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RESEARCH PRODUCT

PO-146 Multiple myeloma-derived exosomes carry amphiregulin and are responsible for the uncoupled bone remodelling

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Introduction Multiple myeloma (MM) is a hematologic malignancy associated with osteolytic bone disease caused by the perturbation of the functional balance between bone resorption and bone formation. Exosomes, nanosize lipoproteic structures, have been recently recognised as a new mechanism of cell to cell communication during tumour growth and progression. We have previously shown that MM-exosomes are involved in osteolytic lesions but the underlying mechanism is still understood. We hypothesise that the epidermal growth factor receptor ligand Amphiregulin (AREG) can be delivered by multiple myeloma-derived exosomes and participate in modulating the response of the bone microenvironment to the tumour. Material and methods Exosomes were isolated from the conditioned medium of MM1 cell line and from BM plasma samples of patients. In order to test whether MM-exosomes could affect osteoclastogenesis through the activation of the EGFR pathway, primary CD14 +monocytes and a murine cell line (RAW264.7) were used as osteoclast (OC) models. Cells were treated with exosomes from both MM1 and plasma samples, pre-treated or not with anti-AREG neutralising antibodies and OC specific markers were measured. In addition, to further explore whether exosomes were able to promote osteoclastogenesis by affecting mesenchymal stem cells, hTERT-MSC were treated with exosomes; the conditioned medium were collected to measure the secretion of IL8 and to stimulate primary CD14 +monocytes. Results and discussions We found that AREG was specifically enriched in exosome samples, leading to the activation of EGFR in pre-OC. In addition we showed a significant increase of the expression of the OC markers Cathepsin K, Matrix Metalloproteinases 9 and Tartrate-resistant Acid Phosphatase in RAW 264.7 and CD14 +cells after treatment with MM-derived exosomes as compared to the control. The effects of MM-derived exosomes on OC activation were significantly abrogated by exosome pre-treatment with anti-AREG neutralising Ab directly on pre-osteoclast cells and indirectly by inhibiting IL8 release in MSC. Conclusion Taken together our data indicate that MM-derived exosomes are responsible for the uncoupled bone remodelling, affecting directly osteoclast function and promoting IL8 release from mesenchymal stromal cells. In this context, AREG packed into MM-derived exosomes, represents a potential new player in MM-induced bone resorption.