Tumor necrosis factor alpha stimulates insulin-like growth factor binding protein 3 expression in cultured porcine Sertoli cells

The present study was undertaken to analyze how a cytokine, the tumor necrosis factor alpha (TNF alpha), antagonizes the stimulatory action of insulin-like growth factor-I (IGF-I) on FSH receptor levels in testicular Sertoli cells. To achieve this purpose, we measured, in a model of primary culture of porcine Sertoli cells, the effects of TNF alpha on the IGF system that includes IGF-I and IGF-II, IGF binding proteins (IGFBPs), and IGF-I receptor (IGF-I R). We report that while TnF alpha had no consistent effect on the levels of IGF-I, IGF-II, or on IGF-I receptor [protein and messenger RNA (mRNA)], it stimulated IGFBP activity and particularly IGFBP-3. TNF alpha stimulated predominantly IGFBP-3 (about 4-fold) both in terms of mRNA (a 2.6-kilobase transcript, measured by Northern blotting analysis), and protein (a doublet of 40-44 kDa, assessed by ligand blotting analysis). Such a stimulatory effect on IGFBP-3 was detected with a concentration as low as 0.1 ng/ml (5.5 pM) of TNF alpha. The stimulatory action of the cytokine was time dependent and was maximal at 7 h and 48 h, for IGFBP-3 mRNA and protein, respectively. Such an increase in IGFBP-3 in TNF alpha-treated Sertoli cells results probably in a decrease in IGF-I bioavailability for its receptors and thus in a decrease in IGF-I action. Indeed, addition of recombinant human IGFBP-3 (10 nM) suppressed completely the stimulatory action of IGF-I (3 nM) on FSH binding to cultured porcine Sertoli cells. Together, the present findings indicate that, in Sertoli cells, TNF alpha antagonizes IGF-I action through the modulation of IGFBPs and particularly through an increase in IGFBP-3. Because of the local production of both TNF alpha and components of the IGF system, such an interaction between the IGF system and the cytokine probably occurs in the context of physiological testicular somatic-germ cell interactions.