Resilient Phenotype in Chronic Mild Stress Paradigm Is Associated with Altered Expression Levels of miR-18a-5p and Serotonin 5-HT1a Receptor in Dorsal Part of the Hippocampus

Clinical Insights into MicroRNAs in Depression: Bridging Molecular Discoveries and Therapeutic Potential

Depression is a major contributor to the overall global burden of disease. The discovery of biomarkers for diagnosis or prediction of treatment responses and as therapeutic agents is a current priority. Previous studies have demonstrated the importance of short RNA molecules in the etiology of depression. The most extensively researched of these are microRNAs, a major component of cellular gene regulation and function. MicroRNAs function in a temporal and tissue-specific manner to regulate and modify the post-transcriptional expression of target mRNAs. They can also be shuttled as cargo of extracellular vesicles between the brain and the blood, thus informing about relevant mechanisms in the CNS through the periphery. In fact, studies have already shown that microRNAs identified peripherally are dysregulated in the pathological phenotypes seen in depression. Our article aims to review the existing evidence on microRNA dysregulation in depression and to summarize and evaluate the growing body of evidence for the use of microRNAs as a target for diagnostics and RNA-based therapies.

The potential role of miRNAs in the pathogenesis of schizophrenia - A focus on signaling pathways interplay

microRNAs (miRNAs) play a crucial role in brain growth and function. Hence, research on miRNA has the potential to reveal much about the etiology of neuropsychiatric diseases. Among these, schizophrenia (SZ) is a highly intricate and destructive neuropsychiatric ailment that has been thoroughly researched in the field of miRNA. Despite being a relatively recent area of study about miRNAs and SZ, this discipline has advanced enough to justify numerous reviews that summarize the findings from the past to the present. However, most reviews cannot cover all research, thus it is necessary to synthesize the large range of publications on this topic systematically and understandably. Consequently, this review aimed to provide evidence that miRNAs play a role in the pathophysiology and progression of SZ. They have also been investigated for their potential use as biomarkers and therapeutic targets.

Comparison of Oncogenes, Tumor Suppressors, and MicroRNAs Between Schizophrenia and Glioma: The Balance of Power

The risk of cancer in schizophrenia has been controversial. Confounders of the issue are cigarette smoking in schizophrenia, and antiproliferative effects of antipsychotic medications. The author has previously suggested comparison of a specific cancer like glioma to schizophrenia might help determine a more accurate relationship between cancer and schizophrenia. To accomplish this goal, the author performed three comparisons of data; the first a comparison of conventional tumor suppressors and oncogenes between schizophrenia and cancer including glioma. This comparison determined schizophrenia has both tumor-suppressive and tumor-promoting characteristics. A second, larger comparison between brain-expressed microRNAs in schizophrenia with their expression in glioma was then performed. This identified a core carcinogenic group of miRNAs in schizophrenia offset by a larger group of tumor-suppressive miRNAs. This proposed "balance of power" between oncogenes and tumor suppressors could cause neuroinflammation. This was assessed by a third comparison between schizophrenia, glioma and inflammation in asbestos-related lung cancer and mesothelioma (ALRCM). This revealed that schizophrenia shares more oncogenic similarity to ALRCM than glioma.

Whole-Transcriptome Analysis of Repeated Low-Level Sarin-Exposed Rat Hippocampus and Identification of Cerna Networks to Investigate the Mechanism of Sarin-Induced Cognitive Impairment

Sarin is a potent organophosphorus nerve agent that causes cognitive dysfunction, but its underlying molecular mechanisms are poorly understood. In this study, a rat model of repeated low-level sarin exposure was established using the subcutaneous injection of 0.4 × LD₅₀ for 21 consecutive days. Sarin-exposed rats showed persistent learning and memory impairment and reduced hippocampal dendritic spine density. A whole-transcriptome analysis was applied to study the mechanism of sarin-induced cognitive impairment, and a total of 1035 differentially expressed mRNA (DEmRNA), including 44 DEmiRNA, 305 DElncRNA, and 412 DEcircRNA, were found in the hippocampus of sarin-treated rats. According to Gene Ontology (GO) annotation, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, and Protein-Protein Interaction (PPI) analysis, these DERNAs were mainly involved in neuronal synaptic plasticity and were related to the pathogenesis of neurodegenerative diseases. The circRNA/lncRNA-miRNA-mRNA ceRNA network was constructed, in which Circ_Fmn1, miR-741-3p, miR-764-3p, miR-871-3p, KIF1A, PTPN11, SYN1, and MT-CO3 formed one circuit, and Circ_Cacna1c, miR-10b-5p, miR-18a-5p, CACNA1C, PRKCD, and RASGRP1 constituted another circuit. The balance between the two circuits was crucial for maintaining synaptic plasticity and may be the regulatory mechanism by which sarin causes cognitive impairment. Our study reveals the ceRNA regulation mechanism of sarin exposure for the first time and provides new insights into the molecular mechanisms of other organophosphorus toxicants.

MicroRNA schizophrenia: Etiology, biomarkers and therapeutic targets

The three sets of symptoms associated with schizophrenia-positive, negative, and cognitive-are burdensome and have serious effects on public health, which affects up to 1% of the population. It is now commonly believed that in addition to the traditional dopaminergic mesolimbic pathway, the etiology of schizophrenia also includes neuronal networks, such as glutamate, GABA, serotonin, BDNF, oxidative stress, inflammation and the immune system. Small noncoding RNA molecules called microRNAs (miRNAs) have come to light as possible participants in the pathophysiology of schizophrenia in recent years by having an impact on these systems. These small RNAs regulate the stability and translation of hundreds of target transcripts, which has an impact on the entire gene network. There may be improved approaches to treat and diagnose schizophrenia if it is understood how these changes in miRNAs alter the critical related signaling pathways that drive the development and progression of the illness.

The hippocampus in stress susceptibility and resilience: Reviewing molecular and functional markers

Understanding the individual variability that comes with the likelihood of developing stress-related psychopathologies is of paramount importance when addressing mechanisms of their neurobiology. This article focuses on the hippocampus as a region that is highly influenced by chronic stress exposure and that has strong ties to the development of related disorders, such as depression and post-traumatic stress disorder. We first outline three commonly used animal models that have been used to separate animals into susceptible and resilient cohorts. Next, we review molecular and functional hippocampal markers of susceptibility and resilience. We propose that the hippocampus plays a crucial role in the differences in the processing and storage of stress-related information in animals with different stress susceptibilities. These hippocampal markers not only help us attain a more comprehensive understanding of the various facets of stress-related pathophysiology, but also could be targeted for the development of new treatments.

Proteostasis and resilience: on the interphase between individual's and intracellular stress

A long proportion of the population is resilient to the negative consequences of stress. Glucocorticoids resulting from endocrine responses to stress are essential adaptive mediators, but also drive alterations to brain function, negatively impacting neuronal connectivity, synaptic plasticity, and memory-related processes. Recent evidence has indicated that organelle function and cellular stress responses are relevant determinant of vulnerability and resistance to environmental stress. At the molecular level, a fundamental mechanism of cellular stress adaptation is the maintenance of proteostasis, which also have key roles in sustaining basal neuronal function. Here, we discuss recent evidence suggesting that proteostasis unbalance at the level of the endoplasmic reticulum, the main site for protein folding in the cell, represents a possible mechanistic link between individuals and cellular stress.

Chronic mild stress paradigm as a rat model of depression: facts, artifacts, and future perspectives

RATIONALE

The chronic mild stress (CMS) paradigm was first described almost 40 years ago and has become a widely used model in the search for antidepressant drugs for major depression disorder (MDD). It has resulted in the publication of almost 1700 studies in rats alone. Under the original CMS procedure, the expression of an anhedonic response, a key symptom of depression, was seen as an essential feature of both the model and a depressive state. The prolonged exposure of rodents to unpredictable/uncontrollable mild stressors leads to a reduction in the intake of palatable liquids, behavioral despair, locomotor inhibition, anxiety-like changes, and vegetative (somatic) abnormalities. Many of the CMS studies do not report these patterns of behaviors, and they often fail to include consistent molecular, neuroanatomical, and physiological phenotypes of CMS-exposed animals.

OBJECTIVES

To critically review the CMS studies in rats so that conceptual and methodological flaws can be avoided in future studies.

RESULTS

Analysis of the literature supports the validity of the CMS model and its impact on the field. However, further improvements could be achieved by (i) the stratification of animals into 'resilient' and 'susceptible' cohorts within the CMS animals, (ii) the use of more refined protocols in the sucrose test to mitigate physiological and physical artifacts, and (iii) the systematic evaluation of the non-specific effects of CMS and implementation of appropriate adjustments within the behavioral tests.

CONCLUSIONS

We propose methodological revisions and the use of more advanced behavioral tests to refine the rat CMS paradigm, which offers a valuable tool for developing new antidepressant medications.

MicroRNAs as Critical Biomarkers of Major Depressive Disorder: A Comprehensive Perspective

Major Depressive Disorder (MDD) represents a major global health concern, a body-mind malady of rising prevalence worldwide nowadays. The complex network of mechanisms involved in MDD pathophysiology is subjected to epigenetic changes modulated by microRNAs (miRNAs). Serum free or vesicles loaded miRNAs have starred numerous publications, denoting a key role in cell-cell communication, systematically and in brain structure and neuronal morphogenesis, activity and plasticity. Upregulated or downregulated expression of these signaling molecules may imply the impairment of genes implicated in pathways of MDD etiopathogenesis (neuroinflammation, brain-derived neurotrophic factor (BDNF), neurotransmitters, hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, circadian rhythms...). In addition, these miRNAs could serve as potential biomarkers with diagnostic, prognostic and predictive value, allowing to classify severity of the disease or to make decisions in clinical management. They have been considered as promising therapy targets as well and may interfere with available antidepressant treatments. As epigenetic malleable regulators, we also conclude emphasizing lifestyle interventions with physical activity, mindfulness and diet, opening the door to new clinical management considerations.

Oligonucleotides as therapeutic tools for brain disorders: Focus on major depressive disorder and Parkinson's disease

Remarkable advances in understanding the role of RNA in health and disease have expanded considerably in the last decade. RNA is becoming an increasingly important target for therapeutic intervention; therefore, it is critical to develop strategies for therapeutic modulation of RNA function. Oligonucleotides, including antisense oligonucleotide (ASO), small interfering RNA (siRNA), microRNA mimic (miRNA), and anti-microRNA (antagomir) are perhaps the most direct therapeutic strategies for addressing RNA. Among other mechanisms, most oligonucleotide designs involve the formation of a hybrid with RNA that promotes its degradation by activation of endogenous enzymes such as RNase-H (e.g., ASO) or the RISC complex (e.g. RNA interference - RNAi for siRNA and miRNA). However, the use of oligonucleotides for the treatment of brain disorders is seriously compromised by two main limitations: i) how to deliver oligonucleotides to the brain compartment, avoiding the action of peripheral RNAses? and once there, ii) how to target specific neuronal populations? We review the main molecular pathways in major depressive disorder (MDD) and Parkinson's disease (PD), and discuss the challenges associated with the development of novel oligonucleotide therapeutics. We pay special attention to the use of conjugated ligand-oligonucleotide approach in which the oligonucleotide sequence is covalently bound to monoamine transporter inhibitors (e.g. sertraline, reboxetine, indatraline). This strategy allows their selective accumulation in the monoamine neurons of mice and monkeys after their intranasal or intracerebroventricular administration, evoking preclinical changes predictive of a clinical therapeutic action after knocking-down disease-related genes. In addition, recent advances in oligonucleotide therapeutic clinical trials are also reviewed.

Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases?

Serotonin (5-HT) is one of the fundamental neurotransmitters that contribute to the information essential for an organism's normal, physiological function. Serotonin acts centrally and systemically. The 5-HT_1A receptor is the most widespread serotonin receptor, and participates in many brain-related disorders, including anxiety, depression, and cognitive impairments. The 5-HT_1A receptor can activate several different biochemical pathways and signals through both G protein-dependent and G protein-independent pathways. Preclinical experiments indicate that distinct signaling pathways in specific brain regions may be crucial for antidepressant-like, anxiolytic-like, and procognitive responses. Therefore, the development of new ligands that selectively target a particular signaling pathway(s) could open new possibilities for more effective and safer pharmacotherapy. This review discusses the current state of preclinical studies focusing on the concept of functional selectivity (biased agonism) regarding the 5-HT_1A receptor and its role in antidepressant-like, anxiolytic-like, and procognitive regulation. Such work highlights not only the differential effects of targeted autoreceptors, vs. heteroreceptors, but also the importance of targeting specific downstream intracellular signaling processes, thereby enhancing favorable over unfavorable signaling activation.

Effect of chronic unpredictable mild stress on the expression profile of serotonin receptors in rats and mice: a meta-analysis

Chronic-stress-induced depression is recognized as a widespread public health concern. Selective serotonin reuptake inhibitors (SSRIs) have been the most common treatment for this illness. However, the role of 5-hydroxytryptamine (5-HT) receptor subtypes in stress-induced depression remains unclear. Evidence from Animal studies has reported a variety of results regarding the effects of chronic unpredictable mild stress (CUMS) on serotonin signaling pathways and 5-HT receptor subtypes. This divergence may rely on differences in protocols, methods, and studied pathways. Thus, the aim of this systematic review was to weigh the currently available findings regarding serotonin receptor changes in animal models of CUMS. Overall, our meta-analysis results showed the association of altered expression of 5-HT_1A receptors in the frontal cortex and 5-HT_2A receptors both in the whole cortex and the hypothalamus of rats following CUMS. Moreover, by using a qualitative-structured analysis and the application of risk-of-bias tools, we identified possible sources of data variation between the studied literature, which should be taken into account in future animal studies of chronic-stress induced depression.

[18F]MPPF and [18F]FDG μPET imaging in rats: impact of transport and restraint stress

Background

Stress exposure can significantly affect serotonergic signaling with a particular impact on 5-HT_1A receptor expression. Positron emission tomography (PET) provides opportunities for molecular imaging of alterations in 5-HT_1A receptor binding following stress exposure. Considering the possible role of 5-HT_1A receptors in stress coping mechanisms, respective imaging approaches are of particular interest.

Material and methods

For twelve consecutive days, Sprague Dawley rats were exposed to daily transport with a 1 h stay in a laboratory or daily transport plus 1 h restraint in a narrow tube. Following, animals were subjected to μPET imaging with 2′-methoxyphenyl-(N-2′-pyridinyl)-p-[¹⁸F]fluoro-benzamidoethylpiperazine ([¹⁸F]MPPF) and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG). Behavioral and biochemical parameters were analyzed to obtain additional information.

Results

In rats with repeated transport, hippocampal [¹⁸F]MPPF binding exceeded that in the naive group, while no difference in [¹⁸F]FDG uptake was detected between the groups. A transient decline in body weight was observed in rats with transport or combined transport and restraint. Thereby, body weight development correlated with [¹⁸F]MPPF binding.

Conclusions

Mild-to-moderate stress associated with daily transport and exposure to a laboratory environment can trigger significant alterations in hippocampal binding of the 5-HT_1A receptor ligand [¹⁸F]MPPF. This finding indicates that utmost care is necessary to control and report transport and associated handling procedures for animals used in μPET studies analyzing the serotonergic system in order to enhance the robustness of conclusions and allow replicability of findings. In view of earlier studies indicating that an increase in hippocampal 5-HT_1A receptor expression may be associated with a resilience to stress, it would be of interest to further evaluate 5-HT_1A receptor imaging approaches as a candidate biomarker for the vulnerability to stress.

Early Life Stress Induced DNA Methylation of Monoamine Oxidases Leads to Depressive-Like Behavior

Major depressive disorder (MDD) is coming to be the regarded as one of the leading causes for human disabilities. Due to its complicated pathological process, the etiology is still unclear and the treatment is still targeting at the monoamine neurotransmitters. Early life stress has been known as a major cause for MDD, but how early life stress affects adult monoaminergic activity is not clear either. Recently, DNA methylation is considered to be the key mechanism of epigenetics and might play a role in early life stress induced mental illness. DNA methylation is an enzymatic covalent modification of DNA, has been one of the main epigenetic mechanisms investigated. The metabolic enzyme for the monoamine neurotransmitters, monoamine oxidases A/B (MAO A/MAO B) are the prime candidates for the investigation into the role of DNA methylation in mental disorders. In this review, we will review recent advances about the structure and physiological function of monoamine oxidases (MAO), brief narrative other factors include stress induced changes, early life stress, perinatal depression (PD) relationship with other epigenetic changes, such as DNA methylation, microRNA (miRNA). This review will shed light on the epigenetic changes involved in MDD, which may provide potential targets for future therapeutics in depression pathogenesis.

PBMCs to Stress-Associated miR-18a-5p and miR-22-3p Ratios as New Indicators of Metabolic Syndrome

Purpose

Metabolic syndrome (MetS) is associated with chronic stress. miR-18a-5p and miR-22-3p are two miRNAs which can target the glucocorticoid receptor. This study looked at the changes in metabolic parameters and the predictive value of the peripheral blood mononuclear cells (PBMCs) to stress-associated miRNA ratios as new indicators in subjects with and without MetS in southern China. Patients and Methods. There were 81 participants (39 with MetS and 42 without MetS) in this cross-sectional study. The potential miRNAs were filtrated in the GEO database. The expression of miR-18a-5p and miR-22-3p in PBMCs was evaluated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The risk of miRNA and PBMCs to stress-associated miRNA ratios contributing to the presence of MetS was estimated by univariate and multivariate logistic regression models. The area under the receiver operating characteristic curve (AUC) was used to evaluate diagnostic accuracy.

Results

MetS was positively correlated with cortisol, IL-6, lymphocyte to miR-18a-5p ratio (LT18R), lymphocyte to miR-22-3p ratio (LT22R), monocyte to miR-18a-5p ratio (MT18R), monocyte to miR-22-3p ratio (MT22R), PBMCs to miR-18a-5p ratio (PT18R), and PBMCs to miR-22-3p ratio (PT22R) and negatively associated with the expression levels of miR-18a-5p and miR-22-3p (P < 0.05). In addition, PT18R (odds ratio: 0.894; 95% CI: 0.823-0.966; P < 0.001) and PT22R (odds ratio: 0.809; 95% CI: 0.717-0.900; P < 0.001) were independent predictors of MetS, respectively. A receiver operating characteristic (ROC) curve analysis was performed to assess the value of the PT18R-PT22R (PMR) panel (odds ratio: 0.905; 95% CI: 0.838-0.971; P < 0.001) for predicting MetS. The area under the curve yielded a cut-off value of 0.608, with sensitivity of 74.4% and specificity of 95.2% (P < 0.001).

Conclusion

In summary, miR-18a-5p and miR-22-3p in PBMCs may be important biomarkers of stress reaction and may play a role in vulnerability to MetS. Besides, the inflammatory cells to the two miRNA ratios demonstrated high accuracy in the diagnosis of MetS.