Molecular Mechanisms of IRE1α-ASK1 Pathway Reactions to Unfolded Protein Response in DRN Neurons of Post-Traumatic Stress Disorder Rats

Endoplasmic reticulum stress, autophagy, neuroinflammation, and sigma 1 receptors as contributors to depression and its treatment

The etiological factors contributing to depression and other neuropsychiatric disorders are largely undefined. Endoplasmic reticulum stress pathways and autophagy are well-defined mechanisms that play critical functions in recognizing and resolving cellular stress and are possible targets for the pathophysiology and treatment of psychiatric and neurologic illnesses. An increasing number of studies indicate the involvement of endoplasmic reticulum stress and autophagy in the control of neuroinflammation, a contributing factor to multiple neuropsychiatric illnesses. Initial inflammatory triggers induce endoplasmic reticulum stress, leading to neuroinflammatory responses. Subsequently, induction of autophagy by neurosteroids and other signaling pathways that converge on autophagy induction are thought to participate in resolving neuroinflammation. The aim of this review is to summarize our current understanding of the molecular mechanisms governing the induction of endoplasmic reticulum stress, autophagy, and neuroinflammation in the central nervous system. Studies focused on innate immune factors, including neurosteroids with anti-inflammatory roles will be reviewed. In the context of depression, animal models that led to our current understanding of molecular mechanisms underlying depression will be highlighted, including the roles of sigma 1 receptors and pharmacological agents that dampen endoplasmic reticulum stress and associated neuroinflammation.

Sodium aescinate improve behavioral performance by inhibiting dorsal raphe nucleus NLRP3 inflammasome in Post-traumatic stress disorder Rat Model

Growing evidence suggest that NLRP3 inflammasome activation in hippocampus and amygdala is involved in the pathophysiology of PTSD. Our previous studies have demonstrated that apoptosis of dorsal raphe nucleus (DRN) contributes to the pathological progression of PTSD. Recent studies by others have shown that in brain injury sodium aescinate (SA) has a protective effect on neurons by inhibiting inflammatory response pathways, thereby relieving symptoms. Here, we extend the therapeutic effects of SA to PTSD rats. We found that PTSD was associated with significant activation of the NLRP3 inflammasome in DRN, whereas administration of SA significantly inhibited DRN NLRP3 inflammasome activation and reduced DRN apoptosis level. SA also improved learning and memory ability and reduced anxiety and depression level in PTSD rats. In addition, NLRP3 inflammasome activation in DRN of PTSD rats impaired mitochondria function by inhibiting ATP synthesis and increasing ROS production, whereas SA can effectively reverse the pathological progression of mitochondria. We recommend SA as a new candidate for the pharmacological treatment of PTSD.

Activated cell-cycle CDK4/CyclinD1-pRB-E2F1 signaling pathway is involved in the apoptosis of dorsal raphe nucleus in the rat model of PTSD

Dysregulation of the dorsal raphe nucleus (DRN) has been revealed to contribute to cognitive and arousal impairments associated with post-traumatic stress disorder (PTSD) in an animal model. In our research an acute exposure to single prolonged stress (SPS) was used to establish PTSD rat model and the effects related to cell-cycle signaling pathway in DRN were examined. Apoptosis in DRN was detected by TUNEL staining, showing that DRN apoptosis number was sharply increased after SPS. SPS triggered cell-cycle CDK4/CyclinD1-pRB-E2F1 signal pathway. Treatment with CDK4 inhibitor Abemaciclib successfully attenuated the DRN apoptosis and rescued decreased spatial learning and memory abilities in SPS rats, indicating that activation of CDK4/CyclinD1-pRB-E2F1 pathway was involved in DRN apoptosis, which may be one of the pathogenesis for PTSD.

Icarrin prevents cardiomyocyte apoptosis in spontaneously hypertensive rats by inhibiting endoplasmic reticulum stress pathways

OBJECTIVES

This study aimed to explore whether icarrin (ICA) can protect cardiomyocytes from hypertension-induced damage by inhibiting endoplasmic reticulum stress (ERS).

METHODS

Spontaneously hypertensive rats (SHRs) were orally administered water or ICA at 10, 20 and 40 mg/kg once daily for 12 weeks, and Wistar-Kyoto (WKY) rats were used as control. Changes in the growth and blood pressure of rats were assessed. Cardiac function was determined by ultrasound and the left ventricle mass was calculated. Myocardial tissue structure was assessed by haematoxylin and eosin staining, cardiomyocyte apoptosis was observed by TUNEL staining and the expression of ERS-related proteins was determined by western blotting.

RESULTS

In the SHR group, blood pressure was significantly high, left ventricular function decreased and left ventricular mass index increased. Additionally, left ventricular cardiomyocyte hypertrophy, disordered myofilament arrangement and increased cardiomyocyte apoptosis were observed by histological staining. ERS-induced proteins associated with apoptosis, including GRP78, PERK, ATF-6, ATF-4, CHOP, DR5, Caspase 12, c-JUN and ASK-1 were found to be highly expressed. ICA treatment reduced blood pressure and regulated the expression of proteins induced by ERS. Cardiomyocyte apoptosis decreased and left ventricular function improved.

CONCLUSIONS

ICA can inhibit ERS-induced apoptosis of cardiomyocytes and protect ventricular function in SHR.

The roles of inducible chromatin and transcriptional memory in cellular defense system responses to redox-active pollutants

People are exposed to wide range of redox-active environmental pollutants. Air pollution, heavy metals, pesticides, and endocrine disrupting chemicals can disrupt cellular redox status. Redox-active pollutants in our environment all trigger their own sets of specific cellular responses, but they also activate a common set of general stress responses that buffer the cell against homeostatic insults. These cellular defense system (CDS) pathways include the heat shock response, the oxidative stress response, the hypoxia response, the unfolded protein response, the DNA damage response, and the general stress response mediated by the stress-activated p38 mitogen-activated protein kinase. Over the past two decades, the field of environmental epigenetics has investigated epigenetic responses to environmental pollutants, including redox-active pollutants. Studies of these responses highlight the role of chromatin modifications in controlling the transcriptional response to pollutants and the role of transcriptional memory, often referred to as "epigenetic reprogramming", in predisposing previously exposed individuals to more potent transcriptional responses on secondary challenge. My central thesis in this review is that high dose or chronic exposure to redox-active pollutants leads to transcriptional memories at CDS target genes that influence the cell's ability to mount protective responses. To support this thesis, I will: (1) summarize the known chromatin features required for inducible gene activation; (2) review the known forms of transcriptional memory; (3) discuss the roles of inducible chromatin and transcriptional memory in CDS responses that are activated by redox-active environmental pollutants; and (4) propose a conceptual framework for CDS pathway responsiveness as a readout of total cellular exposure to redox-active pollutants.

Cronobacter sakazakii Infection in Early Postnatal Rats Impaired Contextual-Associated Learning: a Putative Role of C5a-Mediated NF-κβ and ASK1 Pathways

This study was designed to test whether the Cronobacter sakazakii infection-impaired contextual learning and memory are mediated by the activation of the complement system; subsequent activation of inflammatory signals leads to alternations in serotonin transporter (SERT). To test this, rat pups (postnatal day, PND 15) were treated with either C. sakazakii (10⁷ CFU) or Escherichia coli OP50 (10⁷ CFU) or Luria bertani broth (100 μL) through oral gavage and allowed to stay with their mothers until PND 24. Experimental groups' rats were allowed to explore (PNDs 31-35) and then trained in contextual learning task (PNDs 36-43). Five days after training, individuals were tested for memory retention (PNDs 49-56). Observed behavioural data showed that C. sakazakii infection impaired contextual-associative learning and memory. Furthermore, our analysis showed that C. sakazakii infection activates complement system complement anaphylatoxin (C5a) (a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS1)) and mitogen-activated protein kinase kinase1 (MEKK1). Subsequently, MEKK1 induces pro-inflammatory signals possibly through apoptosis signal-regulating kinase-1 (ASK-1), c-Jun N-terminal kinase (JNK1/3) and protein kinase B gamma (AKT-3). In parallel, activated nuclear factor kappa-light-chain-enhancer B cells (NF-κB) induces interleukin-6 (IL-6) and IFNα-1, which may alter the level of serotonin transporter (SERT). Observed results suggest that impaired contextual learning and memory could be correlated with C5a-mediated NF-κβ and ASK1 pathways.

Role of apoptosis in the Post-traumatic stress disorder model-single prolonged stressed rats

Post-traumatic stress disorder (PTSD) is a stress-related mental disorder which occurs following exposure to traumatic events. A number of brain neuroimaging studies have revealed that PTSD patients have reduced volume and abnormal functions in the hippocampus and the amygdala. However, the pathogenesis of abnormalities in certain brain regions, as induced by PTSD, remains unclear. Recent studies, using the single prolonged stress (SPS) model, an animal model of PTSD, have found that abnormal apoptosis in certain brain regions, including the hippocampus, the amygdala, and the medial prefrontal cortex (mPFC); these areas are closely associated with emotion and cognition. In this review, we summarize the mechanism of apoptosis in SPS rats, including the endoplasmic reticulum (ER) and the mitochondria pathways. For the ER pathway, three individual pathways: PERK, IRE1, and ATF6 showed different roles on apoptosis and neuroprotection. Three key factors are thought to be involved in the mitochondrial pathway and PTSD-induced apoptosis: corticosteroid receptors, apoptosis-related factors, and anti-apoptosis factors. We have investigated the role of these factors and have attempted to identify which factors of the pathways are more focused towards neuronal protection, and which are more direct towards apoptosis. We also discussed the role of autophagy and the specific differences between autophagy and apoptosis in SPS rats. Finally, we discussed emerging researches related to anti-apoptosis treatment, including PERK inhibitors, IRE1 inhibitors, and metformin; collectively, these were exciting, but limited, This review provides a summary of the current understanding of apoptosis in SPS rats and the potential anti-apoptosis treatment strategies for PTSD.

Hydrogen Sulfide Inhibits Cigarette Smoke-Induced Endoplasmic Reticulum Stress and Apoptosis in Bronchial Epithelial Cells

Background: Apoptosis of lung structural cells contributes to the process of lung damage and remodeling in chronic obstructive pulmonary disease (COPD). Our previous studies demonstrated that exogenous hydrogen sulfide (H₂S) can reduce the lung tissue pathology score, anti-inflammation and anti-oxidation effects in COPD, but the effect of H₂S in regulating cigarette smoke (CS) induced bronchial epithelial cell apoptosis and the underlying mechanisms are not clear.

Objectives: To investigate the effect of H₂S on CS induced endoplasmic reticulum stress (ERS) and bronchial epithelial cell apoptosis.

Methods: Male Sprague–Dawley rats randomly divided into four groups for treatment: control, CS, NaHS + CS, and propargylglycine (PPG) + CS. The rats in the CS group were exposed to CS generated from 20 commercial unfiltered cigarettes for 4 h/day, 7 days/week for 4 months. Since the beginning of the third month, freshly prepared NaHS (14 μmol/kg) and PPG (37.5 mg/kg) were intraperitoneally administered 30 min before CS-exposure in the NaHS and PPG groups. 16HBE cells were pretreated with Taurine (10 mM), 5 mmol/L 4-phenylbutyric acid (4-PBA) or NaHS (100, 200, and 400 μM) for 30 min, and then cells were exposed to 40 μmol/L nicotine for 72 h. ERS markers (GRP94, GRP78) and ERS-mediated apoptosis markers 4-C/EBP homologous protein (CHOP), caspase-3 and caspase-12 were assessed in rat lung tissues and human bronchial epithelial cells. The apoptotic bronchial epithelial cells were detected by Hoechst staining in vitro and TUNEL staining in vivo.

Results: In CS exposed rats, peritoneal injection of NaHS significantly inhibited CS induced overexpression ERS-mediated apoptosis markers and upregulation of apoptotic rate in rat lungs, and inhibiting the endogenous H2S production by peritoneal injection of PPG exacerbated these effects. In the nicotine-exposed bronchial epithelial cells, appropriate concentration of NaHS and ERS inhibitors taurine and 4-PBA inhibited nicotine-induced upregulation of apoptotic rate and overexpression of ERS-mediated apoptosis markers.

Conclusion: H₂S inhibited lung tissue damage by attenuating CS induced ERS in rat lung and exogenous H₂S attenuated nicotine induced ERS-mediated apoptosis in bronchial epithelial cells.