Transient postnatal over nutrition induces long-term alterations in cardiac NLRP3-inflammasome pathway

BACKGROUND AND AIMS

The prevalence of obesity is increasing worldwide at an alarming rate. Altered early nutrition, in particular postnatal overfeeding (PNOF), is a risk factor for impaired cardiac function in adulthood. In the understanding of the initiation or progression of heart diseases, NLRP3 inflammasome and non-coding RNAs have been proposed as key players. In this context, the aim of this study was to decipher the role of NLRP3 inflammasome and its post transcriptional control by micro-RNAs in the regulation of cardiac metabolic function induced by PNOF in mice.

METHODS AND RESULTS

Based on a model of mice exposed to PNOF through litter size reduction, we observed increased cardiac protein expression levels of NLRP3 and ETS-1 associated with alterations in insulin signaling. Additionally, miR-193b levels were down-regulated in the adult hearts of overfed animals. In a cardiomyocyte cell line, transfection with miR-193b induced down-regulation of ETS-1 and NLRP3 and improved insulin signaling.

CONCLUSIONS

These findings suggest that the miR-193b could be involved in cardiac phenotypic changes observed in adulthood induced by PNOF likely through the regulation of ETS-1 and NLRP3 expression, and through this of insulin signaling.

Effect of testosterone supplementation on nitroso-redox imbalance, cardiac metabolism markers, and S100 proteins expression in the heart of castrated male rats

The aim of this study was to investigate the effects of castration and testosterone supplementation on nitroso-redox status, cardiac metabolism markers, and S100 proteins expression in the heart of male rats. 50 male Wistar rats were randomized into five groups with ten animals each: group 1: control intact (CON); group 2: sham operated (Sh-O); group 3: sesame oil-treated rats (S-oil); group 4: gonadoectomized (GDX); and group 5: gonadoectomized rats treated with testosterone (GDX-T) for 8 weeks. Our results showed myofibrillar weaving, apoptosis, inflammation, and fibrosis (as reflected by increased activity of MMP 9 and MMP 2) in the heart of gonadoectomized rats. Testosterone supplementation restored the normal structure of the heart. In addition, a state of nitroso-redox imbalance was observed in the heart of castrated rats with increased NO (425.1 ± 322.8 vs. 208 ± 67.06, p ˂ 0.05) and MDA (33.18 ± 9.45 vs. 22.04 ± 7.13, p ˂ 0.05) and decreased GSH levels (0.71 ± 0.13 vs. 1.09 ± 0.19, p = 0.001). Testosterone treatment leads to a re-establish of only NO levels (425.1 ± 322.8 vs. 210.4 ± 114.3, p > 0.05). Markers of cardiac metabolism showed an enhancement of LDH activity (12725 ± 4604 vs. 5381 ± 3122, p ˂ 0.05) in the heart of castrated rats. This was inversed by testosterone replacement (12725 ± 4604 vs. 5781 ± 5187, p ˂ 0.05). Furthermore, castration induced heart's accumulation of triglycerides (37.24 ± 6.17 vs. 27.88 ± 6.47, p ˂ 0.05) and total cholesterol (61.44 ± 3.59 vs. 54.11 ± 7.55, p ˂ 0.05), which were significantly reduced by testosterone supplementation (29.03 ± 2.47 vs. 37.24 ± 6.17, p ˂ 0.05) and (47.9 ± 4.15 vs. 61.44 ± 3.59, p ˂ 0.001). Cardiomyocytes of castrated rats showed a decreased immunoexpression of S100 proteins compared to control animals. A restoration of S100 proteins immunostaining in cardiomyocyte cytoplasm was observed after testosterone supplementation. These findings confirm the deleterious effects of testosterone deficiency on cardiac function and highlight the involvement of nitric oxide, metalloproteinases 2 and 9, and S100 proteins.

Tumor necrosis factor-308 polymorphism increases the embryo implantation rate in women undergoing in vitro fertilization

STUDY QUESTION

Do TNF-308 and -238 polymorphisms impact the embryo implantation rate after in vitro fertilization (IVF) in women without female infertility factor?

SUMMARY ANSWER

The presence of the TNF-308A allele is associated with high implantation and multiple pregnancy rates in women without known infertility factors after ovarian hyperstimulation with exogenous FSH.

WHAT IS ALREADY KNOWN

Multiple pregnancies are frequent after the use of Assisted Reproductive Technologies. Single embryo transfer (SET) has been proposed as a simple way to prevent these risks. However, the extension of SET indications to patients not selected based on specific criteria is controversial because of reduced pregnancy rates. To date, the predictive value of the parameters used for SET (age, gynecological history of the patient and uterine characteristics) allows a pregnancy rate of ~30%.

STUDY DESIGN, SIZE, DURATION

The potential predictive value of TNF polymorphisms (-308, rs1800629 and -238, rs361525) on implantation rate was evaluated in 424 women requiring IVF due to male fertility factors. This cohort retrospective study was conducted over 4 years in University-affiliated hospitals.

PARTICIPANTS, SETTING, METHODS

The entire patient group included 424 women undergoing intracytoplasmic sperm injection (ICSI) due to male fertility factors without the contribution of any female factor. From among this group, a selected patient group included 120 women with a normal karyotype, age under 38 years, serum follicle-stimulating hormone (Day-3 FSH) levels below 10 IU/l, a long agonist desensitization protocol associated with recombinant FSH treatment and a Caucasian background.

MAIN RESULTS AND THE ROLE OF CHANCE

The TNF-238 polymorphism was not associated with implantation rate. In contrast, the presence of the TNF-308A allele was associated with increased Day 3-E2 levels as well as higher implantation and multiple pregnancy rates after fresh embryo transfer in women from the entire and selected patient groups. Moreover, in the selected patient group, the presence of the TNF-308A allele was also associated with a decrease in the miscarriage rate. The benefit of the TNF-308A allele in predicting implantation rates was not observed after the use of frozen embryos.

LIMITATIONS, REASONS FOR CAUTION

Future studies are needed to evaluate whether the TNF-308A allele might also be a biomarker in women with infertility factors.

WIDER IMPLICATIONS OF THE FINDING

The TNF-308A allele may represent a good candidate for a potential predictive, non-invasive biomarker in the SET strategy. However, its impact should be evaluated in prospective studies.

STUDY FUNDING/COMPETING INTEREST

This study was conducted with financial support from the French Institute for Health and Medical Research (INSERM), Organon France for a FARO (Fond d'Aide à la Recherche Organon) fellowship (to V.T.) and CHU Nice PHRC (PHRC 09-279).There are no competing interests.

Inhibition of TGF-beta signaling by IL-15: a new role for IL-15 in the loss of immune homeostasis in celiac disease

BACKGROUND AND AIMS

Interleukin (IL)-15 delivers signals that drive chronic inflammation in several diseases, including celiac disease. Smad3-transforming growth factor-beta (TGF-beta) signaling is instrumental to counteract proinflammatory signals and maintain immune homeostasis. Our goal has been to investigate why the proinflammatory effects of IL-15 cannot be efficiently controlled by TGF-beta in celiac disease.

METHODS

The impact of IL-15 on TGF-beta signaling in T cells and in the intestinal mucosa of celiac disease patients was analyzed by combining cell and organ cultures, immunohistochemistry, flow cytometry, real-time polymerase chain reaction, electromobility gel shift, and Western blot.

RESULTS

IL-15 impaired Smad3-dependent TGF-beta signaling in human T lymphocytes downstream from Smad3 nuclear translocation. IL-15-mediated inhibition was associated with a long-lasting activation of c-jun-N-terminal kinase and reversed by c-jun antisense oligonucleotides, consistent with the demonstrated inhibitory effect of phospho-c-jun on the formation of Smad3-DNA complexes. In active celiac disease, intestinal lymphocytes showed impaired TGF-beta-Smad3-dependent transcriptional responses and up-regulation of phospho-c-jun. Anti-IL-15 antibody and c-jun antisense both downmodulated phospho-c-jun expression and restored TGF-beta-Smad-dependent transcription in biopsies of active celiac disease. c-jun antisense decreased interferon gamma transcription.

CONCLUSIONS

Impairment of TGF-beta-mediated signaling by IL-15 might promote and sustain intestinal inflammation in celiac disease. More generally, our data provide a new rationale for the potent proinflammatory effects of IL-15, and further support the concept that IL-15 is a meaningful therapeutic target in inflammatory diseases associated with irreducible elevation of IL-15.

Effets à long terme des perturbateurs endocriniens environnementaux sur la fertilité masculine

Several epidemiologic studies have demonstrated during the last 50 years an increased incidence in testis cancer, male genital tract malformations (cryptorchidism and hypospadias) and a decrease in sperm quality in men. These three pathologies seem to be linked and to belong to the testicular dysgenesis syndrome (TDS). It was suggested that TDS is a consequence of intra-uterine exposure to environmental compounds that disrupt the metabolism of native hormones. Such substances are so called endocrine disruptors (EDs). EDs are present in our daily environment such as food and water (through the use of pesticides), cosmetics, house-care products etc. Experimental models have been carried out to (i) establish a link between EDs exposure and SDT and (ii) identify the mechanisms that are involved in. After a brief definition of EDs and having underlined the importance of the window of exposure to EDs, several mechanisms will be described such as (i) intergenerational transmission (epigenetic), (ii) programmed cell death of testicular cells, (iii) modification of the androgenic signal and (iv) role of the germ cells-nourishing cells. To conclude, we will try to propose some biomarkers that would be useful to identify the potential link between fetal exposure to anti-androgenic EDs and male testicular pathology.

Evidence for specific TRPM8 expression in human prostate secretory epithelial cells: functional androgen receptor requirement

TRPM8 (melastatine-related transient receptor potential member 8), a member of the transient receptor potential (TRP) superfamily of cation channels, has been shown to be a calcium-channel protein. TRPM8 mRNA has also been shown to be overexpressed in prostate cancer and is considered to play an important role in prostate physiology. This study was designed to determine the androgen-regulation mechanisms for TRPM8 mRNA expression and to identify the phenotype of TRPM8-expressing cells in the human prostate. Our findings show that trpm8 gene expression requires a functional androgen receptor. Furthermore, this article argues strongly in favour of the fact that the trpm8 gene is a primary androgen-responsive gene. Single-cell reverse transcriptase PCR and immunohistochemical experiments also showed that the trpm8 gene was mainly expressed in the apical secretory epithelial cells of the human prostate and trpm8 down-regulation occurred during the loss of the apical differentiated phenotype of the primary cultured human prostate epithelial cells. The androgen-regulated trpm8 expression mechanisms are important in understanding the progression of prostate cancer to androgen-independence. These findings may contribute to design a strategy to predict prostate cancer status from the TRPM8 mRNA level. Furthermore, as the TRPM8 channel is localized in human prostate cells, it will be interesting to understand its physiological function in the normal prostate and its potential role in prostate cancer development.

[Genomic instability and male infertility]

Knowledge of the human genome has opened the genomic era. The genome instability, its causes and the possible consequences especially about fertility start to be understood. This instability can be observed on chromosome structure but also on genes. Different chromosomes rearrangements involved in infertility including translocations and Y chromosome deletions are described. The Y chromosome is a model of instability, and this instability is the source of its evolution. All those rearrangements are the results of illegitimate recombinations between homologous sequences. On genes we find punctual and dynamic mutations, polymorphisms and epigenetic abnormalities. They all are the results of ADN replication mistakes not corrected by the cellular machine. This machinery is the guardian of the genome integrity and in case of abnormality the programmed cellular death is induced. The knowledge of all these instability mechanisms is essential to appreciate the risk for the offspring after intracytoplasmic sperm injection. Indeed we go round physiological barriers without a complete understanding of the mechanisms involved. Thus, this is an important challenge for research teams but also for all assisted reproduction centers, dealing with ART. Genome is unstable - the very basis of its evolution. But this is also the cause of mistakes with pathological consequences like infertility and mental retardation.

The mitochondrial-dependent pathway is chronically affected in testicular germ cell death in adult rats exposed in utero to anti-androgens

In utero exposure to exogenous anti-androgenic compounds induces a wide range of abnormalities of the reproductive system, including hypospermatogenesis, cryptorchidism and hypospadias. By using rats exposed in utero to the anti-androgenic compound flutamide (0.4, 2 or 10 mg/kg per day), it has been shown that hypospermatogenesis in adult testes could be related to (i) a long-term apoptosis in germ cells but not in somatic Leydig and Sertoli cells as evidenced by the TUNEL approach and (ii) alterations in the mRNA and protein expression of pro- (Bax, Bak, Bid) and anti-apoptotic (Bcl-2, Bcl-w) members of the Bcl-2 family. Indeed, the number of apoptotic germ cells increased with the dose of flutamide administered and the apoptotic germ cells were mainly detected at androgen-dependent stages VII-VIII. Moreover, for the Bcl-2-related proteins that were expressed mainly in the germ cells, a decrease in the levels of anti-apoptotic peptides Bcl-w (60%, P=0.003) and Bcl-2 (90%, P=0.0001) was observed at 2 mg/kg per day flutamide and an increase in levels of the pro-apoptotic Bax (2.3-fold, P=0.0004) was detected at 10 mg/kg per day. In contrast, the levels of pro-apoptotic peptide Bak that was mainly expressed in somatic cells decreased (70%, P=0.0008) at 10 mg/kg per day. Such alterations in Bcl-2-related peptides occurred mainly at the protein level except for Bcl-2 (72%, P=0.0001) and Bak (43%, P=00002) transcripts. Together, these results showed that the apoptosis observed in adult germ cells from rats exposed in utero to flutamide may result from a long-term alteration in the balance between pro- and anti-apoptotic Bcl-2-related molecules in favour of pro-apoptotic proteins. These data further supported the concept of an androgen-dependent fetal programming that is in relation with an alteration of the expression of Bcl-2-related genes/proteins promoting apoptosis in testicular germ cells of adult rats with fetal androgen disruption.

Regulation of aromatase gene expression in purified germ cells of adult male rats: effects of transforming growth factor beta, tumor necrosis factor alpha, and cyclic adenosine 3',5'-monosphosphate

Estrogens are key regulators of sexual differentiation and development in vertebrates. The P450 aromatase (P450arom) is the steroidogenic enzyme responsible for the synthesis of estrogens from androgens. In the adult rat testis, aromatase transcripts and activity have been observed in somatic cells and germ cells, including pachytene spermatocytes (PS) and round spermatids (RS), but little is known concerning regulation of the aromatase gene expression, especially in germ cells. The quality of germ cell preparations was assessed by the absence of androgen-binding protein and stem cell factor transcripts, two specific markers for Sertoli cells. By employing a competitive quantitative reverse transcriptase-polymerase chain reaction technique, we confirmed that germ cells contained P450arom transcripts and demonstrated that the aromatase gene was up-regulated by cAMP. Conversely, transforming growth factor (TGF) beta1 inhibited Cyp19 gene expression in a dose- and a time-dependent manner in both PS and RS. The addition of tumor necrosis factor (TNF) alpha to purified germ cells induced an increase of the amount of P450arom mRNA in PS, although an inhibitory effect was observed in RS. When PS were treated with dexamethasone (Dex), a similar enhancement of the aromatase transcript level was observed, whereas an inhibitory effect was recorded for RS. Furthermore, in either TGFbeta1- or TNFalpha-treated germ cells, the addition of Dex stimulated the aromatase gene transcription. Experiments using 5' rapid amplification of cDNA ends suggested that promoter PII is mainly concerned in the regulation of the aromatase gene expression in germ cells of adult male rats; however, the presence of other promoters could not be excluded.

Leukemia inhibitory factor is a key signal for injury-induced neurogenesis in the adult mouse olfactory epithelium

The mammalian olfactory epithelium (OE) is composed of primary olfactory sensory neurons (OSNs) that are renewed throughout adulthood by local, restricted neuronal progenitor cells. The molecular signals that control this neurogenesis in vivo are unknown. Using olfactory bulb ablation (OBX) in adult mice to trigger synchronous mitotic stimulation of neuronal progenitors in the OE, we show the in vivo involvement of a cytokine in the cellular events leading to the regeneration of the OE. We find that, of many potential mitogenic signals, only leukemia inhibitory factor (LIF) is induced before the onset of neuronal progenitor proliferation. The rise in LIF mRNA expression peaks at 8 hr after OBX, and in situ RT-PCR and immunocytochemistry indicate that LIF is upregulated, in part, in the injured neurons themselves. This rise in LIF is necessary for injury-induced neurogenesis, as OBX in the LIF knock-out mouse fails to stimulate cell proliferation in the OE. Moreover, delivery of exogenous LIF to the intact adult OE using an adenoviral vector stimulates BrdU labeling in the apical OE. Taken together, these results suggest that injured OSNs release LIF as a stimulus to initiate their own replacement.

Tumor necrosis factor-alpha inhibits glutathione S-transferase-alpha expression in cultured porcine Sertoli cells

Glutathione S-transferases (GSTs) are a family of soluble enzymes of detoxification that use reduced glutathione in conjugation and reduction reactions. Toxic electrophiles are substrates for the GSTs. GSTalpha is expressed at high levels in different tIssues such as the testis. Among the different GSTs present in the testis, GSTalpha is specifically expressed in Leydig and Sertoli cells known to be under the control of hormonal and local regulatory factors. The present study investigated the regulatory action of tumor necrosis factor-alpha (TNFalpha) on basal and hormone (FSH and testosterone)-stimulated GSTalpha expression in cultured Sertoli cells. Treatment with TNFalpha (0-20 ng/ml, 48 h) induced a decrease in basal GSTalpha mRNA levels in a dose-dependent manner (fivefold decrease; P<0.001). The maximal and half maximal effects were observed at 20 ng/ml and 7 ng/ml respectively. The inhibitory effect of TNFalpha was also time-dependent with a maximal inhibitory effect (threefold decrease; P<0.001) observed at 48 h. The inhibitory effect of the cytokine was also observed on basal GSTalpha protein (28 kDa) levels. TNFalpha also inhibited the hormone-stimulated GSTalpha expression in Sertoli cells. The treatment of cultured Sertoli cells with both FSH and TNFalpha (100 ng/ml and 10 ng/ml respectively, 48 h) resulted in a complete suppression of the stimulatory action of FSH on GSTalpha mRNA levels. Similarly, in Sertoli cells treated with testosterone or its non-aromatizable metabolite dihydrotestosterone (100 ng/ml, 24 h), TNFalpha reduced the hormone-stimulated GSTalpha mRNA and protein levels. TNFalpha inhibited basal GSTalpha expression without affecting mRNA stability. Indeed, the decay curves (mRNA half-life time=18 h) for the GSTalpha basal mRNA levels in Sertoli cells was similar in the absence or presence of TNFalpha (10 ng/ml, 48 h). Testosterone increased GSTalpha mRNA without affecting the enzyme mRNA stability. TNFalpha antagonized the androgen-stimulated GSTalpha mRNA levels without affecting the enzyme mRNA stability, suggesting that the interaction between the androgen and the cytokine is mostly exerted at a transcriptional level. FSH increased GSTalpha mRNA levels through an increase in mRNA stability (increased mRNA half-life times to 119 h). TNFalpha antagonized the stimulatory effect of FSH on GSTalpha mRNA levels by antagonizing the stabilizing effect exerted by the hormone on GSTalpha mRNA. Together, these results suggest that the increase in the cytokine levels within the testis would alter the detoxification processes against genotoxic products during spermatogenesis.

Somatostatin receptor expression profile as a potential criterion for discrimination between seminoma and non-seminoma testicular tumors

The expression of five (sst1-sst5) somatostatin (SRIF) receptor mRNAs was compared between normal and tumoral testicular samples diagnosed as either seminoma or non-seminoma. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicated that all testicular tissues studied (total of 24) contained sst5 receptor transcripts, whereas the sst2 was absent in all of them. In contrast to the normal tissue samples, both types of tumors (total of 12) did not contain sst4 transcripts. sst3 mRNA was expressed in normal and non-seminoma samples, but not in seminomas. sst1 transcripts were not found in normal and seminoma tissues. However, all studied non-seminomas contained this mRNA. Our data thus points to a specific pattern of SRIF receptor mRNA expression in each type of the samples analyzed. Moreover, they further indicate that the presence of sst1 and sst3 transcripts might be used as an additional criterion to distinguish between seminoma and nonseminoma tumors.

Expression of hMLH1 and hMSH2 and assessment of microsatellite instability in testicular and mediastinal germ cell tumours

The aim of this study was to investigate DNA mismatch repair deficiency in male germ cell tumours. We analysed the expression of two mismatch repair proteins, human mutL homologue 1 (hMLH1) and human mutS homologue 2 (hMSH2), and evaluated the frequency of microsatellite instability with 10 mononucleotide and two dinucleotide repeat sequences, in 39 paired tumour/normal DNA samples obtained from 17 testicular and two mediastinal germ cell tumours. In all 19 cases, hMLH1 and hMSH2 both showed nuclear immunolocalization in invasive and testicular in-situ tumours. In non-neoplastic seminiferous tubules, hMLH1 was expressed only in premeiotic germ cells, while hMSH2 was seen in all stages of spermatogenesis. Genetic analysis of dinucleotide markers revealed loss of heterozygosity in one of two testicular yolk sac tumours at D18S58 and an allelic shift at D2S123 in two of three testicular embryonal carcinomas, while none of the 12 seminomas exhibited a genetic abnormality at these loci. No abnormalities were demonstrated with the 10 mononucleotide markers. The two mediastinal germ cell tumours showed no genetic instability or allelic loss with all 12 markers. We suggest that genetic alterations as assessed by microsatellite analysis in germ cell tumours may reflect tissue maturation and phenotypic differentiation rather than tumour progression. In addition, we suggest that hMLH1 and hMSH2 genes may not be implicated in the genesis of germ cell tumours.

Aromatase expression in male germ cells

The cytochrome P450 aromatase (P450arom) is the terminal enzyme responsible for the formation of estrogens from androgens. According to the age, aromatase activity has been measured in immature and mature rat Leydig cells, as well as in Sertoli cells whereas in pig, ram and human the aromatase is mainly present in Leydig cells. In the rat testis, we have immunolocalised the P450arom not only in Leydig cells but also in germ cells and especially in elongated spermatids. Related to the stage of germ cell maturation, we have shown that the level of P450arom mRNA transcripts decreases, it is much more abundant in younger than in mature germ cells whereas the aromatase activity is two- to four-fold greater in spermatozoa when compared to the two other enriched-germ cell preparations. Moreover, we have reported the existence of alternative splicing events of P450arom mRNA in pachytene spermatocytes and round spermatids giving rise to two isoforms lacking the last coding exon which, therefore, cannot encode functional aromatase molecules. In rat germ cells, the aromatase gene expression is not only under androgen control but also subjected to cytokine (TNFalpha) and growth factor (TGFbeta) regulation. In the bank-vole testis, we have evidenced a synchronisation between a fully developed spermatogenesis and a strong positive immunoreactivity for both P450arom and estrogen receptor (ERbeta) in spermatids. Therefore, the aromatase gene expression and its translation in a fully active protein in rodent germ cells evidence an additional site for estrogen production within the testis. Our recent data showing that human ejaculated spermatozoa expressed specific transcripts for P450arom reinforced the observations reported in germ cells of other mammalian species. Together with the widespread distribution of ERs in testicular cells these data bring enlightenments on the hormonal regulation of male reproductive function. Indeed these female hormones (or the ratio androgens/estrogens) do play a physiological role (either directly on germ cells or via testicular somatic cells) in the maintenance of male gonadal functions and obviously, several steps are concerned particularly the spermatid production and the epididymal sperm maturation.

Somatostatin inhibits stem cell factor messenger RNA expression by Sertoli cells and stem cell factor-induced DNA synthesis in isolated seminiferous tubules

Immature porcine Sertoli cells have been reported to be targets for the regulatory peptide somatostatin (SRIF), which inhibits the basal and FSH-induced proliferation of Sertoli cells through a decrease of cAMP production. In the present study, we show that SRIF inhibits both basal and FSH-stimulated expression of the stem cell factor (SCF), a Sertoli cell-specific gene. The SRIF-mediated inhibition of forskolin-triggered, but not of 8-bromoadenosine-cAMP-triggered, SCF mRNA expression demonstrates the involvement of adenylyl cyclase in underlying peptide actions. Moreover, these effects require functional coupling of specific plasma membrane receptors to adenylyl cyclase via inhibitory G proteins, because pertussis toxin prevents SRIF-mediated inhibition of SCF mRNA expression. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assays suggest the involvement of sst2 receptors in SRIF actions on Sertoli cells. The biological relevance of these data is supported by an SRIF-mediated decrease in SCF-induced incorporation of [(3)H]thymidine in isolated seminiferous tubules. In situ hybridization and confocal microscopy show that, in seminiferous tubules only, spermatogonia display both c-kit and sst2 receptors. Taken together, these results suggest that SCF-stimulated DNA synthesis can be inhibited by SRIF in spermatogonia, but not in Sertoli and peritubular cells. Combined RT-PCR and immunohistochemical approaches point toward spermatogonia and Leydig cells as the source of testicular SRIF. These data argue in favor of paracrine/autocrine SRIF actions in testis.

Leukemia inhibitory factor antagonizes gonadotropin induced-testosterone synthesis in cultured porcine leydig cells: sites of action

In the present report, the action of leukemia inhibitory factor (LIF) on testicular steroid hormone formation was studied. For this purpose, the direct effects of LIF were evaluated on basal and human (h)CG-stimulated testosterone synthesis by cultured, purified Leydig cells isolated from porcine testes. LIF reduced (more than 60%) hCG-stimulated testosterone synthesis. This inhibitory effect was exerted in a dose- and time-dependent manner. The maximal and half-maximal effects were obtained with, respectively, 10 ng/ml (0.5 nM ) and 2.5 ng/ml (0.125 nM ) of LIF after a 48-h treatment of the Leydig cells. Such an effect of the cytokine was not a cytotoxic effect, because it was reversible and Leydig cells recovered most of their steroidogenic activity after the removal of LIF. Considering the sites of action of LIF in inhibiting gonadotropin-stimulated testosterone formation, it was shown that LIF significantly (P < 0.002) reduced, in a comparable range (about 60% decrease), testosterone synthesis stimulated with LH/hCG or with pharmacological agents that enhance cAMP levels (cholera toxin, forskolin, and PG E2), and testosterone synthesis stimulated with 8-bromo-cAMP. Such an observation indicates that the antigonadotropic action of the cytokine is exerted in a predominant manner at a step (or steps) located beyond cAMP formation. Furthermore, incubation of Leydig cells with 22R-hydroxycholesterol (5 microg/ml, 2 h), a cholesterol substrate derivative that does not need an assisted process to be delivered to the inner mitochondrial membrane, reversed most of the inhibitory effect of LIF on the steroid hormone formation. Such results indicate that LIF acts by reducing cholesterol substrate availability in the mitochondria. Consequently, LIF action was tested on steroidogenic acute regulatory protein and PBR (peripheral benzodiazepine receptor) shown to be potentially involved in such a cholesterol transfer. LIF reduced, in a dose- and time-dependent manner, LH/hCG-induced steroidogenic acute regulatory protein messenger RNA levels. The maximal inhibitory effect was obtained with 6.6 ng/ml of LIF after 48 h of treatment. In contrast, LIF had no effect on PBR messenger RNA expression or PBR binding. This inhibitory effect of LIF on Leydig cell steroidogenesis is probably exerted via an auto/paracrine action of the cytokine. Indeed, by immunohistochemistry, LIF and LIF receptor proteins were identified in Leydig and Sertoli cells but not in other testicular cell types, except for LIF receptor in spermatogonia. Furthermore, the presence of LIF and its receptor in Leydig cells at the neonatal and adult periods suggests that the inhibitory effect of LIF on androgen formation reported here probably occurs in both the fetal and the adult Leydig cell populations during testicular development.

Differential expression of growth factors in irradiated mouse testes

PURPOSE

By using as an experimental model the male mouse gonad, which contains both radiosensitive (germ) and radioresistant (somatic) cells, we have studied the growth factor (and/or receptor) expression of transforming growth factor-beta receptor (TGFbeta RI), stem cell factor (SCF), c-kit, Fas-L, Fas, tumor necrosis factor receptor (TNF R55), and leukemia inhibiting factor receptor (LIF-R) after local irradiation.

METHODS AND MATERIALS

Adult male mice were locally irradiated on the testes. Induction of apoptosis in the different testicular cell types following X-ray radiation was identified by the TdT-mediated dUTP Nick End Labeling (TUNEL) approach. Growth factor expression was evidenced by semiquantitative RT-PCR and Western blot analyses.

RESULTS

Apoptosis, identified through the TUNEL approach, occurred in radiosensitive testicular (premeotic) germ cells with the following kinetics: the number of apoptotic cells increased after 24 h (p < 0.001) and was maximal 48 h after a 2-Gy ionizing radiation (p < 0.001). Apoptotic cells were no longer observed 72 h after a 2-Gy irradiation. The number of apoptotic cells increased with the dose of irradiation (1-4 Gy). In the seminiferous tubules, the growth factor expression in premeiotic radiosensitive germ cells was modulated by irradiation. Indeed Fas, c-kit, and LIF-R expression, which occurs in (radiosensitive) germ cells, decreased 24 h after a 2-Gy irradiation, and the maximal decrease was observed with a 4-Gy irradiation. The decrease in Stra8 expression occurred earlier, at 4 h after a 2-Gy irradiation. In addition, a significant (p < 0.03) decrease in Stra8 mRNA levels was observed at the lowest dose used (0.5 Gy, 48 h). Moreover, concerning a growth factor receptor, such as TGFbeta RI, which is expressed both in radiosensitive and radioresistant cells, we observed a differential expression depending on the cell radiosensitivity after irradiation. Indeed, TGFbeta RI expression was increased after irradiation in interstitial radioresistant testicular cells in a dose- and time-dependent manner, while it decreased in seminiferous radiosensitive (germ cells) testicular cells. Such a differential expression between radioresistant and radiosensitive cells in TGFbeta RI levels was observed in terms of both mRNA and protein. In contrast, the growth factors specifically expressed in the somatic radioresistant (Sertoli) cells in the seminiferous tubules (SCF, Fas-L, TNF R55) were not affected by ionizing radiation (up to 4 Gy, 72 h).

CONCLUSION

Growth factor expression decreased in the radiosensitive testicular cells after irradiation. Such a decrease occurred before the detection of apoptosis using the TUNEL approach. TGFbeta RI mRNA levels decreased in the radiosensitive cells, whereas it increased in the radioresistant cells, suggesting that TGFbeta RI may represent a biomarker of the intrinsic radiosensitivity of cells.

Up-regulation of mitochondrial peripheral benzodiazepine receptor expression by tumor necrosis factor alpha in testicular leydig cells. Possible involvement in cell survival

Porcine Leydig cells in primary cultures are resistant to tumor necrosis factor alpha (TNFalpha) cytotoxicity. Here we report that these cells can be rendered sensitive to TNFalpha killing by treatment with the translational inhibitor cycloheximide, suggesting the existence of proteins that can suppress the death stimulus induced by the cytokine. In search of these cytoprotective proteins, we focused on the constituents of the mitochondrial permeability transition pore (PT pore), whose opening has been shown to play a critical role in the TNFalpha-mediated death pathway. We found that TNFalpha up-regulated mRNA and protein expression of the mitochondrial peripheral benzodiazepine receptor (PBR), an outer membrane-derived constituent of the pore. A strong correlation was established between the resistance of the cells to TNFalpha killing and the density of PBR-binding sites. Concomitantly, TNFalpha down-regulated Bcl-2 mRNA and protein expression. As Bcl-2 has been shown to be an endogenous inhibitor of the PT pore, we hypothesize that the TNFalpha-induced up-regulation of PBR expression may compensate for the decrease in Bcl-2 levels to prevent the opening of the PT pore.

Role of sphingosine in the tumor necrosis factor alpha stimulatory effect on lactate dehydrogenase A expression and activity in porcine Sertoli cells

In this study, the intracellular signaling mechanisms through which TNFalpha increases LDH(A4) activity/expression in primary cultures of porcine testicular Sertoli cells were investigated. Studies were focused on sphingomyelin hydrolysis pathway. Treatment of [(14)C]serine-labeled cells with TNFalpha (15 ng/ml, 0.8 nM) resulted in a transient decrease (approximately 20%) in cellular [(14)C]sphingomyelin and in an increase (approximately 27%) in [(14)C]sphingosine that remained elevated for at least 75 min. In the same experiments, no significant changes were detected in ceramide levels. Exogenous sphingosine stimulated LDH(A4) activity and LDHA expression in a dose-dependent manner (ED(50) = 8 microM of sphingosine). Such an increase in LDHA messenger RNA levels and LDH(A4) activity was detected at 24 h and was maximal after 48 h of treatment. Kinetically, the increase in LDH(A4) activity was similar whether Sertoli cells were treated with sphingosine (12 microM) or with TNFalpha (20 ng/ml). Although sphingosine mimicked the action of TNFalpha on Sertoli cells LDH(A4) activity and expression, the maximal stimulatory effect represented about 30% of TNFalpha maximal activity. Sphingomyelinase, C2 ceramide, sphingosine 1-phosphate, N, N-dimethylsphingosine, and phosphorylcholine had no significant effect on LDHA expression/LDH(A4) activity. Exogenous C2 ceramide increased LDH(A4) activity only in cytokine-treated cells, suggesting its involvement as sphingosine precursor in TNFalpha-stimulated LDH(A4) activity via the sphingomyelin hydrolysis pathway. The LDH(A4) activity stimulated by TNFalpha was decreased by 36.2% by an inhibitor of sphingosine formation, NH4Cl (4 mM), supporting a role of sphingosine in the TNFalpha effect. Moreover, bisindolylmaleimide (100 nM), a protein kinase C (PKC) inhibitor decreased significantly by 28.7% the TNFalpha effect on LDH(A4) activity but had no effect on the stimulating action of sphingosine, suggesting that if PKC is involved in TNFalpha action, the sphingosine effect on LDH(A4) is unrelated to the PKC activity or inhibition. Together, the present data suggest that in primary Sertoli cell cultures, TNFalpha stimulating action on LDHA expression is partly exerted via sphingomyelin hydrolysis pathway, sphingosine being the active metabolite.

Developmental and hormonal regulation of the expression of oligodendrocyte-specific protein/claudin 11 in mouse testis

The proliferation and differentiation of testicular progenitor stem cells into highly specialized germ cells (spermatozoa) are largely controlled by the hormonally (FSH and testosterone) regulated adjacent supporting Sertoli cells. However, the factors involved in this control remain largely unknown. In the present study, the technique of differential display PCR was used to identify target transcripts to FSH action in cultured murine Sertoli cells. Among these target transcripts, we identified the oligodendrocyte-specific protein (OSP), also known as claudin 11, which had recently been shown to play a key role in the formation of the hematotesticular barrier. Our data show that the testicular expression of OSP is dependent upon male gonad development and systemic and local signaling molecules. Indeed, OSP is expressed early in fetal development in Sertoli cells, immediately after the peak of SRY (sex-determining region, Y gene) expression, but just before that of the anti-Mullerian hormone. Postnatally, OSP expression starts to increase from day 3 to reach a plateau between days 6 and 16 postnatally. In the prepubertal and adult testes, an apparent decline in OSP messenger RNA (mRNA) levels was found, probably because of the increasing number of germ cells (which do not express OSP). Among the signaling molecules that control testicular OSP expression, we have identified FSH and tumor necrosis factor-alpha (TNFalpha). Indeed, using a model of purified cultured mouse Sertoli cells, we demonstrate that FSH inhibits, in a dose (ED50 = 4 ng/ml)- and time (maximal effect after 24 h)-dependent manner, the levels of OSP mRNA. Such an inhibitory effect was mimicked by 8-bromo-cAMP, suggesting that FSH may use the cAMP/protein kinase A pathway to inhibit OSP mRNA levels. TNFalpha was also shown to inhibit OSP expression in cultured Sertoli cells. The maximal effect was observed after 48 h of TNFalpha treatment with an ED50 of 4.5 ng/ml. Together, our results indicate that OSP expression 1) starts during fetal life at a critical period, probably under SRY control and during testicular formation; and 2) is regulated by hormones (FSH) and cytokines (TNFalpha) in the adult testis, suggesting a critical role for these molecules in the (re)modeling process of the hematotesticular barrier during spermatogenesis.

Somatostatin inhibits follicle-stimulating hormone-induced adenylyl cyclase activity and proliferation in immature porcine Sertoli cell via sst2 receptor

The potential involvement of somatostatin (SRIF) in testicular function was studied by using as a model primary cultures of purified immature porcine Sertoli cells. In the present report we show that Sertoli cells express mRNA for sst2 SRIF receptor and display SRIF-sensitive adenylyl cyclase. Sensitivity of adenylyl cyclase to SRIF and its analogues is compatible with the pharmacological profile of this receptor type. Relevant cAMP production is similarly inhibited by SRIF in both basal and stimulated (by gonadotropin FSH or by forskolin) conditions. Moreover, the observed SRIF actions on Sertoli cells require functional coupling of specific membrane receptors to adenylyl cyclase via Gi proteins because pertussis toxin prevents SRIF-dependent inhibition of adenylyl cyclase in either basal or FSH-stimulated conditions. Given the potent antiproliferative actions of SRIF in other cell types, we further assessed the possible SRIF-dependent modulation of [(3)H]thymidine incorporation by Sertoli cells. Our data point to SRIF-mediated inhibition of both basal and FSH-stimulated [(3)H]thymidine uptake. This inhibition of Sertoli cell proliferation is, at least in basal conditions, also blocked by pertussis toxin pretreatment. Altogether, these data suggest that SRIF may play a role as an (local) inhibitor of FSH actions in testicular development.

Transforming growth factor-beta receptor types I and II in cultured porcine leydig cells: expression and hormonal regulation

The steroidogenic activity of testicular Leydig cells is controlled both by the pituitary hormone (LH) and by growth factors such as transforming growth factor-beta peptides (TGFbeta1, -2, and -3; inhibin/activin; and anti-Mullerian hormone). By using primary cultures of porcine Leydig cells as a model, the aim of the study was to identify and characterize the TGFbeta receptors and to study their regulation by LH/hCG. TGFbeta receptors have been identified and characterized through three different approaches, including cross-linking experiments and Western and Northern blotting analyses. In cross-linking experiments, labeled TGFbeta was shown to bind to three different molecular species of 300, 80, and 53 kDa, which may correspond to the protein betaglycan (also known as TGFbeta type III receptor) and TGFbeta type II and I receptors (TGFbetaRII and TGFbetaRI), respectively. The presence of TGFbetaRI and -RII was further demonstrated by Western blotting analysis using specific polyclonal antibodies. Finally, the expression of betaglycan, TGFbetaRII, and TGFbetaRI messenger RNAs, was confirmed by Northern blotting analysis, as shown by the presence of 6.4-, 4.6-, and 5.8-kb messenger RNAs, respectively. By using a RT-PCR approach, the mediators of the TGFbeta signal, Smads 1-7, were also detected in cultured Leydig cells. TGFbetaRI and TGFbetaRII protein levels were enhanced by hCG/LH in a dose-dependent (maximal effect with 0.3 ng/ml hCG) and time-dependent (maximal effect observed after 48 h of hCG treatment) manner. Furthermore, to determine whether the stimulatory effect of LH/hCG was mediated by testosterone, use was made of aminogluthetimide, an inhibitor of cytochrome P450scc. The inhibition oftestosterone formation did not affect the stimulatory effect of LH/hCG on TGFbetaRI and -RII levels, suggesting that the gonadotropin action is not mediated by the steroid hormone. Together, the present findings demonstrate that the TGFbeta receptors are expressed and are under hormonal (gonadotropin) control in cultured porcine Leydig cells.

Evidence for a selective loss of somatostatin receptor subtype expression in male germ cell tumors of seminoma type

Somatostatin (SRIF) is a potent antiproliferative signal for both normal and tumoral mammalian cells and an alteration in the SRIF receptor expression pattern has been associated with carcinogenesis. In the present study, the relevance of SRIF signaling to human male germ cell tumors was assessed at the receptor level. The expression of five SRIF receptor (sst1-sst5) mRNAs was estimated by RT-PCR and compared between normal and tumoral testes. All 12 normal testicular tissues studied contained sst3 and sst5 receptor transcripts whereas sst4 was present in almost all (11 of 12). sst1 transcripts were consistently absent while the majority (11/12) of normal samples studied did not contain sst2 mRNA. Parallel assessment of SRIF receptor mRNAs in 10 seminoma testicular germ cell tumors showed expression of a single receptor type, sst5, in all samples analyzed. All seminoma samples were depleted in transcripts corresponding to sst1 and sst2 receptors while either sst3 or sst4 mRNAs were absent in almost all (9 of 10) tumoral samples studied. The comparison of SRIF receptor expression between normal tissue and seminoma tumors thus points to a selective loss of sst3 and sst4 mRNA expression in seminomas. Altogether these data indicate that: (i) normal human testes are putative SRIF targets; (ii) loss of sst3 and sst4 SRIF receptor expression might be associated with seminoma carcinogenesis.

A novel SMAD4 gene mutation in seminoma germ cell tumors

Transforming growth factor (TGF)-beta is known as an antiproliferative factor in the majority of mammalian cells, including stem germ cells. Lack of TGF-beta-induced growth inhibition has been associated with disruptions of TGF-beta receptors and SMADs. In the present study, we performed a mutational analysis of the TGF-beta signaling system, including TGF-beta receptor type I and type II and SMADs (SMAD1-SMAD7), in 20 seminoma germ cell tumors. Using reverse transcription-PCR, single-strand conformational polymorphism, and sequencing analysis, the COOH-terminal domain of SMAD4 was found to be mutated: a single thymine was inserted between nt 1521 and 1522 in 2 of 20 tumors analyzed. This addition of a thymine creates a frameshift and a new stop signal at codon 492, which leads to premature termination of the encoded protein. Such a mutation potentially abrogates signaling from TGF-beta as well as the other TGF-beta family members, including activin and bone morphogenetic protein, which all use the SMAD pathway. Immunohistological analysis confirmed the loss of expression of SMAD4 protein in the seminoma tissues with the insertional mutation. To our knowledge, this is the first description of a novel SMAD4 insertional mutation in seminoma testicular germ cell tumors. This mutational inactivation of SMAD4/COOH-terminal domain may cause TGF-beta unresponsiveness. It could thus provide a basis for understanding the potential role of the TGF-beta system in germ cell tumorigenesis.

Epidermal growth factor regulates glucose metabolism through lactate dehydrogenase A messenger ribonucleic acid expression in cultured porcine Sertoli cells

In a previous work, we reported that lactate dehydrogenase A4 (LDH A4) activity is a key step in the stimulatory effect of epidermal growth factor (EGF) on lactate production in cultured Sertoli cells. Here, we further investigated the regulatory mechanisms involved in EGF action on LDH A mRNA expression. Steady-state levels of LDH A mRNA analyzed by Northern blot hybridization were induced to 2. 9-fold in response to a 36-h incubation with EGF (ED(50) = 4 ng/ml, 0.63 x 10(-9) M). Whether EGF-induced increases of LDH A mRNA levels are the result of increased transcription and/or altered mRNA stability was investigated. The decay curves for the 1.5-kilobase LDH A mRNA transcript in Sertoli cells were not different in the absence or presence of EGF, suggesting that EGF did not affect LDH A mRNA stability. Inhibitors of protein synthesis (cycloheximide) and RNA synthesis (actinomycin D, and 5,6-dichloro-1-beta-ribofuranosyl benzimidazole) completely abrogated the EGF-induced LDH A mRNA expression, indicating that EGF increased LDH A mRNA levels through a transcriptional mechanism, which probably involves protein synthesis. Finally, the partial inhibitory effect of a protein kinase C (PKC) inhibitor, bisindolylmaleimide, on EGF-stimulated LDH A mRNA supports a partial involvement of PKC in the action of the growth factor. Since EGF is produced in Sertoli and in germ cells, its action is probably exerted in a context of a local control. As EGF also regulates other parameters involved in glucose metabolism, its effect on LDH A might be viewed in a general context related to the control of energy metabolism by the growth factor in the testicular cells.

Stem cell factor/c-kit system in spermatogenesis

One of the major unresolved questions with male infertility is the identification of the molecular origin of a great majority of the spermatogenetic arrests currently diagnosed as idiopathic male infertility. During the past years, several families of regulating factors have been implicated in spermatogenesis defects observed essentially in animal models. Among these factors are signalling molecules, and particularly the stem cell factor (SCF)/c-kit system. The SCF and its receptor c-kit are an appropriate example to illustrate the role of signalling molecules in the physiology and pathology of spermatogenesis. The SCF/c-kit regulates primordial germ cell migration, proliferation and apoptosis during fetal gonadal development. The SCF/c-kit also regulates spermatogonia proliferation in the adult animal. In mutant mice, abnormalities of the SCF/c-kit gene expression, such as gene deletion, point mutation, alternative splicing defect, lead to different types of spermatogenesis alterations (e.g. decrease in primordial germ cell migration, decrease in spermatogonia proliferation). More recently, defects in SCF/c-kit gene expression have also been shown in human testicular dysfunctions. Indeed, a reduction in SCF/c-kit expression has been evidenced in oligozoospermia/azoospermia associated with an increase in the germ cell apoptosis process. In addition, c-kit seems to be a good marker of seminoma testicular tumours. This review reports a large number of data--obtained essentially in animal models--that suggest an important role for the SCF/c-kit system in spermatogenesis and, as a corollary, its potential involvement in spermatogenic defects.

Cellular mechanisms of calcium phosphate ceramic degradation

Calcium phosphate (CaP) ceramics are widely used for bone substitution in orthopedic, maxillofacial and dental surgery. Many environmental factors are involved in the gradual degradation of calcium phosphate ceramic after implantation, including physiocochemical processes (dissolution-precipitation) and the effects of various cell types. Several of these cell types degrade ceramics by phagocytotic mechanisms (fibroblasts, osteoblasts, monocytes/macrophages) or by an acidic mechanism with a proton pump to reduce the pH of the microenvironment and resorb these synthetic substrates (osteoclasts). Various mesenchymal cells located at the implantation sites can induce the solubilization of CaP ceramics. Crystal-cell contacts were required to induce such crystal dissolution. Mesenchymal cells such as fibroblastic cells are also actively involved in the ceramic degradation process. In this context, CaP crystals underwent dissolution into the phagosome. If osteoclasts resorb CaP ceramics similarly to the natural bone, they possess a phagocytic capability. This phagocytosis mechanism consisted of three steps: crystal phagocytosis, disappearance of the endophagosome envelope membrane and fragmentation of phagocytosed crystals within the cytoplasm. Similar phenomenons have been observed during the phagocytic mechanism induced by monocytes/macrophages. The cellular mechanisms of CaP ceramic degradation are modulated by various parameters, such as the properties of the ceramic itself, the implantation sites and the presence of various proteins (cytokines, hormones, vitamins, ions, etc.). The cells involved in these mechanisms could intervene directly or indirectly through their cytokine/growth factor secretions and their sensitivity to the same molecules. This article reviews recent knowledge on the cellular mechanisms of calcium phosphate ceramic degradation.

Tumor necrosis factor-alpha stimulates lactate dehydrogenase A expression in porcine cultured sertoli cells: mechanisms of action

In the present study, we investigated the regulatory action of tumor necrosis factor-alpha (TNFalpha) on lactate dehydrogenase A (LDH A), a key enzyme involved in lactate production. To this end, use was made of a primary culture system of porcine testicular Sertoli cells. TNFalpha stimulated LDH A messenger RNA (mRNA) expression in a dose (ED50 = 2.5 ng/ml; 0.1 nM TNFalpha)-dependent manner. This stimulatory effect was time dependent, with an effect detected after 6 h of TNFalpha treatment and maximal after 48 h of exposition (5-fold; P<0.001). The direct effect of TNFalpha on LDH A mRNA could not be accounted for by an increase in mRNA stability (half-life = 9 h), but was probably due to an increase in LDH A gene transcription. Inhibitors of protein synthesis (cycloheximide), gene transcription (actinomycin D and dichlorobenzimidazole riboside), tyrosine kinase (genistein), and protein kinase C (bisindolylmaleimide) abrogated completely (actinomycin D, dichlorobenzimidazole riboside, cycloheximide, and genistein) or partially (bisindolylmaleimide) TNFalpha-induced LDH A mRNA expression. These observations suggest that the stimulatory effect of TNFalpha on LDH A mRNA expression requires protein synthesis and may involve a protein tyrosine kinase and protein kinase C. In addition, we report that LDH A mRNA levels were increased in Sertoli cells treated with FSH. However, although the cytokine enhances LDH A mRNA levels through increased gene transcription, the hormone exerts its stimulatory action through an increase in LDH A mRNA stability. The regulatory actions of the cytokine and the hormone on LDH A mRNA levels and therefore on lactate production may operate in the context of the metabolic cooperation between Sertoli and postmeiotic germ cells in the seminiferous tubules.

Seminal transforming growth factor-beta in normal and infertile men

Transforming growth factor-beta (TGFbeta) is a cytokine with autocrine and paracrine action in the testis and potent immunoregulatory and anti-inflammatory activities. In the present study, we examined the concentration of latent (acid-activatable) and free (active) TGFbeta in seminal plasma from normal subjects (n = 23) and infertile (n = 40) patients, by using a TGFbeta specific immunoenzymological assay, and a bioassay (CCL64 cell line growth inhibition) detecting any form of TGFbeta. Free TGFbeta1 was present in normal subjects at a concentration (1.82 +/- 1.06 ng/ml) close to that known to give maximal stimulation in vitro. In pathological groups, the mean concentrations were not significantly different from the normal ones. Latent TGFbeta1 was present in normal seminal plasma at a high concentration (92.4 +/- 29.2 ng/ml). In subjects with pathologies of both testis and genital apparatus, or with epididymal occlusion, mean latent TGFbeta1 concentrations were normal, whereas transferrin concentrations were lower. The concentrations found in the epididymal occlusion group indicate that TGFbeta1 is, for a large part, secreted by the genital tract. In the testicular pathology group, TGFbeta1 concentrations were 130.7 +/- 61.2 ng/ml, a mean not statistically different from normal, although higher. No differences were found between patients with high and normal blood plasma follicle stimulating hormone, and this is consistent with the notion that most TGFbeta1 in seminal plasma is not of testicular origin. The TGFbeta bioassay ensured that immunologically detected TGFbeta was present in a bioactive or bioactivatable form. Furthermore, the values found in normal and pathological seminal plasmas were usually higher than those detected by the immunoassay, suggesting that other forms of TGFbeta might be present. Together, the present data show that very large amounts of TGFbeta are present in human seminal plasma. The TGFbeta ligand assay in the seminal plasma appears to indicate no differences between normal and infertile subjects.

Prolactin receptors are expressed and hormonally regulated in rat Sertoli cells

In this study, the protein and mRNA expression of the short and long forms of Prolactin (PRL) receptors (PRL-R) were examined by means of Northern and Western blotting analyses in rat testicular Sertoli cells. Transcripts for the short and long forms of PRL-R were detected with specific probes, five major mRNA species of about 1.9, 2.6, 3.0, 3.7 and 5 kb for the short form and two of about 10 and 1.3 kb for the long form. Under reducing conditions, the use of a specific antibody for the short form revealed a major molecular species of approximately 45 kDa. Two groups of molecular species were detected for the long form, several bands with high molecular masses (110-300 kDa) and others about 45-60 kDa. Finally, the expression of the long form of PRL-R was shown to be hormonally regulated as it was inhibited by follicle stimulating hormone (FSH) (ED50 = 5 ng/ml). Together, the localisation of PRL receptors to Sertoli cells as well as the regulatory action of FSH on these receptors suggest that PRL and or (a) PRL-like activity(ies) might be considered as (a) potential regulator(s) of spermatogenesis.

In vitro regulation of rat Sertoli cell transferrin expression by tumor necrosis factor alpha and retinoic acid

In the present study, we examined the in vitro regulation of 20-day-old rat Sertoli cell transferrin expression by tumor necrosis factor alpha (TNFalpha), a paracrine factor produced by germ cells. Addition of TNFalpha to highly purified cultured Sertoli cells resulted in a dose and time-dependent enhancement in the levels of transferrin mRNA (Northern-blot) and protein (RadioImmunoAssay) with an ED50 of 120 pM. Co-treatment of Sertoli cells with the optimal dose of retinoic acid (RA, a potent inducer of transferrin) and TNFalpha induced a stimulation of transferrin that was significantly higher than the FIRT combination, a well known mixture of transferrin activators. Actinomycin D inhibited the effects of TNFalpha and of RA, suggesting that ongoing RNA synthesis was required to enhance transferrin. We next demonstrated that RA and TNFalpha exerted additive effects on transferrin expression as assessed by dose-response and kinetics studies. Moreover pre-treatment with RA, while greatly increasing the amount of transferrin produced, did not modify Sertoli cell responsiveness to TNFalpha. Together these results show that TNFalpha and RA are likely to act independently, additively and at least at the transcriptional level to increase transferrin expression.

Regulation by pH of the alternative splicing of the stem cell factor pre-mRNA in the testis

Proliferation and differentiation of progenitor stem cells are mainly controlled by diffusible and adhesion molecules. Stem cell factor (SCF), an essential regulator of spermatogenesis produced by Sertoli cells, utilize both modes of cell to cell communication. Indeed, SCF exists in soluble (SCFs) and membrane-bound (SCFm) forms, which are required for a complete spermatogenesis, and are generated by alternative splicing of optional exon 6, encoding sites of proteolysis. We show that in the mouse testis, the alternative splicing of SCF is developmentally regulated. SCFs predominates in fetal and neonatal gonads and is then replaced by SCFm in the prepubertal and adult gonads. By sequencing SCF exon 6, we show that the flanking intronic sequences perfectly follow the gt-at rule, suggesting that the basal splicing machinery might not be responsible by itself for exon 6 skipping. Moreover, freshly isolated Sertoli cells mainly express SCFm, but a switch to SCFs occurs after 48 h of culture. We found that this change can be prevented by acidification of the culture medium at pH 6.3 or by addition of lactate. The sustained synthesis of SCFm at low pH was no longer observed in the presence of cycloheximide, suggesting that SCF exon 6 skipping requires de novo protein synthesis. Accordingly, UV cross-linking experiments show that nuclear Sertoli cell protein(s) bind in a sequence-specific manner to exon 6. Together, our data allow the proposal of an integrated mechanism in which the synthesis of lactate by Sertoli cells is used in the same time as an energetic substrate for germ cells and as a promoter of their survival/proliferation through the production of SCFm.

Interleukin 1alpha stimulates lactate dehydrogenase A expression and lactate production in cultured porcine sertoli cells

By using cultured porcine Sertoli cells as a model, the action of interleukin 1alpha (IL-1alpha) on lactate production and the site of this action were studied. IL-1alpha stimulated Sertoli cell lactate production in a time- and dose-dependent manner (with a half-maximal effect [ED50] of 6 pM). Two major sites involved in IL-1alpha action were identified. First, IL-1alpha was shown to increase the uptake of glucose substrate in a time- and dose-dependent manner. The maximal effect, with an ED50 of 10 pM, was observed after 24 h of treatment. Second, IL-1alpha increased the activity of the lactate dehydrogenase (LDH) A4 isoform, which is involved in the conversion of pyruvate into lactate. This increase in LDH A4 activity was detected at 12 h and was maximal, with an ED50 of 9 pM, after 24-h treatment with IL-1alpha. The increase was related to an increase in LDH A4 expression, since IL-1alpha stimulated LDH A mRNA (size: 1.5 kilobases, evidenced through Northern blotting analysis) in a dose- and time-dependent manner. Assuming that IL-1alpha might be produced in the seminiferous tubules by both Sertoli and germ cells, which utilize lactate for their energy metabolism, we suggest that these results together show 1) that the cytokine may represent a signal in the metabolic cooperation existing between Sertoli cells and germ cells, and 2) that a redistribution of LDH isoforms in favor of LDH A4 under IL-1alpha control is a key mechanism(s) in such cooperation used by germ cells to enhance lactate production in Sertoli cells.

Residual bodies stimulate rat Sertoli cell plasminogen activator activity

Previous studies suggested indirectly that residual bodies (RB) may play a role in the regulation of the proteolytic system within the testis and in the coordination of the spermatogenetic process. In the present study, we examined the effects of RB recovered from adult rat testes by centrifugal elutriation on Sertoli cell plasminogen activator (PA) levels, by zymography and ELISA procedures. Addition of RB to Sertoli cell cultures prepared from 20-day-old rat testes resulted in a dramatic stimulation of PA. Effects were dose- and time-dependent. Phagocytosis of RB by Sertoli cells leads to a rapid stimulation of Sertoli cell interleukin-1alpha (IL-1alpha), a cytokine potentially involved in the regulation of spermatogenesis; the effects of IL-1alpha were investigated. We found that IL-1alpha augmented PA levels and that immunodepletion of Sertoli cell-RB cocultures with anti-IL-1alpha antibodies abrogated the stimulatory effects of RB on PA. Together, the present findings indicate that RB enhance Sertoli cell PA and that IL-1alpha may be involved in that control.

Plasminogen activator inhibitor-1 is expressed in cultured rat Sertoli cells

Sertoli cells secrete plasminogen activators (PAs) on both sides of the blood-testis barrier, i.e., in the basal and apical compartments of the seminiferous tubules, whereas peritubular cells secrete plasminogen activator inhibitor-1 (PAI-1), a fast-acting and specific PA inhibitor. While it is likely that PAI-1 produced by peritubular cells counteracts the basal secretion of PA, the nature of the PA inhibitor acting in the apical compartment remains to be demonstrated. In the present study, we showed that Sertoli cells recovered from 20-day-old rats and cultured contained a transcript of 3-3.2 kilobases, which hybridized specifically to a PAI-1 cDNA probe (Northern blot). We verified that the observed PAI-1 transcript could not result solely from the peritubular cells (weakly contaminating the Sertoli cell cultures), by comparing PAI-1 mRNA levels of Sertoli and peritubular cells recovered from 20-day-old rats and cultured. We also demonstrated that cultured Sertoli cells secreted a protein that complexed with tissue-type PA (zymography), indicating that it was biologically active. This protein comigrated with purified PAI-1 as a doublet of 46 and 49 kDa (Western blot). The trophic hormone FSH decreased PAI-1 messenger RNA as well as immunoreactive PAI-1 protein (probably via the cAMP protein kinase A pathway), whereas transforming growth factor ss1 and basic fibroblast growth factor (in a nanomolar concentration) increased both of these. These observations support the hypothesis that PAI-1 is expressed by Sertoli cells and is under a complex hormonal (FSH) and paracrine and/or autocrine control exerted at least by basic fibroblast growth factor and transforming growth factor ss1.