BACKGROUND Billions of dollars are invested annually by pharmaceutical companies in search of new options for treating hair loss conditions; nevertheless, the challenge remains. One major limitation to hair follicle research is the lack of effective and efficient drug screening systems using human cells. Organoids, three-dimensional in vitro structures derived from stem cells, provide new opportunities for studying organ development, tissue regeneration, and disease pathogenesis. The present study focuses on the formation of human hair follicle organoids. METHODS Scalp-derived dermal progenitor cells mixed with foreskin-derived epidermal stem cells at a 2:1 ratio aggregated in suspension to form hair follicle-like organoids, which were confirmed by immunostaining of hair follicle markers and by molecular dye labeling assays to analyze dermal and epidermal cell organization in those organoids. The hair-forming potential of organoids was examined using an in vivo transplantation assay. RESULTS Pre-aggregation of dermal and epidermal cells enhanced hair follicle formation in vivo. In vitro pre-aggregation initiated the interactions of epidermal and dermal progenitor cells resulting in activation of the WNT pathway and the formation of pear-shape structures, named type I aggregates. Cell-tracing analysis showed that the dermal and epidermal cells self-assembled into distinct epidermal and dermal compartments. Histologically, the type I aggregates expressed early hair follicle markers, suggesting the hair peg-like phase of hair follicle morphogenesis. The addition of recombinant WNT3a protein to the medium enhanced the formation of these aggregates, and the Wnt effect could be blocked by the WNT inhibitor, IWP2. CONCLUSIONS In summary, our system supports the rapid formation of a large number of hair follicle organoids (type I aggregates). This system provides a platform for studying epithelial-mesenchymal interactions, for assessing inductive hair stem cells and for screening compounds that support hair follicle regeneration.

中文翻译：

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头皮祖真皮和表皮干细胞的预聚集激活 WNT 通路并促进体外和体内系统中毛囊的形成。

背景技术制药公司每年投资数十亿美元寻找治疗脱发病症的新选择；尽管如此，挑战依然存在。毛囊研究的一个主要限制是缺乏使用人体细胞的有效且高效的药物筛选系统。类器官是源自干细胞的三维体外结构，为研究器官发育、组织再生和疾病发病机制提供了新的机会。目前的研究重点是人类毛囊类器官的形成。方法 将头皮来源的真皮祖细胞与包皮来源的表皮干细胞以 2:1 的比例混合，在悬浮液中聚集形成毛囊样类器官，通过毛囊标记物的免疫染色和分子染料标记分析来分析真皮以及这些类器官中的表皮细胞组织。使用体内移植测定检查类器官的毛发形成潜力。结果 真皮和表皮细胞的预聚集增强了体内毛囊的形成。体外预聚集引发表皮和真皮祖细胞的相互作用，导致 WNT 通路激活并形成梨形结构，称为 I 型聚集体。细胞示踪分析表明真皮和表皮细胞自组装成不同的表皮和真皮区室。在组织学上，I 型聚集体表达早期毛囊标记，表明毛囊形态发生处于毛栓样阶段。向培养基中添加重组 WNT3a 蛋白可增强这些聚集体的形成，并且 Wnt 抑制剂 IWP2 可以阻断 Wnt 效应。结论 总之，我们的系统支持大量毛囊类器官（I 型聚集体）的快速形成。该系统为研究上皮-间质相互作用、评估诱导性毛发干细胞和筛选支持毛囊再生的化合物提供了一个平台。