Hormonal regulation of proteins secreted by cultured pig Sertoli cells: characterization by two-dimensional polyacrylamide gel electrophoresis

Transferrin and inhibin mRNA in mature pig Sertoli cells

Aims:  There is increasing concern about the effect of environmental toxins and endocrine disrupters on human spermatogenesis but ethical considerations prohibit direct research. Therefore, we developed a method of isolating mature pig Sertoli cells and studying the levels of mRNA of transferrin and inhibin, markers of Sertoli cell function, using real-time polymerase chain reaction analysis. Methods:  Sertoli cells from mature Meishan boars were isolated and cultured. The mRNA was isolated from the cells after 3 days of treatment with follicle-stimulating hormone (FSH), testosterone and β-estradiol. The amounts of transferrin and inhibin mRNA were analyzed by real-time polymerase chain reaction and the relative level of mRNA was calculated. Results:  FSH tended to increase the levels of transferrin and inhibin mRNA, as did the combinations of FSH and the steroids. The effect of testosterone and β-estradiol alone on the level of mRNA was less than that of FSH. Beta-estradiol treatment resulted in a dose-dependent decrease in mRNA. Conclusion:  The Sertoli cell culture used in the present study appears to have a normal secretory function because the mRNA levels of both markers increased after FSH treatment. The suppressive effect of β-estradiol on inhibin mRNA level suggests that β-estradiol has an effect on the function of Sertoli cells. (Reprod Med Biol 2005; 4: 259 -264).

Receptors for anti-müllerian hormone on Leydig cells are responsible for its effects on steroidogenesis and cell differentiation

Strong overexpression of anti-Müllerian hormone (AMH) in transgenic mice leads to incomplete fetal virilization and decreased serum testosterone in the adult. Conversely, AMH-deficient mice exhibit Leydig cell hyperplasia. To probe the mechanism of action of AMH on Leydig cell steroidogenesis, we have studied the expression of mRNA for steroidogenic proteins in vivo and in vitro and performed a morphometric analysis of testicular tissue in mice overexpressing the hormone. We show that overexpression of AMH in male transgenic mice blocks the differentiation of Leydig cell precursors. Expression of steroidogenic protein mRNAs, mainly cytochrome P450 17 alpha-hydroxylase/C17-20 lyase (P450c17), is decreased in transgenic mice overexpressing AMH and in AMH-treated purified Leydig cells. In contrast, transgenic mice in whom the AMH locus has been disrupted show increase expression of P450c17. In vitro, but not in vivo, AMH also decreases the expression of the luteinizing hormone receptor. The effect of AMH is explained by the presence of its receptor on Leydig cells. Our results provide insight into the action of AMH as a negative modulator of Leydig cell differentiation and function.

Enhancement of testosterone secretion by normal adult human Leydig cells by co-culture with enriched preparations of normal adult human Sertoli cells

An in-vitro method was developed to study Sertoli-Leydig cell interactions in man, using testes removed at the time kidneys were removed for transplantation from 6 young adult men (aged 17-45 years) after cerebral death. After collagenase digestion of testicular tissue, Leydig cells were purified on discontinuous Percoll gradients. Two fractions of Leydig cells, 'L2' and 'L3' which differed in their buoyant density (1.05 g < L2 < 1.06 g and 1.06 g < L3 < 1.08 g), were obtained. The Sertoli cell-enriched preparation was obtained from seminiferous tubular fragments after sequential treatment with glycine buffer to remove peritubular-myoid cells, a second collagenase digestion, mechanical fragmentation and washes to remove germ cells. Purified Leydig cells were then cultured either alone or together with Sertoli cells in culture dishes coated with collagen, fibronectin and laminin in a chemically defined medium without serum. The influence of co-culture on basal testosterone secretion was examined in 3 successive 48 h periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal and paracrine regulation of gamma-glutamyl transpeptidase in rat Sertoli cells

The effects of follicle-stimulating hormone (FSH) and testosterone on Sertoli cell gamma-glutamyl transpeptidase (gamma-GTP) activity have been studied in vitro. Addition of FSH to Sertoli cell cultures for 5 days induced stimulation of gamma-GTP activity. No testosterone effect was observed alone or in combination with different doses of FSH. Time course studies for a supramaximal dose of FSH showed that enzyme induction could be achieved after a 48 h stimulation. Furthermore, a gradual stimulation of gamma-GTP activity in response to increasing numbers of germinal cells (GC) added in coculture, was observed. Stimulation was also demonstrated with germinal cell-conditioned medium (GCCM). Stimulatory effects of GC and GCCM were additive with those of FSH, suggesting that different mechanisms were involved.

Leydig cell and extracellular matrix effects on Sertoli cell function: biochemical and morphologic studies

The reciprocal influence between Leydig and Sertoli cells prepared from pig testis were studied by coculture of both types of cells in either plastic dishes or dishes coated with basement membrane matrix. After 2-3 days in plastic dishes, Sertoli cells produced an increase in the steroidogenic response of Leydig cells to hCG. Pretreatment of the coculture with pFSH enhanced the steroidogenic capacity of Leydig cells and increased the number of hCG receptors. Similarly, the number of FSH binding sites and the FSH-induced plasminogen activator activity secretion of Sertoli cells cocultured with Leydig cells were increased. Pretreatment of the coculture with hCG further enhanced both parameters. The positive reciprocal tropic effects between Leydig cells and Sertoli cells were significantly enhanced when the coculture was carried out on the top of extracellular matrix. In addition, when cells were cocultured under these conditions, but not on plastic dishes, they were organized in cell clusters or island structures, with most of the Leydig cells located in the outer area, whereas Sertoli cells were located inside the islands.

Protein secretions of Sertoli cells

As was stated in the introduction, many of the functions of the Sertoli cells are apparently carried out by the protein secretions of these cells. The use of Sertoli cell cultures and appropriate biochemical and immunological techniques has allowed the characterization of some of these secretion products. It is likely that many of the functions of the Sertoli cells are necessary because of the presence of the blood-testis barrier. Many growth and nutritive factors which are necessary for cell viability are available to most cells via the serum. The germinal cells within the adluminal compartment do not have access to serum factors and one of the functions of the Sertoli cells is to synthesize serum-like components and secrete them into the adluminal compartment. The historical description of Sertoli cells as "nurse cells" thus appears to have been accurate. The nurse-cell function is most clearly demonstrated by the proposed mechanism by which germinal cells obtain ferric ions. The Sertoli cells have developed a system to move serum-derived iron through their own cytoplasm and to secrete it bound to newly synthesized testicular transferrin molecules which can deliver it to specific receptors on the germinal cell surface (Huggenvik et al., 1984). Functionally, all of the secreted proteins from Sertoli cells which have been characterized or proposed fall into one of five basic classes. First, Sertoli cells secrete a number of transport proteins including transferrin, ceruloplasmin, and ABP. The proposed function of these proteins is the transport of Fe3+, Cu2+, and androgens to the germinal cells or to the epididymis (ABP). Second, Sertoli cells synthesize and secrete a number of proteins which have a hormone-like or growth factor-like activity. AMH is a clear and well-documented example of this type of product while the evidence for inhibin, somatomedin C, EGF-like growth factor, and seminiferous growth factor will require further corroboration. Third, Sertoli cells secrete proteins which have enzymatic activities. Plasminogen activator is the best characterized example of this class of products and the alpha-lactalbumin-like activity is of potential interest. The fourth class of Sertoli cell secretion products includes those proteins which contribute to the basement membrane, namely, type IV collagen and laminin. Finally, there is a very important group of Sertoli cell secretion products for which there is, as yet, no evidence for a defined function. This group includes SGP-1 and SGP-2 which are the major sertoli cell products in rats and which have been well-characterized biochemically.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of Leydig cell functions by culture with Sertoli cells or with Sertoli cell-conditioned medium: effect of insulin, somatomedin-C and FSH

The potential regulatory action of Sertoli cells on Leydig cell functions has been investigated by using a coculture system of Leydig and Sertoli cells obtained from immature pig or by culturing Leydig cells with Sertoli cell-conditioned medium (SCCM). Coculture of Leydig and Sertoli cells for 48 h in the absence of insulin or somatomedin-C (Sm-C), produced a small but significant increase in both hCG receptors and hCG-induced testosterone production. Addition to the medium of pFSH (100 ng/ml), insulin (5 micrograms/ml) or somatomedin-C (50 ng/ml) produced a marked increase in these two parameters of Leydig cell function. A further significant increase was observed when pFSH was associated with insulin or Sm-C. In contrast, coculture of Leydig cells with aortic endothelial cells decreased both the hCG receptor number and the hCG responsiveness. SCCM stimulated Leydig cell testosterone production following a 4 h incubation. The stimulation depended upon the amount of SCCM used and the conditions in which Sertoli cells were cultured. The most active was the medium from cells cultured in the presence of pFSH and insulin at high concentrations. Since pig Sertoli cells have specific somatomedin-C receptors, but not insulin receptors, it is likely that the effect of micromolar concentrations of insulin are exerted through Sm-C receptors. In addition, SCCM produced a long-term effect after 48 h incubation. SCCM from cells cultured in the absence of insulin and pFSH inhibited both the hCG receptor number and hCG responsiveness. A similar inhibition was observed with SCCM medium from cells cultured without insulin but with pFSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatomedin-C/insulin-like growth factor 1: a differentiating factor of testicular function

Using primary culture in a chemically defined medium of somatic testicular cells from immature pig, we were able to demonstrate synthesis and secretion of Somatomedin-C/Insulin-Like Growth Factor 1 (Sm-C/IGF-1) by Sertoli cells, a process that is stimulated by Fibroblast Growth Factor (FGF). The presence of IGF type 1 receptor was demonstrated on Sertoli cells. Sm-C/IGF-1 stimulates and potentiates the effects of FGF on both cell multiplication and secretion of plasminogen activator. The presence of both IGF type 1 and insulin receptors was also documented on immature Leydig cells. Pre-incubation of immature Leydig cells for 48 hours with Sm-C/IGF-1 resulted in a dramatic dose-dependent increment of both the LH receptor number and steroidogenic response to LH as well as a clear stimulation of DNA synthesis. These data provide new important insights on the role played by Sm-C, a growth and differentiating factor, on the maturation of the male gonad endocrine function.

Processing of follitropin and its receptor by cultured pig Sertoli cells. Effect of monensin

Immature pig Sertoli cells, cultured in a chemically defined medium, are able to maintain many of their functional characteristics for at least two weeks. This model was used to investigate the binding, internalization and degradation of 125I-labelled human follitropin (hFSH) and the effects of pig FSH (pFSH) on its own receptors. The binding of 125I-labelled hFSH was dependent on time, temperature and concentration. At 4 degrees C, the apparent steady state was reached in 8-12 h and remained constant for at least 24 h, whereas at 33 degrees C the apparent equilibrium was reached in 4-6 h. Thereafter the total binding declined and by 24 h it was less than 50% of the maximum binding. At 33 degrees C the binding for the hormone to its surface receptor was followed by internalization of the hormone (half-life approximately equal to 1 h) and its degradation (half-life approximately equal to 3 h). The receptor-mediated internalization of hFSH was blocked by phenylarsine oxide. In the presence of the ionophore monensin (20 microM) the rates of binding and internalization were not modified but the degradation rate was much lower (half-life approximately equal to 18 h). Thus, in the presence of monensin, maximum binding increased twofold to threefold, and remained constant for 24 h. This increase was mainly due to an increase of the internalized hormone. When Sertoli cells were exposed to pFSH there was a loss of its own receptor, which was both dose-dependent (ED50 = 250 ng/ml) and time-dependent (t 1/2 = 14 h). Cycloheximide did not modify the FSH-induced down-regulation, whereas monensin enhanced the down-regulation process. These results show that FSH, like other ligands, is internalized and degraded by its target cells and indicate that the hormone-mediated down-regulation is related to the internalization process. However, the discrepancy between the rate of internalization and of hormone-induced down-regulation, suggests that some of the internalized receptors are recycled.