Bone Marrow Adipogenesis in Response to Chemotherapy and Resultant Effect on Tumour Cell Growth

Abstract

The bone marrow microenvironment is highly saturated with bone marrow adipocytes (BMA), which differentiate from their precursor, mesenchymal stem cells (MSC). Evidence from patient trials suggests that bone marrow adiposity is increased following chemotherapy. Moreover, BMA can confer chemotherapeutic resistance to tumour cells, thereby ascribing a tumour-supportive role to BMA. We hypothesize that chemotherapy promotes bone marrow adipogenesis and in turn contributes to enhanced tumour cell growth in bone. We investigated the effect of doxorubicin on adipogenesis of human MSC in vitro and the effects in turn on tumour cell proliferation. Doxorubicin treatment of adipogenic differentiating MSC led to an increased percentage of mature BMA confirmed by increased levels of lipid droplet containing cells and the adipocyte marker, PPARG. RNA-sequencing, metabolomics and lipidomics were employed to assess global changes in gene expression and metabolite levels in the doxorubicin treated adipogenic differentiated MSC. Significant alterations in gene expression and metabolite levels were identified. Most notably, we identified increased expression of fibroblast growth factor (FGF) pathway genes in the doxorubicin treated cells. Endogenous and secreted FGF2 levels were significantly increased with doxorubicin treatment and siRNA-mediated inhibition of FGF2 impeded doxorubicin-enhanced formation of lipid droplet containing BMA. Doxorubicin also enhanced alkaline phosphatase staining of osteoblastic differentiating MSC but did not correspond to normal osteoblast morphology. Direct and conditioned supernatant transfer coculture models tested and confirmed that secreted factors from doxorubicin-treated adipogenic differentiated MSC enhanced PC3 prostate tumour cell proliferation. Furthermore, this phenotype was abrogated when FGF2 was depleted from the differentiating MSC. Pilot in vivo models were employed however further optimization is required to recapitulate the phenotype observed in vitro. Our findings suggest that chemotherapy can actively promote bone marrow MSC adipogenesis in part by increase of FGF2 which directly enhances adipogenesis and leads to enhanced prostate tumour cell growth as a result.