Direct Regulating Effects of Transforming Growth Factor-β 1 on Lactate Production in Cultured Porcine Sertoli Cells*

Abstract

In the present study we have tested the direct effects of transforming growth factor-beta 1 (TGF beta 1) on lactate production by Sertoli cells isolated from immature porcine testes. In Sertoli cells cultured in a defined medium, TGF beta 1 was shown to stimulate lactate production in a time- and dose-dependent manner. The maximal and half-maximal effects of TGF beta 1 on lactate production were obtained in the picomolar concentration range, respectively 24 and 8 pM TGF beta 1. TGF beta 1 action was found closely related to that of insulin since 1) both TGF beta 1 (40 pM) and insulin (1 microgram/ml) induced the secretion of similar and nonadditive amounts of lactate; and 2) TGF beta 1 and insulin induced comparable increases in lactate production in FSH (1 microgram/ml)-treated Sertoli cells. Because lactate is derived from glucose, 2-deoxy-D-glucose (2-DOG) was used to investigate the hexose transport system of Sertoli cells after insulin, FSH, and TGF beta 1 treatments. Insulin (1 microgram/ml) and FSH (1 microgram/ml) were found to stimulate 2-DOG transport with a similar time course, with an effect detected up to 30 min and maximal at 150 min. In contrast, although TGF beta 1 also enhanced 2-DOG uptake by Sertoli cells, the increase in glucose transport was delayed, since the TGF beta 1 effect was first detected at 150 min and was maximal at 360 min. These effects of TGF beta 1 action on Sertoli cell activity are exerted through specific membrane TGF beta 1 receptors. Scatchard analysis of the binding of TGF beta 1 to cultured Sertoli cells revealed the presence of both a high affinity (Kd, approximately 180 pM) and a low affinity binding site systems for TGF beta 1. Affinity labeling of these receptors by covalent attachment to [125I] TGF beta 1 with disuccinimidyl suberate and subsequent electrophoretic analysis of the labeled complexes revealed the specific binding of [125I] TGF beta 1 to three predominant molecules of 260, 130, and 70 kDa. In conclusion, the present study demonstrates that testicular Sertoli cells are targets for TGF beta 1 action. In view of the importance of lactate as a substrate for germ cells, it is suggested that TGF beta 1 might also be involved in the development of normal germinal epithelium.