The Production of Transforming Growth Factor-β by Chick Growth Plate Chondrocytes in Short Term Monolayer Culture*

Abstract

Transforming growth factor-.beta. (TGF.beta.) is capable of regulating the proliferation and phenotypic expression of growth plate chondrocytes in culture. Chondrocytes were isolated from the growth plates from the long bones of 3- to 5-week-old chicks. Conditioned medium was harvested from short term monolayer cultures for the assay of TGF.beta. production by these cells. A receptor competition assay using [125I]TGF.beta. was used to quantitate the amount of TGF.beta. in the conditioned medium. Acid-activated conditioned medium contained 5.0 .+-. 0.4 ng/ml TGF.beta., while conditioned medium that had not been exposed to acid had undetectable levels of the peptide by this assay. The initial cell plating density was inversely related to the amount of TGF.beta. produced on a per cell basis. Growth plate chondrocytes separated by countercurrent centrifugal elutriation into maturationally distinct subpopulations had different rates of TGF.beta. production; hypertropic chondrocytes produced significantly more TGF.beta. (4.5 ng/106 cells) than the smallest chondrocytes isolated (2.3 ng/106 cells). A variety of other growth mediators were tested for their ability to influence of TGF.beta. production by chondrocytes, and it was found that only basic fibroblast growth factor could significantly influence TGF.beta. production, producing a 6-fold increase in TGF.beta. recovered in the conditioned medium. The production of TGF.beta. by growth plate chondrocytes implicates it as an important autocrine or paracrine regulator in the process of endochondral calcification.