Ceramide Metabolism and Photoreceptor Homeostasis

说明(申请人提供)：鞘氨醇是所有真核细胞膜不可或缺的成分；其中许多如神经酰胺、鞘氨醇、1-磷酸鞘氨醇(S-1-P)也是生物活性脂类，调节从细胞凋亡到血管生成的各种细胞功能。我们的长期目标是全面了解控制正常鞘磷脂代谢的酶的功能，以及它们与参与细胞生长、分化和信号传递的其他途径的整合。为了达到我们的目标，我们以果蝇为模型系统，研究了鞘脂生物合成的酶。 这一建议是基于对鞘磷脂代谢在光感受器存活中发挥重要作用的观察得出的。我们的发现表明，通过神经鞘脂脂生物合成途径的遗传调节来降低神经酰胺水平可以抑制一组光转导突变体中的视网膜退化。最近在人类患者中的研究表明，神经酰胺代谢酶的突变会导致视网膜色素变性和遗传性感觉神经病。基于这些发现，本项目的重点是了解神经酰胺代谢如何有助于维持光感受器稳态和其他细胞功能。我们将阐明三种降低神经酰胺水平的酶在体内的作用--将神经酰胺转化为鞘氨醇的神经酰胺酶，将神经酰胺转化为神经酰胺-1-磷酸的神经酰胺酶，以及将鞘氨醇转化为S-1-P的鞘氨醇激酶。神经酰胺和鞘氨醇具有促死亡作用，而S-1-P具有促生长作用。由生物合成酶调节的这些拮抗代谢物的相对水平决定了细胞的生存或死亡。该项目的具体目标是(1)研究神经酰胺酶下游的成分在抑制视网膜变性中的作用，并利用突变体阐明神经酰胺酶的功能(2)产生神经酰胺酶突变体和转基因果蝇以研究其功能(3)产生并分析突变体和转基因果蝇以确定鞘氨醇激酶在调节鞘磷脂代谢产物水平中的作用。

DESCRIPTION (provided by applicant): Sphingolipids are integral components of all eukaryotic cell membranes; many of them like ceramide, sphingosine, sphingosine-1 -phosphate (S-1-P) are also bioactive lipids regulating cellular functions ranging from apoptosis to angiogenesis. Our long-term goal is to comprehensively understand functions of enzymes that control normal sphingolipid metabolism and their integration into other pathways involved in cell growth, differentiation and signaling. To address our goal, we study enzymes of sphingolipid biosynthesis using Drosophila as a model system. This proposal is based on the observation that sphingolipid metabolism plays an important role in survival of photoreceptors. Our findings show that decreasing ceramide levels by genetic modulation of the sphingolipid biosynthetic pathway suppresses retinal degeneration in a set of phototransduction mutants. Recent studies in human patients show that mutations in enzymes of ceramide metabolism cause Retinitis Pigmentosa and Hereditary Sensory Neuropathy. Based on these findings, the focus of this project is to understand how ceramide metabolism contributes to maintenance of photoreceptor homeostasis and other cellular functions. We will elucidate in vivo functions of three enzymes that decrease ceramide levels - ceramidase that converts ceramide to sphingosine, ceramide kinase that converts ceramide to ceramide-1-phosphate and sphingosine kinase that converts sphingosine to S-1-P. While ceramide and sphingosine are pro-death, S-1-P is pro-growth. The relative level of these antagonistic metabolites, regulated by the biosynthetic enzymes, determines whether a cell survives or dies. The specific aims of the project are (1) study components downstream of ceramidase in suppression of retinal degeneration and elucidate ceramidase function using a mutant (2) generate ceramide kinase mutant and transgenic flies to study its functions (3) generate and analyze mutant and transgenic flies to define the role of sphingosine kinase in regulating levels of sphingolipid metabolites.