Induction of chondrogenesis and expression of superficial zone protein (SZP)/lubricin by mesenchymal progenitors in the infrapatellar fat pad of the knee joint treated with TGF-β1 and BMP-7

Superficial zone protein (SZP) is a key mediator of boundary lubrication of articular cartilage in joints. In this investigation, we made the unexpected discovery that SZP was expressed in infrapatellar fat pad (IFP) from bovine knee. Quantitative analysis of secreted proteins in the medium of the IFP stromal cells demonstrated a significant stimulation by TGF-β1 and BMP-7. Real-time PCR analysis revealed the SZP expression was up-regulated by TGF-β1 and BMP-7. Chondrogenically differentiated IFP progenitor cells were stimulated by TGF-β1 and BMP-7 to synthesize and secrete SZP. SZP mRNA was significantly up-regulated by chondrogenic induction for 21 days. These findings indicate that the stimulation of SZP expression by TGF-β and BMP-7 may lead to functional improvement of damaged intraarticular tissues and that IFP progenitor cells may be a potential useful source for inducing superficial zone of articular cartilage by tissue engineering for regeneration of damaged articular cartilage due to osteoarthritis.