Bernard Bruno A
L'Oréal Recherche, Centre C. Zviak, 90, rue du Général Roguet, 92110 Clichy, France.
Med Sci (Paris). 2006 Feb;22(2):138-43. doi: 10.1051/medsci/2006222138.
The human hair follicle is a unique appendage which results from epithelio-mesenchymal interactions initiated around the 3rd month of development. This appendage has a very complex structure, with a dermal compartment and an epithelial compartment. The dermal compartment comprises the connective tissue sheath and the dermal papilla, both of which are irrigated by microvessels. The epithelial compartment is made of highly replicating matrix cells giving rise to three concentrical domains, namely the outer root sheath, the inner root sheath and the hair shaft. The pigmentation unit, responsible for hair color, is made of fully active melanocytes located on top of the dermal papilla. Altogether a hair follicle contains more than 20 different cell types, engaged in different differentiation pathways and/or interacting with each other. This complex appendage has a unique behavior in mammals since, after a hair production phase, it involutes in place before entering a resting phase after which it renews itself under a cyclical but stochastic way, out of a double reservoir of pluripotent stem cells able to also regenerate epidermis. For yet unknown reasons, this well ordered process can be disturbed, provoking alopecia. The pigmentation unit also renews itself under a cyclical way, out of a melanocyte progenitor reservoir which progressively declines with time, provoking the hair whitening process. Finally, the shape of the hair shaft is programmed from the bulb. What makes this appendage unique and fascinating is its high degree of autonomy, its incredibly complex though stable structure, the number of different cell types interacting under an equilibrated way and its potential of regeneration. It represents a true paradigm of tissue homeostasis, exemplifying in a small living cylinder all the fundamental laws of cell-cell and tissue interactions. This life is revealed in this short synthesis.
人类毛囊是一种独特的附属器，它源于发育第三个月左右开始的上皮 - 间充质相互作用。这个附属器结构非常复杂，有一个真皮部分和一个上皮部分。真皮部分包括结缔组织鞘和真皮乳头，两者均由微血管供血。上皮部分由高度增殖的基质细胞组成，这些细胞形成三个同心区域，即外根鞘、内根鞘和毛干。负责头发颜色的色素生成单位由位于真皮乳头顶部的完全活跃的黑素细胞组成。总之，一个毛囊包含20多种不同类型的细胞，它们参与不同的分化途径和/或相互作用。这种复杂的附属器在哺乳动物中具有独特的行为，因为在毛发产生阶段之后，它会在原位退化，然后进入静止期，在此之后它会以周期性但随机的方式自我更新，这源于一个能够再生表皮的多能干细胞双储备库。由于未知原因，这个有序的过程可能会受到干扰，从而引发脱发。色素生成单位也以周期性方式自我更新，其黑素细胞祖细胞储备会随着时间逐渐减少，从而引发头发变白的过程。最后，毛干的形状由毛囊球部决定。这个附属器的独特和迷人之处在于它高度的自主性、极其复杂却稳定的结构、以平衡方式相互作用的不同细胞类型的数量以及它的再生潜力。它代表了组织稳态的一个真正范例，在一个小小的活体圆柱体中例证了细胞 - 细胞和组织相互作用的所有基本规律。这种生命在这个简短的综述中得以展现。
