PPARs and LXR Regulate Epidermal Differentiation

描述（由申请人提供）： 表皮面临着一项艰巨的任务，即产生一个渗透屏障，使哺乳动物能够在干旱的陆地环境中生存。为了实现这一目标，表皮产生角质层（SC），其具有高度疏水性、富含脂质的细胞外基质，在刚性角质细胞之间组织成层状双层。为了产生这些独特的保护结构，角质形成细胞必须合成大量的胆固醇、脂肪酸和神经酰胺，以与SC近似等摩尔的比例递送，同时形成角质形成细胞，富含交联形成角质层包膜的蛋白质。尽管产生这种功能性的双室SC至关重要，但协调调节角质细胞和细胞外板层膜平行形成的机制在很大程度上仍然未知。 我们的假设是，NHR脂质传感器（PPAR-alpha、-β/ delta、-gamma和LXR）通过首先传感脂质水平，然后协调调节角质形成细胞形成所需的结构蛋白和调节Cer的酶蛋白的表达来调节角质形成细胞分化/GlcCer合成，共同导致功能性SC的形成。 我们建议确定：1）PPAR-alpha、-δ和-γ以及LXR的活化是否刺激Cer/GlcCer合成/板层体形成和角质形成细胞形成; 2）PPARs和LXR的活化刺激角质形成细胞蛋白表达的分子机制; 3）PPARs和LXR的活化剂上调Cer/GlcCer产生的分子机制;最后，4）评估脂质和蛋白质的产生是否进一步协调，使得FA和/或Chol合成的波动协调调节角质细胞蛋白质的产生;即，以表皮分化为特征的脂质和蛋白质合成的整合。 由于角质化和表皮屏障脂质的形成，以及随后产生的细胞外板层，是表皮分化的后期步骤，因此所提出的研究将导致关于成熟SC生成和表皮稳态的协调调节的重要新信息。

DESCRIPTION (provided by applicant): The epidermis is faced with the daunting task of generating a permeability barrier that allows survival of mammals in a xeric, terrestrial environment. To accomplish this goal, the epidermis generates the stratum corneum (SC), with its highly hydrophobic, lipid-enriched extracellular matrix, organized into lamellar bilayers between rigid corneocytes. To generate these unique protective structures, keratinocytes must synthesize extensive quantities of cholesterol, fatty acids, and ceramides, delivered in an approximately equimolar ratio to the SC, simultaneous with formation of corneocytes, enriched in proteins that are crosslinked to form the cornified envelope. Despite the critical importance of generating this functional, two-compartment SC, the mechanisms that coordinately regulate the parallel formation of corneocytes and the extracellular lamellar membranes remain largely unknown. It is our hypothesis that NHR liposensors (PPAR-alpha, -beta/ delta, -gamma, and LXR) regulate keratinocyte differentiation by first sensing lipid levels, and then coordinately regulating the expression of structural proteins required for corneocyte formation and enzyme proteins that regulate Cer/ GIcCer synthesis, together leading to formation of a functional SC. We propose to determine: 1) whether activation of PPAR-alpha, -delta, and -gamma, and LXR stimulate Cer/ GIcCer synthesis/ lamellar body formation and corneocyte formation; 2) the molecular mechanisms by which activation of PPARs and LXR stimulate expression of corneocyte proteins; 3) the molecular mechanisms by which activators of PPARs and LXR upregulate Cer/ GIcCer production; and finally, 4) to assess whether lipid and protein production are further co-ordinated, such that fluctuations in FA and/ or Chol synthesis co-ordinately regulate corneocyte protein production; i.e., the integration of lipid and protein syntheses that characterizes epidermal differentiation. Since cornification and formation of epidermal barrier lipids, with subsequent generation of the extracellular lamellae, are late steps in epidermal differentiation, the proposed studies will result in significant new information regarding the coordinate regulation of mature SC generation and epidermal homeostasis.