INHIBITION OF PROTEOGLYCAN SYNTHESIS INDUCES AN INCREASE IN FOLLICLE-STIMULATING-HORMONE (FSH)-STIMULATED ESTRADIOL PRODUCTION BY IMMATURE RAT SERTOLI CELLS

In order to define the possible involvement of proteoglycans (PG) in the regulation of Sertoli cell functions, we have examined the effect of para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis, on follicle stimulating hormone (FSH)-dependent estradiol production by immature rat Sertoli cells. Addition of PNPX to the culture medium induced a dose-dependent inhibition of S-35-labeled PG synthesis in Sertoli cells both in the medium and the cell layer. Simultaneously there was a drastic increase in S-35- labeled secreted glycosaminoglycans. By 1 mM PNPX, syntheses of chondroitin sulfate proteoglycans released into culture medium and of heparan sulfate proteoglycans associated with the cell layer were 35% of values from untreated cells. Simultaneously, PNPX induced a twofold (mean of seven experiments, range 17-250%) enhancement of FSH (100 ng/ml)-stimulated estradiol production. In each individual experiment, there was an inverse relationship between the amplitude of PNPX-induced increase in FSH responsiveness and the FSH capability to stimulate basal estradiol production in cultured rat Sertoli cells. The effect of PNPX on FSH-stimulated aromatase activity was not mimicked by para-nitrophenyl-beta-D-galactoside, a structural analog of PNPX that has no effect on PG synthesis. The (Bu)(2)cAMP-stimulated estradiol synthesis was not modified in the presence of PNPX. Moreover, PNPX enhancement of FSH-stimulated estradiol synthesis disappeared when Sertoli cells were cultured in the presence of 1-methyl-3-isobutylxanthine, an inhibitor of phosphodiesterase activity. These findings suggest that inhibition of PC synthesis under PNPX conditions did not affect signal transduction steps distal to cAMP but rather decreased the phosphodiesterase activity in Sertoli cells. These results strongly support the idea that PGs associated with the plasma membrane and/or extracellular matrix are involved in the repression of FSH-dependent activities in prepubertal rat Sertoli cells.