ATRT-13. ASSESSMENT OF MITOCHONDRIAL BIOENERGETICS AND FISSION-FUSION DYNAMICS IN ETMR

BACKGROUND: Embryonal tumor with multilayered rosettes (ETMR) is a deadly pediatric brain tumor with limited available therapeutic options. Dysregulated mitochondrial bioenergetics and dynamics have been linked to the initiation and progression of diverse human cancers, however, their role in ETMR pathobiology remains unknown. We used the primary ETMR cell line, BT183, and an in-house developed human neural stem cell (NSC) line to evaluate mitochondrial morphology, bioenergetics and fission-fusion dynamics involved in ETMR growth and aggression. METHODS: Mitochondrial morphology was determined by widefield immunofluorescence and dSTORM super-resolution microscopy in BT183 and NSC monolayers and by TEM in BT183 and NSCs grown as neurospheres. Relative expression of mitochondrial proteins were quantified in BT183 and NSC lysates by western blotting. RESULTS: Widefield immunofluorescence and super-resolution imaging revealed profound differences in mitochondrial morphology in BT183 compared to NSCs. BT183 mitochondria appear as fragmented, rounded structures, with little interconnectivity, while NSC mitochondria present a typical elongated, filamentous morphology. These findings were corroborated by TEM image analysis of BT183 and NSC neurospheres, which revealed additional morphological alterations in BT183 mitochondria at the ultrastructural level, including aberrant cristae structure. Western blot analysis of BT183 and NSC lysates showed up to 5-fold differential expression of mitochondrial OXPHOS, glycolytic and fission-fusion proteins in the two cell types. Fission promoters phospho-Drp1 and MFF displayed significantly higher expression in BT183 relative to NSCs, whereas fusion-inducing proteins Opa1 and Miro2 showed significantly lower differential expression in BT183. CONCLUSIONS: BT183 cells exhibited striking mitochondrial fragmentation and differential expression of proteins involved in fission-fusion, OXPHOS and glycolysis when compared to normal human NSCs. Ongoing studies include the analysis of mitochondrial structure and morphology in patient samples to validate our in-vitro findings, in addition to in-vitro metabolic flux analysis and targeted protein depletion studies to identify druggable pathways based on mitochondrial function and dynamics.