Diametric effects of bacterial endotoxin lipopolysaccharide on adrenal and Leydig cell steroidogenic acute regulatory protein

How Does Maternal Lipopolysaccharide Exposure Impact Prenatal Testicular Development in Rats, and Could α-Tocopherol Provide a Protective Effect? A Histological, Immunohistochemical and Biochemical Study

BACKGROUND

Lipopolysaccharides or endotoxins trigger proinflammatory cytokines and nitric oxide release, whereas α-tocopherol protects cells from oxidative damage. This study investigated the effects of maternal lipopolysaccharide exposure on prenatal testicular development in male rat offspring and assessed α-tocopherol's protective role.

METHODS

Forty pregnant female rats were divided into four groups. Group I (control) included a negative control receiving normal saline and a positive control receiving 30 mg/kg of α-tocopherol intraperitoneally from the 3rd to 18th gestational day. Group II received 50 mg/kg of lipopolysaccharides intraperitoneally from the 13th to 17th gestational day, whereas Group III received both α-tocopherol and lipopolysaccharides at the same dosages. On the seventh day postpartum, fetuses were weighed, sexed, and dissected; sera from male fetuses were collected for biochemical analysis, and fetal testes were used for histology, immunohistochemistry, and morphometry.

RESULTS

Rats treated with lipopolysaccharide showed reduced body weight, testosterone, and luteinizing hormone levels, with histopathological changes, including thickened testicular capsules and abnormalities in the number, size, shape, and cellular components of seminiferous tubules. These adverse effects were improved by α-tocopherol supplementation.

CONCLUSION

We concluded that lipopolysaccharide exposure during pregnancy impairs testicular development and steroidogenesis, which are ameliorated by α-tocopherol coadministration.

Responses of testosterone hormone and important inflammatory cytokines in bucks after challenge with Mannheimia haemolytica A2 and its LPS endotoxin

Previous studies have shown that Mannheimia haemolytica A2 is the principal microorganism causing pneumonic mannheimiosis, a major bacterial respiratory disease among sheep and goats. The effect of this bacteria on the respiratory system is well-established. However, its effect on the reproductive physiology remains unclear. Therefore, this study aimed to determine the alterations in the level of pro-inflammatory cytokines and testosterone hormone post-inoculation with M. haemolytica serotype A2 and its lipopolysaccharide (LPS) endotoxin which were hypothesized to affect the reproductive functions of bucks. Twelve clinically healthy adult male goats were divided equally into three groups. Goats in group 1 were treated with 2 ml of sterile phosphate-buffered saline (PBS) pH 7.0 intranasally (negative control), group 2 with 2 ml of 10⁹ colony-forming unit (CFU) of M. haemolytica serotype A2 intranasally (positive control), and group 3 were treated with 2 ml of lipopolysaccharide extracted from 10⁹ CFU of M. haemolytica serotype A2 intravenously. Following inoculation, blood samples were collected via jugular venipuncture into plain tubes at pre-determined intervals for serum collection to determine the concentration of interleukin (IL)-1β, IL6, tumor necrosis factor (TNF)-α, and testosterone hormone by using commercial ELISA test kits. Results from this study demonstrated that the inoculation of M. haemolytica A2 and its LPS increases the concentration of pro-inflammatory cytokines but decreases the concentration of testosterone hormone in challenged animals at most time points throughout the 56 days experimental period (p < 0.05). This study suggests that the M. haemolytica A2 and its LPS could alter the concentration of pro-inflammatory cytokines and testosterone hormone, which in turn, may negatively affect the reproductive functions of bucks.

Obesity related metabolic endotoxemia is associated with oxidative stress and impaired sperm DNA integrity

Background

Obesity is known to be associated with inflammation, oxidative stress and a resulting reduction in sperm DNA integrity. Importantly, obesity is also reported to be associated with an increase in intestinal permeability with the passage of intestinal bacteria into the circulation (metabolic endotoxemia) that triggers a systemic state of inflammation and resultant oxidative stress. Therefore, we hypothesised that this obesity related increase in intestinal permeability and resultant metabolic endotoxemia (ME) may activate inflammation within the male reproductive tract, leading to increased reactive oxygen species production, sperm oxidative stress and a decline in DNA integrity.

Results

Our pilot study of 37 infertile men confirmed a significant positive correlation between body mass index (BMI), increased intestinal permeability (serum zonulin), metabolic endotoxaemia (LBP), sperm DNA oxidative damage (seminal 8 OhDG) and increasing levels of sperm DNA fragmentation (Halosperm). Metabolic endotoxemia was positively correlated with increasing levels of sperm DNA oxidative damage with this relationship remaining significant, even after adjustment for relevant confounders such as age, BMI and days of abstinence. These observations suggest that metabolic endotoxemia and its associated oxidative stress may be a key driver of sperm DNA damage in obese men.

Conclusion

This study confirms a link between obesity, increasing intestinal permeability and endotoxin exposure, and oxidative mediated sperm DNA damage. This warrants further investigation to fully understand the effect of metabolic endotoxemia on male reproductive function which could result in the new therapies to improve male fertility potential.

A test of the effects of androgens on immunity: No relationship between 11-ketotestosterone and immune performance in bluegill (Lepomis macrochirus)

The immunosuppressive effects of androgens are a key component of the immunocompetence handicap hypothesis (ICHH). Here, we use bluegill sunfish (Lepomis macrochirus) to test two predictions arising from this hypothesis: (1) natural circulating concentrations of the androgen 11-ketotestosterone (11-KT) will be negatively related with measures of immunity, and (2) immune stimulation will lower circulating 11-KT concentration. We found no evidence for a relationship between natural circulating 11-KT concentration and measures of immunity (lymphocyte and granulocyte counts, respiratory burst, cytokine mRNA levels), and an immune stimulation with Vibrio vaccine did not affect circulating 11-KT concentration. We also performed a meta-analysis of immune stimulation studies to help interpret our results, and report evidence suggesting that immune stimulation has weaker effects on androgen levels in fishes compared to other vertebrates. These results suggest that the ICHH may not apply to all vertebrates, although it remains premature to state what factors account for the weaker evidence in fishes that androgens are immunosuppressive.

Endotoxin-initiated inflammation reduces testosterone production in men of reproductive age

Inflammation, both acute and chronic, is associated with testosterone deficiency, raising the possibility of a direct causal link. One potential trigger for inflammation in obese men is the passage of intestinal bacteria into the circulation due to a breakdown in mucosal barrier integrity. Recently, we hypothesized that this endotoxin exposure may cause androgen deficiency in obese men. To test this hypothesis, we analyzed the relationship between serum levels of lipopolysaccharide-binding protein (LBP), an indirect measure of endotoxin exposure, against male reproductive hormones, inflammatory markers (C-reactive protein, IL-1β, IL-6, TNF-α), and adiposity in 75 men. Adiposity was positively correlated with endotoxin exposure (LBP) and inflammation (C-reactive protein, IL-6) and negatively correlated with testosterone. Furthermore, endotoxemia (LBP) was negatively correlated with serum testosterone but positively correlated with IL-6. Multivariate analysis revealed a significant, negative correlation between serum IL-6 and free testosterone. In a second interventional study, low-dose endotoxin challenge in lean men produced a transient inflammatory response that was followed by a decline in serum testosterone, without changes in LH or FSH, providing further evidence that endotoxin-driven inflammation may result in impaired Leydig cell function.

Histomorphometric evaluation of mice testicular tissue following short- and long-term effects of lipopolysaccharide-induced endotoxemia

Objective(s)::

Lipopolysaccharide (LPS)-induced endotoxemia is known to cause male infertility. This study was designed to explore the effects of bacterial LPS on histomorphometric changes of mice testicular tissues.

Materials and Methods:

In experiment 1, a pilot dose responsive study was performed with mice that were divided into five groups, receiving 36000, 18000, 9000, and 6750 µg/kg body weight (B.W) of LPS or only saline (control). White blood cells (WBC) were observed for 3 days after LPS inoculation. In experiment 2, two groups of mice were treated with 6750 µg/kg B.W of LPS or only saline (control). Five cases from each experimental group were sacrificed at 3, 30, and 60 days after LPS inoculation. Left testes were fixed in Bouin’s solution, and stained for morphometrical assays.

Results:

Time-course changes of WBC obtained from different doses of LPS-treated mice showed that inoculation of 6750 µg/kg B.W produced a reversible endotoxemia that lasts for 72 hr and so it was used in the second experiment. In experiment 2, during the first 3 days, no significant changes were observed in the evaluated parameters instead of seminiferous tubules diameter. Spermatogenesis, Johnsen’s score, meiotic index, and epithelial height were significantly affected at 30^th day. However, complete recovery was only observed for the spermatogenesis at day 60. Interestingly, deleterious effects of LPS on spermatogonia were only seen at 60^th day (P<0.05).

Conclusion:

Endotoxemia induced by LPS has long-term detrimental effects on spermatogonia and later stage germ cells, which are reversible at the next spermatogenic cycle.

A high-fat diet impairs reproduction by decreasing the IL1β level in mice treated at immature stage

Obesity causes low-grade inflammation that is involved in male infertility. Interleukin 1 beta (IL1β) plays an important role in this process. A high-fat diet (HFD) is the most common cause of obesity. However, the effect of a HFD on IL1β and its consequence in reproduction remain unclear. We established a HFD model in mice treated at immature stage (mice-TIS) and mice treated at mature stage (mice-TMS). Surprisingly, we found that a HFD decreased IL1β levels and was accompanied by an increase in testosterone in mice-TIS, while the reverse results were observed in mice-TMS. In addition, a HFD caused a reduction in testis macrophages and in the expression of inflammasome-related genes and proteins in mice-TIS. Furthermore, we found that IL1β inhibited testosterone secretion through down-regulating the gene expression of P450SCC and P450c17. However, the influence on mice-TIS that were induced by a HFD was recovered by stopping the HFD. In this study, we are the first to report that a HFD impairs the reproductive system by decreasing IL1β and enhancing testosterone levels in mice-TIS, which are different from the effects in mice-TMS. This provides new ideas for the treatment of obesity-induced infertility.

Effect of Lipopolysaccharide (LPS) Exposure on the Reproductive Organs of Immature Female Rats

Lipopolysaccharide (LPS), an endotoxin, elicits strong immune responses in mammals. Several lines of evidence demonstrate that LPS challenge profoundly affects female reproductive function. For example, LPS exposure affects steroidogenesis and folliculogenesis, resulting in delayed puberty onset. The present study was conducted to clarify the mechanism underlying the adverse effect of LPS on the delayed puberty in female rats. LPS was daily injected for 5 days (50 μg/kg, PND 25-29) to treated animals and the date at VO was evaluated through daily visual examination. At PND 39, animals were sacrificed, and the tissues were immediately removed and weighed. Among the reproductive organs, the weights of the ovaries and oviduct from LPS-treated animals were significantly lower than those of control animals. There were no changes in the weights of uterus and vagina between the LPS-treated and their control animals. Immunological challenge by LPS delayed VO. Multiple corpora lutea were found in the control ovaries, indicating ovulations were occurred. However, none of corpus luteum was present in the LPS-treated ovary. The transcription level of steroidogenic acute regulatory protein (StAR), CYP11A1, CYP17A1 and CYP19 were significantly increased by LPS treatment. On the other hand, the levels of 3β- HSD, 17β-HSD and LH receptor were not changed by LPS challenge. In conclusion, the present study demonstrated that the repeated LPS exposure during the prepubertal period could induce multiple alterations in the steroidogenic machinery in ovary, and in turn, delayed puberty onset. The prepubertal LPS challenge model used in our study is useful to understand the reciprocal regulation of immune (stress) - reproductive function in early life.

Gut Endotoxin Leading to a Decline IN Gonadal function (GELDING) - a novel theory for the development of late onset hypogonadism in obese men

Obesity is an increasing public health problem, with two-thirds of the adult population in many Western countries now being either overweight or obese. Male obesity is associated with late onset hypogonadism, a condition characterised by decreased serum testosterone, sperm quality plus diminished fertility and quality of life. In this paper we propose a novel theory underlying the development of obesity related hypogonadism- the GELDING theory (Gut Endotoxin Leading to a Decline IN Gonadal function). Several observational studies have previously reported an association between obesity related hypogonadism (low testosterone) and systemic inflammation. However, for the first time we postulate that the trans-mucosal passage of bacterial lipopolysaccharide (LPS) from the gut lumen into the circulation is a key inflammatory trigger underlying male hypogonadism. Obesity and a high fat/high calorie diet are both reported to result in changes to gut bacteria and intestinal wall permeability, leading to the passage of bacterial endotoxin (lipopolysaccharide- LPS) from within the gut lumen into the circulation (metabolic endotoxaemia), where it initiates systemic inflammation. Endotoxin is known to reduce testosterone production by the testis, both by direct inhibition of Leydig cell steroidogenic pathways and indirectly by reducing pituitary LH drive, thereby also leading to a decline in sperm production. In this paper we also highlight the novel evolutionary benefits of the GELDING theory. Testosterone is known to be a powerful immune-suppressive, decreasing a man's ability to fight infection. Therefore we postulate that the male reproductive axis has evolved the capacity to lower testosterone production during times of infection and resulting endotoxin exposure, decreasing the immunosuppressive influence of testosterone, in turn enhancing the ability to fight infection. While this response is adaptive in times of sepsis, it becomes maladaptive in the setting of "non-infectious" obesity related metabolic endotoxaemia.

IGF1R signaling is necessary for FSH-induced activation of AKT and differentiation of human Cumulus granulosa cells

CONTEXT

FSH is routinely administered to in vitro fertilization patients to induce follicle maturation. During this process, granulosa cells differentiate and acquire specific functional characteristics that are required to coordinate ovulation and oocyte maturation.

OBJECTIVE

The objective of the study was to gain insight into the molecular mechanisms regulating human granulosa cell differentiation. Design, Setting, Patients, and Interventions: Cumulus and mural granulosa cells were isolated from the follicular aspirates of in vitro fertilization patients and analyzed immediately or cultured in serum-free media in the presence of FSH, IGFs, or an inhibitor of type I IGF receptor (IGF1R) activity.

MAIN OUTCOME

We quantified the mRNA and protein levels of steroidogenic enzymes, components of the IGF system, and gonadotropin receptors; measured 17β-estradiol levels; and examined the activation of intracellular signaling pathways to assess the granulosa cell differentiation as well as the FSH and IGF actions in both cumulus and mural cells.

RESULTS

In freshly isolated cells, LH receptor (Lhr) and steroidogenic acute regulator (Star) were expressed at lower levels in cumulus than mural cells, whereas FSH receptor (Fshr) and anti-Müllerian hormone (Amh) were expressed at higher levels in cumulus than mural cells. In vitro, the expression of Igf2, the differentiation markers Lhr, Star, and Cyp19a1 (aromatase) as well as 17β-estradiol production remained low in untreated cumulus cells but increased significantly after FSH treatment. Strikingly, this stimulatory effect of FSH was abolished by the inhibition of IGF1R activity. FSH-induced activation of v-akt murine thymoma viral oncogene homolog 3 (AKT) required IGF1R activity, and overexpression of constitutively active AKT rescued the induction of differentiation markers and 17β-estradiol production by FSH in the presence of the IGF1R inhibitor.

CONCLUSIONS

The cumulus cell response to FSH resembles the differentiation of preantral to preovulatory granulosa cells. This differentiation program requires IGF1R activity and subsequent AKT activation.

Induction of androgen formation in the male by a TAT-VDAC1 fusion peptide blocking 14-3-3ɛ protein adaptor and mitochondrial VDAC1 interactions

Low testosterone (T), a major cause of male hypogonadism and infertility, is linked to mood changes, fatigue, osteoporosis, reduced bone-mass index, and aging. The treatment of choice, T replacement therapy, has been linked with increased risk for prostate cancer and luteinizing hormone (LH) suppression, and shown to lead to infertility, cardiovascular diseases, and obesity. Alternate methods to induce T with lower side effects are desirable. In search of the mechanisms regulating T synthesis in the testes, we identified the 14-3-3ɛ protein adaptor as a negative regulator of steroidogenesis. Steroidogenesis begins in mitochondria. 14-3-3ɛ interacts with the outer mitochondrial membrane voltage-dependent anion channel (VDAC1) protein, forming a scaffold that limits the availability of cholesterol for steroidogenesis. We report the development of a tool able to induce endogenous T formation. Peptides able to penetrate testes conjugated to 14-3-3ɛ site of interaction with VDAC1 blocked 14-3-3ɛ-VDAC1 interactions while at the same time increased VDAC1-translocator protein (18 kDa) interactions that induced steroid formation in rat testes, leading to increased serum T levels. These peptides rescued intratesticular and serum T formation in adult male rats treated with gonadotropin-releasing hormone antagonist, which dampened LH and T production.

Effect of chocolate and Propolfenol on rabbit spermatogenesis and sperm quality following bacterial lipopolysaccharide treatment

The aims of the study were to evaluate the effects of chocolate and propolis-enriched diets on rabbit spermatogenesis, sperm motility, and ultrastructure following bacterial lipopolysaccharide (LPS) treatment. Thirty-two New Zealand White rabbits were divided into four groups. The LPS-Propolfenol(®) group received propolis (500 mg/kg/day) in their diet for 15 days, while the LPS-chocolate group was fed 70% cacao chocolate (1 g/1 kg/day) for the same period. Following the diet treatments, rabbits in the LPS-Propolfenol(®) and LPS-chocolate groups, and an LPS group received a single intraperitoneal dose of 50 μg/kg LPS, and the control group received only saline. Kinematic sperm traits were evaluated with a computer assisted sperm analyzer (CASA) system, and ultrastructural characteristics were examined by transmission electron microscopy (TEM). Testicular and epididymal tissues were observed by light microscopy and TEM and multiplex real time reverse transcriptase-polymerase chain reaction (RT-PCR) assay was used to detect and quantify toll-like receptor-4 (TLR-4) gene expression. The values of the analyzed semen parameters of rabbits treated with LPS-Propolfenol(®) and LPS-chocolate did not show any variations compared with the control group, but they were lower in rabbits treated only with LPS. Alterations observed in the testicular tissue of LPS treated-rabbits were not detected in specimens from the LPS-chocolate and LPS-Propolfenol(®) groups, which showed normal spermatogenesis. The TLR-4 mRNA expression was similar in controls, in LPS treated, and in LPS-chocolate groups, but it was significantly (p < 0.01) decreased in LPS-Propolfenol(®) rabbits. In conclusion, a chocolate and propolis-enriched diet showed a protective effect on the spermatogenetic process of buck rabbits following LPS treatment.

Immunoprotective properties of primary Sertoli cells in mice: potential functional pathways that confer immune privilege

Primary Sertoli cells isolated from mouse testes survive when transplanted across immunological barriers and protect cotransplanted allogeneic and xenogeneic cells from rejection in rodent models. In contrast, the mouse Sertoli cell line (MSC-1) lacks immunoprotective properties associated with primary Sertoli cells. In this study, enriched primary Sertoli cells or MSC-1 cells were transplanted as allografts into the renal subcapsular area of naive BALB/c mice, and their survival in graft sites was compared. While Sertoli cells were detected within the grafts with 100% graft survival throughout the 20-day study, MSC-1 cells were rejected between 11 and 14 days, with 0% graft survival at 20 days posttransplantation. Nonetheless, the mechanism for primary Sertoli cell survival and immunoprotection remains unresolved. To identify immune factors or functional pathways potentially responsible for immune privilege, gene expression profiles of enriched primary Sertoli cells were compared with those of MSC-1 cells. Microarray analysis identified 2369 genes in enriched primary Sertoli cells that were differentially expressed at ±4-fold or higher levels than in MSC-1 cells. Ontological analyses identified multiple immune pathways, which were used to generate a list of 340 immune-related genes. Three functions were identified in primary Sertoli cells as potentially important for establishing immune privilege: suppression of inflammation by specific cytokines and prostanoid molecules, slowing of leukocyte migration by controlled cell junctions and actin polymerization, and inhibition of complement activation and membrane-associated cell lysis. These results increase our understanding of testicular immune privilege and, in the long-term, could lead to improvements in transplantation success.

Effects of apigenin on steroidogenesis and steroidogenic acute regulatory gene expression in mouse Leydig cells

Previous studies reported that the age-related decline in testosterone biosynthesis is associated with a decrease in the steroidogenic acute regulatory (StAR) protein which regulates the rate-limiting step of testosterone biosynthesis. To explore the possibility of delaying this decline using a dietary approach, we have examined the effect of a natural flavonoid, apigenin, on StAR gene expression in mouse Leydig cells. Incubation of these cells with the flavonoid enhanced cyclic adenosine monophosphate (cAMP)-induced steroidogenesis and StAR protein expression. The results from the analyses of StAR mRNA by reverse transcription-polymerase chain reaction and the luciferase assays of StAR promoter activity indicated that this flavonoid enhanced StAR gene expression at the level of transcription. Further studies showed that apigenin blocked the thromboxane A2 receptor and interrupted the signaling through the cyclooxygenase-2-thromboxane A synthase-thromboxane A2-receptor pathway, resulting in a reduction of DAX-1 (dosage sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene-1) protein, a transcriptional repressor of StAR gene expression. When DAX-1 protein was reduced, the sensitivity of the Leydig cells was dramatically enhanced, with sub-threshold level of cAMP being able to induce maximal levels of StAR protein expression and steroid hormone production. The present study suggests a potential application of apigenin to improve StAR protein expression and steroidogenic sensitivity of aging Leydig cells.

Localization and functional activity of cytochrome P450 side chain cleavage enzyme (CYP11A1) in the adult rat kidney

Cumulative evidence demonstrated effective downstream metabolism of pregnenolone in renal tissue. The aim of this study was to evaluate the expression and functional activity of cytochrome P450 side chain cleavage enzyme (CYP11A1), which converts cholesterol into pregnenolone, in adult rat kidney. Immunohistochemical labeling for CYP11A1 was observed in renal cortex and medulla, on structures identified as distal convoluted tubule and thick ascending limb of Henle's loop, respectively. Immunoblotting analysis corroborated the renal expression of the protein in inner mitochondrial membrane fractions. The incubation of isolated mitochondria with the membrane-permeant cholesterol analogue 22R-hydroxycholesterol resulted in efficient formation of pregnenolone, the immediate precursor for the synthesis of all the steroid hormones. The low progesterone production rate observed in these experiments suggested a poor activity of 3β-hydroxysteroid dehydrogenase enzyme in renal mitochondria. The steroidogenic acute regulatory protein (StAR), involved in the mitochondrial import of cholesterol, was detected in renal tissue at both mRNA and protein level. Immunostaining for StAR showed similar distribution to that observed for CYP11A1. The expression of StAR and CYP11A1 was found to be higher in medulla than in cortex. This enhanced expression of steroidogenesis-related proteins correlated with a greater pregnenolone synthesis rate and higher steroid hormones tissular content measured in medulla. In conclusion, we have established the expression and localization of StAR and CYP11A1 protein, the ability of synthesizing pregnenolone and a region-specific content of sex hormones in the adult rat kidney. These data clearly show that the kidney is a steroid hormones synthesizing organ. It is proposed that the existence in the kidney of complete steroidogenic machinery would respond to a physiological significance.

Sildenafil treatment in vivo stimulates Leydig cell steroidogenesis via the cAMP/cGMP signaling pathway

Sildenafil citrate (Viagra), a cGMP-selective phosphodiesterase (PDE) inhibitor, is widely used to treat erectile dysfunction and pulmonary arterial hypertension. In contrast to its well established action on erectile dysfunction, little is known on the action of sildenafil on cGMP/cAMP signaling and testicular steroidogenesis. This study was designed to assess the effects of prolonged sildenafil treatment on NO synthase-dependent signaling and steroidogenic function of rat Leydig cells. Male adult rats were treated with Viagra (1.25 mg/kg body wt) daily for 30 days. In our studies, serum testosterone and ex vivo testosterone production significantly increased in sildenafil-treated animals. Human chorionic gonadotropin-stimulated testosterone production and cAMP accumulation were also significantly higher in Leydig cells obtained from sildenafil-treated rats. The expression of soluble guanylyl cyclase (GUCY1) subunits (Gucy1a1, Gucy1b1) significantly increased; cAMP-specific Pde4a, cGMP-specific Pde6c, and dual Pde1c and Nos2 were inhibited and expression of Nos3, protein kinase G1 (Pkg1), and Pde5 remained unchanged. Treatment of purified Leydig cells with NO donor caused a dose-dependent increase in both testosterone and cGMP production. Testosterone and cGMP production was significantly higher in Leydig cells obtained from sildenafil-treated animals. The stimulatory effect of NO donor was significantly enhanced by saturating concentrations of hCG in both Leydig cells obtained from control and sildenafil-treated animals. Occurrence of mature steroidogenic acute regulatory protein also increased in sildenafil treated animals in accord with increased cAMP and cGMP production. In summary, inhibition of PDE activity during prolonged sildenafil treatment increased serum testosterone level and Leydig cells' steroidogenic capacity by coordinated stimulatory action on cAMP and cGMP signaling pathway.

Blocking L-type calcium channels reduced the threshold of cAMP-induced steroidogenic acute regulatory gene expression in MA-10 mouse Leydig cells

Previous studies have reported the roles of Ca(2+) in steroidogenesis. The present study has investigated an inhibitory effect of Ca(2+) influx through L-type Ca(2+) channels on gene expression of steroidogenic acute regulatory (STAR) protein that regulates the transfer of substrate cholesterol to the inner mitochondrial membrane for steroidogenesis. Blocking Ca(2+) influx through L-type Ca(2+) channels using the selective Ca(2+) channel blocker, nifedipine, markedly enhanced cAMP-induced STAR protein expression and progesterone production in MA-10 mouse Leydig cells. This was confirmed by utilization of different L-type Ca(2+) channel blockers. Reverse transcription-PCR analyses of Star mRNA and luciferase assays of Star promoter activity indicated that blocking Ca(2+) influx through L-type Ca(2+) channels acted at the level of Star gene transcription. Further studies showed that blocking the Ca(2+) channel enhanced Star gene transcription by depressing the expression of DAX-1 (NR0B1 as listed in the MGI Database) protein, a transcriptional repressor of Star gene expression. It was also observed that there is a synergistic interaction between nifedipine and cAMP. Normally, sub-threshold levels of cAMP are unable to induce steroidogenesis, but in the presence of the L-type Ca(2+) channel blocker, they increased STAR protein and steroid hormone to the maximal levels. However, in the absence of minimal levels of cAMP, none of the L-type Ca(2+) channel blockers are able to induce Star gene expression. These observations indicate that Ca(2+) influx through L-type Ca(2+) channels is involved in an inhibitory effect on Star gene expression. Blocking L-type Ca(2+) channel attenuated the inhibition and reduced the threshold of cAMP-induced Star gene expression in Leydig cells.

Targeting and insertion of the cholesterol-binding translocator protein into the outer mitochondrial membrane

Translocator protein (18 kDa, TSPO), previously known as the peripheral-type benzodiazepine receptor, is an outer mitochondrial membrane (OMM) protein necessary for cholesterol import and steroid production. We reconstituted the mitochondrial targeting and insertion of TSPO into the OMM to analyze the signals and mechanisms required for this process. Initial studies indicated the formation of a mitochondrial 66 kDa complex through Blue Native-PAGE analysis. The formation of this complex was found to be dependent on the presence of ATP and the cytosolic chaperone Hsp90. Through mutational analysis we identified two areas necessary for TSPO targeting, import, and function: amino acids 103-108 (Schellman motif), which provide the necessary structural orientation for import, and the cholesterol-binding C-terminus required for insertion. Although the translocase of the outer mitochondrial membrane (TOM) complex proteins Tom22 and Tom40 were present in the OMM, the TOM complex did not interact with TSPO. In search of proteins involved in TSPO import, we analyzed complexes known to interact with TSPO by mass spectrometry. Formation of the 66 kDa complex was found to be dependent on an identified protein, Metaxin 1, for formation and TSPO import. The level of import of TSPO into steroidogenic cell mitochondria was increased following treatment of the cells with cAMP. These findings suggest that the initial targeting of TSPO to mitochondria is dependent upon the presence of cytosolic chaperones interacting with the import receptor Tom70. The C-terminus plays an important role in targeting TSPO to mitochondria, whereas its import into the OMM is dependent upon the presence of the Schellman motif. Final integration of TSPO into the OMM occurs via its interaction with Metaxin 1. Import of TSPO into steroidogenic cell mitochondria is regulated by cAMP.

Involvement of the thromboxane A2 receptor in the regulation of steroidogenic acute regulatory gene expression in murine Leydig cells

Recent studies suggested an involvement of thromboxane A2 in cyclooxygenase-2-dependent inhibition of steroidogenic acute regulatory (StAR) gene expression. The present study further investigated the role of thromboxane A2 receptor in StAR gene expression and steroidogenesis in testicular Leydig cells. The thromboxane A2 receptor was detected in several Leydig cell lines. Blocking thromboxane A2 binding to the receptor using specific antagonist SQ29548 or BM567 resulted in dose-dependent increases in StAR protein and steroid production in MA-10 mouse Leydig cells. The results were confirmed with Leydig cells isolated from rats. StAR promoter activity and StAR mRNA level in the cells were also increased after the treatments, suggesting an involvement of the thromboxane A2 receptor in StAR gene transcription. Furthermore study indicated that blocking the thromboxane A2 receptor reduced dosage sensitive sex reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene 1 protein, a transcriptional repressor of StAR gene expression. Specific binding of the antagonists to the receptors on cellular membrane was demonstrated by binding assays using (3)H-SQ29548 and binding competition between (3)H-SQ29548 and BM567. Whereas SQ29548 enhanced cAMP-induced StAR gene expression, in the absence of cAMP, it was unable to increase StAR protein and steroidogenesis. However, when the receptor was blocked by the antagonist, subthreshold levels of cAMP were able to induce maximal levels of StAR protein expression, suggesting that blocking the thromboxane A2 receptor increase sensitivity of MA-10 cells to cAMP stimulation. Taken together, the results from the present and previous studies suggest an autocrine loop, involving cyclooxygenase-2, thromboxane A synthase, and thromboxane A2 and its receptor, in cyclooxygenase-2-dependent inhibition of StAR gene expression.

Expression and modulation of translocator protein and its partners by hypoxia reoxygenation or ischemia and reperfusion in porcine renal models

Translocator protein (TSPO), formerly known as the peripheral-type benzodiazepine receptor, is an 18-kDa drug- and cholesterol-binding protein localized to the outer mitochondrial membrane and implicated in a variety of cell and mitochondrial functions. To determine the role of TSPO in ischemia-reperfusion injury (IRI), we used both in vivo and in vitro porcine models: an in vivo renal ischemia model where different conservation modalities were tested and an in vitro model where TSPO-transfected porcine proximal tubule LLC-PK(1) cells were exposed to hypoxia and oxidative stress. The expression of TSPO and its partners in steroidogenic cells, steroidogenic acute regulatory protein (StAR) and cytochrome P-450 side chain cleavage CYP11A1, as well as the impact of TSPO overexpression and exposure to TSPO ligands in vitro in hypoxia-ischemia conditions were investigated. Hypoxia induced caspase activation, reduction of ATP content, and LLC-PK(1) cell death. Transfection and overexpression of TSPO rescued the cells from the detrimental effects of hypoxia and reoxygenation. Moreover, TSPO overexpression was accompanied by a reduction of H(2)O(2)-induced necrosis. TSPO drug ligands did not affect TSPO-mediated functions. In vivo, TSPO expression was modulated by IRI and during regeneration particularly in proximal tubule cells, which do not express this protein at the basal level. Under the same conditions, StAR and CYP11A1 protein and gene expression was reduced without apparent relation to TSPO changes. Pregnenolone was identified and measured in the pig kidney. Pregnenolone synthesis was not affected by the experimental conditions used. Taken together, these results indicate that changes in TSPO expression in kidney regenerating tissue could be important for renal protection and maintenance of kidney function.

Immune activation suppresses plasma testosterone level: a meta-analysis

Females often select mates on the basis of sexual signals, which can be reliable indicators of male quality when the costliness of these signals prevents cheating. The immunocompetence handicap hypothesis (ICHH) provides a mechanistic explanation of these costs, by proposing a trade-off between immune function and sexual displays. This trade-off arises because testosterone enhances sexual signals, but suppresses immune function. Many studies have investigated the ICHH by administrating testosterone, and a recent meta-analysis found little evidence that testosterone suppressed immune function. However, another component of the ICHH, which has received less empirical interest, suggests that there may also be an interaction in the other direction, with immune activation suppressing testosterone levels. We present a meta-analysis to test for this effect. Overall, there was a strong suppressive effect of experimental immune activation on testosterone levels (r=-0.52), regardless of whether live pathogens or non-pathogenic antigens were used to challenge the immune system. The latter is important because it shows that immune activation per se suppresses testosterone levels. Thus, a trade-off between immunocompetence and sexual displays may primarily be generated by the effect of immune activation on testosterone, rather than the opposite effect that has received most attention.

The adaptive response of adult rat Leydig cells to repeated immobilization stress: the role of protein kinase A and steroidogenic acute regulatory protein

The ability of immobilization stress (IMO) to decrease Leydig cell steroidogenesis and serum androgen concentration has been previously observed, but the possible mechanism(s) involved in the adaptation to prolonged or repeated stress have not been identified. In this study, we investigated whether the Leydig cells obtained from adult rats subjected to acute (15 min, 30 min or 2 h) and repeated (2 or 10 days, 2 h daily) IMO show adaptive mechanism(s) in response to stress-impaired steroidogenesis. The results showed that basal and human chorionic gonadotropin-stimulated cAMP production by Leydig cells isolated from rats exposed to both acute and repeated IMO was significantly reduced. Despite the reduced cAMP production, immunoblot analysis revealed increased immunoreactivity for both protein kinase A (PKA) and steroidogenic acute regulatory (StAR) protein in Leydig cells obtained from rats repeatedly exposed to IMO. Also, the phosphorylation and production of mature StAR protein was evident during exposure of rats to repeated IMO treatment. Treatment with cholesterol, the steroid substrate transported into mitochondria by StAR, significantly increased androgen and progesterone production by Leydig cells isolated from rats exposed to repeated IMO. In contrast, when other steroid substrates (22(R)-OH-cholesterol, pregnenolone, progesterone, Delta4-androstenedione) were present in the culture media, Leydig cell steroidogenesis was still reduced by IMO. Thus, PKA-mediated phosphorylation of StAR protein is an important mechanism in the adaptive response of Leydig cells to repeated IMO.

Morphological relationships and leukocyte influence on steroid production in the epigonal organ-ovary complex of the skate, Leucoraja erinacea

In elasmobranchs, a unique association exists between an immune tissue, the epigonal organ (EO), and the gonads. In this study, the histological and vascular relationships of the EO and ovarian follicles of the little skate, Leucoraja erinacea, were assessed. Perfusions of Evans blue dye and Batson's monomer showed a shared vascular pathway from the gonadal artery into the epigonal-ovary complex, with blood first entering the EO and then perfusing the ovarian follicles. Histological studies demonstrated direct cellular contact between epigonal leukocytes and the follicle wall (FW), as well as the presence of leukocytes between the steroidogenic theca and granulosa cells. In vitro analyses demonstrated that epigonal cells co-cultured with FW cells cause a dose-dependent inhibition of estrogen (E2) and testosterone (T) production. In contrast, conditioned media from epigonal leukocytes, stimulated or unstimulated with lipopolysaccharide (10 microg/ml), increase the production of E2 and T from FW cells of the ovaries. These studies provide a basis for further investigations of leukocyte secreted factors and cell contact modulation of follicular steroid production.

Protein kinase G-mediated stimulation of basal Leydig cell steroidogenesis

The androgen-secreting Leydig cells produce cGMP, but the pathways responsible for generation and actions of this intracellular messenger have been incompletely characterized in these cells. Here, we show the presence of mRNA transcripts for the membrane-bound and soluble guanylyl cyclases (sGC), the cGMP-specific phosphodiesterase 5, and the cGMP-dependent protein kinase I (PKG I) and PKG II in purified rat Leydig cells from adult animals. Stimulation of both guanylyl cyclases and inhibition of phosphodiesterase 5 in vitro were accompanied by elevations in cGMP and androgen production, whereas inhibition of sGC and PKG led to a decrease in steroidogenesis. The stimulatory action of cGMP on steroidogenesis was preserved in cells with inhibited cAMP-dependent protein kinases. Experiments with exogenously added substrates revealed the dependence of cGMP-induced progesterone and androgen synthesis on cholesterol but not on 22-OH cholesterol, pregnenolone, progesterone, and Delta(4)-androstenedione. Treatment with nitric oxide donor increased phosphorylation of the steroidogenic acute regulatory protein (StAR). In contrast, inhibition of sGC and PKG, but not protein kinase A, significantly reduced StAR phosphorylation. These results suggest that cGMP contributes to the control of basal steroidogenesis in Leydig cells through the PKG-dependent modification of the StAR protein.

Permethrin may disrupt testosterone biosynthesis via mitochondrial membrane damage of Leydig cells in adult male mouse

Permethrin, a popular synthetic pyrethroid insecticide used to control noxious insects in agriculture, forestry, households, horticulture, and public health throughout the world, poses risks of environmental exposure. Here we evaluate the reproductive toxicity of cis-permethrin in adult male ICR mice that were orally administered cis-permethrin (0, 35, or 70 mg/kg d) for 6 wk. Caudal epididymal sperm count and sperm motility in the treated groups were statistically reduced in a dose-dependent manner. Testicular testosterone production and plasma testosterone concentration were significantly and dose-dependently decreased with an increase in LH, and a significant regression was observed between testosterone levels and cis-permethrin residues in individual mice testes after exposure. However, no significant changes were observed in body weight, reproductive organ absolute and relative weights, sperm morphology, and plasma FSH concentration after cis-permethrin treatment. Moreover, cis-permethrin exposure significantly diminished the testicular mitochondrial mRNA expression levels of peripheral benzodiazepine receptor (PBR), steroidogenic acute regulatory protein (StAR), and cytochrome P450 side-chain cleavage (P450scc) and enzyme and protein expression levels of StAR and P450scc. At the electron microscopic level, mitochondrial membrane damage was found in Leydig cells of the exposed mouse testis. Our results suggest that the insecticide permethrin may cause mitochondrial membrane impairment in Leydig cells and disrupt testosterone biosynthesis by diminishing the delivery of cholesterol into the mitochondria and decreasing the conversion of cholesterol to pregnenolone in the cells, thus reducing subsequent testosterone production.

Energized, polarized, and actively respiring mitochondria are required for acute Leydig cell steroidogenesis

The first and rate-limiting step in the biosynthesis of steroid hormones is the transfer of cholesterol into mitochondria, which is facilitated by the steroidogenic acute regulatory (StAR) protein. Recent study of Leydig cell function has focused on the mechanisms regulating steroidogenesis; however, few investigations have examined the importance of mitochondria in this process. The purpose of this investigation was to determine which aspects of mitochondrial function are necessary for acute cAMP-stimulated Leydig cell steroidogenesis. MA-10 cells were treated with 8-bromoadenosine 3',5'-cyclic monophosphate (cAMP) and different site-specific agents that disrupt mitochondrial function, and the effects on acute cAMP-stimulated progesterone synthesis, StAR mRNA and protein, mitochondrial membrane potential (Deltapsim), and ATP synthesis were determined. cAMP treatment of MA-10 cells resulted in significant increases in both cellular respiration and Deltapsim. Dissipating Deltapsim with carbonyl cyanide m-chlorophenyl hydrazone resulted in a profound reduction in progesterone synthesis, even in the presence of newly synthesized StAR protein. Preventing electron transport in mitochondria with antimycin A significantly reduced cellular ATP, potently inhibited steroidogenesis, and reduced StAR protein levels. Inhibiting mitochondrial ATP synthesis with oligomycin reduced cellular ATP, inhibited progesterone synthesis and StAR protein, but had no effect on Deltapsim. Disruption of intramitochondrial pH with nigericin significantly reduced progesterone production and StAR protein but had minimal effects on Deltapsim. 22(R)-hydroxycholesterol-stimulated progesterone synthesis was not inhibited by any of the mitochondrial reagents, indicating that neither P450 side-chain cleavage nor 3beta-hydroxysteroid dehydrogenase activity was inhibited. These results indicate that Deltapsim, mitochondrial ATP synthesis, and mitochondrial pH are all required for acute steroid biosynthesis. These results suggest that mitochondria must be energized, polarized, and actively respiring to support Leydig cell steroidogenesis, and alterations in the state of mitochondria may be involved in regulating steroid biosynthesis.

Activation of a neural brain-testicular pathway rapidly lowers Leydig cell levels of the steroidogenic acute regulatory protein and the peripheral-type benzodiazepine receptor while increasing levels of neuronal nitric oxide synthase

Activation of a neural brain-testicular pathway by the intracerebroventricular injection of the beta-adrenergic agonist isoproterenol (ISO), the hypothalamic peptide corticotropin-releasing factor (CRF), or alcohol (EtOH) rapidly decreases the testosterone (T) response to human chorionic gonadotropin. To elucidate the intratesticular mechanisms responsible for this phenomenon, we investigated the influence of intracerebroventricular-injected ISO, CRF, or EtOH on levels of the steroidogenic acute regulatory (StAR) protein, the peripheral-type benzodiazepine receptor (PBR), and the cytochrome P450 side-chain cleavage enzyme in semipurified Leydig cells. ISO (10 microg), CRF (5 microg), or EtOH (5 microl of 200 proof, a dose that does not induce neuronal damage nor leaks to the periphery) rapidly decreased StAR and PBR but not cytochrome P450 side-chain cleavage enzyme protein levels. Levels of the variant of the neuronal nitric oxide synthase (nNOS) that is restricted to Leydig cells, TnNOS, significantly increased in response to ISO, CRF, and EtOH over the time course of altered StAR/PBR concentrations. However, pretreatment of the rats with N(w)nitro-arginine methylester, which blocked ISO-induced increases in TnNOS, neither restored the T response to human chorionic gonadotropin nor prevented the decreases in StAR and PBR. These results provide evidence of concomitant changes in Leydig cell StAR and PBR levels in live rats. They also indicate that activation of a neural brain-testicular pathway rapidly decreases concentrations of these steroidogenic proteins while up-regulating testicular NO production. However, additional studies are necessary to elucidate the functional role played by this gas in our model.

Bacterial endotoxin lipopolysaccharide and reactive oxygen species inhibit Leydig cell steroidogenesis via perturbation of mitochondria

Chronic inflammatory disease and acute infection are well known to inhibit gonadal steroidogenesis. Previous studies have demonstrated that immune activation in response to lipopolysaccharide (LPS) results in reductions in serum testosterone, and this is a direct effect on the Leydig cell. We hypothesize that during the early onset of LPS endotoxemia in vivo, testicular macrophages produce reactive oxygen species (ROS) leading to perturbation of Leydig cell mitochondria and an inhibition in steroidogenesis. To investigate the mechanism of LPS inhibition of Leydig cell steroidogenesis, alterations in mitochondria and markers of oxi-dative stress were assessed in vivo and in Leydig cell pri- mary culture. After a single injection of mice with LPS, serum testosterone was significantly decreased within 2 h. LPS injection of mice resulted in significant reductions in steroidogenic acute regulatory protein (StAR) and 3beta-hydroxysteroid dehydogenase-Delta4-Delta5 isomerase (3beta-HSD) proteins. LPS significantly increased lipid peroxidation of Leydig cell membranes, indicating that LPS results in oxidative damage in vivo. Mitochondria in Leydig cells isolated from LPS-injected mice were disrupted and showed a marked reduction in the mitochondrial membrane potential (DeltaPsim). Similar to the effects of LPS, treatment of Leydig cells with hydrogen peroxide acutely inhibited steroidogenesis, reduced StAR and 3beta-HSD protein levels, and disrupted DeltaPsim. These results suggest that LPS acutely inhibits Leydig cell function by ROS-mediated disruption of Leydig cell mitochondria. Taken together, these results demonstrate the necessity of having respiring mitochondria with an intact DeltaPsim to facilitate StAR function and Leydig cell steroidogenesis. The acute effects of LPS demonstrate how sensitive Leydig cell mitochondrial steroidogenesis is to inflammation-induced oxidative stress.

The steroidogenic acute regulatory protein is expressed in steroidogenic cells of the day-old brain

Although recent research has focused on the fundamental role(s) of steroids synthesized de novo in the brain on development, the mechanism by which production of these neurosteroids is regulated remains unclear. Steroid production in peripheral tissues is acutely regulated by the steroidogenic acute regulatory (StAR) protein, which mediates the rate-limiting step in steroid biosynthesis: the intramitochondrial delivery of cholesterol to cytochrome P450scc for conversion to steroid. We recently demonstrated that StAR is present in discrete cell types in the adult brain, suggesting that neurosteroid production is mediated by StAR. Nevertheless, little is known regarding the presence of StAR in the developing brain. In the present study, the presence of StAR and for the first time, its homolog, the putative cholesterol transport protein metastatic lymph node 64 (MLN64), were defined in the neonatal mouse brain using immunocytochemical techniques. Both StAR and MLN64 were found to be present in the brain with staining patterns characteristic to each protein, indicating the authenticity of StAR and MLN64 immunoreactivity. Furthermore, we found MLN64 to be expressed in the adult brain as well, apparently at higher levels than StAR. Importantly, StAR protein is present in cells that also express P450scc. These data suggest that, as with the adult, neurosteroid production during development occurs through a StAR-mediated pathway.

Intratesticular delivery of tumor necrosis factor-alpha and ceramide directly abrogates steroidogenic acute regulatory protein expression and Leydig cell steroidogenesis in adult rats

Systemic or intratesticular release of TNF alpha and IL1 beta have been implicated in the reduced testosterone biosynthesis and impaired production of competent spermatozoa found in human patients suffering from sepsis or chronic inflammation. Although in vitro and in vivo studies have demonstrated that TNF alpha and IL1 beta intercept the hypothalamic-pituitary testis axis at different levels, the site(s) of action and relative contribution of each cytokine to the overall testicular failure associated to systemic inflammatory processes remains poorly defined. In this study we show that intratesticular delivery of TNF alpha induced a rapid (4 h) and sustained (up to 24 h) reduction in steroidogenic acute regulatory (StAR) protein expression and testosterone biosynthesis in nonstimulated or human chorionic gonadotropin-treated intact or hypophysectomized rats. Bilateral treatment with cell-permeant short-chain ceramides (C2-cer or C6-cer) reproduced the early (4 h) inhibitory action of TNFalpha on testosterone biosynthesis and testicular StAR expression. The inhibitory action of C2-cer or C6-cer was not observed in animals treated with inactive analogs (dihydroceramide), phosphorylcholine, sphingosine, or sphingosine-1P. In sharp contrast to the previously described ability of IL1 beta to prevent human chorionic gonadotropin-stimulated Leydig cell steroidogenesis in vitro, serum testosterone and testicular StAR protein expression remained unchanged in animals bilaterally injected with this cytokine. These data support the concept that TNF alpha triggers different effector mechanisms to directly inhibit Leydig cell StAR expression and steroidogenesis, which ultimately contribute to the global reproductive failure associated with chronic inflammation and sepsis.

Steroidogenic acute regulatory protein in the rat brain: cellular distribution, developmental regulation and overexpression after injury

The central nervous system synthesizes steroids which regulate the development and function of neurons and glia and have neuroprotective properties. The first step in this process involves the delivery of free cholesterol to the inner mitochondrial membrane where it can be converted into pregnenolone. This delivery is mediated by steroidogenic acute regulatory protein (StAR). Here, we present a detailed analysis of the distribution of StAR expression in neurons and glia, in the developing, adult and aged male rat brain. Immunohistochemical analysis revealed that StAR is widely distributed throughout the brain, although in each brain area it is restricted to very specific neuronal and astroglial populations. In most regions expressing StAR, immunoreactivity appeared at P10 and the levels of expression then either increased or remained constant until adulthood. In 2-year-old rat brains, StAR immunoreactivity was increased compared to young adults. StAR was expressed in the subventricular zone of the adult brain, in proliferating cells which incorporate BrdU as well as in germinal layers in the developing brain. These findings indicate that StAR expression is developmentally regulated and that StAR may play some function in regulating cell proliferation in the brain. Furthermore, StAR mRNA and protein levels were acutely and transiently increased in the hippocampus following excitotoxic brain injury induced by the administration of kainic acid. This raises the possibility that the up-regulation of StAR expression and the subsequent modifications in steroidogenesis may be part of the mechanisms used by the brain to cope with neurodegeneration.

Reactive oxygen disrupts mitochondria in MA-10 tumor Leydig cells and inhibits steroidogenic acute regulatory (StAR) protein and steroidogenesis

Reactive oxygen species (ROS) are involved in a variety of pathophysiological conditions of the testis, and oxidative stress is known to inhibit ovarian and testicular steroidogenesis. The site of ROS-mediated inhibition of steroidogenesis in the corpus luteum and MA-10 tumor Leydig cells was shown to be the hormone-sensitive mitochondrial cholesterol transfer step. The purpose of this study was to examine the effects of ROS on steroidogenic acute regulatory (StAR) protein in MA-10 cells and determine the extent to which MA-10 cell mitochondria are sensitive to oxidative stress. cAMP-stimulated progesterone production was inhibited in a dose-dependent manner in MA-10 cells exposed to H(2)O(2). StAR protein, but not mRNA levels, was decreased in parallel to changes in progesterone production. Even at the highest concentrations of H(2)O(2) tested, there was no effect on P450 side-chain cleavage enzyme protein levels. Oxidative stress from exposure to exogenous xanthine oxidase and xanthine resulted in the inhibition of both progesterone production and StAR protein expression. The mature 30- and 32-kDa intramitochondrial forms of StAR were decreased relative to the 37-kDa extramitochondrial precursor form of StAR, indicating that the ROS-mediated inhibition of StAR protein was due, in part, to the inhibition of mitochondrial import and processing. Vital staining with the fluorescent dye tetramethylrhodamine ethyl ester was used to visualize changes in the mitochondrial electrochemical gradient-dependent membrane potential (Deltapsim). ROS caused a significant dissipation of Deltapsi(m) and time-dependent loss of tetramethylrhodamine ethyl ester fluorescence. The inhibitory effects of H(2)O(2) were transient. There was no evidence for ROS-induced cell death, and following H(2)O(2) removal in the presence of continuous treatment with 8-bromo-cAMP, StAR protein levels and progesterone production were restored. In addition, there was no loss of cell viability following treatment with H(2)O(2) or xanthine/xanthine oxidase as determined by trypan blue exclusion. H(2)O(2) did not cause a significant decrease in total cellular ATP levels. These data indicate that oxidative stress-mediated perturbation of the mitochondria and dissipation of Deltapsi(m) results in the inhibition of StAR protein expression and its import, processing, and cholesterol transfer activity. These findings confirm earlier studies demonstrating the requirement for maintenance of an intact Deltapsi(m) for StAR protein function in cholesterol transport. The significant reduction in the 32- to 30-kDa mature forms of StAR, cessation of cholesterol transport, and loss of Deltapsi(m) are consistent with mitochondrial perturbation because of oxidative stress. This mechanism likely contributes to a host of pathophysiological events evident in testicular disorders such as infection, reperfusion injury, aging, cryptorchidism, and varicocele.

Follicle-stimulating hormone activates extracellular signal-regulated kinase but not extracellular signal-regulated kinase kinase through a 100-kDa phosphotyrosine phosphatase

In this report we sought to elucidate the mechanism by which the follicle-stimulating hormone (FSH) receptor signals to promote activation of the p42/p44 extracellular signal-regulated protein kinases (ERKs) in granulosa cells. Results show that the ERK kinase MEK and upstream intermediates Raf-1, Ras, Src, and L-type Ca(2+) channels are already partially activated in vehicle-treated cells and that FSH does not further activate them. This tonic stimulatory pathway appears to be restrained at the level of ERK by a 100-kDa phosphotyrosine phosphatase that associates with ERK in vehicle-treated cells and promotes dephosphorylation of its regulatory Tyr residue, resulting in ERK inactivation. FSH promotes the phosphorylation of this phosphotyrosine phosphatase and its dissociation from ERK, relieving ERK from inhibition and resulting in its activation by the tonic stimulatory pathway and consequent translocation to the nucleus. Consistent with this premise, FSH-stimulated ERK activation is inhibited by the cell-permeable protein kinase A-specific inhibitor peptide Myr-PKI as well as by inhibitors of MEK, Src, a Ca(2+) channel blocker, and chelation of extracellular Ca(2+). These results suggest that FSH stimulates ERK activity in immature granulosa cells by relieving an inhibition imposed by a 100-kDa phosphotyrosine phosphatase.

An essential component in steroid synthesis, the steroidogenic acute regulatory protein, is expressed in discrete regions of the brain

Recent data implicate locally produced steroids, termed neurosteroids, as regulators of neuronal function. Adrenal and gonadal steroidogenesis is controlled by changes in the steroidogenic acute regulatory protein (StAR); however, little is known about the regulation of neurosteroid production. We now demonstrate unequivocally that StAR mRNA and protein are expressed within glia and neurons in discrete regions of the mouse brain, and that glial StAR expression is inducible. Consistent with a role in de novo neurosteroidogenesis, StAR colocalizes with the cholesterol side-chain cleavage enzyme P450(scc) in both mouse and human brains. These data support a role for StAR in the production of neurosteroids and identify potential sites of active de novo steroid synthesis in the brain.

The life cycle of the steroidogenic acute regulatory (StAR) protein: from transcription through proteolysis

The Steroidogenic Acute Regulatory (StAR) protein is a mitochondrial protein required for the transport of cholesterol substrate to the P450scc enzyme located in the inner mitochondrial membranes of steroid producing cells. This study suggests that the acute regulation of the rodent StAR gene in the ovary is mediated by two factors, C/EBPbeta and GATA-4. Once translated, the StAR precursor protein is either imported into the mitochondria, or it is rapidly degraded in the cytosol. We predicted that in order to perpetuate StAR activity cycles, imported StAR should turn over rapidly to avoid a potentially harmful accumulation of the protein in sub-mitochondrial compartments. Pulse-chase experiments in metabolically labeled cells showed that: (a) the turnover rate of mature mitochondrial StAR protein (30 kDa) is much faster (t(1/2) = 4-5 h) than that of other mitochondrial proteins; (b) dissipation of the inner membrane potential (-delta psi) by carbonyl cyanide m-chlorophenylhydrazone (mCCCP) accelerates the mitochondrial degradation of StAR; (c) unexpectedly, the mitochondrial degradation of StAR is inhibited by MG132 and lactacystin, but not by epoxomicin. Furthermore, StAR degradation becomes inhibitor-resistant two hours after import. Therefore, these studies suggest a bi-phasic route of StAR turnover in the mitochondria. Shortly after import, StAR is degraded by inhibitor-sensitive protease(s) (phase I), whereas at later times, StAR turnover proceeds to completion through an MG132-resistant proteolytic activity (phase II). Collectively, this study defines StAR as a unique protein that can authentically be used to probe multiple proteolytic activities in mammalian mitochondria.

Relationship Between Steroidogenic Acute Regulatory Protein Expression and Progesterone Production in Hen Granulosa Cells During Follicle Development1

The present studies were conducted to address cellular mechanisms responsible for regulating steroidogenic acute regulatory protein (StAR) expression and progesterone synthesis at maturational stages corresponding to both the time of hen follicle selection, as well as before and after the LH surge in preovulatory follicle granulosa cells. A recently published report has established that mitogen-activated protein (MAP) kinase signaling induced by transforming growth factor alpha (TGFalpha) treatment blocks FSH-induced differentiation and StAR expression in cultured hen granulosa cells, whereas inhibitors of MAP kinase signaling enhance FSH-induced differentiation. The present in vitro studies demonstrate that in addition to MAP kinase signaling, activation of protein kinase C (PKC) blocks both FSH-induced StAR expression and the initiation of progesterone production in prehierarchal follicle granulosa cells, whereas the pharmacologic inhibitor of PKC, GF109203X, potentiates FSH-induced StAR expression and, as a consequence, the initiation of progesterone synthesis. Moreover, we demonstrate in granulosa cells collected from preovulatory follicles that although an acute increase in progesterone production in response to LH treatment requires rapid transcription and translation of StAR, the magnitude of progesterone production is rate-limited by one or more factors other than StAR (e.g., the P450 cholesterol side-chain enzyme). Finally, the rapid turnover of StAR protein, such as occurs following the withdrawal of LH, provides an additional mechanism for the tight regulation of progesterone production that occurs during the hen ovulatory cycle, and explains the rapid loss of steroidogenesis in the postovulatory follicle. In summary, data reported herein support the proposal that paracrine/autocrine factors (including but not necessarily limited to TGFalpha) prevent premature expression of StAR in prehierarchal follicle granulosa cells by more than one receptor-mediated signaling pathway. Furthermore, subsequent to follicle selection into the preovulatory hierarchy, StAR transcription and translation is necessary but not sufficient for the full potentiation of the preovulatory surge of serum progesterone.

Regulation of steroidogenic genes by insulin-like growth factor-1 and follicle-stimulating hormone: differential responses of cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, and 3beta-hydroxysteroid dehydrogenase/isomerase in rat granulosa cells

The present study sought to characterize the concerted action of FSH and insulin-like growth factor-1 (IGF-1) on functional differentiation of prepubertal rat ovarian granulosa cells in culture. To this end, we examined the regulation of three key genes encoding pivotal proteins required for progesterone biosynthesis, namely, side-chain cleavage cytochrome P450 (P450(scc)), steroidogenic acute regulatory (StAR) protein, and 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD). Time-dependent expression profiles showed that P450(scc), StAR, and 3beta-HSD gene products accumulate in chronic, acute, and constitutive patterns, respectively. Each of these genes responded to FSH and/or IGF-1 in a characteristic manner: A synergistic action of IGF-1 was indispensable for FSH induction of P450(scc) mRNA and protein; IGF-1 did not affect FSH-mediated upregulation of StAR products; and IGF-1 alone was enough to promote expression of 3beta-HSD. The responsiveness of the genes to IGF-1 correlated well with their apparent susceptibility to the inhibitory impact of tyrphostin AG18, a potent inhibitor of protein tyrosine kinase receptors. Thus, IGF-1-dependent P450(scc) and 3beta-HSD expression was completely arrested in the presence of AG18, whereas StAR expression was unaffected in the presence of tyrphostin. These findings suggest that FSH/cAMP signaling and IGF-1/tyrosine phosphorylation events are interwoven in rat ovarian cells undergoing functional differentiation. We also sought the mechanism of IGF-1 synergy with FSH. In this regard, our studies were unable to demonstrate a stabilizing effect of IGF-1 on P450(scc) mRNA, nor could IGF-1 augment FSH-induced transcription examined using a proximal region of the P450(scc) promoter (-379/+6). Thus, the mechanism of IGF-1 and FSH synergy remains enigmatic and provides a major challenge for future studies.

Acute signaling by the LH receptor is independent of protein kinase C activation

LH receptor activation leads to the phosphorylation/activation of p42/44 MAPK in preovulatory granulosa cells. As the LH receptor can activate both adenylyl cyclase and phospholipase C, we hypothesized that the LH receptor could elicit phosphorylation of p42/44 MAPK through activation of protein kinase A (PKA) and/or protein kinase C (PKC). Preovulatory granulosa cells in serum-free primary cultures were treated with ovulatory concentrations of human chorionic gonadotropin (hCG), an LH receptor agonist, with or without various inhibitors. The PKA inhibitor H89 as well as the myristoylated PKA inhibitor peptide PKI strongly inhibited hCG-stimulated p42/44 MAPK phosphorylation, whereas the PKC inhibitor GF109203X had no effect on p42/44 MAPK phosphorylation. LH receptor-stimulated phosphorylation of cAMP response element-binding protein (CREB), histone H3, and MAPK kinase (MEK) was also strongly inhibited by H89 and not by GF109203X. The extent of PKC activation was assessed in preovulatory granulosa cells using three criteria: translocation of PKC isoforms to the membrane fraction, phosphorylation of a known PKC substrate, and autophosphorylation of PKC delta on an activation-related site. By all three criteria PKCs were partially activated before hCG stimulation, and hCG treatment failed to elicit further PKC activation, in vitro or in vivo. Taken together, these results indicate that, under primary culture conditions where physiological levels of signaling proteins are present, hCG signals to activate MEK, p42/44 MAPK, CREB, and histone H3 in a predominantly PKA-dependent and PKC-independent manner. Unexpectedly, PKCs were partially activated in the absence of LH receptor activation, and LH receptor activation did not elicit further detectable PKC activation.

Regulation of steroidogenic acute regulatory protein and luteinizing hormone receptor messenger ribonucleic acid in hen granulosa cells

The regulation of steroidogenic acute regulatory protein (StAR) in vitro by gonadotropins was investigated in granulosa cells from prehierarchal and preovulatory hen follicles. Basal levels of StAR messenger RNA (mRNA) in undifferentiated granulosa cells from prehierarchal (6- to 8-mm) follicles were consistently low, but detectable, and were significantly increased by treatment with 8-bromo-cAMP and FSH (but not LH) within 3-6 h of culture. After 20 h of culture, 8-bromo-cAMP, FSH, and LH each increased StAR mRNA levels above those in control cultured cells, and the delayed response to LH treatment was associated with increased levels of LH receptor (LH-R) mRNA. On the other hand, inhibition of mitogen-activated protein (MAP) kinase signaling, using the MAP kinase kinase inhibitors U0126 and PD98059, in the presence of FSH further increased StAR mRNA and protein levels, LH-R mRNA levels, and progesterone synthesis compared with those in cells cultured with FSH alone. The highest basal expression of StAR mRNA during follicle development was found in granulosa from the largest (F1) preovulatory follicle, with comparatively lower levels in granulosa from less mature (F2 plus F3) preovulatory follicles. Treatment with LH rapidly increased StAR mRNA and protein (but not LH-R mRNA) expression in cultures of F1 granulosa and in combined F2 plus F3 granulosa within 3 h, although the magnitude of stimulation was greater in F2 plus F3 granulosa. Compared with results from granulosa cells from prehierarchal follicles cultured for 20 h, inhibition of MAP kinase signaling in the presence of LH for 1 h failed to further enhance levels of StAR or LH-R expression or progesterone production in F2 plus F3 follicle granulosa compared with the effect of LH treatment alone. These results demonstrate that StAR expression in the hen ovary is up-regulated by gonadotropins at least in part via cAMP signaling. The ability of MAP kinase kinase inhibitors to potentiate gonadotropin-induced StAR and LH-R expression plus progesterone synthesis in prehierarchal follicle granulosa cells in vitro suggests that inhibition of paracrine or autocrine factor-mediated MAP kinase signaling in vivo may be a prerequisite for the full potentiation of granulosa cell steroidogenesis that occurs after recruitment into the preovulatory hierarchy. Finally, these results fail to support a role for MAP kinase signaling in acutely modulating LH-mediated StAR expression or progesterone production in hierarchal follicles, such as occurs during the preovulatory surge of progesterone.

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.