its function in plant development is unknown. Here, we report the map-based cloning and characterization of Narrow Leaf and Dwarfism 1 (NLD1), which encodes the ER membrane-localized protein membralin and specifically interacts with maize homologs of RNF185 and related components. The nld1 mutant shows defective leaf and root development due to reduced cell number. The defects of nld1 were largely restored by expressing membralin genes from Arabidopsis thaliana and mice, highlighting the conserved roles of membralin proteins in animals and plants. The excessive accumulation of β-hydroxy β-methylglutaryl-CoA reductase in nld1 indicates that the enzyme is a membralin-mediated ERAD target. The activation of bZIP60 mRNA splicing-related unfolded protein response signaling and marker gene expression in nld1, as well as DNA fragment and cell viability assays, indicate that membralin deficiency induces ER stress and cell death in maize, thereby affecting organogenesis. Our findings uncover the conserved, indispensable role of the membralin-mediated branch of the ERAD pathway in plants. In addition, ZmNLD1 contributes to plant architecture in a dose-dependent manner, which can serve as a potential target for genetic engineering to shape ideal plant architecture, thereby enhancing high-density maize yields.

Kaempferol attenuates particle-induced osteogenic impairment by regulating ER stress via the IRE1α-XBP1s pathway

Periprosthetic osteolysis and subsequent aseptic loosening are the primary causes of failure following total joint arthroplasty. Wear particle-induced osteogenic impairment is recognized as an important contributing factor in the development of osteolysis, with endoplasmic reticulum (ER) stress emerging as a pivotal underlying mechanism. Hence, searching for potential therapeutic targets and agents capable of modulating ER stress in osteoblasts is crucial for preventing aseptic loosening. Kaempferol (KAE), a natural flavonol compound, has shown promising osteoprotective effects and anti-ER stress properties in diverse diseases. However, the influence of KAE on ER stress-mediated osteogenic impairment induced by wear particles remains unclear. In this study, we observed that KAE effectively relieved TiAl6V4 particles-induced osteolysis by improving osteogenesis in a mouse calvarial model. Furthermore, we demonstrated that KAE could attenuate ER stress-mediated apoptosis in osteoblasts exposed to TiAl6V4 particles, both in vitro and in vivo. Mechanistically, our results revealed that KAE mitigated ER stress-mediated apoptosis by upregulating the IRE1α-XBP1s pathway while concurrently partially inhibiting the IRE1α-regulated RIDD and JNK activation. Collectively, our findings suggest that KAE is a prospective therapeutic agent for treating wear particle-induced osteolysis and highlight the IRE1α-XBP1s pathway as a potential therapeutic target for preventing aseptic loosening.

p20BAP31 promotes cell apoptosis via interaction with GRP78 and activating the PERK pathway in colorectal cancer

Colorectal cancer (CRC) is the second most deadly cancer worldwide. Although various treatments for CRC have made progress, they have limitations. Therefore, the search for new effective molecular targets is important for the treatment of CRC. p20BAP31 induces apoptosis through diverse pathways and exhibits greater sensitivity in CRC. Therefore, a comprehensive exploration of the molecular functions of p20BAP31 is important for its application in anti-tumor therapy. In this study, we showed that exogenous p20BAP31 was still located in the ER and significantly activated the unfolded protein response (UPR) through the PERK pathway. The activation of the PERK pathway is prominent in p20BAP31-induced reactive oxygen species (ROS) accumulation and apoptosis. We found, for the first time, that p20BAP31 leads to ER stress and markedly attenuates tumor cell growth in vivo. Importantly, mechanistic investigations indicated that p20BAP31 competitively binds to GRP78 from PERK and causes hyperactivation of the UPR. Furthermore, p20BAP31 upregulates the expression of GRP78 by promoting HSF1 nuclear translocation and enhancing its binding to the GRP78 promoter. These findings reveal p20BAP31 as a regulator of ER stress and a potential target for tumor therapy, and elucidate the underlying mechanism by which p20BAP31 mediates signal transduction between ER and mitochondria.

IRE1α regulates macrophage polarization in type 2 diabetic periodontitis through promoting endoplasmic reticulum stress

OBJECTIVES

The aim of this study was to investigate the effect of 4μ8c, an inhibitor targeting the endoplasmic reticulum stress-associated factor IRE1α, on macrophage polarization in an experimental model of diabetic periodontitis through ex vivo experiments.

MATERIALS AND METHODS

Local alveolar bone parameters were evaluated using Micro-CT following intraperitoneal administration of 4μ8c in mice with experimental diabetic periodontitis. Surface markers indicating macrophage polarization were identified using immunofluorescence. In vitro experiments were performed employing bone marrow-derived macrophages and gingival fibroblasts. Macrophage polarization was determined using flow cytometry. Principal impacted signaling pathways were identified through Western blot analysis.

RESULTS

Results from both in vitro and in vivo experiments demonstrated that 4μ8c mitigated alveolar bone resorption and inflammation in mice with diabetic periodontitis. Furthermore, it modulated macrophage polarization towards the M2 phenotype and augmented M2 macrophage polarization through the MAPK signaling pathway.

CONCLUSIONS

These findings suggest that inhibiting IRE1α can modulate macrophage polarization and alleviate ligature-induced diabetic periodontitis via the MAPK signaling pathway. This unveils a novel mechanism, offering a scientific foundation for the treatment of experimental diabetic periodontitis.

FICD deficiency protects mice from hypertrophy-induced heart failure via BiP-mediated activation of the UPR ER and ER-phagy

Cardiomyocytes require the HSP70 chaperone BiP to maintain proteostasis in the endoplasmic reticulum (ER) following cardiac stress. The adenylyl transferase (AMPylase) FICD is increasingly recognized to regulate BiP activity through the post-translational addition of an adenosine monophosphate moiety to BiP surface residues. However, the physiological impact of FICD-mediated BiP regulation in the context of cardiovascular health is unknown. Here, we find that FICD deficiency prevents pressure overload-associated heart failure, hypertrophy, and fibrosis, and that FICD knockout mice maintain normal cardiac function after cardiac pressure overload. At a cellular level, we observe that FICD-mediated BiP AMPylation blunts the induction of the unfolded protein response (UPR ER ) and impairs BiP interaction with FAM134B, an ER-phagy receptor, thus limiting ER-phagy induction under stress. In contrast, FICD loss significantly increases BiP-dependent UPR ER induction and ER-phagy in stressed cardiomyocytes. We also uncover cell type-specific consequences of FICD activity in response to ER stress, positioning FICD as a critical proteostasis regulator in cardiac tissue. Our results highlight a novel regulatory paradigm controlling stress resilience in cardiomyocytes and offer a rationale to consider FICD as a therapeutic target to treat cardiac hypertrophy.

Irisin Ameliorate Acute Pancreatitis and Acinar Cell Viability through Modulation of the Unfolded Protein Response (UPR) and PPARγ-PGC1α-FNDC5 Pathways

Acute pancreatitis (AP) entails pancreatic inflammation, tissue damage and dysregulated enzyme secretion, including pancreatic lipase (PL). The role of irisin, an anti-inflammatory and anti-apoptotic cytokine, in AP and exocrine pancreatic stress is unclear. We have previously shown that irisin regulates PL through the PPARγ-PGC1α-FNDC5 pathway. In this study, we investigated irisin and irisin's pathway on AP in in vitro (AR42J-B13) and ex vivo (rat primary acinar) models using molecular, biochemical and immunohistochemistry methodology. Pancreatitis induction (cerulein (cer)) resulted in a significant up-regulation of the PPARγ-PGC1α-FNDC5 axis, PL expression and secretion and endoplasmic reticulum (ER) stress unfolded protein response (UPR) signal-transduction markers (CHOP, XBP-1 and ATF6). Irisin addition in the cer-pancreatitis state resulted in a significant down-regulation of the PPARγ-PGC1α-FNDC5 axis, PPARγ nucleus-translocation and inflammatory state (TNFα and IL-6) in parallel to diminished PL expression and secretion (in vitro and ex vivo models). Irisin addition up-regulated the expression of pro-survival UPR markers (ATF6 and XBP-1) and reduced UPR pro-apoptotic markers (CHOP) under cer-pancreatitis and induced ER stress (tunicamycin), consequently increasing cells viability. Irisin's pro-survival effect under cer-pancreatitis state was abolished under PPARγ inhibition. Our findings suggest irisin as a potential therapeutic option for AP via its ability to up-regulate pro-survival UPR signals and activate the PPARγ-PGC1α-FNDC5 pathway.