Primary cultures of Leydig cells from rat, mouse and pig: advantages of porcine cells for the study of gonadotropin regulation of Leydig cell function

Optimization of a Method to Isolate and Culture Adult Porcine, Rats and Mice Müller Glia in Order to Study Retinal Diseases

Müller cells are the predominant glial elements in the retina, extending vertically across this structure, and they fulfill a wealth support roles that are critical for neurons. Alterations to the behavior and phenotype of Müller glia are often seen in animal models of retinal degeneration and in retinal tissue from patients with a variety of retinal disorders. Thus, elucidating the mechanisms underlying the development of retinal diseases would help better understand the cellular processes involved in such pathological changes. Studies into Müller cell activity in vitro have been hindered by the difficulty in obtaining pure cell populations and the tendency of these cells to rapidly differentiate in culture. Most protocols currently used to isolate Müller glia use neonatal or embryonic tissue but here, we report an optimized protocol that facilitates the reliable and straightforward isolation and culture of Müller cells from adult pigs, rats and mice. The protocol described here provides an efficient method for the rapid isolation of adult mammalian Müller cells, which represents a reliable platform to study therapeutic targets and to test the effects of drugs that might combat retinal diseases.

Cloning and mRNA expression of NPB and its effect on hormone secretion of the reproductive cells in the pig

Neuropeptide B (NPB) is an endogenous ligand for the orphan G protein-coupled receptors NPBWR1 (GPR7) and NPBWR2 (GPR8). Some reports have investigated the role of NPB in the regulation of feeding, energy metabolism and hormone secretion in many species. However, few papers reported the physiological function of NPB in the pig. In this study, we cloned and sequenced the NPB mRNA from a pig, which was found to consist of 123 bases. NPB mRNA expression was detected in central and peripheral tissues by the quantitative fluorescence method. The results showed that NPB mRNA expression was higher in hippocampus, cerebellum, spinal cord, thymus, tonsil, duodenum, cecum, colon, ovary and testis. The distribution of NPB suggested that it may be involved in the regulation of reproductive functions in the pig. Subsequently, the expression and distribution of NPBWR1 and NPBWR2 were found in Leydig cells and ovarian granular cells. We then investigated the direct effect of NPB on pig reproductive cells in vitro. The results showed that different concentrations of NPB (10^-12, 10^-10, 10^-8 and 10^-6 M) promoted the secretion of testosterone in Leydig cells in concentration-dependent manner. Different doses of NPB could promote the secretion of progesterone in ovarian granulosa cells in dose-dependent manner. Low concentrations of NPB (10^-8 and 10^-10 M) promoted estradiol secretion, but high concentrations of NPB (10^-6 M) inhibited its secretion. All the results suggested that the NPB/NPBWR1 or NPBWR2 system may play a role in modulating the reproductive activity in the pig.

Involvement of the Multidrug and Toxic Compound Extrusion Transporter in Testosterone Release from Cultured Pig Leydig Cells

Testosterone is considered to be released from Leydig cells via passive diffusion because of its hydrophobicity; however, the exact mechanism underlying testosterone secretion and the transporter involved are both unknown. Multidrug and toxic compound extrusion (MATE) transporters are predominantly found in the kidneys and liver and are thought to function in the elimination of metabolic organic cations during the final step of excretion in the kidney. In contrast, mMATE2 has been shown to be predominantly expressed in testicular Leydig cells. Although the physiological function of mMATE2 in Leydig cells is unknown, we hypothesized that mMATE2 acts as a testosterone exporter and is responsible for the secretion of testosterone from Leydig cells. Therefore, in the present study, we investigated the involvement of the MATE transporter in testosterone secretion from pig Leydig cells. Immunohistochemical analysis with anti-pig MATE2 antiserum indicated that the MATE transporter is present in pig Leydig cells. Additionally, treatment with the MATE inhibitors cimetidine and pyrimethamine reduced the testosterone secretion from pig Leydig cells but increased the intracellular testosterone levels. Estradiol release and intracellular estradiol level induced by human chorionic gonadotropin (hCG) further increased with cimetidine treatment. These results indicated that testosterone produced by hCG treatment is secreted from Leydig cells via the MATE transporter; however, in the presence of cimetidine or pyrimethamine, this MATE transporter-mediated secretion was inhibited, resulting in increased intracellular testosterone levels and estradiol production in Leydig cells. Thus, the MATE transporter may be responsible for testosterone secretion from Leydig cells.

The toxicological effects of bisphenol A and octylphenol on the reproductive system of prepubertal male rats

The aim of the present study was to assess and compare the individual adverse effects of bisphenol A (BPA) and octylphenol (OP) on the reproductive system of prepubertal male rats. Rats were exposed to BPA and OP at doses of 125 and 250 mg/kg/day, by gavage, for 90 days. At the end of the study, the testes, epididymis, prostate gland, and seminal vesicle were removed and examined histopathologically. Also, 3-β-hydroxysteroid dehydrogenase expressions were analyzed and serum testosterone and luteinizing hormone (LH) levels were measured. Sperm head count of caput epididymis was performed using a hemocytometer. Seminiferous and epididymal round tubules were evaluated for tubule diameter, lumen diameter, and height of tubule epithelium. There were significant increases in relative testes weights in BPA125, OP125, and OP250 groups compared with the control. Atrophic tubules, pyknotic tubules, combined tubules, congestion, vacuolization of Sertoli cell, cell debris in the lumen, tubules without sperm, and degeneration of tubules were noted in the tissue specimens obtained from the treatment groups compared with the control group. Sperm head counts were decreased in all treatment groups except for the low-dose BPA group. Testosterone (T) levels decreased in the BPA and high-dose OP treatment groups. LH levels increased in BPA treatment groups and the low-dose OP treatment group and decreased in the high-dose OP group. Epithelial height of high-dose BPA and OP treatment groups increased compared with the control group. Furthermore tubular height of low-dose BPA and high-dose OP groups increased with respect to control levels. In the OP250 treatment group, thyroxine hormone level was increased compared to other groups. Also, in the OP125 treatment group, triiodothyronine hormone level was increased compared with other groups.

The results of this study showed that BPA and OP affect the steroidogenic enzyme expression and T production in Leydig cells. In conclusion, BPA and OP have adverse effects on the male reproductive system of prepubertal rats.

The nuclear genes Mtfr1 and Dufd1 regulate mitochondrial dynamic and cellular respiration

Dufd1 (DUF729 domain containing 1) is related to Mtfr1 (mitochondrial fission regulator 1), a gene involved in the regulation of antioxidant activity in the mouse testis. The present study was undertaken to better understand their role in regulating mitochondrial architecture and function in the mouse. We show that Dufd1 is expressed as a 2 kb mRNA and has a more specific tissue pattern compared to Mtfr1, with highest level of expression in testes, lower level in spleen, and negligible levels in other organs and/or tissues. In the male gonad, Dufd1 mRNA expression increases during postnatal development, similarly to Mtfr1. In situ hybridization and real-time PCR analyses show that Dufd1 is expressed in the seminiferous tubules by middle-late pachytene spermatocytes and spermatids. In transfected cells, the Dufd1-tagged protein is located in mitochondria, associated with the tips of mitochondrial tubules and to tubules constrictions, and induces mitochondrial fission although with a lesser efficiency than Mtfr1. We also found that both endogenous Dufd1 and Mtfr1 proteins are associated with membrane-enriched subcellular fractions, including mitochondria. Inhibition of Mtfr1 and/or Dufd1 expression, in a testicular germ cells line, severely impairs O(2) consumption and indicates that both genes are required for mitochondrial respiration. Accordingly, analysis of testes mitochondria from Mtfr1-deficient mice reveals severely reduced O(2) consumption and ATP synthesis compared to wt animals. These data show that, in murine testis, Dufd1 and Mtfr1 have redundant functions related to mitochondrial physiology and represent genes with a potential role in testicular function.

Morphology and function of human Leydig cells in vitro. Immunocytochemical and radioimmunological analyses

The aim of our study was to show whether the cells isolated from testes of patients underwent bilateral orchiectomy for prostatic cancer are able to grown in vitro, and if so, are functionally active. Immuncytochemistry was performed to show the functional status of human cultured cells. In detail, immunolocalization of luteinizing hormone receptors (LHR), mitochondria, and cytoskeletal elements was demonstrated. Moreover, radioimmunological assay was used to measure testosterone secretion by cultured Leydig cells. Using Nomarski interference contrast and fine immunofluorescence analysis the positive immunostaining for LHR was observed in almost all Leydig cells, however it was of various intensity in individual cells. Testosterone measurement revealed significant difference between testosterone secretion by hCG-stimulated and unstimulated Leydig cells (p<0.05). Moreover, testosterone levels were significantly higher in 24- and 48-hour-cultures than in those of 72 hrs (p<0.05). Morphological analysis of Leydig cells in culture revealed the presence of mononuclear and multinucleate cells. The latter cells occurred in both hCG-stimulated and unstimulated cultures. In Leydig cells labeled with a molecular marker MitoTtracker, an abundance of mitochondria and typical distribution of microtubules and microfilaments were observed irrespective of the number of nuclei within the cell, suggesting no functional differences between mono- and multinucleate human Leydig cells in vitro. Since the percentage of multinucleate cells was similar in both hCG-stimulated and unstimulated cultures (23.70% and 22.80%), respectively, the appearance of these cell population seems to be independent of hormonal stimulation.

Culture of rodent spermatogonial stem cells, male germline stem cells of the postnatal animal

Spermatogonial stem cells (SSCs), postnatal male germline stem cells, are the foundation of spermatogenesis, during which an enormous number of spermatozoa is produced daily by the testis throughout life of the male. SSCs are unique among stem cells in the adult body because they are the only cells that undergo self-renewal and transmit genes to subsequent generations. In addition, SSCs provide an excellent and powerful model to study stem cell biology because of the availability of a functional assay that unequivocally identifies the stem cell. Development of an in vitro culture system that allows an unlimited supply of SSCs is a crucial technique to manipulate genes of the SSC to generate valuable transgenic animals, to study the self-renewal mechanism, and to develop new therapeutic strategies for infertility. In this chapter, we describe a detailed protocol for the culture of mouse and rat SSCs. A key factor for successful development of the SSC culture system was identification of in vitro growth factor requirements for the stem cell using a defined serum-free medium. Because transplantation assays using immunodeficient mice demonstrated that extrinsic factors for self-renewal of SSCs appear to be conserved among many mammalian species, culture techniques for SSCs of other species, including farm animals and humans, are likely to be developed in the coming 5-10 years.

Impaired expression of genes coding for reactive oxygen species scavenging enzymes in testes of Mtfr1/Chppr-deficient mice

Mtfr1/Chppris a nuclear gene coding for a mitochondrial protein capable of inducing fission of this organelle in a sequence-specific manner. Here we show that in mice,Mtfr1/Chppris ubiquitously expressed and displays the highest level of expression in pubertal and adult testes and in particular in spermatids and Leydig cells. To investigateMtfr1functionin vivo, we analyzed homozygous mice null for this gene obtained through a gene trap approach. We show that these mice fail to expressMtfr1and that in their testes several genes coding for enzymes involved in the defense against oxidative stress are downregulated. Among these, we studied in particular glutathione peroxidase 3 and show its expression in selected testis cell types. Furthermore, we demonstrate oxidative DNA damage specifically in testes ofMtfr1-deficient mice likely resulting from a reduced antioxidant activity. As a whole, these data suggest thatMtfr1protects the male gonads against oxidative stress.

Triphenyltin and Tributyltin inhibit pig testicular 17beta-hydroxysteroid dehydrogenase activity and suppress testicular testosterone biosynthesis

We previously reported that tributyltin chloride (TBT) and triphenyltin chloride (TPT) powerfully suppressed human chorionic gonadotropin- and 8-bromo-cAMP-stimulated testosterone production in pig Leydig cells at concentrations that were not cytotoxic [Nakajima Y, Sato Q, Ohno S, Nakajin S. Organotin compounds suppress testosterone production in Leydig cells from neonatal pig testes. J Health Sci 2003;49:514-9]. This study investigated the effects of these organotin compounds on the activity of enzymes involved in testosterone biosynthesis in pig testis. At relatively low concentrations of TPT, 17beta-hydroxysteroid dehydrogenase (17beta-HSD; IC(50)=2.6microM) and cytochrome P450 17alpha-hydroxylase/C(17-20) lyase (IC(50)=117microM) activities were inhibited, whereas cholesterol side-chain cleavage cytochrome P450 and 3beta-HSD/Delta(4)-Delta(5) isomerase activities were less sensitive. Overall, TPT was more effective than TBT. TPT also inhibited both ferredoxin reductase and P450 reductase activities at concentrations over 30microM; however, TBT had no effect, even at 100microM. The IC(50) values of TPT were estimated to be 25.7 and 22.8microM for ferredoxin reductase and P450 reductase, respectively. The inhibitory effect of TPT (30microM) on microsomal 17beta-HSD activity from pig testis was eliminated by pretreatment with the reducing agents dithiothreitol (1mM) and dithioerythritol (1mM). On the other hand, TPT (0.03microM) or TBT (0.1microM) exposure suppressed the testosterone production from androstenedione in pig Leydig cells indicating that these organotins inhibit 17beta-HSD activity in vivo as well as in vitro, and the IC(50) values of TPT and TBT for 17beta-HSD activity were estimated to be 48 and 114nM, respectively. Based on these results, it appears possible that the effects of TBT and TPT are largely due to direct inhibition of 17beta-HSD activity in vivo.

Tributyltin chloride suppresses the P450cl7 transcription involved in testosterone production induced by gonadotropin stimulation in cultured pig Leydig cells

We previously reported that organotin compounds, such as tributyltin chloride (TBT), dibutyltin dichloride and triphenyltin chloride, strongly suppressed the testosterone production level in isolated neonatal pig testicular Leydig cells at a concentration without cytotoxicity. In this report, the action mechanisms of suppressive effect of the testosterone production by TBT were investigated. TBT (0.1μM) exposure to pig Leydig cells for 4h significantly decreased the intracellular cAMP level stimulated by human chorionic gonadotropin (hCG; 10IU/ml) and also the level stimulated by forskolin (25μM). In the same way, TBT exposure for 6 and 24h significantly decreased the 17α-hydroxylase/17,20-lyase (P450cl7) mRNA level stimulated by hCG. However, TBT exposure did not affect the mRNA levels of other steroidogenic enzymes, such as cholesterol side chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase/Δ(4)-Δ(5) isomerase, 17β-hydroxysteroid dehydrogenase, and steroidogenic acute regulatory protein, estimated by RT-PCR. These results suggest that TBT exposure inhibits the adenyl cyclase activity of Leydig cells, which in turn suppresses testosterone production due to a decrease in the P450cl7 transcription level induced by decreasing intracellular cAMP levels.

Endocrine and paracrine control of Leydig cell steroidogenesis and proliferation in the wall lizard: an in vitro study

The present in vitro study, for the first time, demonstrates the endocrine as well as paracrine control of Leydig cell steroidogenesis and proliferation in the wall lizard Hemidactylus flaviviridis. Unlike mammals, Leydig cell activity in the wall lizard seems to be directly controlled by ovine follicle-stimulating hormone (FSH)-like molecule, since FSH increased the testosterone production and tritiated thymidine ([(3)H]TdR) incorporation by Leydig cells. In addition, Sertoli cell paracrine factor or factors play important roles in controlling Leydig cell activities as non-activated Sertoli cell-conditioned medium (SCCM) alone stimulated testosterone production by both non-activated and FSH-preactivated Leydig cells. As far as the proliferation was concerned, non-activated SCCM did not influence [(3)H]TdR uptake by non-activated or FSH-preactivated Leydig cells, while FSH-preactivated SCCM was able to stimulate proliferation of activated Leydig cells. It may be concluded that FSH, besides directly controlling, also regulates Leydig cell activities indirectly through stimulating the secretion of Sertoli cell paracrine factors. Moreover, steroidogenic factor is different from mitogenic factor because non-activated Leydig cells were responsive to steroidogenic factor but nonresponsive to mitogenic factor.

Defining the spermatogonial stem cell

Through the use of donor cells from transgenic rats expressing GFP exclusively in the germline, we have defined culture conditions where male germ cells lose (on STO cells) or maintain (on MSC-1 cells) stem cell activity. A cadre of germ cell transcripts strikingly decrease in relative abundance as a function of testis age or culture time on STO cells, but only a subset of these transcripts (approximately 248) remain elevated when cultured on MSC-1 cells. If specific gene expression regulates stem cell activity, some or all of these transcripts are candidates as such regulators. We establish a spermatogonial stem cell index (SSCI) that reliably predicts relative stem cell activity in rat or mouse testis cell cultures, and through the use of an antibody to a robust signal (Egr3) within the index find intense signals in single or paired cells. As germ cells form longer interconnected chains (incomplete cytokinesis), the Egr3 signal disappears coincident with a loss of stem cell activity. Thus, molecular markers specific for spermatogonial stem cells establish a reliable and rapid means by which to define these cells in culture and alleviate the need for laborious testicular transfers in initial cell culture studies.

A multitude of genes expressed solely in meiotic or postmeiotic spermatogenic cells offers a myriad of contraceptive targets

Understanding mammalian spermatozoan development and the events surrounding fertilization has grown slowly, in part because of uncertainty about the number and identity of the cellular components involved. Determination of those transcripts expressed specifically by germ cells should provide an inclusive list of probable critical proteins. Here, total mouse testis transcript profiles were trimmed of transcripts found in cultures enriched in Sertoli or interstitial cells to yield a germ cell-enriched transcript profile. Monitoring of changes of this profile in the developing testis identified 1,652 genes whose transcript abundance increased markedly coincident with the onset of meiosis. Remarkably, 351 of these genes (approximately equal to 20%) appear to be expressed only in the male germline. Germ cell-specific transcripts are much less common earlier in testis development. Further analysis of the UniGene EST database coupled with quantitative PCR indicates that approximately 4% of the mouse genome is dedicated to expression in postmeiotic male germ cells. Most or many of the protein products of these transcripts are probably retained in mature spermatozoa. Targeted disruption of 19 of these genes has indicated that a majority have roles critical for normal fertility. Thus, we find an astonishing number of genes expressed specifically by male germ cells late in development. This extensive group provides a plethora of potential targets for germ cell-directed contraception and a staggering number of candidate proteins that could be critical for fertilization.

Establishment of Leydig cell line, TTE1, from transgenic mice harboring temperature-sensitive simian virus 40 large T-antigen gene

A Leydig cell line, TTE1, has been established from transgenic mice harboring a temperature-sensitive simian virus 40 (tsSV40) large T-antigen gene. The cells grew at a permissive temperature (33 degrees C), but growth was markedly prevented at a nonpermissive temperature (39 degrees C). T-antigen was expressed in the nuclei at 33 degrees C but disappeared at 39 degrees C, indicating that the cells show a temperature-sensitive growth phenotype reflected by the tsSV40 large T-antigen. TTE1 cells did not show any colony-forming activity in soft agar and form tumors in subcutaneous tissue in nude mice, indicating that the cells were not transformed. Alkaline phosphatase and 3beta-hydroxysteroid dehydrogenase (HSD) activities or expression of cytokeratin and vimentin were observed. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that TTE1 cells expressed mRNAs encoding 17beta-HSD types 1 and 3, and inhibin-alpha. The cells with unique characteristics, therefore, should serve useful model study the function of Leydig cell.

D-Aspartate stimulation of testosterone synthesis in rat Leydig cells

D-Aspartate increases human chorionic gonadotropin-induced testosterone production in purified rat Leydig cells. L-Aspartate, D-,L-glutamate or D-,L-asparagine could not substitute for D-aspartate and this effect was independent of glutamate receptor activation. Testosterone production was enhanced only in cells cultured with D-aspartate for more than 3 h. The increased production of testosterone was well correlated with the amounts of D-aspartate incorporated into the Leydig cells, and L-cysteine sulfinic acid, an inhibitor of D-aspartate uptake, suppressed both testosterone production and intracellular D-aspartate levels. D-Aspartate therefore is presumably taken up into cells to increase steroidogenesis. Intracellular D-aspartate probably acts on cholesterol translocation into the inner mitochondrial membrane, the rate-limiting process in steroidogenesis.

Endocytosis of lutropin by Leydig cells through a pathway distinct from the high-affinity receptor

In porcine Leydig cells in primary culture, 95% of the internalization of [125I]porcine lutropin ([125I]pLH, which bears sulfated GalNAc) could not be ascribed to the high-affinity LH receptor (LHR). In contrast, >40% of [125I]human choriogonadotropin (hCG, with sialylated sugar chains) uptake was performed by the LHR itself. When the LHR was down-regulated by excess unlabeled hormone, the LHR-independent incorporation of [125I]pLH could be inhibited in a dose-dependent fashion by sulfated polysaccharides such as fucoidan or chondroitin-(4 or 6)-sulfate, but not by other polyanionic compounds, nor by sulfated chondroitin disaccharides. Endocytosis occurred through a clathrin-dependent pathway and was inhibited by low temperature, endocytosis inhibitors, increased ionic strength, or by EDTA and dithiothreitol. Taken together, these results suggest that a Leydig cell membrane protein (possibly a lectin, or a glycosaminoglycan receptor) could perform specific LH clearance in the testis via recognition of its sulfated sugars.

Modulation of Leydig cell testosterone production by secretory products of macrophages

Unstimulated macrophages from testes inhibited the production of testosterone by Leydig cells from adult, but not immature, Sprague-Dawley rats (significant after 48 h). Similar results were observed with unstimulated macrophage-conditioned media, suggesting that the observed effect was mediated by one or more secretory products. None of these substances was interleukin-1, since macrophage supernatants tested negative in an interleukin-1 alpha and interleukin-1 beta sensitive, thymocyte assay. Interleukin-6 was detected by a B cell proliferation assay. After stimulation by LPS, testicular macrophages enhanced testosterone production by Leydig cells from adult and immature rats. This enhancement was dose-dependent and required low concentrations (but over 2.5%) of conditioned media. Interleukin-1 and interleukin-6 activities were detected in LPS-stimulated macrophage supernatants. Supernatants of LPS-stimulated, human monocytes had similar effects on Leydig cells. They were rich in interleukin-1, interleukin-1 receptor antagonist and interleukin-6. The present study suggests that, in adult rats, testicular macrophages modulate Leydig cell steroidogenesis by secretory products whose secretion depends on the physiological state of macrophages. The factor or factors responsible for stimulation are not species-specific. The effect cannot be accounted for by variations in the concentration of the above mentioned interleukins in macrophage supernatants.

Isolation and culture of highly enriched populations of Leydig cells from guinea-pig (Cavia porcellus) testes

Leydig cells were isolated from adult male guinea-pig testes using a multi-step procedure involving enzymatic dissociation and Percoll-gradient centrifugation. The following description is the first account of a successful isolation of adolescent guinea-pig Leydig cells. The enriched Leydig-cell preparation routinely isolated from six intact testicles yielded approximately 5.0 x 10(6) +/- 0.7 x 10(6) (+/- SEM) Leydig cells with a viability of 98.0 +/- 0.4% as determined using the trypan-blue exclusion method. The purity of the isolated cell population as assessed by 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) staining averaged 82.5 +/- 0.8%. Under light microscopy, guinea-pig Leydig cells were polyhedral in shape with a large prominent nucleus and a distinct nucleolus. The acidophilic cytoplasm contained numerous lipid-filled vesicles. Ultrastructurally, guinea-pig Leydig cells displayed an eccentrically located ovoid nucleus with dark-staining peripheral heterochromatin. Large quantities of mitochondria, smooth endoplasmic reticulum and particulate-laden lipid droplets were also evident. The steroidogenic potential of the isolated Leydig cells was verified using a maximally stimulating dose of ovine LH (100 ng ml-1) and human CG (200 mIU ml-1). Leydig cells incubated in a shaking (120 cycles min-1) water bath for 3 h at 37 degrees C in capped polypropylene microcentrifuge tubes produced 233 +/- 21 ng and 223 +/- 18 ng testosterone per 1 x 10(6) cells when maximally stimulated with oLH or hCG, respectively. The inclusion of low (1-5 microM) levels of sodium ascorbate during culture enhanced significantly Leydig-cell viability vs. control values.

Transformation and immortalization of Leydig cells from the Sprague-Dawley rat by an early genetic region of simian virus 40 DNA

Two transformed cell lines of rat Leydig cells were established by transfection of primary cells with the transforming region of simian virus (SV40) DNA. Normal adult Leydig cells are non-proliferating cells and cease to grow after the first trypsinization for cell culturing. The cell lines, NWL2 and NWL15, continued to proliferate and subsequently needed subculturing every 2 weeks (split ratio 1:2). No crisis was observed after 35 passages for 18 months. Nile red staining showed the presence of lipid droplets in both normal and transformed cells, although the transformed cells had 2-3-fold higher amounts than the normal cells. The integration of T-antigen DNA has taken place in at least 2 and 1 sites in NWL2 and NWL15, respectively. Both cell lines expressed T-antigen mRNA. The cell lines expressed luteinizing hormone receptor (LH-R) (a Leydig cell-specific gene), insulin-like growth factor-I, insulin-like growth factor-I receptor (IGF-I-R) and insulin-like growth factor binding protein-2 (IGFBP-2) genes. The amounts of transcripts of LH-R were lower in the transformed cells as compared to the normal cells. The IGF-I-R mRNA levels were comparable to those of the normal Leydig cells. NWL2 and NWL15 cells also expressed IGF-I mRNA although to a lesser extent than the normal Leydig cells. IGFBP-2 mRNA levels were much higher in both the transformed cell lines than in the normal Leydig cells. The transformed cells were evaluated for the expression of P450scc, which catalyzes the conversion of cholesterol to pregnenolone.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic AMP regulates expression of the rat gene for steroid 17 alpha-hydroxylase/C17-20 lyase P-450 (CYP17) in rat Leydig cells

The upstream region of the rat CYP17 gene shows significant homology to the upstream regions of the bovine and human genes, 53 and 60 percent, respectively. The start site of transcription was determined by primer extension and S1 nuclease protection to be 41 base pairs (bp) upstream of the initiating methionine codon. Expression vectors were constructed by ligation of upstream sequences into promoterless chloramphenicol acetyl transferase (CAT) vectors. Transient transfection studies using primary cultures of rat Leydig cells indicate a strong cAMP-responsive element located within the -26/+65 region. Stimulation by cyclic AMP was abolished when sequences upstream of -264 were included in expression vectors. No significant expression was seen in Leydig cells in the absence of dbcAMP nor was there any expression in the presence or absence of dbcAMP in rat skin fibroblasts or in mouse adrenal (Y-1) cells in which CYP17 is not normally expressed. Three possible regulatory elements were found in the 5' upstream region: a CRE/ATF consensus sequence (GACGTCA) starting at position -57; a GRE consensus sequence (TGTTCT) starting at position -501; and a consensus sequence for AP-1 binding (TTAGTCA) starting at position -659. It was concluded that the CRE/ATF at -57 is not responsible for increased transcription in the presence of cyclic AMP.

Pathways of internalization of the hCG/LH receptor: immunoelectron microscopic studies in Leydig cells and transfected L-cells

Monoclonal anti-receptor antibodies were used to study the cellular traffic of the hCG/LH receptor by immunoelectron microscopy. The LHR38 antibody was shown to bind to the extracellular domain of the receptor but not to interfere with hormone binding, adenylate cyclase activation or with the rate of internalization of the receptor. Pig Leydig cells and a permanent L-cell line expressing the LH receptor were used for the study. Incubation with LHR38-gold complexes showed the LH receptors to be randomly distributed over the cell surface including the clathrin coated pits. The LH receptors were internalized via a route including coated pits, coated vesicles and multivesicular bodies to lysosomes. This route is different from that observed for beta-adrenergic, muscarinic, and yeast mating factor receptors and considered previously as possibly general for G-protein-coupled receptors. The use of [125I]LHR38 allowed precise measurement of the rate of internalization, showing the existence of a constitutive pathway which was increased 11-fold by hormone administration. Double labeling experiments suggested that the hormone (hCG-Au15nm) and the receptor (labeled with LHR38-Au5nm) have similar routes of endocytosis, both of them being degraded in lysosomes. Studies of the reappearance of LHR38-Au5nm on the surface of the cells and the use of monensin indicated that only a very small proportion of the receptor molecules were recycled to the cell surface. The distribution and the intracellular pathways of LH receptors are very similar in Leydig cells and transfected L-cells. This opens the possibility of using the latter to study, by in vitro mutagenesis, the molecular mechanisms involved in the cellular traffic of LH receptors.

Gene for 17 alpha-hydroxylase/C (17-20) lyase P-450: complete nucleotide sequence of the porcine gene and 5' upstream sequence of the rat gene

We describe the isolation and characterization of a full-length clone for the porcine 17 alpha-hydroxylase/C(17-20) lyase (CYP17) gene. The complete exon and partial intron sequences are presented including approx. 1000 bp of the 5' upstream sequence. In addition we describe the isolation and characterization of the 5' upstream region of the rat CYP17 gene. The sequences of the first exon, part of the first intron, and approx. 3.5 kb of the 5' upstream region are presented.

Adult rat Leydig cell cultures: minimum requirements for maintenance of luteinizing hormone responsiveness and testosterone production

The aim of this study was to establish the minimum conditions required to maintain adult rat Leydig cell testosterone production and luteinizing hormone (LH) responsiveness in short term culture, at a level similar to that observed in vivo, which could be used to study factors which may have a delayed or chronic effect on Leydig cell function. Percoll gradient-purified adult rat Leydig cells (5.0 x 10(4)/250 microliters) were cultured in Dulbecco's modified Eagle's medium/Ham's F12 (DMEM/F12) with 0.1% bovine serum albumin at 32 degrees C for up to 3 days, with daily medium changes. A combination of submaximal rat LH (0.1 ng/ml) and a maximal concentration of rat serum lipoproteins (0.5 mg/ml) maintained testosterone production at between 5 and 15 ng/10(6) cells/h; subsequent stimulation of the Leydig cells with a maximum dose of rat LH (8 ng/ml) over 24 h resulted in testosterone production of 75-240 ng/10(6) cells/h on all 3 days of culture. However, the addition of 0.1% fetal calf serum instead of rat lipoproteins could not maintain LH-stimulated testosterone production in the same culture period. In cultures containing submaximal LH and lipoproteins, levels of testosterone production and responses to maximal LH stimulation were constant over the culture period when expressed as either testosterone production per 10(6) cells plated, or testosterone production per microgram DNA recovered at end of incubation. Reduction of the oxygen tension from 19% to 5%, or to 1% did not significantly alter testosterone production by Leydig cells under these established conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Pig Leydig cell culture: a useful in vitro test for evaluating the testicular toxicity of compounds

In vivo studies have shown that the testis is a target organ for drugs and chemicals. In order to evaluate the testicular toxicity of compounds and to identify the mechanisms of their toxicity, we have developed a miniaturized primary culture of immature pig Leydig cells. Five well-known drugs with differing mechanisms of toxicity on testicular functions were tested to validate the model. Testosterone and progesterone secretion were measured to evaluate testicular function. Cell viability was assessed quantitatively using a colorimetric assay based on the reduction of a tetrazolium salt (3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide) which stains viable cells only, thus allowing discrimination between specific inhibitors of Leydig cell function and nonspecific cytotoxic drugs. Ketoconazole and aminoglutethimide inhibited both testosterone and progesterone secretion, but without modifying cell viability. Spironolactone specifically blocked testosterone secretion and increased progesterone concentration without inducing cell mortality. Cycloheximide altered testicular steroid secretion by another mechanism of action. Chlorpromazine, which interferes with the secretion of gonadotropins in vivo, produced a significant inhibition of progesterone and testosterone secretion as a result of the cytotoxic effects of the drug. In conclusion, this in vitro test enables one to discriminate accurately between specific and nonspecific inhibitors of steroidogenesis and could reduce the number of false positives when screening for potential testicular toxins.

Effect of cortisol on testosterone production by immature pig Leydig cells

The direct effects of hydrocortisone (HS) and adrenocorticotropin (ACTH) on testicular testosterone production were studied in purified immature pig Leydig cells in vitro. Leydig cells were obtained from 3- to 4-week-old piglet testes by enzymatical dispersion followed by discontinuous Percoll gradient centrifugation. Leydig cells were treated with HS and ACTH in the absence or presence of luteinizing hormone (LH) after 12 h of incubation. Media were collected 48 h later for testosterone and cyclic adenosine 3',5'-monophosphate (cAMP) measurement. Treatment of Leydig cells with increasing concentrations (0.001-10.0 micrograms/ml) of HS for 48 h resulted in a dose-dependent increase in basal and LH-stimulated testosterone production. Increasing duration (6-72 h) of treatment with HS (100 ng/ml) led to a time-dependent increase in basal and LH-stimulated testosterone production, achieving statistical significance by 48 and 24 h, respectively. HS increased LH-stimulated cAMP production. HS also increased testosterone production induced by (Bu)2 cAMP. Forskolin stimulated testosterone production to an extent comparable to that attained with LH, and HS augmented forskolin-stimulated testosterone production. HS enhanced the conversion of exogenous 17 alpha-hydroxyprogesterone to testosterone, but did not affect the conversion of pregnenolone and progesterone to testosterone, suggesting a specific stimulation of 17,20-desmolase. Porcine ACTH had no influence on basal and LH-stimulated testosterone production. These results suggest that HS directly stimulates immature pig Leydig cell steroidogenesis, at least in part via an enhancement of the generation of cAMP, leading to an increase in the activity of 17,20-desmolase.

Regulation by growth factors of Leydig cell differentiated functions

In this paper the effects of growth factors on the differentiated function of pig Leydig cells and other steroidogenic cells are reviewed. Two types of action have been observed, i.e. positive or negative acute effects on testosterone secretion, and long-term trophic effects of hCG receptor and responsiveness to hCG. Among the growth factors, insulin-like growth factor I (IGF-I) and transforming growth factor beta (TGF beta-1) are of particular interest. IGF-I is required for the maintenance and probably the expression of differentiated functions of several steroidogenic cells, including the Leydig cells. TGF beta-1 has effects opposite to IGF-I on Leydig cell functions. When considering effects of growth factors on Leydig cells, caution should be taken in extrapolating results obtained in one species to another.

Maintenance of testosterone production by purified adult rat Leydig cells for 3 days in vitro

Using a preparation of highly purified, adult rat Leydig cells and conditions of culture which we found to optimize testosterone production during 24 h, we sought to maintain optimal testosterone production for 3 d. Leydig cells cultured on Cytodex 3 beads at 19% O2 in Dulbecco's modified Eagle's medium-Ham's nutrient mixture F12 (1:1; vol/vol) containing 0.5 mg/ml total bovine lipoproteins (less than 1.222 g/ml) with maximal luteinizing hormone (LH) stimulation failed to maintain a constant amount of testosterone for 3 d. These cells did however secrete a similar amount of total delta 4-3-ketosteroids on each of the 3 culture d, indicating that their viability was preserved. The predominance of progesterone and 170H-progesterone relative to the amount of androstenedione found on Days 2 and 3 suggested that the activity of the cytochrome P450 C17-hydroxylase-C17,20-lyase enzyme in the smooth endoplasmic reticulum was diminished when Leydig cells were maintained in our primary culture for longer than 24 h. Decreasing the oxygen tension of the cultures from 19 to 5%, and decreasing the concentration of LH used to stimulate the Leydig cells from 100 to 0.1 ng/ml, were necessary to achieve maintenance of testosterone secretion without accumulation of other delta 4-3-ketosteroids during a 3-d period. Cells cultured in this fashion were still able to respond to maximal LH stimulation during Day 3, producing as much testosterone as if cultured for 24 h on Day 1 at 19% O2 with 100 ng/ml LH stimulation.

Steroidogenesis expression depends on negative control(s): analysis in Leydig X adrenal intraspecific cell hybrids

Hybrids constructed by fusing mouse Leydig cells with mouse adrenal Y1 cells were able to randomly express all the parental specific traits but for the response to gonadotropin (hCG) and corticotropin (ACTH): three of them, YDYL 14, 17 and 19, metabolized both progesterone and dehydroepiandrosterone into testosterone accounting for 17 alpha-hydroxylase, 17-20-lyase, 17-ketoreductase and 3 beta-hydroxysteroid dehydrogenase activities. Under basal conditions, 17 alpha-hydroxylase and 17-20-lyase activities were high in the three clones as compared to parental Leydig cells, and were no longer stimulated by cAMP in YDYL 17 and 19. The hybrids responded to various hormones such as prostaglandin E2 (PGE2), vasoactive intestinal peptide (VIP) and prolactin (PRL) which are not directly implicated in the expression of steroidogenesis; they generally retained the Y1 morphological response to 8-bromo cAMP. On extended culture, reexpression of ACTH sensitivity occurred in one clone, YDYL 9. This reexpression was correlated with a Robertsonian translocation between mouse chromosomes 2 and 11, while extinction required the presence of an intact mouse chromosome 11.

The effects of reduced O2 and antioxidants on steroidogenic capacity of cultured rat Leydig cells

We have examined the effects of reduced O2 tension and the antioxidant dimethylsulfoxide (DMSO) to determine if O2-derived free radicals are the cause of decreased steroidogenic capacity (testosterone and progesterone production) of cultured rat Leydig cells. Rat Leydig cells were initially cultured under standard conditions of 5% CO2, 95% air (19% O2) with or without DMSO. Addition of DMSO resulted in increased basal testosterone production on days 2, 3 and 4 of culture. hCG (10 mIU)-stimulated testosterone secretion was 2-3 times greater on days 2 and 3 in the presence of DMSO. Lowering the O2 concentration to 5% in the presence of DMSO resulted in even greater hCG-stimulated testosterone production on days 1 to 3. However, the effect of DMSO or low O2 and DMSO were not seen after 5 days. The reduced O2 concentration resulted in an increase in hCG (10 mIU)-stimulated progesterone synthesis throughout the culture, particularly on days 4 to 8. Also, when total steroid (progesterone and testosterone) was determined, cells cultured under reduced O2 conditions responded with increased steroid production on days 1 to 8 in comparison to controls (19% O2). These results demonstrate that lowered O2 concentration and DMSO provide a protective effect resulting in the maintenance of testosterone production and an increase in progesterone synthesis. These findings suggest that free radical-mediated damage of enzymes may result in decreased steroidogenic capacity of cultured Leydig cells.

Optimizing testosterone production by purified adult rat Leydig cells in vitro

We sought to establish conditions that increased the duration of testosterone production by fully differentiated adult rat Leydig cells in primary culture. A freshly isolated suspension of highly purified adult rat Leydig cells produced 83 ng testosterone/10(6) Leydig cells.h-1 when incubated in Medium 199 in a 1.5 ml microfuge tube with shaking for 3 h with a maximally stimulating concentration of ovine luteinizing hormone (LH). Unfortunately, adult rat Leydig cells that were allowed to attach only to a plastic culture dish flattened out, and testosterone production diminished rapidly. Leydig cells in Dulbecco's modified Eagles' medium-Ham's F12 (1:1; vol/vol) containing Cytodex 3 beads pre-equilibrated in culture medium containing fetal bovine serum attached to the beads and remained viable, but produced only 30 ng testosterone/10(6) Leydig cells.h-1 when incubated for 24 h with similar stimulation. Leydig cells similarly cultured and maximally stimulated with LH, responded to bovine lipoproteins (less than 1.222 g/ml) producing 105 ng of testosterone/10(6) Leydig cells.h-1 when incubated with 1 mg/ml bovine lipoprotein. Therefore, lipoproteins maintain the steroidogenic capacity of purified adult rat Leydig cells in primary culture for 24 h.

Detection of cell proliferation in pig testis and intestine sections using monoclonal anti-bromodeoxyuridine antibody and immunogold silver staining

For the first time a monoclonal antibody against 5-bromodeoxyuridine was used to detect cell proliferation in pig testis and intestine sections. The influence of several parameters such as mode of injection, addition of thymidine biosynthesis inhibitor, tissue fixation, hydrolysis and revelation was examined. The technique of choice consisted in intravenously injecting the animals with 50 mg/kg BUdR added to 10 mg/kg FUdR 2 h before tissue collection and Bouin fixation; hydrolysis of sections was performed by HC1 4N: Ethanol 70 degrees (1:1 v/v); revelation of BUdR was made by a secondary antibody linked to colloidal gold particles, followed by a silver enhancement step. The data were superior when compared to those obtained by direct immunofluorescence and by the PAP technique. The described method is convenient and sensitive, provides an intense nuclear labelling without background and allows simultaneous examination of histology. The advantages over the technique using tritiated thymidine are particularly obvious when fast screening of numerous samples is required or when new experimental protocols are developing.

Construction of a Leydig cell line synthesizing testosterone under gonadotropin stimulation: a complex endocrine function immortalized by cell hybridization

Hybridization between a mouse Leydig tumor cell line, MA-10, which produces cyclic AMP and progesterone under human chorionic gonadotropin (hCG) stimulation, and freshly isolated mouse Leydig cells gave rise to 54 hybrid clones, one of which, LK17, was capable of hCG-stimulated testosterone production. Subcloning of this hybrid resulted in the emergence of a subclone, K9, whose testosterone production is more than 10 times that of parent clone LK17, after hCG stimulation, with an ED50 of 37 pM. Testosterone synthesis by K9 cells was multiplied by 25 after gonadotropin stimulation, and binding of hCG declined after prolonged exposure to the hormone. These similarities with murine Leydig cells in primary culture make the K9 clone an attractive alternative for physiological studies.

Relationship between the exposure of Leydig cells to factor(s) present in testicular interstitial fluid and changes in their capacity to secrete testosterone during culture or after hCG-induced desensitization

This study has evaluated whether the decrease in capacity of Leydig cells to secrete testosterone that occurs during culture or after desensitization with hCG in vivo, is a consequence of the removal of a stimulatory factor(s) in testicular interstitial fluid (IF) to which Leydig cells are normally exposed. When Percoll-purified rat Leydig cells were cultured for 3 days in vitro, there was a progressive reduction in their ability to respond to hCG in terms of either testosterone or progesterone production. In contrast, culture of the cells in the presence of 10% charcoal-stripped IF maintained responsiveness to hCG either partially or completely. This effect was attributable to a factor(s) in IF with a molecular weight of greater than 30 kDa; a comparable fraction from serum had little or no effect. Crude Leydig cells from rats injected 24 h previously with 50 IU hCG showed a 70% reduction in their testosterone response to hCG in vitro and, compared to controls, increased testosterone production poorly in response to increasing concentrations of IF. However, progesterone secretion was increased considerably in response to IF. As in controls, fractionation of crude Leydig cells from hCG-desensitized rats on Percoll gradients resulted in three bands of Leydig cells, except that the yields of band 2 and 3 cells (containing about 40 and 85% Leydig cells, respectively) were reduced by 75% and 90%, respectively, with the majority of Leydig cells remaining in band 1 (which comprises poorly responsive cells). Band 2 and 3 cells from hCG-desensitized rats were not greatly different to cells from control rats in terms of their testosterone response to hCG +/- IF, although they produced considerably more progesterone. It is concluded that the reduced capacity of Leydig cells to secrete testosterone during culture may be attributable to some extent to the removal of a factor(s) in IF to which the cells are normally exposed. In contrast, the reduced in vivo exposure of Leydig cells to such factors, as occurs after hCG injection, cannot explain the poor testosterone response of these cells when they are isolated and cultured.

Direct stimulatory effects of insulin-like growth factor-I on Leydig cell steroidogenesis in primary culture

Insulin-like growth factor-I (IGF-I) in concentration as low as 10 ng/ml significantly increased basal testosterone formation and 100 ng/ml of IGF-I increased testosterone production more than two fold in primary cultures of purified mature Leydig cells. IGF-I also markedly potentiated hCG-induced testosterone formation in a dose-dependent manner. Furthermore, IGF-I enhanced 8-bromo cyclic AMP induced steroidogenesis and hCG-stimulated cyclic AMP formation. The binding of 125I-IGF-I to purified Leydig cells was linear with a binding affinity of 0.56 +/- 0.07 X 10(9) M-1 and a capacity of 167 +/- 10.2 fmol/mg protein. Insulin and multiplication-stimulating activity were less potent than IGF-I in competing the binding of 125I-IGF-I to purified Leydig cells. This suggests that Leydig cells contain specific type I IGF receptor and IGF-I could modulate Leydig cell steroidogenesis.

Systematic shut-off of the hormone receptors in intraspecific adrenal x Leydig cell hybrids

The mouse Y1 adrenal cell line was fused with mouse Leydig cells in primary culture. The selected hybrids were examined for their response to gonadotropin (hCG) and ACTH. None of them bound specifically [125I]hCG, nor did they augment their cAMP production in response to gonadotropin or ACTH stimulation, whereas their adenylate cyclase remained responsive to forskolin and cholera toxin, thus indicating a repression of hCG receptor synthesis and probably a loss of ACTH receptors, rather than a lesion of the coupling between the hormone receptor complex and the adenylate cyclase. Basal pregnenolone production in 17 hybrids was close to that of Leydig and Y1 cells and was enhanced after 8-bromo adenosine 3',5'-monophosphate (8-Br-cAMP) stimulation in 11 of them. Therefore, the negative control leading to the extinction of both parental functions acts preferentially at the first step of steroidogenesis, i.e., the gene(s) coding for the hormone receptors.

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.

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

Using a primary culture of immature porcine Sertoli cells, we studied the effect of porcine FSH (pFSH), testosterone and retinoic acid on the labelled secreted protein. Cells were cultured in a chemically defined medium for 3 days and, on day 3, they were incubated for different times in another medium containing labelled amino acids either in the presence or absence of pFSH (50 ng/ml or 2 micrograms/ml), or testosterone (10(-6) M), or retinoic acid (10(-7) M), either alone or in several combinations. After 4 and 8 h of incubation, 20 and 30 secreted peptides were detected respectively by a two-dimensional polyacrylamide gel electrophoresis of the radiolabelled secreted proteins. During these 2 periods, the effect of pFSH was negligible. After 25 h, about 84 spots (pI in the range of 5-8) were identified on the autoradiograms. pFSH (2 micrograms/ml) induced an increase of 14 spots, and a decrease of 7, but at 50 ng/ml only 5 spots were increased and one decreased. Retinoic acid alone induced the increase of one peptide, while testosterone alone or in combination with pFSH (50 ng/ml) did not modify the electrophoretic pattern. When pig Sertoli cells were treated with retinoic acid, testosterone and pFSH (50 ng/ml), the effects on secreted proteins were higher than those induced by pFSH (50 ng/ml) alone.

FSH regulates cultured Leydig cell function via Sertoli cell proteins: an in vitro study

The effects of follicular stimulating hormone (FSH) on testicular steroidogenic activity has been studied by testing the capacity of conditioned medium (CM) by both unstimulated (control) Sertoli cells (C-CM) and FSH stimulated Sertoli cells (FSH-CM) to influence porcine cultured Leydig cell activity. Leydig cells cultured in FSH-CM for 48 hrs, as compared to C-CM, show a significant (P less than 0.05) increase in [125I]-hCG binding (150% +/- 4) and hCG-stimulated testosterone (T) secretion (266% +/- 42). In addition, the stimulating effect of FSH-CM on Leydig cell function as compared to C-CM, is trypsin sensitive, non dialyzable, heat stable, acid resistant and is chromatographed following gel filtration (Sephadex G 100) into two different peaks of activity. These data suggest that FSH regulates Leydig cell function via (at least two types of) Sertoli cell secreted proteins.

Modulation of cultured mouse Leydig cells adenylate cyclase by forskolin and hCG

The diterpene, forskolin, stimulated cAMP accumulation about 15-fold over basal levels in purified mouse Leydig cells; however, it remained far less potent than hCG. Simultaneous addition of forskolin and hCG resulted in a striking synergistic stimulation of cAMP production. In contrast, forskolin-enhanced testosterone accumulation was never synergistic with that produced by maximal concentrations of hCG. hCG (3 X 10(-9) M) lowered about 6-fold the ED50 for forskolin-elicited cAMP accumulation and increased the maximal response to forskolin about 16-fold. Conversely, forskolin 10(-6) M) reduced the ED50 for hCG 2-fold but had a much smaller effect (2-3-fold) on maximal response. Moreover, pretreatment with hCG induced only a homologous desensitization of adenylate cyclase, whereas the enzyme became partially resistant to both hCG and forskolin in cells pretreated with forskolin. The homologous hCG-induced desensitization and the partial heterologous one induced by forskolin suggest that more than the catalytic unit of the cyclase is required for the diterpene activation.

Relationships between unconjugated and sulphated steroids in porcine primary Leydig cell culture

Steroidogenesis in immature porcine Leydig cells was investigated in primary culture at 48-84 h under basal conditions and in the presence of hCG. The basal accumulation of unconjugated steroids was close to linear only during the first 4 h of study, whereas the sulphate-conjugated steroids accumulated essentially linearly over the 36 h experimental period. At the last time point, 95% of the steroids measured were sulphated. Stimulation with hCG (1 ng/ml) led to a still more pronounced sulphate conjugation, and approx 99% of the steroids measured were sulphated at 36 h. Under maximal stimulation with hCG (100 ng/ml) the sulphates accounted for 74% of the total steroids measured at 36 h. Testosterone, androstenedione, dehydroepiandrosterone, 5-androstene-3 beta, 17 beta-diol and estrone were usually quantitatively the most important unconjugated steroids, and sulphated dehydroepiandrosterone, estrone, testosterone and 5-androstene-3 beta, 17 beta-diol were the most important steroid sulphates, especially following maximal stimulation of the cultures. These data emphasize the importance of steroid sulphates in porcine testicular steroid metabolism. Under stimulation with hCG, there was a rapid response in testicular steroidogenesis, initially seen as a rapid increase in the secretion of unconjugated and sulphated steroids. At approx 4-12 h, the rate of sulphate conjugation appeared to reach or even to exceed that of steroid biosynthesis, which lead to stabilisation or a decrease in the concentrations of unconjugated steroids. Only high doses of hCG, 10-100 ng/ml, were then able to lead to a net accumulation of unconjugated steroids, at 24-36 h of incubation with hCG.

The functional activity of adult mouse Leydig cells in monolayer culture: effect of lipoproteins, pregnenolone and cholera-toxin

Further studies were carried out on purified mouse Leydig cells to determine why they lose their hormone responsiveness after several days in monolayer culture. The effects of cholera-toxin on cyclic AMP and testosterone production were examined. It was found that cyclic AMP production could still be maximally stimulated by cholera-toxin after 4 days in culture when response to luteinizing hormone (LH) has declined. Testosterone production was, however, not maintained. Because this decline in testosterone production may have been due to the lack of a suitable substrate after several days in culture, cells were cultured initially in the presence of exogenous pregnenolone and low-density lipoproteins (LDL). Both substances were found to enhance basal and LH-stimulated testosterone production and to extend responsiveness of the cells until at least day 4, but by day 7 response was lost. Cells were then cultured in the presence of rat and human LDL and HDL and in both cases LDL was found to enhance consistently testosterone production, but HDL was much less effective. Scanning and transmission electron micrographs showed that changes in cell shape occurred during culture, but indicated that the cells were not depleted of lipid droplets by the end of culture or after LH stimulation. It is concluded that the eventual decline in testosterone synthesis is not due to lack of substrate, although the addition of exogenous substrate does extend the period of responsiveness. Nor is it due to a decrease in adenylate cyclase activity. At least part of the lesion is caused by a decrease in the enzymes required for the conversion of pregnenolone to testosterone.

Cultured Sertoli cell-mediated FSH stimulatory effect on Leydig cell steroidogenesis

To determine the precise role of Sertoli cells in the stimulating effects of follicle stimulating hormone (FSH) on Leydig cell activity, porcine purified Leydig and Sertoli cells were cultured separately or together in a chemically defined medium in the absence or presence of porcine, FSH 50 ng/ml. Leydig cell activity was evaluated using two parameters: human chorionic gonadotropin (hCG) binding sites; and hCG-stimulated cAMP production and testosterone secretion. First, it was found that FSH increases Leydig cell activity in crude Leydig cell preparations (40-60% of Leydig cells), whereas it exerts no effect on purified Leydig cells (greater than 90% of Leydig cells). Second, FSH stimulates the activity of Leydig cells cocultured with Sertoli cells, whereas it remains without effect on purified Leydig cells cultured alone. This stimulating effect of FSH on Leydig cell activity is dependent on the Sertoli cell number in the coculture. These data 1) show that the stimulating effect of FSH on Leydig cell function is mediated by Sertoli cells and 2) support the concept of local control of Leydig cell function originating from Sertoli cells.

FSH stimulation of cytosolic protein synthesis in cultured pig Sertoli cells

The effects of FSH on the cytosolic protein synthesis by a primary culture of immature porcine Sertoli cells were studied. Cells were cultured in a chemically-defined medium for 3 days and, on day 3, they were incubated for 40 h in another medium containing labelled amino-acids either in the presence or absence of 50 ng/ml porcine FSH (pFSH). In control cells, about 107 spots (pI in the range of 5 to 8) were identified by a two-dimensional polyacrylamide gel electrophoresis of the radiolabelled cytosolic proteins. pFSH treatment produced a marked increase of seven proteins whose molecular weights and isoelectric points are respectively comprised between 25 to 58 K and 5.5 to 5.8. In addition, pFSH treatment induced a slight but constant increase of two other proteins (mol. wt: 24 and 12 K and isoelectric point: 5.3).

Relationship between hCG receptors disappearance and steroid accumulation during long term hCG stimulation in porcine Leydig cell cultures

LH-hCG receptors and steroidogenesis can be maintained for more than a week in porcine Leydig cell culture (chemically defined medium). Free receptors and steroid accumulation were measured following long time exposure to hCG. As expected, the percent of receptor disappearance increases with the hCG concentration in the incubation medium. However, the steroidogenesis was also proportional to hCG concentration for 24 hours as well as 48 hours. A 50% receptor disappearance was obtained for 0.5 ng hCG/ml which led to a steroid accumulation of 50% of the maximal accumulation obtained with 100 ng/ml. A very significative positive correlation (rho) was observed between receptor occupancy (internalized and/or irreversibly occupied receptors) and steroid accumulation (T and DHAS) during a 24 or 48 hour period (rho = 0.97 and 0.98 for T, and rho = 0.96 and 0.94 for DHAS). Following 24 or 48 hour exposure to increasing hCG concentration, the cells were acutely stimulated by 25 ng hCG/ml for 4 hours. The steroidogenic response obtained to this acute stimulation was inversely proportional to the concentration of hCG during the previous period. A negative correlation was found between receptor occupancy and acute steroidogenic response (rho : -0.96 and -0.98 for T). These results indicate that during long term stimulation as well as during acute restimulation the absolute number of occupied receptors conditioned the steroidogenic response. These results do not fit into the concept of spare receptors and suggest that in these immature cells all receptors are potentially active in the regulation of steroidogenesis.