Proteomics Profiling of Exosomes from Primary Mouse Osteoblasts under Proliferation versus Mineralization Conditions and Characterization of Their Uptake into Prostate Cancer Cells

Osteoblasts communicate both with normal cells in the bone marrow and with tumor cells that metastasized to bone. Here we show that osteoblasts release exosomes, we termed osteosomes, which may be a novel mechanism by which osteoblasts communicate with cells in their environment. We have isolated exosomes from undifferentiated/proliferating (D0 osteosomes) and differentiated/mineralizing (D24 osteosomes) primary mouse calvarial osteoblasts. The D0 and D24 osteosomes were found to be vesicles of 130–140 nm by dynamic light scattering analysis. Proteomics profiling using tandem mass spectrometry (LC–MS/MS) identified 206 proteins in D0 osteosomes and 336 in D24 osteosomes. The proteins in osteosomes are mainly derived from the cytoplasm (∼47%) and plasma membrane (∼31%). About 69% of proteins in osteosomes are also found in Vesiclepedia, and these canonical exosomal proteins include tetraspanins and Rab family proteins. We found that there are differences in both protein content and levels in exosomes isola...