Transforming growth factor β induces chondrogenesis of precartilaginous stem cells

Abstract

Objective To investigate the possibility of transforming growth factor β (TGF-p) inducing chondrogenesis of precartilaginous stem cells (PSCs) and discuss expression mechanism of extracel-luar matrix. Methods PSCs were induced into a chondrogenic pathway in alginate bead culture in the absence of serum and in the presence of TGF-β1, β2, or-β3. The temporal pattern of expression of cartilage-specific extracellular matrix during chondrogenesis were analyzed by immunocytochemistry, immunoflu-orescence, RT-PCR, immunoprecipitation, Western blot and spectrophotometer. Results Type Ⅱ collagen staining was positive at days 7, 14 and 21 in alginate bead culture, showing most intense staining in the TGF-p3-treated culture. Expression of type Ⅱ collagen was increased in TGF-β3 group. Immunocytochemi-cal analysis of a number of other extracellular matrix components showed widespread expressions of aggre-can, fibromodulin and COMP in alginate bead culture that presented TGF-p3 for 21 days. The expressions of Aggrcan, fibromodulin, type Ⅰ and ⅹ collagen, and COMP were detected by RT-PCR in TGF-β3 group within 8 days, while type Ⅱ collagen began expression at days 8-21. COMP or type X collagen was present in TGF-β3 group at days 7, 14 and 21 by immunoprecipitation or Western blot analysis respectively. The extracted glycosaminoglycan content or the glycosaminoglycan/DNA rate in TGF-βl group was significantly lower than those in TGF-β2 group or TGF-β3 group at days 14 and 21 (P <0.01). Conclusions TGF-β can evocate chondrogenesis of PSCs, when rapid deposition of cartilage-specific extracellular matrix is involved. The sequential events in this pathway leading from the undifferentiated stem cells to mature chon-drocytes can be investigated by analysis of key matrix elements. Key words: Stem cells; Transforming growth factor β; Extracellular matrix; Chondrocytes; Chondrogenesis