Dihydroceramide desaturase regulates the compartmentalization of Rac1 for neuronal oxidative stress

• Published in: Cell reports (Cambridge) 2021-04, Vol.35 (2), p.108972-108972, Article 108972
• Main Authors: Tzou, Fei-Yang, Su, Tsu-Yi, Lin, Wan-Syuan, Kuo, Han-Chun, Yu, Yu-Lian, Yeh, Yu-Han, Liu, Chung-Chih, Kuo, Ching-Hua, Huang, Shu-Yi, Chan, Chih-Chiang
• Format: Article
• Language: English
• Subjects: Animals; Cell Line, Tumor; Ceramides - metabolism; DEGS1; dihydroceramide; Drosophila melanogaster - genetics; Drosophila melanogaster - metabolism; Drosophila Proteins - deficiency; Drosophila Proteins - genetics; Electroretinography; Fatty Acid Desaturases - antagonists & inhibitors; Fatty Acid Desaturases - genetics; Fatty Acid Desaturases - metabolism; Gene Expression Regulation; Humans; Membrane Proteins - deficiency; Membrane Proteins - genetics; NADPH Oxidases - genetics; NADPH Oxidases - metabolism; neurodegeneration; Neurons - metabolism; Neurons - pathology; Oxidative Stress; Photoreceptor Cells, Invertebrate - metabolism; Photoreceptor Cells, Invertebrate - pathology; Point Mutation; Protein Binding; rac1 GTP-Binding Protein - genetics; rac1 GTP-Binding Protein - metabolism; Rac1 mislocalization; Reactive Oxygen Species - metabolism; Retina - metabolism; Retina - pathology; RNA, Small Interfering - genetics; RNA, Small Interfering - metabolism; Signal Transduction
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2021.108972

Disruption of sphingolipid homeostasis is known to cause neurological disorders, but the mechanisms by which specific sphingolipid species modulate pathogenesis remain unclear. The last step of de novo sphingolipid synthesis is the conversion of dihydroceramide to ceramide by dihydroceramide desaturase (human DEGS1; Drosophila Ifc). Loss of ifc leads to dihydroceramide accumulation, oxidative stress, and photoreceptor degeneration, whereas human DEGS1 variants are associated with leukodystrophy and neuropathy. In this work, we demonstrate that DEGS1/ifc regulates Rac1 compartmentalization in neuronal cells and that dihydroceramide alters the association of active Rac1 with organelle-mimicking membranes. We further identify the Rac1-NADPH oxidase (NOX) complex as the major cause of reactive oxygen species (ROS) accumulation in ifc-knockout (ifc-KO) photoreceptors and in SH-SY5Y cells with the leukodystrophy-associated DEGS1H132R variant. Suppression of Rac1-NOX activity rescues degeneration of ifc-KO photoreceptors and ameliorates oxidative stress in DEGS1H132R-carrying cells. Therefore, we conclude that DEGS1/ifc deficiency causes dihydroceramide accumulation, resulting in Rac1 mislocalization and NOX-dependent neurodegeneration. [Display omitted] •Lack of dihydroceramide desaturase activity induces cytoplasmic ROS•Rac1-NADPH oxidase-elicited ROS mediates leukodystrophy-related neuronal death•DEGS1/ifc defects cause mislocalization of Rac1 to the endolysosomes•Dihydroceramide alters binding of active Rac1 to reconstituted organelle membranes Deficient dihydroceramide desaturase activity causes oxidative stress-mediated neurological disorders. Tzou et al. show that dihydroceramide accumulation leads to mislocalization of active Rac1, and inhibition of Rac1-NOX can ameliorate associated oxidative stress and neuronal defects. Thus, NOX inhibitors may provide a therapeutic approach for patients with DEGS1 variants.