|Ph.D Student||Zarfati Moran|
|Subject||The Role of Myeloma-Derived Microvesicles on Disease|
|Department||Department of Medicine||Supervisors||Assistant Professor Anat Aharon|
|Dr. Tamar Katz|
|Full Thesis text|
Multiple myeloma (MM) is an incurable, genetically heterogeneous malignancy of plasma cells (PCs) characterized by their proliferation in the bone marrow microenvironment (BMMe). PCs secrete non-functioning immunoglobulins and present high proteasome activity. The interaction between MM cells (MMCs) and other cells in the BMMe leads to an increased expression of adhesion molecules, pro-angiogenic and inflammatory cytokines, which results in increased BM angiogenesis and a hypercoagulant state characteristic of MM patients. Proteasome inhibitors (PI) such as Bortezomib, are used for treating MM patients. Bortezomib is known for its anti-proliferative, anti-angiogenic activity and is associated with a low risk for venous thromboembolism (VTE).
Extracellular vesicles (EVs) that are vesicles released from cells include exosomes (30-100 nm) and microparticles (0.1-1 micron).
In the current study exosomes and microparticles are collectively termed microvesicles (MVs). They contain growth factors, adhesion molecules, and genetic material that reflect their cell origin and can be transferred to other cells.
The goal of the study was to investigate the potential involvement of MVs in MM progression, their profiles, and their interaction with BM cells that may indicate their ability to affect tumor microenvironment, thrombosis, and angiogenesis processes. We furthermore aimed to explore the effect that MVs exert on these aspects following drug treatment. An evaluation of the mechanisms by which MVs interact with BM cells may explain MVs’ effect on BM cell functions. In order to accomplish these goals, we used a myeloma cell line, peripheral blood (PB), and BM aspirate samples from MM patients, and compared them to samples from PB and BM of healthy donors, respectively. Endothelial cells (ECs) and BM Mesenchymal Stem Cells (MSCs) were used in order to assess MV effects. This study demonstrated that MMCs generated MVs. We found an increased quantity of PB MVs from MM patients compared to MVs from healthy donors. MVs from both MM cell line and patients were found to contain proteasomes that were functionally active. We also found a difference in profiles between PB MVs and BM MVs obtained from MM patients. MVs obtained from cell lines and from MM patients presented pro-coagulant and pro-angiogenic profiles. We demonstrated that MVs were able to internalize to ECs, and to affect their MAPK signaling cascades; this interaction of MVs with ECs and MSCs results in triggering migration, proliferation, and coagulation processes associated with cancer. MVs exposed to bortezomib display lower levels of angiogenic factors and proteasome activity and a reduced EC and MSC migration and proliferation rates.
To conclude, MM is characterized by a high shedding rate of MVs. MM-MVs contain high levels of angiogenic/inflammatory factors that affect MSCs and ECs, and induce migration and proliferation via specific signal transduction pathways. Bortezomib-induced MVs revealed lower levels of angiogenic factors that limit EC and MSC functions, suggesting that MVs in fact reflect the efficacy of the therapy and the disease' dynamics. Exploring MV cargo, their effect on BM cells and their mechanism, would allow us to understand their role in myeloma and find new targets for therapy.