FSH activates phosphatidylinositol 3-kinase/protein kinase B signaling pathway in 20-day-old Sertoli cells independently of IGF-I.
The gonadotropin FSH plays a key role in the control of Sertoli cell function. The FSH molecular mechanism of action is best recognized for its stimulation of the adenylyl cyclase/cAMP pathway. However, other signaling events have also been demonstrated in Sertoli cells. We have recently presented evidence that FSH can stimulate the phosphatidylinositol 3-kinase/protein kinase B (PI3K/PKB) pathway in 20-day-old Sertoli cells. At the same time, it was proposed that in 8-day-old Sertoli cells the effects of FSH on phosphorylated PKB (P-PKB) levels can be explained by a combination of increased secretion of endogenous IGF-I, decreased IGF-binding protein-3 (IGFBP-3) production, and a synergistic action of FSH on IGF-I-dependent PI3K activation. The aim of the present study was to determine whether the effect of FSH on 20-day-old Sertoli cells is mediated by IGF-I secretion. Twenty-day-old rat Sertoli cell cultures were used. FSH stimulation produced a time-dependent increment in P-PKB levels reaching maximal values in 60-min incubations. IGF-I stimulation was also time-dependent reaching maximal values in 15-min incubations. On the other hand, stimulation of the cultures with FSH showed time-dependent inhibition in phosphorylated mitogen-activated protein kinase (P-MAPK) levels. In sharp contrast, stimulation of the cultures with IGF-I showed time-dependent increments in P-MAPK levels reaching maximal stimulus in 15-min incubations. In order to rule out an IGF-I action on FSH stimulation of P-PKB levels, the effect of a specific IGF-I antibody on the ability of both hormones to increase P-PKB levels was evaluated. As expected, the antibody inhibited IGF-I stimulation of P-PKB levels. However, simultaneous addition of an IGF-I antibody with FSH did not modify the ability of the hormone to increase P-PKB levels. The next set of experiments intended to analyze the relevance of a PI3K/PKB pathway to two biological responses of Sertoli cells to FSH and IGF-I. The PI3K inhibitor, wortmannin, dose-dependently decreased FSH-stimulated lactate and transferrin production. On the other hand, wortmannin was not able to modify the ability of IGF-I to stimulate these metabolic events. In addition, the analysis of the participation of a MAPK pathway in IGF-I regulation of Sertoli cell biological responses showed that the MAPK kinase inhibitors, PD98059 and U0126, decreased IGF-I-stimulated transferrin secretion while not modifying IGF-I-stimulated lactate levels. In summary, results obtained so far support the hypothesis that FSH action on P-PKB levels and Sertoli cell metabolism in 20-day-old animals is not mediated by autocrine regulation of an IGF-I/ IGFBP-3 axis as previously proposed in 8-day-old Sertoli cells.
Meroni
S B
SB
Centro de Investigaciones Endocrinológicas (CEDIE), Hospital de Niños 'R. Gutiérrez', Gallo 1330, 1425 Buenos Aires, Argentina.
Riera
M F
MF
Pellizzari
E H
EH
Galardo
M N
MN
Cigorraga
S B
SB
D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D005640:Follicle Stimulating Hormone / Q000378:metabolism / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D012708:Sertoli Cells / Q000378:metabolism*
D005640:Follicle Stimulating Hormone; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt