细胞外信号调节激酶通路在帕金森病运动并发症中的作用

目的 探讨细胞外信号调节激酶(ERK)通路在左旋多巴诱发的运动并发症中的作用.方法 通过6-羟多巴胺立体定向注射至大鼠前脑内侧前脑束建立帕金森病(PD)动物模型.对建模成功的PD大鼠每日2次左旋多巴(50 mg/kg 加12.5 mg/kg苄丝肼)腹腔注射,持续22 d.在第23天注射左旋多巴前,给予PD大鼠ERK特异性的抑制剂PD98059处理.评估旋转反应时间及剂峰旋转圈数,采用蛋白免疫印迹法检测纹状体区ERK1/2 磷酸化表达情况.结果 长期使用左旋多巴处理使PD大鼠损伤侧纹状体ERK1/2 磷酸化水平显著增强(155.6%±6.5%), 而PD98059 可明显降低ERK1/2磷酸化水平(85.4%±5.6%).同时,PD98059逆转了左旋多巴所诱导的PD大鼠旋转时间的缩短,减少了剂峰旋转次数.此外,蛋白激酶C(PKC)抑制剂能部分减轻ERK1/2磷酸化水平(101.2%±6.2%,与左旋多巴+溶剂组相比较t=3.2,P<0.05).结论 PD运动并发症的发生可能与纹状体ERK通路的激活有关,并且ERK通路的激活部分是PKC所依赖的;抑制ERK通路活性的药物可能是治疗PD运动并发症的一种新的治疗方式.     

FRK通过抑制ERK信号通路对脑胶质瘤细胞增殖作用的研究

目的研究FRK是否通过抑制ERK信号通路进而影响脑胶质瘤细胞的增殖。方法应用PolyJet~(TM)将FRK质粒转染入脑胶质瘤U251细胞中,Western blot(WB)检测转染效率及P-ERK、ERK蛋白水平的变化,EDU实验观察脑胶质瘤细胞增殖能力的变化;用ERK抑制剂PD98059处理U251细胞,WB检测细胞中FRK、P-ERK、ERK的蛋白水平,EDU实验检测脑胶质瘤细胞增殖能力的变化。结果 WB检测显示FRK质粒转染成功,过表达FRK使U251细胞增殖能力降低。过表达FRK降低了P-ERK的蛋白水平,但对ERK总蛋白水平无影响。与对照组相比,ERK抑制剂PD98059组P-ERK的蛋白水平明显降低,但对FRK的蛋白水平无明显影响。ERK抑制剂PD98059处理后,脑胶质瘤U251细胞增殖能力明显降低。结论 FRK可以通过抑制ERK的活性,从而降低脑胶质瘤细胞的增殖。     

脊髓来源神经干细胞分离培养及向雪旺氏细胞的诱导分化

目的 探讨新生大鼠脊髓来源神经干细胞(NSCs)的分离培养及在体外一定条件下向周围神经雪旺氏细胞分化的可行性. 方法 分离新生大鼠的脊髓组织,在含有B27(终浓度1%)、碱性成纤维细胞生长因子(bFGF)和表皮生长因子(EGF)(终浓度均为20 μg/L)培养基中分离培养出NSCs.用复合诱导因子(10%FBS+5 μmol/L血小板凝集抑制剂+10 ng/mL bFGF+5 ng/mE血小板源性生长因子)在体外诱导NSCs分化为雪旺氏细胞.免疫荧光细胞化学方法[一抗为p75、S-100、神经胶质纤维酸性蛋白(GFAP)]鉴定体外诱导分化结果.结果 培养的新生大鼠脊髓组织细胞nestin染色表达阳性;分离培养的大鼠脊髓来源NSCs经诱导分化后形态类似雪旺氏细胞,免疫荧光细胞化学方法显示诱导后细胞表达雪旺氏细胞的表面标志,GFAP、S-100和P75表达阳性.结论 新生大鼠脊髓来源NSCs可以在体外诱导分化为雪旺氏细胞.     

MAPK信号通路在创伤性脑损伤中的作用

目的通过建立小鼠创伤性脑损伤(TBI)模型,研究丝裂原活化蛋白激酶(MAPKs)通路中的细胞外调节蛋白激酶1/2(ERK1/2)通路、JNK通路和p38通路的激活及在TBI中的作用及机制。方法建立小鼠TBI模型,通过Western blot检测ERK1/2、JNK和p38的相对磷酸化水平,确定TBI后MAPK通路的激活情况;分别加入ERK1/2通路抑制剂(PD98059,500μmol/L)、JNK通路抑制剂(SP600125,500μmol/L)和p38通路抑制剂(SB203580,500μmol/L),通过脑干湿重检测、神经功能学评分和TUNEL染色评估不同抑制剂对TBI的作用,并通过Western blot检测ERK1/2、JNK和p38的相对磷酸化水平,明确ERK1/2通路、JNK通路和p38通路之间的相互调节作用。结果 TBI可分别引起ERK1/2通路、JNK通路和p38通路的激活;抑制ERK通路和JNK通路可减轻TBI引起的脑水肿、神经功能损伤和细胞凋亡,而抑制p38通路则加重TBI引起的脑水肿、神经功能损伤和细胞凋亡;抑制JNK通路可减少ERK1/2的相对磷酸化水平,而抑制p38通路可增加ERK1/2的相对磷酸化水平。结论 TBI后,ERK1/2通路和JNK通路的激活发挥促进损伤形成的作用,而p38通路的激活则起到神经保护的作用;ERK1/2通路的激活受到JNK通路的促进和p38通路的抑制,表明MAPK通路之间存在相互调节。     

ERK1/2信号传导通路介导碱性成纤维细胞生长因子诱导人晶状体上皮细胞中环氧合酶2的表达**☆

背景：碱性成纤维细胞生长因子在各种白内障形成中都起着重要的作用,可促进晶状体上皮细胞的增殖并化生为纤维细胞,但其信号通路尚不清楚。 目的：探讨ERK1/2信号转导通路在碱性成纤维细胞生长因子诱导的人晶状体上皮细胞环氧合酶2表达中的作用。 方法：使用10 μg/L的碱性成纤维细胞生长因子干预培养的人晶状体上皮细胞0,1,3,6,12,24 h,RT-PCR检测刺激不同时间人晶状体上皮细胞环氧合酶2 mRNA的表达,Western blot检测细胞中环氧合酶2及磷酸化ERK1/2的表达。在阻断实验中应用特异性ERK1/2的阻断剂PD98059 阻断ERK信号转导通路1 h,再用10 μg/L碱性成纤维细胞生长因子刺激细胞6 h,Western blot检测细胞中环氧合酶2的表达。 结果与结论：碱性成纤维细胞生长因子刺激后的人晶状体上皮细胞中环氧合酶2 mRNA及其蛋白的表达显著增加(P < 0.01),同时碱性成纤维细胞生长因子诱导人晶状体上皮细胞磷酸化ERK1/2活性增强,表达水平随作用时间而增加,30 min时达到最高峰(P < 0.01),6 h后恢复至基线水平;PD98059可抑制人晶状体上皮细胞环氧合酶2的表达 (P < 0.01)。说明ERK1/2信号转导通路参与了碱性成纤维细胞生长因子诱导的人晶状体上皮细胞中环氧合酶2的表达,在后发性白内障的形成过程中起着重要作用。     

ERK1/2信号通路对缺血后适应大鼠皮层的作用

目的研究脑缺血大鼠缺血后适应模型中大脑皮质的ERK1/2通路表达特点及应用ERK1/2特异性抑制剂PD98059后对缺血后适应神经保护作用的影响,研究缺血后适应是否通过ERK1/2信号通路介导对急性缺血性脑梗死再灌注后的神经保护作用。方法将20只SD大鼠随机分为假手术组、缺血2h再灌注组、缺血2h后适应组以及PD98059+缺血2h后适应组(PD+2h后适应组),每组5只,用线栓法建立急性大脑中动脉闭塞的缺血性脑梗死模型,4组分别进行不同形式的实验。对比4组大鼠再灌注1h、24h的神经功能评分及再灌注24h后的梗死体积。每组另增加15只大鼠,分别于再灌注后2h、6h、24h留取缺血大脑皮质;Western blot检测再灌注2h、6h、24h后总T-ERK1/2、P-ERK1/2表达。结果 PD+2h后适应组与缺血2h再灌注组神经功能缺损评分高于缺血2h后适应组,脑梗死体积大于缺血2h后适应组。缺血后适应组再灌注2h、6h、24h后P-ERK1/2表达明显高于缺血2h再灌注组及PD+2h后适应组;以上表明,缺血后适应通过ERK1/2信号通路减轻大鼠缺血性脑损伤,应用P-ERK1/2的阻滞剂PD98059后,阻断了缺血后适应的脑保护作用。结论通过对本实验研究数据的分析后发现,缺血后适应对大鼠急性缺血性脑梗死具有神经保护作用,应用ERK1/2特异性抑制剂PD98059后,缺血后适应神经保护效应减弱,说明缺血后适应对急性缺血性脑梗死再灌注损伤的保护作用与MAPK/ERK信号通路具有深层次紧密关系。     

骨髓间充质干细胞增殖与成骨分化中电磁场激活ERK通路的作用*

背景：研究表明电磁场可调节骨髓间充质干细胞的增殖和分化,但其具体机制尚不清楚。 目的：从ERK信号途径探讨电磁场诱导大鼠骨髓间充质干细胞增殖与分化成骨的作用。 方法：取第3代生长良好的大鼠骨髓间充质干细胞,暴磁组给予15 Hz、1 mT的正弦波电磁场刺激,PD98059+暴磁组在电磁场刺激前给予20 μmol/L ERK阻断剂PD98059,PD98059组仅给PD98059不进行电磁场刺激,对照组正常培养。电磁场刺激后,收集各组细胞,Western blot法检测ERK通路的活性,MTT法检测细胞增殖活性,碱性磷酸酶试剂盒检测细胞碱性磷酸酶活性。 结果与结论：电磁场刺激后,细胞ERK1/2磷酸化水平、细胞的增殖活性、及碱性磷酸酶活性均明显升高(P < 0.01);PD98059可明显抑制ERK1/2磷酸化水平及细胞增殖活性的升高(P < 0.01),而在一定程度上提高细胞的碱性磷酸酶活性(P < 0.01)。说明电磁场刺激可通过激活骨髓间充质干细胞ERK信号通路,并且主要通过该途径促进骨髓间充质干细胞的增殖;而在脉冲电磁场促进骨髓间充质干细胞分化成骨的过程中,激活ERK信号通路所起的作用较小。     

细胞外信号调节激酶信号通路对癫痫大鼠海马内HIF-1α表达的调控作用

目的 探讨细胞外信号调节激酶(ERK)信号通路是否参与调节癫痫大鼠海马内低氧诱导因子-1α(HIF-1α)的表达. 方法 208只21d龄SD大鼠按随机数字表法分为癫痫持续状态(SE)组(96只)、对照组(96只)和PD98059组(16只),SE组腹腔注射戊四氮(PTZ)溶液制作SE模型,对照组注射等剂量生理盐水,造模后0.5、1、1.5、6、12、24h采用RT-PCR、Western blotting分别检测2组大鼠海马内HIF-1α、ERK1/2 mRNA和蛋白的表达;PD98059组大鼠腹腔注射PD98059,10min后腹腔注射PTZ溶液制作SE模型,造模成功后1h采用RT-PCR检测大鼠海马内HIF-1α、ERK1/2mRNA的表达,造模成功后1.5 h采用Western blotting检测其相应蛋白的表达. 结果 与对照组比较,SE组大鼠海马内HIF-1α、ERK1/2 mRNA及其蛋白的表达明显升高,差异均有统计学意义(P＜0.05);其中ERK1/2 mRNA的表达高峰(1.112±0.126)在SE后1h,蛋白的表达高峰(1.127±0.155)在SE后1.5 h;而HIF-1α mRNA的表达高峰(0.589±0.090)在SE后1.5 h,蛋白的表达高峰(0.230±0.052)在SE后6h.与SE组相比,PD98059组大鼠海马内HIF-1αmRNA、ERK1/2 mRNA和蛋白的表达均降低,差异均有统计学意义(P＜0.05).SE组大鼠中,T-ERK 1/2与HIF-1αmRNA的表达呈正相关(r=0.688,P=0.000). 结论 戊四氮诱导发育期大鼠SE后ERK信号通路被激活,参与了海马内HIF-1α的表达调控.     

三七总皂甙通过细胞外信号调节蛋白激酶1/2信号通路促进大鼠

背景：三七总皂甙对骨髓基质细胞向神经样细胞分化的效应及相关信号通路目前尚不明确。 目的：探讨细胞外信号调节蛋白激酶1/2信号通路对三七总皂甙调节大鼠骨髓基质细胞向神经细胞增殖、分化的作用。 设计、时间及地点：细胞学体外观察,于2008-05/10在汕头大学医学院分子生物学实验室完成。 材料：4~6周龄雄性SD大鼠9只,由汕头大学医学院实验动物中心提供。三七总皂甙为广西梧州制药集团股份有限公司产品,细胞外信号调节蛋白激酶的抑制剂PD98059为Cell Signaling Tech 公司产品。 方法：全骨髓法体外分离纯化大鼠骨髓基质细胞,取传至第3代细胞进行诱导分化,设立3组：单纯诱导组向培养液中加入10 μg/L碱性成纤维细胞生长因子,预诱导24 h后全量换为正式诱导液(含10 μg/L碱性成纤维细胞生长因子、2% DMSO、200 μmol/L丁羟回醚的α-MEM培养基),每24 h半量换诱导液1次;三七总皂甙组向预诱导液和正式诱导液内加入终浓度100 mg/L三七总皂甙;PD98059组在三七总皂甙组培养液基础上加入10 μmol/L PD98059。 主要观察指标：细胞形态学观察,MTT法检测细胞增殖情况,免疫组织化学方法鉴定细胞Nestin的表达。 结果：诱导6 h后,少数细胞呈锥形,细胞突起增多伸长,类似神经元,继续诱导培养后细胞突起增多,突起相互连接成网状。与单纯诱导组、PD98059组比较,诱导6,12,24 h三七总皂甙组细胞均明显增殖(P < 0.05),且随诱导时间延长呈递增趋势(P < 0.05);单纯诱导组、PD98059组间比较无明显差异(P > 0.05)。与单纯诱导组比较,诱导24 h后三七总皂甙组Nestin阳性率明显升高(P < 0.05),PD98059组Nestin阳性率明显降低(P < 0.05)。 结论：三七总皂甙可以促进骨髓基质细胞的神经分化和分化后增殖,细胞外信号调节蛋白激酶1/2的特异性抑制剂PD98059能够拮抗三七总皂甙促增殖分化作用,提示细胞外信号调节蛋白激酶1/2信号通路是三七总皂甙促进骨髓基质细胞向神经细胞分化和增殖的重要环节。     

MCPG在神经元氧糖剥夺模型中的抗凋亡作用

目的通过神经元氧糖剥夺模型研究Ⅰ组代谢型谷氨酸受体拮抗剂α-甲基-4-羧苯基甘氨酸（MCPG）对神经元损伤的保护作用,并初步探讨其机制。方法大鼠皮层神经元原代培养2w后,采用氧糖剥夺法建立损伤模型,通过乳酸脱氢酶（LDH）活性测定及碘化丙啶（PI）/Hoechst33342双染鉴定神经元损伤程度;加入Ⅰ组代谢型谷氨酸受体拮抗剂MCPG（1mmol/L）,通过脱氧核糖核苷酸末端转移酶介导的缺口末端标记法（TUNEL）检测神经元凋亡情况,并采用蛋白印迹法研究凋亡相关因子caspase-3、细胞外信号调节激酶1/2（ERK1/2）、磷酸化ERK1/2（p-ERK1/2）的表达变化,讨论MCPG抗凋亡作用与ERK1/2信号通路的关系。结果 MCPG能抑制ERK1/2信号通路的活化并降低凋亡相关因子caspase-3的表达,减轻氧糖剥夺造成的神经元凋亡。结论 MCPG能够通过ERK1/2信号通路减轻氧糖剥夺造成的神经元凋亡。     

Epalrestat protects against diabetic peripheral neuropathy by alleviating oxidative stress and inhibiting polyol pathway

Epalrestat is a noncompetitive and reversible aldose reductase inhibitor used for the treatment of diabetic neuropathy. This study assumed that epalrestat had a protective effect on diabetic peripheral nerve injury by suppressing the expression of aldose reductase in peripheral nerves of diabetes mellitus rats. The high-fat and high-carbohydrate model rats were established by intraperitoneal injection of streptozotocin. Peripheral neuropathy occurred in these rats after sustaining high blood glucose for 8 weeks. At 12 weeks after streptozotocin injection, rats were intragastrically administered epalrestat 100 mg/kg daily for 6 weeks. Transmission electron microscope revealed that the injuries to myelinated nerve fibers, non-myelinated nerve fibers and Schwann cells of rat sciatic nerves had reduced compared to rats without epalrestat administuation. Western blot assay and immunohistochemical results demonstrated that after intervention with epalrestat, the activities of antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase gradually increased, but aldose reductase protein expression gradually diminished. Results confirmed that epalrestat could protect against diabetic peripheral neuropathy by relieving oxidative stress and suppressing the polyol pathway.     

3-N-Butylphthalide mitigates high glucose-induced injury to Schwann cells:association with nitrosation and apoptosis

A high glucose state readily causes peripheral axon atrophy, demyelination, loss of nerve fiber function, and delayed regeneration. However, few studies have examined whether nitration is also critical for diabetic peripheral neuropathy. Therefore, this study investigated the effects of high glucose on proliferation, apoptosis, and 3-nitrotyrosine levels of Schwann cells treated with butylphthalide. In addition, we explored potential protective mechanisms of butylphthalide on peripheral nerves. Schwann cells were cultured in vitro with high glucose then stimulated with the peroxynitrite anion inhibitors uric acid and 3-n-butylphthalide for 48 hours. Cell Counting Kit-8 and flow cytometry were used to investigate the effects of uric acid and 3-n-butylphthalide on proliferation and apoptosis of Schwann cells exposed to a high glucose environment. Effects of uric acid and 3-n-butylphthalide on levels of 3-nitrotyrosine in Schwann cells were detected by enzyme-linked immunosorbent assay. The results indicated that Schwann cells cultured in high glucose showed decreased proliferation, but increased apoptosis and intracellular 3-nitrotyrosine levels. However, intervention with uric acid or 3-n-butylphthalide could increase proliferation of Schwann cells cultured in high glucose, and inhibited apoptosis and intracellular 3-nitrotyrosine levels. According to our data, 3-n-butylphthalide may inhibit cell nitrification and apoptosis, and promote cell proliferation, thereby reducing damage to Schwann cells caused by high glucose.     

Quercetin alleviates high glucose-induced Schwann cell damage by autophagy

Quercetin can reverse high glucose-induced inhibition of neural cell proliferation, and therefore may have a neuroprotective effect in diabetic peripheral neuropathy. It is difficult to obtain pri- mary Schwann cells and RSC96 cells could replace primary Schwann cells in studies of the role of autophagy in the mechanism underlying diabetic peripheral neuropathy. Here, we show that under high glucose conditions, there are fewer autophagosomes in immortalized rat RSC96 cells and primary rat Schwann ceils than under control conditions, the proliferative activity of both cell types is significantly impaired, and the expression of Berlin- 1 and LC3, the molecular mark- ers for autophagy, is significantly lower. After intervention with quercetin, the autophagic and proliferative activity of both cell types is rescued. These results suggest that quercetin can allevi- ate high glucose-induced damage to Schwann cells by autophagy.     

Baculoviral inhibitor of apoptosis protein repeat-containing protein 3 delays early Wallerian degeneration after sciatic nerve injury

Wallerian degeneration is a complex biological process that occurs after nerve injury,and involves nerve degeneration and regeneration.Schwann cells play a crucial role in the cellular and molecular events of Wallerian degeneration of the peripheral nervous system.However,Wallerian degeneration regulating nerve injury and repair remains largely unknown,especially the early response.We have previously reported some key regulators of Wallerian degeneration after sciatic nerve injury.Baculoviral inhibitor of apoptosis protein repeat-containing protein 3(BIRC3)is an important factor that regulates apoptosis-inhibiting protein.In this study,we established rat models of right sciatic nerve injury.In vitro Schwann cell models were also established and subjected to gene transfection to inhibit and overexpress BIRC3.The data indicated that BIRC3 expression was significantly up-regulated after sciatic nerve injury.Both BIRC3 upregulation and downregulation affected the migration,proliferation and apoptosis of Schwan cells and affected the expression of related factors through activating c-fos and ERK signal pathway.Inhibition of BIRC3 delayed early Wallerian degeneration through inhibiting the apoptosis of Schwann cells after sciatic nerve injury.These findings suggest that BIRC3 plays an important role in peripheral nerve injury repair and regeneration.The study was approved by the Institutional Animal Care and Use Committee of Nantong University,China(approval No.2019-nsfc004)on March 1,2019.     

Therapeutic Effects of Aldose Reductase Inhibitor on Experimental Diabetic Neuropathy through Synthesis/Secretion of Nerve Growth Factor

We investigated alterations in nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF) contents during treatment with epalrestat, an aldose reductase inhibitor (ARI), on streptozotocin (STZ)-induced diabetic neuropathy in rats. Diabetic rats showed a statistically significant reduction in H-wave-related sensory nerve conduction velocity (HSNCV) and in NGF content in sciatic nerves during the experiment of 8 weeks. No reduction in the CNTF content in sciatic nerves was seen in the diabetic rats. The epalrestat treatment, which started 4 weeks after STZ injection, resulted in a significantly greater NGF content and faster HSNCV than those in untreated diabetic rats. But no statistically significant alterations of motor nerve conduction velocity (MNCV) or CNTF content were seen during the treatment. ARI showed the stimulating effect for NGF synthesis/secretion in rat Schwann cell culturein vitro.These findings suggest that decreased levels of NGF in diabetic sciatic nerves may be involved in the pathogenesis of diabetic neuropathy in these rats and further show that epalrestat treatment can be useful for the treatment of diabetic neuropathy through NGF-induction in Schwann cells and/or inhibition of the polyol pathway.     

Schwann cells express erythropoietin receptor and represent a major target for Epo in peripheral nerve injury

Erythropoietin (Epo) expresses potent neuroprotective activity in the peripheral nervous system; however, the underlying mechanism remains incompletely understood. In this study, we demonstrate that Epo is upregulated in sciatic nerve after chronic constriction injury (CCI) and crush injury in rats, largely due to local Schwann cell production. In uninjured and injured nerves, Schwann cells also express Epo receptor (EpoR), and its expression is increased during Wallerian degeneration. CCI increased the number of Schwann cells at the injury site and the number was further increased by exogenously administered recombinant human Epo (rhEpo). To explore the activity of Epo in Schwann cells, primary cultures were established. These cells expressed cell-surface Epo receptors, with masses of 71 and 62 kDa, as determined by surface protein biotinylation and affinity precipitation. The 71-kDa species was rapidly but transiently tyrosine-phosphorylated in response to rhEpo. ERK/MAP kinase was also activated in rhEpo-treated Schwann cells; this response was blocked by pharmacologic antagonism of JAK-2. RhEpo promoted Schwann cell proliferation, as determined by BrdU incorporation. Cell proliferation was ERK/MAP kinase-dependent. These results support a model in which Schwann cells are a major target for Epo in injured peripheral nerves, perhaps within the context of an autocrine signaling pathway. EpoR-induced cell signaling and Schwann cell proliferation may protect injured peripheral nerves and promote regeneration.     

Changes in the BAG1 Expression of Schwann Cells After Sciatic Nerve Crush

Bcl-2-associated athanogene-1 (BAG1), a co-chaperone for Hsp70/Hsc70, is a multifunctional protein, which has been shown to suppress apoptosis and enhance neuronal differentiation. However, the expression and roles of BAG1 in peripheral system lesions and repair are still unknown. In this study, we investigated the dynamic changes in BAG1 expression in an acute sciatic nerve crush model in adult rats. Western blot analysis revealed that BAG1 was expressed in normal sciatic nerves. BAG1 expression increased progressively after sciatic nerve crush, reached a peak 2 weeks post-injury, and then returned to the normal level 4 weeks post-injury. Spatially, we observed that BAG1 was mainly expressed in Schwann cells and that BAG1 expression increased in Schwann cells after injury. In vitro, we found that BAG1 expression increased during the cyclic adenosine monophosphate (cAMP)-induced Schwann cell differentiation process. BAG1-specific siRNA inhibited cAMP-induced Schwann cell differentiation. In conclusion, we speculated that BAG1 was upregulated in the sciatic nerve after crush, which was associated with Schwann cell differentiation.     

Impaired peripheral nerve regeneration in type‐2 diabetic mouse model

Peripheral neuropathy is one of the most common and serious complications of type‐2 diabetes. Diabetic neuropathy is characterized by a distal symmetrical sensorimotor polyneuropathy, and its incidence increases in patients 40 years of age or older. In spite of extensive research over decades, there are few effective treatments for diabetic neuropathy besides glucose control and improved lifestyle. The earliest changes in diabetic neuropathy occur in sensory nerve fibers, with initial degeneration and regeneration resulting in pain. To seek its effective treatment, here we prepared a type‐2 diabetic mouse model by giving mice 2 injections of streptozotocin and nicotinamide and examining the ability for nerve regeneration by using a sciatic nerve transection‐regeneration model previously established by us. Seventeen weeks after the last injection, the mice exhibited symptoms of type‐2 diabetes, that is, impaired glucose tolerance, decreased insulin level, mechanical hyperalgesia, and impaired sensory nerve fibers in the plantar skin. These mice showed delayed functional recovery and nerve regeneration by 2 weeks compared with young healthy mice and by 1 week compared with age‐matched non‐diabetic mice after axotomy. Furthermore, type‐2 diabetic mice displayed increased expression of PTEN in their DRG neurons. Administration of a PTEN inhibitor at the cutting site of the nerve for 4 weeks promoted the axonal transport and functional recovery remarkably. This study demonstrates that peripheral nerve regeneration was impaired in type‐2 diabetic model and that its combination with sciatic nerve transection is suitable for the study of the pathogenesis and treatment of early diabetic neuropathy.     

The Neuregulin‐Rac‐MKK7 pathway regulates antagonistic c‐jun/Krox20 expression in Schwann cell dedifferentiation

Schwann cells respond to nerve injury by dedifferentiating into immature states and producing neurotrophic factors, two actions that facilitate successful regeneration of axons. Previous reports have implicated the Raf‐ERK cascade and the expression of c‐jun in these Schwann cell responses. Here we used cultured primary Schwann cells to demonstrate that active Rac1 GTPase (Rac) functions as a negative regulator of Schwann cell differentiation by upregulating c‐jun and downregulating Krox20 through the MKK7‐JNK pathway, but not through the Raf‐ERK pathway. The activation of MKK7 and induction of c‐jun in sciatic nerves after axotomy was blocked by Rac inhibition. Microarray experiments revealed that the expression of regeneration‐associated genes, such as glial cell line‐derived neurotrophic factor and p75 neurotrophin receptor, after nerve injury was dependent on Rac but not on ERK. Finally, the inhibition of ErbB2 signaling prevented MKK7 activation, c‐jun induction, and Rac‐dependent gene expression in sciatic nerve explant cultures. Taken together, our results indicate that the neuregulin‐Rac‐MKK7‐JNK/c‐jun pathway regulates Schwann cell dedifferentiation following nerve injury.     

Role of ERK activation in cisplatin-induced apoptosis in A172 human glioma cells

Cisplatin activates multiple signal transduction pathways associated with cell survival and apoptosis in various cell types. The present study was undertaken to determine the role of extracellular signal-regulated protein kinase (ERK), a member of the mitogen-activated protein kinase family, in cisplatin-induced apoptosis in human glioma cells. Cisplatin resulted in apoptosis in a dose- and time-dependent manner. Cisplatin-induced apoptosis was prevented by the hydrogen peroxide scavenger pyruvate and the antioxidant N-acetylcysteine, but not by the superoxide scavenger tiron. Western blot analysis demonstrated that cisplatin treatment induced time-dependent activation of ERK, which was inhibited by chemical inhibitors of the MEK signaling pathway (PD98059 and U0126) and N-acetylcysteine. These inhibitors prevented cisplatin-induced cell death. Transient transfection of constitutive active MEK1 increased cisplatin-induced apoptosis. Cisplatin resulted in a reduction in mitochondrial membrane potential and its effect was prevented by N-acetylcysteine and PD98059. Caspase inhibitors (Boc-D-FMK and zDEVD-FMK) protected against cisplatin-induced cell death. Cisplatin-induced activation of caspase-3 was inhibited by N-acetylcysteine and PD98059. Taken together, these findings suggest that the ERK activation plays an active role in mediating cisplatin-induced apoptosis of human glioma cells and functions upstream of mitochondrial dysfunction and caspase activation to the initiate the apoptotic signal.