ENHANCEMENT OF LONG-TERM TESTOSTERONE SECRETION AND STEROIDOGENIC ENZYME EXPRESSION IN HUMAN LEYDIG-CELLS BY COCULTURE WITH HUMAN SERTOLI CELL-ENRICHED PREPARATIONS

We have shown previously that long-term testosterone secretion, which decreases when human Leydig cells are cultured alone, increases when p urified human Leydig and Sertoli cells are cultured together. In this work, human Leydig cell functions were studied further during in vitro culture, either alone or with human Sertoli cells, on a basal membran e derived from bovine corneal endothelial cells. The secretion of test osterone increased during the first week of co-culture and remained el evated up to day 12 of culture. In one prolonged co-culture, testoster one secretion decreased progressively after day 12 and, after 1 month of culture, was at a level similar to that observed during the first 4 8 h. After culture for 48 h, testosterone secretion in the co-culture was enhanced by 162 +/- 5% (p < 0.0001) compared with values observed when Leydig cells were cultured alone (42.6 +/- 10.6 ng/10(6) Leydig c ells/48 h; mean +/- SEM). This change was associated with increase in mRNA levels for 3 beta-hydroxysteroid dehydrogenase Delta 5-Delta 4-is omerase (2.49 +/- 0.58-fold), cytochrome P450c17 (2.81 +/- 0.99-fold), cytochrome P450scc (5.20 +/- 0.13-fold) and cytochrome P450 aromatase (1.73 +/- 0.21-fold) when Leydig cells were co-cultured with Sertoli cells (p < 0.05 for each enzyme). IGF-I mRNA levels were higher (2.77 +/- 0.72-fold for 7.6 kb and 1.41 +/- 0.07-fold for 1.1-1.3 kb transcr ipts) in the Leydig-Sertoli cell co-cultures than the sum of the level s in Leydig and in Sertoli cells cultured alone. Both basal and hCG-in duced testosterone secretion were enhanced by treatment of the co;cult ure with human recombinant FSH (50mIU/mL). For basal testosterone secr etion, this increase amounted to 163 +/- 5% compared with Leydig cells cultured alone (p < 0.0001) and by 112 +/- 4% compared with non-FSH t reated co-cultures (p < 0.01); for hCG-stimulated testosterone secreti on this increase was 220 +/- 12% compared with Leydig cells cultured a lone (p < 0.0001) and 132 +/- 8% compared with non-FSH treated co-cult ures (p < 0.01). This study confirms the enhancement of long-term test osterone secretion by adult human Leydig cells by co-culture with adul t human Sertoli cells and shows that this effect is associated with an enhancement of the expression of several steroidogenic enzymes; it mi ght be mediated, as in other species, through increased production of IGF-I by co-culture.