The Adult Stem Cell Niche

Tissue-specific adult stem cells generally exist in a quiescent state with only a small percentage actively dividing to meet the demand of homeostatic tissue replacement. However, a significant number of stem cells can be recruited into cycle in response to injury. The actively dividing stem cell pool will produce cells that differentiate to replace the mature cells that were damaged, but will also rigorously maintain a critical number of stem cells. Given that stem cells have tremendous potential for use in tissue repair and replacement, understanding of how these stem cell fates are controlled has become an area of intense research. However, our ability to expand stem cells ex vivo for therapeutic purposes is still poorly developed, probably due to a lack of understanding of critical factors that maintain pluripotency. Much of our understanding of stem cell regulation comes from studies of the hematopoietic system, including the concept of a stem cell niche, a specialized microenvironment that maintains stem cells in the pluripotent state. In this chapter, we will review the major concepts that have emerged regarding the identity of the cellular/secreted components that influence stem cell fate.

组织特异性成体干细胞通常处于静止状态，只有一小部分会积极分裂以满足组织稳态更替的需求。然而，大量干细胞可在受到损伤时被募集进入细胞周期。积极分裂的干细胞库会产生分化的细胞，以替代受损的成熟细胞，但同时也会严格维持一定数量的关键干细胞。鉴于干细胞在组织修复和替代方面具有巨大潜力，了解这些干细胞命运是如何被调控的，已成为一个热门研究领域。然而，我们在体外扩增干细胞用于治疗的能力仍然很有限，这可能是由于对维持多能性的关键因素缺乏了解。我们对干细胞调控的认识，很大程度上来自对造血系统的研究，其中包括干细胞龛这一概念，即一种能使干细胞维持多能状态的特殊微环境。在本章中，我们将回顾关于影响干细胞命运的细胞/分泌成分特性的主要观点。