Effect of extracellular matrix proteins on in vitro testosterone production by rat Leydig cells

The aim of this study was to detect the effect of extracellular matrix (ECM) proteins on rat Leydig cell shape, adhesion, expression of integrin subunits and testosterone production, in vitro. Leydig cells isolated from adult rats were cultured on plates uncoated or coated with different concentrations of laminin-1, fibronectin, or type IV collagen in the presence or absence of hCG for 3 or 24 hr. A significant increase of cell adhesion and of alpha3, alpha5, and beta1 integrin subunit expression was observed when cells were cultured on ECM proteins, compared to those grown on uncoated plates. Leydig cells cultured on glass coverslips coated with ECM proteins for 24 hr exhibited elongated shapes with long cell processes (spreading), while cells cultured on uncoated plates showed few cell processes. A significant decrease in testosterone production was observed when basal and hCG-stimulated Leydig cells were cultured for 3 or 24 hr on plates coated with type IV collagen (12 and 24 microg/cm(2)) compared to uncoated plates. A significant though a slighter decrease in testosterone production was also observed in cells cultured on plates coated with fibronectin (12 and 24 microg/cm(2)), compared to uncoated plates. Laminin-1 did not modify testosterone production under basal or hCG stimulated conditions. These results suggest that ECM proteins are able to modulate Leydig cell steroidogenesis, in vitro.

Immunodetection of cell adhesion molecules in rat Sertoli cell cultures

PROBLEM

The presence of cell adhesion molecules (CAMs) in Sertoli cells has not been explored extensively. The expression of CAMs involved in cell-matrix and cell-to-cell interactions in Sertoli cell cultures was examined.

METHOD OF STUDY

Immunohistochemical and Western blot techniques were applied to rat Sertoli cell cultures using specific antibodies to alpha 3, alpha 5, and alpha 6 integrin subunits; NCAM; and cadherins.

RESULTS

Expression of alpha 3 and alpha 6 integrin subunits (mainly laminin receptors) and lack of expression of alpha 5 integrin subunit (fibronectin receptor) was observed in Sertoli cells by immunohistochemistry. These cells also expressed neural CAM (NCAM) and N-cadherin. By Western blot analysis, Sertoli cell extracts reacted with antibodies to alpha 3 integrin subunit revealed a band approximately 130 kDa, whereas no expression of alpha 5 integrin subunit was detected. Cell extracts incubated with antibodies to pan cadherin exhibited a band approximately 120 kDa, whereas bands of 180, 140, and 120 kDa were observed with antibodies to NCAM.

CONCLUSION

New data about the expression of receptors for extracellular matrix proteins (alpha 3 and alpha 6 integrin subunits) as well as cell-to-cell adhesion molecules (NCAM and cadherins) are reported in rat Sertoli cell cultures.

Regulation of gamma-glutamyl transpeptidase activity by Ca(2+)- and protein kinase C-dependent pathways in Sertoli cells

gamma-Glutamyl transpeptidase (gamma-GTP) activity in Sertoli cells can be stimulated by FSH. This cAMP-dependent metabolic event can be enhanced when Sertoli cells are co-cultured with germ cells, suggesting that different signal transduction pathways may be involved in the regulation of gamma-GTP activity. In this study we examined the participation of Ca(2+)- and protein kinase C (pkC)-dependent signal transduction pathways in the regulation of basal and FSH-stimulated gamma-GTP activity. Under basal conditions, the increase in extracellular Ca2+ concentration or the addition of the Ca2+ ionophore 4Br-A23187 produced a decrease in gamma-GTP activity. Conversely, blockage of voltage-dependent Ca2+ channels with verapamil or nifedipine or inhibition of Ca(2+)-calmodulin dependent processes with trifluoperazine resulted in an increase in gamma-GTP activity. To study the role of a pkC-dependent pathway the effects of low doses of staurosporine were evaluated. Under these experimental conditions an increase in gamma-GTP activity was observed. It was then investigated whether these signal transduction pathways could interact with the FSH-stimulated cAMP-dependent pathway to regulate gamma-GTP activity. Increase in extracellular Ca2+ concentration, the addition of 4Br-A23187 or the blockage of voltage-dependent Ca2+ channels did not modify FSH-stimulated gamma-GTP activity. However, staurosporine produced an additional increase in FSH-stimulated gamma-GTP activity and this effect was also observed when cells were stimulated with dbcAMP. In summary, our data are consistent with an inhibitory role of Ca(2+)-calmodulin- and pkC-dependent pathways in the regulation of basal gamma-GTP activity. Similar to what has been shown for other Sertoli cell parameters, a pkC-dependent pathway can interact with the FSH-stimulated cAMP-dependent pathway. The precise steps involved in this interaction are still unknown.

Immunodetection of cell adhesion molecules and extracellular matrix proteins in rat Leydig cell cultures

Cell adhesion molecules (CAMs) as well as extracellular matrix (ECM) proteins were identified in Leydig cell cultures using immunohistochemical and Western blot analysis. Leydig cells were isolated from 60-day-old rats and cultured for 4 days. For immunofluorescence and immunoperoxidase techniques, Leydig cells were incubated with antisera to ECM proteins (antibodies to laminin, type IV collagen and fibronectin); antisera to integrins (antibodies to beta 1, alpha 3, alpha 5 and alpha 6 integrin subunits) and antisera to cell-to-cell adhesion molecules (antibodies to N-CAM and N-cadherin). Results of the two immunohistochemical techniques were similar. Laminin and type IV collagen were detected in the perinuclear area of Leydig cell cytoplasm and cell processes as bright granular immunofluorescence or as a brown reaction product using the immunoperoxidase technique. Leydig cells expressed alpha 3 and alpha 6 integrin subunits (mainly laminin receptors), while no reaction was detected with antibodies to the alpha 5 integrin subunit (fibronectin receptor). Leydig cells also expressed cell-to-cell adhesion molecules such as N-CAM and N-cadherin. Using Western blot analysis, Leydig cell extracts incubated with antibodies to laminin revealed two bands of around 200 kDa, which is characteristic of laminin 1 light chains. A band with electrophoretic mobility similar to that of the alpha 2 (IV) collagen chain from EHS sarcoma and a band of around 230 kDa similar to fibronectin were also detected in Leydig cell extracts using specific antisera. Leydig cells incubated with antibodies to the alpha 3 integrin subunit revealed two bands below 120 kDa. Finally, Western blot results showed that Leydig cells expressed N-CAM as two faint bands of around 140 kDa and N-cadherin as a 120 kDa band. The present data suggest that Leydig cells in culture are able to synthesize ECM proteins and express ECM receptors (integrins), as well as cell-to-cell adhesion molecules such as N-CAM and N-cadherin.

Isolation of human Leydig cell mesenchymal precursors from patients with the androgen insensitivity syndrome: testosterone production and response to human chorionic gonadotropin stimulation in culture

Mature Leydig cells, the main source of testicular testosterone in mammals, arise from immature mesenchymal precursors through an LH-dependent differentiation process. In order to study the steroidogenic potential of these precursors, undifferentiated mesenchymal cells were obtained from the testicular interstitium of two patients with androgen insensitivity syndrome. After double digestion with collagenase and separation of the suspensions in a Percoll density gradient, the cells were cultured in Ham's F12 medium: Dulbecco's Modified Eagle Medium (1:1) supplemented with antibiotics, transferrin, insulin, hydrocortisone, and vitamin E with or without 1 IU of hCG/ml. At 11 days in culture, samples were removed for morphological characterization and determination of 3 beta-hydroxysteroid dehydrogenase activity (3 beta-HSD). Testosterone concentration was determined by RIA in the culture medium at different intervals. Cultured cells were mesenchymal in appearance, elongated in shape, with numerous processes running in different directions. No mature Leydig cells were present. In basal conditions, the percentages of 3 beta-HSD-positive cells at 11 days on patients 1 and 2 were 33% and 28%, respectively, and the testosterone concentrations in the culture media were 4.8 and 8.4 ng.10(6) cells.24 h, respectively. In cultures stimulated with hCG, there was an increase of histochemical reactivity (47% and 42% in patients 1 and 2, respectively) and in the amount of testosterone secreted (10.2 and 12.0 ng.10(6) cells, respectively). Electron microscopic studies of cultures grown in the absence of hCG demonstrated a homogenous population of poorly differentiated, fibroblastic-type mesenchymal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of rat testicular gamma-glutamyl-transpeptidase "in vivo" and "in vitro"

The hormonal regulation of gamma-glutamyl transpeptidase (gamma-GTP), an enzyme marker of Sertoli cells, was studied in immature rats that received 50 micrograms/day of testosterone propionate (TP) during 6 days to suppress pituitary LH and FSH. Suppression of LH was monitored indirectly by the determination of intratesticular levels of testosterone and suppression of FSH by radioimmunoassay of serum FSH. Enzyme activity in the testis decreased in parallel to intratesticular testosterone suppression, and it did recover up to control values when animals received 500 micrograms/day of TP, a dose that was able to maintain intratesticular testosterone at normal levels. beta-glucuronidase, another enzyme marker of Sertoli cells, was not affected by these treatments. A significant decrease in gamma-GTP was detected 24h after significant suppression of intratesticular testosterone and it returned to control levels 2 days after increasing the dose of TP to 500 micrograms/day. Administration of FSH to rats with depletion of intratesticular testosterone was able to maintain testicular gamma-GTP at control levels. An stimulatory action of FSH could also be demonstrated in primary Sertoli cell cultures. It is concluded that testicular gamma-GTP is under the regulation of both androgens and FSH while beta-glucuronidase is not. Eventhough the function of gamma-GTP in the testis is not known, the key role that it plays in other tissues suggests that it might be important in the regulation of Sertoli cell-germ cell interactions.

Relative cellular distribution of particulate androgen binding between sertoli and germ cells in rat testis

An androgen binding activity with characteristics similar to ABP is present in a particulate fraction (105,000 g pellet) obtained by differential centrifugation of seminiferous tubules, impure Sertoli cells and impure germ cells homogenates. Purification of germ cells through albumin gradients, results in almost a complete loss of androgen binding activity in the purified germ cell suspensions. Furthermore, Sertoli cell enriched testes from 22-, 32- and 40-day old rats showed increases in particulate androgen binding, when compared to matched controls, parallel to increments in the activity of a Sertoli cell marker enzyme (beta-glucuronidase). These results suggest that particulate androgen binding activity is only present in Sertoli cells and this protein may play a role in the compartmentalization of androgens in the testis.

Androgen binding to subcellular particles of rat testis

Androgen binding activity was evaluated in different subcellular particulate fractions obtained by differential centrifugation of 32-day-old rat seminiferous tubules homogenates. After eliminating heavy particles by centrifugation at 4300 g during 4 min in 0.25 M sucrose buffer, a 27,000 g pellet was obtained and layered on 1.05 M sucrose buffer. The relatively light particulate interface (LPF) formed during centrifugation at 27,000 g 60 min, showed the highest androgen binding activity among particulate fractions. This binding was associated with the plasma membrane marker 5'-nucleotidase and it did not follow any of six other subcellular structure markers: DNA for nuclei, succinate dehydrogenase for mitochondria, acid phosphatase for lysosomes, NADPH-cytochrome C reductase for smooth endoplasmic reticulum, RNA for rough endoplasmic reticulum and lactate dehydrogenase for cytosol. In LPF, concentrations of sites were estimated to be 328 +/- 54 fmol per mg proteins and affinity constant 0.78 +/- 0.23 10(9) M-1. Heat stability, steroid specificity, affinity constant and rate of dissociation were similar to the well known androgen binding protein, ABP. Presence of ABP or a similar protein in subcellular particles might play a role in the mechanism of action of androgens in seminiferous tubules of maturing rats.

Inhibition of follicle-stimulating hormone receptor binding by circulating immunoglobulins

We have characterized a circulating inhibitor of FSH receptor binding found in two patients with hypergonadotropic amenorrhea and myasthenia gravis. The inhibitor behaves as an immunoglobulin according to several criteria, including precipitation by 30% ammonium sulfate, migration on DEAE-cellulose chromatography, specific binding to protein A-Sepharose, characterization as a 7S protein in sucrose density gradients, and immunoprecipitation with specific antihuman immunoglobulin G. Evidence suggests that these antibodies are directed at determinants on or near the FSH receptor, and they may be responsible for the observed clinical FSH resistance.