Memantine ameliorates cognitive impairment induced by exposure to chronic hypoxia environment at high altitude by inhibiting excitotoxicity

Therapeutic effects of a new bithiophene against aluminum -induced Alzheimer's disease in a rat model: Pathological and ultrastructural approach

Alzheimer's disease (AD) remains of unknown etiology and lacks a cure. This study aimed to evaluate the therapeutic potential of a novel bithiophene derivative at two doses against AlCl3-induced AD in a rat model. Adult male rats (Rattus norvegicus) were divided into six groups (n=6): Group one consisted of naïve animals, group two received bithiophene (1 mg/kg) every other day for 30 days, and groups 3-6 were subjected to AlCl3 (100 mg/kg, equivalent to 20.23 mg Al3+) for 45 consecutive days. Groups four and five received low (0.5 mg/kg) or high (1 mg/kg) doses of bithiophene, respectively. Group six received memantine (20 mg/kg) daily for 30 days. All treatments were administered orally. Aluminum exposure resulted in severe degeneration of both histological and ultrastructural aspects of cells. Administration of the low dose of bithiophene significantly restored the number of CA1 pyramidal cells and the thickness of the stratum granulosum of the dentate gyrus. However, the high dose of bithiophene increased viable CA1 pyramidal cell numbers significantly without restoring the thickness of the stratum granulosum or reducing vacuolization or pyknotic changes. The low dose of bithiophene restored the normal histological and cytological structure of both cortical and hippocampal neurons affected by dementia. Further investigation is required to explore the molecular mechanisms underlying the ameliorative effects on Alzheimer's disease-induced deteriorations in the cortex and hippocampus.

Nitronyl Nitroxide Ameliorates Hypobaric Hypoxia-Induced Cognitive Impairment in Mice by Suppressing the Oxidative Stress, Inflammatory Response and Apoptosis

Abundant investigations have shown that hypobaric hypoxia (HH) causes cognitive impairment, mostly attributed to oxidative stress, inflammation, and apoptosis. HPN (4'-hydroxyl-2-subsitiuted phenylnitronyl nitroxide) is an excellent free radical scavenger with anti-inflammatory and anti-apoptotic activities. Our previous study has found that HPN exhibited neuroprotective effect on HH induced brain injury. In the present study, we examined the protective effect and potential mechanism of HPN on HH-induced cognitive impairment. Male mice were exposed to HH at 8000 m for 3 days with and without HPN treatment. Cognitive performance was assessed by the eight-arm radical maze. The histological changes were assayed by Nissle staining. The hippocampus cell apoptosis was detected by Tunnel staining. The levels of inflammatory cytokines and oxidative stress markers were detected. The expression of oxidative stress, inflammation-related and apoptosis-related proteins was determined by western blot. HPN administration significantly and mitigated HH induced histological damages and spatial memory loss with the evidence of decreased working memory error (WME), reference memory error (RME), total errors (TE) and total time (TT). In addition, HPN treatment significantly decreased the content of H2O2 and MDA, increased the levels of SOD, CAT, GSH-Px and GSH, and inhibited the synthesis of TNF-α, IL-1β and IL-6. Moreover, HPN administration could down-regulate the expression of NF-κB, TNF-α, Bax, and cleaved caspase-3 and up-regulate the expression of Nrf2, HO-1 and Bcl-2. The number of apoptotic cells was also significantly decreased in the hippocampus of mice in the HPN group. There results indicate that HPN improve HH-induced cognitive impairment by alleviating oxidative stress damage, suppressing inflammatory response and apoptosis and may be a powerful candidate compound for alleviating memory loss induced by HH.

Oxygen metabolism abnormality and Alzheimer's disease: An update

Oxygen metabolism abnormality plays a crucial role in the pathogenesis of Alzheimer's disease (AD) via several mechanisms, including hypoxia, oxidative stress, and mitochondrial dysfunction. Hypoxia condition usually results from living in a high-altitude habitat, cardiovascular and cerebrovascular diseases, and chronic obstructive sleep apnea. Chronic hypoxia has been identified as a significant risk factor for AD, showing an aggravation of various pathological components of AD, such as amyloid β-protein (Aβ) metabolism, tau phosphorylation, mitochondrial dysfunction, and neuroinflammation. It is known that hypoxia and excessive hyperoxia can both result in oxidative stress and mitochondrial dysfunction. Oxidative stress and mitochondrial dysfunction can increase Aβ and tau phosphorylation, and Aβ and tau proteins can lead to redox imbalance, thus forming a vicious cycle and exacerbating AD pathology. Hyperbaric oxygen therapy (HBOT) is a non-invasive intervention known for its capacity to significantly enhance cerebral oxygenation levels, which can significantly attenuate Aβ aggregation, tau phosphorylation, and neuroinflammation. However, further investigation is imperative to determine the optimal oxygen pressure, duration of exposure, and frequency of HBOT sessions. In this review, we explore the prospects of oxygen metabolism in AD, with the aim of enhancing our understanding of the underlying molecular mechanisms in AD. Current research aimed at attenuating abnormalities in oxygen metabolism holds promise for providing novel therapeutic approaches for AD.

Neuroprotective Effects of Moderate Hypoxia: A Systematic Review

Emerging evidence highlights moderate hypoxia as a candidate treatment for brain disorders. This systematic review examines findings and the methodological quality of studies investigating hypoxia (10-16% O2) for ≥14 days in humans, as well as the neurobiological mechanisms triggered by hypoxia in animals, and suggests optimal treatment protocols to guide future studies. We followed the preferred reporting items for systematic reviews and meta-analysis (PRISMA) 2020. Searches were performed on PubMed/MEDLINE, PsycInfo, EMBASE, and the Cochrane Library, in May-September 2023. Two authors independently reviewed the human studies with the following tools: (1) revised Cochrane collaboration's risk of bias for randomized trials 2.0; (2) the risk of bias in nonrandomized studies of interventions. We identified 58 eligible studies (k = 8 human studies with N = 274 individuals; k = 48 animal studies) reporting the effects of hypoxia on cognition, motor function, neuroimaging, neuronal/synaptic morphology, inflammation, oxidative stress, erythropoietin, neurotrophins, and Alzheimer's disease markers. A total of 75% of human studies indicated cognitive and/or neurological benefits, although all studies were evaluated ashigh risk of bias due to a lack of randomization and assessor blinding. Low-dose intermittent or continuous hypoxia repeated for 30-240 min sessions, preferably in combination with motor-cognitive training, produced beneficial effects, and high-dose hypoxia with longer (≥6 h) durations and chronic exposure produced more adverse effects. Larger and methodologically stronger translational studies are warranted.

Brain-aging related protein expression and imaging characteristics of mice exposed to chronic hypoxia at high altitude

Objective

To determine changes in protein expression related to brain aging and imaging features in mice after chronic hypoxia exposure at high altitude.

Method

A total of 24 healthy 4-week-old mice were randomly divided into high altitude hypoxia (HH) and plain control (PC) groups (n = 8 per group). HH mice were transported from Xi'an (450 m above sea level) to Maduo (4,300 m above sea level) while PC mice were raised in Xi'an. After 6 months, 7.0T magnetic resonance imaging (MRI) was performed. All mice completed T2-weighted imaging (T2WI), diffusion tensor imaging (DTI), resting-state functional MRI (rs-fMRI), arterial spin labeling (ASL), and magnetic resonance angiography (MRA) examinations. Next, brain slices were prepared and Nissl staining was used to observe morphological changes in neurons. Ultrastructural changes in neurons were observed by transmission electron microscopy. Expression changes of Caspase-3, klotho, P16, P21, and P53 at the gene and protein levels were detected by real-time PCR (RT-PCR) and Western blot.

Results

The number of neuronal Nissl bodies in the hippocampus and frontal cortex was significantly decreased in the HH group compared to the PC group. Some hippocampal and frontal cortical neurons were apoptotic, the nuclei were wrinkled, chromatin was aggregated, and most mitochondria were mildly swollen (crista lysis, fracture). Compared with the PC group, the HH group showed elevated expression of caspase-3 mRNA, P16 mRNA, P21 mRNA, and P53 mRNA in the hippocampus and frontal cortex. Expression of Klotho mRNA in the frontal cortex was also significantly decreased. Western blot results showed that caspase-3 protein expression in the hippocampus and frontal cortex of the HH group was increased compared with the PC group. Moreover, there was decreased Klotho protein expression and significantly increased P-P53 protein expression. Compared with the PC group, expression of P16 protein in the frontal cortex of the HH group was increased and the gray matter (GM) volume in the left visceral area, left caudate nucleus, and left piriform cortex was decreased. Furthermore, the amplitude of low frequency fluctuation was decreased in the left posterior nongranular insular lobe, right small cell reticular nucleus, left flocculus, left accessory flocculus, and left primary auditory area, but increased in the GM layer of the left superior colliculus. Regional homogeneity was decreased in the left and right olfactory regions, but increased in the left bed nucleus. After exposure to high altitude, functional connectivity (FC) between the bilateral caudate nucleus and thalamus, corpus callosum, cingulate gyrus, anterior limbic cortex, globus pallidus, and hippocampus was weakened. FC between the right caudate nucleus and hypothalamus and entorhinal cortex was also weakened. The fractional anisotropy value of the left hippocampus was decreased in the HH group. Compared with the PC group, the HH group showed significantly increased inner diameters of the bilateral common carotid artery and left internal carotid artery. The cerebral blood flow values of the bilateral cortex and bilateral hippocampus in the HH group did not change significantly.

Conclusion

Taken together, our findings show that chronic hypoxia exposure at high altitude may promote neuronal apoptosis and abnormal expression of related proteins, changing the structure and function of brain. These changes may contribute to brain aging.

Mechanism, prevention and treatment of cognitive impairment caused by high altitude exposure

Hypobaric hypoxia (HH) characteristics induce impaired cognitive function, reduced concentration, and memory. In recent years, an increasing number of people have migrated to high-altitude areas for work and study. Headache, sleep disturbance, and cognitive impairment from HH, severely challenges the physical and mental health and affects their quality of life and work efficiency. This review summarizes the manifestations, mechanisms, and preventive and therapeutic methods of HH environment affecting cognitive function and provides theoretical references for exploring and treating high altitude-induced cognitive impairment.

CX3CL1/CX3CR1 signal mediates M1-type microglia and accelerates high-altitude-induced forgetting

Introduction

Hypoxia-induced neuronal damage is the primary cause of cognitive impairment induced by high-altitude exposure. Microglia play a crucial regulatory role in the central nervous system (CNS) homeostasis and synaptic plasticity. M1-type polarized microglia are suspected to be responsible for CNS injury under hypoxic conditions, but the exact molecular mechanism is still unelucidated.

Methods

CX3CR1 knock out and wide type mice were exposed to a simulated plateau at 7000 m for 48 h to construct the model of hypobaric hypoxia-induced memory impairment. The memory impairment of mice was assessed by Morris water maze. The dendritic spine density in the hippocampus was examined by Golgi staining. The synapses in the CA1 region and the number of neurons in the DG region were examined by immunofluorescence staining. The synapses in microglia activation and phagocytosis were examined by immunofluorescence. The levels of CX3CL1/CX3CR1 and their downstream proteins were detected. CX3CR1 knockout primary microglia were treated with CX3CL1 combined with 1% O₂. The levels of proteins related to microglial polarization, the uptake of synaptosome and phagocytotic ability of microglia were detected.

Results

In this study, mice exposed to a simulated 7000 m altitude for 48 h developed significant amnesia for recent memories, but no significant change in their anxiety levels was observed. Hypobaric hypoxia exposure (7000 m altitude above sea level for 48 h) resulted in synapse loss in the CA1 region of the hippocampus, but no significant changes occurred in the total number of neurons. Meanwhile, microglia activation, increased phagocytosis of synapses by microglia, and CX3CL1/CX3CR1 signal activation were observed under hypobaric hypoxic exposure. Further, we found that after hypobaric hypoxia exposure, CX3CR1-deficient mice showed less amnesia, less synaptic loss in the CA1 region, and less increase in M1 microglia, compared to their wildtype siblings. CX3CR1-deficient microglia did not exhibit M1-type polarization in response to either hypoxia or CX3CL1 induction. Both hypoxia and CX3CL1 induced the phagocytosis of synapses by microglia through the upregulation of microglial phagocytosis.

Discussion

The current study demonstrates that CX3CL1/CX3CR1 signal mediates the M1-type polarization of microglia under high-altitude exposure and upregulates microglial phagocytosis, which increases the phagocytosis of synapses in the CA1 region of the hippocampus, causing synaptic loss and inducing forgetting.

NMDA Receptor Activation Stimulates Hypoxia-Induced TRPM2 Channel Activation, Mitochondrial Oxidative Stress, and Apoptosis in Neuronal Cell Line: Modular Role of Memantine

TRPM2 channel is activated by the increase of hypoxia (HYP)-mediated excessive mitochondrial (mROS) and cytosolic (cROS) free reactive oxygen species generation and intracellular free Ca²⁺ ([Ca²⁺]_i) influx. The stimulations of the N-methyl-d-aspartate(NMDA) receptor and TRPM2 channel induce mROS and apoptosis in the neurons, although their inhibitions via the treatments of memantine (MEM) and MK-801 decrease mROS and apoptosis. However, the molecular mechanisms underlying MEM treatment and NMDA inhibition' neuroprotection via TRPM2 inhibition in the HYP remain elusive. We investigated the modulator role of MEM and NMDA via the modulation of TRPM2 on oxidative neurodegeneration and apoptosis in SH-SY5Y neuronal cells. Six groups were induced in the SH-SY5Y and HEK293 cells as follows: Control, MEM, NMDA blocker (MK-801), HYP (CoCl₂), HYP + MEM, and HYP + MK-801. The HYP caused to the increases of TRPM2 and PARP-1 expressions, and TRPM2 agonist (H₂O₂ and ADP-ribose)-induced TRPM2 current density and [Ca²⁺]_i concentration via the upregulation of mitochondrial membrane potential, cROS, and mROS generations. The alterations were not observed in the absence of TRPM2 in the HEK293 cells. The increase of cROS, mROS, lipid peroxidation, cell death (propidium iodide/Hoechst) rate, apoptosis, caspase -3, caspase -8, and caspase -9 were restored via upregulation of glutathione and glutathione peroxidase by the treatments of TRPM2 antagonists (ACA or 2-APB), MEM, and MK-801. In conclusion, the inhibition of NMDA receptor via MEM treatment modulated HYP-mediated mROS, apoptosis, and TRPM2-induced excessive [Ca²⁺]_i and may provide an avenue for protecting HYP-mediated neurodegenerative diseases associated with the increase of mROS, [Ca²⁺]_i, and apoptosis.

Theaflavin-3,3'-digallate ameliorates learning and memory impairments in mice with premature brain aging induced by D-galactose

Age-related neurodegenerative diseases accompanied by learning and memory deficits are growing in prevalence due to population aging. Cellular oxidative stress is a common pathomechanism in multiple age-related disorders, and various antioxidants have demonstrated therapeutic efficacy in patients or animal models. Many plants and plant extracts possess potent antioxidant activity, but the compounds responsible are frequently unknown. Identification and evaluation of these phytochemicals is necessary for optimal targeted therapy. A recent study identified theaflavin-3,3'-digallate (TFDG) as the most potent among a large series of phytochemical antioxidants. Here we examined if TFDG can mitigate learning and memory impairments in the D-galactose model of age-related neurodegeneration. Experimental mice were injected subcutaneously with D-galactose (120 mg/kg) for 56 days. In treatment groups, different doses of TFDG were administered daily by gavage starting on day 29 of D-galactose injection. Model mice exhibited poor learning and memory in the novel object recognition and Y-maze tests, reduced brain/body mass ratio, increased brain glutamate concentration and acetylcholinesterase activity, decreased brain acetylcholine concentration, and lower choline acetyltransferase, glutaminase, and glutamine synthetase activities. Activities of antioxidant enzymes glutathione peroxidase and superoxide dismutase were also reduced, while the concentration of malondialdehyde, a lipid peroxidation product, was elevated. Further, antioxidant genes Nrf2, Prx2, Gsh-px1, and Sod1 were downregulated in brain. Each one of these changes was dose-dependently reversed by TFDG. TFDG is an effective antioxidant response inducer and neuroprotectant that can restore normal neurotransmitter metabolism and ameliorate learning and memory dysfunction in the D-galactose model of age-related cognitive decline.

Chondroitin sulfate proteoglycan is a potential target of memantine to improve cognitive function via the promotion of adult neurogenesis

BACKGROUND AND PURPOSE

Chondroitin sulfate proteoglycan (CSPG) constitutes the neurogenic niche in the hippocampus. The reduction of hippocampal neurogenesis is involved in aging-related cognitive decline and dementia. The purpose of this study is to find candidates that improve cognitive function by analyzing the effects of memantine (MEM), a therapeutic agent for Alzheimer's disease, on CSPG and adult hippocampal neurogenesis.

EXPERIMENTAL APPROACH

The effects of MEM on neurogenesis-related cells and CSPG content were assessed in the hippocampus of middle-aged mice. The MEM-induced alterations in gene expressions of neurotrophins and enzymes associated with biosynthesis and degradation of CSPG in the hippocampus were also measured. The effects of MEM on cognitive function were estimated using a behavioral test battery. The same set of behavioral tests was applied to evaluate the effects of pharmacological depletion of CSPG in the hippocampus.

KEY RESULTS

The densities of newborn granule cells and content of CSPG in the hippocampus were increased by MEM. The expression levels of the enzyme responsible for the biosynthesis CSPG were increased by MEM. The neurotrophin-related molecules were activated by MEM. Short- and long-term memory performance was improved by MEM. Pharmacological depletion of CSPG impairs the effects of MEM on cognitive improvement in middle-aged mice.

CONCLUSIONS AND IMPLICATIONS

MEM regulates the biosynthesis and degradation of CSPG, which may underlie the improvement of cognitive function via the promotion of adult hippocampal neurogenesis. These results imply that CSPG-related enzymes may be potentially attractive candidates for the treatment of aging-related cognitive decline.

Effects of Chronic Hypoxic Environment on Cognitive Function and Neuroimaging Measures in a High-Altitude Population

Objective

This study aimed to investigate the effects of long-term hypoxic environment exposure on cognitive ability and neuroimaging characteristics in a highland population in China.

Methods

Health system workers in Maduo County (4,300 m above sea level) and Minhe County (1,700 m above sea level) were selected as research participants and divided into a high-altitude (HA) group and low-altitude (LA) group, respectively. Cognitive ability was assessed using the Montreal Cognitive Assessment (MoCA), Verbal Fluency Test (VFT), Symbol Digit Modalities Test (SDMT), Trail Making Test A and B (TMT), Digit Span Test (DST), and Rey Auditory Verbal Learning Test (RAVLT). All participants underwent a magnetic resonance imaging (MRI) scan, resting state functional MRI scan, and diffusion tensor imaging to clarify changes in regional gray matter (GM) volume, anisotropy index (FA), local consistency (ReHo), and low-frequency oscillation amplitude (ALFF).

Results

The HA group had significantly lower MoCA, DST, VFT, RAVLT, and TMT scores compared to the control group. No significant differences were found in SDMT score. Furthermore, compared to the LA group, the HA group had significantly lower GM density of the left olfactory cortex, right medial orbital superior frontal gyrus, bilateral insula, left globus pallidus, and temporal lobe (left superior temporal gyrus temporal pole, bilateral middle temporal gyrus temporal pole, and right middle temporal gyrus). In terms of FA, compared with the LA group, the HA group had lower values for the corpus callosum, corpus callosum knee, bilateral radiative corona, and left internal capsule. The HA group had lower ALFF values of the left cerebellum, left putamen, left orbital inferior frontal gyrus, and left precuneus, but higher ALFF values of the left fusiform gyrus, bilateral inferior temporal gyrus, left orbital superior frontal gyrus and medial superior frontal gyrus, compared to the LA group. There was no significant group difference in ReHo values.

Conclusion

Our findings suggest that a chronic hypoxic environment can induce extensive cognitive impairment. Decreased GM density in multiple brain regions, damaged nerve fibers, and unbalanced neuronal activity intensity in different brain regions may be the structural and functional basis of cognitive impairment due to hypoxia.

A Multimodal MR Imaging Study of the Effect of Hippocampal Damage on Affective and Cognitive Functions in a Rat Model of Chronic Exposure to a Plateau Environment

Prolonged exposure to high altitudes above 2500 m above sea level (a.s.l.) can cause cognitive and behavioral dysfunctions. Herein, we sought to investigate the effects of chronic exposure to plateau hypoxia on the hippocampus in a rat model by using voxel-based morphometry, creatine chemical exchange saturation transfer (CrCEST) and dynamic contrast-enhanced MR imaging techniques. 58 healthy 4-week-old male rats were randomized into plateau hypoxia rats (H group) as the experimental group and plain rats (P group) as the control group. H group rats were transported from Chengdu (500 m a.s.l.), a city in a plateau located in southwestern China, to the Qinghai-Tibet Plateau (4250 m a.s.l.), Yushu, China, and then fed for 8 months there, while P group rats were fed in Chengdu (500 m a.s.l.), China. After 8 months of exposure to plateau hypoxia, open-field and elevated plus maze tests revealed that the anxiety-like behavior of the H group rats was more serious than that of the P group rats, and the Morris water maze test revealed impaired spatial memory function in the H group rats. Multimodal MR imaging analysis revealed a decreased volume of the regional gray matter, lower CrCEST contrast and higher transport coefficient Ktrans in the hippocampus compared with the P group rats. Further correlation analysis found associations of quantitative MRI parameters of the hippocampus with the behavioral performance of H group rats. In this study, we validated the viability of using noninvasive multimodal MR imaging techniques to evaluate the effects of chronic exposure to a plateau hypoxic environment on the hippocampus.

Application value and challenge of traditional Chinese medicine carried by ZIF-8 in the therapy of ischemic stroke

Stroke is a group of major diseases that cause death or disability in adults, with high incidence and lack of available therapeutic strategies. Although traditional Chinese medicine (TCM) has continuously achieved good effects in the therapy of stroke while there is still not convincing due to the limitation of blood-brain permeability, as well as the individual differences in usage and dosage. With the improvement of nanotechnology, TCM nanopreparation has gradually become a research hotspot in various fields due to its advantages in permeating the blood-brain barrier, targeting delivery, enhancing sustained-release drug delivery, changing the distribution in the body, and improving bioavailability. Zeolitic imidazolate framework-8 (ZIF-8) is an ideal nano-drug delivery system for adsorption, catalysis, and drug loading, which is a biocompatible metal-organic framework framed by 2-methylimidazole and zinc ions. At present, ZIF-8 was wildly used in the treatment of ischemic stroke. However, challenges remain persists for its clinical application, such as preparation technology, detection technology in vivo, targeting specificity, safety and stability, and so forth. Therefore, more efforts need to overcome the above problems to develop the application of TCM nanopreparations in the therapy of ischemia/reperfusion in the future.

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

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