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Role of FABP7 and DHA in Glioblastoma Cell Migration
- Author / Creator
- Xu, Xia
Glioblastoma (GBM) is the most common primary brain malignancy and has a dismal prognosis. Despite advanced therapies, including surgery and concurrent radiotherapy with temozolomide (TMZ), GBM patients only have a 14.6-month median survival time. This dismal outcome can be attributed to the highly infiltrative nature and tumour heterogeneity in GBM, with the tumour cells infiltrating surrounding brain parenchyma at early stages of the disease. Brain fatty acid binding protein (B-FABP or FABP7) is highly expressed in GBM neural stem-like cells (GSCs), correlating with increased GBM cell migration/invasion and a poor clinical prognosis. Long chain polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and arachidonic acid (AA) are abundant in GBM tissues, with a considerably lower DHA content compared to normal adult brain. DHA and AA are preferred ligands of FABP7, with DHA having the stronger affinity for FABP7. Our combined studies have revealed that FABP7 affects GBM migration through several possible PUFA-dependent mechanisms, including membrane lipid remodeling, PUFA storage and energy production, and FABP7 cargo transport via GBM microtubes.
FABP7 is involved in both DHA and AA transport from membrane to cytosol. In Chapter 2, we used a quantitative fluorescence microscopy technique (Laurdan) and super-resolution STED microscopy to investigate FABP7-mediated DHA effect on the GBM cell membrane fluidity, GBM cell membrane FABP7 nanoscale domain formation and the impact of these biophysical properties on GBM cell migration. Our results demonstrate that FABP7 expression in GBM cells correlates with increased membrane lipid order and punctate FABP7 nanodomains, which are particularly enriched at the migrating front of GBM cells. High-DHA/low-AA supplemented culture conditions result in dramatically diminished lipid order and disrupted FABP7 nanodomains.
In Chapter 3, we examine the role of FABP7 in the uptake of DHA from the culture medium. Using gas-chromatography and FABP7-depleted GSCs, we show that FABP7 expression facilitates: (i) uptake of DHA into GSC lipids, (ii) formation of lipid droplets, (iii) increasing the ω-3:ω-6 ratio in lipids (2-fold, p < 0.0001), and (iv) mitigating migration of GSCs. DHA supplementation in FABP7-expressing GSCs also inhibits their migration. Our results demonstrate that it may be possible to increase the DHA content in GSCs which are believed to drive GBM infiltrative properties.
Experiments in Chapters 2 and 4 also show that a preferred FABP7 subcellular localization in GBM cells is mitochondria, suggesting a role for FABP7 in mitochondrial PUFA β-oxidation and energy production. Using a highly aggressive patient-derived GSC line, A4-007N, we show that FABP7 affects GSC microtube formation. Microtubes serve as intercellular communication channels in GBM tumours. We propose that microtubes may also facilitate the transport of FABP7/PUFA across the tumour and perhaps into neighboring brain parenchyma.
We propose a model whereby FABP7 and relative levels of DHA versus AA in the tumour microenvironment determines GBM migratory/invasive properties, particularly in GBM patient-derived GSCs. The mechanistic insight into the role of FABP7 and its ligands provided by our study suggests that dietary intervention using a DHA-rich diet combined with the current standard therapy, may benefit GBM patients by slowing down infiltration of GSCs in the brain.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
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