Description

Isocitrate dehydrogenase 1 (IDH1) catalyzes the NADP+-dependent conversion of isocitrate to α-ketoglutarate (α-KG) in the cytosol and peroxisomes. Mutations in IDH1 drive a variety of cancers, most notably gliomas and glioblastoma, and lead to production of D-2-hydroxyglutarate, an oncometabolite, and also prevent its normal activity, leading to decreased α-KG and NADPH. Catalysis of isocitrate by wild type IDH1 yields the primary source of NADPH in peroxisomes, which are intracellular organelles found in virtually all eukaryotic cells. Peroxisomes are involved in β-oxidation of very long chain fatty acids, α-oxidation of phytanic acid, degradation of H2O2, and biosynthesis of ether lipids. Peroxisomes are a crucial organelle involved in lipid processing reactions which require NADPH. Because lipid biosynthesis is dependent on IDH1-derived NADPH, we hypothesize that cells expressing mutant IDH1 have dysregulated lipid levels due to NADPH deficiency. We predict that these dysregulated lipid levels may affect organelle morphology due to the known interface of lipid metabolism and controlling Golgi morphology. Our lab has generated stable cell lines expressing wild type IDH1 with two IDH1 mutants and R132Q in U87MG glioma cells. Using transmission electron microscopy, we demonstrate that R132Q IDH1 mutant cells have disrupted organelle physiology compared to cells with wild type IDH1 activity. In addition, both R132H and R132Q mutations exhibit retained lipid droplets and membrane abnormalities. Additionally, we demonstrate significant oxidative lipid degradation in R132H and R132Q in a lipid peroxidation study. Both these studies help us characterize the intracellular consequences affected by mutant IDH1-driven tumors.