Dysfunctional mitochondria are exported from myeloma cells to the bone marrow microenvironment
Session type: Poster / e-Poster / Silent Theatre session
Multiple myeloma (MM) is an incurable malignancy of terminally differentiated plasma cells which is highly dependent on the bone marrow microenvironment (BMM). MM tumour survival, proliferation and drug resistance are mitochondrial dependent processes, and accumulation of dysfunctional mitochondria can result in apoptosis. Mitochondria are highly dynamic organelles and cellular fitness is regulated through the maintenance of a healthy mitochondrial pool. Here, we hypothesise that myeloma cells export their damaged, non-functional mitochondria to the bone marrow microenvironment in order to maintain intra-tumoural mitochondrial homeostasis and thus protect the tumour cells from apoptosis.
Primary MM were obtained from bone marrow aspirates following informed consent (UK, Health Research Authority approval LRECref07/H0310/146). Mitochondrial membrane potential (ΔΨm) was measured by tetramethylrhodamine methyl ester (TMRM) and 3,3′-dihexyloxacarbocyanine iodide (DIOC6). In vivo experiments were performed using U266 cell line and the NSG mouse model.
Mitochondria transfer was monitored in vivo using MM cell lines transduced with rLV.EF1 mCherry-mito-9 lentivirus. Extracted bone marrow shows that mCherry-mito-9 to be detected in both bone marrow stromal cells (CD45-CD105+) and M2 macrophages (F4/80+, CD206+ and CD68-) but not M1 macrophages or other haematopoietc cells. In-vitro experiments, using confocal microscopy, confirmed that mitochondria from MM cells are transferred to BMSC via the formation of GAP junctions. To understand the mechanism regulating transfer we examined ΔΨm. We found that primary MM cells have increased TMRM and DIOC6 staining, but not overall mitochondrial content, compared to non-malignant cells of the bone marrow. This suggests that MM cells have hypopolarised mitochondria. Finally, we report that decreasing ΔΨm using FCCP blocks the export of mitochondrial and increases MM apoptosis.
These results show that myeloma cells export dysfunctional mitochondria to the BMM. Moreover we report that in MM mitochondria are selected for export through an increase in ΔΨm.