Differential regulation of osteoadherin (OSAD) by TGF-β1 and BMP-2

Osteoadherin (OSAD) is a member of the small leucine rich-repeat proteoglycan (SLRP) family. SLRPs are normally found in extracellular matrices, but OSAD is the only member restricted to mineralized tissues. We investigated the promoter region of OSAD by in silico analysis and found that the proximal promoter region contains sites for Smad-3, Smad-4, and AP-1. All are effectors of TGF-β family signalling. We tested sensitivity of the promoter to the two TGF-β family members TGF-β1 and BMP-2. We found TGF-β1 to down regulate OSAD, while BMP-2 up regulates OSAD. As a consequence of how OSAD is regulated by TGF-β1 and BMP-2 and its temporal expression pattern in osteoblasts and bone development, we can conclude OSAD as an early marker for terminally differentiated matrix producing osteoblasts.