OMEGA HYDROXY CERAMIDES IN EPIDERMAL DIFFERENTIATION AND FUNCTION

表皮分化产生不透水角质层（SC），这是一个双室系统，由脂质耗尽的角质层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），这是一个富含神经酰胺的小叶，它与凝固包膜的外表面蛋白质共价结合。由于omega-羟基神经酰胺是LBE的主要脂质成分，酰化的omega- oh神经酰胺是细胞外层的关键成分，这些独特的脂质物种对于形成有效屏障至关重要。然而，尽管它们具有明显的重要性，但无论是导致omega-OH神经酰胺的代谢途径，还是它们的生成调控都没有得到解决。此外，它们在形成LE和SC的片层膜结构中的假设作用仍未得到解决。因此，我们假设omega-OH神经酰胺的合成，通过细胞色素P450 omega-羟化酶（CYP4A）的活性，以及随后生成的脂质结合包膜和酰基神经酰胺，受到表皮分化、通透性屏障需求和子宫内表皮屏障发育程序的严格调节，其中核激素受体家族成员是主要的调节因子。在这一提议中，我们将研究独特的表皮ω - oh神经酰胺的产生是否对角质层的LBE和板层膜的形成至关重要。具体来说，我们将解决：1)在表皮分化过程中导致omega- OH神经酰胺生成的关键酶促步骤（即表皮CYP4A的omega-羟基化）的调控；2) - oh神经酰胺合成对小鼠通透性屏障稳态的调节和要求；3)胎儿屏障形成过程中对CYP4A和ω - oh神经酰胺合成的调节和需求；此外，加速表皮屏障发育的因素是否调节omega-OH神经酰胺的生成；4)核激素受体家族成员对omega-羟基化和CYP4a表达的调控；最后，5)在LBE的形成过程中，锥形包膜蛋白和omega-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片层的产生是表皮分化的后期阶段，因此提出的研究应该会带来关于表皮结构、功能和体内平衡的重要新信息。

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.