growth factor

Growth factors are a group of cytokines, containing members like Transforming Growth Factor β-1 (TGFβ-1), Insulin-like Growth Factor I (IGF-I), Bone Morphogenic Protein 2 (BMP-2), Bone Morphogenic Protein 7 (BMP-7), and Fibroblastic Growth Factor 2 (FGF-2). TGFβ and IGF-I have been shown to stimulate the production of proteoglycans (anabolic). Additionally, IGF-I has been shown to increase chondrocyte proliferation (mitogenic). BMP-2 and BMP-7 have been shown to enhance proteoglycan synthesis, and it has been indicated that BMP-7 maybe also increase the synthesis of hyaluronic acid and its receptor CD44. FGF-2 can help the regenerative capacity of chondrocytes, as it will stimulate proliferation and redifferentiation once the chondrocytes are moved from monolayer culture to a 3D culture in a scaffold. Moreover, studies by the Loeser laboratory have shown that growth factors IGF-I and TGFβ-1 when added exogenously to the culture medium can enhance the expression of certain integrins, increasing the adhesivity of the cells to the matrix; however, TGFβ-1 had the opposite effect on the α1β1 integrin, decreasing chondrocyte affinity to collagen VI.

Growth factors play important roles in both positively and negatively regulating proliferation of a variety of cell types in tissue growth, differentiation, and tumorigenesis. It is thought that growth factors have an important central function in mitosis and cell differentiation because growth factors have been found in the three trophoblastic forms in immunohistochemical analyses. Moreover, an autocrine and paracrine function has been suggested in the regulation of the implantation of the blastocyst, owing to the presence of common receptors found in the human endometrium, decidual and implantation zones. Growth factors have a physiological role in fetal growth.
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