TGF-β ALTERS COLLAGEN XII and XIV mRNA LEVEL IN EQUINE TENOCYTE CULTURES

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The effects of TGF-β1, β2 and β3 (TGF-β) on levels of mRNA corresponding to the α chains of type XII and type XIV collagens in equine tenocyte cultures were assessed using the ribonuclease protection assay (RPA). The level of α1(XII) mRNA in untreated monolayer cultures was approximately 50 to 100-fold greater than α1 (XIV) mRNA level. Addition of TGF-β resulted in an increase in the amount of α1 (XII) present and a decrease of α1 (XIV) mRNA in a dose-dependent manner. Specifically, the level of α1(XII) mRNA was doubled, but α1(XIV) was decreased to 30% of control by the addition of 2 ng/ml of TGF-β1 to the cultures. These effects were completely abrogated by neutralizing antibody specific for TGF-β. In addition, electron microscopy demonstrated that bundled collagen fibers were formed in the intercellular spaces of multilayered tenocyte which had been cultured for two weeks in the presence of exogenous TGF-β1 together with ascorbic acid phosphate. These results suggest that type XII and/or type XIV collagens modulate the structure of ECM formed by tenocytes in culture.