Prostate cancer exosomes differentiate BM-MSCs into pro-angiogenic and pro-Invasive myofibroblasts

The reactive stroma in prostate cancer is predominantly composed of myofibroblasts, which are thought to be required for tumour progression. Bone-marrow derived mesenchymal stem cells (BM-MSCs) are known to migrate into the tumour and are one of the many potential precursors of myofibroblasts. The factors secreted by cancer cells which may drive myofibroblastic differentiation of MSC, however are poorly understood. The aim of this thesis was to explore for the first time, the impact of TGF-β1 expressing exosomes (nano-sized vesicles) secreted by prostate cancer cells in directing the differentiation of BM-MSCs and subsequently the functions of exosome differentiated BM-MSCs. Exosomes isolated from prostate cancer cells skewed BM-MSCs away from differentiating into adipocytes, and instead towards alpha-smooth muscle actin (α-SMA) positive myofibroblasts. BM-MSCs treated with exosomes exhibited enhanced secretion of VEGF-A, HGF and had an altered transcript profile with heightened matrix metalloproteinases (MMP-1, -3 and -13). Impairing the secretion of exosomes by Rab27a knockdown or depleting exosomes from prostate cancer cells culture media by high speed ultracentrifugation, attenuated myofibroblastic differentiation of BM-MSCs, demonstrating exosomes as the key driving factor for this. Furthermore, differentiation of BM-MSCs into myofibroblasts was dependent on exosomally tethered TGF-β1, however BM-MSCs treated with soluble TGF-β1 at the same dose, failed to obtain the same myofibroblastic phenotype. The exosome-differentiated MSCs enhanced endothelial and cancer cell proliferation and migration, supported endothelial vessel formation and promoted tumour cell invasion into peri-tumoural matrix in vitro. In conclusion, this study reports prostate cancer exosomes expressing TGF-β1, to dominantly modulate the fate of BM-MSCs, generating cells with tumour promoting myofibroblastic traits