Protein kinase G-mediated stimulation of basal Leydig cell steroidogenesis

Epitope-tagged and phosphomimetic mouse models for investigating natriuretic peptide-stimulated receptor guanylyl cyclases

The natriuretic peptide receptors NPR1 and NPR2, also known as guanylyl cyclase A and guanylyl cyclase B, have critical functions in many signaling pathways, but much remains unknown about their localization and function in vivo. To facilitate studies of these proteins, we developed genetically modified mouse lines in which endogenous NPR1 and NPR2 were tagged with the HA epitope. To investigate the role of phosphorylation in regulating NPR1 and NPR2 guanylyl cyclase activity, we developed mouse lines in which regulatory serines and threonines were substituted with glutamates, to mimic the negative charge of the phosphorylated forms (NPR1-8E and NPR2-7E). Here we describe the generation and applications of these mice. We show that the HA-NPR1 and HA-NPR2 mice can be used to characterize the relative expression levels of these proteins in different tissues. We describe studies using the NPR2-7E mice that indicate that dephosphorylation of NPR2 transduces signaling pathways in ovary and bone, and studies using the NPR1-8E mice that indicate that the phosphorylation state of NPR1 is a regulator of heart, testis, and adrenal function.

Stress alters the transcriptional activity of Leydig cells dependently on the diurnal time

The increasing amount of data points to the circadian timing system as an essential part of processes regulating androgen homeostasis. However, the relationship between stress response, timekeeping-, and steroidogenesis-related systems is unexplored. Here, the stress-response of the testosterone-producing rat Leydig cells depending on the time of stressful events was studied. The study analyzes the effects of 3-hour immobilization (IMO) applied at different periods during the day. The IMO performed once (1xIMO) or repeated in 10 consecutive days (10xIMO). Both types of IMO increased corticosterone and decreased testosterone blood level. However, the effect of 10xIMO occurring in the active phase on blood testosterone was less pronounced. This is related to different sensitivity to IMO-events depending on the diurnal time. Most steroidogenesis-related genes (Lhcgr, Cyp11a1, Hsd3b1/2, Cyp17a1) were down-regulated in the inactive but unchanged or even up-regulated in the active phase of the day. Both types of IMO stimulated the expression of clock elements Bmal1/BMAL1, Per1/PER1 regardless of the day's stage and reduced Rev-erba in the inactive phase. The principal-component-analysis (PCA) confirmed a major shift, for both IMO-types, in the transcription of the genes across the passive/active stage. Further, 10xIMO changed a diurnal pattern of the glucocorticoid receptor (Nr3c1/GR) expression while the observed time-dependent IMO-response of the Leydig cells correlated with different corticosterone engagements. Altogether, the Leydig cell's stress-response depends on the daytime of the stressful event, emphasizing the importance of the circadian-system in supporting androgen homeostasis and male fertility.

Phosphodiesterase (PDE) 5 inhibitors sildenafil, tadalafil and vardenafil impact cAMP-specific PDE8 isoforms-linked second messengers and steroid production in a mouse Leydig tumor cell line

Type 5 phosphodiesterase (PDE5) blockade by inhibitors (PDE5i) results in intracellular cyclic guanosine monophosphate (cGMP) increase and smooth muscle relaxation and are used for the treatment of men erectile dysfunction. Although they have high specificity for PDE5, these inhibitors are suspected to cross-interact also with cyclic adenosine monophosphate (cAMP)-specific PDEs, inducing the intracellular accumulation of this cyclic nucleotide and related testosterone increase, positively impacting male reproductive parameters. However, the link between the use of PDE5i and the activation of cAMP-mediated steroidogenesis is still unclear. We have investigated whether three PDE5i, sildenafil, tadalafil and vardenafil, cross-interacts with the high affinity cAMP-specific enzymes type 8A and 8B PDEs (PDE8A and PDE8B), in live, transfected mouse Leydig tumor (mLTC1) and human embryonic kidney (HEK293) cell lines in vitro. The PDE5i-induced production of cAMP-dependent testosterone and its precursor progesterone was evaluated as well. We have developed PDE8A/B biosensors and modified cyclic nucleotides confirming enzyme binding to cAMP, but not to cGMP, in our cell models. cAMP binding to PDE8A/B was displaced upon cell treatment with PDE5i, revealing that sildenafil, tadalafil and vardenafil have similar effectiveness in live cells, in vitro. The cross-interaction between PDE5i and PDE8A/B supports the gonadotropin-enhanced intracellular cAMP increase, occurring together with cGMP increase, as well as steroid synthesis. Indeed, we found that Leydig cell treatment by PDE5i increases progesterone and testosterone production triggered by gonadotropins. We demonstrated that PDE5i may interact with the cAMP-specific PDE8A and PDE8B, possibly inducing intracellular cAMP and sex steroid hormone increase. These findings support clinical data suggesting that PDE5i might increase testosterone levels in men.

Stress-induced glucocorticoids alter the Leydig cells' timing and steroidogenesis-related systems

The study aimed to analyze the time-dependent consequences of stress on gene expression responsible for diurnal endocrine Leydig cell function connecting them to the glucocorticoid-signaling. In the first 24h after the stress event, a daily variation of blood corticosterone increased, and testosterone decreased; the testosterone/corticosterone were lowest at the end of the stress session overlapping with inhibition of Leydig cells' steroidogenesis-related genes (Nr3c1/GR, Hsd3b1/2, Star, Cyp17a1) and changed circadian activity of the clock genes (the increased Bmal1/BMAL1 and Per1/2/PER1 and decreased Cry1 and Rev-erba). The glucocorticoid-treated rats showed a similar response. The principal-component-analysis (PCA) displayed an absence of significant differences between treatments especially on Per1 and Rev-erba, the findings confirmed by the in vivo blockade of the testicular glucocorticoid receptor (GR) during stress and ex vivo treatment of the Leydig cells with hydrocortisone and GR-blocker. In summary, stressful stimuli can entrain the clock in the Leydig cells through glucocorticoid-mediated communication.

Aging-Related Increase of cGMP Disrupts Mitochondrial Homeostasis in Leydig Cells

Since mitochondria play an essential role in the testosterone biosynthesis, serve as power centers and are a source of oxidative stress, a possible mitochondrial dysfunction could be connected with decreased activity of Leydig cells and lowered testosterone production during aging. Here we chronologically analyzed age-related alterations of mitochondrial function in Leydig cells correlated by the progressive rise of cGMP signaling and with respect to testosterone synthesis. To target cGMP signaling in Leydig cells, acute or long-term in vivo or ex vivo treatments with sildenafil (phosphodiesterase 5 [PDE5] inhibitor) were performed. Aging-related accumulation of cGMP in the Leydig cells is associated with mitochondrial dysfunction illustrated by reduced ATP and steroid production, lowered O2 consumption, increased mitochondrial abundance and mtDNA copies number, decreased expression of genes that regulate mitochondrial biogenesis (Ppargc1a/PGC1a-Tfam-Nrf1/NRF1), mitophagy (Pink1), fusion (Mfn1, Opa1), and increased Nrf2/NRF2. Acute in vivo PDE5 inhibition overaccumulated cGMP and stimulated testosterone but reduced ATP production in Leydig cells from adult, middle-aged, and old rats. The increased ATP/O ratio observed in cells from old compared to adult rats was diminished after stimulation of cGMP signaling. Opposite, long-term PDE5 inhibition decreased cGMP signaling and improved mitochondrial function/dynamics in Leydig cells from old rats. Mitochondrial abundance in Leydig cells decreased while ATP levels increased. Chronic treatment elevated Tfam, Nrf1, Nrf2, Opa1, Mfn1, Drp1, and normalized Pink1 expression. Altogether, long-term PDE5 inhibition prevented age-related NO and cGMP elevation, improved mitochondrial dynamics/function, and testosterone production. The results pointed on cGMP signaling in Leydig cells as a target for pharmacological manipulation of aging-associated changes in mitochondrial function and testosterone production.

Gametogenic and steroidogenic action of kisspeptin-10 in the Asian catfish, Clarias batrachus: Putative underlying mechanistic cascade

Unlike mammals, two kisspeptins genes encoding, kiss1 and kiss2 are detected in fishes with highly varied and contradictory difference in their reproductive activities. The present study was undertaken to examine the direct action of kisspeptin-10 and its role in gonadal activities in the gonadally quiescent Asian catfish using native mammalian kisspeptin decapeptide (KP-10) involving in vivo and in vitro approaches. The in vivo KP-10 treatment caused precocious onset of gametogenesis and its rapid progression, as was evident from the appearance of advanced stages of ovarian follicles in ovary, and advanced germ cells (spermatocytes/ spermatids) in the testis of the treated Clarias batrachus in comparison to the control gonads. It also elevated the steroid levels in gonads of the catfish in vivo and in vitro conditions. Simultaneously, it increased the expressions of key steroidogenic enzymes like 3β-HSD, 17β-HSD, and StAR protein, responsible for transfer of cholesterol from outer to inner membrane of the mitochondria of steroidogenic cells. Concurrently, it augmented the activities of 3β-HSD and 17β-HSD in the ovarian explants. The expressions of MAPK component (pERK1/2 and ERK1/2) were also up-regulated by KP-10 in gonadal explants. Thus, the data suggest that kisspeptin-10 stimulates gametogenesis by enhancing gonadal steroid production. The study also describes the putative mechanistic cascade of steroidogenic actions of kisspeptin-10 in the catfish so much so in teleost fish. The study also suggests that, kisspeptin may act locally to regulate gonadal activities in an autocrine/paracine manner, independent of known extra-gonadal factors in the catfish.

Testicular steroidogenesis is suppressed during experimental autoimmune encephalomyelitis in rats

Multiple sclerosis (MS) is an autoimmune disease that usually occurs during the reproductive years in both sexes. Many male patients with MS show lower blood testosterone levels, which was also observed in male rats during experimental autoimmune encephalomyelitis (EAE), an animal model of MS. To better understand the causes of decreased testosterone production during EAE, we investigated the expression status of genes and proteins associated with steroidogenesis in the testes. No changes in the number of interstitial cells were observed in EAE animals, but the expression of the insulin-like 3 gene was reduced at the peak of the disease, implying that the Leydig cell functional capacity was affected. Consistent with this finding, the expression of most steroidogenic enzyme genes and proteins was reduced during EAE, including StAR, CYP11A1, CYP17A1 and HSD3B. No signs of testicular inflammation were observed. Recovery of steroidogenesis was observed after injection of hCG, the placental gonadotropin, or buserelin acetate, a gonadotropin-releasing hormone analogue, at the peak of EAE. Together, our results are consistent with the hypothesis that impaired testicular steroidogenesis originates upstream of the testes and that low serum LH is the main cause of decreased testosterone levels during EAE.

Growing Up Under Constant Light: A Challenge to the Endocrine Function of the Leydig Cells

The factors influencing Leydig cell maturity and the acquisition of functional capacity are incompletely defined. Here we analyzed the constant light (LL) influence on Leydig cells' endocrine function during reproductive maturation. Rats were exposed to LL from P21 to P90. Data were collected at juvenile (P35), peri/pubertal (P42, P49), and adult (P90) stages of life. The results proved the effect of LL on rats' physiology by changing of bimodal voluntary activity pattern into free-running. Additionally, the peripheral clock in Leydig cells changed in LL condition, indicating disturbed rhythm: the positive element (Bmal1) increased in pre-/pubertal but decreased in the adult period, while negative elements (Per2 and Reverba) were increased. The effects of LL were most prominent in puberty: pituitary genes encoding gonadotropic hormones (Cga, Lhb, Fshb) decreased; serum corticosterone increased, while serum androgens and mass of testicular and sex accessory organs reduced; markers of Leydig cells maturity/differentiation (Insl3, Lhcgr) and steroidogenesis-related genes (Scarb1, Star, Cyp11a1, Cyp17a1) decreased; the steroidogenic and energetic capacity of the Leydig cell mitochondria decreased; the mtDNA copy number reduced, and mitochondrial dynamics markers changed: fusion decreased (Opa1 and Mfn2), and mitophagy increased (Pink1). In adults, the negative effect of LL on mitochondrial function and steroidogenic capacity persists in adult Leydig cells while other parameters reached control values. Altogether, the results indicate that LL slows down Leydig cells' maturation by reducing the endocrine and energy capacity of cells leading to the delay of reproductive development.

Dependence of Leydig Cell's Mitochondrial Physiology on Luteinizing Hormone Signaling

Knowledge about the relationship between steroidogenesis and the regulation of the mitochondrial bioenergetics and dynamics, in steroidogenic cells, is not completely elucidated. Here we employed in vivo and ex vivo experimental models to analyze mitochondrial physiology in Leydig cells depending on the different LH-cAMP environments. Activation of LH-receptor in rat Leydig cells ex and in vivo triggered cAMP, increased oxygen consumption, mitoenergetic and steroidogenic activities. Increased mitoenergetic activity i.e., ATP production is achieved through augmented glycolytic ATP production and a small part of oxidative phosphorylation (OXPHOS). Transcription of major genes responsible for mitochondrial dynamics was upregulated for Ppargc1a (regulator of mitogenesis and function) and downregulated for Drp1 (main fission marker), Prkn, Pink1 and Tfeb (mitophagy markers). Leydig cells from gonadotropin-treated rats show increased mitogenesis confirmed by increased mitochondrial mass, increased mtDNA, more frequent mitochondria observed by a transmission electron microscope and increased expression of subunits of respiratory proteins Cytc/CYTC and COX4. Opposite, Leydig cells from hypogonadotropic-hypogonadal rats characterized by low LH-cAMP, testosterone, and ATP production, reduced markers of mitogenesis and mitofusion (Mfn1/2, Opa1) associated with reduced mtDNA content. Altogether results underline LH-cAMP signaling as an important regulator of mitochondrial physiology arranging mitochondrial dynamics, bioenergetic and steroidogenic function in Leydig cells.

Expression patterns of C1ql4 and its cell-adhesion GPCR Bai3 in the murine testis and functional roles in steroidogenesis

C1q-like 4 (C1QL4), a novel member of the C1q- and TNF-related protein family, was found to be highly expressed in rodent and human testis. However, the localization, developmental, and hormonally regulated expression and biologic function of C1ql4 in the testis have not been investigated. Here, we demonstrated that C1ql4 mRNA and protein levels in murine testes gradually increased from the postnatal period to the adult stage and were up-regulated by LH in vivo. In situ hybridization demonstrated that the distribution and expression levels of C1ql4 mRNA varied at different developmental stages, although C1ql4 mRNA was detected in the seminiferous tubule and interstitial Leydig cells. Recombinant C1QL4 did not affect cell proliferation but did increase testosterone production in TM3 Leydig cells, as well as in cultured seminiferous tubules. C1QL4-induced testosterone secretion in Leydig cells was accompanied by increased expression of steroidogenic acute regulatory (StAR) protein and steroidogenic enzymes. During this process, the c-Raf/extracellular signal-regulated protein kinase kinases 1 and 2/ERK1/2/mitogen- and stress-activated protein kinase-1 and cAMP/PKA/cAMP-responsive element binding protein signaling cascades were activated by C1QL4. The cell-adhesion GPCR brain-specific angiogenesis inhibitor 3 (BAI3), a putative receptor of C1QL4, was detected in the seminiferous tubule and interstitial Leydig cells during testicular development. Knockdown of Bai3 expression in Leydig cells led to a reduction in Star expression, accompanied by increases in phosphorylation of ERK1/2 and intercellular cAMP levels. However, C1QL4-induced StAR expression was not completely suppressed in the Bai3-deficient Leydig cells, and phosphorylation of ERK1/2 and intercellular cAMP levels were not significantly changed before and after C1QL4 stimulation. Our results suggested that although BAI3 played a role in C1QL4-induced steroidogenesis, there was an unidentified receptor that mediated C1QL4-activated testosterone secretion in Leydig cells through phosphorylation of ERK1/2 and up-regulation of intracellular cAMP levels. Taken together, our results showed, for the first time to our knowledge, that C1QL4 served as a novel acute regulator of testosterone secretion, and BAI3 functioned as a new receptor that is involved in steroidogenesis in Leydig cells. BAI3-independent ERK1/2 activation and cAMP activation mediated C1QL4-induced testosterone secretion. This study expanded the reproductive roles and mechanisms of C1QL4 and BAI3 signaling pathways.-Tan, A., Ke, S., Chen, Y., Chen, L., Lu, X., Ding, F., Yang, L., Tang, Y., Yu, Y. Expression patterns of C1ql4 and its cell-adhesion GPCR Bai3 in the murine testis and functional roles in steroidogenesis.

Androgen Deficiency and Phosphodiesterase Type 5 Expression Changes in Aging Male: Therapeutic Implications

The age-related decline of serum T occurs in ~20-30% of adult men and it is today defined as late-onset hypogonadism (LOH). In the elderly, such decline becomes more prevalent (up to 60%) and shows-up with erectile dysfunction (ED) and hypoactive sexual desire. A large body of experimental evidences have shown that the combination of T replacement therapy (TRT) and phosphodiesterase type 5 inhibitors (PDE5i) is, usually, effective in restoring erectile function in patients with LOH and ED who have not responded to monotherapy for sexual disturbances. In fact, PDE5is potentiate the action of nitric oxide (NO) produced by endothelial cells, resulting in a vasodilator effect, while T facilitates PDE5i effects by increasing the expression of PDE5 in corpora cavernosa. Meta-analytic data have recognized to PDE5i a protective role on the cardiovascular health in patients with decreased left ventricular ejection fraction. In addition, several studies have shown pleiotropic beneficial effects of these drugs throughout the body (i.e., on bones, urogenital tract and cerebral, metabolic, and cardiovascular levels). TRT itself is able to decrease endothelial dysfunction, oxidative stress and inflammation, thus lowering the cardiovascular risk. Furthermore, untreated hypogonadism could be the cause of PDE5i ineffectiveness especially in the elderly. For these reasons, aging men complaining ED who have LOH should undergo TRT before or at the moment when PDE5i treatment is started.

The role of PKG in oocyte maturation of zebrafish

Recently the importance of cyclic guanosine monophosphate (cGMP) signaling pathway in oocyte maturation has been well demonstrated in several species. However, as the primary downstream effector of the cGMP signaling pathway, little is known on the role of cGMP-dependent protein kinase (PKG) in oocyte maturation. In the present study, the expression, regulation and function of PKG in oocyte maturation was investigated in zebrafish. We identified four distinct PKG coding genes (named Prkg1a, Prkg1b, Prkg2, and Prkg3) in zebrafish. All prkgs are expressed in the ovary, and both prkg1a and prkg1b could be regulated by human chronic gonadotropin in follicular cells during oocyte maturation. We found that a cGMP analogue, 8-Br-cGMP, could stimulate oocyte maturation in a dose- and time-dependent manner. Such stimulatory effects of cGMP could be totally blocked by a PKG specific inhibitor, KT-5823. Intriguingly, we further found KT5823 could significantly attenuate spontaneous oocyte maturation in intact follicles but not in the denuded oocytes, suggesting that the activity of PKG in follicular cells is important for oocyte maturation. All of these results clearly demonstrate that PKG is involved in oocyte maturation in zebrafish.

Aphrodisiac Activity of Eulophia macrobulbon Extract on Erectile Dysfunction in Male Aged Rats

This study investigated the effect of Eulophia macrobulbon (EM) extract on sexual performance in aged-related erectile dysfunction (ED) rats. The ethanol EM extract at the doses of 15, 150, and 450 and sildenafil citrate at the dose of 5 mg/kg body weight (BW) were administered orally to the aged male rats once daily for 21 days. Mating parameters and intracavernosal pressure (ICP) were measured to evaluate their sexual and erection functions. Numbers of sperm and sperm motility as well as the diameter of seminiferous tubules were observed. The serum testosterone and 3',5'-cyclic guanosine monophosphate (cGMP) concentration in the rat penile tissue were analyzed. The results showed the significant increased sexual motivation, copulatory performance, and ICP of aged rats treated with sildenafil citrate and all doses of EM extract as compared to control aged rats. Moreover, their serum testosterone levels were slightly increased and significant increase in penile cGMP concentration was observed in these aged rats treated with sildenafil citrate and EM extract. The results suggest that treatment with EM could inhibit activity of PDE5 in penile tissue resulting in the increased cGMP level and bring to the improvement of erectile function and sexual performance.

Long-term inhibition of PDE5 ameliorates aging-induced changes in rat testis

NO-cGMP signaling pathway has been implicated in reduction of testicular steroidogenesis during aging. Here we analyzed the effect of PDE5 inhibition on old testicular phenotype formation. The old phenotype exhibited low testosterone and increased nitrite levels in circulation, increased cGMP accumulation in testicular interstitial fluid (TIF), progressive atrophy of testicular seminiferous tubules and enlargement of interstitial area followed by rise in blood vessel density and slight increase in the number of Leydig cells and macrophages. Leydig cells have reduced steroidogenic capacity, increased MAP kinases expression (MEK, ERK1/2, JNK) and antiapoptotic PRKG1 and AKT, suggesting increased proliferation/survival and accumulation of senescent Leydig cells in testis. In 12 month-old rats, a long-term treatment with sildenafil (PDE5 inhibitor) normalized testosterone/nitrite levels in circulation and cGMP accumulation in TIF; improved Leydig cell steroidogenic capacity; decreased MEK, ERK1/2 and PRKG1 expression; prevented an increase in the Leydig cells number and atrophy of seminiferous tubules leading to histological appearance of young rat testes. In 18 month-old rats, long-term PDE5 inhibition partially recovered testosterone and nitrite levels in serum; normalized PRKG1 expression without effect on MEK and ERK1/2; and slowed down Leydig cell and macrophage accumulation and regressive tubular changes. Culturing of primary Leydig cells from aged rats in presence of PDE5-inhibitor stimulated steroidogenic and MAPK gene expression. Taking together, results indicate that cGMP targeting alter both steroidogenesis and signaling pathways associated with cell proliferation/survival. The long-term PDE5 inhibition improves testicular steroidogenesis and slows-down regressive changes in testes during aging.

Nitric oxide modulates ATP-evoked currents in mouse Leydig cells

Testosterone synthesis within Leydig cells is a calcium-dependent process. Intracellular calcium levels are regulated by different processes including ATP-activated P2X purinergic receptors, T-type Ca²⁺ channels modulated by the luteinizing hormone, and intracellular calcium storages recruited by a calcium-induced calcium release mechanism. On the other hand, nitric oxide (NO) is reported to have an inhibitory role in testosterone production. Based on these observations, we investigated the interaction between the purinergic and nitrergic systems in Leydig cells of adult mice. For this purpose, we recorded ATP-evoked currents in isolated Leydig cells using the whole cell patch clamp technique after treatment with L-NAME (300 μM and 1 mM), L-arginine (10, 100, 300, and 500 μM), ODQ (300 μM), and 8-Br-cGMP (100 μM). Our results show that NO produced by Leydig cells in basal conditions is insufficient to change the ATP-evoked currents and that extra NO provided by adding 300 μM L-arginine positively modulates the current through a mechanism involving the NO/cGMP signaling pathway. Thus, we report an interaction between the nitrergic and purinergic systems in Leydig cells and suggest that Ca²⁺ entry via the purinergic receptors can be regulated by NO.

Effects of chronic administration of the phosphodiesterase inhibitor vardenafil on serum levels of adrenal and testicular steroids in men with type 2 diabetes mellitus

To investigate whether long-term, chronic treatment with the phosphodiesterase-5 inhibitor vardenafil affects adrenal and testicular steroidogenesis in diabetic men, using liquid chromatography-tandem mass spectrometry. A longitudinal, prospective, investigator-started, randomized, placebo-controlled, double-blind, clinical-trial was carried out, enrolling 54 male patients affected by type 2 diabetes mellitus diagnosed within the last 5 years. In total, 26 and 28 patients were followed for 1 year and assigned to the study and placebo group, respectively. Progesterone, 17-hydroxyprogesterone, androstenedione, testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulfate, corticosterone, 11-deoxycortisol and cortisol, were evaluated using liquid chromatography-tandem mass spectrometry. No differences were seen in sex testicular steroids between study and control group. As for the adrenal gland, steroids were considered according to the zona in which they are produced. No significant differences were seen in steroid produced in zona fasciculata. For the zona reticularis, dehydroepiandrosterone significantly decreased during treatment only in the study group (p = 0.007), with higher levels at visit 2 and 8 than other visits. The dehydroepiandrosterone sulfate/dehydroepiandrosterone ratio significantly increased during treatment only in the verum group. Considering the adrenal zona glomerulosa, corticosterone significantly changed among visits both in both groups (p < 0.001), with higher levels at visit 2 (p = 0.028), 8 (p = 0.003), and 10 (p = 0.044), i.e., in coincidence with the complete clinical and instrumental examination performed only at these visits according to the study protocol. Chronically administered vardenafil reduces dehydroepiandrosterone levels and increases dehydroepiandrosterone sulfate/dehydroepiandrosterone ratio as possible consequences of modulation of steroidogenic enzymes by tissue changes in cyclic adenosine monophosphate and cyclic guanosine monophosphate availability. A possibly stress-related increase in corticosterone is suggested for the first time.

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

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

Effects of taking tadalafil 5 mg once daily on erectile function and total testosterone levels in patients with metabolic syndrome

We aimed to evaluate the efficacy of tadalafil 5 mg once-daily treatment on testosterone levels in patients with erectile dysfunction (ED) accompanied by the metabolic syndrome. A total of 40 men with metabolic syndrome were evaluated for ED in this study. All the patients received 5 mg tadalafil once a day for 3 months. Erectile function was assessed using the five-item version of the International Index of Erectile Function (IIEF) questionnaire. Serum testosterone, follicle-stimulating hormone and luteinising hormone levels were also evaluated, and blood samples were taken between 08.00 and 10.00 in the fasting state. All participants have three or more criteria of metabolic syndrome. At the end of 3 months, mean testosterone values and IIEF scores showed an improvement from baseline values (from 3.6 ± 0.5 to 5.2 ± 0.3, from 11.3 ± 1.9 to 19 ± 0.8 respectively). After the treatment, serum LH levels were decreased (from 5.6 ± 0.6 to 4.6 ± 0.5). There was significantly difference in terms of baseline testosterone and luteinising hormone values and IIEF scores (p < .05). Based on our findings, we recommend tadalafil 5 mg once daily in those men with erectile dysfunction especially low testosterone levels accompanied by metabolic syndrome.

Pro-steroidogenic and pro-spermatogenic actions of nitric oxide (NO) on the catfish, Clarias batrachus: An in vivo study

In an earlier study we have demonstrated reproductive-stage dependent, cell specific existence of inducible nitric oxide synthase (iNOS) and neuronal nitric oxide synthase (nNOS)/NO system in testis of the catfish, Clarias batrachus. The present study is an extension to examine the role of NO in steroidogenesis and spermatogenesis through in vivo administration of a NO donor, sodium nitroprusside (SNP) and a NOS inhibitor, N-nitro-l-arginine methyl ester (l-NAME) during the quiescence and recrudescence phase of the reproductive cycle of the catfish. Effects of these chemicals were assessed on the gonadosomatic index (GSI), levels of circulating & testicular testosterone, NO, activities of 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD) in testis, expression of different NOS isoforms and testicular morphology in relation to spermatogenesis. SNP treatment increased the GSI, testicular and circulating testosterone & NO, activities of testicular 3β-HSD & 17β-HSD, and expression of NOS isoforms. It also increased the area and perimeters of interstitium and seminiferous tubules in the testis. It accelerated the spermatogenesis, as was evident from the large number of spermatids/spermatozoa in seminiferous tubules and very few spermatogonial cells/primary spermatocytes in comparison to the control testis. On the contrary, l-NAME significantly suppressed GSI, testosterone & NO levels in serum and testis, and activities of testicular 3β-HSD & 17β-HSD. It also suppressed the expression of NOSs in testis. Though l-NAME did not alter the spermatogonial mitotic proliferation with the advancement of testicular recrudescence, it halted the progression of spermatogenesis (meiotic division and spermatozoa formation) as was clear from the increase in spermatogonial cells and very few advanced germ cells in the seminiferous tubules in l-NAME treated testis, compared to the control testis. The above noted effects were highly pronounced in the recrudescing catfish. Their effects were very marginal and at a particular dose levels of SNP and l-NAME in the quiescent testis. This study distinctly provides evidence of pro-steroidogenic and pro-spermatogenic role of NO. This study also demonstrates the existence of eNOS in fish testis for the first time. The positive feedback control of expression of all isoform of NOS in testis by NO is also noteworthy.

Effect of Molybdenum Nanoparticles on Blood Cells, Liver Enzymes, and Sexual Hormones in Male Rats

Despite an increasing surge in application of nanoparticles in industries, there is a serious lack of information concerning their impact on human health and the environment. The present study investigated effects of molybdenum nanoparticles (Mo NPs) injected intraperitoneally into Sprague-Dawley rats at different doses of Mo NPs (5, 10, and 15 mg/kg BW per day) during a period of 28 days. Hematological and biochemical parameters as well as sexual hormones and histopathological examinations of the liver and testis were assessed and compared with control group. The results showed that the serum levels of testosterone decreased significantly in both groups of 10 and 15 mg (Mo NPs)/kg BW in comparison with the control group (p < 0.05). However, there were insignificant differences observed in luteinizing hormone (LH) levels and hematological parameters when compared with the control group (p > 0.05). The results of liver enzymes showed that serum levels of aspartate aminotransferase (AST) decreased significantly in both dosage groups of 5 and 10 mg/kg BW (Mo NPs) when compared with the control group (p < 0.05), and significant decrease obtained in lactate dehydrogenase (LDH) levels at dose of 5 mg/kg BW in comparison with the control group (p < 0.05). The histopathological examination of testis showed a decrease in number of Leydig cells. Also, the number of chronic inflammatory cells increased in portal triad and parenchyma in liver tissue of rats exposed to Mo NPs.

Aging has the opposite effect on cAMP and cGMP circadian variations in rat Leydig cells

The Leydig cell physiology displays a circadian rhythm driven by a complex interaction of the reproductive axis hormones and circadian system. The final output of this regulatory process is circadian pattern of steroidogenic genes expression and testosterone production. Aging gradually decreases robustness of rhythmic testosterone secretion without change in pattern of LH secretion. Here, we analyzed effect of aging on circadian variation of cAMP and cGMP signaling in Leydig cells. Results showed opposite effect of aging on cAMP and cGMP daily variation. Reduced amplitude of cAMP circadian oscillation was probably associated with changed expression of genes involved in cAMP production (increased circadian pattern of Adcy7, Adcy9, Adcy10 and decreased Adcy3); cAMP degradation (increased Pde4a, decreased Pde8b, canceled rhythm of Pde4d, completely reversed circadian pattern of Pde7b and Pde8a); and circadian expression of protein kinase A subunits (Prkac/PRKAC and Prkar2a). Aging stimulates expression of genes responsible for cGMP production (Nos2, Gucy1a3 and Gucy1b3/GUCYB3) and degradation (Pde5a, Pde6a and Pde6h) but the overall net effect is elevation of cGMP circadian oscillations in Leydig cells. In addition, the expression of cGMP-dependent kinase, Prkg1/PRKG1 is up-regulated. It seems that aging potentiate cGMP- and reduce cAMP-signaling in Leydig cells. Since both signaling pathways affect testosterone production and clockwork in the cells, further insights into these signaling pathways will help to unravel disorders linked to the circadian timing system, aging and reproduction.

Molecular regulation of steroidogenesis in endocrine Leydig cells

Steroid hormones regulate essential physiological processes and inadequate levels are associated with various pathological conditions. Consequently, the process of steroid hormone biosynthesis is finely regulated. In the testis, the main steroidogenic cells are the Leydig cells. There are two distinct populations of Leydig cells that arise during development: fetal and adult Leydig cells. Fetal Leydig cells are responsible for masculinizing the male urogenital tract and inducing testis descent. These cells atrophy shortly after birth and do not contribute to the adult Leydig cell population. Adult Leydig cells derive from undifferentiated precursors present after birth and become fully steroidogenic at puberty. The differentiation of both Leydig cell populations is controlled by locally produced paracrine factors and by endocrine hormones. In fully differentially and steroidogenically active Leydig cells, androgen production and hormone-responsiveness involve various signaling pathways and downstream transcription factors. This review article focuses on recent developments regarding the origin and function of Leydig cells, the regulation of their differentiation by signaling molecules, hormones, and structural changes, the signaling pathways, kinases, and transcription factors involved in their differentiation and in mediating LH-responsiveness, as well as the fine-tuning mechanisms that ensure adequate production steroid hormones.

Melatonin replacement restores the circadian behavior in adult rat Leydig cells after pinealectomy

Melatonin actions on oscillators in reproductive organs are poorly understood. Here we analyzed melatonin effects on rhythmic expression of clock and steroidogenesis-related genes in adult rat Leydig cells (LCs). The effect of melatonin was tested both in vivo using pinealectomized and melatonin-substituted rats and in vitro on isolated LCs. Data revealed 24-h-rhythmic expression of clock genes (Bmal1, Per1,2,3, Rev-erba,b, Rorb), steroidogenic genes (Star, Cyp11a1, Cyp17a1), and genes of steroidogenic regulators (positive-Nur77, negative-Arr19). Pinealectomy increased 24-h-oscillations of serum testosterone and LC's cAMP levels, expression of Insl3, Per1, Star/StAR, Hsd3b1/2, Nur77, decreased Arr19 and canceled Per2 oscillatory expression pattern. At hypothalamic-pituitary level, pinealectomy increased mesor of Gnrh, Lhb and rhythm robustness of Mntr1a expression. All parameters disturbed were restored by melatonin-replacement. In vitro studies did not confirm direct melatonin effects on neither clock nor steroidogenic genes. Accordingly, melatonin influence 24-h-rhythmic LC-function likely through hypothalamic-pituitary axis and consequently cAMP-signaling in LCs.

Molecular adaptations of testosterone-producing Leydig cells during systemic in vivo blockade of the androgen receptor

This study systematically evaluates the effects of androgen receptor (AR) blockade on molecular events in Leydig cells. Results showed that intramuscular administration of testosterone-enanthate, at clinically relevant dose, decreased testosterone in interstitial fluid and Leydig cells from adult rats. AR-blocker (Androcur) prevented this effect and testosterone-reduced Leydig cells steroidogenic capacity/activity. Testosterone-reduced expression of some steroidogenic enzymes/proteins (Tspo,StAR,Hsd3b1/2) and transcription factors (Nur77,Gata4,Dax1) was completely abrogated, while decreased expression of Star,Cyp11a1,Cyp17a1,Hsd17b4,Creb1a was partially prevented. In the same cells, increased expression of Hsd3b5/HSD3B and Ar/AR was abolished. Androcur-treatment abolished testosterone-reduced cAMP, coupled with a changed expressional milieu of cAMP signaling elements. Results from in vitro experiments suggest that some of these effects are testosterone-AR dependent, while others could be due to disturbed LH and/or other signals. Presented data provide new molecular insight into Leydig cells function and are important in terms of human reproductive health and the wide-spread use of Androcur as well as use/abuse of testosterone-enanthate.

Age related changes of cAMP and MAPK signaling in Leydig cells of Wistar rats

Here, we chronologically analyzed age-associated changes of cAMP- and MAPK-signaling in Leydig cells (LCs) in relation with decreased testosterone (T) production. In Wistar rats, decreased serum T observed in 12 to 24-month-old rats was not related to decreased serum LH concentration but to reduced luteinizing hormone receptor (Lhr/LHR) and time-coordinated reduction of steroidogenic gene expression (decreased Cyp11a1, Cyp17a1 in 12-month-old rats followed by decreased Star/StAR, Hsd3b/HSD3B, Hsd17b4, and increased Cyp19a1 later in life). The predecessors of age-related changes noted in LCs from 6 to 12-month-old rats were increased level of soluble adenylate cyclase (Adcy/AC) 10, increased JNK phosphorylation but suppressed P38 MAPK. At approximately the same time changed mRNA abundance for transcription factors important for steroidogenesis was detected (increased Nur77 and decreased Sf1, Dax1). Aging caused biphasic expression pattern of ERK1/2 and Nur77: increased in 12-month but decreased in LCs from 24-month-old rats. Further, decreased basal cAMP level observed from 12 to 24th month coincidence with increased expression of cAMP-specific phosphodiesterase (Pde)4a, Pde4b and regulatory subunit of protein kinase A (Prkar/PKAR). Exposing of senescent LCs to permeable cAMP-analog improved transcription of Sf1, Nur77, Star, Cyp11a1,Cyp17a1, but without effect on aging pattern of Dax1, Pde4a/b, Prkar2a, Lhr and MAPK genes. Collectively, results indicated that age-related LC dysfunction is accompanied with changes in MAPK and cAMP signaling and coordinated reduction in the expression of many of the genes that participate in T synthesis. The predecessors of aged-related changes are increased ratio of pJNK/JNK, AC10 and decreased P38 level in LCs from 6-month-old rats.

The opposing roles of nitric oxide and cGMP in the age-associated decline in rat testicular steroidogenesis

The molecular mechanism of the aging-associated dysfunction of Leydig cells (LCs) is complex and poorly understood. In this study, we analyzed the contribution of nitric oxide (NO) and cGMP signaling to the age-dependent decline in LC function. Significant (>50%) decreases in serum, intratesticular, and LC androgens in aging rats (15-24 months) were accompanied by a proportional increase in NO production, an up-regulation of cGMP levels, and the expression of soluble guanylyl cyclase-1B and protein kinase G1 in LCs. In contrast, LC cAMP levels decreased with age, most likely reflecting the up-regulation of cAMP-specific phosphodiesterase expression. Moreover, the expression of genes encoding enzymes responsible for cholesterol transport and its conversion to T were reduced. Exposing LCs from aged animals to NO further increased cGMP levels and decreased cAMP and androgen production, whereas the addition of cell-permeable 8-bromoguanosine-cGMP alone had the opposite effect. In vivo inhibition of cGMP-specific phosphodiesterase-5 for 3 and 6 months in aged rats led to a partial restoration of androgens, NO, and cyclic nucleotide levels, as well as the expression of steroidogenic and NO/cGMP signaling genes. These results indicate that a progressive increase in NO production contributes to the age-dependent decrease in steroidogenesis in a cGMP-independent manner, whereas the sustained elevation in cGMP levels significantly slows the decline in LC function.

Sildenafil increases serum testosterone levels by a direct action on the testes

Phosphodiesterase-5-inhibitors, such as sildenafil, increase intracavernosal cyclic guanosine monophosphate levels, which results in corporal smooth muscle relaxation and penile erection. Here, we determined the effects of sildenafil administration on the hypothalamic-pituitary-gonadal axis in men with erectile dysfunction and low testosterone levels. The Testosterone and Erectile Dysfunction trial (ClinicalTrials.gov # NCT00512707) initially administered an optimized dose of sildenafil to 140 men, aged 40-70 years with erectile dysfunction, low serum total testosterone (<11.4 nmol/L; 330 ng/dL) and/or free testosterone (<173 pmol/L; 50 pg/mL) over 3-7 weeks. Sex steroids and gonadotropins were measured at baseline and after sildenafil optimization in a longitudinal study without a separate control group. Serum testosterone, dihydrotestosterone (DHT) and oestrogens were measured using liquid chromatography-tandem mass spectrometry. Administration of an optimized dose of sildenafil was associated with mean increases of 3.6 nmol/L (103 ng/dL; p < 0.001) and 110 pmol/L (31.7 pg/mL; p < 0.001) in total and free testosterone levels respectively. This was accompanied by parallel increases in serum DHT (0.17 nmol/L; 4.9 ng/dL; p < 0.001) and oestradiol (14 pmol/L; 3.7 pg/mL; p < 0.001) and significant suppression of luteinizing hormone (change -1.3 units/L; p = 0.003) levels, suggesting a direct effect at the testicular level. Androstenedione and oestrone increased by 1.3 nmol/L (38 ng/dL; p = 0.011) and 10.7 pmol/L (2.9 pg/mL; p = 0.012), respectively, supporting a possible effect of sildenafil on adrenal steroidogenesis. In conclusion, sildenafil administration was associated with increased testosterone levels likely ascribable to a direct effect on the testis.

Oxidative stress in testis of animals during aging with and without reproductive activity

The free radical theory of aging postulates that an imbalance between reactive oxygen species (ROS) and reactive nitrogen species (RNS) and antioxidant defenses is important in senescence. To address this issue and gain insight into the aging process, we have evaluated the antioxidant defenses and have assessed oxidative damage in testis tissues in aging male rats. In order to relate aging and reproduction, animals with and without reproductive activity were studied. In reproductive animals the results showed a progressive increase in antioxidant enzyme activity until 12 months of age followed by an abrupt fall at 24 months. In non-reproductive animals, antioxidant activity was stable through 12 months of age, but again, fell abruptly at 24 months of age. In addition, increased aconitase activity and increased testosterone levels were found among reproductively active animals. The data demonstrate the existence of metabolic differences in testis of reproductively experienced animals and reproductively naïve animals.

Male germ cell-specific knockout of cholesterogenic cytochrome P450 lanosterol 14α-demethylase (Cyp51)

Cytochrome P450 lanosterol 14α-demethylase (CYP51) and its products, meiosis-activating sterols (MASs), were hypothesized by previous in vitro studies to have an important role in regulating meiosis and reproduction. To test this in vivo, we generated a conditional male germ cell-specific knockout of the gene Cyp51 in the mouse. High excision efficiency of Cyp51 allele in germ cells resulted in 85-89% downregulation of Cyp51 mRNA and protein levels in germ cells. Quantitative metabolic profiling revealed significantly higher levels of CYP51 substrates lanosterol and 24,25-dihydrolanosterol and substantially diminished levels of MAS, the immediate products of CYP51. However, germ cell-specific ablation of Cyp51, leading to lack of MAS, did not affect testicular morphology, daily sperm production, or reproductive performance in males. It is plausible that due to the similar structures of cholesterol intermediates, previously proposed biological function of MAS in meiosis progression can be replaced by some other yet-unidentified functionally redundant lipid molecule(s). Our results using the germ cell-specific knockout model provide first in vivo evidence that the de novo synthesis of MAS and cholesterol in male germ cells is most likely not essential for spermatogenesis and reproduction and that MASs, originating from germ cells, do not cell-autonomously regulate spermatogenesis and fertility.

Acute effects of hexabromocyclododecane on Leydig cell cyclic nucleotide signaling and steroidogenesis in vitro

Hexabromocyclododecane (HBCDD), an additive brominated flame retardant routinely added to various consumer products, was reported to have toxic effects upon biota, including endocrine disruption. In this study, the potential toxicity of HBCDD was tested in peripubertal rat Leydig cells in vitro during 6h exposure. HBCDD inhibited human chorionic gonadotropin- and forskolin-supported cAMP accumulation and steroidogenesis. It also inhibited basal cAMP production, but elevated basal steroidogenesis. The expression of several cAMP-dependent genes, including steroidogenic acute regulatory protein, cholesterol side chain cleavage enzyme, and 3β-hydroxysteroid dehydrogenase, was also inhibited by HBCDD treatment. Nevertheless, this was not accompanied by a decrease in steroidogenic acute regulatory protein expression, as documented by western blot analysis, and activity of steroidogenic enzymes, as documented by unaffected steroidogenesis in the presence of permeable 22(R)-hydroxycholesterol. However, HBCDD caused significant decrease in mitochondrial membrane potential in untreated and human chorionic gonadotropin-treated cells. This indicates that HBCDD acute toxicity in Leydig cells reflects changes in mitochondrial membrane potential-dependent cAMP production and basal and cAMP-regulated cholesterol transport. This in turn facilitates basal but inhibits cAMP-dependent steroidogenesis. Acute effects of HBCDD treatment on transcription are also indicative of its sustained effects on Leydig cell function.

Orally applied doxazosin disturbed testosterone homeostasis and changed the transcriptional profile of steroidogenic machinery, cAMP/cGMP signalling and adrenergic receptors in Leydig cells of adult rats

Doxazosin (Doxa) is an α1-selective adrenergic receptor (ADR) antagonist widely used, alone or in combination, to treat high blood pressure, benign prostatic hyperplasia symptoms, and recently has been suggested as a potential drug for prostate cancer prevention/treatment. This study was designed to evaluate the effect of in vivo Doxa po-application, in clinically relevant dose, on: (i) steroidogenic machinery homeostasis; (ii) cAMP/cGMP signalling; (iii) transcription profile of ADR in Leydig cells of adult rats. The results showed that po-application of Doxa for once (1×Doxa), or for two (2×Doxa) or 10 (10×Doxa) consecutive days significantly disturbed steroidogenic machinery homeostasis in Leydig cells. Doxa po-application significantly decreased circulating luteinizing hormone and androgens levels. The level of androgens in testicular interstitial fluid and that extracted from testes obtained from 1×Doxa/2×Doxa rats decreased, although it remained unchanged in 10×Doxa rats. Similarly, the ex vivo basal androgen production followed in testes isolated from 1×Doxa/2×Doxa rats decreased, while remained unchanged in 10×Doxa rats. Differently, ex vivo testosterone production and steroidogenic capacity of Leydig cells isolated from 1×Doxa/2×Doxa rats was stimulated, while 10×Doxa had opposite effect. In the same cells, cAMP content/release showed similar stimulatory effect, but back to control level in Leydig cells of 10×Doxa. 1×Doxa/2×Doxa decreased transcripts for cAMP specific phosphodiesterases Pde7b/Pde8b, whereas 10×Doxa increased Pde4d. All types of treatment reduced the expression of genes encoding protein kinase A (PRKA) regulatory subunit (Prkar2b), whereas only 10×Doxa stimulated catalytic subunit (Prkaca). Doxa application more affected cGMP signalling: stimulated transcription of constitutive nitric oxide synthases (Nos1, Nos3) in time-dependent manner, whereas reduced inducible Nos2. 10×Doxa increased guanylyl cyclase 1 transcript and PRKG1 protein in Leydig cells. Orally applied Doxa significantly disturbed the transcriptional 'signature' of steroidogenic machinery, cAMP/cGMP signalling and ADRs and β-ADRs kinases in Leydig cells, thus giving new molecular insights into the role of cAMP/cGMP/adrenalin signalling in Leydig cells homeostasis.

Sickling cells, cyclic nucleotides, and protein kinases: the pathophysiology of urogenital disorders in sickle cell anemia

Sickle cell anemia is one of the best studied inherited diseases, and despite being caused by a single point mutation in the HBB gene, multiple pleiotropic effects of the abnormal hemoglobin S production range from vaso-occlusive crisis, stroke, and pulmonary hypertension to osteonecrosis and leg ulcers. Urogenital function is not spared, and although priapism is most frequently remembered, other related clinical manifestations have been described, such as nocturia, enuresis, increased frequence of lower urinary tract infections, urinary incontinence, hypogonadism, and testicular infarction. Studies on sickle cell vaso-occlusion and priapism using both in vitro and in vivo models have shed light on the pathogenesis of some of these events. The authors review what is known about the deleterious effects of sickling on the genitourinary tract and how the role of cyclic nucleotides signaling and protein kinases may help understand the pathophysiology underlying these manifestations and develop novel therapies in the setting of urogenital disorders in sickle cell disease.

Repeated immobilization stress disturbed steroidogenic machinery and stimulated the expression of cAMP signaling elements and adrenergic receptors in Leydig cells

This study was designed to evaluate the effect of acute (2 h daily) and repeated (2 h daily for 2 or 10 consecutive days) immobilization stress (IMO) on: 1) the steroidogenic machinery homeostasis; 2) cAMP signaling; and the expression of receptors for main markers of 3) adrenergic and 4) glucocorticoid signaling in Leydig cells of adult rats. The results showed that acute IMO inhibited steroidogenic machinery in Leydig cells by downregulation of Scarb1 (scavenger receptor class B), Cyp11a1 (cholesterol side-chain cleavage enzyme), Cyp17a1 (17α-hydroxylase/17,20 lyase), and Hsd17b3 (17β-hydroxysteroid dehydrogenase) expression. In addition to acute IMO effects, repeated IMO increased transcription of Star (steroidogenic acute regulatory protein) and Arr19 (androgen receptor corepressor 19 kDa) in Leydig cells. In the same cells, the transcription of adenylyl cyclases (Adcy7, Adcy9, Adcy10) and cAMP-specific phosphodiesterases (Pde4a, Pde4b, Pde4d, Pde7a, Pde8a) was stimulated, whereas the expression of the genes encoding protein kinase A subunits were unaffected. Ten times repeated IMO increased the levels of all adrenergic receptors and β-adrenergic receptor kinase (Adrbk1) in Leydig cells. The transcription analysis was supported by cAMP/testosterone production. In this signaling scenario, partial recovery of testosterone production in medium/content was detected. The physiological significance of the present results was proven by ex vivo application of epinephrine, which increased cAMP/testosterone production by Leydig cells from control rats in greater fashion than from stressed. IMO did not affect the expression of transcripts for Crhr1/Crhr2 (corticotropin releasing hormone receptors), Acthr (adrenocorticotropin releasing hormone receptor), Gr (glucocorticoid receptor), and Hsd11b1 [hydroxysteroid (11-β) dehydrogenase 1], while all types of IMO stimulated the expression of Hsd11b2, the unidirectional oxidase with high affinity to inactivate glucocorticoids. Thus, presented data provide new molecular/transcriptional base for "fight/adaptation" of Leydig cells and new insights into the role of cAMP, epinephrine, and glucocorticoid signaling in recovery of stress-impaired Leydig cell steroidogenesis.

Transient rise of serum testosterone level after single sildenafil treatment of adult male rats

INTRODUCTION

Phosphodiesterase type 5 (PDE5) inhibitors have been established in therapy for a variety of physiological disorders including erectile dysfunction. Despite its popularity and wide usage in erectile dysfunction treatment, the short-term effect of PDE5 inhibition on Leydig cell functionality and testosterone dynamics is missing.

AIM

This study was designed to assess the acute in vivo effects of sildenafil citrate (Viagra) treatment on testosterone production.

METHODS

Male adult rats were given sildenafil (1.25 mg/kg BW) per os, and testosterone production were analyzed 30, 60, 120, and 180 minutes after treatment. Additionally, in vitro effect of sildenafil extract on Leydig cell steroidogenesis was estimated.

MAIN OUTCOME MEASURES

The formation of testicular interstitial fluid (TIF), and testosterone, cyclic guanosine monophosphate (cGMP), cyclic adenosine monophosphate (cAMP) content was followed. Occurrence and phosphorylation of mature steroidogenic acute regulatory protein (StAR) and interaction with protein kinase G 1 (PRKG1) were assessed by immunoprecipitation and Western blot.

RESULTS

Serum testosterone was increased 60 and 120 minutes after sildenafil treatment. In 60 minutes, TIF volume was doubled and stayed increased till the end of the experimental period. cGMP and testosterone content in TIF were increased 30 minutes after treatment, and cAMP decreased in 60 minutes. Further, sildenafil-induced stimulation of testosterone production was abolished by ex vivo addition of PRKG1 inhibitor but not by protein kinase A inhibitor. Sildenafil treatment increased the level of phosphorylated and total StAR protein. Moreover, co-immunoprecipitation of StAR and PRKG1 was increased following sildenafil treatment suggesting the active role of this kinase in initiation of testosterone synthesis. Additionally, sildenafil extract applied in vitro on primary Leydig cell culture increased cGMP accumulation and testosterone production in time- and dose-dependent manner without effect on cAMP level.

CONCLUSION

Acute sildenafil treatment enlarged TIF volume but also stimulated testosterone production which may be significant considering the positive testosterone effect in regulation of sexual activity.

The roles of cyclic nucleotide phosphodiesterases (PDEs) in steroidogenesis

The second messenger, cAMP, is one of the most important regulatory signals for control of steroidogenesis. This review focuses on current knowledge about regulation of cyclic nucleotides by phosphodiesterases (PDEs) in steroidogenic tissues. The first PDE known to directly regulate steroidogenesis was PDE2, the cGMP-stimulated PDE. PDE2 mediates ANP/cGMP-induced decreases in aldosterone production. Recently, the PDE8 family has been shown to control steroidogenesis in two tissues. Specifically, PDE8A regulates testosterone production by itself and in concert with additional IBMX-sensitive PDEs. PDE8B modulates basal corticosterone synthesis via acute and chronic mechanisms. In addition to cAMP-dependent pathways, cGMP signaling also can promote steroidogenesis, and PDE5 modulates this process. Finally, PDE mutations may lead to several human diseases characterized by abnormal steroid levels.

eNOS activation and NO function: differential control of steroidogenesis by nitric oxide and its adaptation with hypoxia

Nitric oxide (NO) plays a role in a wide range of physiological processes. Aside from its widely studied function in the regulation of vascular function, NO has been shown to impact steroidogenesis in a number of different tissues. The goal of this review is to explore the effects of NO on steroid production and further, to discern its source(s) and mechanism of action. Attention will be given to the regulation of NO synthases in specific endocrine tissues including ovaries, testes, and adrenal glands. The effects of hypoxia on generation of NO and subsequent effects on steroid biosynthesis will also be examined. Finally, a potential model for the interaction of hypoxia on NO synthesis and steroid production is proposed.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.

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.

Testosterone-induced modulation of nitric oxide-cGMP signaling pathway and androgenesis in the rat Leydig cells

Testosterone, acting as a systemic and local factor, is one of the major regulatory molecules that initiate and maintain testicular function. In the present study, different experimental approaches were used to evaluate the role of testosterone in regulation of the nitric oxide (NO)-cGMP pathway in Leydig cells derived from normal and hypogonadotropic male rats treated with testosterone for 24 h and 2 wk. Real-time quantitative PCR and Western blot analysis revealed increased inducible NO synthase (NOS2) expression followed by increased NO secretion from Leydig cells ex vivo after continuous treatment with testosterone for 2 wk in vivo. The cGMP-specific phosphodiesterases Pde5, Pde6, and Pde9 were up-regulated, whereas PRKG1 protein was decreased after a 2-wk testosterone treatment. Induction of Nos2 and Pde5 in Leydig cells was blocked by androgen receptor antagonist. In experimental hypogonadotropic hypogonadism, expression of NOS2 was significantly reduced, and treatment with testosterone increased NOS2 expression above control levels. PDE5 protein level was unchanged in hypogonadal rats, whereas treatment of hypogonadal rats with testosterone significantly increased it. In contrast, hypogonadism and testosterone replacement reduced PRKG1 protein in Leydig cells. In vitro treatment with testosterone caused gradually increased Nos2 gene expression followed by increased nitrite and cGMP production by purified Leydig cells. In summary, testosterone up-regulated NO signaling via increased NOS2 expression and contributed to down-regulation of cGMP signaling in Leydig cells. Thus, testosterone-induced modulation of NO-cGMP signaling may serve as a potent autocrine regulator of testicular steroidogenesis.

Chronic treatment with sildenafil stimulates Leydig cell and testosterone secretion

The phosphodiesterase type 5 (PDE5) inhibitor, Sildenafil, is a novel, oral treatment approach for pulmonary hypertension. As Leydig cells present PDE5, this study was conducted to investigate the effects of the chronic treatment with Sildenafil (25 mg/kg) on male Swiss Webster mice steroidogenesis. After a 4-week long experimental design, Leydig cells were analysed by morphological and immunocytochemical procedures. Serum testosterone was assayed by radioimmunoassay. Leydig cells presented noteworthy ultrastructural alterations, such as a vesicular smooth endoplasmic reticulum, large vacuoles scattered through the cytoplasm, enlarged mitochondria with discontinue cristaes and whorle membranes with vesicles at the periphery, which are typical characteristics of an activated steroid-secreting cell. Important immunocytochemical labelling for steroidogenic acute regulatory protein, cytochrome P450 side-chain cleavage enzyme and testosterone were detected in isolated Leydig cells. In addition, Sildenafil-treated mice showed significant increased levels of total testosterone. The results obtained in the present study are consistent with the hypothesis that the accumulation of cyclic guanosine monophosphate by PDE5 inhibition could be involved in the androgen biosynthesis stimulation. Important clinical implications of hormonal disorders should be taken into account for patients with pulmonary hypertension.

cGK substrates

Signalling of cGK (cGMP-dependent protein kinases) are mediated through phosphorylation of specific substrates. Several substrates of cGKI and cGKII were identified meanwhile. Some cGKI substrates are specifically regulated by the cGKIalpha or the cGKIbeta isozyme. In various cells and tissues, different cGK substrates exist that are essential for the regulation of diverse functions comprising tissue contractility, cell motility, cell contact, cellular secretion, cell proliferation, and cell differentiation. On the molecular level, cGKI substrates fulfill various cellular functions regulating e.g. the intracellular calcium and potassium concentration, the calcium sensitivity, and the organisation of the intracellular cytoskeleton. cGKII substrates are involved e.g. in chloride transport, sodium/proton transport and transcriptional regulation. The understanding of cGK signalling and function depends strongly on the identification of further specific substrates. In the last years, diverse approaches ranging from biochemistry to genetic deletion lead to the identification and establishment of several substrates, which raised new insights in the molecular mechanisms of cGK functions and elucidated new cellular cGK functions. However, the analysis of the dynamic signalling of cGK in tissues and cells will be necessary to discover new signalling pathways and substrates.

Activation of Cl- channels by human chorionic gonadotropin in luteinized granulosa cells of the human ovary modulates progesterone biosynthesis

Chloride permeability pathways and progesterone (P4) secretion elicited by human chorionic gonadotropin (hCG) in human granulosa cells were studied by electrophysiological techniques and single-cell volume, membrane potential and Ca2+i measurements. Reduction in extracellular Cl(-) and equimolar substitution by the membrane-impermeant anions glutamate or gluconate significantly increased hCG-stimulated P4 accumulation. A similar result was achieved by exposing the cells to hCG in the presence of a hypotonic extracellular solution. Conversely, P4 accumulation was drastically reduced in cells challenged with hCG exposed to a hypertonic solution. Furthermore, conventional Cl(-) channel inhibitors abolished hCG-mediated P4 secretion. In contrast, 25-hydroxycholesterol-mediated P4 accumulation was unaffected by Cl(-) channel blockers. In human granulosa cells, hCG triggered the activation of a tamoxifen-sensitive outwardly rectifying Cl(-) current comparable to the volume-sensitive outwardly rectifying Cl(-) current. Exposure of human granulosa cells to hCG induced a rapid 4,4'-diisothiocyanatostilbene-2,2-disulphonic acid-sensitive cell membrane depolarization that was paralleled with an approximately 20% decrease in cell volume. Treatment with hCG evoked oscillatory and nonoscillatory intracellular Ca2+ signals in human granulosa cells. Extracellular Ca2+ removal and 4,4'-diisothiocyanatostilbene-2,2-disulphonic acid abolished the nonoscillatory component while leaving the Ca2+ oscillations unaffected. It is concluded that human granulosa cells express functional the volume-sensitive outwardly rectifying Cl(-) channels that are activated by hCG, which are critical for plasma membrane potential changes, Ca2+ influx, and P4 production.