| Summary: | 碩士 === 國立臺灣大學 === 生理學研究所 === 106 === Sphingolipid is an essential component of cell membrane. Infertile crescent (Ifc) is an evolutionarily conserved dihydroceramide desaturase, which converts dihydroceramide to ceramide. Previously we have found that loss of ifc in Drosophila photoreceptors results in activity-dependent neurodegeneration, elevation of reactive oxygen species (ROS), and activation of autophagy.
To investigate the source of ROS, a NADPH oxidase (NOX)-specific inhibitor was fed to flies with ifc-KO photoreceptors. Apocynin-feeding reduced the level of ROS and partially rescued the neurodegeneration caused by loss of Ifc. Furthermore, with clonal analysis, we observe that Rac1 is activated in ifc-KO photoreceptors. Genetically decreasing the level of Rac1 or NOX partially rescued the function of the degenerated ifc-KO photoreceptors. These results indicate that Rac1-NOX pathway mediates ROS production which causes neurodegeneration in ifc-KO photoreceptors. We also used co-immunoprecipitation to detect the physical interaction between Rac1 and Ifc, but the interaction was not observed, indicating non-association or weak interaction between the two proteins. Interestingly, we have observed the colocalization of Ifc and autophagosome in the photoreceptor. With co-immunoprecipitation, we observed the physical interaction of Ifc and autophagosome. Also, Ifc is predicted to have four LC3-interactiong regions (LIRs) and Ifc with four mutated LIRs failed to rescue the lethality of ifc-KO flies, indicating the importance of Ifc to associate with autophagosomes.
These results support that ROS and activity-dependent neurodegeneration is generated through Rac1-NOX pathway upon loss of Ifc in photoreceptors, and the ability of Ifc to interact with autophagosomes is critical for their survival.
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