The endoplasmic reticulum stress and the HIF-1 signalling pathways are involved in the neuronal damage caused by chemical hypoxia

Newsights of endoplasmic reticulum in hypoxia

The endoplasmic reticulum (ER) is important to cells because of its essential functions, including synthesizing three major nutrients and ion transport. When cellular homeostasis is disrupted, ER quality control (ERQC) system is activated effectively to remove misfolded and unfolded proteins through ER-phagy, ER-related degradation (ERAD), and molecular chaperones. When unfolded protein response (UPR) and ER stress are activated, the cell may be suffering a huge blow, and the most probable consequence is apoptosis. The membrane contact points between the ER and sub-organelles contribute to communication between the organelles. The decrease in oxygen concentration affects the morphology and structure of the ER, thereby affecting its function and further disrupting the stable state of cells, leading to the occurrence of disease. In this study, we describe the functions of ER-, ERQC-, and ER-related membrane contact points and their changes under hypoxia, which will help us further understand ER and treat ER-related diseases.

Transcriptomic Analyses of Neurotoxic Astrocytes Derived from Adult Triple Transgenic Alzheimer's Disease Mice

Neurodegenerative diseases such as Alzheimer's disease have been classically studied from a purely neuronocentric point of view. More recent evidences support the notion that other cell populations are involved in disease progression. In this sense, the possible pathogenic role of glial cells like astrocytes is increasingly being recognized. Once faced with tissue damage signals and other stimuli present in disease environments, astrocytes suffer many morphological and functional changes, a process referred as reactive astrogliosis. Studies from murine models and humans suggest that these complex and heterogeneous responses could manifest as disease-specific astrocyte phenotypes. Clear understanding of disease-associated astrocytes is a necessary step to fully disclose neurodegenerative processes, aiding in the design of new therapeutic and diagnostic strategies. In this work, we present the transcriptomics characterization of neurotoxic astrocytic cultures isolated from adult symptomatic animals of the triple transgenic mouse model of Alzheimer's disease (3xTg-AD). According to the observed profile, 3xTg-AD neurotoxic astrocytes show various reactivity features including alteration of the extracellular matrix and release of pro-inflammatory and proliferative factors that could result in harmful effects to neurons. Moreover, these alterations could be a consequence of stress responses at the endoplasmic reticulum and mitochondria as well as of concomitant metabolic adaptations. Present results support the hypothesis that adaptive changes of astrocytic function induced by a stressed microenvironment could later promote harmful astrocyte phenotypes and further accelerate or induce neurodegenerative processes.

Treponema pallidum lipoprotein Tp0768 promotes the migration and adhesion of THP-1 cells to vascular endothelial cells through stress of the endoplasmic reticulum and the NF-κB/HIF-1α pathway

Endothelial cell injury is a key factor in the spread of infection and pathogenicity of Treponema pallidum. The migration and adhesion reaction mediated by T. pallidum lipoprotein plays an important role. This study aimed to systematically explore the migration and adhesion effect of T. pallidum lipoprotein Tp0768 and its molecular mechanism. Stimulating vascular endothelial cells with Tp0768 increased the expression of ICAM-1, MCP-1, and IL-8. Moreover, it promoted the migration and adhesion of THP-1 cells to vascular endothelial cells. Our results revealed that Tp0768 promoted the THP-1 cells migrating and adhering to vascular endothelial cells by the PERK and IRE-1α pathways of endoplasmic reticulum (ER) stress. We further demonstrated that the inhibition of the NF-κB pathway and the downregulation of hypoxia-inducible factor 1 alpha (HIF-1α) reduced the mRNA levels of ICAM-1, MCP-1, and IL-8 induced by Tp0768. Also, the adhesion rate of THP-1 cells to endothelial cells decreased. After inhibiting ER stress, NF-κB p65 nuclear translocation was weakened, and the mRNA level of HIF-1α was also significantly downregulated. Our results indicated that T. pallidum lipoprotein Tp0768 promoted the migration and adhesion of THP-1 cells to vascular endothelial cells through ER stress and NF-κB/HIF-1α pathway.

Role of Ero1α in cognitive impairment induced by chronic hypoxia

Recent reports suggested the endoplasmic reticulum stress (ERS)-associated pathway is involved with cognitive impairment in hypoxia condition. ERO1-like protein alpha (Ero1α), an endoplasmic reticulum membrane-bound N-glycoprotein, has been reported to promote oxidative protein folding. However, no studies have reported whether the Ero1α is trapped in hypoxia-induced neuronal loss through the ERS-associated pathways. In our study, this effect of Ero1α was investigated using C57BL/6J mice, the HT22 cells and primary rat neurons. C57BL/6J mice were modeled in a hypoxic chamber for 4 weeks. Behavioral tests were then carried out to test cognitive functions, including the Morris water maze and fear conditioning test. Proteomics showed that Ero1α distinctly upregulated compared with normoxia group and verified using western blotting. Flow cytometry and immunofluorescence were used to analyze the neuroprotective effect of inhibitor EN460 of Ero1α in the HT22 cells. In C57BL/6J mice, hypoxia significantly caused cognitive decline. Brain slice staining results were also used to confirm this effect. Western blot analysis demonstrated that Ero1α, ERS-associated proteins and apoptosis-associated proteins significantly increased in the hypoxia treated groups, further proliferation-related marker protein decreased. EN460, a selective endoplasmic reticulum oxidation 1 (ERO1) inhibitor, counteracted neuronal apoptosis and ameliorated neuronal cell proliferation in the HT22 cells. Taken together, our data indicate that hypoxia induces cognitive impairment, at least in part, by upregulating Ero1α which contributes to neuronal apoptosis through ERS signaling pathway, providing preliminary experimental evidence that the Ero1α is a promising therapeutic target in hypoxia-induced cognitive deficits.

Thiamine insufficiency induces Hypoxia Inducible Factor-1α as an upstream mediator for neurotoxicity and AD-like pathology

Insufficiencies of the micronutrient thiamine (Vitamin B1) have been associated with inducing Alzheimer's disease (AD)-like neuropathology. The hypometabolic state associated with chronic thiamine insufficiency (TI) has been demonstrated to be a contributor towards the development of amyloid plaque deposition and neurotoxicity. However, the molecular mechanism underlying TI induced AD pathology is still unresolved. Previously, we have established that TI stabilizes the metabolic stress transcriptional factor, Hypoxia Inducible Factor-1α (HIF1α). Utilizing neuronal hippocampal cells (HT22), TI-induced HIF1α activation triggered the amyloidogenic cascade through transcriptional expression and increased activity of β-secretase (BACE1). Knockdown and pharmacological inhibition of HIF1α during TI significantly reduced BACE1 and C-terminal Fragment of 99 amino acids (C99) formation. TI also increased the expression of the HIF1α regulated pro-apoptotic protein, BCL2/adenovirus E1B 19 kDa protein-interacting protein (BNIP3). Correspondingly, cell toxicity during TI conditions was significantly reduced with HIF1α and BNIP3 knockdown. The role of BNIP3 in TI-mediated toxicity was further highlighted by localization of dimeric BNIP3 into the mitochondria and nuclear accumulation of Endonuclease G. Subsequently, TI decreased mitochondrial membrane potential and enhanced chromatin fragmentation. However, cell toxicity via the HIF1α/BNIP3 cascade required TI induced oxidative stress. HIF1α, BACE1 and BNIP3 expression was induced in 3xTg-AD mice after TI and administration with the HIF1α inhibitor YC1 significantly attenuated HIF1α and target genes levels in vivo. Overall, these findings demonstrate a critical stress response during TI involving the induction of HIF1α transcriptional activity that directly promotes neurotoxicity and AD-like pathology.

A β-Cyclodextrin-Based Nanoparticle with Very High Transfection Efficiency Unveils siRNA-Activated TLR3 Responses in Human Prostate Cancer Cells

Synthetic double-stranded small interfering RNAs (siRNAs) mimic interference RNAs (RNAi) and can bind target mRNAs with a high degree of specificity, leading to selective knockdown of the proteins they encode. However, siRNAs are very labile and must be both protected and transported by nanoparticles to be efficiently delivered into cells. In this work, we used a Janus-type polycationic amphiphilic β-cyclodextrin derivative to efficiently transfect siRNAs targeting mRNAs encoding mitogen-activated protein kinase (p42-MAPK) or Ras homolog enriched in brain (Rheb) into different cancer cell lines as well as astrocytes. We took advantage of this high transfection efficiency to simultaneously knock down p42-MAPK and Rheb to boost docetaxel (DTX)-mediated toxicity in two human prostate cancer cell lines (LNCaP and PC3). We found that double knockdown of p42-MAPK and Rheb increased DTX-toxicity in LNCaP but not in PC3 cells. However, we also observed the same effect when scramble siRNA was used, therefore pointing to an off-target effect. Indeed, we found that the siRNA we used in this work induced toll-like receptor 3 activation, leading to β-interferon production and caspase activation. We believe that this mechanism could be very useful as a general strategy to elicit an immune response against prostate cancer cells.

Salubrinal Protects Against Cisplatin-Induced Cochlear Hair Cell Endoplasmic Reticulum Stress by Regulating Eukaryotic Translation Initiation Factor 2α Signalling

Objective

Cisplatin is a broad-spectrum anti-tumour drug commonly used in clinical practice. However, its ototoxicity greatly limits its clinical application, and no effective method is available to prevent this effect. Endoplasmic reticulum stress (ERS) is reportedly involved in cisplatin ototoxicity, but the exact mechanism remains unclear. Therefore, this study aimed to investigate the role of eukaryotic translation initiation factor 2α (eIF2α) signalling and its dephosphorylation inhibitor salubrinal in cisplatin ototoxicity.

Methods

We evaluated whether salubrinal could protect against cisplatin-induced damage in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and mouse cochlear explants. By knocking down eIF2α, we elucidated the vital role of eIF2α in cisplatin-induced damage in HEI-OC1 cells. Whole-mount immunofluorescent staining and confocal microscopy of mouse cochlear explants and HEI-OC1 cells were performed to analyse cisplatin-induced damage in cochlear hair cells and the auditory cell line.

Results

Data suggested salubrinal attenuated cisplatin-induced hair cell injury by inhibiting apoptosis. In addition, salubrinal significantly reduced ERS levels in hair cells via eIF2α signalling, while eIF2α knockdown inhibited the protective effect of salubrinal.

Significance

Salubrinal and eIF2α signalling play a role in protecting against cisplatin-induced ototoxicity, and pharmacological inhibition of eIF2α-mediated ERS is a potential treatment for cisplatin-induced damage in the cochlea and HEI-OC1 cells.

Endoplasmic Reticulum Stress and the Unfolded Protein Response in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an acute cerebrovascular disease characterized by sudden interruption of blood flow in a certain part of the brain, leading to serious disability and death. At present, treatment methods for ischemic stroke are limited to thrombolysis or thrombus removal, but the treatment window is very narrow. However, recovery of cerebral blood circulation further causes cerebral ischemia/reperfusion injury (CIRI). The endoplasmic reticulum (ER) plays an important role in protein secretion, membrane protein folding, transportation, and maintenance of intracellular calcium homeostasis. Endoplasmic reticulum stress (ERS) plays a crucial role in cerebral ischemia pathophysiology. Mild ERS helps improve cell tolerance and restore cell homeostasis; however, excessive or long-term ERS causes apoptotic pathway activation. Specifically, the protein kinase R-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways are significantly activated following initiation of the unfolded protein response (UPR). CIRI-induced apoptosis leads to nerve cell death, which ultimately aggravates neurological deficits in patients. Therefore, it is necessary and important to comprehensively explore the mechanism of ERS in CIRI to identify methods for preserving brain cells and neuronal function after ischemia.

IL-6/STAT3 Induced Neuron Apoptosis in Hypoxia by Downregulating ATF6 Expression

Background: Neuron apoptosis, regulated by endoplasmic reticulum (ER) stress in the hippocampus, is an essential factor influencing the cognitive impairment induced by hypobaric hypoxia. Hypoxia mainly changes the activating transcription factor (ATF6) pathway of ER stress. However, the role of ATF6 in neuron survival, apoptosis, and upstream regulation is still controversial. Methods: We established a hypobaric hypoxia-induced C57BL/6 murine model and cell lines exposed to 1% hypoxia, including PC12 and HT22. First, we tested the expressions of interleukin 6 (IL-6), IL-1β, and IL-10 in C57BL/6 mice's hippocampus under hypoxia using enzyme-linked immunosorbent assay (ELISA). We determined the signal transducer and activator of transcription 3 (STAT3) phosphorylation at tyrosine (Tyr)705 by western blot and the expression of ATF6, 78-kDa glucose-regulated protein (GRP78), and C/-EBP homologous protein (CHOP) related to ER stress by immunofluorescence (IF), western blot, and qRT-PCR; they were then verified on the cell model. Additionally, IL-6 (40 ng/mL) and STAT3 siRNA were used to treat the PC12 cells for 48 and 4 h to activate or silence STAT3, respectively. Subsequently, the cells of siRNA group were exposed to 1% hypoxia for 48 h. Furthermore, the ATF6 and CHOP expressions were detected with western blot and qRT-PCR. Finally, we examined the binding of STAT3 to the ATF6 promoter by chromatin immunoprecipitation (ChIP)-seq. Results: The results showed that IL-6 increased, IL-10 decreased in the hypoxia group, and IL-1β showed no difference between the hypoxia and the normoxia groups. Neuron apoptosis was significantly elevated by exposure to hypoxia for 48h in PC12 cells. The hypobaric hypoxia-induced ER stress proteins, ATF6, GRP78, and CHOP, and the p-STAT3 (Tyr705) expressions increased both in in vivo and in vitro. Besides, STAT3 silencing significantly promoted the ATF6 expression and inhibited CHOP, while STAT3 activation downregulated the expression of ATF6 and upregulated CHOP in PC12 cells. The ChIP-seq assay demonstrated that p-STAT3 (Tyr705) protein could bind to the ATF6 promoter region in HT22 cells. Conclusion: Phosphorylation of STAT3 at the Tyr705 site contributes to hypoxia-induced neuron apoptosis by downregulating ATF6, which might explain the inflammatory reaction and apoptosis of the hippocampal neurons induced by ER stress.

Dexmedetomidine Protects Human Renal Tubular Epithelial HK-2 Cells against Hypoxia/Reoxygenation Injury by Inactivating Endoplasmic Reticulum Stress Pathway

Objective

The study was aimed to investigate the effects and potential mechanisms of Dexmedetomidine (Dex) on hypoxia/reoxygenation (H/R) injury in human renal tubular epithelial HK-2 cells.

Materials and Methods

In this experimental study, HK-2 cells were divided into four groups: control group, Dex group, H/R group, and Dex+H/R group. The cells in control group received no treatment, and cells in Dex group were only treated with 0.1 nmol/L Dex. The cells in H/R group and Dex+H/R group were all treated with H/R (hypoxia for 24 hours and normoxia for 4 hours), and only the cells in Dex+H/R group were pre-administrated with 0.1 nmol/L Dex. Following treatments at 37˚C for 28 hours, cell viability and apoptosis were measured by MTT assay and flow cytometry, respectively. Also, the expressions of hypoxia-inducible factor 1 (HIF-1α), glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), caspase-12 and cleaved caspase-3 were determined by western blot.

Results

The cell viability was significant decreased in H/R group compared with control group (P<0.05), while was significantly increased in Dex+H/R group compared with that in H/R group (P<0.05). However, the change tendency of the cell apoptosis was opposite to that of cell viability. Compared with H/R group, the expression of HIF-1α was evidently up-regulated, while GRP78, CHOP, capase-12 and cleaved caspase-3 expressions were all obviously down- regulated in Dex+H/R group (P<0.05). In addition, the concentrations of malondialdehyde (MDA) in H/R group and Dex+H/R group were 1.68 ± 0.22 nmol/mgprot and 0.85 ± 0.16 nmol/mgprot, respectively. The superoxide dismutase (SOD) activity was higher in Dex+H/R group (121 ± 11 U/L), which which was more than twice larger than that in H/R group (57 ± 10 U/L).

Conclusion

Dex could promote cell viability and inhibit apoptosis through up-regulating HIF-1α, reducing endoplasmic reticulum (ER) stress and mediating oxidative stress, thus ameliorating the H/R injury.

Roles of ERK/Akt signals in mitochondria-dependent and endoplasmic reticulum stress-triggered neuronal cell apoptosis induced by 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene, a major active metabolite of bisphenol A

Bisphenol A (BPA) is recognized as a harmful pollutant in the worldwide. Growing studies have reported that BPA can cause adverse effects and diseases in human, and link to a potential risk factor for development of neurodegenerative diseases (NDs). 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), which generated in the mammalian liver after BPA exposure, is a major active metabolite of BPA. MBP has been suggested to exert greater toxicity than BPA. However, the molecular mechanism of MBP on the neuronal cytotoxicity remains unclear. In this study, MBP exposure significantly reduced Neuro-2a cell viability and induced apoptotic events that MBP (5-15 μM) exhibited greater neuronal cytotoxicity than BPA (50-100 μM). The mitochondria-dependent apoptotic signals including the decrease in mitochondrial membrane potential (MMP) and the increase in cytosolic apoptosis-induced factor (AIF), cytochrome c release, and Bax protein expression were involved in MBP (10 μM)-induced Neuro-2a cell death. Exposure of Neuro-2a cells to MBP (10 μM) also triggered endoplasmic reticulum (ER) stress through the induction of several key molecules including glucose-regulated protein (GRP)78, C/EBP homologous protein (CHOP), X-box binding protein (XBP)-1, protein kinase R-like ER kinase (PERK), eukaryotic initiation factor 2α (eIF2α), inositol-requiring enzyme(IRE)-1, activation transcription factor(AFT)4 and ATF6, and caspase-12. Pretreatment with 4-PBA (an ER stress inhibitor) and specific siRNAs for GRP78, CHOP, and XBP-1 significantly suppressed the expression of these ER stress-related proteins and the activation of caspase-12/-3/-7 in MBP-exposed Neuro-2a cells. Furthermore, MBP (10 μM) exposure dramatically increased the activation of extracellular regulated protein (ERK)1/2 and decreased Akt phosphorylation. Pretreatment with PD98059 (an ERK1/2 inhibitor) and transfection with the overexpression of activation of Akt1 (myr-Akt1) effectively suppressed MBP-induced apoptotic and ER stress-related signals. Collectively, these results demonstrate that MBP exposure exerts neuronal cytotoxicity via the interplay of ERK activation and Akt inactivation-regulated mitochondria-dependent and ER stress-triggered apoptotic pathway, which ultimately leads to neuronal cell death.

Methane supplementation improves graft function in experimental heart transplantation

BACKGROUND

Maintenance of cell viability during cold storage is a key issue in organ transplantation. Methane (CH₄) bioactivity has recently been recognized in ischemia/reperfusion conditions; we therefore hypothesized that cold storage in CH₄-enriched preservation solution can provide an increased defense against organ dysfunction during experimental heart transplantation (HTX).

METHODS

The hearts of donor Lewis rats were stored for 60 minutes in cold histidine-tryptophan-ketoglutarate (Custodiol [CS]) or CH₄-saturated CS solution (CS-CH₄) (n = 12 each). Standard heterotopic HTX was performed, and 60 minutes later, the left ventricular (LV) pressure-volume relationships LV systolic pressure (LVSP), systolic pressure increment (dP/dtmax), diastolic pressure decrement, and coronary blood flow (CBF) were measured. Tissue samples were taken to detect proinflammatory parameters, structural damage (by light microscopy), endoplasmic reticulum (ER) stress, and apoptosis markers (CCAAT/enhancer binding protein [C/EBP] homologous protein, GRP78, glycogen synthase kinase-3β, very low-density lipoprotein receptor, caspase 3 and 9, B-cell lymphoma 2, and bcl-2-like protein 4), whereas mitochondrial functional changes were analyzed by high-resolution respirometry.

RESULTS

LVSP and dP/dtmax increased significantly at the largest pre-load volumes in CS-CH₄ grafts as compared with the CS group (114.5 ± 16.6 mm Hg vs 82.8 ± 4.6 mm Hg and 3,133 ± 430 mm Hg/s vs 1,739 ± 169 mm Hg/s, respectively); the diastolic function and CBF (2.4 ± 0.4 ml/min/g vs 1.3 ± 0.3 ml/min/g) also improved. Mitochondrial oxidative phosphorylation capacity was more preserved (58.5 ± 9.4 pmol/s/ml vs 27.7 ± 6.6 pmol/s/ml), and cytochrome c release was reduced in CS-CH₄ storage. Signs of HTX-caused myocardial damage, level of ER stress, and the transcription of proapoptotic proteins were significantly lower in CS-CH₄ grafts.

CONCLUSION

The addition of CH₄ during 1 hour of cold storage improved early in vitro graft function and reduced mitochondrial dysfunction and activation of inflammation. Evidence shows that CH₄ reduced ER stress-linked proapoptotic signaling.

Differential susceptibility of PC12 and BRL cells and the regulatory role of HIF-1α signaling pathway in response to acute methylmercury exposure under normoxia

Hypoxia-inducible factor 1 (HIF-1) is a critical nuclear transcription factor for adaptation to hypoxia; its regulatable subunit, HIF-1α, is a cytoprotective regulatory factor. We examined the effects of methylmercury (MeHg) in rat adrenal pheochromocytoma (PC12) cells and the rat hepatocyte cell line BRL. MeHg treatment led to time- and concentration-dependent toxicity in both lines with statistically significant cytotoxic effects at 5 μM and 10 μM in PC12 and BRL, respectively, at 0.5 h. HIF-1α protein levels were significantly decreased at 2.5 (PC12) and 5 (BRL) μM MeHg. Furthermore, MeHg reduced the protein levels of HIF-1α and its target genes (glucose transporter-1, vascular endothelial growth factor-A and erythropoietin). Overexpression of HIF-1α significantly attenuated MeHg-induced toxicity in both cell types. Notably, cobalt chloride, a pharmacological inducer of HIF-1α, significantly attenuated MeHg-induced toxicity in BRL but not PC12. In both cell lines, an inhibitor of prolyl hydroxylase, 3, 4-dihydroxybenzoic acid, and the proteasome inhibitor carbobenzoxy-L-leucyl-L-leucyl-L-leucinal(MG132), antagonized MeHg toxicity, while 2-methoxyestradiol, a HIF-1α inhibitor, significantly increased it. These data establish that: (a) neuron-like PC12 cells are more sensitive to MeHg than non-neuronal BRL cells; (b) HIF-1α plays a similar role in MeHg-induced toxicity in both cell lines; and (c) upregulation of HIF-1α offers general cytoprotection against MeHg toxicity in PC12 and BRL cell lines.

Association of the Hepatitis B Virus Large Surface Protein with Viral Infectivity and Endoplasmic Reticulum Stress-mediated Liver Carcinogenesis

Hepatitis B is the most prevalent viral hepatitis worldwide, affecting approximately one-third of the world’s population. Among HBV factors, the surface protein is the most sensitive biomarker for viral infection, given that it is expressed at high levels in all viral infection phases. The large HBV surface protein (LHBs) contains the integral pre-S1 domain, which binds to the HBV receptor sodium taurocholate co transporting polypeptide on the hepatocyte to facilitate viral entry. The accumulation of viral LHBs and its prevalent pre-S mutants in chronic HBV carriers triggers a sustained endoplasmic reticulum (ER) overload response, leading to ER stress-mediated cell proliferation, metabolic switching and genomic instability, which are associated with pro-oncogenic effects. Ground glass hepatocytes identified in HBV-related hepatocellular carcinoma (HCC) patients harbor pre-S deletion variants that largely accumulate in the ER lumen due to mutation-induced protein misfolding and are associated with increased risks of cancer recurrence and metastasis. Moreover, in contrast to the major HBs, which is decreased in tumors to a greater extent than it is in peritumorous regions, LHBs is continuously expressed during tumorigenesis, indicating that LHBs serves as a promising biomarker for HCC in people with CHB. Continuing efforts to delineate the molecular mechanisms by which LHBs regulates pathological changes in CHB patients are important for establishing a correlation between LHBs biomarkers and HCC development.

Gestational Hypoxia Inhibits Pregnancy-Induced Upregulation of Ca2+ Sparks and Spontaneous Transient Outward Currents in Uterine Arteries Via Heightened Endoplasmic Reticulum/Oxidative Stress

Hypoxia during pregnancy profoundly affects uterine vascular adaptation and increases the risk of pregnancy complications, including preeclampsia and fetal intrauterine growth restriction. We recently demonstrated that increases in Ca2+ sparks and spontaneous transient outward currents (STOCs) played an essential role in pregnancy-induced uterine vascular adaptation. In the present study, we hypothesize that gestational hypoxia suppresses Ca2+ sparks/STOCs coupling leading to increased uterine vascular tone via enhanced endoplasmic reticulum (ER)/oxidative stress. Uterine arteries were obtained from nonpregnant and near-term pregnant sheep residing in low altitude or acclimatizing to high-altitude (3801 m) hypoxia for ≈110 days. High-altitude hypoxia suppressed pregnancy-induced upregulation of RyR1 and RyR2 (ryanodine receptor 1 and 2) protein abundance, Ca2+ sparks, and STOCs in uterine arteries. Inhibition of Ca2+ sparks/STOCs with the RyR inhibitor ryanodine significantly increased pressure-dependent myogenic tone in uterine arteries from low-altitude normoxic pregnant animals but not those from high-altitude hypoxic pregnant animals. Gestational hypoxia significantly increased ER/oxidative stress in uterine arteries. Of importance, the hypoxia-mediated suppression of Ca2+ sparks/STOCs and increase in myogenic tone in uterine arteries of pregnant animals were reversed by inhibiting ER/oxidative stress. Of great interest, the impaired sex hormonal regulation of STOCs in high-altitude animals was annulled by scavenging reactive oxygen species but not by inhibiting ER stress. Together, the findings reveal the differential mechanisms of ER and oxidative stresses in suppressing Ca2+ sparks/STOCs and increasing myogenic tone of uterine arteries in hypoxia during gestation, providing new insights into the understanding of pregnancy complications associated with hypoxia.

IL13Rα1 protects against rheumatoid arthritis by combating the apoptotic resistance of fibroblast-like synoviocytes

Background

Endoplasmic reticulum (ER) stress is closely related with the pathological progression of rheumatoid arthritis (RA), and fibroblast-like synoviocytes (FLSs) are known as its resistance against ER stress-induced apoptosis. Studies on overcoming such resistance would provide a novel treatment strategy for RA in a clinical setting.

Methods

IL13Rα1 expression was assessed in the synovial tissue by RT-qPCR, immunohistology, and Western blot. Gain or loss of functional analysis was applied to evaluate the biological roles of IL13Rα1 in RA FLSs. Cell viability and apoptosis were assessed by MTS, Western blot, and flow cytometry. The therapeutic effects of IL13Rα1 on the severity of type II collagen-induced arthritis (CIA) in DBA-/1 mouse model were evaluated by scoring synovitis, hyperplasia, cartilage degradation, and bone destruction.

Results

IL13Rα1 expression was selectively downregulated when RA FLSs were stimulated by ER stress inducers. Functionally, IL13Rα1 overexpression could inhibit the viability, but induce the apoptosis of RA FLSs in the presence of ER stress inducers. Mechanistically, IL13Rα1 promotes cell apoptosis via transcriptionally activating trail expression. Besides, IL13Rα1 could interact and stabilize DR5 protein, thus forming a positive loop involving trail and DR5 to render RA FLSs more susceptible to apoptosis. Additionally, intraarticular injection of IL13Rα1 conferred therapeutic effects in CIA models and showed a limited degree of synovial proliferation and joint destruction.

Conclusions

Together, our data establishes a regulatory role for IL13Rα1 to combat the apoptotic resistance of RA FLSs against ER stress. The inhibitory effects of IL13Rα1 on arthritis progression suggest the therapeutic potential in RA.

Protective effect of the extremolytes ectoine and hydroxyectoine in a porcine organ culture

Purpose

Hypoxic damage to the retina is a relevant component of neurodegenerative pathologies such as glaucoma or retinal ischemia. In porcine retina organ cultures, hypoxic damage can be induced by applying cobalt chloride (CoCl₂). The aim of our study was to investigate possible neuroprotective effects of the extremolytes ectoine and hydroxyectoine in this hypoxia-damaged retina model.

Methods

To simulate hypoxia, porcine retina organ cultures were damaged with 300 μM CoCl₂ for 48 h starting on day 1 (n = 8–9/group). In order to investigate the possible neuroprotective effects of ectoine and hydroxyectoine, 0.5 mM of each extremolyte was added to the culture at the same time as the stressor and for the same duration. On day 8, the retina organ cultures were taken for (immuno)-histochemical examinations. Retinal ganglion cells (RGCs), macroglia, and apoptotic and hypoxic cells were detected with appropriate markers followed by cell counts and group comparisons.

Results

Treatment with ectoine resulted in RGC protection (p < 0.05) and reduced rate of apoptosis (p < 0.001) in hypoxia-treated retina organ cultures. However, the macroglia area and the amount of hypoxic, HIF-1α⁺ cells were unaffected by the ectoine treatment (p = 0.99). Treatment with hydroxyectoine also protected RGCs (p < 0.01) by inhibiting apoptosis (p < 0.001). In addition, the number of hypoxic, HIF-1α⁺ cells could be significantly reduced by treatment with hydroxyectoine (p < 0.05). The macroglia area on the other hand was unchanged after CoCl₂ and treatment with hydroxyectoine.

Conclusion

Both extremolytes had a protective effect on CoCl₂-induced hypoxia in the porcine retina organ culture. Regarding the reduction of hypoxic stress, hydroxyectoine appears to be more effective. Thus, both extremolytes represent an interesting potential new therapeutic approach for patients with ocular diseases in which hypoxic processes play a significant role.

Neuroprotective Effect of the Inhibitor Salubrinal after Cardiac Arrest in a Rodent Model

Cardiac arrest (CA) yields poor neurological outcomes. Salubrinal (Sal), an endoplasmic reticulum (ER) stress inhibitor, has been shown to have neuroprotective effects in both in vivo and in vitro brain injury models. This study investigated the neuroprotective mechanisms of Sal in postresuscitation brain damage in a rodent model of CA. In the present study, rats were subjected to 6 min of CA and then successfully resuscitated. Either Sal (1 mg/kg) or vehicle (DMSO) was injected blindly 30 min before the induction of CA. Neurological status was assessed 24 h after CA, and the cortex was collected for analysis. As a result, we observed that, compared with the vehicle-treated animals, the rats pretreated with Sal exhibited markedly improved neurological performance and cortical mitochondrial morphology 24 h after CA. Moreover, Sal pretreatment was associated with the following: (1) upregulation of superoxide dismutase activity and a reduction in maleic dialdehyde content; (2) preserved mitochondrial membrane potential; (3) amelioration of the abnormal distribution of cytochrome C; and (4) an increased Bcl-2/Bax ratio, decreased cleaved caspase 3 upregulation, and enhanced HIF-1α expression. Our findings suggested that Sal treatment improved neurological dysfunction 24 h after CPR (cardiopulmonary resuscitation), possibly through mitochondrial preservation and stabilizing the structure of HIF-1α.

Deep insights into the response of human cervical carcinoma cells to a new cyano enone-bearing triterpenoid soloxolone methyl: a transcriptome analysis

Semisynthetic triterpenoids, bearing cyano enone functionality in ring A, are considered now as novel promising anti-tumor agents. However, despite the large-scale studies, their effects on cervical carcinoma cells and, moreover, mechanisms underlying cell death activation by such compounds in this cell type have not been fully elucidated. In this work, we attempted to reconstitute the key pathways and master regulators involved in the response of human cervical carcinoma KB-3-1 cells to the novel glycyrrhetinic acid derivative soloxolone methyl (SM) by a transcriptomic approach. Functional annotation of differentially expressed genes, analysis of their cis^- regulatory sequences and protein-protein interaction network clearly indicated that stress of endoplasmic reticulum (ER) is the central event triggered by SM in the cells. A range of key ER stress sensors and transcription factor AP-1 were identified as upstream transcriptional regulators, controlling the response of the cells to SM. Additionally, by using Gene Expression Omnibus data, we showed the ability of SM to modulate the expression of key genes involved in regulation of the high proliferative rate of cervical carcinoma cells. Further Connectivity Map analysis revealed similarity of SM's effects with known ER stress inducers thapsigargin and geldanamycin, targeting SERCA and Grp94, respectively. According to the molecular docking study, SM could snugly fit into the active sites of these proteins in the positions very close to that of both inhibitors. Taken together, our findings provide a basis for the better understanding of the intracellular processes in tumor cells switched on in response to cyano enone-bearing triterpenoids.

SQSTM1/p62-Directed Metabolic Reprogramming Is Essential for Normal Neurodifferentiation

Neurodegenerative disorders are an increasingly common and irreversible burden on society, often affecting the aging population, but their etiology and disease mechanisms are poorly understood. Studying monogenic neurodegenerative diseases with known genetic cause provides an opportunity to understand cellular mechanisms also affected in more complex disorders. We recently reported that loss-of-function mutations in the autophagy adaptor protein SQSTM1/p62 lead to a slowly progressive neurodegenerative disease presenting in childhood. To further elucidate the neuronal involvement, we studied the cellular consequences of loss of p62 in a neuroepithelial stem cell (NESC) model and differentiated neurons derived from reprogrammed p62 patient cells or by CRISPR/Cas9-directed gene editing in NESCs. Transcriptomic and proteomic analyses suggest that p62 is essential for neuronal differentiation by controlling the metabolic shift from aerobic glycolysis to oxidative phosphorylation required for neuronal maturation. This shift is blocked by the failure to sufficiently downregulate lactate dehydrogenase expression due to the loss of p62, possibly through impaired Hif-1α downregulation and increased sensitivity to oxidative stress. The findings imply an important role for p62 in neuronal energy metabolism and particularly in the regulation of the shift between glycolysis and oxidative phosphorylation required for normal neurodifferentiation.

The Role of High Mobility Group Box 1 in Ischemic Stroke

High-mobility group box 1 protein (HMGB1) is a novel, cytokine-like, and ubiquitous, highly conserved, nuclear protein that can be actively secreted by microglia or passively released by necrotic neurons. Ischemic stroke is a leading cause of death and disability worldwide, and the outcome is dependent on the amount of hypoxia-related neuronal death in the cerebral ischemic region. Acting as an endogenous danger-associated molecular pattern (DAMP) protein, HMGB1 mediates cerebral inflammation and brain injury and participates in the pathogenesis of ischemic stroke. It is thought that HMGB1 signals via its presumed receptors, such as toll-like receptors (TLRs), matrix metalloproteinase (MMP) enzymes, and receptor for advanced glycation end products (RAGEs) during ischemic stroke. In addition, the release of HMGB1 from the brain into the bloodstream influences peripheral immune cells. However, the role of HMGB1 in ischemic stroke may be more complex than this and has not yet been clarified. Here, we summarize and review the research into HMGB1 in ischemic stroke.

Diminished apoptosis in hypoxic porcine retina explant cultures through hypothermia

Simulation of hypoxic processes in vitro can be achieved through cobalt chloride (CoCl2), which induces strong neurodegeneration. Hypoxia plays an important role in the progression of several retinal diseases. Thus, we investigated whether hypoxia can be reduced by hypothermia. Porcine retinal explants were cultivated for four and eight days and hypoxia was mimicked by adding 300 µM CoCl2 from day one to day three. Hypothermia treatment (30 °C) was applied simultaneously. Retinal ganglion, bipolar and amacrine cells, as well as microglia were evaluated via immunohistological and western blot analysis. Furthermore, quantitative real-time PCR was performed to analyze cellular stress and apoptosis. In addition, the expression of specific marker for the previously described cell types were investigated. A reduction of ROS and stress markers HSP70, iNOS, HIF-1α was achieved via hypothermia. In accordance, an inhibition of apoptotic proteins (caspase 3, caspase 8) and the cell cycle arrest gene p21 was found in hypothermia treated retinae. Furthermore, neurons of the inner retina were protected by hypothermia. In this study, we demonstrate that hypothermia lowers hypoxic processes and cellular stress. Additionally, hypothermia inhibits apoptosis and protects neurons. Hence, this seems to be a promising treatment for retinal neurodegeneration.

HIF-1α triggers ER stress and CHOP-mediated apoptosis in alveolar epithelial cells, a key event in pulmonary fibrosis

Endoplasmic Reticulum (ER) stress of alveolar epithelial cells (AECs) is recognized as a key event of cell dysfunction in pulmonary fibrosis (PF). However, the mechanisms leading to AECs ER stress and ensuing unfolded protein response (UPR) pathways in idiopathic PF (IPF) remain unclear. We hypothesized that alveolar hypoxic microenvironment would generate ER stress and AECs apoptosis through the hypoxia-inducible factor-1α (HIF-1α). Combining ex vivo, in vivo and in vitro experiments, we investigated the effects of hypoxia on the UPR pathways and ER stress-mediated apoptosis, and consecutively the mechanisms linking hypoxia, HIF-1α, UPR and apoptosis. HIF-1α and the pro-apoptotic ER stress marker C/EBP homologous protein (CHOP) were co-expressed in hyperplastic AECs from bleomycin-treated mice and IPF lungs, not in controls. Hypoxic exposure of rat lungs or primary rat AECs induced HIF-1α, CHOP and apoptosis markers expression. In primary AECs, hypoxia activated UPR pathways. Pharmacological ER stress inhibitors and pharmacological inhibition or silencing of HIF-1α both prevented hypoxia-induced upregulation of CHOP and apoptosis. Interestingly, overexpression of HIF-1α in normoxic AECs increased UPR pathways transcription factors activities, and CHOP expression. These results indicate that hypoxia and HIF-1α can trigger ER stress and CHOP-mediated apoptosis in AECs, suggesting their potential contribution to the development of IPF.

Effects of curcumin on hypoxia-inducible factor as a new therapeutic target

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that consists of two subunits, the HIF-1α and HIF-1β (ARNT). Under hypoxic conditions, HIF-1 is an adaptive system that regulates the transcription of multiple genes associated with growth, angiogenesis, proliferation, glucose transport, metabolism, pH regulation and cell death. However, aberrant HIF-1 activation contributes to the pathophysiology of several human diseases such as cancer, ischemic cardiovascular disorders, and pulmonary and kidney diseases. A growing body of evidence indicates that curcumin, a natural bioactive compound of turmeric root, significantly targets both HIF-1 subunits, but is more potent against HIF-1α. In this review, we have summarized the knowledge about the pharmacological effects of curcumin on HIF-1 and the related molecular mechanisms that may be effective candidates for the development of multi-targeted therapy for several human diseases.

Interacting Cancer Machineries: Cell Signaling, Lipid Metabolism, and Epigenetics

Cancer-specific perturbations of signaling, metabolism, and epigenetics can be a cause and/or consequence of malignant transformation. Evidence indicates that these regulatory systems interact with each other to form highly flexible and robust cybernetic networks that promote malignant growth and confer treatment resistance. Deciphering these plexuses using holistic approaches known from systems biology can be instructive for the future design of novel anticancer strategies. In this review, I discuss novel findings elucidating the multiple molecular interdependence among cancer-specific signaling, cell metabolism, and epigenetics to provide an insightful understanding of how major cancer machineries interact with each other during cancer development and progression, and how this knowledge may be used for future co-targeting strategies.

Inhibition of endoplasmic reticulum stress alleviates secondary injury after traumatic brain injury

Apoptosis after traumatic brain injury has been shown to be a major factor influencing prognosis and outcome. Endoplasmic reticulum stress may be involved in mitochondrial mediated neuronal apoptosis. Therefore, endoplasmic reticulum stress has become an important mechanism of secondary injury after traumatic brain injury. In this study, a rat model of traumatic brain injury was established by lateral fluid percussion injury. Fluorescence assays were used to measure reactive oxygen species content in the cerebral cortex. Western blot assays were used to determine expression of endoplasmic reticulum stress-related proteins. Hematoxylin-eosin staining was used to detect pathological changes in the cerebral cortex. Transmission electron microscopy was used to measure ultrastructural changes in the endoplasmic reticulum and mitochondria. Our results showed activation of the endoplasmic reticulum stress-related unfolded protein response. Meanwhile, both the endoplasmic reticulum stress response and mitochondrial apoptotic pathway were activated at different stages post-traumatic brain injury. Furthermore, pretreatment with the endoplasmic reticulum stress inhibitor, salubrinal (1 mg/kg), by intraperitoneal injection 30 minutes before injury significantly inhibited the endoplasmic reticulum stress response and reduced apoptosis. Moreover, salubrinal promoted recovery of mitochondrial function and inhibited activation of the mitochondrial apoptotic pathway post-traumatic brain injury. These results suggest that endoplasmic reticulum stress might be a key factor for secondary brain injury post-traumatic brain injury.

Transcription Factor C/EBP Homologous Protein in Health and Diseases

C/EBP homologous protein (CHOP), known also as DNA damage-inducible transcript 3 and as growth arrest and DNA damage-inducible protein 153 (GADD153), is induced in response to certain stressors. CHOP is universally acknowledged as a main conduit to endoplasmic reticulum stress-induced apoptosis. Ongoing research established the existence of CHOP-mediated apoptosis signaling networks, for which novel downstream targets are still being determined. However, there are studies that contradict this notion and assert that apoptosis is not the only mechanism by which CHOP plays in the development of pathologies. In this review, insights into the roles of CHOP in pathophysiology are summarized at the molecular and cellular levels. We further focus on the newest advances that implicate CHOP in human diseases including cancer, diabetes, neurodegenerative disorders, and notably, fibrosis.

Salubrinal attenuated retinal neovascularization by inhibiting CHOP-HIF1α-VEGF pathways

Retinal neovascularization (RNV) related disease is the leading cause of irreversible blindness in the world. The aim of this study is to identify whether salubrinal could attenuate RNV by inhibiting CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP)- hypoxia inducible factors 1α (HIF1α) -vascular endothelial growth factor (VEGF) pathways in both mouse retinal microvascular endothelial cells (mRMECs) and oxygen-induced retinopathy (OIR) mouse model. After being treated with salubrinal (20μmol/L) or CHOP-siRNA, mRMECs were exposed to a hypoxia environment. OIR mice were intraperitoneally injected with salubrinal (0.5 mg/kg/day) from P12 to P17. With salubrinal or CHOP-siRNA treatment, the elevated CHOP protein and mRNA levels in hypoxia-induced mRMECs were significantly decreased. HIF1α-VEGF pathways were activated under hypoxia condition, then HIF1α protein was degraded and VEGF secretion was down-regulated after salubrinal or CHOP-siRNA treatment. In OIR mice, the areas of RNV were markedly decreased with salubrinal treatment. Moreover, elevated expressions of CHOP, HIF1α and VEGF in retinas of OIR mice were all reduced after salubrinal treatment. It suggested that salubrinal attenuated RNV in mRMECs and OIR mice by inhibiting CHOP-HIF1α-VEGF pathways and could be a potential therapeutic target for hypoxia-induced retinal microangiopathy.

Cross talk between increased intracellular zinc (Zn2+) and accumulation of reactive oxygen species in chemical ischemia

Both zinc (Zn²⁺) and reactive oxygen species (ROS) have been shown to accumulate during hypoxic-ischemic stress and play important roles in pathological processes. To understand the cross talk between the two of them, here we studied Zn²⁺ and ROS accumulation by employing fluorescent probes in HeLa cells to further the understanding of the cause and effect relationship of these two important cellular signaling systems during chemical-ischemia, stimulated by oxygen and glucose deprivation (OGD). We observed two Zn²⁺ rises that were divided into four phases in the course of 30 min of OGD. The first Zn²⁺ rise was a transient, which was followed by a latent phase during which Zn²⁺ levels recovered; however, levels remained above a basal level in most cells. The final phase was the second Zn²⁺ rise, which reached a sustained plateau called Zn²⁺ overload. Zn²⁺ rises were not observed when Zn²⁺ was removed by TPEN (a Zn²⁺ chelator) or thapsigargin (depleting Zn²⁺ from intracellular stores) treatment, indicating that Zn²⁺ was from intracellular storage. Damaging mitochondria with FCCP significantly reduced the second Zn²⁺ rise, indicating that the mitochondrial Zn²⁺ accumulation contributes to Zn²⁺ overload. We also detected two OGD-induced ROS rises. Two Zn²⁺ rises preceded two ROS rises. Removal of Zn²⁺ reduced or delayed OGD- and FCCP-induced ROS generation, indicating that Zn²⁺ contributes to mitochondrial ROS generation. There was a Zn²⁺-induced increase in the functional component of NADPH oxidase, p47^phox, thus suggesting that NADPH oxidase may mediate Zn²⁺-induced ROS accumulation. We suggest a new mechanism of cross talk between Zn²⁺ and mitochondrial ROS through positive feedback processes that eventually causes excessive free Zn²⁺ and ROS accumulations during the course of ischemic stress.

Degenerative effects of cobalt-chloride treatment on neurons and microglia in a porcine retina organ culture model

In order to understand the pathological processes of retinal diseases, experimental models are necessary. Cobalt, as part of the vitamin B12 complex, is important for neuronal integrity. However, it is known that high quantities of cobalt induce cytotoxic mechanisms via hypoxia mimicry. Therefore, we tested the degenerative effect of cobalt chloride (CoCl₂) on neurons and microglia in a porcine retina organ culture model. Organotypic cultures of porcine retinas were cultured and treated with different concentrations of CoCl₂ (0, 100, 300 and 500 μM) for 48 h. After four and eight days, CoCl₂ induced a strong degeneration of the porcine retina, starting at 300 μM. A loss of retinal ganglion cells (RGCs, Brn-3a), amacrine cells (calretinin) and bipolar cells (PKCα) was observed. Additionally, a high expression of hypoxia induced factor-1a (HIF-1a) and heat shock protein 70 (HSP70) was noted at both points in time. Also, the Caspase 3 protein was activated and P21 expression was induced. However, only at day four, the Bax/Bcl-2 ratio was increased. The effect of CoCl₂ was not restricted to neurons. CoCl₂ concentrations reduced the microglia amount (Iba1) and activity (Iba1 + Fc_γ-Receptor) at both points in time. These damaging effects on microglia were surprising, since CoCl₂ causes hypoxia and a pro-inflammatory environment. However, high concentrations of CoCl₂ also seem to be toxic to these cells. Similar degenerative mechanisms as in comparison to retinal ischemia animal models were observed. In summary, an effective and reproducible hypoxia-mimicking organotypic model for retinal degeneration was established, which is easy to handle and ready for drug studies.

Lack of mitochondrial DNA impairs chemical hypoxia-induced autophagy in liver tumor cells through ROS-AMPK-ULK1 signaling dysregulation independently of HIF-1α

Alterations in mitochondrial DNA (mtDNA) and autophagy activation are common events in tumors. Here we have investigated the effect of mitochondrial genome depletion on chemical hypoxia-induced autophagy in liver tumor cells. Human SK-Hep-1 wild-type and mtDNA-depleted (Rho) cells were exposed to the hypoxia mimetic agents CoCl₂ and deferoxamine (DFO). Up-regulation of HIF-1α, but not HIF-2α was observed. The expression of several HIF-1α target genes was also found. In human SK-Hep-1 and mouse Hepa 1-6 liver tumor cells, but not in the counterpart Rho derived lines, chemical hypoxia increased the abundance of autophagosomes and autolysosomes. In wild-type and Rho cells, chemical hypoxia induced down-regulation of HIF-1α-dependent autophagy inhibitors Bcl-2 and mTOR, whereas activation of AMPK/ULK1-mediated pro-autophagy pathway occurred only in wild-type cells. Chemical (compound C) and genetic (shRNA) inhibition of AMPK activation resulted in reduced autophagy. ATP levels were similar in both cell types, whereas constitutive and chemical hypoxia-induced reactive oxygen species (ROS) generation was lower in Rho cells. In wild-type cells, the antioxidant N-acetylcysteine blocked CoCl₂- and DFO-induced AMPK and autophagy activation, but not endoplasmic reticulum stress induced by CoCl₂. Enhanced Bax-α/Bcl-2 ratio and cell death was induced by hypoxia mimetic agents more markedly in wild-type than in Rho cells. Upon blocking autophagy activation with 3-methyladenine, DFO-induced cell death was partially prevented whereas that induced by CoCl₂ was increased, but only in wild-type cells. These results suggest that mitochondrial dysfunction associated with the lack of mtDNA impairs the signaling pathways mediated by ROS, controlling autophagy activation in liver tumor cells, which may contributes to cancer development.

Baclofen Protects Primary Rat Retinal Ganglion Cells from Chemical Hypoxia-Induced Apoptosis Through the Akt and PERK Pathways

Retinal ganglion cells (RGCs) consume large quantities of energy to convert light information into a neuronal signal, which makes them highly susceptible to hypoxic injury. This study aimed to investigate the potential protection by baclofen, a GABA_B receptor agonist of RGCs against hypoxia-induced apoptosis. Cobalt chloride (CoCl₂) was applied to mimic hypoxia. Primary rat RGCs were subjected to CoCl₂ with or without baclofen treatment, and RNA interference techniques were used to knock down the GABA_B2 gene in the primary RGCs. The viability and apoptosis of RGCs were assessed using cell viability and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, Hoechst staining, and flow cytometry. The expression of cleaved caspase-3, bcl-2, bax, Akt, phospho-Akt, protein kinase RNA (PKR)-like ER kinase (PERK), phospho-PERK, eIF2α, phospho-eIF2α, ATF-4 and CCAAT/enhancer-binding protein homologous protein (CHOP) were measured using western blotting. GABA_B2 mRNA expression was determined using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Our study revealed that CoCl₂ significantly induced RGC apoptosis and that baclofen reversed these effects. CoCl₂-induced reduction of Akt activity was also reversed by baclofen. Baclofen prevented the activation of the PERK pathway and the increase in CHOP expression induced by CoCl₂. Knockdown of GABA_B2 and the inactivation of the Akt pathway by inhibitors reduced the protective effect of baclofen on CoCl₂-treated RGCs. Taken together, these results demonstrate that baclofen protects RGCs from CoCl₂-induced apoptosis by increasing Akt activity and by suppressing the PERK pathway and CHOP activation.

Amelioration of ER stress by 4-phenylbutyric acid reduces chronic hypoxia induced cardiac damage and improves hypoxic tolerance through upregulation of HIF-1α

While endoplasmic reticulum (ER) stress has been observed in several human diseases, few studies have reported the involvement of ER stress in chronic hypoxia (CH) induced cardiac damage. Hypoxia, such as that prevalent at high altitude (HA), forms the underlying cause of several maladies including cardiovascular diseases. While the role of hypoxia inducible factor-1 (HIF-1α) in the adaptive responses to hypoxia is known, the role of the unfolded protein response (UPR) is only recently being explored in the HA pathophysiologies. The present study investigates the effect of ER stress modulation on CH mediated injury and the cardioprotective action of 4-phenylbutyric acid (PBA) in enhancing survival response under hypoxia. Here, we observed that exposure of rats, for 1, 7 and 14days CH to a simulated altitude of 7620m, led to cardiac hypertrophy and significant protein oxidation. This induced the activation of UPR signaling mechanisms, mediated by PERK, IRE1α and ATF6. By 14days, there was a marked upregulation of apoptosis, evident in increased CHOP and caspase-3/9 activity. PBA reduced CH induced right ventricular enlargement and apoptosis. Further, in contrast to tunicamycin, PBA considerably enhanced hypoxic tolerance. An elevation in the level of antioxidant enzymes, HIF-1α and its regulated proteins (HO-1, GLUT-1) was observed in the PBA administered animals, along with a concomitant suppression of UPR markers. Our study thus emphasizes upon the attenuation of ER stress by PBA as a mechanism to diminish CH induced cardiac injury and boost hypoxic survival, providing an insight into the novel relationship between the HIF-1α and UPR under hypoxia.

Quinolinic acid induces cell apoptosis in PC12 cells through HIF-1-dependent RTP801 activation

Neurological disease comprises a series of disorders featuring brain dysfunction and neuronal cell death. Among the factors contributing to neuronal death, excitotoxicity induced by excitatory amino acids, such as glutamate, plays a critical role. However, the mechanisms about how the excitatory amino acids induce neuronal death remain elucidated. In this study, we investigated the role of HIF-1α (hypoxia inducible factor-1α) and RTP801 in cell apoptosis induced by quinolinic acid (QUIN), a glutamatergic agonist, in PC12 cells. We found that QUIN at 5 μM increased the expression of HIF-1α significantly with a peak at 24 h. After the treatment with QUIN (5-20 μM) for 24 h, the cells exhibited decreased viability and cell apoptosis with a concomitant increased expression of apoptosis related proteins. QUIN treatment also induced the generation of intracellular reactive oxygen species and RTP801 up-regulation in a HIF-1α-dependent manner that were inhibited by 2-methoxyestradiol, a HIF-1α inhibitor. Importantly, HIF-1 or RTP801 invalidation by siRNA rescued the cell apoptosis induced by QUIN or cobalt chloride, a chemical inducer of HIF-1. Taken together, these findings support the concept that neurotoxicity induced by QUIN is associated with HIF-1-dependent RTP801 activation and provide insight into the potential of RTP801 inhibitor in treatment of neurological disorders.

Endoplasmic reticulum stress as a novel inducer of hypoxia inducible factor-1 activity: its role in the susceptibility to myocardial ischemia-reperfusion induced by chronic intermittent hypoxia

BACKGROUND

Obstructive sleep apnea (OSA) is a highly prevalent disease and a risk factor for myocardial infarction expansion in humans. Intermittent hypoxia (IH) is known to be the most important OSA feature in terms of cardiovascular morbi-mortality. Since ER stress and HIF-1 are known to be involved in cardiomyocyte life or death, this study investigates the role of ER stress on HIF-1 activation in myocardial susceptibility to ischemia-reperfusion (I/R) induced by IH.

METHODS

C57Bl6J, HIF-1α(+/-) and their respective control mice were exposed to 14 days of IH (21-5% FiO2, 60 scycle, 8h/day). Myocardial inter-organelle calcium exchanges, ER stress and HIF-1 activity were investigated and in vivo I/R was performed to measure infarct size. In additional groups, tauroursodeoxycholic acid (TUDCA, 75 mg·kg(-1)), an ER stress inhibitor, was administered daily during exposure.

RESULTS

In C57Bl6J mice, chronic IH induced an increase in ER-Ca(2+) content, ER stress markers and HIF-1 activity, associated with an enhanced infarct size (33.7 ± 9.4 vs. 61.0 ± 5.6% in N and IH, respectively, p<0.05). IH failed to increase infarct size in HIF-1α deficient mice (42.4 ± 2.7 and 24.7 ± 3.4% N and IH, respectively). Finally, TUDCA totally abolished the IH-induced increase in HIF-1 activity (1.3 ± 0.04 vs. 0.14 ± 0.02 fold increase in IH vs. IH-TUDCA respectively, p<0.0001) and in infarct size (55.5 ± 7.6 vs. 49.9 ± 3.0 in N-TUDCA and IH-TUDCA, respectively).

CONCLUSION

This novel regulatory mechanism of HIF-1 activity by ER stress should be considered as a potential diagnostic tool for cardiovascular complications in OSA patients as well as a therapeutic target to limit myocardial ischemic damage.