How does a telogen-elevated growth factor regulate hair growth?

毛囊反复循环经历生长期（生长期）、退化期（退化期）和休止期（休止期）。 虽然参与生长期和生长期-退化期转变的信号分子已经被广泛研究，但控制休止期的信号仅被部分理解。在这里，我们表明，成纤维细胞生长因子（Fgf）18在整个休止期的毛发干细胞龛中表达，并且它通过非生长阶段调节毛发周期。当小鼠角蛋白5阳性上皮细胞中的Fgf18基因被有条件地敲除时，休止期变得非常短，从而引起毛发周期的惊人快速连续。在野生型小鼠中，毛发生长期的毛囊生长受到局部FGF18蛋白的强烈抑制。我们的研究结果表明，上皮细胞FGF18信号转导及其在毛干细胞环境中的减少分别对静止期和生长期的维持至关重要。

Hair follicles repeatedly cycle through growth (anagen), regression (catagen), and resting (telogen) phases. Although the signaling molecules involved in the anagen and anagen–catagen transition have been studied extensively, the signaling that controls telogen is only partly understood. Here we show that fibroblast growth factor (Fgf)18 is expressed in a hair stem cell niche throughout telogen, and that it regulates the hair cycle through the non-growth phases. When the Fgf18 gene is conditionally knocked out in keratin 5-positive epithelial cells in mice, telogen becomes very short, giving rise to a strikingly rapid succession of hair cycles. In wild-type mice, hair follicle growth during anagen is strongly suppressed by local delivery of FGF18 protein. Our results demonstrate that epithelial FGF18 signaling and its reduction in the milieu of hair stem cells are crucial for the maintenance of resting and growth phase, respectively.