Dual roles of IRE1α inhibition in reversing mitochondrial ROS-induced CD8+ T-cell senescence and exerting direct antitumor effects in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is characterized by the proliferation of malignant plasma cells within the bone marrow (BM) microenvironment, which significantly contributes to immune suppression of CD8+ T cells. Our previous research identified that dysregulation of the IRE1α-XBP1s-SLC38A2 axis leads to decreased glutamine uptake and senescence of CD8+ T cells in MM. However, the underlying mechanisms of T-cell senescence remain unclear.

METHODS

Single-cell RNA sequencing was used to analyze mitochondrial function in CD8+ T cells in MM. The effects of XBP1s and SLC38A2 on mitochondrial reactive oxygen species (mtROS) were evaluated by flow cytometry under loss-of-function experiments. An IRE1α inhibitor (17#) was administered to explore its effects on T-cell senescence and MM cell growth. RNA sequencing was employed to disclose pathway alterations in T cells treated with 17#. The Vk*MYC mouse model was used to assess the impact of 17# on CD8+ T cell senescence and anti-myeloma effects.

RESULTS

BM-derived CD8+ T cells from patients with MM exhibited downregulated expressions of genes critical for glutamine transport (SLC38A2), mitochondrial respiratory chain, and ATP synthesis, while genes associated with ROS were upregulated. Suppression of XBP1s in CD8+ T cells resulted in decreased mtROS levels, whereas inhibition of SLC38A2 increased mtROS levels. Compound 17# significantly reduced senescence marker KLRG1 expression and increased perforin expression in nutrient-deprived BM CD8+ T cells from healthy donors and in BM CD8+ T cells from patients with MM, while promoting T-cell proliferation. Importantly, 17# did not impair the viability of peripheral blood mononuclear cells from healthy donors or alter the immune phenotypes of healthy CD8+ T cells. The NPR2-cGMP-PKG pathway was activated by IRE1α inhibition in restoring T-cell function. Furthermore, 17# exhibited direct inhibitory effects on MM cells. In Vk*MYC mouse model, 17# decreased mtROS levels in BM CD8+ T cells, reduced the proportion of senescent (KLRG1+CD57+CD28-) T cells, and resulted in a lower tumor burden.

CONCLUSION

Inhibiting IRE1α represents a promising strategy to reverse the senescence of CD8+ T cells by mitigating mtROS production. This dual mechanism not only rejuvenates T cells but also directly targets myeloma cells, offering a novel therapeutic approach for MM treatment.

MiR-204-5p mediates PERK inhibition to suppress growth and induce apoptosis in ovarian cancer through the eIF2α/ATF-4/CHOP pathway

The unfolded protein response (UPR) is crucial in maintaining cell survival during stressful conditions, but prolonged ER stress can lead to apoptosis. Based on the evidence acquired, it has been suggested that inhibiting the protein kinase RNA-like ER kinase (PERK) pathway, which constitutes an adaptive branch of UPR, may represent a viable approach for impeding the proliferation of neoplastic cells. This study assesses the influence of PERK inhibition mediated by miR-204-5p on the growth of ovarian cancer cell lines, OVCAR3 and SKOV3. We demonstrated that miR-204-5p significantly downregulated the expression of PERK at the RNA and protein levels. The suppression of PERK, mediated by miR-204-5p, significantly diminished cellular viability and enhanced apoptotic cell death in cells exposed to Tunicamycin (Tm). We ascertained that the inhibition of PERK by miR-204-5p decreased eukaryotic initiation factor 2alpha (eIF2α) phosphorylation. Moreover, activating transcription factor 4 (ATF4) and CCAAT-enhancer-binding homologous protein (CHOP) expression levels were notably elevated in response to miR-204-5p. The expression of Bax and caspase-12 was found to be upregulated, while the expression of Bcl-2 was reduced. This study is the first to demonstrate that silencing the PERK gene through miR-204-5p significantly inhibits cell growth and promotes ER-stress-induced apoptosis in ovarian cancer cells.

Chrysin-loaded PEGylated liposomes protect against alloxan-induced diabetic neuropathy in rats: the interplay between endoplasmic reticulum stress and autophagy

BACKGROUND

Diabetic neuropathy (DN) is recognized as a significant complication arising from diabetes mellitus (DM). Pathogenesis of DN is accelerated by endoplasmic reticulum (ER) stress, which inhibits autophagy and contributes to disease progression. Autophagy is a highly conserved mechanism crucial in mitigating cell death induced by ER stress. Chrysin, a naturally occurring flavonoid, can be found abundantly in honey, propolis, and various plant extracts. Despite possessing advantageous attributes such as being an antioxidant, anti-allergic, anti-inflammatory, anti-fibrotic, and anticancer agent, chrysin exhibits limited bioavailability. The current study aimed to produce a more bioavailable form of chrysin and discover how administering chrysin could alter the neuropathy induced by Alloxan in male rats.

METHODS

Chrysin was formulated using PEGylated liposomes to boost its bioavailability and formulation. Chrysin PEGylated liposomes (Chr-PLs) were characterized for particle size diameter, zeta potential, polydispersity index, transmission electron microscopy, and in vitro drug release. Rats were divided into four groups: control, Alloxan, metformin, and Chr-PLs. In order to determine Chr- PLs' antidiabetic activity and, by extension, its capacity to ameliorate DN, several experiments were carried out. These included measuring acetylcholinesterase, fasting blood glucose, insulin, genes dependent on autophagy or stress in the endoplasmic reticulum, and histopathological analysis.

RESULTS

According to the results, the prepared Chr-PLs exhibited an average particle size of approximately 134 nm. They displayed even distribution of particle sizes. The maximum entrapment efficiency of 90.48 ± 7.75% was achieved. Chr-PLs effectively decreased blood glucose levels by 67.7% and elevated serum acetylcholinesterase levels by 40% compared to diabetic rats. Additionally, Chr-PLs suppressed the expression of ER stress-related genes (ATF-6, CHOP, XBP-1, BiP, JNK, PI3K, Akt, and mTOR by 33%, 39.5%, 32.2%, 44.4%, 40.4%, 39.2%, 39%, and 35.9%, respectively). They also upregulated the miR-301a-5p expression levels by 513% and downregulated miR-301a-5p expression levels by 65%. They also boosted the expression of autophagic markers (AMPK, ULK1, Beclin 1, and LC3-II by 90.3%, 181%, 109%, and 78%, respectively) in the sciatic nerve. The histopathological analysis also showed that Chr-PLs inhibited sciatic nerve degeneration.

CONCLUSION

The findings suggest that Chr-PLs may be helpful in the protection against DN via regulation of ER stress and autophagy.

Arrestin beta-2 deficiency exacerbates periodontal inflammation by mediating activating transcription factor 6 activation and abnormal remodelling of the extracellular matrix

AIM

To investigate the specific role of arrestin beta-2 (ARRB2) in the progression of periodontitis and the underlying mechanisms.

MATERIALS AND METHODS

Single-cell RNA sequencing data were used to analyse gene expression in periodontal tissues from healthy controls and patients with periodontitis. Real-time quantitative polymerase chain reaction, Western blotting and immunohistochemical staining were performed to detect the expression of ARRB2. Furthermore, a ligature-induced periodontitis model was created. Using radiographic and histological methods, RNA sequencing and luciferase assay, the role of ARRB2 in periodontitis and the underlying mechanisms were explored. Finally, the therapeutic effect of melatonin, an inhibitor of activating transcription factor 6 (ATF6), on periodontitis in mice was assessed in both in vivo and in vitro experiments.

RESULTS

ARRB2 expression was up-regulated in inflammatory periodontal tissue. In the ligature-induced mouse model, Arrb2 knockout exacerbated alveolar bone loss (ABL) and extracellular matrix (ECM) degradation. ARRB2 exerted a negative regulatory effect on ATF6, an essential targeted gene. Melatonin ameliorated ABL and an imbalance in ECM remodelling in Arrb2-deficient periodontitis mice.

CONCLUSIONS

ARRB2 mediates ECM remodelling via inhibition of the ATF6 signalling pathway, which ultimately exerts a protective effect on periodontal tissues.

Single-cell RNA sequencing reveals XBP1-SLC38A2 axis as a metabolic regulator in cytotoxic T lymphocytes in multiple myeloma

The mechanisms underlying the functional impairment and metabolic reprogramming of T lymphocytes in multiple myeloma (MM) have not been fully elucidated. In this study, single-cell RNA sequencing was used to compare gene expression profiles in T cells in bone marrow and peripheral blood of 10 newly diagnosed MM patients versus 3 healthy donors. Unbiased bioinformatics analysis revealed 9 cytotoxic T cell clusters. All 9 clusters in MM had higher expression of senescence markers (e.g., KLRG1 and CTSW) than the healthy control; some had higher expression of exhaustion-related markers (e.g., LAG3 and TNFRSF14). Pathway enrichment analyses showed downregulated amino acid metabolism and upregulated unfolded protein response (UPR) pathways, along with absent expression of glutamine transporter SLC38A2 and increased expression of UPR hallmark XBP1 in cytotoxic T cells in MM. In vitro studies revealed that XBP1 inhibited SLC38A2 by directly binding to its promoter, and silencing SLC38A2 resulted in decreased glutamine uptake and immune dysfunction of T cells. This study provided a landscape description of the immunosuppressive and metabolic features in T lymphocytes in MM, and suggested an important role of XBP1-SLC38A2 axis in T cell function.

Apelin/APJ system: an emerging therapeutic target for neurological diseases

Apelin, an endogenous ligand for the G protein-coupled receptor APJ, is extensively expressed in various systems, especially the nervous system. This article reviews the role of apelin/APJ system in neurological diseases. In detail, apelin/APJ system can relieve acute brain injury including subarachnoid hemorrhage, traumatic brain injury, and ischemic stroke. Also, apelin/APJ system has therapeutic effects on chronic neurodegenerative disease models, involving the regulation of neurotrophic factors, neuroendocrine, oxidative stress, neuroinflammation, neuronal apoptosis, and autophagy. In addition, through different routes of administration, apelin/APJ system has a biphasic effect on depression, epilepsy, and pain. However, apelin/APJ system exacerbates the proliferation and invasion of glioblastoma. Thus, apelin/APJ system is expected to be a therapeutic target for the treatment of nervous system diseases.

Melatonin Can Modulate Neurodegenerative Diseases by Regulating Endoplasmic Reticulum Stress

As people age, their risks of developing degenerative diseases such as cancer, diabetes, Parkinson's Disease (PD), Alzheimer's Disease (AD), rheumatoid arthritis, and osteoporosis are generally increasing. Millions of people worldwide suffer from these diseases as they age. In most countries, neurodegenerative diseases are generally recognized as the number one cause afflicting the elderly. Endoplasmic reticulum (ER) stress has been suggested to be associated with some human neurological diseases, such as PD and AD. Melatonin, a neuroendocrine hormone mainly synthesized in the pineal gland, is involved in pleiotropically biological functions, including the control of the circadian rhythm, immune enhancement, and antioxidant, anti-aging, and anti-tumor effects. Although there are many papers on the prevention or suppression of diseases by melatonin, there are very few papers about the effects of melatonin on ER stress in neurons and neurodegenerative diseases. This paper aims to summarize and present the effects of melatonin reported so far, focusing on its effects on neurons and neurodegenerative diseases related to ER stress. Studies have shown that the primary target molecule of ER stress for melatonin is CHOP, and PERK and GRP78/BiP are the secondary target molecules. Therefore, melatonin is crucial in protecting neurons and treating neurodegeneration against ER stress.

MicroRNA-30c-2-3p regulates ER stress and induces apoptosis in ovarian cancer cells underlying ER stress

Ovarian cancer is a common gynecologic cancer with a high rate of recurrence, drug resistance, and mortality, thereby necessitating novel molecular target therapies. Ovarian cancer as a solid tumor has constantly been challenged by endoplasmic reticulum stress (ERS). Currently, XBP1 as a therapeutic target in solid tumors plays a key role in adaptation to ERS. Single-stranded RNAs usually modulate posttranscriptional of the gene activity. miR-30c-2-3p has been demonstrated to inhibit the expression of XBP1. Here, we evaluated the effect of miR-30c-2-3p on controlling XBP1-CHOP-BIM and its apoptotic effects on ovarian cancer cell lines during ERS. The ER stress was assessed using Thioflavin T staining in OVCAR3 and SKOV3 cells. The expression of ER stress genes was measured by QRT-PCR. The protein levels of XBP1(s), BIP/GRP78, CHOP, and BIM were evaluated using Western blotting. Cell viability and apoptosis in STF-083010 and Tunicamycin (Tm) co-treated cells were evaluated using BrdU, MTT, Annexin V-FITC/PI staining, and caspase-12 and -3 activities assays. We found that miR-30c-2-3p significantly decreased the folding capacity of ER, leading to ERS intensification (P<0.05). Additionally, the Western blot analysis showed the modest up-regulation of CHOP and BIM with pro-apoptotic activity and down-regulation of the BIP protein. Furthermore, mimic miR-30c-2-3p transfection not only decreased cell proliferation but also induced cell death in ovarian cancer cells in response to the Tm-treatment. Our results indicated that the apoptotic pathway was induced possibly through activation of caspases -12 and -3 and elevation of the Bax/Bcl-2 ratio. Overall, the present paper adds new evidence to the possible treatment of miR-30c-2-3p via impeding the XBP1 transcription in ovarian cancer cells provoking apoptotic pathways by XBP1/CHOP/BIM mediators.

Melatonin and its anti-glioma functions: a comprehensive review

Melatonin (N-acetyl-5-methoxytryptamine) is a naturally synthesized hormone secreted from the pineal gland in a variety of animals and is primarily involved in the regulation of the circadian rhythm, which is the natural cycle controlling sleep in organisms. Melatonin acts on specific receptors and has an important role in overall energy metabolism. This review encompasses several aspects of melatonin activity, such as synthesis, source, structure, distribution, function, signaling and its role in normal physiology. The review highlights the cellular signaling and messenger systems involved in melatonin's action on the body and their wider implications, the distribution and diverse action of different melatonin receptors in specific areas of the brain, and the pharmacological agonists and antagonists that have specific action on these melatonin receptors. This review also incorporates the antitumor effects of melatonin in considerable detail, emphasizing on melatonin's role as an adjuvant therapeutic agent in glioma treatment. We conclude that the diminishing levels of melatonin have significant debilitating effects on normal physiology and can also be associated with malignant conditions such as glioma. Based on the review of the available evidence, our study provides a broad platform for a better understanding of the specific roles of melatonin and serves as a starting point for further investigation into the therapeutic effect of melatonin in glioma as an adjuvant therapeutic agent.

Celastrol ameliorates endoplasmic stress-mediated apoptosis of osteoarthritis via regulating ATF-6/CHOP signalling pathway

Objectives

Osteoarthritis (OA) is a common degenerative joint disease with the pathological features of the reduced cartilage cellularity. Celastrol, a compound from Tripterygium wilfordii, exerted therapeutic effects on arthritis, but the potential mechanism remains unclear.

Methods

Tunicamycin was used to establish a model of OA in vitro, and ACLT surgery model in rats was applied to verify the mechanism. Chondrocytes were isolated from the knee articular cartilage of rabbit. MTT and flow cytometry assay were used to detect cell viability and apoptosis rate. Haematoxylin–eosin staining was used to assess for the histopathological changes. The activity and expression of apoptosis-related factors and ERs (endoplasmic reticulum stress)-related factors were detected by ELISA, WB, PCR and IHC, respectively.

Key findings

Celastrol exhibited significant enhancement on cell viability and reduced the rate of apoptosis in Tm-exposed chondrocytes. Celastrol reduced enzyme activity and protein expression of caspase-3, caspase-6 and caspase-9, decreased Bip, Atf6, Chop and Xbp-1 expression both at protein and mRNA levels. Celastrol showed a more significant effect on cell apoptosis rate and mRNA expression in the combination with 4-PBA.

Conclusions

This study reveals that celastrol may prevent OA by inhibiting the ERs-mediated apoptosis. All these might supply beneficial hints for celastrol on OA treatment.

Mechanism of inositol-requiring enzyme 1-alpha inhibition in endoplasmic reticulum stress and apoptosis in ovarian cancer cells

IRE1α endonuclease is a key regulator of endoplasmic reticulum (ER) stress that controls cell survival/apoptosis in cancers. Inhibition of IRE1α endonuclease leads to decreased splice XBP1 which decreases cell proliferation and increases cell death in cancer cells. Therefore, this study investigated the effects and mechanism of STF-083010 (an IRE1α inhibitor) on the cell growth/apoptosis of ovarian malignant cells via the XBP1-CHOP-Bim pathway following the induction of ER stress (ERS). ERS in OVCAR3 and SKOV3 cells was measured using Thioflavin T staining. The expression of ER stress response genes was evaluated by QRT-PCR. The levels of XBP1(s), PERK, phospho-PERK, p-PP2A, ATF4, BIP/GRP78, CHOP, and Bim proteins were evaluated using western blotting. Cell viability and apoptosis in STF-083010 and Tunicamycin (Tm) co-treated cells were assessed using BrdU, MTT, Annexin V-FITC/PI staining, and caspases-12 and -3 activity assays. The results showed increased XBP1, CHOP, and ATF-4 mRNA expression levels as well as high protein aggregation in STF-083010 and Tm co-treated cells. The IRE1α inhibitor down-regulated sXBP1 and BIP proteins, while XBP-1, p-PERK, ATF-4, CHOP, and Bim proteins were up-regulated. STF-083010 reduced cell proliferation and induced apoptosis through the activation of caspases-12 and -3 and Bax/Bcl-2 protein expression. In summary, the present data revealed the effects of STF-083010 in ER stress and apoptosis as well as signaling via XBP1/CHOP/Bim mediators. Thus, STF-083010 is proposed as a new target for the control of ERS in ovarian cancer cells.

Lupenone Protects Neuroblastoma SH-SY5y Cells Against Methamphetamine-Induced Apoptotic Cell Death via PI3K/Akt/mTOR Signaling Pathway

Methamphetamine (METH) is an addictive psychostimulant showing neurotoxicity through neuronal apoptosis and the neuro-inflammatory pathway. Lupenone, a lupane triterpenoid, is an isolated compound exhibiting anti-oxidative, anti-inflammation, and anti-diabetic activities. However, whether lupenone plays a protective role against apoptosis induced by METH in SH-SY5y neuroblastoma cells remains unknown. In the present study, we elucidated that lupenone had no toxicity to SH-SY5y cells at different concentrations. On the other hand, we found that the treatment of SH-SY5y cells with an optimal concentration of lupenone could lead to protection against cell death induced by METH. AnnexinV/PI apoptosis analysis revealed a dramatically reduced level of the apoptotic cell population in lupenon and METH treated SH-SY5y cells. Moreover, diminished expression of anti-apoptotic proteins, including Bcl-2, Caspase3, Caspase7, and Caspase8 in METH-exposed SH-SY5y cells, was significantly recovered by treatment with lupenone. This protection in the expression of anti-apoptotic proteins was due to an increased phosphorylation level of PI3K/Akt in METH-treated SH-SY5y cells pre-incubated with lupenone. These findings suggest that lupenone can protect SH-SY5y cells against METH-induced neuronal apoptosis through the PI3K/Akt pathway.

Relevance of Translation Initiation in Diffuse Glioma Biology and its Therapeutic Potential

Cancer cells are continually exposed to environmental stressors forcing them to adapt their protein production to survive. The translational machinery can be recruited by malignant cells to synthesize proteins required to promote their survival, even in times of high physiological and pathological stress. This phenomenon has been described in several cancers including in gliomas. Abnormal regulation of translation has encouraged the development of new therapeutics targeting the protein synthesis pathway. This approach could be meaningful for glioma given the fact that the median survival following diagnosis of the highest grade of glioma remains short despite current therapy. The identification of new targets for the development of novel therapeutics is therefore needed in order to improve this devastating overall survival rate. This review discusses current literature on translation in gliomas with a focus on the initiation step covering both the cap-dependent and cap-independent modes of initiation. The different translation initiation protagonists will be described in normal conditions and then in gliomas. In addition, their gene expression in gliomas will systematically be examined using two freely available datasets. Finally, we will discuss different pathways regulating translation initiation and current drugs targeting the translational machinery and their potential for the treatment of gliomas.

Identification of cytotoxic markers in methamphetamine treated rat C6 astroglia-like cells

Methamphetamine (METH) is a powerfully addictive psychostimulant that has a pronounced effect on the central nervous system (CNS). The present study aimed to assess METH toxicity in differentiated C6 astroglia-like cells through biochemical and toxicity markers with acute (1 h) and chronic (48 h) treatments. In the absence of external stimulants, cellular differentiation of neuronal morphology was achieved through reduced serum (2.5%) in the medium. The cells displayed branched neurite-like processes with extensive intercellular connections. Results indicated that acute METH treatment neither altered the cell morphology nor killed the cells, which echoed with lack of consequence on reactive oxygen species (ROS), nitric oxide (NO) or inhibition of any cell cycle phases except induction of cytoplasmic vacuoles. On the other hand, chronic treatment at 1 mM or above destroyed the neurite-like processors and decreased the cell viability that paralleled with increased levels of ROS, lipid peroxidation and lactate, depletion in glutathione (GSH) level and inhibition at G0/G1 phase of cell cycle, leading to apoptosis. Pre-treatment of cells with N-acetyl cysteine (NAC, 2.5 mM for 1 h) followed by METH co-treatment for 48 h rescued the cells completely from toxicity by decreasing ROS through increased GSH. Our results provide evidence that increased ROS and GSH depletion underlie the cytotoxic effects of METH in the cells. Since loss in neurite connections and intracellular changes can lead to psychiatric illnesses in drug users, the evidence that we show in our study suggests that these are also contributing factors for psychiatric-illnesses in METH addicts.

The role of melatonin in targeting cell signaling pathways in neurodegeneration

Neurodegenerative diseases are typified by neuronal loss associated with progressive dysfunction and clinical presentation. Neurodegenerative diseases are characterized by the intra- and extracellular conglomeration of misfolded proteins that occur because of abnormal protein dynamics and genetic manipulations; these trigger processes of cell death in these disorders. The disrupted signaling mechanisms involved are oxidative stress-mediated mitochondrial and calcium signaling deregulation, alterations in immune and inflammatory signaling, disruption of autophagic integrity, proteostasis dysfunction, and anomalies in the insulin, Notch, and Wnt/β-catenin signaling pathways. Herein, we accentuate some of the contemporary translational approaches made in characterizing the underlying mechanisms of neurodegeneration. Melatonin-induced cognitive enhancement and inhibition of oxidative signaling substantiates the efficacy of melatonin in combating neurodegenerative processes. Our review considers in detail the possible roles of melatonin in understanding the synergistic pathogenic mechanisms between aggregated proteins and in regulating, modulating, and preventing the altered signaling mechanisms discovered in cellular and animal models along with clinical evaluations pertaining to neurodegeneration. Furthermore, this review showcases the therapeutic potential of melatonin in preventing and treating neurodegenerative diseases with optimum prognosis.

Melatonin Protects Against Neuronal Apoptosis via Suppression of the ATF6/CHOP Pathway in a Rat Model of Intracerebral Hemorrhage

Neuronal apoptosis is an important factor accounting for the poor outcomes of intracerebral hemorrhage (ICH). This study first showed that inhibition of activating transcription factor 6 (ATF6) could alleviate secondary brain injury through anti-apoptosis after ICH in rats. Melatonin, ATF6 and CCAAT/enhancer-binding protein homologous protein (CHOP) siRNAs were applied in this study. Brain edema, neurological functions, blood-brain barrier (BBB) integrity were evaluated at 24 h after ICH. Western blot analysis was used to evaluate the protein level of target proteins (ATF6, CHOP, Bip, Bcl-2, Bax, and cleaved caspase-3). Reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the mRNA level of ATF6, CHOP and cleaved caspase-3. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and caspase-3 immunofluorescence staining were applied to evaluate the neuronal cell death. The results suggested that the levels of ATF6 and its downstream protein, CHOP, were upregulated and reached the peak at 24 h after ICH. ATF6 was highly expressed in neurons. The administration of melatonin significantly decreased the mRNA and protein levels of ATF6, and its downstream targets, CHOP and cleaved caspase-3, but increased the Bcl-2/Bax ratio, which ameliorated the neurological functions. The CHOP siRNA significantly reversed the pro-apoptotic effect induced by the increased ATF6 level after ICH. Melatonin could protect against neuronal apoptosis via suppression of ATF6/CHOP arm of ER-stress-response pathway.

Apelin-13 Alleviates Early Brain Injury after Subarachnoid Hemorrhage via Suppression of Endoplasmic Reticulum Stress-mediated Apoptosis and Blood-Brain Barrier Disruption: Possible Involvement of ATF6/CHOP Pathway

Neuronal apoptosis plays important roles in the early brain injury after subarachnoid hemorrhage (SAH). This study first showed that inhibition of activating transcription factor 6 (ATF6) by apelin-13 could reduce endoplasmic reticulum (ER)-stress-mediated apoptosis and blood-brain-barrier (BBB) disruption after SAH. We chose apelin-13, ATF6 and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) siRNAs to verify the hypothesis. Brain water content, neurological behavior and Evans Blue (EB) were assessed at 24 h after SAH. Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) were applied to evaluate the expression of targets in both protein and mRNA levels. Neuronal apoptosis was assessed with Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) and caspase-3 staining. The results showed that the levels of ATF6, and its downstream protein, CHOP were upregulated and reached the peak at 24 h after SAH. ATF6 was highly expressed in neurons. The administration of apelin-13 could significantly reduce the mRNA and protein levels of ATF6, and its downstream targets, CHOP and caspase-3, but increase the Bcl-2/Bax ratio, Claudin-5, Occludin and ZO-1. What's more, the administration of apelin-13 could reduce brain edema, ameliorate BBB disruption and improve neurological functions. However, the CHOP siRNA could significantly reverse the pro-apoptotic effect induced by the increased ATF6 level after SAH. Apelin-13 could exert its neuroprotective effects via suppression of ATF6/CHOP arm of ER-stress-response pathway in the early brain injury after SAH.

Methamphetamine exposure triggers apoptosis and autophagy in neuronal cells by activating the C/EBPβ-related signaling pathway

Methamphetamine (Meth) is a widely abused psychoactive drug that primarily damages the nervous system, notably causing dopaminergic neuronal apoptosis. CCAAT-enhancer binding protein (C/EBPβ) is a transcription factor and an important regulator of cell apoptosis and autophagy. Insulin-like growth factor binding protein (IGFBP5) is a proapoptotic factor that mediates Meth-induced neuronal apoptosis, and Trib3 (tribbles pseudokinase 3) is an endoplasmic reticulum (ER) stress-inducible gene involved in autophagic cell death through the mammalian target of rapamycin (mTOR) signaling pathway. To test the hypothesis that C/EBPβ is involved in Meth-induced IGFBP5-mediated neuronal apoptosis and Trib3-mediated neuronal autophagy, we measured the protein expression of C/EBPβ after Meth exposure and evaluated the effects of silencing C/EBPβ, IGFBP5, or Trib3 on Meth-induced apoptosis and autophagy in neuronal cells and in the rat striatum after intrastriatal Meth injection. We found that, at relatively high doses, Meth exposure increased C/EBPβ protein expression, which was accompanied by increased neuronal apoptosis and autophagy; triggered the IGFBP5-mediated, p53-up-regulated modulator of apoptosis (PUMA)-related mitochondrial apoptotic signaling pathway; and stimulated the Trib3-mediated ER stress signaling pathway through the Akt-mTOR signaling axis. We also found that autophagy is an early response to Meth-induced stress upstream of apoptosis and plays a detrimental role in Meth-induced neuronal cell death. These results suggest that Meth exposure induces C/EBPβ expression, which plays an essential role in the neuronal apoptosis and autophagy induced by relatively high doses of Meth; however, relatively low concentrations of Meth did not change the expression of C/EBPβ in vitro. Further studies are needed to elucidate the role of C/EBPβ in low-dose Meth-induced neurotoxicity.-Xu, X., Huang, E., Luo, B., Cai, D., Zhao, X., Luo, Q., Jin, Y., Chen, L., Wang, Q., Liu, C., Lin, Z., Xie, W.-B., Wang, H. Methamphetamine exposure triggers apoptosis and autophagy in neuronal cells by activating the C/EBPβ-related signaling pathway.

Endoplasmic Reticulum Stress Mediates Methamphetamine-Induced Blood-Brain Barrier Damage

Methamphetamine (METH) abuse causes serious health problems worldwide, and long-term use of METH disrupts the blood-brain barrier (BBB). Herein, we explored the potential mechanism of endoplasmic reticulum (ER) stress in METH-induced BBB endothelial cell damage in vitro and the therapeutic potential of endoplasmic reticulum stress inhibitors for METH-induced BBB disruption in C57BL/6J mice. Exposure of immortalized BMVEC (bEnd.3) cells to METH significantly decreased cell viability, induced apoptosis, and diminished the tightness of cell monolayers. METH activated ER stress sensor proteins, including PERK, ATF6, and IRE1, and upregulated the pro-apoptotic protein CHOP. The ER stress inhibitors significantly blocked the upregulation of CHOP. Knockdown of CHOP protected bEnd.3 cells from METH-induced cytotoxicity. Furthermore, METH elevated the production of reactive oxygen species (ROS) and induced the dysfunction of mitochondrial characterized by a Bcl2/Bax ratio decrease, mitochondrial membrane potential collapse, and cytochrome c. ER stress release was partially reversed by ROS inhibition, and cytochrome c release was partially blocked by knockdown of CHOP. Finally, PBA significantly attenuated METH-induced sodium fluorescein (NaFluo) and Evans Blue leakage, as well as tight junction protein loss, in C57BL/6J mice. These data suggest that BBB endothelial cell damage was caused by METH-induced endoplasmic reticulum stress, which further induced mitochondrial dysfunction, and that PBA was an effective treatment for METH-induced BBB disruption.

Melatonin Mediates Protective Effects against Kainic Acid-Induced Neuronal Death through Safeguarding ER Stress and Mitochondrial Disturbance

Kainic acid (KA)-induced neuronal death is linked to mitochondrial dysfunction and ER stress. Melatonin is known to protect hippocampal neurons from KA-induced apoptosis, but the exact mechanisms underlying melatonin protective effects against neuronal mitochondria disorder and ER stress remain uncertain. In this study, we investigated the sheltering roles of melatonin during KA-induced apoptosis by focusing on mitochondrial dysfunction and ER stress mediated signal pathways. KA causes mitochondrial dynamic disorder and dysfunction through calpain activation, leading to neuronal apoptosis. Ca²⁺ chelator BAPTA-AM and calpain inhibitor calpeptin can significantly restore mitochondrial morphology and function. ER stress can also be induced by KA treatment. ER stress inhibitor 4-phenylbutyric acid (PBA) attenuates ER stress-mediated apoptosis and mitochondrial disorder. It is worth noting that calpain activation was also inhibited under PBA administration. Thus, we concluded that melatonin effectively inhibits KA-induced calpain upregulation/activation and mitochondrial deterioration by alleviating Ca²⁺ overload and ER stress.