Astrocytic miR-324-5p is essential for synaptic formation by suppressing the secretion of CCL5 from astrocytes

Targeting epigenetic mechanisms in amyloid-β-mediated Alzheimer's pathophysiology: unveiling therapeutic potential

Alzheimer's disease is a prominent chronic neurodegenerative condition characterized by a gradual decline in memory leading to dementia. Growing evidence suggests that Alzheimer's disease is associated with accumulating various amyloid-β oligomers in the brain, influenced by complex genetic and environmental factors. The memory and cognitive deficits observed during the prodromal and mild cognitive impairment phases of Alzheimer's disease are believed to primarily result from synaptic dysfunction. Throughout life, environmental factors can lead to enduring changes in gene expression and the emergence of brain disorders. These changes, known as epigenetic modifications, also play a crucial role in regulating the formation of synapses and their adaptability in response to neuronal activity. In this context, we highlight recent advances in understanding the roles played by key components of the epigenetic machinery, specifically DNA methylation, histone modification, and microRNAs, in the development of Alzheimer's disease, synaptic function, and activity-dependent synaptic plasticity. Moreover, we explore various strategies, including enriched environments, exposure to non-invasive brain stimulation, and the use of pharmacological agents, aimed at improving synaptic function and enhancing long-term potentiation, a process integral to epigenetic mechanisms. Lastly, we deliberate on the development of effective epigenetic agents and safe therapeutic approaches for managing Alzheimer's disease. We suggest that addressing Alzheimer's disease may require distinct tailored epigenetic drugs targeting different disease stages or pathways rather than relying on a single drug.

Spotlight on pro-inflammatory chemokines: regulators of cellular communication in cognitive impairment

Cognitive impairment is a decline in people's ability to think, learn, and remember, and so forth. Cognitive impairment is a global health challenge that affects the quality of life of thousands of people. The condition covers a wide range from mild cognitive impairment to severe dementia, which includes Alzheimer's disease (AD) and Parkinson's disease (PD), among others. While the etiology of cognitive impairment is diverse, the role of chemokines is increasingly evident, especially in the presence of chronic inflammation and neuroinflammation. Although inflammatory chemokines have been linked to cognitive impairment, cognitive impairment is usually multifactorial. Researchers are exploring the role of chemokines and other inflammatory mediators in cognitive dysfunction and trying to develop therapeutic strategies to mitigate their effects. The pathogenesis of cognitive disorders is very complex, their underlying causative mechanisms have not been clarified, and their treatment is always one of the challenges in the field of medicine. Therefore, exploring its pathogenesis and treatment has important socioeconomic value. Chemokines are a growing family of structurally and functionally related small (8-10 kDa) proteins, and there is growing evidence that pro-inflammatory chemokines are associated with many neurobiological processes that may be relevant to neurological disorders beyond their classical chemotactic function and play a crucial role in the pathogenesis and progression of cognitive disorders. In this paper, we review the roles and regulatory mechanisms of pro-inflammatory chemokines (CCL2, CCL3, CCL4, CCL5, CCL11, CCL20, and CXCL8) in cognitive impairment. We also discuss the intrinsic relationship between the two, hoping to provide some valuable references for the treatment of cognitive impairment.

FABP7 drives an inflammatory response in human astrocytes and is upregulated in Alzheimer's disease

Alzheimer's disease (AD), the most common cause of dementia in the elderly, is characterized by the accumulation of intracellular neurofibrillary tangles, extracellular amyloid plaques, and neuroinflammation. In partnership with microglial cells, astrocytes are key players in the regulation of neuroinflammation. Fatty acid binding protein 7 (FABP7) belongs to a family of conserved proteins that regulate lipid metabolism, energy homeostasis, and inflammation. FABP7 expression is largely restricted to astrocytes and radial glia-like cells in the adult central nervous system. We observed that treatment of primary hippocampal astrocyte cultures with amyloid β fragment 25-35 (Aβ25-35) induces FABP7 upregulation. In addition, FABP7 expression is upregulated in the brain of APP/PS1 mice, a widely used AD mouse model. Co-immunostaining with specific astrocyte markers revealed increased FABP7 expression in astrocytes. Moreover, astrocytes surrounding amyloid plaques displayed increased FABP7 staining when compared to non-plaque-associated astrocytes. A similar result was obtained in the brain of AD patients. Whole transcriptome RNA sequencing analysis of human astrocytes differentiated from induced pluripotent stem cells (i-astrocytes) overexpressing FABP7 identified 500 transcripts with at least a 2-fold change in expression. Gene Ontology enrichment analysis identified (i) positive regulation of cytokine production and (ii) inflammatory response as the top two statistically significant overrepresented biological processes. We confirmed that wild-type FABP7 overexpression induces an NF-κB-driven inflammatory response in human i-astrocytes. On the other hand, the expression of a ligand-binding impaired mutant FABP7 did not induce NF-κB activation. Together, our results suggest that the upregulation of FABP7 in astrocytes could contribute to the neuroinflammation observed in AD.

Identification of novel microRNAs in the embryonic mouse brain using deep sequencing

Many advances in small RNA-seq technology and bioinformatics pipelines have been made recently, permitting the discovery of novel miRNAs in the embryonic day 15.5 (E15.5) mouse brain. We aimed to improve miRNA discovery in this tissue to expand our knowledge of the regulatory networks that underpin normal neurodevelopment, find new candidates for neurodevelopmental disorder aetiology, and deepen our understanding of non-coding RNA evolution. A high-quality small RNA-seq dataset of 458 M reads was generated. An unbiased miRNA discovery pipeline identified fifty putative novel miRNAs, six of which were selected for further validation. A combination of conservation analysis and target functional prediction was used to determine the authenticity of novel miRNA candidates. These findings demonstrate that miRNAs remain to be discovered, particularly if they have the features of other small RNA species.

Mir324 knockout regulates the structure of dendritic spines and impairs hippocampal long-term potentiation

MicroRNAs are an emerging class of synaptic regulators. These small noncoding RNAs post-transcriptionally regulate gene expression, thereby altering neuronal pathways and shaping cell-to-cell communication. Their ability to rapidly alter gene expression and target multiple pathways makes them interesting candidates in the study of synaptic plasticity. Here, we demonstrate that the proconvulsive microRNA miR-324-5p regulates excitatory synapse structure and function in the hippocampus of mice. Both Mir324 knockout (KO) and miR-324-5p antagomir treatment significantly reduce dendritic spine density in the hippocampal CA1 subregion, and Mir324 KO, but not miR-324-5p antagomir treatment, shift dendritic spine morphology, reducing the proportion of thin, "unstable" spines. Western blot and quantitative Real-Time PCR revealed changes in protein and mRNA levels for potassium channels, cytoskeletal components, and synaptic markers, including MAP2 and Kv4.2, which are important for long-term potentiation (LTP). In line with these findings, slice electrophysiology revealed that LTP is severely impaired in Mir324 KO mice, while neurotransmitter release probability remains unchanged. Overall, this study demonstrates that miR-324-5p regulates dendritic spine density, morphology, and plasticity in the hippocampus, potentially via multiple cytoskeletal and synaptic modulators.

Age-Dependent Regulation of Dendritic Spine Density and Protein Expression in Mir324 KO Mice

Dendritic spines are small, dynamic protrusions along the dendrite that comprise more than 90% of excitatory connections in the brain, making them essential sites for neuronal communication. These synaptic sites change throughout the process of development, reducing in density and shifting morphology as synapses are refined. One important class of dendritic spine regulators is microRNA (miRNA), small-noncoding RNAs that post-transcriptionally regulate gene expression. Several studies suggest that miRNA-324-5p regulates dendritic spine formation. In addition, we have previously shown that miR-324-5p plays a role in seizure and long-term potentiation, both of which involve dendritic spine changes. In this study, we aimed to characterize the role of miRNA-324-5p in developmental spine regulation by assessing the effect of Mir324 knockout (KO) on dendritic spine density and expression of a subset of dendritic proteins at select developmental time points. We show that miR-324-5p expression is developmentally regulated and peaks at 4 weeks of age. We demonstrate that loss of miR-324-5p expression leads to differential changes in both target protein expression and spine density at different time points during development, disrupting the pattern of spine density changes and leading to a premature loss of dendritic spines in KO mice, which is compensated later. Our findings indicate that miR-324-5p plays a role in synaptic refinement across development. Additionally, our data illustrate the importance of context in the study of miRNA, as regulation by and/or of miRNA can vary dramatically across development and in disease.

Age-dependent regulation of dendritic spine density and protein expression in Mir324 KO mice

Dendritic spines are small, dynamic protrusions along the dendrite that comprise more than 90% of excitatory connections in the brain, making them essential sites for neuronal communication. These synaptic sites change throughout the process of development, reducing in density and shifting morphology as synapses are refined. One important class of dendritic spine regulators is microRNA (miRNA), small noncoding RNAs that post-transcriptionally regulate gene expression. Several studies suggest that miRNA-324-5p regulates dendritic spine formation. In addition, we have previously shown that miR-324-5p plays a role in seizure and long-term potentiation, both of which involve dendritic spine changes. In this study, we aimed to characterize the role of miRNA-324-5p in developmental spine regulation by assessing the effect of Mir324 knockout (KO) on dendritic spine density and expression of a subset of dendritic proteins at select developmental time points. We show that miR-324-5p expression is developmentally regulated and peaks at four weeks of age. We demonstrate that loss of miR-324-5p expression leads to differential changes in both target protein expression and spine density at different time points during development, disrupting the pattern of spine density changes and leading to a premature loss of dendritic spines in KO mice, which is compensated later. Our findings indicate that miR-324-5p plays a role in synaptic refinement across development. Additionally, our data illustrate the importance of context in the study of miRNA, as regulation by and/or of miRNA can vary dramatically across development and in disease.

MicroRNA: A Linking between Astrocyte Dysfunction, Mild Cognitive Impairment, and Neurodegenerative Diseases

Simple Summary

Neurodegenerative diseases are complex neurological disorders with a high incidence worldwide in older people, increasing hospital visits and requiring expensive treatments. As a precursor phase of neurodegenerative diseases, cognitive impairment needs to be studied to understand the factors that influence its development and improve patients’ quality of life. The present review compiles possible factors and biomarkers for diagnosing mild cognitive impairment based on the most recent studies involving miRNAs. These molecules can direct the gene expression in multiple cells, affecting their behavior under certain conditions, such as stressing factors. This review encourages further research into biomarkers that identify cognitive impairment in cellular models such as astrocytes, which are brain cells capable of maintaining the optimal conditions for the central nervous system functioning.

Abstract

The importance of miRNAs in cellular processes and their dysregulation has taken significant importance in understanding different pathologies. Due to the constant increase in the prevalence of neurodegenerative diseases (ND) worldwide and their economic impact, mild cognitive impairment (MCI), considered a prodromal phase, is a logical starting point to study this public health problem. Multiple studies have established the importance of miRNAs in MCI, including astrocyte regulation during stressful conditions. Additionally, the protection mechanisms exerted by astrocytes against some damage in the central nervous system (CNS) lead to astrocytic reactivation, in which a differential expression of miRNAs has been shown. Nevertheless, excessive reactivation can cause neurodegeneration, and a clear pattern defining the equilibrium point between a neuroprotective or detrimental astrocytic phenotype is unknown. Therefore, the miRNA expression has gained significant attention to understand the maintenance of brain balance and improve the diagnosis and treatment at earlier stages in the ND. Here, we provide a comprehensive review of the emerging role of miRNAs in cellular processes that contribute to the loss of cognitive function, including lipotoxicity, which can induce chronic inflammation, also considering the fundamental role of astrocytes in brain homeostasis.

A review on the role of miRNA-324 in various diseases

Recent studies have revealed important functions of several microRNAs (miRNAs) in the pathogenesis of human diseases. miR-324 is an example of miRNAs with crucial impacts on the pathogenesis of a wide range of disorders. Gene ontology studies have indicated possible role of miR-324 in responses of cells to the leukemia inhibitory factor, long-term synaptic potentiation, positive regulation of cytokines production and sensory perception of sound. In human, miR-324 is encoded by MIR324 gene which resides on chromosome 17p13.1. In the current manuscript, we provide a concise review of the role of miR-324 in the pathogenesis of cancers as well as non-cancerous conditions such as aneurysmal subarachnoid hemorrhage, diabetic nephropathy, epilepsy, pulmonary/renal fibrosis, ischemic stroke and ischemia reperfusion injuries. Moreover, we summarize the role of this miRNA as a prognostic marker for malignant disorders.

Plasma microRNA vary in association with the progression of Alzheimer's disease

Introduction

Early intervention in Alzheimer's disease (AD) requires the development of an easily administered test that is able to identify those at risk. Focusing on microRNA robustly detected in plasma and standardizing the analysis strategy, we sought to identify disease‐stage specific biomarkers.

Methods

Using TaqMan microfluidics arrays and a statistical consensus approach, we assessed plasma levels of 185 neurodegeneration‐related microRNA, in cohorts of cognitively normal amyloid β‐positive (CN‐Aβ+), mild cognitive impairment (MCI), and Alzheimer's disease (AD) participants, relative to their respective controls.

Results

Distinct disease stage microRNA biomarkers were identified, shown to predict membership of the groups (area under the curve [AUC] >0.8) and were altered dynamically with AD progression in a longitudinal study. Bioinformatics demonstrated that these microRNA target known AD‐related pathways, such as the Phosphoinositide 3‐kinase (PI3K‐Akt) signalling pathway. Furthermore, a significant correlation was found between miR‐27a‐3p, miR‐27b‐3p, and miR‐324‐5p and amyloid beta load.

Discussion

Our results show that microRNA signatures alter throughout the progression of AD, reflect the underlying disease pathology, and may prove to be useful diagnostic markers.

Cytokine Signalling at the Microglial Penta-Partite Synapse

Microglial cell processes form part of a subset of synaptic contacts that have been dubbed microglial tetra-partite or quad-partite synapses. Since tetrapartite may also refer to the presence of extracellular matrix components, we propose the more precise term microglial penta-partite synapse for synapses that show a microglial cell process in close physical proximity to neuronal and astrocytic synaptic constituents. Microglial cells are now recognised as key players in central nervous system (CNS) synaptic changes. When synaptic plasticity involving microglial penta-partite synapses occurs, microglia may utilise their cytokine arsenal to facilitate the generation of new synapses, eliminate those that are not needed anymore, or modify the molecular and structural properties of the remaining synaptic contacts. In addition, microglia–synapse contacts may develop de novo under pathological conditions. Microglial penta-partite synapses have received comparatively little attention as unique sites in the CNS where microglial cells, cytokines and other factors they release have a direct influence on the connections between neurons and their function. It concerns our understanding of the penta-partite synapse where the confusion created by the term “neuroinflammation” is most counterproductive. The mere presence of activated microglia or the release of their cytokines may occur independent of inflammation, and penta-partite synapses are not usually active in a neuroimmunological sense. Clarification of these details is the main purpose of this review, specifically highlighting the relationship between microglia, synapses, and the cytokines that can be released by microglial cells in health and disease.

Emerging Role of microRNAs in Stroke Protection Elicited by Remote Postconditioning

Remote ischemic conditioning (RIC) represents an innovative and attractive neuroprotective approach in brain ischemia. The purpose of this intervention is to activate endogenous tolerance mechanisms by inflicting a subliminal ischemia injury to the limbs, or to another “remote” region, leading to a protective systemic response against ischemic brain injury. Among the multiple candidates that have been proposed as putative mediators of the protective effect generated by the subthreshold peripheral ischemic insult, it has been hypothesized that microRNAs may play a vital role in the infarct-sparing effect of RIC. The effect of miRNAs can be exploited at different levels: (1) as transducers of protective messages to the brain or (2) as effectors of brain protection. The purpose of the present review is to summarize the most recent evidence supporting the involvement of microRNAs in brain protection elicited by remote conditioning, highlighting potential and pitfalls in their exploitation as diagnostic and therapeutic tools. The understanding of these processes could help provide light on the molecular pathways involved in brain protection for the future development of miRNA-based theranostic agents in stroke.

SMA-miRs (miR-181a-5p, -324-5p, and -451a) are overexpressed in spinal muscular atrophy skeletal muscle and serum samples

Background:

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by the degeneration of the second motor neuron. The phenotype ranges from very severe to very mild forms. All patients have the homozygous loss of the SMN1 gene and a variable number of SMN2 (generally 2–4 copies), inversely related to the severity. The amazing results of the available treatments have made compelling the need of prognostic biomarkers to predict the progression trajectories of patients. Besides the SMN2 products, few other biomarkers have been evaluated so far, including some miRs.

Methods:

We performed whole miRNome analysis of muscle samples of patients and controls (14 biopsies and 9 cultures). The levels of muscle differentially expressed miRs were evaluated in serum samples (51 patients and 37 controls) and integrated with SMN2 copies, SMN2 full-length transcript levels in blood and age (SMA-score).

Results:

Over 100 miRs were differentially expressed in SMA muscle; 3 of them (hsa-miR-181a-5p, -324-5p, -451a; SMA-miRs) were significantly upregulated in the serum of patients. The severity predicted by the SMA-score was related to that of the clinical classification at a correlation coefficient of 0.87 (p<10^-5).

Conclusions:

miRNome analyses suggest the primary involvement of skeletal muscle in SMA pathogenesis. The SMA-miRs are likely actively released in the blood flow; their function and target cells require to be elucidated. The accuracy of the SMA-score needs to be verified in replicative studies: if confirmed, its use could be crucial for the routine prognostic assessment, also in presymptomatic patients.

Funding:

Telethon Italia (grant #GGP12116).

Role of miRNA-324-5p-Modified Adipose-Derived Stem Cells in Post-Myocardial Infarction Repair

Background and Objectives

To seek out the role of mircoRNA (miR)-324-5p-modified adipose-derived stem cells (ADSCs) in post-myocardial infarction (MI) myocardial repair.

Methods and Results

Rat ADSCs were cultivated and then identified by morphologic observation, osteogenesis and adipogenesis induction assays and flow cytometry. Afterwards, ADSCs were modified by miR-324-5p lentiviral vector, with ADSC proliferation and migration measured. Then, rat MI model was established, which was treated by ADSCs or miR-324-5p-modified ADSCs. Subsequently, the function of miR-324-5p-modified ADSCs in myocardial repair of MI rats was assessed through functional assays. Next, the binding relation of miR-324-5p and Toll-interacting protein (TOLLIP) was validated. Eventually, functional rescue assay of TOLLIP was performed to verify the role of TOLLIP in MI. First, rat ADSCs were harvested. Overexpressed miR-324-5p improved ADSC viability. ADSC transplantation moderately enhanced cardiac function of MI rats, reduced enzyme levels and decreased infarct size and apoptosis; while miR-324-5p-modified ADSCs could better promote post-MI repair. Mechanically, miR-324-5p targeted TOLLIP in myocardial tissues. Moreover, TOLLIP overexpression debilitated the promotive role of miR-324-5p-modified ADSCs in post-MI repair in rats.

Conclusions

miR-324-5p-modified ADSCs evidently strengthened post-MI myocardial repair by targeting TOLLIP in myocardial tissues.

Long-Lasting Changes in Glial Cells Isolated From Rats Subjected to the Valproic Acid Model of Autism Spectrum Disorder

Synaptic alterations concomitant with neuroinflammation have been described in patients and experimental models of autism spectrum disorder (ASD). However, the role of microglia and astroglia in relation to synaptic changes is poorly understood. Male Wistar rats prenatally exposed to valproic acid (VPA, 450 mg/kg, i.p.) or saline (control) at embryonic day 10.5 were used to study synapses, microglia, and astroglia in the prefrontal cortex (PFC) at postnatal days 3 and 35 (PND3 and PND35). Primary cultures of cortical neurons, microglia, and astroglia isolated from control and VPA animals were used to study each cell type individually, neuron-microglia and microglia-astroglia crosstalk. In the PFC of VPA rats, synaptic changes characterized by an increase in the number of excitatory synapses were evidenced at PND3 and persisted until PND35. At PND3, microglia and astroglia from VPA animals were morphologically similar to those of age-matched controls, whereas at PND35, reactive microgliosis and astrogliosis were observed in the PFC of VPA animals. Cortical neurons isolated from VPA rats mimicked in vitro the synaptic pattern seen in vivo. Cortical microglia and astroglia isolated from VPA animals exhibited reactive morphology, increased pro-inflammatory cytokines, and a compromised miRNA processing machinery. Microglia from VPA animals also showed resistance to a phagocytic challenge. In the presence of neurons from VPA animals, microglia isolated from VPA rats revealed a non-reactive morphology and promoted neurite outgrowth, while microglia from control animals displayed a reactive profile and promoted dendritic retraction. In microglia-astroglia co-cultures, microglia from VPA animals displayed a reactive profile and exacerbated astrocyte reactivity. Our study indicates that cortical microglia from VPA animals are insensitive or adapted to neuronal cues expressed by neurons from VPA animals. Further, long-term in vivo microgliosis could be the result of altered microglia-astroglia crosstalk in VPA animals. Thus, our study highlights cortical microglia-astroglia communication as a new mechanism implicated in neuroinflammation in ASD; consequently, we propose that this crosstalk is a potential target for interventions in this disorder.

Functions of noncoding RNAs in glial development

Glia are widely distributed in the central nervous system and are closely related to cell metabolism, signal transduction, support, cell migration, and other nervous system development processes and functions. Glial development is complex and essential, including the processes of proliferation, differentiation, and migration, and requires precise regulatory networks. Noncoding RNAs (ncRNAs) can be deeply involved in glial development through gene regulation. Here, we review the regulatory roles of ncRNAs in glial development. We briefly describe the classification and functions of noncoding RNAs and focus on microRNAs (miRNAs) and long ncRNAs (lncRNAs), which have been reported to participate extensively during glial formation. The highlight of this summary is that miRNAs and lncRNAs can participate in and regulate the signaling pathways of glial development. The review not only describes how noncoding RNAs participate in nervous system development but also explains the processes of glial development, providing a foundation for subsequent studies on glial development and new insights into the pathogeneses of related neurological diseases.

Multifaceted Regulation of MicroRNA Biogenesis: Essential Roles and Functional Integration in Neuronal and Glial Development

MicroRNAs (miRNAs) are small, non-coding RNAs that function as endogenous gene silencers. Soon after the discovery of miRNAs, a subset of brain-enriched and brain-specific miRNAs were identified and significant advancements were made in delineating miRNA function in brain development. However, understanding the molecular mechanisms that regulate miRNA biogenesis in normal and diseased brains has become a prevailing challenge. Besides transcriptional regulation of miRNA host genes, miRNA processing intermediates are subjected to multifaceted regulation by canonical miRNA processing enzymes, RNA binding proteins (RBPs) and epitranscriptomic modifications. Further still, miRNA activity can be regulated by the sponging activity of other non-coding RNA classes, namely circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs). Differential abundance of these factors in neuronal and glial lineages partly underlies the spatiotemporal expression and function of lineage-specific miRNAs. Here, we review the continuously evolving understanding of the regulation of neuronal and glial miRNA biogenesis at the transcriptional and posttranscriptional levels and the cooperativity of miRNA species in targeting key mRNAs to drive lineage-specific development. In addition, we review dysregulation of neuronal and glial miRNAs and the detrimental impacts which contribute to developmental brain disorders.

Dicer Deletion in Astrocytes Inhibits Oligodendroglial Differentiation and Myelination

Increasing evidence has shown that astrocytes are implicated in regulating oligodendrocyte myelination, but the underlying mechanisms remain largely unknown. To understand whether microRNAs in astrocytes function in regulating oligodendroglial differentiation and myelination in the developing and adult CNS, we generated inducible astrocyte-specific Dicer conditional knockout mice (hGFAP-CreERT; Dicer fl/fl). By using a reporter mouse line (mT/mG), we confirmed that hGFAP-CreERT drives an efficient and astrocyte-specific recombination in the developing CNS, upon tamoxifen treatment from postnatal day 3 (P3) to P7. The Dicer deletion in astrocytes resulted in inhibited oligodendroglial differentiation and myelination in the developing CNS of Dicer cKO mice at P10 and P14, and did not alter the densities of neurons or axons, indicating that Dicer in astrocytes is required for oligodendrocyte myelination. Consequently, the Dicer deletion in astrocytes at P3 resulted in impaired spatial memory and motor coordination at the age of 9 weeks. To understand whether Dicer in astrocytes is also required for remyelination, we induced Dicer deletion in 3-month-old mice and then injected lysolecithin into the corpus callosum to induce demyelination. The Dicer deletion in astrocytes blocked remyelination in the corpus callosum 14 days after induced demyelination. Together, our results indicate that Dicer in astrocytes is required for oligodendroglia myelination in both the developing and adult CNS.

Silencing of miR-324-5p alleviates rat spinal cord injury by Sirt1

MicroRNAs (miRNAs) are implicated in the pathogenesis of spinal cord injury (SCI) as primary regulators. Previous studies have reported that miR-324-5p is involved in the modulation of neural injury, while the underlying mechanisms of miR-324-5p in SCI remain unclear. In a SCI rat model, miR-324-5p was significantly upregulated in the spinal cord tissues after SCI. Downregulation of miR-324-5p via injection of adeno-associated viruses (AAV) expressing miR-324-5p inhibitor relieved animal motor deficits and pathological changes in the tissues. Furthermore, downregulation of miR-324-5p significantly altered the expression of genes regulating neural growth, apoptosis, and the inflammatory and antioxidant response, which are implicated in SCI pathogenesis. In a H₂O₂-induced cell injury model, miR-324-5p silencing rescued the elevated apoptosis of PC12 cells. Finally, miR-324-5p directly targeted the 3'-untranslated region of NAD-dependent protein deacetylase sirtuin-1 (Sirt1) and negatively regulated the levels of Sirt1, an anti-inflammatory protein involved in SCI. Silencing of Sirt1 aggravated SCI and rescued the effects of miR-324-5p downregulation in rats. Overall, our findings indicated that silencing of miR-324-5p alleviates the loss of animal locomotion and concurrently mediates several degenerative processes relevant to the pathogenesis of SCI by Sirt1, which may provide clues for SCI treatment.

MicroRNAs Instruct and Maintain Cell Type Diversity in the Nervous System

Characterizing the diverse cell types that make up the nervous system is essential for understanding how the nervous system is structured and ultimately how it functions. The astonishing range of cellular diversity found in the nervous system emerges from a small pool of neural progenitor cells. These progenitors and their neuronal progeny proceed through sequential gene expression programs to produce different cell lineages and acquire distinct cell fates. These gene expression programs must be tightly regulated in order for the cells to achieve and maintain the proper differentiated state, remain functional throughout life, and avoid cell death. Disruption of developmental programs is associated with a wide range of abnormalities in brain structure and function, further indicating that elucidating their contribution to cellular diversity will be key to understanding brain health. A growing body of evidence suggests that tight regulation of developmental genes requires post-transcriptional regulation of the transcriptome by microRNAs (miRNAs). miRNAs are small non-coding RNAs that function by binding to mRNA targets containing complementary sequences and repressing their translation into protein, thereby providing a layer of precise spatial and temporal control over gene expression. Moreover, the expression profiles and targets of miRNAs show great specificity for distinct cell types, brain regions and developmental stages, suggesting that they are an important parameter of cell type identity. Here, we provide an overview of miRNAs that are critically involved in establishing neural cell identities, focusing on how miRNA-mediated regulation of gene expression modulates neural progenitor expansion, cell fate determination, cell migration, neuronal and glial subtype specification, and finally cell maintenance and survival.

Epigenetic Regulation of the Hippocampus, with Special Reference to Radiation Exposure

The hippocampus is crucial in learning, memory and emotion processing, and is involved in the development of different neurological and neuropsychological disorders. Several epigenetic factors, including DNA methylation, histone modifications and non-coding RNAs, have been shown to regulate the development and function of the hippocampus, and the alteration of epigenetic regulation may play important roles in the development of neurocognitive and neurodegenerative diseases. This review summarizes the epigenetic modifications of various cell types and processes within the hippocampus and their resulting effects on cognition, memory and overall hippocampal function. In addition, the effects of exposure to radiation that may induce a myriad of epigenetic changes in the hippocampus are reviewed. By assessing and evaluating the current literature, we hope to prompt a more thorough understanding of the molecular mechanisms that underlie radiation-induced epigenetic changes, an area which can be further explored.

[miR-324-5p inhibits lipopolysaccharide-induced proliferation of rat glomerular mesangial cells by regulating the Syk/Ras/c-fos pathway]

OBJECTIVE

To investigate the effect of miR-324-5p on the proliferation of rat glomerular mesangial (HBZY-1) cells and the role of Syk/Ras/c-fos signaling pathway in mediating this effect.

METHODS

HBZY-1 cells cultured in vitro were transiently transfected with miR-324-5p mimics or miR-324-5p-mimics-NC followed by treatment with lipopolysaccharide (LPS). MTT assay was used to detect the proliferation activity of HBZY-1 cells, and RT-qPCR was used to detect the expressions of miR-324-5p and the mRNA expressions of Syk, Ras, MEK1/2, ERK1/2 and c-fos mRNA. The protein expressions of p-Syk, Ras, p-MEK1/2, p-ERK1/2 and c-Fos were detected by Western blotting and immunofluorescence assay.

RESULTS

MTT assay showed that exposure to LPS significantly enhanced the proliferative activity of HBZY-1 cells. Compared with the cells treated with LPS and LPS + mimics NC, the cells transfected with miR-324-5p mimics prior to LPS exposure exhibited significantly lowered proliferative activity. Transfection with miR-324-5p mimics significantly lowered the mRNA expressions of Syk, Ras, MEK1/2, ERK1/2 and c-fos and the protein expressions of p-Syk, Ras, MEK1/2, ERK1/2 and c-Fos (P < 0.05), and reduced numbers of cells positive for p-Syk, Ras, p-MEK1/2, p-ERK1/2 and c-Fos proteins following LPS exposure.

CONCLUSIONS

miR-324-5p can inhibit the proliferation of rat chronic glomerulonephritis cells induced by LPS by inhibiting Syk/Ras/c-fos signaling pathway and may potentially serve as a diagnostic indicator and a therapeutic target for chronic glomerulonephritis.

Remote postconditioning ameliorates stroke damage by preventing let-7a and miR-143 up-regulation

Remote limb ischemic postconditioning (RLIP) is a well-established neuroprotective strategy able to protect the brain from a previous harmful ischemic insult through a sub-lethal occlusion of the femoral artery. Neural and humoral mechanisms have been proposed as mediators required to transmit the peripheral signal from limb to brain. Moreover, different studies suggest that protection observed at brain level is associated to a general genetic reprogramming involving also microRNAs (miRNAs) intervention.

Methods: Brain ischemia was induced in male rats by transient occlusion of the middle cerebral artery (tMCAO), whereas RLIP was achieved by one cycle of temporary occlusion of the ipsilateral femoral artery after tMCAO. The expression profile of 810 miRNAs was evaluated in ischemic brain samples from rats subjected either to tMCAO or to RLIP. Among all analyzed miRNAs, there were four whose expression were upregulated after stroke and returned to basal level after RLIP, thus suggesting a possible involvement in RLIP-induced neuroprotection. These selected miRNAs were intracerebroventricularly infused in rats subjected to remote ischemic postconditioning, and their effect was evaluated in terms of brain damage, neurological deficit scores and expression of putative targets.

Results: Twenty-one miRNAs, whose expression was significantly affected by tMCAO and by tMCAO plus RLIP, were selected based on microarray microfluidic profiling. Our data showed that: (1) stroke induced an up-regulation of let-7a and miR-143 (2) these two miRNAs were involved in the protective effects induced by RLIP and (3) HIF1-α contributes to their protective effect. Indeed, their expression was reduced after RLIP and the exogenous intracerebroventricularly infusion of let-7a and miR-143 mimics prevented neuroprotection and HIF1-α overexpression induced by RLIP.

Conclusions: Prevention of cerebral let-7a and miR-143 overexpression induced by brain ischemia emerges as new potential strategy in stroke intervention.

MicroRNAs and target genes in epileptogenesis

Epilepsy is a chronic brain dysfunction. Current antiepileptic medicines cannot prevent epileptogenesis. Increasing data have shown that microRNAs (miRNAs) are selectively altered within the epileptic hippocampi of experimental models and human tissues, and these alterations affect the genes that control epileptogenesis. Furthermore, manipulation of miRNAs in animal models can modify epileptogenesis. As a result, miRNAs have been proposed as promising targets for treating epilepsy. We searched PubMed using the terms "microRNAs/miRNAs AND epilepsy", "microRNAs/miRNAs AND epileptogenesis", and "microRNAs/miRNAs AND seizure". We selected the articles in which the relationship between miRNAs and target gene(s) was validated and manipulation of miRNAs in in vivo epilepsy models modified epileptogenesis during the chronic phase via gene regulation. A total of 13 miRNAs were found in the present review. Based on the current analysis of miRNAs and their target gene(s), each miRNA has limitations as a potential epilepsy target. Importantly, miR-211 or miR-128 transgenic mice displayed seizures. These findings highlight new developments for epileptogenesis prevention. Developing novel strategies to modify epileptogenesis will be effective in curing epilepsy patients. This article provides an overview of the clinical application of miRNAs as novel targets for epilepsy.

The MicroRNA Centrism in the Orchestration of Neuroinflammation in Neurodegenerative Diseases

MicroRNAs (miRNAs) are small non-coding RNAs with a unique ability to regulate the transcriptomic profile by binding to complementary regulatory RNA sequences. The ability of miRNAs to enhance (proinflammatory miRNAs) or restrict (anti-inflammatory miRNAs) inflammatory signalling within the central nervous system is an area of ongoing research, particularly in the context of disorders that feature neuroinflammation, including neurodegenerative diseases (NDDs). Furthermore, the discovery of competing endogenous RNAs (ceRNAs) has led to an increase in the complexity of miRNA-mediated gene regulation, with a paradigm shift from a unidirectional to a bidirectional regulation, where miRNA acts as both a regulator and is regulated by ceRNAs. Increasing evidence has revealed that ceRNAs, including long non-coding RNAs, circular RNAs, and pseudogenes, can act as miRNA sponges to regulate neuroinflammation in NDDs within complex cross-talk regulatory machinery, which is referred to as ceRNA network (ceRNET). In this review, we discuss the role of miRNAs in neuroinflammatory regulation and the manner in which cellular and vesicular ceRNETs could influence neuroinflammatory dynamics in complex multifactorial diseases, such as NDDs.