Hormonal stimulation alters the type of plasminogen activator produced by Sertoli cells

Primary cultures of immature rat Sertoli cells, maintained in serum-free medium, secrete two types of plasminogen activator (PA). When cultured under basal conditions, the preparations predominantly produce PA having a relative molecular weight (Mr) of 45,000 to 48,000. This PA activity is inactivated by antiserum against urokinase-type PA. When Sertoli cells are stimulated by follicle-stimulating hormone (FSH) or by dibutyryl cyclic adenosine 3',5'-monophosphate (dbcAMP), PA secretion is increased. The PA produced under these conditions has an Mr of 70,000, and is inactivated by antiserum against tissue-type PA but not by antiserum against urokinase-type PA. We conclude that, under basal conditions, Sertoli cells primarily secrete PA having the characteristics of urokinase-like PA (mu PA), and that Sertoli cells stimulated by FSH or by dbcAMP predominantly produce PA having the properties of tissue-type PA (tPA). Segments of adult rat seminiferous tubules, at defined stages of the cycle of the seminiferous epithelium, also produce and secrete two types of PA into the medium when maintained in organ culture. Segments at all stages examined release primarily mu PA in preparations cultured under basal conditions. In contrast, segments cultured in the presence of FSH synthesize larger amounts of PA, predominantly of the tPA type. An additional protease, which is independent of plasminogen, is secreted by tubule segments stimulated by FSH. The activity of this novel protease is not detectable in cultures maintained under basal conditions. We discuss the data in relation to the possible role of proteases in the restructuring of the seminiferous tubule during spermatogenesis.     

Stimulatory effect of Sertoli cell culture medium on the FSH release by pituitary halves in vitro

The influence of the medium collected from cultured rat Sertoli cells on the spontaneous and LHRH-stimulated release of gonadotropins by incubated rat pituitary halves was examined. The homogeneity of the cultured population of Sertoli cells taken from 20-day-old rats ranged up to 98%. The cells in culture responded to FSH stimulation with characteristic morphological changes and with increased secretion of estradiol-17 beta. The hemi-pituitaries obtained from sexually mature male rats were incubated for 5 hours in the presence of Sertoli cell culture medium (SCCM) or its fractions obtained by use of ultrafiltration. The SCCM fraction deprived of MW less than 10 kD compounds exhibited a typical inhibin-like activity, whereas crude SCCM as well as its low-molecular-weight fraction stimulated the basal FSH release to about 150% and 175% of the control values, respectively. These fractions exerted an inhibitory effect on the LHRH-stimulated secretion of both LH and FSH. It is concluded that Sertoli cells cultured in chemically defined medium release, apart from inhibin, a non-steroidal, heat-labile substance of MW less than 10 kD which stimulates the basal secretion of FSH and LH and inhibits the LHRH-stimulated secretion of both gonadotropins from incubated rat hemi-pituitaries.     

Interaction between Leydig and Sertoli cells in vitro

The interaction between Leydig and Sertoli cells grown in co-culture was studied. After 3 to 4 days in culture, Leydig and Sertoli cells formed monolayers. To distinguish functional Leydig cells from Sertoli cells, a histochemical test for delta 5,3 beta-HSD activity was performed, and cells which showed a positive reaction were defined as Leydig cells, in contrast to Sertoli cells which did not manifest enzyme activity. Testosterone and oestradiol levels in culture media were determined by radioimmunological assays. Sertoli cells in co-culture showed a tendency to organize themselves as in vivo, forming a kind of pseudo-wall of the tubule. This process becomes more evident with the time of culture. Co-cultures secreted more androgens than Leydig cells alone and more oestradiol than Sertoli cells alone. This influence was strengthened by the presence of follicle stimulating hormone (FSH) in the culture medium, which was not the case in cultures of Leydig and Sertoli cells cultured separately.     

Spent media from immature seminiferous tubules and Sertoli cells inhibit adult rat Leydig cell aromatase activity

Adult rat Leydig cell aromatase activity is stimulated 2.5 fold by LH or dbcAMP. Spent media prepared from seminiferous tubules or Sertoli cells of immature rats depress both the basal and the LH stimulated estradiol syntheses (25 and 20% decreases, respectively). These inhibitory effects are further enhanced when FSH is added to the culture medium of seminiferous tubules or Sertoli cells. Rat serum as well as culture media from other cell lines are ineffective while seminiferous tubule media from other immature animals (mouse, guinea-pig, calf) inhibit the aromatase activity. This Sertoli cell factor is a heat stable protein (molecular weight greater than 10 kDa), different from the LHRH-like Sertoli cell compound, which acts on the aromatase activity at a step beyond the adenylate cyclase.     

Increase by FSH hormone and depression by testosterone of the diffusional coupling between Sertoli cells from immature rat testis in primary culture

Previous studies have suggested that FSH promotes the intercellular coupling of Sertoli cells from immature rat testis in primary culture ([1], [2]). In order to test this hypothesis, we have investigated the diffusional coupling between Sertoli cells in primary culture with the FRAP technique. The coupling is low in unstimulated cells but increases in the presence of FSH. This effect is not reversed by returning to the control medium. Testosterone decreases this coupling, an effect which is reversed by a new exposure to FSH. Taken together these data show that FSH initiates diffusional coupling in Sertoli cells and that testosterone antagonizes this effect.     

Transglutaminase activity in testicular homogenates and serum-free Sertoli cell cultures

Transglutaminase (EC 2.3.2.13) (TGase) activity has been localized in homogenates of rat Leydig cells and seminiferous tubules and is present in cytosol and membrane fractions. The enzyme has a requirement for Ca2+ and when the acceptor substrate casein was deleted from the assay mixture, incorporation of [14C]putrescine into cytosolic and membrane fractions occurred. Transglutaminase was also detected in Sertoli cells cultured in serum-free medium. Sertoli cells reside within the seminiferous tubule and are involved in normal spermatogenesis. Sertoli cell TGase has a strict requirement for Ca2+ and is not activated by Mg2+. Activation of the enzyme occurs with as little as 0.3 microM Ca2+; however, consistent with intracellular calcium levels, maximum stimulation occurred at 1.9 mM Ca2+. Sertoli cell TGase activity is markedly stimulated if the cells are cultured in 10% fetal bovine serum rather than in serum-free medium. Inhibition of Sertoli cell TGase by monodansylcadaverine concomitantly decreased the response of the cells to follicle-stimulating hormone (FSH)-induced secretion of cAMP but did not change basal cAMP levels. These data suggest that TGase may play a facilitative rather than an absolute role in activation of Sertoli cells by FSH and the resultant secretion of cellular products. This may occur through modulation of activities of membrane and cytosolic components by TGase.     

Secreted metalloproteinases in testicular cell culture

It is well known that cultured Sertoli cells secrete plasminogen activators (Lacroix et al., Mol Cell Endocrinol 1977; 9:227-236; Hettle et al., Biol Reprod 1986; 34:895-904). We now show that testicular cells in culture also secrete gelatinolytic metalloproteinases. Gelatin zymographic analysis of concentrated culture medium proteins reveals that Sertoli cells secrete gelatinases of 185 kDa, 110 kDa, 83 kDa, 76 kDa, and 72 kDa in addition to plasminogen activators (PAs). Gelatinase 185 kDa is induced by FSH. Media from Sertoli (epithelial)/peritubular (mesenchymal) cell cocultures contain the Sertoli cell gelatinases and one FSH-stimulated gelatinase of 50 kDa, indicating that gelatinase 50 kDa is regulated by both FSH and cell-cell interactions. A 50-kDa fibronectinolytic activity is also present in the coculture medium from cells grown in the presence of FSH. Casein zymography demonstrates a prominent 30-kDa protease only in media from cocultures. Peritubular cells secrete urokinase-type plasminogen activator (u-PA) and exhibit slight degrading activity at 86 kDa and 74 kDa. The gelatinases are most active in the pH range 7.3-8.5 and are completely or partially inhibited by metal ion chelators indicating that they are metalloproteinases. Our data demonstrate that testicular cells in culture secrete several gelatinases in addition to PAs, and that FSH and coculture conditions regulate some of these secreted proteases. We suggest that the highly regulated secretion of these proteases may well be of physiological importance during testicular development and spermatogenesis.     

The Sertoli cell in vivo and in vitro

The Sertoli cell extends from the basement membrane of the seminiferous tubule towards its lumen; it sends cytoplasmic processes which envelop different generations of germ cells. The use of Sertoli cell culture began to develop in 1975. To reduce germ cell contamination immature animals are generally used as Sertoli cell donors. Sertoli cell mitosis essentially occurs in sexually immature testes in mammals; mitosis of these cells is observed in vitro during a limited period of time. Sertoli cells in vivo perform an impressive range of functions: structural support of the seminiferous epithelium, displacement of germ cells and release of sperm; formation of the Sertoli cell blood-testis barrier; secretion of factors and nutrition of germ cells; phagocytosis of degenerating germ cells and of germ cell materials. Some of the Sertoli cell functions can be studied in vitro. The recent development of Sertoli cell culture on permeable supports (with or without extracellular matrix) has resulted in progress in understanding the vectorial secretion of several Sertoli cell markers. In addition to FSH and testosterone, several other humoral factors are known to influence Sertoli cell function. Furthermore, myoid cells bordering the tubules as well as germ cells are capable of regulating Sertoli cell activity. Sertoli cells are the most widely used testicular cells for in vitro toxicology. The testis is highly vulnerable to xenobiotics and radiations, yet the number of studies undertaken in this field is insufficient and should be drastically increased.     

Isolation of cyclic protein-2 from rat seminiferous tubule fluid and Sertoli cell culture medium

Cyclic Protein-2 (CP-2), a stage-specific secretory product of the rat seminiferous epithelium, has been isolated from seminiferous tubule fluid (STF) and Sertoli cell culture medium. Isolation from STF was accomplished by mixing STF with radiolabeled proteins secreted by Stage VI-VII seminiferous tubules and sequential fractionation of these proteins by hydroxylapatite, DEAE-agarose, and quaternary amine ion-exchange chromatography. Radiolabeled proteins were used to identify the chromatographic fractions that contained CP-2. Through use of these procedures, a highly purified preparation of radioinert CP-2 was obtained from seminiferous tubule fluid. Cyclic Protein-2 was also isolated from Sertoli cell culture medium, indicating that the Sertoli cell is its most likely source. Preliminary characterization of CP-2 was conducted. First, CP-2 appeared to be highly enriched in methionine. Second, the molecular weight of CP-2 was found to be 20,000. Third, analysis by reverse-phase hydrophobic chromatography indicated that CP-2 was relatively hydrophobic. We conclude that CP-2 is a small hydrophobic glycoprotein secreted in vivo and in vitro in a stage-specific manner by Sertoli cells.     

FSH-initiated differentiation of newt spermatogonia to primary spermatocytes in germ-somatic cell reaggregates cultured within a collagen matrix

We previously cultured fragments of newt testes in chemically defined media and showed that mammalian follicle-stimulating hormone (FSH) stimulates proliferation of spermatogonia as well as their differentiation into primary spermatocytes (Ji et al., 1992; Abe and Ji, 1994). Next, we indicated in cultures composed of spermatogonia and somatic cells (mainly Sertoli cells) that FSH stimulates germ cell proliferation via Sertoli cells (Maekawa et al., 1995). However, the spermatogonia did not differentiate into primary spermatocytes, but instead died. In the present study, we embedded large reaggregates of spermatogonia and somatic cells (mainly Sertoli cells) within a collagen matrix and cultured the reaggregates on a filter that floated on chemically defined media containing FSH; in this revised culture system, spermatogonia proliferated and differentiated into primary spermatocytes. The viability and percentage of germ cells differentiating into primary spermatocytes were proportional to the percentage of somatic cells in the culture, indicating that differentiation of spermatogonia into primary spermatocytes is mediated by Sertoli cells.     

Paracrine control of Leydig cell activity by FSH dependent proteins from Sertoli cells: an in vitro study

The regulating effect of follicle-stimulating hormone (FSH) on Leydig cell function was studied using a model of immature porcine Leydig and Sertoli cells cultured in a hormone supplemented defined medium. FSH pretreatment for 2 days of Leydig cells cultured alone was with no effect. FSH pretreatment of Leydig cells cocultured with Sertoli cells increases Leydig cell activity in an FSH dose-dependent manner with a maximal effect observed at 50 ng/ml porcine FSH (pFSH). Leydig cells cultured for 2 days in conditioned medium (CM) by FSH stimulated (FSH-CM) Sertoli cells, as compared to CM by unstimulated (control) (C-CM) Sertoli cells show an increase of their activity with a maximal effect observed at 50 ng/ml pFSH. Leydig cells cultured in CM as compared to non CM, show a marked development of organelles (smooth endoplasmic reticulum and mitochondria) involved in the steroidogenic activity. The activity of FSH-CM as compared to C-CM on Leydig cell function was non dialyzable and trypsin sensitive. These data suggest that Sertoli cells exert a regulatory action on Leydig cell steroidogenic activity via FSH dependent secreted proteins.     

Actions of extracellular matrix on Sertoli cell morphology and function

Sertoli cells were isolated and cultured in the absence or presence of extracellular matrix (ECM) to determine whether ECM may influence Sertoli cell function on a molecular level. As previously described, a morphological analysis of the cells indicated that ECM allows the expression of a columnar histotype and the formation of junctional complexes. The combined actions of ECM and hormones were found to have a profound effect in promoting the expression of a polarized Sertoli cell morphology. In our investigation of the effects of ECM on Sertoli cells, we used transferrin and androgen-binding protein (ABP) production as biochemical markers of Sertoli cell function. The presence of ECM was found to cause a 25% increase in the basal level of transferrin production; however, ECM had no effect on the basal level of ABP production by Sertoli cells. Regulatory agents such as follicle-stimulating hormone (FSH) and a combination of FSH, insulin, retinol, and testosterone stimulated the production of both transferrin and ABP. The ability of hormones to stimulate these Sertoli cell functions was not influenced by the presence of ECM. Similar results were obtained with 2-microns- or 50-microns-thick ECM and with a seminiferous tubule biomatrix preparation. ECM was found to increase the maintenance of long-term Sertoli cell cultures; however, the decline in Sertoli cell functional integrity, which occurs during cell culture, was not affected by the presence of ECM. An additional functional parameter examined was the radiolabeled proteins secreted by Sertoli cells. ECM did not promote the production or affect the electrophoretic profile of Sertoli cell-secreted proteins under basal or hormonally stimulated conditions. Combined results indicated that although ECM allowed the expression of a normal Sertoli cell histotype, ECM had no major effects on the Sertoli cell functions analyzed nor on the hormonal regulation of these functions. The inability of ECM to affect Sertoli cell function on a molecular level is discussed with regard to environmental as opposed to regulatory cellular interactions. Our observations imply that dramatic effects of ECM on cell morphology do not necessarily correlate to subsequent effects on cellular function.     

The effects of various hormones on the surface morphology of testicular cells in culture.

The purpose of this investigation was to study the effects of various hormones on the surface morphology of 20-day-old rat testicular cells in culture. Aggregates containing primarily Sertoli cells and germinal cells were obtained by enzymatic digestion. The surface morphology of the cells composing these aggregates was characterized under various culture conditions using light microscopy and scanning electron microscopy. The cytoplasmic processes of Sertoli cells became highly branched and filamentous after being cultured in the presence of rat, human or ovine FSH. Identical branching and filamentation was observed when Sertoli cells were cultured in rat TSH. Finally, numerous large blebs were observed on the surfaces of germinal cells cultured in the presence of insulin. These results suggest that the branching and filamentation of Sertoli cell cytoplasm observed after FSH stimulation are not specific for that hormone.     

Purification of ovine transferrin and study of the hormonal control of its secretion in enriched cultures of ovine Sertoli cells.

Ovine transferrin (o-transferrin) was purified from sheep serum by fractionated precipitation with ammonium sulphate, ion-exchange chromatography on DEAE trisacryl and finally by affinity chromatography on Affigel blue to remove albumin. Ovine transferrin was identified by its apparent molecular weight in sodium dodecyl sulphate polyacrylamide gel electrophoresis and by its N-terminal amino-acid sequence. The procedure presented in this report permits the preparation of highly purified o-transferrin with a good recovery (52% of initial total immunoactivity). An antiserum against o-transferrin was then raised in rabbits, using this highly purified preparation. A specific radioimmunoassay was set up using 125I-labelled o-transferrin. Its detection threshold (4 ng/ml) was low enough to measure o-transferrin in spent culture media of ovine Sertoli cells, which ranged between 15 and 600 ng/ml. Sheep seminiferous tubule cells, containing approximately 80% Sertoli cells, were cultured at a high density (1.5 x 10(6) cells/cm2) on a thin layer of reconstituted basement membrane. Kinetic studies showed that basal daily secretion of o-transferrin was reduced by half (-49%) between Day 1 and Day 2 of culture, and progressively decreased thereafter. Under FIRT (500 ng ovine follicle-stimulating hormone (FSH)/ml + 10 micrograms insulin/ml + 500 ng retinol/ml + 5 x 10(-7) mol/l testosterone) stimulation, the ratio of stimulated to basal secretions increased 11-fold between Day 1 (1.1) and Day 6 (12). When 10% fetal calf serum was added, mean o-transferrin secretion was a third of that in serum-free medium, suggesting that fetal calf serum contains factors that inhibit secretion of ovine Sertoli cell transferrin. In the presence of serum, the ratio of FIRT-stimulated to basal secretions doubled between Day 1 (1.0) and Day 4-6 (2.0). Between Days 2 and 4 of culture, insulin had a slight stimulatory effect on o-transferrin secretion (128% of control at 10 micrograms insulin/ml), as well as epidermal growth factor (124% of control at 50 ng/ml). Testosterone at up to 5 x 10(-7) mol/l had no effect; 500 ng retinol/ml doubled o-transferrin secretion (218% of control) as did 500 ng FSH/ml (220% of control). A combination of retinol and FSH increased the secretion 4-fold, indicating that maximal stimulation of o-transferrin secretion by ovine Sertoli cells requires the combined actions of mechanisms dependent and independent of cAMP.     

Extracellular matrix promotes rat Sertoli cell histotypic expression in vitro

We describe procedures for the preparation of a cell-free seminiferous tubule biomatrix, and provide evidence demonstrating that this material constitutes a useful substratum for maintaining the normal architecture of Sertoli cells in primary culture. Seminiferous tubule biomatrix, which has the morphological appearance of a fibrillar network rich in filaments and amorphous substance, is shown to consist of about 50% protein, most of which is collagen and glycoproteins. Fibronectin and laminin are also present in the seminiferous tubule biomatrix, as judged by immunofluorescence microscopy. Sertoli cell aggregates plated on this substratum retain a cuboidal to columnar shape, spread very slowly to form a monolayer, and survive for at least 3 weeks when cultured in a hormone-free, serum-free, chemically defined medium. In contrast, Sertoli cells plated onto uncoated polystyrene readily spread to form a monolayer of flat squamous cells which do not survive as well. Other morphological and ultrastructural characteristics are described which indicate that cells cultured on the seminiferous tubule biomatrix more closely resemble those of Sertoli cells in vivo than do cells plated on uncoated plastic. These differences in cell structure, including the maintenance of normal polarity as indicated by the presence of basolateral tight junctional complexes, remain evident for periods of 10 to 14 days after plating Sertoli cells onto biomatrix substratum. Rates of DNA synthesis by immature Sertoli cells plated onto biomatrix are less than rates by cells plated onto uncoated plastic. The data are discussed in relation to the role of substratum in the preservation of normal functions and histotype of Sertoli cells.     

Temporal sequence of cell shape changes in cultured rat sertoli cells after experimental elevation of intracellular cAMP

The ability of FSH and pharmacological agents to induce changes in the shape of cultured rat Sertoli cells has been studied by using time-lapse phase-contrast microscopy and scanning electron microscopy (SEM). Morphological studies were combined with an immunocytochemical method for the localization of cAMP in Sertoli cells and the results correlated with determinations of protein-bound cAMP in Sertoli cells. A variable number of Sertoli cells were converted from a flat, epithelial-like morphology into a stellate morphology after exposure to FSH, isobutyl-methylxanthine (MIX), dibutyryl cyclic AMP (db-cAMP) and an FSH-MIX mixture. The morphological changes followed a time- and biological agent-dependent alteration and recovery pattern. While a 120 min exposure to FSH induced shape changes in 38% of the cells, MIX, db-cAMP and FSH-MIX effected shape changes in 75 % of cells. The morphological conversion induced by MIX, db-cAMP and FSH-MIX persisted as long as these biological agents were present in the medium, whereas the effects induced by FSH alone were transient. The flat-to-stellate transition was preceded by an increase in intracellular protein-bound cAMP, a form of cyclic nucleotide which may account for cAMP immunoreactivity observed in morphologically responsive and non-responsive Sertoli cells. From these data and from previous experimental findings of androgen-binding protein (ABP) immunoreactivity in the cytoplasm of responsive and non-responsive Sertoli cells, we conclude that a surge of cAMP triggers a still undefined mechanism by which Sertoli cells modify their shape in coincidence with a progressive depletion of cytoplasmic secretory granules.     

Regulation by FSH and dibutyryl cyclic AMP of the formation of androgen-binding protein in Sertoli cell-enriched cultures.

Sertoli cell-enriched preparations from testes of 20-day-old rats were cultured in a defined medium in the presence and absence of FSH or dibutyryl cyclic AMP (dcAMP). Androgen-binding activity was assayed in the culture medium, and related to testicular androgen-binding protein (ABP). The production and secretion of ABP by the Sertoli cell-enriched preparation was increased after FSH or dcAMP treatment of the primary culture. It is concluded that ABP is produced by Sertoli cells. The possibility of involvement of other cell types in the testis in ABP production is discussed.     

Isolation and culture of FSH responsive Sertoli cells.

Methods for the isolation and culture of enriched populations of Sertoli cells from 20-60 day old rats are described. The identity of the Sertoli cells was verified by bright light and electron microscopy. Freshly isolated Sertoli cells specifically bound follicle stimulating hormone (FSH) but not luteinizing hormone (LH) and responded to FSH stimulation with dramatic increase in cyclic AMP level. Isolated Sertoli cells, maintained in culture for 11 days, showed no evidence of proliferation but retained their characteristic ultrastructural features and FSH binding ability. Incubation of cultured cells with FSH resulted in a significant stimulation of cyclic AMP and androgen binding protein (ABP). Since the freshly isolated or cultured cells were predominantly (greater than 80%) Sertoli cells, these results provide direct evidence that the Sertoli cells represent a primary target site for FSH activity in the testes. The culture method also provides a valuable in vitro model for the study of chronic effects of various agents on the Sertoli cell.