Endoplasmic reticulum stress plays critical role in brain damage after chronic intermittent hypoxia in growing rats

Tauroursodeoxycholic acid attenuates endoplasmic reticulum stress and protects the liver from chronic intermittent hypoxia induced injury

Obstructive sleep apnea that characterized by chronic intermittent hypoxia (CIH) has been reported to associate with chronic liver injury. Tauroursodeoxycholic acid (TUDCA) exerts liver-protective effects in various liver diseases. The purpose of this study was to test the hypothesis that TUDCA could protect liver against CIH injury. C57BL/6 mice were subjected to intermittent hypoxia for eight weeks and applied with TUDCA by intraperitoneal injection. The effect of TUDCA on liver histological changes, liver function, oxidative stress, inflammatory response, hepatocyte apoptosis and endoplasmic reticulum (ER) stress were investigated. The results showed that administration of TUDCA attenuated liver pathological changes, reduced serum alanine aminotransferase and aspartate aminotransferase level, suppressed reactive oxygen species activity, decreased tumor necrosis factor-α and interleukin-1β level and inhibited hepatocyte apoptosis induced by CIH. TUDCA also inhibited CIH-induced ER stress in liver as evidenced by decreased expression of ER chaperone 78 kDa glucose-related protein, unfolded protein response transducers and ER proapoptotic proteins. Altogether, the present study described a liver-protective effect of TUDCA in CIH mice model, and this effect seems at least partly through the inhibition of ER stress.

Effect of Hypoxic Injury in Mood Disorder

Hypoxemia is a common complication of the diseases associated with the central nervous system, and neurons are highly sensitive to the availability of oxygen. Neuroplasticity is an important property of the neural system controlling breathing, memory, and cognitive ability. However, the underlying mechanism has not yet been clearly elucidated. In recent years, several pieces of evidence have highlighted the effect of hypoxic injury on neuronal plasticity in the pathogenesis and treatment of mood disorder. Therefore, the present study reviewed the relevant articles regarding hypoxic injury and neuronal plasticity and discussed the pathological changes and physiological functions of neurons in hypoxemia in order to provide a translational perspective to the relevance of hypoxic injury and mood disorder.

Integrated Stress Response as a Therapeutic Target for CNS Injuries

Central nervous system (CNS) injuries, caused by cerebrovascular pathologies or mechanical contusions (e.g., traumatic brain injury, TBI) comprise a diverse group of disorders that share the activation of the integrated stress response (ISR). This pathway is an innate protective mechanism, with encouraging potential as therapeutic target for CNS injury repair. In this review, we will focus on the progress in understanding the role of the ISR and we will discuss the effects of various small molecules that target the ISR on different animal models of CNS injury.

Expression of Glucose-Regulated Protein 78 and miR-199a in Rat Brain After Fatal Ligature Strangulation

The roles of endoplasmic reticulum (ER) stress and microRNA in the brain tissue after fatal mechanical asphyxia have not been clearly elucidated. We examined the expression of glucose-regulated protein 78 (GRP78), the key regulator of unfolded protein response, and miR-199a in the brain tissues of rats subjected to fatal ligature strangulation to understand the roles of ER stress and microRNA in ligature strangulation. The expressions of GRP78 and miR-199a in rat cortex, hippocampi, and midbrain were measured by immunohistochemistry and Western blot analysis in a rat model of ligature strangulation. Furthermore, the levels of miR-199a-3p and miR-199a-5p were detected by real-time fluorescent quantitative polymerase chain reaction. Glucose-regulated protein 78 was highly expressed in the cortex and midbrain in the ligature strangulation group (P < 0.01) when compared with the control group. The expression of GRP78 in the hippocampi showed no significant difference between the 2 groups. miR-199a-3p in the cortex and midbrain was significantly down-regulated in the ligature strangulation group (P < 0.01). However, miR-199a-5p in each brain region showed no significant difference between the 2 groups. In conclusion, ER stress was involved in the physiological and pathological processes of ligature strangulation. Furthermore, upstream miR-199a may play an important regulatory role in mechanical asphyxia.

Neuroprotection and Blood-Brain Barrier Restoration by Salubrinal After a Cortical Stab Injury

Following a central nervous system (CNS) injury, restoration of the blood-brain barrier (BBB) integrity is essential for recovering homeostasis. When this process is delayed or impeded, blood substances and cells enter the CNS parenchyma, initiating an additional inflammatory process that extends the initial injury and causes so-called secondary neuronal loss. Astrocytes and profibrotic mesenchymal cells react to the injury and migrate to the lesion site, creating a new glia limitans that restores the BBB. This process is beneficial for the resolution of the inflammation, neuronal survival, and the initiation of the healing process. Salubrinal is a small molecule with neuroprotective properties in different animal models of stroke and trauma to the CNS. Here, we show that salubrinal increased neuronal survival in the neighbourhood of a cerebral cortex stab injury. Moreover, salubrinal reduced cortical blood leakage into the parenchyma of injured animals compared with injured controls. Adjacent to the site of injury, salubrinal induced immunoreactivity for platelet-derived growth factor subunit B (PDGF-B), a specific mitogenic factor for mesenchymal cells. This effect might be responsible for the increased immunoreactivity for fibronectin and the decreased activation of microglia and macrophages in injured mice treated with salubrinal, compared with injured controls. The immunoreactivity for PDGF-B colocalized with neuronal nuclei (NeuN), suggesting that cortical neurons in the proximity of the injury were the main source of PDGF-B. Our results suggest that after an injury, neurons play an important role in both, the healing process and the restoration of the BBB integrity. J. Cell. Physiol. 232: 1501-1510, 2017. © 2016 Wiley Periodicals, Inc.

Curcumin inhibits lipolysis via suppression of ER stress in adipose tissue and prevents hepatic insulin resistance

Curcumin is natural polyphenol with beneficial effects on lipid and glucose metabolism and this study aimed to investigate the effects of curcumin on lipolysis and hepatic insulin resistance. Endoplasmic reticulum (ER) stress and lipolysis signaling in adipose and FFA influx, lipid deposits, and glucose production in liver were examined. Palmitate challenge and high-fat diet feeding evoked ER stress-associated lipolysis with cAMP accumulation in adipose tissue. Curcumin treatment inhibited adipose tissue ER stress by dephosphorylation of inositol-requiring enzyme 1α and eukaryotic initiation factor 2α and reduced cAMP accumulation by preserving phosphodiesterase 3B induction. Knockdown of mitogen-activated protein kinase α1/2α with siRNAs diminished such effects of curcumin. As a result from downregulation of cAMP, curcumin blocked protein kinase (PK)A/hormone-sensitive lipase lipolysis signaling, and thereby reduced glycerol and FFA release from adipose tissue. Curcumin reduced FFA influx into the liver by blocking FFA trafficking, and then prevented diacylglycerol deposits and PKCε translocation in the liver, resultantly improving insulin action in the suppression of hepatic gluconeogenesis. Curcumin decreased adipose lipolysis by attenuating ER stress through the cAMP/PKA pathway, reduced FFA influx into the liver by blocking FFA trafficking, and thereby improved insulin sensitivity to inhibit hepatic glucose production. These findings suggested a novel pathway of curcumin to prevent lipid deposits and insulin resistance in liver by beneficial regulation of adipose function.

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.

Bone Marrow Mesenchymal Stem Cells Attenuate Mitochondria Damage Induced by Hypoxia in Mouse Trophoblasts

Objective

We aimed to observe the change of mitochondrial function and structure as well as the cell function induced by hypoxia in mouse trophoblasts, and moreover, to validate the restoration of these changes after co-culture with bone marrow mesenchymal stem cells (hereinafter referred to as “MSCs”). Further, we explored the mechanism of MSCs attenuating the functional damage of trophoblasts caused by hypoxia.

Methods

Cells were divided into two groups, trophoblasts and MSCs+trophoblasts respectively, and the two groups of cells were incubated with normoxia or hypoxia. Chemiluminescence was used to assay the β-HCG and progesterone in cell culture supernatants quantitatively. Western blotting and PCR were applied to detect the expression of Mfn2, MMP-2, MMP-9 and integrin β1 in the two groups. The mitochondrial membrane potential of each group of cells was detected with JC-1 dye and the ATP content was measured by the phosphomolybdic acid colorimetric method. We utilized transmission electron microscopy for observing the ultrastructure of mitochondria in trophoblasts. Finally, we assessed the cell apoptosis with flow cytometry (FCM) and analyzed the expression of the apoptosis related genes—Bcl-2, Bax, Caspase3 and Caspase9 by western blotting.

Results

The results showed that the Mfn2 expression was reduced after 4 h in hypoxia compared with that in normoxia, but increased in the co-culture group when compared with that in the separated-culture group (p<0.05). In addition, compared with the separated-culture group, theβ-HCG and progesterone levels in the co-culture group were significantly enhanced (p<0.05), and so were the expressions of MMP-2, MMP-9 and integrin β1 (p<0.05). Moreover, it exhibited significantly higher in ATP levels and intensified about the mitochondrial membrane potential in the co-culture group. TEM revealed disorders of the mitochondrial cristae and presented short rod-like structure and spheroids in hypoxia, however, in the co-culture group, the mitochondrial cristae had a relatively regular arrangement and the mitochondrial ultrastructure showed hyperfusion. The expression of Bax, Caspase3 and Caspase9 was decreased in the co-culture group when compared with that in trophoblast cells cultured alone (p<0.05), while the Bcl-2 levels and the Apoptosis Index (AI) were markedly increased in the co-culture group (p<0.05).

Conclusion

Bone marrow mesenchymal stem cells can attenuate mitochondria damage and cell apoptosis induced by hypoxia; the mechanism could be upregulating the expression of Mfn2 in mouse trophoblasts and changing mitochondrial structure.

PERK-eIF2α-ATF4 pathway mediated by endoplasmic reticulum stress response is involved in osteodifferentiation of human periodontal ligament cells under cyclic mechanical force

To prevent excess accumulation of unfolded proteins in endoplasmic reticulum (ER), eukaryotic cells have signaling pathways from the ER to the cytosol or nucleus. These processes are known as the endoplasmic reticulum stress (ERS) response. Protein kinase R like endoplasmic reticulum kinase (PERK) is a major transducer of the ERS response and it directly phosphorylate α-subunit of eukaryotic initiation factor 2 (eIF2α), resulting in translational attenuation. Phosphorylated eIF2α specifically promoted the translation of the activating transcription factor 4 (ATF4). ATF4 is a known important transcription factor which plays a pivotal role in osteoblast differentiation and bone formation. Furthermore, ATF4 is a downstream target of PERK. Studies have shown that PERK-eIF2α-ATF4 signal pathway mediated by ERS was involved in osteoblastic differentiation of osteoblasts. We have known that orthodontic tooth movement is a process of periodontal ligament cells (PDLCs) osteodifferentiation and alveolar bone remodeling under mechanical force. However, the involvement of PERK-eIF2α-ATF4 signal pathway mediated by ERS in osteogenic differentiation of PDLCs under mechanical force has not been unclear. In our study, we applied the cyclic mechanical force at 10% elongation with 0.5Hz to mimic occlusal force, and explored whether PERK-eIF2α-ATF4 signaling pathway mediated by ERS involved in osteogenic differentiation of PDLCs under mechanical force. Firstly, cyclic mechanical force will induce ERS and intensify several osteoblast marker genes (ATF4, OCN, and BSP). Next, we found that PERK overexpression increased eIF2α phosphorylation and expression of ATF4, furthermore induced BSP, OCN expression, thus it will promote osteodifferentiation of hPDLCs; mechanical force could promote this effect. However, PERK(-/-) cells showed the opposite changes, which will inhibit osteodifferentiation of hPDLCs. Taken together, our study proved that PERK-eIF2α-ATF4 signaling pathway mediated by ERS involved in osteoblast differentiation of PDLCs under cyclic mechanical force.

Bone Age and Serum Osteocalcin Levels in Children With Obstructive Sleep Apnea Hypopnea Syndrome Before and After Adenotonsillectomy

Our aim was to study the changes in bone age and serum osteocalcin levels before and after adenotonsillectomy (AT) in children with obstructive sleep apnea hypopnea syndrome (OSAHS). A total of 58 OSAHS children (37 males and 21 females) with the mean age of 6.68 ± 1.11 years were enrolled and assessed by x-ray-based bone age estimation and enzyme-linked immunosorbent assay-based measurement of serum osteocalcin levels, before surgery and 6 months after AT. SPSS 19.0 software was used for statistical analysis. Our results revealed that bone age and serum osteocalcin levels in OSAHS patients were significantly lower than normal controls before AT (P < 0.05). Within 6 months after surgery, the bone age and the serum osteocalcin levels were significantly elevated in OSAHS patients (P < 0.05), compared with those before surgery. Serum osteocalcin levels and bone age are negatively correlated with apnea-hypopnea index, oxygen desaturation index, the percentage of the total recorded time spent below 90% oxygen saturation, and Epworth sleepiness scale scores (all P < 0.05). Our findings suggested that bone age and serum osteocalcin levels may be correlated with the development of OSAHS in children. AT may improve bone age and serum osteocalcin levels in OSAHS children.

Celecoxib induces apoptosis but up-regulates VEGF via endoplasmic reticulum stress in human colorectal cancer in vitro and in vivo

PURPOSE

In our previous study, we found that celecoxib, a kind of COX-2 inhibitor, led to cell apoptosis while up-regulating the expression of vascular endothelial growth factor (VEGF) in colorectal cancer HCT116 cells (COX-2 deficient), and endoplasmic reticulum (ER) stress was involved in the mechanism. Thus, we would like to explore whether these results are universal for other colorectal cancer cells, especially for COX-2-expressing ones, and whether the results in vitro and in vivo are matched.

METHODS

HT29 cells (COX-2 expressing) were treated with celecoxib under different conditions to evaluate cell apoptosis, VEGF expression and the activation of ER stress. HT29 and HCT116 xenograft tumor models were established to evaluate anti-tumor effects and verify the experiment results we obtained in vitro.

RESULTS

Celecoxib (≥60 µM) up-regulated the expression of ER stress markers (GRP78 and CHOP) and induced cell apoptosis accompanying with a correlated increased expression of VEGF in HT29 cells. Celecoxib-induced gene expression and cell apoptosis were inhibited by an ER stress inhibitor, PBA. In xenograft models, celecoxib treatment inhibited tumor growth with increased GRP78 and VEGF, which was consistent with the results in vitro.

CONCLUSIONS

Celecoxib, both in vitro and in vivo, induced apoptosis of colorectal cancer cells but increased the VEGF levels at the same time in a COX-2-independent manner, namely by activating ER stress. The increased VEGF would impair the effect of celecoxib and bring drug resistant; hence, the optimal schedule of the combination of celecoxib with anti-VEGF drugs needs to be explored.

P2X7 Receptor Antagonism Attenuates the Intermittent Hypoxia-induced Spatial Deficits in a Murine Model of Sleep Apnea Via Inhibiting Neuroinflammation and Oxidative Stress

Background:

The mechanism of the neural injury caused by chronic intermittent hypoxia (CIH) that characterizes obstructive sleep apnea syndrome (OSAS) is not clearly known. The purpose of this study was to investigate whether P2X7 receptor (P2X7R) is responsible for the CIH-induced neural injury and the possible pathway it involves.

Methods:

Eight-week-old male C57BL/6 mice were used. For each exposure time point, eight mice divided in room air (RA) and IH group were assigned to the study of P2X7R expression. Whereas in the 21 days-Brilliant Blue G (BBG, a selective P2X7R antagonist) study, 48 mice were randomly divided into CIH group, BBG-treated CIH group, RA group and BBG-treated RA group. The hippocampus P2X7R expression was determined by Western blotting and real-time polymerase chain reaction (PCR). The spatial learning was analyzed by Morris water maze. The nuclear factor kappa B (NFκB) and NADPH oxidase 2 (NOX2) expressions were analyzed by Western blotting. The expressions of tumor necrosis factor α, interleukin 1β (IL-β), IL-18, and IL-6 were measured by real-time PCR. The malondialdehyde and superoxide dismutase levels were detected by colorimetric method. Cell damage was evaluated by Hematoxylin and Eosin staining and Terminal Transferase dUTP Nick-end Labeling method.

Results:

The P2X7R mRNA was elevated and sustained after 3-day IH exposure and the P2X7R protein was elevated and sustained after 7-day IH exposure. In the BBG study, the CIH mice showed severer neuronal cell damage and poorer performance in the behavior test. The increased NFκB and NOX2 expressions along with the inflammation injury and oxidative stress were also observed in the CIH group. BBG alleviated CIH-induced neural injury and consequent functional deficits.

Conclusions:

The P2X7R antagonism attenuates the CIH-induced neuroinflammation, oxidative stress, and spatial deficits, demonstrating that the P2X7R is an important therapeutic target in the cognition deficits accompanied OSAS.

Efficacy of atorvastatin on hippocampal neuronal damage caused by chronic intermittent hypoxia: Involving TLR4 and its downstream signaling pathway

Hippocampal neuronal damage is critical for the initiation and progression of neurocognitive impairment accompanied obstructive sleep apnea syndrome (OSAS). Toll-like receptor 4 (TLR4) plays an important role in the development of several hippocampus-related neural disorders. Atorvastatin was reported beneficially regulates TLR4. Here, we examined the effects of atorvastatin on hippocampal injury caused by chronic intermittent hypoxia (CIH), the most characteristic pathophysiological change of OSAS. Mice were exposed to intermittent hypoxia with or without atorvastatin for 4 weeks. Cell damage, the expressions of TLR4 and its two downstream factors myeloid differentiation factor 88 (MYD88) and TIR-domain-containing adapter-inducing interferon-β (TRIF), inflammatory agents (tumor necrosis factor α and interleukin 1β), and the oxidative stress (superoxide dismutase and malondialdehyde) were determined. Atorvastatin decreased the neural injury and the elevation of TLR4, MyD88, TRIF, pro-inflammatory cytokines and oxidative stress caused by CIH. Our study suggests that atorvastatin may attenuate CIH induced hippocampal neuronal damage partially via TLR4 and its downstream signaling pathway.

IRE1α-XBP1 Pathway Is Activated Upon Induction of Single-Prolonged Stress in Rat Neurons of the Medial Prefrontal Cortex

Endoplasmic reticulum stress (ERS) is associated with many nervous system diseases. IRElα is considered as ERS sensor that, upon activation, initiates the nonconventional splicing of the precursor unspliced form of X-box binding protein 1 (XBP1u) messenger RNA (mRNA) to yield an active transcription factor-XBP1s. The goal of this study is to detect whether there is activation of IRE1α-XBP1 pathway in the medial prefrontal cortex (mPFC) of posttraumatic stress disorder (PTSD) model rats. This study adopted single-prolonged stress (SPS) model. Behavioral functions including anxiety-like behavior, exploration behavior, and spatial memory were assessed by open field test and Morris water maze test. We detected the IRE1α and XBP1 by using methods of double-labeling immunofluorescence, Western blot, and quantitative real-time reverse transcription-PCR (qRT-PCR). We also observed neuronal apoptosis by transferase-mediated dUTP Nick-end-labeling (TUNEL) staining and the expression of caspase-12 by qRT-PCR. Our results showed that the expression of IRE1α, XBP1u, and total XBP1 significantly increased at 1 day after SPS and then decreased gradually. At the same time, XBP1s appeared and peaked at 4 days after SPS, which indicated that IRE1α-XBP1 pathway was activated upon induction of SPS stimulation. We also noted that the mRNA of caspase-12 was upregulated after SPS. Our study preliminarily showed that ERS mediated by IRE1α-XBP1 pathway was closely related to PTSD and it might be a pathogenesis of PTSD.

Intermittent hypoxia in childhood: the harmful consequences versus potential benefits of therapeutic uses

Intermittent hypoxia (IH) often occurs in early infancy in both preterm and term infants and especially at 36-44 weeks postmenstrual age. These episodes of IH could result from sleep-disordered breathing or may be temporally unrelated to apnea or bradycardia events. There are numerous reports indicating adverse effects of IH on development, behavior, academic achievement, and cognition in children with sleep apnea syndrome. It remains uncertain about the exact causative relationship between the neurocognitive and behavioral morbidities and IH and/or its associated sleep fragmentation. On the other hand, well-controlled and moderate IH conditioning/training has been used in sick children for treating their various forms of bronchial asthma, allergic dermatoses, autoimmune thyroiditis, cerebral palsy, and obesity. This review article provides an updated and impartial analysis on the currently available evidence in supporting either side of the seemingly contradictory scenarios. We wish to stimulate a comprehensive understanding of such a complex physiological phenomenon as intermittent hypoxia, which may be accompanied by other confounding factors (e.g., hypercapnia, polycythemia), in order to prevent or reduce its harmful consequences, while maximizing its potential utility as an effective therapeutic tool in pediatric patients.

Chronic intermittent hypoxia-induced neuronal apoptosis in the hippocampus is attenuated by telmisartan through suppression of iNOS/NO and inhibition of lipid peroxidation and inflammatory responses

Obstructive sleep apnea syndrome (OSAS) plays a critical role in the initiation and progression of Alzheimer׳s disease (AD), but little is known about the precise mechanism of OSAS-induced AD. Nitric oxide synthase (NOS) and nitric oxide (NO) are known to play key roles in the development of AD. Several studies have confirmed that an angiotensin II type 1 receptor blocker, telmisartan, beneficially regulates NOS and NO. Here, we examined the neuroprotective effects of telmisartan against hippocampal apoptosis induced by chronic intermittent hypoxia (CIH), the most characteristic pathophysiological change of OSAS. Adult male Sprague Dawley rats were subjected to 8h of intermittent hypoxia per day with or without telmisartan for eight weeks. Neuronal apoptosis in the hippocampal CA1 region, NOS activity, NO content, and the presence of inflammatory agents and radical oxygen species in the hippocampus were determined. The results showed that CIH activated inducible nitric oxide synthase (iNOS), increased NO content, and enhanced lipid peroxidation and inflammatory responses in the hippocampus. Treatment with telmisartan inhibited excessive iNOS and NO generation and reduced lipid peroxidation and inflammatory responses. In addition, telmisartan significantly ameliorated the hippocampal apoptosis induced by CIH. In conclusion, Pre-CIH telmisartan administration attenuated CIH-induced hippocampal apoptosis partly by regulating NOS activity, inhibiting excessive NO generation, and reducing lipid peroxidation and inflammatory responses.