The microRNA miR-34 modulates ageing and neurodegeneration in Drosophila

Analysis of the microRNA transcriptome of Daphnia pulex during aging

Daphnia pulex is an important food organism that exhibits a particular mode of reproduction known as cyclical parthenogenesis (asexual) and sexual reproduction. Regulation of the aging process by microRNAs (miRNAs) is a research hotspot in miRNA studies. To investigate a possible role of miRNAs in regulating aging and senescence, we used Illumina HiSeq to sequence two miRNA libraries from 1-day-old (1d) and 25-day-old (25d) D. pulex specimens. In total, we obtained 11,218,097 clean reads and 28,569 unique miRNAs from 1d specimens and 11,819,106 clean reads and 44,709 unique miRNAs from 25d specimens. Bioinformatic analyses was used to identify 1335 differentially expressed miRNAs from known miRNAs, including 127 miRNAs that exhibited statistically significant differences (P < 0.01); 92 miRNAs were upregulated and 35 were downregulated. Quantitative real-time (qRT)-PCR experiments were performed for nine miRNAs from five samples (1d, 5d, 10d, 15d, 20d and 25d) during the aging process, and the sequencing and qRT-PCR data were found to be consistent. Ninety-four miRNAs were predicted to correspond to 2014 target genes in known miRNAs with 4032 target gene sites. Sixteen pathways changed significantly (P < 0.05) at different developmental stages, revealing many important principles of the miRNA regulatory aging network of D. pulex. Overall, the difference in miRNA expression profile during aging of D. pulex forms a basis for further studies aimed at understanding the role of miRNAs in regulating aging, reproductive transformation, senescence, and longevity.

Importance of miRNA stability and alternative primary miRNA isoforms in gene regulation during Drosophila development

Mature microRNAs (miRNAs) are processed from primary transcripts (pri-miRNAs), and their expression is controlled at transcriptional and post-transcriptional levels. However, how regulation at multiple levels achieves precise control remains elusive. Using published and new datasets, we profile a time course of mature and pri-miRNAs in Drosophila embryos and reveal the dynamics of miRNA production and degradation as well as dynamic changes in pri-miRNA isoform selection. We found that 5' nucleotides influence stability of mature miRNAs. Furthermore, distinct half-lives of miRNAs from the mir-309 cluster shape their temporal expression patterns, and the importance of rapid degradation of the miRNAs in gene regulation is detected as distinct evolutionary signatures at the target sites in the transcriptome. Finally, we show that rapid degradation of miR-3/-309 may be important for regulation of the planar cell polarity pathway component Vang. Altogether, the results suggest that complex mechanisms regulate miRNA expression to support normal development.

The lncRNA male-specific abdominal plays a critical role in Drosophila accessory gland development and male fertility

Although thousands of long non-coding RNAs (lncRNA) have been identified in the genomes of higher eukaryotes, the precise function of most of them is still unclear. Here, we show that a >65 kb, male-specific, lncRNA, called male-specific abdominal (msa) is required for the development of the secondary cells of the Drosophila male accessory gland (AG). msa is transcribed from within the Drosophila bithorax complex and shares much of its sequence with another lncRNA, the iab-8 lncRNA, which is involved in the development of the central nervous system (CNS). Both lncRNAs perform much of their functions via a shared miRNA embedded within their sequences. Loss of msa, or of the miRNA it contains, causes defects in secondary cell morphology and reduces male fertility. Although both lncRNAs express the same miRNA, the phenotype in the secondary cells and the CNS seem to reflect misregulation of different targets in the two tissues.

In many animals, the male seminal fluid induces physiology changes in the mated female that increase a male’s reproductive success. These changes are often referred to as the post-mating response (PMR). In Drosophila, the seminal fluid proteins responsible for generating the PMR are made in a specialized gland, analogous to the mammalian seminal vesicle and prostate, called the accessory gland (AG). In this work, we show that a male-specific, long, non-coding RNA (lncRNA), called msa, plays a critical role in the development and function of this gland, primarily through a microRNA (miRNA) encoded within its sequence. This same miRNA had previously been shown to be expressed in the central nervous system (CNS) via an alternative promoter, where its ability to repress homeotic genes is required for both male and female fertility. Here, we present evidence that the targets of this miRNA in the AG are likely different from those found in the CNS. Thus, the same miRNA seems to have been selected to affect Drosophila fertility through two different mechanisms. Although many non-coding RNAs have now been identified, very few can be shown to have function. Our work highlights a lncRNA that has multiple biological functions, affecting cellular morphology and fertility.

MicroRNAs regulate the sesquiterpenoid hormonal pathway in Drosophila and other arthropods

Arthropods comprise the majority of all described animal species, and understanding their evolution is a central question in biology. Their developmental processes are under the precise control of distinct hormonal regulators, including the sesquiterpenoids juvenile hormone (JH) and methyl farnesoate. The control of the synthesis and mode of action of these hormones played important roles in the evolution of arthropods and their adaptation to diverse habitats. However, the precise roles of non-coding RNAs, such as microRNAs (miRNAs), controlling arthropod hormonal pathways are unknown. Here, we investigated the miRNA regulation of the expression of the juvenile hormone acid methyltransferase gene (JHAMT), which encodes a rate-determining sesquiterpenoid biosynthetic enzyme. Loss of function of the miRNA bantam in the fly Drosophila melanogaster increased JHAMT expression, while overexpression of the bantam repressed JHAMT expression and resulted in pupal lethality. The male genital organs of the pupae were malformed, and exogenous sesquiterpenoid application partially rescued the genital deformities. The role of the bantam in the regulation of sesquiterpenoid biosynthesis was validated by transcriptomic, qPCR and hormone titre (JHB3 and JH III) analyses. In addition, we found a conserved set of miRNAs that interacted with JHAMT, and the sesquiterpenoid receptor methoprene-tolerant (Met) in different arthropod lineages, including insects (fly, mosquito and beetle), crustaceans (water flea and shrimp), myriapod (centipede) and chelicerate (horseshoe crab). This suggests that these miRNAs might have conserved roles in the post-transcriptional regulation of genes in sesquiterpenoid pathways across the Panarthropoda. Some of the identified lineage-specific miRNAs are potential targets for the development of new strategies in aquaculture and agricultural pest control.

Epigenetic drift of H3K27me3 in aging links glycolysis to healthy longevity in Drosophila

Epigenetic alteration has been implicated in aging. However, the mechanism by which epigenetic change impacts aging remains to be understood. H3K27me3, a highly conserved histone modification signifying transcriptional repression, is marked and maintained by Polycomb Repressive Complexes (PRCs). Here, we explore the mechanism by which age-modulated increase of H3K27me3 impacts adult lifespan. Using Drosophila, we reveal that aging leads to loss of fidelity in epigenetic marking and drift of H3K27me3 and consequential reduction in the expression of glycolytic genes with negative effects on energy production and redox state. We show that a reduction of H3K27me3 by PRCs-deficiency promotes glycolysis and healthy lifespan. While perturbing glycolysis diminishes the pro-lifespan benefits mediated by PRCs-deficiency, transgenic increase of glycolytic genes in wild-type animals extends longevity. Together, we propose that epigenetic drift of H3K27me3 is one of the molecular mechanisms that contribute to aging and that stimulation of glycolysis promotes metabolic health and longevity.

Genomic Instabilities, Cellular Senescence, and Aging: In Vitro, In Vivo and Aging-Like Human Syndromes

As average life span and elderly people prevalence in the western world population is gradually increasing, the incidence of age-related diseases such as cancer, heart diseases, diabetes, and dementia is increasing, bearing social and economic consequences worldwide. Understanding the molecular basis of aging-related processes can help extend the organism’s health span, i.e., the life period in which the organism is free of chronic diseases or decrease in basic body functions. During the last few decades, immense progress was made in the understanding of major components of aging and healthy aging biology, including genomic instability, telomere attrition, epigenetic changes, proteostasis, nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and intracellular communications. This progress has been made by three spear-headed strategies: in vitro (cell and tissue culture from various sources), in vivo (includes diverse model and non-model organisms), both can be manipulated and translated to human biology, and the study of aging-like human syndromes and human populations. Herein, we will focus on current repository of genomic “senescence” stage of aging, which includes health decline, structural changes of the genome, faulty DNA damage response and DNA damage, telomere shortening, and epigenetic alterations. Although aging is a complex process, many of the “hallmarks” of aging are directly related to DNA structure and function. This review will illustrate the variety of these studies, done in in vitro, in vivo and human levels, and highlight the unique potential and contribution of each research level and eventually the link between them.

The Role of microRNAs in Alzheimer's Disease and Their Therapeutic Potentials

MicroRNAs (miRNAs) are short, endogenous, non-coding RNAs that post-transcriptionally regulate gene expression by base pairing with mRNA targets. Altered miRNA expression profiles have been observed in several diseases, including neurodegeneration. Multiple studies have reported altered expressions of miRNAs in the brains of individuals with Alzheimer’s disease (AD) as compared to those of healthy elderly adults. Some of the miRNAs found to be dysregulated in AD have been reported to correlate with neuropathological changes, including plaque and tangle accumulation, as well as altered expressions of species that are known to be involved in AD pathology. To examine the potentially pathogenic functions of several dysregulated miRNAs in AD, we review the current literature with a focus on the activities of ten miRNAs in biological pathways involved in AD pathogenesis. Comprehensive understandings of the expression profiles and activities of these miRNAs will illuminate their roles as potential therapeutic targets in AD brain and may lead to the discovery of breakthrough treatment strategies for AD.

A Glio-Protective Role of mir-263a by Tuning Sensitivity to Glutamate

Glutamate is a ubiquitous neurotransmitter, mediating information flow between neurons. Defects in the regulation of glutamatergic transmission can result in glutamate toxicity, which is associated with neurodegeneration. Interestingly, glutamate receptors are expressed in glia, but little is known about their function, and the effects of their misregulation, in these non-neuronal cells. Here, we report a glio-protective role for Drosophila mir-263a mediated by its regulation of glutamate receptor levels in glia. mir-263a mutants exhibit a pronounced movement defect due to aberrant overexpression of CG5621/Grik, Nmdar1, and Nmdar2. mir-263a mutants exhibit excitotoxic death of a subset of astrocyte-like and ensheathing glia in the CNS. Glial-specific normalization of glutamate receptor levels restores cell numbers and suppresses the movement defect. Therefore, microRNA-mediated regulation of glutamate receptor levels protects glia from excitotoxicity, ensuring CNS health. Chronic low-level glutamate receptor overexpression due to mutations affecting microRNA (miRNA) regulation might contribute to glial dysfunction and CNS impairment.

miR-34a deficiency in APP/PS1 mice promotes cognitive function by increasing synaptic plasticity via AMPA and NMDA receptors

MicroRNA (miR)-34a was recently determined to contribute to the pathological development of Alzheimer's disease (AD). miR-34a deficiency significantly attenuates cognitive deficits in amyloid precursor protein (APP)/presenilin 1 (PS1) mice; however, its role in early AD pathology and the underlying mechanisms remain elusive. Here, we confirmed that the increase of miR-34a expression in APP/PS1 mice was earlier than the relevant AD pathological characteristics, such as amyloid-β production, amyloid plaque deposition, and cognitive deficits. Furthermore, because predicted miR-34a target genes were broadly linked to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) receptors, we evaluated synaptic plasticity by investigating high-frequency conditioning tetanus-induced excitatory postsynaptic potential, which revealed that synaptic plasticity was promoted in miR-34a knockout/APP/PS1 mice. Therefore, we assessed the expression of the presynaptic components synaptophysin and postsynaptic density protein 95 (PSD95) and found that synaptophysin and PSD95 were not altered by miR-34a deficiency. Additionally, the synaptic strength (vesicular fusion, vesicular docking, and transporting) was either not significantly changed. We also evaluated the levels of AMPA and NMDA receptors, which showed that the expression of AMPA and NMDA receptors was markedly upregulated in APP/PS1 mice with miR-34a deficiency. We conclude that miR-34a is involved in synaptic deficits in AD pathological development, which was, at least in part, due to the inhibition of NMDA (by miR-34a-5p) and AMPA (by miR-34a-3p) receptor expression.

MicroRNA-10a inhibits A30P α-synuclein aggregation and toxicity by targeting proapoptotic protein BCL2L11

Parkinson's disease (PD) is the second most common neurodegenerative disorder around the world, and is characterized by progressive loss of nigrostriatal dopaminergic neurons. Certain microRNAs (miRNAs) are aberrantly expressed in the post-mortem brain tissues of patients with PD and in vivo PD model mice. However, the role of brain-enriched miRNA (miR)-10a in PD has not been studied. To investigate the regulatory role of miR-10a on α-synuclein (α-syn) in the pathology of PD, the present study aimed to examine whether upregulation of miR-10a attenuated A30P α-syn mutant aggregation and cellular toxicity. miRNA expression analysis by reverse transcription-quantitative polymerase chain reaction demonstrated that miR-10a expression was decreased in the midbrain of A30P α-syn transgenic mice and in SH-SY5Y human neuroblastoma cells transfected with A30P α-syn. In addition, miR-10a mimics were used to upregulate miR-10a expression. It was revealed that the upregulation of miR-10a suppressed α-syn intracellular accumulation and toxicity in α-syn-overexpressing SH-SY5Y cells. In addition, miR-10a overexpression resulted in a reversal of the A30P α-syn-induced upregulation of proapoptotic protein Bcl-2-associated X protein and cleaved caspase-3 expression and downregulation of antiapoptotic protein B-cell lymphoma-2 (BCL2) expression. A luciferase reporter assay demonstrated that BCL2-like 11 (BCL2L11), an apoptosis inducer, was a novel target gene of miR-10a. A30P α-syn aggregation and toxicity were alleviated by knocking down endogenous BCL2L11 in SH-SY5Y cells using a small interfering RNA specific for BCL2L11. In conclusion, these results demonstrate that miR-10a may serve a functional role in α-syn-induced neuronal pathology by inhibiting expression of BCL2L11 and that upregulation of miR-10a expression may be a useful therapeutic strategy for the treatment of PD.

MicroRNAs and Presbycusis

Presbycusis (age-related hearing loss) is the most universal sensory degenerative disease in elderly people caused by the degeneration of cochlear cells. Non-coding microRNAs (miRNAs) play a fundamental role in gene regulation in almost every multicellular organism, and control the aging processes. It has been identified that various miRNAs are up- or down-regulated during mammalian aging processes in tissue-specific manners. Most miRNAs bind to specific sites on their target messenger-RNAs (mRNAs) and decrease their expression. Germline mutation may lead to dysregulation of potential miRNAs expression, causing progressive hair cell degeneration and age-related hearing loss. Therapeutic innovations could emerge from a better understanding of diverse function of miRNAs in presbycusis. This review summarizes the relationship between miRNAs and presbycusis, and presents novel miRNAs-targeted strategies against presbycusis.

Autophagy and Longevity

Autophagy is an evolutionally conserved cytoplasmic degradation system in which varieties of materials are sequestered by a double membrane structure, autophagosome, and delivered to the lysosomes for the degradation. Due to the wide varieties of targets, autophagic activity is essential for cellular homeostasis. Recent genetic evidence indicates that autophagy has a crucial role in the regulation of animal lifespan. Basal level of autophagic activity is elevated in many longevity paradigms and the activity is required for lifespan extension. In most cases, genes involved in autophagy and lysosomal function are induced by several transcription factors including HLH-30/TFEB, PHA-4/FOXA and MML-1/Mondo in long-lived animals. Pharmacological treatments have been shown to extend lifespan through activation of autophagy, indicating autophagy could be a potential and promising target to modulate animal lifespan. Here we summarize recent progress regarding the role of autophagy in lifespan regulation.

Identification of miR-305, a microRNA that promotes aging, and its target mRNAs in Drosophila

MicroRNAs (miRNAs) are involved in the regulation of important biological processes. Here, we describe a novel Drosophila miRNAs involved in aging. We selected eight Drosophila miRNAs, displaying high homology with seed sequences of aging-related miRNAs characterized in other species, and investigated whether the over-expression of these miRNAs affected aging in Drosophila adult flies. The lifespan of adults over-expressing miR-305, a miRNA showing high homology with miR-239 in C. elegans, was significantly shorter. Conversely, a reduction in miR-305 expression led to a longer lifespan than that in control flies. miR-305 over-expression accelerated the impairment of locomotor activity and promoted the age-dependent accumulation of poly-ubiquitinated protein aggregates in the muscle, as flies aged. Thus, we show that the ectopic expression of miR-305 has a deleterious effect on aging in Drosophila. To identify the targets of miR-305, we performed RNA-Seq. We discovered several mRNAs encoding antimicrobial peptides and insulin-like peptides, whose expression changed in adults upon miR-305 over-expression. We further confirmed, by qRT-PCR, that miR-305 over-expression significantly decreases the mRNA levels of four antimicrobial peptides. As these mRNAs contain multiple sequences matching the seed sequence of miR-305, we speculate that a reduction in target mRNA levels, caused by ectopic miRNA expression, promotes aging.

Circular RNA DLGAP4 Ameliorates Ischemic Stroke Outcomes by Targeting miR-143 to Regulate Endothelial-Mesenchymal Transition Associated with Blood-Brain Barrier Integrity

Circular RNAs (circRNAs) are highly expressed in the CNS and regulate physiological and pathophysiological processes. However, the potential role of circRNAs in stroke remains largely unknown. Here, we show that the circRNA DLGAP4 (circDLGAP4) functions as an endogenous microRNA-143 (miR-143) sponge to inhibit miR-143 activity, resulting in the inhibition of homologous to the E6-AP C-terminal domain E3 ubiquitin protein ligase 1 expression. circDLGAP4 levels were significantly decreased in the plasma of acute ischemic stroke patients (13 females and 13 males) and in a mouse stroke model. Upregulation of circDLGAP4 expression significantly attenuated neurological deficits and decreased infarct areas and blood-brain barrier damage in the transient middle cerebral artery occlusion mouse stroke model. Endothelial-mesenchymal transition contributes to blood-brain barrier disruption and circDLGAP4 overexpression significantly inhibited endothelial-mesenchymal transition by regulating tight junction protein and mesenchymal cell marker expression. Together, the results of our study are illustrative of the involvement of circDLGAP4 and its coupling mechanism in cerebral ischemia, providing translational evidence that circDLGAP4 serves as a novel therapeutic target for acute cerebrovascular protection.SIGNIFICANCE STATEMENT Circular RNAs (circRNAs) are involved in the regulation of physiological and pathophysiological processes. However, whether circRNAs are involved in ischemic injury, particularly cerebrovascular disorders, remains largely unknown. Here, we demonstrate a critical role for circular RNA DLGAP4 (circDLGAP4), a novel circular RNA originally identified as a sponge for microRNA-143 (miR-143), in ischemic stroke outcomes. Overexpression of circDLGAP4 significantly attenuated neurological deficits and decreased infarct areas and blood-brain barrier damage in the transient middle cerebral artery occlusion mouse stroke model. To our knowledge, this is the first report describing the efficacy of circRNA injection in an ischemic stroke model. Our investigation suggests that circDLGAP4 may serve as a novel therapeutic target for acute ischemic injury.

Epigenetic profiles in polyglutamine disorders

The dominant polyglutamine (polyQ) disorders are a group of progressive and incurable neurodegenerative disorders, which are caused by unstable expanded CAG trinucleotide repeats in the coding regions of their respective causative genes. The most prevalent polyQ disorders worldwide are Huntington’s disease and spinocerebellar ataxia type 3. Epigenetic mechanisms, such as DNA methylation, histone modifications and chromatin remodeling and noncoding RNA regulation, regulate gene expression or genome function. Epigenetic dysregulation has been suggested to play a pivotal role in the pathogenesis of polyQ disorders. Here, we summarize the current knowledge of epigenetic changes present in several representative polyQ disorders and discuss the potentiality of miRNAs as therapeutic targets for the clinic therapy of these disorders.

MicroRNAs mir-184 and let-7 alter Drosophila metabolism and longevity

MicroRNAs (miRNAs) are small RNA molecules that regulate gene expression associated with many complex biological processes. By comparing miRNA expression between long‐lived cohorts of Drosophila melanogaster that were fed a low‐nutrient diet with normal‐lived control animals fed a high‐nutrient diet, we identified miR‐184, let‐7, miR‐125, and miR‐100 as candidate miRNAs involved in modulating aging. We found that ubiquitous, adult‐specific overexpression of these individual miRNAs led to significant changes in fat metabolism and/or lifespan. Most impressively, adult‐specific overexpression of let‐7 in female nervous tissue increased median fly lifespan by ~22%. We provide evidence that this lifespan extension is not due to alterations in nutrient intake or to decreased insulin signaling.

Impact of Dietary Interventions on Noncoding RNA Networks and mRNAs Encoding Chromatin-Related Factors

Dietary interventions dramatically affect metabolic disease and lifespan in various aging models. Here, we profiled liver microRNA (miRNA), coding, and long non-coding RNA (lncRNA) expression by high-throughput deep sequencing in mice across multiple energy intake and expenditure interventions. Strikingly, three dietary intervention network design patterns were uncovered: (1) lifespan-extending interventions largely repressed the expression of miRNAs, lncRNAs, and transposable elements; (2) protein-coding mRNAs with expression positively correlated with long lifespan are highly targeted by miRNAs; and (3) miRNA-targeting interactions mainly target chromatin-related functions. We experimentally validated miR-34a, miR-107, and miR-212-3p targeting of the chromatin remodeler Chd1 and further demonstrate that Chd1 knockdown mimics high-fat diet and aging-induced gene expression changes and activation of transposons. Our findings demonstrate lifespan-extending diets repress miRNA-chromatin remodeler interactions and safeguard against deregulated transcription induced by aging and lifespan shortening diets, events linked by microRNA, chromatin, and ncRNA crosstalk.

An intestinal microRNA modulates the homeostatic adaptation to chronic oxidative stress in C. elegans

Adaptation to an environmental or metabolic perturbation is a feature of the evolutionary process. Recent insights into microRNA function suggest that microRNAs serve as key players in a robust adaptive response against stress in animals through their capacity to fine-tune gene expression. However, it remains largely unclear how a microRNA-modulated downstream mechanism contributes to the process of homeostatic adaptation. Here we show that loss of an intestinally expressed microRNA gene, mir-60, in the nematode C. elegans promotes an adaptive response to chronic - a mild and long-term - oxidative stress exposure. The pathway involved appears to be unique since the canonical stress-responsive factors, such as DAF-16/FOXO, are dispensable for mir-60 loss to enhance oxidative stress resistance. Gene expression profiles revealed that genes encoding lysosomal proteases and those involved in xenobiotic metabolism and pathogen defense responses are up-regulated by the loss of mir-60. Detailed genetic studies and computational microRNA target prediction suggest that endocytosis components and a bZip transcription factor gene zip-10, which functions in innate immune response, are directly modulated by miR-60 in the intestine. Our findings suggest that the mir-60 loss facilitates adaptive response against chronic oxidative stress by ensuring the maintenance of cellular homeostasis.

CRISPR-Cas9-mediated functional dissection of 3'-UTRs

Many studies using reporter assays have demonstrated that 3′ untranslated regions (3′-UTRs) regulate gene expression by controlling mRNA stability and translation. Due to intrinsic limitations of heterologous reporter assays, we sought to develop a gene editing approach to investigate the regulatory activity of 3′-UTRs in their native context. We initially used dual-CRISPR (clustered, regularly interspaced, short palindromic repeats)-Cas9 targeting to delete DNA regions corresponding to nine chemokine 3′-UTRs that destabilized mRNA in a reporter assay. Targeting six chemokine 3′-UTRs increased chemokine mRNA levels as expected. However, targeting CXCL1, CXCL6 and CXCL8 3′-UTRs unexpectedly led to substantial mRNA decreases. Metabolic labeling assays showed that targeting these three 3′-UTRs increased mRNA stability, as predicted by the reporter assay, while also markedly decreasing transcription, demonstrating an unexpected role for 3′-UTR sequences in transcriptional regulation. We further show that CRISPR–Cas9 targeting of specific 3′-UTR elements can be used for modulating gene expression and for highly parallel localization of active 3′-UTR elements in the native context. Our work demonstrates the duality and complexity of 3′-UTR sequences in regulation of gene expression and provides a useful approach for modulating gene expression and for functional annotation of 3′-UTRs in the native context.

MicroRNAs and the metabolic hallmarks of aging

Aging, the natural process of growing older, is characterized by a progressive deterioration of physiological homeostasis at the cellular, tissue, and organismal level. Metabolically, the aging process is characterized by extensive changes in body composition, multi-tissue/multi-organ insulin resistance, and physiological declines in multiple signaling pathways including growth hormone, insulin/insulin-like growth factor 1, and sex steroids regulation. With this review, we intend to consolidate published information about microRNAs that regulate critical metabolic processes relevant to aging. In certain occasions we uncover relationships likely relevant to aging, which has not been directly described before, such as the miR-451/AMPK axis. We have also included a provocative section highlighting the potential role in aging of a new designation of miRNAs, namely fecal miRNAs, recently discovered to regulate intestinal microbiota in mammals.

Sirtuins, epigenetics and longevity

Aging of organisms begins from a single cell at the molecular level. It includes changes related to telomere shortening, cell senescence and epigenetic modifications. These processes accumulate over the lifespan. Research studies show that epigenetic signaling contributes to human disease, tumorigenesis and aging. Epigenetic DNA modifications involve changes in the gene activity but not in the DNA sequence. An epigenome consists of chemical modifications to the DNA and histone proteins without the changes in the DNA sequence. These modifications strongly depend on the environment, could be reversible and are potentially transmittable to daughter cells. Epigenetics includes DNA methylation, noncoding RNA interference, and modifications of histone proteins. Sirtuins, a family of nicotine adenine dinucleotide (NAD+)-dependent enzymes, are involved in the cell metabolism and can regulate many cellular functions including DNA repair, inflammatory response, cell cycle or apoptosis. Literature shows the strong interconnection between sirtuin expression and aging processes. However, the direct relationship is still unknown. Here, we would like to summarize the existing knowledge about epigenetic processes in aging, especially those related to sirtuin expression. Another objective is to explain why some negative correlations between sirtuin activity and the rate of aging can be assumed.

MicroRNA-101 Modulates Autophagy and Oligodendroglial Alpha-Synuclein Accumulation in Multiple System Atrophy

Synucleinopathies, neurodegenerative disorders with alpha-synuclein (α-syn) accumulation, are the second leading cause of neurodegeneration in the elderly, however no effective disease-modifying alternatives exist for these diseases. Multiple system atrophy (MSA) is a fatal synucleinopathy characterized by the accumulation of toxic aggregates of α-syn within oligodendroglial cells, leading to demyelination and neurodegeneration, and the reduction of this accumulation might halt the fast progression of MSA. In this sense, the involvement of microRNAs (miRNAs) in synucleinopathies is yet poorly understood, and the potential of manipulating miRNA levels as a therapeutic tool is underexplored. In this study, we analyzed the levels of miRNAs that regulate the expression of autophagy genes in MSA cases, and investigated the mechanistic correlates of miRNA dysregulation in in vitro models of synucleinopathy. We found that microRNA-101 (miR-101) was significantly increased in the striatum of MSA patients, together with a reduction in the expression of its predicted target gene RAB5A. Overexpression of miR-101 in oligodendroglial cell cultures resulted in a significant increase in α-syn accumulation, along with autophagy deficits. Opposite results were observed upon expression of an antisense construct targeting miR-101. Stereotaxic delivery of a lentiviral construct expressing anti-miR-101 into the striatum of the MBP-α-syn transgenic (tg) mouse model of MSA resulted in reduced oligodendroglial α-syn accumulation and improved autophagy. These results suggest that miRNA dysregulation contributes to MSA pathology, with miR-101 alterations potentially mediating autophagy impairments. Therefore, therapies targeting miR-101 may represent promising approaches for MSA and related neuropathologies with autophagy dysfunction.

Fifty-Hertz Magnetic Field Affects the Epigenetic Modulation of the miR-34b/c in Neuronal Cells

The exposure to extremely low-frequency magnetic fields (ELF-MFs) has been associated to increased risk of neurodegenerative diseases, although the underlying molecular mechanisms are still undefined. Since epigenetic modulation has been recently encountered among the key events leading to neuronal degeneration, we here aimed at assessing if the control of gene expression mediated by miRNAs, namely miRs-34, has any roles in driving neuronal cell response to 50-Hz (1 mT) magnetic field in vitro. We demonstrate that ELF-MFs drive an early reduction of the expression level of miR-34b and miR-34c in SH-SY5Y human neuroblastoma cells, as well as in mouse primary cortical neurons, by affecting the transcription of the common pri-miR-34. This modulation is not p53 dependent, but attributable to the hyper-methylation of the CpG island mapping within the miR-34b/c promoter. Incubation with N-acetyl-l-cysteine or glutathione ethyl-ester fails to restore miR-34b/c expression, suggesting that miRs-34 are not responsive to ELF-MF-induced oxidative stress. By contrast, we show that miRs-34 control reactive oxygen species production and affect mitochondrial oxidative stress triggered by ELF-MFs, likely by modulating mitochondria-related miR-34 targets identified by in silico analysis. We finally demonstrate that ELF-MFs alter the expression of the α-synuclein, which is specifically stimulated upon ELF-MFs exposure via both direct miR-34 targeting and oxidative stress. Altogether, our data highlight the potential of the ELF-MFs to tune redox homeostasis and epigenetic control of gene expression in vitro and shed light on the possible mechanism(s) producing detrimental effects and predisposing neurons to degeneration.

Activation of miR-34a impairs autophagic flux and promotes cochlear cell death via repressing ATG9A: implications for age-related hearing loss

Age-related hearing loss is a major unresolved public health problem. We have previously elucidated that the activation of cochlear miR-34a is correlated with age-related hearing loss in C57BL/6 mice. A growing body of evidence points that aberrant autophagy promotes cell death during the development of multiple age-related diseases. The aim of this study was to investigate the role of miR-34a-involved disorder of autophagy in the pathogenesis of age-related hearing loss. Our results showed that miR-34a expression was markedly upregulated in the aging cochlea accompanied with impairment of autophagic flux. In the inner ear HEI-OC1 cell line, miR-34a overexpression resulted in an accumulation of phagophores and impaired autophagosome-lysosome fusion, and led to cell death subsequently. Notably, autophagy-related protein 9A (ATG9A), an autophagy protein, was significantly decreased after miR-34a overexpression. Knockdown of ATG9A inhibited autophagy flux, which is similar to the effects of miR-34a overexpression. Moreover, ursodeoxycholic acid significantly rescued miR-34a-induced HEI-OC1 cell death by restoring autophagy activity. Collectively, these findings increase our understanding of the biological effects of miR-34a in the development of age-related hearing loss and highlight miR-34a as a promising therapeutic target for its treatment.

HSF-1 is a regulator of miRNA expression in Caenorhabditis elegans

The ability of an organism to sense and adapt to environmental stressors is essential for proteome maintenance and survival. The highly conserved heat shock response is a survival mechanism employed by all organisms, including the nematode Caenorhabditis elegans, upon exposure to environmental extremes. Transcriptional control of the metazoan heat shock response is mediated by the heat shock transcription factor HSF-1. In addition to regulating global stress-responsive genes to promote stress-resistance and survival, HSF-1 has recently been shown to regulate stress-independent functions in controlling development, metabolism, and longevity. However, the indirect role of HSF-1 in coordinating stress-dependent and -independent processes through post-transcriptional regulation is largely unknown. MicroRNAs (miRNAs) have emerged as a class of post-transcriptional regulators that control gene expression through translational repression or mRNA degradation. To determine the role of HSF-1 in regulating miRNA expression, we have performed high-throughput small RNA-sequencing in C. elegans grown in the presence and absence of hsf-1 RNAi followed by treatment with or without heat shock. This has allowed us to uncover the miRNAs regulated by HSF-1 via heat-dependent and -independent mechanisms. Integrated miRNA/mRNA target-prediction analyses suggest HSF-1 as a post-transcriptional regulator of development, metabolism, and longevity through regulating miRNA expression. This provides new insight into the possible mechanism by which HSF-1 controls these processes. We have also uncovered oxidative stress response factors and insulin-like signaling factors as a common link between processes affected by HSF-1-regulated miRNAs in stress-dependent and -independent mechanisms, respectively. This may provide a role for miRNAs in regulating cross-talk between various stress responses. Our work therefore uncovers an interesting potential role for HSF-1 in post-transcriptionally controlling gene expression in C. elegans, and suggests a mechanism for cross-talk between stress responses.

Aging as an Epigenetic Phenomenon

INTRODUCTION

Hypermethylation of genes associated with promoter CpG islands, and hypomethylation of CpG poor genes, repeat sequences, transposable elements and intergenic genome sections occur during aging in mammals. Methylation levels of certain CpG sites display strict correlation to age and could be used as "epigenetic clock" to predict biological age. Multi-substrate deacetylases SIRT1 and SIRT6 affect aging via locus-specific modulations of chromatin structure and activity of multiple regulatory proteins involved in aging. Random errors in DNA methylation and other epigenetic marks during aging increase the transcriptional noise, and thus lead to enhanced phenotypic variation between cells of the same tissue. Such variation could cause progressive organ dysfunction observed in aged individuals. Multiple experimental data show that induction of NF-κB regulated gene sets occurs in various tissues of aged mammals. Upregulation of multiple miRNAs occurs at mid age leading to downregulation of enzymes and regulatory proteins involved in basic cellular functions, such as DNA repair, oxidative phosphorylation, intermediate metabolism, and others.

CONCLUSION

Strong evidence shows that all epigenetic systems contribute to the lifespan control in various organisms. Similar to other cell systems, epigenome is prone to gradual degradation due to the genome damage, stressful agents, and other aging factors. But unlike mutations and other kinds of the genome damage, age-related epigenetic changes could be fully or partially reversed to a "young" state.

Regulation of longevity by FGF21: Interaction between energy metabolism and stress responses

Fibroblast growth factor 21 (FGF21) is a hormone-like member of FGF family which controls metabolic multiorgan crosstalk enhancing energy expenditure through glucose and lipid metabolism. In addition, FGF21 acts as a stress hormone induced by endoplasmic reticulum stress and dysfunctions of mitochondria and autophagy in several tissues. FGF21 also controls stress responses and metabolism by modulating the functions of somatotropic axis and hypothalamic-pituitary-adrenal (HPA) pathway. FGF21 is a potent longevity factor coordinating interactions between energy metabolism and stress responses. Recent studies have revealed that FGF21 treatment can alleviate many age-related metabolic disorders, e.g. atherosclerosis, obesity, type 2 diabetes, and some cardiovascular diseases. In addition, transgenic mice overexpressing FGF21 have an extended lifespan. However, chronic metabolic and stress-related disorders involving inflammatory responses can provoke FGF21 resistance and thus disturb healthy aging process. First, we will describe the role of FGF21 in interorgan energy metabolism and explain how its functions as a stress hormone can improve healthspan. Next, we will examine both the induction of FGF21 expression via the integrated stress response and the molecular mechanism through which FGF21 enhances healthy aging. Finally, we postulate that FGF21 resistance, similarly to insulin resistance, jeopardizes human healthspan and accelerates the aging process.

miR-34a knockout attenuates cognitive deficits in APP/PS1 mice through inhibition of the amyloidogenic processing of APP

The noncoding miRNA-34a (miR-34a) is involved in Alzheimer's disease (AD) pathologenesis and shows potential for application as a biomarker for early diagnosis and intervention. Here, we established miR-34a knockout mice in an APP/PS1 background (APP/PS1-miR-34a KO mice) by crossbreeding miR-34a^-/- mice with APP/PS1 mice. We then investigated cognitive impairment and related pathologies. The results showed that the level of miR-34a was increased at about 6months in APP/PS1 mice, consistent with the increase in amyloid β (Aβ), and cognitive function was significantly improved in mice when miR-34a was knocked out in 9-month-old and 12-month-old mice, indicating that miR-34a is a potential candidate for determining the progression of AD. Furthermore, we assessed the processing of amyloid precursor protein (APP) and the results suggest that cognitive improvement by miR-34a knock out was mainly triggered by depression of γ-secretase activity, without affecting β- and α-secretase activities, indicating that miR-34a plays an important role in AD pathology, mainly by inhibiting the amyloidogenic processing of APP, without altering the non-amyloidogenic processing of APP.

The microRNA machinery regulates fasting-induced changes in gene expression and longevity in Caenorhabditis elegans

Intermittent fasting (IF) is a dietary restriction regimen that extends the lifespans of Caenorhabditis elegans and mammals by inducing changes in gene expression. However, how IF induces these changes and promotes longevity remains unclear. One proposed mechanism involves gene regulation by microRNAs (miRNAs), small non-coding RNAs (∼22 nucleotides) that repress gene expression and whose expression can be altered by fasting. To test this proposition, we examined the role of the miRNA machinery in fasting-induced transcriptional changes and longevity in C. elegans We revealed that fasting up-regulated the expression of the miRNA-induced silencing complex (miRISC) components, including Argonaute and GW182, and the miRNA-processing enzyme DRSH-1 (the ortholog of the Drosophila Drosha enzyme). Our lifespan measurements demonstrated that IF-induced longevity was suppressed by knock-out or knockdown of miRISC components and was completely inhibited by drsh-1 ablation. Remarkably, drsh-1 ablation inhibited the fasting-induced changes in the expression of the target genes of DAF-16, the insulin/IGF-1 signaling effector in C. elegans Fasting-induced transcriptome alterations were substantially and modestly suppressed in the drsh-1 null mutant and the null mutant of ain-1, a gene encoding GW182, respectively. Moreover, miRNA array analyses revealed that the expression levels of numerous miRNAs changed after 2 days of fasting. These results indicate that components of the miRNA machinery, especially the miRNA-processing enzyme DRSH-1, play an important role in mediating IF-induced longevity via the regulation of fasting-induced changes in gene expression.

Pervasive Behavioral Effects of MicroRNA Regulation in Drosophila

Picao-Osorio et al. reveal pervasive effects of microRNA regulation on complex locomotor behaviors in Drosophila larvae: over 40% of microRNAs display...

The effects of microRNA (miRNA) regulation on the genetic programs underlying behavior remain largely unexplored. Despite this, recent work in Drosophila shows that mutation of a single miRNA locus (miR-iab4/iab8) affects the capacity of the larva to correct its orientation if turned upside down (self-righting, SR), suggesting that other miRNAs might also be involved in behavioral control. Here we explore this possibility, studying early larval SR behavior in a collection of 81 Drosophila miRNA mutants covering almost the entire miRNA complement of the late embryo. Unexpectedly, we observe that >40% of all miRNAs tested significantly affect SR time, revealing pervasive behavioral effects of miRNA regulation in the early larva. Detailed analyses of those miRNAs affecting SR behavior (SR-miRNAs) show that individual miRNAs can affect movement in different ways, suggesting that specific molecular and cellular elements are affected by individual miRNA mutations. Furthermore, gene expression analysis shows that the Hox gene Abdominal-B (Abd-B) represents one of the targets deregulated by several SR-miRNAs. Our work thus reveals pervasive effects of miRNA regulation on a complex innate behavior in Drosophila and suggests that miRNAs may be core components of the genetic programs underlying behavioral control in other animals too.

Systemic antimiR-337-3p delivery inhibits cerebral ischemia-mediated injury

Modulation of miRNA expression has been shown to be beneficial in the context of multiple diseases. The purpose of this study was to determine if an inhibitor of miR-337-3p is neuroprotective for hypoxic injury after tail vein injection. We evaluated miR-337-3p expression levels and in brain tissue in vivo before and after permanent middle cerebral artery occlusion (pMCAO) in mice. Subsequently, a custom locked nucleic acid (LNA) antimir-337-3p oligonucleotide was developed and tested in vitro after induction of oxygen glucose-deprivation (OGD) and in vivo by injection into the mouse tail vein for 3 consecutive days before pMCAO. Ischemic lesion volume was measured by TTC staining. We show that systemically administered LNA antimir-337-3p crosses the blood brain-brain-barrier (BBB), penetrates into neurosn, downregulates endogenous miR-337-3p expression and reduces ischemic brain injury. The findings support the use of similar antimir-LNA constructs as novel therapies in neurological disease.

High-throughput sequencing of pituitary and hypothalamic microRNA transcriptome associated with high rate of egg production

Background

MicroRNAs exist widely in viruses, plants and animals. As endogenous small non-coding RNAs, miRNAs regulate a variety of biological processes. Tissue miRNA expression studies have discovered numerous functions for miRNAs in various tissues of chicken, but the regulation of miRNAs in chicken pituitary and hypothalamic development related to high and low egg-laying performance has remained unclear.

Results

In this study, using high-throughput sequencing technology, we sequenced two tissues (pituitary and hypothalamus) in 3 high- and 3 low-rate egg production Luhua chickens at the age of 300 days. By comparing low- and high-rate egg production chickens, 46 known miRNAs and 27 novel miRNAs were identified as differentially expressed (P < 0.05). Six differentially expressed known miRNAs, which are expressed in both tissues, were used in RT-qPCR validation and SNP detection. Among them, seven SNPs in two miRNA precursors (gga-miR-1684a and gga-miR-1434) were found that might enhance or reduce the production of the mature miRNAs. In addition, 124 and 30 reciprocally expressed miRNA-target pairs were identified by RNA-seq in pituitary and hypothalamic tissues, respectively and randomly selected candidate miRNA and miRNA-target pairs were validated by RT-qPCR in Jiuyuan black fowl. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation illustrated that a large number of egg laying-related pathways were enriched in the high-rate egg production chickens, including ovarian steroidogenesis and steroid hormone biosynthesis.

Conclusions

These differentially expressed miRNAs and their predicted target genes, especially identified reciprocally expressed miRNA-target pairs, advance the study of miRNA function and egg production associated miRNA identification. The analysis of the miRNA-related SNPs and their effects provided insights into the effects of SNPs on miRNA biogenesis and function. The data generated in this study will further our understanding of miRNA regulation mechanisms in the chicken egg-laying process.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3644-3) contains supplementary material, which is available to authorized users.

MicroRNA miR-29 controls a compensatory response to limit neuronal iron accumulation during adult life and aging

Background

A widespread modulation of gene expression occurs in the aging brain, but little is known as to the upstream drivers of these changes. MicroRNAs emerged as fine regulators of gene expression in many biological contexts and they are modulated by age. MicroRNAs may therefore be part of the upstream drivers of the global gene expression modulation correlated with aging and aging-related phenotypes.

Results

Here, we show that microRNA-29 (miR-29) is induced during aging in short-lived turquoise killifish brain and genetic antagonism of its function induces a gene-expression signature typical of aging. Mechanicistically, we identified Ireb2 (a master gene for intracellular iron delivery that encodes for IRP2 protein), as a novel miR-29 target. MiR-29 is induced by iron loading and, in turn, it reduces IRP2 expression in vivo, therefore limiting intracellular iron delivery in neurons. Genetically modified fish with neuro-specific miR-29 deficiency exhibit increased levels of IRP2 and transferrin receptor, increased iron content, and oxidative stress.

Conclusions

Our results demonstrate that age-dependent miR-29 upregulation is an adaptive mechanism that counteracts the expression of some aging-related phenotypes and its anti-aging activity is primarily exerted by regulating intracellular iron homeostasis limiting excessive iron-exposure in neurons.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0354-x) contains supplementary material, which is available to authorized users.

Cortical Morphogenesis during Embryonic Development Is Regulated by miR-34c and miR-204

The porcine brain closely resembles the human brain in aspects such as development and morphology. Temporal miRNA profiling in the developing embryonic porcine cortex revealed a distinct set of miRNAs, including miR-34c and miR-204, which exhibited a highly specific expression profile across the time of cortical folding. These miRNAs were found to target Doublecortin (DCX), known to be involved in neuron migration during cortical folding of gyrencephalic brains. In vivo modulation of miRNA expression in mouse embryos confirmed that miR-34c and miR-204 can control neuronal migration and cortical morphogenesis, presumably by posttranscriptional regulation of DCX.

MicroRNAs underlying memory deficits in neurodegenerative disorders

Neurodegenerative disorders are defined by neuronal loss and often associated with dementia. Understanding the multifactorial nature of cognitive decline is of particular interest. Cell loss is certainly a possibility but also an early imbalance in the complex gene networks involved in learning and memory. The small (~22nt) non-coding microRNAs play a major role in gene expression regulation and have been linked to neuronal survival and cognition. Interestingly, changes in microRNA signatures are associated with neurodegenerative disorders. In this review, we explore the role of three microRNAs, namely miR-132, miR-124 and miR-34, which are dysregulated in major neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Interestingly, these microRNAs have been associated with both memory impairment and neuronal survival, providing a potential common molecular mechanism contributing to dementia.

Alzheimer's disease: presence and role of microRNAs

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that accounts for the most cases of dementia. AD affects more than 25 million people globally and is predicted to affect nearly one in 85 people worldwide by 2050. AD is characterized by the accumulation of dense plaques of β-amyloid peptide (Aβ) and neurofibrillary tangles of hyperphosphorylated tau that cause impairment in memory, cognition, and daily activities. Although early-onset AD has been linked to several mutations, reliable genetic markers for late-onset AD are lacking. Further, the diagnosis of AD biomarkers has its limitations and cannot detect early-stage AD. The identification of accurate, early, and non-invasive biomarkers for AD is, therefore, an unmet challenge. Recently, microRNAs (miRNAs) have emerged as a novel class of gene regulatory elements with conserved roles in development and disease. Recent discoveries have uncovered roles of miRNAs in several model organisms during aging and have identified potential miRNAs biomarkers of AD. Here we will discuss this emerging field of miRNAs associated with AD and prospects for the future.

MicroRNAs in brain aging

Brain aging is one of the most crucial biological processes that affect the physiological balance between health and disease. Age-associated dysfunction of brain leads to severe health problems in current aging society. MicroRNAs (miRNAs) have emerged as important regulators in most physiological processes including fine-tuning of the short-term, cellular regulatory functions as well as modulation of long-term organismal lifespan. In this review, we discuss critical roles of miRNAs in the progression of normal and pathological brain aging. 50% of all known miRNAs are found in brain including cortex and hippocampus. A significant number of expressed miRNAs were differentially regulated during aging, implicating miRNAs as regulators of brain aging. The ability of miRNAs to regulate multiple targets within a pathway or even multiple pathways allows for coordinated regulation of brain functions. miRNA-mediated, brain functional changes are evident in cognition, inflammation, neuroprotection, lipid metabolism, mitochondrial function and lifespan. Dysregulation of brain miRNAs contributes to accelerated cognitive decline and increased neurological disorders. Elucidating mechanisms by which miRNAs and their multiple targets are temporally and spatially regulated in normal and pathological brain aging will provide a deeper understanding on the process of interrelated pathways of brain aging, and a new insight into therapeutic interventions.

Regulation of miR-34 Family in Neuronal Development

Differentiation of neural stem cells (NSC's) to mature and functional neurons requires coordinated expression of mRNA, microRNAs (miRNAs) and regulatory proteins. Our earlier unbiased miRNA profiling studies have identified miR-200, miR-34 and miR-221/222 as maximally up-regulated miRNA families in differentiating PC12 cells and demonstrated the capability of miR-200 family in inducing neuronal differentiation (J. Neurochem, 2015, 133, 640-652). In present study, we have investigated role of miR-34 family in neuronal differentiation and identified P53 as mediator of nerve growth factor (NGF) induced miR-34a expression in differentiating PC12 cells. Our studies have shown that NGF induced miR-34a, arrests proliferating PC12 cells to G1 phase, which is pre-requisite for neuronal differentiation. Our studies have also shown that increased expression of miR-34a controls the P53 level in differentiated PC12 cells in feedback inhibition manner, which probably prevents differentiated cells from P53 induced apoptosis. Expression profiling of miR-34 family in different neuronal, non-neuronal and developing cells have identified differentiated and aged brain cells as richest source of miR-34, which also indicates that higher expression of miR-34 family helps in maintaining the mature neurons in non-proliferative stage. In conclusion, our studies have shown that miR-34 is brain enriched miRNA family, which up-regulates with neuronal maturation and brain ageing and co-operative regulation of P53 and miR-34a helps in neuronal differentiation by arresting cells in G1 phase.

MiRNAs in β-Cell Development, Identity, and Disease

Pancreatic β-cells regulate glucose metabolism by secreting insulin, which in turn stimulates the utilization or storage of the sugar by peripheral tissues. Insulin insufficiency and a prolonged period of insulin resistance are usually the core components of type 2 diabetes (T2D). Although, decreased insulin levels in T2D have long been attributed to a decrease in β-cell function and/or mass, this model has recently been refined with the recognition that a loss of β-cell “identity” and dedifferentiation also contribute to the decline in insulin production. MicroRNAs (miRNAs) are key regulatory molecules that display tissue-specific expression patterns and maintain the differentiated state of somatic cells. During the past few years, great strides have been made in understanding how miRNA circuits impact β-cell identity. Here, we review current knowledge on the role of miRNAs in regulating the acquisition of the β-cell fate during development and in maintaining mature β-cell identity and function during stress situations such as obesity, pregnancy, aging, or diabetes. We also discuss how miRNA function could be harnessed to improve our ability to generate β-cells for replacement therapy for T2D.

Drosophila microRNA-34 Impairs Axon Pruning of Mushroom Body γ Neurons by Downregulating the Expression of Ecdysone Receptor

MicroRNA-34 (miR-34) is crucial for preventing chronic large-scale neurite degeneration in the aged brain of Drosophila melanogaster. Here we investigated the role of miR-34 in two other types of large-scale axon degeneration in Drosophila: axotomy-induced axon degeneration in olfactory sensory neurons (OSNs) and developmentally related axon pruning in mushroom body (MB) neurons. Ectopically overexpressed miR-34 did not inhibit axon degeneration in OSNs following axotomy, whereas ectopically overexpressed miR-34 in differentiated MB neurons impaired γ axon pruning. Intriguingly, the miR-34-induced γ axon pruning defect resulted from downregulating the expression of ecdysone receptor B1 (EcR-B1) in differentiated MB γ neurons. Notably, the separate overexpression of EcR-B1 or a transforming growth factor- β receptor Baboon, whose activation can upregulate the EcR-B1 expression, in MB neurons rescued the miR-34-induced γ axon pruning phenotype. Future investigations of miR-34 targets that regulate the expression of EcR-B1 in MB γ neurons are warranted to elucidate pathways that regulate axon pruning, and to provide insight into mechanisms that control large-scale axon degeneration in the nervous system.

MicroRNA mir-34 provides robustness to environmental stress response via the DAF-16 network in C. elegans

Diverse stresses and aging alter expression levels of microRNAs, suggesting a role for these posttranscriptional regulators of gene expression in stress modulation and longevity. Earlier studies demonstrated a central role for the miR-34 family in promoting cell cycle arrest and cell death following stress in human cells. However, the biological significance of this response was unclear. Here we show that in C. elegans mir-34 upregulation is necessary for developmental arrest, correct morphogenesis, and adaptation to a lower metabolic state to protect animals against stress-related damage. Either deletion or overexpression of mir-34 lead to an impaired stress response, which can largely be explained by perturbations in DAF-16/FOXO target gene expression. We demonstrate that mir-34 expression is regulated by the insulin signaling pathway via a negative feedback loop between miR-34 and DAF-16/FOXO. We propose that mir-34 provides robustness to stress response programs by controlling noise in the DAF-16/FOXO-regulated gene network.

miR-34 Modulates Innate Immunity and Ecdysone Signaling in Drosophila

microRNAs are endogenous small regulatory RNAs that modulate myriad biological processes by repressing target gene expression in a sequence-specific manner. Here we show that the conserved miRNA miR-34 regulates innate immunity and ecdysone signaling in Drosophila. miR-34 over-expression activates antibacterial innate immunity signaling both in cultured cells and in vivo, and flies over-expressing miR-34 display improved survival and pathogen clearance upon Gram-negative bacterial infection; whereas miR-34 knockout animals are defective in antibacterial defense. In particular, miR-34 achieves its immune-stimulatory function, at least in part, by repressing the two novel target genes Dlg1 and Eip75B. In addition, our study reveals a mutual repression between miR-34 expression and ecdysone signaling, and identifies miR-34 as a node in the intricate interplay between ecdysone signaling and innate immunity. Lastly, we identify cis-regulatory genomic elements and trans-acting transcription factors required for optimal ecdysone-mediated repression of miR-34. Taken together, our study enriches the repertoire of immune-modulating miRNAs in animals, and provides new insights into the interplay between steroid hormone signaling and innate immunity.

Current progress on microRNAs-based therapeutics in neurodegenerative diseases

MicroRNAs (miRNAs)-based therapy has recently emerged as a promising strategy in the treatments of neurodegenerative diseases. Thus, in this review, the most recent and important challenges and advances on the development of miRNA therapeutics for brain targeting are discussed. In particular, this review highlights current knowledge and progress in the field of manufacturing, recovery, isolation, purification, and analysis of these therapeutic oligonucleotides. Finally, the available miRNA delivery systems are reviewed and an analysis is presented in what concerns to the current challenges that have to be addressed to ensure their specificity and efficacy. Overall, it is intended to provide a perspective on the future of miRNA-based therapeutics, focusing the biotechnological approach to obtain miRNAs. WIREs RNA 2017, 8:e1409. doi: 10.1002/wrna.1409 For further resources related to this article, please visit the WIREs website.

Expressed microRNA associated with high rate of egg production in chicken ovarian follicles

MicroRNA (miRNA) is a highly conserved class of small noncoding RNA about 19-24 nucleotides in length that function in a specific manner to post-transcriptionally regulate gene expression in organisms. Tissue miRNA expression studies have discovered a myriad of functions for miRNAs in various aspects, but a role for miRNAs in chicken ovarian tissue at 300 days of age has not hitherto been reported. In this study, we performed the first miRNA analysis of ovarian tissues in chickens with low and high rates of egg production using high-throughput sequencing. By comparing low rate of egg production chickens with high rate of egg production chickens, 17 significantly differentially expressed miRNAs were found (P < 0.05), including 11 known and six novel miRNAs. We found that all 11 known miRNAs were involved mainly in pathways of reproduction regulation, such as steroid hormone biosynthesis and dopaminergic synapse. Additionally, expression profiling of six randomly selected differentially regulated miRNAs were validated by quantitative real-time polymerase chain reaction (RT-qPCR). Some miRNAs, such as gga-miR-34b, gga-miR-34c and gga-miR-216b, were reported to regulate processes such as proliferation, cell cycle, apoptosis and metastasis and were expressed differentially in ovaries of chickens with high rates of egg production, suggesting that these miRNAs have an important role in ovary development and reproductive management of chicken. Furthermore, we uncovered that a significantly up-regulated miRNA-gga-miR-200a-3p-is ubiquitous in reproduction-regulation-related pathways. This miRNA may play a special central role in the reproductive management of chicken, and needs to be further studied for confirmation.