Sevoflurane induces cognitive impairments via the MiR-27b/LIMK1-signaling pathway in developing rats

Electroacupuncture improves postoperative cognitive dysfunction by inhibiting ferroptosis via the TFR1-DMT1-FPN pathway

OBJECTIVE

The aim of this study was to investigate the role of ferroptosis in the occurrence of postoperative cognitive dysfunction (POCD) using a mouse model and to elucidate whether electroacupuncture (EA) can improve POCD by suppressing ferroptosis via the transferrin receptor 1 (TFR1)-divalent metal transporter 1 (DMT1)-ferroportin (FPN) pathway.

METHODS

The experiment involved three groups: the control group, the POCD group and the POCD + EA group. The POCD animal model was established using sevoflurane anesthesia and tibial fracture. Cognitive and behavioral changes in mice were assessed using the novel object recognition test (NORT) and the Morris water maze (MWM) test, 1 and 3 days after surgery. Transmission electron microscopy was performed to observe changes in the mitochondrial structure of hippocampal tissue. Enzyme-linked immunosorbent assay was conducted to determine the levels of glutathione (GSH) and iron ion (Fe) concentrations. Western blot analysis was used to measure the expression of TFR1, DMT1 and iron pump protein. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was employed to detect the mRNA levels of DMT1 and FPN.

RESULTS

Based on the experimental results of the MWM test and the NORT, we found that EA can improve POCD in mice. Observation by projection electron microscopy showed that EA improved the mitochondrial structure in the hippocampus. The enzyme-linked immunosorbent assay (ELISA) results showed that EA suppressed ferroptosis in the hippocampal area. The qRT-PCR and Western blot results suggested that EA suppresses ferroptosis by regulating the TFR1-DMT1-FPN pathway.

CONCLUSION

This study reveals that sevoflurane and tibial fractures cause cognitive damage through the mechanism of ferroptosis, while EA may inhibit ferroptosis through the TFR1-DMT1-FPN pathway and improve POCD when induced in this way.

The duration-dependent and sex-specific effects of neonatal sevoflurane exposure on cognitive function in rats

Clinical studies have found that neonatal sevoflurane exposure can increase the risk of cognitive dysfunction. However, recent studies have found that it can exhibit neuroprotective effects in some situations. In this study, we aimed to explore the effects of sevoflurane neonatal exposure in rats. A total of 144 rat pups (72 males and 72 females) were assigned to six groups and separately according to sevoflurane exposure of different times on the seventh day after birth. Blood gas analysis and western blot detection in the hippocampus were conducted after exposure. The Morris water maze test was conducted on the 32nd to 38th days after birth. The expression of PSD95 and synaptophysin in the hippocampus was detected after the Morris water maze test. We found that neonatal exposure to sevoflurane promoted apoptosis in the hippocampus, and Bax and caspase-3 were increased in a dose-dependent manner. The 2-h exposure had the greatest effects on cognitive dysfunction. However, with the extension of exposure time to 6 h, the effects on cognitive function were partly compensated. In addition, sevoflurane exposure decreased synaptogenesis in the hippocampus. However, as the exposure time was extended, the suppression of synaptogenesis was attenuated. In conclusion, neonatal sevoflurane exposure exhibited duration-dependent effects on cognitive function via Bax-caspase-3-dependent apoptosis and bidirectional effects on synaptogenesis in rats.

Sequencing Reveals miRNAs Enriched in the Developing Mouse Enteric Nervous System

The enteric nervous system (ENS) is an essential network of neurons and glia in the bowel wall. Defects in ENS development can result in Hirschsprung disease (HSCR), a life-threatening condition characterized by severe constipation, abdominal distention, bilious vomiting, and failure to thrive. A growing body of literature connects HSCR to alterations in miRNA expression, but there are limited data on the normal miRNA landscape in the developing ENS. We sequenced small RNAs (smRNA-seq) and messenger RNAs (mRNA-seq) from ENS precursor cells of mid-gestation Ednrb-EGFP mice and compared them to aggregated RNA from all other cells in the developing bowel. Our smRNA-seq results identified 73 miRNAs that were significantly enriched and highly expressed in the developing ENS, with miR-9, miR-27b, miR-124, miR-137, and miR-488 as our top 5 miRNAs that are conserved in humans. However, contrary to prior reports, our follow-up analyses of miR-137 showed that loss of Mir137 in Nestin-cre, Wnt1-cre, Sox10-cre, or Baf53b-cre lineage cells had no effect on mouse survival or ENS development. Our data provide important context for future studies of miRNAs in HSCR and other ENS diseases and highlight open questions about facility-specific factors in development.

Hippocampal LIMK1-mediated Structural Synaptic Plasticity in Neurobehavioral Deficits Induced by a Low-dose Heavy Metal Mixture

Humans are commonly exposed to the representative neurotoxic heavy metals lead (Pb), cadmium (Cd), and mercury (Hg). These three substances can be detected simultaneously in the blood of the general population. We have previously shown that a low-dose mixture of these heavy metals induces rat learning and memory impairment at human exposure levels, but the pathogenic mechanism is still unclear. LIM kinase 1 (LIMK1) plays a critical role in orchestrating synaptic plasticity during brain function and dysfunction. Hence, we investigated the role of LIMK1 activity in low-dose heavy metal mixture-induced neurobehavioral deficits and structural synaptic plasticity disorders. Our results showed that heavy metal mixture exposure altered rat fear responses and spatial learning at general population exposure levels and that these alterations were accompanied by downregulation of LIMK1 phosphorylation and structural synaptic plasticity dysfunction in rat hippocampal tissues and cultured hippocampal neurons. In addition, upregulation of LIMK1 phosphorylation attenuated heavy metal mixture-induced structural synaptic plasticity, dendritic actin dynamics, and cofilin phosphorylation damage. The potent LIMK1 inhibitor BMS-5 yielded similar results induced by heavy metal mixture exposure and aggravated these impairments. Our findings demonstrate that LIMK1 plays a crucial role in neurobehavioral deficits induced by low-dose heavy metal mixture exposure by suppressing structural synaptic plasticity.

Recent progress on the role of non-coding RNA in postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD), especially in elderly patients, is a serious complication characterized by impairment of cognitive and sensory modalities after surgery. The pathogenesis of POCD mainly includes neuroinflammation, neuronal apoptosis, oxidative stress, accumulation of Aβ, and tau hyperphosphorylation; however, the exact mechanism remains unclear. Non-coding RNA (ncRNA) may play an important role in POCD. Some evidence suggests that microRNA, long ncRNA, and circular RNA can regulate POCD-related processes, making them promising biomarkers in POCD diagnosis, treatment, and prognosis. This article reviews the crosstalk between ncRNAs and POCD, and systematically discusses the role of ncRNAs in the pathogenesis and diagnosis of POCD. Additionally, we explored the possible mechanisms of ncRNA-associated POCD, providing new knowledge for developing ncRNA-based treatments for POCD.

Electroacupuncture ameliorates postoperative cognitive dysfunction and associated neuroinflammation via NLRP3 signal inhibition in aged mice

Background

Postoperative cognitive dysfunction (POCD) is associated with worsened prognosis especially in aged population. Clinical and animal studies suggested that electroacupuncture (EA) could improve POCD. However, the underlying mechanisms especially EA’s regulatory role of inflammasomes remain unclear.

Methods

The model of POCD was established by partial hepatectomy surgery in 18‐month mice with or without postoperative EA treatment to the Baihui acupoint (GV20) for 7 days. Cognitive functions were assessed by Morris water maze test, and proinflammatory cytokines IL‐1β and IL‐6 and microglia activity were assayed by qPCR, ELISA, or immunohistochemistry. Tight junction proteins, NLRP3 inflammasome and downstream proteins, and NF‐κB pathway proteins were evaluated by western blotting.

Results

EA markedly preserved cognitive dysfunctions in POCD mice, associated with the inhibition of neuroinflammation as evidenced by reduced microglial activation and decreased IL‐1β and IL‐6 levels in brain tissue. EA also preserved hippocampal neurons and tight junction proteins ZO‐1 and claudin 5. Mechanistically, the activation of NLRP3 inflammasome and NF‐κB was inhibited by EA, while NLRP3 activation abolished EA’s treatment effects on cognitive function.

Conclusion

EA alleviates POCD‐mediated cognitive dysfunction associated with ameliorated neuroinflammation. Mechanistically, EA’s treatment effects are dependent on NLRP3 inhibition.

Sevoflurane-Induced miR-211-5p Promotes Neuronal Apoptosis by Inhibiting Efemp2

Sevoflurane exposure can result in serious neurological side effects including neuronal apoptosis and cognitive impairment. Although the microRNA miR-211-5p is profoundly upregulated following sevoflurane exposure in neonatal rodent models, the impact of miR-211-5p on neuronal apoptosis and cognitive impairment postsevoflurane exposure has not yet been elucidated. Here, we found that sevoflurane upregulated miR-211-5p and downregulated EGF-Containing Fibulin Extracellular Matrix Protein 2 (Efemp2, Fibulin-4) levels in vitro and in vivo. Sevoflurane's effect on miR-211-5p expression was based on enhancing primary miR-211 transcription. miR-211-5p targets Efemp2's mRNA 3′-untranslated region, reducing Efemp2 expression. RNA immunoprecipitation revealed significant enrichment of the miR-211-5p:Efemp2 mRNA dyad in the RNA-induced silencing complex. miR-211-5p mimics downregulated Efemp2, leading to phosphorylation of Smad2 and Smad3, upregulation of pro-apoptotic Bim, and mitochondrial release of allograft inflammatory factor 1 and cytochrome C. In contrast, miR-211-5p hairpin inhibitor (AntimiR-211-5p) negatively regulated this apoptotic pathway and reduced neuronal apoptosis in an Efemp2-dependent manner. Sevoflurane-exposed mice administered AntimiR-211-5p displayed reduced cortical apoptosis levels and near-term cognitive impairment. In conclusion, sevoflurane-induced miR-211-5p promotes neuronal apoptosis via Efemp2 inhibition. Summary statement: This study revealed the significance of sevoflurane-induced increases in miR-211-5p on the promotion of neuronal apoptosis via inhibition of Efemp2 and its downstream targets.

The importance of non-coding RNAs in environmental stress-related developmental brain disorders: A systematic review of evidence associated with exposure to alcohol, anesthetic drugs, nicotine, and viral infections

Brain development is a dynamic and lengthy process that includes cell proliferation, migration, neurogenesis, gliogenesis, synaptogenesis, and pruning. Disruption of any of these developmental events can result in long-term outcomes ranging from brain structural changes, to cognitive and behavioral abnormality, with the mechanisms largely unknown. Emerging evidence suggests non-coding RNAs (ncRNAs) as pivotal molecules that participate in normal brain development and neurodevelopmental disorders. NcRNAs such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are transcribed from the genome but not translated into proteins. Many ncRNAs have been implicated as tuners of cell fate. In this review, we started with an introduction of the current knowledge of lncRNAs and miRNAs, and their potential roles in brain development in health and disorders. We then reviewed and discussed the evidence of ncRNA involvement in abnormal brain development resulted from alcohol, anesthetic drugs, nicotine, and viral infections. The complex connections among these ncRNAs were also discussed, along with potential overlapping ncRNA mechanisms, possible pharmacological targets for therapeutic/neuroprotective interventions, and potential biomarkers for brain developmental disorders.

Sevoflurane induces inflammation of microglia in hippocampus of neonatal rats by inhibiting Wnt/β-Catenin/CaMKIV pathway

OBJECTIVE

To investigate the effect of sevoflurane on inflammation of microglia in hippocampus of neonatal rats, and to investigate whether the related mechanism is related to Wnt/β-Catenin/CaMKIV pathway.

METHODS

Neonatal rats were anesthetized with 2% or 3% sevoflurane for 4 h a day for 3 consecutive days. Water maze test was used to detect the effect of sevoflurane anesthesia on memory function of neonatal rats. H&E and Nissl staining were used to observe the pathological damage of hippocampal area of neonatal rats induced by sevoflurane anesthesia. The expression of microglial marker Iba-1 was detected by Immunofluorescence. Immunofluorescence and WB were used to detect the expression CD32b, CD86, TNF-α, IL-6, Wnt3a, β-Catenin and CaMKIV in hippocampus. To further explore the related mechanism, Wnt-3α inhibitor and activator was treated to study the effect of sevoflurane on microglial inflammation in hippocampus of neonatal rats.

RESULTS

Sevoflurane anesthesia significantly increased escape latency time, reduced platform crossing times, and damaged the learning and memory ability of neonatal rats. H&E and Nissl staining results showed that sevoflurane anesthesia caused obvious damage to the hippocampus of neonatal rats. Sevoflurane anesthesia promoted the expression of Iba-1 and activated microglia. Sevoflurane anesthesia not only significantly increased the positive expression of CD32b, CD86, TNF-α and IL-6, but also decreased the expression of Wnt3a, β-Catenin and CaMKIV. These results suggested that sevoflurane inhibited Wnt/β-Catenin/CaMKIV pathway.

CONCLUSION

Sevoflurane induces inflammation of microglia in hippocampus of neonatal rats by inhibiting Wnt/β-Catenin/CaMKIV pathway.

LncRNA Rian ameliorates sevoflurane anesthesia-induced cognitive dysfunction through regulation of miR-143-3p/LIMK1 axis

Sevoflurane could stimulate neurotoxicity and result in postoperative cognitive dysfunction (POCD). Long non-coding RNAs (lncRNAs) have been implicated in the regulation of nervous system disease. This study was performed to investigate role and mechanism of lncRNA Rian (RNA imprinted and accumulated in nucleus) in sevoflurane anesthesia-induced cognitive dysfunction. Mice post-sevoflurane anesthesia showed cognitive impairments and neuronal damage and apoptosis. However, intracerebroventricularly injection with Adenovirus (Ad) for the over-expression of Rian ameliorated sevoflurane-induced neuronal damage and apoptosis. Cognitive impairments induced by sevoflurane were attenuated by injection with Ad-Rian. Moreover, transfection with Ad-Rian also protected isolated primary hippocampal neurons against sevoflurane-induced decrease of cell viability and increase of lactic acid dehydrogenase (LDH) and apoptosis. Mechanistically, Rian bind to miR-143-3p, and decreased expression of LIMK1 (Lim kinase 1) through negative regulation of miR-143-3p. Knockdown of LIMK1 aggravated sevoflurane-induced decrease of cell viability and increase of LDH and apoptosis in neurons, while over-expression attenuated LIMK1 silence-induced neuronal damage post-sevoflurane anesthesia. In conclusion, Rian demonstrated neuroprotective effects against sevoflurane anesthesia-induced cognitive dysfunction through regulation of miR-143-3p/LIMK1 axis, providing promising target for sevoflurane anesthesia-induced cognitive dysfunction.

Exosomal lncRNA H19 promotes the progression of hepatocellular carcinoma treated with Propofol via miR-520a-3p/LIMK1 axis

Background

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer‐related deaths globally. Herein, we explored the underlying mechanism by which Propofol inhibited the development of HCC.

Methods

3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay was carried out to detect the viability and proliferation. Quantitative real‐time polymerase chain reaction (qRT‐PCR) and Western blot were performed to detect the expression of long noncoding RNA (lncRNA) H19, microRNA‐520a‐3p (miR‐520a‐3p), LIM domain kinase 1 (LIMK1), metastasis‐associated markers (Snail, Twist, Vimentin and E‐cadherin) and exosome markers (CD9 and CD81). Transmission electron microscopy (TEM) was used to observe the morphology and structure of exosomes. The apoptosis and metastasis were measured by flow cytometry and transwell assays. StarBase software was utilized to predict the targets of H19 and miR‐520a‐3p. Dual‐luciferase reporter assay was performed to confirm the interaction between miR‐520a‐3p and H19 or LIMK1. Nude mice bearing tumors were used to validate the role of exosomal H19.

RESULTS

The high expression of exosomal H19 accelerated the proliferation and motility while hampering the apoptosis of HCC cells. MiR‐520a‐3p could bind with H19. Exosomal H19 exacerbated HCC through sponging miR‐520a‐3p. The 3’ untranslated region (3’UTR) of LIMK1 could bind to miR‐520a‐3p. MiR‐520a‐3p mimic transfection reversed the inhibitory effect of high expression of exosomal LIMK1 on the apoptosis of HCC cells and the promoting effects on the proliferation and metastasis of HCC cells. The mRNA and protein levels of LIMK1 were regulated by H19/miR‐520a‐3p signaling. The high level of exosomal H19 promoted the growth of HCC tumors in vivo.

Conclusion

Circulating H19 promoted the proliferation, migration and invasion and inhibited the apoptosis of HCC cells treated with Propofol through upregulating LIMK1 via sponging miR‐520a‐3p.

Role of the GABAA receptors in the long-term cognitive impairments caused by neonatal sevoflurane exposure

Sevoflurane is a widely used inhalational anesthetic in pediatric surgeries, which is considered reasonably safe and reversible upon withdrawal. However, recent preclinical studies suggested that peri-neonatal sevoflurane exposure may cause developmental abnormalities in the brain. The present review aimed to present and discuss the accumulating experimental data regarding the undesirable effects of sevoflurane on brain development as revealed by the laboratory studies. First, we summarized the long-lasting side effects of neonatal sevoflurane exposure on cognitive functions. Subsequently, we presented the structural changes, namely, neuroapoptosis, neurogenesis and synaptogenesis, following sevoflurane exposure in the immature brain. Finally, we also discussed the potential mechanisms underlying subsequent cognitive impairments later in life, which are induced by neonatal sevoflurane exposure and pointed out potential strategies for mitigating sevoflurane-induced long-term cognitive impairments. The type A gamma-amino butyric acid (GABAA) receptor, the main targets of sevoflurane, is excitatory rather than inhibitory in the immature neurons. The excitatory effects of the GABAA receptors have been linked to increased neuroapoptosis, elevated serum corticosterone levels and epigenetic modifications following neonatal sevoflurane exposure in rodents, which might contribute to sevoflurane-induced long-term cognitive abnormalities. We proposed that the excitatory GABAA receptor-mediated HPA axis activity might be a novel mechanism underlying sevoflurane-induced long-term cognitive impairments. More studies are needed to investigate the effectiveness and mechanisms by targeting the excitatory GABAA receptor as a prevention strategy to alleviate cognitive deficits induced by neonatal sevoflurane exposure in future.

Up-regulation of miR-106a targets LIMK1 and contributes to cognitive impairment induced by isoflurane anesthesia in mice

BACKGROUND

Postoperative cognitive dysfunction (POCD) had a great relationship with anesthesia during surgery, and miRNAs have been found involved in anesthesia-induced cognitive impairment.

OBJECTIVE

To explore the role and potential mechanism of miR-106a in isoflurane anesthesia-induced cognitive impairment.

METHODS

Adult male mice were treated with isoflurane anesthesia; Morris water maze tests and fear conditioning tests were performed; and expression levels of miR-106a and LIMK1 were determined by quantitative real-time PCR (qRT-PCR) and western blot. Dual luciferase reporter assay was used to determine the binding of miR-106a and 3'UTR of LIMK1. To verify the role of miR-106a, antagomir of miR-106a were intrahippocampally injected. Finally, expression of BCL2 apoptosis regulator (Bcl-2), LIM domain kinase 1 (LIMK1), BCL2-associated X, apoptosis regulator (Bax) and cleaved caspase3 was determined by western blot.

RESULTS

In isoflurane anesthesia-treated group (IS), the percentage of target quadrant dwell time was significantly lower and the escape latency was significantly higher than in the control group (sham), and the freezing behavior of IS was significantly less in contextual fear conditioning tests. Expression levels of miR-106a were increased and those of LIMK1 were decreased in response to IS. Dual luciferase reporter assay showed that miR-106a could bind with the 3'UTR of LIMK1. Decreased expression levels of miR-106a improved the cognitive impairment of the mice treated with isoflurane. Intrahippocampally injected antagomir of miR-106a also increased LIMK1 and Bcl-2 levels, decreased the BAX and cleaved caspase3 expression levels in the mice treated with isoflurane.

CONCLUSION

Decrease of LIMK1 expression by miR-106a played an important role in isoflurane anesthesia-induced cognitive impairment.

miR-27a/b is a posttranscriptional regulator of Gpr126 (Adgrg6)

Gpr126 (Adgrg6), a member of the adhesion G protein-coupled receptor family, has been associated with a variety of human diseases. Yet, despite its clinical importance, the mechanisms regulating Gpr126 expression are poorly understood. Here, we aimed at identifying upstream regulatory mechanisms of Gpr126 expression utilizing the heart as model organ in which Gpr126 regulates trabeculation. Here, we focused on possible regulation of Gpr126 regulation by microRNAs, which have emerged as key players in regulating development, have a critical role in disease progression, and might serve as putative therapeutic targets. In silico analyses identified one conserved binding site in the 3' UTR of Gpr126 for microRNA 27a and 27b (miR-27a/b). In addition, miR-27a/b and Gpr126 expression were differentially expressed during rat heart development. A regulatory role of miR-27a/b in controlling Gpr126 expression was substantiated by reduced Gpr126 mRNA levels upon ectopic expression of miR-27a/b in HEK293T cells and miR-27b in zebrafish embryos. Regulation of Gpr126 expression by direct binding of miR-27a/b to the 3' UTR of Gpr126 was verified by luciferase reporter assays in HEK293T cells. Finally, the modulation of gpr126 expression in zebrafish by injection of either miR-27b or miR-27b inhibitor in single cell-stage embryos resulted in hypo- or hypertrabeculation, respectively. Collectively, the data indicate that Gpr126 expression is regulated by miR-27a/b.

Cognitive impairment and transcriptomic profile in hippocampus of young mice after multiple neonatal exposures to sevoflurane

Children with repeated inhalational anesthesia may develop cognitive disorders. This study aimed to investigate the transcriptome-wide response of hippocampus in young mice that had been exposed to multiple sevoflurane in the neonatal period. Mice received 3% sevoflurane for 2 h on postnatal day (PND) 6, 8, and 10, followed by arterial blood gas test on PND 10, behavioral experiments on PND 31–36, and RNA sequencing (RNA-seq) of hippocampus on PND 37. Functional annotation and protein-protein interaction analyses of differentially expressed genes (DEGs) and quantitative reverse transcription polymerase chain reaction (qPCR) were performed. Neonatal sevoflurane exposures induced cognitive and social behavior disorders in young mice. RNA-seq identified a total of 314 DEGs. Several enriched biological processes (ion channels, brain development, learning, and memory) and signaling pathways (oxytocin signaling pathway and glutamatergic, cholinergic, and GABAergic synapses) were highlighted. As hub-proteins, Pten was involved in nervous system development, synapse assembly, learning, memory, and behaviors, Nos3 and Pik3cd in oxytocin signaling pathway, and Cdk16 in exocytosis and phosphorylation. Some top DEGs were validated by qPCR. This study revealed a transcriptome-wide profile in mice hippocampus after multiple neonatal exposures to sevoflurane, promoting better understanding of underlying mechanisms and investigation of preventive strategies.

Mesenchymal stromal cells attenuate sevoflurane-induced apoptosis in human neuroglioma H4 cells

BACKGROUND

Inhalation of sevoflurane can induce neuronal apoptosis, cognitive impairment and abnormal behaviors. Bone marrow mesenchymal stem cells (MSCs) can secret neurotrophic factors and cytokines to protect from oxidative stress-related neuronal apoptosis. However, whether MSCs can protect from sevoflurane-induced neuronal apoptosis and the potential mechanisms are unclear.

METHODS

A non-contact co-culture of MSCs with human neuroglioma H4 cells (H4 cells) was built. H4 cells were co-cultured with MSCs or without MSCs (control) for 24 h. The co-cultured H4 cells were exposed to 4% sevoflurane for 6 h. The levels of caspase-3, reactive oxygen species (ROS), adenosine triphosphate (ATP), and the release of cytochrome C were determined by Western blot and fluorescence assay.

RESULTS

Sevoflurane exposure significantly elevated the levels of cleaved caspase 3 and Bax in H4 cells. However, these phenomena were significantly offset by the co-culture with MSCs in H4 cells. Co-culture with MSCs before, but not after, sevoflurane exposure, significantly attenuated sevoflurane-induced ROS production in H4 cells. MSCs prevented sevoflurane-mediated release of cytochrome C from the mitochondria and production of ATP in H4 cells.

CONCLUSIONS

Our study indicated that soluble factors secreted by MSCs attenuated the sevoflurane-induced oxidative stress and apoptosis of neuronal cells by preserving their mitochondrial function.

Different doses of sevoflurane facilitate and impair learning and memory function through activation of the ERK pathway and synthesis of ARC protein in the rat hippocampus

BACKGROUND

Sevoflurane has been shown to stimulate or depress memory in adult rats; however, the cellular mechanism of this bidirectional effect has not been fully investigated.

METHODS

We used an intra-hippocampal microinfusion of U0126 to suppress ERK activation. Male SD rats were randomly assigned to four groups: Sham, 0.11%SEV, 0.3%SEV and 0.3%+U0126. They received bilateral injections of U0126 or saline. Rats were anesthetized, and Inhibitory Avoidance (IA) training was performed immediately after anesthesia. The memory retention latency was observed 24 h later. In another experiment, the hippocampus was removed 45 min after IA training to assess ARC expression, the synapsin 1 protein levels and the phosphorylation level of ERK.

RESULTS

Treatment with 0.11%SEV led to rapid phosphorylation of ERK, while 0.3%SEV inhibited phosphorylation; the latter change was reversed by the microinfusion of U0126 in the hippocampus. The memory latency result had similar tendencies. The local infusion of U0126 abolished the 0.3%SEV-induced memory impairment and ERK inhibition. Selective upregulations of ARC and synapsin 1 proteins were observed in the 0.3%SEV group compared with the 0.11%SEV group.

CONCLUSIONS

The results indicate that different doses of sevoflurane trigger synaptic plasticity-related cytoskeleton proteins through the ERK signaling pathway. This novel modulation by inhalational agents may help to reduce their side-effects on memory function.

MicroRNA-27a-3p suppression of peroxisome proliferator-activated receptor-γ contributes to cognitive impairments resulting from sevoflurane treatment

Sevoflurane is the most widely used anaesthetic administered by inhalation. Exposure to sevoflurane in neonatal mice can induce learning deficits and abnormal social behaviours. MicroRNA (miR)-27a-3p, a short, non-coding RNA that functions as a tumour suppressor, is up-regulated after inhalation of anaesthetic, and peroxisome proliferator-activated receptor γ (PPAR-γ) is one of its target genes. The objective of this study was to investigate how the miR-27a-3p-PPAR-γ interaction affects sevoflurane-induced neurotoxicity. A luciferase reporter assay was employed to identify the interaction between miR-27a-3p and PPAR-γ. Primary hippocampal neuron cultures prepared from embryonic day 0 C57BL/6 mice were treated with miR-27a-3p inhibitor or a PPAR-γ agonist to determine the effect of miR-27a-3p and PPAR-γ on sevoflurane-induced cellular damage. Cellular damage was assessed by a flow cytometry assay to detect apoptotic cells, immunofluorescence to detect reactive oxygen species, western blotting to detect NADPH oxidase 1/4 and ELISA to measure inflammatory cytokine levels. In vivo experiments were performed using a sevoflurane-induced anaesthetic mouse model to analyse the effects of miR-27a-3p on neurotoxicity by measuring the number of apoptotic neurons using the Terminal-deoxynucleoitidyl Transferase Mediated Nick End Labeling (TUNEL) method and learning and memory function by employing the Morris water maze test. Our results revealed that PPAR-γ expression was down-regulated by miR-27a-3p following sevoflurane treatment in hippocampal neurons. Down-regulation of miR-27a-3p expression decreased sevoflurane-induced hippocampal neuron apoptosis by decreasing inflammation and oxidative stress-related protein expression through the up-regulation of PPAR-γ. In vivo tests further confirmed that inhibition of miR-27a-3p expression attenuated sevoflurane-induced neuronal apoptosis and learning and memory impairment. Our findings suggest that down-regulation of miR-27a-3p expression ameliorated sevoflurane-induced neurotoxicity and learning and memory impairment through the PPAR-γ signalling pathway. MicroRNA-27a-3p may, therefore, be a potential therapeutic target for preventing or treating sevoflurane-induced neurotoxicity.

Neuroprotective Role of Exogenous Brain-Derived Neurotrophic Factor in Hypoxia-Hypoglycemia-Induced Hippocampal Neuron Injury via Regulating Trkb/MiR134 Signaling

Hypoxic-ischemic brain injury is an important cause of neonatal mortality and morbidity. Brain-derived neurotrophic factor (BDNF) has been reported to play a neuroprotective role in hypoxic-ischemic brain injury; however, the specific effects and mechanism of BDNF on hypoxic-hypoglycemic hippocampal neuron injury remains unknown. The current study investigated the action of BDNF in regulating cerebral hypoxic-ischemic injury by simulating hippocampal neuron ischemia and hypoxia. We found that BDNF, p-Trkb, and miR-134 expression levels decreased, and that exogenous BDNF increased survival and reduced apoptosis in hypoxic-hypoglycemic hippocampal neurons. The results also show that BDNF inhibits MiR-134 expression by activating the TrkB pathway. Transfection with TrkB siRNA and pre-miR-134 abrogated the neuroprotective role of BDNF in hypoxic-hypoglycemic hippocampal neurons. Our results suggest that exogenous BDNF alleviates hypoxic-ischemic brain injury through the Trkb/MiR-134 pathway. These findings may help to identify a potential therapeutic agent for the treatment of hypoxic-ischemic brain injury.