A guide to assessing endoplasmic reticulum homeostasis and stress in mammalian systems

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.

A rare missense p.C125Y mutation in the TNFRSF1A gene identified in a Chinese family with tumor necrosis factor receptor-associated periodic fever syndrome

Background

Tumor necrosis factor receptor-associated periodic syndrome (TRAPS) is a rare autosomal dominant disorder with a low incidence in Asia. The most frequent clinical manifestations include fever, rash, myalgia, joint pain and abdominal pain. Misdiagnosis rates are high because of the clinical and genetic variability of the disease. The pathogenesis of TRAPS is complex and yet to be fully defined. Early genetic diagnosis is the key to precise treatment.

Methods

In this study, a Chinese family with suspected TRAPS were analyzed by genome-wide SNP genotyping, linkage analysis and targeted sequencing for identification of mutations in causative genes. To study the pathogenicity of the identified gene mutation, we performed a conservation analysis of the mutation site and protein structure analysis. Flow cytometry was used to detect TNFRSF1A shedding and quantitative real-time PCR were used to assess the activation of unfolded protein response (UPR) in the mutation carriers and healthy individuals.

Results

A typical TRAPS family history, with a pattern of autosomal dominant inheritance, led to the identification of a rare mutation in the TNFRSF1A gene (c.G374A [p.Cys125Tyr]) with unknown significance. The patient responded well to corticosteroids, and long-term therapy with colchicine effectively reduced the inflammatory attacks. No amyloid complications occurred during the 6-year follow-up. In silico protein analysis showed that the mutation site is highly conversed and the mutation prevents the formation of intrachain disulfide bonds in the protein. Despite a normal shedding of the TNFRSF1A protein from stimulated monocytes in the TRAPS patients with p.C125Y mutation, the expression of CHOP and the splicing of XBP1 was significantly higher than healthy controls, suggesting the presence of an activation UPR.

Conclusion

This is the first report of a Chinese family with the rare p.C125Y mutation in TNFRSF1A. The p.C125Y mutation does not result in aberrant receptor shedding, but instead is associated with an activated UPR in these TRAPS patients, which may provide new insights into the pathogenesis of this rare mutation in TRAPS.

RNASeq highlights ATF6 pathway regulators for CHO cell engineering with different impacts of ATF6β and WFS1 knockdown on fed-batch production of IgG1

Secretion levels required of industrial Chinese hamster ovary (CHO) cell lines can challenge endoplasmic reticulum (ER) homeostasis, and ER stress caused by accumulation of misfolded proteins can be a bottleneck in biomanufacturing. The unfolded protein response (UPR) is initiated to restore homeostasis in response to ER stress, and optimization of the UPR can improve CHO cell production of therapeutic proteins. We compared the fed-batch growth, production characteristics, and transcriptomic response of an immunoglobulin G1 (IgG1) producer to its parental, non-producing host cell line. We conducted differential gene expression analysis using high throughput RNA sequencing (RNASeq) and quantitative polymerase chain reaction (qPCR) to study the ER stress response of each cell line during fed-batch culture. The UPR was activated in the IgG1 producer compared to the host cell line and our analysis of differential expression profiles indicated transient upregulation of ATF6α target mRNAs in the IgG1 producer, suggesting two upstream regulators of the ATF6 arm of the UPR, ATF6β and WFS1, are rational engineering targets. Although both ATF6β and WFS1 have been reported to negatively regulate ATF6α, this study shows knockdown of either target elicits different effects in an IgG1-producing CHO cell line. Stable knockdown of ATF6β decreased cell growth without decreasing titer; however, knockdown of WFS1 decreased titer without affecting growth. Relative expression measured by qPCR indicated no direct relationship between ATF6β and WFS1 expression, but upregulation of WFS1 in one pool was correlated with decreased growth and upregulation of ER chaperone mRNAs. While knockdown of WFS1 had negative impacts on UPR activation and product mRNA expression, knockdown of ATF6β improved the UPR specifically later in fed-batch leading to increased overall productivity.

Natural compound Alternol actives multiple endoplasmic reticulum stress-responding pathways contributing to cell death

Background: Alternol is a small molecular compound isolated from the fermentation of a mutant fungus obtained from Taxus brevifolia bark. Our previous studies showed that Alternol treatment induced reactive oxygen species (ROS)-dependent immunogenic cell death. This study conducted a comprehensive investigation to explore the mechanisms involved in Alternol-induced immunogenic cell death. Methods: Prostate cancer PC-3, C4-2, and 22RV1 were used in this study. Alternol interaction with heat shock proteins (HSP) was determined using CETSA assay. Alternol-regulated ER stress proteins were assessed with Western blot assay. Extracellular adenosine triphosphate (ATP) was measured using ATPlite Luminescence Assay System. Results: Our results showed that Alternol interacted with multiple cellular chaperone proteins and increased their expression levels, including endoplasmic reticulum (ER) chaperone hypoxia up-regulated 1 (HYOU1) and heat shock protein 90 alpha family class B member 1 (HSP90AB1), as well as cytosolic chaperone heat shock protein family A member 8 (HSPA8). These data represented a potential cause of unfolded protein response (UPR) after Alternol treatment. Further investigation revealed that Alternol treatment triggered ROS-dependent (ER) stress responses via R-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α). The double-stranded RNA-dependent protein kinase (PKR) but not activating transcription factor 6 (ATF6) cascades, leading to ATF-3/ATF-4 activation, C/EBP-homologous protein (CHOP) overexpression, and X-box binding protein XBP1 splicing induction. In addition, inhibition of these ER stress responses cascades blunted Alternol-induced extracellular adenosine triphosphate (ATP) release, one of the classical hallmarks of immunogenic cell death. Conclusion: Taken together, our data demonstrate that Alternol treatment triggered multiple ER stress cascades, leading to immunogenic cell death.

An increase in ER stress and unfolded protein response in iPSCs-derived neuronal cells from neuronopathic Gaucher disease patients

Gaucher disease (GD) is a lysosomal storage disorder caused by a mutation in the GBA1 gene, responsible for encoding the enzyme Glucocerebrosidase (GCase). Although neuronal death and neuroinflammation have been observed in the brains of individuals with neuronopathic Gaucher disease (nGD), the exact mechanism underlying neurodegeneration in nGD remains unclear. In this study, we used two induced pluripotent stem cells (iPSCs)-derived neuronal cell lines acquired from two type-3 GD patients (GD3-1 and GD3-2) to investigate the mechanisms underlying nGD by biochemical analyses. These iPSCs-derived neuronal cells from GD3-1 and GD3-2 exhibit an impairment in endoplasmic reticulum (ER) calcium homeostasis and an increase in unfolded protein response markers (BiP and CHOP), indicating the presence of ER stress in nGD. A significant increase in the BAX/BCL-2 ratio and an increase in Annexin V-positive cells demonstrate a notable increase in apoptotic cell death in GD iPSCs-derived neurons, suggesting downstream signaling after an increase in the unfolded protein response. Our study involves the establishment of iPSCs-derived neuronal models for GD and proposes a possible mechanism underlying nGD. This mechanism involves the activation of ER stress and the unfolded protein response, ultimately leading to apoptotic cell death in neurons.

PBA alleviates cadmium-induced mouse spermatogonia apoptosis by suppressing endoplasmic reticulum stress

OBJECTIVE

Endoplasmic reticulum (ER) stress mediates Cd-caused germ cell apoptosis in testis. The effects of 4-phenylbutyric acid (PBA), a classical chaperone, were investigated on Cd-induced apoptosis in mouse GC-1 spermatogonia cells.

METHODS

The cells were pretreated with PBA before Cd exposure. TUNEL and flow cytometry assays were applied to determine apoptosis. Some key biomarkers of ER stress were analyzed using RT-PCR and western blot.

RESULTS

as expected, the apoptotic cells exposed to Cd apparently increased. The mRNA and protein expression levels of GRP78 and ATF6α, were elevated in the Cd groups. Additional experiments displayed that Cd notably increased IRE1α and JNK phosphorylation, and upregulated XBP-1 mRNA and protein expression. Moreover, p-eIF2α and CHOP expressions were clearly elevated in the Cd groups. Interestingly, PBA almost completely inhibited ER stress and protected spermatogonia against apoptosis induced by Cd.

CONCLUSION

PBA alleviated Cd-induced ER stress and spermatogonia apoptosis, and may have the therapeutic role in Cd-induced male reproductive toxicity.

Unraveling the interplay between vital organelle stress and oxidative stress in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease characterized by excessive accumulation of extracellular matrix, leading to irreversible fibrosis. Emerging evidence suggests that endoplasmic reticulum (ER) stress, mitochondrial stress, and oxidative stress pathways play crucial roles in the pathogenesis of IPF. ER stress occurs when the protein folding capacity of the ER is overwhelmed, triggering the unfolded protein response (UPR) and contributing to protein misfolding and cellular stress in IPF. Concurrently, mitochondrial dysfunction involving dysregulation of key regulators, including PTEN-induced putative kinase 1 (PINK1), Parkin, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and sirtuin 3 (SIRT3), disrupts mitochondrial homeostasis and impairs cellular energy metabolism. This leads to increased reactive oxygen species (ROS) production, release of pro-fibrotic mediators, and activation of fibrotic pathways, exacerbating IPF progression. The UPR-induced ER stress further disrupts mitochondrial metabolism, resulting in altered mitochondrial mechanisms that increase the generation of ROS, resulting in further ER stress, creating a feedback loop that contributes to the progression of IPF. Oxidative stress also plays a pivotal role in IPF, as ROS-mediated activation of TGF-β, NF-κB, and MAPK pathways promotes inflammation and fibrotic responses. This review mainly focuses on the links between ER stress, mitochondrial dysfunctions, and oxidative stress with different signaling pathways involved in IPF. Understanding these mechanisms and targeting key molecules within these pathways may offer promising avenues for intervention.

DUSP1 mRNA modulation during porcine circovirus type 2 and porcine reproductive and respiratory syndrome virus co-infection regulates viruses replication

The effects of porcine circovirus type 2b (PCV2b) and porcine reproductive and respiratory syndrome virus (PRRSV) co-infection in epithelial cells of the swine respiratory tract is unknown. In the present study, the newborn pig trachea cell line NPTr-CD163, which is permissive to both viruses, was persistently infected with PCV2b and then with PRRSV. Viral replication, cell viability, cytokines' mRNA expression, and modulation of cellular genes expression were evaluated in infected cells. In NPTr-CD163 co-infection model, PCV2b replication was enhanced while PRRSV replication was suppressed. Cell viability was significantly decreased during PCV2b single infection and co-infection compared to mock-infected and PRRSV single infected cells. However, no difference was observed in cell viability between PCV2b and PCV2b/PRRSV infected cells. The IL6, IL8 and IL10 mRNA expression was significantly higher in co-infected cells compared to PCV2b and PRRSV single infected cells. Moreover, the IFN-α/β expression was significantly reduced in co-infected cells compared to PCV2b infected cells whereas it remained higher compared to PRRSV infected cells. The differential gene expression analysis revealed that the mRNA expression level of the cellular gene DUSP1 was significantly higher in all PRRSV infection models compared to PCV2b single infected cells. Knockdown of DUSP1 expression in co-infected cells significantly reduced PCV2b replication, suggesting a role for DUSP1 in PCV2b/PRRSV pathogenesis.

Performance of Green Desymmetrization Methods toward Bioactive Cephalostatin Analogues

Since the discovery of cephalostatins, which have shown remarkable activity against human cancer cells, they have attracted the attention of researchers to target the synthesis of such impressive, complicated molecules using the green desymmetrization approach. In the current review, we report the progress in the desymmetrization of symmetrical bis-steroidal pyrazines (BSPs) as an approach toward potentially active anti-- cancer agents, namely cephalostatins/ ritterazines. The achievement of synthesizing a gram-scaled prodrug with comparable activity to the potent natural cephalostatins using green methods is our primary target. These synthetic methods can be scaled up based on the symmetrical coupling (SC) of two steroidal units of the same type. Our secondary target is the discovery of new green pathways that help in structural reconstruction programming toward the total synthesis of at least one potentially active family member. The strategy is based on functional group interconversions with high flexibility and brevity using green selective methods. The introduction of controlling groups using nontrivial reconstruction methodologies forms the backbone of our work. After certain modifications to the symmetrical BSP starting material, the resulting analogs underwent several chemoselective transformations through three main routes in rings F, D, and C. One of these routes is the chemoselective spiroketal opening (ring-F). The second route was the functionalization of the Δ14,15 bond (ring-D), including chlorination/dechlorination, in addition to epoxidation/ oxygenation processes. Finally, the introduction of the C-11 methoxy group as a directing group on ring-C led to several chemoselective transformations. Moreover, certain transformations on C-12 (ring-C), such as methylenation, followed by hydroboration- oxidation, led to a potentially active analog. The alignment of these results directs us toward the targets. Our efforts culminated in preparing effective anti-cancer prodrugs (8, 24, 30, and 31), which are able to overcome cancer drug resistance (chemoresistance) by inducing the atypical endoplasmic reticulum-mediated apoptosis pathway, which works through the release of Smac/Diablo and the activation of caspase-4.

DNAJB12 and DNJB14 are non-redundant Hsp40 redox chaperones involved in endoplasmic reticulum protein reflux

BACKGROUND

The endoplasmic reticulum (ER) transmembrane chaperones DNAJB12(B12) and DNAJB14(B14) are cofactors that cooperate with cytosolic Heat Shock-70 protein (HSC70) facilitating folding/degradation of nascent membrane proteins and supporting the ER-membrane penetration of viral particles. Here, we assessed structural/functional features of B12/B14 with respect to their regulation by ER stress and their involvement in ER stress-mediated protein reflux.

METHODS

We investigated the effect of Unfolded Protein Response(UPR)-eliciting drugs on the expression/regulation of B12-B14 and their roles in ER-to-cytosol translocation of Protein Disulfide Isomerase-A1(PDI).

RESULTS

We show that B12 and B14 are similar but do not seem redundant. They share predicted structural features and show high homology of their cytosolic J-domains, while their ER-lumen DUF1977 domains are quite dissimilar. Interactome analysis suggested that B12/B14 associate with different biological processes. UPR activation did not significantly impact on B12 gene expression, while B14 transcripts were up-regulated. Meanwhile, B12 and B14 (33.4 kDa isoform) protein levels were degraded by the proteasome upon acute reductive challenge. Also, B12 degradation was impaired upon sulfenic-acid trapping by dimedone. We originally report that knockdown of B12/B14 and their cytosolic partner SGTA in ER-stressed cells significantly impaired the amount of the ER redox-chaperone PDI in a cytosolic-enriched fraction. Additionally, B12 but not B14 overexpression increased PDI relocalization in non-stressed cells.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Our findings reveal that B12/B14 regulation involves thiol redox processes that may impact on their stability and possibly on physiological effects. Furthermore, we provide novel evidence that these proteins are involved in UPR-induced ER protein reflux.

Endoplasmic Reticulum Stress and Its Impact on Adipogenesis: Molecular Mechanisms Implicated

Endoplasmic reticulum (ER) stress plays a pivotal role in adipogenesis, which encompasses the differentiation of adipocytes and lipid accumulation. Sustained ER stress has the potential to disrupt the signaling of the unfolded protein response (UPR), thereby influencing adipogenesis. This comprehensive review illuminates the molecular mechanisms that underpin the interplay between ER stress and adipogenesis. We delve into the dysregulation of UPR pathways, namely, IRE1-XBP1, PERK and ATF6 in relation to adipocyte differentiation, lipid metabolism, and tissue inflammation. Moreover, we scrutinize how ER stress impacts key adipogenic transcription factors such as proliferator-activated receptor γ (PPARγ) and CCAAT-enhancer-binding proteins (C/EBPs) along with their interaction with other signaling pathways. The cellular ramifications include alterations in lipid metabolism, dysregulation of adipokines, and aged adipose tissue inflammation. We also discuss the potential roles the molecular chaperones cyclophilin A and cyclophilin B play in adipogenesis. By shedding light on the intricate relationship between ER stress and adipogenesis, this review paves the way for devising innovative therapeutic interventions.

The interaction network of the proteasome assembly chaperone PSMD9 regulates proteostasis

Functional networks in cells are created by physical, genetic, and regulatory interactions. Mapping them and annotating their functions by available methods remains a challenge. We use affinity purification mass spectrometry (AP-MS) coupled with SLiMFinder to discern such a network involving 26S proteasome non-ATPase regulatory subunit 9 (PSMD9), a chaperone of proteasome assembly. Approximately 20% of proteins within the PSMD9 interactome carry a short linear motif (SLiM) of the type 'EXKK'. The binding of purified PSMD9 with the peptide sequence ERKK, proteins heterogeneous nuclear ribonucleoproteins A2/B1 (hnRNPA2B1; containing ERKK), and peroxiredoxin-6 (PRDX6; containing EAKK) provided proof of principle for this motif-driven network. The EXKK motif in the peptide primarily interacts with the coiled-coil N domain of PSMD9, a unique interaction not reported for any coiled-coil domain. PSMD9 knockout (KO) HEK293 cells experience endoplasmic reticulum (ER) stress and respond by increasing the unfolded protein response (UPR) and reducing the formation of aggresomes and lipid droplets. Trans-expression of PSMD9 in the KO cells rescues lipid droplet formation. Overexpression of PSMD9 in HEK293 cells results in reduced UPR, and increased lipid droplet and aggresome formation. The outcome argues for the prominent role of PSMD9 in maintaining proteostasis. Probable mechanisms involve the binding of PSMD9 to binding immunoglobulin protein (BIP/GRP78; containing EDKK), an endoplasmic reticulum chaperone and key regulator of the UPR, and fatty acid synthase (FASN; containing ELKK), involved in fatty acid synthesis/lipid biogenesis. We propose that PSMD9 acts as a buffer in the cellular milieu by moderating the UPR and enhancing aggresome formation to reduce stress-induced proteotoxicity. Akin to waves created in ponds that perpetuate to a distance, perturbing the levels of PSMD9 would cause ripples down the networks, affecting final reactions in the pathway, one of which is altered proteostasis.

Silicon dioxide-induced endoplasmic reticulum stress of alveolar macrophages and its role on the formation of silicosis fibrosis: a review article

Silicosis is a chronic lung inflammatory disease induced by long-term inhalation of high concentrations of silicon dioxide (SiO2), characterized by pulmonary fibrosis. Inhalation of silica invades alveolar macrophages (AMs) and changes the micro-environment of the cell, resulting in abnormal morphology and dysfunction of the endoplasmic reticulum (ER). Once beyond the range of cell regulation, the endoplasmic reticulum stress (ERS) will occur, which will lead to cell damage, necrosis, and apoptosis, eventually causing silicosis fibrosis through various mechanisms. This is a complex and delicate process accompanied by various macrophage-derived cytokines. Unfortunately, the details have not been systematically summarized yet. In this review, we systematically introduce the basic two processes: the process of inducing ERS by inhaling SiO2 and the process of inducing pulmonary fibrosis by ERS. Moreover, the underlying mechanism of the above two sequential events is also be discussed. We conclude that the ERS of alveolar macrophages caused by silica dust are involved deeply in the pathogenesis of silicosis. Therefore, changing the states of SiO2-induced ERS of macrophage may be an attractive therapeutic target for silicosis fibrosis.

The Role of Endoplasmic Reticulum Stress in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD), which is involved in osteogenic reprogramming of valvular interstitial cells, is the most common form of valve disease. It still lacks effective pharmacologic intervention, as its cellular biological mechanisms remain unclear. Congenital abnormality (bicuspid valve) and older age are considered to be the most powerful risk factors for CAVD. Aortic valve sclerosis (AVS) and calcific aortic stenosis (CAS), 2 subclinical forms of CAVD, represent 2 distinct stages of aortic valve calcification. During the AVS stage, the disease is characterised by endothelial activation/damage, inflammatory response, and lipid infiltration accompanied by microcalcification. The CAS stage is dominated by calcification, resulting in valvular dysfunction and severe obstruction to cardiac outflow, which is life threatening if surgery is not performed in time. Endoplasmic reticulum (ER) stress, a state in which conditions disrupting ER homeostasis cause an accumulation of unfolded and misfolded proteins in the ER lumen, has been shown to promote osteogenic differentiation and aortic valve calcification. Therefore, identifying targets or drugs for suppressing ER stress may be a novel approach for CAVD treatment.

Different Dietary Sources of Selenium Alleviate Hepatic Lipid Metabolism Disorder of Heat-Stressed Broilers by Relieving Endoplasmic Reticulum Stress

As global warming continues, the phenomenon of heat stress (HS) in broilers occurs frequently. The alleviating effect of different selenium (Se) sources on HS-induced hepatic lipid metabolism disorders in broilers remains unclear. This study compared the protective effects of four Se sources (sodium selenite; selenium yeast; selenomethionine; nano-Se) on HS-induced hepatic lipid metabolism disorder and the corresponding response of selenotranscriptome in the liver of broilers. The results showed that HS-induced liver injury and hepatic lipid metabolism disorder, which were reflected in the increased activity of serum alanine aminotransferase (ALT), the increased concentration of triacylglycerol (TG) and total cholesterol (TC), the increased activity of acetyl-CoA carboxylase (ACC), diacylglycerol O-acyltransferase (DGAT) and fatty acid synthase (FAS), and the decreased activity of hepatic lipase (HL) in the liver. The hepatic lipid metabolism disorder was accompanied by the increased mRNA expression of lipid synthesis related-genes, the decreased expression of lipidolysis-related genes, and the increased expression of endoplasmic reticulum (ER) stress biomarkers (PERK, IRE1, ATF6, GRP78). The dietary supplementation of four Se sources exhibited similar protective effects. Four Se sources increased liver Se concentration and promoted the expression of selenotranscriptome and several key selenoproteins, enhanced liver antioxidant capacity and alleviated HS-induced ER stress, and thus resisted the hepatic lipid metabolism disorders of broilers exposed to HS. In conclusion, dietary supplementation of four Se sources (0.3 mg/kg) exhibited similar protective effects on HS-induced hepatic lipid metabolism disorders of broilers, and the protective effect is connected to the relieving of ER stress.

Role of endoplasmic reticulum stress-related unfolded protein response and its implications in dengue virus infection for biomarker development

Dengue virus (DENV) causes debilitating disease in humans, which varies at different rates in host cells, such as monocytes, macrophages, dendritic cells, Langerhans cells, and other cell types. Such heterogeneity in DENV infection in cells could be attributed to a range of factors, including host cell immune response, anti-viral cellular proteins, and virus mediated cellular autophagy. This review delineates an important feature of every cell, the unfolded protein response (UPR) that is attributed to the accumulation of several viral and unfolded/misfolded proteins, such as in DENV infection. UPR is a normal process to counteract endoplasmic reticulum (ER) stress that leads to cell autophagy; though the phenomenon is markedly upregulated during DENV infection. This could be attributed to the uncontrolled activation of the key UPR signaling pathways: inositol-requiring transmembrane kinase/endoribonuclease 1 (IRE1), protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), and activating transcription factor-6 (ATF6), which promote cell autophagy under normal and diseased conditions through the downstream regulation of apoptosis promoting factors such as X-box binding protein (XBP1), GADD34, and ATF-6. Because DENV can modulate these signaling cascades, by promoting dysregulated cell autophagy, the ER stress mediated UPR pathways and the inherent agents could play an important role in delineating the severity of dengue infection with a potential for developing DENV targeted therapeutics.

Cadmium-induced pyroptosis is mediated by PERK/TXNIP/NLRP3 signaling in SH-SY5Y cells

Cadmium (Cd) is a hypertoxic heavy metal that may be exposed to environmental pollutants by humans and animals. It can lead to cognitive disfunction, and is linked to neurodegenerative diseases. Cadmium reportedly can induce endoplasmic reticulum (ER) stress, but few studies have concentrated on it in nerve cells, and the connection between ER stress and neuroinflammation. In this study, in vitro experiments on SH-SY5Y neuroblastoma cells were carried out. We aimed at exploring whether Cd attributed to the cell pyroptosis and the role of PERK in promoting this form of cell damage which can induce strong inflammatory responses. Our results demonstrated that CdCl2 treatment induced excess reactive oxygen species (ROS) production, caused significant modifications in the expression of PERK and increased TXNIP, NLRP3, IL-1β, IL-18, and caspase1 in SH-SY5Y cells. In addition, scavenging ROS with N-acetylcysteine or inhibiting the expression of PERK by using GSK2606414, rescued the SH-SY5Y cells from cadmium-induced pyroptosis. In conclusion, the results suggest that Cd induces pyroptotic death of SH-SY5Y cells through ER stress, and this may be the potential mechanism of Cd incurring neurological diseases.

Inflammatory ER stress responses dictate the immunopathogenic progression of systemic candidiasis

Recognition of pathogen-associated molecular patterns can trigger the inositol-requiring enzyme 1 α (IRE1α) arm of the endoplasmic reticulum (ER) stress response in innate immune cells. This process maintains ER homeostasis and also coordinates diverse immunomodulatory programs during bacterial and viral infections. However, the role of innate IRE1α signaling in response to fungal pathogens remains elusive. Here, we report that systemic infection with the human opportunistic fungal pathogen Candida albicans induced proinflammatory IRE1α hyperactivation in myeloid cells that led to fatal kidney immunopathology. Mechanistically, simultaneous activation of the TLR/IL-1R adaptor protein MyD88 and the C-type lectin receptor dectin-1 by C. albicans induced NADPH oxidase-driven generation of ROS, which caused ER stress and IRE1α-dependent overexpression of key inflammatory mediators such as IL-1β, IL-6, chemokine (C-C motif) ligand 5 (CCL5), prostaglandin E2 (PGE2), and TNF-α. Selective ablation of IRE1α in leukocytes, or treatment with an IRE1α pharmacological inhibitor, mitigated kidney inflammation and prolonged the survival of mice with systemic C. albicans infection. Therefore, controlling IRE1α hyperactivation may be useful for impeding the immunopathogenic progression of disseminated candidiasis.

Macrophage Reprogramming via the Modulation of Unfolded Protein Response with siRNA-Loaded Magnetic Nanoparticles in a TAM-like Experimental Model

New therapeutic strategies are required in cancer therapy. Considering the prominent role of tumor-associated macrophages (TAMs) in the development and progression of cancer, the re-education of TAMs in the tumor microenvironment (TME) could represent a potential approach for cancer immunotherapy. TAMs display an irregular unfolded protein response (UPR) in their endoplasmic reticulum (ER) to endure environmental stress and ensure anti-cancer immunity. Therefore, nanotechnology could be an attractive tool to modulate the UPR in TAMs, providing an alternative strategy for TAM-targeted repolarization therapy. Herein, we developed and tested polydopamine-coupled magnetite nanoparticles (PDA-MNPs) functionalized with small interfering RNAs (siRNA) to downregulate the protein kinase R (PKR)-like ER kinase (PERK) expression in TAM-like macrophages derived from murine peritoneal exudate (PEMs). After the evaluation of the cytocompatibility, the cellular uptake, and the gene silencing efficiency of PDA-MNPs/siPERK in PEMs, we analyzed their ability to re-polarize in vitro these macrophages from M2 to the M1 inflammatory anti-tumor phenotype. Our results indicate that PDA-MNPs, with their magnetic and immunomodulator features, are cytocompatible and able to re-educate TAMs toward the M1 phenotype by PERK inhibition, a UPR effector contributing to TAM metabolic adaptation. These findings can provide a novel strategy for the development of new tumor immunotherapies in vivo.

Phytohormones Affect Differentiation Status of Human Skin Fibroblasts via UPR Activation

Normalization of secretory activity and differentiation status of mesenchymal cells, including fibroblasts, is an important biomedical problem. One of the possible solutions is modulation of unfolded protein response (UPR) activated during fibroblast differentiation. Here, we investigated the effect of phytohormones on the secretory activity and differentiation of cultured human skin fibroblasts. Based on the analysis of expression of genes encoding UPR markers, abscisic acid (ABA) upregulated expression of the GRP78 and ATF4 genes, while gibberellic acid (GA) upregulated expression of CHOP. Evaluation of the biosynthetic activity of fibroblasts showed that ABA promoted secretion and synthesis of procollagen I and synthesis of fibronectin, as well as the total production of collagen and non-collagen proteins of the extracellular matrix (ECM). ABA also stimulated the synthesis of smooth muscle actin α (α-SMA), which is the marker of myofibroblasts, and increased the number of myofibroblasts in the cell population. On the contrary, GA increased the level of fibronectin secretion, but reduced procollagen I synthesis and the total production of the ECM collagen proteins. GA downregulated the synthesis of α-SMA and decreased the number of myofibroblasts in the cell population. Our results suggest that phytohormones modulate the biosynthetic activity of fibroblasts and affect their differentiation status.

Molecular Mechanism of Tocotrienol-Mediated Anticancer Properties: A Systematic Review of the Involvement of Endoplasmic Reticulum Stress and Unfolded Protein Response

BACKGROUND

Tocotrienol, a type of vitamin E, is well known for its anti-cancer and other biological activities. This systematic review aims to summarize the involvement of endoplasmic reticulum stress (ERS) and subsequent unfolded protein response (UPR) as the underlying molecular mechanisms for the anticancer properties of tocotrienol.

METHOD

A comprehensive literature search was performed in March 2023 using the PubMed, Scopus, Web of Science, and EMBASE databases. In vitro, in vivo, and human studies were considered.

RESULT

A total of 840 articles were retrieved during the initial search, and 11 articles that fit the selection criteria were included for qualitative analysis. The current mechanistic findings are based solely on in vitro studies. Tocotrienol induces cancer cell growth arrest, autophagy, and cell death primarily through apoptosis but also through paraptosis-like cell death. Tocotrienol-rich fractions, including α-, γ- and δ-tocotrienols, induce ERS, as evidenced by upregulation of UPR markers and/or ERS-related apoptosis markers. Early endoplasmic reticulum calcium ion release, increased ceramide level, proteasomal inhibition, and upregulation of microRNA-190b were suggested to be essential in modulating tocotrienol-mediated ERS/UPR transduction. Nevertheless, the upstream molecular mechanism of tocotrienol-induced ERS is largely unknown.

CONCLUSION

ERS and UPR are essential in modulating tocotrienol-mediated anti-cancer effects. Further investigation is needed to elucidate the upstream molecular mechanism of tocotrienol-mediated ERS.

LINP1 represses unfolded protein response by directly inhibiting eIF2α phosphorylation to promote cutaneous squamous cell carcinoma

BACKGROUND

Endoplasmic reticulum stress (ER stress) may destroy endoplasmic reticulum homeostasis (ER homeostasis) and leads to programmable cell death. Unfolded protein response (UPR) originally stimulated by ER stress is critical for the survival of tumor cells through trying to re-establish ER homeostasis as an adaption to harsh microenvironment. However, mechanisms involving key regulators in modulating UPR remain underexplored.

METHODS

The expression of LINP1 in cutaneous squamous cell carcinoma (cSCC) tissues and cell lines was assessed. Subsequently, LINP1 was knocked out, knocked down or overexpressed in cSCC cells. CCK-8 assays, colony forming assays, transwell migration assays and invasiveness measurement by matrigel-coated transwell were performed to examine the role of LINP1 in cSCC development through gain-of-function and loss-of-function experiments. Transcriptomic sequencing (RNA-Seq) was conducted and indicated the key downstream signaling events regulated by LINP1 including UPR and apoptosis signaling. Furthermore, the direct interaction between LINP1 and eIF2α to modulate UPR and apoptosis was confirmed by RNA pulldown, RNA immunoprecipitation (RIP), ChIP-qPCR and in vitro phosphorylation assays.

RESULTS

In this study, LncRNA in non-homologous end joining pathway 1 (LINP1) was identified to be one of the top ten highest-expressed LncRNAs in cSCC, the second most common cancer in the world. Functional studies using in vitro and in vivo models revealed that LINP1 functions as an oncogene to promote cell proliferation, colony formation, migration and invasiveness while inhibiting cell apoptosis in cSCC. Transcriptomic sequencing after knockdown of LINP1 indicated LINP1 negatively regulates UPR-related pathways involving key effectors for activating UPR and the apoptosis following the prolonged UPR. Mechanistic study showed LINP1 physically interacts with eIF2α to inhibit its phosphorylation for avoiding unmitigated UPR. Loss of LINP1 followed by enhanced eIF2α phosphorylation led to overactivated UPR and induced DDIT3 expression, contributing to ER stress-induced apoptosis and suppression of cSCC development.

CONCLUSIONS

Our findings demonstrate a novel regulatory hierarchy of UPR by demonstrating LINP1 as a critical modulator for eIF2α phosphorylation and a suppressor of UPR-mediated apoptosis, which suggests a novel therapeutic target for cSCC treatment.

Tunicamycin induces depression-like behaviors in male rats, accompanied by initiated chaperon-mediated autophagy and decreased synaptic protein expression in the hippocampus

BACKGROUND AND AIM

Endoplasmic reticulum (ER) stress participates in the occurrence and development of depression, but the underlying mechanism is not fully understood. This study aimed to investigate the behavioral performance and intracerebral molecular changes in an ER stress model of male rats.

METHODS

Intrahippocampal injection of tunicamycin (TM) was performed on male rats as a model of ER stress. The body weight was determined, and behavioral tests, including sucrose preference test (SPT), open field test (OFT), and forced swimming test (FST), were performed to evaluate depressive and anxiety-like phenotypes within 8 days after injection. The levels of chaperone-mediated autophagy (CMA), synaptic proteins, and neuroinflammation related factors in this model were measured via real-time quantitative PCR and Western blot analysis.

RESULTS

Intrahippocampal injection of TM (2 or 1 μg) induced depression-like behaviors in rats, as indicated by the reduced body weight, sucrose preference in SPT, central time in OFT, and increased immobility time in FST. The mRNA and protein levels of GRP78, ATF4, CHOP, LAMP2A, IL-1β, IL-6, and TNF-α were significantly increased, while the expressions of MEF2D, PSD95, SYN, p-CREB (Ser133), and BDNF were significantly decreased in the hippocampus in the model group compared with the sham group.

CONCLUSIONS

These results confirmed that intrahippocampal injection of TM was a valid method to induce an ER stress rat model with depression-like behaviors accompanied by decreased synaptic protein expression and neuroinflammation. The alteration in CMA-related proteins in this ER stress depression model indicated the involvement of CMA in the development of depression.

Ammonium induces oxidative stress, endoplasmic reticulum stress, and apoptosis of hepatocytes in the liver cell line of grass carp (Ctenopharyngodon idella)

Under unfavorable agricultural conditions, ammonia toxicity has become a major problem, resulting in a large number of deaths. Ammonia has been shown to be hepatotoxic. Research has also shown that ammonia can damage the livers of carp, but the mechanism is unclear. In this study, normal grass carp hepatocytes (L8824) were exposed to ammonia water to investigate the effect of ammonia on hepatocyte injury and apoptosis and its mechanism. The results showed that ammonia (50 mM) reduced the viability of L8824 cells and increased glutamic pyruvic transaminase (ALT, up 144.95%, P < 0.01) and glutamic oxalacetic transaminase (AST, up 65.27%, P < 0.01). Furthermore, exposure to ammonia induced oxidative stress and endoplasmic reticulum (ER) stress in L8824 cells. Elevated levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and decreased mitochondrial membrane potential indicated that L8824 cells suffered oxidative damage. Endoplasmic reticulum stress manifests as increased expression degrees of PERK, ATF4, and IRE-1α. These results confirmed the toxicity of ammonia to hepatocytes. In addition, the rate of apoptosis in L8824 cells was increased 69.66% after exposure to ammonia (50 mM, P < 0.01). However, pretreatment of L8824 cells with ER stress inhibitor 2-APB reduced ammonia-induced calcium release (26.50%, P < 0.01) in endoplasmic reticulum. These results indicate that ammonia can exert toxic effects on L8824 cells through inducing endoplasmic reticulum stress and oxidative stress, resulting in apoptosis in L8824 cells.

Dysregulated UPR and ER Stress Related to a Mutation in the Sdf2l1 Gene Are Involved in the Pathophysiology of Diet-Induced Diabetes in the Cohen Diabetic Rat

The Cohen Diabetic rat is a model of type 2 diabetes mellitus that consists of the susceptible (CDs/y) and resistant (CDr/y) strains. Diabetes develops in CDs/y provided diabetogenic diet (DD) but not when fed regular diet (RD) nor in CDr/y given either diet. We recently identified in CDs/y a deletion in Sdf2l1, a gene that has been attributed a role in the unfolded protein response (UPR) and in the prevention of endoplasmic reticulum (ER) stress. We hypothesized that this deletion prevents expression of SDF2L1 and contributes to the pathophysiology of diabetes in CDs/y by impairing UPR, enhancing ER stress, and preventing CDs/y from secreting sufficient insulin upon demand. We studied SDF2L1 expression in CDs/y and CDr/y. We evaluated UPR by examining expression of key proteins involved in both strains fed either RD or DD. We assessed the ability of all groups of animals to secrete insulin during an oral glucose tolerance test (OGTT) over 4 weeks, and after overnight feeding (postprandial) over 4 months. We found that SDF2L1 was expressed in CDr/y but not in CDs/y. The pattern of expression of proteins involved in UPR, namely the PERK (EIF2α, ATF4 and CHOP) and IRE1 (XBP-1) pathways, was different in CDs/y DD from all other groups, with consistently lower levels of expression at 4 weeks after initiation of DD and coinciding with the development of diabetes. In CDs/y RD, insulin secretion was mildly impaired, whereas in CDs/y DD, the ability to secrete insulin decreased over time, leading to the development of the diabetic phenotype. We conclude that in CDs/y DD, UPR participating proteins were dysregulated and under-expressed at the time point when the diabetic phenotype became overt. In parallel, insulin secretion in CDs/y DD became markedly impaired. Our findings suggest that under conditions of metabolic load with DD and increased demand for insulin secretion, the lack of SDF2L1 expression in CDs/y is associated with UPR dysregulation and ER stress which, combined with oxidative stress previously attributed to the concurrent Ndufa4 mutation, are highly likely to contribute to the pathophysiology of diabetes in this model.

In vitro methods in autophagy research: Applications in neurodegenerative diseases and mood disorders

Background

Autophagy is a conserved physiological intracellular mechanism responsible for the degradation and recycling of cytoplasmic constituents (e.g., damaged organelles, and protein aggregates) to maintain cell homeostasis. Aberrant autophagy has been observed in neurodegenerative diseases, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Huntington's Disease (HD), and recently aberrant autophagy has been associated with mood disorders, such as depression. Several in vitro methods have been developed to study the complex and tightly regulated mechanisms of autophagy. In vitro methods applied to autophagy research are used to identify molecular key players involved in dysfunctional autophagy and to screen autophagy regulators with therapeutic applications in neurological diseases and mood disorders. Therefore, the aims of this narrative review are (1) to compile information on the cell-based methods used in autophagy research, (2) to discuss their application, and (3) to create a catalog of traditional and novel in vitro methods applied in neurodegenerative diseases and depression.

Methods

Pubmed and Google Scholar were used to retrieve relevant in vitro studies on autophagy mechanisms in neurological diseases and depression using a combination of search terms per mechanism and disease (e.g., "macroautophagy" and "Alzheimer's disease"). A total of 37 studies were included (14 in PD, 8 in AD, 5 in ALS, 5 in %, and 5 in depression).

Results

A repertoire of traditional and novel approaches and techniques was compiled and discussed. The methods used in autophagy research focused on the mechanisms of macroautophagy, microautophagy, and chaperone-mediated autophagy. The in vitro tools presented in this review can be applied to explore pathophysiological mechanisms at a molecular level and to screen for potential therapeutic agents and their mechanism of action, which can be of great importance to understanding disease biology and potential therapeutic options in the context of neurodegenerative disorders and depression.

Conclusion

This is the first review to compile, discuss, and provide a catalog of traditional and novel in vitro models applied to neurodegenerative disorders and depression.

Assessment of HDAC Inhibitor-Induced Endoplasmic Reticulum (ER) Stress

The endoplasmic reticulum (ER) is a multifunctional cell organelle which is important for the folding and processing of proteins. Different endogenous and exogenous factors can disturb the ER homeostasis, causing ER stress and activating the unfolded protein response (UPR) to remove misfolded proteins and aggregates. ER stress and the UPR are associated with several human diseases, such as diabetes, Alzheimer's or Parkinson's disease, and cancer. Histone deacetylase inhibitors (HDACi) are used to treat cancer and were shown to induce ER stress/to modulate the UPR, although the exact mechanism is not fully understood and needs further research. Several approaches to monitoring ER stress exist. Here we describe methods including qPCR, Western blot, transmission electron microscopy, and fluorescence microscopy to analyze changes in mRNA and protein expression levels as well as defects in ER structures after HDAC inhibitor-induced ER stress.

Neurodegenerative Diseases: From Dysproteostasis, Altered Calcium Signalosome to Selective Neuronal Vulnerability to AAV-Mediated Gene Therapy

Despite intense research into the multifaceted etiology of neurodegenerative diseases (ND), they remain incurable. Here we provide a brief overview of several major ND and explore novel therapeutic approaches. Although the cause (s) of ND are not fully understood, the accumulation of misfolded/aggregated proteins in the brain is a common pathological feature. This aggregation may initiate disruption of Ca⁺⁺ signaling, which is an early pathological event leading to altered dendritic structure, neuronal dysfunction, and cell death. Presently, ND gene therapies remain unidimensional, elusive, and limited to modifying one pathological feature while ignoring others. Considering the complexity of signaling cascades in ND, we discuss emerging therapeutic concepts and suggest that deciphering the molecular mechanisms involved in dendritic pathology may broaden the phenotypic spectrum of ND treatment. An innovative multiplexed gene transfer strategy that employs silencing and/or over-expressing multiple effectors could preserve vulnerable neurons before they are lost. Such therapeutic approaches may extend brain health span and ameliorate burdensome chronic disease states.

Endoplasmic Reticulum Stress Underlies Nanosilver-Induced Neurotoxicity in Immature Rat Brain

The growing production of silver nanoparticles (AgNPs), and their widespread use in medical and consumer products, poses a potential threat to the environment and raises questions about biosafety. Immature organisms are particularly susceptible to various insults during development. The biological characteristics of immature organisms are different from those of adults, and dictate the consequences of exposure to various toxic substances, including AgNPs. Nanoparticles are highly reactive and can easily cross the blood–brain barrier (BBB) to accumulate in brain tissues. It is therefore important to investigate the molecular mechanisms of AgNP-induced neurotoxicity in the developing brain. Immature 2-week-old rats were exposed to a low dose of AgNPs (0.2 mg/kg b.w.) over a long period. Subsequently, brain tissues of the animals were subjected to ultrastructural and molecular analyses to determine endoplasmic reticulum (ER) stress. Ultrastructural markers of ER stress, such as pathological alterations in the ER and elongated forms of mitochondria accompanied by autophagy structures, were confirmed to be present in AgNP-exposed rat brain. Evidence for induction of ER stress in neurons was also provided by molecular markers. Upregulation of genes related to the ER-stress-induced unfolded protein response (UPR) pathway, such as GRP78, PERK, and CHOP ATF-6, was observed at the transcriptional and translational levels. The results show that prolonged exposure of immature rats to a low dose of AgNPs during the developmental period leads to induction of ER stress in the neurons of the developing brain. Simultaneously, in response to AgNP-induced ER stress, neurons promote protective mechanisms that partially compensate for ER stress by regulating the biodynamic processes of mitochondria and autophagy.

Molecular and cellular mechanisms in diabetic heart failure: Potential therapeutic targets

Diabetes Mellitus (DM) is a worldwide health issue that can lead to a variety of complications. DM is a serious metabolic disorder that causes long-term microvascular and macro-vascular complications, as well as the failure of various organ systems. Diabetes-related cardiovascular diseases (CVD) including heart failure cause significant morbidity and mortality worldwide. Concurrent hypertensive heart disease and/or coronary artery disease have been thought to be the causes of diabetic heart failure in DM patients. However, heart failure is extremely common in DM patients even in the absence of other risk factors such as coronary artery disease and hypertension. The occurrence of diabetes-induced heart failure has recently received a lot of attention. Understanding how diabetes increases the risk of heart failure and how it mediates major cellular and molecular alteration will aid in the development of therapeutics to prevent these changes. Hence, this review aimed to summarize the current knowledge and most recent findings in cellular and molecular mechanisms of diabetes-induced heart failure.

The Role of Endoplasmic Reticulum Stress in Differentiation of Cells of Mesenchymal Origin

Endoplasmic reticulum (ER) is a multifunctional membrane-enclosed organelle. One of the major ER functions is cotranslational transport and processing of secretory, lysosomal, and transmembrane proteins. Impaired protein processing caused by disturbances in the ER homeostasis results in the ER stress. Restoration of normal ER functioning requires activation of an adaptive mechanism involving cell response to misfolded proteins, the so-called unfolded protein response (UPR). Besides controlling protein folding, UPR plays a key role in other physiological processes, in particular, differentiation of cells of connective, muscle, epithelial, and neural tissues. Cell differentiation is induced by the physiological levels of ER stress, while excessive ER stress suppresses differentiation and can result in cell death. So far, it remains unknown whether UPR activation induces cell differentiation or if UPR is initiated by the upregulated synthesis of secretory proteins during cell differentiation. Cell differentiation is an important stage in the development of multicellular organisms and is tightly controlled. Suppression or excessive activation of this process can lead to the development of various pathologies in an organism. In particular, impairments in the differentiation of connective tissue cells can result in the development of fibrosis, obesity, and osteoporosis. Recently, special attention has been paid to fibrosis as one of the major complications of COVID-19. Therefore, studying the role of UPR in the activation of cell differentiation is of both theoretical and practical interest, as it might result in the identification of molecular targets for selective regulation of cell differentiation stages and as well as the potential to modulate the mechanisms involved in the development of various pathological states.

Potential role of endoplasmic reticulum stress in the pathophysiology of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is an endocrine disorder that affects million women worldwide, presenting a complex pathophysiology that has not been fully elucidated yet. Recently, it has been suggested that PCOS triggers the endoplasmic reticulum (ER) stress, thus being associated with unfolded protein response (UPR) activation. Indeed, the UPR response has been associated with several pathological conditions, including in the reproductive system. Several studies demonstrated that ovarian UPR markers are upregulated in PCOS, being associated with worst ovarian outcomes, and this was ameliorated by ER stress inhibition. In this review, we aim to summarize the main findings from previous studies covering this topic, in an attempt to clarify the potential role of ER stress and the UPR response in the pathophysiology of PCOS.

Modulation of autophagy by melatonin via sirtuins in stroke: From mechanisms to therapies

Sirtuins perform an important effect on the neural cell fate following stroke. Several mechanisms that have been correlated with stroke are oxidative stress, apoptosis, necrosis and autophagy. Autophagy is usually regarded as unitary of the neural cell survival mechanisms. Recently, the importance of the sirtuins effect on autophagy by antioxidant agents for stroke treatment mentioned in various studies. One of these agents is melatonin. Melatonin can modulate autophagy by changing on sirtuin pathways. Melatonin and its metabolites adjust various sirtuins pathways related to apoptosis, proliferation, metastases, autophagy and inflammation in case of stroke. In this review, we will discuss about the modulation of autophagy by melatonin via sirtuins in stroke.

XAF1 drives apoptotic switch of endoplasmic reticulum stress response through destabilization of GRP78 and CHIP

X-linked inhibitor of apoptosis-associated factor-1 (XAF1) is a stress-inducible tumor suppressor that is commonly inactivated in many human cancers. Despite accumulating evidence for the pro-apoptotic role for XAF1 under various stressful conditions, its involvement in endoplasmic reticulum (ER) stress response remains undefined. Here, we report that XAF1 increases cell sensitivity to ER stress and acts as a molecular switch in unfolded protein response (UPR)-mediated cell-fate decisions favoring apoptosis over adaptive autophagy. Mechanistically, XAF1 interacts with and destabilizes ER stress sensor GRP78 through the assembly of zinc finger protein 313 (ZNF313)-mediated destruction complex. Moreover, XAF1 expression is activated through PERK-Nrf2 signaling and destabilizes C-terminus of Hsc70-interacting protein (CHIP) ubiquitin E3 ligase, thereby blocking CHIP-mediated K63-linked ubiquitination and subsequent phosphorylation of inositol-required enzyme-1α (IRE1α) that is involved in in the adaptive ER stress response. In tumor xenograft assays, XAF1^-/- tumors display substantially lower regression compared to XAF1^+/+ tumors in response to cytotoxic dose of ER stress inducer. XAF1 and GRP78 expression show an inverse correlation in human cancer cell lines and primary breast carcinomas. Collectively this study uncovers an important role for XAF1 as a linchpin to govern the sensitivity to ER stress and the outcomes of UPR signaling, illuminating the mechanistic consequence of XAF1 inactivation in tumorigenesis.

Saturated Fatty Acid-Induced Endoplasmic Reticulum Stress and Insulin Resistance Are Prevented by Imoxin in C2C12 Myotubes

In obesity, plasma free fatty acids (FFAs) levels are elevated due to enlarged adipose tissue mass. Saturated fatty acids can induce prolonged ER stress and insulin resistance. Double-stranded RNA-dependent Protein Kinase (PKR) is activated under stress conditions in skeletal muscle. The current study aimed to investigate the effect of imoxin (IMX), a selective PKR inhibitor, on palmitate-induced ER stress and insulin resistance in C2C12 myotubes. Cells were treated with 5 μM imoxin and exposed to 0.5 mM bovine serum albumin (BSA)-conjugated PA for 24 h. A subset of cells was stimulated with 50 nM insulin for the last 15 min. Glucose uptake was monitored and protein levels involved in ER stress and insulin signaling were measured by Western blotting. Palmitate stimulated PKR phosphorylation, which was prevented by imoxin. Moreover, imoxin reduced protein levels of ER stress-related markers including glucose-regulating protein 78 (GRP78), CCAAT-enhancer-binding protein homologous protein (CHOP), activating transcription factor 6 (ATF6) and spliced X-box binding protein 1 (XBP-1s) which were induced by palmitate. Furthermore, imoxin ameliorated palmitate-induced suppression of phospho-insulin receptor beta (p-IRβ) and Akt phosphorylation in myotubes. In addition, imoxin promoted glucose uptake in response to insulin under palmitate exposure. Furthermore, imoxin reduced phospho-c-Jun N-terminal kinase (p-JNK) induced by palmitate treatment. These findings suggest that imoxin may protect against saturated fatty acid-induced ER stress and insulin resistance in skeletal muscle, which are potentially mediated by PKR.

PKA/ATGL signaling pathway is involved in ER stress-mediated lipolysis in adipocytes of grass carp (Ctenopharyngodon idella)

The relationship between endoplasmic reticulum stress (ER stress) and lipolysis in mammals has been widely studied, but it is relatively scarce in fish. The present study used grass carp Ctenopharyngodon idella as a model to investigate the effect of ER stress on lipolysis in adipocytes of fish. We found that ER stress evoked by tunicamycin (TM) treatment significantly induced lipolysis in adipocytes. Subsequently, in order to further investigate whether protein kinase A (PKA) is involved in ER stress-induced lipolysis, we treated adipocytes with PKA activator forskolin and inhibitor H89. The results showed that the mechanism was related to the activation of PKA, especially the catalytic subunit PRKACBa. Notably, we also found that PKA regulates lipolysis by targeting mRNA level and protein and enzyme activities of adipotriglyceride lipase (ATGL). Taken together, our findings suggest that PKA/ATGL signaling pathway is involved in ER stress-mediated lipolysis of grass carp adipocytes. It provides a theoretical basis for further study on the mechanism of lipolysis in fish and other vertebrates.

Mefloquine induces ER stress and apoptosis in BRAFi-resistant A375-BRAFV600E /NRASQ61K malignant melanoma cells targeting intracranial tumors in a bioluminescent murine model

Molecularly targeted therapeutics have revolutionized the treatment of BRAFV600E -driven malignant melanoma, but the rapid development of resistance to BRAF kinase inhibitors (BRAFi) presents a significant obstacle. The use of clinical antimalarials for the investigational treatment of malignant melanoma has shown only moderate promise, attributed mostly to inhibition of lysosomal-autophagic adaptations of cancer cells, but identification of specific antimalarials displaying single-agent antimelanoma activity has remained elusive. Here, we have screened a focused library of clinically used artemisinin-combination therapeutic (ACT) antimalarials for the apoptotic elimination of cultured malignant melanoma cell lines, also examining feasibility of overcoming BRAFi-resistance comparing isogenic melanoma cells that differ only by NRAS mutational status (BRAFi-sensitive A375-BRAFV600E /NRASQ61 vs. BRAFi-resistant A375-BRAFV600E /NRASQ61K ). Among ACT antimalarials tested, mefloquine (MQ) was the only apoptogenic agent causing melanoma cell death at low micromolar concentrations. Comparative gene expression-array analysis (A375-BRAFV600E /NRASQ61 vs. A375-BRAFV600E /NRASQ61K ) revealed that MQ is a dual inducer of endoplasmic reticulum (ER) and redox stress responses that precede MQ-induced loss of viability. ER-trackerTM DPX fluorescence imaging and electron microscopy indicated ER swelling, accompanied by rapid induction of ER stress signaling (phospho-eIF2α, XBP-1s, ATF4). Fluo-4 AM-fluorescence indicated the occurrence of cytosolic calcium overload observable within seconds of MQ exposure. In a bioluminescent murine model employing intracranial injection of A375-Luc2 (BRAFV600E /NRASQ61K ) cells, an oral MQ regimen efficiently antagonized brain tumor growth. Taken together, these data suggest that the clinical antimalarial MQ may be a valid candidate for drug repurposing aiming at chemotherapeutic elimination of malignant melanoma cells, even if metastasized to the brain and BRAFi-resistant.

Protodioscin Induces Mitochondrial Apoptosis of Human Hepatocellular Carcinoma Cells Through Eliciting ER Stress-Mediated IP3R Targeting Mfn1/Bak Expression

Objective

Protodioscin (PD), a steroidal saponin, has a diverse pharmacological activity including neuroprotection, male fertility improvement, and cytotoxicity against various cancers cell lines of different origins. However, the effect of PD on hepatocellular carcinoma (HCC) is still unclear.

Methods

Cell viability, colony formation and flow cytometry analysis for apoptosis profile, mitochondrial membrane potential endoplasmic reticulum (ER) expansion were employed to determine the effect of PD against HCC cells. Transient transfection of siRNA, immunofluorescent imaging and immunoprecipitation were used to elucidate the anti-cancer mechanism of PD. The in vivo toxicity and efficacy of PD were assessed by a xenograft mouse model.

Results

PD induced apoptosis, loss of mitochondrial membrane potential and ER expansion in HCC cells. Either downregulation of Mfn1 or Bak reversed PD-induced apoptosis and loss of mitochondrial membrane potential. Further analysis revealed that Mfn1 and Bak will form a complex with IP3R to facilitate the transfer of Ca²⁺ from ER to mitochondria and apoptosis. In addition, our tumour xenograft model further verifies the in vivo anti-tumour effect of PD.

Conclusion

Our study sheds light on the understanding of the anti-HCC effects of PD and may open new aspects for the development of novel treatment for human hepatocellular carcinoma.

Organelle specific fluorescent phenomics and transcriptomic profiling to evaluate cellular response to tris(1,3 dichloro 2 propyl)phosphate

Tris(1,3-dichloro-2-propyl)phosphate (TDCPP) has been suspected to cause toxicity invertebrates, but its phenotypic effects and the underlying regulatory mechanism have not been fully revealed. Generally, cellular responses tightly control and affect various phenotypes. The scope of the whole organism or cellular toxicological phenotyping, however, has been limited, and quantitative analysis methods using phenotype data have not been fully established. Here, we demonstrated that fluorescence imaging of sub-organelle-based phenomic analysis together with transcriptomic profiling can enable a comprehensive understanding of correlations between molecular and phenomic events. To reveal the cellular response to TDCPP exposure, we obtained three sub-organelle images as fluorescent phenotypes. Transcriptomic perturbation data were measured from the RNA-seq experiment, and both profiling results were analyzed together. Interestingly, organelle phenomic data showed a unique fluorescent intensity increase in the endoplasmic reticulum (ER), and pathway analysis using transcriptomic data also revealed that ER was significantly enriched in gene ontology terms. Following the series of analyses, RNA-seq data also revealed potential carcinogenic effects of TDCPP. Our multi-dimensional profiling approach for organophosphate chemicals can uniquely correlate phenotypic changes with transcriptomic perturbations.

Hydroxy Selenomethionine Alleviates Hepatic Lipid Metabolism Disorder of Pigs Induced by Dietary Oxidative Stress via Relieving the Endoplasmic Reticulum Stress

This study used 40 castrated male pigs to determine the protective effects of a new selenium molecule (hydroxy selenomethionine, OH-SeMet) on dietary oxidative stress (DOS) induced hepatic lipid metabolism disorder, and corresponding response of selenotranscriptome. The pigs were randomly grouped into 5 dietary treatments and fed a basal diet formulated with either normal corn and oils or oxidized diet in which the normal corn and oils were replaced by aged corn and oxidized oils, and supplemented with OH-SeMet at 0.0, 0.3, 0.6 and 0.9 mg Se/kg for a period of 16 weeks (n = 8). The results showed that DOS induced liver damage, increased serum alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels, decreased serum triacylglycerol (TG) level, suppressed antioxidant capacity in the liver, and changed lipid metabolism enzyme activity, thus causing lipid metabolism disorder in the liver. The DOS-induced lipid metabolism disorder was accompanied with endoplasmic reticulum (ER) stress, changes in lipid metabolism-related genes and selenotranscriptome in the liver. Dietary Se supplementation partially alleviated the negative impact of DOS on the lipid metabolism. These improvements were accompanied by increases in Se concentration, liver index, anti-oxidative capacity, selenotranscriptome especially 11 selenoprotein-encoding genes, and protein abundance of GPX1, GPX4 and SelS in the liver, as well as the decrease in SelF abundance. The Se supplementation also alleviated ER stress, restored liver lipid metabolism enzyme activity, increased the mRNA expression of lipid synthesis-related genes, and decreased the mRNA levels of lipidolysis-related genes. In conclusion, the dietary Se supplementation restored antioxidant capacity and mitigated ER stress induced by DOS, thus resisting hepatic lipid metabolism disorders that are associated with regulation of selenotranscriptome.

Endoplasmic reticulum stress is involved in lipid accumulation induced by oleic acid in adipocytes of grass carp (Ctenopharyngodon idella): focusing on the transcriptional level

It has been extensively claimed that endoplasmic reticulum stress (ER stress) is related to lipid accumulation in mammals, but little is known in fish. This study aims at elucidating the role of ER stress in mediating lipid accumulation induced by monounsaturated oleic acid (OA) with a focus on the transcriptional level. We treated the adipocytes of grass carp with 200 μM and 400 μM OA, respectively, while the control group was treated with 2% bovine serum albumin (BSA). The results showed that cell viability was significantly improved, while 400 μM OA treatment promoted neutral lipid accumulation along with stimulating ER stress more obviously. Although lipolysis and fatty acid β-oxidation were activated simultaneously, the primary effect of OA seems to be promotion of lipid accumulation. To further explore whether ER stress affects lipid accumulation, 4-phenyl butyric acid (4-PBA), an effective inhibitor of ER stress, was used to pretreat the cells for 4 h. Unsurprisingly, it was found that the mRNA expressions of genes linked with ER stress were decreased. Intracellular triglyceride (TG) content was also decreased, which was in accordance with the mRNA expressions of adipogenic and lipogenic transcription factors as well as their target genes. Collectively, our data shows that ER stress may take part in OA-induced lipid accumulation in adipocytes via activating adipogenesis and lipogenesis. Based on this, strategies for protecting ER could be used to alleviate excessive accumulation of lipid in grass carp adipose tissue.

Deep Learning-Based Morphological Classification of Endoplasmic Reticulum Under Stress

Endoplasmic reticulum stress (ER stress) is a condition that is defined by abnormal accumulation of unfolded proteins. It plays an important role in maintaining cellular protein, lipid, and ion homeostasis. By triggering the unfolded protein response (UPR) under ER stress, cells restore homeostasis or undergo apoptosis. Chronic ER stress is implicated in many human diseases. Despite extensive studies on related signaling mechanisms, reliable image biomarkers for ER stress remain lacking. To address this deficiency, we have validated a morphological image biomarker for ER stress and have developed a deep learning-based assay to enable automated detection and analysis of this marker for screening studies. Specifically, ER under stress exhibits abnormal morphological patterns that feature ring-shaped structures called whorls (WHs). Using a highly specific chemical probe for unfolded and aggregated proteins, we find that formation of ER whorls is specifically associated with the accumulation of the unfolded and aggregated proteins. This confirms that ER whorls can be used as an image biomarker for ER stress. To this end, we have developed ER-WHs-Analyzer, a deep learning-based image analysis assay that automatically recognizes and localizes ER whorls similarly as human experts. It does not require laborious manual annotation of ER whorls for training of deep learning models. Importantly, it reliably classifies different patterns of ER whorls induced by different ER stress drugs. Overall, our study provides mechanistic insights into morphological patterns of ER under stress as well as an image biomarker assay for screening studies to dissect related disease mechanisms and to accelerate related drug discoveries. It demonstrates the effectiveness of deep learning in recognizing and understanding complex morphological phenotypes of ER.

Oxidative stress and endoplasmic reticulum stress contributed to hepatotoxicity of decabromodiphenyl ethane (DBDPE) in L-02 cells

Decabromodiphenyl ethane (DBDPE) is one of the most commonly used novel brominated flame retardants (NBFRs), and its mass production and widespread application have caused health threats to the human being. Existing studies have shown that DBDPE has hepatotoxicity. And we have found that DBDPE could change cytochrome P450 3A (CYP3A) expression levels in rat livers, whereas the mechanism is unclear. In this study, we exposed human normal hepatocyte (L-02) to DBDPE to further study the effect and mechanism of DBDPE on hepatocellular injury and liver metabolic enzyme CYP3A changes in vitro. The results showed that DBDPE caused L-02 cell viability decrease, lactate dehydrogenase (LDH) and transaminase release, ultrastructural damage, and apoptosis. Moreover, DBDPE exposure induced oxidative stress (i.e., increased ROS generation and MDA levels and decreased GSH content, SOD activity, and mitochondrial membrane potential) and endoplasmic reticulum (ER) stress in L-02 cells as evidenced by the elevated PERK and IRE-1α expression levels. These results confirmed that DBDPE is toxic to hepatocytes. Besides, the CYP3A expression level was decreased in DBDPE exposed L-02 cells. However, pretreatment of L-02 cells with antioxidant N-Acetyl-l-cysteine (NAC) and endoplasmic reticulum stress inhibitor 4-PBA inhibited DBDPE-induced oxidative stress, endoplasmic reticulum stress, CYP3A expression decrease, and apoptosis. Therefore, we demonstrated that DBDPE could exert toxic effects and decrease CYP3A expression on L-02 cells by inducing ER stress and oxidative stress.

The E3 Ubiquitin Ligase Ring Finger Protein 5 Ameliorates NASH Through Ubiquitin-Mediated Degradation of 3-Hydroxy-3-Methylglutaryl CoA Reductase Degradation Protein 1

BACKGROUND AND AIMS

NAFLD is the most prevalent chronic liver disease worldwide, but no effective pharmacological therapeutics are available for clinical use. NASH is the more severe stage of NAFLD. During this progress, dysregulation of endoplasmic reticulum (ER)-related pathways and proteins is one of the predominant hallmarks. We aimed to reveal the role of ring finger protein 5 (RNF5), an ER-localized E3 ubiquitin-protein ligase, in NASH and to explore its underlying mechanism.

APPROACH AND RESULTS

We first inspected the expression level of RNF5 and found that it was markedly decreased in livers with NASH in multiple species including humans. We then introduced adenoviruses for Rnf5 overexpression or knockdown into primary mouse hepatocytes and found that palmitic acid/oleic acid (PAOA)-induced lipid accumulation and inflammation in hepatocytes were markedly attenuated by Rnf5 overexpression but exacerbated by Rnf5 gene silencing. Hepatocyte-specific Rnf5 knockout significantly exacerbated hepatic steatosis, inflammatory response, and fibrosis in mice challenged with diet-induced NASH. Mechanistically, we identified 3-hydroxy-3-methylglutaryl CoA reductase degradation protein 1 (HRD1) as a binding partner of RNF5 by systematic interactomics analysis. RNF5 directly bound to HRD1 and promoted its lysine 48 (K48)-linked and K33-linked ubiquitination and subsequent proteasomal degradation. Furthermore, Hrd1 overexpression significantly exacerbated PAOA-induced lipid accumulation and inflammation, and short hairpin RNA-mediated Hrd1 knockdown exerted the opposite effects. Notably, Hrd1 knockdown significantly diminished PAOA-induced lipid deposition, and up-regulation of related genes resulted from Rnf5 ablation in hepatocytes.

CONCLUSIONS

These data indicate that RNF5 inhibits NASH progression by targeting HRD1 in the ubiquitin-mediated proteasomal pathway. Targeting the RNF5-HRD1 axis may provide insights into the pathogenesis of NASH and pave the way for developing strategies for NASH prevention and treatment.

Artemisinins induce endoplasmic reticulum stress in acute leukaemia cells in vitro and in vivo

Loss of endoplasmic reticulum (ER) homeostasis leads to ER stress, thus prolonged activation can lead to apoptosis. Herein, artesunate (ART) induced ER stress in leukaemia cells, resulting in eIF2α phosphorylation, activation of transcription factor 4, subsequent CHOP upregulation and XBP1 splicing. Furthermore, in vitro cyclin/CDKs reduction induced G1‐phase arrest. An in vivo xenograft model showed a consistent pattern of ART in reducing tumour burden, supporting roles in the UPR pathway, which we speculate could lead to apoptosis by NOXA activation. Moreover, ART were capable of increasing the survival of mice. Taken together, our data indicate that ART may represent an interesting weapon to fight leukaemia.

p62/sequestosome 1 attenuates methylmercury-induced endoplasmic reticulum stress in mouse embryonic fibroblasts

Methylmercury (MeHg) is a hazardous environmental pollutant that causes serious toxicity in humans and animals, as well as proteotoxic stress. In our previous study, we found that MeHg induces the expression of p62/sequestosome 1 (p62) that selectively targets ubiquitinated proteins for degradation via autophagy, and that p62 might protect cells against MeHg toxicity. To further investigate the role of p62 in MeHg-induced stress responses, we evaluated the role of p62 in MeHg-induced endoplasmic reticulum (ER) stress in p62 knockout (p62KO) mouse embryonic fibroblasts (MEFs). Treatment of wild-type (WT) MEFs were treated with MeHg (1 μM) increased mRNA levels of Chop encoding C/EBP homologous protein, Trib3 encoding Tribbles homolog 3, and Dnajb9 encoding DnaJ heat-shock protein family (Hsp40) member B9 increased, suggesting that ER stress is elicited by MeHg stress. Additionally, p62KO MEFs treated with MeHg showed a higher mRNA expression of Chop and Trib3 relative to that in WT MEFs. Furthermore, knock-in of GFP-p62 to p62KO cells diminished the Chop and Trib3 induction responses to MeHg stress and resulted in a higher cell viability than that of p62KO MEFs. These results suggest that the protective role of p62 against MeHg toxicity is partly mediated by suppressing the ER stress response.

Profound architectural and functional readjustments of the secretory pathway in decidualization of endometrial stromal cells

Certain cell types must expand their exocytic pathway to guarantee efficiency and fidelity of protein secretion. A spectacular case is offered by decidualizing human endometrial stromal cells (EnSCs). In the midluteal phase of the menstrual cycle, progesterone stimulation induces proliferating EnSCs to differentiate into professional secretors releasing proteins essential for efficient blastocyst implantation. Here, we describe the architectural rearrangements of the secretory pathway of a human EnSC line (TERT-immortalized human endometrial stromal cells (T-HESC)). As in primary cells, decidualization entails proliferation arrest and the coordinated expansion of the entire secretory pathway without detectable activation of unfolded protein response (UPR) pathways. Decidualization proceeds also in the absence of ascorbic acid, an essential cofactor for collagen biogenesis, despite also the secretion of some proteins whose folding does not depend on vitamin C is impaired. However, even in these conditions, no overt UPR induction can be detected. Morphometric analyses reveal that the exocytic pathway does not increase relatively to the volume of the cell. Thus, differently from other cell types, abundant production is guaranteed by a coordinated increase of the cell size following arrest of proliferation.

Recent advances in cell homeostasis by African swine fever virus-host interactions

African swine fever (ASF) is an acute hemorrhagic disease caused by the infection of domestic swine and wild boar by the African swine fever virus (ASFV), with a mortality rate close to 90-100%. ASFV has been spreading in the world and poses a severe economic threat to the swine industry. There is no high effective vaccine commercially available or drug for this disease. However, attenuated ASFV isolates may infect pigs by chronic infection, and the infected pigs will not be lethal, which may indicate that pigs can produce protective immunity to resistant ASFV. Immunity acquisition and virus clearances are the central pillars to maintain the host normal cell activities and animal survival dependent on virus-host interactions, which has offered insights into the biology of ASFV. This review is organized around general themes including native immunity, endoplasmic reticulum stress, cell apoptosis, ubiquitination, autophagy regarding the intricate relationship between ASFV protein-host. Elucidating the multifunctional role of ASFV proteins in virus-host interactions can provide more new insights on the initial virus sensing, clearance, and cell homeostasis, and contribute to understanding viral pathogenesis and developing novel antiviral therapeutics.

AMPK: restoring metabolic homeostasis over space and time

The evolution of AMPK and its homologs enabled exquisite responsivity and control of cellular energetic homeostasis. Recent work has been critical in establishing the mechanisms that determine AMPK activity, novel targets of AMPK action, and the distribution of AMPK-mediated control networks across the cellular landscape. The role of AMPK as a hub of metabolic control has led to intense interest in pharmacologic activation as a therapeutic avenue for a number of disease states, including obesity, diabetes, and cancer. As such, critical work on the compartmentalization of AMPK, its downstream targets, and the systems it influences has progressed in recent years. The variegated distribution of AMPK-mediated control of metabolic homeostasis has revealed key insights into AMPK in normal biology and future directions for AMPK-based therapeutic strategies.

MEF2D-NR4A1-FAM134B2-mediated reticulophagy contributes to amino acid homeostasis

We recently identified FAM134B2, which is an N-terminal truncated reticulophagy receptor highly induced by starvation such as fasting of mice and treatment of mammalian cells with a starvation medium that does not contain amino acids, glucose and growth factors. However, which starvation signal mediates the induction of FAM134B2 is still obscure. In this study, we found that amino acid deficiency (AAD) could mimic the starvation condition to induce FAM134B2 expression. Unexpectedly, EIF2AK4/GCN2-mediated integrated signal response (ISR) and MTOR (mechanistic target of rapamycin kinase) signals, which constitute two major signaling pathways that respond to AAD, did not contribute to AAD-induced FAM134B2 induction. mRNA-seq and siRNA screenings identified two ISR-independent transcription factors, MEF2D (myocyte enhancer factor 2D) and NR4A1 (nuclear receptor subfamily 4 group A member 1), involved in AAD-induced FAM134B2 expression. AAD induces MEF2D, resulting in the induction of NR4A1, which in turn induces FAM134B2-mediated reticulophagy to maintain intracellular amino acid levels. In conclusion, the MEF2D-NR4A1-FAM134B2 cascade is a critical signal in amino acid homeostasis.