Somatomedin C/insulin-like growth factor 1 as a possible intratesticular regulator of Leydig cell activity

Abstract

By using immature porcine Sertoli cells cultured in serum-free defined medium, we report that Sertoli cell-conditioned medium (SCCM) contains immunoreactive somatomedin C/insulin-like growth factor 1 (ir-SmC/IGF 1) which dilutes in parallel with purified human SmC/IGF 1. The release of ir-SmC/IGF 1 in the culture medium was dependent on the exposure time to Sertoli cells: no measurable ir-SmC/IGF 1 at 8 h, 12.1 ± 1.2 ng/10 6 cells at 24 h and 33.9 ± 5.3 ng/10 6 cells at 48 h of incubation. Moreover, ir-SmC/IGF 1 was also evidenced in SCCM following high performance liquid chromatography using a μC18 Bondapak column; ir-SmC/IGF 1 Sertoli cell-conditioned medium co-eluted with pure human SmC/IGF, suggesting a high homology between the two peptides. The effects of SmC/IGF 1 on testicular steroidogenesis were studied by incubating immature porcine Leydig cells with a biosynthetic human SmC/IGF 1. SmC/IGF 1 exerted a dose- and time-dependent stimulating effect on Leydig cell function with a maximal response at 50 ng/ml after 48 h of treatment. SmC/IGF 1 increased both LH/hCG binding (4.3-fold), basal testosterone (4-fold) and DMAS- and hCG-stimulated testosterone and DHAS (dehydroepiandrosterone sulfate) production (15.5- and 6.4-fold respectively). The slight effect of SmC/IGF 1 (100 ng for 48 h) on cell number (1.3-fold) and incorporation of [ 3H]thymidine into DNA (1.5-fold) in comparison with the high steroidogenic effect, supports the concept that SmC/IGF 1 acts as a cytodifferentiative factor rather than as a growth factor. The steroidogenic action of SmC/IGF 1 was not suppressed by cytosine arabinoside C (ARA-C) (10 −5 M), a DNA synthesis inhibitor, thereby strengthening the concept that this peptide plays a cytodifferentiative role. In conclusion, the release by cultured Sertoli cells of SmC/IGF 1 associated with the stimulating effect exerted by this peptide on Leydig cell function suggests that SmC/IGF 1 could be a potential intratesticular regulator of Leydig cell differentiation.