Myeloma-modified adipocytes exhibit a senescent-associated secretory phenotype

Bone marrow -adipocytes (BMAs) have recently been implicated in accelerating bone metastatic cancers such as AML and breast cancer. Importantly, bone marrow adipose tissue (BMAT) expands with aging and obesity- two key risk factors in multiple myeloma (MM) disease prevalence- suggesting that BMAs influence and are influenced by myeloma cells in the marrow. Here we examined how myeloma cells affect adipocytes and provide evidence that MM cells alter adipocyte gene expression and cytokine secretion profiles, creating a “MM-associated” adipocyte (MM-adipocyte) phenotype. Our findings indicate that: (1) Multiple myeloma cells decrease BM adiposity in vitro, in myeloma animal models, and in clinical samples, (2) myeloma induces widespread gene expression and phenotypic changes in adipocytes in vitro, most notable, the induction of a senescent-like phenotype in BMAs, (3) MM-adipocytes affect myeloma cell cycle, drug sensitivity, and aggressiveness, illuminating a new driver of MM cell evolution in a drug resistant clone. We demonstrate that myeloma cells exposed to MM-adipocytes are rescued from dexamethasone-induced cell cycle arrest and have increased expression of FKBP5, a potential drug resistance gene. Our findings in patients confirm that BMAs are dynamic during myeloma disease progression (decrease during MM initiation, recover during disease remission) and that the interactions between BMAs and MM cells have previously unappreciated implications in the understanding and treatment of myeloma. Overall design: Primary human mesenchymal stromal cells (MSCs) were isolated from bone marrow samples received from deidentified male and female donors after total hip arthroplasty. MSCs were isolated by surface adherence, and seeded into 6-well plates at a density of 150,000 cells/well and grown until 80-90% confluent. To generate bone marrow adipocytes (BMAs), MSCs were differentiated for 21 days in hMSC adipogenic media consisting of DMEM/F12 supplemented with FBS, antibiotic/antimycotic, 500 µM IBMX, 50 µM indomethacin, 1 µM dexamethasone, and 1 µM insulin. After 21 days, cells were washed and myeloma cells (OPM-2, MM.1S, and RPMI-8226) were added via transwell co-culture (0.4 µm pores) at a density of 500,000 cells/well in RPMI-1640 media containing FBS and antibiotic/antimycotic for 72 hours. Following co-culture the individual cell types were then pooled (n=2 wells) prior to RNA extraction.