Ablation of coactivator Med1 regulates bulge keratinocyte stem cells and accelerates epidermal regeneration after injury [10wk skin]

Transcriptional coactivator Mediator complex facilitates transcription of various transcription factors. Previously, we have generated Med1 conditional null mice, where a critical subunit of Mediator, Med1, is removed from keratinocytes. Here we present evidence that ablation of Med1 accelerated epidermal regeneration after injury. As bulge keratinocyte stem cells are important contributors to regenerate epidermis, we first analyzed properties of stem cells in Med1 null mice. BrdU long retaining analysis revealed that deletion of Med1 still maintained quiescence of bulge keratinocyte stem cells, despite of general hyperplasia observed in Med1 deficient keratinocytes. Gene expression analysis demonstrated that a series of niche matrix proteins decreased in Med1 deficient keratinocytes. In contrast, the expression of stem cell marker Sox9 was not altered, suggesting stem cells are present but activated because of abnormal niche surrounding stem cells. In addition, Med1 deletion suppressed injury induced inflammatory reaction, which indirectly regulates epidermal regeneration. We also indicated that TGFβ1 significantly decreased in both bulge and epidermal keratinocytes upon Med1 deletion. Our study demonstrates that coactivator Med1 has a critical role to maintain bulge stem cells and epidermal regeneration presumably through regulation in TGFβ signaling. n=4 WT and KO (each sample contain RNA from one mouse)转录共激活因子Mediator复合物（Transcriptional coactivator Mediator complex）可促进多种转录因子的转录过程。本课题组此前已构建Med1条件性敲除小鼠，该模型中Mediator的关键亚基Med1可在角质形成细胞中被特异性敲除。本研究证实，敲除Med1可加速损伤后表皮再生进程。鉴于毛囊隆突部角质形成干细胞（bulge keratinocyte stem cells）是表皮再生的重要细胞来源，我们首先对Med1敲除小鼠的干细胞特性进行了分析。BrdU长期滞留标记分析结果显示，尽管Med1缺陷型角质形成细胞存在广泛性增生，但Med1的缺失仍可维持毛囊隆突部角质形成干细胞的静息状态。基因表达分析表明，Med1缺陷型角质形成细胞中一系列干细胞微环境基质蛋白的表达水平出现下调。与之相反，干细胞标志物Sox9的表达未发生改变，提示干细胞仍正常存在，但其激活状态因干细胞周围微环境异常而发生改变。此外，Med1敲除可抑制损伤诱导的炎症反应，而该反应可间接调控表皮再生进程。我们同时发现，在Med1缺失的毛囊隆突部及表皮角质形成细胞中，转化生长因子β1（TGFβ1）的表达水平显著降低。本研究证实，共激活因子Med1在维持毛囊隆突部干细胞稳态及表皮再生过程中发挥关键作用，其分子机制可能与调控转化生长因子β（TGFβ）信号通路有关。本实验每组设置4例野生型（WT）与敲除型（KO）样本，每份样本包含1只小鼠的组织RNA。