Sodium 4-phenylbutyrate protects against spinal cord ischemia by inhibition of endoplasmic reticulum stress

Particulate matter induced cognitive impairments via endoplasmic reticulum stress-mediated damage to mitochondria-associated endoplasmic reticulum membranes in immature rats

Particulate matter (PM) exposure has been increasingly recognized as detrimental to cognitive function and is associated with neurodevelopmental disorders. Mitochondria-associated endoplasmic reticulum membranes (MAMs) form an integrated interface between mitochondria and the endoplasmic reticulum (ER), facilitating crucial cellular functions. Prolonged ER stress (ERS) is implicated in various pathological states in the nervous system. MAMs and ERS may play vital roles in adverse effects of early-life PM exposure on cognitive abilities. This study investigated whether ERS plays a role in PM-induced MAMs dysfunction, leading to neuronal damage and cognitive impairments in early postnatal rats. Using a rat model with PM exposure concentrations of 2 and 10 mg/kg from postnatal Day 3 (PND3) to PND28, we observed that PM exposure resulted in anxiety-like behavior and impaired spatial working memory. The protein levels of ERS markers, including GRP78 and CHOP, were significantly increased in response to PM exposure. Western blot, transmission electron microscopy (TEM), and immunofluorescence analyses revealed decreased MAMs-related proteins and disrupted MAM structure and function caused by PM exposure. Administration of the ERS inhibitor 4-phenylbutyric acid (4-PBA) ameliorated these effects, restoring MAMs integrity and improving cognitive deficits. These findings highlighted the key role of ERS-MAMs dysfunction in PM-induced neurotoxicity and cognitive impairments, providing a new perspective and strategy for the prevention of cognitive deficits in early age with PM exposure.

RGC-specific ATF4 and/or CHOP deletion rescues glaucomatous neurodegeneration and visual function

Endoplasmic reticulum (ER) stress has been linked with various acute and chronic neurodegenerative diseases. We previously found that optic nerve (ON) injury and diseases induce neuronal ER stress in retinal ganglion cells (RGCs). We further demonstrated that germline deletion of CHOP preserves the structure and function of both RGC somata and axons in mouse glaucoma models. Here we report that RGC-specific deletion of CHOP and/or its upstream regulator ATF4 synergistically promotes RGC and ON survival and preserves visual function in mouse ON crush and silicone oil-induced ocular hypertension (SOHU) glaucoma models. Consistently, topical application of the ATF4/CHOP chemical inhibitor ISRIB or RGC-specific CRISPR-mediated knockdown of the ATF4 downstream effector Gadd45a also delivers significant neuroprotection in the SOHU glaucoma model. These studies suggest that blocking the neuronal intrinsic ATF4/CHOP axis of ER stress is a promising neuroprotection strategy for neurodegeneration.

Control of immune cell function by the unfolded protein response

Initiating and maintaining optimal immune responses requires high levels of protein synthesis, folding, modification and trafficking in leukocytes, which are processes orchestrated by the endoplasmic reticulum. Importantly, diverse extracellular and intracellular conditions can compromise the protein-handling capacity of this organelle, inducing a state of 'endoplasmic reticulum stress' that activates the unfolded protein response (UPR). Emerging evidence shows that physiological or pathological activation of the UPR can have effects on immune cell survival, metabolism, function and fate. In this Review, we discuss the canonical role of the adaptive UPR in immune cells and how dysregulation of this pathway in leukocytes contributes to diverse pathologies such as cancer, autoimmunity and metabolic disorders. Furthermore, we provide an overview as to how pharmacological approaches that modulate the UPR could be harnessed to control or activate immune cell function in disease.

4-Phenyl-butyric Acid Inhibits Japanese Encephalitis Virus Replication via Inhibiting Endoplasmic Reticulum Stress Response

Japanese encephalitis virus (JEV) infection causes host endoplasmic reticulum stress (ERS) reaction, and then induces cell apoptosis through the UPR pathway, invading the central nervous system and causing an inflammation storm. The endoplasmic reticulum stress inhibitor, 4-phenyl-butyric acid (4-PBA), has an inhibitory effect on the replication of flavivirus. Here, we studied the effect of 4-PBA on JEV infection both in vitro and vivo. The results showed that 4-PBA treatment could significantly decrease the titer of JEV, inhibit the expression of the JEV NS3 protein (in vitro, p < 0.01) and reduce the positive rate of the JEV E protein (in vivo, p < 0.001). Compared to the control group, 4-PBA treatment can restore the weight of JEV-infected mice, decrease the level of IL-1β in serum and alleviate the abnormalities in brain tissue structure. Endoplasmic reticulum stress test found that the expression level of GRP78 was much lower and activation levels of PERK and IRE1 pathways were reduced in the 4-PBA treatment group. Furthermore, 4-PBA inhibited the UPR pathway activated by NS3, NS4b and NS5 RdRp. The above results indicated that 4-PBA could block JEV replication and inhibit ER stress caused by JEV. Interestingly, 4-PBA could reduce the expression of NS5 by inhibiting transcription (p < 0.001), but had no effect on the expression of NS3 and NS4b. This result may indicate that 4-PBA has antiviral activity independent of the UPR pathway. In summary, the effect of 4-PBA on JEV infection is related to the inhibition of ER stress, and it may be a promising drug for the treatment of Japanese encephalitis.

Spinal Stroke: Outcome Attenuation by Erythropoietin and Carbamylated Erythropoietin and Its Prediction by Sphingosine-1-Phosphate Serum Levels in Mice

Spinal strokes may be associated with tremendous spinal cord injury. Erythropoietin (EPO) improves the neurological outcome of animals after spinal cord ischemia (SCI) and its effects on ischemia-induced endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are considered possible molecular mechanisms. Furthermore, sphingosin-1-phosphate (S1P) is suggested to correlate with SCI. In this study, the effect of recombinant human EPO (rhEPO) and carbamylated EPO (cEPO-Fc) on the outcome of mice after SCI and a prognostic value of S1P were investigated. SCI was induced in 12-month-old male mice by thoracic aortal cross-clamping after administration of rhEPO, cEPO-Fc, or a control. The locomotory behavior of mice was evaluated by the Basso mouse scale and S1P serum levels were measured by liquid chromatography-tandem mass spectrometry. The spinal cord was examined histologically and the expressions of key UPR proteins (ATF6, PERK, and IRE1a, caspase-12) were analyzed utilizing immunohistochemistry and real-time quantitative polymerase chain reaction. RhEPO and cEPO-Fc significantly improved outcomes after SCI. The expression of caspase-12 significantly increased in the control group within the first 24 h of reperfusion. Animals with better locomotory behavior had significantly higher serum levels of S1P. Our data indicate that rhEPO and cEPO-Fc have protective effects on the clinical outcome and neuronal tissue of mice after SCI and that the ER is involved in the molecular mechanisms. Moreover, serum S1P may predict the severity of impairment after SCI.

TSG-6 released from adipose stem cells-derived small extracellular vesicle protects against spinal cord ischemia reperfusion injury by inhibiting endoplasmic reticulum stress

Background

Spinal cord ischemia reperfusion injury (SCIRI) is a complication of aortic aneurysm repair or spinal cord surgery that is associated with permanent neurological deficits. Mesenchymal stem cell (MSC)-derived small extracellular vesicles (sEVs) have been shown to be potential therapeutic options for improving motor functions after SCIRI. Due to their easy access and multi-directional differentiation potential, adipose‐derived stem cells (ADSCs) are preferable for this application. However, the effects of ADSC-derived sEVs (ADSC-sEVs) on SCIRI have not been reported.

Results

We found that ADSC-sEVs inhibited SCIRI-induced neuronal apoptosis, degradation of tight junction proteins and suppressed endoplasmic reticulum (ER) stress. However, in the presence of the ER stress inducer, tunicamycin, its anti-apoptotic and blood–spinal cord barrier (BSCB) protective effects were significantly reversed. We found that ADSC-sEVs contain tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) whose overexpression inhibited ER stress in vivo by modulating the PI3K/AKT pathway.

Conclusions

ADSC-sEVs inhibit neuronal apoptosis and BSCB disruption in SCIRI by transmitting TSG-6, which suppresses ER stress by modulating the PI3K/AKT pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02963-4.

4-Phenylbutyrate restores localization and membrane repair to human dysferlin mutations

Dysferlinopathies are muscular dystrophies caused by recessive loss-of-function mutations in dysferlin (DYSF), a membrane protein involved in skeletal muscle membrane repair. We describe a cell-based assay in which human DYSF proteins bearing missense mutations are quantitatively assayed for membrane localization by flow cytometry and identified 64 localization-defective DYSF mutations. Using this platform, we show that the clinically approved drug 4-phenylbutryric acid (4-PBA) partially restores membrane localization to 25 mutations, as well as membrane repair to cultured myotubes expressing 2 different mutations. Two-day oral administration of 4-PBA to mice homozygous for one of these mutations restored myofiber membrane repair. 4-PBA may hold therapeutic potential for treating a subset of humans with muscular dystrophy due to dysferlin deficiency.

Histological Findings After Aortic Cross-Clamping in Preclinical Animal Models

Spinal cord ischemic injury and paralysis are devastating complications after open surgical repair of thoracoabdominal aortic aneurysms. Preclinical models have been developed to simulate the clinical paradigm to better understand the neuropathophysiology and develop therapeutic treatment. Neuropathological findings in the preclinical models have not been comprehensively examined before. This systematic review studies the past 40 years of the histological findings after open surgical repair in preclinical models. Our main finding is that damage is predominantly in the grey matter of the spinal cord, although white matter damage in the spinal cord is also reported. Future research needs to examine the neuropathological findings in preclinical models after endovascular repair, a newer type of surgical repair used to treat aortic aneurysms.

Inhibition of MALT1 Alleviates Spinal Ischemia/Reperfusion Injury-Induced Neuroinflammation by Modulating Glial Endoplasmic Reticulum Stress in Rats

PURPOSE

Glial activation and the disorders of cytokine secretion induced by endoplasmic reticulum stress (ERS) are crucial pathogenic processes in establishing ischemia/reperfusion (I/R) injury of the brain and spinal cord. This present study aimed to investigate the effects of mucous-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) on spinal cord ischemia/reperfusion (SCI/R) injury via regulating glial ERS.

METHODS

SCI/R was induced by thoracic aorta occlusion-reperfusion in rats. The MALT1-specific inhibitor MI-2 or human recombinant MALT1 protein (hrMALT1) was administrated for three consecutive days after the surgery. Immunofluorescent staining was used to detect the localization of MALT1 and ERS profiles in activated astrocyte and microglia of spinal cord. The ultrastructure of endoplasmic reticulum (ER) was examined by transmission electron microscopy. Blood-spinal cord barrier (BSCB) disruption and noninflammatory status were assessed. The neuron loss and demyelination in the spinal cord were monitored, and the hindlimb motor function was evaluated in SCI/R rats.

RESULTS

Intraperitoneally postoperative MI-2 treatment down-regulated phos-NF-κB (p65) and Bip (ERS marker protein) expression in the spinal cord after SCI/R in rats. Intraperitoneal injection MI-2 attenuated the swelling/dilation of ER of the glia in SCI/R rats. Furthermore, MI-2 attenuated I/R-induced Evans blue (EB) leakage and microglia M1 polarization in spinal cord, implying a role for MALT1 in the BSCB destruction and neuroinflammation after SCI/R in rats. Furthermore, intrathecal injection of hrMALT1 aggravated the fragmentation of neuron, loss of neurofibrils and demyelination caused by I/R, while 4-PBA, an ERS inhibitor, co-treatment with hrMALT1 reversed these effects in SCI/R rats. hrMALT1 administration aggravated the motor deficit index (MDI) scoring, while 4-PBA co-treatment improved SCI/R-induced motor deficits in rats.

CONCLUSION

Inhibition of MALT1 alleviates SCI/R injury-induced neuroinflammation by modulating glial endoplasmic reticulum stress in rats.

Sodium 4-Phenylbutyrate Protects Hypoxic-Ischemic Brain Injury via Attenuating Endoplasmic Reticulum Stress in Neonatal Rats

Neonatal hypoxic-ischemic (HI) brain injury is associated with long-term neurological disorders, and protective strategies are presently scarce. Sodium 4-phenylbutyrate (4-PBA) reportedly acts as a chemical chaperone that alleviates endoplasmic reticulum (ER) stress, which plays a critical role in neurological diseases. The present study aimed to evaluate the neuroprotective effects of 4-PBA on HI-induced neonatal brain injury in a rat model, and to characterize possible underlying mechanisms. The HI brain injury model was established by ligating the left common carotid artery in 7-day-old rats, followed by exposure to 8% oxygen for 2 h. The 4-PBA or vehicle was administered by an intracerebroventricular injection 30 min before HI. The protein expression levels of ER stress markers (GRP78, ATF6, and CHOP) were detected by western blotting at 24 h after HI insult. The activation of cAMP-response element-binding protein (CREB) was evaluated by western blotting and immunofluorescence. TUNEL and Nissl staining were performed to detect the histomorphological changes in the hippocampal neurons at 24 h and 7 days, respectively, after HI injury. From days 29 to 34 after brain HI, rats underwent Morris water maze tests to assess cognitive functioning. The results showed that pretreatment with 4-PBA decreased HI-induced excessive ER stress and neuronal injury. Moreover, CREB activation might be involved in the beneficial effects of 4-PBA on HI-induced learning and memory deficits in rats. In conclusion, the present study suggested a potential therapeutic approach of ER stress inhibition in the treatment of neonatal HI brain injury.

MicroRNA-211-5p attenuates spinal cord injury via targeting of activating transcription factor 6

The recovery of spinal cord injury (SCI) involves multiple factors, of which miRNAs take an important part. In this study, we evaluated the function of microRNA-211-5p (miR-211-5p) on SCI in a rat model. SCI model was established using modified Allen's weight-drop method and Basso-Bcattie-Bresnahan score was applied to assess the locomotor function. MiR-211-5p agomir was utilized to increase miR-211-5p expression and endoplasmic reticulum (ER) stress inhibitor, 4-PBA (4-phenylbutyric acid), was utilized to suppress ER stress. Neuron apoptosis and the expressions of miR-211-5p, activating transcription factor 6 (ATF6), apoptosis-related proteins, pro-inflammatory cytokines and endoplasmic reticulum stress-related proteins were detected. Dual luciferase reporter gene assay was performed to verify the binding between miR-211-5p and ATF6. The results showed that miR-211-5p directly targeted ATF6. MiR-211-5p was down-regulated and ATF6 was up-regulated in SCI rats. Both interferences with miR-211-5p agomir and 4-PBA effectively attenuated neuron apoptosis and reversed the expressions of apoptosis, inflammation and endoplasmic reticulum stress-related molecules post SCI in rats. These findings demonstrated that miR-211-5p could effectively alleviate SCI-induced neuron apoptosis and inflammation via directly targeting ATF-6 and regulating ER stress.

Baicalein Attenuates Pyroptosis and Endoplasmic Reticulum Stress Following Spinal Cord Ischemia-Reperfusion Injury via Autophagy Enhancement

Background

Spinal cord ischemia-reperfusion injury (SCIRI) is the main complication after the repair of a complex thoracoabdominal aortic aneurysm. Many clinical treatments are not ideal due to the complex pathophysiological process of this injury. Baicalein (BA), a component derived from the roots of the herb Scutellaria baicalensis, may contribute to the successful treatment of ischemia/reperfusion injury.

Purpose

In the present study, the effects of BA on spinal cord ischemia-reperfusion injury and the underlying mechanisms were assessed.

Materials and Methods

Spinal cord ischemia was induced in C57BL/6 mice by blocking the aortic arch. Fifty-five mice were then randomly divided into four groups: Sham, SCIR+Vehicle, SCIR+BA, and SCIR+BA +3MA groups. At 0 and 24 h pre-SCIRI and at 24 h and 7 days post-SCIRI, evaluations with the Basso mouse scale (BMS) were performed. On postoperative 24 h, the spinal cord was harvested to assess pyroptosis, endoplasmic reticulum stress mediated apoptosis and autophagy.

Results

BA enhanced the functional recovery of spinal cord ischemia-reperfusion injury. In addition, BA attenuated pyroptosis, alleviated endoplasmic reticulum stress-mediated apoptosis, and activated autophagy. However, the effects of BA on the functional recovery of SCIRI, pyroptosis and endoplasmic reticulum stress-mediated apoptosis were reversed by the inhibition of autophagy.

Conclusions

In general, our findings revealed that BA enhances the functional recovery of spinal cord ischemia-reperfusion injury by dampening pyroptosis and alleviating endoplasmic reticulum stress-mediated apoptosis, which are mediated by the activation of autophagy.

Adipose-Derived Stem Cells Protect Ischemia-Reperfusion and Partial Hepatectomy by Attenuating Endoplasmic Reticulum Stress

Ischemia-reperfusion (IR) is an inevitable complication of liver surgery. Recent studies indicate a critical role of endoplasmic reticulum stress (ERS) in hepatic IR. Mesenchymal stem cells (MSCs) have proven to be an effective tool for tissue regeneration and treatment of various diseases, including that of the liver. However, the mechanisms underlying the therapeutic effects of stem cells on hepatic IR injury (IRI) are still poorly understood, especially in the context of ERS. In this study, we established a porcine model of hepatic IRI and partial hepatectomy, and transplanted the animals with adipose-derived mesenchymal stem cells (ADSCs) isolated from miniature pigs. ADSCs not only alleviated the pathological changes in the liver parenchyma following IRI, but also protected the resident hepatocytes from damage. Mechanistically, the ADSCs significantly downregulated ERS-related proteins, including GRP78, p-eIF2α, ATF6 and XBP1s, as well as the proteins involved in ERS-induced apoptosis like p-JNK, ATF4 and CHOP. Taken together, ADSCs can alleviate hepatic IRI by inhibiting ERS and its downstream apoptotic pathways in the hepatocytes, indicating its therapeutic potential in liver diseases.

4-PBA Enhances Autophagy by Inhibiting Endoplasmic Reticulum Stress in Recombinant Human Beta Nerve Growth Factor-Induced PC12 cells After Mechanical Injury via PI3K/AKT/mTOR Signaling Pathway

OBJECTIVE

To investigate mechanism of endoplasmic reticulum (ER) stress-mediated autophagy in spinal cord injury (SCI).

METHODS

An in vitro model of spinal cord injury (SCI) was established by recombinant human beta nerve growth factor (NGF)-induced PC12 cells. Immunofluorescence was used to detect properties of PC12 cells induced by NGF. Western blot assay was used to detect expressions of the autophagy-related protein microtubule-associated protein 1 light chain 3 (LC3)I/II, the ER stress-related protein (HSPA5/GRP78), as well as the PI3K/AKT/mTOR signaling pathway-related proteins after mechanical injury at different time points. Then the sample assigned into sham, SCI, LY294002, SCI+LY294002, 4-PBA (4-phenylbutyric acid), and SCI+4-PBA groups. The expressions of the LC3I/II and PI3K/AKT/mTOR signaling pathway-related proteins were detected by Western blot assay.

RESULTS

NGF-induced PC12 cells have neurophysiological characteristics. After administration of the PI3K-specific inhibitor LY294002, phosphorylation levels of AKT and mTOR decreased, and the ratio of LC3II/I was higher in the inhibitor-treated injury group than the simple-injury group. After administration of the ER stress inhibitor 4-PBA, the results were similar to LY294002 group's results compared with SCI group.

CONCLUSIONS

Our study showed that NGF-induced PC12 cells can induce autophagy and ER stress after mechanical injury. ER stress inhibitor 4-PBA obtained similar effects to PI3K inhibitor LY294002, enhanced autophagy via PI3K/AKT/mTOR signaling pathway.

Xanthatin induces glioma cell apoptosis and inhibits tumor growth via activating endoplasmic reticulum stress-dependent CHOP pathway

Xanthatin is a natural sesquiterpene lactone purified from Xanthium strumarium L., which has shown prominent antitumor activity against a variety of cancer cells. In the current study, we investigated the effect of xanthatin on the growth of glioma cells in vitro and in vivo, and elucidated the underlying mechanisms. In both rat glioma C6 and human glioma U251 cell lines, xanthatin (1–15 μM) dose-dependently inhibited cell viability without apparent effect on the cell cycle. Furthermore, xanthatin treatment dose-dependently induced glioma cell apoptosis. In nude mice bearing C6 glioma tumor xenografts, administration of xanthatin (10, 20, 40 mg·kg⁻¹·d⁻¹, ip, for 2 weeks) dose-dependently inhibited the tumor growth, but did not affect the body weight. More importantly, xanthatin treatment markedly increased the expression levels of the endoplasmic reticulum (ER) stress-related markers in both the glioma cell lines as well as in C6 xenografts, including glucose-regulated protein 78, C/EBP-homologous protein (CHOP), activating factor 4, activating transcription factor 6, spliced X-box binding protein-1, phosphorylated protein kinase R-like endoplasmic reticulum kinase, and phosphorylated eukaryotic initiation factor 2a. Pretreatment of C6 glioma cells with the ER stress inhibitor 4-phenylbutyric acid (4-PBA, 7 mM) or knockdown of CHOP using small interfering RNA significantly attenuated xanthatin-induced cell apoptosis and increase of proapoptotic caspase-3. These results demonstrate that xanthatin induces glioma cell apoptosis and inhibits tumor growth via activating the ER stress-related unfolded protein response pathway involving CHOP induction. Xanthatin may serve as a promising agent in the treatment of human glioma.

Systemic hypoxia led to little retinal neuronal loss and dramatic optic nerve glial response

Vision loss is a devastating consequence of systemic hypoxia, but the cellular mechanisms are unclear. We investigated the impact of acute hypoxia in the retina and optic nerve. We induced systemic hypoxia (10% O₂) in 6-8w mice for 48 h and performed in vivo imaging using optical coherence tomography (OCT) at baseline and after 48 h to analyze structural changes in the retina and optic nerve. We analyzed glial cellular and molecular changes by histology and immunofluorescence and the impact of pretreatment with 4-phenylbutyric acid (4-PBA) in oligodendroglia survival. After 48 h hypoxia, we found no change in ganglion cell complex thickness and no loss of retinal ganglion cells. Despite this, there was significantly increased expression of CCAAT-enhancer-binding protein homologous protein (CHOP), a marker of endoplasmic reticulum stress, in the retina and optic nerve. In addition, hypoxia induced obvious increase of GFAP expression in the anterior optic nerve, where it co-localized with CHOP, and significant loss of Olig2⁺ oligodendrocytes. Pretreatment with 4-PBA, which has been shown to reduce endoplasmic reticulum stress, rescued total Olig2⁺ oligodendrocytes and increased the pool of mature (CC-1⁺) but not of immature (PDGFRa+) oligodendrocytes. Consistent with a selective vulnerability of the retina and optic nerve in hypoxia, the most striking changes in the 48 h murine model of hypoxia were in glial cells in the optic nerve, including increased CHOP expression in the astrocytes and loss of oligodendrocytes. Our data support a model where glial dysfunction is among the earliest events in systemic hypoxia - suggesting that glia may be a novel target in treatment of hypoxia.

Dexmedetomidine attenuates neuronal injury after spinal cord ischaemia-reperfusion injury by targeting the CNPY2-endoplasmic reticulum stress signalling

Dexmedetomidine (Dex) has been proven to exert protective effects on multiple organs in response to ischaemia-reperfusion injury, but the specific mechanism by which this occurs has not been fully elucidated. The purpose of this study was to investigate whether Dex attenuates spinal cord ischaemia-reperfusion injury (SCIRI) by inhibiting endoplasmic reticulum stress (ERS). Our team established a model of SCIRI and utilized the endoplasmic reticulum agonist thapsigargin. Dex (25 g/kg) was intraperitoneally injected 30 minutes before spinal cord ischaemia. After 45 minutes of ischaemia, the spinal cord was reperfused for 24 hours. To evaluate the neuroprotective effect of Dex on SCIRI, neurological function scores were assessed in rats and apoptosis of spinal cord cells was determined by TUNEL staining. To determine whether the endoplasmic reticulum apoptosis pathway CNPY2-PERK was involved in the neuroprotective mechanism of Dex, the expression levels of related proteins (CNPY2, GRP78, PERK, CHOP, caspase-12, caspase-9 and caspase-3) were detected by western blot analysis and RT-PCR. We observed that Dex significantly increased the neurological function scores after SCIRI and decreased apoptosis of spinal cord cells. The expression of ERS-related apoptosis proteins was significantly increased by SCIRI but was significantly decreased in response to Dex administration. Taken together, the results of this study indicate that Dex may attenuate SCIRI by inhibiting the CNPY2-ERS apoptotic pathway.

Increased ER Stress After Experimental Ischemic Optic Neuropathy and Improved RGC and Oligodendrocyte Survival After Treatment With Chemical Chaperon

Purpose

Increased endoplasmic reticulum (ER) stress is one of the earliest subcellular changes in neuro-ophthalmic diseases. In this study, we investigated the expression of key molecules in the ER stress pathways following nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults over 50, and assessed the impact of chemical chaperon 4-phenylbutyric acid (4-PBA) in vivo.

Methods

We induced AION using photochemical thrombosis in adult mice and performed histologic analyses of key molecules in the ER stress pathway in the retina and optic nerve. We also assessed the effects of daily intraperitoneal injections of 4-PBA after AION.

Results

In the retina at baseline, there was low proapoptotic transcriptional regulator C/EBP homologous protein (CHOP) and high prosurvival chaperon glucose-regulated protein 78 (GRP78) expression in retinal ganglion cells (RGCs). One day after AION, there was significantly increased CHOP and reduced GRP78 expressions in the ganglion cell layer. In the optic nerve at baseline, there was little CHOP and high GRP78 expression. One day after AION, there was significantly increased CHOP and no change in GRP78 expression. Treatment immediately after AION using daily intraperitoneal injection of chemical chaperone 4-PBA for 19 days significantly rescued Brn3A⁺ RGCs and Olig2⁺ optic nerve oligodendrocytes.

Conclusions

We showed for the first time that acute AION resulted in increased ER stress and differential expression of ER stress markers CHOP and GRP78 in the retina and optic nerve. Rescue of RGCs and oligodendrocytes with 4-PBA provides support for ER stress reduction as possible treatment for AION.

Effect of endoplasmic reticulum stress involved in manganese‑induced neurotoxicity in rats

The aim of the present study was to probe the mechanism of apoptosis induced by endoplasmic reticulum stress (ERS) in manganese‑induced rats. A total of 60 Sprague‑Dawley rats were randomly divided into a Vehicle group, LoMag group, HiMag group, and HiMag + 4‑phenylbutyrate (PBA) group. Manganese content was measured by Inductively Coupled Plasma‑Atomic Emission Spectrometry. Pathogenic morphology, the cellular structure of the striatum and ER were observed by hematoxylin and eosin staining and electron microscopy. The TUNEL method was used to examine neuronal apoptosis in the rat striatum. The expression levels of glucose‑regulated protein 78KD (GRP78), C/EBP homologous protein (CHOP), c‑Jun N‑terminal kinase (JNK) and caspase‑12 were analyzed by western blot analysis. The results revealed that striatal manganese concentrations in the LoMag and HiMag groups were higher than that in the Vehicle group (P<0.01). Rat striatal neuronal structure and apoptotic rates in the LoMag and HiMag groups were higher than those in the Vehicle group (P<0.05). 4‑PBA treatment effectively reduced the apoptotic cell number (P<0.05). In addition, ER swelling and vacuolization in the HiMag + PBA group was reduced compared with that in the HiMag group. In addition, the protein expression levels of GRP78, CHOP, JNK and caspase‑12 in the LoMag and HiMag groups were higher than those in the Vehicle group (P<0.05). However, the expression of these four proteins was reduced by 4‑PBA treatment (P<0.05). In conclusion, 4‑PBA significantly reduced the damage and apoptosis induced by manganese exposure in rats.

4-Phenylbutyric Acid Protects Against Ethanol-Induced Damage in the Developing Mouse Brain

BACKGROUND

Ethanol (EtOH) exposure during pregnancy may result in fetal alcohol spectrum disorders (FASD). One of the most deleterious consequences of EtOH exposure is neuronal loss in the developing brain. Previously, we showed that EtOH exposure induced neuroapoptosis in the brain of postnatal day 4 (PD4) mice but not PD12 mice. This differential susceptibility may result from an insufficient cellular stress response system such as unfolded protein response (also known as endoplasmic reticulum [ER] stress) in PD4 mice. In this study, we compared the effect of EtOH on ER stress in PD4 and PD12 mice and determined whether the inhibition of ER stress could protect the developing brain against EtOH damage.

METHODS

We used a third-trimester equivalent mouse model of FASD. PD4 and PD12 C57BL/6 mice were subcutaneously injected with saline (control), EtOH, EtOH plus 4-phenylbutyric acid (4-PBA), a chemical chaperone known as ER stress inhibitor, and 4-PBA alone. The expression of apoptosis marker, ER stress markers, and markers for glial cell activation was examined in the cerebral cortex.

RESULTS

EtOH induced neuroapoptosis and increased the expression of ER stress markers, such as activating transcription factor 6, 78-kDa glucose-regulated protein, inositol-requiring enzyme 1α, mesencephalic astrocyte-derived neurotrophic factor, and caspase-12 in PD4 but not PD12 mice. EtOH exposure also activated microglia and astrocytes. Interestingly, treatment with 4-PBA attenuated EtOH-induced neuroapoptosis. Moreover, 4-PBA inhibited the expression of the aforementioned ER stress markers and EtOH-induced glial activation in PD4 mice.

CONCLUSIONS

ER stress plays an important role in EtOH-induced damage to the developing brain. Inhibition of ER stress is neuroprotective and may provide a new therapeutic strategy for treating FASD.

Inhibition of Endoplasmic Reticulum Stress Preserves the Integrity of Blood-Spinal Cord Barrier in Diabetic Rats Subjected to Spinal Cord Injury

The blood-spinal cord barrier (BSCB) plays significance roles in recovery following spinal cord injury (SCI), and diabetes mellitus (DM) impairs endothelial cell function and integrity of BSCS. Endoplasmic reticulum (ER) stress occurs in the early stages of SCI and affects prognosis and cell survival. However, the relationship between ER stress and the integrity of BSCB in diabetic rats after SCI remains unclear. Here we observed that diabetic rats showed increased extravasation of Evans Blue (EB) dye, and loss of endothelial cells and pericytes 1 day after SCI compared to non-diabetic rats. Diabetes was also shown to induce activation of ER stress. Similar effects were observed in human brain microvascular endothelial cells. 4-phenylbutyric acid (4-PBA), an ER stress inhibitor lowered the adverse effect of diabetes on SCI, reduced EB dye extravasation, and limited the loss of endothelial cells and pericytes. Moreover, 4-PBA treatment partially reversed the degradation of tight junction and adherens junction both in vivo and in vitro. In conclusion, diabetes exacerbates the disruption of BSCB after SCI via inducing ER stress, and inhibition of ER stress by 4-PBA may play a beneficial role on the integrity of BSCB in diabetic SCI rats, leading to improved prognosis.

Inhibition of Endoplasmic Reticulum Stress Alleviates Lung Injury Induced by Brain Death

Brain death (BD) can induce inflammation and injury of organs. Endoplasmic reticulum (ER) stress is associated with a variety of diseases. However, little is known about how ER stress is implicated in brain death (BD)-induced lung injury. In this study, a stable BD rat model was constructed to investigate the role of ER stress on BD-induced lung injury. H&E staining demonstrated that BD can induce lung injury in rats. The results of Western blot and immunohistochemistry showed that apoptosis was observed in the lung tissues of BD rats. And the level of GRP78, p-PERK, p-eIF2α, CHOP, and Caspase-12 was highly expressed in BD rats compared with the control group. Inhibition of ER stress with salubrinal reduced the BD-induced lung inflammation. Moreover, BD-induced increase of NF-κB activity was lowered by inhibition of ER stress. These results suggested that inhibition of ER stress alleviates BD-induced lung inflammation by regulating NF-κB signaling pathway.

ER stress and the unfolded protein response in neurodegeneration

The clinical manifestation of neurodegenerative diseases is initiated by the selective alteration in the functionality of distinct neuronal populations. The pathology of many neurodegenerative diseases includes accumulation of misfolded proteins in the brain. In physiological conditions, the proteostasis network maintains normal protein folding, trafficking and degradation; alterations in this network - particularly disturbances to the function of endoplasmic reticulum (ER) - are thought to contribute to abnormal protein aggregation. ER stress triggers a signalling reaction known as the unfolded protein response (UPR), which induces adaptive programmes that improve protein folding and promote quality control mechanisms and degradative pathways or can activate apoptosis when damage is irreversible. In this Review, we discuss the latest advances in defining the functional contribution of ER stress to brain diseases, including novel evidence that relates the UPR to synaptic function, which has implications for cognition and memory. A complex concept is emerging wherein the consequences of ER stress can differ drastically depending on the disease context and the UPR signalling pathway that is altered. Strategies to target specific components of the UPR using small molecules and gene therapy are in development, and promise interesting avenues for future interventions to delay or stop neurodegeneration.

4-Phenylbutyrate Benefits Traumatic Hemorrhagic Shock in Rats by Attenuating Oxidative Stress, Not by Attenuating Endoplasmic Reticulum Stress

OBJECTIVE

Vascular dysfunction such as vascular hyporeactivity following severe trauma and shock is a major cause of death in injured patients. Oxidative stress and endoplasmic reticulum stress play an important role in vascular dysfunction. The objective of the present study was to determine whether or not 4-phenylbutyrate can improve vascular dysfunction and elicit antishock effects by inhibiting oxidative and endoplasmic reticulum stress.

DESIGN

Prospective, randomized, controlled laboratory experiment.

SETTING

State key laboratory of trauma, burns, and combined injury.

SUBJECTS

Five hundred and fifty-two Sprague-Dawley rats.

INTERVENTIONS

Rats were anesthetized, and a model of traumatic hemorrhagic shock was established by left femur fracture and hemorrhage. The effects of 4-phenylbutyrate (5, 20, 50, 100, 200, and 300 mg/kg) on vascular reactivity, animal survival, hemodynamics, and vital organ function in traumatic hemorrhagic shock rats and cultured vascular smooth muscle cells, and the relationship to oxidative stress and endoplasmic reticulum stress was observed.

MEASUREMENTS AND MAIN RESULTS

Lower doses of 4-phenylbutyrate significantly improved the vascular function, stabilized the hemodynamics, and increased the tissue blood flow and vital organ function in traumatic hemorrhagic shock rats, and markedly improved the survival outcomes. Among all dosages observed in the present study, 20 mg/kg of 4-phenylbutyrate had the best effect. Further results indicated that 4-phenylbutyrate significantly inhibited the oxidative stress, decreased shock-induced oxidative stress index such as the production of reactive oxygen species, increased the antioxidant enzyme levels such as superoxide dismutase, catalase, and glutathione, and improved the mitochondrial function by inhibiting the opening of the mitochondrial permeability transition pore in rat artery and vascular smooth muscle cells. In contrast, 4-phenylbutyrate did not affect the changes of endoplasmic reticulum stress markers following traumatic hemorrhagic shock. Furthermore, 4-phenylbutyrate increased the nuclear levels of nuclear factor-E2-related factor 2, and decreased the nuclear levels of nuclear factor κB in hypoxic vascular smooth muscle cells.

CONCLUSIONS

4-phenylbutyrate has beneficial effects for traumatic hemorrhagic shock including improving animal survival and protecting organ function. These beneficial effects of 4-phenylbutyrate in traumatic hemorrhagic shock result from its vascular function protection via attenuation of the oxidative stress and mitochondrial permeability transition pore opening. Nuclear factor-E2-related factor 2 and nuclear factor-κB may be involved in 4-phenylbutyrate-mediated inhibition of oxidative stress.

Mitochondrial and endoplasmic reticulum dysfunction and related defense mechanisms in critical illness-induced multiple organ failure

Patients with critical illness-induced multiple organ failure suffer from a very high morbidity and mortality, despite major progress in intensive care. The pathogenesis of this condition is complex and incompletely understood. Inadequate tissue perfusion and an overwhelming inflammatory response with pronounced cellular damage have been suggested to play an important role, but interventions targeting these disturbances largely failed to improve patient outcome. Hence, new therapeutic perspectives are urgently needed. Cellular dysfunction, hallmarked by mitochondrial dysfunction and endoplasmic reticulum stress, is increasingly recognized as an important contributor to the development of organ failure in critical illness. Several cellular defense mechanisms are normally activated when the cell is in distress, but may fail or respond insufficiently to critical illness. This insight may open new therapeutic options by stimulating these cellular defense mechanisms. This review summarizes the current understanding of the role of mitochondrial dysfunction and endoplasmic reticulum stress in critical illness-induced multiple organ failure and gives an overview of the corresponding cellular defense mechanisms. Therapeutic perspectives based on these cellular defense mechanisms are discussed. This article is part of a Special Issue entitled: Immune and Metabolic Alterations in Trauma and Sepsis edited by Dr. Raghavan Raju.

ENDOPLASMIC RETICULUM STRESS IN SEPSIS

Sepsis is an enormous public health issue and the leading cause of death in critically ill patients in intensive care units. Overwhelming inflammation, characterized by cytokine storm, oxidative threats, and neutrophil sequestration, is an underlying component of sepsis-associated organ failure. Despite recent advances in sepsis research, there is still no effective treatment available beyond the standard of care and supportive therapy. To reduce sepsis-related mortality, a better understanding of the biological mechanism associated with sepsis is essential. Endoplasmic reticulum (ER), a subcellular organelle, is responsible for the facilitation of protein folding and assembly and involved in several other physiological activities. Under stress and inflammatory conditions, ER loses homeostasis in its function, which is termed ER stress. During ER stress, unfolded protein response (UPR) is activated to restore ER function to its normal balance. However, once stress is beyond the compensatory capacity of UPR or protracted, apoptosis would be initiated by triggering cell injuries, even cell death. As such, ER stress and UPR are reported to be implicated in several pathological and inflammatory conditions. Although the detrimental role of ER stress during infections has been demonstrated, there is growing evidence that ER stress participates in the pathogenesis of sepsis. In this review, we summarize current research in the context of ER stress and UPR signaling associated with sepsis and its related clinical conditions, such as trauma-hemorrhage and ischemia/reperfusion injury. We also discuss the potential implications of ER stress as a novel therapeutic target and prognostic marker in patients with sepsis.

Effect of a chemical chaperone, tauroursodeoxycholic acid, on HDM-induced allergic airway disease

Endoplasmic reticulum (ER) stress-induced unfolded protein response plays a critical role in inflammatory diseases, including allergic airway disease. However, the benefits of inhibiting ER stress in the treatment of allergic airway disease are not well known. Herein, we tested the therapeutic potential of a chemical chaperone, tauroursodeoxycholic acid (TUDCA), in combating allergic asthma, using a mouse model of house dust mite (HDM)-induced allergic airway disease. TUDCA was administered during the HDM-challenge phase (preventive regimen), after the HDM-challenge phase (therapeutic regimen), or therapeutically during a subsequent HDM rechallenge (rechallenge regimen). In the preventive regimen, TUDCA significantly decreased HDM-induced inflammation, markers of ER stress, airway hyperresponsiveness (AHR), and fibrosis. Similarly, in the therapeutic regimen, TUDCA administration efficiently decreased HDM-induced airway inflammation, mucus metaplasia, ER stress markers, and AHR, but not airway remodeling. Interestingly, TUDCA administered therapeutically in the HDM rechallenge regimen markedly attenuated HDM-induced airway inflammation, mucus metaplasia, ER stress markers, methacholine-induced AHR, and airway fibrotic remodeling. These results indicate that the inhibition of ER stress in the lungs through the administration of chemical chaperones could be a valuable strategy in the treatment of allergic airway diseases.

Injury to the nervous system: A look into the ER

Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities that still lack an effective treatment. Although injury to the nervous system involves multiple and complex molecular factors, alteration to protein homeostasis is emerging as a relevant pathological mechanism. In particular, chronic endoplasmic reticulum (ER) stress is proposed as a possible driver of neuronal dysfunction in conditions such as spinal cord injury, stroke and damage to peripheral nerves. Importantly, manipulation of the unfolded protein response (UPR), a homeostatic pathway engaged by ER stress, has proved effective in improving cognitive and motor recovery after nervous system injury. Here we provide an overview on recent findings depicting a functional role of the UPR to the functional recovery after injury in the peripheral and central nervous systems. This article is part of a Special Issue entitled SI:ER stress.

4‑Phenylbutyrate protects rat skin flaps against ischemia‑reperfusion injury and apoptosis by inhibiting endoplasmic reticulum stress

4-phenylbutyrate (4-PBA) is a low molecular weight fatty acid, which has been demonstrated to regulate endoplasmic reticulum (ER) stress. ER stress-induced cell apoptosis has an important role in skin flap ischemia; however, a pharmacological approach for treating ischemia-induced ER dysfunction has yet to be reported. In the present study, the effects of 4-PBA-induced ER stress inhibition on ischemia-reperfusion injury were investigated in the skin flap of rats, and transcriptional regulation was examined. 4-PBA attenuated ischemia-reperfusion injury and inhibited cell apoptosis in the skin flap. Furthermore, 4-PBA reversed the increased expression levels of two ER stress markers: CCAAT/enhancer-binding protein-homologous protein and glucose-regulated protein 78. These results suggested that 4-PBA was able to protect rat skin flaps against ischemia-reperfusion injury and apoptosis by inhibiting ER stress marker expression and ER stress-mediated apoptosis. The beneficial effects of 4-PBA may prove useful in the treatment of skin flap ischemia-reperfusion injury.

Hyperbaric Oxygen Treatment Protects Against Spinal Cord Injury by Inhibiting Endoplasmic Reticulum Stress in Rats

STUDY DESIGN

Experimental animal study of treatment of SCI.

OBJECTIVE

To explore whether HBO treatment protects against secondary SCI by inhibiting the ER stress response.

SUMMARY OF BACKGROUND DATA

SCI is a neurological disorder that can severely limit the execution of the simplest day-to-day functions. ER stress plays an important role in the induction of neuronal apoptosis after SCI. HBO treatment can alleviate secondary injury and benefit neurological recovery after SCI, but the effect of HBO on ER stress response after SCI is yet to be characterized.

METHODS

The spinal cord of rats was injured via T10 laminectomy. Experimental animals were randomly assigned to 1 of 3 groups: sham-operated, SCI, and SCI+HBO. Each group was analyzed 1, 2, 3, 7, and 14 days after injury. Neurological recovery was evaluated using the Basso-Beattie-Bresnahan (BBB) scoring system and the TdT-mediated dUTP nick-end labeling reaction was carried out to visualize apoptotic cells. The expression of ER stress-related factors was evaluated by immunohistochemical, western blot, and real-time reverse transcription-polymerase chain reaction analyses.

RESULTS

SCI-induced apoptosis and an increase in the levels of CCAAT-enhancer-binding protein homologous protein (CHOP), and caspase-12 and caspase-3 compared with the sham-operated group. HBO treatment decreased CHOP and caspase-12 and caspase-3 expression as well as apoptosis compared with the SCI group. In addition, BBB scores were improved in the SCI+HBO relative to the SCI group at 7 and 14 days.

CONCLUSION

These results suggest that HBO treatment alleviates secondary injury to the spinal cord by inhibiting ER stress induced apoptosis, thereby promoting the recovery of neurological function.

LEVEL OF EVIDENCE

N/A.

4-Phenylbutyric Acid (4-PBA) and Lithium Cooperatively Attenuate Cell Death during Oxygen-Glucose Deprivation (OGD) and Reoxygenation

Hypoxia is an important cause of brain injury in ischemic stroke. It is known that endoplasmic reticulum (ER) stress is an important determinant of cell survival or death during hypoxia. However, the signaling pathways and molecular mechanisms involved remain to be studied in more detail. To investigate whether inhibition of ER stress promotes neuroprotection pathways, we applied an in vitro oxygen-glucose deprivation (OGD) followed by reoxygenation model of human SK-N-MC neuronal cell cultures in this study. Our results showed that neuronal cell death was induced in this model during the OGD reoxygenation by the sustained ER stress, but not during OGD phase. However, treatment of the cultures with lithium with the OGD reoxygenation insult did not result in neuroprotection, whereas concomitant treatment of chemical chaperon 4-phenylbutyric acid (4-PBA) provides protective effects in ER stress-exposed cells. Moreover, 4-PBA rescued ER stress-suppressed Akt protein biosynthesis, which works cooperatively with lithium in the activation of Akt downstream signaling by inhibition of autophagy-induced cell death. Taken together, our finding provides a possible mechanism by which 4-PBA and lithium contribute to mediate neuroprotection cooperatively. This result may potentially be a useful therapeutic strategy for ischemic stroke.

Targeting the unfolded protein response for disease intervention

INTRODUCTION

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) generates a stress condition that engages the unfolded protein response (UPR). The UPR is an adaptive reaction that aims to reestablish ER proteostasis by recovering the folding capacity of the cell. However, chronic ER stress results in apoptosis.

AREAS COVERED

This review focuses on discussing the emerging role of the UPR as a driver of several human pathologies including diabetes, neurodegenerative diseases and cancer. The involvement of specific UPR signaling components on different diseases is highlighted based on preclinical models and pharmacological and genetic manipulation of the pathway.

EXPERT OPINION

Therapeutic strategies directed to regulate the activity of different UPR signaling arms may reduce stress levels with a therapeutic gain. Recent drug discovery efforts have identified small molecules that target specific UPR components, providing protection on various disease models. However, important side effects are predicted in the chronic administration due to the fundamental role of the UPR in highly secretory organs such as liver and pancreas. To overcome these problems, we propose the use of combinatorial treatments of selected drugs with natural compounds that are known to modulate the ER proteostasis network.

Endoplasmic reticulum stress: relevance and therapeutics in central nervous system diseases

Endoplasmic reticulum (ER) stress plays an important role in a range of neurological disorders, such as neurodegenation diseases, cerebral ischemia, spinal cord injury, sclerosis, and diabetic neuropathy. Protein misfolding and accumulation in the ER lumen initiate unfolded protein response in energy-starved neurons which are relevant to toxic effects. In neurological disorders, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, ER dysfunction is well recognized, but the mechanisms remain unclear. In stroke and ischemia, spinal cord injury, and amyotrophic lateral sclerosis, chronic activation of ER stress is considered as main pathogeny which causes neuronal disorders. By targeting components of these ER signaling responses, to explore clinical treatment strategies or new drugs in CNS neurological diseases might become possible and valuable in the future.

ATF6 mediates a pro-inflammatory synergy between ER stress and TLR activation in the pathogenesis of liver ischemia-reperfusion injury

Although the roles of the metabolic stress in organ ischemia-reperfusion injury (IRI) have been well recognized, the question of whether and how these stress responses regulate innate immune activation against IR remains unclear. In a murine liver partial warm ischemia mode, we showed that prolonged ischemia triggered endoplasmic reticulum (ER) stress response, particularly, the activating transcription factor 6 (ATF6) branch, in liver Kupffer cells (KCs) and altered their responsiveness against Toll-like receptor (TLR) stimulation. Ischemia-primed cells increased pro-, but decreased anti-, inflammatory cytokine productions. Alleviation of ER stress in vivo by small chemical chaperon 4-phenylbutyrate or ATF6 small interfering RNA (siRNA) diminished the pro-inflammatory priming effect of ischemia in KCs, leading to the inhibition of liver immune response against IR and protection of livers from IRI. In vitro, ATF6 siRNA abrogated the ER stress-mediated pro-inflammatory enhancement of macrophage TLR4 response, by restricting NF-κB and restoring Akt activations. Thus, ischemia primes liver innate immune cells by ATF6-mediated ER stress response. The IR-induced metabolic stress and TLR activation function in synergy to activate tissue inflammatory immune response.

Disturbance of endoplasmic reticulum proteostasis in neurodegenerative diseases

The unfolded protein response (UPR) is a homeostatic mechanism by which cells regulate levels of misfolded proteins in the endoplasmic reticulum (ER). Although it is well characterized in non-neuronal cells, a proliferation of papers over the past few years has revealed a key role for the UPR in normal neuronal function and as an important driver of neurodegenerative diseases. A complex scenario is emerging in which distinct UPR signalling modules have specific and even opposite effects on neurodegeneration depending on the disease context. Here, we provide an overview of the most recent findings addressing the biological relevance of ER stress in the nervous system.

Neuronal endoplasmic reticulum stress in axon injury and neurodegeneration

Injuries to central nervous system axons result not only in Wallerian degeneration of the axon distal to the injury, but also in death or atrophy of the axotomized neurons, depending on injury location and neuron type. No method of permanently avoiding these changes has been found, despite extensive knowledge concerning mechanisms of secondary neuronal injury. The autonomous endoplasmic reticulum (ER) stress pathway in neurons has recently been implicated in retrograde neuronal degeneration. In addition to the emerging role of ER morphology in axon maintenance, we propose that ER stress is a common neuronal response to disturbances in axon integrity and a general mechanism for neurodegeneration. Thus, manipulation of the ER stress pathway could have important therapeutic implications for neuroprotection.

Bone marrow stromal cells inhibit caspase-12 expression in rats with spinal cord injury

The mechanisms underlying the potentially beneficial effect of bone marrow stem cells (BMSCs) on spinal cord injury (SCI) are unknown. Therefore, the aim of the present study was to explore the protective effect of BMSCs in rats with SCI. A total of 45 adult male Sprague-Dawley rats were randomly divided into three groups; the SCI group (n=15), the BMSC group (n=15) and the sham-operation group (n=15). In the SCI and BMSC treatment groups, a modified Allen’s weight-drop technique was used to induce SCI. The BMSC treatment group received an injection of BMSCs using a microneedle into the epicenter of the spinal cord 24 h after injury. Rats in the sham-operation group were not subjected to SCI; however, the corresponding vertebral laminae were removed. Seven days after transplantation, a rapid recovery was observed in the Basso, Beattie and Bresnahan (BBB) scores of the BMSC treatment group, whereas the BBB scores in the SCI group remained low (P<0.05). Caspase-12 expression in the SCI group was increased compared with that in the sham-operation group, whereas caspase-12 expression was attenuated 24 h after transplantation in the BMSC treatment group (P<0.05). In conclusion, the transplantation of BMSCs may improve locomotor function and attenuate caspase-12 expression following SCI. Therefore, it is likely to be an effective strategy for preventing severe injury of the spinal cord.

Inhibition of endoplasmic reticulum stress alleviates lipopolysaccharide-induced lung inflammation through modulation of NF-κB/HIF-1α signaling pathway

Lipopolysaccharide (LPS) is involved in a variety of inflammatory disorders. Under stress conditions, endoplasmic reticulum (ER) loses the homeostasis in its functions, which is defined as ER stress. Little is known how ER stress is implicated in LPS-induced lung inflammation. In this study, effects of inhibition of ER stress on LPS-induced lung inflammation and transcriptional regulation were examined. An ER stress regulator, 4-phenylbutyrate (PBA) reduced LPS-induced increases of various ER stress markers in the lung. Furthermore, inhibition of ER stress reduced the LPS-induced lung inflammation. Moreover, LPS-induced increases of NF-κB and HIF-1α activity were lowered by inhibition of ER stress. These results suggest that inhibition of ER stress ameliorates LPS-induced lung inflammation through modulation of NF-κB/IκB and HIF-1α signaling pathway.

Endoplasmic reticulum stress modulates liver inflammatory immune response in the pathogenesis of liver ischemia and reperfusion injury

BACKGROUND

Although endoplasmic reticulum (ER) stress has been implicated in the pathophysiology of organ ischemia-reperfusion injury (IRI), the underlying mechanisms have yet to be fully elucidated. In particular, because tissue proinflammatory immune response is the key mediator of local IRI, how ER stress impacts liver immune cell activation cascade remains to be determined.

METHODS

In vitro, ER stress in macrophages and hepatocytes were induced by pharmacological agents. Macrophage Toll-like receptor 4 and hepatocyte tumor necrosis factor α responses were studied. In vivo, the induction of ER stress by ischemia-reperfusion and the impact of ER stress amelioration by a small molecule chaperon 4-phenylbutyric acid on liver immune response were studied in a murine partial liver warm ischemia model.

RESULTS

ER-stressed macrophages generated a significantly enhanced proinflammatory immune response against Toll-like receptor 4 stimulation, whereas ER-stressed hepatocytes became more susceptible to tumor necrosis factor α-induced cell death. Ischemia-reperfusion resulted in up-regulations of spliced X-box binding protein 1 and activating transcription factor 6 levels in affected livers. Mice pretreated with 4-phenylbutyric acid were protected from liver IRI, in parallel with diminished local proinflammatory gene induction program.

CONCLUSIONS

Our study documents a potential immune regulatory role of ER stress in the mechanism of liver IRI and provides a rationale for targeting stress response as a new therapeutic means to ameliorate tissue inflammation in organ transplant recipients.

Determination of phenylbutyric acid and its metabolite phenylacetic acid in different tissues of mouse by liquid chromatography with tandem mass spectrometry and its application in drug tissue distribution

Endoplasmic reticulum (ER) stress is associated with various human diseases. Phenylbutyric acid (PBA) is a well-known chemical chaperone that regulates ER stress. The main objective of this study was to develop a simple, rapid, and sensitive method for the simultaneous determination of phenylbutyric acid and its metabolite, phenylacetic acid (PAA). A LC-MS/MS analysis using negative electrospray ionization was used. Samples were analyzed by multiple reaction monitoring (MRM) in 15 min of total run time, using d11-PBA and d7-PAA as internal standards. The limit of quantification was 1 μg/g for tissue and 0.8 μg/mL for plasma. Recoveries for plasma and tissues were higher than 81% for both PBA and PAA. The inter-day and intra-day accuracy and precision were within ±15%. We then further successfully validated this method by applying it to determine the tissue distribution of PBA and its metabolite PAA after i.p. injection of PBA at a dose of 500 mg/kg in mice. The maximum concentrations of PBA and PAA in plasma and tissues were seen at 15 min and 45 min, respectively. The PBA plasma concentration was 15-fold higher than the concentration in the kidney, whereas the PAA plasma concentration was 6-fold higher than the concentration in the liver. The area under the curve decreased in the order of plasma > kidney > liver > heart > muscle > lung for PBA and plasma > liver > kidney > heart > muscle > lung for PAA. The tissue to plasma ratio ranged from 0.007 to 0.063 for PBA and 0.016 to 0.109 for PAA. In summary, the LC-ESI-MS method developed in this study is simple, sensitive and reliable.

Potential of chromatin modifying compounds for the treatment of Alzheimer's disease

Alzheimer's disease is a very common progressive neurodegenerative disorder affecting the learning and memory centers in the brain. The hallmarks of disease are the accumulation of β-amyloid neuritic plaques and neurofibrillary tangles formed by abnormally phosphorylated tau protein. Alzheimer's disease is currently incurable and there is an intense interest in the development of new potential therapies. Chromatin modifying compounds such as sirtuin modulators and histone deacetylase inhibitors have been evaluated in models of Alzheimer's disease with some promising results. For example, the natural antioxidant and sirtuin 1 activator resveratrol has been shown to have beneficial effects in animal models of disease. Similarly, numerous histone deacetylase inhibitors including Trichostatin A, suberoylanilide hydroxamic acid, valproic acid and phenylbutyrate reduction have shown promising results in models of Alzheimer's disease. These beneficial effects include a reduction of β-amyloid production and stabilization of tau protein. In this review we provide an overview of the histone deacetylase enzymes, with a focus on enzymes that have been identified to have an important role in the pathobiology of Alzheimer's disease. Further, we discuss the potential for pharmacological intervention with chromatin modifying compounds that modulate histone deacetylase enzymes.

Activation of the unfolded protein response enhances motor recovery after spinal cord injury

Spinal cord injury (SCI) is a major cause of paralysis, and involves multiple cellular and tissular responses including demyelination, inflammation, cell death and axonal degeneration. Recent evidence suggests that perturbation on the homeostasis of the endoplasmic reticulum (ER) is observed in different SCI models; however, the functional contribution of this pathway to this pathology is not known. Here we demonstrate that SCI triggers a fast ER stress reaction (1–3 h) involving the upregulation of key components of the unfolded protein response (UPR), a process that propagates through the spinal cord. Ablation of X-box-binding protein 1 (XBP1) or activating transcription factor 4 (ATF4) expression, two major UPR transcription factors, leads to a reduced locomotor recovery after experimental SCI. The effects of UPR inactivation were associated with a significant increase in the number of damaged axons and reduced amount of oligodendrocytes surrounding the injury zone. In addition, altered microglial activation and pro-inflammatory cytokine expression were observed in ATF4 deficient mice after SCI. Local expression of active XBP1 into the spinal cord using adeno-associated viruses enhanced locomotor recovery after SCI, and was associated with an increased number of oligodendrocytes. Altogether, our results demonstrate a functional role of the UPR in SCI, offering novel therapeutic targets to treat this invalidating condition.

Endoplasmic reticulum stress and lipid metabolism: mechanisms and therapeutic potential

The endoplasmic reticulum (ER) plays a crucial role in protein folding, assembly, and secretion. Disruption of ER homeostasis may lead to accumulation of misfolded or unfolded proteins in the ER lumen, a condition referred to as ER stress. In response to ER stress, a signal transduction pathway known as the unfolded protein response (UPR) is activated. UPR activation allows the cell to cope with an increased protein-folding demand on the ER. Recent studies have shown that ER stress/UPR activation plays a critical role in lipid metabolism and homeostasis. ER-stress-dependent dysregulation of lipid metabolism may lead to dyslipidemia, insulin resistance, cardiovascular disease, type 2 diabetes, and obesity. In this paper, we examine recent findings illustrating the important role ER stress/UPR signalling pathways play in regulation of lipid metabolism, and how they may lead to dysregulation of lipid homeostasis.

Sodium phenylbutyrate ameliorates focal cerebral ischemic/reperfusion injury associated with comorbid type 2 diabetes by reducing endoplasmic reticulum stress and DNA fragmentation

Endoplasmic reticulum (ER) stress has been postulated to play a crucial role in the pathophysiology of cerebral ischemic/reperfusion (I/R) injury and diabetes. Diabetes is a major risk factor and also common amongst the people who suffer from stroke. In this study, we have investigated the neuroprotective potential of sodium 4-phenylbutyrate (SPB; 30-300mg/kg), a chemical chaperone by targeting ER stress in a rat model of transient focal cerebral ischemia associated with comorbid type 2 diabetes. Intraperitoneal treatment with SPB (100 and 300mg/kg) significantly ameliorated brain I/R damage as evidenced by reduction in cerebral infarct and edema volume. It also significantly improved the functional recovery of various neurobehavioral impairments (neurological deficit score, grip strength and rota rod) evoked by I/R compared with vehicle-treatment. Further, SPB (100mg/kg) significantly reduced the DNA fragmentation as shown by prominent reduction in terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive cells. This effect was observed concomitantly with significant attenuation in upregulation of 78kDa glucose regulated protein (GRP78), CCAAT/enhancer binding protein homologous protein or growth arrest DNA damage-inducible gene 153 (CHOP/GADD153) and activation of caspase-12, specific markers of ER stress/apoptosis. The neuroprotection observed with SPB was independent of its effect on cerebral blood flow and blood glucose. In conclusion, this study demonstrates the neuroprotective effect of SPB owing to amelioration of ER stress and DNA fragmentation. It also suggest that targeting ER stress might offer a promising therapeutic approach and benefits against ischemic stroke associated with comorbid type 2 diabetes.

Protein folding stress in neurodegenerative diseases: a glimpse into the ER

Several neurodegenerative diseases share common neuropathology, primarily featuring the presence in the brain of abnormal protein inclusions containing specific misfolded proteins. Recent evidence indicates that alteration in organelle function is a common pathological feature of protein misfolding disorders, highlighting perturbations in the homeostasis of the endoplasmic reticulum (ER). Signs of ER stress have been detected in most experimental models of neurological disorders and more recently in brain samples from human patients with neurodegenerative disease. To cope with ER stress, cells activate an integrated signaling response termed the unfolded protein response (UPR), which aims to reestablish homeostasis in part through regulation of genes involved in protein folding, quality control and degradation pathways. Here we discuss the particular mechanisms currently proposed to be involved in the generation of protein folding stress in different neurodegenerative conditions and speculate about possible therapeutic interventions.