Overexpressing GRP78 influences Ca2+ handling and function of mitochondria in astrocytes after ischemia-like stress

Heat shock proteins in cerebral ischemia-reperfusion injury: Mechanisms and therapeutic implications

Cerebral ischemia-reperfusion injury (CIRI) remains a significant challenge in ischemic stroke treatment. Heat shock proteins (HSPs), a cadre of molecular chaperones, have emerged as pivotal regulators in this pathological cascade. This review synthesizes the latest research on HSPs in CIRI from 2013 to 2024 focusing on their multifaceted roles and therapeutic potential. We explore the diverse cellular functions of HSPs, including regulation of oxidative stress, apoptosis, necroptosis, ferroptosis, autophagy, neuroinflammation, and blood-brain barrier integrity. Key HSPs, such as HSP90, HSP70, HSP32, HSP60, HSP47, and small HSPs, are investigated for their specific mechanisms of action in CIRI. Potential therapeutic strategies targeting HSPs, including HSP inhibitors, traditional Chinese medicine components, and gene therapy, are discussed. This review provides a comprehensive understanding of HSPs in CIRI and offers insights into the development of innovative neuroprotective treatments.

Regulation of N-degron recognin-mediated autophagy by the SARS-CoV-2 PLpro ubiquitin deconjugase

Viral proteases play critical roles in the host cell and immune remodeling that allows virus production. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) papain-like protease (PLpro) encoded in the large nonstructural protein 3 (Nsp3) also possesses isopeptidase activity with specificity for ubiquitin and ISG15 conjugates. Here, we interrogated the cellular interactome of the SARS-CoV-2 PLpro catalytic domain to gain insight into the putative substrates and cellular functions affected by the viral deubiquitinase. PLpro was detected in protein complexes that control multiple ubiquitin and ubiquitin-like (UbL) regulated signaling and effector pathways. By restricting the analysis to cytosolic and membrane-associated ubiquitin ligases, we found that PLpro interacts with N-recognin ubiquitin ligases and preferentially rescues type I N-degron substrates from proteasomal degradation. PLpro stabilized N-degron carrying HSPA5/BiP/GRP78, which is arginylated in the cytosol upon release from the endoplasmic reticulum (ER) during ER stress, and enhanced the Arg-HSPA5-driven oligomerization of the N-recognin SQSTM1/p62 that serves as a platform for phagophore assembly. However, while in addition to Arg-HSPA5 and SQSTM1/p62, ATG9A, WIPI2, and BECN1/Beclin 1 were detected in PLpro immunoprecipitates, other components of the autophagosome biogenesis machinery, such as the ATG12-ATG5-ATG16L1 complex and MAP1LC3/LC3 were absent, which correlated with proteolytic inactivation of ULK1, impaired production of lipidated LC3-II, and inhibition of reticulophagy. The findings highlight a novel mechanism by which, through the reprogramming of autophagy, the PLpro deubiquitinase may contribute to the remodeling of intracellular membranes in coronavirus-infected cells.

Astrogliosis and glial scar in ischemic stroke - focused on mechanism and treatment

Ischemic stroke is a kind of neurological dysfunction caused by cerebral ischemia. Astrocytes, as the most abundant type of glial cells in the central nervous system, are activated into reactive astrocytes after cerebral ischemia, and this process involves the activation or change of a series of cell surface receptors, ion channels and ion transporters, GTPases, signaling pathways, and so on. The role of reactive astrocytes in the development of ischemic stroke is time-dependent. In the early stage of ischemia, reactive astrocytes proliferate moderately and surround the ischemic tissue to prevent the spread of the lesion. At the same time, reactive astrocytes release neuroprotective factors, ultimately relieving brain injury. In the late stage of ischemia, reactive astrocytes excessively proliferate and migrate to form dense glial scar tissue, which hinders the repair of damaged tissue. At the same time, reactive astrocytes in the glial scar release a large number of neurotoxic factors, ultimately aggravating ischemic stroke. In this paper, we focus on the molecular mechanism of astrogliosis and glial scar formation after cerebral ischemia, and explore the relevant studies using glial scar as a therapeutic target, providing a reference for the selection of therapeutic strategies for ischemic stroke and further research directions.

Glucose-Regulated Protein 78, via Releasing β-Catenin from Adherens Junctions, Facilitates Its Interaction with STAT3 in Mediating Retinal Neovascularization

Retinopathy due to neovascularization is one of the major causes of vision loss. To understand the mechanisms underlying retinal neovascularization the oxygen-induced retinopathy (OIR) model was used. Two-dimensional gel matrix-assisted laser desorption/ionization time-of-flight/time-of-flight analysis of normoxic and 24-hour post-OIR mice pups' retinas revealed that glucose-regulated protein 78 (GRP78) was one of the several molecules induced by OIR in the retinal endothelial cells (ECs). Vascular endothelial growth factor A (VEGFA) also induced GRP78 expression independent of endoplasmic reticulum stress response in human retinal microvascular endothelial cells, and its depletion reduced VEGFA-induced EC angiogenic responses. Consistent with these observations, EC-specific deletion of GRP78 inhibited OIR-induced retinal neovascularization. GRP78 bound with vascular endothelial-cadherin and released adherens junction, but not Wnt-mediated, β-catenin. β-catenin, in turn, via interacting with STAT3, triggered cyclin D1 expression. Furthermore, depletion of β-catenin or cyclin D1 levels negated VEGFA-induced EC angiogenic responses and OIR-induced retinal neovascularization. EC-specific deletion of GRP78 also suppressed OIR-induced vascular leakage. Studies of upstream signaling indicated that activating transcription factor 6 mediated GRP78 induction in the modulation of VEGFA-induced EC angiogenic responses and OIR-induced retinal neovascularization. Together, these observations revealed that GRP78, independent of its response to endoplasmic reticulum stress, is involved in mediating EC angiogenic responses by VEGFA and retinal neovascularization by OIR. In view of these findings, GRP78 emerges as a desirable target for drug development against diabetic retinopathy.

GRP78 mediates mitochondrial fusion and fission in cigarette smoke-induced inflammatory responses in airway epithelial cells

OBJECTIVE

Chronic obstructive pulmonary disease (COPD) is characterized by persistent airway inflammation, with cigarette smoke being a major contributor to epithelial injury. Recent studies have shown that abnormal mitochondrial function is closely linked to the onset and progression of airway inflammation. This study aims to explore the role and underlying molecular mechanisms of mitochondrial dynamics in cigarette smoke-induced airway inflammation.

MATERIALS AND METHODS

Human bronchial epithelial (HBE) cells were exposed to cigarette smoke extract (CSE) to assess the expression of mitochondrial fusion markers MFN2 and OPA1, the fission marker DRP1, and the glucose-regulated protein GRP78. The siRNA and pharmaceutics targeting DRP1, MFN2, and GRP78 were employed. Both cells and supernatants were analyzed for inflammatory factor levels and the related signaling pathways.

RESULTS

In this study, HBE cells exposed to CSE showed a significant decrease in the proteins MFN2 and OPA1 and an increase in DRP1. The inhibition of DRP1 expression mitigated inflammation while silencing MFN2 exacerbated it. This was similarly corroborated by the use of the DRP1 inhibitor mdivi-1 and the MFN2 activator leflunomide. Additionally, we proved that GRP78 played an important regulatory role as an essential endoplasmic reticulum protein, regulating the mitochondrial fusion/fission process and subsequently activating the NF-κB pathway to regulate airway inflammation.

DISCUSSION AND CONCLUSION

Taken together, these results suggested that the GRP78-mediated mitochondrial fusion and fission process played a vital role in cigarette smoke-induced airway inflammation and might be a potential therapeutic target in this regard.

Atrogin-1 promotes muscle homeostasis by regulating levels of endoplasmic reticulum chaperone BiP

Skeletal muscle wasting results from numerous pathological conditions affecting both the musculoskeletal and nervous systems. A unifying feature of these pathologies is the upregulation of members of the E3 ubiquitin ligase family, resulting in increased proteolytic degradation of target proteins. Despite the critical role of E3 ubiquitin ligases in regulating muscle mass, the specific proteins they target for degradation and the mechanisms by which they regulate skeletal muscle homeostasis remain ill-defined. Here, using zebrafish loss-of-function models combined with in vivo cell biology and proteomic approaches, we reveal a role of atrogin-1 in regulating the levels of the endoplasmic reticulum chaperone BiP. Loss of atrogin-1 resulted in an accumulation of BiP, leading to impaired mitochondrial dynamics and a subsequent loss in muscle fiber integrity. We further implicated a disruption in atrogin-1-mediated BiP regulation in the pathogenesis of Duchenne muscular dystrophy. We revealed that BiP was not only upregulated in Duchenne muscular dystrophy, but its inhibition using pharmacological strategies, or by upregulating atrogin-1, significantly ameliorated pathology in a zebrafish model of Duchenne muscular dystrophy. Collectively, our data implicate atrogin-1 and BiP in the pathogenesis of Duchenne muscular dystrophy and highlight atrogin-1's essential role in maintaining muscle homeostasis.

ER chaperone GRP78/BiP translocates to the nucleus under stress and acts as a transcriptional regulator

Cancer cells are commonly subjected to endoplasmic reticulum (ER) stress. To gain survival advantage, cancer cells exploit the adaptive aspects of the unfolded protein response such as upregulation of the ER luminal chaperone GRP78. The finding that when overexpressed, GRP78 can escape to other cellular compartments to gain new functions regulating homeostasis and tumorigenesis represents a paradigm shift. Here, toward deciphering the mechanisms whereby GRP78 knockdown suppresses EGFR transcription, we find that nuclear GRP78 is prominent in cancer and stressed cells and uncover a nuclear localization signal critical for its translocation and nuclear activity. Furthermore, nuclear GRP78 can regulate expression of genes and pathways, notably those important for cell migration and invasion, by interacting with and inhibiting the activity of the transcriptional repressor ID2. Our study reveals a mechanism for cancer cells to respond to ER stress via transcriptional regulation mediated by nuclear GRP78 to adopt an invasive phenotype.

The essential role of N6-methyladenosine RNA methylation in complex eye diseases

There are many complex eye diseases which are the leading causes of blindness, however, the pathogenesis of the complex eye diseases is not fully understood, especially the underlying molecular mechanisms of N6-methyladenosine (m6A) RNA methylation in the eye diseases have not been extensive clarified. Our review summarizes the latest advances in the studies of m6A modification in the pathogenesis of the complex eye diseases, including cornea disease, cataract, diabetic retinopathy, age-related macular degeneration, proliferative vitreoretinopathy, Graves' disease, uveal melanoma, retinoblastoma, and traumatic optic neuropathy. We further discuss the possibility of developing m6A modification signatures as biomarkers for the diagnosis of the eye diseases, as well as potential therapeutic approaches.

Chronic Cerebral Hypoperfusion-Induced Disturbed Proteostasis of Mitochondria and MAM Is Reflected in the CSF of Rats by Proteomic Analysis

Declining cerebral blood flow leads to chronic cerebral hypoperfusion which can induce neurodegenerative disorders, such as vascular dementia. The reduced energy supply of the brain impairs mitochondrial functions that could trigger further damaging cellular processes. We carried out stepwise bilateral common carotid occlusions on rats and investigated long-term mitochondrial, mitochondria-associated membrane (MAM), and cerebrospinal fluid (CSF) proteome changes. Samples were studied by gel-based and mass spectrometry-based proteomic analyses. We found 19, 35, and 12 significantly altered proteins in the mitochondria, MAM, and CSF, respectively. Most of the changed proteins were involved in protein turnover and import in all three sample types. We confirmed decreased levels of proteins involved in protein folding and amino acid catabolism, such as P4hb and Hibadh in the mitochondria by western blot. We detected reduced levels of several components of protein synthesis and degradation in the CSF as well as in the subcellular fractions, implying that hypoperfusion-induced altered protein turnover of brain tissue can be detected in the CSF by proteomic analysis.

Inhibition of microRNA-200c preserves astrocyte sirtuin-1 and mitofusin-2, and protects against hippocampal neurodegeneration following global cerebral ischemia in mice

Memory impairment remains a leading disability in survivors of global cerebral ischemia, occurring secondary to delayed neurodegeneration of hippocampal cornu ammonis-1 (CA1) neurons. MicroRNA-200c (miR-200c) is induced following ischemic stress and we have previously demonstrated that pre-treatment with anti-miR-200c is protective against embolic stroke in mice. In the present study we assessed the role of miR-200c on CA1 neurodegeneration, sirtuin-1 (SIRT1), and mitochondrial dynamic protein expression in a mouse model of transient global cerebral ischemia and in vitro in primary mouse astrocyte cultures after simulated ischemia. Mice were subjected to 10 min bilateral common carotid artery occlusion plus hypotension with 5% isoflurane. After 2 h recovery mice were treated with intravenous injection of either anti-miR-200c or mismatch control. Memory function was assessed by Barnes maze at post-injury days 3 and 7. Mice were sacrificed at post-injury day 7 for assessment of brain cell-type specific expression of miR-200c, SIRT1, and the mitochondrial fusion proteins mitofusin-2 (MFN2) and OPA1 via complexed fluorescent in situ hybridization and fluorescent immunohistochemistry. Global cerebral ischemia induced significant loss of CA1 neurons, impaired memory performance and decreased expression of CA1 SIRT1, MFN2, and OPA1. Post-injury treatment with anti-miR-200c significantly improved survival, prevented CA1 neuronal loss, improved post-injury performance in Barnes maze, and was associated with increased post-injury expression of CA1 SIRT1 and MFN2 in astrocytes. In vitro, primary mouse astrocyte cultures pre-treated with miR-200c inhibitor prior to oxygen/glucose deprivation preserved expression of SIRT1 and MFN2, and decreased reactive oxygen species generation, whereas pre-treatment with miR-200c mimic had opposite effects that could be reversed by co-treatment with SIRT1 activator. These results suggest that miR-200c regulates astrocyte mitochondrial homeostasis via targeting SIRT1, and that CA1 astrocyte mitochondria and SIRT1 represent potential post-injury therapeutic targets to preserve cognitive function in survivors of global cerebral ischemia.

Balancing energy and protein homeostasis at ER-mitochondria contact sites

The endoplasmic reticulum (ER) is the largest organelle of the cell and participates in multiple essential functions, including the production of secretory proteins, lipid synthesis, and calcium storage. Sustaining proteostasis requires an intimate coupling with energy production. Mitochondrial respiration evolved to be functionally connected to ER physiology through a physical interface between both organelles known as mitochondria-associated membranes. This quasi-synaptic structure acts as a signaling hub that tunes the function of both organelles in a bidirectional manner and controls proteostasis, cell death pathways, and mitochondrial bioenergetics. Here, we discuss the main signaling mechanisms governing interorganellar communication and their putative role in diseases including cancer and neurodegeneration.

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.

A novel ND1 mitochondrial DNA mutation is maternally inherited in growth hormone transgenesis in amago salmon (Oncorhynchus masou ishikawae)

Growth hormone (GH) transgenesis can be used to manipulate the growth performance of fish and mammals. In this study, homozygous and hemizygous GH-transgenic amago salmon (Oncorhynchus masou ishikawae) derived from a single female exhibited hypoglycemia. Proteomic and signal network analyses using iTRAQ indicated a decreased NAD⁺/NADH ratio in transgenic fish, indicative of reduced mitochondrial ND1 function and ROS levels. Mitochondrial DNA sequencing revealed that approximately 28% of the deletion mutations in the GH homozygous- and hemizygous-female-derived mitochondrial DNA occurred in ND1. These fish also displayed decreased ROS levels. Our results indicate that GH transgenesis in amago salmon may induce specific deletion mutations that are maternally inherited over generations and alter energy production.

Early Aerobic Exercise Promotes Neurological Function Recovery of Rats after Cerebral Ischemia/Reperfusion by Upregulating the Expression of Heat Shock Protein A5

OBJECTIVE

The neuroprotective function of heat shock protein A5 (HSPA5) in ischemic stroke has been confirmed. This study aimed to investigate the effects of early aerobic exercise on neurological function recovery from cerebral ischemia/reperfusion and to determine whether these effects are associated with the expression level of HSPA5 in the ischemic penumbra.

METHODS

A total of 72 male Sprague-Dawley rats were randomly assigned to the ischemia and exercise group [middle cerebral artery occlusion (MCAO)-Ex, n=18], ischemia and sedentary group (MCAO-St, n=18), sham-surgery and exercise group (Sham-Ex, n=18), or sham-surgery and sedentary group (Sham-St, n=18). The MCAO-Ex and MCAO-St groups were subjected to MCAO for 60 min, whereas the Sham-Ex and Sham-St groups were subjected to an identical operation without MCAO. Rats in the MCAO-Ex and Sham-Ex groups then ran on a treadmill for 30 min once a day for 5 consecutive days. After reperfusion, the motor function of the rats was scored by the Bederson neurological function test, balance beam test, and screen test. Nissl staining was conducted to assess morphological and structural change of nerve cells in the ischemic penumbra. The reverse transcription-quantitative polymerase chain reaction was applied to detect the mRNA expression of HSPA5. Western blot analysis was conducted to determine the protein expression of HSPA5. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining was carried out in the ischemic penumbra after MCAO.

RESULTS

Rats receiving early treadmill exercise had lower Bederson neurological function, balance beam, and screen test scores on the 3rd, 7th, and 14th days after MCAO; in addition, more neurons survived in the ischemic penumbra after MCAO, and higher mRNA and protein expression of HSPA5 and fewer TUNEL-positive stained cells were observed.

CONCLUSION

Our study demonstrated that early aerobic exercise can improve neurological function recovery after ischemia/reperfusion. Furthermore, the increased level of HSPA5 in the ischemic penumbra might be one of the mechanisms of enhanced neurological function recovery.

The role of endoplasmic reticulum stress in astrocytes

Astrocytes are glial cells that support neurological function in the central nervous system (CNS), in part, by providing structural support for neuronal synapses and blood vessels, participating in electrical and chemical transmission, and providing trophic support via soluble factors. Dysregulation of astrocyte function contributes to neurological decline in CNS diseases. Neurological diseases are highly heterogeneous but share common features of cellular stress including the accumulation of misfolded proteins. Endoplasmic reticulum (ER) stress has been reported in nearly all neurological and neurodegenerative diseases. ER stress occurs when there is an accumulation of misfolded proteins in the ER lumen and the protein folding demand of the ER is overwhelmed. ER stress initiates the unfolded protein response (UPR) to restore homeostasis by abating protein translation and, if the cell is irreparably damaged, initiating apoptosis. Although protein aggregation and misfolding in neurological disease has been well described, cell-specific contributions of ER stress and the UPR in physiological and disease states are poorly understood. Recent work has revealed a role for active UPR signaling that may drive astrocytes toward a maladaptive phenotype in various model systems. In response to ER stress, astrocytes produce inflammatory mediators, have reduced trophic support, and can transmit ER stress to other cells. This review will discuss the current known contributions and consequences of activated UPR signaling in astrocytes.

GRP78 Overexpression Triggers PINK1-IP3R-Mediated Neuroprotective Mitophagy

An experimental model of spinal root avulsion (RA) is useful to study causal molecular programs that drive retrograde neurodegeneration after neuron-target disconnection. This neurodegenerative process shares common characteristics with neuronal disease-related processes such as the presence of endoplasmic reticulum (ER) stress and autophagy flux blockage. We previously found that the overexpression of GRP78 promoted motoneuronal neuroprotection after RA. After that, we aimed to unravel the underlying mechanism by carrying out a comparative unbiased proteomic analysis and pharmacological and genetic interventions. Unexpectedly, mitochondrial factors turned out to be most altered when GRP78 was overexpressed, and the abundance of engulfed mitochondria, a hallmark of mitophagy, was also observed by electronic microscopy in RA-injured motoneurons after GRP78 overexpression. In addition, GRP78 overexpression increased LC3-mitochondria tagging, promoted PINK1 translocation, mitophagy induction, and recovered mitochondrial function in ER-stressed cells. Lastly, we found that GRP78-promoted pro-survival mitophagy was mediated by PINK1 and IP3R in our in vitro model of motoneuronal death. This data indicates a novel relationship between the GRP78 chaperone and mitophagy, opening novel therapeutical options for drug design to achieve neuroprotection.

Expression of the Endoplasmic Reticulum Stress Marker GRP78 in the Normal Retina and Retinal Degeneration Induced by Blue LED Stimuli in Mice

Retinal degeneration is a leading cause of blindness. The unfolded protein response (UPR) is an endoplasmic reticulum (ER) stress response that affects cell survival and death and GRP78 forms a representative protective response. We aimed to determine the exact localization of GRP78 in an animal model of light-induced retinal degeneration. Dark-adapted mice were exposed to blue light-emitting diodes and retinas were obtained at 24 h and 72 h after exposure. In the normal retina, we found that GRP78 was rarely detected in the photoreceptor cells while it was expressed in the perinuclear space of the cell bodies in the inner nuclear and ganglion cell layers. After injury, the expression of GRP78 in the outer nuclear and inner plexiform layers increased in a time-dependent manner. However, an increased GRP78 expression was not observed in damaged photoreceptor cells in the outer nuclear layer. GRP78 was located in the perinuclear space and ER lumen of glial cells and the ER developed in glial cells during retinal degeneration. These findings suggest that GRP78 and the ER response are important for glial cell activation in the retina during photoreceptor degeneration.

Neuroprotective Role of Akt in Hypoxia Adaptation in Andeans

Chronic mountain sickness (CMS) is a disease that potentially threatens a large segment of high-altitude populations during extended living at altitudes above 2,500 m. Patients with CMS suffer from severe hypoxemia, excessive erythrocytosis and neurologic deficits. The cellular mechanisms underlying CMS neuropathology remain unknown. We previously showed that iPSC-derived CMS neurons have altered mitochondrial dynamics and increased susceptibility to hypoxia-induced cell death. Genome analysis from the same population identified many ER stress-related genes that play an important role in hypoxia adaptation or lack thereof. In the current study, we showed that iPSC-derived CMS neurons have increased expression of ER stress markers Grp78 and XBP1s under normoxia and hyperphosphorylation of PERK under hypoxia, alleviating ER stress does not rescue the hypoxia-induced CMS neuronal cell death. Akt is a cytosolic regulator of ER stress with PERK as a direct target of Akt. CMS neurons exhibited lack of Akt activation and lack of increased Parkin expression as compared to non-CMS neurons under hypoxia. By enhancing Akt activation and Parkin overexpression, hypoxia-induced CMS neuronal cell death was reduced. Taken together, we propose that increased Akt activation protects non-CMS from hypoxia-induced cell death. In contrast, impaired adaptive mechanisms including failure to activate Akt and increase Parkin expression render CMS neurons more susceptible to hypoxia-induced cell death.

TFIIB-related factor 2 regulates glucose-regulated protein 78 expression in acquired middle ear cholesteatoma

Acquired middle ear cholesteatoma leads to hearing loss, ear discharge, ear pain, and more serious intracranial complications. However, there is still no effective treatment other than surgery. TFIIB-related factor 2 (BRF2) acted as a redox sensor overexpressing in oxidative stress which linked endoplasmic reticulum (ER) stress, while glucose-regulated protein 78 (GRP78) was a biomarker of ER stress in cancer, atherosclerosis and inflammation. In our study, we investigated the roles of BRF2 and GRP78 in acquired middle ear cholesteatoma. Our results revealed that the expression of BRF2 was significant increased in acquired middle ear cholesteatoma, and which was positively correlated with the expression of GRP78. In addition, BRF2 and GRP78 showed colocalization in epithelium of acquired middle ear cholesteatomas and HaCaT cells. Prolongation of LPS stimulation in HaCaT cells escalated the expression of BRF2 and GRP78. To confirm the role of BRF2 and GRP78, we transfected si-BRF2 into HaCaT cells. All results indicated that BRF2 expression positively regulates the expression of GRP78 and may participate in the pathogenesis of acquire middle ear cholesteatoma.

1% Isoflurane and 1.2 μg/ml of Propofol: A Combination of Anesthetics That Causes the Least Damage to Hypoxic Neurons

Backgrounds: Aging-related impairment of cerebral blood flow regulation leads to the disruption of neuronal micro-environmental homeostasis. Anesthetics should be carefully selected for aging patients since they have less cognition capacity. Effects and mechanisms of propofol or isoflurane have been widely investigated. However, how different combinations of propofol and isoflurane affect neurons and the mechanism still needs to be demonstrated.

Methods: We cultured rat hippocampal neurons and established a hypoxic injury model to imitate the micro-environment of aging brains. Three different combinations of propofol and isoflurane were applied to find out an optimum group via Cell Counting Kit-8 (CCK8) assay, lactic acid dehydrogenase (LDH) assay, real-time qPCR, and immunofluorescence of key proteins. Then BiP was silenced by small interfering RNA (siRNA) to explore the mechanism of how isoflurane and propofol affect neurons. Endoplasmic reticulum (ER) stress was measured by Western blot and immunofluorescence. To detect GABA_AR α1 subunit proteostasis and its function, real-time qPCR, immunoprecipitation, and Western blot were carried out.

Results: Hypoxic neurons showed no different changes on cell viability, LDH leakage, and ER stress after treatment with 1% isoflurane and 1.2 μg/ml of propofol. Hypoxic neurons showed a sharp increase of LDH leakage and ER stress and a decrease of cell viability after treatment with 1.4% isoflurane and 0.6 μg/ml of propofol or 0.5% isoflurane and 1.8 μg/ml of propofol. After knockdown of BiP, the application of 1% isoflurane and 1.2 μg/ml of propofol led to the decrease of GABA_AR α1 subunit protein content and viability of cell, as well as aggravation of ER stress.

Conclusion: A combination of 1% isoflurane and 1.2 μg/ml of propofol causes the least damage than do other dosages of both two drugs, and endogenous BiP plays an important role in this process.

Combination of Isoflurane and Propofol as General Anesthesia During Orthopedic Surgery of Perioperative Cerebral Hypoperfusion Rats to Avoid Cognitive Impairment

Background: Perioperative cerebral hypoperfusion (CH) is common, although the underlying mechanism of cognitive impairment that results due to perioperative cerebral hypoperfusion remains to be determined. Isoflurane anesthesia induces neuronal injury via endoplasmic reticulum (ER) stress, whereas a sub-anesthetic dose of propofol improves postoperative cognitive function. However, the effects of the combination of isoflurane plus propofol, which is a common aesthetic combination administered to patients, on ER stress and cognition remain unknown. Methods: We sought to determine the effects of isoflurane plus propofol on ER stress and cognitive function in rats insulted by cerebral hypoperfusion. Ligation of the bilateral common carotid arteries (CCA) was adopted to develop the cerebral hypoperfusion rat model. A second surgery, open reduction and internal fixation (ORIF), requiring general anesthesia, was performed 30 days later so that the effects of anesthetics on the cognitive function of CH rats could be assessed. Rats received isoflurane alone (1.9%), propofol alone (40 mg·kg^-1·h^-1) or a combination of isoflurane and propofol (1% and 20 mg·kg^-1·h^-1 or 1.4% and 10 mg·kg^-1·h^-1). Behavioral studies (contextual fear conditioning [FC] test), histological analyses (Nissl staining) and biochemical analyses (western blotting of the harvested rat brain tissues) were employed. Results: Hippocampus-dependent memory of rats in group IP₁ (1% isoflurane plus 20 mg·kg^-1·h^-1 propofol) was not impaired, and expression level of γ-aminobutyric acid A type receptor α1 subunit, a key cognition-related protein, remained normal. ER stress alleviator, binding immunoglobulin protein, increased extremely while ER stress transcription factor, C/EBP homologous protein, showed no statistical difference compared with the control group. Numbers of surviving neurons confirmed the substantial neuronal damage caused by propofol or isoflurane alone. Conclusions: These data suggest that ER stress contributes to the underlying mechanism of cognitive impairment and that the combination of isoflurane and propofol did not aggravate cognitive impairment and ER stress in aging rats with CH that were further subjected to ORIF surgery.

MERCs. The Novel Assistant to Neurotransmission?

In neuroscience, much attention is paid to intercellular interactions, in particular, to synapses. However, many researchers do not pay due attention to the contribution of intracellular contacts to the work of intercellular interactions. Nevertheless, along with synapses, intracellular contacts also have complex organization and a tremendous number of regulatory elements. Mitochondria-endoplasmic reticulum contacts (MERCs) are a specific site of interaction between the two organelles; they provide a basis for a large number of cellular functions, such as calcium homeostasis, lipid metabolism, autophagy, and apoptosis. Despite the presence of these contacts in various parts of neurons and glial cells, it is yet not known whether they fulfill the same functions. There are still many unsolved questions about the work of these intracellular contacts, and one of the most important among them is if MERCs, with their broad implication into synaptic events, can be considered the assistant to neurotransmission?

Zika virus infection leads to mitochondrial failure, oxidative stress and DNA damage in human iPSC-derived astrocytes

Zika virus (ZIKV) has been extensively studied since it was linked to congenital malformations, and recent research has revealed that astrocytes are targets of ZIKV. However, the consequences of ZIKV infection, especially to this cell type, remain largely unknown, particularly considering integrative studies aiming to understand the crosstalk among key cellular mechanisms and fates involved in the neurotoxicity of the virus. Here, the consequences of ZIKV infection in iPSC-derived astrocytes are presented. Our results show ROS imbalance, mitochondrial defects and DNA breakage, which have been previously linked to neurological disorders. We have also detected glial reactivity, also present in mice and in post-mortem brains from infected neonates from the Northeast of Brazil. Given the role of glia in the developing brain, these findings may help to explain the observed effects in congenital Zika syndrome related to neuronal loss and motor deficit.

Glucose-Regulated Protein 78 in the Aqueous Humor of Patients with Diabetic Macular Edema

PURPOSE

We identified the associations between levels of aqueous glucose-regulated protein 78 (GRP78) and systemic or ocular factors in patients with center-involving diabetic macular edema (CIDME).

METHODS

We measured the aqueous concentrations of GRP78, interleukin- (IL-) 1β, IL-2, IL-8, IL-10, and IL-17, placental growth factor, and vascular endothelial growth factor (VEGF). We explored the associations between aqueous GRP78 levels and those of other aqueous factors, optical coherence tomography (OCT) findings, and systemic parameters in CIDME patients.

RESULTS

In multivariate regression analysis, aqueous GRP78 levels were associated with aqueous VEGF levels (p = 0.007), length of EZ disruption (p = 0.007), length of EZ disruption (p = 0.007), length of EZ disruption (p = 0.007), length of EZ disruption (.

CONCLUSIONS

Aqueous GRP78 levels correlated with VEGF levels in the aqueous humor and EZ disruption on OCT. However, GRP78 levels were not associated with those of inflammatory biomarkers in the aqueous humor or OCT findings. Additionally, GRP78 could not serve as a biomarker to predict short-term prognosis of anti-VEGF agent.

Imbalance of ER and Mitochondria Interactions: Prelude to Cardiac Ageing and Disease?

Cardiac disease is still the leading cause of morbidity and mortality worldwide, despite some exciting and innovative improvements in clinical management. In particular, atrial fibrillation (AF) and heart failure show a steep increase in incidence and healthcare costs due to the ageing population. Although research revealed novel insights in pathways driving cardiac disease, the exact underlying mechanisms have not been uncovered so far. Emerging evidence indicates that derailed proteostasis (i.e., the homeostasis of protein expression, function and clearance) is a central component driving cardiac disease. Within proteostasis derailment, key roles for endoplasmic reticulum (ER) and mitochondrial stress have been uncovered. Here, we describe the concept of ER and mitochondrial stress and the role of interactions between the ER and mitochondria, discuss how imbalance in the interactions fuels cardiac ageing and cardiac disease (including AF), and finally assess the potential of drugs directed at conserving the interaction as an innovative therapeutic target to improve cardiac function.

ER Stress and the UPR in Shaping Intestinal Tissue Homeostasis and Immunity

An imbalance in the correct protein folding milieu of the endoplasmic reticulum (ER) can cause ER stress, which leads to the activation of the unfolded protein response (UPR). The UPR constitutes a highly conserved and intricately regulated group of pathways that serve to restore ER homeostasis through adaptation or apoptosis. Numerous studies over the last decade have shown that the UPR plays a critical role in shaping immunity and inflammation, resulting in the recognition of the UPR as a key player in pathological processes including complex inflammatory, autoimmune and neoplastic diseases. The intestinal epithelium, with its many highly secretory cells, forms an important barrier and messenger between the luminal environment and the host immune system. It is not surprising, that numerous studies have associated ER stress and the UPR with intestinal diseases such as inflammatory bowel disease (IBD) and colorectal cancer (CRC). In this review, we discuss our current understanding of the roles of ER stress and the UPR in shaping immune responses and maintaining tissue homeostasis. Furthermore, the role played by the UPR in disease, with emphasis on IBD and CRC, is described here. As a key player in immunity and inflammation, the UPR has been increasingly recognized as an important pharmacological target in the development of therapeutic strategies for immune-mediated pathologies. We summarize available strategies targeting the UPR and their therapeutic implications. Understanding the balance between homeostasis and pathophysiology, as well as means of manipulating this balance, provides an important avenue for future research.

Organellar Calcium Handling in the Cellular Reticular Network

Ca²⁺ is an important intracellular messenger affecting diverse cellular processes. In eukaryotic cells, Ca²⁺ is handled by a myriad of Ca²⁺-binding proteins found in organelles that are organized into the cellular reticular network (CRN). The network is comprised of the endoplasmic reticulum, Golgi apparatus, lysosomes, membranous components of the endocytic and exocytic pathways, peroxisomes, and the nuclear envelope. Membrane contact sites between the different components of the CRN enable the rapid movement of Ca²⁺, and communication of Ca²⁺ status, within the network. Ca²⁺-handling proteins that reside in the CRN facilitate Ca²⁺ sensing, buffering, and cellular signaling to coordinate the many processes that operate within the cell.

Glucocorticoid-induced leucine zipper protects noise-induced apoptosis in cochlear cells by inhibiting endoplasmic reticulum stress in rats

Endoplasmic reticulum (ER) stress-mediated apoptosis has been reported to be involved in the noise-induced hearing loss (NIHL). Glucocorticoid-induced leucine zipper (GILZ) protein has been reported to have different regulatory effects on apoptosis according to cell types. However, whether GILZ regulates apoptosis in cochlear cells is unclear. Our study aimed to investigate the mechanism by which GILZ protected ER stress-mediated cochlear apoptosis induced by noise exposure. In our trials, forty-eight male Spraque-Dawley rats were randomized into the noise, OE-GILZ-rLV + noise (ON), shRNA-GILZ-rLV + noise (SN), and control group. Rats in noise and control groups were pre-treated by administration of Blank-rLV. Before and on days 1, 4, 14 after noise exposure, auditory brainstem response (ABR) and cochlear apoptosis were detected. Changes in GILZ, GRP78, CHOP, Bcl-xL, Bax, and cleaved caspase-3 levels were investigated. Noise exposure increased ABR threshold shifts and cochlear apoptosis in parallel with downregulation of Bcl-xL and upregulation of GRP78, CHOP, Bax and cleaved caspase-3. GILZ overexpression significantly reduced ABR threshold shifts and apoptotic cochlear cells owing to noise exposure. GILZ overexpression in the cochlea further increased GRP78 elevation, decreased expression of CHOP, Bax and cleaved caspase-3, and increased expression of Bcl-xL. GILZ silencing demonstrated the opposite effect on these effects. GILZ protects cochlea from ER stress-mediated apoptosis induced by noise exposure through reduction of CHOP and regulation of ER stress-associated apoptotic proteins.

The roles of mitochondria-associated membranes in mitochondrial quality control under endoplasmic reticulum stress

The endoplasmic reticulum (ER) and mitochondria are two important organelles in cells. Mitochondria-associated membranes (MAMs) are lipid raft-like domains formed in the ER membranes that are in close apposition to mitochondria. They play an important role in signal transmission between these two essential organelles. When cells are exposed to internal or external stressful stimuli, the ER will activate an adaptive response called the ER stress response, which has a significant effect on mitochondrial function. Mitochondrial quality control is an important mechanism to ensure the functional integrity of mitochondria and the effect of ER stress on mitochondrial quality control through MAMs is of great significance. Therefore, in this review, we introduce ER stress and mitochondrial quality control, and discuss how ER stress signals are transmitted to mitochondria through MAMs. We then review the important roles of MAMs in mitochondrial quality control under ER stress.

Proteostasis and Beyond: ATF6 in Ischemic Disease

Endoplasmic reticulum (ER) stress is a pathological hallmark of numerous ischemic diseases, including stroke and myocardial infarction (MI). In these diseases, ER stress leads to activation of the unfolded protein response (UPR) and subsequent adaptation of cellular physiology in ways that dictate cellular fate following ischemia. Recent evidence highlights a protective role for the activating transcription factor 6 (ATF6) arm of the UPR in mitigating adverse outcomes associated with ischemia/reperfusion (I/R) injury in multiple disease models. This suggests ATF6 as a potential therapeutic target for intervening in diverse ischemia-related disorders. Here, we discuss the evidence demonstrating the importance of ATF6 signaling in protecting different tissues against ischemic damage and discuss preclinical results focused on defining the potential for pharmacologically targeting ATF6 to intervene in such diseases.

The Interplay Between Pattern Recognition Receptors and Autophagy in Inflammation

Pattern recognition receptors (PRRs) are sensors of exogenous and endogenous "danger" signals from pathogen-associated molecular patterns (PAMPs), and damage associated molecular patterns (DAMPs), while autophagy can respond to these signals to control homeostasis. Almost all PRRs can induce autophagy directly or indirectly. Toll-like receptors (TLRs), Nod-like receptors (NLRs), retinoic acid-inducible gene-I-like receptors (RLRs), and cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) pathway can induce autophagy directly through Beclin-1 or LC3-dependent pathway, while the interactions with the receptor for advanced glycation end products (RAGE)/high mobility group box 1 (HMGB1), CD91/Calreticulin, and TLRs/HSPs are achieved by protein, Ca2⁺, and mitochondrial homeostasis. Autophagy presents antigens to PRRs and helps to clean the pathogens. In addition, the induced autophagy can form a negative feedback regulation of PRRs-mediated inflammation in cell/disease-specific manner to maintain homeostasis and prevent excessive inflammation. Understanding the interaction between PRRs and autophagy in a specific disease will promote drug development for immunotherapy. Here, we focus on the interactions between PRRs and autophagy and how they affect the inflammatory response.

Mitochondrial Neuroglobin Is Necessary for Protection Induced by Conditioned Medium from Human Adipose-Derived Mesenchymal Stem Cells in Astrocytic Cells Subjected to Scratch and Metabolic Injury

Astrocytes are specialized cells capable of regulating inflammatory responses in neurodegenerative diseases or traumatic brain injury. In addition to playing an important role in neuroinflammation, these cells regulate essential functions for the preservation of brain tissue. Therefore, the search for therapeutic alternatives to preserve these cells and maintain their functions contributes in some way to counteract the progress of the injury and maintain neuronal survival in various brain pathologies. Among these strategies, the conditioned medium from human adipose-derived mesenchymal stem cells (CM-hMSCA) has been reported with a potential beneficial effect against several neuropathologies. In this study, we evaluated the potential effect of CM-hMSCA in a model of human astrocytes (T98G cells) subjected to scratch injury. Our findings demonstrated that CM-hMSCA regulates the cytokines IL-2, IL-6, IL-8, IL-10, GM-CSF, and TNF-α, downregulates calcium at the cytoplasmic level, and regulates mitochondrial dynamics and the respiratory chain. These actions are accompanied by modulation of the expression of different proteins involved in signaling pathways such as AKT/pAKT and ERK1/2/pERK, and may mediate the localization of neuroglobin (Ngb) at the cellular level. We also confirmed that Ngb mediated the protective effects of CM-hMSCA through regulation of proteins involved in survival pathways and oxidative stress. In conclusion, regulation of brain inflammation combined with the recovery of fundamental cellular aspects in the face of injury makes CM-hMSCA a promising candidate for the protection of astrocytes in brain pathologies.

Spatiotemporal Expression of GRP78 in the Blood Vessels of Rats Treated With 3-Nitropropionic Acid Correlates With Blood-Brain Barrier Disruption

Glucose-regulated protein (GRP78) or BiP, a 78-kDa chaperone protein located in the endoplasmic reticulum (ER), has recently been reported to be involved in the neuroglial response to ischemia-induced ER stress. The present study was designed to study the expression patterns of this protein and the cell types involved in the induction of GRP78 expression in rats treated with the mitochondrial toxin 3-nitropropionic acid (3-NP). GRP78 immunoreactivity was almost exclusively localized to striatal neurons in saline-treated controls, but GRP78 expression was induced in activated glial cells, including reactive astrocytes and activated microglia/macrophages, in the striata of rats treated with 3-NP. In the lesion core, increased GRP78 immunoreactivity was observed in the vasculature; this was evident in the lesion periphery of the core at 3 days after lesion induction, and was evenly distributed throughout the lesion core by 7 days after lesion induction. Vascular GRP78 expression was correlated, both temporally and spatially, with infiltration of activated microglia into the lesion core. In addition, this was coincident with the time and pattern of blood-brain barrier (BBB) leakage, detected by the extravasation of fluorescein isothiocyanate-albumin, an established BBB permeability marker. Vascular GRP78-positive cells in the lesion core were identified as endothelial cells, smooth muscle cells, and adventitial fibroblast-like cells, in which GRP78 protein was specifically localized to the cisternae of the rough ER and perinuclear cisternae, but not to other organelles such as mitochondria or nuclei. Thus, our data provide novel insights into the phenotypic and functional heterogeneity of GRP78-positive cells within the lesion core, suggesting the involvement of GRP78 in the activation/recruitment of activated microglia/macrophages and its potential role in BBB impairment in response to a 3-NP-mediated neurotoxic insult.

Elucidating sex differences in response to cerebral ischemia: immunoregulatory mechanisms and the role of microRNAs

Cerebral ischemia remains a major cause of death and disability worldwide, yet therapeutic options remain limited. Differences in sex and age play an important role in the final outcome in response to cerebral ischemia in both experimental and clinical studies: males have a higher risk and worse outcome than females at younger ages and this trend reverses in older ages. Although the molecular mechanisms underlying sex dimorphism are complex and are still not well understood, studies suggest steroid hormones, sex chromosomes, differential cell death and immune pathways, and sex-specific microRNAs may contribute to the outcome following cerebral ischemia. This review focuses on differential effects between males and females on cell death and immunological pathways in response to cerebral ischemia, the central role of innate sex differences in steroid hormone signaling, and upstreamregulation of sexually dimorphic gene expression by microRNAs.

Suppression of stress induction of the 78-kilodalton glucose regulated protein (GRP78) in cancer by IT-139, an anti-tumor ruthenium small molecule inhibitor

In many cancers, combination therapy regimens are successfully improving response and survival rates, but the challenges of toxicity remain. GRP78, the master regulator of the unfolded protein response, is emerging as a target that is upregulated in tumors, specifically following treatment, and one that impacts tumor cell survival and disease recurrence. Here, we show IT-139, an antitumor small molecule inhibitor, suppresses induction of GRP78 from different types of endoplasmic reticulum (ER) stress in a variety of cancer cell lines, including those that have acquired therapeutic resistance, but not in the non-cancer cells being tested. We further determined that IT-139 treatment exacerbates ER stress while at the same time suppresses GRP78 induction at the transcriptional level. Our studies revealed a differential effect of IT-139 on chaperone protein family expression at multiple levels in different cancer cell lines. In xenograft studies, IT-139 decreased BRAF inhibitor upregulation of GRP78 expression in the tumor, while having minimal effect on GRP78 expression in the adjacent normal cells. The preferential decrease in GRP78 levels in tumor cells over normal cells, supported by the manageable safety profile seen in the Phase 1 clinical trial, reinforce the value IT-139 brings to combination therapies as it continues its clinical development.

Astroglial Modulation of Hydromineral Balance and Cerebral Edema

Maintenance of hydromineral balance (HB) is an essential condition for life activity at cellular, tissue, organ and system levels. This activity has been considered as a function of the osmotic regulatory system that focuses on hypothalamic vasopressin (VP) neurons, which can reflexively release VP into the brain and blood to meet the demand of HB. Recently, astrocytes have emerged as an essential component of the osmotic regulatory system in addition to functioning as a regulator of the HB at cellular and tissue levels. Astrocytes express all the components of osmoreceptors, including aquaporins, molecules of the extracellular matrix, integrins and transient receptor potential channels, with an operational dynamic range allowing them to detect and respond to osmotic changes, perhaps more efficiently than neurons. The resultant responses, i.e., astroglial morphological and functional plasticity in the supraoptic and paraventricular nuclei, can be conveyed, physically and chemically, to adjacent VP neurons, thereby influencing HB at the system level. In addition, astrocytes, particularly those in the circumventricular organs, are involved not only in VP-mediated osmotic regulation, but also in regulation of other osmolality-modulating hormones, including natriuretic peptides and angiotensin. Thus, astrocytes play a role in local/brain and systemic HB. The adaptive astrocytic reactions to osmotic challenges are associated with signaling events related to the expression of glial fibrillary acidic protein and aquaporin 4 to promote cell survival and repair. However, prolonged osmotic stress can initiate inflammatory and apoptotic signaling processes, leading to glial dysfunction and a variety of brain diseases. Among many diseases of brain injury and hydromineral disorders, cytotoxic and osmotic cerebral edemas are the most common pathological manifestation. Hyponatremia is the most common cause of osmotic cerebral edema. Overly fast correction of hyponatremia could lead to central pontine myelinolysis. Ischemic stroke exemplifies cytotoxic cerebral edema. In this review, we summarize and analyze the osmosensory functions of astrocytes and their implications in cerebral edema.

Cellular and Subcellular Localization of Endoplasmic Reticulum Chaperone GRP78 Following Transient Focal Cerebral Ischemia in Rats

The 78-kDa glucose-regulated protein (GRP78), a chaperone protein located in the endoplasmic reticulum (ER), has been reported to have neuroprotective effects in the injured central nervous system. Our aim was to examine the expression profiles and subcellular distributions of GRP78 and its association with the neuroglial reaction in the rat striatum after transient, focal cerebral ischemia. In sham-operated rats, constitutive, specific immunoreactivity for GRP78 was almost exclusively localized to the rough ER of striatal neurons, with none in the resting, ramified microglia or astrocytes. At 1 day post reperfusion, increased expression was observed in ischemia-resistant cholinergic interneurons, when most striatal neurons had lost GRP78 expression (this occurred earlier than the loss of other neuronal markers). By 3 days post reperfusion, GRP78 expression had re-emerged in association with the activation of glial cells in both infarct and peri-infarct areas but showed different patterns in the two regions. Most of the expression induced in the infarct area could be attributed to brain macrophages, while expression in the peri-infarct area predominantly occurred in neurons and reactive astrocytes. A gradual, sustained induction of GRP78 immunoreactivity occurred in reactive astrocytes localized to the astroglial scar, lasting for at least 28 days post reperfusion. Using correlative light- and electron-microscopy, we found conspicuous GRP78 protein localized to abnormally prominent, dilated rough ER in both glial cell types. Thus, our data indicate a link between GRP78 expression and the activated functional status of neuroglial cells, predominantly microglia/macrophages and astrocytes, occurring in response to ischemia-induced ER stress.

Endoplasmic reticulum chaperone GRP78 mediates cigarette smoke-induced necroptosis and injury in bronchial epithelium

Introduction

Bronchial epithelial cell death and airway inflammation induced by cigarette smoke (CS) have been involved in the pathogenesis of COPD. GRP78, belonging to heat shock protein 70 family, has been implicated in cell death and inflammation, while little is known about its roles in COPD. Here, we demonstrate that GRP78 regulates CS-induced necroptosis and injury in bronchial epithelial cells.

Materials and methods

GRP78 and necroptosis markers were examined in human bronchial epithelial (HBE) cell line, primary mouse tracheal epithelial cells, and mouse lungs. siRNA targeting GRP78 gene and necroptosis inhibitor were used. Expression of inflammatory cytokines, mucin MUC5AC, and related signaling pathways were detected.

Results

Exposure to CS significantly increased the expression of GRP78 and necroptosis markers in HBE cell line, primary mouse tracheal epithelial cells, and mouse lungs. Inhibition of GRP78 significantly suppressed CS extract (CSE)-induced necroptosis. Furthermore, GRP78–necroptosis cooperatively regulated CSE-induced inflammatory cytokines such as interleukin 6 (IL6), IL8, and mucin MUC5AC in HBE cells, likely through the activation of nuclear factor (NF-κB) and activator protein 1 (AP-1) pathways, respectively.

Conclusion

Taken together, our results demonstrate that GRP78 promotes CSE-induced inflammatory response and mucus hyperproduction in airway epithelial cells, likely through upregulation of necroptosis and subsequent activation of NF-κB and AP-1 pathways. Thus, inhibition of GRP78 and/or inhibition of necroptosis could be the effective therapeutic approaches for the treatment of COPD.

Calbindin-D28k in the Brain Influences the Expression of Cellular Prion Protein

The phenotypes of calbindin-D9k- (CaBP-9k-) knockout (KO), calbindin-D28k- (CaBP-28k-) KO, and CaBP-9k/28k-KO mice are similar to those of wild-type (WT) mice due to the compensatory action of other calcium transport proteins. In this study, we investigated the expression of cellular prion protein (PrP^C) in the brains of CaBP-9k-, CaBP-28k-, and CaBP-9k/28k-KO mice. PrP^C expression was significantly upregulated in the brain of all three strains. Levels of phospho-Akt (Ser473) and phospho-Bad (Ser136) were significantly elevated, but those of phospho-ERK and phospho-Bad (Ser155 and 112) were significantly reduced in the brains of CaBP-9k-, CaBP-28k-, and CaBP-9k/28k-KO mice. The expressions of the Bcl-2, p53, Bax, Cu/Zn-SOD, and Mn-SOD proteins were decreased in the brains of all KO mice. Expression of the endoplasmic reticulum marker protein BiP/GRP78 was decreased, and that of the CHOP protein was increased in the brains of those KO mice. To identify the roles of CaBP-28k, we transfected PC12 cells with siRNA for CaBP-28k and found increased expression of the PrP^C protein compared to the levels in control cells. These results suggest that CaBP-28k expression may regulate PrP^C protein expression and these mice may be vulnerable to the influence of prion disease.

Conditioned Medium of Human Adipose Mesenchymal Stem Cells Increases Wound Closure and Protects Human Astrocytes Following Scratch Assay In Vitro

Astrocytes perform essential functions in the preservation of neural tissue. For this reason, these cells can respond with changes in gene expression, hypertrophy, and proliferation upon a traumatic brain injury event (TBI). Different therapeutic strategies may be focused on preserving astrocyte functions and favor a non-generalized and non-sustained protective response over time post-injury. A recent strategy has been the use of the conditioned medium of human adipose mesenchymal stem cells (CM-hMSCA) as a therapeutic strategy for the treatment of various neuropathologies. However, although there is a lot of information about its effect on neuronal protection, studies on astrocytes are scarce and its specific action in glial cells is not well explored. In the present study, the effects of CM-hMSCA on human astrocytes subjected to scratch assay were assessed. Our findings indicated that CM-hMSCA improved cell viability, reduced nuclear fragmentation, and preserved mitochondrial membrane potential. These effects were accompanied by morphological changes and an increased polarity index thus reflecting the ability of astrocytes to migrate to the wound stimulated by CM-hMSCA. In conclusion, CM-hMSCA may be considered as a promising therapeutic strategy for the protection of astrocyte function in brain pathologies.

Transient Oxygen/Glucose Deprivation Causes a Delayed Loss of Mitochondria and Increases Spontaneous Calcium Signaling in Astrocytic Processes

Recently, mitochondria have been localized to astrocytic processes where they shape Ca(2+) signaling; this relationship has not been examined in models of ischemia/reperfusion. We biolistically transfected astrocytes in rat hippocampal slice cultures to facilitate fluorescent confocal microscopy, and subjected these slices to transient oxygen/glucose deprivation (OGD) that causes delayed excitotoxic death of CA1 pyramidal neurons. This insult caused a delayed loss of mitochondria from astrocytic processes and increased colocalization of mitochondria with the autophagosome marker LC3B. The losses of neurons in area CA1 and mitochondria in astrocytic processes were blocked by ionotropic glutamate receptor (iGluR) antagonists, tetrodotoxin, ziconotide (Ca(2+) channel blocker), two inhibitors of reversed Na(+)/Ca(2+) exchange (KB-R7943, YM-244769), or two inhibitors of calcineurin (cyclosporin-A, FK506). The effects of OGD were mimicked by NMDA. The glutamate uptake inhibitor (3S)-3-[[3-[[4-(trifluoromethyl)benzoyl]amino]phenyl]methoxy]-l-aspartate increased neuronal loss after OGD or NMDA, and blocked the loss of astrocytic mitochondria. Exogenous glutamate in the presence of iGluR antagonists caused a loss of mitochondria without a decrease in neurons in area CA1. Using the genetic Ca(2+) indicator Lck-GCaMP-6S, we observed two types of Ca(2+) signals: (1) in the cytoplasm surrounding mitochondria (mitochondrially centered) and (2) traversing the space between mitochondria (extramitochondrial). The spatial spread, kinetics, and frequency of these events were different. The amplitude of both types was doubled and the spread of both types changed by ∼2-fold 24 h after OGD. Together, these data suggest that pathologic activation of glutamate transport and increased astrocytic Ca(2+) through reversed Na(+)/Ca(2+) exchange triggers mitochondrial loss and dramatic increases in Ca(2+) signaling in astrocytic processes.

SIGNIFICANCE STATEMENT

Astrocytes, the most abundant cell type in the brain, are vital integrators of signaling and metabolism. Each astrocyte consists of many long, thin branches, called processes, which ensheathe vasculature and thousands of synapses. Mitochondria occupy the majority of each process. This occupancy is decreased by ∼50% 24 h after an in vitro model of ischemia/reperfusion injury, due to delayed fragmentation and mitophagy. The mechanism appears to be independent of neuropathology, instead involving an extended period of high glutamate uptake into astrocytes. Our data suggest that mitochondria serve as spatial buffers, and possibly even as a source of calcium signals in astrocytic processes. Loss of mitochondria resulted in drastically altered calcium signaling that could disrupt neurovascular coupling and gliotransmission.

Endoplasmic reticulum chaperones tweak the mitochondrial calcium rheostat to control metabolism and cell death

The folding of secretory proteins is a well-understood mechanism, based on decades of research on endoplasmic reticulum (ER) chaperones. These chaperones interact with newly imported polypeptides close to the ER translocon. Classic examples for these proteins include the immunoglobulin binding protein (BiP/GRP78), and the lectins calnexin and calreticulin. Although not considered chaperones per se, the ER oxidoreductases of the protein disulfide isomerase (PDI) family complete the folding job by catalyzing the formation of disulfide bonds through cysteine oxidation. Research from the past decade has demonstrated that ER chaperones are multifunctional proteins. The regulation of ER-mitochondria Ca²⁺ crosstalk is one of their additional functions, as shown for calnexin, BiP/GRP78 or the oxidoreductases Ero1α and TMX1. This function depends on interactions of this group of proteins with the ER Ca²⁺ handling machinery. This novel function makes perfect sense for two reasons: i. It allows ER chaperones to control mitochondrial apoptosis instantly without a lengthy bypass involving the upregulation of pro-apoptotic transcription factors via the unfolded protein response (UPR); and ii. It allows the ER protein folding machinery to fine-tune ATP import via controlling the speed of mitochondrial oxidative phosphorylation. Therefore, the role of ER chaperones in regulating ER-mitochondria Ca²⁺ flux identifies the progression of secretory protein folding as a central regulator of cell survival and death, at least in cell types that secrete large amount of proteins. In other cell types, ER protein folding might serve as a sentinel mechanism that monitors cellular well-being to control cell metabolism and apoptosis. The selenoprotein SEPN1 is a classic example for such a role. Through the control of ER-mitochondria Ca²⁺-flux, ER chaperones and folding assistants guide cellular apoptosis and mitochondrial metabolism.

GRP78 at the Centre of the Stage in Cancer and Neuroprotection

The 78-kDa glucose-regulated protein GRP78, also known as BiP and HSP5a, is a multifunctional protein with activities far beyond its well-known role in the unfolded protein response (UPR) which is activated after endoplasmic reticulum (ER) stress in the cells. Most of these newly discovered activities depend on its position within the cell. GRP78 is located mainly in the ER, but it has also been observed in the cytoplasm, the mitochondria, the nucleus, the plasma membrane, and secreted, although it is dedicated mostly to engage endogenous cytoprotective processes. Hence, GRP78 may control either UPR and macroautophagy or may activated phosphatidylinositol 3-kinase (PI3K)/AKT pro-survival pathways. GRP78 influences how tumor cells survive, proliferate, and develop chemoresistance. In neurodegeneration, endogenous mechanisms of neuroprotection are frequently insufficient or dysregulated. Lessons from tumor biology may give us clues about how boosting endogenous neuroprotective mechanisms in age-related neurodegeneration. Herein, the functions of GRP78 are revealed at the center of the stage of apparently opposite sites of the same coin regarding cytoprotection: neurodegeneration and cancer. The goal is to give a comprehensive and critical review that may serve to guide future experiments to identify interventions that will enhance neuroprotection.

Bovine and murine models highlight novel roles for SLC25A46 in mitochondrial dynamics and metabolism, with implications for human and animal health

Neuropathies are neurodegenerative diseases affecting humans and other mammals. Many genetic causes have been identified so far, including mutations of genes encoding proteins involved in mitochondrial dynamics. Recently, the “Turning calves syndrome”, a novel sensorimotor polyneuropathy was described in the French Rouge-des-Prés cattle breed. In the present study, we determined that this hereditary disease resulted from a single nucleotide substitution in SLC25A46, a gene encoding a protein of the mitochondrial carrier family. This mutation caused an apparent damaging amino-acid substitution. To better understand the function of this protein, we knocked out the Slc25a46 gene in a mouse model. This alteration affected not only the nervous system but also altered general metabolism, resulting in premature mortality. Based on optic microscopy examination, electron microscopy and on biochemical, metabolic and proteomic analyses, we showed that the Slc25a46 disruption caused a fusion/fission imbalance and an abnormal mitochondrial architecture that disturbed mitochondrial metabolism. These data extended the range of phenotypes associated with Slc25a46 dysfunction. Moreover, this Slc25a46 knock-out mouse model should be useful to further elucidate the role of SLC25A46 in mitochondrial dynamics.

Mitochondria are essential organelles, the site of numerous biochemical reactions, with a critical role in delivering energy to cells, particularly in the nervous system. Consequently, disrupted mitochondrial function often results in neurodegenerative diseases, in humans and in other mammals. Herein, we determined that the “Turning calves syndrome”, a new hereditary sensorimotor polyneuropathy in the French Rouge-des-Prés cattle breed was due to a single substitution in SLC25A46, a gene encoding a protein of the mitochondrial carrier family. We created a mouse knock-out model and determined that disruption of this gene dramatically disturbed mitochondrial dynamics in various organs that resulted in altered metabolism and early death, indirectly confirming the gene identification in cattle. Moreover, our novel findings extended the range of phenotypes associated with polymorphisms of this gene and help to elucidate the role of SLC25A46 in mitochondrial function.

Blockade of Neuroglobin Reduces Protection of Conditioned Medium from Human Mesenchymal Stem Cells in Human Astrocyte Model (T98G) Under a Scratch Assay

Previous studies have indicated that paracrine factors (conditioned medium) increase wound closure and reduce reactive oxygen species in a traumatic brain injury in vitro model. Although the beneficial effects of conditioned medium from human adipose tissue-derived mesenchymal stem cells (hMSCA-CM) have been previously suggested for various neurological diseases, their actions on astrocytic cells are not well understood. In this study, we have explored the effect of hMSCA-CM on human astrocyte model (T98G cells) subjected to scratch assay. Our results indicated that hMSCA-CM improved cell viability, reduced nuclear fragmentation, attenuated the production of reactive oxygen species, and preserved mitochondrial membrane potential and ultrastructural parameters. In addition, hMSCA-CM upregulated neuroglobin in T98G cells and the genetic silencing of this protein prevented the protective action of hMSCA-CM on damaged cells, suggesting that neuroglobin is mediating, at least in part, the protective effect of hMSCA-CM. Overall, this evidence suggests that the use of hMSCA-CM is a promising therapeutic strategy for the protection of astrocytic cells in central nervous system (CNS) pathologies.

Effects of Prolonged GRP78 Haploinsufficiency on Organ Homeostasis, Behavior, Cancer and Chemotoxic Resistance in Aged Mice

GRP78, a multifunctional protein with potent cytoprotective properties, is an emerging therapeutic target to combat cancer development, progression and drug resistance. The biological consequences of prolonged reduction in expression of this essential chaperone which so far has been studied primarily in young mice, was investigated in older mice, as older individuals are likely to be important recipients of anti-GRP78 therapy. We followed cohorts of Grp78+/+ and Grp78+/- male and female mice up to 2 years of age in three different genetic backgrounds and characterized them with respect to body weight, organ integrity, behavioral and memory performance, cancer, inflammation and chemotoxic response. Our results reveal that body weight, organ development and integrity were not impaired in aged Grp78+/- mice. No significant effect on cancer incidence and inflammation was observed in aging mice. Interestingly, our studies detected some subtle differential trends between the WT and Grp78+/- mice in some test parameters dependent on gender and genetic background. Our studies provide the first evidence that GRP78 haploinsufficiency for up to 2 years of age has no major deleterious effect in rodents of different genetic background, supporting the merit of anti-GRP78 drugs in treatment of cancer and other diseases affecting the elderly.

[Protective effects of heat shock protein 70 against hypoxic pulmonary hypertension in neonatal rats]

OBJECTIVE

To investigate the protective effect of heat shock protein 70 (HSP70) against hypoxic pulmonary hypertension (HPH) in neonatal rats.

METHODS

A total of 128 neonatal rats were randomly divided into blank control group, HPH model group, empty virus group, and HSP70 group, with 32 rats in each group. Before the establishment of an HPH model, the rats in the blank control group and HPH model group were given caudal vein injection of 5 μL sterile saline, those in the empty virus group were given caudal vein injection of 5 μL Ad-GFP (1 010 PFU/mL), and those in the HSP70 group were given caudal vein injection of 5 μL Ad-HSP70 (1 010 PFU/mL). HPH model was prepared in the HPH model, empty virus, and HSP70 groups after transfection. At 3, 7, 10, and 14 days after model establishment, a multi-channel physiological recorder was used to record mean pulmonary arterial pressure (mPAP), optical and electron microscopes were used to observe the structure and remodeling parameters of pulmonary vessels, and Western blot was used to measure the protein expression of HSP70, hypoxia-inducible factor-1α (HIF-1α), endothelin-1 (ET-1), and inducible nitric oxide synthase (iNOS) in lung tissues.

RESULTS

At 3, 7, 10, and 14 days after model establishment, the HPH model group and the empty virus group had a significantly higher mPAP than the blank control group (P<0.05). On days 7 and 10 of hypoxia, the blank control group and the HSP70 group had significantly lower MA% and MT% than the HPH model group and the empty virus group (P<0.01); on day 14 of hypoxia, the HPH model group, empty virus group, and HSP70 group had similar MA% and MT% (P>0.05), but had significantly higher MA% and MT% than the blank control group (P<0.01). On days 3, 7 and 10 of hypoxia, the HSP70 group had significantly higher protein expression of HSP70 than the HPH model group, empty virus group, and blank control group (P<0.01); the HSP70 group had significantly lower expression of HIF-1α, ET-1, and iNOS than the HPH model group and the empty virus group (P<0.05) and similar expression of HIF-1α, ET-1, and iNOS as the blank control group (P>0.05).

CONCLUSIONS

In neonatal rats with HPH, HSP70 transfection can increase the expression of HSP70 in lung tissues, downregulate the expression of HIF-1α, ET-1, and iNOS, alleviate pulmonary vascular remodeling, and reduce pulmonary artery pressure; therefore, it may become a new strategy for the treatment of HPH in neonates.

Profibrotic IHG-1 complexes with renal disease associated HSPA5 and TRAP1 in mitochondria

The highly conserved mitochondrial protein induced in high glucose-1 (IHG-1) functions to maintain mitochondrial quality and is associated with the development of fibrosis in diabetic nephropathy. Towards identifying novel approaches to treating diabetic kidney disease, IHG-1-protein-protein interactions were investigated using epitope-tagged immunoprecipitation analyses followed by mass spectrometry. Here we show that IHG-1 is solely expressed in mitochondria and localised to the inner mitochondrial membrane, the region where mitochondrial reactive oxygen species are generated. Chaperones HSPA5 and TRAP1 and cold shock protein YBX1 were identified as IHG-1 binding partners. All three proteins are important in the cellular response to oxidative stress and play important roles in mitochondrial transcription and DNA repair. Both redox imbalance and IHG-1 stimulate TGF-β signalling. IHG-1, HSPA5 and YBX1 all show increased expression in diabetic nephropathy, chronic kidney disease and in the Unilateral Ureteral Obstruction model of kidney fibrosis. Increased IHG-1 expression in UUO correlated with loss of TRAP1 expression. IHG-1 may target TRAP1 for degradation. When IHG-1 is no longer localised to mitochondria, it retains the ability to interact with the cold shock protein YBX1, facilitating anti-fibrotic actions in the nucleus. Targeting these proteins may offer alternative treatments for fibrotic kidney disease.