Dexmedetomidine-up-regulated microRNA-381 exerts anti-inflammatory effects in rats with cerebral ischaemic injury via the transcriptional factor IRF4

Dexmedetomidine (Dex) possesses analgesic and anaesthetic values and reported being used in cerebral ischaemic injury therapeutics. Accumulating studies have determined the effect of microRNAs (miRNAs) on the cerebral ischaemic injury. Thus, the present study aimed to unravel the molecular mechanism of miR-381 and Dex in cerebral ischaemic injury. For this purpose, the cerebral ischaemic injury rat model was established by induction of middle cerebral artery occlusion (MCAO) and expression of miR-381 and IRF4 was determined. Thereafter, MCAO rats were treated with Dex, miR-381 mimic, miR-381 inhibitor and oe-IRF4 respectively, followed by evaluation of neurological function. Furthermore, neuron cells were isolated from the hippocampus of rats and subjected to oxygen-glucose deprivation (OGD). Then, OGD-treated neuron cells and primary neuron cells were examined by gain- and loss-of-function assay. Neuron cell apoptosis was detected using TUNEL staining and flow cytometry. The correlation between interferon regulatory factor 4 (IRF4) and interleukin (IL)-9 was detected. Our results showed down-regulated miR-38 and up-regulated IRF4 in MCAO rats. Besides, IRF4 was targeted by miR-381 in neuron cells. Dex and overexpressed miR-381, or silenced IRF4 improved the neurological function and inhibited neuron cell apoptosis in MCAO rats. Additionally, in MCAO rats, Dex was found to increase the miR-381 expression and reduced IRF4 expression to decrease the IL-9 expression, which suppressed the inflammatory response and cell apoptosis both in vivo and in vitro. Importantly, our study demonstrated that Dex elevated the expression of miR-381, which ultimately results in the inhibition of inflammation response in rats with cerebral ischaemic injury.     

Downregulation of microRNA-103a reduces microvascular endothelial cell injury in a rat model of cerebral ischemia by targeting AXIN2

Multiple microRNAs (miRNAs) have been found to be linked with cerebral ischemia. Thus, this study was employed to characterize the capabilities of miRNA-103a (miR-103a) on the brain microvascular endothelial cells (BMECs) injury in rat models of middle cerebral artery occlusion (MCAO) by regulating AXIN2. The MCAO rat model was developed by the suture method, where normal saline, miR-103a inhibitors, or its negative control were separately injected into the lateral ventricle to assess the function of miR-103a inhibitors in BMECs apoptosis, microvessel density, as well as angiogenesis. In addition, the oxygen-glucose deprivation model was induced in primarily cultured BMECs to unearth the functions of miR-103a inhibitors on cell viability and apoptosis, lactate dehydrogenase (LDH) release and tube formation ability. Furthermore, the relationship between miR-103a and AXIN2 was verified. The modeled rats of MCAO showed robustly expressed miR-103a, poorly expressed AXIN2, severe neurological deficits, accelerated apoptosis and reduced angiogenesis. miR-103a expression had a negative correlation with AXIN2 messenger RNA expression (r = −0.799; p < .05). In response to the treatment of miR-103a inhibitors, the BMECs apoptosis was suppressed and angiogenesis was restored, corresponding to upregulated Bcl-2, VEGF, and Ang-1, in addition to downregulated caspase-3 and Bax. Meanwhile, AXIN2 was verified to be the miR-103a's target gene. More important, miR-103a inhibitors led to promoted BMEC viability and tube formation and suppressed apoptosis and LDH release rate. This study highlights that miR-103a targets and negatively regulates AXIN2, whereby reducing BMEC injury in cerebral ischemia.     

Serum Exosomal mir-340-5p Promotes Angiogenesis in Brain Microvascular Endothelial Cells During Oxygen-Glucose Deprivation

Ischemic stroke (IS) is a cerebrovascular disease with high morbidity, recurrence, and mortality. The purpose of the present study was to investigate the role and mechanism of human serum exosomes on angiogenesis after IS. The middle cerebral artery occlusion (MCAO) in vivo model and oxygen-glucose deprivation (OGD) in vitro model were established. Human serum exosomes from healthy samples (NC-exo) and IS samples (IS-exo) were injected into MCAO mice. Neurobehavioral tests were performed to assess the extent of neurological deficits. The infarct volume was assessed by 2,3,5-triphenyl tetrazolium chloride (TTC) staining, and the levels of inflammatory cytokines were analyzed by enzyme-linked immunosorbent assay (ELISA). In addition, human serum exosomes were cocultured with brain microvascular endothelial cells (BMECs). Cell Counting Kit-8 (CCK-8), Transwell, and tubule formation assays were performed to investigate the proliferation, migration, invasion, length, and branching of BMECs. The miRNA expression profiles of NC-exo and IS-exo were analyzed by high-throughput sequencing and compared. Bioinformatics and luciferase reporter assays were performed to evaluate the relationship between miR-340-5p and CD147. Serum NC-exo and IS-exo had protective effects on IS injury and promoted BMEC angiogenesis. Interestingly, the protective effect of IS-exo was weaker than that of NC-exo. In addition, miR-340-5p was downregulated in IS-exo, and miR-340-5p accelerated angiogenesis of BMECs after OGD. Mechanistically, CD147 was confirmed as a direct target of miR-340-5p. Finally, miR-340-5p promoted angiogenesis by directly targeting CD147. Serum exosome-derived miR-340-5p promote angiogenesis in OGD-induced BMECs by targeting CD147.

     

MiR‐377 Regulates Inflammation and Angiogenesis in Rats After Cerebral Ischemic Injury

Ischemic stroke is the leading cause of disabilities worldwide. MicroRNA‐377 (miR‐377) plays important roles in ischemic injury. The present study focused on the mechanisms of miR‐377 in protecting ischemic brain injury in rats. Cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in rats. Primary rat microglial cells and brain microvascular endothelial cells (BMECs) were exposed to oxygen‐glucose deprivation (OGD). The concentrations of cytokines (TNF‐α, IL‐1β, IL‐6, IFN‐γ, TGF‐β, MMP2, COX2, and iNOS) in the culture medium were measured by specific ELISA. Tube formation assay was for the in vitro study of angiogenesis. Luciferase reporter assay was performed to confirm whether VEGF and EGR2 were direct targets of miR‐377. The MCAO rats were intracerebroventricular (ICV) injection of miR‐377 inhibitor to assess its protective effects in vivo. MiR‐377 levels were decreased in the rat brain tissues at 1, 3, and 7 d after MCAO. Both microglia cells and BMECs under OGD showed markedly lower expression levels of miR‐377 while higher expression levels of EGR2 and VEGF compared to those under normoxia conditions. Knockdown of miR‐377 inhibited microglial activation and the release of pro‐inflammatory cytokines after OGD. Suppression of miR‐377 promoted the capillary‐like tube formation and cell proliferation and migration of BMECs. The anti‐inflammation effect of EGR2 and the angiogenesis effect of VEGF were regulated by miR‐377 after OGD. Inhibition of miR‐377 decreased cerebral infarct volume and suppressed cerebral inflammation but promoted angiogenesis in MCAO rats. Knockdown of miR‐377 lessened the ischemic brain injury through promoting angiogenesis and suppressing cerebral inflammation. J. Cell. Biochem. 119: 327–337, 2018. © 2017 Wiley Periodicals, Inc.     

MiR-539 Targets MMP-9 to Regulate the Permeability of Blood–Brain Barrier in Ischemia/Reperfusion Injury of Brain

Cerebral ischemia/reperfusion (I/R) injury severely threatens human life, while the potential mechanism underlying it is still need further exploration. The rat model of cerebral I/R injury was established using middle cerebral artery occlusion (MCAO). The rat microvascular endothelial cell line bEND.3 was exposed to oxygen–glucose deprivation/reperfusion (OGD/R) to mimic ischemic condition in vitro. Evans blue was performed to determine the blood–brain barrier (BBB) permeability. Real-time PCR and western blot were performed to determine gene expression in mRNA and protein level, individually. Luciferase reporter assay was conducted to determine the relationship between miR-539 and MMP-9. The infarct volume and BBB permeability of cerebral (I/R) rats were significantly greater than Sham group. The expression of miR-539 was decreased, while MMP-9 was increased in the brain tissues of I/R injury rats and OGD/R pretreated bEND.3. Up-regulated miR-539 in OGD/R pretreated bEND.3 significantly promoted the BBB permeability. MiR-539 targets MMP-9 to regulate its expression. OGD/R treatment significantly promoted the BBB permeability in bEND.3, miR-539 mimic transfection abolished the effects of OGD/R, while co-transfected with pcDNA-MMP-9 abolished the effects of miR-539 mimic. MiR-539 targets MMP-9 and further regulates the BBB permeability in cerebral I/R injury.     

MicroRNA-449b-5p targets HMGB1 to attenuate hepatocyte injury in liver ischemia and reperfusion

MicroRNAs (miRNAs) participate in the pathological process of liver ischemia/reperfusion (I/R) injury. MiR-449b-5p is the target miRNA of high mobility group box 1 (HMGB1). Its role and molecular mechanism in liver I/R injury remain unidentified. In this study, we found a protective effect of miR-449b-5p against hepatic I/R injury. HMGB1 expression significantly increased, whereas miR-449b-5p dramatically decreased in patients after liver transplant and in L02 cells exposed to hypoxia/reoxygenation (H/R). A dual-luciferase reporter assay confirmed the direct interaction between miR-449b-5p and the 3′ untranslated region of HMGB1 messenger RNA. We also found that overexpression of miR-449b-5p significantly promoted cell viability and inhibited cell apoptosis of L02 cells exposed to H/R. Moreover, miR-449b-5p repressed HMGB1 protein expression and nuclear factor-κB (NF-κB) pathway activation in these L02 cells. In an in vivo rat model of hepatic I/R injury, overexpression of miR-449b-5p significantly decreased alanine aminotransferase and aspartate aminotransferase and inhibited the HMGB1/NF-κB pathway. Our study thus suggests that miR-449b-5p alleviated hepatic I/R injury by targeting HMGB1 and deactivating the NF-κB pathway, which may provide a novel and promising therapeutic target for hepatic I/R injury.     

急性脑缺血诱导的Sirt3蛋白表达下调通过破坏线粒体功能导致神经元损伤

本文旨在观察急性脑缺血对神经元沉默信息调节因子2相关酶类3(silent mating type information regulator 2 homolog 3,Sirt3)蛋白表达水平的影响,并阐明Sirt3在急性脑缺血中的病理意义.建立小鼠大脑中动脉栓塞(middle cerebral artery occlu...     

MicroRNA‐130a regulates neurological deficit and angiogenesis in rats with ischaemic stroke by targeting XIAP

MicroRNAs (miRNAs) have already been proposed to be implicated in the development of ischaemic stroke. We aim to investigate the role of miR‐130a in the neurological deficit and angiogenesis in rats with ischaemic stroke by regulating X‐linked inhibitor of apoptosis protein (XIAP). Middle cerebral artery occlusion (MCAO) models were established by suture‐occluded method, and MCAO rats were then treated with miR‐130a mimics/inhibitors or/and altered XIAP for detection of changes of rats’ neurological function, nerve damage and angiogenesis in MCAO rats. The oxygen‐glucose deprivation (OGD) cellular models were established and respectively treated to determine the roles of miR‐130a and XIAP in neuronal viability and apoptosis. The expression levels of miR‐130a and XIAP in brain tissues of MCAO rats and OGD‐treated neurons were detected. The binding site between miR‐130a and XIAP was verified by luciferase activity assay. MiR‐130a was overexpressed while XIAP was down‐regulated in MCAO rats and OGD‐treated neurons. In animal models, suppressed miR‐130a improved neurological function, alleviated nerve damage and increased new vessels in brain tissues of rats with MCAO. In cellular models, miR‐130a inhibition promoted neuronal viability and suppressed apoptosis. Inhibited XIAP reversed the effect of inhibited miR‐130a in both MCAO rats and OGD‐treated neurons. XIAP was identified as a target of miR‐130a. Our study reveals that miR‐130a regulates neurological deficit and angiogenesis in rats with MCAO by targeting XIAP.     

Upregulation of miR-1306-5p decreases cerebral ischemia/reperfusion injury in vitro by targeting BIK

ABSTRACT

MiR-1306-5p is involved in the progression of acute heart failure, but its role in ischemic stroke remains unclear. Here, SH-SY5Y cells were exposed to oxygen–glucose deprivation (OGD) for 4, 8, and 12 h, respectively, and then reoxygenation for 12 h to construct OGD/R induced cell injury model. Cell viability, cell death, and cell apoptosis were assessed with CCK-8 assay, LDH assay, ?ow cytometry, and caspase-3 activity assay. The target gene of miR-1306-5p was confirmed by luciferase reporter assay. We found miR-1306-5p expression was significantly down-regulated in OGD/R-induced SH-SY5Y cell model. Moreover, miR-1306-5p protected SH-SY5Y cell against OGD/R-induced injury. Mechanistically, Bcl2-interacting killer (BIK) was the direct target gene of miR-1306-5p. Furthermore, BIK knockdown mimicked, while overexpression reversed the protective effects of miR-1306-5p against OGD/R induced injury. Our findings thus provide an experimental basis miR-1306-5p targeting BIK-based therapy for cerebral I/R injury.     

miR-96-5p靶向FOXO1调节脑缺血再灌注损伤机制

摘要 目的：探究miR-96-5p在脑缺血再灌注损伤（CIRI）中的作用及机制。方法：通过qRT-PCR检测36例确诊的缺血性脑卒中患者（IS患者组）和30例健康体检者（健康组）的血清miR-96-5p水平。将PC12细胞分为5组：对照组、NC-ag组、miR-96-5p-ag组、NC-an组、miR-96-5p-an组。采用Lipofectamine 2000对PC12细胞进行转染,通过qRT-PCR验证转染效率。将PC12细胞分为6组：对照组、氧糖剥夺/复氧复糖（OGD/R）组、OGD/R+NC-ag组、OGD/R+miR-ag组、OGD/R+NC-an组、OGD/R+miR-an组。根据分组对PC12细胞进行OGD/R处理和转染。通过MTT法检测PC12细胞活力,TUNEL法检测PC12细胞凋亡。采用改良Longa法建立大鼠CIRI模型,然后将大鼠分为假手术组、CIRI组、CIRI+NC-an组和CIRI+miR-an组。假手术组和CIRI组大鼠尾静脉注射生理盐水,CIRI+NC-an组和CIRI+miR-an组大鼠分别尾静脉注射NC-antagomir和miR-96-5p-antagomir。然后检测各组大鼠的神经功能评分、脑梗死体积和脑组织细胞凋亡情况。按照试剂盒说明书测定PC12细胞和大鼠脑组织中MDA、SOD和GSH-Px的含量。通过qRT-PCR检测PC12细胞和大鼠脑组织miR-96-5p和Forkhead box O1（FOXO1） mRNA水平,通过Western blot检测FOXO1、Ac-FOXO1、Bax和Bcl-2的蛋白表达水平。结果：与Health组比较,IS组患者的血清miR-96-5p水平显著升高（P<0.001）。与对照组和NC-ag组比较,miR-96-5p-ag组的miR-96-5p水平升高,FOXO1的mRNA和蛋白表达水平均降低,FOXO1的乙酰化水平升高（P<0.05）。与对照组和NC-an组比较,miR-96-5p-an组的miR-96-5p水平降低,FOXO1的mRNA和蛋白表达水平均升高,FOXO1的乙酰化水平降低（P<0.05）。与OGD/R组和OGD/R+NC-an组比较,OGD/R+miR-an组的相对细胞活力升高,TUNEL阳性率降低,Bax的蛋白相对表达量降低,Bcl-2的蛋白相对表达量升高,MDA水平降低,SOD和GSH-Px水平升高,miR-96-5p水平降低,FOXO1的mRNA和蛋白表达水平升高,FOXO1的乙酰化水平降低（P<0.05）。与CIRI组和CIRI+NC-an组比较,CIRI+miR-an组大鼠的神经功能评分和脑梗死体积降低,TUNEL阳性率降低,Bax的蛋白相对表达量降低,Bcl-2的蛋白相对表达量升高,MDA水平降低,SOD和GSH-Px水平升高,miR-96-5p水平降低,FOXO1的mRNA和蛋白表达水平升高,FOXO1的乙酰化水平降低（P<0.05）。结论：miR-96-5p在CIRI发生过程中表达上调,而下调miR-96-5p表达可能通过负调控FOXO1以减轻CIRI程度。     

miR-374 improves cerebral ischemia reperfusion injury by targeting Wnt5a

To date, studies have demonstrated the potential functions of microRNAs in cerebral ischemia reperfusion (IR) injury. Herein, we established a middle cerebral artery occlusion (MCAO) model in rats and then subjected them to reperfusion to explore the role of microRNA-374 (miR-374) in cerebral IR injury. After reperfusion, the endogenous miR-374 level decreased, and the expression of its target gene, Wnt5a, increased in brain tissues. Intracerebral pretreatment of miR-374 agomir attenuated cerebral damage induced by IR, including neurobehavioral deficits, infarction, cerebral edema and blood-brain barrier disruption. Moreover, rats pretreated with miR-374 agomir showed a remarkable decrease in apoptotic neurons, which was further confirmed by reduced BAX expression as well as increased BCL-2 and BCL-XL expression. A dual-luciferase reporter assay substantiated that Wnt5a was the target gene of miR-374. miR-374 might protect against brain injury by downregulating Wnt5a in rats after IR. Thus, our study provided a novel mechanism of cerebral IR injury from the perspective of miRNA regulation.     

Decreased expression of sirtuin 6 is associated with release of high mobility group box-1 after cerebral ischemia

Sirtuin 6 (SIRT6) belongs to the sirtuin family of NAD⁺-dependent deacetylases and has been implicated in the regulation of metabolism, inflammation, and aging. Here, we found that SIRT6 was predominantly expressed in neuronal cells throughout the entire brain. Ischemia models using transient middle cerebral artery occlusion in rats and oxygen/glucose deprivation (OGD) in SH-SY5Y neuronal cells showed that ischemia reduced SIRT6 expression and induced the release of high mobility group box-1 (HMGB1) from cell nuclei. The reduced expression of SIRT6 via treatment with SIRT6 siRNA dramatically enhanced the OGD-induced release of HMGB1 in SH-SY5Y cells. Together, our data suggest that SIRT6 may serve as a potential therapeutic target for HMGB1-mediated inflammation after cerebral ischemia.     

Arctium lappa L. roots ameliorates cerebral ischemia through inhibiting neuronal apoptosis and suppressing AMPK/mTOR-mediated autophagy

BackgroundArctium lappa L. roots are very popular cultivated vegetables, which possesses various pharmacological activities. Our previous studies have demonstrated that Arctium lappa L. roots exerted protective effects against H₂O₂, glutamate and N-methyl-D-aspartic acid (NMDA)-induced neuronal injury in vitro. However, whether Arctium lappa L. roots could prevent against cerebral ischemia and the underlying mechanism remain unclear.PurposeThe objective of the present study was to investigate the neuroprotective effects of ethyl acetate extract of Arctium lappa L. roots (EAL) and the active ingredient 4,5-O-dicaffeoyl-1-O-[4-malic acid methyl ester]-quinic acid (DCMQA) in EAL against cerebral ischemia and explore the underlying mechanism.Study DesignThe neuroprotective effects of EAL and DCMQA were investigated in rats with permanent middle cerebral artery occlusion (MCAO) and in oxygen glucose deprivation/reoxygenation (OGD/R)-stimulated SH-SY5Y cells, respectively.MethodsThe infarct volume, brain edema and neurological deficits were measured following MCAO. TUNEL and Nissl staining were performed to detect neuronal loss and apoptosis of neurons in rat brains. Cell survival was measured by MTT and LDH assay. In addition, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) levels were determined by DCFH-DA and JC-1 fluorescent probe, respectively. Hoechst 33342 staining and Annexin V-FITC/PI double staining were performed to evaluate neuronal apoptosis. The expression levels of proteins were evaluated by western blot.ResultsEAL reduced brain infarct volume, ameliorated brain edema and improved neurological deficits in MCAO rats. In addition, EAL inhibited oxidative stress and inflammatory responses following MCAO. Besides, active compound DCMQA alleviated cytotoxicity as well as inhibited over-production of intracellular ROS and loss of MMP induced by OGD/R in SH-SY5Y cells. Moreover, EAL and DCMQA inhibited apoptosis by decreasing the expressions of pro-apoptotic proteins including bax, cytochrome c and cleaved caspase-3 while promoting the bcl-2 expression in MCAO rats and OGD/R-stimulated neurons, respectively. In addition, DCMQA suppressed the production of autophagosomes and down-regulated expression of Beclin 1 and LC3. Furthermore, inhibiting AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling pathway contributed to DCMQA-mediated suppression of autophagy induced by OGD/R.ConclusionOur findings demonstrate that Arctium lappa L. roots protect against cerebral ischemia through inhibiting apoptosis and AMPK/mTOR-mediated autophagy in vitro and in vivo, providing a theoretical basis for the development of CQAs in Arctium lappa L. roots as neuroprotective drugs for the prevention and treatment of ischemic stroke.     

Retracted: MicroRNA-150 contributes to ischemic stroke through its effect on cerebral cortical neuron survival and function by inhibiting ERK1/2 axis via Mal

Ischemic stroke, caused by the blockage of blood supply, is a major cause of death worldwide. For identifying potential candidates, we explored the effects microRNA-150 (miR-150) has on ischemic stroke and its underlying mechanism by developing a stable middle cerebral artery occlusion (MCAO) rat model. Gene expression microarray analysis was performed to screen differentially expressed genes associated with MCAO. We evaluated the expression of miR-150 and Mal and the status of ERK1/2 axis in the brain tissues of MCAO rats. Then the cerebral cortical neurons (CCNs) were obtained and introduced with elevated or suppressed miR-150 or silenced Mal to validate regulatory mechanisms for miR-150 governing Mal in vitro. The relationship between miR-150 and Mal was verified by dual luciferase reporter gene assay. Besides, cell growth and apoptosis of CCNs were detected by means of MTT assay and flow cytometry analyses. We identified Mal as a downregulated gene in MCAO, based on the microarray data of GSE16561. MiR-150 was over-expressed and negatively targeted Mal in the brain tissues obtained from MCAO rats and their CCNs. Increasing miR-150 blocked the ERK1/2 axis, resulting in an inhibited cell growth of CNNs but an enhanced apoptosis. Furthermore, MiR-150 inhibition was observed to have effects on CNNs as opposed to those inhibited by miR-150 promotion. The key findings of this study support the notion that miR-150 under-expression-mediated direct promotion of Mal protects CNN functions through the activation of the ERK1/2 axis, and underscore the concept that miR-150 may represent a novel pharmacological target for ischemic stroke intervention.     

Sufentanil alleviates cerebral ischemia-reperfusion injury by inhibiting inflammation and protecting the blood-brain barrier in rats

Stroke is a brain system disease with a high fatality rate and disability rate. About 80% of strokes are ischemic strokes. Cerebral ischemia-reperfusion injury (CIRI) caused by ischemic stroke seriously affects the prognosis of stroke patients. The purpose of this study is to investigate the effect of sufentanil (SUF) on CIRI model rats. We used middle cerebral artery occlusion (MCAO) to make the CIRI model in rats and monitored region cerebral blood flow (rCBF) to ensure that blood flow was blocked and recanalized. We used ELISA and RT-PCR to detect the expression of inflammatory factors in rat serum and brain tissue. In addition, we detected the expression of metalloproteinase (MMP) 2, MMP9 and collagen IV in brain tissues and performed Evans blue (EB) assay to determine the permeability of the blood-brain barrier (BBB). Finally, we clarified the apoptosis of brain tissue through the TUNEL staining and the detection of caspase 3, Bcl2 and Bax. Various concentrations of SUF, especially 5, 10 and 25μg/kg of SUF, all alleviated the infarct size, neurological function and brain edema of MCAO rats. SUF pretreatment also effectively reduced the expression of inflammatory cytokines in MCAO rats, including interleukin (IL)-1β, IL-4, IL-6, IL-8, IL-10 and tumor necrosis factor (TNF)-α. In addition, SUF also inhibited MMP2 and MMP9 and promoted the expression of collagen IV, indicating that SUF attenuated the destruction of the BBB. SUF also inhibited caspase 3 and Bax rats and promoted Bcl2 in MCAO rats, thus inhibiting cell apoptosis. SUF pretreatment effectively improved the neurological function and cerebral infarction of MCAO rats, inhibited excessive inflammation in rats, protected the BBB, and inhibited cell apoptosis in brain tissue.Key words: Sufentanil, cerebral ischemia-reperfusion injury, inflammation, blood-brain barrier     

Induction of autophagy contributes to the neuroprotection of nicotinamide phosphoribosyltransferase in cerebral ischemia

Recent reports indicate that autophagy serves as a stress response and may participate in pathophysiology of cerebral ischemia. Nicotinamide phosphoribosyltransferase (Nampt, also known as visfatin), the rate-limiting enzyme in mammalian NAD⁺ biosynthesis, protects against ischemic stroke through inhibiting neuronal apoptosis and necrosis. This study was taken to determine the involvement of autophagy in neuroprotection of Nampt in cerebral ischemia. Middle cerebral artery occlusion (MCAO) in rats and oxygen-glucose deprivation (OGD) in cultured cortical neurons were performed. Nampt was overexpressed or knocked-down using lentivirus-mediated gene transfer in vivo and in vitro. Immunochemistry (LC3-II), electron microscope and immunoblotting assays (LC3-II, beclin-1, mammalian target of rapamycin [mTOR], S6K1 and tuberous sclerosis complex-2 [TSC2]) were performed to assess autophagy. We found that overexpression of Nampt increased autophagy (LC3 puncta immunochemistry staining, LC3-II/beclin-1 expression and autophagosomes number) both in vivo and in vitro at 2 hours after MCAO. At the early stage of OGD, autophagy inducer rapamycin protected against neuronal injury induced by Nampt knockdown, whereas autophagy inhibitor 3-methyladenine abolished the neuroprotective effect of Nampt partly. Overexpression or knockdown of Nampt regulated the phosphorylation of mTOR and S6K1 signaling pathway upon OGD stress through enhancing phosphorylation of TSC2 at Ser1387 but not Thr1462 site. Furthermore, in cultured SIRT1-knockout neurons, the regulation of Nampt on autophagic proteins LC3-II and beclin-1 was abolished. Our results demonstrate that Nampt promotes neuronal survival through inducing autophagy via regulating TSC2-mTOR-S6K1 signaling pathway in a SIRT1-dependent manner during cerebral ischemia.