OMEGA HYDROXY CERAMIDES IN EPIDERMAL DIFFERENTIATION AND FUNCTION

表皮分化产生不可渗透的角质层（SC），这是一个双室系统，由脂质耗尽的角质细胞和脂质富集的细胞外板层膜组成。在这两个隔室的界面处是脂质结合包膜（LBE），一种富含神经酰胺的小叶，其与皮质包膜的外表面蛋白共价结合。由于ω-羟基神经酰胺是LBE的主要脂质成分，并且酰化ω-OH神经酰胺是细胞外膜的关键组分，因此这些独特的脂质种类对于形成有效屏障必须是关键的。然而，尽管其明显的重要性，既没有导致ω-OH神经酰胺的代谢途径，也没有其产生的调节已经解决。此外，他们假设的作用都在形成LE和层状膜结构的SC仍然没有得到解决。因此，我们假设，通过细胞色素P450 ω-羟化酶（CYP 4A）的活性合成ω-OH神经酰胺，随后产生脂质结合包膜和酰基神经酰胺，受到表皮分化、渗透性屏障要求和子宫内表皮屏障发育程序的严格调控，以核激素受体家族的成员作为主要的调节调节剂。在这个提议中，我们将研究是否生成独特的表皮ω-OH神经酰胺是关键的LBE和角质层的层状膜的形成。具体来说，我们将解决：1）关键酶促步骤的调节（即，通过表皮CYP 4A的ω-羟基化），导致表皮分化期间ω- OH神经酰胺的产生; 2）调节和需要ω-OH神经酰胺合成以实现鼠渗透性屏障稳态; 3）调节和需要胎儿屏障个体发育期间的CYP 4A和ω-OH神经酰胺合成;此外，加速表皮屏障发育的因素是否调节ω-OH神经酰胺的产生; 4）核激素受体家族成员对ω-羟基化和CYP 4a表达的调节;以及最后，5）在LBE的形成中皮质包膜蛋白和ω-OH神经酰胺之间的相互作用。由于LBE的形成和随后的细胞外板层的产生是表皮分化的晚期步骤，因此拟议的研究应导致关于表皮结构、功能和稳态的重要新信息。

Epidermal differentiation generates the impermeable stratum corneum (SC), a two-compartment system, composed of lipid-depleted corneocytes and lipid-enriched, extracelluar lamellar membranes. At the interface of these two compartments lies the lipid-bound envelope (LBE), a ceramide-enriched leaflet, that is covalently bound to the outer surface proteins of the cornified envelope. Since omega-hydroxy ceramides re both the predominant lipid constituents of the LBE, and the acylated-omega-OH ceramides are critical components of the extracellular lamellae, these unique lipid species, must be critical for the formation of a competent barrier. However, despite their apparent importance, neither the metabolic pathways leading to omega-OH ceramides, nor the regulation of their generation has been addressed. Moreover, their hypothesized role both in forming the LE and the lamellar membrane structures of the SC remain unresolved. Therefore, we hypothesize that the synthesis of omega-OH ceramides, through the activity of a cytochrome P450 omega-hydroxylase (CYP4A), with the subsequent generation of the lipid-bound envelope and acyl-ceramides, are tightly regulated by epidermal differentiation, permeability barrier requirements, and the program of epidermal barrier development in utero, with members of the nuclear hormone receptor family as the principle regulatory regulators. In this proposal, we will examine whether the generation of the unique epidermal omega-Oh ceramides is critical for formation of both the LBE and the lamellar membranes of the stratum corneum. Specifically, we will address: 1) the regulation of the key enzymatic step (i.e., omega- hydroxylation by epidermal CYP4A) leading to the generation of omega- OH ceramides during epidermal differentiation; 2) the regulation of , and requirement of, omega-OH ceramide synthesis for murine permeability barrier homeostasis; 3) the regulation of, and requirement for, CYP4A and omega-OH ceramide synthesis during fetal barrier ontogenesis; in addition, whether factors that accelerate epidermal barrier development modulate omega-OH ceramide generations; 4) the regulation of omega-hydroxylation and CYP4a expression by members of the nuclear hormone receptor family; and finally, 5) the interaction between the cornified envelope protein(s) and omega-OH ceramides in the formation of the LBE. Since the formation of the LBE, and subsequent generation of the extracellular lamellae, are late steps in epidermal differentiation, the proposed studies should result in significant new information regarding epidermal structure, function, and homeostasis.