Stem cell activity is subject to non-cell-autonomous regulation from the local microenvironment, or niche. In adaption to varying physiological conditions and the ever-changing external environment, the stem cell niche has evolved with multifunctionality that enables stem cells to detect these changes and to communicate with remote cells/tissues to tailor their activity for organismal needs. The cyclic growth of hair follicles is powered by hair follicle stem cells (HFSCs). Using HFSCs as a model, we categorize niche cells into 3 functional modules, including signaling, sensing and message-relaying. Signaling modules, such as dermal papilla cells, immune cells and adipocytes, regulate HFSC activity through short-range cell-cell contact or paracrine effects. Macrophages capacitate the HFSC niche to sense tissue injury and mechanical cues and adipocytes seem to modulate HFSC activity in response to systemic nutritional states. Sympathetic nerves implement the message-relaying function by transmitting external light signals through an ipRGC-SCN-sympathetic circuit to facilitate hair regeneration. Hair growth can be disrupted by niche pathology, e.g. dysfunction of dermal papilla cells in androgenetic alopecia and influx of auto-reacting T cells in alopecia areata and lichen planopilaris. Understanding the functions and pathological changes of the HFSC niche can provide new insight for the treatment of hair loss.

中文翻译：

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毛囊干细胞生态位的功能复杂性和针对生态位功能障碍的头发再生治疗目标。

干细胞的活性受当地微环境或生态位的非细胞自主调节的影响。为了适应不断变化的生理条件和不断变化的外部环境，干细胞生态位已发展成具有多功能性，使干细胞能够检测到这些变化并与偏远的细胞/组织进行交流，以适应其机体需求。毛囊的周期性生长由毛囊干细胞（HFSC）推动。使用HFSC作为模型，我们将小生境细胞分类为3个功能模块，包括信令，感测和消息中继。诸如真皮乳头细胞，免疫细胞和脂肪细胞之类的信号模块通过短距离细胞-细胞接触或旁分泌作用来调节HFSC活性。巨噬细胞吞噬了HFSC的生态位，以感知组织损伤和机械提示，而脂肪细胞似乎响应系统的营养状态而调节HFSC的活性。交感神经通过ipRGC-SCN交感神经回路传输外部光信号，从而促进毛发再生，从而实现了信息传递功能。利基病理会破坏头发的生长，例如雄激素性脱发中的真皮乳头细胞功能障碍以及斑秃和扁平苔藓中自体反应性T细胞的流入。了解HFSC利基的功能和病理变化可以为脱发的治疗提供新的见解。交感神经通过ipRGC-SCN交感神经回路传输外部光信号，从而促进毛发再生，从而实现了信息传递功能。利基病理会破坏头发的生长，例如雄激素性脱发中的真皮乳头细胞功能障碍以及斑秃和扁平苔藓中自体反应性T细胞的流入。了解HFSC利基的功能和病理变化可以为脱发的治疗提供新的见解。交感神经通过ipRGC-SCN交感神经回路传输外部光信号，从而促进毛发再生，从而实现了信息传递功能。利基病理会破坏头发的生长，例如雄激素性脱发中的真皮乳头细胞功能障碍以及斑秃和扁平苔藓中自体反应性T细胞的流入。了解HFSC利基的功能和病理变化可以为脱发的治疗提供新的见解。