OS03.6.A MITOCHONDRIA TRANSFER IN GBM IS MEDIATED BY TGF-Β AND PROMOTES INCREASED INVASIVENESS

Abstract BACKGROUND Acquisition of intact mitochondria from the tumor microenvironment (TME) is a ubiquitious phenomenon in tumors of glioblastoma multiforme (GBM),promoting mitochondrial respiration and metabolic pathways tied to proliferation and tumorigenicity 1. The Transforming growth factor β (TGFβ) pathway is a major molecular pathway upregulated in GBM compared to low grade gliomas 2 and recent studies have shown its involvement in invasion associated microtube (MT) formation 3. We hypothesized that TGFβ affects the mitochondria transfer process between GBM and members in the TME, namely astrocytes. We speculated that mitochondria transfer would lead to increased invasiveness as oxidative metabolism has been previously linked to invasion 1. Furthermore, we postulated that inducing metabolic stress conditions via mitochondria depletion would have an impact on the GBM-TME mitochondria transfer process. METHODOLOGY We utilised specifically transduced cell lines, immunofluorescence, confocal imaging and flow cytometry to measure mitochondria transfer under TGFβ treatment, MT formation and downstream SMAD signaling. Invasion data was elucidated via collagen invasion assays. Mitochondria depletion experiments in vitro were conducted using electron transport chain inhibitor treatment and flow cytometry. Orthotopic xenograft models were utilised to study this mitochondria depletion in vivo, and immunohistochemical analyses were performed to quantify mitotransfer. RESULTS Our in vitro results show that treatment of GBM - astrocyte cocultures with TGFβ directly impacted mitotransfer rates, MT formation and downstream SMAD signaling. Results obtained from collagen assays show promoted invasion in GBM with acquired mitochondria from the TME. Our mitochondria depletion model experiments show an amplified transfer of mitochondria from the TME by mitochondria deficient GBM cells - further characterizing the reliance of GBM on this process to promote its aggressive tumorigenic phenotype. CONCLUSION We identified a new mediating role of TGFβ in GBM interactions with the TME and canonical SMAD as a specific downstream signaling pathway involved. Our collagen invasion and mitochondria depletion studies also demonstrated the importance of mitochondria transfer from TME astrocytes to GBM in cellular functions related to proliferation, invasion and cell rescue. REFLECTION The findings of our study provide new insights into GBM disease progression and therapy resistance, indicating new opportunities for treatment development.