通过单毛囊多组学技术鉴定人类头发变白的多种机制

随着年龄的增长，每个成年人或多或少都有些头发会变白。白发早生发生在青年人身上，对青年人的心理和社交有一定影响。已有研究表明，多种不同的因素可以导致头发变白:(1)在头发毛囊的毛乳头附近的毛发基质中，产生黑色素的黑色素细胞有损耗或功能有障碍;(2)基因毒性压力导致的黑色素干细胞自我更新有缺陷;(3)伴随活跃的毛发生长的氧化应激。虽然现有研究发现了毛发变白的多种机制，但是正常人的不同头发变白是否有相似的机制还不清楚;同时我们也不清楚来自不同人的头发变白是否更倾向于不同的机制。为了解决这些难题，我们进行了单毛囊转录组测序和单毛囊染色质可及性测序在单毛囊水平上分析这些毛囊在不同人之间的差异。

我们分析了来自 12 个志愿者的 123 个毛囊(97 个白发毛囊和 26 个黑发毛囊)的转录组。同时，我们分析了来自 13 个志愿者的 63 个毛囊(33个黑发毛囊和 30 个白发毛囊)的 ATAC-seq 数据。对所有单毛囊转录组样本进行方差分析发现志愿者间没有显著差异，黑发样本和白发样本之间有显著差别(P=0.012)。另一方面，通过单毛囊转录组分析，我们发现白发毛囊间差异显著大于黑发毛囊间差异(P<2.2×10-16)。黑发毛囊的基因表达模式相似而白发毛囊转录组差异较大可能意味着不同的头发变白有不同的基因表达改变，即多种的头发变白机制。主成分分析发现黑发分布相对集中，而白发分布比较离散，支持我们的头发变白机制多样性假说。我们在每个主成分中选取基因进行 GO (gene ontology)分析，通过这种分析鉴定的头发变白机制包括氧化磷酸化、角质化、细胞应激反应、细胞粘附和肌动蛋白丝改变等。但染色质可及性数据并未观察到明显差异。简言之，我们通过建立单毛囊多组学技术发现多种机制导致每个人的头发变白。

Every adult has more or less some gray hairs as they age. Gray hair occurs in young people, and has a certain impact on their major psychosocial and socioeconomic repercussion. It has been shown that a number of different factors can lead to hair graying: (1) depletion or dysfunction of melanocytes producing melanin in the hair matrix near the dermal papilla of the hair follicle (HF); (2) defective hair bulge Melanocyte Stem Cell self-maintenance via genotoxic stress; (3) oxidative stress associated with active hair growth. Although various mechanisms of hair graying have been found, it is not clear whether there are similar mechanisms in different gray hairs in normal people. It is also unknown if different people tend to have different mechanisms contributing to hair graying. To address these challenges, we performed single- follicle transcriptome sequencing and single-follicle chromatin accessibility sequencing to analyze the differences of these hair follicles at the single-follicle level.

We analyzed the transcriptomes of 123 hair follicles (97 gray hairs and 26 black hairs) from 12 volunteers. At the same time, we analyzed ATAC-seq data from 63 hair follicles (33 black hairs and 30 gray hairs) from 13 volunteers. From the analysis of variance of transcriptomic data, we found no significant difference among volunteers, and significant difference between black hairs and gray hairs (P=0.012). On the other hand, transcriptome analysis of single hair follicles showed that the difference among gray hair follicles was significantly greater than that among black hair follicles (P<2.2×10-16). Similar gene expression patterns in black hair follicles and large differences in the transcriptome of gray hair follicles may indicate that different hair graying have different gene expression changes, i.e., multiple hair graying mechanisms. Principal component analysis showed that the distribution of black hairs was relatively concentrated, while the distribution of gray hairs was relatively discrete, which supported our hypothesis of diversity of hair graying mechanism. GO analysis of genes selected from each principle component was performed to identify different mechanisms. The mechanisms of hair graying identified by this analysis included oxidative phosphorylation, keratinization, cellular responses to stress, cell-cell adhesion and actin filament-based process and others. However, the peak annotation and read distribution in the peaks between black hairs and gray hairs were similar. In short, we discovered the multiple mechanisms that caused hair graying by a single follicle multi-omics technique.

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