Mitigate Endoplasmic Reticulum Stress Research Articles

FAM134B-induced endoplasmic reticulum (ER)-phagy exacerbates cisplatin-insulted hair cell apoptosis ：Possible relation to excessive ER stress

AimsFAM134B, the initial endoplasmic reticulum (ER)-phagy receptor identified, facilitates ER-phagy during ER stress. The malfunction of FAM134B has been demonstrated to have a crucial role in the pathological mechanisms of diverse human ailments. However, the role of FAM134B-mediated ER-phagy in ototoxicity, particularly in cisplatin-induced ototoxicity, remains unclear. The present study endeavors to investigate whether FAM134B is expressed in House Ear Institute-Organ of Corti 1 (HEI-OC1) and C57BL/6 murine cochlear hair cells (HCs), and to explore its potential function in cisplatin-mediated ototoxicity, with the aim of discovering new insights that can mitigate or forestall the irreversible adverse effect of cisplatin. MethodsImmunofluorescence (IF) staining was used to test the expression pattern of FAM134B, levels of C/EBP-homologous protein (CHOP), autophagy, and co-localization ratio of lysosomes and ER. Western blotting was employed to measure changes in expression levels of FAM134B, LC3B, ER stress-related proteins, LAMP1 and apoptotic mediators. Cell apoptosis was examined using transferase dUTP nick end labeling (TUNEL) assay and flow cytometry. ResultsIn the present investigation, it was observed that FAM134B exhibited a diffuse expression pattern in the cytoplasm and nuclei of control HEI-OC1 cells. Following cisplatin administration, FAM134B was found to accumulate and form distinct dots around the nuclei, concomitant with increased levels of ER-phagy, ER stress, unfolded protein response (UPR), and cell apoptosis. Additionally, knockdown of FAM134B resulted in reduced ER-phagy, mitigated ER stress and UPR, and decreased apoptotic activity in HEI-OC1 cells following cisplatin exposure. ConclusionsCollectively, the findings of this study demonstrate that FAM134B-mediated ER-phagy enhances the susceptibility of HCs to ER stress and apoptosis in response to cisplatin-induced stress. This suggests a sequential progression of ER-phagy, ER stress and apoptosis following cisplatin stimulus, and implies the potential therapeutic benefit of inhibiting of FAM134B-mediated ER-phagy in the prevention of cisplatin-related ototoxicity.

Epigallocatechin-3-Gallate Reduces Cd-Induced Developmental Toxicity of Bodysize in Caenorhabditis elegans via the PEK-1/eIF-2α/ATF-4 Pathway.

Cadmium (Cd), a harmful heavy metal that has no biological purpose, can harm healthy fetal and child development. Epigallocatechin-3-gallate (EGCG), the most abundant polyphenol in tea, has been shown to increase cell viability under Cd exposure and ameliorate Cd-induced kidney injury in adult male rats. Using the Caenorhabditis elegans (C. elegans) model, we demonstrated that EGCG mitigated Cd-induced body size developmental toxicity through a mechanism that did not involve chelation with EGCG and was not associated with Cd accumulation and efflux. Our research indicated that the beneficial effects of EGCG on Cd-induced body size developmental toxicity were associated with the mitigation of endoplasmic reticulum stress. Furthermore, our observations indicate that EGCG reduced Cd-induced developmental toxicity in C. elegans via the PEK-1/eIF-2α/ATF-4 pathway. Our results provide important evidence for the potential benefits of consuming tea as a detoxification agent.

SQLE promotes pancreatic cancer growth by attenuating ER stress and activating lipid rafts-regulated Src/PI3K/Akt signaling pathway

Pancreatic cancer (PC), a highly lethal malignancy, commonly exhibits metabolic reprogramming that results in therapeutic vulnerabilities. Nevertheless, the mechanisms underlying the impacts of aberrant cholesterol metabolism on PC development and progression remain elusive. In this study, we found that squalene epoxidase (SQLE) is a crucial mediator of cholesterol metabolism in PC growth. We observed a profound upregulation of SQLE in PC tissues, and its high expression was correlated with poor patient outcomes. Our functional experiments demonstrated that SQLE facilitated cell proliferation, induced cell cycle progression, and inhibited apoptosis in vitro, while promoting tumor growth in vivo. Mechanistically, SQLE was found to have a dual role. First, its inhibition led to squalene accumulation-induced endoplasmic reticulum (ER) stress and subsequent apoptosis. Second, it enhanced de novo cholesterol biosynthesis and maintained lipid raft stability, thereby activating the Src/PI3K/Akt signaling pathway. Significantly, employing SQLE inhibitors effectively suppressed PC cell proliferation and xenograft tumor growth. In summary, this study reveals SQLE as a novel oncogene that promotes PC growth by mitigating ER stress and activating lipid raft-regulated Src/PI3K/Akt signaling pathway, highlighting the potential of SQLE as a therapeutic target for PC.

The Activation of Reticulophagy by ER Stress through the ATF4-MAP1LC3A-CCPG1 Pathway in Ovarian Granulosa Cells Is Linked to Apoptosis and Necroptosis.

Female infertility is caused by premature ovarian failure (POF), which is triggered by the endoplasmic reticulum (ER) stress-mediated apoptosis of granulosa cells. The ER unfolded protein response (UPRer) is initiated to promote cell survival by alleviating excessive ER stress, but cellular apoptosis is induced by persistent or strong ER stress. Recent studies have reported that reticulophagy is initiated by ER stress. Whether reticulophagy is activated in the ER stress-mediated apoptosis of granulosa cells and which pathway is initiated to activate reticulophagy during the apoptosis of granulosa cells are unknown. Therefore, the role of reticulophagy in granulosa cell death and the relationship between ER stress and reticulophagy were investigated in this work. Our results suggest that the ER stress inducer tunicamycin causes POF in mice, which is attributed to the apoptosis of granulosa cells and is accompanied by the activation of UPRer and reticulophagy. Furthermore, granulosa cells were treated with tunicamycin, and granulosa cell apoptosis was triggered and increased the expression of UPRer and reticulophagy molecules. The expression of ATF4 was then downregulated by RNAi, which decreased the levels of autophagy and the reticulophagy receptor CCGP1. Furthermore, ATF4 targets MAP1LC3A, as revealed by the ChIP sequencing results, and co-IP results demonstrated that MAP1LC3A interacts with CCPG1. Therefore, reticulophagy was activated by ER stress through the ATF4-MAP1LC3A-CCPG1 pathway to mitigate ER stress. Additionally, the role of reticulophagy in granulosa cells was investigated by the knockdown of CCPG1 with RNAi. Interestingly, only a small number of granulosa cells died by apoptosis, whereas the death of most granulosa cells occurred by necroptosis triggered by STAT1 and STAT3 to impair ER proteostasis and the ER protein quality control system UPRer. Taken together, the results indicate that the necroptosis of granulosa cells is triggered by up- and downregulating the reticulophagy receptor CCPG1 through STAT1/STAT3-(p)RIPK1-(p)RIPK3-(p)MLKL and that reticulophagy is activated by ER stress through the ATF4-MAP1LC3A-CCPG1 pathway.

Pterostilbene Prevents Tunicamycin-Induced Intestinal Barrier Damage by Targeting Endoplasmic Reticulum Stress, Oxidative Stress, Autophagy, and Gut Microbiota.

Endoplasmic reticulum (ER) stress is a crucial factor in the pathogenesis of intestinal diseases. Pterostilbene (PT) has been demonstrated to mitigate ER stress and protect against intestinal disorders. Here, we investigated the effects of PT on tunicamycin (TM)-induced intestinal ER stress and intestinal barrier damage in vivo in piglets and in vitro in intestinal porcine epithelial cell-jejunum 2 (IPEC-J2) cells. Results indicated that PT prevented TM-induced body weight loss (-0.67 ± 0.16 vs -0.48 ± 0.08 kg) and improved intestinal barrier integrity and goblet cell function of the TM-challenged piglets (P < 0.05). PT also inhibited ER stress, restored redox homeostasis and autophagic flux, and decreased apoptosis in the TM-challenged jejunum and the TM-exposed IPEC-J2 cells (P < 0.05). However, these attenuating effects of PT in the TM-treated IPEC-J2 cells were blunted by the knockdown of sirtuin 1 (P < 0.05). Moreover, PT increased the Ace index (390.12 ± 60.05 vs 460.27 ± 42.83) and downregulated the prevalence of the phylum Proteobacteria (48.73% ± 12.62% vs 32.10% ± 11.08%) of cecal microbiota of the TM-challenged piglets (P < 0.05). In conclusion, PT alleviated TM-induced intestinal barrier damage by regulating ER homeostasis, oxidative stress, autophagic flux, and gut microbiota.

Inhibition of Endoplasmic Reticulum Stress Improves Acetylcholine-Mediated Relaxation in the Aorta of Type-2 Diabetic Rats.

Endoplasmic reticulum (ER) stress contributes to insulin resistance and macro- and microvascular complications associated with diabetes. This study aimed to evaluate the effect of ER stress inhibition on endothelial function in the aorta of type-2 diabetic rats. Type-2 diabetes was developed in male Sprague–Dawley rats using a high-fat diet and low-dose streptozotocin. Rat aortic tissues were harvested to study endothelial-dependent relaxation. The mechanisms for acetylcholine-mediated relaxation were investigated using pharmacological blockers, Western blotting, oxidative stress, and inflammatory markers. Acetylcholine-mediated relaxation was diminished in the aorta of diabetic rats compared to control rats; supplementation with TUDCA improved relaxation. In the aortas of control and diabetic rats receiving TUDCA, the relaxation was mediated via eNOS/PI3K/Akt, NAD(P)H, and the KATP channel. In diabetic rats, acetylcholine-mediated relaxation involved eNOS/PI3K/Akt and NAD(P)H, but not the KATP channel. The expression of ER stress markers was upregulated in the aorta of diabetic rats and reduced with TUDCA supplementation. The expression of eNOS and Akt were lower in diabetic rats but were upregulated after supplementation with TUDCA. The levels of MDA, IL-6, and SOD activity were higher in the aorta of the diabetic rats compared to control rats. This study demonstrated that endothelial function was impaired in diabetes, however, supplementation with TUDCA improved the function via eNOS/Akt/PI3K, NAD(P)H, and the KATP channel. The improvement of endothelial function was associated with increased expressions of eNOS and Akt. Thus, ER stress plays a crucial role in the impairment of endothelial-dependent relaxation. Mitigating ER stress could be a potential strategy for improving endothelial dysfunction in type-2 diabetes.

4-PBA rescues hyperoxaluria induced nephrolithiasis by modulating urinary glycoproteins: Cross talk between endoplasmic reticulum, calcium homeostasis and mitochondria

AimUrinary glycoproteins such as Tamm Horsfall Protein (THP) and Osteopontin (OPN) are well established key regulators of renal stone formation. Additionally, recent revelations have highlighted the influence of Endoplasmic Reticulum (ER) and mitochondria of crucial importance in nephrolithiasis. However, till date conclusive approach highlighting the influence of ER stress on urinary glycoproteins and chaperone in nephrolithiasis remains elusive. Therefore, the present study was focussed on deciphering the possible effect of 4-PBA mitigating ER stress on urinary glycoproteins and calnexin (chaperone) with emphasis on interlinking calcium homeostasis in hyperoxaluric rats. Material and methodsPost 9 days of treatment, animals were sacrificed, and renal tissues were investigated for urinary glycoproteins, calnexin, calcium homeostasis, ER environment, redox status, and mitochondrial linkage. Key findings4-PBA appreciably reversed the altered levels of THP, OPN, and calnexin observed along with curtailing the disrupted calcium homeostasis when assessed for SERCA activity and intra-cellular calcium levels. Additionally, significant improvement in the perturbed ER environment as verified by escalated ER stress markers, disturbed protein folding-aggregation-degradation (congo red assay) pathway, and redox status was found post 4-PBA intervention. Interestingly, linkage of ER stress and mitochondria was established under hyperoxaluric conditions when assessed for protein levels of VDAC1 and GRP75. Significance4-PBA treatment resulted in rectifying the repercussions of ER-mitochondrial caused distress when assessed for protein folding/aggregation/degradation events along with disturbed calcium homeostasis. The present study advocates the necessity to adopt a holistic vision towards hyperoxaluria with emphasis on glycoproteins and ER environment.

SARS-CoV-2 ORF8 reshapes the ER through forming mixed disulfides with ER oxidoreductases

The replication machinery of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is closely associated with the endoplasmic reticulum (ER) in host cells. Activation of the unfolded protein response (UPR) is a strategy hijacked by coronavirus to facilitate its replication and suppress host innate immunity. Here, we have found that SARS-CoV-2 ORF8 protein accumulates in the ER and escapes the degradation system by forming mixed disulfide complexes with ER oxidoreductases. ORF8 induces the activation of three UPR pathways through targeting key UPR components, remodels ER morphology and accelerates protein trafficking. Moreover, small molecule reducing agents release ORF8 from the mixed disulfide complexes and facilitate its degradation, therefore mitigate ER stress. Our study reveals a unique mechanism by which SARS-CoV-2 ORF8 escapes degradation by host cells and regulates ER reshaping. Targeting ORF8-involved mixed disulfide complexes could be a new strategy to alleviate SARS-CoV-2 induced ER stress and related diseases.

Small Molecule-mediated Insulin Hypersecretion Induces Transient ER Stress Response and Loss of Beta Cell Function.

Pancreatic islet beta cells require a fine-tuned endoplasmic reticulum (ER) stress response for normal function; abnormal ER stress contributes to diabetes pathogenesis. Here, we identified a small molecule, SW016789, with time-dependent effects on beta cell ER stress and function. Acute treatment with SW016789 potentiated nutrient-induced calcium influx and insulin secretion, while chronic exposure to SW016789 transiently induced ER stress and shut down secretory function in a reversible manner. Distinct from the effects of thapsigargin, SW016789 did not affect beta cell viability or apoptosis, potentially due to a rapid induction of adaptive genes, weak signaling through the eIF2α kinase PERK, and lack of oxidative stress gene Txnip induction. We determined that SW016789 acted upstream of voltage-dependent calcium channels (VDCCs) and potentiated nutrient- but not KCl-stimulated calcium influx. Measurements of metabolomics, oxygen consumption rate, and G protein-coupled receptor signaling did not explain the potentiating effects of SW016789. In chemical cotreatment experiments, we discovered synergy between SW016789 and activators of protein kinase C and VDCCs, suggesting involvement of these pathways in the mechanism of action. Finally, chronically elevated calcium influx was required for the inhibitory impact of SW016789, as blockade of VDCCs protected human islets and MIN6 beta cells from hypersecretion-induced dysfunction. We conclude that beta cells undergoing this type of pharmacological hypersecretion have the capacity to suppress their function to mitigate ER stress and avoid apoptosis. These results have the potential to uncover beta cell ER stress mitigation factors and add support to beta cell rest strategies to preserve function.

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.

Montelukast ameliorated pemetrexed-induced cytotoxicity in hepatocytes by mitigating endoplasmic reticulum (ER) stress and nucleotide oligomerization domain-like receptor protein 3 (NLRP3) activation

ABSTRACT Pemetrexed (PEM) is an effective chemotherapeutic drug used for the treatment of clinical non-small-cell lung cancer (NSCLC) and is reported to induce severe hepatotoxicity. Exploring potential drugs which could counteract the side effects of PEM is of great clinical interest. Here, we aim to examine the beneficial effects of Montelukast, a novel anti-asthma drug, against PEM-induced cytotoxicity in hepatocytes, and to explore the underlying mechanism. We found that Montelukast reduces cytotoxicity of PEM in hepatocytes, confirmed by its increasing cell viability and reducing lactate dehydrogenase (LDH) release. In addition, Montelukast attenuated PEM-induced oxidative stress by reducing mitochondrial reactive oxygen species (ROS), increasing reduced glutathione (GSH), and downregulating NADPH oxidase 4 (NOX-4) expression. Importantly, Montelukast suppressed PEM-induced activation of the nucleotide oligomerization domain-like receptor protein 3 (NLRP3) inflammasome and mitigated endoplasmic reticulum (ER) stress by reducing NLRP3, growth arrest, and DNA damage-inducible protein 34 (GADD34), CEBP-homologous protein (CHOP), and also blocking the eukaryotic initiation factor 2 (eIF-2α)/activating transcription factor 4 (ATF4) signaling pathway. Lastly, we found that Montelukast inhibited the transcriptional activity of nuclear factor kappa-B (NF-κB). Montelukast exerted a protective action against PEM-induced cytotoxicity in hepatocytes by mitigating ER stress and NLRP3 activation.

Modulation of heterologous protein secretion in the thermotolerant methylotrophic yeast Ogataea thermomethanolica TBRC 656 by CRISPR-Cas9 system.

The thermotolerant methylotrophic yeast Ogataea thermomethanolica TBRC 656 is a potential host strain for industrial protein production. Heterologous proteins are often retained intracellularly in yeast resulting in endoplasmic reticulum (ER) stress and poor secretion, and despite efforts to engineer protein secretory pathways, heterologous protein production is often lower than expected. We hypothesized that activation of genes involved in the secretory pathway could mitigate ER stress. In this study, we created mutants defective in protein secretory-related functions using clustered regularly interspaced short palindromic repeats (CRISPR)–CRISPR-associated protein 9 (Cas9) tools. Secretion of the model protein xylanase was significantly decreased in loss of function mutants for oxidative stress (sod1Δ) and vacuolar and protein sorting (vps1Δ and ypt7Δ) genes. However, xylanase secretion was unaffected in an autophagy related atg12Δ mutant. Then, we developed a system for sequence-specific activation of target gene expression (CRISPRa) in O. thermomethanolica and used it to activate SOD1, VPS1 and YPT7 genes. Production of both non-glycosylated xylanase and glycosylated phytase was enhanced in the gene activated mutants, demonstrating that CRISPR-Cas9 systems can be used as tools for understanding O. thermomethanolica genes involved in protein secretion, which could be applied for increasing heterologous protein secretion in this yeast.

SIMP1 modulates salt tolerance by elevating ERAD efficiency through UMP1A-mediated proteasome maturation in plants.

Salt stress significantly induces accumulation of misfolded or unfolded proteins in plants. Endoplasmic reticulum (ER)-associated protein degradation (ERAD) and other degradative machineries function in the degradation of these abnormal proteins, leading to enhanced salt tolerance in plants. Here we characterise that a novel receptor-like kinase, Salt-Induced Malectin-like domain-containing Protein1 (SIMP1), elevates ERAD efficiency during salt stress through UMP1A, a putative proteasome maturation factor in Arabidopsis. SIMP1 loss-of-function caused a salt-hypersensitive phenotype. SIMP1 interacts and phosphorylates UMP1A, and the protein stability of UMP1A is positively regulated by SIMP1. SIMP1 modulates the 26S proteasome maturation possibly through enhancing the recruitment of specific β subunits of the core catalytic particle to UMP1A. Functionally, the SIMP1-UMP1A module plays a positive role in ERAD efficiency in Arabidopsis. The degradation of misfolded/unfolded proteins was impaired in both simp1 and ump1a mutants during salt stress. Consistently, both simp1 and ump1a plants exhibited reduced ER stress tolerance. Phenotypic analysis revealed that SIMP1 regulates salt tolerance through UMP1A at least in part. Taken together, our work demonstrated that SIMP1 modulates plant salt tolerance by promoting proteasome maturation via UMP1A, therefore mitigating ER stress through enhanced ERAD efficiency under saline conditions.

Exercise training mitigates ER stress and UCP2 deficiency-associated coronary vascular dysfunction in atherosclerosis

Endoplasmic reticulum (ER) stress and uncoupling protein-2 (UCP2) activation are opposing modulators of endothelial dysfunction in atherosclerosis. Exercise reduces atherosclerosis plaques and enhances endothelial function. Our aim was to understand how exercise affects ER stress and UCP2 activation, and how that relates to endothelial dysfunction in an atherosclerotic murine model. Wild type (C57BL/6, WT) and apolipoprotein-E-knockout (ApoEtm1Unc, ApoE KO) mice underwent treadmill exercise training (EX) or remained sedentary for 12 weeks. Acetylcholine (ACh)-induced endothelium-dependent vasodilation was determined in the presence of an eNOS inhibitor (L-NAME), UCP2 inhibitor (genipin), and ER stress inducer (tunicamycin). UCP2, ER stress markers and NLRP3 inflammasome signaling were quantified by western blotting. p67phox and superoxide were visualized using immunofluorescence and DHE staining. Nitric oxide (NO) was measured by nitrate/nitrite assay. ACh-induced vasodilation was attenuated in coronary arterioles of ApoE KO mice but improved in ApoE KO-EX mice. Treatment of coronary arterioles with L-NAME, tunicamycin, and genipin significantly attenuated ACh-induced vasodilation in all mice except for ApoE KO mice. Exercise reduced expression of ER stress proteins, TXNIP/NLRP3 inflammasome signaling cascades, and Bax expression in the heart of ApoE KO-EX mice. Further, exercise diminished superoxide production and NADPH oxidase p67phox expression in coronary arterioles while simultaneously increasing UCP2 expression and nitric oxide (NO) production in the heart of ApoE KO-EX mice. Routine exercise alleviates endothelial dysfunction in atherosclerotic coronary arterioles in an eNOS, UCP2, and ER stress signaling specific manner, and resulting in reduced TXNIP/NLRP3 inflammasome activity and oxidative stress.

The Mammalian Ecdysoneless Protein Interacts with RNA Helicase DDX39A To Regulate Nuclear mRNA Export.

ABSTRACTThe mammalian orthologue of ecdysoneless (ECD) protein is required for embryogenesis, cell cycle progression, and mitigation of endoplasmic reticulum stress. Here, we identified key components of the mRNA export complexes as binding partners of ECD and characterized the functional interaction of ECD with key mRNA export-related DEAD BOX protein helicase DDX39A. We find that ECD is involved in RNA export through its interaction with DDX39A. ECD knockdown (KD) blocks mRNA export from the nucleus to the cytoplasm, which is rescued by expression of full-length ECD but not an ECD mutant that is defective in interaction with DDX39A. We have previously shown that ECD protein is overexpressed in ErbB2+ breast cancers (BC). In this study, we extended the analyses to two publicly available BC mRNA The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) data sets. In both data sets, ECD mRNA overexpression correlated with short patient survival, specifically ErbB2+ BC. In the METABRIC data set, ECD overexpression also correlated with poor patient survival in triple-negative breast cancer (TNBC). Furthermore, ECD KD in ErbB2+ BC cells led to a decrease in ErbB2 mRNA level due to a block in its nuclear export and was associated with impairment of oncogenic traits. These findings provide novel mechanistic insight into the physiological and pathological functions of ECD.

Aeration mitigates endoplasmic reticulum stress in Saccharomyces cerevisiae even without mitochondrial respiration

Saccharomyces cerevisiae is a facultative anaerobic organism that grows well under both aerobic and hypoxic conditions in media containing abundant fermentable nutrients such as glucose. In order to deeply understand the physiological dependence of S. cerevisiae on aeration, we checked endoplasmic reticulum (ER)-stress status by monitoring the splicing of HAC1 mRNA, which is promoted by the ER stress-sensor protein, Ire1. HAC1-mRNA splicing that was caused by conventional ER-stressing agents, including low concentrations of dithiothreitol (DTT), was more potent in hypoxic cultures than in aerated cultures. Moreover, growth retardation was observed by adding low-dose DTT into hypoxic cultures of ire1Δ cells. Unexpectedly, aeration mitigated ER stress and DTT-induced impairment of ER oxidative protein folding even when mitochondrial respiration was halted by the ρo mutation. An ER-located protein Ero1 is known to directly consume molecular oxygen to initiate the ER protein oxidation cascade, which promotes oxidative protein folding of ER client proteins. Our further study using ero1-mutant strains suggested that, in addition to mitochondrial respiration, this Ero1-medaited reaction contributes to mitigation of ER stress by molecular oxygen. Taken together, here we demonstrate a scenario in which aeration acts beneficially on S. cerevisiae cells even under fermentative conditions.

Emc3 maintains intestinal homeostasis by preserving secretory lineages

Intestinal exocrine secretory lineages, including goblet cells and Paneth cells, provide vital innate host defense to pathogens. However, how these cells are specified and maintained to ensure intestinal barrier function remains poorly defined. Here we show that endoplasmic reticulum membrane protein complex subunit 3 (Emc3) is essential for differentiation and function of exocrine secretory lineages. Deletion of Emc3 in intestinal epithelium decreases mucus production by goblet cells and Paneth cell population, along with gut microbial dysbiosis, which result in spontaneous inflammation and increased susceptibility to DSS-induced colitis. Moreover, Emc3 deletion impairs stem cell niche function of Paneth cells, thus resulting in intestinal organoid culture failure. Mechanistically, Emc3 deficiency leads to increased endoplasmic reticulum (ER) stress. Mitigating ER stress with tauroursodeoxycholate acid alleviates secretory dysfunction and restores organoid formation. Our study identifies a dominant role of Emc3 in maintaining intestinal mucosal homeostasis.

Apigenin Ameliorates Insulin Resistance and Lipid Accumulation by Endoplasmic Reticulum Stress and SREBP-1c/SREBP-2 Pathway in Palmitate-Induced HepG2 Cells and High-Fat Diet-Fed Mice.

Insulin resistance (IR) is the common basis of diabetes and cardiovascular diseases, and its development is closely associated with lipid metabolism disorder. Flavonoids have definite chemical defense effects, including anti-inflammatory effects, anticancer effects, and antimutation effects. However, the function and mechanism of apigenin (AP, a kind of flavonoid) in IR are still unclear. In our study, intracellular fat accumulation model cells and high-fat diet (HFD)-fed model mice were established using palmitate (PA) and HFD. Mechanistically, we first demonstrated that AP could notably downregulate sterol regulatory element-binding protein 1c (SREBP-1c), sterol regulatory element-binding protein 2 (SREBP-2), fatty acid synthase, stearyl-CoA desaturase 1, and 3-hydroxy-3-methyl-glutaryl-CoA reductase in PA-induced hyperlipidemic cells and mice. Functionally, we verified that AP could markedly reduce lipid accumulation in PA-induced hyperlipidemic cells and decrease the body weight, visceral fat weight, IR, and lipid accumulation in HFD-induced hyperlipidemic mice. Besides, we showed that PA could significantly downregulate endoplasmic reticulum stress (ERS)-related proteins and inhibit ERS. Furthermore, we proved that AP could reduce blood lipids by inhibiting ERS in PA-induced hyperlipidemic cells. Meanwhile, 4-phenyl butyric acid (also called ERS alleviator), like AP, could significantly reduce blood lipids and alleviate IR in HFD-fed model mice. Therefore, we concluded that AP could substantially improve the disorder of lipid metabolism, and its mechanism might be related to the decrease of SREBP-1c, SREBP-2, and downstream genes, the inhibition of ERS, and the reduction of blood lipids and IR. SIGNIFICANCE STATEMENT: Apigenin, a nontoxic and naturally sourced flavonoid, has antihyperlipidemic properties in mice and hepatocyte. This study highlights a new mechanism of apigenin and proposes that these hypolipidemic effects are associated with the mitigation of endoplasmic reticulum stress and insulin resistance in diet-induced obesity. This study might provide translational insight into the prevention and treatment of apigenin in hyperlipidemia-related diseases.

Regulation of the early stages of endoplasmic reticulum inheritance during ER stress.

The endoplasmic reticulum (ER) is one of the largest cytoplasmic organelles in eukaryotic cells and plays a role in many cellular processes, such as the production and quality control of secretory protein, lipid synthesis, and calcium homeostasis. The ER cannot be generated de novo, and thus its proper inheritance during cell division is paramount to the health and survival of the daughter cells. Although previous work has uncovered the cytoskeletal components involved, we still lack a comprehensive understanding of the intricate steps of and the cytoplasmic and membrane-bound components involved in ER inheritance. To directly address these issues, we utilized microfluidics and genetic analyses to show that before nuclear migration, early ER inheritance can be further divided into three distinctive steps. Moreover, we demonstrated that perturbing each of these steps affects the cell’s ability to mitigate ER stress. Thus, proper ER inheritance is essential to ensuring a healthy, functional cell.

Alpha-fetoprotein/endoplasmic reticulum stress signaling mitigates injury in hepatoma cells.

Alpha-fetoprotein (AFP) and endoplasmic reticulum (ER) stress play multiple roles in hepatocellular carcinoma. Here, we analyzed the crosstalk between AFP and ER stress in human hepatoma cells. We induced ER stress in human hepatoma cell lines (HepG2 and SK-Hep1 cells) with thapsigargin (TG, an ER stress inducer), and mitigated ER stress with 4-phenylbutyrate acid (4-PBA, an ER stress inhibitor). AFP expression was knocked down by AFP short hairpin RNA and rescued by the pCI-AFP vector. AFP expression and ER stress were examined, and their roles in apoptosis, necroptosis, and proliferation were analyzed. TG significantly induced ER stress, apoptosis, necroptosis, and intracellular AFP protein levels, and reduced proliferation and AFP mRNA expression as well as supernatant AFP protein levels in HepG2 and SK-Hep1 cells. 4-PBA pretreatment partially reversed those changes in HepG2 cells. By contrast to AFP overexpression, knockdown of AFP significantly exacerbated TG-induced ER stress, apoptosis, and necroptosis, and decreased proliferation and the expression of activating transcription factor 6 alpha. In conclusion, ER stress causes the accumulation of AFP protein, which may be related to the reduction of AFP secretion. Accumulated AFP mitigates apoptosis and necroptosis and restores the proliferation of hepatoma cells by reducing ER stress.