Data_Sheet_1_Dietary Vitamin A Impacts Refractory Telogen.PDF

Hair follicles cycle through periods of growth (anagen), regression (catagen), rest (telogen), and release (exogen). Telogen is further divided into refractory and competent telogen based on expression of bone morphogenetic protein 4 (BMP4) and wingless-related MMTV integration site 7A (WNT7A). During refractory telogen hair follicle stem cells (HFSC) are inhibited. Retinoic acid synthesis proteins localized to the hair follicle and this localization pattern changed throughout the hair cycle. In addition, excess retinyl esters arrested hair follicles in telogen. The purpose of this study was to further define these hair cycle changes. BMP4 and WNT7A expression was also used to distinguish refractory from competent telogen in C57BL/6J mice fed different levels of retinyl esters from two previous studies. These two studies produced opposite results; and differed in the amount of retinyl esters the dams consumed and the age of the mice when the different diet began. There were a greater percentage of hair follicles in refractory telogen both when mice were bred on an unpurified diet containing copious levels of retinyl esters (study 1) and consumed excess levels of retinyl esters starting at 12 weeks of age, as well as when mice were bred on a purified diet containing adequate levels of retinyl esters (study 2) and remained on this diet at 6 weeks of age. WNT7A expression was consistent with these results. Next, the localization of vitamin A metabolism proteins in the two stages of telogen was examined. Keratin 6 (KRT6) and cellular retinoic acid binding protein 2 (CRABP2) localized almost exclusively to refractory telogen hair follicles in study 1. However, KRT6 and CRABP2 localized to both competent and refractory telogen hair follicles in mice fed adequate and high levels of retinyl esters in study 2. In mice bred and fed an unpurified diet retinol dehydrogenase SDR16C5, retinal dehydrogenase 2 (ALDH1A2), and cytochrome p450 26B1 (CYP26B1), enzymes and proteins involved in RA metabolism, localized to BMP4 positive refractory telogen hair follicles. This suggests that vitamin A may contribute to the inhibition of HFSC during refractory telogen in a dose dependent manner.

毛囊的生长周期依次历经生长期（anagen）、退行期（catagen）、休止期（telogen）与脱落期（exogen）。根据骨形态发生蛋白4（bone morphogenetic protein 4, BMP4）与无翅型MMTV整合位点家族成员7A（wingless-related MMTV integration site 7A, WNT7A）的表达特征，休止期可进一步划分为难治性休止期（refractory telogen）与感受态休止期（competent telogen）。在难治性休止期阶段，毛囊干细胞（hair follicle stem cells, HFSC）的活性受到抑制。视黄酸合成相关蛋白定位于毛囊组织，且其定位模式随毛囊周期动态改变。此外，过量摄入视黄基酯可使毛囊停滞于休止期。本研究旨在进一步阐明毛囊周期中的上述变化。
研究团队借助BMP4与WNT7A的表达水平，对两项既往研究中饲喂不同剂量视黄基酯的C57BL/6J小鼠的两类休止期毛囊进行区分。两项研究所得实验结果截然相反，差异体现在母鼠摄入的视黄基酯剂量，以及不同饮食干预启动时小鼠的周龄两个方面。结果显示，无论是在未纯化日粮（视黄基酯含量充足）中繁育、并于12周龄起饲喂过量视黄基酯的小鼠（研究1），还是在纯化日粮（视黄基酯含量达标）中繁育、并自6周龄起持续饲喂该日粮的小鼠（研究2）中，处于难治性休止期的毛囊占比均更高。WNT7A的表达结果与上述结论相符。
随后，本研究检测了维生素A代谢相关蛋白在两种休止期阶段的定位特征。在研究1中，角蛋白6（keratin 6, KRT6）与细胞视黄酸结合蛋白2（cellular retinoic acid binding protein 2, CRABP2）几乎仅特异性定位于难治性休止期毛囊。而在研究2中，饲喂达标与高剂量视黄基酯的小鼠，其KRT6与CRABP2同时定位于感受态与难治性休止期毛囊。在饲喂未纯化日粮的小鼠体内，参与视黄酸代谢的酶与蛋白：视黄醇脱氢酶SDR16C5、视网膜脱氢酶2（aldehyde dehydrogenase 1A2, ALDH1A2）以及细胞色素P450 26B1（cytochrome p450 26B1, CYP26B1），均定位于BMP4阳性的难治性休止期毛囊。
上述结果提示，维生素A可能以剂量依赖的方式，参与难治性休止期阶段HFSC的抑制过程。