Systematic Review of miRNA as Biomarkers in Alzheimer's Disease

A Machine Learning Approach to Identify a Circulating MicroRNA Signature for Alzheimer Disease

BACKGROUND

Accurate diagnosis of Alzheimer disease (AD) involving less invasive molecular procedures and at reasonable cost is an unmet medical need. We identified a serum miRNA signature for AD that is less invasive than a measure in cerebrospinal fluid.

METHODS

From the Oxford Project to Investigate Memory and Aging (OPTIMA) study, 96 serum samples were profiled by a multiplex (>500 analytes) microRNA (miRNA) reverse transcription quantitative PCR analysis, including 51 controls, 32 samples from patients with AD, and 13 samples from patients with mild cognitive impairment (MCI). Clinical diagnosis of a subset of AD and the controls was confirmed by postmortem (PM) histologic examination of brain tissue. In a machine learning approach, the AD and control samples were split 70:30 as the training and test cohorts. A multivariate random forest statistical analysis was applied to construct and test a miRNA signature for AD identification. In addition, the MCI participants were included in the test cohort to assess whether the signature can identify early AD patients.

RESULTS

A 12-miRNA signature for AD identification was constructed in the training cohort, demonstrating 76.0% accuracy in the independent test cohort with 90.0% sensitivity and 66.7% specificity. The signature, however, was not able to identify MCI participants. With a subset of AD and control participants with PM-confirmed diagnosis status, a separate 12-miRNA signature was constructed. Although sample size was limited, the PM-confirmed signature demonstrated improved accuracy of 85.7%, largely owing to improved specificity of 80.0% with comparable sensitivity of 88.9%.

CONCLUSION

Although additional and more diverse cohorts are needed for further clinical validation of the robustness, the miRNA signature appears to be a promising blood test to diagnose AD.

NF-κB-Induced Upregulation of miR-146a-5p Promoted Hippocampal Neuronal Oxidative Stress and Pyroptosis via TIGAR in a Model of Alzheimer's Disease

Alzheimer’s disease (AD) is a common neurodegenerative disorder that places a heavy burden on patients and society. Hippocampal neuronal loss is a hallmark of AD progression. Therefore, understanding the mechanism underlying hippocampal neuronal death would be of great importance for the diagnosis and treatment of AD. This study aimed to explore the molecular mechanism via which nuclear factor kappa β (NF-κB) promotes hippocampal neuronal oxidative stress and pyroptosis in AD. We collected serum samples from 101 healthy elderly people and 112 patients with AD at the Affiliated Hospital of Kunming University of Science and Technology between January 2017 and January 2020. Commercially available human hippocampal neurons (HHNs) were used to establish an AD model (AD-HHN) following Aβ25–35 treatment. The mRNA expression levels of NF-κB and pyroptosis markers [NLR family pyrin domain-containing 3, caspase-1, interleukin (IL)-1β, and interleukin-18] mRNA and the expression level of miR-146a-5p in the serum samples of patients with AD and AD-HHNs were determined by quantitative reverse transcription polymerase chain reaction. Oxidative stress indices (reactive oxygen species, malondialdehyde, nicotinamide adenine dinucleotide phosphate, superoxide dismutase, glutathione, and catalase) were measured by Enzyme-Linked Immunosorbent Assay (ELISA). The expression of proteins [NF-κB, TP53-induced glycolysis and apoptosis regulator (TIGAR), and pyroptosis markers] was tested by western blotting. The relationship between miR-146a-5p and TIGAR was investigated using a dual luciferase reporter gene assay. We found that NF-κB and miR-146a-5p were highly expressed, while TIGAR was low expressed in patients with AD and AD-HHNs. In addition, there was a significant positive correlation between the expression levels of NF-κB and miR-146a-5p, but a negative correlation between NF-κB mRNA and TIGAR mRNA in patients with AD, as well as miR-146a-5p and TIGAR mRNA in patients with AD. In AD-HNNs, miR-146a-5p targeted and downregulated the expression of TIGAR. Knockdown of NF-κB or overexpression of TIGAR markedly attenuated oxidative stress and pyroptosis in AD-HHNs, while concurrent overexpression of miR-146a-5p inhibited these effects. In conclusion, NF-κB-induced upregulation of miR-146a-5p promoted oxidative stress and pyroptosis in AD-HNNs by targeting TIGAR.

MicroRNA-221 Upregulates the Expression of P-gp and Bcl-2 by Activating the Stat3 Pathway to Promote Doxorubicin Resistance in Osteosarcoma Cells

MicroRNA-221 (miRNA-221) is upregulated in several malignant tumors and is associated with poor patient prognosis. Therefore, the present study aimed to investigate the role and underlying mechanism of miRNA-221 in doxorubicin (DOX) resistance in osteosarcoma cells. We constructed DOX-resistant Saos-2/DOX cells and treated them with DOX. Cell viability was determined by performing a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cells were transfected with either miRNA-221 mimic or miRNA-221 inhibitor; quantitative (q)RT-PCR was performed to detect the expression of miRNA-221. Flow cytometry and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick-end labeling (TUNEL) staining were used to detect cell apoptosis. The immunofluorescence method was also used to detect cell signal transduction and activator of transcription 3 (Stat3) protein expression distribution. In addition, Western blotting was used to detect changes in the expression of each protein. We found that miRNA-221 was upregulated in Saos-2/DOX cells. Moreover, the miRNA-221 mimic induced DOX resistance in Saos-2 cells, whereas the miRNA-221 inhibitor enhanced DOX sensitivity in Saos-2/DOX cells. The miRNA-221 mimic upregulated the expression of phosphorylated-Stat3, P-glycoprotein (P-gp), and B-cell lymphoma-2 (Bcl-2) proteins in Saos-2 cells and induced the entry of Stat3 into the nucleus, whereas the miRNA-221 inhibitor exerted the opposite effect. Pretreatment with the Stat3 chemical inhibitor, STAT3-IN-3, significantly inhibited the upregulation of P-gp and Bcl-2 protein expression induced by the miRNA-221 mimic in Saos-2 cells; it also caused the Saos-2 cells to overcome DOX resistance induced by the miRNA-221 mimic. Thus, miRNA-221 increased the expression of P-gp and Bcl-2 by activating the Stat3 pathway to promote DOX resistance in osteosarcoma cells, indicating a potential use of miRNA-221 in osteosarcoma treatment.

Effect of Intranasal Administration of Multipotent Mesenchymal Stromal Cell Exosomes on Memory of Mice in Alzheimer's Disease Model

We studied the effect of intranasal administration of exosomes obtained by culturing of multipotent mesenchymal stromal cells (MMSC) isolated from the Wharton's jelly of the human umbilical cord on spatial memory of olfactory bulbectomized mice demonstrating the basic signs of a sporadic form of Alzheimer's disease. Intranasal administration of isolated exosomes expressing typical markers CD9, CD63 and CD81 improved spatial memory in bulbectomized animals, which manifested in a significant increase in the number of visits to the target sector and the time spent there in comparison with indifferent sectors. After administration, labeled exosomes were found in the hippocampus and neocortex, the structures playing an important role in learning and memory processes and affected by Alzheimer's disease. The advantages of exosomes in comparison with MMSC are their small size, low immunogenicity, and inability to cause cell transformation together with high therapeutic efficacy.

Peripheral Blood Biomarkers CXCL12 and TNFRSF13C Associate with Cerebrospinal Fluid Biomarkers and Infiltrating Immune Cells in Alzheimer Disease

Neuroinflammation-induced neurodegeneration and immune cell infiltration are two features of Alzheimer disease (AD). This study aimed to identify potential peripheral biomarkers that interact with cerebrospinal fluid (CSF) and infiltrating immune cells in AD. Blood and CSF data were downloaded from the Alzheimer's disease Neuroimaging Initiative database. We identified differentially expressed genes (DEGs) in AD and assessed infiltrating immune cells using the Immune Cell Abundance Identifier (ImmuCellAI) algorithm. Blood-brain barrier (BBB) and immune-related genes were identified from medical databases, and common genes were used to construct a protein-protein interaction network (PPI). Potential biomarkers reflecting the clinical features of AD were screened using Pearson correlations and logistic regression analysis. We identified 210 DEGs in the AD group. ImmuCellAI indicated that blood samples from patients with AD had a higher abundance of exhausted T (Tex; 0.196 vs. 0.132) and induced regulatory T (iTreg; 0.180 vs. 0.137) cells than controls. Thirty-two genes overlapped between the BBB and immune-related genes, and 27 genes in the PPI network were associated with eight pathways, including the cytokine-cytokine receptor interaction pathway (hsa04060) and the chemokine signaling pathway (hsa04062). Pearson correlations showed that five genes were associated with the CSF biomarkers, Aβ, total, and phosphorylated tau. Logistics analysis showed that the B cell-associated genes, CXCL12 and TNFRSF13C, were independent risk factors for AD diagnosis. Peripheral CXCL12 and TNFRSF13C genes that correlated with immune cell infiltration in AD might serve as easily accessible biomarkers for the early diagnosis of AD.

Human neural stem cell-derived extracellular vesicles mitigate hallmarks of Alzheimer's disease

Background

Regenerative therapies to mitigate Alzheimer’s disease (AD) neuropathology have shown very limited success. In the recent era, extracellular vesicles (EVs) derived from multipotent and pluripotent stem cells have shown considerable promise for the treatment of dementia and many neurodegenerative conditions.

Methods

Using the 5xFAD accelerated transgenic mouse model of AD, we now show the regenerative potential of human neural stem cell (hNSC)-derived EVs on the neurocognitive and neuropathologic hallmarks in the AD brain. Two- or 6-month-old 5xFAD mice received single or two intra-venous (retro-orbital vein, RO) injections of hNSC-derived EVs, respectively.

Results

RO treatment using hNSC-derived EVs restored fear extinction memory consolidation and reduced anxiety-related behaviors 4–6 weeks post-injection. EV treatment also significantly reduced dense core amyloid-beta plaque accumulation and microglial activation in both age groups. These results correlated with partial restoration of homeostatic levels of circulating pro-inflammatory cytokines in the AD mice. Importantly, EV treatment protected against synaptic loss in the AD brain that paralleled improved cognition. MiRNA analysis of the EV cargo revealed promising candidates targeting neuroinflammation and synaptic function.

Conclusions

Collectively, these data demonstrate the neuroprotective effects of systemic administration of stem cell-derived EVs for remediation of behavioral and molecular AD neuropathologies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00791-x.

MicroRNAs in central nervous system disorders: current advances in pathogenesis and treatment

MicroRNAs (miRNAs) are a class of short, non-coding, regulatory RNA molecules that function as post transcriptional regulators of gene expression. Altered expression of multiple miRNAs was found to be extensively involved in the pathogenesis of different neurological disorders including Alzheimer’s disease, Parkinson’s disease, stroke, epilepsy, multiple sclerosis, amyotrophic lateral sclerosis, and Huntington’s disease. miRNAs are implicated in the pathogenesis of excitotoxicity, apoptosis, oxidative stress, inflammation, neurogenesis, angiogenesis, and blood–brain barrier protection. Consequently, miRNAs can serve as biomarkers for different neurological disorders. In recent years, advances in the miRNA field led to identification of potentially novel prospects in the development of new therapies for incurable CNS disorders. MiRNA-based therapeutics include miRNA mimics and inhibitors that can decrease or increase the expression of target genes. Better understanding of the mechanisms by which miRNAs are implicated in the pathogenesis of neurological disorders may provide novel targets to researchers for innovative therapeutic strategies.

A critical review of the epidemiological evidence of effects of air pollution on dementia, cognitive function and cognitive decline in adult population

Dementia is arguably the most pressing public health challenge of our age. Since dementia does not have a cure, identifying risk factors that can be controlled has become paramount to reduce the personal, societal and economic burden of dementia. The relationship between exposure to air pollution and effects on cognitive function, cognitive decline and dementia has stimulated increasing scientific interest in the past few years. This review of the literature critically examines the available epidemiological evidence of associations between exposure to ambient air pollutants, cognitive performance, acceleration of cognitive decline, risk of developing dementia, neuroimaging and neurological biomarker studies, following Bradford Hill guidelines for causality. The evidence reviewed has been consistent in reporting associations between chronic exposure to air pollution and reduced global cognition, as well as impairment in specific cognitive domains including visuo-spatial abilities. Cognitive decline and dementia incidence have also been consistently associated with exposure to air pollution. The neuro-imaging studies reviewed report associations between exposure to air pollution and white matter volume reduction. Other reported effects include reduction in gray matter, larger ventricular volume, and smaller corpus callosum. Findings relating to ischemic (white matter hyperintensities/silent cerebral infarcts) and hemorrhagic (cerebral microbleeds) markers of cerebral small vessel disease have been heterogeneous, as have observations on hippocampal volume and air pollution. The few studies available on neuro-inflammation tend to report associations with exposure to air pollution. Several effect modifiers have been suggested in the literature, but more replication studies are required. Traditional confounding factors have been controlled or adjusted for in most of the reviewed studies. Additional confounding factors have also been considered, but the inclusion of these has varied among the different studies. Despite all the efforts to adjust for confounding factors, residual confounding cannot be completely ruled out, especially since the factors affecting cognition and dementia are not yet fully understood. The available evidence meets many of the Bradford Hill guidelines for causality. The reported associations between a range of air pollutants and effects on cognitive function in older people, including the acceleration of cognitive decline and the induction of dementia, are likely to be causal in nature. However, the diversity of study designs, air pollutants and endpoints examined precludes the attribution of these adverse effects to a single class of pollutant and makes meta-analysis inappropriate.

Identification of miRNA-Target Gene Pairs in the Parietal and Frontal Lobes of the Brain in Patients with Alzheimer's Disease Using Bioinformatic Analyses

Alzheimer's disease (AD) is a growing health concern worldwide. MicroRNAs (miRNAs) have been extensively studied in many diseases, including AD. To identify differentially expressed miRNAs (DEmiRNAs) and genes specific to AD, we used bioinformatic analyses to investigate candidate miRNA-mRNA pairs involved in the pathogenesis of AD. We focused on differentially expressed genes (DEGs) that are targets of DEmiRNAs. The GEO2R tool and the HISAT2-DESeq2 software were used to identify DEmiRNAs and DEGs. Bioinformatic tools available online, such as TAM and the Database for Annotation, Visualization and Integrated Discovery (DAVID), were used to perform functional annotation and enrichment analysis. Targets of miRNAs were predicted using the miRTarBase. The Search Tool for the Retrieval of Interacting Genes (STRING) and Cytoscape, which are available online, were utilized to construct protein-protein interaction (PPI) networks and identify hub genes. Furthermore, transcription factors (TFs) encoded by the DEGs were predicted using the TransmiR database and TF-miRNA-mRNA networks were constructed. Finally, the expression profile of a hub gene in peripheral blood mononuclear cells was compared between healthy individuals and AD patients. We identified 26 correlated miRNA-mRNA pairs. In the parietal lobe, miRNA-mRNA pairs involved in protein folding were enriched, and in the frontal lobe, miRNA-mRNA pairs involved in synaptic transmission, abnormal protein degradation, and apoptosis were enriched. In addition, HSP90AB1 in peripheral blood mononuclear cells was found to be significantly downregulated in AD patients, and this was consistent with its expression profile in the parietal lobe of AD patients. Our results provide brain region-specific changes in miRNA-mRNA associations in AD patients, further our understanding of potential underlying molecular mechanisms of AD, and reveal promising diagnostic and therapeutic targets for AD.

Biomarker Testing: Piercing the Fog of Alzheimer's and Related Dementia

Alzheimer's disease (AD) and related dementia is one of the growing threats to the sustainability of health and care systems in developed countries, and efforts to find therapies have had scant success. The main reasons for this are lack of efficient therapy, which is linked to too late discovery of the disease itself. With this in mind, biomarkers are recognised as an element which can bring a major contribution to research, helping elucidate the disease and the search for treatments. They are also playing an increasing role in early detection and timely diagnosis, which are considered the principal hopes of effective management in the absence of an effective drug. The current arsenal of biomarkers could already, if more widely deployed, provide an effective minimum service to patients and health systems. A concerted action by policy makers and stakeholders could drive progress in access to AD biomarker testing to provide an optimum service in the medium term. This paper discusses how to improve the use of and access to biomarker testing in the detection and diagnosis of AD and other diseases featuring dementia, and how EU healthcare systems could benefit. It outlines the challenges, lists the achievements to date, and highlights the actions needed to allow biomarker testing to deliver more fully on their potential in AD.

Programmable DNA Nanodevices for Applications in Neuroscience

The broad area of neuroscience has witnessed an increasing exploitation of a variety of synthetic biomaterials with controlled nanosized features. Different bionanomaterials offer very peculiar physicochemical and biochemcial properties contributing to the development of novel imaging devices toward imaging the brain, or as smartly functionalized scaffolds, or diverse tools contributing toward a better understanding of nervous tissue and its functions. DNA nanotechnology-based devices and scaffolds have emerged as ideal materials for cellular and tissue engineering due to their very biocompatible properties, robust adaptation with diverse biological systems, and biosafety in terms of reduced immune response triggering. Here we present technologies with respect to DNA nanodevices that are designed to better interact with nervous systems like neural cells, advanced molecular imaging technologies for imaging brain, biomaterials in neural regeneration, neuroprotection, and targeted delivery of drugs and small molecules across the blood-brain barrier. Along with comments regarding the progress of DNA nanotechnology in neuroscience, we also present a perspective on challenges and opportunities for applying DNA nanotechnology in applications pertaining to neurosciences.

MicroRNA-149 is downregulated in Alzheimer's disease and inhibits β-amyloid accumulation and ameliorates neuronal viability through targeting BACE1

Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) plays a critical role in Alzheimer's disease (AD) pathogenesis. This study aimed to investigate the relationship between microRNA-149 (miR-149) and BACE1, and evaluate the clinical significance and biological function of miR-149 in AD progression. Bioinformatics analysis and a luciferase reporter assay were used to confirm the interaction between miR-149 and BACE1. Expression of miR-149 and BACE1 was estimated using quantitative real-time PCR. The clinical significance of miR-149 in AD diagnosis and severity determination was evaluated using ROC analysis. The effect of miR-149 on Aβ accumulation and neuronal viability was analyzed in Aβ-treated SH-SY5Y cells. miR-149 was found directly binding the 3'-UTR of BACE1 and was negatively correlated with BACE1 in AD patients and cell model. Serum miR-149 expression was downregulated in AD patients and served as a potential diagnostic biomarker. The overexpression of miR-149 in Aβ-treated SH-SY5Y cells resulted in inhibited Aβ accumulation and enhanced neuronal viability. This study demonstrated that serum miR-149 is decreased in AD patients and serves as a candidate diagnostic biomarker, and that the overexpression of miR-149 may suppress Aβ accumulation and promote neuronal viability by targeting BACE1 in AD model cells.

MicroRNA-149 is downregulated in Alzheimer's disease and inhibits β-amyloid accumulation and ameliorates neuronal viability through targeting BACE1

Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) plays a critical role in Alzheimer’s disease (AD) pathogenesis. This study aimed to investigate the relationship between microRNA-149 (miR-149) and BACE1, and evaluate the clinical significance and biological function of miR-149 in AD progression. Bioinformatics analysis and a luciferase reporter assay were used to confirm the interaction between miR-149 and BACE1. Expression of miR-149 and BACE1 was estimated using quantitative real-time PCR. The clinical significance of miR-149 in AD diagnosis and severity determination was evaluated using ROC analysis. The effect of miR-149 on Aβ accumulation and neuronal viability was analyzed in Aβ-treated SH-SY5Y cells. miR-149 was found directly binding the 3’-UTR of BACE1 and was negatively correlated with BACE1 in AD patients and cell model. Serum miR-149 expression was downregulated in AD patients and served as a potential diagnostic biomarker. The overexpression of miR-149 in Aβ-treated SH-SY5Y cells resulted in inhibited Aβ accumulation and enhanced neuronal viability. This study demonstrated that serum miR-149 is decreased in AD patients and serves as a candidate diagnostic biomarker, and that the overexpression of miR-149 may suppress Aβ accumulation and promote neuronal viability by targeting BACE1 in AD model cells.

microRNAs as Early Biomarkers of Alzheimer's Disease: A Synaptic Perspective

Pathogenic processes underlying Alzheimer's disease (AD) affect synaptic function from initial asymptomatic stages, long time before the onset of cognitive decline and neurodegeneration. Therefore, reliable biomarkers enabling early AD diagnosis and prognosis are needed to maximize the time window for therapeutic interventions. MicroRNAs (miRNAs) have recently emerged as promising cost-effective and non-invasive biomarkers for AD, since they can be readily detected in different biofluids, including cerebrospinal fluid (CSF) and blood. Moreover, a growing body of evidence indicates that miRNAs regulate synaptic homeostasis and plasticity processes, suggesting that they may be involved in early synaptic dysfunction during AD. Here, we review the current literature supporting a role of miRNAs during early synaptic deficits in AD, including recent studies evaluating their potential as AD biomarkers. Besides targeting genes related to Aβ and tau metabolism, several miRNAs also regulate synaptic-related proteins and transcription factors implicated in early synaptic deficits during AD. Furthermore, individual miRNAs and molecular signatures have been found to distinguish between prodromal AD and healthy controls. Overall, these studies highlight the relevance of considering synaptic-related miRNAs as potential biomarkers of early AD stages. However, further validation studies in large cohorts, including longitudinal studies, as well as implementation of standardized protocols, are needed to establish miRNA-based biomarkers as reliable diagnostic and prognostic tools.

miR-204-3p/Nox4 Mediates Memory Deficits in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder leading to dementia in the elderly, and the mechanisms of AD are not fully defined. MicroRNAs (miRNAs) have been shown to contribute to memory deficits in AD. In this study, we identified that miR-204-3p was downregulated in the hippocampus and plasma of 6-month-old APPswe/PS1dE9 (APP/PS1) mice. miR-204-3p overexpression attenuated memory and synaptic deficits in APP/PS1 mice. The amyloid levels and oxidative stress were decreased in the hippocampus of APP/PS1 mice after miR-204-3p overexpression. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (Nox4) was a target of miR-204-3p, and Nox4 inhibition by GLX351322 protected neuronal cells against Aβ1-42-induced neurotoxicity. Furthermore, GLX351322 treatment rescued synaptic and memory deficits, and decreased oxidative stress and amyloid levels in the hippocampus of APP/PS1 mice. These results revealed that miR-204-3p attenuated memory deficits and oxidative stress in APP/PS1 mice by targeting Nox4, and miR-204-3p overexpression and/or Nox4 inhibition might be a potential therapeutic strategy for AD treatment.

[Mechanism of glutathione production in neurons]

Glutathione (GSH) is a tripeptide consisting of glutamate, cysteine, and glycine that acts as an important neuroprotective molecule in the central nervous system. In neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, GSH levels in the brain would be decreased before the onset, and GSH dysregulation is considered to be involved in the development of these neurodegenerative diseases. Cysteine uptake into neurons is the rate-limiting step for GSH synthesis. Excitatory amino acid carrier 1 (EAAC1), which is a glutamate/cysteine cotransporter, is responsible for the neuronal cysteine uptake, and EAAC1 dysfunction reduces GSH levels in the brain and has a significant influence on the process of neurodegeneration. Since miR-96-5p, which is one of microRNAs, suppresses EAAC1 expression, it is conceivable that miR-96-5p inhibitor suppresses the onset or slows the progression of neurodegenerative diseases by increasing EAAC1 levels leading to promoting neuronal GSH production.

Enhanced Expression of miR-34c in Peripheral Plasma Associated with Diabetic Foot Ulcer in Type 2 Diabetes Patients

OBJECTIVE

To explore the correlation between the expression of miR-34c in peripheral blood of patients with type 2 diabetes mellitus (T2DM) and the onset of diabetic foot ulcer (DFU) and diabetic foot osteomyelitis (DFO).

METHODS

Sixty newly diagnosed patients with T2DM without DFU (T2DM group), 112 T2DM patients with DFU (DFU group) and 60 controls with normal glucose tolerance (NC group). The DFU group patients were subdivided into DFO (n=64) and NDFO (n=48) groups. Quantitative real-time PCR (qRT-PCR) method was used to determine miR-34c expression levels in the peripheral blood of subjects to analyze the clinical characteristics of DFU and DFO risk factors.

RESULTS

MiR-34c expression level in the T2DM group was marked higher than the NC group [2.99 (1.45-6.22) vs 1.01 (0.89-1.52)] (P < 0.05). However, the expression level of miR-34c in the DFU group was significantly higher than the T2DM group [9.65 (6.15-18.63) vs 2.99 (1.45-6.22)] (P < 0.01). Compared with the NDFO group, the expression level of miR-34c in the DFO group was also obviously increased [13.46 (8.89-19.11) vs 6.02 (5.93-14.72)] (P < 0.01). The expression level of miR-34c in DFU patients was positively correlated with the amputation rate of foot ulcers (P=0.030) and was negatively correlated with the healing rate of foot ulcers after eight weeks (P=0.025). Multifactorial logistic regression analysis showed that increased expression of miR-34c was an independent risk factor for DFU and DFO (OR_DFU=3.47, OR_DFO=4.25, P < 0.01). Meanwhile, the ROC curve analysis indicated that the AUC of miR-34c for the diagnosis of DFU and DFO was 0.803 and 0.904, the optimum sensitivity being was 100% and 98.7%, the optimum specificity was 98.4% and 98.4%, respectively.

CONCLUSION

The increased expression of miR-34c in peripheral blood of T2DM patients is closely related to the occurrence, development and prognosis of DFU and DFO.

MiR-130a-3p Has Protective Effects in Alzheimer's Disease via Targeting DAPK1

The present study investigated the role and potential mechanisms of miR-130a-3p in AD. SH-SY5Y cells were treated with Aβ 1-42 to construct AD cell models. APP/PS1 mice were used for the animal experiments.  MiR-130a-3p was downregulated in Aβ-induced SH-SY5Y cells. Overexpression of miR-130a-3p attenuates Aβ induced SH-SY5Y cell apoptosis. Low miR-130a-3p expression was detected in the hippocampus tissues of AD mice. The Morris water maze (MWM) results indicated that miR-130a-3p upregulation reduced the escape latency time and increased the time of AD mice spent in the target quadrant. DAPK1 was the target gene of miR-130a-3p. High DAPK1 mRNA level was detected in Aβ treated PC 12 cells and in the hippocampus tissues of AD mice. It was concluded that overexpression of miR-130a-3p may attenuate Aβ-induced neurotoxicity and improve the cognitive function of AD mice via targeting DAPK1.

Identification and validation of endogenous control miRNAs in plasma samples for normalization of qPCR data for Alzheimer's disease

Background

MicroRNAs (miRNAs) are noncoding RNAs that are highly relevant as disease biomarkers. Several studies that explored the role of miRNAs in Alzheimer’s disease (AD) demonstrated their usefulness in clinical identification. Nevertheless, miRNAs that may act as endogenous controls (ECs) have not yet been established. The identification of ECs would contribute to the standardization of these biomarkers in AD. The objective of the study was to identify miRNAs that can be used as ECs in AD.

Methods

We evaluated 145 patients divided into two different cohorts. One was a discovery cohort of 19 women diagnosed with mild to moderate AD (Mini-Mental State Examination (MMSE) score ≥ 20) and with confirmed pathologic levels of Aβ42 in CSF. The stability assessment cohort consisted of 126 individuals: 24 subjects without AD or any kind of dementia and negative for all core CSF biomarkers of AD, 25 subjects with MCI and negative for CSF biomarkers (MCI −), 22 subjects with MCI and positive for CSF biomarkers (MCI +), and 55 subjects with AD and positive for CSF biomarkers. In the discovery cohort, a profile of 384 miRNAs was determined in the plasma by TaqMan low-density array. The best EC candidates were identified by mean-centering and concordance correlation restricted normalization methods. The stability of the EC candidates was assessed using the GeNorm, BestKeeper, and NormFinder algorithms.

Results

Nine miRNAs (hsa-miR-324-5p, hsa-miR-22-5p, hsa-miR-103a-2-5p, hsa-miR-362-5p, hsa-miR-425-3p, hsa-miR-423-5p, hsa-let-7i-3p, hsa-miR-532-5p, and hsa-miR-1301-3p) were identified as EC candidates in the discovery cohort. The validation results indicated that hsa-miR-103a-2-5p was the best EC, followed by hsa-miR-22-5p, hsa-miR-1301-3p, and hsa-miR-425-3p, which had similar stability values in all three algorithms.

Conclusions

We identified a profile of four miRNAs as potential plasma ECs to be used for normalization of miRNA expression data in studies of subjects with cognitive impairment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-020-00735-x.

Neuroprotective effects of miR-331-3p through improved cell viability and inflammatory marker expression: Correlation of serum miR-331-3p levels with diagnosis and severity of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a common neurodegenerative disease with an increasing incidence rate. Numerous microRNAs (miRNAs) have been found to be involved in AD progression. This study aimed to investigate the expression and diagnostic value of microRNA-331-3p (miR-331-3p) in AD patients and to explore the effects of miR-331-3p on neuronal viability and neuroinflammation.

METHODS

This study recruited AD patients and used Aβ_1-40 treated SH-SY5Y cells mimicking AD characteristics. The expression of miR-331-3p was estimated using reverse transcription quantitative PCR. A receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic value of miR-331-3p, and the correlation of miR-331-3p with patients' Mini-Mental State Examination (MMSE) scores and serum proinflammatory cytokines were analyzed. The effects of miR-331-3p on neuronal viability and inflammatory response were explored in SH-SY5Y cells by in vitro analysis.

RESULTS

In AD patients and Aβ_1-40 treated SH-SY5Y cells, the expression of miR-331-3p was significantly downregulated. Serum miR-331-3p had certain diagnostic potential and was correlated with the MMSE scores and serum proinflammatory cytokine levels of AD patients. In Aβ_1-40-treated SH-SY5Y cells, the overexpression of miR-331-3p enhanced cell viability and inhibited inflammatory responses.

CONCLUSION

The data of this study indicated that serum expression of miR-331-3p is decreased in AD patients, and is correlated with the MMSE scores and proinflammatory cytokine levels of AD patients. In addition, miR-331-3p can regulate the cell viability and the expression of pro-inflammatory cytokines of Aβ_1-40 treated SH-SY5Y cells, indicating the potential neuroprotective role of miR-331-3p.

RNA and Oxidative Stress in Alzheimer's Disease: Focus on microRNAs

Oxidative stress (OS) is one of the major pathomechanisms of Alzheimer's disease (AD), which is closely associated with other key events in neurodegeneration such as mitochondrial dysfunction, inflammation, metal dysregulation, and protein misfolding. Oxidized RNAs are identified in brains of AD patients at the prodromal stage. Indeed, oxidized mRNA, rRNA, and tRNA lead to retarded or aberrant protein synthesis. OS interferes with not only these translational machineries but also regulatory mechanisms of noncoding RNAs, especially microRNAs (miRNAs). MiRNAs can be oxidized, which causes misrecognizing target mRNAs. Moreover, OS affects the expression of multiple miRNAs, and conversely, miRNAs regulate many genes involved in the OS response. Intriguingly, several miRNAs embedded in upstream regulators or downstream targets of OS are involved also in neurodegenerative pathways in AD. Specifically, seven upregulated miRNAs (miR-125b, miR-146a, miR-200c, miR-26b, miR-30e, miR-34a, miR-34c) and three downregulated miRNAs (miR-107, miR-210, miR-485), all of which are associated with OS, are found in vulnerable brain regions of AD at the prodromal stage. Growing evidence suggests that altered miRNAs may serve as targets for developing diagnostic or therapeutic tools for early-stage AD. Focusing on a neuroprotective transcriptional repressor, REST, and the concept of hormesis that are relevant to the OS response may provide clues to help us understand the role of the miRNA system in cellular and organismal adaptive mechanisms to OS.

Biomarkers: Our Path Towards a Cure for Alzheimer Disease

Over the last decade, biomarkers have significantly improved our understanding of the pathophysiology of Alzheimer disease (AD) and provided valuable tools to examine different disease mechanisms and their progression over time. While several markers of amyloid, tau, neuronal, synaptic, and axonal injury, inflammation, and immune dysregulation in AD have been identified, there is a relative paucity of biomarkers which reflect other disease mechanisms such as oxidative stress, mitochondrial injury, vascular or endothelial injury, and calcium-mediated excitotoxicity. Importantly, there is an urgent need to standardize methods for biomarker assessments across different centers, and to identify dynamic biomarkers which can monitor disease progression over time and/or response to potential disease-modifying treatments. The updated research framework for AD, proposed by the National Institute of Aging- Alzheimer’s Association (NIA-AA) Work Group, emphasizes the importance of incorporating biomarkers in AD research and defines AD as a biological construct consisting of amyloid, tau, and neurodegeneration which spans pre-symptomatic and symptomatic stages. As results of clinical trials of AD therapeutics have been disappointing, it has become increasingly clear that the success of future AD trials will require the incorporation of biomarkers in participant selection, prognostication, monitoring disease progression, and assessing response to treatments. We here review the current state of fluid AD biomarkers, and discuss the advantages and limitations of the updated NIA-AA research framework. Importantly, the integration of biomarker data with clinical, cognitive, and imaging domains through a systems biology approach will be essential to adequately capture the molecular, genetic, and pathological heterogeneity of AD and its spatiotemporal evolution over time.

Hypoperfusion is a potential inducer of immunosuppressive network in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease which causes a non-reversible cognitive impairment and dementia. The primary cause of late-onset AD remains unknown although its pathology was discovered over a century ago. Recently, the vascular hypothesis of AD has received backing from evidence emerging from neuroimaging studies which have revealed the presence of a significant hypoperfusion in the brain regions vulnerable to AD pathology. In fact, hypoxia can explain many of the pathological changes evident in AD pathology, e.g. the deposition of β-amyloid plaques and chronic low-grade inflammation. Hypoxia-inducible factor-1α (HIF-1α) stimulates inflammatory responses and modulates both innate and adaptive immunity. It is known that hypoxia-induced inflammation evokes compensatory anti-inflammatory response involving tissue-resident microglia/macrophages and infiltrated immune cells. Hypoxia/HIF-1α induce immunosuppression by (i) increasing the expression of immunosuppressive genes, (ii) stimulating adenosinergic signaling, (iii) enhancing aerobic glycolysis, i.e. lactate production, and (iv) augmenting the secretion of immunosuppressive exosomes. Interestingly, it seems that these common mechanisms are also involved in the pathogenesis of AD. In AD pathology, an enhanced immunosuppression appears, e.g. as a shift in microglia/macrophage phenotypes towards the anti-inflammatory M2 phenotype and an increase in the numbers of regulatory T cells (Treg). The augmented anti-inflammatory capacity promotes the resolution of acute inflammation but persistent inflammation has crucial effects not only on immune cells but also harmful responses to the homeostasis of AD brain. I will examine in detail the mechanisms of the hypoperfusion/hypoxia-induced immunosuppressive state in general and especially, in its association with AD pathogenesis. These immunological observations support the vascular hypothesis of AD pathology.

MiR-485-3p serves as a biomarker and therapeutic target of Alzheimer's disease via regulating neuronal cell viability and neuroinflammation by targeting AKT3

BACKGROUND

Numerous microRNAs (miRNAs) have been identified as functional molecules in Alzheimer's disease (AD) pathogenesis. This study aimed to investigate the diagnostic value of microRNA-485-3p (miR-485-3p) in AD patients, evaluate the effect of miR-485-3p on neuronal viability and neuroinflammation, as well as the underlying molecular mechanisms.

METHODS

Quantitative Real-Time PCR was used to estimate expression of miR-485-3p and AKT3. A ROC analysis was used to evaluate the diagnostic value of miR-485-3p. The correlation of miR-485-3p with patients' MMSE score and inflammatory response was analyzed. Using Aβ-treated SH-SY5Y and BV2 cells models, the effects of miR-485-3p on neuronal proliferation, apoptosis, and neuroinflammation were explored. A luciferase reporter assay was used to confirm the target gene of miR-485-3p in both SH-SY5Y and BV2 cells.

RESULTS

Serum miR-485-3p expression was significantly upregulated in AD patients and cell models, which had a high diagnostic accuracy and correlated with MMSE score and inflammatory response in AD patients. The knockdown of miR-485-3p in SH-SY5Y and BV2 cells was found to significantly reverse the effect of Aβ treatment on neuronal viability and neuroinflammation. AKT3 was determined as a target of miR-485-3p, which might mediate the biological function of miR-485-3p in AD pathogenesis.

CONCLUSION

All the data indicated that increased serum miR-485-3p serves as a diagnostic biomarker in AD patients, and knockdown of miR-485-3p exerts a neuroprotective role by improving neuronal viability and weakening neuroinflammation, which may be mediated by AKT3. This study may provide a novel biomarker and therapeutic target for AD therapy.

Blood-based Biomarkers of Alzheimer's Disease: The Long and Winding Road

BACKGROUND

Blood-based biomarkers can be very useful in formulating new diagnostic and treatment proposals in the field of dementia, especially in Alzheimer's disease (AD). However, due to the influence of several factors on the reproducibility and reliability of these markers, their clinical use is still very uncertain. Thus, up-to-date knowledge about the main blood biomarkers that are currently being studied is extremely important in order to discover clinically useful and applicable tools, which could also be used as novel pharmacological strategies for the AD treatment.

METHODS

A narrative review was performed based on the current candidates of blood-based biomarkers for AD to show the main results from different studies, focusing on their clinical applicability and association with AD pathogenesis.

OBJECTIVE

The aim of this paper was to carry out a literature review on the major blood-based biomarkers for AD, connecting them with the pathophysiology of the disease.

RESULTS

Recent advances in the search of blood-based AD biomarkers were summarized in this review. The biomarkers were classified according to the topics related to the main hallmarks of the disease such as inflammation, amyloid, and tau deposition, synaptic degeneration and oxidative stress. Moreover, molecules involved in the regulation of proteins related to these hallmarks were described, such as non-coding RNAs, neurotrophins, growth factors and metabolites. Cells or cellular components with the potential to be considered as blood-based AD biomarkers were described in a separate topic.

CONCLUSION

A series of limitations undermine new discoveries on blood-based AD biomarkers. The lack of reproducibility of findings due to the small size and heterogeneity of the study population, different analytical methods and other assay conditions make longitudinal studies necessary in this field to validate these structures, especially when considering a clinical evaluation that includes a broad panel of these potential and promising blood-based biomarkers.

Prognosis prediction model for conversion from mild cognitive impairment to Alzheimer's disease created by integrative analysis of multi-omics data

BACKGROUND

Mild cognitive impairment (MCI) is a precursor to Alzheimer's disease (AD), but not all MCI patients develop AD. Biomarkers for early detection of individuals at high risk for MCI-to-AD conversion are urgently required.

METHODS

We used blood-based microRNA expression profiles and genomic data of 197 Japanese MCI patients to construct a prognosis prediction model based on a Cox proportional hazard model. We examined the biological significance of our findings with single nucleotide polymorphism-microRNA pairs (miR-eQTLs) by focusing on the target genes of the miRNAs. We investigated functional modules from the target genes with the occurrence of hub genes though a large-scale protein-protein interaction network analysis. We further examined the expression of the genes in 610 blood samples (271 ADs, 248 MCIs, and 91 cognitively normal elderly subjects [CNs]).

RESULTS

The final prediction model, composed of 24 miR-eQTLs and three clinical factors (age, sex, and APOE4 alleles), successfully classified MCI patients into low and high risk of MCI-to-AD conversion (log-rank test P = 3.44 × 10^-4 and achieved a concordance index of 0.702 on an independent test set. Four important hub genes associated with AD pathogenesis (SHC1, FOXO1, GSK3B, and PTEN) were identified in a network-based meta-analysis of miR-eQTL target genes. RNA-seq data from 610 blood samples showed statistically significant differences in PTEN expression between MCI and AD and in SHC1 expression between CN and AD (PTEN, P = 0.023; SHC1, P = 0.049).

CONCLUSIONS

Our proposed model was demonstrated to be effective in MCI-to-AD conversion prediction. A network-based meta-analysis of miR-eQTL target genes identified important hub genes associated with AD pathogenesis. Accurate prediction of MCI-to-AD conversion would enable earlier intervention for MCI patients at high risk, potentially reducing conversion to AD.

Extracellular Vesicles Loaded miRNAs as Potential Modulators Shared Between Glioblastoma, and Parkinson's and Alzheimer's Diseases

Glioblastoma (GBM) is the deadliest brain tumor. Its poor prognosis is due to cell heterogeneity, invasiveness, and high vascularization that impede an efficient therapeutic approach. In the past few years, several molecular links connecting GBM to neurodegenerative diseases (NDDs) were identified at preclinical and clinical level. In particular, giving the increasing critical role that epigenetic alterations play in both GBM and NDDs, we deeply analyzed the role of miRNAs, small non-coding RNAs acting epigenetic modulators in several key biological processes. Specific miRNAs, transported by extracellular vesicles (EVs), act as intercellular communication signals in both diseases. In this way, miRNA-loaded EVs modulate GBM tumorigenesis, as they spread oncogenic signaling within brain parenchyma, and control the aggregation of neurotoxic protein (Tau, Aβ-amyloid peptide, and α-synuclein) in NDDs. In this review, we highlight the most promising miRNAs linking GBM and NDDs playing a significant pathogenic role in both diseases.

Urinary Biomarkers for Neurodegenerative Diseases

Global incidence of neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD) and Parkinson's disease (PD) is rapidly increasing, but the diagnosis of these diseases at their early stage is challenging. Therefore, the availability of reproducible and reliable biomarkers to diagnose such diseases is more critical than ever. In addition, biomarkers could be used not only to diagnose diseases but also to monitor the development of disease therapeutics. Urine is an excellent biofluid that can be utilized as a source of biomarker to diagnose not only several renal diseases but also other diseases because of its abundance in invasive sampling. However, urine was conventionally regarded as inappropriate as a source of biomarker for neurodegenerative diseases because it is anatomically distant from the central nervous system (CNS), a major pathologic site of NDD, in comparison to other biofluids such as cerebrospinal fluid (CSF) and plasma. However, recent studies have suggested that urine could be utilized as a source of NDD biomarker if an appropriate marker is predetermined by metabolomic and proteomic approaches in urine and other samples. In this review, we summarize such studies related to NDD.

microRNA-Based Biomarkers in Alzheimer's Disease (AD)

Alzheimer's disease (AD) is a multifactorial, age-related neurological disease characterized by complex pathophysiological dynamics taking place at multiple biological levels, including molecular, genetic, epigenetic, cellular and large-scale brain networks. These alterations account for multiple pathophysiological mechanisms such as brain protein accumulation, neuroinflammatory/neuro-immune processes, synaptic dysfunction, and neurodegeneration that eventually lead to cognitive and behavioral decline. Alterations in microRNA (miRNA) signaling have been implicated in the epigenetics and molecular genetics of all neurobiological processes associated with AD pathophysiology. These changes encompass altered miRNA abundance, speciation and complexity in anatomical regions of the CNS targeted by the disease, including modified miRNA expression patterns in brain tissues, the systemic circulation, the extracellular fluid (ECF) and the cerebrospinal fluid (CSF). miRNAs have been investigated as candidate biomarkers for AD diagnosis, disease prediction, prognosis and therapeutic purposes because of their involvement in multiple brain signaling pathways in both health and disease. In this review we will: (i) highlight the significantly heterogeneous nature of miRNA expression and complexity in AD tissues and biofluids; (ii) address how information may be extracted from these data to be used as a diagnostic, prognostic and/or screening tools across the entire continuum of AD, from the preclinical stage, through the prodromal, i.e., mild cognitive impairment (MCI) phase all the way to clinically overt dementia; and (iii) consider how specific miRNA expression patterns could be categorized using miRNA reporters that span AD pathophysiological initiation and disease progression.

Body Fluid Biomarkers for Alzheimer's Disease-An Up-To-Date Overview

Neurodegeneration is a highly complex process which is associated with a variety of molecular mechanisms related to ageing. Among neurodegenerative disorders, Alzheimer's disease (AD) is the most common, affecting more than 45 million individuals. The underlying mechanisms involve amyloid plaques and neurofibrillary tangles (NFTs) deposition, which will subsequently lead to oxidative stress, chronic neuroinflammation, neuron dysfunction, and neurodegeneration. The current diagnosis methods are still limited in regard to the possibility of the accurate and early detection of the diseases. Therefore, research has shifted towards the identification of novel biomarkers and matrices as biomarker sources, beyond amyloid-β and tau protein levels within the cerebrospinal fluid (CSF), that could improve AD diagnosis. In this context, the aim of this paper is to provide an overview of both conventional and novel biomarkers for AD found within body fluids, including CSF, blood, saliva, urine, tears, and olfactory fluids.

Neuro-protective roles of long non-coding RNA MALAT1 in Alzheimer's disease with the involvement of the microRNA-30b/CNR1 network and the following PI3K/AKT activation

Long non-coding RNAs (lncRNAs) have been increasingly found to fulfill key functions in neurodegenerative diseases. This study aimed to probe the function of lncRNA MALAT1 in neuronal recovery in Alzheimer's disease (AD). Aβ25-35 was used to induce AD in a rat model and neuronal injury in PC12 and C6 cells. Aberrantly expressed lncRNAs/microRNAs (miRNAs) in AD rats were screened out by microarray analyses. Altered expression of MALAT1, miR-30b and CNR1 was performed to explore their roles in neuronal recovery in rat and cell models. Consequently, LncRNA MALAT1 and CNR1 were poorly expressed while miR-30b was highly expressed in Aβ25-35-induced rat models and cells. Overexpression of MALAT1 or CNR1 reduced neuronal injury in rat hippocampus. It increased viability and decreased apoptosis in injured PC12 and C6 cells, and decreased the secretion of pro-inflammatory factor IL-6 and TNF-α but increased IL-10 production. However, overexpression of miR-30b reversed these trends. MALAT1 could served as a sponge for mR-30b to up-regulate CNR1 expression. The phosphorylation of PI3K and AKT was stimulated when MALAT1 or CNR1 was overexpressed. To sum up, we found MALAT1 could promote neuronal recovery following AD through the miR-30b/CNR1 network and the PI3K/AKT signaling activation.

Bridging the Gap Between Fluid Biomarkers for Alzheimer's Disease, Model Systems, and Patients

Alzheimer’s disease (AD) is a debilitating neurodegenerative disease characterized by the accumulation of two proteins in fibrillar form: amyloid-β (Aβ) and tau. Despite decades of intensive research, we cannot yet pinpoint the exact cause of the disease or unequivocally determine the exact mechanism(s) underlying its progression. This confounds early diagnosis and treatment of the disease. Cerebrospinal fluid (CSF) biomarkers, which can reveal ongoing biochemical changes in the brain, can help monitor developing AD pathology prior to clinical diagnosis. Here we review preclinical and clinical investigations of commonly used biomarkers in animals and patients with AD, which can bridge translation from model systems into the clinic. The core AD biomarkers have been found to translate well across species, whereas biomarkers of neuroinflammation translate to a lesser extent. Nevertheless, there is no absolute equivalence between biomarkers in human AD patients and those examined in preclinical models in terms of revealing key pathological hallmarks of the disease. In this review, we provide an overview of current but also novel AD biomarkers and how they relate to key constituents of the pathological cascade, highlighting confounding factors and pitfalls in interpretation, and also provide recommendations for standardized procedures during sample collection to enhance the translational validity of preclinical AD models.

MicroRNA: A Key Player for the Interplay of Circadian Rhythm Abnormalities, Sleep Disorders and Neurodegenerative Diseases

Circadian rhythms are endogenous 24-h oscillators that regulate the sleep/wake cycles and the timing of biological systems to optimize physiology and behavior for the environmental day/night cycles. The systems are basically generated by transcription-translation feedback loops combined with post-transcriptional and post-translational modification. Recently, evidence is emerging that additional non-coding RNA-based mechanisms are also required to maintain proper clock function. MicroRNA is an especially important factor that plays critical roles in regulating circadian rhythm as well as many other physiological functions. Circadian misalignment not only disturbs the sleep/wake cycle and rhythmic physiological activity but also contributes to the development of various diseases, such as sleep disorders and neurodegenerative diseases. The patient with neurodegenerative diseases often experiences profound disruptions in their circadian rhythms and/or sleep/wake cycles. In addition, a growing body of recent evidence implicates sleep disorders as an early symptom of neurodegenerative diseases, and also suggests that abnormalities in the circadian system lead to the onset and expression of neurodegenerative diseases. The genetic mutations which cause the pathogenesis of familial neurodegenerative diseases have been well studied; however, with the exception of Huntington's disease, the majority of neurodegenerative diseases are sporadic. Interestingly, the dysfunction of microRNA is increasingly recognized as a cause of sporadic neurodegenerative diseases through the deregulated genes related to the pathogenesis of neurodegenerative disease, some of which are the causative genes of familial neurodegenerative diseases. Here we review the interplay of circadian rhythm disruption, sleep disorders and neurodegenerative disease, and its relation to microRNA, a key regulator of cellular processes.

Early Biomarkers of Neurodegenerative and Neurovascular Disorders in Diabetes

Diabetes mellitus (DM) is a common disease worldwide. There is a strong association between DM and neurovascular and neurodegenerative disorders. The first group mainly consists of diabetic retinopathy, diabetic neuropathy and stroke, whereas, the second group includes Alzheimer's disease, Parkinson's disease, mild cognitive impairment and dementia. The aforementioned diseases have a common pathophysiological background including insulin resistance, oxidative stress, atherosclerosis and vascular injury. The increasing prevalence of neurovascular and neurodegenerative disorders among diabetic patients has resulted in an urgent need to develop biomarkers for their prediction and/or early detection. The aim of this review is to present the potential application of the most promising biomarkers of diabetes-related neurodegenerative and neurovascular disorders, including amylin, β-amyloid, C-reactive protein (CRP), dopamine, gamma-glutamyl transferase (GGT), glycogen synthase kinase 3β, homocysteine, microRNAs (mi-RNAs), paraoxonase 1, phosphoinositide 3-kinases, tau protein and various growth factors. The most clinically promising biomarkers of neurovascular and neurodegenerative complications in DM are hsCRP, GGT, homocysteine and miRNAs. However, all biomarkers discussed in this review could become a part of the potential multi-biomarker screening panel for diabetic patients at risk of neurovascular and neurodegenerative complications.

Clinical significance of miR-433 in the diagnosis of Alzheimer's disease and its effect on Aβ-induced neurotoxicity by regulating JAK2

BACKGROUND

Numerous microRNAs (miRNAs) have been investigated in the progression of Alzheimer's disease (AD). The purpose of this study was to analyze the expression of miR-433 and its diagnostic value in patients with AD, and to explore the neuroprotective effect of miR-433 in amyloid β (Aβ)-treated SH-SY5Y and SK-N-SH cells.

METHODS

AD patients and AD cell model that established by Aβ treatment were used in this study. Quantitative real-time PCR was used to measure the expression of miR-433. The diagnostic value of miR-433 was evaluated using the receiver operating characteristic analysis. MTT assay was used to examine the viability of Aβ-treated SH-SY5Y and SK-N-SH cells. Bioinformatics and luciferase activity analyses were used to confirm the target gene that might be involved in the mechanisms of miR-433 in AD.

RESULTS

Expression levels of miR-433 were decreased in AD patients and cells compared with the corresponding controls. The decreased miR-433 expression levels in serum and cerebrospinal fluid (CS) were positively correlated with MMSE scores and had relatively high diagnostic accuracy in AD patients. The gain-of-function experiments found that the overexpression of miR-433 could rescue the Aβ-induced inhibition in neuronal viability in SH-SY5Y and SK-N-SH cells. The luciferase activity results showed that JAK2 was a target gene of miR-433 in neuronal cells.

CONCLUSION

All the data of this study showed that miR-433 serves as a candidate diagnostic biomarker for AD patients, and may have the potential as a novel therapeutic target by ameliorating Aβ-induced neurotoxicity.

MicroRNAs in Alzheimer's Disease: Function and Potential Applications as Diagnostic Biomarkers

Alzheimer’s disease (AD) is the most common form of dementia. Although the incidence of AD is high, the rates of diagnosis and treatment are relatively low. Moreover, effective means for the diagnosis and treatment of AD are still lacking. MicroRNAs (miRNAs, miRs) are non-coding RNAs that play regulatory roles by targeting mRNAs. The expression of miRNAs is conserved, temporal, and tissue-specific. Impairment of microRNA function is closely related to AD pathogenesis, including the beta-amyloid and tau hallmarks of AD, and there is evidence that the expression of some microRNAs differs significantly between healthy people and AD patients. These properties of miRNAs endow them with potential diagnostic and therapeutic value in the treatment of this debilitating disease. This review provides comprehensive information about the regulatory function of miRNAs in AD, as well as potential applications as diagnostic biomarkers.

Toxoplasmosis and Psychiatric and Neurological Disorders: A Step toward Understanding Parasite Pathogenesis

Toxoplasmosis, a disease that disrupts fetal brain development and severely affects the host's brain, has been linked to many behavioral and neurological disorders. There is growing interest in how a single-celled neurotropic parasite, Toxoplasma gondii, can control or change the behavior of the host as well as how it dominates the host's neurons. Secrets beyond these could be answered by decoding the Toxoplasma gondii genome, unravelling the function of genomic sequences, and exploring epigenetics and mRNAs alterations, as well as the postulated mechanisms contributing to various neurological and psychiatric symptoms caused by this parasite. Substantial efforts have been made to elucidate the action of T. gondii on host immunity and the biology of its infection. However, the available studies on the molecular aspects of toxoplasmosis that affect central nervous system (CNS) circuits remain limited, and much research is still needed on this interesting topic. In my opinion, this parasite is a gift for studying the biology of the nervous system and related diseases. We should utilize the unique features of Toxoplasma, such as its abilities to modulate brain physiology, for neurological studies or as a possible tool or approach to cure neurological disease.

MicroRNA Expression Signature in Mild Cognitive Impairment Due to Alzheimer's Disease

Mild cognitive impairment (MCI) defines an intermediate state between normal ageing and dementia, including Alzheimer’s disease (AD). Identification of MCI subjects who will progress to AD (MCI-AD) is today of crucial importance, especially in light of the possible development of new pathogenic therapies. Several evidences suggest that miRNAs could play relevant roles in the biogenesis of AD, and the links between selected miRNAs and specific pathogenic aspects have been partly explored. In this study, we analysed the composition of microRNA transcriptome in blood, serum and cerebrospinal fluid samples from MCI-AD subjects, from an enriched small RNA library. Real-time qPCR from MCI-AD and AD patients and normal controls was performed to profile miRNA expression. In particular, four microRNAs, hsa-mir-5588-5p, hsa-mir-3658, hsa-mir-567 and hsa-mir-3908, among all selected microRNAs, are dysregulated. Hsa-mir-567 was found to be differentially expressed in cerebrospinal fluid samples, blood and serum from MCI-AD patients, showing the highest fold change and statistical significance. Target prediction analysis have been performed to evaluate mRNAs whose expression was controlled by miRNAs found to be dysregulated here, showing that hsa-mir-567 target genes are functionally active in neuronal cells. We propose that miRNA profiles found in samples from MCI-AD patients might be relevant for a better understanding of AD-related cognitive decline and could lead to set up suitable and potential biomarkers for MCI-AD progression to AD.

Vesicular Transport of Encapsulated microRNA between Glial and Neuronal Cells

Exosomes (EXs) and extracellular microvesicles (EMVs) represent a diverse assortment of plasma membrane-derived nanovesicles, 30–1000 nm in diameter, released by all cell lineages of the central nervous system (CNS). They are examples of a very active and dynamic form of extracellular communication and the conveyance of biological information transfer essential to maintain homeostatic neurological functions and contain complex molecular cargoes representative of the cytoplasm of their cells of origin. These molecular cargoes include various mixtures of proteins, lipids, proteolipids, cytokines, chemokines, carbohydrates, microRNAs (miRNA) and messenger RNAs (mRNA) and other components, including end-stage neurotoxic and pathogenic metabolic products, such as amyloid beta (Aβ) peptides. Brain microglia, for example, respond to both acute CNS injuries and degenerative diseases with complex reactions via the induction of a pro-inflammatory phenotype, and secrete EXs and EMVs enriched in selective pathogenic microRNAs (miRNAs) such as miRNA-34a, miRNA-125b, miRNA-146a, miRNA-155, and others that are known to promote neuro-inflammation, induce complement activation, disrupt innate–immune signaling and deregulate the expression of neuron-specific phosphoproteins involved in neurotropism and synaptic signaling. This communication will review our current understanding of the trafficking of miRNA-containing EXs and EMVs from astrocytes and “activated pro-inflammatory” microglia to target neurons in neurodegenerative diseases with an emphasis on Alzheimer’s disease wherever possible.

Molecular and Imaging Biomarkers in Alzheimer's Disease: A Focus on Recent Insights

Alzheimer’s disease (AD) is the most common neurodegenerative disease among the elderly, affecting millions of people worldwide and clinically characterized by a progressive and irreversible cognitive decline. The rapid increase in the incidence of AD highlights the need for an easy, efficient and accurate diagnosis of the disease in its initial stages in order to halt or delay the progression. The currently used diagnostic methods rely on measures of amyloid-β (Aβ), phosphorylated (p-tau) and total tau (t-tau) protein levels in the cerebrospinal fluid (CSF) aided by advanced neuroimaging techniques like positron emission tomography (PET) and magnetic resonance imaging (MRI). However, the invasiveness of these procedures and the high cost restrict their utilization. Hence, biomarkers from biological fluids obtained using non-invasive methods and novel neuroimaging approaches provide an attractive alternative for the early diagnosis of AD. Such biomarkers may also be helpful for better understanding of the molecular mechanisms underlying the disease, allowing differential diagnosis or at least prolonging the pre-symptomatic stage in patients suffering from AD. Herein, we discuss the advantages and limits of the conventional biomarkers as well as recent promising candidates from alternative body fluids and new imaging techniques.

microRNA-146a Signaling in Alzheimer's Disease (AD) and Prion Disease (PrD)

The mouse- and human-brain-resident, nuclear factor kappa B (NF-κB)-regulated, micro RNA-146a-5p (miRNA-146a-5p) is an inducible, 22-nucleotide, single-stranded non-coding RNA (sncRNA) easily detected in several brain and immunological cell types, and an important epigenetic modulator of inflammatory signaling and the innate-immune response in several neurological disorders. Among all studied microRNAs, miRNA-146a-5p (typically referred to as just miRNA-146a) has been well characterized and its pathological function in progressive, age-related, and lethal human inflammatory neurodegenerative disease states is well documented. This communication will review our current understanding of miRNA-146a, its induction by the NF-kB-stimulating actions of inflammatory mediators, including the secretory products of certain microbial species such as viral vectors, and Gram-negative bacteria (such as Bacteroides fragilis) that are normal residents of the human gastrointestinal (GI) tract microbiome, and how miRNA-146a appears to contribute to neuro-pathological, neuro-inflammatory, and altered neuro-immunological aspects of both Alzheimer's disease (AD) and prion disease (PrD).

Identification of the Potential Key Circular RNAs in Elderly Patients With Postoperative Cognitive Dysfunction

Background

Postoperative cognitive dysfunction (POCD) is one of the severe complications after surgery, inducing low life quality and high mortality, especially in elderly patients. However, the underlying molecular mechanism of POCD remains largely unknown, and the ideal biomarker for clinical diagnosis and prognosis is lacking. Circular RNAs (circRNAs), as a unique class of non-coding RNAs, were characterized by its stability and conservativeness, serving as novel biomarkers in various diseases. Nevertheless, the role of circRNAs in the occurrence of POCD remains elusive.

Methods

To investigate the differentially expressed circRNAs in the serum of POCD patients and its potential role in the development of POCD, we performed a circRNA microarray to screen the differentially expressed circRNAs in the serum samples from three patients of the POCD group and three paired patients of the non-POCD group. Subsequently, quantitative real-time polymerase chain reaction analysis (qRT-PCR) was utilized to verify the microarray data with the serum samples from 10 paired patients. Cytoscape software was used to construct the circRNA–miRNA–mRNA network for circRNAs with different expression levels as well as the target genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed the biological functions of the differentially expressed circRNAs target genes.

Results

In total, we have analyzed 10,198 circRNAs through the microarray. Compared with the non-POCD patient group, there were 210 differentially expressed circRNAs with 133 upregulated and 77 downregulated in the POCD group (≥2-fold differential expression, P ≤ 0.05). The qRT-PCR confirmed 10 circRNAs with different expressed levels, and the results were consistent with the microarray findings. Among them, hsa_circRNA_001145, hsa_circRNA_101138, and hsa_circRNA_061570 had the highest magnitude of change. The GO analysis showed that the differentially expressed circRNAs were associated with the regulation of the developmental process, cell-to-cell adhesion, and nervous system development. The KEGG analysis showed that the target genes of circRNAs were enriched in the MAPK signaling pathway and RAS signaling pathway. According to the targetscan7.1 and mirdbV5 databases, the circRNA–miRNA–mRNA network was constructed, and these results provided a vital landscape of circRNA expression profile in POCD.

Conclusions

Our study provides an essential perspective for the differential expression of circRNAs in POCD patients. Further studies need to be performed to explore their potential therapeutic roles in the development of POCD.

MicroRNA-146a Is a Wide-Reaching Neuroinflammatory Regulator and Potential Treatment Target in Neurological Diseases

Progressive functional deterioration and loss of neurons underlies neurological diseases and constitutes an important cause of disability and death worldwide. The causes of various types of neurological diseases often share several critical nerve-related cellular mechanisms and pathological features, particularly the neuroinflammatory response in the nervous system. A rapidly growing body of evidence indicates that various microRNAs play pivotal roles in these processes in neurological diseases and might be viable therapeutic targets. Among these microRNAs, microRNA-146a (miR-146a) stands out due to the rapid increase in recent literature on its mechanistic involvement in neurological diseases. In this review, we summarize and highlight the critical role of miR-146a in neurological diseases. MiR-146a polymorphisms are associated with the risk of neurological disease. Alterations in miR-146a expression levels are crucial events in the pathogenesis of numerous neurological diseases that are spatially and temporally diverse. Additionally, the target genes of miR-146a are involved in the regulation of pathophysiological processes in neurological diseases, particularly the neuroinflammatory response. In summary, miR-146a mainly plays a critical role in neuroinflammation during the progression of neurological diseases and might be a prospective biomarker and therapeutic target. Understanding the mechanisms by which miR-146a affects the neuroinflammatory response in different neurological injuries, different cell types, and even different stages of certain neurological diseases will pave the way for its use as a therapeutic target in neurodegenerative diseases.

How the enriched get richer? Experience-dependent modulation of microRNAs and the therapeutic effects of environmental enrichment

Environmental enrichment and physical exercise have many well-established health benefits. Although these environmental manipulations are known to delay symptom onset and progression in a variety of neurological and psychiatric conditions, the mechanisms underlying these effects remain poorly understood. A notable candidate molecular mechanism is that of microRNA, a family of small noncoding RNAs that are important regulators of gene expression. Research investigating the many diverse roles of microRNAs has greatly expanded over the past decade, with several promising preclinical and clinical studies highlighting the role of dysregulated microRNA expression (in the brain, blood and other peripheral systems) in understanding the aetiology of disease. Altered microRNA levels have also been described following environmental interventions such as exercise and environmental enrichment in non-clinical populations and wild-type animals, as well as in some brain disorders and associated preclinical models. Recent studies exploring the effects of stimulating environments on microRNA levels in the brain have revealed an array of changes that are likely to have important downstream effects on gene expression, and thus may regulate a variety of cellular processes. Here we review literature that explores the differential expression of microRNAs in rodents following environmental enrichment and exercise, in both healthy control animals and preclinical models of relevance to neurological and psychiatric disorders.

An update on blood-based biomarkers for non-Alzheimer neurodegenerative disorders

Cerebrospinal fluid analyses and neuroimaging can identify the underlying pathophysiology at the earliest stage of some neurodegenerative disorders, but do not have the scalability needed for population screening. Therefore, a blood-based marker for such pathophysiology would have greater utility in a primary care setting and in eligibility screening for clinical trials. Rapid advances in ultra-sensitive assays have enabled the levels of pathological proteins to be measured in blood samples, but research has been predominantly focused on Alzheimer disease (AD). Nonetheless, proteins that were identified as potential blood-based biomarkers for AD, for example, amyloid-β, tau, phosphorylated tau and neurofilament light chain, are likely to be relevant to other neurodegenerative disorders that involve similar pathological processes and could also be useful for the differential diagnosis of clinical symptoms. This Review outlines the neuropathological, clinical, molecular imaging and cerebrospinal fluid features of the most common neurodegenerative disorders outside the AD continuum and gives an overview of the current status of blood-based biomarkers for these disorders.

Study on the mechanism of curcumin to reduce the inflammatory response of temporal lobe in Alzheimer's disease by regulating miR-146a

BACKGROUND

To explore the potential mechanism of curcumin in the treatment of Alzheimer's disease and clarify the role of miR-146a in the neuroinflammatory response to Alzheimer's disease.

METHODS

Clinical case study: 20 AD patients and 20 age-gender matched non-inflammatory and non-dementia patients in the department of neurology of our hospital were included, peripheral venous blood and cerebrospinal fluid were collected, and mir-146a levels in peripheral blood and cerebrospinal fluid were detected by real-time fluorescence quantitative PCR. Animal experimental study group: There were 3 groups, including APP/PS1 mice control group, APP/PS1 mice low-dose curcumin treatment group, and C57BL/6J mice wild-type (WT) control group, with 10 mice in each group. mir-146a levels in mice brain tissue were detected by quantitative real-time PCR. Aβ, APP, complement factor H (CFH) and M1 microglia labeled IL-1 β and iNOS in temporal lobe tissues of mice were detected by using Westernblot method.

RESULTS

The plasma miRNA-146a level in AD group was 39.10 ±12.97 fmol/L, and that in control group was 60.54 ±13.16 fmol/L. The plasma miRNA-146a level in AD group was significantly lower than that in control group. The level of miRNA-146a in cerebrospinal fluid of AD group (25.16 ± 5.16 fmol/L) was significantly higher than that of control group (11.35 ±3.58 fmol/L). After treatment with low dose curcumin, the level of miRNA-146a in APP/PS1 mice decreased significantly, and the expression of A β and APP/PS1 in temporal lobe of mice detected by Western blot decreased significantly, the levels of IL-1 β and iNOS protein decreased significantly, and the protein of CFH increased signifanctly.

CONCLUSIONS

miRNA-146a can be used as one of the potential biomarkers of AD. Low dose curcumin can significantly reduce the level of neuropro-inflammatory miR-146A, up-regulate the expression of CFH protein, inhibit the phenotype of M1 microglia, and play a role in the treatment of AD by promoting the phagocytosis and clearance mechanism of A β.

Activating miRNA-mRNA network in gemcitabine-resistant pancreatic cancer cell associates with alteration of memory CD4+ T cells

Background

To identify key microRNAs (miRNAs) and their target mRNAs related to gemcitabine-resistant pancreatic cancer (PC) and investigate the association between gemcitabine-resistant-related miRNAs and mRNAs and immune infiltration.

Methods

Expression profiles of miRNAs and mRNAs were obtained from the Gene Expression Omnibus (GEO) database. The differentially expressed miRNAs and mRNAs (referred to as "DEmiRNAs" and "DEmRNAs", respectively) were distinguished between gemcitabine-resistant PC cells and its parental cells. The DEmRNAs targeted by the DEmiRNAs were retrieved using miRDB, microT, and Targetscan. Furthermore, GO and KEGG pathway enrichment analysis and GSEA were performed. The Kaplan-Meier plotter was used to analyze the prognosis of key DEmiRNAs and DEmRNAs on PC patients. The relationship between the key DEmRNAs and tumor-infiltrating immune cells in PC was investigated using CIBERSORT method using the LM22 signature as reference. Key infiltrating immune cells were further analyzed for the associations with prognosis of TCGA PAAD patients.

Results

Four DEmiRNAs, including hsa-miR-3178, hsa-miR-485-3p, hsa-miR-574-5p, and hsa-miR-584-5p, were identified to target seven DEmRNAs, including MSI2, TEAD1, GNPDA1, RND3, PRKACB, TRIM68, and YKT6, individually, in gemcitabine-resistant PC cells versus parental cells. Gemcitabine-resistant PC cells were enriched in proteasome-related, immune-related, and memory CD4⁺ T cell-related pathways, indicating a gemcitabine therapeutic effect on PC cells. All four DEmiRNAs and almost all DEmRNAs had an impact on the prognosis of PC patients. All seven DEmRNAs had remarkable effects on CD4⁺ memory T cells, which were affected by the gemcitabine therapeutic effect. Effector memory CD4⁺ T cells rather than central memory CD4⁺ T cells predicted a good prognosis according to the TCGA PAAD dataset.

Conclusions

Gemcitabine resistance can alter the fraction of memory CD4⁺ T cells via hsa-miR-3178, hsa-miR-485-3p, hsa-miR-574-5p and hsa-miR-584-5p targeted MSI2, TEAD1, GNPDA1, RND3, PRKACB, TRIM68, and YKT6 network in PC.

Fetal malnutrition-induced catch up failure is caused by elevated levels of miR-322 in rats

If sufficient nutrition is not obtained during pregnancy, the fetus changes its endocrine system and metabolism to protect the brain, resulting in a loss of body size. The detailed mechanisms that determine the success or failure of growth catch-up are still unknown. Therefore, we investigated the mechanism by which catch-up growth failure occurs. The body weights of rat pups at birth from dams whose calorie intake during pregnancy was reduced by 40% were significantly lower than those of controls, and some offspring failed to catch up. Short-body-length and low-bodyweight rats showed blood IGF-1 levels and mRNA expression levels of IGF-1 and growth hormone receptor (GHR) in the liver that were lower than those in controls. The next generation offspring from low-bodyweight non-catch-up (LBW-NCG) rats had high expression of miR-322 and low expression of GHR and IGF-1. The expression of miR-322 showed a significant negative correlation with GHR expression and body length, and overexpression of miR-322 suppressed GHR expression. We found that insufficient intake of calories during pregnancy causes catch-up growth failure due to increased expression of miR-322 and decreased expression of GHR in the livers of offspring, and this effect is inherited by the next generation.

miRNAs as Influencers of Cell-Cell Communication in Tumor Microenvironment

microRNAs (miRNAs) are small noncoding RNAs that regulate gene expression at the posttranscriptional level, inducing the degradation of the target mRNA or translational repression. MiRNAs are involved in the control of a multiplicity of biological processes, and their absence or altered expression has been associated with a variety of human diseases, including cancer. Recently, extracellular miRNAs (ECmiRNAs) have been described as mediators of intercellular communication in multiple contexts, including tumor microenvironment. Cancer cells cooperate with stromal cells and elements of the extracellular matrix (ECM) to establish a comfortable niche to grow, to evade the immune system, and to expand. Within the tumor microenvironment, cells release ECmiRNAs and other factors in order to influence and hijack the physiological processes of surrounding cells, fostering tumor progression. Here, we discuss the role of miRNAs in the pathogenesis of multicomplex diseases, such as Alzheimer’s disease, obesity, and cancer, focusing on the contribution of both intracellular miRNAs, and of released ECmiRNAs in the establishment and development of cancer niche. We also review growing evidence suggesting the use of miRNAs as novel targets or potential tools for therapeutic applications.