Nature：科学家发现指甲隐藏着肢体重生重要线索

哺乳动物拥有指尖再生的非凡能力，这种能力也在指甲、神经、甚至骨头的再生上表现着。人类的指尖断了可以在两个月时间内再长出来。直到现在，人们对这个能力还知之甚少。

近日在一篇发表于《自然》期刊上的论文中，纽约大学医学中心的研究人员阐明了哺乳动物这一非凡的再生能力，利用基因工程改造的老鼠首次证明了指尖再生这一能力隐藏的生物化学链。该研究为截肢患者带去了希望。

伊藤真由美教授和其研究队伍已经发现了指尖再生过程的重要线索——指甲基质（nail matrix）中自我更新干细胞的数量。指甲基质是甲床（人指甲或是趾甲覆盖的那块皮肤）的一部分，而甲床内富含刺激指甲生长作用的神经末梢和血管。此外，科学家们还发现这些干细胞依赖于一种被称为“Wnt信号网”的蛋白质家族来再生指尖的骨头。而该蛋白质也在毛发和组织再生过程中发挥关键作用。

哺乳动物拥有指尖再生的非凡能力，包括了指甲、神经、甚至骨头的再生

伊藤真由美博士称：“当我们阻断断了指尖的老鼠的Wnt信号途径时，其指甲和骨头并不能像正常的那样再生。“更有趣的是，科学家还发现了他们可以操纵Wnt信号途径来刺激指尖下方骨头和组织再生。这些发现意味着Wnt信号对于指尖再生非常重要，也为能帮助人类肢体再生的疗法的发明指明了道路。

研究人员下一步将研究控制“Wnt信号途径如何与指甲干细胞发生相互作用从而影响骨头和指甲生长”的分子机制。

Wnt activation in nail epithelium couples nail growth to digit regeneration
The tips of mammalian digits can regenerate after amputation1, 2, like those of amphibians. It is unknown why this capacity is limited to the area associated with the nail2, 3, 4. Here we show that nail stem cells (NSCs) reside in the proximal nail matrix and that the mechanisms governing NSC differentiation are coupled directly with their ability to orchestrate digit regeneration. Early nail progenitors undergo Wnt-dependent differentiation into the nail. After amputation, this Wnt activation is required for nail regeneration and also for attracting nerves that promote mesenchymal blastema growth, leading to the regeneration of the digit. Amputations proximal to the Wnt-active nail progenitors result in failure to regenerate the nail or digit. Nevertheless, β-catenin stabilization in the NSC region induced their regeneration. These results establish a link between NSC differentiation and digit regeneration, and suggest that NSCs may have the potential to contribute to the development of novel treatments for amputees.

How nails regenerate lost fingertips
If a salamander loses its leg, it can grow a new one. Humans and other mammals are not so fortunate, but we can regenerate the tips of our digits, as long as enough of the nail remains. This was first shown some 40 years ago; today researchers finally reveal why it is that nails are necessary.
Working with mice, researchers led by Mayumi Ito at New York University have identified a population of stem cells lying beneath the base of the nail that can orchestrate the restoration of a partially amputated digit. However, the cells can do so only if sufficient nail epithelium — the tissue that lies immediately below the nail — remains. The results are published on Nature's website today....