Identification of Circulating miR-125b as a Potential Biomarker of Alzheimer's Disease in APP/PS1 Transgenic Mouse

Epigallocatechin-3-Gallate Inhibits Oxidative Stress Through the Keap1/Nrf2 Signaling Pathway to Improve Alzheimer Disease

Alzheimer disease (AD) is a common neurodegenerative disease with an intricate pathophysiological mechanism. Oxidative stress has been shown in several investigations as a significant factor in AD progression. For instance, studies have confirmed that oxidative stress inhibition may considerably improve AD symptoms, with potent antioxidants being touted as a possible interventional strategy in the search for AD treatment. Epigallocatechin-3-gallate (EGCG) acts as a natural catechin that has antioxidant effect. It activates the kelch-like epichlorohydrin-associated proteins (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway to inhibit oxidative stress. The Keap1/Nrf2 signal pathway is not only an upstream signaling target for a variety of antioxidant enzymes, but also minimizes high levels of reactive oxygen species. This report analyzes the antioxidant effect of EGCG in AD, elaborates its specific mechanism of action, and provides a theoretical basis for its clinical application in AD.

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.

A hypothesis about interrelations of epigenetic factors and transposable elements in memory formation

The review describes the hypothesis that the drivers of epigenetic regulation in memory formation are transposable elements that influence the expression of specific genes in the brain. The hypothesis is confirmed by research into transposon activation in neuronal stem cells during neuronal differentiation. These changes occur in the hippocampus dentate gyrus, where a pronounced activity of transposons and their insertion near neuron-specific genes have been detected. In experiments on changing the activity of histone acetyltransferase and inhibition of DNA methyltransferase and reverse transcriptase, the involvement of epigenetic factors and retroelements in the mechanisms of memory formation has been shown. Also, a number of studies on different animals have revealed the preservation of long-term memory without the participation of synaptic plasticity. The data obtained suggest that transposons, which are genome sensors highly sensitive to various environmental and internal influences, form memory at the nuclear coding level. Therefore, long-term memory is preserved after elimination of synaptic connections. This is confirmed by the fact that the proteins involved in memory formation, including the transfer of genetic information through synapses between neurons (Arc protein), originate from transposons. Long non-coding RNAs and microRNAs also originate from transposons; their role in memory consolidation has been described. Pathological activation of transposable elements is a likely cause of neurodegenerative diseases with memory impairment. Analysis of the scientific literature allowed us to identify changes in the expression of 40 microRNAs derived from transposons in Alzheimer's disease. For 24 of these microRNAs, the mechanisms of regulation of genes involved in the functioning of the brain have been described. It has been suggested that the microRNAs we identified could become potential tools for regulating transposon activity in the brain in order to improve memory.

MicroRNA (miRNA) as a biomarker for diagnosis, prognosis, and therapeutics molecules in neurodegenerative disease

Neurodegenerative diseases that include Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), Huntington's disease (HD), and multiple sclerosis (MS) that arise due to numerous causes like protein accumulation and autoimmunity characterized by neurologic depletion which lead to incapacity in normal physiological function such as thinking and movement in these patients. Glial cells perform an important role in protective neuronal function; in the case of neuroinflammation, glial cell dysfunction can promote the development of neurodegenerative diseases. miRNA that participates in gene regulation and plays a vital role in many biological processes in the body; in the central nervous system (CNS), it can play an essential part in neural maturation and differentiation. In neurodegenerative diseases, miRNA dysregulation occurs, enhancing the development of these diseases. In this review, we discuss neurodegenerative disease (Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS)) and how miRNA is preserved as a diagnostic biomarker or therapeutic agent in these disorders. Finally, we highlight miRNA as therapy.

Systemic analysis of the prognostic significance and interaction network of miR-26b-3p in cholangiocarcinoma

MicroRNAs (miRNAs) reportedly play significant roles in the progression of various cancers and hold huge potential as both diagnostic tools and therapeutic targets. Given the ongoing uncertainty surrounding the precise functions of several miRNAs in cholangiocarcinoma (CCA), this research undertakes a comprehensive analysis of CCA data sourced from Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases. The present study identified a novel miRNA, specifically miR-26b-3p, which exhibited prognostic value for individuals with CCA. Notably, miR-26b-3p was upregulated within CCA samples, with an inverse correlation established with patient prognosis (Hazard Ratio = 8.19, p = 0.018). Through a combination of functional enrichment analysis, analysis of the LncRNA-miR-26b-3p-mRNA interaction network, and validation by qRT PCR and western blotting, this study uncovered the potential of miR-26b-3p in potentiating the malignant progression of CCA via regulation of essential genes (including PSMD14, XAB2, SLC4A4) implicated in processes such as endoplasmic reticulum (ER) stress and responses to misfolded proteins. Our findings introduce novel and valuable insights that position miR-26b-3p-associated genes as promising biomarkers for the diagnosis and treatment of CCA.

Serum Exosomal miRNA-125b and miRNA-451a are Potential Diagnostic Biomarker for Alzheimer's Diseases

Aim

To explore the diagnostic value of serum-derived exosomal miRNAs and predict the roles of their target genes in Alzheimer's disease (AD) based on the expression of miRNAs in AD patients.

Methods

We determined the relative concentration of exosomal miRNAs by High-throughput Second-generation Sequencing and real-time quantitative real-time PCR.

Results

71 AD patients and 71 ND subjects were collected. The study demonstrated that hsa-miR-125b-1-3p, hsa-miR-193a-5p, hsa-miR-378a-3p, hsa-miR-378i and hsa-miR-451a are differentially expressed in the serum-derived exosomes of AD patients compared with healthy subjects. According to ROC analysis, hsa-miR-125b-1-3p has an AUC of 0.765 in the AD group compared to the healthy group with a sensitivity and specificity of 82.1-67.7%, respectively. Enrichment analysis of its target genes showed that they were related to neuroactive ligand-receptor interactions, the PI3K-Akt signaling pathway, the Hippo signaling pathway and nervous system-related pathways. And, hsa-miR-451a had an AUC of 0.728 that differentiated the AD group from the healthy group with a sensitivity and specificity of 67.9% and 72.6%, respectively. Enrichment analysis of its target genes showed a relationship with cytokine-cytokine receptor interactions and the PI3K-Akt signaling pathway.

Conclusion

The dysregulation of serum exosomal microRNAs in patients with AD may promote the diagnosis of AD. The target genes of miRNAs may be involved in the occurrence and development of AD through various pathways.

Involvement of transposable elements in Alzheimer's disease pathogenesis

Alzheimer's disease affects an average of 5 % of the population with a significant increase in prevalence with age, suggesting that the same mechanisms that underlie aging may influence this pathology. Investigation of these mechanisms is promising for effective methods of treatment and prevention of the disease. Possible participants in these mechanisms are transposons, which serve as drivers of epigenetic regulation, since they form species-specific distributions of non-coding RNA genes in genomes in evolution. Study of miRNA involvement in Alzheimer's disease pathogenesis is relevant, since the associations of protein-coding genes (APOE4, ABCA7, BIN1, CLU, CR1, PICALM, TREM2) with the disease revealed as a result of GWAS make it difficult to explain its complex pathogenesis. Specific expression changes of many genes were found in different brain parts of Alzheimer's patients, which may be due to global regulatory changes under the influence of transposons. Experimental and clinical studies have shown pathological activation of retroelements in Alzheimer's disease. Our analysis of scientific literature in accordance with MDTE DB revealed 28 miRNAs derived from transposons (17 from LINE, 5 from SINE, 4 from HERV, 2 from DNA transposons), the expression of which specifically changes in this disease (decreases in 17 and increases in 11 microRNA). Expression of 13 out of 28 miRNAs (miR-151a, -192, -211, -28, -31, -320c, -335, -340, -378a, -511, -576, -708, -885) also changes with aging and cancer development, which indicates the presence of possible common pathogenetic mechanisms. Most of these miRNAs originated from LINE retroelements, the pathological activation of which is associated with aging, carcinogenesis, and Alzheimer's disease, which supports the hypothesis that these three processes are based on the primary dysregulation of transposons that serve as drivers of epigenetic regulation of gene expression in ontogeny.

Unraveling the role of miRNAs in the diagnosis, progression, and therapeutic intervention of Alzheimer's disease

Alzheimer's disease (AD) is a multifaceted, advancing neurodegenerative illness that is responsible for most cases of neurological impairment and dementia in the aged population. As the disease progresses, affected individuals may experience cognitive decline, linguistic problems, affective instability, and behavioral changes. The intricate nature of AD reflects the altered molecular mechanisms participating in the affected human brain. MicroRNAs (miRNAs, miR) are essential for the intricate control of gene expression in neurobiology. miRNAs exert their influence by modulating the transcriptome of brain cells, which typically exhibit substantial genetic activity, encompassing gene transcription and mRNA production. Presently, comprehensive studies are being conducted on AD to identify miRNA-based signatures that are indicative of the disease pathophysiology. These findings can contribute to the advancement of our understanding of the mechanisms underlying this disorder and can inform the development of therapeutic interventions based on miRNA and related RNA molecules. Therefore, this comprehensive review provides a detailed holistic analysis of the latest advances discussing the emerging role of miRNAs in the progression of AD and their possible application as potential biomarkers and targets for therapeutic interventions in future studies.

Understanding the multifaceted role of miRNAs in Alzheimer's disease pathology

Small non-coding RNAs (miRNAs) regulate gene expression by binding to mRNA and mediating its degradation or inhibiting translation. Since miRNAs can regulate the expression of several genes, they have multiple roles to play in biological processes and human diseases. The majority of miRNAs are known to be expressed in the brain and are involved in synaptic functions, thus marking their presence and role in major neurodegenerative disorders, including Alzheimer's disease (AD). In AD, amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) are known to be the major hallmarks. The clearance of Aβ and tau is known to be associated with miRNA dysregulation. In addition, the β-site APP cleaving enzyme (BACE 1), which cleaves APP to form Aβ, is also found to be regulated by miRNAs, thus directly affecting Aβ accumulation. Growing evidences suggest that neuroinflammation can be an initial event in AD pathology, and miRNAs have been linked with the regulation of neuroinflammation. Inflammatory disorders have also been associated with AD pathology, and exosomes associated with miRNAs are known to regulate brain inflammation, suggesting for the role of systemic miRNAs in AD pathology. Several miRNAs have been related in AD, years before the clinical symptoms appear, most of which are associated with regulating the cell cycle, immune system, stress responses, cellular senescence, nerve growth factor (NGF) signaling, and synaptic regulation. Phytochemicals, especially polyphenols, alter the expression of various miRNAs by binding to miRNAs or binding to the transcriptional activators of miRNAs, thus control/alter various metabolic pathways. Awing to the sundry biological processes being regulated by miRNAs in the brain and regulation of expression of miRNAs via phytochemicals, miRNAs and the regulatory bioactive phytochemicals can serve as therapeutic agents in the treatment and management of AD.

Non-Coding RNA in Microglia Activation and Neuroinflammation in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by complex pathophysiological features. Amyloid plaques resulting from extracellular amyloid deposition and neurofibrillary tangles formed by intracellular hyperphosphorylated tau accumulation serve as primary neuropathological criteria for AD diagnosis. The activation of microglia has been closely associated with these pathological manifestations. Non-coding RNA (ncRNA), a versatile molecule involved in various cellular functions such as genetic information storage and transport, as well as catalysis of biochemical reactions, plays a crucial role in microglial activation. This review aims to investigate the regulatory role of ncRNAs in protein expression by directly targeting genes, proteins, and interactions. Furthermore, it explores the ability of ncRNAs to modulate inflammatory pathways, influence the expression of inflammatory factors, and regulate microglia activation, all of which contribute to neuroinflammation and AD. However, there are still significant controversies surrounding microglial activation and polarization. The categorization into M1 and M2 phenotypes may oversimplify the intricate and multifaceted regulatory processes in microglial response to neuroinflammation. Limited research has been conducted on the role of ncRNAs in regulating microglial activation and inducing distinct polarization states in the context of neuroinflammation. Moreover, the regulatory mechanisms through which ncRNAs govern microglial function continue to be refined. The current understanding of ncRNA regulatory pathways involved in microglial activation remains incomplete and may be influenced by spatial, temporal, and tissue-specific factors. Therefore, further in-depth investigations are warranted. In conclusion, there are ongoing debates and uncertainties regarding the activation and polarization of microglial cells, particularly concerning the categorization into M1 and M2 phenotypes. The study of ncRNA regulation in microglial activation and polarization, as well as its mechanisms, is still in its early stages and requires further investigation. However, this review offers new insights and opportunities for therapeutic approaches in AD. The development of ncRNA-based drugs may hold promise as a new direction in AD treatment.

Platelet MicroRNA-484 as a Novel Diagnostic Biomarker for Acute Coronary Syndrome

OBJECTIVE

Platelet microRNAs (miRs) have been indicated as a diagnostic biomarker in various diseases, including acute coronary syndrome (ACS). This study aimed to investigate the expression of miR-223-5p, miR-126-5p, miR-484, and miR-130a-3p in individuals with coronary artery disease (CAD).

METHODS

Forty subjects with CAD and 13 healthy individuals were under study. The expression of miR-223-5p, miR-126-5p, miR-484, and miR-130a-3p was measured in platelets by quantitative reverse transcription-polymerase chain reaction. The relationship between miRNA expression and various parameters of the subjects was analyzed using analysis of variance and Spearman and t-tests.

RESULTS

The miR-484 expression was significantly upregulated in the ACS subjects (P = .0097). Moreover, miR-484 had diagnostic value for screening subjects with unstable angina vs controls (area under the curve [AUC] = 0.978, 95% confidence interval [CI] 0.92-1, P = .0006) and NSTEMI patients versus controls (AUC = 0.910, 95% CI 0.74-1, P = .005).

CONCLUSION

The results of this study indicate that the upregulated expression of miR-484 in ACS patients might be used as a diagnostic biomarker in ACS.

Therapeutic actions of tea phenolic compounds against oxidative stress and inflammation as central mediators in the development and progression of health problems: A review focusing on microRNA regulation

Many health problems including chronic diseases are closely associated with oxidative stress and inflammation. Tea has abundant phenolic compounds with various health benefits including antioxidant and anti-inflammatory properties. This review focuses on the present understanding of the impact of tea phenolic compounds on the expression of miRNAs, and elucidates the biochemical and molecular mechanisms underlying the transcriptional and post-transcriptional protective actions of tea phenolic compounds against oxidative stress- and/or inflammation-mediated diseases. Clinical studies showed that drinking tea or taking catechin supplement on a daily basis promoted the endogenous antioxidant defense system of the body while inhibiting inflammatory factors. The regulation of chronic diseases based on epigenetic mechanisms, and the epigenetic-based therapies involving different tea phenolic compounds, have been insufficiently studied. The molecular mechanisms and application strategies of miR-27 and miR-34 involved in oxidative stress response and miR-126 and miR-146 involved in inflammation process were preliminarily investigated. Some emerging evidence suggests that tea phenolic compounds may promote epigenetic changes, involving non-coding RNA regulation, DNA methylation, histone modification, ubiquitin and SUMO modifications. However, epigenetic mechanisms and epigenetic-based disease therapies involving phenolic compounds from different teas, and the potential cross-talks among the epigenetic events, remain understudied.

Alzheimer’s disease: insights and new prospects in disease pathophysiology, biomarkers and disease-modifying drugs

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases that affect millions of people worldwide, with both prevalence and incidence increasing with age. It is characterized by cognitive decline associated, specifically, with degeneration of cholinergic neurons. The problem of this disease is even more fundamental as the available therapies remain fairly limited and mainly focused on symptoms' relief. Although the aetiology of the disease remains elusive, two main pathological hallmarks are described: i) presence of neurofibrillary tangles formed by unfolded protein aggregates (hyperphosphorylated Tau protein) and ii) presence of extracellular aggregates of amyloid-beta peptide. Given the complexity surrounding the pathogenesis of the disease, several potential targets have been highlighted and interrelated upon its progression, such as oxidative stress and the accumulation of metal ions. Thus, advances have been made on the development of innovative multitarget therapeutical compounds to delay the disease progression and restore cell function. This review focuses the ongoing research on new insights and emerging disease-modifying drugs for AD treatment. Furthermore, classical and novel potential biomarkers for early diagnosis of the disease, and their role in assisting on the improvement of targeted therapies will also be approached.

Profiling microRNA from peripheral blood mononuclear cells in early-onset familial Alzheimer's disease

MicroRNAs (miRNAs) refer to short in-length, noncoding RNAs that regulate numerous cellular functions by targeting mRNA, and numerous types of research have shown that miRNA is vitalin Alzheimer's disease. For identifying differentially expressed miRNAs in the peripheral blood mononuclear cell (PBMC) of early-onset familial Alzheimer's disease (EOFAD), we conducted this study which might give a reference for potential therapeutic targets or biomarkers for this disease. On the basis of high-throughput sequencing, we screened the miRNAs expression profiles in PBMC regarding both EOFAD patients and healthy controls, and the biological information was analyzed. Compared with the PBMC of healthy controls, 142 miRNAs were differentially expressed in EOFAD patients ( P  < 0.05), including 48 significantly differentially expressed miRNAs, 37 of which were significantly upregulated, including miR-3614-5p, miR-193A-5p, miR-2115-5p, miR-143-3p, etc. and 11 were significantly downregulated, including miR-484, miR-708-5p, miR-205-5p, miR-31-5p, etc. According to biological information analysis, 768 miRNA target genes were differentially expressed, which may be involved in multiple gene functions and cell cycle, cell senescence, and several signaling pathways, including FoxO, MAPK, Ras, mTOR, neurotrophin, etc. There are differential expressions of miRNAs in PBMC of EOFAD patients and controls, revealing their importance in Alzheimer's disease as indicated by co-expression network analysis; this may support basic information for new biomarkers or treatment exploring.

Neuroprotective Effects and Therapeutic Potential of the Citrus Flavonoid Hesperetin in Neurodegenerative Diseases

Neurodegenerative disorders affect more than fifty million Americans each year and represent serious health threats as the population ages. Neuroinflammation and oxidative stress are critical in the onset, progression, and pathogenesis of neurodegenerative diseases such as Alzheimer’s (AD), Parkinson’s (PD), and amyotrophic lateral sclerosis (ALS). A wide range of natural compounds has been investigated because of their antioxidant, anti-inflammatory, and neuroprotective properties. The citrus flavonoid hesperetin (HPT), an aglycone of hesperidin found in oranges, mandarins, and lemons, has been extensively reported to exert neuroprotective effects in experimental models of neurogenerative diseases. This review has compiled multiple studies on HPT in both in vivo and in vitro models to study neurodegeneration. We focused on the modulatory effects of hesperetin on the release of cellular anti-inflammatory and antioxidative stress mediators. Additionally, this review discusses the hesperetin effect in maintaining the levels of microRNA (miRNA) and modulating autophagy as it relates to hesperetin’s protective mechanisms against neurodegeneration. Moreover, this review is focused on providing experimental data for hesperetin’s potential as a neuroprotective compound and discusses reported evidence that HPT crosses the blood–brain barrier. In summary, this review shows the evidence available in the literature to indicate the efficacy of hesperetin in delaying the onset of neurodegenerative diseases.

Nucleic acid liquid biopsies in Alzheimer's disease: current state, challenges, and opportunities

Alzheimer's disease (AD) is the most common neurodegenerative disease and affects persons of all races, ethnic groups, and sexes. The disease is characterized by neuronal loss leading to cognitive decline and memory loss. There is no cure and the effectiveness of existing treatments is limited and depends on the time of diagnosis. The long prodromal period, during which patients' ability to live a normal life is not affected despite neuronal loss, often leads to a delayed diagnosis because it can be mistaken for normal aging of the brain. In order to make a substantial impact on AD patient survival, early diagnosis may provide a greater therapeutic window for future therapies to slow AD-associated neurodegeneration. Current gold standards for disease detection include magnetic resonance imaging and positron emission tomography scans, which visualize amyloid β and phosphorylated tau depositions and aggregates. Liquid biopsies, already an active field of research in precision oncology, are hypothesized to provide early disease detection through minimally or non-invasive sample collection techniques. Liquid biopsies in AD have been studied in cerebrospinal fluid, blood, ocular, oral, and olfactory fluids. However, most of the focus has been on blood and cerebrospinal fluid due to biomarker specificity and sensitivity attributed to the effects of the blood-brain barrier and inter-laboratory variation during sample collection. Many studies have identified amyloid β and phosphorylated tau levels as putative biomarkers, however, advances in next-generation sequencing-based liquid biopsy methods have led to significant interest in identifying nucleic acid species associated with AD from liquid tissues. Differences in cell-free RNAs and DNAs have been described as potential biomarkers for AD and hold the potential to affect disease diagnosis, treatment, and future research avenues.

Microglial activation in Alzheimer's disease: The role of flavonoids and microRNAs

Alzheimer's disease (AD) is the most common form of senile dementia and is characterized by progressive cognitive impairment and neuronal degeneration. Microglial activation is an important pathologic hallmark of AD. During disease progression, microglial cells switch from an alternative or anti-inflammatory and neuroprotective profile (M2) to a classic or proinflammatory and neurotoxic profile (M1). Phenotypically, M1 microglia is characterized by the activation of inflammatory signaling pathways that cause increased expression of proinflammatory genes, including those coding for cytokines and chemokines. This microglia-mediated neuroinflammation contributes to neuronal cell death. Recent studies in microglial cells have shown that a group of plant-derived compounds, known as flavonoids, possess anti-inflammatory properties and therefore exert a neuroprotective effect through regulating microglia activation. Here, we discuss how flavonoids can promote the switch from an inflammatory M1 phenotype to an anti-inflammatory M2 phenotype in microglia and how this represents a valuable opportunity for the development of novel therapeutic strategies to blunt neuroinflammation and boost neuronal recovery in AD. We also review how certain flavonoids can inhibit neuroinflammation through their action on the expression of microglia-specific microRNAs (miRNAs), which also constitute a key therapeutic approach in different neuropathologies involving an inflammatory component, including AD. Finally, we propose novel targets of microglia-specific miRNAs that may be considered for AD treatment.

Epigallocatechin-3-Gallate (EGCG): New Therapeutic Perspectives for Neuroprotection, Aging, and Neuroinflammation for the Modern Age

Alzheimer’s and Parkinson’s diseases are the two most common forms of neurodegenerative diseases. The exact etiology of these disorders is not well known; however, environmental, molecular, and genetic influences play a major role in the pathogenesis of these diseases. Using Alzheimer’s disease (AD) as the archetype, the pathological findings include the aggregation of Amyloid Beta (Aβ) peptides, mitochondrial dysfunction, synaptic degradation caused by inflammation, elevated reactive oxygen species (ROS), and cerebrovascular dysregulation. This review highlights the neuroinflammatory and neuroprotective role of epigallocatechin-3-gallate (EGCG): the medicinal component of green tea, a known nutraceutical that has shown promise in modulating AD progression due to its antioxidant, anti-inflammatory, and anti-aging abilities. This report also re-examines the current literature and provides innovative approaches for EGCG to be used as a preventive measure to alleviate AD and other neurodegenerative disorders.

Deregulated mitochondrial microRNAs in Alzheimer's disease: Focus on synapse and mitochondria

Alzheimer's disease (AD) is the most common cause of dementia and is currently one of the biggest public health concerns in the world. Mitochondrial dysfunction in neurons is one of the major hallmarks of AD. Emerging evidence suggests that mitochondrial miRNAs potentially play important roles in the mitochondrial dysfunctions, focusing on synapse in AD progression. In this meta-analysis paper, a comprehensive literature review was conducted to identify and discuss the (1) role of mitochondrial miRNAs that regulate mitochondrial and synaptic functions; (2) the role of various factors such as mitochondrial dynamics, biogenesis, calcium signaling, biological sex, and aging on synapse and mitochondrial function; (3) how synapse damage and mitochondrial dysfunctions contribute to AD; (4) the structure and function of synapse and mitochondria in the disease process; (5) latest research developments in synapse and mitochondria in healthy and disease states; and (6) therapeutic strategies that improve synaptic and mitochondrial functions in AD. Specifically, we discussed how differences in the expression of mitochondrial miRNAs affect ATP production, oxidative stress, mitophagy, bioenergetics, mitochondrial dynamics, synaptic activity, synaptic plasticity, neurotransmission, and synaptotoxicity in neurons observed during AD. However, more research is needed to confirm the locations and roles of individual mitochondrial miRNAs in the development of AD.

MiR-191-5p alleviates microglial cell injury by targeting Map3k12 (mitogen-activated protein kinase kinase kinase 12) to inhibit the MAPK (mitogen-activated protein kinase) signaling pathway in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Multiple reports have elucidated that microRNAs are promising biomarkers for AD diagnosis and treatment. Herein, the effect of miR-191-5p on microglial cell injury and the underlying mechanism were explored. APP/PS1 transgenic mice were utilized to establish mouse model of AD. Amyloid-β protein 1-42 (Aβ1-42)-treated microglia were applied to establish in vitro cell model of AD. MiR-191-5p expression in hippocampus and microglia was measured by reverse transcription quantitative polymerase chain reaction. The viability and apoptosis of microglia were evaluated by Cell Counting Kit-8 assays and flow cytometry analyses, respectively. The binding relationship between miR-191-5p and its downstream target mitogen-activated protein kinase kinase kinase 12 (Map3k12) was determined by luciferase reporter assays. Pathological degeneration of hippocampus was tested using hematoxylin-eosin staining and Nissl staining. Aβ expression in hippocampus was examined via immunohistochemistry. In this study, miR-191-5p was downregulated in Aβ1-42-stimulated microglia and hippocampal tissues of APP/PS1 mice. MiR-191-5p overexpression facilitated cell viability and inhibited apoptosis rate of Aβ1-42-treated microglia. Mechanically, miR-191-5p targeted Map3k12 3'-untranslated region to downregulate Map3k12 expression. MiR-191-5p inhibited Aβ1-42-induced microglial cell injury and inactivated the MAPK signaling by downregulating Map3k12. Overall, miR-191-5p alleviated Aβ1-42-induced microglia cell injury by targeting Map3k12 to inhibit the MAPK signaling pathway in microglia.

Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives

Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.

Identification of Potential Diagnostic miRNAs Biomarkers for Alzheimer Disease Based on Weighted Gene Coexpression Network Analysis

BACKGROUND

Alzheimer disease (AD) is an age-related neurodegenerative disease that accounts for nearly three fourths of dementia cases. Searching for potential biomarkers will help clinicians in the early diagnosis and treatment of AD.

METHODS

Firstly, we downloaded detailed AD data from the Gene Expression Omnibus (GEO) database for identification of differentially expressed microribonucleic acids (DEmiRNAs) and differentially expressed messenger ribonucleic acids (DEmRNAs). Secondly, functional enrichment analysis was used to identify the biological functions of DEmRNAs. Thirdly, weighted gene coexpression network analysis was used to identify important modules and hub miRNAs. In addition, the miRNA-mRNA regulatory network was constructed. Fourthly, the GSE120584 dataset was used for electronic expression verification and diagnostic analysis. Finally, real-time polymerase chain reaction in vitro verification was performed.

RESULTS

We obtained 1005 DEmiRNAs and 97 DEmRNAs, respectively. Functional enrichment found that DEmRNAs was enriched in the N-glycan biosynthesis pathway, which was associated with AD. In the weighted gene coexpression network analysis, we found that the brown module was the optimal module. Moreover, 11 hub miRNAs were identified. A total of 216 negatively regulated miRNA-mRNA regulation effects are involved. Hub miRNAs were found to have potential diagnostic value in the receiver operating characteristic analysis.

CONCLUSION

Eleven hub miRNAs were identified, and DEmRNAs was found to be significantly enriched in the N-glycan biosynthesis pathway, which contributes to the early diagnosis and treatment of AD.

Reduced serum miR-202 may promote the progression of Alzheimer's disease patients via targeting amyloid precursor protein

The current study investigated whether the expression of miR-202 was abnormal in the serum of patients with Alzheimer's disease (AD) and evaluated the potential clinical significance, thereby shedding light on the diagnosis of AD. Here, our data showed that the level of miR-202 decreased significantly in the serum of AD patients (n = 121) compared with that of healthy controls (n = 86). Further analysis showed that the level of serum miR-202 was gradually decreased in the mild AD group (n = 31), moderate AD group (n = 52) and severe AD group (n = 38) compared with the healthy control group. Receiver operating characteristic (ROC) curve analysis demonstrated that serum miR-202 could differentiate AD patients from healthy controls, with an AUC of 0.892. Spearman correlation analysis showed that serum miR-202 was positively correlated with the Mini-Mental State Examination (MMSE). Based on TargetScan, a conserved binding site was identified in the 3'UTR of amyloid precursor protein (APP). The dual luciferase assay showed that miR-202 suppressed the relative luciferase activity of pmirGLO-APP-3'UTR. Western blot assays indicated that overexpression of miR-202 suppressed the expression of APP, while the expression of APP was enhanced after inhibition of miR-202 in PC12 cells, indicating that APP was a possible target gene of miR-202. Moreover, the cell apoptosis induced by transfection of miR-202 inhibitor was abolished by silencing APP. In summary, we showed novel data that downregulation of serum miR-202 may be used as a potential biomarker for AD and may promote the development of AD by targeting APP.

Adipocyte, Immune Cells, and miRNA Crosstalk: A Novel Regulator of Metabolic Dysfunction and Obesity

Obesity is characterized as a complex and multifactorial excess accretion of adipose tissue (AT) accompanied with alterations in the immune response that affects virtually all age and socioeconomic groups around the globe. The abnormal accumulation of AT leads to several metabolic diseases, including nonalcoholic fatty liver disorder (NAFLD), low-grade inflammation, type 2 diabetes mellitus (T2DM), cardiovascular disorders (CVDs), and cancer. AT is an endocrine organ composed of adipocytes and immune cells, including B-Cells, T-cells and macrophages. These immune cells secrete various cytokines and chemokines and crosstalk with adipokines to maintain metabolic homeostasis and low-grade chronic inflammation. A novel form of adipokines, microRNA (miRs), is expressed in many developing peripheral tissues, including ATs, T-cells, and macrophages, and modulates the immune response. miRs are essential for insulin resistance, maintaining the tumor microenvironment, and obesity-associated inflammation (OAI). The abnormal regulation of AT, T-cells, and macrophage miRs may change the function of different organs including the pancreas, heart, liver, and skeletal muscle. Since obesity and inflammation are closely associated, the dysregulated expression of miRs in inflammatory adipocytes, T-cells, and macrophages suggest the importance of miRs in OAI. Therefore, in this review article, we have elaborated the role of miRs as epigenetic regulators affecting adipocyte differentiation, immune response, AT browning, adipogenesis, lipid metabolism, insulin resistance (IR), glucose homeostasis, obesity, and metabolic disorders. Further, we will discuss a set of altered miRs as novel biomarkers for metabolic disease progression and therapeutic targets for obesity.

Neuronal Development-Related miRNAs as Biomarkers for Alzheimer's Disease, Depression, Schizophrenia and Ionizing Radiation Exposure

Radiation exposure may induce Alzheimer's disease (AD), depression or schizophrenia. A number of experimental and clinical studies suggest the involvement of miRNA in the development of these diseases, and also in the neuropathological changes after brain radiation exposure. The current literature review indicated the involvement of 65 miRNAs in neuronal development in the brain. In the brain tissue, blood, or cerebral spinal fluid (CSF), 11, 55, or 28 miRNAs are involved in the development of AD respectively, 89, 50, 19 miRNAs in depression, and 102, 35, 8 miRNAs in schizophrenia. We compared miRNAs regulating neuronal development to those involved in the genesis of AD, depression and schizophrenia and also those driving radiation-induced brain neuropathological changes by reviewing the available data. We found that 3, 11, or 8 neuronal developmentrelated miRNAs from the brain tissue, 13, 16 or 14 miRNAs from the blood of patient with AD, depression and schizophrenia respectively were also involved in radiation-induced brain pathological changes, suggesting a possibly specific involvement of these miRNAs in radiation-induced development of AD, depression and schizophrenia respectively. On the other hand, we noted that radiationinduced changes of two miRNAs, i.e., miR-132, miR-29 in the brain tissue, three miRNAs, i.e., miR- 29c-5p, miR-106b-5p, miR-34a-5p in the blood were also involved in the development of AD, depression and schizophrenia, thereby suggesting that these miRNAs may be involved in the common brain neuropathological changes, such as impairment of neurogenesis and reduced learning memory ability observed in these three diseases and also after radiation exposure.

Molecular Changes in Circulating microRNAs' Expression and Oxidative Stress in Adults with Mild Cognitive Impairment: A Biochemical and Molecular Study

BACKGROUND

The release of miRNAs in tissue fluids significantly recommends its use as non-invasive diagnostic biomarkers for the progression and pathogenesis of mild cognitive impairment (MCI) in aged patients.

OBJECTIVE

The potential role of circulated miRNAs in the pathogenesis of MCI and its association with cellular oxidative stress, apoptosis, and circulated BDNF, Sirtuin 1 (SIRT1), and dipeptidyl peptidase-4 (DPP4) were evaluated in older adults with MCI.

METHODS

A total of 150 subjects aged 65.4±3.7 years were recruited in this study. The participants were classified into two groups: healthy normal (n=80) and MCI (n=70). Real-time PCR analysis was performed to estimate the relative expression of miRNAs; miR-124a, miR-483-5p, miR-142-3p, and miR-125b, and apoptotic-related genes Bax, Bcl-2, and caspase-3 in the sera of MCI and control subjects. In addition, oxidative stress parameters; MDA, NO, SOD, and CAT; as well as plasma DPP4 activity, BDNF, SIRT1 levels were colorimetrically estimated.

RESULTS

The levels of miR-124a and miR-483-5p significantly increased and miR-142-3p and miR-125b significantly reduced in the serum of MCI patients compared to controls. The expressed miRNAs significantly correlated with severe cognitive decline, measured by MMSE, MoCA, ADL, and memory scores. The expression of Bax, and caspase-3 apoptotic inducing genes significantly increased and Bcl-2 antiapoptotic gene significantly reduced in MCI subjects compared to controls. In addition, the plasma levels of MDA, NO, and DPP4 activity significantly increased, and the levels of SOD, CAT, BDNF, and SIRT1 significantly reduced in MCI subjects compared to controls. The expressed miRNAs correlated positively with NO, MDA, DPP4 activity, BDNF, and SIRT-1, and negatively with the levels of CAT, SOD, Bcl-2, Bax, and caspase-3 genes.

CONCLUSION

Circulating miR-124a, miR-483-5p, miR-142-3p, and miR-125b significantly associated with severe cognitive decline, cellular oxidative stress, and apoptosis in patients with MCI. Thus, it could be potential non-invasive biomarkers for the diagnosis of MCI with high diagnostic performance.

MicroRNA profiling of the pig periaqueductal grey (PAG) region reveals candidates potentially related to sex-dependent differences

Background

MicroRNAs indirectly orchestrate myriads of essential biological processes. A wide diversity of miRNAs of the neurodevelopmental importance characterizes the brain tissue, which, however, exhibits region-specific miRNA profile differences. One of the most conservative regions of the brain is periaqueductal grey (PAG) playing vital roles in significant functions of this organ, also those observed to be sex-influenced. The domestic pig is an important livestock species but is also believed to be an excellent human model. This is of particular importance for neurological research because of the similarity of pig and human brains as well as difficult access to human samples. However, the pig PAG profile has not been characterized so far. Moreover, molecular bases of sex differences connected with brain functioning, including miRNA expression profiles, have not been fully deciphered yet.

Methods

Thus, in this study, we applied next-generation sequencing to characterize pig PAG expressed microRNAs. Furthermore, we performed differential expression analysis between females and males to identify changes of the miRNA profile and reveal candidates underlying sex-related differences.

Results

As a result, known brain-enriched, and new miRNAs which will expand the available profile, were identified. The downstream analysis revealed 38 miRNAs being differentially expressed (DE) between female and male samples. Subsequent pathway analysis showed that they enrich processes vital for neuron growth and functioning, such as long-term depression and axon guidance. Among the identified sex-influenced miRNAs were also those associated with the PAG physiology and diseases related to this region.

Conclusions

The obtained results broaden the knowledge on the porcine PAG miRNAome, along with its dynamism reflected in different isomiR signatures. Moreover, they indicate possible mechanisms associated with sex-influenced differences mediated via miRNAs in the PAG functioning. They also provide candidate miRNAs for further research concerning, i.e., sex-related bases of physiological and pathological processes occurring in the nervous system.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-020-00343-2.

Scratch2, a Snail Superfamily Member, Is Regulated by miR-125b

Scratch2 is a transcription factor expressed in a very restricted population of vertebrate embryonic neural cell precursors involved in their survival, differentiation, and migration. The mechanisms that control its expression remain unknown and could contribute towards our understanding of gene regulation during neural differentiation and evolution. Here we investigate the role of microRNAs (miRNAs) in the Scrt2 post-transcriptional regulatory mechanism. We identified binding sites for miR-125b and -200b in the Scrt2 3′UTR in silico. We confirmed the repressive-mediated activity of the Scrt2 3′UTR through electroporation of luciferase constructs into chick embryos. Further, both CRISPR/Cas9-mediated deletion of miR-125b/-200b responsive elements from chicken Scrt2 3′UTR and expression of miRNAs sponges increased Scrt2 expression field, suggesting a role for these miRNAs as post-transcriptional regulators of Scrt2. The biological effect of miR-125b titration was much more pronounced than that of miR-200b. Therefore, we propose that, after transcription, miR-125b fine-tunes the Scrt2 expression domain.

Long Non-coding RNA MALAT1 Inhibits Neuron Apoptosis and Neuroinflammation While Stimulates Neurite Outgrowth and Its Correlation With MiR-125b Mediates PTGS2, CDK5 and FOXQ1 in Alzheimer's Disease

BACKGROUND

This study aimed to investigate the effect of long noncoding ribonucleic acids (RNAs) metastasis-associated lung adenocarcinoma transcript 1 (lnc-MALAT1) on regulating neuron apoptosis, neurite outgrowth and inflammation, and further explore its molecule mechanism in Alzheimer's disease (AD).

METHODS

Control overexpression, lnc-MALAT1 overexpression, control shRNA, and lnc-MALAT1 shRNA were transfected into NGF-stimulated PC12 cellular AD model and cellular AD model from primary cerebral cortex neurons of rat embryo, which were established by Aβ1-42 insult. Rescue experiments were performed by transferring lnc-MALAT1 overexpression and lnc-MALAT1 overexpression & miR-125b overexpression plasmids. Neuron apoptosis, neurite outgrowth and inflammation were detected by Hoechst-PI/apoptosis marker expressions, and observations were made using microscope and RT-qPCR/Western blot assays. PTGS2, CDK5 and FOXQ1 expressions in rescue experiments were also determined.

RESULTS

In two AD models, lnc-MALAT1 overexpression inhibited neuron apoptosis, promoted neurite outgrowth, reduced IL-6 and TNF-α levels, and increased IL-10 level compared to control overexpression, while lnc-MALAT1 knockdown promoted neuron apoptosis, repressed neurite outgrowth, elevated IL-6 and TNF-α levels, but reduced IL-10 level compared to control shRNA. Additionally, lnc- MALAT1 reversely regulated miR-125b expression, while miR-125b did not influence the lnc- MALAT1 expression. Subsequently, rescue experiments revealed that miR-125b induced neuron apoptosis, inhibited neurite outgrowth and promoted inflammation, also increased PTGS2 and CDK5 expressions but decreased FOXQ1 expression in lnc-MALAT1 overexpression treated AD models.

CONCLUSION

Lnc-MALAT1 might interact with miR-125b to inhibit neuron apoptosis and inflammation while promote neurite outgrowth in AD.

Expression of miR-28-3p in patients with Alzheimer's disease before and after treatment and its clinical value

Expression of miR-28-3p in patients with Alzheimer's disease (AD) before and after treatment and clinical value of miR-28-3p were determined. There were three groups: 68 AD patients treated with donepezil combined with basic therapy in The People's Hospital of Shouguang collected as an AD group, 70 patients with mild cognitive impairment (MCI) as an MCI group, and 75 healthy people as a normal group. Serum miR-28-3p was detected by qRT-PCR. The Montreal cognitive assessment scale (MoCA), mini mental state examination scale (MMSE), activities of daily living scale (ADL) and homocysteine (Hcy) were adopted to assess patients before and after treatment. miR-28-3p in normal group was significantly lower than that in other two groups, and miR-28-3p in MCI group was significantly lower than that in AD group (P<0.001). miR-28-3p correlated with the course and severity of patients. miR-28-3p in AD group after treatment was significantly lower than that before treatment (P<0.001). ADL and Hcy of AD patients after treatment were significantly lower than before treatment (P<0.05), and MMSE and MoCA after treatment were significantly higher than before treatment (P<0.05). Before and after treatment, miR-28-3p was significantly positively correlated with ADL score and Hcy level, but negatively correlated with MMSE score and MoCA score. Analysis of the working characteristic curve of the patients indicated that miR-28-3p can be used for diagnosis of AD patients. Donepezil therapy may reduce miR-28-3p level to alleviate the symptoms of AD patients, and miR-28-3p level can be used as an early diagnosis and prognosis evaluation of AD patients.

Modulation of MicroRNAs as a Potential Molecular Mechanism Involved in the Beneficial Actions of Physical Exercise in Alzheimer Disease

Alzheimer disease (AD) is one of the most common neurodegenerative diseases, affecting middle-aged and elderly individuals worldwide. AD pathophysiology involves the accumulation of beta-amyloid plaques and neurofibrillary tangles in the brain, along with chronic neuroinflammation and neurodegeneration. Physical exercise (PE) is a beneficial non-pharmacological strategy and has been described as an ally to combat cognitive decline in individuals with AD. However, the molecular mechanisms that govern the beneficial adaptations induced by PE in AD are not fully elucidated. MicroRNAs are small non-coding RNAs involved in the post-transcriptional regulation of gene expression, inhibiting or degrading their target mRNAs. MicroRNAs are involved in physiological processes that govern normal brain function and deregulated microRNA profiles are associated with the development and progression of AD. It is also known that PE changes microRNA expression profile in the circulation and in target tissues and organs. Thus, this review aimed to identify the role of deregulated microRNAs in the pathophysiology of AD and explore the possible role of the modulation of microRNAs as a molecular mechanism involved in the beneficial actions of PE in AD.

MicroRNA alterations in neuropathologic cognitive disorders with an emphasis on dementia: Lessons from animal models

Cognitive dysfunction is a state of losing or having difficulties in remembering, learning, focusing, or making decisions that impact individual healthy life. Small single-stranded and nonprotein coding RNAs, microRNAs (miRNAs) participate actively in regulatory processes, incorporate cognitive signaling pathways, and intensely affect cognitive evolution. miRNAs exert their modification activities through translational or transcriptional processes. Reportedly, cognitive impairment and dementia are rising, especially in developing countries. Herein we provided a brief review of original studies addressing miRNA changes in the most common neurological diseases with a focus on dementia and Alzheimer's disease. It must be noted that an increase in the level of certain miRNAs but a decrease in other ones deteriorate cognitive performance. The current review revealed that induction of miR-214-3p, miR-302, miR-21, miR- 200b/c, miR-207, miR-132, miR-188-3p and 5p, and miR-873 improved cognitive impairment in various cognitive tasks. On the other hand, intentionally lowering the level of miR-34a, miR-124, miR-574, and miR-191a enhanced cognitive function and memory. Synaptic dysfunction is a core cause of cognitive dysfunction; miRNA-34, miRNA-34-c, miRNA-124, miRNA-188-5p, miRNA-210-5p, miRNA-335-3p, and miRNA-134 strongly influence synaptic-related mechanisms. The downregulation of miRNA-132 aggregates both amyloid and tau in tauopathy. Concerning the massive burden of neurological diseases worldwide, the future challenge is the translation of animal model knowledge into the detection of pathophysiological stages of neurocognitive disorders and designing efficient therapeutic strategies. While the delivery procedure of agomir or antagomir miRNAs into the brain is invasive and only applied in animal studies, finding a safe and specific delivery route is a priority.

Mitochondrial MicroRNAs in Aging and Neurodegenerative Diseases

MicroRNAs (miRNAs) are important regulators of several biological processes, such as cell growth, cell proliferation, embryonic development, tissue differentiation, and apoptosis. Currently, over 2000 mammalian miRNAs have been reported to regulate these biological processes. A subset of microRNAs was found to be localized to human mitochondria (mitomiRs). Through years of research, over 400 mitomiRs have been shown to modulate the translational activity of the mitochondrial genome. While miRNAs have been studied for years, the function of mitomiRs and their role in neurodegenerative pathologies is not known. The purpose of our article is to highlight recent findings that relate mitomiRs to neurodegenerative diseases, including Alzheimer’s, Parkinson’s, and Huntington’s. We also discuss the involvement of mitomiRs in regulating the mitochondrial genome in age-related neurodegenerative diseases.

MicroRNA-15a-5p serves as a potential biomarker and regulates the viability and apoptosis of hippocampus neuron in children with temporal lobe epilepsy

BACKGROUND

Temporal lobe epilepsy (TLE) is the most common type of epilepsy, usually starting in childhood. The dysregulation of microRNAs (miRNAs) has been identified in neurological disorders. The current study investigated the expression level and clinical significance of miR-15a-5p in TLE children, and explored its function in regulating cell behaviors of hippocampal neurons.

METHODS

The expression level of miR-15a-5p was examined in the serum of 63 TLE children. Primary hippocampal cells were cultured in magnesium-free medium to mimic TLE condition in children. The effect of miR-15a-5p on the viability and apoptosis of hippocampus neuron was assessed using MTT or flow cytometric apoptosis assay.

RESULTS

TLE children had significantly low expression of miR-15a-5p. MiR-15a-5p was of great value for the diagnosis of TLE in children, with high specificity and sensitivity. The expression level of miR-15a-5p was decreased significantly in hippocampal cells treated in the magnesium-free medium. Overexpression of miR-15a-5p attenuated TLE-induced reduction for cell viability, and reversed the cell apoptosis induced by TLE.

CONCLUSIONS

MiR-15a-5p is downregulated in children with TLE, and overexpression of miR-15a-5p promoted the viability and inhibited the apoptosis of hippocampal neuron. MiR-15a-5p may be a promising biomarker for the diagnosis of children TLE.

miR-34a-5p and miR-125b-5p attenuate Aβ-induced neurotoxicity through targeting BACE1

BACKGROUND

Accumulation of β-amyloid (Aβ) could induce neurotoxicity in Alzheimer's disease (AD). microRNA (miR)-34a-5p and miR-125b-5p have been reported to be aberrantly expressed in AD patients. However, the roles and mechanisms of these two miRNAs in AD remain poorly understood.

METHODS

Serum samples of 27 AD patients were collected. Primary mouse cortical neurons (MCN) and Neuro2a (N2a) cells were incubated with Aβ. The expression levels of miR-34a-5p, miR-125b-5p and β-site amyloid precursor protein cleaving enzyme 1 (BACE1) were detected by quantitative real-time polymerase chain reaction and western blot. The effect of miRNAs or epigallocatechin-3-gallate (EGCG) on Aβ-induced neurotoxicity was investigated by cell viability, Caspase 3 activity, apoptosis and intracellular ROS production. The interaction between BACE1 and miR-34a-5p or miR-125b-5p was analyzed by luciferase reporter assay.

RESULTS

miR-34a-5p and miR-125b-5p levels were decreased and BACE1 mRNA expression was increased in AD patients and Aβ-treated MCN and N2a cells. Addition of miR-34a-5p or miR-125b-5p attenuated Aβ-induced apoptosis and oxidative stress. BACE1 acted as a target of miR-34a-5p and miR-125b-5p and its restoration weakened the effect of miR-34a-5p or miR-125b-5p on Aβ-induced neurotoxicity. Moreover, EGCG could mitigate Aβ-induced neurotoxicity, which might be associated with miR-34a-5p and miR-125b-5p.

CONCLUSION

miR-34a-5p and miR-125b-5p inhibited Aβ-induced neurotoxicity by decreasing apoptosis and oxidative stress via targeting BACE1, providing novel targets for treatment of AD.

Regulation of microRNAs by IRE1α in apoptosis: implications for the pathomechanism of neurodegenerative diseases

Although there are large differences in clinical and pathological features, age-related neurodegenerative diseases (NDs) share common pathogenetic mechanisms involving aggregation and deposition of misfolded proteins, which leads to progressive dysfunction and death of neurons. Up to now, it seems that apoptosis is one major form of neuronal cell death. This review provides an overview of recent progress in unfolded protein response (UPR) during apoptosis induced by abnormal protein aggregation and emphasizes on the potential role of inositol requiring enzyme 1 alpha (IRE1α)-microRNAs (miRNAs) mediated apoptosis in NDs, which will provide new insights in the pathogenesis of neurodegenerative diseases and novel therapeutic targets for the treatment of NDs.

The Potential Markers of Circulating microRNAs and long non-coding RNAs in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder and one of the leading causes of disability and mortality in the late life with no curative treatment currently. Thus, it is urgently to establish sensitive and non-invasive biomarkers for AD diagnosis, particularly in the early stage. Recently, emerging number of microRNAs (miRNAs) and long-noncoding RNAs (lncRNAs) are considered as effective biomarkers in various diseases as they possess characteristics of stable, resistant to RNAase digestion and many extreme conditions in circulatory fluid. This review highlights recent advances in the identification of the aberrantly expressed miRNAs and lncRNAs in circulatory network for detection of AD. We summarized the abnormal expressed miRNAs in blood and cerebrospinal fluid (CSF), and detailed discussed the functions and molecular mechanism of serum or plasma miRNAs-miR-195, miR-155, miR-34a, miR-9, miR-206, miR-125b and miR-29 in the regulation of AD progression. In addition, we also elaborated the role of circulating lncRNA major including beta-site APP cleaving enzyme 1 (BACE1) and its antisense lncRNA BACE1-AS in AD pathological advancement. In brief, confirming the aberrantly expressed circulating miRNAs and lncRNAs will provide an effective testing tools for treatment of AD in the future.

Cerebral Amyloid Angiopathy, Alzheimer's Disease and MicroRNA: miRNA as Diagnostic Biomarkers and Potential Therapeutic Targets

The protein molecules must fold into unique conformations to acquire functional activity. Misfolding, aggregation, and deposition of proteins in diverse organs, the so-called "protein misfolding disorders (PMDs)", represent the conformational diseases with highly ordered assemblies, including oligomers and fibrils that are linked to neurodegeneration in brain illnesses such as cerebral amyloid angiopathy (CAA) and Alzheimer's disease (AD). Recent studies have revealed several aspects of brain pathology in CAA and AD, but both the classification and underlying mechanisms need to be further refined. MicroRNAs (miRNAs) are critical regulators of gene expression at the post-transcriptional level. Increasing evidence with the advent of RNA sequencing technology suggests possible links between miRNAs and these neurodegenerative disorders. To provide insights on the small RNA-mediated regulatory circuitry and the translational significance of miRNAs in PMDs, this review will discuss the characteristics and mechanisms of the diseases and summarize circulating or tissue-resident miRNAs associated with AD and CAA.

Extracellular miRNAs: From Biomarkers to Mediators of Physiology and Disease

miRNAs can be found in serum and other body fluids and serve as biomarkers for disease. More importantly, secreted miRNAs, especially those in extracellular vesicles (EVs) such as exosomes, may mediate paracrine and endocrine communication between different tissues and thus modulate gene expression and the function of distal cells. When impaired, these processes can lead to tissue dysfunction, aging, and disease. Adipose tissue is an especially important contributor to the pool of circulating exosomal miRNAs. As a result, alterations in adipose tissue mass or function, which occur in many metabolic conditions, can lead to changes in circulating miRNAs, which then function systemically. Here we review the findings that led to these conclusions and discuss how this sets the stage for new lines of investigation in which extracellular miRNAs are recognized as important mediators of intercellular communication and potential candidates for therapy of disease.

Role of miRNAs in Alzheimer's Disease and Possible Fields of Application

miRNAs (or microRNAs) are a class of single-stranded RNA molecules, responsible for post-transcriptional gene silencing through binding to the coding region as well as 3' and 5' untranslated region of target genes. About 70% of experimentally detectable miRNAs are expressed in the brain and some studies suggest that miRNAs are intimately involved in synaptic function and in specific signals during memory formation. More and more evidence demonstrates the possible involvement of miRNAs in Alzheimer's disease (AD). AD is the most common form of senile dementia, a disease that affects memory and cognitive functions. It is a neurodegenerative disorder characterized by loss of synapses, extracellular amyloid plaques composed of the amyloid-β peptide (Aβ), and intracellular aggregates of hyperphosphorylated TAU protein. This review aims to provide an overview of the in vivo studies of the last 5 years in the literature describing the role of the different miRNAs involved in AD. miRNAs hold huge potential as diagnostic and prognostic biomarkers and, at the same time, their modulation could be a potential therapeutic strategy against AD.

miR-133b is a potential diagnostic biomarker for Alzheimer's disease and has a neuroprotective role

MicroRNAs (miRNAs/miRs) are involved in post-transcriptional gene regulation and aberrant expression of miRNAs has been widely detected in various human diseases. The aim of the present study was to examine the serum levels of miR-133b in patients with Alzheimer's disease (AD), and to explore its diagnostic value and neuroprotective role in AD. Reverse transcription-quantitative PCR was applied to analyze the serum levels of miR-133b in 105 AD patients and 98 healthy controls. A cell model of AD was established by treating SH-SY5Y cells with amyloid β (Aβ)25-35, and the resulting effect on miR-133b expression was determined. Cell viability and apoptosis were also measured. A dual-luciferase assay was used to validate a target gene of miR-133b. Receiver operating characteristic (ROC) curve analysis was also applied to assess the specificity and sensitivity of miR-133b to diagnose AD. The results indicated that the serum levels of miR-133b were significantly downregulated in AD patients and SH-SY5Y cells treated with Aβ25-35 (all P<0.001). A positive correlation between the serum levels of miR-133b and the Mini-Mental State Examination score of AD patients was determined (r=0.8814, P<0.001). The area under the ROC curve for miR-133b regarding the diagnosis of AD was 0.907, with a sensitivity of 90.8% and specificity of 74.3% at the cutoff value of 1.70. Overexpression of miR-133b significantly attenuated the Aβ25-35-induced inhibition of cell viability (P<0.01) and induction of cell apoptosis (P<0.01). The luciferase reporter assay demonstrated that epidermal growth factor receptor (EGFR) is a target gene of miR-133b. In conclusion, miR-133b may serve as a novel diagnostic biomarker for AD and it may have a neuroprotective role in AD and targets EGFR.

Aging-Related Changes in Cognition and Cortical Integrity are Associated With Serum Expression of Candidate MicroRNAs for Alzheimer Disease

Evidence has shown that microRNAs (miRNAs) are involved in molecular pathways responsible for aging and prevalent aging-related chronic diseases. However, the lack of research linking circulating levels of miRNAs to changes in the aging brain hampers clinical translation. Here, we have investigated if serum expression of brain-enriched miRNAs that have been proposed as potential biomarkers in Alzheimer’s disease (AD) (miR-9, miR-29b, miR-34a, miR-125b, and miR-146a) are also associated with cognitive functioning and changes of the cerebral cortex in normal elderly subjects. Results revealed that candidate miRNAs were linked to changes in cortical thickness (miR-9, miR-29b, miR-34a, and miR-125b), cortical glucose metabolism (miR-29b, miR-125b, and miR-146a), and cognitive performance (miR-9, miR-34a, and miR-125b). While both miR-29b and miR-125b were related to aging-related structural and metabolic cortical changes, only expression levels of miR-125b were associated with patterns of glucose consumption shown by cortical regions that correlated with executive function. Together, these findings suggest that serum expression of AD-related miRNAs are biologically meaningful in aging and may play a role as biomarkers of cerebral vulnerability in late life.

Small RNA Sequencing of Sporadic Amyotrophic Lateral Sclerosis Cerebrospinal Fluid Reveals Differentially Expressed miRNAs Related to Neural and Glial Activity

Amyotrophic lateral sclerosis (ALS) is a clinical subtype of motor neurone disease (MND), a fatal neurodegenerative disease involving the loss of both the upper and lower motor neurones from the motor cortex, brainstem, and spinal cord. Identifying specific disease biomarkers would help to not only improve diagnostic delay but also to classify disease subtypes, monitor response to therapeutic drugs and track disease progression. miRNAs are small non-coding RNA responsible for regulating gene expression and ultimately protein expression and have been used as biomarkers for many cancers and neurodegenerative disorders. Investigating the detection of miRNAs in cerebrospinal fluid (CSF), the fluid that bathes the central nervous system (CNS) is a prime target for identifying potential biomarkers for ALS. This is the first study to investigate the expression of miRNAs in the CSF of ALS patients using small RNA sequencing. We detected 11 differentially expressed miRNAs in the CSF of sporadic ALS (sALS) patients related to neural and glial activity. Additionally, miRNAs involved in glucose metabolism and the regulation of oxidative stress were also identified. Detecting the presence of potential CSF derived miRNA biomarkers in sALS could open up a whole new area of knowledge to help gain a better understanding of disease pathophysiology. Additionally, with further investigation, the tracking of CSF miRNA over the disease course could be used to follow the disease progression and monitor the effect of novel therapeutics that could be personalized to an individual disease phenotype.