The miRNome of bipolar disorder

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Progress and Implications from Genetic Studies of Bipolar Disorder

With the advancements in gene sequencing technologies, including genome-wide association studies, polygenetic risk scores, and high-throughput sequencing, there has been a tremendous advantage in mapping a detailed blueprint for the genetic model of bipolar disorder (BD). To date, intriguing genetic clues have been identified to explain the development of BD, as well as the genetic association that might be applied for the development of susceptibility prediction and pharmacogenetic intervention. Risk genes of BD, such as CACNA1C, ANK3, TRANK1, and CLOCK, have been found to be involved in various pathophysiological processes correlated with BD. Although the specific roles of these genes have yet to be determined, genetic research on BD will help improve the prevention, therapeutics, and prognosis in clinical practice. The latest preclinical and clinical studies, and reviews of the genetics of BD, are analyzed in this review, aiming to summarize the progress in this intriguing field and to provide perspectives for individualized, precise, and effective clinical practice.

Role of FKBP5 and its genetic mutations in stress-induced psychiatric disorders: an opportunity for drug discovery

Stress-induced mental health disorders are affecting many people around the world. However, effective drug therapy for curing psychiatric diseases does not occur sufficiently. Many neurotransmitters, hormones, and mechanisms are essential in regulating the body's stress response. One of the most critical components of the stress response system is the hypothalamus-pituitary-adrenal (HPA) axis. The FKBP prolyl isomerase 51 (FKBP51) protein is one of the main negative regulators of the HPA axis. FKBP51 negatively regulates the cortisol effects (the end product of the HPA axis) by inhibiting the interaction between glucocorticoid receptors (GRs) and cortisol, causing reduced transcription of downstream cortisol molecules. By regulating cortisol effects, the FKBP51 protein can indirectly regulate the sensitivity of the HPA axis to stressors. Previous studies have indicated the influence of FKBP5 gene mutations and epigenetic changes in different psychiatric diseases and drug responses and recommended the FKBP51 protein as a drug target and a biomarker for psychological disorders. In this review, we attempted to discuss the effects of the FKBP5 gene, its mutations on different psychiatric diseases, and drugs affecting the FKBP5 gene.

Identification and characterization of noncoding RNAs-associated competing endogenous RNA networks in major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a common and serious mental illness. Many novel genes in MDD have been characterized by high-throughput methods such as microarrays or sequencing. Recently, noncoding RNAs (ncRNAs) were suggested to be involved in the complicated environmental-genetic regulatory network of MDD occurrence; however, the interplay among RNA species, including protein-coding RNAs and ncRNAs, in MDD remains unclear.

AIM

To investigate the RNA expression datasets downloaded from a public database and construct a network based on differentially expressed long noncoding RNA (lncRNAs), microRNAs (miRNAs), and mRNAs between MDD and controls.

METHODS

Gene expression data were searched in NCBI Gene Expression Omnibus using the search term “major depressive disorder.” Six array datasets from humans were related to the search term: GSE19738, GSE32280, GSE38206, GSE52790, GSE76826, and GSE81152. These datasets were processed for initial assessment and subjected to quality control and differential expression analysis. Differentially expressed lncRNAs, miRNAs, and mRNAs were determined, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses were performed, and protein-protein interaction network was generated. The results were analyzed for their association with MDD.

RESULTS

After analysis, 3 miRNAs, 12 lncRNAs, and 33 mRNAs were identified in the competing endogenous RNA network. Two of these miRNAs were earlier shown to be involved in psychiatric disorders, and differentially expressed mRNAs were found to be highly enriched in pathways related to neurogenesis and neuroplasticity as per Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. The expression of hub gene fatty acid 2-hydroxylase was enriched, and the encoded protein was found to be involved in myelin formation, indicating that neurological development and signal transduction are involved in MDD pathogenesis.

CONCLUSION

The present study presents candidate ncRNAs involved in the neurogenesis and neuroplasticity pathways related to MDD.

Genomic regulatory sequences in the pathogenesis of bipolar disorder

The lifetime prevalence of bipolar disorder is estimated to be about 2%. Epigenetics defines regulatory mechanisms that determine relatively stable patterns of gene expression by controlling all key steps, from DNA to messenger RNA to protein. This Mini Review highlights recent discoveries of modified epigenetic control resulting from genetic variants associated with bipolar disorder in genome-wide association studies. The revealed epigenetic abnormalities implicate gene transcription and post-transcriptional regulation. In the light of these discoveries, the Mini Review focuses on the genes PACS1, MCHR1, DCLK3, HAPLN4, LMAN2L, TMEM258, GNL3, LRRC57, CACNA1C, CACNA1D, and NOVA2 and their potential biological role in the pathogenesis of bipolar disorder. Molecular mechanisms under control of these genes do not translate into a unified picture and substantially more research is needed to fill the gaps in knowledge and to solve current limitations in prognosis and treatment of bipolar disorder. In conclusion, the genetic and functional studies confirm the complex nature of bipolar disorder and indicate future research directions to explore possible targeted treatment options, eventually working toward a personalized approach.

Decreased miR-15b-5p/miR-155-5p levels and increased miR-134-5p/miR-652-3p levels among BD patients under lithium treatment

BACKGROUND

There is an increasing interest about the role of miRNAs in the pathogenesis of bipolar disorder (BD). In this study, we aimed to examine the role of miRNAs as potential diagnostic and clinical biomarkers in BD.

METHODS

Fifteen miRNAs in plasmas obtained from BD patients (n = 66) and from the healthy control group (n = 66) were analyzed by a qPCR test. Clinical variables including lithium treatment response were assessed with various test batteries. The correlation of the miRNA levels with the clinical variables and scale scores was examined. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed using the DIANA-miRPath v.3.0 software to identify the possible target genes.

RESULTS

The miR-132, miR-134, miR-152, miR-607, miR-633, and miR-652 levels were significantly increased, whereas the miR-15b and miR-155 levels were found to be significantly decreased in the patient group compared to the controls. The miR-15b-5p and miR-155-5p levels and increases in the miR-134-5p and miR-652-3p levels were calculated to have 83.3 % sensitivity and 78.8 % specificity in determining the risk of BD. miR-155-5p was associated with the disease burden and severity. Fatty acid biosynthesis and metabolism, viral carcinogenesis, the EBV infection, and extracellular matrix and adhesion pathways were highlighted as target pathways.

CONCLUSION

We can conclude that miRNAs may play a role in the pathophysiology of BD through various biological pathways and that miRNAs may be used as a screening test to distinguish bipolar patients from healthy controls. Our findings will provide a basis for long-term follow-up studies with larger samples.

Transcriptomics and miRNomics data integration in lymphoblastoid cells highlights the key role of immune-related functions in lithium treatment response in Bipolar disorder

BACKGROUND

Bipolar Disorder (BD) is a complex mental disease characterized by recurrent episodes of mania and depression. Lithium (Li) represents the mainstay of BD pharmacotherapy, despite the narrow therapeutic index and the high variability in treatment response. However, although several studies have been conducted, the molecular mechanisms underlying Li therapeutic effects remain unclear.

METHODS

In order to identify molecular signatures and biological pathways associated with Li treatment response, we conducted transcriptome and miRNome microarray analyses on lymphoblastoid cell lines (LCLs) from 20 patients diagnosed with BD classified as Li responders (n = 11) or non-responders (n = 9).

RESULTS

We found 335 mRNAs and 77 microRNAs (miRNAs) significantly modulated in BD responders versus non-responders. Interestingly, pathway and network analyses on these differentially expressed molecules suggested a modulatory effect of Li on several immune-related functions. Indeed, among the functional molecular nodes, we found NF-κB and TNF. Moreover, networks related to these molecules resulted overall inhibited in BD responder patients, suggesting anti-inflammatory properties of Li. From the integrative analysis between transcriptomics and miRNomics data carried out using miRComb R package on the same samples from patients diagnosed with BD, we found 97 significantly and negatively correlated mRNA-miRNA pairs, mainly involved in inflammatory/immune response.

CONCLUSIONS

Our results highlight that Li exerts modulatory effects on immune-related functions and that epigenetic mechanisms, especially miRNAs, can influence the modulation of different genes and pathways involved in Li response. Moreover, our data suggest the potentiality to integrate data coming from different high-throughput approaches as a tool to prioritize genes and pathways.

Oxidative Stress and Its Modulation by Ladostigil Alter the Expression of Abundant Long Non-Coding RNAs in SH-SY5Y Cells

Neurodegenerative disorders, brain injury, and the decline in cognitive function with aging are accompanied by a reduced capacity of cells in the brain to cope with oxidative stress and inflammation. In this study, we focused on the response to oxidative stress in SH-SY5Y, a human neuroblastoma cell line. We monitored the viability of the cells in the presence of oxidative stress. Such stress was induced by hydrogen peroxide or by Sin1 (3-morpholinosydnonimine) that generates reactive oxygen and nitrogen species (ROS and RNS). Both stressors caused significant cell death. Our results from the RNA-seq experiments show that SH-SY5Y cells treated with Sin1 for 24 h resulted in 94 differently expressed long non-coding RNAs (lncRNAs), including many abundant ones. Among the abundant lncRNAs that were upregulated by exposing the cells to Sin1 were those implicated in redox homeostasis, energy metabolism, and neurodegenerative diseases (e.g., MALAT1, MIAT, GABPB1-AS1, NEAT1, MIAT, GABPB1-AS1, and HAND2-AS1). Another group of abundant lncRNAs that were significantly altered under oxidative stress included cancer-related SNHG family members. We tested the impact of ladostigil, a bifunctional reagent with antioxidant and anti-inflammatory properties, on the lncRNA expression levels. Ladostigil was previously shown to enhance learning and memory in the brains of elderly rats. In SH-SY5Y cells, several lncRNAs involved in transcription regulation and the chromatin structure were significantly induced by ladostigil. We anticipate that these poorly studied lncRNAs may act as enhancers (eRNA), regulating transcription and splicing, and in competition for miRNA binding (ceRNA). We found that the induction of abundant lncRNAs, such as MALAT1, NEAT-1, MIAT, and SHNG12, by the Sin1 oxidative stress paradigm specifies only the undifferentiated cell state. We conclude that a global alteration in the lncRNA profiles upon stress in SH-SY5Y may shift cell homeostasis and is an attractive in vitro system to characterize drugs that impact the redox state of the cells and their viability.

MicroRNAs, Stem Cells in Bipolar Disorder, and Lithium Therapeutic Approach

Bipolar disorder (BD) is a severe, chronic, and disabling neuropsychiatric disorder characterized by recurrent mood disturbances (mania/hypomania and depression, with or without mixed features) and a constellation of cognitive, psychomotor, autonomic, and endocrine abnormalities. The etiology of BD is multifactorial, including both biological and epigenetic factors. Recently, microRNAs (miRNAs), a class of epigenetic regulators of gene expression playing a central role in brain development and plasticity, have been related to several neuropsychiatric disorders, including BD. Moreover, an alteration in the number/distribution and differentiation potential of neural stem cells has also been described, significantly affecting brain homeostasis and neuroplasticity. This review aimed to evaluate the most reliable scientific evidence on miRNAs as biomarkers for the diagnosis of BD and assess their implications in response to mood stabilizers, such as lithium. Neural stem cell distribution, regulation, and dysfunction in the etiology of BD are also dissected.

Bipolar‐associated miR ‐499‐5p controls neuroplasticity by downregulating the Cav1.2 subunit CACNB2

Bipolar disorder (BD) is a chronic mood disorder characterized by manic and depressive episodes. Dysregulation of neuroplasticity and calcium homeostasis are frequently observed in BD patients, but the underlying molecular mechanisms are largely unknown. Here, we show that miR‐499‐5p regulates dendritogenesis and cognitive function by downregulating the BD risk gene CACNB2. miR‐499‐5p expression is increased in peripheral blood of BD patients, as well as in the hippocampus of rats which underwent juvenile social isolation. In rat hippocampal neurons, miR‐499‐5p impairs dendritogenesis and reduces surface expression and activity of the L‐type calcium channel Cav1.2. We further identified CACNB2, which encodes a regulatory β‐subunit of Cav1.2, as a direct functional target of miR‐499‐5p in neurons. miR‐499‐5p overexpression in the hippocampus in vivo induces short‐term memory impairments selectively in rats haploinsufficient for the Cav1.2 pore forming subunit Cacna1c. In humans, miR‐499‐5p expression is negatively associated with gray matter volumes of the left superior temporal gyrus, a region implicated in auditory and emotional processing. We propose that stress‐induced miR‐499‐5p overexpression contributes to dendritic impairments, deregulated calcium homeostasis, and neurocognitive dysfunction in BD.

Circulating miRNAs as Potential Biomarkers for Patient Stratification in Bipolar Disorder: A Combined Review and Data Mining Approach

Bipolar disorder is a debilitating psychiatric condition that is shaped in a concerted interplay between hereditary and triggering risk factors. Profound depression and mania define the disorder, but high clinical heterogeneity among patients complicates diagnosis as well as pharmacological intervention. Identification of peripheral biomarkers that capture the genomic response to the exposome may thus progress the development of personalized treatment. MicroRNAs (miRNAs) play a prominent role in of post-transcriptional gene regulation in the context of brain development and mental health. They are coordinately modulated by multifarious effectors, and alteration in their expression profile has been reported in a variety of psychiatric conditions. Intriguingly, miRNAs can be released from CNS cells and enter circulatory bio-fluids where they remain remarkably stable. Hence, peripheral circulatory miRNAs may act as bio-indicators for the combination of genetic risk, environmental exposure, and/or treatment response. Here we provide a comprehensive literature search and data mining approach that summarize current experimental evidence supporting the applicability of miRNAs for patient stratification in bipolar disorder.

The molecular pathophysiology of mood disorders: From the analysis of single molecular layers to multi-omic integration

Next-generation sequencing now enables the rapid and affordable production of reliable biological data at multiple molecular levels, collectively referred to as "omics". To maximize the potential for discovery, computational biologists have created and adapted integrative multi-omic analytical methods. When applied to diseases with traceable pathophysiology such as cancer, these new algorithms and statistical approaches have enabled the discovery of clinically relevant molecular mechanisms and biomarkers. In contrast, these methods have been much less applied to the field of molecular psychiatry, although diagnostic and prognostic biomarkers are similarly needed. In the present review, we first briefly summarize main findings from two decades of studies that investigated single molecular processes in relation to mood disorders. Then, we conduct a systematic review of multi-omic strategies that have been proposed and used more recently. We also list databases and types of data available to researchers for future work. Finally, we present the newest methodologies that have been employed for multi-omics integration in other medical fields, and discuss their potential for molecular psychiatry studies.

TINY IN SIZE, BIG IN IMPACT: EXTRACELLULAR VESICLES AS MODULATORS OF MOOD, ANXIETY AND NEURODEVELOPMENTAL DISORDERS

Extracellular Vesicles (EVs) are tiny vesicles used by cells as means of cellular communication, through which the function and state of a given cell can be changed. A body of evidence has suggested that EVs could be culprits in the development and progression of various types of diseases, including neurodegenerative diseases such as Multiple Sclerosis (MS) and Alzheimer's Disease (AD). Unsurprisingly, EVs have also been implicate in mood, anxiety and neurodevelopmental disorders, such as Major Depressive Disorder (MDD), anxiety disorder and Autism-Spectrum Disorder (ASD), respectively. Here, we review the state-of-art regarding the roles of EVs in the aforementioned diseases and focus on the mechanisms by which they can cause and worsen disease. Harnessing the knowledge of EVs is not only important to deliver different cargos to cells in a specific manner to treat these diseases, but also to establish reliable disease biomarkers, which will aid in the early disease diagnosis and treatment, increasing the chance of successful treatment.

Circulating hsa-let-7e-5p and hsa-miR-125a-5p as Possible Biomarkers in the Diagnosis of Major Depression and Bipolar Disorders

Background. Evidence shows that microRNAs (miRNAs) could play a key role in the homeostasis and development of major depressive disorder and bipolar disorder. The present study is aimed at investigating the changes in circulating miRNA expression profiles in a plasma of patients suffering from major depressive disorder (MDD) and bipolar disorder (BD) to distinguish and evaluate these molecules as biomarkers for mood disorders. Methods. A study enrolled a total of 184 subjects: 74 controls, 84 MDD patients, and 26 BD patients. Small RNA sequencing revealed 11 deregulated circulating miRNAs in MDD and BD plasma, of which expression of 5, hsa-miR-139-3p, miRNAs hsa-let-7e-5p, hsa-let-7f-5p, hsa-miR-125a-5p, and hsa-miR-483-5p, were further verified using qPCR. miRNA gene expression data was evaluated alongside the data from clinical assessment questionnaires. Results. hsa-let-7e-5p and hsa-miR-125a-5p were both confirmed upregulated: 0.75-fold and 0.25-fold, respectively, in the MDD group as well as 1.36-fold and 0.68-fold in the BD group. Receiver operating curve (ROC) analysis showed mediocre diagnostic sensitivity and specificity of both hsa-let-7e-5p and hsa-miR-125a-5p with approximate area under the curve (AOC) of 0.66. ROC analysis of combined miRNA and clinical assessment data showed that hsa-let-7e-5p and hsa-miR-125a-5p testing could improve MDD and BD diagnostic accuracy by approximately 10%. Conclusions. Circulating hsa-let-7e-5 and hsa-miR-125a-5p could serve as additional peripheral biomarkers for mood disorders; however, suicidal ideation remains the major diagnostic factor for MDD and BD.

miR-323a regulates ERBB4 and is involved in depression

Major depressive disorder (MDD) is a complex and debilitating illness whose etiology remains unclear. Small RNA molecules, such as micro RNAs (miRNAs) have been implicated in MDD, where they display differential expression in the brain and the periphery. In this study, we quantified miRNA expression by small RNA sequencing in the anterior cingulate cortex and habenula of individuals with MDD and psychiatrically-healthy controls. Thirty-two miRNAs showed significantly correlated expression between the two regions (False Discovery Rate < 0.05), of which four, miR-204-5p, miR-320b, miR-323a-3p, and miR-331-3p, displayed upregulated expression in MDD. We assessed the expression of predicted target genes of differentially expressed miRNAs in the brain, and found that the expression of erb-b2 receptor tyrosine kinase 4 (ERBB4), a gene encoding a neuregulin receptor, was downregulated in both regions, and was influenced by miR-323a-3p in vitro. Finally, we assessed the effects of manipulating miRNA expression in the mouse ACC on anxiety- and depressive-like behaviors. Mice in which miR-323-3p was overexpressed or knocked-down displayed increased and decreased emotionality, respectively. Additionally, these mice displayed significantly downregulated and upregulated expression of Erbb4, respectively. Overall, our findings indicate the importance of brain miRNAs in the pathology of MDD, and emphasize the involvement of miR-323a-3p and ERBB4 in this phenotype. Future studies further characterizing miR-323a-3p and neuregulin signaling in depression are warranted.

Genetic variants in miRNAs differentially expressed during brain development and their relevance to psychiatric disorders susceptibility

OBJECTIVES

MicroRNAs (miRNAs) play an important regulatory role in the expression of genes involved in brain functions during development. Genetic variants in miRNA genes may impact their regulatory function and lead to psychiatric disorders. To evaluate the role of genetic variants in genes of miRNAs differentially expressed during neurodevelopment on autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD), schizophrenia (SCZ), and major depressive disorder (MDD).

METHODS

The miRNAs were identified in the literature. Summary statistics from the most recent genome-wide association studies to date were used to evaluate the association between the selected polymorphisms and each disorder in a look-up approach. In a global analysis, we compared the standardised risk effect of variants in neurodevelopment-related miRNAs with those in the remaining miRNAs from miRBase.

RESULTS

The global analysis showed that variants in neurodevelopment-related miRNAs had higher risk effects compared to the other miRNAs for SCZ (p = 0.010) and ADHD (p = 0.001). MIR33B, MIR29B2, MIR29C, MIR137, and MIR135A1 were significantly associated with SCZ, while 55.9% of the miRNAs were at least nominally associated with one or more psychiatric disorders (p < 0.05).

CONCLUSIONS

Genetic variants in neurodevelopment-related miRNAs play an important role in the genetic susceptibility of psychiatric disorders, mainly SCZ and ADHD.

The "missing heritability"-Problem in psychiatry: Is the interaction of genetics, epigenetics and transposable elements a potential solution?

Psychiatric disorders exhibit an enormous burden on the health care systems worldwide accounting for around one-third of years lost due to disability among adults. Their etiology is largely unknown and diagnostic classification is based on symptomatology and course of illness and not on objective biomarkers. Most psychiatric disorders are moderately to highly heritable. However, it is still unknown what mechanisms may explain the discrepancy between heritability estimates and the present data from genetic analysis. In addition to genetic differences also epigenetic modifications are considered as potentially relevant in the transfer of susceptibility to psychiatric diseases. Though, whether or not epigenetic alterations can be inherited for many generations is highly controversial. In the present article, we will critically summarize both the genetic findings and the results from epigenetic analyses, including also those of noncoding RNAs. We will argue that one possible solution to the "missing heritability" problem in psychiatry is a potential role of retrotransposons, the exploration of which is presently only in its beginnings.

Neurobiology of bipolar disorders: a review of genetic components, signaling pathways, biochemical changes, and neuroimaging findings

Bipolar disorder (BD) is a chronic mental illness characterized by changes in mood that alternate between mania and hypomania or between depression and mixed states, often associated with functional impairment. Although effective pharmacological and non-pharmacological treatments are available, several patients with BD remain symptomatic. The advance in the understanding of the neurobiology underlying BD could help in the identification of new therapeutic targets as well as biomarkers for early detection, prognosis, and response to treatment in BD. In this review, we discuss genetic, epigenetic, molecular, physiological and neuroimaging findings associated with the neurobiology of BD. Despite the advances in the pathophysiological knowledge of BD, the diagnosis and management of the disease are still essentially clinical. Given the complexity of the brain and the close relationship between environmental exposure and brain function, initiatives that incorporate genetic, epigenetic, molecular, physiological, clinical, environmental data, and brain imaging are necessary to produce information that can be translated into prevention and better outcomes for patients with BD.

Long Non-coding RNA TALNEC2 Aggravates Cerebral Ischemia/Reperfusion Injury via Acting as a Competing Endogenous RNAs for miR-650 to Target Apoptotic Peptidase Activating Factor 1

Increasing evidence has indicated that long non-coding RNAs (lncRNAs) play a vital role for adjusting RNA transcripts as competing endogenous RNAs (ceRNAs) for microRNAs (miRNAs). The present study was intended to explore the probable regulation of lncRNA TALNEC2 in ischemic stroke. In this study, we measured the up-regulation of TALNEC2 and down-regulation of miR-650 in mice brains after cerebral ischemia/reperfusion (I/R) operation and in cultured neuroblastoma cells of neuro-2A (N2a) treated with oxygen glucose deprivation/reoxygenation (OGD/R). Then we verified the common predicted binding sites of miR-650 in TALNEC2 and 3'-UTR of apoptotic peptidase activating factor 1 (APAF1), a critical regulator in ischemic neuronal death, with bioinformatics. Overexpression of miR-650 reduced N2a cell apoptosis induced by OGD/R. MiR-650 was confirmed to be a directly target of APAF1 by luciferase reporter assay. It was found that TALNEC2 played a critical role as a ceRNA for miR-650 and bound directly to miR-650 to mediate the APAF1. In result, overexpression of TALNEC2 antagonized the inhibition impact of miR-650 on APAF1 expression and N2a cell apoptosis induced by OGD/R, while TALNEC2 knockdown aggravated the impact. Furthermore, TALNEC2 knockdown reversed brain injury and neurological deficits induced by I/R in vivo. In conclusion, we verified a TALNEC2/miR-650/APAF1 signaling pathway as a key mechanism monitoring cerebral I/R injury.

A miRNome analysis of drug-free manic psychotic bipolar patients versus healthy controls

The lifetime presence of psychotic symptoms is associated with more clinical severity, poorer outcome and biological changes in patients affected by bipolar disorder (BD). Epigenetic mechanisms have been evoked to explain the onset of psychotic symptoms in BD as well as the associated biological changes. The main objective of the present study was to evaluate the expression profiles of circulating microRNAs (miRNAs) in drug-free manic psychotic bipolar patients versus healthy controls (HC), to identify possible non-invasive molecular markers of the disorder. 15 drug-free manic psychotic bipolar patients and 9 HC were enrolled and 800 miRNAs expression profile was measured by Nanostring nCounter technology on plasma samples and validated through qPCR. Overall, twelve miRNAs showed a significantly altered expression between the two groups (p < 0.05). Functional annotation of predicted miRNAs targets by MultiMIR R tool showed repression in bipolar patients of genes with a role in neurodevelopment and neurogenesis, and upregulation of genes involved in metabolism regulation. We identified a signature of circulating miRNA characteristic of manic psychotic bipolar patients, suggesting a possible role in neurodevelopment and metabolic processes regulation.

MicroRNA Alterations in Induced Pluripotent Stem Cell-Derived Neurons from Bipolar Disorder Patients: Pathways Involved in Neuronal Differentiation, Axon Guidance, and Plasticity

Bipolar disorder (BP) is a complex psychiatric condition characterized by severe fluctuations in mood for which underlying pathological mechanisms remain unclear. Family and twin studies have identified a hereditary component to the disorder, but a single causative gene (or set of genes) has not been identified. MicroRNAs (miRNAs) are small, noncoding RNAs ∼20 nucleotides in length, that are responsible for the posttranslational regulation of multiple genes. They have been shown to play important roles in neural development as well as in the adult brain, and several miRNAs have been reported to be dysregulated in postmortem brain tissue isolated from bipolar patients. Because there are no viable cellular models to study BP, we have taken advantage of the recent discovery that somatic cells can be reprogrammed to pluripotency then directed to form the full complement of neural cells. Analysis of RNAs extracted from Control and BP patient-derived neurons identified 58 miRNAs that were differentially expressed between the two groups. Using quantitative polymerase chain reaction we validated six miRNAs that were elevated and two miRNAs that were expressed at lower levels in BP-derived neurons. Analysis of the targets of the miRNAs indicate that they may regulate a number of cellular pathways, including axon guidance, Mapk, Ras, Hippo, Neurotrophin, and Wnt signaling. Many are involved in processes previously implicated in BP, such as cell migration, axon guidance, dendrite and synapse development, and function. We have validated targets of several different miRNAs, including AXIN2, BDNF, RELN, and ANK3 as direct targets of differentially expressed miRNAs using luciferase assays. Identification of pathways altered in patient-derived neurons suggests that disruption of these regulatory networks that may contribute to the complex phenotypes in BP.

Integrative Transcriptomics Reveals Sexually Dimorphic Control of the Cholinergic/Neurokine Interface in Schizophrenia and Bipolar Disorder

RNA sequencing analyses are often limited to identifying lowest p value transcripts, which does not address polygenic phenomena. To overcome this limitation, we developed an integrative approach that combines large-scale transcriptomic meta-analysis of patient brain tissues with single-cell sequencing data of CNS neurons, short RNA sequencing of human male- and female-originating cell lines, and connectomics of transcription factor and microRNA interactions with perturbed transcripts. We used this pipeline to analyze cortical transcripts of schizophrenia and bipolar disorder patients. Although these pathologies show massive transcriptional parallels, their clinically well-known sexual dimorphisms remain unexplained. Our method reveals the differences between afflicted men and women and identifies disease-affected pathways of cholinergic transmission and gp130-family neurokine controllers of immune function interlinked by microRNAs. This approach may open additional perspectives for seeking biomarkers and therapeutic targets in other transmitter systems and diseases.

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Single-cell transcriptomes reveal a unique profile of cortical cholinergic neurons

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Female- and male-derived cells show distinct neurokine-induced miRNA responses

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Differentially enriched microRNA families constitute a self-organizing network

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Integrative analysis identifies mir-10/mir-199 regulators of cholinergic function

Exploiting Circulating MicroRNAs as Biomarkers in Psychiatric Disorders

Non-invasive peripheral biomarkers play a significant role in both disease diagnosis and progression. In the past few years, microRNA (miRNA) expression changes in circulating peripheral tissues have been found to be correlative with changes in neuronal tissues from patients with neuropsychiatric disorders. This is a notable quality of a biomolecule to be considered as a biomarker for both prognosis and diagnosis of disease. miRNAs, members of the small non-coding RNA family, have recently gained significant attention due to their ability to epigenetically influence almost every aspect of brain functioning. Empirical evidence suggests that miRNA-associated changes in the brain are often translated into behavioral changes. Current clinical understanding further implicates their role in the management of major psychiatric conditions, including major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ). This review aims to critically evaluate the potential advantages and disadvantages of miRNAs as diagnostic/prognostic biomarkers in psychiatric disorders as well as in treatment response.

Clinical, genetic, and brain imaging predictors of risk for bipolar disorder in high-risk individuals

Introduction: Early detection and intervention in bipolar disorder (BD) might reduce illness severity, slow its progression, and, in specific cases, even ward off the full-blown disorder. Therefore, identifying at-risk individuals and targeting them promptly before the illness onset is of the utmost importance. In the last decades, there has been a significant effort aimed at identifying genetic and molecular factors able to modulate risk and pharmacological outcomes.Areas covered: We performed a narrative review of articles aimed at identifying clinical, genetics, molecular, and brain imaging markers of BD specifically focusing on samples of individuals at high-risk for BD. Special emphasis was put on studies applying an integrative design, e.g. studies combining different markers such as genetic and brain imaging.Expert opinion: Findings from studies in risk individuals are still too sparse to allow drawing definite conclusions. However, the high potentiality of longitudinal studies in individuals considered at risk to develop BD supports the need for more efforts. Future investigations should focus on more homogeneous subpopulations and evaluate the cross-linking between clinical, genetic, and brain morphostructural/functional neuroimaging characteristics as predictors of risk for BD.

Neurodevelopmental pathways in bipolar disorder

Aberrations in neurodevelopmental trajectories have been implicated in the neurobiology of several mental disorders and evidence indicates a pathophysiological and genetic overlap of schizophrenia and bipolar disorder (BD). In this narrative review, we summarize findings related to developmental and perinatal factors as well as epidemiological, clinical, neuropsychological, brain imaging, postmortem brain and genomic studies that provide evidence for a putative neurodevelopmental pathogenesis and etiology of BD. Overall, aberrations in neurodevelopmental pathways have been more consistently implicated in the pathophysiology of schizophrenia compared to BD. Nevertheless, an accumulating body of evidence indicates that dysfunctional neurodevelopmental pathways may be implicated in the underlying pathophysiology of at least a subset of individuals with BD particularly those with an early age of illness onset and those exhibiting psychotic symptoms. A heuristic neurodevelopmental model for the pathophysiology of BD based on the findings of this review is proposed. Furthermore, we critically discuss clinical and research implications of this model. Finally, further research directions for this emerging field are provided.

Circulating exosomal microRNAs in bipolar disorder

INTRODUCTION

Emerging evidence suggests central roles of miRNAs in the pathogenesis of bipolar disorder (BD). Exosomes are membrane-bound vesicles acting as "biological cargo carriers" of various types of molecules including microRNAs. In this study, we aimed to investigate circulating exosomal microRNAs as potential diagnostic biomarkers for BD.

METHODS

The exosomes were precipitated from plasma samples of patients with BD (n = 69; 15 depressed, 27 manic, 27 euthymic) and healthy controls (n = 41). Total RNA was extracted from the exosomes and the levels of miRNAs were assayed by qPCR. Dysregulated miRNAs were subjected to Kyoto Encyclopedia of Genes and Genomes" (KEGG) pathway analysis by DIANA-miRPath v3.0 to identify the predicted targets and the related pathways.

RESULTS

Thirteen miRNAs showed significant differences between patients with BD and healthy individuals; among these, MiR-484, -652-3p, -142-3p remained significantly downregulated and miR-185-5p remained significantly upregulated after accounting for multiple comparisons and adjustments for potential confounders. There were no significant alterations among different states of BD. The KEEG analysis of four dysregulated miRNAs highlighted several target pathways including PI3K/Akt signaling, fatty acid biosynthesis/metabolism, extracellular matrix and adhesion pathways.

CONCLUSION

Our findings suggest that dysregulation of miRNAs might be involved in the underlying pathophysiology of BD through several biological pathways; and highlight the importance of the exosomal miRNAs for biomarker research in BD. Further longitudinal studies may clarify the roles of exosomal miRNAs and their targets in the neurobiology of BD.

MicroRNA dysregulation in manic and euthymic patients with bipolar disorder

BACKGROUND

Bipolar disorder (BPD) is a major psychiatric disorder with an unclear pathophysiology. Peripheral blood samples are easily drawn, making them are good candidates for diagnosing diseases. MicroRNAs are small non-coding RNA transcripts that regulate gene expression by binding to the 3'- UTR of mRNAs and directing their degradation. The aim of this study was to use blood plasma to investigate microRNA dysregulations in bipolar manic and euthymic patients.

SUBJECTS AND METHODS

Blood samples were collected from 58 patients with bipolar I disorder (19 manic, 39 euthymic) and 51 healthy controls.

RESULTS

Four microRNAs (miR-29a-3p, p = 0.035; miR-106b-5p, p = 0.014; miR-107, p = 0.011; and miR-125a-3p, p = 0.014) were upregulated in the entire bipolar group, compared to the healthy controls. Seven microRNAs (miR-9-5p, p = 0.032; miR-29a-3p, p = 0.001; miR-106a-5p, p = 0.034; miR-106b-5p, p = 0.003; miR-107, p < 0.001; miR-125a-3p, p = 0.016; and miR-125b-5p, p = 0.004) were more upregulated in bipolar manic patients compared to the healthy controls, and two microRNAs (miR-106a-5p, p = 0.013, and miR-107, p = 0.021) showed statistically significant upregulation in the manic patients compared to the euthymic patients.

CONCLUSIONS

Our results showed greater miRNA dysregulation in the manic patients than in the euthymic patients. Two microRNAs could be more selective for bipolar manic episodes. Future studies should include depressive patients along with euthymic and manic patients.

Gene-Environment Interactions in Major Mental Disorders in the Czech Republic

BACKGROUND

Mental disorders affect about one-third of the human population, are typically chronic and significantly decrease the quality of life. Presently, the treatment of mental illnesses is far from adequate with a substantial proportion of the patients being pharmacoresistant and suffering from relapses. One of the reasons for this complicated situation is that we do not precisely know about the causes of mental disorders, so their treatment cannot be causal. The etiology of a mental disorder is typically based on a combination of molecular (genetic) and environmental factors.

AIM

The aim of the project is to discover the gene-environment interactions (GxE) in a wide spectrum of mental disorders.

METHODS

The design of our study is innovative in the sense that we intend to study large groups of associated mental disorders as a whole instead of in isolation. This would enable us to map out the possible environmental causal factors in detail in relation to their character, magnitude and timing. The project also allows a study of genetics (including epigenetics and microbiomes) as well as the environment simultaneously. We plan on involving three study groups: the first group are patients suffering from schizophrenia or a mood disorder such as major depression, recurrent depressive disorder and bipolar affective disorder; the second group of patients have anxiety disorders; and the third group are healthy volunteers from the general population who are genetically unrelated. All of the study subjects will undergo the following assessments: a psychiatric examination, the identification of stressful life events with the aid of a questionnaire, the examination of their reaction to stress, genetic and epigenetic (microRNA) assessments and the analysis of oral and gut microbiome.

CONCLUSION

We expect that some of the genetic as well as environmental factors in the studied mental disorders are shared, while some others are specific. We also expect that the GxE (gene-environment interaction) in schizophrenic and affective disorders will be different from the GxE in anxiety disorders and that the GxE in the studied mental disorders will differ generally from the GxE in healthy volunteers. Our results can help in the prevention and individualized treatment of a range of mental disorders.

Expression alteration of microRNAs in Nucleus Accumbens is associated with chronic stress and antidepressant treatment in rats

BACKGROUND

Nucleus Accumbens (NAc) is a vital brain region for the process of reward and stress, whereas microRNA plays a crucial role in depression pathology. However, the abnormality of NAc miRNA expression during the stress-induced depression and antidepressant treatment, as well as its biological significance, are still unknown.

METHODS

We performed the small RNA-sequencing in NAc of rats from three groups: control, chronic unpredictable mild stress (CUMS), and CUMS with an antidepressant, Escitalopram. We applied an integrative pipeline for analyzing the miRNA expression alternation in different model groups, including differential expression analysis, co-expression analysis, as well as a subsequent pathway/network analysis to discover both miRNA alteration pattern and its biological significance.

RESULT

A total of 423 miRNAs were included in analysis.18/8 differential expressing (DE) miRNA (adjusted p < 0.05, |log2FC| > 1) were observed in controls Vs. depression/depression Vs. treatment, 2 of which are overlapping. 78% (14/18) of these miRNAs showed opposite trends of alteration in stress and treatment. Two micro RNA, miR-10b-5p and miR-214-3p, appeared to be hubs in the regulation networks and also among the top findings in both differential analyses. Using co-expression analysis, we found a functional module that strongly correlated with stress (R = 0.96, P = 0.003), and another functional module with a moderate correlation with anhedonia (R = 0.89, P = 0.02). We also found that predicted targets of these miRNAs were significantly enriched in the Ras signaling pathway, which is associated with both depression, anhedonia, and antidepressant treatment.

CONCLUSION

Escitalopram treatment can significantly reverse NAc miRNA abnormality induced by chronic stress. However, the novel miRNA alteration that is absent in stress pathology also emerges, which means that antidepressant treatment is unlikely to bring miRNA expression back to the same level as the controls. Also, the Ras-signaling pathway may be involved in explaining the depression disease etiology, the clinical symptom, and treatment response of stress-induced depression.

Genetic Advance in Depressive Disorder

Major depressive disorder (MDD) and bipolar disorder (BPD) are both chronic, severe mood disorder with high misdiagnosis rate, leading to substantial health and economic burdens to patients around the world. There is a high misdiagnosis rate of bipolar depression (BD) just based on symptomology in depressed patients whose previous manic or mixed episodes have not been well recognized. Therefore, it is important for psychiatrists to identify these two major psychiatric disorders. Recently, with the accumulation of clinical sample sizes and the advances of methodology and technology, certain progress in the genetics of major depression and bipolar disorder has been made. This article reviews the candidate genes for MDD and BD, genetic variation loci, chromosome structural variation, new technologies, and new methods.

MicroRNA-34a Acutely Regulates Synaptic Efficacy in the Adult Dentate Gyrus In Vivo

Activity-dependent synaptic plasticity involves rapid regulation of neuronal protein synthesis on a time-scale of minutes. miRNA function in synaptic plasticity and memory formation has been elucidated by stable experimental manipulation of miRNA expression and activity using transgenic approaches and viral vectors. However, the impact of rapid miRNA modulation on synaptic efficacy is unknown. Here, we examined the effect of acute (12 min), intrahippocampal infusion of a miR-34a antagonist (antimiR) on medial perforant path-evoked synaptic transmission in the dentate gyrus of adult anesthetised rats. AntimiR-34a infusion acutely depressed medial perforant path-evoked field excitatory post-synaptic potentials (fEPSPs). The fEPSP decrease was detected within 9 min of infusion, lasted for hours, and was associated with knockdown of antimiR-34a levels. AntimiR-34a-induced synaptic depression was sequence-specific; no changes were elicited by infusion of scrambled or mismatch control. The rapid modulation suggests that a target, or set of targets, is regulated by miR-34a. Western blot analysis of dentate gyrus lysates revealed enhanced expression of Arc, a known miR-34a target, and four novel predicted targets (Ctip2, PKI-1α, TCF4 and Ube2g1). Remarkably, antimiR-34a had no effect when infused during the maintenance phase of long-term potentiation. We conclude that miR-34a regulates basal synaptic efficacy in the adult dentate gyrus in vivo. To our knowledge, these in vivo findings are the first to demonstrate acute (< 9 min) regulation of synaptic efficacy in the adult brain by a miRNA.

Preliminary investigation of peripheral extracellular vesicles' microRNAs in bipolar disorder

BACKGROUND

The search for biomarkers of bipolar disorder (BD), including epigenetic alterations, has heavily relied on peripheral investigations that do not necessarily reflect brain-specific mechanisms. In this study we aimed to assess peripheral extracellular vesicles (EVs)' microRNAs and determine their use as a novel source of biomarkers in BD.

METHODS

We assessed peripheral blood EVs' microRNAs from 20 patients with BD type I and 21 age- and sex-matched healthy controls by microarray, and further explored the predicted biological functions of significantly differentially expressed microRNAs.

RESULTS

Our results identified 33 nominally significant microRNAs (p < 0.05 and fold-change >1.5) altered in BD patients, including miRNAs previously reported to be altered in post-mortem tissues of patients. Pathway analyses identified some brain-relevant mechanisms enriched in these miRNAs, including axon guidance by netrin and the serotonin receptor pathway.

LIMITATIONS

Relatively small sample size, potential confounding effects of mood states, medication use, and comorbidities, analysis of total rather than brain-specific EVs, and lack of validation of significant miRNAs by other methods.

CONCLUSIONS

This study provides important preliminary evidence of the potential use of EVs as a novel source of biomarkers in BD. Overall, our findings of brain-relevant mechanisms in these vesicles suggest their potential use in living patients as a peripheral window to the brain.

Protein Translation and Psychiatric Disorders

Although historically research has focused on transcription as the central governor of protein expression, protein translation is now increasingly being recognized as a major factor for determining protein levels within cells. The central nervous system relies on efficient updating of the protein landscape. Thus, coordinated regulation of mRNA localization, initiation, or termination of translation is essential for proper brain function. In particular, dendritic protein synthesis plays a key role in synaptic plasticity underlying learning and memory as well as cognitive processes. Increasing evidence suggests that impaired mRNA translation is a common feature found in numerous psychiatric disorders. In this review, we describe how malfunction of translation contributes to development of psychiatric diseases, including schizophrenia, major depression, bipolar disorder, and addiction.

The Missing Link: How Exosomes and miRNAs can Help in Bridging Psychiatry and Molecular Biology in the Context of Depression, Bipolar Disorder and Schizophrenia

MicroRNAs (miRNAs) only recently have been recognized as promising molecules for both fundamental and clinical neuroscience. We provide a literature review of miRNA biomarker studies in three most prominent psychiatric disorders (depression, bipolar disorder and schizophrenia) with the particular focus on depression due to its social and healthcare importance. Our search resulted in 191 unique miRNAs across 35 human studies measuring miRNA levels in blood, serum or plasma. 30 miRNAs replicated in more than one study. Most miRNAs targeted neuroplasticity and neurodevelopment pathways. Various limitations do not allow us to make firm conclusions on clinical potential of studied miRNAs. Based on our results we discuss the rationale for future research investigations of exosomal mechanisms to overcome methodological caveats both in studying etiology and pathogenesis, and providing an objective back-up for clinical decisions.

microRNA-34a (miRNA-34a) Mediated Down-Regulation of the Post-synaptic Cytoskeletal Element SHANK3 in Sporadic Alzheimer's Disease (AD)

Integrating a combination of bioinformatics, microRNA microfluidic arrays, ELISA analysis, LED Northern, and transfection-luciferase reporter assay data using human neuronal-glial (HNG) cells in primary culture we have discovered a set of up-regulated microRNAs (miRNAs) linked to a small family of down-regulated messenger RNAs (mRNAs) within the superior temporal lobe neocortex (Brodmann A22) of sporadic Alzheimer's disease (AD) brain. At the level of mRNA abundance, the expression of a significant number of human brain genes found to be down-regulated in sporadic AD neocortex appears to be due to the increased abundance of a several brain-abundant inducible miRNAs. These up-regulated miRNAs—including, prominently, miRNA-34a—have complimentary RNA sequences in the 3′ untranslated-region (3′-UTR) of their target-mRNAs that results in the pathological down-regulation in the expression of important brain genes. An up-regulated microRNA-34a, already implicated in age-related inflammatory-neurodegeneration–appears to down-regulate key mRNA targets involved in synaptogenesis and synaptic-structure, distinguishing neuronal deficits associated with AD neuropathology. One significantly down-regulated post-synaptic element in AD is the proline-rich SH3 and multiple-ankyrin-repeat domain SHANK3 protein. Bioinformatics, microRNA array analysis and SHANK3-mRNA-3′UTR luciferase-reporter assay confirmed the importance of miRNA-34a in the regulation of SHANK3 expression in HNG cells. This paper reports on recent studies of a miRNA-34a-up-regulation coupled to SHANK3 mRNA down-regulation in sporadic AD superior-temporal lobe compared to age-matched controls. These findings further support our hypothesis of an altered miRNA-mRNA coupled signaling network in AD, much of which is supported, and here reviewed, by recently reported experimental-findings in the scientific literature.

Significant increasing of DISC2 long non-coding RNA expression as a potential biomarker in bipolar disorder

Bipolar disorder (BD) is a mental disorder that is often misdiagnosed with ineffective treatment. It has strong genetic component but unknown pathophysiology. Long non-coding RNAs (lncRNAs) have been recently recognized as one of the important genetic factors and are considered as one of the regulatory mechanisms of nervous system. Given that lncRNAs may be diagnostic biomarkers for BD, we aimed to quantify the levels of DISC1 and DISC2 lncRNA transcripts. The levels of DISC1 and DISC2 lncRNA were tested in peripheral blood mononuclear cells (PBMCs) of 50 BD and 50 controls by real-time PCR. In addition, we performed ROC curve analysis as well as correlation analysis between the gene expression and some clinical features of BD cases. Computational analysis of miRNAs binding sites and CpG Islands on DISC1 and DISC2 lncRNA was performed as well. Significant down-regulation of DISC1 and up-regulation of DISC2 were observed in BD cases compared with controls. The areas under the ROC curve (AUC) for DISC1 and DISC2 lncRNA were 0.76 and 0.68 respectively. There was no significant correlation between the levels of mRNA expression in PBMCs of BD patients and clinical features. These data demonstrated that DISC1 and DISC2 lncRNA expression was potentially associated with an increased risk of bipolar disorder and might involve several molecular mechanisms. Our results revealed that the transcript levels of DISC1 and DISC2 lncRNA could be considered as a good putative biomarker for individuals with bipolar disorder.

Biomarkers for bipolar disorder: current status and challenges ahead

INTRODUCTION

Bipolar disorder (BD) is a chronic psychiatric disorder marked by clinical and pathophysiological heterogeneity. There is a high expectation that personalized approaches can improve the management of patients with BD. For that, identification and validation of potential biomarkers are fundamental. Areas covered: This manuscript will critically review the current status of different biomarkers for BD, including peripheral, genetic, neuroimaging, and neurophysiological candidates, discussing the challenges to move the field forward. Expert commentary: There are no lab or complementary tests currently recommended for the diagnosis or management of patients with BD. Panels composed by multiple biomarkers will probably contribute to stratifying patients according to their clinical stage, therapeutic response, and prognosis.

The FKBP51 Glucocorticoid Receptor Co-Chaperone: Regulation, Function, and Implications in Health and Disease

Among the chaperones and co-chaperones regulating the glucocorticoid receptor (GR), FK506 binding protein (FKBP) 51 is the most intensely investigated across different disciplines. This review provides an update on the role of the different co-chaperones of Hsp70 and Hsp90 in the regulation of GR function. The development leading to the focus on FKBP51 is outlined. Further, a survey of the vast literature on the mechanism and function of FKBP51 is provided. This includes its structure and biochemical function, its regulation on different levels—transcription, post-transcription, and post-translation—and its function in signaling pathways. The evidence portraying FKBP51 as a scaffolding protein organizing protein complexes rather than a chaperone contributing to the folding of individual proteins is collated. Finally, FKBP51’s involvement in physiology and disease is outlined, and the promising efforts in developing drugs targeting FKBP51 are discussed.