Memory Decline and Its Reversal in Aging and Neurodegeneration Involve miR-183/96/182 Biogenesis

Aging alone or combined with obesity increases white adipose tissue inflammatory status in male mice

White adipose tissue (WAT) has been recognized as a fundamental and crucial organ of interest in research focusing on inflammation during obesity or aging. WAT is also proposed as a significant component of cholecalciferol and 25-hydroxyvitamin D (25(OH)D) storage, which participates in the decrease of 25(OH)D plasma levels reported during aging and obesity. In the present study, we evaluated WAT and plasma cholecalciferol and 25(OH)D content together with inflammatory status to highlight the putative relationship between vitamin D status and inflammatory process during aging alone or combined with obesity. Circulating cholecalciferol and 25(OH)D and the stored quantity of cholecalciferol and 25(OH)D in WAT were quantified in young and old mice fed a control or obesogenic diet. The inflammation was assessed by measuring plasma inflammatory cytokines, mRNA, and microRNAs inflammatory-associated in WAT. The combination of aging and obesity decreased 25(OH)D plasma levels but did not modify circulating inflammatory markers. A cumulative effect of aging and obesity was observed in WAT, with rising mRNA inflammatory cytokines, notably Ccl5 and Tnf. Interestingly, aging and obesity-associated were also characterized by increased inflammatory microRNA expression. The inflammatory parameters in WAT were negatively correlated with the plasma 25(OH)D but positively correlated with the quantity of cholecalciferol and 25(OH)D in WAT. These results support the cumulative effect of obesity and aging in aggravation of WAT inflammation and suggest that accumulation of cholecalciferol and 25(OH)D in WAT could constitute a mechanism to counteract WAT inflammation during aging and obesity.

Specific quinone reductase 2 inhibitors reduce metabolic burden and reverse Alzheimer's disease phenotype in mice

Biological aging can be described as accumulative, prolonged metabolic stress and is the major risk factor for cognitive decline and Alzheimer's disease (AD). Recently, we identified and described a quinone reductase 2 (QR2) pathway in the brain, in which QR2 acts as a removable memory constraint and metabolic buffer within neurons. QR2 becomes overexpressed with age, and it is possibly a novel contributing factor to age-related metabolic stress and cognitive deficit. We found that, in human cells, genetic removal of QR2 produced a shift in the proteome opposing that found in AD brains while simultaneously reducing oxidative stress. We therefore created highly specific QR2 inhibitors (QR2is) to enable evaluation of chronic QR2 inhibition as a means to reduce biological age-related metabolic stress and cognitive decline. QR2is replicated results obtained by genetic removal of QR2, while local QR2i microinjection improved hippocampal and cortical-dependent learning in rats and mice. Continuous consumption of QR2is in drinking water improved cognition and reduced pathology in the brains of AD-model mice (5xFAD), with a noticeable between-sex effect on treatment duration. These results demonstrate the importance of QR2 activity and pathway function in the healthy and neurodegenerative brain and what we believe to be the great therapeutic potential of QR2is as first-in-class drugs.

Ageing at Molecular Level: Role of MicroRNAs

The progression of age triggers a vast number of diseases including cardiovascular, cancer, and neurodegenerative disorders. Regardless of our plentiful knowledge about age-related diseases, little is understood about molecular pathways that associate the ageing process with various diseases. Several cellular events like senescence, telomere dysfunction, alterations in protein processing, and regulation of gene expression are common between ageing and associated diseases. Accumulating information on the role of microRNAs (miRNAs) suggests targeting miRNAs can aid our understanding of the interplay between ageing and associated diseases. In the present chapter, we have attempted to explore the information available on the role of miRNAs in ageing of various tissues/organs and diseases and understand the molecular mechanism of ageing.

Posttranscriptional regulation of neurofilament proteins and tau in health and disease

Neurofilament and tau proteins are neuron-specific cytoskeletal proteins that are enriched in axons, regulated by many of the same protein kinases, interact physically, and are the principal constituents of neurofibrillary lesions in major adult-onset dementias. Both proteins share functions related to the modulation of stability and functions of the microtubule network in axons, axonal transport and scaffolding of organelles, long-term synaptic potentiation, and learning and memory. Expression of these proteins is regulated not only at the transcriptional level but also through posttranscriptional control of pre-mRNA splicing, mRNA stability, transport, localization, local translation and degradation. Current evidence suggests that posttranscriptional determinants of their levels are usually regulated by RNA-binding proteins and microRNAs primarily through 3'-untranslated regions of neurofilament and tau mRNAs. Dysregulations of neurofilament and tau expression caused by mutations or pathologies of RNA-binding proteins such as TDP43, FUS and microRNAs are increasingly recognized in association with varied neurological disorders. In this review, we summarize the current understanding of posttranscriptional control of neurofilament and tau by examining the posttranscriptional regulation of neurofilament and tau by RNA-binding proteins and microRNAs implicated in health and diseases.

Regulation of LncRNAs and microRNAs in neuronal development and disease

Non-coding RNAs (ncRNAs) are RNAs that do not encode proteins but play important roles in regulating cellular processes. Multiple studies over the past decade have demonstrated the role of microRNAs (miRNAs) in cancer, in which some miRNAs can act as biomarkers or provide therapy target. Accumulating evidence also points to the importance of long non-coding RNAs (lncRNAs) in regulating miRNA-mRNA networks. An increasing number of ncRNAs have been shown to be involved in the regulation of cellular processes, and dysregulation of ncRNAs often heralds disease. As the population ages, the incidence of neurodegenerative diseases is increasing, placing enormous pressure on global health systems. Given the excellent performance of ncRNAs in early cancer screening and treatment, here we attempted to aggregate and analyze the regulatory functions of ncRNAs in neuronal development and disease. In this review, we summarize current knowledge on ncRNA taxonomy, biogenesis, and function, and discuss current research progress on ncRNAs in relation to neuronal development, differentiation, and neurodegenerative diseases.

The Expression of miRNAs Involved in Long-Term Memory Formation in the CNS of the Mollusk Helix lucorum

Mollusks are unique animals with a relatively simple central nervous system (CNS) containing giant neurons with identified functions. With such simple CNS, mollusks yet display sufficiently complex behavior, thus ideal for various studies of behavioral processes, including long-term memory (LTM) formation. For our research, we use the formation of the fear avoidance reflex in the terrestrial mollusk Helix lucorum as a learning model. We have shown previously that LTM formation in Helix requires epigenetic modifications of histones leading to both activation and inactivation of the specific genes. It is known that microRNAs (miRNAs) negatively regulate the expression of genes; however, the role of miRNAs in behavioral regulation has been poorly investigated. Currently, there is no miRNAs sequencing data being published on Helix lucorum, which makes it impossible to investigate the role of miRNAs in the memory formation of this mollusk. In this study, we have performed sequencing and comparative bioinformatics analysis of the miRNAs from the CNS of Helix lucorum. We have identified 95 different microRNAs, including microRNAs belonging to the MIR-9, MIR-10, MIR-22, MIR-124, MIR-137, and MIR-153 families, known to be involved in various CNS processes of vertebrates and other species, particularly, in the fear behavior and LTM. We have shown that in the CNS of Helix lucorum MIR-10 family (26 miRNAs) is the most representative one, including Hlu-Mir-10-S5-5p and Hlu-Mir-10-S9-5p as top hits. Moreover, we have shown the involvement of the MIR-10 family in LTM formation in Helix. The expression of 17 representatives of MIR-10 differentially changes during different periods of LTM consolidation in the CNS of Helix. In addition, using comparative analysis of microRNA expression upon learning in normal snails and snails with deficient learning abilities with dysfunction of the serotonergic system, we identified a number of microRNAs from several families, including MIR-10, which expression changes only in normal animals. The obtained data can be used for further fundamental and applied behavioral research.

MicroRNAs: a crossroad that connects obesity to immunity and aging

Obesity is characterized by an elevated amount of fat and energy storage in the adipose tissue (AT) and is believed to be the root cause of many metabolic diseases (MDs). Obesity is associated with low-grade chronic inflammation in AT. Like obesity, chronic inflammation and MDs are prevalent in the elderly. The resident immune microenvironment is not only responsible for maintaining AT homeostasis but also plays a crucial role in stemming obesity and related MDs. Mounting evidence suggests that obesity promotes activation in resident T cells and macrophages. Additionally, inflammatory subsets of T cells and macrophages accumulated into the AT in combination with other immune cells maintain low-grade chronic inflammation. microRNAs (miRs) are small non-coding RNAs and a crucial contributing factor in maintaining immune response and obesity in AT. AT resident T cells, macrophages and adipocytes secrete various miRs and communicate with other cells to create a potential effect in metabolic organ crosstalk. AT resident macrophages and T cells-associated miRs have a prominent role in regulating obesity by targeting several signaling pathways. Further, miRs also emerged as important regulators of cellular senescence and aging. To this end, a clear link between miRs and longevity has been demonstrated that implicates their role in regulating lifespan and the aging process. Hence, AT and circulating miRs can be used as diagnostic and therapeutic tools for obesity and related disorders. In this review, we discuss how miRs function as biomarkers and impact obesity, chronic inflammation, and aging.

MicroRNA biomarkers in frontotemporal dementia and to distinguish from Alzheimer's disease and amyotrophic lateral sclerosis

Frontotemporal lobar degeneration describes a group of progressive brain disorders that primarily are associated with atrophy of the prefrontal and anterior temporal lobes. Frontotemporal lobar degeneration is considered to be equivalent to frontotemporal dementia. Frontotemporal dementia is characterized by progressive impairments in behavior, executive function, and language. There are two main clinical subtypes: behavioral-variant frontotemporal dementia and primary progressive aphasia. The early diagnosis of frontotemporal dementia is critical for developing management strategies and interventions for these patients. Without validated biomarkers, the clinical diagnosis depends on recognizing all the core or necessary neuropsychiatric features, but misdiagnosis often occurs due to overlap with a range of neurologic and psychiatric disorders. In the studies reviewed a very large number of microRNAs were found to be dysregulated but with limited overlap between individual studies. Measurement of specific miRNAs singly or in combination, or as miRNA pairs (as a ratio) in blood plasma, serum, or cerebrospinal fluid enabled frontotemporal dementia to be discriminated from healthy controls, Alzheimer's disease, and amyotrophic lateral sclerosis. Furthermore, upregulation of miR-223-3p and downregulation of miR-15a-5p, which occurred both in blood serum and cerebrospinal fluid, distinguished behavioral-variant frontotemporal dementia from healthy controls. Downregulation of miR-132-3p in frontal and temporal cortical tissue distinguished frontotemporal lobar degeneration and frontotemporal dementia, respectively, from healthy controls. Possible strong miRNA biofluid biomarker contenders for behavioral-variant frontotemporal dementia are miR-223-3p, miR-15a-5p, miR-22-3p in blood serum and cerebrospinal fluid, and miR-124 in cerebrospinal fluid. No miRNAs were identified able to distinguish between behavioral-variant frontotemporal dementia and primary progressive aphasia subtypes. Further studies are warranted on investigating miRNA expression in biofluids and frontal/temporal cortical tissue to validate and extend these findings.

Age-dependent expression changes of circadian system-related genes reveal a potentially conserved link to aging

The circadian clock system influences the biology of life by establishing circadian rhythms in organisms, tissues, and cells, thus regulating essential biological processes based on the day/night cycle. Circadian rhythms change over a lifetime due to maturation and aging, and disturbances in the control of the circadian system are associated with several age-related pathologies.

However, the impact of chronobiology and the circadian system on healthy organ and tissue aging remains largely unknown. Whether aging-related changes of the circadian system’s regulation follow a conserved pattern across different species and tissues, hence representing a common driving force of aging, is unclear.

Based on a cross-sectional transcriptome analysis covering 329 RNA-Seq libraries, we provide indications that the circadian system is subjected to aging-related gene alterations shared between evolutionarily distinct species, such as Homo sapiens, Mus musculus, Danio rerio, and Nothobranchius furzeri. We discovered differentially expressed genes by comparing tissue-specific transcriptional profiles of mature, aged, and old-age individuals and report on six genes (per2, dec2, cirp, klf10, nfil3, and dbp) of the circadian system, which show conserved aging-related expression patterns in four organs of the species examined. Our results illustrate how the circadian system and aging might influence each other in various tissues over a long lifespan and conceptually complement previous studies tracking short-term diurnal and nocturnal gene expression oscillations.

RNA Deregulation in Amyotrophic Lateral Sclerosis: The Noncoding Perspective

RNA metabolism is central to cellular physiopathology. Almost all the molecular pathways underpinning biological processes are affected by the events governing the RNA life cycle, ranging from transcription to degradation. The deregulation of these processes contributes to the onset and progression of human diseases. In recent decades, considerable efforts have been devoted to the characterization of noncoding RNAs (ncRNAs) and to the study of their role in the homeostasis of the nervous system (NS), where they are highly enriched. Acting as major regulators of gene expression, ncRNAs orchestrate all the steps of the differentiation programs, participate in the mechanisms underlying neural functions, and are crucially implicated in the development of neuronal pathologies, among which are neurodegenerative diseases. This review aims to explore the link between ncRNA dysregulation and amyotrophic lateral sclerosis (ALS), the most frequent motoneuron (MN) disorder in adults. Notably, defective RNA metabolism is known to be largely associated with this pathology, which is often regarded as an RNA disease. We also discuss the potential role that these transcripts may play as diagnostic biomarkers and therapeutic targets.

SMAD4 Inhibits Granulosa Cell Apoptosis via the miR-183-96-182 Cluster and FoxO1 Axis

The miR-183-96-182 cluster is a polycistronic miRNA cluster necessary for ovarian functions in mammals. However, its transcriptional regulation in the ovary is largely unclear. In this study, we characterized the promoter region of the porcine miR-183-96-182 cluster, and showed that SMAD4 may function as a transcriptional activator of the miR-183-96-182 cluster in GCs through direct binding to SBE motifs in its promoter. SMAD4 may inhibit GC apoptosis via suppression of FoxO1, an effector of GC apoptosis and a direct target of the miR-183-96-182 cluster, by inducing the miR-183-96-182 cluster, and this process may be regulated by the TGF-β/SMAD signaling pathway. Our findings uncovered the regulatory mechanism of miR-183-96-182 cluster expression in GCs and demonstrated that TGF-β1/SMAD4/miR-183-96-182 cluster/FoxO1 may be a potential pathway for regulating follicular atresia and female reproduction.

Interplay of RNA-Binding Proteins and microRNAs in Neurodegenerative Diseases

The number of patients with neurodegenerative diseases (NDs) is increasing, along with the growing number of older adults. This escalation threatens to create a medical and social crisis. NDs include a large spectrum of heterogeneous and multifactorial pathologies, such as amyotrophic lateral sclerosis, frontotemporal dementia, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and multiple system atrophy, and the formation of inclusion bodies resulting from protein misfolding and aggregation is a hallmark of these disorders. The proteinaceous components of the pathological inclusions include several RNA-binding proteins (RBPs), which play important roles in splicing, stability, transcription and translation. In addition, RBPs were shown to play a critical role in regulating miRNA biogenesis and metabolism. The dysfunction of both RBPs and miRNAs is often observed in several NDs. Thus, the data about the interplay among RBPs and miRNAs and their cooperation in brain functions would be important to know for better understanding NDs and the development of effective therapeutics. In this review, we focused on the connection between miRNAs, RBPs and neurodegenerative diseases.

Plasma microRNA signature in presymptomatic and symptomatic subjects with C9orf72-associated frontotemporal dementia and amyotrophic lateral sclerosis

OBJECTIVE

To identify potential biomarkers of preclinical and clinical progression in chromosome 9 open reading frame 72 gene (C9orf72)-associated disease by assessing the expression levels of plasma microRNAs (miRNAs) in C9orf72 patients and presymptomatic carriers.

METHODS

The PREV-DEMALS study is a prospective study including 22 C9orf72 patients, 45 presymptomatic C9orf72 mutation carriers and 43 controls. We assessed the expression levels of 2576 miRNAs, among which 589 were above noise level, in plasma samples of all participants using RNA sequencing. The expression levels of the differentially expressed miRNAs between patients, presymptomatic carriers and controls were further used to build logistic regression classifiers.

RESULTS

Four miRNAs were differentially expressed between patients and controls: miR-34a-5p and miR-345-5p were overexpressed, while miR-200c-3p and miR-10a-3p were underexpressed in patients. MiR-34a-5p was also overexpressed in presymptomatic carriers compared with healthy controls, suggesting that miR-34a-5p expression is deregulated in cases with C9orf72 mutation. Moreover, miR-345-5p was also overexpressed in patients compared with presymptomatic carriers, which supports the correlation of miR-345-5p expression with the progression of C9orf72-associated disease. Together, miR-200c-3p and miR-10a-3p underexpression might be associated with full-blown disease. Four presymptomatic subjects in transitional/prodromal stage, close to the disease conversion, exhibited a stronger similarity with the expression levels of patients.

CONCLUSIONS

We identified a signature of four miRNAs differentially expressed in plasma between clinical conditions that have potential to represent progression biomarkers for C9orf72-associated frontotemporal dementia and amyotrophic lateral sclerosis. This study suggests that dysregulation of miRNAs is dynamically altered throughout neurodegenerative diseases progression, and can be detectable even long before clinical onset.

TRIAL REGISTRATION NUMBER

NCT02590276.

The role of microRNAs in learning and long-term memory

The mechanisms of long-term memory formation and ways to improve it (in the case of its impairment) remain an extremely difficult problem yet to be solved. Over the recent years, much attention has been paid to microRNAs in this regard. MicroRNAs are unique endogenous non-coding RNAs about 22 nucleotides in length; each can regulate translation of hundreds of messenger RNA targets, thereby controlling entire gene networks. MicroRNAs are widely represented in the central nervous system. A large number of studies are currently being conducted to investigate the role of microRNAs in the brain functioning. A number of microRNAs have been shown to be involved in the process of synaptic plasticity, as well as in the long-term memory formation. Disruption of microRNA biogenesis leads to significant cognitive dysfunctions. Moreover, impaired microRNA biogenesis is one of the causes of the pathogenesis of mental disorders, neurodegenerative illnesses and senile dementia, which are often accompanied by deterioration in the learning ability and by memory impairment. Optimistic predictions are made that microRNAs can be used as targets for therapeutic treatment and for diagnosing the above pathologies. The importance of applications related to microRNAs significantly raises interest in studying their functions in the brain. Thus, this review is focused on the role of microRNAs in cognitive processes. It describes microRNA biogenesis and the role of miRNAs in the regulation of gene expression, as well as the latest achievements in studying the functional role of microRNAs in learning and in long-term memory formation, depending on the activation or inhibition of their expression. The review presents summarized data on the effect of impaired microRNA biogenesis on long-term memory formation, including those associated with sleep deprivation. In addition, analysis is provided of the current literature related to the prospects of improving cognitive processes by influencing microRNA biogenesis via the use of CRISPR/Cas9 technologies and active mental and physical exercises.

Electroacupuncture reduces scopolamine-induced amnesia via mediating the miR-210/SIN3A and miR-183/SIN3A signaling pathway

Background

The expression of SIN3A is closely correlated with electroacupuncture (EA) treatment efficacy of scopolamine-induced amnesia (SIA), but its underlying mechanisms remain to be further explored.

Methods

Quantitative real-time PCR was performed to analyze the expression of candidate microRNAs (miRNAs) and SIN3A mRNA in a rat model of SIA. Western blot was carried out to evaluate the differential expression of SIN3A proteins under different circumstances. Luciferase assay was used to explore the inhibitory role of certain miRNAs in SIN3A expression. A novel object recognition (NOR) test was performed to assess the memory function of SIA rats undergoing EA treatment. Immunohistochemistry was carried out to evaluate the expression of SIN3A in the hippocampus of SIA rats.

Results

Rno-miR-183-5p, rno-miR-34c-3p and rno-miR-210-3p were significantly up-regulated in SIA rats treated with EA. In addition, rno-miR-183-5p and rno-miR-210-3p exerted an inhibitory effect on SIN3A expression. EA treatment of SIA rats effectively restored the dysregulated expression of rno-miR-183-5p, rno-miR-210-3p and SIN3A. EA treatment also promoted the inhibited expression of neuronal IEGs including Arc, Egr1, Homer1 and Narp in the hippocampus of SIA rats. Accordingly, the NOR test also confirmed the effect of EA treatment on the improvement of memory in SIA rats.

Conclusion

In summary, the findings of this study demonstrated that scopolamine-induced amnesia was associated with downregulated expression of miR-210/miR-183 and upregulated expression of SIN3A. Furthermore, treatment with EA alleviated scopolamine-induced amnesia in rats and was associated with upregulated expression of miR-210/miR-183 and downregulated expression of SIN3A.

Dopamine-Dependent QR2 Pathway Activation in CA1 Interneurons Enhances Novel Memory Formation

The formation of memory for a novel experience is a critical cognitive capacity. The ability to form novel memories is sensitive to age-related pathologies and disease, to which prolonged metabolic stress is a major contributing factor. Presently, we describe a dopamine-dependent redox modulation pathway within the hippocampus of male mice that promotes memory consolidation. Namely, following novel information acquisition, quinone reductase 2 (QR2) is suppressed by miRNA-182 (miR-182) in the CA1 region of the hippocampus via dopamine D1 receptor (D1R) activation, a process largely facilitated by locus coeruleus activity. This pathway activation reduces ROS generated by QR2 enzymatic activity, a process that alters the intrinsic properties of CA1 interneurons 3 h following learning, in a form of oxidative eustress. Interestingly, novel experience decreases QR2 expression predominately in inhibitory interneurons. Additionally, we find that in aged animals this newly described QR2 pathway is chronically under activated, resulting in miR-182 underexpression and QR2 overexpression. This leads to accumulative oxidative stress, which can be seen in CA1 via increased levels of oxidized, inactivated potassium channel Kv2.1, which undergoes disulfide bridge oligomerization. This newly described interneuron-specific molecular pathway lies alongside the known mRNA translation-dependent processes necessary for long-term memory formation, entrained by dopamine in CA1. It is a process crucial for the distinguishing features of novel memory, and points to a promising new target for memory enhancement in aging and age-dependent diseases.SIGNIFICANCE STATEMENT One way in which evolution dictates which sensory information will stabilize as an internal representation, relies on information novelty. Dopamine is a central neuromodulator involved in this process in the mammalian hippocampus. Here, we describe for the first time a dopamine D1 receptor-dependent quinone reductase 2 pathway in interneurons. This is a targeted redox event necessary to delineate a novel experience to a robust long-term internal representation. Activation of this pathway alone can explain the effect novelty has on "flashbulb" memories, and it can become dysfunctional with age and diseases, such as Alzheimer's disease.

Role of microRNAs in neurodegeneration induced by environmental neurotoxicants and aging

The progressive loss of neuronal structure and functions resulting in the death of neurons is considered as neurodegeneration. Environmental toxicants induced degeneration of neurons is accelerated with aging. In adult brains, most of the neurons are post-mitotic, and their loss results in the development of diseases like amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). Neurodegenerative diseases have several similarities at the sub-cellular and molecular levels, such as synaptic degeneration, oxidative stress, inflammation, and cognitive decline, which are also known in brain aging. Identification of these similarities at the molecular level offers hope for the development of new therapeutics to ameliorate all neurodegenerative diseases simultaneously. Aging is known as the most strongly associated additive factor in the pathogenesis of neurodegenerative diseases. Studies carried out so far identified several genes, which are responsible for selective degeneration of neurons in different neurodegenerative diseases. Countless efforts have been made in identifying therapeutics for neurodegenerative diseases; however, the discovery of effective therapy remains elusive. Findings made in the last two decades identified microRNAs (miRNAs) as the most potent post-transcription regulatory RNA molecule, which can condition protein levels in the cell and tissue-specific manner. Identification of miRNAs, which regulate both neurotoxicant and aging-associated degeneration of brain cells, raises the possibility that roads leading to aging and neurotoxicant induced neurodegeneration cross at some point. Identification of miRNAs, which are common to aging and neurotoxicant induced neurodegeneration, will help in understanding the complex mechanism of neurodegenerative disease development. In the future, the use of natural miRNAs in vivo in therapy will be able to tackle several issues of aging and neurodegeneration. In the present review, we have provided a summary of findings made on the role of miRNAs in neurodegeneration and explored the common link made by miRNAs between aging and neurotoxicants induced neurodegeneration.

Muscarinic-Dependent miR-182 and QR2 Expression Regulation in the Anterior Insula Enables Novel Taste Learning

In a similar manner to other learning paradigms, intact muscarinic acetylcholine receptor (mAChR) neurotransmission or protein synthesis regulation in the anterior insular cortex (aIC) is necessary for appetitive taste learning. Here we describe a parallel local molecular pathway, where GABA_A receptor control of mAChR activation causes upregulation of miRNA-182 and quinone reductase 2 (QR2) mRNA destabilization in the rodent aIC. Damage to long-term memory by prevention of this process, with the use of mAChR antagonist scopolamine before novel taste learning, can be rescued by local QR2 inhibition, demonstrating that QR2 acts downstream of local muscarinic activation. Furthermore, we prove for the first time the presence of endogenous QR2 cofactors in the brain, establishing QR2 as a functional reductase there. In turn, we show that QR2 activity causes the generation of reactive oxygen species, leading to modulation in Kv2.1 redox state. QR2 expression reduction therefore is a previously unaccounted mode of mAChR-mediated inflammation reduction, and thus adds QR2 to the cadre of redox modulators in the brain. The concomitant reduction in QR2 activity during memory consolidation suggests a complementary mechanism to the well established molecular processes of this phase, by which the cortex gleans important information from general sensory stimuli. This places QR2 as a promising new target to tackle neurodegenerative inflammation and the associated impediment of novel memory formation in diseases such as Alzheimer’s disease.

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.

Epigenetic changes during ageing and their underlying mechanisms

As life expectancy increases worldwide, ageing and age-related diseases arise as a major issue for societies around the globe. Understanding the biological mechanisms underlying the ageing process is thus instrumental for the development of efficient interventions aimed to prevent and treat age-related conditions. Current knowledge in the biogerontology field points to epigenetics as a critical component of the ageing process, not only by serving as a bona-fide marker of biological age but also by controlling and conferring inheritability to cellular and organismal ageing. This is reflected by a myriad of evidences demonstrating the relationship between DNA methylation, histone modifications, chromatin remodeling and small non-coding RNAs and several age-related phenotypes. Given the reversibility of epigenetic alterations, epigenetic reprogramming may also be envisioned as a potential approach to treat age-related disorders. Here we review how different types of epigenetic mechanisms are involved in the ageing process. In addition, we highlight how interventions modulate epigenetics and thus promote health- and lifespan.

Characterising the Transcriptional and Translational Impact of the Schizophrenia-Associated miR-1271-5p in Neuronal Cells

MicroRNA (miRNA) coordinate complex gene expression networks in cells that are vital to support highly specialised morphology and cytoarchitecture. Neurons express a rich array of miRNA, including many that are specific or enriched, which have important functions in this context and implications for neurological conditions. While the neurological function of a number of brain-derived miRNAs have been examined thoroughly, the mechanistic basis of many remain obscure. In this case, we investigated the transcriptome-wide impact of schizophrenia-associated miR-1271-5p in response to bidirectional modulation. Alteration of miR-1271-5p induced considerable changes to mRNA abundance and translation, which spanned a diverse range of cellular functions, including directly targeted genes strongly associated with cytoskeletal dynamics and cellular junctions. Mechanistic analyses additionally revealed that upregulation of miR-1271-5p predominantly repressed mRNAs through destabilisation, wherein 3'UTR and coding sequence binding sites exhibited similar efficacy. Knockdown, however, produced no discernible trend in target gene expression and strikingly resulted in increased expression of the highly conserved miR-96-5p, which shares an identical seed region with miR-1271-5p, suggesting the presence of feedback mechanisms that sense disruptions to miRNA levels. These findings indicate that, while bidirectional regulation of miR-1271-5p results in substantial remodeling of the neuronal transcriptome, these effects are not inverse in nature. In addition, we provide further support for the idea that destabilisation of mRNA is the predominant mechanism by which miRNAs regulate complementary mRNAs.

Circulating RNAs as Potential Biomarkers in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a complex multi-system neurodegenerative disorder with currently limited diagnostic and no therapeutic options. Despite the intense efforts no clinically applicable biomarkers for ALS are yet established. Most current research is thus focused, in particular, in identifying potential non-invasive circulating biomarkers for more rapid and accurate diagnosis and monitoring of the disease. In this review, we have focused on messenger RNA (mRNA), non-coding RNAs (lncRNAs), micro RNAs (miRNAs) and circular RNA (circRNAs) as potential biomarkers for ALS in peripheral blood serum, plasma and cells. The most promising miRNAs include miR-206, miR-133b, miR-27a, mi-338-3p, miR-183, miR-451, let-7 and miR-125b. To test clinical potential of this miRNA panel, a useful approach may be to perform such analysis on larger multi-center scale using similar experimental design. However, other types of RNAs (lncRNAs, circRNAs and mRNAs) that, together with miRNAs, represent RNA networks, have not been yet extensively studied in blood samples of patients with ALS. Additional research has to be done in order to find robust circulating biomarkers and therapeutic targets that will distinguish key RNA interactions in specific ALS-types to facilitate diagnosis, predict progression and design therapy.

TDP-43: A Key Therapeutic Target beyond Amyotrophic Lateral Sclerosis

Accumulation of TDP-43 in the cytoplasm of diseased neurons is the pathological hallmark of frontotemporal dementia-TDP (FTLD-TDP) and amyotrophic lateral sclerosis (ALS), two diseases that lack efficacious medicine to prevent or to stop disease progression. The discovery of mutations in the TARDBP gene (encoding the nuclear protein known as TDP-43) in both FTLD and ALS patients provided evidence for a link between TDP-43 alterations and neurodegeneration. Our understanding of TDP-43 function has advanced profoundly in the past several years; however, its complete role and the molecular mechanisms that lead to disease are not fully understood. Here we summarize the recent studies of this protein, its relation to neurodegenerative diseases, and the therapeutic strategies for restoring its homeostasis with small molecules. Finally, we briefly discuss the available cellular and animal models that help to shed light on TDP-43 pathology and could serve as tools for the discovery of pharmacological agents for the treatment of TDP-43-related diseases.

Friend or foe-Post-translational modifications as regulators of phase separation and RNP granule dynamics

Ribonucleoprotein (RNP) granules are membrane-less organelles consisting of RNA-binding proteins (RBPs) and RNA. RNA granules form through liquid-liquid phase separation (LLPS), whereby weak promiscuous interactions among RBPs and/or RNAs create a dense network of interacting macromolecules and drive the phase separation. Post-translational modifications (PTMs) of RBPs have emerged as important regulators of LLPS and RNP granule dynamics, as they can directly weaken or enhance the multivalent interactions between phase-separating macromolecules or can recruit or exclude certain macromolecules into or from condensates. Here, we review recent insights into how PTMs regulate phase separation and RNP granule dynamics, in particular arginine (Arg)-methylation and phosphorylation. We discuss how these PTMs regulate the phase behavior of prototypical RBPs and how, as "friend or foe," they might influence the assembly, disassembly, or material properties of cellular RNP granules, such as stress granules or amyloid-like condensates. We particularly highlight how PTMs control the phase separation and aggregation behavior of disease-linked RBPs. We also review how disruptions of PTMs might be involved in aberrant phase transitions and the formation of amyloid-like protein aggregates as observed in neurodegenerative diseases.

Non-coding RNA influences in dementia

Dementia is a complex clinical syndrome characterised by progressive decline in cognitive function. It usually presents itself as impairment in memory, loss of judgement, abstract thinking and other disturbances that are severe enough to interfere with activities of daily living. It has long been considered as one of the major challenges at present posing an ever-increasing demand on global health and social care systems. Of all the different forms of dementia, Alzheimer's disease (AD) is the most common. The term non-coding RNA (ncRNA) refers to RNA sequences which do not have the ability to be translated into proteins and therefore mainly fall within the realm of the recently acknowledged ‘dark matter’ of the genome. This genomic dark matter encompasses a whole spectrum of differing ncRNA families such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), PIWI-interacting RNAs (piRNAs), transfer RNAs (tRNAs), small nuclear RNAs (snoRNAs) and circular RNAs (circRNAs), to name but a few. Consequently, due to the widespread influences of miRNAs and lncRNAs across all disease pathways, it is of critical importance for researchers in the field of dementia to focus their attention on possible ncRNA-induced pathogeneses, with the ultimate goal of identifying novel diagnostic procedures and drug targets, together with the development of novel therapies to control such a devastating mental condition in the patient population.