The dynamic changes of main cell types in the microenvironment of sciatic nerves following sciatic nerve injury and the influence of let-7 on their distribution

Schwann cells (SCs), fibroblasts and macrophages are the main cells in the peripheral nerve stumps. These three types of cell play important roles in regulating the regeneration microenvironment and improving the regeneration effect through a variety of manual interventions. However, the dynamic distribution of these cells during the different stages of peripheral nerve regeneration remain unclear. In this study, we systematically explored the number/ratio and distribution changes of SCs, fibroblasts, and macrophages at different time points after sciatic nerve injury. Moreover, considering that let-7 is an ideal molecule for regulating the regeneration environment, we further studied the entrance and influence of let-7 antagomir on these three main cell types. Collectively, our current study revealed the cell basis of the microenvironment of peripheral nerve regeneration and indicated that let-7 could modify the regenerative microenvironment by regulating the number/ratio and distribution of SCs, fibroblasts, and macrophages. Our study would help to open a new potential therapeutic window for peripheral nerve injury.

Schwann cells (SCs), fibroblasts and macrophages are the main cells in the peripheral nerve stumps.     

Upgraded Nerve Growth Factor Expression Induced by Low-Intensity Continuous-Wave Ultrasound Accelerates Regeneration of Neurotometicly Injured Sciatic Nerve in Rats

Low-intensity ultrasound (LIU) can stimulate injured nerve regeneration but the mechanism is still unclear. We investigated the stimulating effect and its mechanism of continuous-wave LIU on neurotometic injury of sciatic nerve. The right sciatic nerves of 64 adult Wistar rats were first crushed and then exposed (32 rats) or sham-exposed (32 rats) to LIU at the crush site. The LIU had a spatial averaged and temporal averaged intensity of 0.25W/cm² operated at 1.0 MHz for 1 min every other day. At various stages (the second, fourth, sixth and eighth weeks) after LIU exposure, the sciatic nerve function index (SFI), the sensory nerve conduction velocity (SNCV), the expression of nerve growth factor (NGF) and sample histology were studied. It was found that the density of nerve fibers with myelin sheath, SFI, SNCV and NGF expression of the treatment group were higher than that of control group (p < 0.05). It has been determined that LIU treatment can accelerate the regeneration and functional recovery of neurotometic injured sciatic nerve at earlier stages after injury, the upgraded expression of NGF induced by LIU may be the primary mechanism of the acceleration effects. (E-mail: wangzhibiao@haifu.com.cn)     

微囊化转染神经生长因子基因细胞移植在周围神经再生中的作用

目的探讨应用免疫隔离技术进行转染神经生长因子（NGF）基因的3T3细胞移植促进周围神经损伤后再生的可行性.方法采用海藻酸钠-聚赖氨酸-海藻酸钠（APA）微胶囊包埋NGF-3T3细胞并进行培养;制备坐骨神经横断损伤SD大鼠模型,96只SD大鼠随机分A组（微囊化NGF-3T3细胞组）、B组（空胶囊组）、C组（转染NGF的3T3细胞组）和D组（阴性对照组）.分别采用神经干动作电位（NAP）、神经传导速度（NCV）和坐骨神经功能指数（SFI）检测坐骨神经功能恢复情况.结果微囊化NGF-3T3细胞培养后保持活性和增殖能力,将具有分化潜能的大鼠嗜铬细胞瘤细胞与其共培养,7 d时细胞胞体分化成多边形或锥形,形成突起;培养10 d左右NGF分泌量最高,达269 pg/ml;培育50 d仍然保持在208 pg/ml.移植术后4、8及12周时,A组大鼠的NAP及NCV均大于B、C、D组（P＜0.05）,而B、C、D三组之间无显著性差异（P＞0.05）;A组大鼠的SFI恢复情况优于B、C、D组（P＜0.05）,而B、C、D三组之间无显著性差异（P＞0.05）.结论微囊化NGF-3T3细胞在体外培养一定时间后,仍保持增殖能力和生物活性,移植到大鼠周围神经损伤局部后可长时间存活,并通过持续分泌NGF起到促进周围神经修复的作用.     

Effect of platelet‐rich plasma (PRP) concentration on proliferation,neurotrophic function and migration of Schwann cells in vitro

Platelet‐rich plasma (PRP) contains various growth factors and appears to have the potential to promote peripheral nerve regeneration, but evidence is lacking regarding its biological effect on Schwann cells (SCs). The present study was designed to investigate the effect of PRP concentration on SCs in order to determine the plausibility of using this plasma‐derived therapy for peripheral nerve injury. PRP was obtained from rats by double‐step centrifugation and was characterized by determining platelet numbers and growth factor concentrations. Primary cultures of rat SCs were exposed to various concentrations of PRP (40%, 20%, 10%, 5% and 2.5%). Cell proliferation assays and flow cytometry were performed to study to assess SC proliferation. Quantitative real‐time PCR and ELISA analysis were performed to determine the ability of PRP to induce SCs to produce nerve growth factor (NGF) and glial cell line‐derived neurotrophic factor (GDNF). Microchemotaxis assay was used to analyse the cell migration capacity. The results obtained indicated that the platelet concentration and growth factors in our PRP preparations were significantly higher than in whole blood. Cell culture experiments showed that 2.5–20% PRP significantly stimulated SC proliferation and migration compared to untreated controls in a dose‐dependent manner. In addition, the expression and secretion of NGF and GDNF were significantly increased. However, the above effects of SCs were suppressed by high PRP concentrations (40%). In conclusion, the appropriate concentration of PRP had the potency to stimulate cell proliferation, induced the synthesis of neurotrophic factors and significantly increased migration of SCs dose‐dependently. Copyright © 2013 John Wiley & Sons, Ltd.     

Enhanced in vivo survival of Schwann cells by a synthetic oxygen carrier promotes sciatic nerve regeneration and functional recovery

Local hypoxia in the early stages of peripheral nerve injury is a challenge for axonal regeneration. To address this issue, perfluorotributylamine (PFTBA)‐based oxygen carrying fibrin hydrogel was prepared and injected into Schwann cell (SC)‐seeded collagen‐chitosan conduits to increase oxygen supply to SCs within the conduits. The conduit containing PFTBA‐SC gel was then applied to bridge a 15‐mm sciatic nerve defect in rats. It was observed that most of the GFP‐labeled SCs initially seeded in the PFTBA hydrogel remained alive for approximately 28 days after their in vivo implantation. The number of SCs was significantly higher in the PFTBA‐SC scaffold than that in the SC scaffold without PFTBA. In addition, nerve regeneration and functional recovery were examined after nerve injury repair. We found that the PFTBA‐SC scaffold was capable of promoting axonal regeneration and remyelination of the regenerated axons. Further studies showed the PFTBA‐SC scaffold was able to accelerate the recovery of motor and sensory function of the regenerating nerves. Electrophysiological analysis showed area under the curve of compound muscle action potential and nerve conduction velocity were also improved, and gastrocnemius muscle atrophy was partially reversed by PFTBA‐SC scaffold. Furthermore, microvessel density analysis showed PFTBA‐SC composites were beneficial for microvascular growth, which provided sustained oxygen for regenerating nerve in the later stages of nerve regeneration. In conclusion, enhanced survival of SCs by PFTBA is capable of promoting sciatic nerve regeneration and functional recovery, which provides a new avenue for achieving better functional recovery in the treatment of peripheral nerve injuries. Copyright © 2016 John Wiley & Sons, Ltd.     

坐骨神经损伤后脊髓肝细胞生长因子mRNA及蛋白的表达

目的 研究坐骨神经损伤后再生过程中脊髓肝细胞生长因子（HGF）mRNA和蛋白的表达及经时变化规律，探讨周围神经损伤的机制。方法 采用原位杂交及免疫组化技术检测坐骨神经损伤后再生过程中脊髓HGF的mRNA及蛋白的表达。结果 大鼠坐骨神经损伤模型损伤侧的神经细胞胞质颗粒阳性染色强于未损伤侧；神经损伤后第3，7和14天，感觉。运动和副交感神经元内杂交信号明显增强，以第7天的变化最为显著。HGF蛋白的表达均于坐骨神经损伤后第1周开始增强，第2周时达峰值，然后下降。结论 周围神经损伤后，内源性HGF mRNA和蛋白表达增强，对神经元具有保护作用。     

Changes of pro-inflammatory and anti-inflammatory macrophages after peripheral nerve injury

Macrophages are notable immune cells that are recruited to the injury sites after peripheral nerve injury. Following peripheral nerve injury, increasing numbers of macrophages engulf debris and promote nerve regeneration. However, changes of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages, two types of macrophages with dissimilar biological functions, have not been discovered. In the current study, the expression profiles of M1 and M2 macrophage marker genes in the sciatic nerve stumps and dorsal root ganglions (DRGs) after rat sciatic nerve injury were determined using RNA sequencing. Robust up-regulation of macrophage marker genes was observed in the injured sciatic nerve stumps as compared with in the DRGs. Measurement of the dynamic expression levels of M1 macrophage specific marker genes CD38 and Gpr18 as well as M2 macrophage specific marker genes Egr2 and Myc suggested that M1 macrophages were highly involved at all tested time points after peripheral nerve injury while M2 macrophage might be more involved in the later phase after nerve injury. Dynamic changes of M1 macrophage-inducing miRNAs showed that miR-18a, miR-19b, miR-21, miR-29a, and miR-29b were elevated in the injured nerve stump. These up-regulated miRNAs might mediate macrophage polarization by targeting multiple genes, such as Pten. Collectively, our study explored the unique temporal patterns of pro-inflammatory and anti-inflammatory macrophages after peripheral nerve injury for genetic aspects and provided a deeper understanding of the cellular and molecular basis of microenvironment reconstruction after peripheral nerve injury.

The temporal patterns of pro-inflammatory and anti-inflammatory macrophages after peripheral nerve injury.     

神经生长因子不同给药方式对坐骨神经吻合后修复与再生的影响

背景：神经生长因子对神经损伤后的修复有促进作用,但目前对不同用药方式的优劣性尚有争议。目的：观察鞘膜内与局部应用神经生长因子对兔坐骨神经吻合后修复与再生的影响。方法：将24只新西兰大白兔坐骨神经切断后再缝合,分别向兔鞘膜内或损伤局部注射30μg神经生长因子或等量生理盐水结果与结论：坐骨神经损伤后12周,鞘膜内注射神经生长因子组损伤坐骨神经鞘膜增厚,神经纤维排列较整齐,与正常神经纤维差异不大;且其神经干传导速度、有髓神经纤维数目、髓鞘厚度也明显高于其他组（P〈0.05）,损伤局部注射神经生长因子组次之。说明神经生长因子具有促进外周神经吻合后修复与再生的功能,鞘膜内应用优于局部注射。     

针刺激对大鼠坐骨神经损伤后神经生长因子mRNA表达的影响

目的:探讨针刺对神经生长因子信使RNA(NGF mRNA)表达的影响,并且从这一角度分析评价电针频率的不同,及电针与手针对神经生长的影响。方法:78只雄性SD大鼠随机分为5组,治疗1组(n=18),疏波,电压2V,频率:F1:5Hz。治疗2组(n=18):疏波,电压2V,频率:F1:100Hz。治疗3组(n=18):手针。模型组(n=18):行坐骨神经损伤手术造模,不行治疗。对照组(n=6),正常成年大鼠。治疗组与模型组均行坐骨神经损伤手术造模,术后第2天开始给予电针及针刺治疗,电针正极接在近心端,负极接在远心端。分别夹在"环跳"、"足三里"处的针柄上,每次30min,每日2次。手针针刺相同穴位,每次30min,每日2次。术后1、2、6周取治疗组大鼠神经损伤部位远侧坐骨神经干0.6cm,应用原位杂交的方法和图像分析处理系统定量测定坐骨神经组织中NGF mRNA水平。结果:治疗组NGF mRNA表达明显增加,均高于模型组(均P<0.01);治疗1组NGF mRNA表达始终处于高水平,明显高于模型组(P<0.01)。结论:针刺激是促进周围神经损伤再生的重要手段,其中5Hz低频电针效果最佳。     

The advances in nerve tissue engineering: From fabrication of nerve conduit to in vivo nerve regeneration assays

Peripheral nerve damage is a common clinical complication of traumatic injury occurring after accident, tumorous outgrowth, or surgical side effects. Although the new methods and biomaterials have been improved recently, regeneration of peripheral nerve gaps is still a challenge. These injuries affect the quality of life of the patients negatively. In the recent years, many efforts have been made to develop innovative nerve tissue engineering approaches aiming to improve peripheral nerve treatment following nerve injuries. Herein, we will not only outline what we know about the peripheral nerve regeneration but also offer our insight regarding the types of nerve conduits, their fabrication process, and factors associated with conduits as well as types of animal and nerve models for evaluating conduit function. Finally, nerve regeneration in a rat sciatic nerve injury model by nerve conduits has been considered, and the main aspects that may affect the preclinical outcome have been discussed.     

应用人工神经修复大鼠坐骨神经损伤的实验研究

目的观察应用复合碱性成纤维细胞生长因子(bFGF)-壳聚糖导管修复大鼠周围神经损伤的效果。方法成年Wistar大鼠25 只分为假手术组(n=10)、单纯损伤组(n=5)和人工神经修复组(n=10)。假手术组仅暴露坐骨神经5 mm,单纯损伤组暴露坐骨神经并切断,人工神经修复组以复合bFGF-壳聚糖导管桥接缺损。术后对实验动物的坐骨神经进行大体观察,对运动进行行为观察,以及组织化学和免疫组织化学方法评价神经再生情况和靶肌肉恢复情况。结果术后5 周,与单纯损伤组相比,人工神经修复组运动功能有一定程度恢复。人工神经修复组再生的坐骨神经已经通过bFGF-壳聚糖导管越过缺损并与远端相连接。免疫组织化学方法显示,坐骨神经再生段可观察到神经微丝(NF)阳性和S-100 阳性纤维。应用Masson 染色方法,可观察到人工神经修复组腓肠肌去纤维化程度相对于单纯损伤组有明显改善。结论应用bFGF-壳聚糖导管能有效修复周围神经损伤并使大鼠运动功能得到改善。     

The Effect of Low-Intensity Ultrasound on Brain-Derived Neurotropic Factor Expression in a Rat Sciatic Nerve Crushed Injury Model

Low-intensity ultrasound (LIU) can improve nerve regeneration and functional recovery after peripheral nerve crush injury, but the underlying mechanism is not clear. The objective of this study was to examine the effects of LIU on rat sciatic crush injury and to investigate a possible molecular mechanism. Adult male Sprague-Dawley rats underwent left sciatic nerve crush surgery and were then randomized into two groups: a treatment group that received LIU every other d, and a control group that received sham exposure. Compared with rats in the control group, rats in the treatment group had higher sciatic nerve function indexes, compound muscle action potentials, wet weight ratios of the target muscle and mRNA expression of brain-derived neurotropic factor (BDNF) in the crushed nerve and ipsilateral dorsal root ganglia. Our findings suggest that LIU might promote injured nerve regeneration by stimulating BDNF release.     

电刺激对大鼠脊髓损伤后神经生长因子表达的影响

目的探讨电刺激对成年大鼠脊髓损伤后脊髓灰质神经元神经生长因子(NGF)表达的影响。方法健康成年SD大鼠72只,随机分为正常组、损伤对照组、电刺激组。采用Allen法,将后两组复制为脊髓T9损伤模型。术后对电刺激组大鼠进行电刺激治疗7 d。于术后l d、3 d、5 d、7 d对3组进行BBB评分,免疫组化和Western blot法检测NGF的表达情况。结果 BBB评分结果显示大鼠脊髓损伤后有自行恢复功能,从第5天开始电刺激组与损伤对照组有显著性差异(P<0.05)。脊髓损伤后,电刺激组和损伤对照组NGF表达均持续升高(P<0.05),电刺激组表达多于损伤对照组(P<0.05)。结论脊髓损伤后电刺激诱导损伤区NGF表达,从而创造了有利于神经再生的微环境。     

Neurotrophin releasing single and multiple lumen nerve conduits.

Tissue engineering strategies for nerve repair employ polymer conduits termed guidance channels and bridges to promote regeneration for peripheral nerve injury and spinal cord injury, respectively. An approach for fabrication of nerve conduits with single and multiple lumens capable of controlled release of neurotrophic factors was developed. These conduits were fabricated from a mixture of poly(lactide-co-glycolide) (PLG) microspheres and porogen (NaCl) that was loaded into a mold and processed by gas foaming. The porosity and mechanical properties of the constructs were regulated by the ratio of porogen to polymer microsphere. The neurotrophin, nerve growth factor (NGF), was incorporated into the conduit by either mixing the protein with microspheres or encapsulating the protein within microspheres prior to gas foaming. A sustained release was observed for at least 42 days, with the release rate controlled by method of incorporation and polymer molecular weight. Released NGF retained its bioactivity, as demonstrated by its ability to stimulate neurite outgrowth from primary dorsal root ganglion (DRG). In vivo results indicate that conduits retain their original architecture, and allow for cellular infiltration into the channels. Polymer conduits with controllable lumen diameters and protein release may enhance nerve regeneration by guiding and stimulating neurite outgrowth.     

miR-let-7d attenuates EMT by targeting HMGA2 in silica-induced pulmonary fibrosis

Silicosis is a serious occupational disease characterized by pulmonary chronic inflammation and progressive fibrosis. Epithelial-mesenchymal transition (EMT) of alveolar epithelial cells plays a vital role in silicosis. Recent studies discovered a variety of microRNAs (miRNAs) participating in fibrotic diseases. Here, we aimed to explore the function and mechanism of miRNA let-7d in the EMT process in silica-induced alveolar epithelial cells. To detect whether let-7d and its target HMGA2 were involved in silica-induced EMT, we established a silicosis mouse model and found that let-7d was down-regulated and HMGA2 was up-regulated in the silica-treated group. Then we applied an in vitro co-culture system to imitate the EMT process in A549 cells after silica treatment. The down-regulation of let-7d and up-regulation of HMGA2 were also observed in vitro. The knockdown of HMGA2 significantly inhibited the silica-induced EMT. Furthermore, we found that overexpression of let-7d could reduce the expression of HMGA2 and consequently inhibited the silica-induced EMT, whereas inhibition of let-7d increased the expression of HMGA2 and promoted the silica-induced EMT. In conclusion, let-7d negatively regulated silica-induced EMT and inhibited silica-induced pulmonary fibrosis, which might be partially realized by directly binding to HMGA2. Our data suggested that miRNA let-7d might have a potential protective effect in the fibrotic process and become a new therapeutic target for silicosis or other fibrotic diseases.

Silicosis is a serious occupational disease characterized by pulmonary chronic inflammation and progressive fibrosis.     

内源性神经营养因子促进冷冻保存大鼠坐骨神经异体移植后神经再生的作用

目的 探讨内源性神经营养因子(ENTFs)对冷冻保存大鼠坐骨神经同种异体移植后神经再生的影响。方法 15 mm雌性Sprague-Dawley大鼠坐骨神经置于DMEM溶液中,37 ℃、5% CO₂分别体外预处理1 d、3 d、7 d、14 d和21 d (A组、B组、C组、D组和E组),设置新鲜神经对照组(F组)。Western blotting检测神经的胶质细胞源性神经营养因子(GDNF)、神经生长因子(NGF)、Bcl-2、Bax、Caspase-3、主要组织相容性复合体(MHC)-Ⅰ、MHC-Ⅱ蛋白表达。将上述6组神经置于冷冻保存液中液氮保存4周,Calcein-AM/Propidium Iodide染色、激光共聚焦显微镜观察保存后神经活细胞和死细胞情况。用上述冷冻保存4周的坐骨神经和新鲜坐骨神经(G组),同种异体移植修复雌性Wistar大鼠坐骨神经10 mm缺损(A′组、B′组、C′组、D′组、E′组、F′组和G′组),设置同系移植组(H′组)。移植术后1周,免疫荧光染色观察CD₈⁺T细胞、巨噬细胞入侵移植物情况,ELISA法检测受者血清白细胞介素(IL)-2、干扰素(IFN)-γ、肿瘤坏死因子(TNF)-α水平;移植术后20周,电生理检测肌肉复合动作电位(CMAP)和神经传导速度(NCV),称重计算腓肠肌湿重比,神经丝(NF)200免疫荧光染色、甲苯胺蓝染色和透射电镜观察再生神经组织学。结果 与F组相比,C组、D组和E组GDNF、NGF蛋白表达均增加(P < 0.05);B~E组Bcl-2蛋白表达降低( P < 0.05),Bax和Caspase-3蛋白表达均增加( P < 0.05);A组~E组MHC-Ⅰ、MHC-Ⅱ蛋白表达均降低( P <0.05)。坐骨神经冷冻保存4周后,与F组和G组相比,C组、D组和E组活细胞数量降低。同种异体移植术后1周,与F′组和G′组相比,C′组、D′组和E′组移植物CD₈⁺T细胞、巨噬细胞减少,受者血清IL-2、TNF-α水平降低(P < 0.05)。移植术后20周,C′组、D′组和E′组CMAP、NCV、腓肠肌湿重比、再生有髓神经纤维数及髓鞘厚度均显著优于F′组和G′组( P <0.05),C′组、D′组和E′组移植神经NF200表达高于F′组和G′组。结论 体外预处理大鼠坐骨神经能诱导ENTFs表达,高表达ENTFs的坐骨神经冷冻保存后异体移植能促进受者神经再生和功能恢复。     

Investigating the Optimal Initiation Time of Ultrasound Therapy for Peripheral Nerve Regeneration after Axonotmesis in Rats

This study was aimed at identifying the optimal initiation time of ultrasound (US) therapy for peripheral nerve regeneration after axonotmesis. Thirty-six rats with sciatic nerve crush injury were divided into four groups that received US irradiation initiated 1, 7 or 14 d after injury, or sham stimulation for 4 wk. Motor function analysis was conducted weekly; however, there was no significant improvement attributed to US treatment. Four weeks after injury, compound muscle action potential amplitude values of the group in which US irradiation was initiated 1 d after the injury exhibited significant improvement compared with the sham stimulation group. In addition, myelin sheath thickness was significantly greater in the 1-d group than in other groups. These results indicate that US treatment initiated 1 d after peripheral nerve injury promotes maximum regeneration.