Endoplasmic Reticulum Stress Signaling Pathways: Activation and Diseases

Low-Dose Hexavalent Chromium Exposure Induces Endoplasmic Reticulum Stress-Mediated Apoptosis in Rat Liver

This study investigated the toxic effects of low-dose hexavalent chromium (Cr(VI)) on rat liver. Male specific pathogen-free (SPF) Sprague-Dawley (SD) rats (4-5 weeks of age) were randomly divided into groups: saline, 0.05 mg/kg Cr(VI), and 0.25 mg/kg Cr(VI). The rats were subjected to intratracheal instillation of K2Cr2O7 suspensions or saline once weekly, for a total of five times. The results showed that the accumulation of Cr(VI) in the blood of the 0.25 mg/kg K2Cr2O7 group was significantly higher than that in the saline group. Transmission electron microscopy (TEM) showed that exposure to hexavalent chromium caused endoplasmic reticulum (ER) oedema and a disordered arrangement. The levels of endoplasmic reticulum stress (ERS)-related proteins (ATF6, P-PERK, P-IRE1, Grp78, and CHOP) in the 0.25 mg/kg K2Cr2O7 group were significantly higher than those in the saline group. The expression of apoptosis-inhibitory protein Bcl-2 was significantly lower in the 0.25 mg/kg K2Cr2O7 group than that in the saline group, and the expression of apoptosis protein Bax was significantly higher in the 0.25 mg/kg K2Cr2O7 group than that in the saline group, indicating that Cr(VI) increased apoptosis. These findings revealed that Cr(VI) may be involved in rat liver injury by initiating ERS-mediated apoptosis. The expression of ATF6, P-PERK, P-IRE1, and Bax in the 0.05 mg/kg K2Cr2O7 group was not significantly different from that in the saline group, and the different effects produced by the two different dose groups provide a possible experimental basis for further study of occupational exposure limits.

Endoplasmic reticulum associated degradation preserves neurons viability by maintaining endoplasmic reticulum homeostasis

Endoplasmic reticulum-associated degradation (ERAD) is a principal quality-control mechanism responsible for targeting misfolded ER proteins for cytosolic degradation. Evidence suggests that impairment of ERAD contributes to neuron dysfunction and death in neurodegenerative diseases, many of which are characterized by accumulation and aggregation of misfolded proteins. However, the physiological role of ERAD in neurons remains unclear. The Sel1L-Hrd1 complex consisting of the E3 ubiquitin ligase Hrd1 and its adaptor protein Sel1L is the best-characterized ERAD machinery. Herein, we showed that Sel1L deficiency specifically in neurons of adult mice impaired the ERAD activity of the Sel1L-Hrd1 complex and led to disruption of ER homeostasis, ER stress and activation of the unfold protein response (UPR). Adult mice with Sel1L deficiency in neurons exhibited weight loss and severe motor dysfunction, and rapidly succumbed to death. Interestingly, Sel1L deficiency in neurons caused global brain atrophy, particularly cerebellar and hippocampal atrophy, in adult mice. Moreover, we found that cerebellar and hippocampal atrophy in these mice resulted from degeneration of Purkinje neurons and hippocampal neurons, respectively. These findings indicate that ERAD is required for maintaining ER homeostasis and the viability and function of neurons in adults under physiological conditions.

Deacetylated MDH1 and IDH1 aggravates PANoptosis in acute liver failure through endoplasmic reticulum stress signaling

Acute liver failure (ALF) is a disease with a high mortality rate and poor prognosis, whose pathogenesis is not fully understood. PANoptosis is a recently proposed mode of cell death characterized by pyroptosis, apoptosis, and necroptosis, but it cannot be explained by any of them alone. This study aims to explore the role of PANoptosis in ALF and the impact and mechanism of deacetylated malate dehydrogenase 1 (MDH1) and isocitrate dehydrogenase 1 (IDH1) on PANoptosis. Our results found that, compared with the control group, the cell viability in the lipopolysaccharide (LPS)/D-galactosamine (D-Gal) group decreased, lactate dehydrogenase (LDH) release increased, cell death increased, and the levels of PANoptosis-related molecules RIPK1, GSDMD, caspase-3, MLKL, IL-18, IL-1β increased, indicating that PANoptosis increased during ALF. Deacetylated MDH1 at K118 and IDH1 at K93 increased the expression of PANoptosis-related molecules RIPK1, GSDMD, caspase-3, MLKL, IL-18, and IL-1β in vivo and in vitro. The deacetylation weakened the inhibitory effect of histone deacetylase (HDAC) inhibitor ACY1215 on PANoptosis-related molecules, suggesting that deacetylated MDH1 at K118 and IDH1 at K93 aggravated PANoptosis during ALF. Deacetylated MDH1 at K118 and IDH1 at K93 also promoted the expression of endoplasmic reticulum stress-related molecules BIP, ATF6, XBP1, and CHOP in vivo and in vitro. The use of endoplasmic reticulum stress inhibitor 4-PBA weakened the promotion effect of deacetylated MDH1 K118 and IDH1 K93 on PANoptosis. The results suggested that deacetylated MDH1 at K118 and IDH1 at K93 may aggravate PANoptosis in ALF through endoplasmic reticulum stress signaling. In conclusion, deacetylated MDH1 and IDH1 may aggravate PANoptosis in ALF, and the mechanism may act through endoplasmic reticulum stress signaling.

miRNA-378 Is Downregulated by XBP1 and Inhibits Growth and Migration of Luminal Breast Cancer Cells

X-box binding protein 1 (XBP1) is a transcription factor that plays a crucial role in the unfolded protein response (UPR), a cellular stress response pathway involved in maintaining protein homeostasis in the endoplasmic reticulum (EnR). While the role of XBP1 in UPR is well-characterised, emerging evidence suggests its involvement in endocrine resistance in breast cancer. The transcriptional activity of spliced XBP1 (XBP1s) is a major component of its biological effects, but the targets of XBP1s in estrogen receptor (ER)-positive breast cancer are not well understood. Here, we show that the expression of miR-378 and PPARGC1B (host gene of miR-378) is downregulated during UPR. Using chemical and genetic methods, we show that XBP1s is necessary and sufficient for the downregulation of miR-378 and PPARGC1B. Our results show that overexpression of miR-378 significantly suppressed cell growth, colony formation, and migration of ER-positive breast cancer cells. Further, we found that expression of miR-378 sensitised the cells to UPR-induced cell death and anti-estrogens. The expression of miR-378 and PPARGC1B was downregulated in breast cancer, and higher expression of miR-378 is associated with better outcomes in ER-positive breast cancer. We found that miR-378 upregulates the expression of several genes that regulate type I interferon signalling. Analysis of separate cohorts of breast cancer patients showed that a gene signature derived from miR-378 upregulated genes showed a strong association with improved overall and recurrence-free survival in breast cancer. Our results suggest a growth-suppressive role for miR-378 in ER-positive breast cancer where downregulation of miR-378 by XBP1 contributes to endocrine resistance in ER-positive breast cancer.

Resistance exercise stress: theoretical mechanisms for growth hormone processing and release from the anterior pituitary somatotroph

Heavy resistance exercise (HRE) is the most effective method for inducing muscular hypertrophy and stimulating anabolic hormones, including growth hormone, into the blood. In this review, we explore possible mechanisms within the GH secretory pathway of the pituitary somatotroph, which are likely to modulate the flow of hormone synthesis and packaging as it is processed prior to exocytosis. Special emphasis is placed on the secretory granule and its possible role as a signaling hub. We also review data that summarize how HRE affects the quality and quantity of the secreted hormone. Finally, these pathway mechanisms are considered in the context of heterogeneity of the somatotroph population in the anterior pituitary.

Revolutionizing Radiotoxicity Management with Mesenchymal Stem Cells and Their Derivatives: A Focus on Radiation-Induced Cystitis

Although radiation therapy plays a crucial role in cancer treatment, and techniques have improved continuously, irradiation induces side effects in healthy tissue. Radiation cystitis is a potential complication following the therapeutic irradiation of pelvic cancers and negatively impacts patients' quality of life (QoL). To date, no effective treatment is available, and this toxicity remains a therapeutic challenge. In recent times, stem cell-based therapy, particularly the use of mesenchymal stem cells (MSC), has gained attention in tissue repair and regeneration due to their easy accessibility and their ability to differentiate into several tissue types, modulate the immune system and secrete substances that help nearby cells grow and heal. In this review, we will summarize the pathophysiological mechanisms of radiation-induced injury to normal tissues, including radiation cystitis (RC). We will then discuss the therapeutic potential and limitations of MSCs and their derivatives, including packaged conditioned media and extracellular vesicles, in the management of radiotoxicity and RC.

Dantrolene and ryanodine receptors in COVID-19: The daunting task and neglected warden

Dantrolene (DTN) is a ryanodine receptor (RyR) antagonist that inhibits Ca²⁺ release from stores in the sarcoplasmic reticulum. DTN is mainly used in the management of malignant hyperthermia. RyRs are highly expressed in immune cells and are involved in different viral infections, including severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), because Ca²⁺ is necessary for viral replication, maturation and release. DTN can inhibit the proliferation of SARS-CoV-2, indicating its potential role in reducing entry and pathogenesis of SARS-CoV-2. DTN may increase clearance of SARS-CoV-2 and promote coronavirus disease 2019 (COVID-19) recovery by shortening the period of infection. DTN inhibits N-methyl-D-aspartate (NMDA) mediated platelets aggregations and thrombosis. Therefore, DTN may inhibit thrombosis and coagulopathy in COVID-19 through suppression of platelet NMDA receptors. Moreover, DTN has a neuroprotective effect against SARS-CoV-2 infection-induced brain injury through modulation of NMDA receptors, which are involved in excitotoxicity, neuronal injury and the development of neuropsychiatric disorders. In conclusion, DTN by inhibiting RyRs may attenuate inflammatory disorders in SARS-CoV-2 infection and associated cardio-pulmonary complications. Therefore, DNT could be a promising drug therapy against COVID-19. Preclinical and clinical studies are warranted in this regards.

Endoplasmic reticulum stress in liver diseases

The endoplasmic reticulum (ER) is an intracellular organelle that fosters the correct folding of linear polypeptides and proteins, a process tightly governed by the ER-resident enzymes and chaperones. Failure to shape the proper 3-dimensional architecture of proteins culminates in the accumulation of misfolded or unfolded proteins within the ER, disturbs ER homeostasis, and leads to canonically defined ER stress. Recent studies have elucidated that cellular perturbations, such as lipotoxicity, can also lead to ER stress. In response to ER stress, the unfolded protein response (UPR) is activated to reestablish ER homeostasis ("adaptive UPR"), or, conversely, to provoke cell death when ER stress is overwhelmed and sustained ("maladaptive UPR"). It is well documented that ER stress contributes to the onset and progression of multiple hepatic pathologies including NAFLD, alcohol-associated liver disease, viral hepatitis, liver ischemia, drug toxicity, and liver cancers. Here, we review key studies dealing with the emerging role of ER stress and the UPR in the pathophysiology of liver diseases from cellular, murine, and human models. Specifically, we will summarize current available knowledge on pharmacological and non-pharmacological interventions that may be used to target maladaptive UPR for the treatment of nonmalignant liver diseases.

Gardenia jasminoides Extract GJ-4 Alleviates Memory Deficiency of Vascular Dementia in Rats through PERK-Mediated Endoplasmic Reticulum Stress Pathway

Endoplasmic reticulum stress (ERS) is involved in the pathological process of vascular dementia (VD). GJ-4 is extracted from Gardenia jasminoides J. Ellis and has been reported to have protective roles in ischemia-related brain damage. However, the role of GJ-4 in ERS has not been elucidated. We established a VD rat model through bilateral common carotid arteries occlusion (2-VO). The rats were intragastrically administrated with GJ-4 (10, 25, and 50[Formula: see text]mg/kg) and nimodipine (10[Formula: see text]mg/kg). Data from a Morris water maze test showed that GJ-4 could significantly alleviate learning and memory deficits in VD rats. Nissl and cleaved caspase-3 staining revealed that GJ-4 can inhibit apoptosis and thus exert a protective role in the brain of 2-VO rats. Western blot results suggested that GJ-4 significantly reduced ERS-related protein expression and inhibited apoptosis through suppression of the PERK/eIF2[Formula: see text]/ATF4/CHOP signaling pathway. For in vitro studies, the oxygen-glucose deprivation (OGD) SH-SY5Y model was employed. Western blot and Hoechst 33342/PI double staining were utilized to explore the effects of crocetin, the main active metabolite of GJ-4. Like GJ-4 in vivo, crocetin in vitro also decreased ERS-related protein expression and inhibited the activation of the PERK/eIF2[Formula: see text]/ATF4/CHOP signaling pathway. Thus, crocetin exerted similar protective roles on OGD challenged SH-SY5Y cells in vitro. In summary, GJ-4 and crocetin reduce the ERS in the brain of VD rats and SY5Y cells subjected to OGD and inhibit neuronal apoptosis through suppression of the PERK/eIF2[Formula: see text]/ATF4/CHOP pathway, suggesting that GJ-4 may be useful for the treatment of VD.

Histidine Deficiency Inhibits Intestinal Antioxidant Capacity and Induces Intestinal Endoplasmic-Reticulum Stress, Inflammatory Response, Apoptosis, and Necroptosis in Largemouth Bass (Micropterus salmoides)

This 56-day study aimed to evaluate the effects of histidine levels on intestinal antioxidant capacity and endoplasmic-reticulum stress (ERS) in largemouth bass (Micropterus salmoides). The initial weights of the largemouth bass were (12.33 ± 0.01) g. They were fed six graded levels of histidine: 0.71% (deficient group), 0.89%, 1.08%, 1.26%, 1.48%, and 1.67%. The results showed that histidine deficiency significantly suppressed the intestinal antioxidant enzyme activities, including SOD, CAT, GPx, and intestinal level of GSH, which was supported by significantly higher levels of intestinal MDA. Moreover, histidine deficiency significantly lowered the mRNA level of nrf2 and upregulated the mRNA level of keap1, which further lowered the mRNA levels of the downstream genes sod, cat, and gpx. Additionally, histidine-deficiency-induced intestinal ERS, which was characterized by activating the PEPK-signalling pathway and IRE1-signalling pathway, including increased core gene expression of pepk, grp78, eif2α, atf4, chopα, ire1, xbp1, traf2, ask1, and jnk1. Dietary histidine deficiency also induced apoptosis and necroptosis in the intestine by upregulating the expressions of proapoptotic genes, including caspase 3, caspase 8, caspase 9, and bax, and necroptosis-related genes, including mlkl and ripk3, while also lowering the mRNA level of the antiapoptotic gene bcl-2. Furthermore, histidine deficiency activated the NF-κB-signalling pathway to induce an inflammatory response, improving the mRNA levels of the proinflammatory factors tnf-α, hepcidin 1, cox2, cd80, and cd83 and lowering the mRNA levels of the anti-inflammatory factors tgf-β1 and ikbα. Similarly, dietary histidine deficiency significantly lowered the intestinal levels of the anti-inflammatory factors TGF-β and IL-10 and upregulated the intestinal levels of the proinflammatory factor TNF-α, showing a trend similar to the gene expression of inflammatory factors. However, dietary histidine deficiency inhibited only the level of C3, and no significant effects were observed for IgM, IgG, HSP70, or IFN-γ. Based on the MDA and T-SOD results, the appropriate dietary histidine requirements of juvenile largemouth bass were 1.32% of the diet (2.81% dietary protein) and 1.47% of the diet (3.13% dietary protein), respectively, as determined by quadratic regression analysis.

Chitooligosaccharide prevents vascular endothelial cell apoptosis by attenuation of endoplasmic reticulum stress via suppression of oxidative stress through Nrf2-SOD1 up-regulation

CONTEXT

Endoplasmic reticulum (ER) stress contributes to endothelium pathological conditions. Chitooligosaccharides (COS) have health benefits, but their effect on endothelial cells is unknown. We demonstrate for the first time a protective effect of COS against ER-induced endothelial cell damage.

OBJECTIVE

To evaluate the protective effect of COS on ER stress-induced apoptosis in endothelial cells.

MATERIAL AND METHODS

Endothelial (EA.hy926) cells were pre-treated with COS (250 or 500 μg/mL) for 24 h, and then treated with 0.16 μg/mL of Tg for 24 h and compared to the untreated control. Apoptosis and necrosis were detected by Annexin V-FITC/propidium iodide co-staining. Reactive oxygen species (ROS) were measured with the DCFH₂-DA and DHE probes. The protective pathway and ER stress markers were evaluated by reverse transcription-polymerase chain reaction, western blot, and immunofluorescence analyses.

RESULTS

COS attenuated ER stress-induced cell death. The viability of EA.hy926 cells treated with Tg alone was 44.97 ± 1% but the COS pre-treatment increased cells viability to 74.74 ± 3.95% in the 250 μg/mL COS and 75.34 ± 2.4% in the 500 μg/mL COS treatments. Tg induced ER stress and ROS, which were associated with ER stress-mediated death. Interestingly, COS reduced ROS by upregulating nuclear factor-E2-related factor 2 (Nrf2), and the oxidative enzymes, superoxide dismutase1 (SOD1) and catalase. COS also suppressed up-regulation of the ER-related apoptosis protein, CHOP induced by Tg.

CONCLUSIONS

COS protected against ER stress-induced apoptosis in endothelial cells by suppressing ROS and up-regulation Nrf2 and SOD1. These findings support the use of COS to protect endothelial cells.

Shrimp Lipid Prevents Endoplasmic Reticulum-Mediated Endothelial Cell Damage

Shrimp contains a fat that benefits cardiovascular function and may help in the prevention of diseases. The stress of essential cellular organelle endoplasmic reticulum (ER) is linked to endothelial dysfunction and damage. This research aimed at investigating the effect of shrimp lipid (SL) on endothelial cells in response to ER stress, as well as the underlying mechanisms. Human endothelial cells were pretreated with SL (250 and 500 μg/mL) for 24 h, and treated with 0.16 μg/mL of Thapsigargin (Tg) for 24 h. The apoptosis and necrosis were detected by Hoechst 33342/propidium iodide (PI) co-staining. Cellular signaling pathways and ER stress markers were evaluated by Western blot analysis and immunofluorescence. SL protected against ER-induced endothelial cell apoptosis. According to the results, the viability of EA.hy926 cells treated with Tg alone was 44.97 ± 1%, but SL (250 μg/mL) pretreatment increased cell viability to 77.26 ± 3.9%, and SL (500 μg/mL) increased to 72.42 ± 4.3%. SL suppressed the increase in ER stress regulator glucose-regulated protein 78 (GRP78) and attenuated the RNA-dependent protein kinase-like ER eukaryotic initiation factor-2α kinase (PERK) and inositol-requiring ER-to-nucleus signaling protein 1 (IRE1) pathways. SL could inhibit cell damage by reducing the ER-related apoptosis protein, C/EBPα-homologous protein (CHOP), induced by ER stress. Taken together, we found the protective effect and mechanism of SL in protecting ER stress-induced endothelial cell apoptosis through suppression of the ER stress pathway. The findings may support the potential use of SL as an approach with a protective effect on endothelial cells.

Family with sequence similarity 134 member B-mediated reticulophagy ameliorates hepatocyte apoptosis induced by dithiothreitol

BACKGROUND

Endoplasmic reticulum (ER) stress-related hepatocyte apoptosis is responsible for multiple hepatic diseases. Previous studies have revealed that endoplasmic reticulophagy (ER-phagy) promotes the selective clearance of damaged ER fragments during ER stress, playing a crucial role in maintaining ER homeostasis and inhibiting apoptosis. Family with sequence similarity 134 member B (FAM134B) is a receptor involved in ER-phagy that can form a complex with calnexin (CNX) and microtubule-associated protein 1 light chain 3 (LC3). The complex can mediate the selective isolation of ER fragments to attenuate hepatocyte apoptosis. However, the precise regulatory mechanisms remain unclear.

AIM

To elucidate the effect of FAM134B-mediated ER-phagy on ER stress-induced apoptosis in buffalo rat liver 3A (BRL-3A) rat hepatocytes and the potential regulatory mechanisms.

METHODS

ER stress-related hepatocyte apoptosis was induced using dithiothreitol (DTT). Proteins related to ER stress and autophagy were measured with western blotting. Protein complex interactions with FAM134B were isolated by co-immunoprecipitation. ER-phagy was evaluated in immunofluorescence experiments. Cell cycle distribution and apoptosis were measured by flow cytometry. Mitochondrial Ca²⁺ levels were evaluated by the co-localization of intracellular Ca²⁺-tracker and Mito-tracker. The small interfering RNA against FAM134B was used to knockdown FAM134B in BRL-3A cells.

RESULTS

ER stress-related and autophagy-related proteins in BRL-3A cells were elevated by both short and long-term DTT treatment. Furthermore, co-immunoprecipitation confirmed an interaction between FAM134B, CNX, FAM134B, and LC3 in BRL-3A cells. Immunofluorescence assays revealed that autolysosomes significantly decreased following short-term DTT treatment, but increased after long-term treatment. Mitochondrial Ca²⁺ levels and apoptotic rates were dramatically elevated, and more cells were arrested in the G1 stage after short-term DTT treatment; however, these decreased 48 h later. Moreover, FAM134B downregulation accelerated mitochondrial apoptotic pathway activation and aggravated hepatocyte apoptosis under ER stress.

CONCLUSION

FAM134B-mediated ER-phagy attenuates hepatocyte apoptosis by suppressing the mitochondrial apoptotic pathway. Our findings provide new evidence highlighting the importance of FAM134B-mediated ER-phagy in attenuating hepatocyte apoptosis.

GRP78 blockade overcomes intrinsic resistance to UBA1 inhibitor TAK-243 in glioblastoma

Glioblastoma multiforme (GBM) is the most aggressive malignant primary brain tumor of the central nervous system. Despite continuous progression in treatment options for GBM like surgery, radiotherapy, and chemotherapy, this disease still has a high rate of recurrence. The endoplasmic reticulum (ER) stress pathway is associated with chemotherapeutic drug resistance. The UBA1 inhibitor TAK-243 can induce strong ER stress. However, the sensitivity of TAK-243 varies greatly in different tumor cells. This study evaluated the antitumor effects of the GRP78 inhibitor, HA15, combined with TAK-243 on GBM in the preclinical models. HA15 synergistically enhanced the sensitivity of GBM cells to TAK-243. When compared with TAK-243 monotherapy, HA15 combined with TAK-243 significantly inhibited GBM cell proliferation. It also induced G2/M-phase arrest in the cell cycle. In vivo studies showed that HA15 combined with TAK-243 significantly inhibited the growth of intracranial GBM and prolonged survival of the tumor-bearing mice. Mechanistically, HA15 and TAK-243 synergistically activated the PERK/ATF4 and IRE1α/XBP1 signaling axes, thereby eventually activating PARP and the Caspase families, which induced cell apoptosis. Our data provided a new strategy for improving the sensitivity of GBM to TAK-243 treatment and experimental basis for further clinical trials to evaluate this combination therapy.

Protein Misfolding and Aggregation: The Relatedness between Parkinson's Disease and Hepatic Endoplasmic Reticulum Storage Disorders

Dysfunction of cellular homeostasis can lead to misfolding of proteins thus acquiring conformations prone to polymerization into pathological aggregates. This process is associated with several disorders, including neurodegenerative diseases, such as Parkinson’s disease (PD), and endoplasmic reticulum storage disorders (ERSDs), like alpha-1-antitrypsin deficiency (AATD) and hereditary hypofibrinogenemia with hepatic storage (HHHS). Given the shared pathophysiological mechanisms involved in such conditions, it is necessary to deepen our understanding of the basic principles of misfolding and aggregation akin to these diseases which, although heterogeneous in symptomatology, present similarities that could lead to potential mutual treatments. Here, we review: (i) the pathological bases leading to misfolding and aggregation of proteins involved in PD, AATD, and HHHS: alpha-synuclein, alpha-1-antitrypsin, and fibrinogen, respectively, (ii) the evidence linking each protein aggregation to the stress mechanisms occurring in the endoplasmic reticulum (ER) of each pathology, (iii) a comparison of the mechanisms related to dysfunction of proteostasis and regulation of homeostasis between the diseases (such as the unfolded protein response and/or autophagy), (iv) and clinical perspectives regarding possible common treatments focused on improving the defensive responses to protein aggregation for diseases as different as PD, and ERSDs.

Ghrelin Alleviates Endoplasmic Reticulum Stress in MC3T3E1 Cells by Inhibiting AMPK Phosphorylation

Ghrelin is a gastric endocrine peptide that has been found to be involved in the process of energy homeostasis and bone physiology in recent years. To explore the effects of ghrelin on endoplasmic reticulum stress (ERS) in MC3T3E1 cells and its possible mechanism, an ERS model was induced by tunicamycin (TM) in the osteoblast line MC3T3E1. TM at 1.5 μg/mL was selected as the experimental concentration found by CCK8 assay. Through the determination of apoptosis, reactive oxygen species production, and endoplasmic reticulum stress-related gene expression, we found that ERS induced by TM can be relieved by ghrelin in a concentration-dependent manner (P < 0.001). Compared with the TM group, ghrelin reduced the expression of ERS-related marker genes induced by TM. Compared with the GSK621 + TM group without ghrelin pretreatment, the mRNA expression of genes in the ghrelin pretreatment group decreased significantly (P < 0.001). The results of protein analysis showed that the levels of BIP, p-AMPK, and cleaved-caspase3 in the TM group increased significantly, while the levels decreased after ghrelin pretreatment. In group GSK621 + TM compared with group GSK621 + ghrelin+TM, ghrelin pretreatment significantly reduced the level of p-AMPK, which is consistent with the trend of the ERS-related proteins BIP and cleaved-caspase3. In conclusion, ghrelin alleviates the ERS induced by TM in a concentration-dependent manner and may or at least partly alleviate the apoptosis induced by ERS in MC3T3E1 cells by inhibiting the phosphorylation of AMPK.

A multitude of signaling pathways associated with Alzheimer's disease and their roles in AD pathogenesis and therapy

The exact molecular mechanisms associated with Alzheimer's disease (AD) pathology continue to represent a mystery. In the past decades, comprehensive data were generated on the involvement of different signaling pathways in the AD pathogenesis. However, the utilization of signaling pathways as potential targets for the development of drugs against AD is rather limited due to the immense complexity of the brain and intricate molecular links between these pathways. Therefore, finding a correlation and cross-talk between these signaling pathways and establishing different therapeutic targets within and between those pathways are needed for better understanding of the biological events responsible for the AD-related neurodegeneration. For example, autophagy is a conservative cellular process that shows link with many other AD-related pathways and is crucial for maintenance of the correct cellular balance by degrading AD-associated pathogenic proteins. Considering the central role of autophagy in AD and its interplay with many other pathways, the finest therapeutic strategy to fight against AD is the use of autophagy as a target. As an essential step in this direction, this comprehensive review represents recent findings on the individual AD-related signaling pathways, describes key features of these pathways and their cross-talk with autophagy, represents current drug development, and introduces some of the multitarget beneficial approaches and strategies for the therapeutic intervention of AD.

IRE1 signaling regulates chondrocyte apoptosis and death fate in the osteoarthritis

IRE1 is an important central regulator of unfolded protein response (UPR) in the endoplasmic reticulum (ER) because of its ability to regulate cell fate as a function of stress sensing. When misfolded proteins accumulated in chondrocytes ER, IRE1 disintegrates with BIP/GRP78 and undergoes dimer/oligomerization and transautophosphorylation. These two processes are mediated through an enzyme activity of IRE1 to activate endoribonuclease and generates XBP1 by unconventional splicing of XBP1 messenger RNA. Thereby promoting the transcription of UPR target genes and apoptosis. The deficiency of inositol-requiring enzyme 1α (IRE1α) in chondrocytes downregulates prosurvival factors XBP1S and Bcl-2, which enhances the apoptosis of chondrocytes through increasing proapoptotic factors caspase-3, p-JNK, and CHOP. Meanwhile, the activation of IRE1α increases chondrocyte viability and reduces cell apoptosis. However, the understanding of IRE1 responses and cell death fate remains controversial. This review provides updated data about the role IRE1 plays in chondrocytes and new insights about the potential efficacy of IRE1 regulation in cartilage repair and osteoarthritis treatment.

LINC00665/miR-379-5p/GRP78 regulates cisplatin sensitivity in gastric cancer by modulating endoplasmic reticulum stress

Acquired resistance to cisplatin (DDP)-based chemotherapy greatly hinders the treatment of gastric cancer (GC). LINC00665 serves as an oncogene in GC. Hence, the current study was designed to investigate the regulatory effects of LINC00665 on DDP-resistance of GC. LINC00665 and miR-379-5p expression levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR) and Glucose regulated protein 78 (GRP78) protein level was measured by western blot assay. Interactions between LINC00665 and miR-379-5p or between miR-379-5p and GRP78 were verified by dual luciferase reporter assay. Cell counting kit 8 (CCK-8) assay and flow cytometry assay respectively determine the proliferative ability and apoptosis of GC cells. Western blot analysis was also performed to detect the protein levels of C/EBP-homologous protein (CHOP), X box binding protein (XBP1) and apoptosis-related proteins. In addition, GRP78 expression was evaluated by immunofluorescence. It was observed that the expression levels of LINC00665 and GRP78 were upregulated, and the expression level of miR-379-5p was downregulated in DDP-sensitive and DDP-resistant GC cell lines. What's more, GRP78 expression and the cell growth inhibition rates of DDP-sensitive and DDP-resistant GC cells had a negative correlation. Additionally, miR-379-5p was a target miRNA of LINC00665, and GRP78 was a target mRNA of miR-379-5p. Functional studies revealed that knockdown of LINC00665 inhibited DDP-resistant GC cell proliferation, induced apoptosis as well as suppressed Endoplasmic reticulum (ER) stress. Mechanistically, knockdown of LINC00665 downregulated GRP78 expression by strengthening miR-379-5p. LINC00665 silencing could overcome DPP-resistance of GC cells by downregulating GRP78 via sponging miR-379-5p, indicating that LINC00665 might be a potential therapeutic target for DDP- resistant GC patients.

A Review of the Role of Endo/Sarcoplasmic Reticulum-Mitochondria Ca2+ Transport in Diseases and Skeletal Muscle Function

The physical contact site between a mitochondrion and endoplasmic reticulum (ER), named the mitochondria-associated membrane (MAM), has emerged as a fundamental platform for regulating the functions of the two organelles and several cellular processes. This includes Ca²⁺ transport from the ER to mitochondria, mitochondrial dynamics, autophagy, apoptosis signalling, ER stress signalling, redox reaction, and membrane structure maintenance. Consequently, the MAM is suggested to be involved in, and as a possible therapeutic target for, some common diseases and impairment in skeletal muscle function, such as insulin resistance and diabetes, obesity, neurodegenerative diseases, Duchenne muscular dystrophy, age-related muscle atrophy, and exercise-induced muscle damage. In the past decade, evidence suggests that alterations in Ca²⁺ transport from the ER to mitochondria, mediated by the macromolecular complex formed by IP₃R, Grp75, and VDAC1, may be a universal mechanism for how ER-mitochondria cross-talk is involved in different physiological/pathological conditions mentioned above. A better understanding of the ER (or sarcoplasmic reticulum in muscle)-mitochondria Ca²⁺ transport system may provide a new perspective for exploring the mechanism of how the MAM is involved in the pathology of diseases and skeletal muscle dysfunction. This review provides a summary of recent research findings in this area.

Mesenchymal Stem Cells for Mitigating Radiotherapy Side Effects

Radiation therapy for cancers also damages healthy cells and causes side effects. Depending on the dosage and exposure region, radiotherapy may induce severe and irreversible injuries to various tissues or organs, especially the skin, intestine, brain, lung, liver, and heart. Therefore, promising treatment strategies to mitigate radiation injury is in pressing need. Recently, stem cell-based therapy generates great attention in clinical care. Among these, mesenchymal stem cells are extensively applied because it is easy to access and capable of mesodermal differentiation, immunomodulation, and paracrine secretion. Here, we summarize the current attempts and discuss the future perspectives about mesenchymal stem cells (MSCs) for mitigating radiotherapy side effects.

Boron Attenuates Heat Stress-Induced Apoptosis by Inhibiting Endoplasmic Reticulum Stress in Mouse Granulosa Cells

Heat stress-induced apoptosis in granulosa cells is mediated by multiple apoptotic signaling pathways, including endoplasmic reticulum (ER) stress. Boron is a naturally occurring trace element with several cytoprotective properties. Nonetheless, the molecular mechanisms involved in the protective functions of boron in granulosa cells undergoing apoptosis caused by heat stress (HS) remain unclear. In this study, we investigated the role of boric acid, a predominant chemical form of boron, in HS-induced apoptotic damage in mouse granulosa cells (mGCs) and explored the underlying mechanisms. We found that HS treatment suppressed cell viability; increased the apoptotic rate of cells; potentiated the activity of caspase-3, a key player in the caspase-mediated apoptotic signaling pathway; and activated ER stress markers, including glucose-regulated protein 78 (GRP78) and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) in mGCs. However, boric acid treatment effectively alleviated the effects of both HS-induced and thapsigargin (an ER stress agonist)-induced apoptosis, such as the enhanced activity of caspase-3 and increase in GRP78 and CHOP expression. Moreover, treatment with 4-phenylbutyrate (4-PBA), an ER stress antagonist, significantly attenuated these HS-induced adverse effects in mGCs. In addition, boric acid supplementation in the culture medium significantly restored the decreased estradiol levels in heat-treated mGCs. The administration of boric acid to female mice previously exposed to hyperthermal conditions effectively restored the levels of serum estradiol in vivo. Collectively, these findings suggest that HS induces apoptosis in mGCs via ER stress pathways and that boron has a protective effect against these adverse effects. This study provides novel insights into the benefits of using boron against heat-induced apoptosis.

MicroRNA and ER stress in cancer

The development of biological technologies in genomics, proteomics, and bioinformatics has led to the identification and characterization of the complete set of coding genes and their roles in various cellular pathways in cancer. Nevertheless, the cellular pathways have not been fully figured out like a jigsaw puzzle with missing pieces. The discovery of noncoding RNAs including microRNAs (miRNAs) has provided the missing pieces of the cellular pathways. Likewise, miRNAs have settled many questions of inexplicable patches in the endoplasmic reticulum (ER) stress pathways. The ER stress-caused pathways typified by the unfolded protein response (UPR) are pivotal processes for cellular homeostasis and survival, rectifying uncontrolled proteostasis and determining the cell fate. Although various factors and pathways have been studied and characterized, the understanding of the ER stress requires more wedges to fill the cracks of knowledge about the ER stress pathways. Moreover, the roles of the ER stress and UPR are still controversial in cancer despite their strong potential to promote cancer. The noncoding RNAs, in particular, miRNAs aid in a better understanding of the ER stress and its role in cancer. In this review, miRNAs that are the more-investigated subtype of noncoding RNAs are focused on the interpretation of the ER stress in cancer, following the introduction of miRNA and ER stress.

Stage-specific expression patterns of ER stress-related molecules in mice molars: Implications for tooth development

The endoplasmic reticulum (ER) is a site where protein folding and posttranslational modifications occur, but when unfolded or misfolded proteins accumulate in the ER lumen, an unfolded protein response (UPR) occurs. A UPR activates ER-stress signalling genes, including inositol-requiring enzyme-1 (Ire1), activating transcription factor 6 (Atf6), and double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase (Perk), to maintain homeostasis. The involvement of ER stress molecules in metabolic disease and hard tissue matrix formation has been established; however, an understanding of the role of ER-stress signalling molecules in tooth development is lacking. The aims of this study are to define the stage-specific expression patterns of ER stress-related molecules and to elucidate their putative functions in the organogenesis of teeth. This study leverages knowledge of the tissue morphology and expression patterns of a range of signalling molecules during tooth development. RT-qPCR, in situ hybridization, and immunohistochemistry analyses were performed to determine the stage-specific expression patterns of ER-stress-related signalling molecules at important stages of tooth development. RT-qPCR analyses showed that Atf6 and Perk have similar expression levels during all stages of tooth development; however, the expression levels of Ire1 and its downstream target X-box binding protein (Xbp1) increased significantly from the cap to the secretory stage of tooth development. In situ hybridization results revealed that Atf6 and Xbp1 were expressed in cells that form the enamel knot at cap stage and ameloblasts and odontoblasts at secretory stage in stage-specific patterns. In addition, Atf6, Ire1, and Xbp1 expression exhibited distinct localization patterns in secretory odontoblasts and ameloblasts of PN0 molars. Overall, our results strongly suggest that ER-stress molecules are involved in tooth development in response to protein overload that occurs during signaling modulations from enamel knots at cap stage and extracellular matrix secretion at secretory stage.

The Genetic and Endoplasmic Reticulum-Mediated Molecular Mechanisms of Primary Open-Angle Glaucoma

Glaucoma is a heterogenous, chronic, progressive group of eye diseases, which results in irreversible loss of vision. There are several types of glaucoma, whereas the primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma, accounting for three-quarters of all glaucoma cases. The pathological mechanisms leading to POAG pathogenesis are multifactorial and still poorly understood, but it is commonly known that significantly elevated intraocular pressure (IOP) plays a crucial role in POAG pathogenesis. Besides, genetic predisposition and aggregation of abrogated proteins within the endoplasmic reticulum (ER) lumen and subsequent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent unfolded protein response (UPR) signaling pathway may also constitute important factors for POAG pathogenesis at the molecular level. Glaucoma is commonly known as a ‘silent thief of sight’, as it remains asymptomatic until later stages, and thus its diagnosis is frequently delayed. Thereby, detailed knowledge about the glaucoma pathophysiology is necessary to develop both biochemical and genetic tests to improve its early diagnosis as well as develop a novel, ground-breaking treatment strategy, as currently used medical therapies against glaucoma are limited and may evoke numerous adverse side-effects in patients.