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Rapamycin Ameliorates Defects in Mitochondrial Fission and Mitophagy in Glioblastoma Cells
Paola Lenzi1, Rosangela Ferese2, Francesca Biagioni2
1Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Via Roma 55, 56126 Pisa, Italy.
Abstract:
Glioblastoma (GBM) cells feature mitochondrial alterations, which are documented and quantified in the present study, by using ultrastructural morphometry. Mitochondrial impairment, which roughly occurs in half of the organelles, is shown to be related to mTOR overexpression and autophagy suppression. The novelty of the present study consists of detailing an mTOR-dependent mitophagy occlusion, along with suppression of mitochondrial fission. These phenomena contribute to explain the increase in altered mitochondria reported here. Administration of the mTOR inhibitor rapamycin rescues mitochondrial alterations. In detail, rapamycin induces the expression of genes promoting mitophagy (PINK1, PARKIN, ULK1, AMBRA1) and mitochondrial fission (FIS1, DRP1). This occurs along with over-expression of VPS34, an early gene placed upstream in the autophagy pathway. The topographic stoichiometry of proteins coded by these genes within mitochondria indicates that, a remarkable polarization of proteins involved in fission and mitophagy within mitochondria including LC3 takes place. Co-localization of these proteins within mitochondria, persists for weeks following rapamycin, which produces long-lasting mitochondrial plasticity. Thus, rapamycin restores mitochondrial status in GBM cells. These findings add novel evidence about mitochondria and GBM, while fostering a novel therapeutic approach to restore healthy mitochondria through mTOR inhibition.
Insights
Glioblastoma cells show mitochondrial damage linked to mTOR. Rapamycin treatment restores mitochondrial function by promoting mitophagy and fission, offering a new therapeutic strategy for glioblastoma.
Area of Science:
- Cell Biology
- Neuro-Oncology
- Mitochondrial Biology
Background:
- Glioblastoma (GBM) exhibits significant mitochondrial alterations.
- Mitochondrial dysfunction in GBM is associated with mTOR overexpression and suppressed autophagy.
- Previous studies have documented but not fully detailed the mechanisms of mitochondrial impairment in GBM.
Purpose of the Study:
- To quantify mitochondrial alterations in glioblastoma cells using ultrastructural morphometry.
- To investigate the role of mTOR signaling, mitophagy, and mitochondrial fission in GBM-associated mitochondrial damage.
- To evaluate the therapeutic potential of mTOR inhibition using rapamycin in restoring mitochondrial health in GBM.
Main Methods:
- Ultrastructural morphometry was employed to document and quantify mitochondrial changes in GBM cells.
- Analysis of gene expression related to mitophagy (PINK1, PARKIN, ULK1, AMBRA1) and mitochondrial fission (FIS1, DRP1) pathways.
- Assessment of VPS34 gene expression, a key regulator of autophagy.
- Investigation of protein localization and co-localization within mitochondria, including LC3.
Main Results:
- Approximately half of the mitochondria in GBM cells displayed impairment, correlated with mTOR overexpression and suppressed autophagy.
- A novel finding was the identification of mTOR-dependent mitophagy occlusion and suppressed mitochondrial fission.
- Rapamycin administration reversed mitochondrial alterations by inducing mitophagy and fission gene expression.
- Rapamycin treatment led to VPS34 overexpression and significant co-localization of fission and mitophagy proteins within mitochondria, including LC3.
- These molecular changes resulted in long-lasting mitochondrial plasticity and restoration of mitochondrial status in GBM cells.
Conclusions:
- Mitochondrial impairment in GBM is mechanistically linked to mTOR signaling, mitophagy occlusion, and suppressed fission.
- Rapamycin effectively restores mitochondrial integrity in GBM cells by modulating key autophagy and fission pathways.
- Targeting mTOR offers a promising therapeutic strategy to correct mitochondrial dysfunction in glioblastoma.
