Gene Expression of Small Leucine-Rich Proteoglycans during Differentiation of Human Mesenchymal Stem Cells toward Osteoblasts

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Human mesenchymal stem cells (hMSC) have the capacity to differentiate into osteoblasts. To identify genes involved in the commitment of hMSC to osteoblasts, total RNA from hMSC cultured in osteogenic induction medium was isolated on days 0 and 10 and used to create gene expression profiles with oligonucleotide microarrays. Seven SLRPs were expressed in hMSC during osteoblast differentiation. Asporin, which is a small leucine-rich proteoglycan (SLRP), was the most up-regulated extracellular matrix protein in the mineralization stage. The expression levels of these SLRPs genes were compared in hMSC cultured in osteogenic induction medium and hMSC cultured in MSC growth medium on days 0, 1, 3, and 10. The mRNA levels of asporin and osteomodulin were drastically increased in hMSC cultured in osteogenic induction medium as compared to MSC growth medium. The expression levels of asporin, osteomodulin (OMD), proline arginine rich end leucine rich repeat protein, and decorin on day 10 were significantly increased in osteogenic induction medium culture as compared to MSC growth medium culture. These SLRPs are ECM components in bone and articular cartilage. Thus, these SLRPs, particular OMD and ASPN, may be important matrix molecules during differentiation into osteoblasts and/or mineralization.