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 test icular 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 protein s (IGFBPs), and IGF-I receptor (IGF-I R). We report that while TnF alp ha 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 act ivity and particularly IGFBP-3. TNF alpha stimulated predominantly IGF BP-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 effe ct 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 d ependent 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 Serto li cells results probably in a decrease in IGF-I bioavailability for i ts receptors and thus in a decrease in IGF-I action. Indeed, addition of recombinant human IGFBP-3 (10 nM) suppressed completely the stimula tory 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 i n the context of physiological testicular somatic-germ cell interactio ns.