MicroRNA Expression in the Blood and Brain of Rats Subjected to Transient Focal Ischemia by Middle Cerebral Artery Occlusion

MicroRNAs as potential circulating biomarkers for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a condition primarily characterized by the selective loss of upper and lower motor neurons. Motor neuron loss gives rise to muscle tissue malfunctions, including weakness, spasticity, atrophy, and ultimately paralysis, with death typically due to respiratory failure within 2 to 5 years of symptoms' onset. The mean delay in time from presentation to diagnosis remains at over 1 year. Biomarkers are urgently needed to facilitate ALS diagnosis and prognosis as well as to act as indicators of therapeutic response in clinical trials. MicroRNAs (miRNAs) are small molecules that can influence posttranscriptional gene expression of a variety of transcript targets. Interestingly, miRNAs can be released into the circulation by pathologically affected tissues. This review presents therapeutic and diagnostic challenges associated with ALS, highlights the potential role of miRNAs in ALS, and discusses the diagnostic potential of these molecules in identifying ALS-specific miRNAs or in distinguishing between the various genotypic and phenotypic forms of ALS.

Exosomes/miRNAs as mediating cell-based therapy of stroke

Cell-based therapy, e.g., multipotent mesenchymal stromal cell (MSC) treatment, shows promise for the treatment of various diseases. The strong paracrine capacity of these cells and not their differentiation capacity, is the principal mechanism of therapeutic action. MSCs robustly release exosomes, membrane vesicles (~30–100 nm) originally derived in endosomes as intraluminal vesicles, which contain various molecular constituents including proteins and RNAs from maternal cells. Contained among these constituents, are small non-coding RNA molecules, microRNAs (miRNAs), which play a key role in mediating biological function due to their prominent role in gene regulation. The release as well as the content of the MSC generated exosomes are modified by environmental conditions. Via exosomes, MSCs transfer their therapeutic factors, especially miRNAs, to recipient cells, and therein alter gene expression and thereby promote therapeutic response. The present review focuses on the paracrine mechanism of MSC exosomes, and the regulation and transfer of exosome content, especially the packaging and transfer of miRNAs which enhance tissue repair and functional recovery. Perspectives on the developing role of MSC mediated transfer of exosomes as a therapeutic approach will also be discussed.

The blood-brain barrier-gatekeeper to neuronal homeostasis: clinical implications in the setting of stroke

The blood-brain barrier is part of the neurovascular unit and serves as a functional and anatomical barrier between the blood and the extracellular space. It controls the flow of solutes in and out of the brain thereby providing an optimal environment for neuronal functioning. Paracellular transport between endothelial cells is restricted by tight junctions and transendothelial transport is reduced and more selective compared to capillaries of other organs. Further, the blood-brain barrier is involved in controlling blood flow and it is the site for signaling damage of the nervous system to the peripheral immune system. As an important player in brain homeostasis, blood-brain barrier dysfunction has been implicated in the pathophysiology of many brain diseases including stroke, traumatic brain injury, brain tumors, epilepsy and neurodegenerative disorders. In this article - highlighting recent advances in basic science - we review the features of the blood-brain barrier and their significance for neuronal homeostasis to discuss clinical implications for neurological complications following cerebral ischemia.

Up-regulation of brain-enriched miR-107 promotes excitatory neurotoxicity through down-regulation of glutamate transporter-1 expression following ischaemic stroke

Recent studies have uncovered that accumulation of glutamate after ischaemic stroke is closely associated with the down-regulation of glutamate transporter-1 (GLT-1) expression, suggesting that GLT-1 expression critically controls glutamate accumulation and the abnormal glutamate transport-elicited neuronal cell excitotoxicity in patients with ischaemic stroke. However, it remains unknown how GLT-1 expression is regulated under ischaemic stroke conditions. In the present study, we screened the expression of nine brain-specific or brain-enriched miRNAs in a focal cerebral ischaemia/reperfusion (I/R) injury rat model, which showed glutamate accumulation and down-regulated GLT-1 expression as expected, and revealed that the miR-107 level was elevated in both brain tissue and plasma in the model. Next, we examined the functional relationship of miR-107 with GLT-1 expression in a nerve cell hypoxia/reoxygenation (H/R) injury model. H/R treatment increased apoptosis of the nerve cells concomitant with glutamate accumulation, miR-107 elevation and suppressed GLT-1 expression, mimicking our in vivo findings in the cerebral I/R injury rat model in vitro. Co-treating the cells with an miR-107 inhibitor blocked all of the effects, demonstrating that miR-107 functions to inhibit GLT-1 expression and elevate glutamate accumulation. To extend these animal and cell-based studies to clinical patients, we measured the plasma levels of miR-107 and glutamate, and observed that both miR-107 and glutamate were elevated in patients with ischaemic stroke. On the basis of these observations, we conclude that elevated miR-107 expression after ischaemic stroke accounts, at least partially, for glutamate accumulation through suppression of GLT-1 expression. Our findings also highlight that the plasma level of miR-107 may serve as a novel biomarker for monitoring excitotoxicity in patients with ischaemic stroke.

miR-206 modulates lipopolysaccharide-mediated inflammatory cytokine production in human astrocytes

Astrocyte-derived inflammation is a common component of acute or chronic injury in the central nervous system. MicroRNAs (miRNAs) are small non-coding RNAs that play important regulatory roles in the inflammatory response. In this study, we found that miR-206 is induced upon stimulation with lipopolysaccharide. Overexpression of miR-206 in astrocytes led to increased expression of inflammatory cytokines (interleukin-6, interleukin-1β, CCL5) upon exposure to lipopolysaccharide, whereas knockdown of miR-206 had completely opposite effects. We used a combination of bioinformatics and experimental techniques to demonstrate that NR4A2, which belongs to the nuclear receptor (NR) 4 family of orphan nuclear receptors, is a direct target of miR-206. Overexpression of miR-206 mimics decreased the activity of a luciferase reporter containing the NR4A2 3'-untranslated region and led to decreased NR4A2 mRNA and protein levels. In contrast, ectopic expression of an miR-206 inhibitor led to elevated NR4A2 expression. We also found that miR-206 modulated the lipopolysaccharide-induced proinflammatory response by targeting NR4A2 and activating nuclear factor-kappa B activity. Finally, we demonstrated that the transcription factor AP-1 plays a critical role in lipopolysaccharide-induced expression of miR-206 and that the extracellular signal-regulated kinase signaling pathway contributes to the regulation of miR-206 level in astrocytes. These data demonstrate that miR-206 positively regulates the lipopolysaccharide-induced inflammatory response in human astrocytes.

Repetitive transcranial magnetic stimulation promotes neural stem cell proliferation via the regulation of MiR-25 in a rat model of focal cerebral ischemia

Repetitive transcranial magnetic stimulation (rTMS) has increasingly been studied over the past decade to determine whether it has a therapeutic benefit on focal cerebral ischemia. However, the underlying mechanism of rTMS in this process remains unclear. In the current study, we investigated the effects of rTMS on the proliferation of adult neural stem cells (NSCs) and explored microRNAs (miRNAs) that were affected by rTMS. Our data showed that 10 Hz rTMS significantly increased the proliferation of adult NSCs after focal cerebral ischemia in the subventricular zone (SVZ), and the expression of miR-25 was obviously up-regulated in the ischemic cortex after rTMS. p57, an identified miR-25 target gene that regulates factors linked to NSC proliferation, was also evaluated, and it exhibited down-regulation. To further verify the role of miR-25, rats were injected with a single dose of antagomir-25 and were subjected to focal cerebral ischemia followed by rTMS treatment. The results confirmed that miR-25 could be repressed specifically and could drive the up-regulation of its target gene (p57), which resulted in the inhibition of adult NSC proliferation in the SVZ after rTMS. Thus, our studies strongly indicated that 10 Hz rTMS can promote the proliferation of adult NSCs in the SVZ after focal cerebral ischemia by regulating the miR-25/p57 pathway.

Circulating microRNAs as novel potential biomarkers for early diagnosis of acute stroke in humans

BACKGROUND

Many diseases include microRNAs (miRNAs) as reported biomarkers. The significance of circulating miRNAs for early diagnosis of acute stroke in humans is unknown. We aim to determine whether circulating miRNAs potentially serve as novel biomarkers for acute stroke.

METHODS

We prospectively recruited patients with acute stroke and those with nonstroke disease. Patients with acute stroke were identified using magnetic resonance imaging (MRI) for early diagnosis. If the patient suffered from acute stroke that was detected with diffusion-weighted imaging, the patient was defined as an MRI(+) patient. Otherwise, it was defined as an MRI(-) patient. Circulating miRNAs were measured by miRNA microarray and real-time polymerase chain reaction (PCR) analysis.

RESULTS

A total of 136 patients were included in the study. Testing by miRNA microarray and real-time PCR analyses showed that hsa-miR-106b-5P and hsa-miR-4306 were present with markedly high abundance in patients of acute stroke, whereas hsa-miR-320e and hsa-miR-320d were present with quite low abundance in patients compared with healthy individuals. Compared with healthy individuals, the miRNAs were increased as in patients with acute stroke as follows: hsa-miR-106b-5P, 3.63-fold in MRI(-) patients and 23.90-fold in MRI(+) patients; hsa-miR-4306, 3.19-fold in MRI(-) patients and 5.30-fold in MRI(+) patients; hsa-miR-320e, .33-fold in MRI(-) patients and .13-fold in MRI(+) patients; and hsa-miR-320d, .23-fold in MRI(-) patients and .07-fold in MRI(+) patients.

CONCLUSIONS

Elevated hsa-miR-106b-5P and hsa-miR-4306 and decreased hsa-miR-320e and hsa-miR-320d in plasma may be novel biomarkers for the early detection of acute stroke in humans.

MicroRNAs participate in the murine oligodendroglial response to perinatal hypoxia-ischemia

BACKGROUND

Hypoxic-ischemic injury (HI) to preterm brain results in white matter loss. The endogenous oligodendroglial response to perinatal HI is characterized by increased oligodendroglial progenitor cells (OPCs). MicroRNAs (miRs) are important post-transcriptional regulators of gene expression, and a few miRs have been shown to regulate differentiation of OPCs into mature oligodendroglia. We tested the hypothesis that miRs play a role in the increase in OPCs in response to perinatal HI.

METHODS

We inducibly deleted the miR-processing enzyme Dicer in OPCs using a tamoxifen-inducible NG2CreER(T2) transgene in Dicer(fl/fl) mice. After HI, mice were analyzed for OPC differentiation using immunofluorescence and for white matter formation by Luxol fast blue (LFB) staining. Functional recovery from injury was investigated using digital gait analysis. We also tested whether HI changed miRs known to regulate OPC differentiation using quantitative RT-PCR.

RESULTS

Perinatal HI induced significant increases in miR-138 and miR-338, two miRs known to regulate OPC differentiation. Knockdown of Dicer increased myelin basic protein and LFB staining within the corpus callosum after HI. In addition, there was significant improvement in motor function 14 and 24 d post lesion.

CONCLUSION

Changes in specific mature miRs expressed in OPCs following HI may contribute to white matter injury.

Biomarker development for C9orf72 repeat expansion in ALS

The expanded GGGGCC hexanucleotide repeat in the non-coding region of the C9orf72 gene on chromosome 9p21 has been discovered as the cause of approximately 20-50% of familial and up to 5-20% of sporadic amyotrophic lateral sclerosis (ALS) cases, making this the most common known genetic mutation of ALS to date. At the same time, it represents the most common genetic mutation in frontotemporal dementia (FTD; 10-30%). Because of the high prevalence of mutant C9orf72, pre-clinical efforts in identifying therapeutic targets and developing novel therapeutics for this mutation are highly pursued in the hope of providing a desperately needed disease-modifying treatment for ALS patients, as well as other patient populations affected by the C9orf72 mutation. The current lack of effective treatments for ALS is partially due to the lack of appropriate biomarkers that aide in assessing drug efficacy during clinical trials independent of clinical outcome measures, such as increased survival. In this review we will summarize the opportunities for biomarker development specifically targeted to the newly discovered C9orf72 repeat expansion. While drugs are being developed for this mutation, it will be crucial to provide a reliable biomarker to accompany the clinical development of these novel therapeutic interventions to maximize the chances of a successful clinical trial. This article is part of a Special Issue entitled ALS complex pathogenesis.

Hypoxia-induced miR-210 modulates tissue response to acute peripheral ischemia

AIMS

Peripheral artery disease is caused by the restriction or occlusion of arteries supplying the leg. Better understanding of the molecular mechanisms underpinning tissue response to ischemia is urgently needed to improve therapeutic options. The aim of this study is to investigate hypoxia-induced miR-210 regulation and its role in a mouse model of hindlimb ischemia.

RESULTS

miR-210 expression was induced by femoral artery dissection. To study the role of miR-210, its function was inhibited by the systemic administration of a miR-210 complementary locked nucleic acid (LNA)-oligonucleotide (anti-miR-210). In the ischemic skeletal muscle, anti-miR-210 caused a marked decrease of miR-210 compared with LNA-scramble control, while miR-210 target expression increased accordingly. Histological evaluation of acute tissue damage showed that miR-210 inhibition increased both apoptosis at 1 day and necrosis at 3 days. Capillary density decrease caused by ischemia was significantly more pronounced in anti-miR-210-treated mice; residual limb perfusion decreased accordingly. To investigate the molecular mechanisms underpinning the increased damage triggered by miR-210 blockade, we tested the impact of anti-miR-210 treatment on the transcriptome. Gene expression analysis highlighted the deregulation of mitochondrial function and redox balance. Accordingly, oxidative damage was more severe in the ischemic limb of anti-miR-210-treated mice and miR-210 inhibition increased oxidative metabolism. Further, oxidative-stress resistant p66(Shc)-null mice displayed decreased tissue damage following ischemia.

INNOVATION

This study identifies miR-210 as a crucial element in the adaptive mechanisms to acute peripheral ischemia.

CONCLUSIONS

The physiopathological significance of miR-210 is context dependent. In the ischemic skeletal muscle it seems to be cytoprotective, regulating oxidative metabolism and oxidative stress.

miR-137, a new target for post-stroke depression?

Expression of miR-137 is downregulated in brain tissue from patients with depression and suicidal behavior, and is also downregulated in peripheral blood from stroke patients. However, it is not yet known if miR-137 acts as a bridge between stroke and depression. To test this, we used middle cerebral artery occlusion and chronic mild stress to establish a post-stroke depression model in rats. Compared with controls, we found significantly lower miR-137 levels in the brain and peripheral blood from post-stroke depression rats. Injection of a miR-137 antagonist into the brain ventricles upregulated miR-137 levels, and improved behavioral changes in post-stroke depression rats. Luciferase assays showed miR-137 bound to the 3’UTR of Grin2A, regulating Grin2A expression in a neuronal cell line. Grin2A gene overexpression in the brain of post-stroke depression rats, noticeably suppressed the inhibitory effect of miR-137 on post-stroke depression. Overall, our results show that miR-137 suppresses Grin2A protein expression through binding to Grin2A mRNA, thereby exerting an inhibitory effect on post-stroke depression. Our results offer a new therapeutic direction for post-stroke depression.

microRNAs in spinal cord injury: potential roles and therapeutic implications

microRNAs (miRNAs) are a novel class of small non-coding RNAs that negatively regulate gene expression at the post-transcriptional level. miRNAs can modulate gene expression and thus play important roles in diverse neurobiological processes, such as cell differentiation, growth, proliferation and neural activity, as well as the pathogenic processes of spinal cord injury (SCI) like inflammation, oxidation, demyelination and apoptosis. Results from animal studies have revealed the temporal alterations in the expression of a large set of miRNAs following SCI in adult rats, and the expressional changes in miRNAs following SCI is bidirectional (increase or decrease). In addition, several miRNAs have distinct roles in prognosis of SCI (protective, detrimental and varied). Taken together, the existing evidence suggests that abnormal miRNA expression following SCI contributes to the pathogenesis of SCI, and miRNAs may become potential targets for the therapy of SCI.

The myriad essential roles of microRNAs in cardiovascular homeostasis and disease

According to the World Health Organization, cardiovascular disease accounts for approximately 30% of all deaths in the United States, and is the worldwide leading cause of morbidity and mortality. Over the last several years, microRNAs have emerged as critical regulators of physiological homeostasis in multiple organ systems, including the cardiovascular system. The focus of this review is to provide an overview of the current state of knowledge of the molecular mechanisms contributing to the multiple causes of cardiovascular disease with respect to regulation by microRNAs. A major challenge in understanding the roles of microRNAs in the pathophysiology of cardiovascular disease is that cardiovascular disease may arise from perturbations in intracellular signaling in multiple cell types including vascular smooth muscle and endothelial cells, cardiac myocytes and fibroblasts, as well as hepatocytes, pancreatic β-cells, and others. Additionally, perturbations in intracellular signaling cascades may also have profound effects on heterocellular communication via secreted cytokines and growth factors. There has been much progress in recent years to identify the microRNAs that are both dysregulated under pathological conditions, as well as the signaling pathway(s) regulated by an individual microRNA. The goal of this review is to summarize what is currently known about the mechanisms whereby microRNAs maintain cardiovascular homeostasis and to attempt to identify some key unresolved questions that require further study.

miRNA expression profiles in cerebrospinal fluid and blood of patients with acute ischemic stroke

The aims of the study were (1) to determine whether miRNAs (microRNAs) can be detected in the cerebrospinal fluid (CSF) and blood of patients with ischemic stroke and (2) to compare these miRNA profiles with corresponding profiles from other neurological patients to address whether the miRNA profiles of CSF or blood have potential usefulness as diagnostic biomarkers of ischemic stroke. CSF from patients with acute ischemic stroke (n = 10) and patients with other neurological diseases (n = 10) was collected by lumbar puncture. Blood samples were taken immediately after. Expression profiles in the cell-free fractions of CSF and blood were analyzed by a microarray technique (miRCURY LNA™ microRNA Array, Exiqon A/S, Denmark) using a quantitative PCR (qPCR) platform containing 378 miRNA primers. In total, 183 different miRNAs were detected in the CSF, of which two miRNAs (let-7c and miR-221-3p) were found upregulated in relation to stroke. In the blood, 287 different miRNAs were detected of which two miRNAs (miR-151a-3p and miR-140-5p) were found upregulated and one miRNA (miR-18b-5p) was found downregulated in the stroke group. Some miRNAs occurred exclusively in the CSF including miR-523-3p which was detected in 50 % of the stroke patients, whereas it was completely absent in controls. Our preliminary results demonstrate that it is possible to detect and profile miRNAs in CSF and blood from patients with neurological diseases. Some miRNAs appear differentially expressed in the CSF and others in the blood of stroke patients. Currently, we are validating our results in larger groups of patients.

miRNA functional synergistic network analysis of mice with ischemic stroke

This study aimed to identify potential miRNAs highly associated with the response to brain ischemic stroke. The miRNAs microarray expression profiles data were downloaded from Gene Expression Omnibus database under accession number GSE51586, including three ischemia and three ipsilateral normal samples from mouse brain tissues. Limma package was used to identify differentially expressed miRNAs between ischemia and ipsilateral normal samples. The common target genes of miRNA predicted from TargetScan, PicTar, miRanda and DIANA-microT databases were used as the candidate subset in which functional modules were identified by performing gene ontology enrichment analysis using ClusterProfile. Finally, the miRNA functional synergistic network was constructed by assembling all miRNA synergistic pairs. Fifty-one differentially expressed miRNAs were identified between ischemia and ipsilateral normal samples, including 32 up- and 19 down-regulated miRNAs. Among them, 24 miRNAs can commonly regulate at least one target gene and thus were used to construct a network, which included 274 pairs of co-regulating miRNAs. Further, 242 pairs of miRNAs interaction involving 23 miRNAs were shown to be synergetic in function. Sixteen miRNAs forming 20 miRNAs interaction pairs participated in inflammatory response, such as mir-185 and mir-674-3p. The 16 miRNAs related to inflammatory response during ischemic stroke may provide underlying targets for prevention and treatment of stroke.

Decreased DGCR8 expression and miRNA dysregulation in individuals with 22q11.2 deletion syndrome

Deletion of the 1.5–3 Mb region of chromosome 22 at locus 11.2 gives rise to the chromosome 22q11.2 deletion syndrome (22q11DS), also known as DiGeorge and Velocardiofacial Syndromes. It is the most common micro-deletion disorder in humans and one of the most common multiple malformation syndromes. The syndrome is characterized by a broad phenotype, whose characterization has expanded considerably within the last decade and includes many associated findings such as craniofacial anomalies (40%), conotruncal defects of the heart (CHD; 70–80%), hypocalcemia (20–60%), and a range of neurocognitive anomalies with high risk of schizophrenia, all with a broad phenotypic variability. These phenotypic features are believed to be the result of a change in the copy number or dosage of the genes located in the deleted region. Despite this relatively clear genetic etiology, very little is known about which genes modulate phenotypic variations in humans or if they are due to combinatorial effects of reduced dosage of multiple genes acting in concert. Here, we report on decreased expression levels of genes within the deletion region of chromosome 22, including DGCR8, in peripheral leukocytes derived from individuals with 22q11DS compared to healthy controls. Furthermore, we found dysregulated miRNA expression in individuals with 22q11DS, including miR-150, miR-194 and miR-185. We postulate this to be related to DGCR8 haploinsufficiency as DGCR8 regulates miRNA biogenesis. Importantly we demonstrate that the level of some miRNAs correlates with brain measures, CHD and thyroid abnormalities, suggesting that the dysregulated miRNAs may contribute to these phenotypes and/or represent relevant blood biomarkers of the disease in individuals with 22q11DS.

Expression profiling of RNA transcripts during neuronal maturation and ischemic injury

Neuronal development is a pro-survival process that involves neurite growth, synaptogenesis, synaptic and neuronal pruning. During development, these processes can be controlled by temporal gene expression that is orchestrated by both long non-coding RNAs and microRNAs. To examine the interplay between these different components of the transcriptome during neuronal differentiation, we carried out mRNA, long non-coding RNA and microRNA expression profiling on maturing primary neurons. Subsequent gene ontology analysis revealed regulation of axonogenesis and dendritogenesis processes by these differentially expressed mRNAs and non-coding RNAs. Temporally regulated mRNAs and their associated long non-coding RNAs were significantly over-represented in proliferation and differentiation associated signalling, cell adhesion and neurotrophin signalling pathways. Verification of expression of the Axin2, Prkcb, Cntn1, Ncam1, Negr1, Nrxn1 and Sh2b3 mRNAs and their respective long non-coding RNAs in an in vitro model of ischemic-reperfusion injury showed an inverse expression profile to the maturation process, thus suggesting their role(s) in maintaining neuronal structure and function. Furthermore, we propose that expression of the cell adhesion molecules, Ncam1 and Negr1 might be tightly regulated by both long non-coding RNAs and microRNAs.

Downregulation of miRNA-134 protects neural cells against ischemic injury in N2A cells and mouse brain with ischemic stroke by targeting HSPA12B

MicroRNAs (miRNAs) have emerged as a major regulator in neurological diseases, and understanding their molecular mechanism in modulating cerebral ischemic injury may provide potential therapeutic targets for ischemic stroke. However, as one of 19 differentially expressed miRNAs in mouse brain with middle cerebral artery occlusion (MCAO), the role of miR-134 in ischemic injury is not well understood. In this study, the miR-134 expression level was manipulated both in oxygen-glucose deprivation (OGD)-treated N2A neuroblastoma cells in vitro and mouse brain with MCAO-induced ischemic stroke in vivo, and its possible targets of heat shock protein A5 (HSPA5) and HSPA12B were determined by bioinformatics analysis and dual luciferase assay. The results showed that overexpression of miR-134 exacerbated cell death and apoptosis both in vitro and in vivo. Conversely, downregulating miR-134 levels reduced cell death and apoptosis. Furthermore, non-expression of miR-134 enhanced HSPA12B protein levels in OGD-treated N2A cells as well as in the ischemic region. It could attenuate brain infarction size and neural cell damage, and improve neurological outcomes in mice with ischemic stroke, whereas upregulation of miR-134 had the opposite effect. In addition, HSPA12B was validated to be a target of miR-134 and its short interfering RNAs (siRNAs) could block miR-134 inhibitor-induced neuroprotection in OGD-treated N2A cells. In conclusion, downregulation of miR-134 could induce neuroprotection against ischemic injury in vitro and in vivo by negatively upregulating HSPA12B protein expression.

Advances in astrocyte-targeted approaches for stroke therapy: an emerging role for mitochondria and microRNAS

Astrocytes are critical regulators of neuronal function and an effective target for stroke therapy in animal models. Identifying individual targets with the potential for simultaneous activation of multiple downstream pathways that regulate astrocyte homeostasis may be a necessary element for successful clinical translation. Mitochondria and microRNAs each represent individual targets with multi-modal therapeutic potential. Mitochondria regulate metabolism and apoptosis, while microRNAs have the capacity to bind and inhibit numerous mRNAs. By combining strategies targeted at maintaining astrocyte function during and following cerebral ischemia, a synergistic therapeutic effect may be achieved.

Circulating miRNA profiles provide a biomarker for severity of stroke outcomes associated with age and sex in a rat model

Small non-coding RNA [miRNA (microRNA)] found in the circulation have been used successfully as biomarkers and mechanistic targets for chronic and acute disease. The present study investigated the impact of age and sex on miRNA expression following ischaemic stroke in an animal model. Adult (6 month) and middle-aged (11-12 months) female and male rats were subject to MCAo (middle cerebral artery occlusion) using ET-1 (endothelin-1). Circulating miRNAs were analysed in blood samples at 2 and 5 days post-stroke, and brain miRNAs were analysed at 5 days post-stroke. Although stroke-associated infarction was observed in all groups, infarct volume and sensory-motor deficits were significantly reduced in adult females compared with middle-aged females, adult males or middle-aged males. At 2 days post-stroke, 21 circulating miRNAs were differentially regulated and PCA (principal component analysis) confirmed that most of the variance was due to age. At 5 days post-stroke, 78 circulating miRNAs exhibited significantly different regulation, and most of the variance was associated with sex. A small cohort (five) of miRNAs, miR-15a, miR-19b, miR-32 miR-136 and miR-199a-3p, were found to be highly expressed exclusively in adult females compared with middle-aged females, adult males and middle-aged males. Predicted gene targets for these five miRNAs analysed for KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways revealed that the top ten KEGG pathways were related to growth factor signalling, cell structure and PI3K (phosphoinositide 3-kinase)/Akt and mTOR (mammalian target of rapamycin) signalling. Overall, the pattern of circulating miRNA expression suggests an early influence of age in stroke pathology, with a later emergence of sex as a factor for stroke severity.

miR-146a and miR-196a2 polymorphisms in patients with ischemic stroke in the northern Chinese Han population

MicroRNAs are endogenous non-coding RNAs about 22 nucleotides in length that can repress the expression of proteins by binding to the 3'-untranslated regions of target messenger RNAs. We hypothesized that polymorphisms in miR-146a and miR-196a2 are associated with risk of ischemic stroke in the northern Chinese Han population. In a case-control study of 368 ischemic stroke patients and 381 control subjects that were frequency matched by age and gender, we genotyped two single nucleotide polymorphisms (rs11614913 in miR-196a2 and rs2910164 in miR-146a) using polymerase chain reaction-ligation detection reaction. The frequencies of the rs2910164 CC genotype and C allele within miR-146a were not significantly different in patients with ischemic stroke compared with those in the healthy control group. In subgroup meta-analysis, rs2910164 in miR-146a and large-artery atherosclerosis, rather than small-vessel disease, showed the significant association under the dominant model (CC vs CG+GG, OR 1.694; 95 % CI 1.199-2.395 p = 0.003). After adjusting for confounding risk factors of ischemic stroke by logistic regression analysis, this significant correlation remained. In addition, the distributions of the miR-196a2 genotypes and alleles were not statistically different between ischemic stroke and healthy groups. We also did not find any significant association from stroke subtypes. The CC genotype and C allele of rs2910164 within miR-146a are associated with an increased incidence of large-artery atherosclerotic stroke in the northern Chinese Han population. This study indicates that miR-146a (rs2910164) might contribute to ischemic stroke susceptibility in the northern Chinese Han population.

The role of circulating microRNA-126 (miR-126): a novel biomarker for screening prediabetes and newly diagnosed type 2 diabetes mellitus

Recent studies suggested an association of endothelial microRNA-126 (miR-126) with type 2 diabetes mellitus (T2DM). In the current study, we examined whether circulating miR-126 is associated with T2DM and pre-diabetic syndrome. The study included 82 subjects with impaired glucose tolerance (IGT), 75 subjects with impaired fasting glucose (IFG), 160 patients with newly diagnosed T2DM, and 138 healthy individuals. Quantitative polymerase chain reaction (qPCR) was used to examine serum miR-126. Serum miR-126 was significantly lower in IGT/IFG subjects and T2DM patients than in healthy controls (p < 0.05). After six months of treatment (diet control and exercise in IGT/IFG subjects, insulin plus diet control and exercise in T2DM patients), serum miR-126 increased significantly (p < 0.05). An analysis based on serum miR-126 in the sample revealed a significantly higher odds ratio (OR) for the subjects with the lowest 1/3 of serum miR-126 for T2DM (OR: 3.500, 95% confidence interval: 1.901–6.445, p < 0.05) than subjects within the highest 1/3 of serum miR-126. Such an association was still apparent after adjusting for other major risk factors. The area under the curve (AUC) for the receiver-operating characteristic (ROC) analysis was 0.792 (95% confidence interval: 0.707–0.877, p < 0.001). These results encourage the use of serum miR-126 as a biomarker for pre-diabetes and diabetes mellitus, as well as therapeutic response.

microRNA expression in peripheral blood cells following acute ischemic stroke and their predicted gene targets

Background

microRNA (miRNA) are important regulators of gene expression. In patients with ischemic stroke we have previously shown that differences in immune cell gene expression are present. In this study we sought to determine the miRNA that are differentially expressed in peripheral blood cells of patients with acute ischemic stroke and thus may regulate immune cell gene expression.

Methods

miRNA from peripheral blood cells of forty-eight patients with ischemic stroke and vascular risk factor controls were compared. Differentially expressed miRNA in patients with ischemic stroke were determined by microarray with qRT-PCR confirmation. The gene targets and pathways associated with ischemic stroke that may be regulated by the identified miRNA were characterized.

Results

In patients with acute ischemic stroke, miR-122, miR-148a, let-7i, miR-19a, miR-320d, miR-4429 were decreased and miR-363, miR-487b were increased compared to vascular risk factor controls. These miRNA are predicted to regulate several genes in pathways previously identified by gene expression analyses, including toll-like receptor signaling, NF-κβ signaling, leukocyte extravasation signaling, and the prothrombin activation pathway.

Conclusions

Several miRNA are differentially expressed in blood cells of patients with acute ischemic stroke. These miRNA may regulate leukocyte gene expression in ischemic stroke including pathways involved in immune activation, leukocyte extravasation and thrombosis.

Identification of miRNA-21 and miRNA-24 in plasma as potential early stage markers of acute cerebral infarction

This study investigated the role of microRNA-21 (miR-21) and microRNA-24 (miR-24) in the pathological processes that follow cerebral ischemic injury and examined the potential use of miR-21 and -24 in stroke diagnostics as sensitive plasma biomarkers. An oxygen-glucose deprivation (OGD) model was constructed using mouse N2A neuroblastoma cells (N2A). Western blot analysis and quantitative polymerase chain reaction (qPCR) were employed to detect protein and miRNA expression levels. miR-21 and miR-24 were analyzed in the plasma from 68 patients with acute cerebral infarction (ACI) and 21 healthy individuals. In the present study, it was identified that plasma miR-21 and miR-24 were lower in ACI patients than in the controls (P<0.05). A positive correlation was demonstrated between plasma miR-21 and miR-24, and a negative correlation was revealed between miR-21, miR-24 and the National Institutes of Health Scales Score (NIHSS) within the first day following stroke. In addition, the expression of miR-21 and miR-24 was upregulated by 3.3- and 4.9-fold, respectively, when the reoxygenation time persisted up to 24 h following 3 h of OGD. The expression of Bcl-2 was upregulated following gain of miR-21 function, while X-linked inhibitor of apoptosis protein (XIAP) was downregulated after gain of miR-24 function in N2A cells. The data suggested that miR-21 may have an antiapoptotic effect in N2A neuroblastoma cells following OGD and reoxygenation, while miR-24 may have a pro-apoptotic effect. Therefore, these microRNAs may be potential therapeutic targets for the treatment of post-ischemic injury and may act as diagnostic markers during the early stage of ACI.

Attenuated neuroprotective effect of riboflavin under UV-B irradiation via miR-203/c-Jun signaling pathway in vivo and in vitro

Background

Riboflavin (RF) or vitamin B2 is known to have neuroprotective effects. In the present study, we report the attenuation of the neuroprotective effects of RF under UV-B irradiation. Preconditioning of UV-B irradiated riboflavin (UV-B-RF) showed attenuated neuroprotective effects compared to that of RF in SH-SY5Y neuroblostoma cell line and primary cortical neurons in vitro and a rat model of cerebral ischemia in vivo.

Results

Results indicated that RF pretreatment significantly inhibited cell death and reduced LDH secretion compared to that of the UV-B-RF pretreatment in primary cortical neuron cultures subjected to oxygen glucose deprivation in vitro and cortical brain tissue subjected to ischemic injury in vivo. Further mechanistic studies using cortical neuron cultures revealed that RF treatment induced increased miR-203 expression which in turn inhibited c-Jun expression and increased neuronal cell survival. Functional assays clearly demonstrated that the UV-B-RF preconditioning failed to sustain the increased expression of miR-203 and the decreased levels of c-Jun, mediating the neuroprotective effects of RF. UV-B irradiation attenuated the neuroprotective effects of RF through modulation of the miR-203/c-Jun signaling pathway.

Conclusion

Thus, the ability of UV-B to serve as a modulator of this neuroprotective signaling pathway warrants further studies into its role as a regulator of other cytoprotective/neuroprotective signaling pathways.

miR-376b-5p regulates angiogenesis in cerebral ischemia

The profile of microRNAs (miRNAs) altered following middle cerebral artery occlusion (MCAO) and miRNAs are involved in angiogenesis following cerebral ischemia. miR‑376b‑5p was decreased following MCAO, however, whether miR‑376b‑5p is important in angiogenesis remains to be elucidated. The present study was designed to identify whether miR‑376b‑5p is involved in angiogenesis following cerebral ischemia and to elucidate the underlying mechanisms. A rat MCAO model was established and quantitative polymerase chain reaction was performed to analyze the mRNA expression level of miR‑376b‑5p for 1 to 7 days. In addition, the density of microvessels and the relative mRNA and protein levels of hypoxia‑inducible factor‑1 α (HIF‑1α), vascular endothelial growth factor A (VEGFA) and Notch1 were measured. The miR‑376b‑5p mimic or the miR‑376b‑5p inhibitor were transfected into hypoxic human umbilical vein endothelial cells (HUVECs), and the proliferation, migration and tube formation were measured. To further examine the underlying mechanisms, shRNA was transfected into cells to knock down HIF‑1α, and angiogenesis and the expression of associated molecules, including HIF‑1α, VEGFA and Notch1 were compared between each group. Our results demonstrated that miR‑376b‑5p repressed angiogenesis in vivo and in vitro, and miR‑376b‑5p inhibited angiogenesis in HUVECs by targeting the HIF‑1α‑mediated VEGFA/Notch1 signaling pathway. These findings provide new insights into angiogenesis therapy for cerebral ischemia.

MicroRNAs expression and function in cerebral ischemia reperfusion injury

MicroRNAs (miRNAs) are small (18 ~ 25 nt) noncoding single-stranded RNA molecules that act as negative regulators of gene expression and modulating the stability and/or the translational efficiency of target messenger RNAs. Studies have shown that miRNAs control diverse aspects of brain disease. Recently, several studies have suggested that miRNAs alter the response to ischemia reperfusion injury and regulate the expression of various key elements in cell survival and apoptosis. This review article gives a brief overview of some miRNAs (miR-15a/b, miR-21, miR-29b/c, miR-124, miR-145, miR-181, miR-200 family, miR-338, miR-422a, miR-497, and miR let 7 family) in cerebral ischemia reperfusion injury. Although miRNAs could be potential therapeutic targets for the treatment of ischemia reperfusion injury, their safety and other limitations need further confirmation.

The interplay between microRNAs and histone deacetylases in neurological diseases

Neurological conditions, such as Alzheimer's disease and stroke, represent a prevalent group of devastating illnesses with few treatments. Each of these diseases or conditions is in part characterized by the dysregulation of many genes, including those that code for microRNAs (miRNAs) and histone deacetylases (HDACs). Recently, a complex relationship has been uncovered linking miRNAs and HDACs and their ability to regulate one another. This provides a new avenue for potential therapeutics as the ability to reinstate a careful balance between miRNA and HDACs has lead to improved outcomes in a number of in vitro and in vivo models of neurological conditions. In this review, we will discuss recent findings on the interplay between miRNAs and HDACs and its implications for pathogenesis and treatment of neurological conditions, including amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease and stroke.

Diagnosis, prognosis and therapeutic role of circulating miRNAs in cardiovascular diseases

Cardiovascular diseases (CVD) are the leading cause of morbidity and mortality in the world. Although much progress has been made for cardiovascular diseases in diagnosis, treatment and prognosis during the past two decades, the clinical need for a novel diagnostic biomarker and new therapeutic interventions to decrease the cardiovascular disease incidence is ongoing. MicroRNAs (miRNAs) are endogenous, small (∼22 nucleotides), single-stranded, non-coding RNAs that regulate gene expression and are detectable in whole blood, serum, plasma, urine and other body fluids in a highly stable form. Accumulating evidence suggests that miRNAs are potential novel biomarkers with high sensitivity for early diagnosis and modern treatment for cardiovascular diseases. Altered circulating miRNAs expressions have been reported in acute myocardial infarction (AMI), acute coronary syndrome (ACS), stable coronary artery disease, heart failure, atherosclerosis, essential hypertension and stroke. In the present review, we examine more recent data regarding circulating miRNAs and their potential roles in diagnosis, prognosis and therapeutic strategies for cardiovascular diseases. In addition, we briefly present our own recent experience in detecting circulating miRNAs, and the significance of these miRNAs in AMI prognosis.

Blood brain barrier and neuroinflammation are critical targets of IGF-1-mediated neuroprotection in stroke for middle-aged female rats

Ischemia-induced cerebral infarction is more severe in older animals as compared to younger animals, and is associated with reduced availability of insulin-like growth factor (IGF)-1. This study determined the effect of post-stroke IGF-1 treatment, and used microRNA profiling to identify mechanisms underlying IGF-1’s neuroprotective actions. Post-stroke ICV administration of IGF-1 to middle-aged female rats reduced infarct volume by 39% when measured 24h later. MicroRNA analyses of ischemic tissue collected at the early post-stroke phase (4h) indicated that 8 out of 168 disease-related miRNA were significantly downregulated by IGF-1. KEGG pathway analysis implicated these miRNA in PI3K-Akt signaling, cell adhesion/ECM receptor pathways and T-and B-cell signaling. Specific components of these pathways were subsequently analyzed in vehicle and IGF-1 treated middle-aged females. Phospho-Akt was reduced by ischemia at 4h, but elevated by IGF-1 treatment at 24h. IGF-1 induced Akt activation was preceded by a reduction of blood brain barrier permeability at 4h post-stroke and global suppression of cytokines including IL-6, IL-10 and TNF-α. A subset of these cytokines including IL-6 was also suppressed by IGF-1 at 24h post-stroke. These data are the first to show that the temporal and mechanistic components of post-stroke IGF-1 treatment in older animals, and that cellular components of the blood brain barrier may serve as critical targets of IGF-1 in the aging brain.

MicroRNAs in the Neural Retina

The health and function of the visual system rely on a collaborative interaction between diverse classes of molecular regulators. One of these classes consists of transcription factors, which are known to bind to DNA and control the transcription activities of their target genes. For a long time, it was thought that the transcription factors were the only regulators of gene expression. More recently, however, a novel class of regulators emerged. This class consists of a large number of small noncoding endogenous RNAs, namely, miRNAs. The miRNAs compose an essential component of posttranscriptional gene regulation, since they ultimately control the fate of gene transcripts. The retina, as a part of the central nervous system, is a well-established model for unraveling the molecular mechanisms underlying neuronal and glial functions. Numerous recent efforts have been made towards identification of miRNAs and their inferred roles in the visual pathway. In this review, we summarize the current state of our knowledge regarding the expression and function of miRNA in the neural retina and we discuss their potential uses as biomarkers for some retinal disorders.

Potential roles of HDAC inhibitors in mitigating ischemia-induced brain damage and facilitating endogenous regeneration and recovery

Ischemic stroke is a leading cause of death and disability worldwide, with few available treatment options. The pathophysiology of cerebral ischemia involves both early phase tissue damage, characterized by neuronal death, inflammation, and blood-brain barrier breakdown, followed by late phase neurovascular recovery. It is becoming clear that any promising treatment strategy must target multiple points in the evolution of ischemic injury to provide substantial therapeutic benefit. Histone deacetylase (HDAC) inhibitors are a class of drugs that increase the acetylation of histone and non-histone proteins to activate transcription, enhance gene expression, and modify the function of target proteins. Acetylation homeostasis is often disrupted in neurological conditions, and accumulating evidence suggests that HDAC inhibitors have robust protective properties in many preclinical models of these disorders, including ischemic stroke. Specifically, HDAC inhibitors such as trichostatin A, valproic acid, sodium butyrate, sodium 4-phenylbutyrate, and suberoylanilide hydroxamic acid have been shown to provide robust protection against excitotoxicity, oxidative stress, ER stress, apoptosis, inflammation, and bloodbrain barrier breakdown. Concurrently, these agents can also promote angiogenesis, neurogenesis and stem cell migration to dramatically reduce infarct volume and improve functional recovery after experimental cerebral ischemia. In the following review, we discuss the mechanisms by which HDAC inhibitors exert these protective effects and provide evidence for their strong potential to ultimately improve stroke outcome in patients.

The brain-enriched microRNA miR-124 in plasma predicts neurological outcome after cardiac arrest

Introduction

Early prognostication after successful cardiopulmonary resuscitation is difficult, and there is a need for novel methods to estimate the extent of brain injury and predict outcome. In this study, we evaluated the impact of the cardiac arrest syndrome on the plasma levels of selected tissue-specific microRNAs (miRNAs) and assessed their ability to prognosticate death and neurological disability.

Methods

We included 65 patients treated with hypothermia after cardiac arrest in the study. Blood samples were obtained at 24 hours and at 48 hours. For miRNA-screening purposes, custom quantitative polymerase chain reaction (qPCR) panels were first used. Thereafter individual miRNAs were assessed at 48 hours with qPCR. miRNAs that successfully predicted prognosis at 48 hours were further analysed at 24 hours. Outcomes were measured according to the Cerebral Performance Category (CPC) score at 6 months after cardiac arrest and stratified into good (CPC score 1 or 2) or poor (CPC scores 3 to 5).

Results

At 48 hours, miR-146a, miR-122, miR-208b, miR-21, miR-9 and miR-128 did not differ between the good and poor neurological outcome groups. In contrast, miR-124 was significantly elevated in patients with poor outcomes compared with those with favourable outcomes (P < 0.0001) at 24 hours and 48 hours after cardiac arrest. Analysis of receiver operating characteristic curves at 24 and 48 hours after cardiac arrest showed areas under the curve of 0.87 (95% confidence interval (CI) = 0.79 to 0.96) and 0.89 (95% CI = 0.80 to 0.97), respectively.

Conclusions

The brain-enriched miRNA miR-124 is a promising novel biomarker for prediction of neurological prognosis following cardiac arrest.

Mir-592 regulates the induction and cell death-promoting activity of p75NTR in neuronal ischemic injury

The neurotrophin receptor p75(NTR) has been implicated in mediating neuronal apoptosis after injury to the CNS. Despite its frequent induction in pathologic states, there is limited understanding of the mechanisms that regulate p75(NTR) expression after injury. Here, we show that after focal cerebral ischemia in vivo or oxygen-glucose deprivation in organotypic hippocampal slices or neurons, p75(NTR) is rapidly induced. A concomitant induction of proNGF, a ligand for p75(NTR), is also observed. Induction of this ligand/receptor system is pathologically relevant, as a decrease in apoptosis, after oxygen-glucose deprivation, is observed in hippocampal neurons or slices after delivery of function-blocking antibodies to p75(NTR) or proNGF and in p75(NTR) and ngf haploinsufficient slices. Furthermore, a significant decrease in infarct volume was noted in p75(NTR)-/- mice compared with the wild type. We also investigated the regulatory mechanisms that lead to post-ischemic induction of p75(NTR). We demonstrate that induction of p75(NTR) after ischemic injury is independent of transcription but requires active translation. Basal levels of p75(NTR) in neurons are maintained in part by the expression of microRNA miR-592, and an inverse correlation is seen between miR-592 and p75(NTR) levels in the adult brain. After cerebral ischemia, miR-592 levels fall, with a corresponding increase in p75(NTR) levels. Importantly, overexpression of miR-592 in neurons decreases the level of ischemic injury-induced p75(NTR) and attenuates activation of pro-apoptotic signaling and cell death. These results identify miR-592 as a key regulator of p75(NTR) expression and point to a potential therapeutic candidate to limit neuronal apoptosis after ischemic injury.

MicroRNA dysregulation in spinal cord injury: causes, consequences and therapeutics

Trauma to the spinal cord causes permanent disability to more than 180,000 people every year worldwide. The initial mechanical damage triggers a complex set of secondary events involving the neural, vascular, and immune systems that largely determine the functional outcome of the spinal cord injury (SCI). Cellular and biochemical mechanisms responsible for this secondary injury largely depend on activation and inactivation of specific gene programs. Recent studies indicate that microRNAs function as gene expression switches in key processes of the SCI. Microarray data from rodent contusion models reveal that SCI induces changes in the global microRNA expression patterns. Variations in microRNA abundance largely result from alterations in the expression of the cells at the damaged spinal cord. However, microRNA expression levels after SCI are also influenced by the infiltration of immune cells to the injury site and the death and migration of specific neural cells after injury. Evidences on the role of microRNAs in the SCI pathophysiology have come from different sources. Bioinformatic analysis of microarray data has been used to identify specific variations in microRNA expression underlying transcriptional changes in target genes, which are involved in key processes in the SCI. Direct evidences on the role of microRNAs in SCI are scarcer, although recent studies have identified several microRNAs (miR-21, miR-486, miR-20) involved in key mechanisms of the SCI such as cell death or astrogliosis, among others. From a clinical perspective, different evidences make clear that microRNAs can be potent therapeutic tools to manipulate cell state and molecular processes in order to enhance functional recovery. The present article reviews the actual knowledge on how injury affects microRNA expression and the meaning of these changes in the SCI pathophysiology, to finally explore the clinical potential of microRNAs in the SCI.

MicroRNA-206: a potential circulating biomarker candidate for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a lethal motor neuron disease that progressively debilitates neuronal cells that control voluntary muscle activity. Biomarkers are urgently needed to facilitate ALS diagnosis and prognosis, and as indicators of therapeutic response in clinical trials. microRNAs (miRNAs), small posttranscriptional modifiers of gene expression, are frequently altered in disease conditions. Besides their important regulatory role in variety of biological processes, miRNAs can also be released into the circulation by pathologically affected tissues and display remarkable stability in body fluids. In a mouse model of ALS that expresses mutated human superoxide dismutase 1 (SOD1-G93A) skeletal muscle is one of the tissues affected early by mutant SOD1 toxicity. To find biomarkers for ALS, we studied miRNA alterations from skeletal muscle and plasma of SOD1-G93A mice, and subsequently tested the levels of the affected miRNAs in the serum from human ALS patients. Fast-twitch and slow-twitch muscles from symptomatic SOD1-G93A mice (age 90 days) and their control littermates were first studied using miRNA microarrays and then evaluated with quantitative PCR from five age groups from neonatal to the terminal disease stage (10–120 days). Among those miRNA changed in various age/gender/muscle groups (miR-206, -1, -133a, -133b, -145, -21, -24), miR-206 was the only one consistently altered during the course of the disease pathology. In both sexes, mature miR-206 was increased in fast-twitch muscles preferably affected in the SOD1-G93A model, with highest expression towards the most severely affected animals. Importantly, miR-206 was also increased in the circulation of symptomatic animals and in a group of 12 definite ALS patients tested. We conclude that miR-206 is elevated in the circulation of symptomatic SOD1-G93A mice and possibly in human ALS patients. Although larger scale studies on ALS patients are warranted, miR-206 is a promising candidate biomarker for this motor neuron disease.

MicroRNA responses to focal cerebral ischemia in male and female mouse brain

Stroke occurs with greater frequency in men than in women across diverse ethnic backgrounds and nationalities. Work from our lab and others have revealed a sex-specific sensitivity to cerebral ischemia whereby males exhibit a larger extent of brain damage resulting from an ischemic event compared to females. Previous studies revealed that microRNA (miRNA) expression is regulated by cerebral ischemia in males; however, no studies to date have examined the effect of ischemia on miRNA responses in females. Thus, we examined miRNA responses in male and female brain in response to cerebral ischemia using miRNA arrays. These studies revealed that in male and female brains, ischemia leads to both a universal miRNA response as well as a sexually distinct response to challenge. Target prediction analysis of the miRNAs increased in male or female ischemic brain reveal sex-specific differences in gene targets and protein pathways. These data support that the mechanisms underlying sexually dimorphic responses to cerebral ischemia includes distinct changes in miRNAs in male and female brain, in addition to a miRNA signature response to ischemia that is common to both.

Circulating microRNAs as biomarkers of acute stroke

MicroRNAs have been identified as key regulators of gene expression and thus their potential in disease diagnostics, prognosis and therapy is being actively pursued. Deregulation of microRNAs in cerebral pathogenesis has been reported to a limited extent in both animal models and human. Due to the complexity of the pathology, identifying stroke specific microRNAs has been a challenge. This study shows that microRNA profiles reflect not only the temporal progression of stroke but also the specific etiologies. A panel of 32 microRNAs, which could differentiate stroke etiologies during acute phase was identified and verified using a customized TaqMan Low Density Array (TLDA). Furthermore we also found 5 microRNAs, miR-125b-2*, -27a*, -422a, -488 and -627 to be consistently altered in acute stroke irrespective of age or severity or confounding metabolic complications. Differential expression of these 5 microRNAs was also observed in rat stroke models. Hence, their specificity to the stroke pathology emphasizes the possibility of developing these microRNAs into accurate and useful tools for diagnosis of stroke.

MicroRNA-206: a promising theranostic marker

MicroRNAs (miRs) are small non-coding RNAs that negatively regulate gene expression by binding to the 3` untranslated regions (3`UTR) of their target mRNAs. MiRs were shown to play pivotal roles in tissue development and function and are also involved in the pathogenesis of various diseases including cancer. MicroRNA-206, which belongs to the group of so-called "myomiRs", is one of the most studied miRs thus far. In addition to being involved in skeletal muscle development and pathology, it has also been established that it is involved in the pathogenesis of numerous diseases including heart failure, chronic obstructive pulmonary disease, Alzheimer's disease and various types of cancers. The aim of this review is to provide a complex overview of microRNA-206, including regulating its expression, a brief description of its known functions in skeletal muscle and a complex overview of its roles in the biology and pathology of other tissues, emphasizing its significant diagnostic and therapeutic potential.

The role of microRNAs in human diseases

About 20 years have passed since the discovery of the first microRNA (miRNA) and by now microRNAs are implicated in a variety of physiological and pathological processes. Since the discovery of the powerful effect miRNAs have on biological processes, it has been suggested that mutations affecting miRNA function may play a role in the pathogenesis of human diseases. Over the past several years microRNAs have been found to play a major role in various human diseases. In addition, many studies aim to apply miRNAs for diagnostic and therapeutic applications in human diseases. In this chapter, we summarize the role of miRNAs in pathological processes and discuss how miRNAs could be used as disease biomarkers.

miR-210: fine-tuning the hypoxic response

Hypoxia is a central component of the tumor microenvironment and represents a major source of therapeutic failure in cancer therapy. Recent work has provided a wealth of evidence that noncoding RNAs and, in particular, microRNAs, are significant members of the adaptive response to low oxygen in tumors. All published studies agree that miR-210 specifically is a robust target of hypoxia-inducible factors, and the induction of miR-210 is a consistent characteristic of the hypoxic response in normal and transformed cells. Overexpression of miR-210 is detected in most solid tumors and has been linked to adverse prognosis in patients with soft-tissue sarcoma, breast, head and neck, and pancreatic cancer. A wide variety of miR-210 targets have been identified, pointing to roles in the cell cycle, mitochondrial oxidative metabolism, angiogenesis, DNA damage response, and cell survival. Additional microRNAs seem to be modulated by low oxygen in a more tissue-specific fashion, adding another layer of complexity to the vast array of protein-coding genes regulated by hypoxia.

miRNAs-19b, -29b-2* and -339-5p show an early and sustained up-regulation in ischemic models of stroke

Stroke, the loss of neurons after ischemic insult to the brain, is one of the leading causes of death and disability worldwide. Despite its prevalence and severity, current therapy is extremely limited, highlighting the importance of further understanding the molecular events underlying ischemia-induced neuronal cell death. An ischemic area can be subdivided into two separate pathophysiological regions: the rapidly dying necrotic core, and the potentially salvageable apoptotic penumbra. Understanding molecular events occurring in the apoptotic ischemic penumbra may give greater insight into mechanisms controlling this salvageable tissue. miRNAs are known to have key roles in the regulation of gene expression in numerous pathological conditions, including the modulation of distinct pathways in stroke. However, previous studies have profiled miRNAs in the whole ischemic infarct, and do not differentiate between miRNA regulation in the necrotic core versus the apoptotic penumbra. We asked if there were unique miRNAs that are differentially regulated following ischemic insults in the salvageable apoptotic penumbra. miRNA expression profiles were compared in the whole infarct from in vivo stroke models, using the three vessel occlusion approach, to an in vitro model of the ischemic penumbra, prior to apoptotic induction. Multiple miRNAs were found to be differentially regulated following ischemic insults in each system. However, miR-19b, miR-29b-2* and miR-339-5p were significantly up-regulated in both model systems. Further, we confirmed these results in a neuroblastoma cell line subjected to a penumbra-like ischemic insult that induced the apoptotic cell death pathway. The data show that miR-19b, miR-29b-2* and miR-339-5p are up-regulated following ischemic insults and may be regulating gene expression to control important cellular pathways in the salvageable ischemic penumbra. Further investigation of their role and mRNA target identification may lead to new insights into the molecular mechanisms taking place in the salvageable apoptotic penumbra.

MicroRNAs in Cerebral Ischemia

Pathogenesis of cerebral ischemia has so far been described in the context of proteins and the pathways that they regulate. The discovery of biomarkers has also been focussed mainly on proteins and to some extent on the mRNAs that encode them. The knowledge on the role of microRNAs in understanding the pathogenesis of cerebral ischemia is still at its infancy. In this study, using rat models subjected to middle cerebral artery occlusion, we have profiled the microRNAs at different reperfusion times (0 to 48 h) to understand the progression of cerebral ischemia. We have also attempted to correlate the expression of microRNAs to treatment with an NMDA antagonist (MK801) and to protein expression with the hope of demonstrating the potential use of microRNAs as early biomarkers of stroke.

Inhibition of microRNA-181 reduces forebrain ischemia-induced neuronal loss

MicroRNA (miRNA), miR-181a, is enriched in the brain, and inhibition of miR-181a reduced astrocyte death in vitro and infarct volume after stroke in vivo. This study investigated the role of miR-181a in neuronal injury in vitro and hippocampal neuronal loss in vivo after forebrain ischemia. miR-181a levels were altered by transfection with mimic or antagomir. N2a cells subjected to serum deprivation and oxidative stress showed less cell death when miR-181a was reduced and increased death when miR-181a increased; protection was associated with increased Bcl-2 protein. In contrast, transfected primary neurons did not show altered levels of cell death when miR-181a levels changed. Naive male rats and rats stereotactically infused with miR-181a antagomir or control were subjected to forebrain ischemia and cornus ammonis (CA)1 neuronal survival and protein levels were assessed. Forebrain ischemia increased miR-181a expression and decreased Bcl-2 protein in the hippocampal CA1 region. miR-181a antagomir reduced miR-181a levels, reduced CA1 neuronal loss, increased Bcl-2 protein, and significantly prevented the decrease of glutamate transporter 1. Thus, miR-181a antagomir reduced evidence of astrocyte dysfunction and increased CA1 neuronal survival. miR-181a inhibition is thus a potential target in the setting of forebrain or global cerebral ischemia as well as focal ischemia.