Osteolyse beim Multiplen Myelom : Untersuchungen am Zellmodell
Myeloma is characterized by bone disease leading to severe bone pain and pathologic fractures. Only over the last few years the biochemistry of osteolysis in multiple myeloma has become clearer. A basic cytokine network responsible for balancing ostgenesis and osteolysis has been described consisting of a receptor called receptor activator of NF-?B (RANK), its ligand (RANKL) and the soluble decoy receptor osteoprotegerin (OPG). Binding of RANKL to RANK leads to osteoclastogenesis and osteolysis whereas binding to OPG inactivates RANKL. Myeloma cells seem to disturb bone marrow microenvironment in a manner tipping the balance towards osteolysis. On one hand syndecan 1 (SDC1), a transmembrane heparan sulfate proteoglycan on myeloma cells, is able to sequester OPG and to mediate internalization and degradation of OPG in myeloma cells. On the other hand, myeloma cells are thought to imbalance the OPG/RANKL system by influencing bone marrow stromal cells, the major source of OPG and RANKL in bone marrow microenvironment. This thesis presents a sufficient procedure for investigating expression of OPG, RANKL and SDC1 on the mRNA level based on semiquantitative realtime RT-PCR. Using this method we show that treatment of human foreskin fibroblasts with myeloma cell contitioned media and fibroblast/myeloma cell coculture both lead to a significant decrease in expression of OPG mRNA in fibroblasts. These data indicate that myeloma cells influence OPG expression in fibroblasts as a model for bone marrow stromal cells and, thus, disrupt RANKL/OPG cytokine axis to trigger bone destruction. In contrast to the published literature, this happens through a soluble factor as demonstrated by the conditioned media experiments. Moreover fibroblasts and U-266 both are negative for RANKL even if grown in coculture. The levels of SDC1 mRNA in myeloma cell lines U-266 and IM-9 are not affected by enhancing the autocrine IL-6 loop or by enhancing or interrupting the autocrine IL-15 loop. Furthermore treatment of U-266 with fibroblast conditioned media or myeloma cell/fibroblast coculture does not alter expression of SDC1 mRNA significantly. A polarized expression of SDC1 protein on U-266 cell surface can be confirmed by immune fluorescence staining. Cytokine and contactmediated interactions between myeloma cells and mesenchymal cells shift the balance towards osteolysis within the microenvironment of myeloma infiltrates. Disruption of the OPG/RANKL cytokine axis seems to be of major importance. Expression of SDC1 by myeloma cells is not affected by mesenchymal cells and is independent of IL-6 or IL-15 autocrine loop.
info:eu-repo/classification/ddc/610, Medizin, Myelom, Plasmozytom, Osteolyse, OPG, Osteoprotegerin, SDC, Syndecan, Knochenmarksmikromillieu
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