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. 2022 Jul 22;10:933370. doi: 10.3389/fcell.2022.933370

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Copyright © 2022 Park.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Niches of hair follicles. (A) Mature hair follicles have many niche components around them. In addition to DP, there are dermal sheath (DS) cells, regulatory T (Treg) cells, macrophages, preadipocytes, adipocytes, and arrector pili muscle (APM). These components of the niches regulate the homeostasis of hair follicles, cooperatively. (B) In terms of hair follicles from wound-induced hair neogenesis (WIHN), Wnt2 and FGF9 form a positive feedback loop and enhance the new hair generation. Most of the niches are composed, but melanocytes and APM are absent. Therefore, functional differences exist, such as being able to create only gray hairs. (C) In the case of hair follicles made by organoids, the structures of hair follicles and DPs are similar to those of general hair follicles. Due to the limitations of the organoid culture methods, circulatory systems, including blood and lymphatic vessels, do not exist. In addition, other cellular and non-cellular components are not perfect, such as immune cells and extracellular matrix (ECM). However, unlike the WIHN-derived hair follicles, melanocytes exist and hair follicles from the organoid can produce pigmented hairs.