Voluntary exercise prior to traumatic brain injury alters miRNA expression in the injured mouse cerebral cortex

Role of exercise on ncRNAs and exosomal ncRNAs in preventing neurodegenerative diseases: a narrative review

Engaging in activity has proven to have beneficial effects on different facets of well-being, such as conditions related to the deterioration of the nervous system. Non-coding RNAs (ncRNAs) and exosomal ncRNAs associated with vesicles have been recognized as influencers of gene expression and cell signaling, potentially contributing to the positive impact of physical activity on neurodegenerative conditions. It is hypothesized that exercise-induced changes in ncRNA expression may regulate key processes involved in neuroprotection, including neuroinflammation, oxidative stress, protein aggregation, and synaptic function. Exercise has shown promise in preventing neurodegenerative diseases (NDs), and ncRNAs and exosomal ncRNAs are emerging as potential mediators of these benefits. In review, we explored how ncRNAs and exosomal ncRNAs play a role in enhancing the impacts of activity on neurodegenerative disorders for future treatments. Research studies, both preclinical and clinical, that have documented the use of various exercises and their effects on ncRNAs and exosomal ncRNAs for the treatment of NDs have been compiled and enlisted from the PubMed database, spanning the time period from the year 2000 up to the current time. Studies show that manipulating specific ncRNAs or harnessing exercise-induced changes in ncRNA expression and exosomal cargo could potentially be utilized as therapeutic strategies for preventing or treating NDs. In conclusion, studies suggest that various exercise modalities, including aerobic, resistance, and high-intensity interval training, can modulate the expression of ncRNAs and exosomal ncRNAs in the context of NDs. The altered ncRNA profiles may contribute to the neuroprotective and therapeutic effects observed with exercise interventions. However, more research is needed to fully understand the underlying mechanisms and to further explore the potential of exercise-induced ncRNA signatures as biomarkers and therapeutic targets for neurodegenerative disorders.

Unveiling the predictive power of biomarkers in traumatic brain injury: A narrative review focused on clinical outcomes

Traumatic brain injury (TBI) has long-term consequences, including neurodegenerative disease risk. Current diagnostic tools are limited in detecting subtle brain damage. This review explores emerging biomarkers for TBI, including those related to neuronal injury, inflammation, EVs, and ncRNAs, evaluating their potential to predict clinical outcomes like mortality, recovery, and cognitive impairment. It addresses challenges and opportunities for implementing biomarkers in clinical practice, aiming to improve TBI diagnosis, prognosis, and treatment.

The Ambivalent Role of miRNA-21 in Trauma and Acute Organ Injury

Since their initial recognition, miRNAs have been the subject of rising scientific interest. Especially in recent years, miRNAs have been recognized to play an important role in the mediation of various diseases, and further, their potential as biomarkers was recognized. Rising attention has also been given to miRNA-21, which has proven to play an ambivalent role as a biomarker. Responding to the demand for biomarkers in the trauma field, the present review summarizes the contrary roles of miRNA-21 in acute organ damage after trauma with a specific focus on the role of miRNA-21 in traumatic brain injury, spinal cord injury, cardiac damage, lung injury, and bone injury. This review is based on a PubMed literature search including the terms "miRNA-21" and "trauma", "miRNA-21" and "severe injury", and "miRNA-21" and "acute lung respiratory distress syndrome". The present summary makes it clear that miRNA-21 has both beneficial and detrimental effects in various acute organ injuries, which precludes its utility as a biomarker but makes it intriguing for mechanistic investigations in the trauma field.

Can exercise benefits be harnessed with drugs? A new way to combat neurodegenerative diseases by boosting neurogenesis

Adult hippocampal neurogenesis (AHN) is affected by multiple factors, such as enriched environment, exercise, ageing, and neurodegenerative disorders. Neurodegenerative disorders can impair AHN, leading to progressive neuronal loss and cognitive decline. Compelling evidence suggests that individuals engaged in regular exercise exhibit higher production of proteins that are essential for AHN and memory. Interestingly, specific molecules that mediate the effects of exercise have shown effectiveness in promoting AHN and cognition in different transgenic animal models. Despite these advancements, the precise mechanisms by which exercise mimetics induce AHN remain partially understood. Recently, some novel exercise molecules have been tested and the underlying mechanisms have been proposed, involving intercommunications between multiple organs such as muscle-brain crosstalk, liver-brain crosstalk, and gut-brain crosstalk. In this review, we will discuss the current evidence regarding the effects and potential mechanisms of exercise mimetics on AHN and cognition in various neurological disorders. Opportunities, challenges, and future directions in this research field are also discussed.

Recent advances in the role of miRNAs in post-traumatic stress disorder and traumatic brain injury

Post-traumatic stress disorder (PTSD) is usually considered a psychiatric disorder upon emotional trauma. However, with the rising number of conflicts and traffic accidents around the world, the incidence of PTSD has skyrocketed along with traumatic brain injury (TBI), a complex neuropathological disease due to external physical force and is also the most common concurrent disease of PTSD. Recently, the overlap between PTSD and TBI is increasingly attracting attention, as it has the potential to stimulate the emergence of novel treatments for both conditions. Of note, treatments exploiting the microRNAs (miRNAs), a well-known class of small non-coding RNAs (ncRNAs), have rapidly gained momentum in many nervous system disorders, given the miRNAs' multitudinous and key regulatory role in various biological processes, including neural development and normal functioning of the nervous system. Currently, a wealth of studies has elucidated the similarities of PTSD and TBI in pathophysiology and symptoms; however, there is a dearth of discussion with respect to miRNAs in both PTSD and TBI. In this review, we summarize the recent available studies of miRNAs in PTSD and TBI and discuss and highlight promising miRNAs therapeutics for both conditions in the future.

Voluntary running exercise modifies astrocytic population and features in the peri-infarct cortex

Rehabilitative exercise following a brain stroke has beneficial effects on the morphological plasticity of neurons. Particularly, voluntary running exercise after focal cerebral ischemia promotes functional recovery and ameliorates ischemia-induced dendritic spine loss in the peri-infarct motor cortex layer 5. Moreover, neuronal morphology is affected by changes in the perineuronal environment. Glial cells, whose phenotypes may be altered by exercise, are known to play a pivotal role in the formation of this perineuronal environment. Herein, we investigated the effects of voluntary running exercise on glial cells after middle cerebral artery occlusion. Voluntary running exercise increased the population of glial fibrillary acidic protein-positive astrocytes born between post-operative days (POD) 0 and 3 on POD15 in the peri-infarct cortex. After exercise, transcriptomic analysis of post-ischemic astrocytes revealed 10 upregulated and 70 downregulated genes. Furthermore, gene ontology analysis showed that the 70 downregulated genes were significantly associated with neuronal morphology. In addition, exercise reduced the number of astrocytes expressing lipocalin 2, a regulator of dendritic spine density, on POD15. Our results suggest that exercise modifies the composition of astrocytic population and their phenotype.

Lower and higher volumes of physical exercise build up brain reserves against memory deficits triggered by a head injury in mice

Decreasing neurotrophic support and impaired mitochondrial bioenergetics are key mechanisms for long-term neurodegeneration and cognitive decline after traumatic brain injury (TBI). We hypothesize that preconditioning with lower and higher volumes of physical exercise upregulates the CREB-BDNF axis and bioenergetic capability, which might serve as neural reserves against cognitive impairment after severe TBI. Using a running wheel mounted in the home cage, mice were engaged in lower (LV, 48 h free access, and 48 h locked) and higher (HV, daily free access) exercise volumes for thirty days. Subsequently, LV and HV mice remained for additional thirty days in the home cage with the running wheel locked and were euthanized. The sedentary group had the running wheel always locked. For the same type of exercise stimulus in a given time, daily workout presents higher volume than alternate days workout. The total distance ran in the wheel was the reference parameter to confirm distinct exercise volumes. On average, LV exercise ran 27.522 m and HV exercise ran 52.076 m. Primarily, we investigate whether LV and HV protocols increase neurotrophic and bioenergetic support in the hippocampus thirty days after exercise ceased. Regardless of volume, exercise increased hippocampal pCREBSer133-CREB-proBDNF-BDNF signaling and mitochondrial coupling efficiency, excess capacity, and leak control, that may compose the neurobiological basis for neural reserves. Further, we challenge these neural reserves against secondary memory deficits triggered by a severe TBI. After thirty days of exercise LV and HV, and sedentary (SED) mice were submitted to the CCI model. Mice remained for additional thirty days in the home cage with the running wheel locked. The mortality after severe TBI was approximately 20% in LV and HV, while in the SED was 40%. Also, LV and HV exercise sustained hippocampal pCREBSer133-CREB-proBDNF-BDNF signaling, mitochondrial coupling efficiency, excess capacity, and leak control for thirty days after severe TBI. Corroborating these benefits, the mitochondrial H2O2 production linked to complexes I and II was attenuated by exercise regardless of the volume. These adaptations attenuated spatial learning and memory deficits caused by TBI. In summary, preconditioning with LV and HV exercise builds up long-lasting CREB-BDNF and bioenergetic neural reserves that preserve memory fitness after severe TBI.

Non-coding RNAs and Exosomal Non-coding RNAs in Traumatic Brain Injury: the Small Player with Big Actions

Nowadays, there is an increasing concern regarding traumatic brain injury (TBI) worldwide since substantial morbidity is observed after it, and the long-term consequences that are not yet fully recognized. A number of cellular pathways related to the secondary injury in brain have been identified, including free radical production (owing to mitochondrial dysfunction), excitotoxicity (regulated by excitatory neurotransmitters), apoptosis, and neuroinflammatory responses (as a result of activation of the immune system and central nervous system). In this context, non-coding RNAs (ncRNAs) maintain a fundamental contribution to post-transcriptional regulation. It has been shown that mammalian brains express high levels of ncRNAs that are involved in several brain physiological processes. Furthermore, altered levels of ncRNA expression have been found in those with traumatic as well non-traumatic brain injuries. The current review highlights the primary molecular mechanisms participated in TBI that describes the latest and novel results about changes and role of ncRNAs in TBI in both clinical and experimental research.

Serum microRNAs associated with concussion in football players

Mild Traumatic Brain Injury (mild TBI)/concussion is a common sports injury, especially common in football players. Repeated concussions are thought to lead to long-term brain damage including chronic traumatic encephalopathy (CTE). With the worldwide growing interest in studying sport-related concussion the search for biomarkers for early diagnosis and progression of neuronal injury has also became priority. MicroRNAs are short, non-coding RNAs that regulate gene expression post-transcriptionally. Due to their high stability in biological fluids, microRNAs can serve as biomarkers in a variety of diseases including pathologies of the nervous system. In this exploratory study, we have evaluated changes in the expression of selected serum miRNAs in collegiate football players obtained during a full practice and game season. We found a miRNA signature that can distinguish with good specificity and sensitivity players with concussions from non-concussed players. Furthermore, we found miRNAs associated with the acute phase (let-7c-5p, miR-16-5p, miR-181c-5p, miR-146a-5p, miR-154-5p, miR-431-5p, miR-151a-5p, miR-181d-5p, miR-487b-3p, miR-377-3p, miR-17-5p, miR-22-3p, and miR-126-5p) and those whose changes persist up to 4 months after concussion (miR-17-5p and miR-22-3p).

Physical exercise and the functions of microRNAs

MicroRNAs (miRNAs) control RNA translation and are a class of small, tissue-specific, non-protein-coding RNAs that maintain cellular homeostasis through negative gene regulation. Maintenance of the physiological environment depends on the proper control of miRNA expression, as these molecules influence almost all genetic pathways, from the cell cycle checkpoint to cell proliferation and apoptosis, with a wide range of target genes. Dysregulation of the expression of miRNAs is correlated with several types of diseases, acting as regulators of cardiovascular functions, myogenesis, adipogenesis, osteogenesis, hepatic lipogenesis, and important brain functions. miRNAs can be modulated by environmental factors or external stimuli, such as physical exercise, and can eventually induce specific and adjusted changes in the transcriptional response. Physical exercise is used as a preventive and non-pharmacological treatment for many diseases. It is well established that physical exercise promotes various benefits in the human body such as muscle hypertrophy, mental health improvement, cellular apoptosis, weight loss, and inhibition of cell proliferation. This review highlights the current knowledge on the main miRNAs altered by exercise in the skeletal muscle, cardiac muscle, bone, adipose tissue, liver, brain, and body fluids. In addition, knowing the modifications induced by miRNAs and relating them to the results of prescribed physical exercise with different protocols and intensities can serve as markers of physical adaptation to training and responses to the effects of physical exercise for some types of chronic diseases. This narrative review consists of randomized exercise training experiments with humans and/or animals, combined with analyses of miRNA modulation.

Exercise mimetics: harnessing the therapeutic effects of physical activity

Exercise mimetics are a proposed class of therapeutics that specifically mimic or enhance the therapeutic effects of exercise. Increased physical activity has demonstrated positive effects in preventing and ameliorating a wide range of diseases, including brain disorders such as Alzheimer disease and dementia, cancer, diabetes and cardiovascular disease. This article discusses the molecular mechanisms and signalling pathways associated with the beneficial effects of physical activity, focusing on effects on brain function and cognitive enhancement. Emerging therapeutic targets and strategies for the development of exercise mimetics, particularly in the field of central nervous system disorders, as well as the associated opportunities and challenges, are discussed.

The Effect of Eight Weeks of Endurance Training with Saffron on miR133bFC, miR29aFC in the Hippocampus Tissue and Depression in Rats with Alzheimer’s Disease

Background: Recent studies indicate that deregulation of microRNAs (miRNAs) expression is associated with neurological and cognitive disorders, but physical activity and medicinal plants have favorable effects on physiological and psychological factors in these patients. Objectives: Therefore, we aimed to investigate the effect of endurance training (ET) with saffron (S) on miR133bFC, miR29aFC in the hippocampus tissue and depression of rats with Alzheimer’s disease (AD). Methods: Forty AD rats with the mean age of eight weeks and mean weight of 250 ± 30.65 g were randomly divided into five groups of eight rats including: (1) control (C), (2) ET, (3) ET + S, (4) S, and (5) sham (normal saline) (Sh). During eight weeks, groups 2 and 3 ran on a treadmill for three sessions per week, each session lasting for 15 - 30 minutes, at a speed of 20 - 15 m/min, and groups 3 and 4 received 25 mg/kg daily aqueous extract of S peritoneally. Depression was evaluated by the forced swim test. Results: The levels of miR29aFC were higher in the ET + S group than in the C (P = 0.002), Sh (P = 0.003), ET (P = 0.003), and S (P = 0.001) groups. The levels of miR133bFC in the S (P = 0.02) and ET (P = 0.005) groups were lower than the C group. The mobility time in the ET (P = 0.001), S (P = 0.001), and ET + S (P = 0.001) groups was higher than the C group; in the ET + S group, the mobility time was higher than in the ET (P = 0.001) and S (P = 0.001) groups, and in the S group the mobility time was higher than in the ET group (P = 0.001). Conclusions: It seems that ET and S administration alone do not have favorable effects on miR29aFC and miR133bFC expression levels, but both can decrease depression; however, the simultaneous administration S and ET has interactive effects on improving miR29aFC expression and reducing depression.

miRNAs as Potential Biomarkers for Traumatic Brain Injury: Pathway From Diagnosis to Neurorehabilitation

BACKGROUND

Biomarkers that can advance precision neurorehabilitation of the traumatic brain injury (TBI) are needed. MicroRNAs (miRNAs) have biological properties that could make them well suited for playing key roles in differential diagnoses and prognoses and informing likelihood of responsiveness to specific treatments.

OBJECTIVE

To review the evidence of miRNA alterations after TBI and evaluate the state of science relative to potential neurorehabilitation applications of TBI-specific miRNAs.

METHODS

This scoping review includes 57 animal and human studies evaluating miRNAs after TBI. PubMed, Scopus, and Google Scholar search engines were used.

RESULTS

Gold standard analytic steps for miRNA biomarker assessment are presented. Published studies evaluating the evidence for miRNAs as potential biomarkers for TBI diagnosis, severity, natural recovery, and treatment-induced outcomes were reviewed including statistical evaluation. Growing evidence for specific miRNAs, including miR21, as TBI biomarkers is presented.

CONCLUSIONS

There is evidence of differential miRNA expression in TBI in both human and animal models; however, gaps need to be filled in terms of replication using rigorous, standardized methods to isolate a consistent set of miRNA changes. Longitudinal studies in TBI are needed to understand how miRNAs could be implemented as biomarkers in clinical practice.

Brain Perfusion Mediates the Relationship Between miRNA Levels and Postural Control

Transcriptomics, regional cerebral blood flow (rCBF), and a virtual reality-based spatial motor task were integrated using mediation analysis in a novel demonstration of “imaging omics.” Data collected in National Collegiate Athletic Association (NCAA) Division I football athletes cleared for play before in-season training showed significant relationships in 1) elevated levels of miR-30d and miR-92a to elevated putamen rCBF, 2) elevated putamen rCBF to compromised Balance scores, and 3) compromised Balance scores to elevated microRNA (miRNA) levels. rCBF acted as a consistent mediator variable (Sobel’s test P < 0.05) between abnormal miRNA levels and compromised Balance scores. Given the involvement of these miRNAs in inflammation and immune function and that vascular perfusion is a component of the inflammatory response, these findings support a chronic inflammatory model in these athletes with 11 years of average football exposure. rCBF, a systems biology measure, was necessary for miRNA to affect behavior.

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

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

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.

Chronic Regulation of miR-124-3p in the Perilesional Cortex after Experimental and Human TBI

Traumatic brain injury (TBI) dysregulates microRNAs, which are the master regulators of gene expression. Here we investigated the changes in a brain-enriched miR-124-3p, which is known to associate with major post-injury pathologies, such as neuroinflammation. RT-qPCR of the rat tissue sampled at 7 d and 3 months in the perilesional cortex adjacent to the necrotic lesion core (aPeCx) revealed downregulation of miR-124-3p at 7 d (fold-change (FC) 0.13, p < 0.05 compared with control) and 3 months (FC 0.40, p < 0.05) post-TBI. In situ hybridization confirmed the downregulation of miR-124-3p at 7 d and 3 months post-TBI in the aPeCx (both p < 0.01). RT-qPCR confirmed the upregulation of the miR-124-3p target Stat3 in the aPeCx at 7 d post-TBI (7-fold, p < 0.05). mRNA-Seq revealed 312 downregulated and 311 upregulated miR-124 targets (p < 0.05). To investigate whether experimental findings translated to humans, we performed in situ hybridization of miR-124-3p in temporal lobe autopsy samples of TBI patients. Our data revealed downregulation of miR-124-3p in individual neurons of cortical layer III. These findings indicate a persistent downregulation of miR-124-3p in the perilesional cortex that might contribute to post-injury neurodegeneration and inflammation.

Overexpression Of miR138 Ameliorates Spared Sciatic Nerve Injury-Induced Neuropathic Pain Through The Anti-Inflammatory Response In Mice

Background

The emerging role of inflammation in the initiation and maintenance of neuropathic pain has been confirmed. Previous studies have reported that miR138 has neuroprotective and anti-inflammatory effects in animal models of spinal cord injury and in human coronary artery endothelial cell injury, while its effect on neuropathic pain is still not known. As the mechanism of neuropathic pain remains unclear, we investigated whether miR138 is involved in the development of neuropathic pain and the role of miR138 in the modulation of inflammation in the spinal cord in a mouse model of neuropathic pain induced by spared sciatic nerve injury (SNI).

Materials and methods

Firstly, the expression of miR138 in spinal cord was evaluated on days 1, 3, 5, 7, 9 and 14 after SNI. And then, LV-miR-control and LV-miR138 were intrathecally injected 1 week before the surgery followed by investigation of the expression of miR138, mechanical allodynia and thermal hyperalgesia on day 1, 3, 5, 7, 9, 14 after SNI. Ipsilateral L4-L6 spinal cord tissue was harvested on day 14 post-SNI and detected by Western blotting, enzyme-linked immunosorbent assay or immunohischemistry.

Results

We observed decreased expression of miR138 and increased expression of proinflammatory cytokines, along with activated microglia, astrocytes and nuclear factor-κВ (NF-κВ), in the spinal cord dorsal horn after SNI. Moreover, the intrathecal upregulation of miR138 significantly alleviated SNI-induced mechanical allodynia and thermal hyperalgesia, downregulated the production of proinflammatory cytokines, and deactivated microglia, astrocytes and NF-κВ.

Conclusion

The results indicate that miR138 contributes to the development of neuropathic pain and that the overexpression of miR138 alleviates pain hypersensitivity by inhibiting proinflammatory cytokine production and glial activation, which suggests a novel target for reducing neuropathic pain.

A Review of MicroRNA Biomarkers in Traumatic Brain Injury

There is growing public concern surrounding traumatic brain injury (TBI). TBI can cause significant morbidity, and the long-term sequelae are poorly understood. TBI diagnosis and management rely on patient-reported symptoms and subjective clinical assessment. There are no biologic tools to detect mild TBI or to track brain recovery. Emerging evidence suggests that microRNAs (miRNAs) may provide information about the injured brain. These tiny epigenetic molecules are expressed throughout the body. However, they are particularly important in neurons, can cross the blood-brain barrier, and are securely transported from cell to cell, where they regulate gene expression. miRNA levels may identify patients with TBI and predict symptom duration. This review synthesizes miRNA findings from 14 human studies. We distill more than 291 miRNAs to 17 biomarker candidates that overlap across multiple studies and multiple biofluids. The goal of this review is to establish a collective understanding of miRNA biology in TBI and identify clinical priorities for future investigations of this promising biomarker.

The critical role of microRNAs in stress response: Therapeutic prospect and limitation

Stress response refers to the systemic nonspecific response upon exposure to strong stimulation or chronic stress, such as severe trauma, shock, infection, burn, major surgery or improper environment, which disturb organisms and damage their physical and psychological health. However, the pathogenesis of stress induced disorder remains complicated and diverse under different stress exposure. Recently, studies have revealed a specific role of microRNAs (miRNAs) in regulating cellular function under different types of stress, suggesting a significant role in the treatment and prevention of stress-related diseases, such as stress ulcer, posttraumatic stress disorder, stress-induced cardiomyopathy and so on. This paper have reviewed the literature on microRNA related stress diseases in different databases including PubMed, Web of Science, and the MiRbase. It considers only peer-reviewed papers published in English between 2004 and 2018. This review summarizes new advances in principles and mechanisms of miRNAs regulating stress signalling pathway and the role of miRNAs in human stress diseases. This comprehensive review is to provide an integrated account of how different stresses affect miRNAs and how stress-miRNA pathways may, in turn, be linked with disease, which offers some potential strategies for stress disorder treatment. Furthermore, the limitation of current studies and challenges for clinical use are discussed.

miR-124-3p is a chronic regulator of gene expression after brain injury

Traumatic brain injury (TBI) initiates molecular and cellular pathologies that underlie post-injury morbidities, including hippocampus-related memory decline and epileptogenesis. Non-coding small RNAs are master regulators of gene expression with the potential to affect multiple molecular pathways. To evaluate whether hippocampal gene expression networks are chronically regulated by microRNAs after TBI, we sampled the dentate gyrus of rats with severe TBI induced by lateral fluid-percussion injury 3 months earlier. Ingenuity pathway analysis revealed 30 upregulated miR-124-3p targets, suggesting that miR-124-3p is downregulated post-TBI (z-score = - 5.146, p < 0.05). Droplet digital polymerase chain reaction (ddPCR) and in situ hybridization confirmed the chronic downregulation of miR-124-3p (p < 0.05). Quantitative PCR analysis of two targets, Plp2 and Stat3, indicated that their upregulation correlated with the miR-124-3p downregulation (r = - 0.647, p < 0.05; r = - 0.629, p < 0.05, respectively). Immunohistochemical staining of STAT3 confirmed the increased protein expression. STRING analysis showed that 9 of the 30 miR-124-3p targets belonged to a STAT3 network. Reactome analysis and data mining connected the targets especially to inflammation and signal transduction. L1000CDS2 software revealed drugs (e.g., importazole, trichostatin A, and IKK-16) that could reverse the observed molecular changes. The translational value of our data was emphasized by in situ hybridization showing chronic post-traumatic downregulation of miR-124-3p in the dentate gyrus of TBI patients. Analysis of another brain injury model, status epilepticus, highlighted the fact that chronic downregulation of miR-124 is a common phenomenon after brain injury. Together, our findings indicate that miR-124-3p is a chronic modulator of molecular networks relevant to post-injury hippocampal pathologies in experimental models and in humans.

MicroRNA-21 in the Pathogenesis of Traumatic Brain Injury

MicroRNAs (miRNAs), an abundant class of small noncoding RNA molecules, which regulate gene expression by functioning as post-transcriptional regulatory factors, have been identified as key components of traumatic brain injury (TBI) progression. MicroRNA-21 (miR-21) is a recently identified typical miRNA that is involved in the signaling pathways of inflammation, neuronal apoptosis, reactive gliosis, disruption of blood brain barrier, angiogenesis and recovery process induced by physical exercises in TBI. Hence, miR-21 is now considered as a potential therapeutic target of TBI. We review the correlative literature and research progress regarding the roles of miR-21 in TBI in this article.

MicroRNA Signature of Traumatic Brain Injury: From the Biomarker Discovery to the Point-of-Care

Traumatic brain injury (TBI) is a serious problem that causes high morbidity and mortality around the world. Currently, no reliable biomarkers are used to assess the severity and predict the recovery. Many protein biomarkers were extensively studied for diagnosis and prognosis of different TBI severities such as S-100β, glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), neurofilament light chain (NFL), cleaved tau protein (C-tau), and ubiquitin C-terminal hydrolase-L1 (UCH-L1). However, none of these candidates is currently used in the clinical practice, due to relatively low sensitivity, for the diagnosis of mild TBI (mTBI) or mild to moderate TBI (MMTBI) patients who are clinically well and do not have a detectable intracranial pathology on the scans. MicroRNAs (miRNAs or miRs) are a class of small endogenous molecular regulators, which showed to be altered in different pathologies, including TBI and for this reason, their potential role in diagnosis, prognosis and therapeutic applications, is explored. Promising miRNAs such as miR-21, miR-16 or let-7i were identified as suitable candidate biomarkers for TBI and can differentiate mild from severe TBI. Also, they might represent new potential therapeutic targets. Identification of miRNA signature in tissue or biofluids, for several pathological conditions, is now possible thanks to the introduction of new high-throughput technologies such as microarray platform, Nanostring technologies or Next Generation Sequencing. This review has the aim to describe the role of microRNA in TBI and to explore the most commonly used techniques to identify microRNA profile. Understanding the strengths and limitations of the different methods can aid in the practical use of miRNA profiling for diverse clinical applications, including the development of a point-of-care device.

Exercise and epigenetic inheritance of disease risk

Epigenetics is the study of gene expression changes that occur in the absence of altered genotype. Current evidence indicates a role for environmentally induced alterations to epigenetic modifications leading to health and disease changes across multiple generations. This phenomenon is called intergenerational or transgenerational epigenetic inheritance of health or disease. Environmental insults, in the form of toxins, plastics and particular dietary interventions, perturb the epigenetic landscape and influence the health of F1 through to F4 generations in rodents. There is, however, the possibility that healthy lifestyles and environmental factors, such as exercise training, could lead to favourable, heritable epigenetic modifications that augment transcriptional programmes protective of disease, including metabolic dysfunction, heart disease and cancer. The health benefits conferred by regular physical exercise training are unquestionable, yet many of the molecular changes may have heritable health implications for future generations. Similar to other environmental factors, exercise modulates the epigenome of somatic cells and researchers are beginning to study exercise epigenetics in germ cells. The germ cell epigenetic modifications affected by exercise offer a molecular mechanism for the inheritance of health and disease risk. The aims of this review are to: (i) provide an update on the expanding field of exercise epigenetics; (ii) offer an overview of data on intergenerational/transgenerational epigenetic inheritance of disease by environmental insults; (iii) to discuss the potential of exercise-induced intergenerational inheritance of health and disease risk; and finally, outline potential mechanisms and avenues for future work on epigenetic inheritance through exercise.

Non-coding RNAs and neuroprotection after acute CNS injuries

Accumulating evidence indicates that various classes of non-coding RNAs (ncRNAs) including microRNAs (miRNAs), PIWI-interacting RNAs (piRNAs) and long non-coding RNAs (lncRNAs) play important roles in normal state as well as the diseases of the CNS. Interestingly, ncRNAs have been shown to interact with messenger RNA, DNA and proteins, and these interactions could induce epigenetic modifications and control transcription and translation, thereby adding a new layer of genomic regulation. The ncRNA expression profiles are known to be altered after acute CNS injuries including stroke, traumatic brain injury and spinal cord injury that are major contributors of morbidity and mortality worldwide. Hence, a better understanding of the functional significance of ncRNAs following CNS injuries could help in developing potential therapeutic strategies to minimize the neuronal damage in those conditions. The potential of ncRNAs in blood and CSF as biomarkers for diagnosis and/or prognosis of acute CNS injuries has also gained importance in the recent years. This review highlighted the current progress in the understanding of the role of ncRNAs in initiation and progression of secondary neuronal damage and their application as biomarkers after acute CNS injuries.

MicroRNAs as diagnostic markers and therapeutic targets for traumatic brain injury

Traumatic brain injury (TBI) is characterized by primary damage to the brain from the external mechanical force and by subsequent secondary injury due to various molecular and pathophysiological responses that eventually lead to neuronal cell death. Secondary brain injury events may occur minutes, hours, or even days after the trauma, and provide valuable therapeutic targets to prevent further neuronal degeneration. At the present time, there is no effective treatment for TBI due, in part, to the widespread impact of numerous complex secondary biochemical and pathophysiological events occurring at different time points following the initial injury. MicroRNAs control a range of physiological and pathological functions such as development, differentiation, apoptosis and metabolism, and may serve as potential targets for progress assessment and intervention against TBI to mitigate secondary damage to the brain. This has implications regarding improving the diagnostic accuracy of brain impairment and long-term outcomes as well as potential novel treatments. Recent human studies have identified specific microRNAs in serum/plasma (miR-425-p, -21, -93, -191 and -499) and cerebro-spinal fluid (CSF) (miR-328, -362-3p, -451, -486a) as possible indicators of the diagnosis, severity, and prognosis of TBI. Experimental animal studies have examined specific microRNAs as biomarkers and therapeutic targets for moderate and mild TBI (e.g., miR-21, miR-23b). MicroRNA profiling was altered by voluntary exercise. Differences in basal microRNA expression in the brain of adult and aged animals and alterations in response to TBI (e.g., miR-21) have also been reported. Further large-scale studies with TBI patients are needed to provide more information on the changes in microRNA profiles in different age groups (children, adults, and elderly).

Differential expression of microRNAs in the brains of mice subjected to increasing grade of mild traumatic brain injury

OBJECTIVE

To investigate the effect of heterogeneity in mTBI on miRNA expression in mouse brain and to identify molecular pathways targeted by the modulated miRNAs.

METHODS

A weight drop device was used to induce four increasing grades of mTBI. MiRNA expression was evaluated using TaqMan rodent miRNA arrays. Bioinformatics analysis was done using the DIANA miRPath tool and Ingenuity Pathway Analysis software. Histology of brain sections was evaluated using H&E staining.

RESULTS

No histologic lesions were observed in the brains of injured mice; however, significant modulation in miRNA expression profile was observed. Global miRNA profiling indicated a trend of decrease in the number of modulated miRNAs from 24 hours to day 7 post-injury, except for the most severe grade of mTBI. Canonical pathways like calcium signalling, synaptic pathways and axon guidance pathway were the major targets of the modulated miRNAs. Network correlation analyses indicated an interaction between the modulated miRNAs and putative protein biomarkers of TBI.

CONCLUSIONS

The data demonstrated that varying intensities of mTBI induced a differential miRNA expression profile in the brain post-injury. Pathways such as calcium and synaptic signalling were major targets of modulated miRNAs and may play a role in the pathophysiology of mTBI.

Non-coding RNAs as Emerging Regulators of Neural Injury Responses and Regeneration

Non-coding RNAs (ncRNAs) are a large cluster of RNAs that do not encode proteins, but have multiple functions in diverse cellular processes. Mounting evidence indicates the involvement of ncRNAs in the physiology and pathophysiology of the central and peripheral nervous systems. It has been shown that numerous ncRNAs, especially microRNAs and long non-coding RNAs, are differentially expressed after insults such as acquired brain injury, spinal cord injury, and peripheral nerve injury. These ncRNAs affect neuronal survival, neurite regrowth, and glial phenotype primarily by targeting specific mRNAs, resulting in translation repression or degradation of the mRNAs. An increasing number of studies have investigated the regulatory roles of microRNAs and long non-coding RNAs in neural injury and regeneration, and thus a new research field is emerging. In this review, we highlight current progress in the field in an attempt to provide further insight into post-transcriptional changes occurring after neural injury, and to facilitate the potential use of ncRNAs for improving neural regeneration. We also suggest potential directions for future studies.