Effects of transforming growth factor‐β1 and fibroblast growth factor on DNA synthesis in growth plate chondrocytes are enhanced by insulin‐like growth factor‐I

Abstract

The local tissue metabolism is controlled through the complex interaction between systemic and local growth factors. In recent years, an increasing number of autocrine or paracrine growth regulators have been identified in physeal cartilage. While these factors act to alter chondrocytes phenotypically and presumably are important mediators in the process of endochondral ossification, the manner in which they interact with the systemically regulated growth factor insulin-like growth factor-I is unknown. In the present study, the interactive effects of insulin-like growth factor-I with transforming growth factor-beta 1 or basic fibroblast growth factor were examined in short-term monolayer cultures of chick growth plate chondrocytes. [3H]thymidine incorporation was maximally stimulated 11-fold by fibroblast growth factor (10 ng/ml) and 3.5-fold by transforming growth factor-beta 1 following a 24-hour exposure in serum-containing cultures. The effects of transforming growth factor-beta 1 and fibroblast growth factor at both high and low concentrations were enhanced in a dose-dependent manner by insulin-like growth factor-I, with a 40-50% increase in DNA synthesis in the presence of 100 ng/ml of insulin-like growth factor-I. Since insulin-like growth factor-I increased [3H]thymidine incorporation after 48 hours (50% increase) but not after 24 hours of exposure, these observations represent a synergistic interaction. Total DNA in cultures treated for 5 days confirmed the modulating effect of insulin-like growth factor-I with transforming growth factor-beta 1 and fibroblast growth factor. The growth factors were further examined for their effects on markers of chondrocyte differentiation. While all three caused a dose-dependent inhibition of alkaline phosphatase activity, the effects of insulin-like growth factor-I were additive only to those of transforming growth factor-beta 1 and fibroblast growth factor. Similarly, insulin-like growth factor-I did not affect the sulfate incorporation stimulated by fibroblast growth factor or transforming growth factor-beta 1. Insulin-like growth factor-I had no effect on total protein synthesis after 24 hours and, although type-II collagen mRNA levels were stimulated, it had no effect on type-X collagen mRNA, as determined by quantitative in situ hybridization. Finally, insulin-like growth factor-I did not alter the dose-dependent stimulation of noncollagen protein synthesis and the inhibition of collagen synthesis caused by fibroblast growth factor and transforming growth factor-beta 1 in 24-hour cultures. Thus, the data suggest that insulin-like growth factor-I may have a role in augmenting the effects of other growth factors found in cartilage.(ABSTRACT TRUNCATED AT 400 WORDS)

Bone morphogenetic protein-2 and -9 regulate the interaction of insulin-like growth factor-I with growth plate chondrocytes

“…This augmentation occurred at lower concentrations of BMP-9 than of BMP-2. In prior studies, epidermal growth factor (EGF) increased both IGF-I binding and IGF-I responsiveness in growth plate chondrocytes (31), and IGF-I enhanced the mitogenic effect of TGF-ß1 and fibroblast growth factor (FGF) on these cells (32). Taken together, these data support the view that growth factor interaction may be an important mechanism of cell regulation, including the regulation of growth plate chondrocytes.…”

Role of Growth Factors in the Development of Mandible

“…45 Although several studies indicate a stimulatory effect of TGF-β on chondrocyte proliferation and matrix production in vitro, others report an inhibitory effect. 46,47 The specific effects seem to depend on factors like concentration, culture period and the differentiation state of the cells. 48 In general, TGF-β 1 is a potent inhibitor of chondrocyte maturation and hypertrophy, and reduces alkaline phosphatase activity.…”

BMP signaling stimulates chondrocyte maturation and the expression of Indian hedgehog

“…This developmental process continues throughout adolescence and is recapitulated during fracture repair. Several factors, including insulin-like growth factor-1 (IGF-I), fibroblast growth factors (FGFs), and transforming growth factor-p (TGF-P) are produced within the cartilage and regulate chondrocyte proliferation [8,11,28,33]. As chondrocytes mature, they cease proliferating and express high levels of type X collagen and alkaline phosphatase activity.…”