Artemisinin ameliorates cognitive decline by inhibiting hippocampal neuronal ferroptosis via Nrf2 activation in T2DM mice.

BACKGROUND: Neuronal ferroptosis plays a critical role in the pathogenesis of cognitive deficits. The present study explored whether artemisinin protected type 2 diabetes mellitus (T2DM) mice from cognitive impairments by attenuating neuronal ferroptosis in the hippocampal CA1 region. METHODS: STZ-induced T2DM mice were treated with artemisinin (40 mg/kg, i.p.), or cotreated with artemisinin and Nrf2 inhibitor MEL385 or ferroptosis inducer erastin for 4 weeks. Cognitive performance was determined by the Morris water maze and Y maze tests. Hippocampal ROS, MDA, GSH, and Fe2+ contents were detected by assay kits. Nrf2, p-Nrf2, HO-1, and GPX4 proteins in hippocampal CA1 were assessed by Western blotting. Hippocampal neuron injury and mitochondrial morphology were observed using H&E staining and a transmission electron microscope, respectively. RESULTS: Artemisinin reversed diabetic cognitive impairments, decreased the concentrations of ROS, MDA and Fe2+, and increased the levels of p-Nr2, HO-1, GPX4 and GSH. Moreover, artemisinin alleviated neuronal loss and ferroptosis in the hippocampal CA1 region. However, these neuroprotective effects of artemisinin were abolished by Nrf2 inhibitor ML385 and ferroptosis inducer erastin. CONCLUSION: Artemisinin effectively ameliorates neuropathological changes and learning and memory decline in T2DM mice; the underlying mechanism involves the activation of Nrf2 to inhibit neuronal ferroptosis in the hippocampus.

ASIC1/RIP1 accelerates atherosclerosis via disrupting lipophagy.

INTRODUCTION: Atherosclerosis, a major contributor to cardiovascular disease, remains a significant health concern worldwide. While previous research has shown that acid-sensing ion channel 1 (ASIC1) impedes macrophage cholesterol efflux, its precise role in atherogenesis and the underlying mechanisms have remained elusive. OBJECTIVES: This study aimed to investigate the role of ASIC1 in atherosclerosis and its underlying mechanisms. METHODS: First, data from a single-cell RNA sequencing (scRNA-seq) database were used to explore the relationships between ASIC1 differential expression and lipophagy in human atherosclerotic lesions. Finally, we validated the role of ASIC1/RIP1 signaling in lipophagy in vivo (human and mice) and in vitro (RAW264.7 and HTP-1 cells). RESULT: Our results demonstrated a significant increase in ASIC1 protein levels within CD68+ macrophages in both human aortic lesions and AopE-/- mouse lesion areas compared to nonlesion regions. Concurrently, there was a notable decrease in lipophagy, a crucial process for lipid metabolism. In vitro assays further elucidated that ASIC1 interaction with RIP1 (receptor-interacting protein 1) promoted the phosphorylation of RIP1 at serine 166 and transcription factor EB (TFEB) at serine 142, leading to disrupted lipophagy and increased lipid accumulation. Intriguingly, all these events were reversed upon ASIC1 deficiency and RIP1 inhibition. Furthermore, in ApoE-/- mouse models of atherosclerosis, silencing ASIC1 expression or inhibiting RIP1 activation not only significantly attenuated atherogenesis but also restored TFEB-mediated lipophagy in aortic tissues. This was evidenced by reduced TFEB Ser-142 phosphorylation, decreased LC3II and LAMP1 protein expression, increased numbers of lipophagosomes, and a decrease in lipid droplets. CONCLUSION: Our findings unveil the critical role of macrophage ASIC1 in interacting with RIP1 to inhibit lipophagy, thereby promoting atherogenesis. Targeting ASIC1 represents a promising therapeutic avenue for the treatment of atherosclerosis.

Critical role of dysfunctional mitochondria and defective mitophagy in autism spectrum disorders.

Autism spectrum disorders (ASDs) are a group of complex neurodevelopmental disorders, including autistic disorder, Asperger's syndrome, pervasive developmental disorder and childhood disintegrative disorder. Mitochondria not only provide neurons with energy in the form of ATP to sustain neuron growth, proliferation and neurodevelopment, but also regulate neuron apoptosis, intracellular calcium ion (Ca2+) homeostasis, and reactive oxygen species (ROS) clearance. Due to their postmitotic state and high energy-demanded feature, neurons are particularly prone to mitophagy and mitochondrial disfunction. Mitophagy, a selective autophagy, is critical for sustaining mitochondrial turnover and quality control via eliminating unwanted and dysfunctional mitochondria in neurons. Dysfunctional mitochondria and dysregulated mitophagy have been closely associated with the onset of ASDs. In this review, we summarize the mechanism of mitophagy and its role in neurons, and the consequence of mitophagy dysfunction in ASDs. Deeper appreciation of the role of mitophagy in ASDs pathology is required for developing new therapeutic approaches.

Acid-Sensing Ion Channel 1/Calpain1 Activation Impedes Macrophage ATP-Binding Cassette Protein A1-Mediated Cholesterol Efflux Induced by Extracellular Acidification.

BACKGROUND: Extracellular acidification is a common feature of atherosclerotic lesions, and such an acidic microenvironment impedes ATP-binding cassette transporter A1 (ABCA1)-mediated cholesterol efflux and promotes atherogenesis. However, the underlying mechanism is still unclear. Acid-sensing ion channel 1 (ASIC1) is a critical H+ receptor, which is responsible for the perception and transduction of extracellular acidification signals. AIM: In this study, we explored whether or how ASIC1 influences extracellular acidification-induced ABCA1-mediated cholesterol efflux from macrophage-derived foam cells. METHODS: RAW 264.7 macrophages were cultured in an acidic medium (pH 6.5) to generate foam cells. Then the intracellular lipid deposition, cholesterol efflux, and ASIC1/calpain1/ABCA1 expressions were evaluated. RESULTS: We showed that extracellular acidification enhanced ASIC1 expression and translocation, promoted calpain1 expression and lipid accumulation, and decreased ABCA1 protein expression as well as ABCA1-mediated cholesterol efflux. Of note, inhibiting ASIC1 activation with amiloride or Psalmotoxin 1 (PcTx-1) not only lowered calpain1 protein level and lipid accumulation but also enhanced ABCA1 protein levels and ABCA1-mediated cholesterol efflux of macrophages under extracellular acidification conditions. Furthermore, similar results were observed in macrophages treated with calpain1 inhibitor PD150606. CONCLUSION: Extracellular acidification declines cholesterol efflux via activating ASIC1 to promote calpain1-mediated ABCA1 degradation. Thus, ASIC1 may be a novel therapeutic target for atherosclerosis.

Lipophagy in atherosclerosis.

Atherosclerosis results from the excessive accumulation of lipids within the arterial wall. Lipophagy, referred to as the autophagic degradation of lipids, is a critical mechanism that regulates lipid metabolism in numerous cell types. The contribution of lipophagy to intracellular lipid turnover makes it a major player in the development and progression of atherosclerosis. This review addresses recent advances in lipid metabolism via lipophagy. The relationship between lipophagy and atherosclerosis is discussed focusing on the roles of lipophagy in vascular endothelial cell injury, vascular smooth muscle cells phenoypic shift, and macrophage lipid accumulation. A further understanding of lipophagy in these processes may provide promising new therapeutic options for atherosclerotic diseases.

Autophagy in chronic stress induced atherosclerosis.

Atherosclerosis, a complex multifactorial disease, is the leading cause of acute cardiovascular events. Substantial evidence confirms that chronic stress plays a pivot role in the occurrence and development of atherosclerosis, but the specific mechanism remains unclear. Autophagy serves as a safeguard mechanism for sustaining cellular homeostasis via eliminating unnecessary or/and harmful components, and damaged organelles in response to various stress. An increasing number of studies indicate that autophagy plays vital roles in the development of atherosclerosis. Therefore, understanding the role of chronic stress in the regulation of autophagy may provide new insight into prevention and treatment atherosclerotic disease, especially with respect to emerging targeted therapy. In present review, we focus on changes in autophagic function under chronic stress and its relationship to atherosclerosis.

Acid-sensing ion channels: Linking extracellular acidification with atherosclerosis.

Extracellular acidification in atherosclerosis-prone regions of arterial walls is considered pro-atherosclerotic by exerting detrimental effect on macrophages, endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). Acid-sensing ion channels (ASICs), a family of extracellular H+ (proton)-gated cation channels, are present extensively in the nervous system and other tissues, implying physiologic as well as pathophysiologic importance. Aberrant activation of ASICs is thought to be associated in EC dysfunction, macrophage phenotypic switch, and VSMC migration and proliferation. Although in vitro evidence acknowledges the contribution of ASIC activation in atherosclerosis, no direct evidence confirms their pro-atherosclerotic roles in vivo. In this review, the effect of extracellular acidity on three major contributors, ECs, macrophages, and VSMCs, is discussed focusing on the potential roles of ASICs in atherosclerotic development and underlying pathology. A more comprehensive understanding of ASICs in these processes may provide promising new therapeutic targets for treatment and prevention of atherosclerotic diseases.

Hydrogen Sulfide Ameliorates Cognitive Dysfunction in Formaldehyde-Exposed Rats: Involvement in the Upregulation of Brain-Derived Neurotrophic Factor.

OBJECTIVE: To investigate whether hydrogen sulfide (H2S) counteracts formaldehyde (FA)-induced cognitive defects and whether the underlying mechanism is involved in the upregulation of hippocampal brain-derived neurotrophic factor (BDNF) expression. METHODS: The cognitive function of rats was evaluated by the Morris water maze (MWM) test and the novel object recognition test. The content of superoxide dismutase (SOD) and malondialdehyde (MDA) in the hippocampus were detected by enzyme-linked immunosorbent assay (ELISA). The neuronal apoptosis in the hippocampal CA1 region was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end (TUNEL) staining. The expression of the BDNF protein was detected by Western blot and immunohistochemistry. RESULTS: We found that sodium hydrosulfide (NaHS, a donor of H2S) significantly reversed the impairment in the function of learning and memory in the MWM test and the novel objective recognition task induced by intracerebroventricular injection of FA. We also showed that NaHS significantly reduced the level of MDA, elevated the level of SOD, and decreased the amount of TUNEL-positive neurons in the hippocampus of FA-exposed rats. Moreover, NaHS markedly increased the expression of hippocampal BDNF in FA-exposed rats. CONCLUSIONS: H2S attenuates FA-induced dysfunction of cognition and the underlying mechanism is involved in the reduction of hippocampal oxidative damage and apoptosis as well as upregulation of hippocampal BDNF.

Corticosterone induces neurotoxicity in PC12 cells via disrupting autophagy flux mediated by AMPK/mTOR signaling.

AIMS: Our previous study indicated that chronic stress caused autophagy impairment and subsequent neuron apoptosis in hippocampus. However, the mechanism underlying the stress-induced damage to neurons is unclear. In present work, we investigated whether stress-level glucocorticoids (GCs) GCs promoted PC12 cell damage via AMPK/mTOR signaling-mediated autophagy. METHODS: Chronic stress-induced PC12 cell injury model was built by treatment with high level corticosterone (CORT). Cell injury was evaluated by flow cytometry assay and transmission electron microscopy observation. RESULTS: Autophagy flux was measured based on the changes in LC3-II and P62 protein expressions, and the color alteration of mCherry-GFP-LC3-II transfection. Our results showed that CORT not only increased cell injury and apoptosis, but also dysregulated AMPK/mTOR signaling-mediated autophagy flux, as indicated by the upregulated expression of LC3-II and P62 proteins, and the lowered ration of autolysosomes to autophagosomes. Mechanistically, our results demonstrated that autophagy activation by AMPK activator metformin or mTOR inhibitor rapamycin obviously promotes cell survival and autophagy flux, improved mitochondrial ultrastructure, and reduced expression of Cyt-C and caspase-3 in CORT-induced PC12 cells. CONCLUSION: These results indicate that high CORT triggers PC12 cell damage through disrupting AMPK/mTOR-mediated autophagy flux. Targeting this signaling may be a promising approach to protect against high CORT and chronic stress-induced neuronal impairment.

Chronic Unpredictable Mild Stress Promotes Atherosclerosis via HMGB1/TLR4-Mediated Downregulation of PPARγ/LXRα/ABCA1 in ApoE-/- Mice.

Background: Although our previous studies have confirmed that the activation of TLR4 is implicated in the development of atherosclerosis induced by chronic unpredicted mild stress (CUMS), the underling mechanism is largely unclear. Here, we hypothesized that CUMS accelerates atherosclerotic development through lowering PPARγ/LXRα-ABCA1 expression via HMGB1/TLR4 signaling. Methods: In present study, CUMS atherosclerotic animal models were established with AopE-/- mice, and CUMS Raw 264.7 macrophage models were mimicked by high corticosterone treatment, These models were treated with Ethyl pyruvate (EP, an inhibitor of HMGB1), TLR4 inhibitor TAK-242, and PPARγ agonist RSG (Rosiglitazone) to test our hypothesis, respectively. Results: Our results indicated that the protein levels of HMGB1, TLR4, and pro-inflammatory cytokines including IL-1ß, TNF-α were elevated with the development of atherosclerosis in CUMS mice, while the expressions of PPARγ, LXRα, and ABCA1 declined. Notably, HMGB1 inhibition by EP reversed CUMS-induced atherosclerotic development, pro-inflammatory cytokines upregulation, and PPARγ/LXRα-ABCA1 downregulation. The same trend was observed in the stressed mice treatment with TAK-242. Further experimental evidences indicated that EP, TAK-242, and RSG treatment notably corrected foam cell formation, HMGB1 release, and down-regulation of LXRα and ABCA1 in CUMS Raw 264.7 macrophage model. Conclusion: These results indicate that CUMS exacerbates atherosclerosis is likely via HMGB1-mediated downregulation of PPARγ/LXRα-ABCA1 through TLR4. These data reveal a novel mechanism by which CUMS aggravates atherosclerosis and may offer a potential therapeutic target for this disease.

Tissue factor pathway inhibitor in atherosclerosis.

Tissue factor pathway inhibitor (TFPI) reduces the development of atherosclerosis by regulating tissue factor (TF) mediated coagulation pathway. In this review, we focus on recent findings on the inhibitory effects of TFPI on endothelial cell activation, vascular smooth muscle cell (VSMC) proliferation and migration, inflammatory cell recruitment and extracellular matrix which are associated with the development of atherosclerosis. Meanwhile, we are also concerned about the impact of TFPI levels and genetic polymorphisms on clinical atherogenesis. This article aims to explain the mechanism in inhibiting the development of atherosclerosis and clinical effects of TFPI, and provide new ideas for the clinical researches and mechanism studies of atherothrombosis.

Nicotinate-curcumin ameliorates cognitive impairment in diabetic rats by rescuing autophagic flux in CA1 hippocampus.

INTRODUCTION: Our previous study has confirmed that a novel curcumin derivate nicotinate-curcumin (NC) can facilitate autophagic flux in THP-1 cells induced by oxidized low-density lipoprotein. AIMS: Given that autophagy plays critical roles in neurodegenerative diseases, the present study was carried out to investigate whether NC can improve cognitive function of rats with diabetes mellitus (DM) via restoring autophagic flux in CA1 hippocampus. RESULTS: Our results showed that NC treatment improved cognitive deficit and attenuated neuronal loss as well as cellular ultrastructure impairment in the CA1 region of DM rats induced by streptozotocin. Moreover, NC lowered the expressions of the apoptosis-related proteins Bcl-2, Bax, Cyt-c, and cleaved Caspase-3. Notably, NC treatment reversed autophagic flux impairment as evidenced by the deceases in LC3-II and p62 protein levels, and autophagosome accumulation in the hippocampal CA1 region of DM rats. However, these protective effects of NC were abolished by cotreatment with 3-methyladenine (an autophagy inhibitor) and chloroquine (an autophagic flux inhibitor), respectively. Furthermore, NC treatment decreased the expressions of phosphorylated mammalian target of rapamycin (mTOR) and p70 ribosomal protein S6 kinase (p70S6k) proteins in the CA1 region of DM rats. CONCLUSIONS: These results indicate that NC ameliorates DM-induced cognitive function impairment via restoring autophagic flux might by inhibiting mTOR/p70S6k activation in the CA1 region, and NC may be a promising agent for diabetic cognitive dysfunction prevention and treatment.

Hydrogen sulfide ameliorates cognitive dysfunction in streptozotocin-induced diabetic rats: involving suppression in hippocampal endoplasmic reticulum stress.

Diabetes induces impairment in cognitive function. There is substantial evidence that hippocampal endoplasmic reticulum (ER) stress is involved in diabetic cognitive impairment. Hydrogen sulfide (H2S) attenuates the learning and memory decline in experimental Alzheimer's disease and inhibits the hippocampal ER stress in homocysteine-exposed rats. Therefore, this aim of the present work was to investigate whether H2S ameliorates the diabetic cognitive dysfunction involving inhibition of hippocampal ER stress. In the present work, we found that stretozotocin (STZ, 40 mg/kg)-induced diabetic rats exhibited impairment in cognitive function, as judged by the novel objective recognition task (NOR) test, the Y-maze test and the Morris water maze (MWM) test. Notably, treatment of diabetic rats with sodium hydrosulfide (NaHS, a donor of H2S, 30 or 100 µmol/kg/d, for 30 d) significantly reversed diabetes-induced impairment in cognitive function. We also found that STZ (40 mg/kg)-induced diabetic rats exhibited hippocampal ER stress, as evidenced by upregulations of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and cleaved caspase-12 in the hippocampus. However, treatment with NaHS (30 or 100 µmol/kg/d, for 30 d) markedly suppressed the increases in GRP78, CHOP, and cleaved caspase-12 expressions in the hippocampus of diabetic rats. In addition, we noted that NaHS (30 or 100 µmol/kg/d, for 30 d) significantly enhanced the generation of hippocampal endogenous H2S in STZ-induced diabetic rats. These results suggest that H2S exhibits therapeutic potential for diabetes-associated cognitive dysfunction, which is most likely related to its protective effects against hippocampal ER stress.

Hydrogen Sulfide Inhibits Chronic Unpredictable Mild Stress-Induced Depressive-Like Behavior by Upregulation of Sirt-1: Involvement in Suppression of Hippocampal Endoplasmic Reticulum Stress.

Background: Hydrogen sulfide (H2S) is a crucial signaling molecule with a wide range of physiological functions. Previously, we confirmed that stress-induced depression is accompanied with disturbance of H2S generation in hippocampus. The present work attempted to investigate the inhibitory effect of H2S on chronic unpredictable mild stress-induced depressive-like behaviors and the underlying mechanism. Methods: We established the rat model of chronic unpredictable mild stress to simulate depression. Open field test, forced swim test, and tail suspension test were used to assess depressive-like behaviors. The expression of Sirt-1 and three marked proteins related to endoplasmic reticulum stress (GRP-78, CHOP, and cleaved caspase-12) were detected by western blot. Results: We found that chronic unpredictable mild stress-exposed rats exhibit depression-like behavior responses, including significantly increased immobility time in the forced swim test and tail suspension test, and decreased climbing time and swimming time in the forced swim test. In parallel, chronic unpredictable mild stress-exposed rats showed elevated levels of hippocampal endoplasmic reticulum stress and reduced levels of Sirt-1. However, NaHS (a donor of H2S) not only alleviated chronic unpredictable mild stress-induced depressive-like behaviors and hippocampal endoplasmic reticulum stress, but it also increased the expression of hippocampal Sirt-1 in chronic unpredictable mild stress-exposed rats. Furthermore, Sirtinol, an inhibitor of Sirt-1, reversed the protective effects of H2S against chronic unpredictable mild stress-induced depression-like behaviors and hippocampal endoplasmic reticulum stress. Conclusion: These results demonstrated that H2S has an antidepressant potential, and the underlying mechanism is involved in the inhibition of hippocampal endoplasmic reticulum stress by upregulation of Sirt-1 in hippocampus. These findings identify H2S as a novel therapeutic target for depression.

Inhibition of ALDH2 protects PC12 cells against formaldehyde-induced cytotoxicity: involving the protection of hydrogen sulphide.

Formaldehyde (FA), a common environmental contaminant, has toxic effects on the central nervous system (CNS). We have previously found that hydrogen sulphide (H2 S), the third endogenous gaseous mediator, protects neuron against the toxicity of FA. However, the underlying mechanism is poor. Aldehyde-dehydrogenase-2 (ALDH2) plays a major role in detoxification of reactive aldehyde in a range of organs and cell types. Therefore, we speculated that H2 S antagonizes FA-induced neurotoxicity by modulating ALDH2. In the present study, we found that the exposure of PC12 cells to FA causes increase in ALDH2 expression and activity. Daidzin, an inhibitor of ALDH2, significantly antagonizes FA-exerted cytotoxicity and oxidative stress including the accumulation of intracellular reactive oxygen species (ROS), 4-hydroxy-2-trans-nonenal (4-HNE), and malondialdehyde (MDA), in PC12 cells. We also showed that daidzin markedly attenuated FA-induced apoptosis in PC12 cells. Furthermore, we found that H2 S reverses FA-elicited upregulation of ALDH2 in PC12 cells. Our results demonstrated the involvement of downregulation of ALDH2 in the protection of H2 S against FA neurotoxicity.

Oxidized low-density lipoprotein induced mouse hippocampal HT-22 cell damage via promoting the shift from autophagy to apoptosis.

AIMS: Although oxidized low-density lipoprotein (ox-LDL) in the brain induces neuronal death, the mechanism underlying the damage effects remains largely unknown. Given that the ultimate outcome of a cell is depended on the balance between autophagy and apoptosis, this study was performed to explore whether ox-LDL induced HT-22 neuronal cell damage via autophagy impairment and apoptosis enhancement. METHODS: Flow cytometry and transmission electron microscopy (TEM) were used to evaluate changes in cell apoptosis and autophagy, respectively. The protein expression of LC3-II, p62, Bcl-2, and Bax in HT-22 cells was measured by Western bolt analysis. RESULTS: Our study confirmed that 100 µg/mL of ox-LDL not only promoted TH-22 cell apoptosis, characterized by elevated cell apoptosis rate and Bax protein expression, decreased Bcl-2 protein expression, and damaged cellular ultrastructures, but also impaired autophagy as indicated by the decreased LC3-II levels and the increased p62 levels. Importantly, all of these effects of ox-LDL were significantly aggravated by cotreatment with chloroquine (an inhibitor of autophagy flux). In contrast, cotreatment with rapamycin (an inducer of autophagy) remarkably reversed these effects of ox-LDL. CONCLUSIONS: Taken together, our results indicated that ox-LDL-induced shift from autophagy to apoptosis contributes to HT-22 cell damage.

Hydrogen Sulfide Ameliorates Homocysteine-Induced Cognitive Dysfunction by Inhibition of Reactive Aldehydes Involving Upregulation of ALDH2.

Background: Homocysteine, a risk factor for Alzheimer's disease, induces cognitive dysfunction. Reactive aldehydes play an important role in cognitive dysfunction. Aldehyde-dehydrogenase 2 detoxifies reactive aldehydes. Hydrogen sulfide, a novel neuromodulator, has neuroprotective effects and regulates learning and memory. Our previous work confirmed that the disturbance of hydrogen sulfide synthesis is invovled in homocysteine-induced defects in learning and memory. Therefore, the present work was to explore whether hydrogen sulfide ameliorates homocysteine-generated cognitive dysfunction and to investigate whether its underlying mechanism is related to attenuating accumulation of reactive aldehydes by upregulation of aldehyde-dehydrogenase 2. Methods: The cognitive function of rats was assessed by the Morris water maze test and the novel object recognition test. The levels of malondialdehyde, 4-hydroxynonenal, and glutathione as well as the activity of aldehyde-dehydrogenase 2 were determined by enzyme linked immunosorbent assay; the expression of aldehyde-dehydrogenase 2 was detected by western blot. Results: The behavior experiments, Morris water maze test and novel objects recognition test, showed that homocysteine induced deficiency in learning and memory in rats, and this deficiency was reversed by treatment of NaHS (a donor of hydrogen sulfide). We demonstrated that NaHS inhibited homocysteine-induced increases in generations of MDA and 4-HNE in the hippocampus of rats and that hydrogen sulfide reversed homocysteine-induced decreases in the level of glutathione as well as the activity and expression of aldehyde-dehydrogenase 2 in the hippocampus of rats. Conclusion: Hydrogen sulfide ameliorates homocysteine-induced impairment in cognitive function by decreasing accumulation of reactive aldehydes as a result of upregulations of glutathione and aldehyde-dehydrogenase 2.

Hydrogen sulfide inhibits MPP+-induced aldehyde stress and endoplasmic reticulum stress in PC12 cells: involving upregulation of BDNF.

We have previously demonstrated the protective action of hydrogen sulfide (H2S) in 1-Methy-4-Phenylpyridinium Ion (MPP+)-induced neurotoxicity. However, the exact mechanisms of this protection remain largely unknown. Aldehyde stress and endoplasmic reticulum (ER) stress play significant roles in the neurotoxicity of MPP+. Brain derived neurotrophic factor (BDNF) is an important endogenous neuroprotectant. Therefore, we speculated that the protection of H2S against MPP+ neurotoxicity results from inhibiting MPP+-induced aldehyde stress and ER stress via upregulation of BDNF. In the present study, we found that NaHS, a donor of H2S, inhibited MPP+-induced aldehyde stress (the accumulations of the intracellular 4-HNE and MDA) and ER stress (the increases in the expressions of GRP78 and Cleaved-caspase-12) in PC12 cells and upregulated the BDNF expression in MPP+-exposed PC12 cells. Furthermore, we found that pretreatment of PC12 cells with K252a, an inhibitor of the BDNF receptor TrkB, not only markedly reversed the inhibitiory role of NaHS in MPP+-induced aldehyde stress and ER stress, but also ablated the protection of NaHS against MPP+-induced neurotoxicity. These data demonstrated that the protective role of H2S against MPP+-induced neurotoxicity by inhibiting aldehyde stress and ER stress, which is involved in upregulation of BDNF.

Hydrogen Sulfide Protects against Chronic Unpredictable Mild Stress-Induced Oxidative Stress in Hippocampus by Upregulation of BDNF-TrkB Pathway.

Chronic unpredictable mild stress (CUMS) induces hippocampal oxidative stress. H2S functions as a neuroprotectant against oxidative stress in brain. We have previously shown the upregulatory effect of H2S on BDNF protein expression in the hippocampus of rats. Therefore, we hypothesized that H2S prevents CUMS-generated oxidative stress by upregulation of BDNF-TrkB pathway. We showed that NaHS (0.03 or 0.1 mmol/kg/day) ameliorates the level of hippocampal oxidative stress, including reduced levels of malondialdehyde (MDA) and 4-hydroxy-2-trans-nonenal (4-HNE), as well as increased level of glutathione (GSH) and activity of superoxide dismutase (SOD) in the hippocampus of CUMS-treated rats. We also found that H2S upregulated the level of BDNF and p-TrkB protein in the hippocampus of CUMS rats. Furthermore, inhibition of BDNF signaling by K252a, an inhibitor of the BDNF receptor TrkB, blocked the antioxidant effects of H2S on CUMS-induced hippocampal oxidative stress. These results reveal the inhibitory role of H2S in CUMS-induced hippocampal oxidative stress, which is through upregulation of BDNF/TrkB pathway.

Arecoline Induces Neurotoxicity to PC12 Cells: Involvement in ER Stress and Disturbance of Endogenous H2S Generation.

Arecoline is a major alkaloid of areca nut and has been effect on central nervous system. Although arecoline-induced neurotoxicity has been reported, the possible underlying neurotoxic mechanisms have not yet been elucidated. Increasing evidences have shown that both excessive endoplasmic reticulum (ER) stress and disturbance of hydrogen sulfide (H2S) production are involved in the pathophysiology of numerous neurodegenerative diseases. Here, the purpose of present study was to verify whether ER stress and the disturbance of endogenous H2S generation are also involved in arecoline-caused neurotoxicity. We found that treatment of PC12 cells with arecoline induced the down-regulation of cells viability and up-regulation of apoptosis and the activity of caspase-3, indicating the neurotoxic role of arecoline to PC12 cells. In addition, arecoline also increased the expression of Bax (pro-apoptotic protein) and attenuated the expression of Bcl-2 (anti-apoptotic protein) in PC12 cells. Simultaneously, arecoline caused excessive ER stress in PC12 cells, as evidenced by the up-regulations of Glucose-regulated protein 78 (GRP78), CCAAT/enhancer binding protein homologous protein (CHOP), and Cleaved caspase-12 expressions. Notably, the level of H2S in the culture supernatant and the expressions of cystathionine ß-synthase and 3-mercaptopyruvate sulfurtransferase (two major enzymes for endogenous H2S generation in PC12 cells) were also reduced by arecoline treatment. These results indicate that arecoline-caused neurotoxicity to PC12 cells is involved in ER stress and disturbance of endogenous H2S generation and suggest that the modulation of ER stress and endogenous H2S generation may be potential therapeutic approach in treatment of arecoline-caused neurotoxicity.