Plasticity-related microRNA and their potential contribution to the maintenance of long-term potentiation

Deciphering the role of miRNAs in Alzheimer's disease: Predictive targeting and pathway modulation - A systematic review

Alzheimer's Disease (AD), a multifaceted neurodegenerative disorder, is increasingly understood through the regulatory lens of microRNAs (miRNAs). This review comprehensively examines the pivotal roles of miRNAs in AD pathogenesis, shedding light on their influence across various pathways. We delve into the biogenesis and mechanisms of miRNAs, emphasizing their significant roles in brain function and regulation. The review then navigates the complex landscape of AD pathogenesis, identifying key genetic, environmental, and molecular factors, with a focus on hallmark pathological features like amyloid-beta accumulation and tau protein hyperphosphorylation. Central to our discussion is the intricate involvement of miRNAs in these processes, highlighting their altered expression patterns in AD and subsequent functional implications, from amyloid-beta metabolism to tau pathology, neuroinflammation, oxidative stress, and synaptic dysfunction. The predictive analysis of miRNA targets using computational methods, complemented by experimental validations, forms a crucial part of our discourse, unraveling the contributions of specific miRNAs to AD. Moreover, we explore the therapeutic potential of miRNAs as biomarkers and in miRNA-based interventions, while addressing the challenges in translating these findings into clinical practice. This review aims to enhance understanding of miRNAs in AD, offering a foundation for future research directions and novel therapeutic strategies.

Functionalizing Dendrimers for Targeted Delivery of Bioactive Molecules to Macrophages: A Potential Treatment for Mycobacterium tuberculosis Infection-A Review

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis that replicates inside human alveolar macrophages. This disease causes significant morbidity and mortality throughout the world. According to the World Health Organization 1.4 million people died of this disease in 2021. This indicates that despite the progress of modern medicine, improvements in diagnostics, and the development of drug susceptibility tests, TB remains a global threat to public health. In this sense, host-directed therapy may provide a new approach to the cure of TB, and the expression of miRNAs has been correlated with a change in the concentration of various inflammatory mediators whose concentrations are responsible for the pathophysiology of M. tuberculosis infection. Thus, the administration of miRNAs may help to modulate the immune response of organisms. However, direct administration of miRNAs, without adequate encapsulation, exposes nucleic acids to the activity of cytosolic nucleases, limiting their application. Dendrimers are a family of highly branched molecules with a well-defined architecture and a branched conformation which gives rise to cavities that facilitate physical immobilization, and functional groups that allow chemical interaction with molecules of interest. Additionally, dendrimers can be easily functionalized to target different cells, macrophages among them. In this sense, various studies have proposed the use of different cell receptors as target molecules to aim dendrimers at macrophages and thus release drugs or nucleic acids in the cell of interest. Based on the considerations, the primary objective of this review is to comprehensively explore the potential of functionalized dendrimers as delivery vectors for miRNAs and other therapeutic agents into macrophages. This work aims to provide insights into the use of functionalized dendrimers as an innovative approach for TB treatment, focusing on their ability to target and deliver therapeutic cargo to macrophages.

Common microRNA regulated pathways in Alzheimer's and Parkinson's disease

MicroRNAs (miRNAs) are small non-coding RNAs involved in gene regulation. Recently, miRNA dysregulation has been found in neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The diagnosis of Alzheimer's and Parkinson's is currently challenging, mainly occurring when pathology is already present, and although treatments are available for both diseases, the role of treatment is primarily to prevent or delay the progress of the diseases instead of fully overcoming the diseases. Therefore, the challenge in the near future will be to determine effective drugs to tackle the dysregulated biological pathways in neurodegenerative diseases. In the present study, we describe the dysregulation of miRNAs in blood of Alzheimer's and Parkinson's patients with the aim to identify common mechanisms between the 2 pathologies and potentially to identify common therapeutic targets which can stop or delay the progression of two most frequent neuropathologies. Two independent systematic reviews, bioinformatic analysis, and experiment validation were performed to identify whether AD and PD share common pathways. A total of 15 common miRNAs were found in the literature and 13 common KEGG pathways. Among the common miRNAs, two were selected for validation in a small cohort of AD and PD patients. Let-7f-5p and miR-29b-3p showed to be good predictors in blood of PD patients.

Electroacupuncture protective effects after cerebral ischemia are mediated through miR-219a inhibition

BACKGROUND

Electroacupuncture (EA) is a complementary and alternative therapy which has shown protective effects on vascular cognitive impairment (VCI). However, the underlying mechanisms are not entirely understood.

METHODS

Rat models of VCI were established with cerebral ischemia using occlusion of the middle cerebral artery or bilateral common carotid artery. The brain structure and function imaging were measured through animal MRI. miRNA expression was detected by chip and qPCR. Synaptic functional plasticity was detected using electrophysiological techniques.

RESULTS

This study demonstrated the enhancement of Regional Homogeneity (ReHo) activity of blood oxygen level-dependent (BOLD) signal in the entorhinal cortical (EC) and hippocampus (HIP) in response to EA treatment. miR-219a was selected and confirmed to be elevated in HIP and EC in VCI but decreased after EA. N-methyl-D-aspartic acid receptor1 (NMDAR1) was identified as the target gene of miR-219a. miR-219a regulated NMDAR-mediated autaptic currents, spontaneous excitatory postsynaptic currents (sEPSC), and long-term potentiation (LTP) of the EC-HIP CA1 circuit influencing synaptic plasticity. EA was able to inhibit miR-219a, enhancing synaptic plasticity of the EC-HIP CA1 circuit and increasing expression of NMDAR1 while promoting the phosphorylation of downstream calcium/calmodulin-dependent protein kinase II (CaMKII), improving overall learning and memory in VCI rat models.

CONCLUSION

Inhibition of miR-219a ameliorates VCI by regulating NMDAR-mediated synaptic plasticity in animal models of cerebral ischemia.

iLoc-miRNA: extracellular/intracellular miRNA prediction using deep BiLSTM with attention mechanism

The location of microRNAs (miRNAs) in cells determines their function in regulation activity. Studies have shown that miRNAs are stable in the extracellular environment that mediates cell-to-cell communication and are located in the intracellular region that responds to cellular stress and environmental stimuli. Though in situ detection techniques of miRNAs have made great contributions to the study of the localization and distribution of miRNAs, miRNA subcellular localization and their role are still in progress. Recently, some machine learning-based algorithms have been designed for miRNA subcellular location prediction, but their performance is still far from satisfactory. Here, we present a new data partitioning strategy that categorizes functionally similar locations for the precise and instructive prediction of miRNA subcellular location in Homo sapiens. To characterize the localization signals, we adopted one-hot encoding with post padding to represent the whole miRNA sequences, and proposed a deep bidirectional long short-term memory with the multi-head self-attention algorithm to model. The algorithm showed high selectivity in distinguishing extracellular miRNAs from intracellular miRNAs. Moreover, a series of motif analyses were performed to explore the mechanism of miRNA subcellular localization. To improve the convenience of the model, a user-friendly web server named iLoc-miRNA was established (http://iLoc-miRNA.lin-group.cn/).

Regulation of microRNA Expression in Sleep Disorders in Patients with Epilepsy

The effects of epilepsy on sleep and the activating effects of sleep on seizures are well documented in the literature. To date, many sleep-related and awake-associated epilepsy syndromes have been described. The relationship between sleep and epilepsy has led to the recognition of polysomnographic testing as an important diagnostic tool in the diagnosis of epilepsy. The authors analyzed the available medical database in search of other markers that assess correlations between epilepsy and sleep. Studies pointing to microRNAs, whose abnormal expression may be common to epilepsy and sleep disorders, are promising. In recent years, the role of microRNAs in the pathogenesis of epilepsy and sleep disorders has been increasingly emphasized. MicroRNAs are a family of single-stranded, non-coding, endogenous regulatory molecules formed from double-stranded precursors. They are typically composed of 21–23 nucleotides, and their main role involves post-transcriptional downregulation of expression of numerous genes. Learning more about the role of microRNAs in the pathogenesis of sleep disorder epilepsy may result in its use as a biomarker in these disorders and application in therapy.

Role of Satb1 and Satb2 Transcription Factors in the Glutamate Receptors Expression and Ca2+ Signaling in the Cortical Neurons In Vitro

Transcription factors Satb1 and Satb2 are involved in the processes of cortex development and maturation of neurons. Alterations in the expression of their target genes can lead to neurodegenerative processes. Molecular and cellular mechanisms of regulation of neurotransmission by these transcription factors remain poorly understood. In this study, we have shown that transcription factors Satb1 and Satb2 participate in the regulation of genes encoding the NMDA-, AMPA-, and KA- receptor subunits and the inhibitory GABA(A) receptor. Deletion of gene for either Satb1 or Satb2 homologous factors induces the expression of genes encoding the NMDA receptor subunits, thereby leading to higher amplitudes of Ca²⁺-signals in neurons derived from the Satb1-deficient (Satb1^fl/+ * Nex^Cre/+) and Satb1-null mice (Satb1^fl/fl * Nex^Cre/+) in response to the selective agonist reducing the EC50 for the NMDA receptor. Simultaneously, there is an increase in the expression of the Gria2 gene, encoding the AMPA receptor subunit, thus decreasing the Ca²⁺-signals of neurons in response to the treatment with a selective agonist (5-Fluorowillardiine (FW)). The Satb1 deletion increases the sensitivity of the KA receptor to the agonist (domoic acid), in the cortical neurons of the Satb1-deficient mice but decreases it in the Satb1-null mice. At the same time, the Satb2 deletion decreases Ca²⁺-signals and the sensitivity of the KA receptor to the agonist in neurons from the Satb1-null and the Satb1-deficient mice. The Satb1 deletion affects the development of the inhibitory system of neurotransmission resulting in the suppression of the neuron maturation process and switching the GABAergic responses from excitatory to inhibitory, while the Satb2 deletion has a similar effect only in the Satb1-null mice. We show that the Satb1 and Satb2 transcription factors are involved in the regulation of the transmission of excitatory signals and inhibition of the neuronal network in the cortical cell culture.

Atrx Deletion in Neurons Leads to Sexually Dimorphic Dysregulation of miR-137 and Spatial Learning and Memory Deficits

ATRX gene mutations have been identified in syndromic and non-syndromic intellectual disabilities in humans. ATRX is known to maintain genomic stability in neuroprogenitor cells, but its function in differentiated neurons and memory processes remains largely unresolved. Here, we show that the deletion of neuronal Atrx in mice leads to distinct hippocampal structural defects, fewer presynaptic vesicles, and an enlarged postsynaptic area at CA1 apical dendrite-axon junctions. We identify male-specific impairments in long-term contextual memory and in synaptic gene expression, linked to altered miR-137 levels. We show that ATRX directly binds to the miR-137 locus and that the enrichment of the suppressive histone mark H3K27me3 is significantly reduced upon the loss of ATRX. We conclude that the ablation of ATRX in excitatory forebrain neurons leads to sexually dimorphic effects on miR-137 expression and on spatial memory, identifying a potential therapeutic target for neurological defects caused by ATRX dysfunction.

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Loss of ATRX in neurons has sexually dimorphic effects on long-term spatial memory

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Targeted deletion of neuronal ATRX in mice causes ultrastructural synaptic defects

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ATRX null neurons show sex-specific changes in miR-137 and target synaptic transcripts

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ATRX directly binds and suppresses miR-137 in males via enrichment of H3K27me3

The Potential Role of miRNAs as Predictive Biomarkers in Neurodevelopmental Disorders

Neurodevelopmental disorders are defined as a set of abnormal brain developmental conditions marked by the early childhood onset of cognitive, behavioral, and functional deficits leading to memory and learning problems, emotional instability, and impulsivity. Autism spectrum disorder, attention-deficit/hyperactivity disorder, Tourette syndrome, fragile X syndrome, and Down's syndrome are a few known examples of neurodevelopmental disorders. Although they are relatively common in both developed and developing countries, very little is currently known about their underlying molecular mechanisms. Both genetic and environmental factors are known to increase the risk of neurodevelopmental disorders. Current diagnostic and screening tests for neurodevelopmental disorders are not reliable; hence, individuals with neurodevelopmental disorders are often diagnosed in the later stages. This negatively affects their prognosis and quality of life, prompting the need for a better diagnostic biomarker. Recent studies on microRNAs and their altered regulation in diseases have shed some light on the possible role they could play in the development of the central nervous system. This review attempts to elucidate our current understanding of the role that microRNAs play in neurodevelopmental disorders with the hope of utilizing them as potential biomarkers in the future.

miR-135a-5p mediates memory and synaptic impairments via the Rock2/Adducin1 signaling pathway in a mouse model of Alzheimer's disease

Aberrant regulation of microRNAs (miRNAs) has been implicated in the pathogenesis of Alzheimer's disease (AD), but most abnormally expressed miRNAs found in AD are not regulated by synaptic activity. Here we report that dysfunction of miR-135a-5p/Rock2/Add1 results in memory/synaptic disorder in a mouse model of AD. miR-135a-5p levels are significantly reduced in excitatory hippocampal neurons of AD model mice. This decrease is tau dependent and mediated by Foxd3. Inhibition of miR-135a-5p leads to synaptic disorder and memory impairments. Furthermore, excess Rock2 levels caused by loss of miR-135a-5p plays an important role in the synaptic disorder of AD via phosphorylation of Ser726 on adducin 1 (Add1). Blocking the phosphorylation of Ser726 on Add1 with a membrane-permeable peptide effectively rescues the memory impairments in AD mice. Taken together, these findings demonstrate that synaptic-related miR-135a-5p mediates synaptic/memory deficits in AD via the Rock2/Add1 signaling pathway, illuminating a potential therapeutic strategy for AD.

Fine-tuning Nanog expression heterogeneity in embryonic stem cells by regulating a Nanog transcript-specific microRNA

In embryonic stem cells (ESCs), the transcription factor Nanog maintains the stemness of ESCs despite exhibiting heterogeneous expression patterns under varied culture conditions. Efficient fine-tuning of Nanog expression heterogeneity could enable ESC proliferation and differentiation along specific lineages to be regulated. Herein, by employing a stochastic modeling approach, we show that Nanog expression heterogeneity can be controlled by modulating the regulatory features of a Nanog transcript-specific microRNA, mir-296. We demonstrate how and why the extent of origin-dependent fluctuations in Nanog expression level can be altered by varying either the binding efficiency of the microRNA-mRNA complex or the expression level of mir-296. Moreover, our model makes experimentally feasible and insightful predictions to maneuver Nanog expression heterogeneity explicitly to achieve cell-type-specific differentiation of ESCs.

Mycobacterium tuberculosis Infection Drives Mitochondria-Biased Dysregulation of Host Transfer RNA-Derived Fragments

BACKGROUND

Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis, causes 10 million infections and 1.5 million deaths per year worldwide. The success of Mtb as a human pathogen is directly related to its ability to suppress host responses, which are critical for clearing intracellular pathogens. Emerging evidence suggests that key response pathways may be regulated by a novel class of small noncoding RNA, called transfer RNA (tRNA)-derived fragments (tRFs). tRFs can complex with Argonaute proteins to target and degrade messenger RNA targets, similarly to micro RNAs, but have thus far been overlooked in the context of bacterial infections.

METHODS

We generated a novel miRge2.0-based tRF-analysis tool, tRFcluster, and used it to analyze independently generated and publicly available RNA-sequencing datasets to assess tRF dysregulation in host cells following infection with Mtb and other intracellular bacterial pathogens.

RESULTS

We found that Mtb and Listeria monocytogenes drive dramatic tRF dysregulation, whereas other bacterial pathogens do not. Interestingly, Mtb infection uniquely increased the expression of mitochondria-derived tRFs rather than genomic-derived tRFs, suggesting an association with mitochondrial damage in Mtb infection.

CONCLUSIONS

tRFs are dysregulated in some, but not all, bacterial infections. Biased dysregulation of mitochondria-derived tRFs in Mtb infection suggests a link between mitochondrial distress and tRF production.

Nociceptive related microRNAs and their role in rheumatoid arthritis

Rheumatoid Arthritis (RA) is an autoimmune disease with unknown etiology and a global incidence around 1%, a positive family history increases the risk of RA roughly three to five times. Pain is one of the first symptoms to appear in this disease. MicroRNAs (miRNAs) belong to the class of small non-coding RNAs; they regulate multiple cellular processes including embryonic development, cellular proliferation, differentiation and apoptosis among others. A great deal of evidence points to the employment of miRNAs as therapeutic targets and biomarkers for several pathologies. The main objective of this Review is to assess how miRNAs participate in the pathogenesis of RA. Two advanced searches were conducted in databases, one using "micro-RNA" and "rheumatoid arthritis" as key words, and another one with "micro-RNA", "pain" and "nociception". In this Review, we describe how six miRNAs: miR-16-5p, miR-23b-3b, miR-124-3p, miR-146a-5p, miR-155-5p and miR-223-3p, involved in the modulation and transmission of the nociceptive input are unregulated in RA patients. Key molecular pathways involved in nociception, inflammation and autoimmune responses, are regulated by these miRNAs; the NF-κB, TNF-α, interleukins and TLR4. By means of gene repression, the miRNAs here described modulate the nociceptive process as well as the autoimmune response that characterize this disease.

From reversible to irreversible bistable switches via bifurcations in a gene regulatory network

The interplay of small, noncoding microRNAs (miRNAs), mRNAs and proteins plays crucial roles in almost all cellular processes. MiR-124, widely known as a memory-related miRNA, can regulate LTM by binding to the mRNA of CREB1 stimulated with 5-HT. In this paper, we establish a regulatory network model of CREB1 and miR-124 stimulated by 5-HT, in which miR-124 inhibits CREB1, which in turn enhances miR-124. Our model validates three protocols based on 5-HT in experiments on the induction of LTM in Aplysia. A steady-state analysis and numerical bifurcations of the abstracted system beyond memory formation, when the fast reaction has been in the equilibrium, can facilitate more abundant dynamical behaviors such as bistability and oscillation. The original system also exhibits bistability under appropriate feedback strengths, which is relevant to the mechanism of LTM formation. Furthermore, we specifically show a change in the transition from a reversible switch to an irreversible switch via bifurcations of the negative regulation of miR-124 on CREB1, which eventually maintains a high phosphorylated CREB1 level after initially elevated by 5-HT. These findings indicate that miR-124 provides an inhibitory constraint on long-term synaptic plasticity through the regulation of CREB1.

Extracellular vesicular MicroRNA-27a* contributes to cardiac hypertrophy in chronic heart failure

Under stress, the heart undergoes extensive remodeling resulting in cardiac fibrosis and hypertrophy, ultimately contributing to chronic heart failure (CHF). Alterations in microRNA levels are associated with dysfunctional gene expression profiles involved in the pathogenesis of heart failure. We previously showed that myocardial infarction-induced microRNA-enriched extracellular vesicles (EVs) contribute to the reduction in antioxidant enzymes by targeting Nrf2 signaling in CHF. MicroRNA-27a (miRNA-27a) is the predominant microRNA contained in cardiac fibroblast-derived EVs contributing to oxidative stress along with hypertrophic gene expression in cardiomyocytes. In the present study, we observed that miRNA-27a passenger strand (miRNA-27a*) was markedly upregulated in the non-infarcted area of the left ventricle of rats with CHF and encapsulated into EVs and secreted into the circulation. Bioinformatic analysis revealed that PDZ and LIM domain 5 (PDLIM5) is one of the major targets of miRNA-27a*, playing a major role in cardiac structure and function, and potentially contributing to the progression of cardiac hypertrophy. Our in vivo data demonstrate that PDLIM5 is down-regulated in the progression of heart failure, accompanied with the upregulation of hypertrophic genes and consistent with alterations in miRNA-27a*. Moreover, exogenous administration of miRNA27a* mimics inhibit PDLIM5 translation in cardiomyocytes whereas a miRNA27a* inhibitor enhanced PDLIM5 expression. Importantly, we confirmed that infarcted hearts have higher abundance of miRNA-27a* in EVs compared to normal hearts and further demonstrated that cultured cardiac fibroblasts secrete miRNA27a*-enriched EVs into the extracellular space in response to Angiotensin II stimulation, which inhibited PDLIM5 translation, leading to cardiomyocyte hypertrophic gene expression. In vivo studies suggest that the administration of a miRNA-27a* inhibitor in CHF rats partially blocks endogenous miR-27a* expression, prevents hypertrophic gene expression and improves myocardial contractility. These findings suggest that cardiac fibroblast-secretion of miRNA27a*-enriched EVs may act as a paracrine signaling mediator of cardiac hypertrophy that has potential as a novel therapeutic target.

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.

Enduring effects of muscarinic receptor activation on adult hippocampal neurogenesis, microRNA expression and behaviour

The cholinergic system is one of the most important neurotransmitter systems in the brain with key roles in autonomic control and the regulation of cognitive and emotional responses. However, the precise mechanism by which the cholinergic system influences behaviour is unclear. Adult hippocampal neurogenesis (AHN) is a potential mediator in this context based on evidence, which has identified this process as putative mechanism of antidepressant action. More recently, post-transcriptional regulation by microRNAs is another candidate mechanism based on its involvement in the regulation of AHN and neurotransmission. Taking into account this background, we evaluated the behavioural effects of a non-convulsant dose of pilocarpine - a non-selective muscarinic receptor (mAChR) agonist - in adult Wistar rats. Furthermore, we quantified the expression of different microRNAs implicated in the regulation of AHN. Our results suggests that pilocarpine treatment increases AHN in the granular cell layer but also induced ectopic neurogenesis. Pilocarpine treatment reduced immobility time in forced swimming test but did not affect fear conditioning response, sucrose preference or novelty supressed feeding behaviour. In addition, treatment with pilocarpine down-regulated the expression of 6 microRNAs implicated in the regulation of neurotrophin signalling and axon guidance pathways. Therefore, we suggest that the low-dose stimulation of the cholinergic system is sufficient to alter AHN of rats through post-transcriptional mechanisms, which might contribute to long-lasting behavioural effects.

The Neuroprotective Effect of miR-181a After Oxygen-Glucose Deprivation/Reperfusion and the Associated Mechanism

The level of miR-181a decreases rapidly in N2a cells following oxygen-glucose deprivation/reperfusion, but its role in this process is unclear. Reelin, a regulator of neuronal migration and synaptogenesis, is a predicted target of miR-181a. We hypothesized that miR-181a reduces neuronal apoptosis and protects neurons by targeting reelin. Second mitochondria-derived activator of caspases (Smac) is a protein located in mitochondria that regulates apoptosis. The pro-apoptotic effect of Smac is achieved by reversing the effects of apoptosis-inhibiting proteins (IAPs), particularly X-linked inhibitor of apoptosis (XIAP). We also evaluated the effect of miR-181a on the Smac/IAP signaling pathway after oxygen-glucose deprivation and reperfusion in N2a cells. The miR-181a level, apoptosis rate, and the levels of reelin mRNA and protein, Smac, and XIAP were assessed in N2a cells subjected to oxygen-glucose deprivation for 4 h and reperfusion for 0, 4, 12, or 24 h with/without an miR-181a mimic, or mismatched control. Direct targeting of reelin by miR-181a was assessed in vitro by dual luciferase assay and immunoblotting. Pre-treatment with miR-181a mimicked the increase in the miR-181a level in N2a cells after oxygen-glucose deprivation/reperfusion, resulting in a significant decrease in the apoptosis rate. Changes in the miR-181a level in N2a cells were inversely correlated with reelin protein expression. Direct targeting of the reelin 3' untranslated region by miR-181a was verified by dual luciferase assay, which showed that miR-181a significantly inhibited luciferase activity. The Smac level was significantly lower in the miR-181a mimics than the normal control and mimics-cont groups (P < 0.01), whereas the level of XIAP was increased slightly. These findings suggest that miR-181a protects neurons from apoptosis by inhibiting reelin expression and regulating the Smac/IAP signaling pathway after oxygen-glucose deprivation/reperfusion injury.

MicroRNA-186-5p controls GluA2 surface expression and synaptic scaling in hippocampal neurons

Homeostatic synaptic scaling is a negative feedback response to fluctuations in synaptic strength induced by developmental or learning-related processes, which maintains neuronal activity stable. Although several components of the synaptic scaling apparatus have been characterized, the intrinsic regulatory mechanisms promoting scaling remain largely unknown. MicroRNAs may contribute to posttranscriptional control of mRNAs implicated in different stages of synaptic scaling, but their role in these mechanisms is still undervalued. Here, we report that chronic blockade of glutamate receptors of the AMPA and NMDA types in hippocampal neurons in culture induces changes in the neuronal mRNA and miRNA transcriptomes, leading to synaptic upscaling. Specifically, we show that synaptic activity blockade persistently down-regulates miR-186-5p. Moreover, we describe a conserved miR-186-5p-binding site within the 3'UTR of the mRNA encoding the AMPA receptor GluA2 subunit, and demonstrate that GluA2 is a direct target of miR-186-5p. Overexpression of miR-186 decreased GluA2 surface levels, increased synaptic expression of GluA2-lacking AMPA receptors, and blocked synaptic scaling, whereas inhibition of miR-186-5p increased GluA2 surface levels and the amplitude and frequency of AMPA receptor-mediated currents, and mimicked excitatory synaptic scaling induced by synaptic inactivity. Our findings elucidate an activity-dependent miRNA-mediated mechanism for regulation of AMPA receptor expression.

Plasticity of Spine Structure: Local Signaling, Translation and Cytoskeletal Reorganization

Dendritic spines are small protrusive structures on dendritic surfaces, and function as postsynaptic compartments for excitatory synapses. Plasticity of spine structure is associated with many forms of long-term neuronal plasticity, learning and memory. Inside these small dendritic compartments, biochemical states and protein-protein interactions are dynamically modulated by synaptic activity, leading to the regulation of protein synthesis and reorganization of cytoskeletal architecture. This in turn causes plasticity of structure and function of the spine. Technical advances in monitoring molecular behaviors in single dendritic spines have revealed that each signaling pathway is differently regulated across multiple spatiotemporal domains. The spatial pattern of signaling activity expands from a single spine to the nearby dendritic area, dendritic branch and the nucleus, regulating different cellular events at each spatial scale. Temporally, biochemical events are typically triggered by short Ca²⁺ pulses (~10–100 ms). However, these signals can then trigger activation of downstream protein cascades that can last from milliseconds to hours. Recent imaging studies provide many insights into the biochemical processes governing signaling events of molecular assemblies at different spatial localizations. Here, we highlight recent findings of signaling dynamics during synaptic plasticity and discuss their roles in long-term structural plasticity of dendritic spines.

MicroRNA-Related Polymorphisms in Infectious Diseases-Tiny Changes With a Huge Impact on Viral Infections and Potential Clinical Applications

MicroRNAs (miRNAs) are single-stranded sequences of non-coding RNA with approximately 22 nucleotides that act posttranscriptionally on gene expression. miRNAs are important gene regulators in physiological contexts, but they also impact the pathogenesis of various diseases. The role of miRNAs in viral infections has been explored by different authors in both population-based as well as in functional studies. However, the effect of miRNA polymorphisms on the susceptibility to viral infections and on the clinical course of these diseases is still an emerging topic. Thus, this review will compile and organize the findings described in studies that evaluated the effects of genetic variations on miRNA genes and on their binding sites, in the context of human viral diseases. In addition to discussing the basic aspects of miRNAs biology, we will cover the studies that investigated miRNA polymorphisms in infections caused by hepatitis B virus, hepatitis C virus, human immunodeficiency virus, Epstein–Barr virus, and human papillomavirus. Finally, emerging topics concerning the importance of miRNA genetic variants will be presented, focusing on the context of viral infectious diseases.

MicroRNA-219 decreases hippocampal long-term potentiation inhibition and hippocampal neuronal cell apoptosis in type 2 diabetes mellitus mice by suppressing the NMDAR signaling pathway

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is a complex polygenic disease that causes hyperglycemia and accounts for 90%-95% of all diabetes mellitus cases. Hence, this study aimed to examine the effects of microRNA-219 (miR-219) on inhibition of long-term potentiation (LTP) and apoptosis of hippocampal neuronal cells in T2DM mice through the N-methyl-d-aspartate receptor (NMDAR) signaling pathway regulation.

METHODS

The T2DM mouse models were established, after which LTP in vivo was recorded by means of electrical biology, and the fasting blood glucose of mice was measured. Next, the density of pyramidal neurons in each group was calculated. Additionally, the expression levels of miR-219, the NMDAR signaling pathway [NMDAR1 (NR) 1, NR2A, and NR2B), downstream target proteins [calmodulin-dependent protein kinase-II (CaMK-II) and cAMP response element binding protein (CREB)], and apoptosis-related factors [Bcl2-associated X protein (Bax), c-caspase-9 and c-caspase-3] in the hippocampal tissues were determined. Finally, immunohistochemistry was applied to detect and measure the positive expression of Bax, caspase-9, and caspase-3 proteins.

RESULTS

The results showed that upregulation of miR-219 increases LTP and density of pyramidal neurons in the hippocampal tissues of mice, while it decreases blood glucose of db/db mice. In addition, miR-219 upregulation also leads to decreased mRNA levels of NR1, NR2A, NR2B, CaMK-II, and CREB and protein levels of NR1, NR2A, NR2B, CaMK-II, CREB, p-CREB, Bax, c-caspase-9, and c-caspase-3. Furthermore, upregulation of miR-219 inhibits positive expression of Bax, caspase-9, and caspase-3 proteins, leading to the suppression of hippocampal neuronal cell apoptosis.

CONCLUSION

The findings from this study indicated that the upregulation of miR-219 decreases LTP inhibition and hippocampal neuronal cell apoptosis in T2DM mice by downregulating the NMDAR signaling pathway, therefore suggesting that MiR-219 might be a future therapeutic strategy for T2DM.

Non-viral based miR delivery and recent developments

miRNAs are promising therapeutic targets or tools for the treatment of numerous diseases, with most prominently, cancer. The inherent capacity of these short nucleic acids to regulate multiple cancer-related pathways simultaneously has prompted strong research on understanding miR functions and their potential use for therapeutic purposes. A key determinant of miR therapeutics' potential for treatment is their delivery. Viral and non-viral vectors attempt to address the major limitations associated with miR delivery, but several hurdles have been identified. Here, we present an overview on the general limitations of miR delivery, and the delivery strategies exploited to overcome them. We provide an introduction on the advantages and disadvantages of viral and non-viral vectors, and we go into detail to analyze the most prominently used non-viral systems. We provide with an update on the most recent research on this topic and we describe the mechanism and limitations of the lipid-, polymer- and inorganic material- based miR delivery systems.

Turing Revisited: Decoding the microRNA Messages in Brain Extracellular Vesicles for Early Detection of Neurodevelopmental Disorders

The prevention of neurodevelopmental disorders (NDD) of prenatal origin suffers from the lack of objective tools for early detection of susceptible individuals and the long time lag, usually in years, between the neurotoxic exposure and the diagnosis of mental dysfunction. Human data on the effects of alcohol, lead, and mercury and experimental data from animals on developmental neurotoxins and their long-term behavioral effects have achieved a critical mass, leading to the concept of the Developmental Origin of Health and Disease (DOHaD). However, there is currently no way to evaluate the degree of brain damage early after birth. We propose that extracellular vesicles (EVs) and particularly exosomes, released by brain cells into the fetal blood, may offer us a non-invasive means of assessing brain damage by neurotoxins. We are inspired by the strategy applied by Alan Turing (a cryptanalyst working for the British government), who created a first computer to decrypt German intelligence communications during World War II. Given the growing evidence that microRNAs (miRNAs), which are among the molecules carried by EVs, are involved in cell-cell communication, we propose that decrypting messages from EVs can allow us to detect damage thus offering an opportunity to cure, reverse, or prevent the development of NDD. This review summarizes recent findings on miRNAs associated with selected environmental toxicants known to be involved in the pathophysiology of NDD.

Role of miR-34c in the cognitive function of epileptic rats induced by pentylenetetrazol

Studies suggest that microRNA (miR)-34c may serve a role in cognitive function in rodent and primate groups. A previous study demonstrated an increase in miR-34c expression in chronic epileptic rats with memory disorders, induced by pentylenetetrazol (PTZ). However, the mechanism underlying the effects of miR-34c on cognitive function in epileptic rats remains unclear. Therefore, the present study investigated alterations in cognitive function in temporal lobe epileptic rats, induced by repeated injections of PTZ, following treatment with an miR-34c agomir compared with a scramble group. Increased expression of miR-34c was observed in the agomir group, in addition to an increased deficit in learning and memory function in the Morris water maze test. Glutamate receptor ionotropic N-methyl-D-aspartate (NMDA) 2B (NR2B), phosphorylated (p)-reduced nicotinamide-adenine dinucleotide phosphate-dependent diflavin oxidoreductase 1 (NR1) and p-glutamate receptor 1 (GluR1) protein expression was detected in the hippocampus using western blotting. Additionally, the downregulation of NR2B, p-NR1 and p-GluR1 in the miR-34c agomir group demonstrated that miR-34c may serve a negative role in cognitive function in epileptic seizures, by dysregulating NMDA and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, which are associated with long-term potentiation.

miR-181a involves in the hippocampus-dependent memory formation via targeting PRKAA1

Post-transcriptional gene regulation by microRNAs (miRNAs) is involved in memory formation. However, the roles of individual miRNAs in these processes remain largely unknown. In this study, we want to clarify the role of miR-181a in hippocampus-dependent memory formation. A transient increase in miR-181a expression was observed after conditioned fear conditioning (CFC) and object location task (OLT) training. Selective overexpression or inhibition of miR-181a in the dorsal hippocampus (DH) via the injection of a miR-181a agomir or antagomir enhanced or impaired the CFC- and OLT-dependent memory formation, respectively. Using bioinformatics and luciferase assays, we identified PRKAA1 as a potential target gene of miR-181a. After CFC or OLT training, the expression and activity of PRKAA1 decreased as miR-181a expression increased and was effectively blocked by the miR-181a antagomir. Moreover, microinjection of the PRKAA1 agonist AICAR or inhibitor compound C in the DH reversed the roles of the miR-181a agomir or antagomir in CFC- and OLT-dependent memory formation. In conclusion, this work provides novel evidence describing the role and mechanism of miR-181a in hippocampus-dependent memory formation, which sheds light on the potential regulation of cognition and future treatments for cognitive disorders.

miR-12 and miR-124 contribute to defined early phases of long-lasting and transient memory

MicroRNAs (miRNAs) are important epigenetic regulators of mRNA translation implicated in long-lasting synaptic plasticity and long-term memory (LTM). Since recent findings demonstrated a role of epigenetic regulation of gene expression in early memory phases we investigated whether epigenetic regulation by miRNAs also contributes to early memory phases. We used the olfactory associative learning paradigm in honeybees and addressed the contribution of miRNAs depending on the conditioning strength. We selected miR-12, miR-124, and miR-125 that have been implicated in processes of neuronal plasticity and analysed their contribution to non-associative and associative learning using miRNA inhibitors. Blocking miR-12, miR-124, or miR125 neither affects gustatory sensitivity nor habituation nor sensitization. Blocking the function of miR-12 and miR-124 during and shortly after 3-trial conditioning impairs different early memory phases. Although different, the function of miR-12 and miR-124 is also required for early phases of transient memory that is induced by 1-trial conditioning. Blocking miR-125 has no effect on early memory independent of the conditioning strength. These findings demonstrate that distinct miRNAs contribute to early phases of both, transient memories as well as long-lasting memories.

MicroRNAs, miR-23a-3p and miR-151-3p, Are Regulated in Dentate Gyrus Neuropil following Induction of Long-Term Potentiation In Vivo

Translation of synaptic mRNA contributes to alterations in the proteome necessary to consolidate long-term potentiation (LTP), a model of memory processes. Yet, how this process is controlled is not fully resolved. MicroRNAs are non-coding RNAs that negatively regulate gene expression by suppressing translation or promoting mRNA degradation. As specific microRNAs are synaptically located, we hypothesized that they are ideally suited to couple synaptic activation, translational regulation, and LTP persistence. The aim of this study was to identify LTP-regulated microRNAs at or near synapses. Accordingly, LTP was induced unilaterally at perforant path-dentate gyrus synapses in awake adult Sprague-Dawley rats. Five hours later, dentate gyrus middle molecular layer neuropil, containing potentiated synapses, was laser-microdissected. MicroRNA expression profiling, using TaqMan Low Density MicroRNA Microarrays (n = 4), identified eight regulated microRNAs. Subsequent individual TaqMan assays confirmed upregulation of miR-23a-3p (1.30 ± 0.10; p = 0.015) and miR-151-3p (1.17 ± 0.19; p = 0.045) in a second cohort (n = 7). Interestingly, bioinformatic analysis indicated that miR-151-3p and miR-23a-3p regulate synaptic reorganisation and transcription, respectively. In summary, we have demonstrated for the first time that microRNAs are regulated in isolated neuropil following LTP induction in vivo, supporting the hypothesis that synaptic, LTP-responsive microRNAs contribute to LTP persistence via regulation of the synaptic proteome.

MicroRNAs in Neurocognitive Dysfunctions: New Molecular Targets for Pharmacological Treatments?

BACKGROUND

Neurodegenerative and cognitive disorders are multifactorial diseases (i.e., involving neurodevelopmental, genetic, age or environmental factors) characterized by an abnormal development that affects neuronal function and integrity. Recently, an increasing number of studies revealed that the dysregulation of microRNAs (miRNAs) may be involved in the etiology of cognitive disorders as Alzheimer, Parkinson, and Huntington's diseases, Schizophrenia and Autism spectrum disorders.

METHODS

From an extensive search in bibliographic databases of peer-reviewed research literature, we identified relevant published studies related to specific key words such as memory, cognition, neurodegenerative disorders, neurogenesis and miRNA. We then analysed, evaluated and summerized scientific evidences derived from these studies.

RESULTS

We first briefly summarize the basic molecular events involved in memory, a process inherent to cognitive disease, and then describe the role of miRNAs in neurodevelopment, synaptic plasticity and memory. Secondly, we provide an overview of the impact of miRNA dysregulation in the pathogenesis of different neurocognitive disorders, and lastly discuss the feasibility of miRNA-based therapeutics in the treatment of these disorders.

CONCLUSION

This review highlights the molecular basis of neurodegenerative and cognitive disorders by focusing on the impact of miRNAs dysregulation in these pathological phenotypes. Altogether, the published reports suggest that miRNAs-based therapy could be a viable therapeutic alternative to current treatment options in the future.

Satb2 determines miRNA expression and long-term memory in the adult central nervous system

SATB2 is a risk locus for schizophrenia and encodes a DNA-binding protein that regulates higher-order chromatin configuration. In the adult brain Satb2 is almost exclusively expressed in pyramidal neurons of two brain regions important for memory formation, the cerebral cortex and the CA1-hippocampal field. Here we show that Satb2 is required for key hippocampal functions since deletion of Satb2 from the adult mouse forebrain prevents the stabilization of synaptic long-term potentiation and markedly impairs long-term fear and object discrimination memory. At the molecular level, we find that synaptic activity and BDNF up-regulate Satb2, which itself binds to the promoters of coding and non-coding genes. Satb2 controls the hippocampal levels of a large cohort of miRNAs, many of which are implicated in synaptic plasticity and memory formation. Together, our findings demonstrate that Satb2 is critically involved in long-term plasticity processes in the adult forebrain that underlie the consolidation and stabilization of context-linked memory.

DOI:http://dx.doi.org/10.7554/eLife.17361.001

Novel microRNA revealed by systematic analysis of the microRNA transcriptome in dentate gyrus granule cells

Post-transcriptional control of gene expression by microRNAs provides an important regulatory system within neurons, allowing co-ordinate and fine-tuned expression of plasticity-related proteins. Indeed, specific microRNAs have been shown to be regulated by synaptic activity in the dentate gyrus, and contribute to the regulated gene expression that underlies the persistence of long-term potentiation (LTP), a model of memory. To fully explore the contribution of microRNAs in synaptic plasticity, it is important to characterize the complete microRNA transcriptome in regions such as the dentate gyrus. Accordingly we used deep sequencing and miRDeep* analysis to search for novel microRNAs expressed in the dentate gyrus granule cell layer. Drawing on combined sequencing and bioinformatics analyses, including hairpin stability and patterns of precursor microRNA processing, we identified nine putative novel microRNAs. We did not find evidence of differential expression of any of these putative microRNAs following LTP at perforant path-granule cell synapses in awake rats (5 h post-tetanus; p > 0.05). Focusing on novel_miR-1, the most abundant novel miRNA, we showed that this sequence could be amplified from RNA extracted from dentate gyrus granule cells by reverse transcription-quantitative polymerase chain reaction. Further, by computationally predicting mRNA targets of this microRNA, we found that this novel microRNA likely contributes to the regulation of proteins that function at synapses.

Transcriptional regulation of long-term potentiation

Long-term potentiation (LTP), the persistent strengthening of synapses following high levels of stimulation, is a form of synaptic plasticity that has been studied extensively as a possible mechanism for learning and memory formation. The strengthening of the synapse that occurs during LTP requires cascades of complex molecular processes and the coordinated remodeling of pre-synaptic and post-synaptic neurons. Despite over four decades of research, our understanding of the transcriptional mechanisms and molecular processes underlying LTP remains incomplete. Identification of all the proteins and non-coding RNA transcripts expressed during LTP may provide greater insight into the molecular mechanisms involved in learning and memory formation.

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.

Rapid reversal of translational silencing: Emerging role of microRNA degradation pathways in neuronal plasticity

As microRNAs silence translation, rapid reversal of this process has emerged as an attractive mechanism for driving de novo protein synthesis mediating neuronal plasticity. Herein, we summarize recent studies identifying neuronal stimuli that trigger rapid decreases in microRNA levels and reverse translational silencing of plasticity transcripts. Although these findings indicate that neuronal stimulation elicits rapid degradation of selected microRNAs, we are only beginning to decipher the molecular pathways involved. Accordingly, we present an overview of several molecular pathways implicated in mediating microRNA degradation: Lin-28, translin/trax, and MCPIP1. As these degradation pathways target distinct subsets of microRNAs, they enable neurons to reverse silencing rapidly, yet selectively.

Prolonged Induction of miR-212/132 and REST Expression in Rat Striatum Following Cocaine Self-Administration

Chronic exposure to cocaine in vivo induces long-term synaptic plasticity associated with the brain’s circuitry that underlies development of repetitive and automatic behaviors called habits. In fact, prolonged drug consumption results in aberrant expression of protein-coding genes and small regulatory RNAs, including miRNAs that are involved in synaptic plasticity and neuroadaptations. However, the mechanisms mediating cocaine use disorder are still not fully understood. The present study is designed to examine the expression of miR-124, miR-132, miR-134, and miR-212, as well as the levels of the Ago2, Pum2, and REST mRNAs and proteins implicated in their regulation. We applied rat cocaine self-administration (SA) and extinction training procedures with a yoked triad to assess the changes in the levels of four miRNAs and three protein-coding genes and corresponding proteins in the dorsal striatum. We demonstrated that elevated expression of mature miR-212 and miR-132 is long-lasting and persists in the drug-free period (till 10-day abstinence). Moreover, mRNA and protein of REST, a regulator of neuronal transcription, was raised selectively in cocaine self-administering rats and Ago2 transcript decreased after cocaine treatment. Unexpectedly, the expression level of Ago2 and Pum2 proteins changed only in the active cocaine-receiving animals. These results point out the important aspects of long-lasting alterations in microRNAs, genes, and protein expressions involved in the control of synaptic plasticity associated with reward and motivation learning related to cocaine addiction.

Exosomes as Novel Regulators of Adult Neurogenic Niches

Adult neurogenesis has been convincingly demonstrated in two regions of the mammalian brain: the sub-granular zone (SGZ) of the dentate gyrus (DG) in the hippocampus, and the sub-ventricular zone (SVZ) of the lateral ventricles (LV). SGZ newborn neurons are destined to the granular cell layer (GCL) of the DG, while new neurons from the SVZ neurons migrate rostrally into the olfactory bulb (OB). The process of adult neurogenesis persists throughout life and is supported by a pool of neural stem cells (NSCs), which reside in a unique and specialized microenvironment known as "neurogenic niche". Neurogenic niches are structured by a complex organization of different cell types, including the NSC-neuron lineage, glial cells and vascular cells. Thus, cell-to-cell communication plays a key role in the dynamic modulation of homeostasis and plasticity of the adult neurogenic process. Specific cell-cell contacts and extracellular signals originated locally provide the necessary support and regulate the balance between self-renewal and differentiation of NSCs. Furthermore, extracellular signals originated at distant locations, including other brain regions or systemic organs, may reach the niche through the cerebrospinal fluid (CSF) or the vasculature and influence its nature. The role of several secreted molecules, such as cytokines, growth factors, neurotransmitters, and hormones, in the biology of adult NSCs, has been systematically addressed. Interestingly, in addition to these well-recognized signals, a novel type of intercellular messengers has been identified recently: the extracellular vesicles (EVs). EVs, and particularly exosomes, are implicated in the transfer of mRNAs, microRNAs (miRNAs), proteins and lipids between cells and thus are able to modify the function of recipient cells. Exosomes appear to play a significant role in different stem cell niches such as the mesenchymal stem cell niche, cancer stem cell niche and pre-metastatic niche; however, their roles in adult neurogenic niches remain virtually unexplored. This review focuses on the current knowledge regarding the functional relationship between cellular and extracellular components of the adult SVZ and SGZ neurogenic niches, and the growing evidence that supports the potential role of exosomes in the physiology and pathology of adult neurogenesis.