Association of X-box binding protein 1 ( XBP1) genotype with morning cortisol and 1-year clinical course after a major depressive episode

Potential antidepressant-like effects of N-3 polyunsaturated fatty acids through inhibition of endoplasmic reticulum stress

RATIONALE

The growing evidence has demonstrated the importance of endoplasmic reticulum stress (ERS) in the pathophysiology of depression. ERS genes were considered to be potential novel therapeutic targets for depression.

OBJECTIVES

To clarify the mechanisms of the chronic unpredictable mild stress (CUMS)-induced ERS response and the potential contributing pathways in depression, and further investigate the potential link between N-3 polyunsaturated fatty acids (PUFAs) and stress-induced ERS disturbances.

METHODS

This study analyzed the expression of ERS-related genes including GRP78, ATF-4, ATF-6, XBP-1, and CHOP, and sigma-1R with real-time PCR in peripheral blood mononuclear cell (PBMC) RNA samples from participants. All of the rats except for those in the control groups were subjected to 5 consecutive weeks of CUMS to establish the depression model, and the antidepressant effects of N-3 PUFAs were observed by behavior tests. Moreover, the effect of diet and stress on the ERS pathways was also investigated using the western blot.

RESULTS

Blood CHOP, ATF-4, and XBP-1 levels were notably elevated in depressed patients relative to healthy individuals. Moreover, increased sigma-1R and decreased ATF-6 implied the protective role of sigma-1R through modulating ERS in patients with depression. Animal studies disclosed the novel findings that supplementary N-3 PUFAs in rats alleviated CUMS-induced disturbance of ERS through the ATF-4/XBP-1/CHOP pathway, implying its potential strategy for depression.

CONCLUSION

CUMS-induced depressive-like behaviors are related to the disturbance of ERS. Furthermore, supplementary N-3 PUFAs might be an effective way to alleviate ERS.

Endoplasmic reticulum stress inhibition ameliorated WFS1 expression alterations and reduced pancreatic islets' insulin secretion induced by high-fat diet in rats

Endoplasmic reticulum (ER) stress is involved in the development of glucose homeostasis impairment. When ER stress occurs, the unfolded protein response (UPR) is activated to cope with it. One of the UPR components is WFS1 (Wolfram syndrome 1), which plays important roles in ER homeostasis and pancreatic islets glucose-stimulated insulin secretion (GSIS). Accordingly and considering that feeding high-fat food has a major contribution in metabolic disorders, this study aimed to investigate the possible involvement of pancreatic ER stress in glucose metabolism impairment induced by feeding high-fat diet (HFD) in male rats. After weaning, the rats were divided into six groups, and fed on normal diet and HFD for 20 weeks, then 4-phenyl butyric acid (4-PBA, an ER stress inhibitor) was administered. Subsequently, in all groups, after performing glucose tolerance test, the animals were dissected and their pancreases were removed to extract ER, islets isolation and assessment of GSIS. Moreover, the pancreatic ER stress [binding of immunoglobulin protein (BIP) and enhancer-binding protein homologous protein (CHOP)] and oxidative stress [malondialdehyde (MDA), glutathione (GSH) and catalase] biomarkers as well as WFS1 expression level were evaluated. HFD decreased pancreatic WFS1 protein and GSH levels, and enhanced pancreatic catalase activity, MDA content, BIP and CHOP protein and mRNA levels as well as Wfs1 mRNA amount. Accordingly, it increased BIP, CHOP and WFS1 protein levels in the extracted ER of pancreas. In addition, the HFD caused glucose intolerance, and decreased the islets' GSIS and insulin content. However, 4-PBA administration restored the alterations. It seems that, HFD consumption through inducing pancreatic ER stress, altered WFS1 expression levels, reduced the islets' GSIS and insulin content and finally impaired glucose homeostasis.

The chemical chaperon 4-phenyl butyric acid restored high-fat diet- induced hippocampal insulin content and insulin receptor level reduction along with spatial learning and memory deficits in male rats

This study assessed the effect of a chronic high-fat diet (HFD) on plasma and hippocampal insulin and corticosterone levels, the hippocampus insulin receptor amount, and spatial learning and memory with or without receiving 4-phenyl butyric acid (4-PBA) in male rats. Rats were divided into high-fat and normal diet groups, then each group was subdivided into dimethyl sulfoxide (DMSO) and 4-PBA groups. After weaning, the rats were fed with HFD for 20 weeks. Then, 4-PBA or DMSO were injected for 3 days. Subsequently, oral glucose tolerance test was done. On the following day, spatial memory tests were performed. Then the hippocampus Bip, Chop, insulin, corticosterone, and insulin receptor levels were determined. HFD increased plasma glucose, leptin and corticosterone concentrations, hippocampus Bip, Chop and corticosterone levels, food intake, abdominal fat weight and body weight along with impaired glucose tolerance. It decreased plasma insulin, and insulin content, and its receptor amount in hippocampus. HFD lengthened escape latency and shortened the duration spent in target zone. 4-PBA administration improved the HFD- induced adverse changes. Chronic HFD possibly through the induction of endoplasmic reticulum (ER) stress and subsequent changes in the levels of hippocampal corticosterone, insulin and insulin receptor along with possible leptin resistance caused spatial learning and memory deficits.

Animal models for the study of depressive disorder

Depressive disorder is one of the most widespread forms of psychiatric pathology, worldwide. According to a report by the World Health Organization, the number of people with depression, globally, is increasing dramatically with each year. Previous studies have demonstrated that various factors, including genetics and environmental stress, contribute to the risk of depression. As such, it is crucial to develop a detailed understanding of the pathogenesis of depressive disorder and animal studies are essential for identifying the mechanisms and genetic disorders underlying depression. Recently, many researchers have reported on the pathology of depression via various models of depressive disorder. Given that different animal models of depression show differences in terms of patterns of depressive behavior and pathology, the comparison between depressive animal models is necessary for progress in the field of the depression study. However, the various animal models of depression have not been fully compared or evaluated until now. In this paper, we reviewed the pathophysiology of the depressive disorder and its current animal models with the analysis of their transcriptomic profiles. We provide insights for selecting different animal models for the study of depression.

The Unfolded Protein Response and Autophagy as Drug Targets in Neuropsychiatric Disorders

Neurons are polarized in structure with a cytoplasmic compartment extending into dendrites and a long axon that terminates at the synapse. The high level of compartmentalization imposes specific challenges for protein quality control in neurons making them vulnerable to disturbances that may lead to neurological dysfunctions including neuropsychiatric diseases. Synapse and dendrites undergo structural modulations regulated by neuronal activity involve key proteins requiring strict control of their turnover rates and degradation pathways. Recent advances in the study of the unfolded protein response (UPR) and autophagy processes have brought novel insights into the specific roles of these processes in neuronal physiology and synaptic signaling. In this review, we highlight recent data and concepts about UPR and autophagy in neuropsychiatric disorders and synaptic plasticity including a brief outline of possible therapeutic approaches to influence UPR and autophagy signaling in these diseases.

Unravelling the GSK3β-related genotypic interaction network influencing hippocampal volume in recurrent major depressive disorder

OBJECTIVE

Glycogen synthase kinase 3β (GSK3β) has been implicated in mood disorders. We previously reported associations between a GSK3β polymorphism and hippocampal volume in major depressive disorder (MDD). We then reported similar associations for a subset of GSK3β-regulated genes. We now investigate an algorithm-derived comprehensive list of genes encoding proteins that directly interact with GSK3β to identify a genotypic network influencing hippocampal volume in MDD.

PARTICIPANTS AND METHODS

We used discovery (N=141) and replication (N=77) recurrent MDD samples. Our gene list was generated from the NetworKIN database. Hippocampal measures were derived using an optimized Freesurfer protocol. We identified interacting single nucleotide polymorphisms using the machine learning algorithm Random Forest and verified interactions using likelihood ratio tests between nested linear regression models.

RESULTS

The discovery sample showed multiple two-single nucleotide polymorphism interactions with hippocampal volume. The replication sample showed a replicable interaction (likelihood ratio test: P=0.0088, replication sample; P=0.017, discovery sample; Stouffer's combined P=0.0007) between genes associated previously with endoplasmic reticulum stress, calcium regulation and histone modifications.

CONCLUSION

Our results provide genetic evidence supporting associations between hippocampal volume and MDD, which may reflect underlying cellular stress responses. Our study provides evidence of biological mechanisms that should be further explored in the search for disease-modifying therapeutic targets for depression.

Epigenetic differences in monozygotic twins discordant for major depressive disorder

Although monozygotic (MZ) twins share the majority of their genetic makeup, they can be phenotypically discordant on several traits and diseases. DNA methylation is an epigenetic mechanism that can be influenced by genetic, environmental and stochastic events and may have an important impact on individual variability. In this study we explored epigenetic differences in peripheral blood samples in three MZ twin studies on major depressive disorder (MDD). Epigenetic data for twin pairs were collected as part of a previous study using 8.1-K-CpG microarrays tagging DNA modification in white blood cells from MZ twins discordant for MDD. Data originated from three geographical regions: UK, Australia and the Netherlands. Ninety-seven MZ pairs (194 individuals) discordant for MDD were included. Different methods to address non independently-and-identically distributed (non-i.i.d.) data were evaluated. Machine-learning methods with feature selection centered on support vector machine and random forest were used to build a classifier to predict cases and controls based on epivariations. The most informative variants were mapped to genes and carried forward for network analysis. A mixture approach using principal component analysis (PCA) and Bayes methods allowed to combine the three studies and to leverage the increased predictive power provided by the larger sample. A machine-learning algorithm with feature reduction classified affected from non-affected twins above chance levels in an independent training-testing design. Network analysis revealed gene networks centered on the PPAR-γ (NR1C3) and C-MYC gene hubs interacting through the AP-1 (c-Jun) transcription factor. PPAR-γ (NR1C3) is a drug target for pioglitazone, which has been shown to reduce depression symptoms in patients with MDD. Using a data-driven approach we were able to overcome challenges of non-i.i.d. data when combining epigenetic studies from MZ twins discordant for MDD. Individually, the studies yielded negative results but when combined classification of the disease state from blood epigenome alone was possible. Network analysis revealed genes and gene networks that support the inflammation hypothesis of MDD.

Altered Expression of Endoplasmic Reticulum Stress Associated Genes in Hippocampus of Learned Helpless Rats: Relevance to Depression Pathophysiology

The unfolded protein response (UPR) is an evolutionarily conserved defensive mechanism that is used by cells to correct misfolded proteins that accumulate in the endoplasmic reticulum. These proteins are misfolded as a result of physical stress on a cell and initiate a host of downstream effects that govern processes ranging from inflammation to apoptosis. To examine whether UPR system plays a role in depression, we examined the expression of genes that are part of the three different pathways for UPR activation, namely GRP78, GRP94, ATF6, XBP-1, ATF4, and CHOP using an animal model system that distinguishes vulnerability (learned helpless, LH) from resistance (non-learned helpless, NLH) to develop depression. Rats were exposed to inescapable shock on days 1 and 7 and were tested for escape latency on day 14. Rats not given shock but tested for escape latency were used as tested control (TC). Plasma corticosterone (CORT) levels were measured. Expression levels of various UPR associated genes were determined in hippocampus using qPCR. We found that the CORT level was higher in LH rats compared with TC and NLH rats. Expression of GRP78, GRP94, ATF6, and XBP-1 were significantly upregulated in LH rats compared with TC or NLH rats, whereas NLH rats did not show such changes. Expression levels of ATF4 and CHOP showed trends toward upregulation but were not significantly altered in LH or NLH group. Our data show strong evidence of altered UPR system in depressed rats, which could be associated with development of depressive behavior.

Psychological stress, cocaine and natural reward each induce endoplasmic reticulum stress genes in rat brain

Our prior research has shown that the transcription of endoplasmic reticulum (ER) stress transcription factors activating transcription factor 3 (ATF3) and ATF4 are induced by amphetamine and restraint stress in rat striatum. However, presently the full extent of ER stress responses to psychological stress or cocaine, and which of the three ER stress pathways is activated is unknown. The current study examines transcriptional responses of key ER stress target genes subsequent to psychological stress or cocaine. Rats were subjected to acute or repeated restraint stress or cocaine treatment and mRNA was isolated from dorsal striatum, medial prefrontal cortex and nucleus accumbens brain tissue. ER stress gene mRNA expression was measured using quantitative polymerase chain reaction (PCR) and RNA sequencing. Restraint stress and cocaine-induced transcription of the classic ER stress-induced genes (BIP, CHOP, ATF3 and GADD34) and of two other ER stress components x-box binding protein 1 (XBP1) and ATF6. In addition, rats living in an enriched environment (large group cage with novel toys changed daily) exhibited rapid induction of GADD34 and ATF3 after 30 min of exploring novel toys, suggesting these genes are also involved in normal non-pathological signaling. However, environmental enrichment, a paradigm that produces protective addiction and depression phenotypes in rats, attenuated the rapid induction of ATF3 and GADD34 after restraint stress. These experiments provide a sensitive measure of ER stress and, more importantly, these results offer good evidence of the activation of ER stress mechanisms from psychological stress, cocaine and natural reward. Thus, ER stress genes may be targets for novel therapeutic targets for depression and addiction.

Sigma-1Rs are upregulated via PERK/eIF2α/ATF4 pathway and execute protective function in ER stress

Sigma-1 receptors (Sig-1Rs) are the ER resident proteins. Sig-1Rs in the brain have been reported to be significantly reduced in patients with schizophrenia. The impediment of regulating Sig-1Rs expression levels increases the risk for schizophrenia. Thus elucidating the mechanism regulating Sig-1Rs expression might provide the strategy to prevent mental disorders. In this study, we have demonstrated that Sig-1Rs were transcriptionally upregulated by ATF4 in ER stress. Moreover, ATF4 directly bounds to the 5' flanking region of Sig-1R gene. The reporter activities using this region were enhanced in ER stress, or by ATF4 alone. The reporter activities with the pathogenic polymorphisms (GC-241-240TT, T-485A) were reduced. In addition, the processing of Caspase-4 was inhibited by Sig-1Rs. These results indicate that Sig-1Rs are transcriptionally upregulated via the PERK/eIF2α/ATF4 pathway and ameliolate cell death signaling. This study is the first report identifying the transcription factor regulating Sig-1Rs expression.