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

Epigenetic Promoter DNA Methylation of miR-124 Promotes HIV-1 Tat-Mediated Microglial Activation via MECP2-STAT3 Axis

The present study demonstrates HIV-1 Tat-mediated epigenetic downregulation of microglial miR-124 and its association with microglial activation. Exposure of mouse primary microglia isolated from newborn pups of either sex to HIV-1 Tat resulted in decreased expression of primary miR-124-1, primary miR-124-2 as well as the mature miR-124. In parallel, HIV-1 Tat exposure to mouse primary microglial cells resulted in increased expression of DNA methylation enzymes, such as DNMT1, DNMT3A, and DNMT3B, which were also accompanied by increased global DNA methylation. Bisulfite-converted genomic DNA sequencing in the HIV-1 Tat-exposed mouse primary microglial cells further confirmed increased DNA methylation of the primary miR-124-1 and primary miR-124-2 promoters. Bioinformatic analyses identified MECP2 as a novel 3'-UTR target of miR-124. This was further validated in mouse primary microglial cells wherein HIV-1 Tat-mediated downregulation of miR-124 resulted in increased expression of MECP2, leading in turn to further repression of miR-124 via the feedback loop. In addition to MECP2, miR-124 also modulated the levels of STAT3 through its binding to the 3'-UTR, leading to microglial activation. Luciferase assays and Ago2 immunoprecipitation determined the direct binding between miR-124 and 3'-UTR of both MECP2 and STAT3. Gene silencing of MECP2 and DNMT1 and overexpression of miR-124 blocked HIV-1 Tat-mediated downregulation of miR-124 and microglial activation. In vitro findings were also confirmed in the basal ganglia of SIV-infected rhesus macaques (both sexes). In summary, our findings demonstrate a novel mechanism of HIV-1 Tat-mediated activation of microglia via downregulation of miR-124, leading ultimately to increased MECP2 and STAT3 signaling.SIGNIFICANCE STATEMENT Despite the effectiveness of combination antiretroviral therapy in controlling viremia, the CNS continues to harbor viral reservoirs. The persistence of low-level virus replication leads to the accumulation of early viral proteins, including HIV-1 Tat protein. Understanding the epigenetic/molecular mechanism(s) by which viral proteins, such as HIV-1 Tat, can activate microglia is thus of paramount importance. This study demonstrated that HIV-1 Tat-mediated DNA methylation of the miR-124 promoter leads to its downregulation with a concomitant upregulation of the MECP2-STAT3-IL6, resulting in microglial activation. These findings reveal an unexplored epigenetic/molecular mechanism(s) underlying HIV-1 Tat-mediated microglial activation, thereby providing a potential target for the development of therapeutics aimed at ameliorating microglial activation and neuroinflammation in the context of HIV-1 infection.

Investigation of candidate long noncoding RNAs and messenger RNAs in the immediate phase of spinal cord injury based on gene expression profiles

Spinal cord injury (SCI) is a serious devastating condition and it has a high mortality rate and morbidity rate. The early pathological changes in the immediate phase of SCI may play a major part in the development of secondary injury. Alterations in the expression of many long noncoding RNAs (lncRNAs) have been shown to play fundamental roles in the diseases of the central nervous system. However, the roles of lncRNAs and messenger RNAs (mRNAs) in the immediate phase of SCI are not clear. We examined the expression of mRNAs and lncRNAs in a rat model at 2 h after SCI and identified the differentially expressed lncRNAs (DE lncRNAs) and differentially expressed mRNAs (DE mRNAs) using microarray analysis. 772 DE lncRNAs and 992 DE mRNAs were identified in spinal cord samples in the immediate phase following SCI compared with control samples. Moreover, Gene Ontology (GO) term annotation results showed that CXCR chemokine receptor binding, neutrophil apoptotic process, neutrophil migration, neutrophil extravasation, macrophage differentiation, monocyte chemotaxis and cellular response to interleukin-1 (IL-1) were the main significantly enriched GO terms. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEGs were enriched in toll-like receptor signaling pathway, p53 signaling pathway, MAPK signaling pathway and Jak-STAT signaling pathway. IL6, MBOAT4, FOS, TNF, JUN, STAT3, CSF2, MYC, CCL2 and FGF2 were the top 10 high-degree hub nodes and may be important targets in the immediate phase of SCI. The current study on provides novel insights into how lncRNAs and mRNAs regulate the pathogenesis of the immediate phase after SCI.

The emerging role of long non-coding RNA in spinal cord injury

Spinal cord injury (SCI) is a significant health burden worldwide which causes permanent neurological deficits, and there are approximately 17,000 new cases each year. However, there are no effective and current treatments that lead to functional recovery because of the limited understanding of the pathogenic mechanism of SCI. In recent years, the biological roles of long non-coding RNAs (lncRNAs) in SCI have attracted great attention from the researchers all over the world, and an increasing number of studies have investigated the regulatory roles of lncRNAs in SCI. In this review, we summarized the biogenesis, classification and function of lncRNAs and focused on the investigations on the roles of lncRNAs involved in the pathogenic processes of SCI, including neuronal loss, astrocyte proliferation and activation, demyelination, microglia activation, inflammatory reaction and angiogenesis. This review will help understand the molecular mechanisms of SCI and facilitate the potential use of lncRNAs as diagnostic markers and therapeutic targets for SCI treatment.

Transcriptome analysis of adherens junction pathway-related genes after peripheral nerve injury

The neural regeneration process is driven by a wide range of molecules and pathways. Adherens junctions are critical cellular junctions for the integrity of peripheral nerves. However, few studies have systematically characterized the transcript changes in the adherens junction pathway following injury. In this study, a rat model of sciatic nerve crush injury was established by forceps. Deep sequencing data were analyzed using comprehensive transcriptome analysis at 0, 1, 4, 7, and 14 days after injury. Results showed that most individual molecules in the adherens junctions were either upregulated or downregulated after nerve injury. The mRNA expression of ARPC1B, ARPC3, TUBA8, TUBA1C, CTNNA2, ACTN3, MET, HGF, NME1 and ARF6, which are involved in the adherens junction pathway and in remodeling of adherens junctions, was analyzed using quantitative real-time polymerase chain reaction. Most of these genes were upregulated in the sciatic nerve stump following peripheral nerve injury, except for CTNNA2, which was downregulated. Our findings reveal the dynamic changes of key molecules in adherens junctions and in remodeling of adherens junctions. These key genes provide a reference for the selection of clinical therapeutic targets for peripheral nerve injury.

Deep Sequencing Reveals the Significant Involvement of cAMP-Related Signaling Pathways Following Sciatic Nerve Crush

Peripheral nerve injury and regeneration is a complex biological process jointly mediated by numerous factors. Cyclic adenosine monophosphate (cAMP) modifies the cellular behaviors of neurons and Schwann cells, and thus may contribute to peripheral nerve regeneration. Despite the importance of cAMP, the temporal and spatial expressions of genes involved in cAMP-related signaling pathways during peripheral nerve regeneration remain unclear. In the current study, by using rat sciatic nerve crush model, we analyzed previously obtained RNA deep sequencing data, explored the significance of cAMP-mediated signaling pathway and protein kinase A (PKA) signaling pathway after peripheral nerve injury, and examined the expression patterns of genes involved in these cAMP-related signaling pathways. Our results, from the genetic aspect, emphasized the critical involvement of cAMP-related signaling pathways, identified the dynamic changes of some key signaling cascades, and may help the discovery of potential therapeutic targets for peripheral nerve repair and regeneration.

Analysis of temporal expression profiles after sciatic nerve injury by bioinformatic method

After Peripheral nerve injuries (PNI), many complicated pathophysiologic processes will happen. A global view of functional changes following PNI is essential for the looking for the adequate therapeutic approaches. In this study, we performed an in-depth analysis on the temporal expression profiles after sciatic nerve injury by bioinformatic methods, including (1) cluster analysis of the samples; (2) identification of gene co-expression modules(CEMs) correlated with the time points; (3) analysis of differentially expressed genes at each time point (DEGs-ET); (4) analysis of differentially expressed genes varying over time (DEGs-OT); (5) creating Pairwise Correlation Plot for the samples; (6) Time Series Regression Analysis; (7) Determining the pathway, GO (gene ontology) and drug by enrichment analysis. We found that at a 3 h "window period" some specific gene expression may exist after PNI, and responses to lipopolysaccharide (LPS) and TNF signaling pathway may play important roles, suggesting that the inflammatory microenvironment exists after PNI. We also found that troglitazone was closely associated with the change of gene expression after PNI. Therefore, the further evaluation of the precise mechanism of troglitazone on PNI is needed and it may contribute to the development of new drugs for patients with PNI.

[Yiqihuoxue prescription promotes nerve regeneration by miR-124-mediated regulation of Wnt signaling in rats]

OBJECTIVE

To investigate the effect of Yiqihuoxue prescription (NLXT) on nerve regeneration in MCAO-R rat models of qi deficiency and blood stasis syndrome and explore the underlying mechanisms.

METHODS

The rats were randomized into 4 groups, namely the control group, model group, NLXT group and TXL group. The rats in NLXT group and TXL group were treated with gavage of NLXT and TXL solutions, respectively. The NFDS, QDSS and BSSS of the rats were evaluated. The regional cerebral blood flow (rCBF) were dynamically monitored with laser Doppler scanning, and the volume of cerebral infarction was detected with TTC-dye; the expression levels of nestin and BrdU were assayed with immunohistochemistry and mmunofluorescent staining. The expressions of miRNA-124, Wnt3a, GSK3β and β-catenin in the rat brain tissue were detected with PCR or Western blotting.

RESULTS

NLXT and TXL both improved the neurological functions of the model rats, reduced NFDS, QDSS, and BSSS scores, decreased the volume of cerebral infarction, and promoted the recovery of the rCBF (P<0.01). Nestin and BrdU expression levels were significantly increased in the rat brain tissue in NLXT group and TXL group. NLXT significantly inhibited high expressions of miRNA-124 and Wnt3a in response to stress, and increased β-catenin expression level (P<0.01). NLXT and TXL produced no obvious effect on GSK3β expression in the model rats (P>0.05).

CONCLUSION

NLXT can activate Wnt signaling by affecting miRNA-124 expression to offer neuroprotection and promote nerve regeneration in rats with cerebral ischemia with qi deficiency and blood stasis syndrome.

Trans-resveratrol enriched maternal diet protects the immature hippocampus from perinatal asphyxia in rats

Trans-resveratrol (tRESV), a polyphenol with antioxidant properties, is common in many food sources, hence easily accessible for study as a maternal dietary supplement in perinatal asphyxia (PA). Hypoxic-ischemic encephalopathy secondary to PA affects especially vulnerable brain areas such as hippocampus and is a leading cause of neonatal morbidity. The purpose of this study is to identify new epigenetic mechanisms of brain inflammation and injury related to PA and to explore the benefit of tRESV enriched maternal diet. The hippocampal interleukin 1 beta (IL-1b), tumour necrosis factor alpha (TNFα) and S-100B protein, at 24-48h after 90min of asphyxia were assessed in postnatal day 6 rats whose mothers received either standard or tRESV enriched diet. The expression of non-coding microRNAs miR124, miR132, miR134, miR146 and miR15a as epigenetic markers of hippocampus response to PA was determined 24h post-asphyxia. Our results indicate that neural response to PA could be epigenetically controlled and that tRESV reduces asphyxia-related neuroinflammation and neural injury. Moreover, tRESV could increase, through epigenetic mechanisms, the tolerance to asphyxia, with possible impact on the neuronal maturation. Our data support the neuroprotective quality of tRESV when used as a supplement in the maternal diet on the offspring's outcome in PA.

miR-30c promotes Schwann cell remyelination following peripheral nerve injury

Differential expression of miRNAs occurs in injured proximal nerve stumps and includes miRNAs that are firstly down-regulated and then gradually up-regulated following nerve injury. These miRNAs might be related to a Schwann cell phenotypic switch. miR-30c, as a member of this group, was further investigated in the current study. Sprague-Dawley rats underwent sciatic nerve transection and proximal nerve stumps were collected at 1, 4, 7, 14, 21, and 28 days post injury for analysis. Following sciatic nerve injury, miR-30c was down-regulated, reaching a minimum on day 4, and was then upregulated to normal levels. Schwann cells were isolated from neonatal rat sciatic nerve stumps, then transfected with miR-30c agomir and co-cultured in vitro with dorsal root ganglia. The enhanced expression of miR-30c robustly increased the amount of myelin-associated protein in the co-cultured dorsal root ganglia and Schwann cells. We then modeled sciatic nerve crush injury in vivo in Sprague-Dawley rats and tested the effect of perineural injection of miR-30c agomir on myelin sheath regeneration. Fourteen days after surgery, sciatic nerve stumps were harvested and subjected to immunohistochemistry, western blot analysis, and transmission electron microscopy. The direct injection of miR-30c stimulated the formation of myelin sheath, thus contributing to peripheral nerve regeneration. Overall, our findings indicate that miR-30c can promote Schwann cell myelination following peripheral nerve injury. The functional study of miR-30c will benefit the discovery of new therapeutic targets and the development of new treatment strategies for peripheral nerve regeneration.

Paradigms and mechanisms of inhalational anesthetics mediated neuroprotection against cerebral ischemic stroke

Cerebral ischemic stroke is a leading cause of serious long-term disability and cognitive dysfunction. The high mortality and disability of cerebral ischemic stroke is urging the health providers, including anesthesiologists and other perioperative professioners, to seek effective protective strategies, which are extremely limited, especially for those perioperative patients. Intriguingly, several commonly used inhalational anesthetics are recently suggested to possess neuroprotective effects against cerebral ischemia. This review introduces multiple paradigms of inhalational anesthetic treatments that have been investigated in the setting of cerebral ischemia, such as preconditioning, proconditioning and postconditioning with a variety of inhalational anesthetics. The pleiotropic mechanisms underlying these inhalational anesthetics-afforded neuroprotection against stroke are also discussed in detail, including the common pathways shared by most of the inhalational anesthetic paradigms, such as anti-excitotoxicity, anti-apoptosis and anti-inflammation. There are also distinct mechanisms involved in specific paradigms, such as preserving blood brain barrier integrity, regulating cerebral blood flow and catecholamine release. The ready availability of these inhalational anesthetics bedside and renders them a potentially translatable stroke therapy attracting great efforts for understanding of the underlying mechanisms.

Cocaine-mediated downregulation of microglial miR-124 expression involves promoter DNA methylation

Neuroinflammation plays a critical role in the development of reward-related behavior in cocaine self-administration rodents. Cocaine, one of most commonly abused drugs, has been shown to activate microglia both in vitro and in vivo. Detailed molecular mechanisms underlying cocaine-mediated microglial activation remain poorly understood. microRNAs (miRs) belonging to a class of small noncoding RNA superfamily have been shown to modulate the activation status of microglia. miR-124, one of the microglia-enriched miRs, functions as an anti-inflammatory regulator that maintains microglia in a quiescent state. To date, the possible effects of cocaine on microglial miR-124 levels and the associated underlying mechanisms have not been explored. In the current study, we demonstrated that cocaine exposure decreased miR-124 levels in both BV-2 cells and rat primary microglia. These findings were further validated in vivo, wherein we demonstrated decreased abundance of miR-124 in purified microglia isolated from cocaine-administered mice brains compared with cells from saline administered animals. Molecular mechanisms underlying these effects involved cocaine-mediated increased mRNA and protein expression of DNMTs in microglia. Consistently, cocaine substantially increased promoter DNA methylation levels of miR-124 precursors (pri-miR-124-1 and -2), but not that of pri-miR-124-3, both in vitro and in vivo. In summary, our findings demonstrated that cocaine exposure increased DNA methylation of miR-124 promoter resulting into its downregulation, which, in turn, led to microglial activation. Our results thus implicate that epigenetic modulation of miR-124 could be considered as a potential therapeutic approach to ameliorate microglial activation and, possibly, the development of cocaine addiction.

Changes in the Expression of miR-34a and its Target Genes Following Spinal Cord Injury In Rats

Background

Results from DNA microarray experiments have shown that the expression of miR-34s undergoes significant changes following spinal cord injury (SCI). The present study was designed to detect changes in the expression of miR-34s and its target genes during the acute and sub-acute stages of SCI.

Material/Methods

Luxol fast blue (LFB) staining for myelin was used to observe the differences in the general morphology of the spinal cord after SCI in a contusion model in rats. qPCR was carried out to determine the expression variation of miR-34s and its target genes during the acute and sub-acute stages of SCI. The mimic technique was used to further confirm the regulatory effect of miR-34a on the potential target genes.

Results

The expression level of miR-34a decreased immediately after SCI and persisted for 21 days after SCI. The expression level of miR-34c began decreasing at day 1 after SCI and persisted until day 14. The expression level of miR-34b did not undergo significant change after SCI. The results of double immunofluorescence and in-situ hybridization suggested that miR-34a was highly expressed in spinal cord neurons. Based on our bioinformatics analysis, we postulated that miR-34a might participate in post-SCI cell apoptosis by regulating the target gene Notch1, and likely participated in the inflammatory response and glial scar formation by regulating the candidate genes Csf1r and PDGFRα, respectively. The expression levels of the candidate genes Csf1r and PDGFRα were consistent with Notch1 after SCI. The mimic technique further confirmed the regulatory effect of miR-34a on the aforementioned target genes.

Conclusions

We postulate that miR-34a and miR-34c might participate in multiple aspects of cytobiological activities following SCI. MiR-34a in particular may participate in cell apoptosis, inflammatory response, and glial scar formation by regulating the target gene Notch1 and candidate target genes Csf1r and PDGFRα respectively.

Global analysis of transcriptome in dorsal root ganglia following peripheral nerve injury in rats

Peripheral nervous system has intrinsic regeneration ability after injury, accompanied with the coordination of numerous cells, molecules and signaling pathways. These post-injury biological changes are complex with insufficient understanding. Thus, to obtain a global perspective of changes following nerve injury and to elucidate the mechanisms underlying nerve regeneration are of great importance. By RNA sequencing, we detected transcriptional changes in dorsal root ganglia (DRG) neurons at 0 h, 3 h, 9 h, 1 d, 4 d and 7 d following sciatic nerve crush injury in rats. Differentially expressed genes were then selected and classified into major clusters according to their expression patterns. Cluster 2 (with genes high expressed before 9 h and then down expressed) and cluster 6 (combination of cluster 4 and 5 with genes low expressed before 1 d and then up expressed) were underwent GO annotation and KEGG pathway analysis. Gene act networks were then constructed for these two clusters and the expression of pivotal genes was validated by quantitative real-time PCR. This study provided valuable information regarding the transcriptome changes in DRG neurons following nerve injury, identified potential genes that could be used for improving axon regeneration after nerve injury, and facilitated to elucidate the biological process and molecular mechanisms underlying peripheral nerve injury.

Regulation of Schwann cell proliferation and migration by miR-1 targeting brain-derived neurotrophic factor after peripheral nerve injury

Peripheral nerve injury is a global problem that causes disability and severe socioeconomic burden. Brain-derived neurotrophic factor (BDNF) benefits peripheral nerve regeneration and becomes a promising therapeutic molecule. In the current study, we found that microRNA-1 (miR-1) directly targeted BDNF by binding to its 3'-UTR and caused both mRNA degradation and translation suppression of BDNF. Moreover, miR-1 induced BDNF mRNA degradation primarily through binding to target site 3 rather than target site 1 or 2 of BDNF 3'-UTR. Following rat sciatic nerve injury, a rough inverse correlation was observed between temporal expression profiles of miR-1 and BDNF in the injured nerve. The overexpression or silencing of miR-1 in cultured Schwann cells (SCs) inhibited or enhanced BDNF secretion from the cells, respectively, and also suppressed or promoted SC proliferation and migration, respectively. Interestingly, BDNF knockdown could attenuate the enhancing effect of miR-1 inhibitor on SC proliferation and migration. These findings will contribute to the development of a novel therapeutic strategy for peripheral nerve injury, which overcomes the limitations of direct administration of exogenous BDNF by using miR-1 to regulate endogenous BDNF expression.

MiR-340 Regulates Fibrinolysis and Axon Regrowth Following Sciatic Nerve Injury

After peripheral nerve injury, the degenerative debris and inflammatory alterations at the injury site may block the elongation of regenerating axons to reach target organs. Tissue plasminogen activator (tPA), a serine protease, has a capability of degrading matrix molecules and cell adhesions. In this study, we found that either tPA or miR-340 was differentially expressed in the injured nerve after sciatic nerve injury, and that the expressions of tPA and miR-340 were negatively correlated to each other. Moreover, miR-340 and tPA were co-localized in sciatic nerve. miR-340 regulated tPA through direct targeting of the 3'-UTR of tPA. Functionally, over- or under-expression of miR-340 reduced or augmented the fibrinolytic activity and migration ability of cultured Schwann cells as well as tPA secretion from the cells, respectively. In rats with sciatic nerve crush injury, dysregulation of the miR-340 expression in the injury site affected the cell debris removal and axonal regrowth. Obviously, unlike many previous studies that investigate the functional impact of miRNAs on peripheral nerve regeneration in the perspective of miRNA regulation of neural cell behaviors, the present study focused on miRNA regulation of debris clearance, thus updating our understanding of the regulatory roles of miRNAs in peripheral nerve regeneration.