Osteoblasts secrete various proteins that make up bone as well as growth factors and cytokines that interact with organs outside of bone. Despite their critical role in bone formation and communication with other organs, the proteins that osteoblasts secrete are not very well understood. Osteoblasts evolve from stem cells in the bone marrow, which are called mesenchymal stem cells. “Mesenchymal stem cells are being introduced into clinical trials, and some of the putative beneficial effects of these cells are related to their secreted factors,” explains Moustapha Kassem at the University Hospital of Odense in Denmark. “However, the nature of these secreted factors and their change during osteoblast differentiation are poorly documented and understood.” So in a recent Molecular & Cellular Proteomics paper, a team led by Kassem and Jens S. Andersen at the University of Southern Denmark described a mass spectrometric analysis of the proteins secreted by osteoblasts over a period of two weeks as the cells developed and matured from mesenchymal stem cells in culture (1). The investigators used an isotope-labeling approach that allowed them to tell apart proteins that were secreted by the cells and contaminants in the culture media. One of the things the investigators established was that a hormone called stanniocalcin 2 behaved in an autocrine fashion to promote the differentiation of the mesenchymal stem cells into osteoblasts. The investigators also discovered nine novel factors that are secreted by mesenchymal stem cells. Kassem says they will now focus on these nine factors to better understand their role in mesenchymal stem cell biology.
- 1. Kristensen, L. P, et al. Mol. Cell. Proteomics DOI: 10.1074/mcp.M111.012138 (2012)
Rajendrani Mukhopadhyay (firstname.lastname@example.org) is the senior science writer for ASBMB Today and the technical editor for The Journal of Biological Chemistry. Follow her on Twitter at www.twitter.com/rajmukhop.