Effects of mechanical stresses on neural differentiation of mesenchymal stem cells

doi:10.3969/j.issn.2095-4344.0501

Abstract

Abstract:

BACKGROUND: Currently, regulation of stem cell differentiation by mechanical stresses or microenvironment has become a popular issue in the tissue engineering and regenerative medicine.
OBJECTIVE: To review the progress in the effects of mechanical stress on neural differentiation of mesenchymal stem cells in the last decade, providing theoretical basis for stem cell replacement therapy in the treatment of degenerative diseases.
METHODS: A search of Web of Science and PubMed database was done to retrieve articles addressing the effects of mechanical stresses on the neural differentiation of mesenchymal stem cells. After systematical analysis and summarization, 104 articles were finally selected and analyzed.
RESULTS AND CONCLUSION: Mechanical stimulation and extracellular physical environment factors have important influence on the neural differentiation of mesenchymal stem cells from the bone marrow, adipose tissues, dental pulp and endometrium. PI3K-AKT-mTOR, Wnt/beta-catenin, Rho, MAPK signaling pathways may be involved in the mechanical stresses regulated neural differentiation. However, the clear molecular mechanism needs further studies.

中国组织工程研究杂志出版内容重点：干细胞；骨髓干细胞；造血干细胞；脂肪干细胞；肿瘤干细胞；胚胎干细胞；脐带脐血干细胞；干细胞诱导；干细胞分化；组织工程

Key words: Mesenchymal Stem Cells, Cell Differentiation, Neurons, Stress, Mechanical, Tissue Engineering

CLC Number:

R394.2

Jiang Jing-yi, Fan Yu-bo, Zheng Li-sha. Effects of mechanical stresses on neural differentiation of mesenchymal stem cells[J]. Chinese Journal of Tissue Engineering Research, 2018, 22(17): 2761-2768.

Figures/Tables 2

2.1 机械应力调控间充质干细胞神经向分化 2.1.1 流动剪切力流动剪切力是组织再生和重建过程中最重要的机械刺激之一。研究表明流动剪切力对维持细胞、组织乃至整个机体正常的生理状态都有重要意义[19-21]。许多实验室根据流变学原理研制了相应的细胞力学实验装置，其中包括近些年研究较广泛的微流控等。目前，微流控细胞培养系统已经用于二维(2D)和三维(3D)细胞培养[22-24]。人类脂肪组织干细胞是一种组织特异性干细胞，可以分化成多种间充质细胞，如骨细胞、软骨细胞、脂肪细胞、肌肉细胞等[25-26]。Choi等[27]利用3D微流控通道芯片培养人脂肪干细胞，并加入神经分化诱导液。结果显示生长在芯片上的人脂肪干细胞形成的神经球比在普通培养皿中培养的细胞多，且诱导细胞产生更多的γ-氨基丁酸，几乎60%的细胞都表达γ-氨基丁酸。此外，芯片/PCR分析表明3D微流控细胞培养系统是通过诱导激活人脂肪干细胞中wnt5A/β-catenin信号通路，从而导致人脂肪干细胞的自我更新和神经向分化。Jeon等[28]连续2 d对接种在微图形化基底上的骨髓间充质干细胞加载3 h 0.1 Pa和0.25 Pa的流动剪切力，然后对细胞进行神经向诱导，结果显示流动剪切力促进了骨髓间充质干细胞中神经元标志物微管蛋白(β-tubulin Ⅲ)、微管相关蛋白2(MAP-2)等分子的表达。然而，另一研究给骨髓间充质干细胞施加1.5 Pa的流动剪切力，然后继续在神经向分化诱导培养基中培养细胞，结果显示流动剪切力并未影响骨髓间充质干细胞的神经向分化效率[29]，可能原因是1 h的加载时间过短。 2.1.2 微重力太空飞行会使宇航员处于微重力环境中，引起许多人体生理的变化[30]。大量研究证明了微重力对细胞内信号通路、细胞分泌物和基因表达的影响机制[31]。目前的研究发现模拟微重力作为一种机械因素可以影响间充质干细胞的分化和功能[32]，并触发细胞在体外进行三维组装，从而模拟体内的状态[31，33-34]，被认为是组织工程和再生医学领域的一种新策略。有学者研究了模拟微重力条件下骨髓间充质干细胞的多向分化能力。研究将骨髓间充质干细胞分为正常重力(NG)组和模拟微重力(SMG)组，模拟微重力组内细胞骨架从纺锤形变成圆形，细胞内干细胞多能性标记物OCT4表达量上调，特别是模拟微重力加载72 h时是最适合骨髓间充质干细胞多向分化的时间点。诱导两组细胞神经向分化，免疫染色和免疫印迹结果发现模拟微重力组内骨髓间充质干细胞分化形成的神经样细胞中MAP-2和神经丝蛋白(NF-H)的表达量均高于正常重力组。因此，该研究认为模拟微重力可能是通过调节细胞骨架和OCT4的表达来诱导骨髓间充质干细胞的分化[35]。Xue等[36]在不同的分化培养基中培养骨髓间充质干细胞72 h或10 d。结果发现短时间的微重力刺激(72 h)可以促进骨髓间充质干细胞向内皮细胞、神经元和脂肪细胞分化；而延长微重力(10 d)的刺激时间则会促进骨髓间充质干细胞分化为成骨细胞。他们还发现，短时间的微重力刺激显著降低了细胞内Ras家族成员RhoA激酶的活性，但长期的微重力刺激却使RhoA激酶的活性显著增加。而当RhoA激酶的活性受到抑制时，长期的微重力作用效果就会被恢复。这些结果表明，微重力刺激通过RhoA激酶相关的信号通路调节骨髓间充质干细胞的神经向分化能力。此外，Chen等[37]研究也表明模拟微重力显著增强了骨髓间充质干细胞成神经向分化的诱导效果。Zarrinpour等[38]使用快速旋转的回转器模拟微重力条件，研究微重力刺激对人脂肪干细胞神经向分化的影响。结果显示无论是神经诱导分化之前还是之后，模拟微重力都可以促进细胞内MAP-2、脑源性神经营养因子(BDNF)和神经营养因子(NT-3)表达量的上调。由以上所有研究结果可见，模拟微重力可以促进间充质干细胞的神经向分化。 2.1.3 牵张力纵观机体所处的力学刺激环境，似乎可以发现一个有趣的现象，即大多数的力学刺激都是有“节奏”的，并常以牵张力的形式表达，譬如心脏规律泵血时外周血管壁的反复牵拉、运动状况下骨骼和肌肉的反复拉伸、口颌系统咀嚼运动时牙周膜组织承受的规律牵张等。近来已有不少相关研究证实了周期性牵张力的生物学重要性。研究发现骨髓间充质干细胞对机械牵张非常敏感，不同振幅、不同频率的牵张会有利于骨髓间充质干细胞向不同的方向分化[39-41]。而Leong等[42]发现只有低频率、低振幅的牵张(0.5 Hz，0.5%)能够在没有额外的诱导培养条件下促进骨髓间充质干细胞的神经向分化，同时，他们还发现该过程是通过活化Rac1而非Rho A来实现的。 2.1.4 次声振动除了上述的机械力刺激对间充质干细胞的神经向分化有影响以外，研究发现次声振动也能影响骨髓间充质干细胞的分化方向。有研究给骨髓间充质干细胞施加了40 Hz的次声振动而不进行诱导培养，持续刺激5 d后发现细胞表现出神经细胞样形态，神经向标志物的表达量显著升高，而且此过程中还伴随着ERK激酶的激活[43]。同样的，在另一研究中，人脂肪组织干细胞无需神经向诱导培养，在30 Hz次声振动持续刺激4 d后，也表现出神经向分化的现象，同时伴随着ERK激酶的活化。上述研究表明次声振动能够通过激活ERK激酶信号通路调控间充质干细胞的神经向分化[44]。 2.2 细胞外基质调控间充质干细胞神经向分化在生物体内，细胞并不是孤立存在的，而是存在于其周围一定的微环境中，这个微环境包括其周围的基质细胞、细胞间质、体液以及各种细胞因子和物理因素等[45-46]。细胞的微环境也被称为细胞生存的细胞外基质[47]，越来越多的证据证明这些物理和化学因素共同影响细胞的命运[48-52]。因此，通过改变细胞外基质的物理环境来调控干细胞的生物学行为，已经成为组织工程和再生医学研究的热点领域。细胞在体内和体外的微环境条件，见图1[53]。"

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