Role of growth factors on extracellular matrix production by chick embryo fibroblasts in vitro. Antagonist effect of TGF-beta through the control of IL-1 and IL-1Ra secretion.

Growth factors and extracellular matrix (ECM) macromolecules create specific environments that regulate cell proliferation and differentiation during embryonic development. This study had two main aims: (1) to characterize the phenotype of 7- and 13-day-old chick embryo fibroblasts treated with interleukin 1 (IL-1) and interleukin 6 (IL-6) evaluating in particular the neosynthesis of the total proteins and of the fibronectin (FN); (2) to examine the mechanisms through which transforming growth factor beta (TGF-beta) antagonizes the action of IL-1. The results show that protein neosynthesis and secretion is modulated by treatment with IL-1 and IL-6 only in 7-day-old fibroblasts. IL-1 favours cellular accumulation, while IL-6 promotes secretion more. FN, isolated by affinity chromatography and analysed by SDS-PAGE and flurography, is produced in greater concentrations by 7-day-old fibroblasts. Treatment with IL-1 promotes the accumulation of FN in the cellular compartment both at 7 and 13 days, while it stimulates the secretion only in 7-day-old fibroblasts. IL-6 only has a stimulating effect on the processes of accumulation and secretion on 13-day-old fibroblasts. The authors show in addition, that TFG-beta blocks the IL-1 induced inhibitory effect on glycosaminoglycan (GAG) and collagen production, evaluated with [3H]glucosamine and [3H]proline incorporation studies, respectively. The effect is evident when TGF-beta is added either before of with the cytokine. Analysis in cell culture supernatants, using specific ELISA kit and the study of the proliferative responses in mouse thymocytes, showed that TGF-beta induces its antagonist effects through a downregulation of IL-1 and/or an upregulation of IL-1 receptor antagonist protein (IL-1Ra). Considered as a whole the data indicate that the ILs and TGF-beta are involved in the physiological age-dependent accumulation of ECM and that the balance between the secreted cytokine network and IL-1Ra amount, may represent a homeostatic mechanism aimed at controlling normal embyrogenesis.