Selective lentiviral-mediated suppression of microRNA124a in the hippocampus evokes antidepressants-like effects in rats

Hippocampal MicroRNA-124 Enhances Chronic Stress Resilience in Mice

Chronic stress-induced aberrant gene expression in the brain and subsequent dysfunctional neuronal plasticity have been implicated in the etiology and pathophysiology of mood disorders. In this study, we examined whether altered expression of small, regulatory, noncoding microRNAs (miRNAs) contributes to the depression-like behaviors and aberrant neuronal plasticity associated with chronic stress. Mice exposed to chronic ultra-mild stress (CUMS) exhibited increased depression-like behaviors and reduced hippocampal expression of the brain-enriched miRNA-124 (miR-124). Aberrant behaviors and dysregulated miR-124 expression were blocked by chronic treatment with an antidepressant drug. The depression-like behaviors are likely not conferred directly by miR-124 downregulation because neither viral-mediated hippocampal overexpression nor intrahippocampal infusion of an miR-124 inhibitor affected depression-like behaviors in nonstressed mice. However, viral-mediated miR-124 overexpression in hippocampal neurons conferred behavioral resilience to CUMS, whereas inhibition of miR-124 led to greater behavioral susceptibility to a milder stress paradigm. Moreover, we identified histone deacetylase 4 (HDAC4), HDAC5, and glycogen synthase kinase 3β (GSK3β) as targets for miR-124 and found that intrahippocampal infusion of a selective HDAC4/5 inhibitor or GSK3 inhibitor had antidepressant-like actions on behavior. We propose that miR-124-mediated posttranscriptional controls of HDAC4/5 and GSK3β expressions in the hippocampus have pivotal roles in susceptibility/resilience to chronic stress.

SIGNIFICANCE STATEMENT

Depressive disorders are a major public health concern worldwide. Although a clear understanding of the etiology of depression is still lacking, chronic stress-elicited aberrant neuronal plasticity has been implicated in the pathophysiology of depression. We show that the hippocampal expression of microRNA-124 (miR-124), an endogenous small, noncoding RNA that represses gene expression posttranscriptionally, controls resilience/susceptibility to chronic stress-induced depression-like behaviors. These effects on depression-like behaviors may be mediated through regulation of the mRNA or protein expression levels of histone deacetylases HDAC4/5 and glycogen synthase kinase 3β, all highly conserved miR-124 targets. Moreover, miR-124 contributes to stress-induced dendritic hypotrophy and reduced spine density of dentate gyrus granule neurons. Modulation of hippocampal miR-124 pathways may have potential antidepressant effects.

The recent progress in animal models of depression

Major depression disorder (MDD) is a debilitating mental illness with significant morbidity and mortality. Despite the growing number of studies that have emerged, the precise underlying mechanisms of MDD remain unknown. When studying MDD, tissue samples like peripheral blood or post-mortem brain samples are used to elucidate underlying mechanisms. Unfortunately, there are many uncontrollable factors with such samples such as medication history, age, time after death before post-mortem tissue was collected, age, sex, race, and living conditions. Although these factors are critical, they introduce confounding variables that can influence the outcome profoundly. In this regard, animal models provide a crucial approach to examine neural circuitry and molecular and cellular pathways in a controlled environment. Further, manipulations with pharmacological agents and gene editing are accepted methods of studying depression in animal models, which is impossible to employ in human patient studies. Here, we have reviewed the most widely used animal models of depression and delineated the salient features of each model in terms of behavioral and neurobiological outcomes. We have also illustrated the current challenges in using these models and have suggested strategies to delineate the underlying mechanism associated with vulnerability or resilience to developing depression.

Hippocampal BDNF overexpression or microR124a silencing reduces anxiety- and autism-like behaviors in rats

MicroRNA124a (miR124a) has emerged recently as a key player for multiple neuropsychiatric disorders including depression, anxiety, alcoholism, and cocaine addiction. Although we have previously reported that miR124a and its target the brain-derived neutrophic factor (BDNF) play an important role in autism-like behaviors, the molecular and behavioral dysfunctions remain unknown. The aim of this study was to understand the effects of sustained decreases in miR124a and increases of BDNF in the dentate gyrus (DG) on neonatal isolation-induced anxiety-and autism like behaviors in rats. Here we report that lentiviral-mediated silencing of miR124a in the adult DG attenuated neonatal isolation-induced anxiety-like behavior in the elevated plus maze (EPM) and open-field (OF) tests. Also, miR124a silencing decreased autism-like phenotype in the marble burying test (MBT), self-grooming (SG), and social interaction tests. Pearson's correlations demonstrated that high levels of BDNF, a direct target of miR124a, were negatively correlated with miR124a expression. Interestingly, viral-mediated BDNF overexpression in the DG also reversed the neonatal isolation-induced anxiety-and autism like phenotypes. Collectively, these findings suggest that miR124a, through its target BDNF, may influence neonatal isolation-induced anxiety-and autism like behaviors. In conclusion, these results do support the hypothesis that miR124a in discrete hippocampal areas contributes to anxiety- and autism-like behaviors and may be involved in the neuroadaptations underlying the development of autism spectrum disorders as a persistent and lasting condition, and therefore provide a clearer mechanistic framework for understanding the physiopathology of such psychiatric illnesses.

Identification of MicroRNA-124-3p as a Putative Epigenetic Signature of Major Depressive Disorder

Major depressive disorder (MDD) is predicted to be the second leading cause of global disease burden by 2030. A large number of MDD patients do not respond to the currently available medication because of its poorly understood etiology. Recently, studies of microRNAs (miRNAs), which act as a molecular switch of gene expression, have shown promise in identifying a molecular network that could provide significant clues to various psychiatric illnesses. Using an in vitro system, a rodent depression model, and a human postmortem brain, we investigated the role of a brain-enriched, neuron-specific miRNA, miR-124-3p, whose expression is highly dysregulated in stressed rodents, and identified a set of target genes involved in stress response and neural plasticity. We also found that miR-124-3p is epigenetically regulated and its interaction with the RNA-induced silencing complex (RISC) is compromised in MDD. Using blood serum, we found similar dysregulation of miR-124-3p in antidepressant-free MDD subjects. Altogether, our study demonstrates potential contribution of miR-124-3p in the pathophysiology of MDD and suggests that this miRNA may serve as a novel target for drug development and a biomarker for MDD pathogenesis.

The link between long noncoding RNAs and depression

The major depressive disorder (MDD) is a relatively common mental disorder from which that hundreds of million people have suffered, leading to displeasing life quality, which is characterized by health damage and even suicidal thoughts. The complicated development and functioning of MDD is still under exploration. Long noncoding RNA (lncRNAs) are highly expressed in the brain, could affect neural stem cell maintenance, neurogenesis and gliogenesis, brain patterning, synaptic and stress responses, and neural plasticity. The dysregulation of certain lncRNAs induces in neurodevelopmental, neurodegenerative and neuroimmunological disorders, primary brain tumors, and psychiatric diseases. Although advances have been made, no fully satisfactory treatments for major depression are available, further investigation is requested. And recently data showed that the expression level of the majority of lncRNAs demonstrated a clear tendency of upregulation, and the certain dysregulated miRNAs and lncRNAs in the MDD have been proved to have a co-synergism mechanism, that is why we speculate lncRNA might get the capability to regulate MDD. Few identified lncRNAs have been deeply studied in detailed experiments up until now, little predictions of their function have been raised, and further researches is calling for discover their signal pathway and related regulatory networks.

Neuroprotective effects of miR-27a against traumatic brain injury via suppressing FoxO3a-mediated neuronal autophagy

MicroRNA-27a (miR-27a) has been reported to be a brain-specific miRNA and aberrantly expressed in the brain suffered from traumatic brain injury (TBI). The present study is designed to investigate the potential role and molecular mechanism of miR-27a in the pathogenesis of TBI. The level of miR-27a in brain was manipulated by intracerebroventricular injection of lentiviral-encoding miR-27a before TBI induction. Real-time PCR was used to detected miR-27a and Forkhead box O3a (FoxO3a) levels in the hippocampus. Then, we evaluated the impact of miR-27a overexpression on neurological function, brain edema, lesion volume and neuronal autophagy after TBI. The blinding of miR-27a to the 3'UTR of FoxO3a mRNA and its effects on FoxO3a translation were analyzed by luciferase reporter assay and Western blot. The downregulation of miR-27a and the increase in FoxO3a level were observed in the hippocampus post-TBI. Overexpression of miR-27a significantly attenuated neurological deficits and brain injury, especially suppressed autophagic activation after TBI. Furthermore, we identified that miR-27a directly targeted the FoxO3a 3'UTR region to reduced FoxO3a protein expression. Knockdown of FoxO3a significantly reversed high levels of autophagy-related genes induced by TBI. Taken together, Overexpression of miR-27a may protect against brain injury via suppressing FoxO3a-mediated neuronal autophagy following TBI.

The microRNA network is altered in anterior cingulate cortex of patients with unipolar and bipolar depression

MicroRNAs (miRNAs) are small, non-coding RNAs acting as post-transcriptional regulators of gene expression. Though implicated in multiple CNS disorders, miRNAs have not been examined in any psychiatric disease state in anterior cingulate cortex (AnCg), a brain region centrally involved in regulating mood. We performed qPCR analyses of 29 miRNAs previously implicated in psychiatric illness (major depressive disorder (MDD), bipolar disorder (BP) and/or schizophrenia (SZ)) in AnCg of patients with MDD and BP versus controls. miR-132, miR-133a and miR-212 were initially identified as differentially expressed in BP, miR-184 in MDD and miR-34a in both MDD and BP (although none survived multiple correction testing and must be considered preliminary). In silico target prediction algorithms identified putative targets of differentially expressed miRNAs. Nuclear Co-Activator 1 (NCOA1), Nuclear Co-Repressor 2 (NCOR2) and Phosphodiesterase 4B (PDE4B) were selected based upon predicted targeting by miR-34a (with NCOR2 and PDE4B both targeted by miR-184) and published relevance to psychiatric illness. Luciferase assays identified PDE4B as a target of miR-34a and miR-184, while NCOA1 and NCOR2 were targeted by miR-34a and 184, respectively. qPCR analyses were performed to determine whether changes in miRNA levels correlated with mRNA levels of validated targets. NCOA1 showed an inverse correlation with miR-34a in BP, while NCOR2 demonstrated a positive correlation. In sum, this is the first study to demonstrate miRNA changes in AnCg in psychiatric illness and validate miR-34a as differentially expressed in CNS in MDD. These findings support a mechanistic role for miRNAs in the regulation of stress-responsive genes disrupted in psychiatric illness.

MicroRNAs and psychiatric disorders: From aetiology to treatment

The emergence of psychiatric disorders relies on the interaction between genetic vulnerability and environmental adversities. Several studies have demonstrated a crucial role for epigenetics (e.g. DNA methylation, post-translational histone modifications and microRNA-mediated post-transcriptional regulation) in the translation of environmental cues into adult behavioural outcome, which can prove to be harmful thus increasing the risk to develop psychopathology. Within this frame, non-coding RNAs, especially microRNAs, came to light as pivotal regulators of many biological processes occurring in the Central Nervous System, both during the neuronal development as well as in the regulation of adult function, including learning, memory and neuronal plasticity. On these basis, in recent years it has been hypothesised a central role for microRNA modulation and expression regulation in many brain disorders, including neurodegenerative disorders and mental illnesses. Indeed, the aim of the present review is to present the most recent state of the art regarding microRNA involvement in psychiatric disorders. We will first describe the mechanisms that regulate microRNA biogenesis and we will report evidences of microRNA dysregulation in peripheral body fluids, in postmortem brain tissues from patients suffering from psychopathology as well as in animal models. Last, we will discuss the potential to consider microRNAs as putative target for pharmacological intervention, using common psychotropic drugs or more specific tools, with the aim to normalize functions that are disrupted in different psychiatric conditions.

Alterations of microRNA-124 expression in peripheral blood mononuclear cells in pre- and post-treatment patients with major depressive disorder

Recently, increasing evidence has indicated that dysfunction of microRNA-124 (miR-124) might be involved in the pathophysiology and treatment of major depressive disorder (MDD) in some animal models of depression. However, the role of miR-124 in MDD patients remains unclear. The objective of this study was to investigate whether the miR-124 expression levels in peripheral blood mononuclear cells (PBMCs) were associated with MDD and to evaluate the effects of antidepressant treatment on miR-124 levels. Quantitative real-time PCR was applied to detect miR-124 expression in 32 pre- and post-treatment MDD patients and 30 healthy controls. Our results showed that expression levels of miR-124 from PBMCs in MDD patients were significantly higher than those in healthy controls (p < 0.001), and that the area under the curve of miR-124 from ROC analysis was 0.762 with a sensitivity of 83.33% and specificity of 66.67% in distinguishing MDD patients from healthy controls. In addition, the expression levels of miR-124 were significantly down-regulated after eight weeks of treatment (p < 0.001). MiRNA target gene prediction and functional annotation analysis indicated that altered miR-124 was involved in affecting some important biological processes and pathways related to MDD. These results provide new information on miR-124 involvement in the biological alterations of MDD and in antidepressant effects.

MicroRNAs Modulate Interactions between Stress and Risk for Cocaine Addiction

Exposure to stress increases vulnerability to drug abuse, as well as relapse liability in addicted individuals. Chronic drug use alters stress response in a manner that increases drug seeking behaviors and relapse. Drug exposure and withdrawal have been shown to alter stress responses, and corticosteroid mediators of stress have been shown to impact addiction-related brain function and drug-seeking behavior. Despite the documented interplay between stress and substance abuse, the mechanisms by which stress exposure and drug seeking interact remain largely unknown. Recent studies indicate that microRNAs (miRNA) play a significant role in stress modulation as well as addiction-related processes including neurogenesis, synapse development, plasticity, drug acquisition, withdrawal and relapse. MiRNAs are short non-coding RNAs that function as bidirectional epigenetic modulators of gene expression through imperfect sequence targeted degradation and/or translational repression of mRNAs. They serve as dynamic regulators of CNS physiology and pathophysiology, and facilitate rapid and long-lasting changes to complex systems and behaviors. MiRNAs function in glucocorticoid signaling and the mesolimbic dopamine reward system, as well as mood disorders related to drug withdrawal. The literature suggests miRNAs play a pivotal role in the interaction between exposures to stress, addiction-related processes, and negative affective states resulting from extended drug withdrawal. This manuscript reviews recent evidence for the role of miRNAs in the modulation of stress and cocaine responses, and discusses potential mediation of the interaction of these systems by miRNAs. Uncovering the mechanism behind the association of stress and drug taking has the potential to impact the treatment of drug abuse and prevention of relapse. Further comprehension of these complex interactions may provide promising new targets for the treatment of drug addiction.

Sustained lentiviral-mediated overexpression of microRNA124a in the dentate gyrus exacerbates anxiety- and autism-like behaviors associated with neonatal isolation in rats

Autism spectrum disorders (ASD) are highly disabling psychiatric disorders. Despite a strong genetic etiology, there are no efficient therapeutic interventions that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of microRNA (miR) machinery may contribute to the underlying molecular mechanisms involved in ASD. Here, we report a stress model demonstrating that neonatal isolation-induced long-lasting hippocampal elevation of miR124a was associated with reduced expression of its target BDNF mRNA. In addition, we investigated the impact of lentiviral-mediated overexpression of miR124a into the dentate gyrus (DG) on social interaction, repetitive- and anxiety-like behaviors in the neonatal isolation (Iso) model of autism. Rats isolated from the dams on PND 1 to PND 11 were assessed for their social interaction, marble burying test (MBT) and repetitive self-grooming behaviors as adults following miR124a overexpression. Also, anxiety-like behavior and locomotion were evaluated in the elevated plus maze (EPM) and open-field (OF) tests. Results show that, consistent with previously published reports, Iso rats displayed decreased social interaction contacts but increased repetitive- and anxiety-like behaviors. Interestingly, across both autism- and anxiety-like behavioral assays, miR124a overexpression in the DG significantly exacerbated repetitive behaviors, social impairments and anxiety with no effect on locomotor activity. Our novel findings attribute neonatal isolation-inducible cognitive impairments to induction of miR124a and consequently suppressed BDNF mRNA, opening venues for intercepting these miR124a-mediated damages. They also highlight the importance of studying microRNAs in the context of ASD and identify miR124a as a novel potential therapeutic target for improving mood disorders.

miR-182 (microRNA-182) suppression in the hippocampus evokes antidepressant-like effects in rats

Depression is a serious and potentially life-threatening mental disorder with unknown etiology. Emerging evidence shows that brain-derived neurotrophic factor (BDNF) and microRNAs (miRNAs) play critical roles in the etiology of depression. However, the molecular mechanisms are not fully understood. Expression of miR-182 and BDNF in the hippocampus were analyzed in a chronic unpredictable mild stress (CUMS) model. Male Wistar rats received bilateral intra-hippocampal infusions of BDNF- and miR-182-expressing (miR-182) or miR-182-silencers (si-miR-182) lentiviral vectors (LV). miR-182 upregulation was correlated with decreased BDNF expression in the hippocampus of a CUMS model. Accordingly, an anti-depressant like effect was observed when LV-BDNF or LV-si-miR-182 was injected into the hippocampus. Moreover, BDNF and its target gene cyclic AMP responsive element binding protein 1 (CREB1) decreased following LV-miR-182 injection and increased upon LV-si-miR-182 injection in rat hippocampus and cultured neuronal cells. In contrast, miR-182 overexpression exacerbated depression-like behaviors and decreased BDNF. Further, luciferase reporter evidence confirmed BDNF was a miR-182 target. Taken together, the current results reveal a potential molecular regulation of miR-182 on BDNF and the pronounced behavioral consequences of this regulation.

Overexpression of brain-derived neurotrophic factor in the hippocampus protects against post-stroke depression

Post-stroke depression is associated with reduced expression of brain-derived neurotrophic factor (BDNF). In this study, we evaluated whether BDNF overexpression affects depression-like behavior in a rat model of post-stroke depression. The middle cerebral artery was occluded to produce a model of focal cerebral ischemia. These rats were then subjected to isolation-housing combined with chronic unpredictable mild stress to generate a model of post-stroke depression. A BDNF gene lentiviral vector was injected into the hippocampus. At 7 days after injection, western blot assay and real-time quantitative PCR revealed that BDNF expression in the hippocampus was increased in depressive rats injected with BDNF lentivirus compared with depressive rats injected with control vector. Furthermore, sucrose solution consumption was higher, and horizontal and vertical movement scores were increased in the open field test in these rats as well. These findings suggest that BDNF overexpression in the hippocampus of post-stroke depressive rats alleviates depression-like behaviors.

Epigenetic mechanisms underlying the role of brain-derived neurotrophic factor in depression and response to antidepressants

Major depressive disorder (MDD) is a devastating neuropsychiatric disorder encompassing a wide range of cognitive and emotional dysfunctions. The prevalence of MDD is expected to continue its growth to become the second leading cause of disease burden (after HIV) by 2030. Despite an extensive research effort, the exact etiology of MDD remains elusive and the diagnostics uncertain. Moreover, a marked inter-individual variability is observed in the vulnerability to develop depression, as well as in response to antidepressant treatment, for nearly 50% of patients. Although a genetic component accounts for some cases of MDD, it is now clearly established that MDD results from strong gene and environment interactions. Such interactions could be mediated by epigenetic mechanisms, defined as chromatin and DNA modifications that alter gene expression without changing the DNA structure itself. Some epigenetic mechanisms have recently emerged as particularly relevant molecular substrates, promoting vulnerability or resilience to the development of depressive-like symptoms. Although the role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of MDD remains unclear, its modulation of the efficacy of antidepressants is clearly established. Therefore, in this review, we focus on the epigenetic mechanisms regulating the expression of BDNF in humans and in animal models of depression, and discuss their role in individual differences in vulnerability to depression and response to antidepressant drugs.

MeCP2 controls hippocampal brain-derived neurotrophic factor expression via homeostatic interactions with microRNA‑132 in rats with depression

Major depressive disorder (MDD) is a considerable public health concern, which affects patients worldwide. MDD is associated with psychosocial impairment, poor quality of life, and significant disability, morbidity and mortality. Stress is a major factor in depression, which impairs the structural and functional plasticity of the hippocampus. Previous studies have demonstrated that chronic unpredictable mild stress is able to downregulate the expression of brain‑derived neurotrophic factor (BDNF) and methyl‑CpG‑binding protein 2 (MeCP2), and alter the expression levels of certain microRNAs (miR). The aim of the present study was to investigate the regulatory association between BDNF, MeCP2 and miR-132 in an animal model of chronic stress‑induced depression. ELISA, western blot and qPCR were used to detect the expression levels of BDNF, MeCP2 and miR-132 in the peripheral blood samples of patients with MDD and in the hippocampi of depressed animals. In addition, a dual luciferase reporter gene system was used to determine whether miR-132 directly targets BDNF or MeCP2. The present study demonstrated that, as compared with normal subjects, miR‑132 expression was increased in the peripheral blood samples of patients with MDD, whereas the expression of MeCP2 and BDNF was decreased; thus, the expression levels of MeCP2 and BDNF were negatively correlated with those of miR‑132. In addition, in an animal model of chronic stress‑induced depression, increased expression levels of miR‑132, and decreased levels of MeCP2 and BDNF were detected in the hippocampi. Furthermore, knockdown of MeCP2 expression in primary hippocampal neurons increased the expression of miR‑132 and decreased the expression levels of BDNF. The results of the present study demonstrated that miR‑132 may directly target MeCP2, but not BDNF, and control its expression at the transcriptional and translational level. miR‑132 was also shown to negatively regulate BDNF expression. The reduced expression levels of BDNF, as induced by MeCP2 knockdown, were enhanced by miR‑132 mimics, and were rescued by miR‑132 inhibitors. These results suggested that homeostatic interactions between MeCP2 and miR‑132 may regulate hippocampal BDNF levels, which may have a role in the pathogenesis of MDD.

Noncoding RNAs and neurobehavioral mechanisms in psychiatric disease

The human genome project has revolutionized our understanding of the underlying mechanisms in psychiatric disease. It is now abundantly clear that neurobehavioral phenotypes are epigenetically controlled by noncoding RNAs (ncRNAs). The microRNA (miRNA) class of ncRNAs are ubiquitously expressed throughout the brain and govern all major neuronal pathways. The attractive therapeutic potential of miRNAs is underscored by their pleiotropic capacities, putatively targeting multiple pathways within a single neuron. Many psychiatric diseases stem from a multifactorial origin, thus conventional drug targeting of single proteins may not prove most effective. In this exciting post-genome sequencing era, many new epigenetic targets are emerging for therapeutic investigation. Here we review the reported roles of miRNAs, as well as other ncRNA classes, in the pathology of psychiatric disorders; there are both common and unique ncRNA mechanisms that influence the various diagnoses. Collectively, these potent epigenetic regulators may clarify the disrupted signaling networks in psychiatric phenotypes.