Biomaterials：皮肤细胞经三维培养变身神经干细胞

日前，中科院遗传与发育生物学研究所戴建武研究组成功利用三维培养，将皮肤细胞变成神经干细胞。相关研究成果发表于《生物材料》。

2006年，山中伸弥利用逆转录病毒转基因的方法实现体细胞重编程，产生诱导性多能干细胞（iPS细胞），开创了基因调控细胞重编程的全新领域。随后大量研究表明，不同基因的联合应用可以诱导体细胞向多种类型细胞转变，如心肌细胞、神经元细胞、神经干细胞、血液祖细胞、胰岛细胞等。这些转分化研究都是通过病毒转染、整合、基因过表达等手段调节细胞命运的，寻找更为安全的转分化方法是重编程技术临床应用亟待解决的重要问题。

三维细胞培养指在一定的环境条件下，将细胞种植在三维支架中，构建出具有特定形态和功能细胞的方法。三维球状形态（或者克隆形态）与干细胞特性密切相关，如胚胎干细胞在滋养层上以克隆形态生长，神经干细胞以神经球的形态生长；克隆形成实验是鉴定干细胞的重要手段，干细胞分化后失去克隆样形态；多项研究也表明三维成球培养可以更好地维持干细胞的自我更新和多向分化特性。然而，学界对于三维成球培养如何影响细胞重编程并不清楚。

为此，戴建武研究组对小鼠成纤维细胞进行了三维成球培养，发现三维成球培养的小鼠成纤维细胞显着上调了Sox2基因的表达，获得了类似于神经前体细胞的特性，并具有分化为神经元、星形胶质细胞和少突胶质细胞的能力。当其被注射到鼠大脑海马部位后，可以存活并在体内分化为神经元、星形胶质细胞和少突胶质细胞。

业内专家表示，这些结果首次表明，不依赖基因、RNA及蛋白的导入，三维成球培养可以诱导成纤维细胞发生重编程，获得神经前体细胞特性，为寻找更安全的转分化方法提供了新思路。

据悉，该项工作受到科技部重大科学研究计划和中科院干细胞与再生医学战略先导科技专项资助。

Biomaterials     DOI： 10.1016/j.biomaterials.2013.04.040

Direct conversion of fibroblasts into neural progenitor-like cells by forced growth into 3D spheres on low attachment surfaces

Guannan Sua, b, 1, Yannan Zhaoa, 1, Jianshu Weia, b, 1, Zhifeng Xiaoa, Bing Chena, Jin Hana, Lei Chena, b, Jian Guanc, Renzhi Wangc, Qun Dongd, Jianwu Daia

Many stem cells grow into three-dimensional (3D) spheres or colonies, such as neural progenitor cells (NPCs) and embryonic stem cells (ESCs). Sphere morphology helps maintaining the stemness of stem cells. Our previous study demonstrated that forced growth of RT4 and HEK293 cells into 3D sphere on low attachment surface could induce stem cell properties. The close relationship between 3D sphere morphology and stem cell stemness drives us to hypothesize that 3D sphere formation induces fibroblasts reprogramming. The key gene Sox2 for reprogramming fibroblasts into NPCs was found to be overexpressed in 3D sphere cultured mouse fibroblasts. These cells exhibited similar morphological and molecular features to NPCs in vitro, were capable of differentiating into neurons, astrocytes and oligodendrocytes, and could generate long-term expandable neurospheres while maintaining differentiation capability. When engrafted into hippocampus of adult rat brain, the 3D sphere cells differentiated into neural cells. Thus, NPCs can be generated from fibroblasts directly through a physical approach without introducing exogenous reprogramming factors.