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

The Emerging Role of Epigenetics in Cerebral Ischemia

Despite great progresses in the treatment and prevention of ischemic stroke, it is still among the leading causes of death and serious long-term disability all over the world, indicating that innovative neural regenerative and neuroprotective agents are urgently needed for the development of therapeutic approaches with greater efficacy for ischemic stroke. More and more evidence suggests that a spectrum of epigenetic processes play an important role in the pathophysiology of cerebral ischemia. In the present review, we first discuss recent developments in epigenetic mechanisms, especially their roles in the pathophysiology of cerebral ischemia. Specifically, we focus on DNA methylation, histone deacetylase, histone methylation, and microRNAs (miRNAs) in the regulation of vascular and neuronal regeneration after cerebral ischemia. Additionally, we highlight epigenetic strategies for ischemic stroke treatments, including the inhibition of histone deacetylase enzyme and DNA methyltransferase activities, and miRNAs. These therapeutic strategies are far from clinic use, but preliminary data indicate that neuroprotective agents targeting these pathways can modulate neural cell regeneration and promote brain repair and functional recovery after cerebral ischemia. A better understanding of how epigenetics influences the process and progress of cerebral ischemia will pave the way for discovering more sensitive and specific biomarkers and new targets and therapeutics for ischemic stroke.

MicroRNA-150 regulates blood-brain barrier permeability via Tie-2 after permanent middle cerebral artery occlusion in rats

The mechanism of blood-brain barrier (BBB) disruption, involved in poststroke edema and hemorrhagic transformation, is important but elusive. We investigated microRNA-150 (miR-150)-mediated mechanism in the disruption of BBB after stroke in rats. We found that up-regulation of miR-150 increased permeability of BBB as detected by MRI after permanent middle cerebral artery occlusion in vivo as well as increased permeability of brain microvascular endothelial cells after oxygen-glucose deprivation in vitro. The expression of claudin-5, a key tight junction protein, was decreased in the ischemic boundary zone after up-regulation of miR-150. We found in brain microvascular endothelial cells that overexpression of miR-150 decreased not only cell survival rate but also the expression levels of claudin-5 after oxygen-glucose deprivation. With dual-luciferase assay, we confirmed that miR-150 could directly regulate the angiopoietin receptor Tie-2. Moreover, silencing Tie-2 with lentivirus-delivered small interfering RNA reversed the effect of miR-150 on endothelial permeability, cell survival, and claudin-5 expression. Furthermore, poststroke treatment with antagomir-150, a specific miR-150 antagonist, contributed to BBB protection, infarct volume reduction, and amelioration of neurologic deficits. Collectively, our findings suggested that miR-150 could regulate claudin-5 expression and endothelial cell survival by targeting Tie-2, thus affecting the permeability of BBB after permanent middle cerebral artery occlusion in rats, and that miR-150 might be a potential alternative target for the treatment of stroke.-Fang, Z., He, Q.-W., Li, Q., Chen, X.-L., Baral, S., Jin, H.-J., Zhu, Y.-Y., Li, M., Xia, Y.-P., Mao, L., Hu, B. MicroRNA-150 regulates blood-brain barrier permeability via Tie-2 after permanent middle cerebral artery occlusion in rats.

Development and regulation of exosome-based therapy products

Recently, various innovative therapies involving the ex vivo manipulation and subsequent reintroduction of exosome-based therapeutics into humans have been developed and validated, although no exosome-based therapeutics have yet to be brought into the clinic. Exosomes are nanosized vesicles secreted by many cells that utilize them for cell-to-cell communications to facilitate transport of proteins and genetic material. Comprised of cellular membranes with multiple adhesive proteins on their surface, exosomes offer distinct advantages that exceptionally position them as highly effective drug carriers. Additionally, exosomes can exert unique biological activity reflective of their origin that may be used for therapy of various diseases. In fact, exosomes have benefits of both synthetic nanocarriers and cell-mediated drug delivery systems, and avoid their limitations. This concise review highlights the recent developments in exosome-based drug delivery systems and the main regulatory considerations for using this type of therapeutic in clinic. WIREs Nanomed Nanobiotechnol 2016, 8:744-757. doi: 10.1002/wnan.1395 For further resources related to this article, please visit the WIREs website.

Inhibition of microRNA-210 provides neuroprotection in hypoxic-ischemic brain injury in neonatal rats

Perinatal hypoxic-ischemic encephalopathy (HIE) is associated with high neonatal mortality and severe long-term neurologic morbidity. Yet the mechanisms of brain injury in infants with HIE remain largely elusive. The present study determined a novel mechanism of microRNA-210 (miR-210) in silencing endogenous neuroprotection and increasing hypoxic-ischemic brain injury in neonatal rats. The study further revealed a potential therapeutic effect of miR-210 inhibition using complementary locked nucleic acid oligonucleotides (miR-210-LNA) in 10-day-old neonatal rats in the Rice-Vannucci model. The underlying mechanisms were investigated with intracerebroventricular injection (i.c.v) of miR-210 mimic, miR-210-LNA, glucocorticoid receptor (GR) agonist and antagonist. Luciferase reporter gene assay was conducted for identification of miR-210 targeting GR 3'untranslated region. The results showed that the HI treatment significantly increased miR-210 levels in the brain, and miR-210 mimic significantly decreased GR protein abundance and exacerbated HI brain injury in the pups. MiR-210-LNA administration via i.c.v. 4h after the HI insult significantly decreased brain miR-210 levels, increased GR protein abundance, reduced HI-induced neuronal death and brain infarct size, and improved long-term neurological function recovery. Of importance, the intranasal delivery of miR-210-LNA 4h after the HI insult produced similar effects in decreasing HI-induced neonatal brain injury and improving neurological function later in life. Altogether, the present study provides evidence of a novel mechanism of miR-210 in a neonatal HI brain injury model, and suggests a potential therapeutic approach of miR-210 inhibition in the treatment of neonatal HIE.

Focus on Extracellular Vesicles: Physiological Role and Signalling Properties of Extracellular Membrane Vesicles

Extracellular vesicles (EVs) are a heterogeneous population of secreted membrane vesicles, with distinct biogenesis routes, biophysical properties and different functions both in physiological conditions and in disease. The release of EVs is a widespread biological process, which is conserved across species. In recent years, numerous studies have demonstrated that several bioactive molecules are trafficked with(in) EVs, such as microRNAs, mRNAs, proteins and lipids. The understanding of their final impact on the biology of specific target cells remains matter of intense debate in the field. Also, EVs have attracted great interest as potential novel cell-free therapeutics. Here we describe the proposed physiological and pathological functions of EVs, with a particular focus on their molecular content. Also, we discuss the advances in the knowledge of the mechanisms regulating the secretion of EV-associated molecules and the specific pathways activated upon interaction with the target cell, highlighting the role of EVs in the context of the immune system and as mediators of the intercellular signalling in the brain.

Early diagnosis of Alzheimer's disease from elevated olfactory mucosal miR-206 level

MicroRNA-206, which suppresses the expression of brain-derived neurotrophic factor, is known to be elevated in the brains of Alzheimer's disease (AD) patients. We performed intranasal biopsy of the olfactory epithelia of early dementia patients (n = 24) and cognitively healthy controls (n = 9). Patients with significant depression (n = 8) were analyzed separately, as their cognitive impairments were thought to be caused by their depression. Real-time PCR was performed on the biopsied tissues. The relative microRNA-206 level exhibited a 7.8-fold increase (P = 0.004) in the mild cognitive impairment group (CDR 0.5; n = 13) and a 41.5-fold increase (P < 0.001) in the CDR 1 group (n = 11). However, this level was not increased in the depression group, even in those with cognitive decline. Using the optimal cutoff value, the sensitivity/specificity for diagnosing CDR 0.5 and CDR 1 dementia were 87.5%/94.1% and 90.9%/93.3%, respectively. In ROC analysis, the AUCs were 0.942 and 0.976 in the CDR 0.5 and CDR 1 groups, respectively. The olfactory mucosal microRNA-206 level and cognitive assessment scores were significantly correlated in the non-depressed subjects with cognitive impairment. In conclusion, the olfactory mucosal microRNA-206 level can be easily measured, and it can be utilized as an excellent biomarker for the diagnosis of early AD, including mild cognitive impairment.

MicroRNAs: a novel promising therapeutic target for cerebral ischemia/reperfusion injury?

To determine the molecular mechanism of cerebral ischemia/reperfusion injury, we examined the microRNA (miRNA) expression profile in rat cortex after focal cerebral ischemia/reperfusion injury using miRNA microarrays and bioinformatic tools to systematically analyze Gene Ontology (GO) function classifications, as well as the signaling pathways of genes targeted by these differentially expressed miRNAs. Our results show significantly changed miRNA expression profiles in the reperfusion period after focal cerebral ischemia, with a total of 15 miRNAs up-regulated and 44 miRNAs down-regulated. Target genes of these differentially expressed miRNAs were mainly involved in metabolic and cellular processes, which were identified as hub nodes of a miRNA-GO-network. The most correlated pathways included D-glutamine and D-glutamate metabolism, the renin-angiotensin system, peroxisomes, the PPAR signaling pathway, SNARE interactions in vesicular transport, and the calcium signaling pathway. Our study suggests that miRNAs play an important role in the pathological process of cerebral ischemia/reperfusion injury. Understanding miRNA expression and function may shed light on the molecular mechanism of cerebral ischemia/reperfusion injury.

MicroRNA-146a Promotes Oligodendrogenesis in Stroke

Stroke induces new myelinating oligodendrocytes that are involved in ischemic brain repair. Molecular mechanisms that regulate oligodendrogenesis have not been fully investigated. MicroRNAs (miRNAs) are small non-coding RNA molecules that post-transcriptionally regulate gene expression. MiR-146a has been reported to regulate immune response, but the role of miR-146a in oligodendrocyte progenitor cells (OPCs) remains unknown. Adult Wistar rats were subjected to the right middle cerebral artery occlusion (MCAo). In situ hybridization analysis with LNA probes against miR-146a revealed that stroke considerably increased miR-146a density in the corpus callosum and subventricular zone (SVZ) of the lateral ventricle of the ischemic hemisphere. In vitro, overexpression of miR-146a in neural progenitor cells (NPCs) significantly increased their differentiation into O4⁺ OPCs. Overexpression of miR-146a in primary OPCs increased their expression of myelin proteins, whereas attenuation of endogenous miR-146a suppressed generation of myelin proteins. MiR-146a also inversely regulated its target gene-IRAK1 expression in OPCs. Attenuation of IRAK1 in OPCs substantially increased myelin proteins and decreased OPC apoptosis. Collectively, our data suggest that miR-146a may mediate stroke-induced oligodendrogenesis.

Time-Course Analysis of Brain Regional Expression Network Responses to Chronic Intermittent Ethanol and Withdrawal: Implications for Mechanisms Underlying Excessive Ethanol Consumption

Long lasting abusive consumption, dependence, and withdrawal are characteristic features of alcohol use disorders (AUD). Mechanistically, persistent changes in gene expression are hypothesized to contribute to brain adaptations leading to ethanol toxicity and AUD. We employed repeated chronic intermittent ethanol (CIE) exposure by vapor chamber as a mouse model to simulate the cycles of ethanol exposure and withdrawal commonly seen with AUD. This model has been shown to induce progressive ethanol consumption in rodents. Brain CIE-responsive expression networks were identified by microarray analysis across five regions of the mesolimbic dopamine system and extended amygdala with tissue harvested from 0-hours to 7-days following CIE. Weighted Gene Correlated Network Analysis (WGCNA) was used to identify gene networks over-represented for CIE-induced temporal expression changes across brain regions. Differential gene expression analysis showed that long-lasting gene regulation occurred 7-days after the final cycle of ethanol exposure only in prefrontal cortex (PFC) and hippocampus. Across all brain regions, however, ethanol-responsive expression changes occurred mainly within the first 8-hours after removal from ethanol. Bioinformatics analysis showed that neuroinflammatory responses were seen across multiple brain regions at early time-points, whereas co-expression modules related to neuroplasticity, chromatin remodeling, and neurodevelopment were seen at later time-points and in specific brain regions (PFC or HPC). In PFC a module containing Bdnf was identified as highly CIE responsive in a biphasic manner, with peak changes at 0 hours and 5 days following CIE, suggesting a possible role in mechanisms underlying long-term molecular and behavioral response to CIE. Bioinformatics analysis of this network and several other modules identified Let-7 family microRNAs as potential regulators of gene expression changes induced by CIE. Our results suggest a complex temporal and regional pattern of widespread gene network responses involving neuroinflammatory and neuroplasticity related genes as contributing to physiological and behavioral responses to chronic ethanol.

Electroacupuncture induces acute changes in cerebral cortical miRNA profile, improves cerebral blood flow and alleviates neurological deficits in a rat model of stroke

Electroacupuncture has been shown to improve cerebral blood flow in animal models of stroke. However, it is unclear whether electroacupuncture alters miRNA expression in the cortex. In this study, we examined changes in the cerebral cortical miRNA profile, cerebral blood flow and neurological function induced by electroacupuncture in a rat model of stroke. Electroacupuncture was performed at Renzhong (GV26) and Neiguan (PC6), with a frequency of 2 Hz, continuous wave, current intensity of 3.0 mA, and stimulation time of 1 minute. Electroacupuncture increased cerebral blood flow and alleviated neurological impairment in the rats. miRNA microarray profiling revealed that the vascular endothelial growth factor signaling pathway, which links cell proliferation with stroke, was most significantly affected by electroacupuncture. Electroacupuncture induced changes in expression of rno-miR-206-3p, rno-miR-3473, rno-miR-6216 and rno-miR-494-3p, and these changes were confirmed by quantitative real-time polymerase chain reaction. Our findings suggest that changes in cell proliferation-associated miRNA expression induced by electroacupuncture might be associated with the improved cerebral blood supply and functional recovery following stroke.

The Diagnostic Value of Circulating Brain-specific MicroRNAs for Ischemic Stroke

Objective Circulating microRNAs have been recognized as promising biomarkers for various diseases. The aim of the present study was to explore the potential role of circulating miR-107, miR-128b and miR-153 as non-invasive biomarkers in the diagnosis of ischemia stroke. Methods One hundred and fourteen ischemic stroke patients (61±11.3 years old) and 58 healthy volunteers (56±3.9 years old) matched for age and sex were enrolled in this study. Total RNA was isolated from plasma with TRIzol reagent. The circulating microRNAs levels were measured by quantitative real-time polymerase chain reaction. Results The circulating levels of miR-107, miR-128b and miR-153 significantly increased 2.78-, 2.13- and 1.83-fold in ischemia stroke patients in comparison to the healthy volunteers, respectively. Receiver operating characteristic (ROC) curves were analyzed using the SPSS software program and revealed the areas under the curve for circulating miR-107, miR-128b and miR-153 to be 0.97, 0.903 and 0.893 in ischemia stroke patients in comparison to healthy volunteers, respectively. The levels of circulating miR-107, miR-128b and miR-153 therefore positively correlated with the severity of stroke as defined by NIHSS classes. Conclusion Our results suggest that circulating miR-107, miR-128b and miR-153 might be used as potential novel non-invasive biomarkers for the diagnosis of ischemia stroke. However, future prospective trials in large-sized patient cohorts are needed before drawing any definitive conclusions.

Blood microRNAs as potential diagnostic and prognostic markers in cerebral ischemic injury

MicroRNAs are a family of small, genome-encoded endogenous RNAs that are transcribed but are not translated into proteins. They serve essential roles in virtually every aspect of brain function, including neurogenesis, neural development, and cellular responses leading to changes in synaptic plasticity. They are also implicated in neurodegeneration and neurological disorders, in responses to hypoxia and ischemia, and in ischemic tolerance induced by ischemic preconditioning. In recent developments, miRNA expression profiling has been examined in stroke, and these studies indicate that miRNAs have emerged as key mediators in ischemic stroke biology. Both increased and decreased miRNA levels may be needed either as prevention or treatment of stroke. Novel approaches are being developed to get miRNA related therapeutics into the brain across an intact blood-brain barrier, including chemical modification, use of targeting molecules and methods to disrupt the blood-brain barrier.

Circulating microRNA 132-3p and 324-3p Profiles in Patients after Acute Aneurysmal Subarachnoid Hemorrhage

Background

Aneurysmal subarachnoid hemorrhage (SAH) is a highly morbid and fatal condition with high rate of cognitive impairment and negative impact in quality of life among survivors. Delayed cerebral infarction (DCI) is one the major factors for these negative outcomes. In this study we compared the circulating microRNA profiles of SAH patients and healthy individuals, and the circulating microRNA profiles of SAH patients with and without DCI.

Methods

Peripheral blood samples on Day 7 after the onset of SAH were subjected to microarray analysis with Affymetrix miRNA 3.0 array and quantitative PCR analysis. SAH patients with (N = 20) and without DCI (N = 20) and Healthy controls (N = 20) were included for analyses.

Results

We demonstrated that 99 miRNAs were found to be dysregulated in the SAH patient group with DCI. 81 miRNAs were upregulated and 18 were downregulated. Findings from KEGG pathway analysis showed that miRNAs and target genes for axon guidance and TGF-beta signaling were involved, implying that the resulted differential miRNA expression pattern reflect the results of SAH instead of etiology of the disease. miR-132-3p and miR-324-3p showed distinctive upregulations in qPCR [miR-132: 9.5 fold (95%CI: 2.3 to 16.7) in DCI group and 3.4 fold (95%CI: 1.0 to 5.8) in Non-DCI group; miR-324: 4924 fold (95%CI: 2620 to 7228) in DCI group and 4545 fold (95%CI: 2408 to 6683) in non-DCI group]. However, there were no significant differences in fold changes between SAH patients with and without DCI [fold change ratios (mean+/-SD): 2.7+/-4.2 and 1.1+/-1.1 for miRNA-132 and miRNA-324].

Conclusion

Our study demonstrated that as compared to healthy control, miR-132 and miR-324 showed a upregulation in both SAH DCI and Non-DCI groups. However, the differences between the SAH DCI and non-DCI groups were not statistically significant.

MicroRNA-9 Mediates the Cell Apoptosis by Targeting Bcl2l11 in Ischemic Stroke

Ischemic strokes occur as a result of an obstruction within a blood vessel supplying blood to the brain and accounts for about 87 % of all cases. During the cerebral ischemia, most of the neurons undergo the necrosis and apoptosis upon the exposure to the dramatic blood flow reduction. Although, it is known that both the intrinsic and extrinsic pathways are involved in the neuronal apoptosis of ischemic brain injury. The complex underlying mechanisms remains less known. MicroRNAs are a class of endogenous small non-coding RNAs and the role of miRNAs in the pathophysiology of stroke has been studied. In this study, we found that miR-9 is downregulated in the mice with middle cerebral artery occlusion (MCAO) brain and oxygen-glucose deprivation (OGD) neurons. Application of miR-9 gamer could restore the neurological scores and reduces the infarct volume, brain water content, and the behavioral impairments. Moreover, upregulation of miR-9 suppresses the neuronal apoptosis in MCAO brain and OGD neurons. Furthermore, we identified that Bcl2l11 as the direct target of miR-9 and manipulation of miR-9 induces the corresponding changing of Bcl2l11 protein level. Finally, we found that the protein level of Bcl2l11 is increased in the MCAO brain and OGD neurons. Our study demonstrated the critical role of miR-9 in the neuronal apoptosis of ischemic brain injury.

MicroRNA-29b is a therapeutic target in cerebral ischemia associated with aquaporin 4

MicroRNA-29b (miR-29b) is involved in regulating ischemia process, but the molecular mechanism is unclear. In this work, we explored the function of miR-29b in cerebral ischemia. The level of miR-29b in white blood cells was evaluated in patients and mice after ischemic stroke. Brain infarct volume and National Institute of Health stroke scale (NIHSS) scores were analyzed to determine the relationship between miR-29b expression and the severity of stroke. The relationship of miR-29b and aquaporin-4 (AQP4) was further studied in mice. We found that miR-29b was significantly downregulated in stroke patients (P<0.05). MiR-29b level negatively associated with NIHSS scores (r=-0.349, P<0.01) and brain infarct volume (r=-0.321, P<0.05). In ischemic mice, miR-29b in the brain and blood were both downregulated (r=0.723, P<0.05). MiR-29b overexpression reduced infarct volume (49.50±6.55 versus 35.48±2.28 mm(3), P<0.05), edema (164±4% versus 108±4%, P<0.05), and blood-brain barrier (BBB) disruption compared with controls (15±9% versus 7±3%, P<0.05). Aquaporin-4 expression greatly decreased after miR-29b overexpression (28±7% versus 11±3%, P<0.05). Dual-luciferase reporter system showed that AQP-4 was the direct target of miR-29b (P<0.05). We concluded that miR-29b could potentially predict stroke outcomes as a novel circulating biomarker, and miR-29b overexpression reduced BBB disruption after ischemic stroke via downregulating AQP-4.

MicroRNA miR124 is required for the expression of homeostatic synaptic plasticity

Homeostatic synaptic plasticity is a compensatory response to alterations in neuronal activity. Chronic deprivation of neuronal activity results in an increase in synaptic AMPA receptors (AMPARs) and postsynaptic currents. The biogenesis of GluA2-lacking, calcium-permeable AMPARs (CP-AMPARs) plays a crucial role in the homeostatic response; however, the mechanisms leading to CP-AMPAR formation remain unclear. Here we show that the microRNA, miR124, is required for the generation of CP-AMPARs and homeostatic plasticity. miR124 suppresses GluA2 expression via targeting its 3′-UTR, leading to the formation of CP-AMPARs. Blockade of miR124 function abolishes the homeostatic response, whereas miR124 overexpression leads to earlier induction of homeostatic plasticity. miR124 transcription is controlled by an inhibitory transcription factor EVI1, acting by association with the deacetylase HDAC1. Our data support a cellular cascade in which inactivity relieves EVI1/HDAC-mediated inhibition of miR124 gene transcription, resulting in enhanced miR124 expression, formation of CP-AMPARs and subsequent induction of homeostatic synaptic plasticity.

GluA2-lacking AMPA receptors are known to play a role in homeostatic plasticity. Here, the authors show that spiking activity blockade disinhibits mir124 transcription, which in turn suppresses GluA2 mRNA translation, thereby contributing to synaptic upscaling in hippocampal cells.

Gene expression profiling in stroke: relevance of blood-brain interaction

Biomarker profiling is utilized to identify diagnostic and prognostic candidates for stroke. Clinical and preclinical biomarker data suggest altered circulating immune responses may illuminate the mechanisms of stroke recovery. However, the relationship between peripheral blood biomarker profile(s) and brain profiles following stroke remains elusive. Data show that neutrophil lymphocyte ratio (NLR) predicts stroke outcome. Neutrophils release Arginase 1 (ARG1) resulting in T lymphocyte suppression in peripheral blood. Interestingly, the cellular response to stroke may have implications for known biomarker profiles. Conversely, preclinical evidence suggests that upregulation of ARG1 in microglia is a marker of M2 macrophages and may influence neuroprotection. Comparing clinical and preclinical studies creates opportunities to explore the molecular mechanisms of blood and brain biomarker interactions in stroke.

MicroRNAs Regulate Mitochondrial Function in Cerebral Ischemia-Reperfusion Injury

Cerebral ischemia-reperfusion injury involves multiple independently fatal terminal pathways in the mitochondria. These pathways include the reactive oxygen species (ROS) generation caused by changes in mitochondrial membrane potential and calcium overload, resulting in apoptosis via cytochrome c (Cyt c) release. In addition, numerous microRNAs are associated with the overall process. In this review, we first briefly summarize the mitochondrial changes in cerebral ischemia-reperfusion and then describe the possible molecular mechanism of miRNA-regulated mitochondrial function, which likely includes oxidative stress and energy metabolism, as well as apoptosis. On the basis of the preceding analysis, we conclude that studies of microRNAs that regulate mitochondrial function will expedite the development of treatments for cerebral ischemia-reperfusion injury.

Identification and Functional Analysis of MicroRNAs in Mice following Focal Cerebral Ischemia Injury

Numerous studies have demonstrated that genes, RNAs, and proteins are involved in the occurrence and development of stroke. In addition, previous studies concluded that microRNAs (miRNAs or miRs) are closely related to the pathological process of ischemic and hypoxic disease. Therefore, the aims of this study were to quantify the altered expression levels of miRNAs in the infarct region 6 h after middle cerebral artery occlusion (MCAO)-induced focal cerebral ischemia in mice using a large-scale miRNAs microarray. Firstly, MCAO-induced cerebral ischemic injuries were investigated by observing the changes of neurological deficits, infarct volume and edema ratio. One hundred and eighteen differentially expressed miRNAs were identified in the infarct region of mice following the MCAOs compared with sham group (p < 0.05 was considered as significant). Among these 118 significantly expressed microRNAs, we found that 12 miRNAs were up-regulated with fold changes lager than two, and 18 miRNAs were down-regulated with fold changes less than 0.5 in the infarct region of mice following the 6 h MCAOs, compared with the sham group. Then, these 30 miRNAs with expression in fold change larger than two or less than 0.5 was predicted, and the functions of the target genes of 30 miRNAs were analyzed using a bioinformatics method. Finally, the miRNA-gene network was established and the functional miRNA-mRNA pairs were identified, which provided insight into the roles of the specific miRNAs that regulated specified genes in the ischemic injuries. The miRNAs identified in this study may represent effective therapeutic targets for stroke, and further study of the role of these targets may increase our understanding of the mechanisms underlying ischemic injuries.

Renal stromal miRNAs are required for normal nephrogenesis and glomerular mesangial survival

MicroRNAs are small noncoding RNAs that post-transcriptionally regulate mRNA levels. While previous studies have demonstrated that miRNAs are indispensable in the nephron progenitor and ureteric bud lineage, little is understood about stromal miRNAs during kidney development. The renal stroma (marked by expression of FoxD1) gives rise to the renal interstitium, a subset of peritubular capillaries, and multiple supportive vascular cell types including pericytes and the glomerular mesangium. In this study, we generated FoxD1^GC;Dicer^fl/fl transgenic mice that lack miRNA biogenesis in the FoxD1 lineage. Loss of Dicer activity resulted in multifaceted renal anomalies including perturbed nephrogenesis, expansion of nephron progenitors, decreased renin-expressing cells, fewer smooth muscle afferent arterioles, and progressive mesangial cell loss in mature glomeruli. Although the initial lineage specification of FoxD1⁺ stroma was not perturbed, both the glomerular mesangium and renal interstitium exhibited ectopic apoptosis, which was associated with increased expression of Bcl2l11 (Bim) and p53 effector genes (Bax, Trp53inp1, Jun, Cdkn1a, Mmp2, and Arid3a). Using a combination of high-throughput miRNA profiling of the FoxD1⁺-derived cells and mRNA profiling of differentially expressed transcripts in FoxD1^GC;Dicer^fl/fl kidneys, at least 72 miRNA:mRNA target interactions were identified to be suppressive of the apoptotic program. Together, the results support an indispensable role for stromal miRNAs in the regulation of apoptosis during kidney development.

The regulatory roles of non-coding RNAs in nerve injury and regeneration

Non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), have attracted much attention since their regulatory roles in diverse cell processes were recognized. Emerging studies demonstrate that many ncRNAs are differentially expressed after injury to the nervous system, significantly affecting nerve regeneration. In this review, we compile the miRNAs and lncRNAs that have been reported to be dysregulated following a variety of central and peripheral nerve injuries, including acquired brain injury, spinal cord injury, and peripheral nerve injury. We also list investigations on how these miRNAs and lncRNAs exert the regulatory actions in neurodegenerative and neuroregenerative processes through different mechanisms involving their interaction with target coding genes. We believe that comprehension of the expression profiles and the possible functions of ncRNAs during the processes of nerve injury and regeneration will help understand the molecular mechanisms responsible for post-nerve-injury changes, and may contribute to the potential use of ncRNAs as a diagnostic marker and therapeutic target for nerve injury.

MiR-207/352 regulate lysosomal-associated membrane proteins and enzymes following ischemic stroke

The role of microRNAs (miRNAs) in lysosome-mediated neuronal death and survival following ischemic stroke remains unknown. Herein, using miRNA and mRNA gene expression profiling microarrays, we identified the differentially expressed 24 miRNAs and 494 genes in the cortical peri-infarct area, respectively. Integrating the miRNA targets and mRNA expression profiles, we found 47 genes of miRNA targets, including lysosomal-associated membrane protein 2 (LAMP2), Hexb, Bcl2, etc. MiR-207 and miR-352 were mainly downregulated after ischemic stroke, followed by a slight return to baseline during post-middle cerebral artery occlusion (MCAO) 1d to 7d. Furthermore, the luciferase reporter assay demonstrated that LAMP2 and Hexb were the direct targets of miR-207 and miR-352, respectively. After lateral ventricle injection with miR-207 agonist mimics, the neurological deficit scores and infarct volumes were attenuated, and the structure of mitochondria ridges was improved. In addition, miR-207 mimics could reduce the number of cellular lysosome and autophagosome, whereas increase the number of autophagic vacuoles, indicating miR-207 might affect the latter part of lysosomal-autophagy pathway and mitochondria-induced apoptosis. These results suggested that miR-207 and miR-352 were involved in lysosomal pathway for mediating ischemic injury and spontaneous recovery. MiR-207 mimics as potential target drugs could protect against autophagic cell death after ischemic stroke.

Using exosomes, naturally-equipped nanocarriers, for drug delivery

Exosomes offer distinct advantages that uniquely position them as highly effective drug carriers. Comprised of cellular membranes with multiple adhesive proteins on their surface, exosomes are known to specialize in cell-cell communications and provide an exclusive approach for the delivery of various therapeutic agents to target cells. In addition, exosomes can be amended through their parental cells to express a targeting moiety on their surface, or supplemented with desired biological activity. Development and validation of exosome-based drug delivery systems are the focus of this review. Different techniques of exosome isolation, characterization, drug loading, and applications in experimental disease models and clinic are discussed. Exosome-based drug formulations may be applied to a wide variety of disorders such as cancer, various infectious, cardiovascular, and neurodegenerative disorders. Overall, exosomes combine benefits of both synthetic nanocarriers and cell-mediated drug delivery systems while avoiding their limitations.

Circulating miR-145 is associated with plasma high-sensitivity C-reactive protein in acute ischemic stroke patients

Stroke is a major cerebrovascular disease threatening human health and life with high morbidity, disability and mortality. We aimed to find effective biomarkers for the early diagnosis on stroke. Nine previously reported stroke-associated miRNAs (miR-21, miR-23a, miR-29b, miR-124, miR-145, miR-210, miR-221, miR-223 and miR-483-5p) were measured by quantitative real time-PCR, and plasma high-sensitivity C-reactive protein (hs-CRP) and serum interleukin 6 (IL-6), the pro-inflammation markers in brain injury, were examined by enzyme-linked immunosorbent assay in 146 acute ischemic stroke patients and 96 healthy blood donors. We found that serum miR-145 was significantly increased within 24 h after stroke onset and serum miR-23a and miR-221 were decreased in patients. Moreover, serum miR-145 was strong positively correlated with plasma hs-CRP and moderate positively correlated with serum IL-6. Meanwhile, serum miR-23a and miR-221 were moderate negatively correlated with plasma hs-CRP but not serum IL-6. Importantly, the combination of hs-CRP and serum miR-145 gained a better sensitivity/spectivity for prediction of acute ischemia stroke (area under receiver operating characteristic curve from 0.794 to 0.896). Conclusively, our preliminary findings indicate that serum miR-145 upregulated in acute ischemic stroke might be a new biomarker for acute ischemia stroke evaluation.

MiR-335 Regulates Hif-1α to Reduce Cell Death in Both Mouse Cell Line and Rat Ischemic Models

Hypoxia inducible factor-1α facilitates cellular adaptation to hypoxic conditions. Hence its tight regulation is crucial in hypoxia related diseases such as cerebral ischemia. Changes in hypoxia inducible factor-1α expression upon cerebral ischemia influence the expression of its downstream genes which eventually determines the extent of cellular damage. MicroRNAs are endogenous regulators of gene expression that have rapidly emerged as promising therapeutic targets in several diseases. In this study, we have identified miR-335 as a direct regulator of hypoxia inducible factor-1α and as a potential therapeutic target in cerebral ischemia. MiR-335 and hypoxia inducible factor-1α mRNA showed an inverse expression profile, both in vivo and in vitro ischemic conditions. Given the biphasic nature of hypoxia inducible factor-1α expression during cerebral ischemia, miR-335 mimic was found to reduce infarct volume in the early time (immediately after middle cerebral artery occlusion) of embolic stroke animal models while the miR-335 inhibitor appears to be beneficial at the late time of stroke (24 hrs after middle cerebral artery occlusion). Modulation of hypoxia inducible factor-1α expression by miR-335 also influenced the expression of crucial genes implicated in neurovascular permeability, cell death and maintenance of the blood brain barrier. These concerted effects, resulting in a reduction in infarct volume bring about a beneficial outcome in ischemic stroke.

Circulating MicroRNAs: Potential and Emerging Biomarkers for Diagnosis of Cardiovascular and Cerebrovascular Diseases

MicroRNAs (miRNAs) are composed of a group of endogenous and noncoding small RNAs which control expression of complementary target mRNAs. The extended functions of miRNAs enhance the complexity of gene-regulatory processes in cardiovascular and cerebrovascular diseases. Indeed, recent studies have shown that miRNAs are closely related to myocardial infarction, heart failure, atrial fibrillation, cardiomyopathy, hypertension, angiogenesis, coronary artery disease, dyslipidaemia, stroke, and so forth. These findings suggest a new therapeutic pointcut for cardiovascular and cerebrovascular diseases and show the extensive therapeutic potential of miRNA regulation. Moreover, it has been shown that circulating extracellular miRNAs are stable in bodily fluids, which indicates circulating miRNAs as potential and emerging biomarkers for noninvasive diagnosis. This review highlights the most recent findings indicative of circulating miRNAs as potential clinical biomarkers for diagnosis of cardiovascular and cerebrovascular diseases.

Elevated plasma CaM expression in patients with acute cerebral infarction predicts poor outcomes and is inversely associated with miR-26b expression

BACKGROUND

Calcium overload plays an important role in ischemia/reperfusion injury during ischemic brain damage and is mediated by calmodulin (CaM). However, the understanding of the regulatory mechanisms of CaM expression at the gene level is limited. The expression levels of miR-26b change significantly during ACI, and bioinformatic analyses predict that miR-26b would be a potential regulator of calmodulin (CALM1) mRNA. This study aimed to determine the expression of miR-26b and CaM in the plasma of patients with ACI and investigate the impact of miR-26b on CALM1 expression.

METHODS

CaM and miR-26b expression analyses from the plasma of patients with ACI and normal controls were performed using ELISA and qRT-PCR, respectively. Correlations between CaM, miR-26b, and NIHSS scores were analyzed. Then, miR-26b mimics and inhibitors were transfected into HUVE cell lines via lipofectamine. CALM1 mRNA expression in HUVECs was detected by RT-PCR, and the protein levels were detected by Western blot.

RESULTS

Plasma CaM expression in patients with ACI was significantly higher when compared with normal controls, and miR-26b expression was significantly lower. The plasma levels of CaM and miR-26b were correlated with the NIHSS scores in ACI patients. miR-26b modulated CALM1 in vitro. The transfected miR-26b mimic and inhibitor significantly altered the expression of CALM1/CAM at the mRNA and protein levels in cultured HUVECs.

CONCLUSIONS

CaM might be a potential novel blood marker in patients with ACI. miR-26b targeted CALM1 and affected the expression of CaM at the post-transcriptional level, which likely contributed to the progression of ACI brain injury.

An updated role of microRNA-124 in central nervous system disorders: a review

MicroRNA-124 (miR-124) is the most abundant miRNA in the brain. Biogenesis of miR-124 displays specific temporal and spatial profiles in various cell and tissue types and affects a broad spectrum of biological functions in the central nervous system (CNS). Recently, the link between dysregulation of miR-124 and CNS disorders, such as neurodegeneration, CNS stress, neuroimmune disorders, stroke, and brain tumors, has become evident. Here, we provide an overview of the specific molecular function of miR-124 in the CNS and a revealing insight for the therapeutic potential of miR-124 in the treatment of human CNS diseases.

Long noncoding RNA SPRY4-IT1 predicts poor patient prognosis and promotes tumorigenesis in gastric cancer

Gastric cancer (GC) is the second common cause of cancer-related death worldwide. Long noncoding RNAs (lncRNAs) are emerging as novel regulators in the cancer paradigm. However, investigation of lncRNAs on GC is still in its infancy. In this study, we focused on lncRNA SPRY4 intronic transcript 1 (SPRY4-IT1) and investigated its expression pattern, clinical significance, biological function, and molecular mechanism in GC. SPRY4-IT1 expression was examined, and its correlation with clinicopathological characteristics and patient prognosis was analyzed. A series of assays were performed to understand the role of SPRY4-IT1 in GC. SPRY4-IT1 expression was elevated in GC tissues and cell lines, and SPRY4-IT1 levels were highly positively correlated with tumor size, invasion depth, distant metastasis, TNM stage, and reduced overall survival (OS) and disease-free survival (DFS). A multivariate analysis showed that SPRY4-IT1 expression is an independent prognostic factor of OS and DFS in patients with GC. Additionally, the results of in vitro assays showed that the suppression of SPRY4-IT1 expression in GC cell line MKN-45 significantly reduced cell proliferation, colony formation, and cell migration/invasion. Moreover, the tumorigenic effects of SPRY4-IT1 were partially mediated by the regulation of certain cyclins and matrix metalloproteinases (MMPs)-related genes. Our data suggest that SPRY4-IT1 plays a critical role in GC tumorigenesis and may represent a novel prognostic marker and potential therapeutic target in patients with GC.

Sexual dimorphism in miR-210 expression and mitochondrial dysfunction in the placenta with maternal obesity

BACKGROUND

Maternal obesity is a major problem in obstetrics, and the placenta is involved in obesity-related complications via its roles at the maternal-fetal interface. We have recently shown a causative role for micro(mi)RNA-210, a so called 'hypoxamir' regulated by HIF-1α, in mitochondrial dysfunction in placentas from women with preeclampsia. We also reported mitochondrial dysfunction in placentas with maternal obesity. Here we hypothesized that expression of miR-210 is dysregulated in the placentas with obesity.

METHODS

Placentas from uncomplicated pregnancies were collected at term from healthy weight or control (CTRL, pre-pregnancy body mass index (BMI)<25), overweight (OW, BMI=25-24.9) and obese (OB, BMI>30) women following C-section with no labor. Expression of miRNA-210 and its target genes was measured by reverse transcription-PCR and Western Blot, respectively. Mitochondrial respiration was assessed by Seahorse Analyzer in syncytiotrophoblast (ST) 72 h after cytotrophoblast isolation.

RESULTS

Expression of miR-210 was significantly increased in placentas of OB and OW women with female but not male fetuses compared with CTRL placentas of females. However, expression of HIF-1α in these placentas remained unchanged. Levels of tumor-necrosis factor-alpha (TNFα) were increased in OW and OB placentas of females but not males, and in silico analysis suggested that activation of miR-210 expression in these placentas might be activated by NFκB1 (p50) signaling. Indeed, chromatin Immunoprecipitation assay showed that NFkB1 binds to placental miR-210 promoter in a fetal sex-dependent manner. Female but not male STs treated with TNFα showed overexpression of miR-210, reduction of mitochondrial target genes and decreased mitochondrial respiration. Pre-treatment of these STs with small interfering RNA to NFkB1 or antagomiR-210 prevented the TNFα-mediated inhibition of mitochondrial respiration.

CONCLUSIONS

Our data suggest that the inflammatory intrauterine environment associated with maternal obesity induces an NFκB1-mediated increase in miR-210 in a fetal sex-dependent manner, leading to inhibition of mitochondrial respiration and placental dysfunction in the placentas of female fetuses.

Effect of sex and age interactions on functional outcome after stroke

Stroke is one of the leading causes of death and disability worldwide. Experimental and clinical studies showed that sex and age play an important role in deciding the outcome after stroke. At younger ages, males were shown to have a higher risk for stroke than females. However, this trend reverses in older ages particularly when females reach menopause. Many preclinical studies indicate that steroid hormones modulate the age-dependent differential stroke outcome. In addition, patterns of cell death pathways activated following cerebral ischemia are distinct between males and females, but independent of steroid hormones. Recent studies also indicate that microRNAs play important roles in mediating sex-specific stroke outcome by regulating stroke-related genes. This review discusses the contribution of sex and age to outcome after stroke with particular emphasis on the experimental studies that examined the effects of steroid hormones, differential cell death pathways, and involvement of sex-specific microRNAs following cerebral ischemia. Current understanding of the role of thrombolytic agents in stroke therapy is also discussed.

Identification of circulating microRNAs as potential biomarkers for detecting acute ischemic stroke

MicroRNAs (miRNAs) are present in serum and have the potential to serve as disease biomarkers. As such, it is important to explore the clinical value of miRNAs in serum as biomarkers for ischemic stroke (IS) and cast light on the pathogenesis of IS. In this study, we screened differentially expressed serum miRNAs from IS and normal people by miRNA microarray analysis, and validated the expression of candidate miRNAs using quantitative reverse-transcriptase polymerase chain reaction assays. Furthermore, we performed gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analyses to disclose functional enrichment of genes predicted to be regulated by the differentially expressed miRNAs. Notably, our results revealed that 115 miRNAs were differentially expressed in IS, among which miR-32-3p, miR-106-5p, and miR-532-5p were first found to be associated with IS. In addition, GO and KEGG pathway analyses showed that genes predicted to be regulated by differentially expressed miRNAs were significantly enriched in several related biological process and pathways, including axon guidance, glioma, MAPK signaling, mammalian target of rapamycin signaling, and ErbB-signaling pathway. In conclusion, we identified the changed expression pattern of miRNAs in IS. Serum miR-32-3p, miR-106-5p, miR-1246, and miR-532-5p may serve as potential diagnostic biomarkers for IS. Our results also demonstrate a novel role for miRNAs in the pathogenesis of IS.

Epigenetic impact of curcumin on stroke prevention

The epigenetic impact of curcumin in stroke and neurodegenerative disorders is curiosity-arousing. It is derived from Curcuma longa (spice), possesses anti-oxidative, anti-inflammatory, anti-lipidemic, neuro-protective and recently shown to exhibit epigenetic modulatory properties. Epigenetic studies include DNA methylation, histone modifications and RNA-based mechanisms which regulate gene expression without altering nucleotide sequences. Curcumin has been shown to affect cancer by altering epigenetic changes but its role as an epigenetic agent in cerebral stroke has not been much explored. Although curcumin possesses remarkable medicinal properties, the bioavailability of curcumin has limited its success in epigenetic studies and clinical trials. The present review is therefore designed to look into epigenetic mechanisms that could be induced with curcumin during stroke, along with its molecular designing with different moieties that may increase its bioavailability. Curcumin has been shown to be encapsulated in exosomes, nano-vesicles (<200 nm), thereby showing its therapeutic effects in brain diseases. Curcumin delivered through nanoparticles has been shown to be neuroregenerative but the use of nanoparticles in brain has limitations. Hence, curcumin-encapsulated exosomes along with curcumin-primed exosomes (exosomes released by curcumin-treated cells) are much needed to be explored to broadly look into their use as a novel therapy for stroke.

Non-Coding RNAs in Stroke and Neuroprotection

This review will focus on the current state of knowledge regarding non-coding RNAs (ncRNA) in stroke and neuroprotection. There will be a brief introduction to microRNAs (miRNA), long ncRNAs (lncRNA), and piwi-interacting RNAs (piRNA), followed by evidence for the regulation of ncRNAs in ischemia. This review will also discuss the effect of neuroprotection induced by a sublethal duration of ischemia or other stimuli given before a stroke (preconditioning) on miRNA expression and the role of miRNAs in preconditioning-induced neuroprotection. Experimental manipulation of miRNAs and/or their targets to induce pre- or post-stroke protection will also be presented, as well as discussion on miRNA responses to current post-stroke therapies. This review will conclude with a brief discussion of future directions for ncRNAs studies in stroke, such as new approaches to model complex ncRNA datasets, challenges in ncRNA studies, and the impact of extracellular RNAs on human diseases such as stroke.

Expression profiles of microRNAs after focal cerebral ischemia/reperfusion injury in rats

Rat models of focal cerebral ischemia/reperfusion injury were established by occlusion of the middle cerebral artery. Microarray analysis showed that 24 hours after cerebral ischemia, there were nine up-regulated and 27 down-regulated microRNA genes in cortical tissue. Bioinformatic analysis showed that bcl-2 was the target gene of microRNA-384-5p and microRNA-494, and caspase-3 was the target gene of microRNA-129, microRNA-320 and microRNA-326. Real-time PCR and western blot analyses showed that 24 hours after cerebral ischemia, bcl-2 mRNA and protein levels in brain tissue were significantly decreased, while caspase-3 mRNA and protein levels were significantly increased. This suggests that following cerebral ischemia, differentially expressed microRNA-384-5p, microRNA-494, microRNA-320, microRNA-129 and microRNA-326 can regulate bcl-2 and caspase-3 expression in brain tissue.

Regulation of microRNAs miR-30a and miR-143 in cerebral vasculature after experimental subarachnoid hemorrhage in rats

BACKGROUND

microRNAs (miRNAs) are important regulators of translation and have been implicated in the pathogenesis of a number of cardiovascular diseases, including stroke, and suggested as possible prognostic biomarkers. Our aim was to identify miRNAs that are differentially regulated in cerebral arteries after subarachnoid hemorrhage (SAH), using a rat injection model of SAH and a qPCR-based screen of 728 rat miRNAs. Additionally, serum was analyzed for a possible spill-over to the circulation of regulated miRNAs from the vessel walls.

RESULTS

We identified 482 different miRNAs expressed in cerebral arteries post-SAH. Two miRNAs, miR-30a and miR-143, were significantly upregulated in cerebral arteries after SAH when compared to sham-operated animals. However, none of these exhibited significantly altered serum levels after SAH versus post-sham surgery. The most robust upregulation was seen for miR-143, which has several predicted targets and is a strong regulator of vascular morphology. We hypothesize that miR-30a and miR-143 may play a role in the vascular wall changes seen after SAH.

CONCLUSIONS

We report that miR-30a and miR-143 in the cerebral arteries show significant changes over time after SAH, but do not differ from sham-operated rats at 24 h post-SAH. Although this finding suggests interesting novel possible mechanisms involved in post-SAH cerebrovascular changes, the lack of regulation of these miRNAs in serum excludes their use as blood-borne biomarkers for cerebrovascular changes following SAH.

MicroRNAs: new biomarkers and therapeutic targets after cardiac arrest?

Despite advances in resuscitation medicine, including target temperature management as part of post-cardiac arrest care, many patients will have a poor neurological outcome, most often resulting in death. It is a commonly held belief that the ability to prognosticate outcome at an early stage after cardiac arrest would allow subsequent health care delivery to be tailored to individual patients. However, currently available predictive methods and biomarkers lack sufficient accuracy and therefore cannot be generally recommended in clinical practice. MicroRNAs have recently emerged as potential biomarkers of cardiovascular diseases. While the biomarker value of microRNAs for myocardial infarction or heart failure has been extensively studied, less attention has been devoted to their prognostic value after cardiac arrest. This review highlights the recent discoveries suggesting that microRNAs may be useful both to predict outcome and to treat patients after cardiac arrest.

Time-dependent profiles of microRNA expression induced by ischemic preconditioning in the gerbil hippocampus

MicroRNAs (miRNAs) are critically important in both normal neuronal development and neurological diseases. Although cerebral ischemia has been shown to alter the miRNA profiles of rats, the role of miRNA in the cornu ammonis 1 region of the gerbil hippocampus under ischemic tolerance has not been studied. In the present study, Mongolian gerbils were subjected to one or three times the nonlethal dose of 2-min transient common carotid artery occlusion (tCCAO). miRNA microarray technology detected 251 miRNAs and the expression of seven of these in terms of ischemic tolerance. They were compared at different time points: 1 day, 7 days, 1 month, and 6 months. mmu-miR-15a-5p, related to neurogenesis, showed increased expression after one dose of 2-min tCCAO and was much higher after three doses. An increase in sha-miR-24 and oan-let-7b-3p, related to transactivation response DNA-binding protein (TDP43), was observed after one dose of 2-min tCCAO, but the peak was accelerated to an earlier period of reperfusion after three doses. In contrast, mmu-miR-125b-5p and mmu-miR-132-5p, related to fused in sarcoma/translocated in liposarcoma (FUS/TLS), showed similar increases at both doses. mmu-miR-181c-5p and mmu-miR-378a-5p, related to heat shock protein 70 (HSP70), also showed accelerated expression after three doses. This data set provides new insight about miRNA expression during neurogenesis, and related to TDP43, FUS/TLS, and HSP70, which may be useful when pursuing further studies on the possible use of miRNAs as biomarkers in cerebral ischemic tolerance and neuroregeneration.

The use of microRNAs to modulate redox and immune response to stroke

SIGNIFICANCE

Cerebral ischemia is a major cause of death and disability throughout the world, yet therapeutic options remain limited. The interplay between the cellular redox state and the immune response plays a critical role in determining the extent of neural cell injury after ischemia and reperfusion. Excessive amounts of reactive oxygen species (ROS) generated by mitochondria and other sources act both as triggers and effectors of inflammation. This review will focus on the interplay between these two mechanisms.

RECENT ADVANCES

MicroRNAs (miRNAs) are important post-transcriptional regulators that interact with multiple target messenger RNAs coordinately regulating target genes, including those involved in controlling mitochondrial function, redox state, and inflammatory pathways. This review will focus on the regulation of mitochondria, ROS, and inflammation by miRNAs in the chain of deleterious intra- and intercellular events that lead to brain cell death after cerebral ischemia.

CRITICAL ISSUES

Although pretreatment using miRNAs was effective in cerebral ischemia in rodents, testing treatment after the onset of ischemia is an essential next step in the development of acute stroke treatment. In addition, miRNA formulation and delivery into the CNS remain a challenge in the clinical translation of miRNA therapy.

FUTURE DIRECTIONS

Future research should focus on post-treatment and potential clinical use of miRNAs.

Angiogenesis-regulating microRNAs and Ischemic Stroke

Stroke is a leading cause of death and disability worldwide. Ischemic stroke is the dominant subtype of stroke and results from focal cerebral ischemia due to occlusion of major cerebral arteries. Thus, the restoration or improvement of reduced regional cerebral blood supply in a timely manner is very critical for improving stroke outcomes and poststroke functional recovery. The recovery from ischemic stroke largely relies on appropriate restoration of blood flow via angiogenesis. Newly formed vessels would allow increased cerebral blood flow, thus increasing the amount of oxygen and nutrients delivered to affected brain tissue. Angiogenesis is strictly controlled by many key angiogenic factors in the central nervous system, and these molecules have been well-documented to play an important role in the development of angiogenesis in response to various pathological conditions. Promoting angiogenesis via various approaches that target angiogenic factors appears to be a useful treatment for experimental ischemic stroke. Most recently, microRNAs (miRs) have been identified as negative regulators of gene expression in a post-transcriptional manner. Accumulating studies have demonstrated that miRs are essential determinants of vascular endothelial cell biology/angiogenesis as well as contributors to stroke pathogenesis. In this review, we summarize the knowledge of stroke-associated angiogenic modulators, as well as the role and molecular mechanisms of stroke-associated miRs with a focus on angiogenesis-regulating miRs. Moreover, we further discuss their potential impact on miR-based therapeutics in stroke through targeting and enhancing post-ischemic angiogenesis.

microRNAs in Cerebrovascular Disease

Cardiovascular diseases are major causes of morbidity and mortality in developed countries. Cerebrovascular diseases, especially stroke, represent major burden of disability and economy impact. Major advances in primary and secondary prevention and therapy are needed in order to tackle this public health problem. Our better understanding of pathophysiology is essential in order to develop novel diagnostic and therapeutic tools and strategies. microRNAs are a family of important post-transcriptional regulators of gene expression and their involvement in the pathophysiology of cerebrovascular diseases has already been reported. Moreover, microRNAs may represent above-mentioned potential diagnostic and therapeutic tools in clinical practice. Within this chapter, we briefly describe basic epidemiology, aetiology and clinical manifestation of following cerebrovascular diseases: extracranial carotid atherosclerosis, acute stroke, intracranial aneurysms and cerebral arterio-venous malformations. Further, in each chapter, the current knowledge about the involvement of specific microRNAs and their potential use in clinical practice will be summarized. More specifically, within the subchapter "miRNAs in carotid atherosclerosis", general information about miRNA involvement in atherosclerosis will be described (miR-126, miR-17-92, miR-155 and others) with special emphasis put on miRNAs affecting carotid plaque progression and stability (e.g. miR-145, miR-146 or miR-217). In the subchapter "miRNAs in acute stroke", we will provide insight into recent knowledge from animal and human studies concerning miRNA profiling in acute stroke and their expression dynamics in brain tissue and extracellular fluids (roles of, e.g. let-7 family, miR-21, miR-29 family, miR-124, miR-145, miR-181 family, miR-210 and miR-223). Subchapters dealing with "miRNAs and AV malformations" and "miRNAs and intracranial aneurysms" will focus on miR-21, miR-26, miR-29 family and miR-143/145.

Circulating microRNAs as Biomarkers in Cardiovascular Diseases

MicroRNAs, key regulators of biological processes, are involved in the pathophysiological mechanisms underlying human diseases, including cardiovascular diseases. Their recent discovery revealed a previously unknown layer of pathophysiologic regulators, which also play a key role in the regulation of several aspects of cardiovascular diseases. More recently, it was demonstrated that circulating microRNAs can be measured in the blood. Hence, the potential use of microRNAs as disease biomarkers attracted many research groups. Indeed, their unusual stability in the bloodstream and during prolonged storage make circulating miRs very interesting as potential biomarkers. Circulating microRNAs are emerging as the next generation "smart" biomarkers and could be helpful in further improving the diagnostic and therapeutic processes of cardiovascular diseases. The present chapter summarizes the most relevant experimental evidence on circulating microRNAs in cardiovascular diseases, including arterial remodeling, restenosis, coronary artery disease, acute coronary syndromes, hypertension, heart failure, and ischemic stroke, highlighting potential pathophysiological correlations to the mechanisms underlying cardiovascular diseases.

MicroRNA-424 protects against focal cerebral ischemia and reperfusion injury in mice by suppressing oxidative stress

BACKGROUND AND PURPOSE

We previously showed that the microRNA miR-424 protects against permanent cerebral ischemic injury in mice by suppressing microglia activation. This study investigated the role of miR-424 in transient cerebral ischemia in mice with a focus on oxidative stress-induced neuronal injury.

METHODS

Transient cerebral ischemia was induced in C57/BL6 mice by middle cerebral artery occlusion for 1 hour followed by reperfusion (ischemia/reperfusion). The miR-424 level in the peri-infarct cortex was quantified. Mice were also administered miR-424 angomir by intracerebroventricular injection. Cerebral infarct volume, neuronal apoptosis, and levels of oxidative stress markers and antioxidants were evaluated. In an in vitro experiment, primary cortical neurons were exposed to H2O2 and treated with miR-424 angomir, nuclear factor erythroid 2-related factor 2 siRNA, and superoxide dismutase (SOD) inhibitor; cell activity, lactate dehydrogenase release, malondialdehyde level, and manganese (Mn)SOD activity were then evaluated.

RESULTS

MiR-424 levels in the peri-infarct cortex increased at 1 and 4 hours then decreased 24 hours after reperfusion. Treatment with miR-424 decreased infarct volume and inhibited neuronal apoptosis after ischemia/reperfusion, reduced reactive oxygen species and malondialdehyde levels in the cortex, and increased the expression and activation of MnSOD as well as the expression of extracellular SOD and the redox-sensitive transcription factor nuclear factor erythroid 2-related factor. In neuronal cultures, miR-424 treatment abrogated H2O2-induced injury, as evidenced by decreased lactate dehydrogenase leakage and malondialdehyde level and increased cell viability and MnSOD activity; the protective effects of miR-424 against oxidative stress were reversed by nuclear factor erythroid 2-related factor knockdown and SOD inhibitor treatment.

CONCLUSIONS

MiR-424 protects against transient cerebral ischemia/reperfusion injury by inhibiting oxidative stress.

Rapid regulation of microRNA following induction of long-term potentiation in vivo

Coordinated regulation of gene expression is essential for consolidation of the memory mechanism, long-term potentiation (LTP). Triggering of LTP by N-methyl-D-aspartate receptor (NMDAR) activation rapidly activates constitutive and inducible transcription factors, which promote expression of genes responsible for LTP maintenance. As microRNA (miRNA) coordinate expression of genes related through seed sites, we hypothesize that miRNA contribute to the regulation of the LTP-induced gene response. MiRNA function primarily as negative regulators of gene expression. As LTP induction promotes a generalized rapid up-regulation of gene expression, we predicted a complementary rapid down-regulation of miRNA levels. Accordingly, we carried out global miRNA expression profiling in the rat dentate gyrus 20 min post-LTP induction in vivo. Consistent with our hypothesis, we found a large number of differentially expressed miRNA, the majority down-regulated. Detailed analysis of miR-34a-5p and miR-132-3p revealed this down-regulation was transient and NMDAR-dependent, whereby block of NMDARs released an activity-associated inhibitory mechanism. Furthermore, down-regulation of mature miR-34a-5p and miR-132-3p occurred solely by post-transcriptional mechanisms, occurring despite an associated up-regulation of the pri-miR-132 transcript. To understand how down-regulation of miR-34a-5p and miR-132-3p intersects with the molecular events occurring following LTP, we used bioinformatics to identify potential targets. Previously validated targets included the key LTP-regulated genes Arc and glutamate receptor subunits. Predicted targets included the LTP-linked kinase, Mapk1, and neuropil-associated transcripts Hn1 and Klhl11, which were validated using luciferase reporter assays. Furthermore, we found that the level of p42-Mapk1, the protein encoded by the Mapk1 transcript, was up-regulated following LTP. Together, these data support the interpretation that miRNA, in particular miR-34a-5p and miR-132-3p, make a surprisingly rapid contribution to synaptic plasticity via dis-inhibition of translation of key plasticity-related molecules.

Transcriptional profiling reveals that C5a alters microRNA in brain endothelial cells

Blood-brain barrier (BBB) disturbance is a crucial occurrence in many neurological diseases, including systemic lupus erythematosus (SLE). Our previous studies showed that experimental lupus serum altered the integrity of the mouse brain endothelial layer, an important constituent of the BBB. Complement activation occurs in lupus with increased circulating complement components. Using a genomics approach, we identified the microRNA (miRNA) altered in mouse brain endothelial cells (bEnd3) by lupus serum and the complement protein, C5a. Of the 318 miRNA evaluated, 23 miRNAs were altered by lupus serum and 32 were altered by C5a alone compared with controls. Seven miRNAs (P < 0 · 05) were differentially expressed by both treatments: mmu-miR-133a*, mmu-miR-193*, mmu-miR-26b, mmu-miR-28*, mmu-miR-320a, mmu-miR-423-3p and mmu-miR-509-5p. The microarray results were validated by quantitative RT-PCR. In line with the in vitro results, expression of miR-26b and miR-28* were also significantly up-regulated in lupus mouse brain which was reduced by C5a receptor inhibition. Target prediction analysis revealed miR gene targets encoding components involved in inflammation, matrix arrangement, and apoptosis, pathways known to play important roles in central nervous system lupus. Our findings suggest that the miRNAs reported in this study may represent novel therapeutic targets in central nervous system lupus and other similar neuroinflammatory settings.