Testicular endocrine function in GH receptor gene disrupted mice

Effects of Growth Hormone on Adult Human Gonads: Action on Reproduction and Sexual Function

Growth hormone (GH), which is commonly considered to be a promoter of growth and development, has direct and indirect effects on adult gonads that influence reproduction and sexual function of humans and nonhumans. GH receptors are expressed in adult gonads in some species including humans. For males, GH can improve the sensitivity of gonadotropins, contribute to testicular steroidogenesis, influence spermatogenesis possibly, and regulate erectile function. For females, GH can modulate ovarian steroidogenesis and ovarian angiogenesis, promote the development of ovarian cells, enhance the metabolism and proliferation of endometrial cells, and ameliorate female sexual function. Insulin-like growth factor-1 (IGF-1) is the main mediator of GH. In vivo, a number of the physiological effects of GH are mediated by GH-induced hepatic IGF-1 and local IGF-1. In this review, we highlight the roles of GH and IGF-1 in adult human gonads, clarify potential mechanisms, and explore the efficacy and the risk of GH supplementation in associated deficiency and assisted reproductive technologies. Besides, the effects of excess GH on adult human gonads are discussed as well.

Increased testicular insulin-like growth factor 1 is associated with gonadal activation by recombinant growth hormone in immature rats

BACKGROUND

In children, recombinant human growth hormone (rhGH) therapy for treatment of short stature has raised concerns of the early onset of puberty. Puberty is initiated by the activation of the hypothalamus-pituitary-gonad axis. Insulin-like growth factor-1 (IGF1) has been known to mediate physiologic effects of GH. To understand the mechanism of precocious sexual maturation following prepubertal GH therapy, the effects of rhGH on the hypothalamus-pituitary-gonad axis were examined in the immature male rats.

METHODS

Immature male rats were given by daily injection of rhGH (1 or 2 IU/kg) from postnatal day (PND) 21 to PND 23 or 30. The effects of rhGH on kisspeptin-GnRH-LH system in the hypothalamus-pituitary axis, systemic and testicular IGF1, spermatogenesis, steroidogenesis, and circulating testosterone levels were examined. The effects of rhGH on the IGF1 expression and steroidogenesis were examined in progenitor LCs in vitro.

RESULTS

Testicular steroidogenic pathway and spermatogenesis marker mRNA levels, number and size of 17β-hydroxysteroid dehydrogenase (+) LCs, and blood testosterone levels of rhGH rats were significantly higher than those of controls on PNDs 24 and 31. Hypothalamic Kiss1 and Gnrh1 mRNA of rhGH rats were significantly higher than those of controls on PND 24, indicating early activation of hypothalamic kisspeptin-GnRH neurons by rhGH. Hypothalamic Igf1 mRNA levels of rhGH rats were significantly higher than those of controls on PND 24 but significantly lower than those of controls on PND 31. Testicular Igf1 mRNA levels were significantly higher in rhGH rats than in the controls on PNDs 24 and 31 whereas circulating IGF1 levels were not. In progenitor LCs, rhGH significantly increased Igf1 and steroidogenic pathway mRNA levels and testosterone production.

CONCLUSIONS

Local increases in testicular IGF1 might be an important mediator of gonadal maturation via activation of LCs steroidogenesis in immature rats given rhGH.

Growth Hormone-induced STAT5B Regulates Star Gene Expression Through a Cooperation With cJUN in Mouse MA-10 Leydig Cells

Leydig cells produce androgens that are essential for male sex differentiation and reproductive function. Leydig cell function is regulated by several hormones and signaling molecules, including growth hormone (GH). Although GH is known to upregulate Star gene expression in Leydig cells, its molecular mechanism of action remains unknown. The STAT5B transcription factor is a downstream effector of GH signaling in other systems. While STAT5B is present in both primary and Leydig cell lines, its function in these cells has yet to be ascertained. Here we report that treatment of MA-10 Leydig cells with GH or overexpression of STAT5B induces Star messenger RNA levels and increases steroid hormone output. The mouse Star promoter contains a consensus STAT5B element (TTCnnnGAA) at -756 bp to which STAT5B binds in vitro (electrophoretic mobility shift assay and supershift) and in vivo (chromatin immunoprecipitation) in a GH-induced manner. In functional promoter assays, STAT5B was found to activate a -980 bp mouse Star reporter. Mutating the -756 bp element prevented STAT5B binding but did not abrogate STAT5B-responsiveness. STAT5B was found to functionally cooperate with DNA-bound cJUN. The STAT5B/cJUN cooperation was only observed in Leydig cells and not in Sertoli or fibroblast cells, indicating that additional Leydig cell-enriched transcription factors are required. The STAT5B/cJUN cooperation was lost only when both STAT5B and cJUN elements were mutated. In addition to identifying the Star gene as a novel target for STAT5B in Leydig cells, our data provide important new insights into the mechanism of GH and STAT5B action in the regulation of Leydig cell function.

GH-induced LH hyporesponsiveness as a potential mechanism for hypogonadism in male patients with acromegaly

Male patients with acromegaly frequently have hypogonadism. However, whether excess GH affects gonadal function remains unclear. We retrospectively compared clinical features affecting total testosterone (TT) and free testosterone (FT) levels between 112 male patients with acromegaly and 100 male patients with non-functioning pituitary adenoma (NFPA) without hyperprolactinemia. Median maximum tumor diameter (14.4 vs. 26.5 mm) and suprasellar extension rate (33 vs. 100%) were lower in acromegaly, but LH, FSH, TT, and FT were not significantly different. In acromegaly, TT was less than 300 ng/dL in 57%, and FT was below the age-specific reference range in 77%. TT and FT were negatively correlated with GH, IGF-1, and the tumor size, and positively correlated with LH. In NFPA, they were positively correlated with IGF-1, LH, FSH, ACTH, cortisol, and free T4, reflecting hypopituitarism. Multiple regression analysis showed that TT and FT had the strongest correlation with GH in acromegaly, and with LH in NFPA. Surgical remission was achieved in 87.5% of 56 follow-up patients with acromegaly. TT and FT increased in 80.4 and 87.5%, respectively, with a significant increase in LH. In acromegaly, the degree of postoperative increase in TT(FT) correlated with the fold increase of TT(FT)/LH ratio, a potential parameter of LH responsiveness, but not with fold increase of LH, whereas in NFPA it correlated with both. These results suggest that excessive GH is the most relevant factor for hypogonadism in male acromegaly, and may cause impaired LH responsiveness as well as the suppression of LH secretion.

Regulatory effects of quercetin on testicular histopathology induced by cyanide in Wistar rats

Several causes of infertility have been identified, and several papers have documented some compounds that cause infertility. One of the compounds reported to be toxic to the reproductive system is cyanide. In the management of infertility, various mechanisms ranging from synthetic drugs, natural products and supplements have been employed. Quercetin is an antioxidant supplement that has been used in the treatment of a variety of ailments. This work is aimed at investigating the role of quercetin in attenuating spermato-toxicity and testicular-histopathology induced by cyanide.

Seventy-two (72) male wistar rat (weight 190 g ± 10 g) were divided into nine groups (n = 8) except for groups 4 and 5 with (n = 16). Group 1 (control) received physiological saline while Groups 2 and 3 received 0.5 and 1 mg/kg body weight (bwt) cyanide respectively for 56 days, groups 4 and 5 received 0.5 and 1 mg/kg bwt cyanide respectively for 30 days. At day 30, eight animals were sacrificed from Groups 4 and 5 and the remaining eight (8) rats were subdivided into groups (6 and 7) and were given 20 and 40 mg/kg bwt of quercetin respectively for twenty-six days. Co-administration of cyanide and quercetin at a dose of 0.5 mg/kg cyanide +20 mg/kg quercetin and 1 mg/kg cyanide +40 mg/kg quercetin were given to group 8 and 9 respectively for 56 days.

Significant decreases in sperm parameters (count, motile and normal sperm) and increases in malondiadehyde concentration were observed in the cyanide treated groups. Testicular histoarchitecture showed few to no spermatozoa in the lumen of rats treated with cyanide. All these effects were attenuated by quercetin.

In conclusion, quercetin regulates testicular histopathology induced by cyanide in Wistar rats. Data from this work suggests potential preventive or therapeutic applications of quercetin for individuals subjected to cyanide environmental pollution.

Mild Calorie Restriction Does Not Affect Testosterone Levels and Testicular Gene Expression in Mutant Mice

The hypothalamic-pituitary-gonadal (HPG) axis and the somatotropic axis are influenced by nutritional factors. Calorie restriction (CR) extends lifespan but suppresses both the HPG and the somatotropic axes. Since most CR studies use a fairly severe (40%–60%) reduction of calorie intake, we hypothesized that a milder CR (20%) might not be deleterious to reproduction in male mice. To test this hypothesis, we evaluated the effects of 20% CR on testicular testosterone content and on testicular expression of genes that are relevant to testicular function and reproductive competence, including insulin-like growth factor-I, cytochrome P450 aromatase (Cyp19a1), androgen receptor, luteinizing hormone receptor, follicle-stimulating hormone receptor, cytochrome P450c17 and 3-β-hydroxysteroid dehydrogenase/isomerase. To relate CR effects to the activity of the somatotropic axis, we have used growth hormone–resistant GHR knockout mice as well as transgenic mice overexpressing GH. Mild CR did not affect testosterone levels in testis homogenates and had little effect on expression of the examined genes in the reproductive organs. Altered activity of the GH/insulin-like growth factor–1 axis had a major impact on the parameters analyzed. The results also suggest that expression of several key genes involved in the control of testicular function is preserved under conditions of mild CR and encourage speculation that mild regimens of CR can produce longevity benefits without impairing reproduction.

Histological changes of testes in growth hormone transgenic mice with high plasma level of GH and insulin-like growth factor-1

INTRODUCTION

Overexpression of growth hormone (GH) leads to increase in insulin-like growth factor-1 (IGF-1) plasma level, stimulation of growth and increase in body size, organomegaly and reduced body fat. The action of GH affects all the organs and transgenic mice that overexpress bovine GH (bGH mice) serve as convenient model to study somatotropic axis. Male mice overexpressing GH are fertile, however, they show reduced overall lifespan as well as reproductive life span. The aim of the study was to evaluate the morphology and expression of androgen receptor (AR) and luteinizing hormone receptor (LHR) of bGH mice testes.

MATERIAL AND METHODS

The experiment was performed on 6 and 12 month-old bGH male mice and 6 and 12 month-old wild type (WT) littermates (8 animals in each group). The morphology of testes was evaluated on deparaffinized sections stained by the periodic acid-Schiff (PAS) method. Expression of AR and LHR was investigated by immunohistochemistry and diameters of seminiferous tubules (ST) were measured on round cross sections of ST.

RESULTS

We noted larger testes in 6-month bGH mice as compared to normal WT littermates. The morpho-logical observations revealed essentially normal structure of Leydig cells, seminiferous epithelium and other morphological structures. However, some changes like tubules containing only Sertoli cells, tubules with arrested spermatogenesis or vacuoles in seminiferous epithelium could be attributed to the overexpression of GH. In contrast to WT mice, 12 month-old bGH mice displayed first symptoms of testicular aging. The immunoexpres-sion of AR and LHR was decreased in 12 month-old bGH males as compared to 12 month-old WT mice and younger animals.

CONCLUSION

Chronic exposure to elevated GH level accelerates testicular aging and thus potentially may change response of Leydig cells to LH and Sertoli and germ cells to testosterone.

Growth hormone and reproduction: a review of endocrine and autocrine/paracrine interactions

The somatotropic axis, consisting of growth hormone (GH), hepatic insulin-like growth factor I (IGF-I), and assorted releasing factors, regulates growth and body composition. Axiomatically, since optimal body composition enhances reproductive function, general somatic actions of GH modulate reproductive function. A growing body of evidence supports the hypothesis that GH also modulates reproduction directly, exerting both gonadotropin-dependent and gonadotropin-independent actions in both males and females. Moreover, recent studies indicate GH produced within reproductive tissues differs from pituitary GH in terms of secretion and action. Accordingly, GH is increasingly used as a fertility adjunct in males and females, both humans and nonhumans. This review reconsiders reproductive actions of GH in vertebrates in respect to these new conceptual developments.

Endocrine parameters and phenotypes of the growth hormone receptor gene disrupted (GHR-/-) mouse

Disruption of the GH receptor (GHR) gene eliminates GH-induced intracellular signaling and, thus, its biological actions. Therefore, the GHR gene disrupted mouse (GHR-/-) has been and is a valuable tool for helping to define various parameters of GH physiology. Since its creation in 1995, this mouse strain has been used by our laboratory and others for numerous studies ranging from growth to aging. Some of the most notable discoveries are their extreme insulin sensitivity in the presence of obesity. Also, the animals have an extended lifespan, which has generated a large number of investigations into the roles of GH and IGF-I in the aging process. This review summarizes the many results derived from the GHR-/- mice. We have attempted to present the findings in the context of current knowledge regarding GH action and, where applicable, to discuss how these mice compare to GH insensitivity syndrome in humans.

Female gonadal function before and after treatment of acromegaly

CONTEXT

The menstrual cycle is often abnormal in women with acromegaly. Gonadotropin deficiency may be due to a tumor mass effect (macroadenomas) and/or hyperprolactinemia and/or GH excess.

AIM OF THE STUDY

The aim of the study was to analyze the causes of ovarian dysfunction in a large series of patients with acromegaly followed up in a single center.

PATIENTS AND METHODS

Gonadal function was assessed on the basis of menstrual status and hormone assays before and after treatment of acromegaly, between 1985 and 2005, in 55 patients aged from 17 to less than 45 yr.

RESULTS

Seventeen women (31%) were considered to be eugonadal because they had regular menstrual cycles and/or conceived spontaneously. The remaining 38 women had anovulatory cycles. Of these, 11 had hyperprolactinemia and six had hypogonadism due to a mass effect. The cause of the menstrual disturbances was mixed or unclassifiable in 14 cases. In the seven remaining cases, the gonadal dysfunction was likely related to the GH/IGF-I excess, which exerts a direct effect on the gonadotropic axis. Two had polycystic ovary syndrome, which disappeared after normalization of serum GH/IGF-I levels, suggesting that GH/IGF-I excess may also have a direct effect on the ovary. Thirty-eight women became pregnant, and all had healthy children, despite active acromegaly in 12 cases (31%).

CONCLUSION

Gonadal dysfunction is very common in premenopausal women with acromegaly. The potential causes include the lactogenic effect of prolactin, GH, or both on gonadotropic axis. Tumor mass effect or direct effect of GH or IGF-I on the ovary may also participate in ovarian dysfunction.

Effect of recombinant bovine somatotropin on plasma concentrations of insulin-like growth factor I, insulin and membrane integrity of bull spermatozoa

This study aimed to evaluate the effect of the exogenous recombinant bovine somatotropin (rbST) on plasma concentrations of insulin-like growth factor I (IGF-I), insulin and semen quality of bulls. Twenty bulls (Aberdeen Angus and Brangus) were divided by breed into two groups. Placebo group was injected with NaCl 0.9% (s.c.) and treatment group with rbST (s.c., 500 mg) at days 0 and 14 of the experiment. Immediately after semen collection, blood samples were taken on days 0, 14, 28, 42 and 56 of the experiment. Semen was also collected on day 70 of the experiment. Evaluation of sperm motility was performed at pre-freezing and post-thawing stage, whereas assessment of sperm membrane integrity was performed after freezing and thawing. Analysis of data revealed that the effect of treatment and treatment-by-collection day on plasma concentrations of IGF-I and insulin was not significant. However, mean plasma concentrations of IGF-I and insulin were affected (p < 0.0001) by days of blood sampling. Effect of treatment and treatment-by-collection day on motility of spermatozoa was similar (p > 0.05) at pre-freezing and post-thawing stage. Intactness of plasmalemma and tail membrane of spermatozoa at post-thawing stage was higher (p < 0.05) in rbST-treated group than in control. In conclusion, rbST did not affect plasma concentrations of IGF-I and insulin, however, it did improve post-thaw sperm membrane integrity.

Age-related alterations in pituitary and testicular functions in long-lived growth hormone receptor gene-disrupted mice

The somatotropic axis, GH, and IGF-I interact with the hypothalamic-pituitary-gonadal axis in health and disease. GH-resistant GH receptor-disrupted knockout (GHRKO) male mice are fertile but exhibit delayed puberty and decreases in plasma FSH levels, testicular content of LH, and prolactin (PRL) receptors, whereas PRL levels are elevated. Because the lifespan of GHRKO mice is much greater than the lifespan of their normal siblings, it was of interest to compare age-related changes in the hypothalamic-pituitary-gonadal axis in GHRKO and normal animals. Plasma IGF-I, insulin, PRL, LH, FSH, androstenedione and testosterone levels, and acute responses to GnRH and LH were measured in young (2-4 and 5-6 months of age) and old (18-19 and 23-26 months of age) male GHRKO mice and their normal siblings. Plasma IGF-I was not detectable in GHRKO mice. Plasma PRL levels increased with age in normal mice but declined in GHRKO males, and did not differ in old GHRKO and normal animals. Plasma LH responses to acute GnRH stimulation were attenuated in GHRKO mice but increased with age only in normal mice. Plasma FSH levels were decreased in GHRKO mice regardless of age. Plasma testosterone responses to LH stimulation were attenuated in old mice regardless of genotype, whereas plasma androstenedione responses were reduced with age only in GHRKO mice. Testicular IGF-I mRNA levels were normal in young and increased in old GHRKO mice, whereas testicular concentrations and total IGF-I levels were decreased in these animals. These findings indicate that GH resistance due to targeted disruption of the GH receptor gene in mice leads to suppression of testicular IGF-I levels, and modifies the effects of aging on plasma PRL levels and responses of the pituitary and testes to GnRH and LH stimulation. Plasma testosterone levels declined during aging in normal but not in GHRKO mice, and the age-related increase in the LH responses to exogenous GnRH was absent in GHRKO mice, perhaps reflecting a delay of aging in these remarkably long-lived animals.

Clinical and biochemical characteristics of a male patient with a novel homozygous STAT5b mutation

CONTEXT

GH insensitivity can be caused by defects in the GH receptor (GHR) or in the postreceptor signaling pathway. Recently, two female patients with severe growth retardation and pulmonary and immunological problems were described with a defect in STAT5b, a critical intermediary of downstream GHR signaling.

OBJECTIVE

The objective was to determine the functional characteristics of a novel STAT5b mutation and describe the phenotype.

PATIENT

We describe an adult male patient with short stature [-5.9 sd score (SDS)], delayed puberty, and no history of pulmonary or immunological problems. GH-binding protein level as well as GH secretion characteristics were normal. Plasma prolactin level was elevated. Extremely low levels of IGF-I (-6.9 SDS), IGF-binding protein-3 (-12 SDS), and acid-labile subunit (-7.5 SDS) were found.

RESULTS

We found a homozygous frameshift mutation in the STAT5b gene (nucleotide 1102-3insC, Q368fsX376), resulting in an inactive truncated protein, lacking most of the DNA binding domain and the SH2-domain.

CONCLUSIONS

This report confirms the essential role of STAT5b in GH signaling in the human. We show for the first time that immunological or pulmonary problems or elevated GH secretion are not obligatory signs of STAT5b deficiency, whereas hyperprolactinemia appears to be part of the syndrome. Therefore, in patients with severe short stature, signs of GH insensitivity, and a normal GHR, analysis of the STAT5b gene is recommended.

The intraovarian actions of estrogen receptor-alpha are necessary to repress the formation of morphological and functional Leydig-like cells in the female gonad

The predisposition of the testis and ovary to primarily synthesize testosterone (T) and estradiol (E2), respectively, is due to gonadal-specific cell types that differentially express the various hydroxysteroid (17beta) dehydrogenase (HSD17B) isoforms. In testes, Leydig cells rely on LH stimulation to maintain expression of the type 3 (HSD17B3) isoform, which specifically converts androstenedione to T. In ovaries, thecal interstitial (TI) cells also rely on LH to induce androgen synthesis but lack HSD17B3 and therefore secrete androgens of low biological activity. Therefore, thecal cells may possess a mechanism to repress the Leydig cell phenotype and HSD17B3 expression. E2 is known to inhibit experimentally Leydig cell function and proliferation. In the current study, we provide evidence that E2 prevents the development of functional Leydig-like cells in the murine ovary and that this action is mediated by estrogen receptor (ER) alpha. ERalpha-null (alphaERKO) female mice exhibit testis-like levels of Hsd17b3 expression in the ovaries and male-like levels of plasma T. Herein, we demonstrate that: 1) Hsd17b3 expression in alphaERKO ovaries is a primary effect of the loss of intraovarian ERalpha actions; 2) alphaERKO ovarian cells produce substantial levels of T in vitro, and this is blocked by a HSD17B3-specific inhibitor; 3) Hsd17b3 expression in alphaERKO ovaries is LH regulated and localized to the secondary interstitial (SI)/TI cells; and 4) alphaERKO SI/TI cells possess Leydig-like ultrastructural features. These data indicate that intraovarian ERalpha actions are required to repress Hsd17b3 expression in the ovary and may be important to maintaining a female phenotype in SI/TI cells.

Aging-related characteristics of growth hormone receptor/binding protein gene-disrupted mice

Since generation of the growth hormone receptor/binding protein (GHR/BP) gene-disrupted mouse nearly 10 years ago, use of this mouse model has become widespread in the elucidation of the physiological roles of GH and insulin-like growth factor-1 (IGF-1). In particular, it serves as a useful model to study mechanisms of aging. This review highlights the evidence demonstrating that the loss of GH signaling leads to lifespan extension in mice, and presents the multiple characteristics of this mouse line that suggest the life extension is due to alteration of the aging process.

Little effects of insulin-like Growth Factor-I on testicular atrophy induced by hypoxia

BACKGROUND

Insulin-like Growth Factor-I (IGF-I) supplementation restores testicular atrophy associated with advanced liver cirrhosis that is a condition of IGF-I deficiency. The aim of this work was to evaluate the effect of IGF-I in rats with ischemia-induced testicular atrophy (AT) without liver disease and consequently with normal serum level of IGF-I.

METHODS

Testicular atrophy was induced by epinephrine (1, 2 mg/Kg intra-scrotal injection five times per week) during 11 weeks. Then, rats with testicular atrophy (AT) were divided into two groups (n = 10 each): untreated rats (AT) receiving saline sc, and AT+IGF, which were treated with IGF-I (2 microg.100 g b.w.(-1).day(-1), sc.) for 28 d. Healthy controls (CO, n = 10) were studied in parallel. Animals were sacrificed on day 29th. Hypophyso-gonadal axis, IGF-I and IGFBPs levels, testicular morphometry and histopathology, immuno-histochemical studies and antioxidant enzyme activity phospholipid hydroperoxide glutathione peroxidase (PHGPx) were assessed.

RESULTS

Compared to controls, AT rats displayed a reduction in testicular size and weight, with histological testicular atrophy, decreased cellular proliferation and transferrin expression, and all of these alterations were slightly improved by IGF-I at low doses. IGF-I therapy increased significantly steroidogenesis and PHGPx activity (p < 0.05). Interestingly, plasma IGF-I did not augment in rats with testicular atrophy treated with IGF-I, while IGFBP3 levels, that reduces IGF-I availability, was increased in this group (p < 0.05).

CONCLUSION

In testicular atrophy by hypoxia, condition without IGF-I deficiency, IGF-treatment induces only partial effects. These findings suggest that IGF-I therapy appears as an appropriate treatment in hypogonadism only when this is associated to conditions of IGF-I deficiency (such as Laron Syndrome or liver cirrhosis).

Scaffold attachment factor B1 functions in development, growth, and reproduction

Scaffold attachment factor B1 (SAFB1) is a multifunctional protein that can bind both DNA and RNA and is involved in RNA processing and stress response. In addition, SAFB1 contains a transcriptional repression domain and can bind certain hormone receptors and repress their activity. To assess the role of SAFB1 in vivo, we generated SAFB1 mutant mice through targeted deletion in embryonic stem cells. While viable homozygous mutant (SAFB1-/-) mice were obtained, genotypic distribution indicated that homozygous deficiency resulted in both prenatal and neonatal lethality. Mice lacking SAFB1 exhibited dwarfism, as a result of in utero growth retardation, and had low serum insulin-like growth factor 1 (IGF1) levels. In agreement with the previous characterization of SAFB1 as a corepressor for hormone receptors, we found that SAFB1-/- mice displayed dramatic defects in the development and function of the reproductive system. Male SAFB1 null mice were infertile, apparently because of low circulating levels of testosterone. SAFB1-/- testes were small and showed progressive degeneration of the germinal epithelium, increased apoptosis of germ cells, and Leydig cell hyperplasia. SAFB-/- female mice were subfertile and showed progressive infertility, in part because of defects in oviductal transport and reduced numbers of follicles. Immortalized SAFB1-/- mouse embryonic fibroblasts showed cell-intrinsic defects including increased transcriptional estrogen receptor alpha activity and enhanced responsiveness to IGF1. Together, these in vivo findings establish a critical role for SAFB1 in development, growth regulation, and reproduction.

Leydig cell injury as a consequence of an acute graft-versus-host reaction

Hematopoietic stem cell transplantation (HSCT) is associated with significant posttransplantation gonadotoxicity. This deficit has been mainly attributed to pretransplantation conditioning, but lower sperm counts in humans also appear to be associated with graft-versus-host disease (GVHD) following allogeneic HSCT. However, the mechanisms leading to diminished spermatocyte levels during GVHD remain unknown. Here we demonstrate that injury to intratesticular cells occurs in unconditioned F1 mice following the infiltration of donor alloreactive T cells during an acute graft-versus-host reaction (GVHR). Using computer-aided quantitative microscopic morphometry we demonstrate that the nadir of Leydig cell volume density coincides with the peak of intratesticular infiltration by donor T cells. Injury to Leydig cells correlates with an intratesticular inflammatory response characterized by interferon-γ and tumor necrosis factor-α production. These results demonstrate impairment of testosterone-producing Leydig cells during a local alloresponse, thus representing a mechanism that contributes to gonadal insufficiency following allogeneic HSCT.

Reproduction and plasma concentrations of leptin, insulin and insulin-like growth factor 1 in growth-hormone-transgenic female sheep before and after artificial insemination

The transgenic sheep used in this study expressed an additional copy of the gene for ovine growth hormone (GH), so they had continuously high plasma concentrations of GH. They were used to test whether the GH transgene affected plasma concentrations of the metabolic hormones leptin, insulin-like growth factor 1 (IGF-1) and insulin, and whether these effects were associated with changes in conception, pregnancy or parturition following artificial insemination. Compared with control animals, the GH-transgenic sheep had higher bodyweight, lower body condition score and less subcutaneous fat (P < 0.05). These sheep also had lower plasma concentrations of leptin, higher plasma concentrations of insulin, and higher plasma concentrations of IGF-1 (P < 0.001). A similar proportion of GH-transgenic and control ewes came into oestrus, but the conception rate to artificial insemination was lower in GH-transgenic ewes than in the controls. Only four live lambs were recovered from 12 GH-transgenic ewes (33%) compared with 38 lambs from 43 controls (88%). This outcome was not associated with any difference in plasma progesterone profile in the period leading up to artificial insemination (Day 0). The GH-transgenic ewes had lower concentrations of FSH at all times measured (Day -19, Day -2 and Day 19). These results indicate that appropriate regulation of GH secretion from pituitary or peripheral tissues is necessary for normal reproduction and normal levels of metabolic hormones. Chronically high concentrations of GH were associated with increased levels of IGF-1 and insulin, and decreased levels of leptin.

Stimulation of steroidogenesis in immature rat Leydig cells evoked by interleukin-1alpha is potentiated by growth hormone and insulin-like growth factors

The cytokine IL-1alpha is produced constitutively by the intact testis, but its function in this organ remains largely unknown. In this study we examined cooperation between IL-1alpha and GH and IGFs with regard to stimulation of steroidogenesis by Leydig cells from 40-d-old rats in vitro. IL-1alpha alone stimulated testosterone (T) and dihydrotestosterone (DHT) production. GH, IGF-I, or IGF-II alone was without effect on T production, but they were found to elevate DHT release, albeit without an obvious dose-response effect. Costimulation with IL-1alpha and GH or with IL-1alpha and IGF-I or IGF-II elevated the rate of steroidogenesis (both T and DHT) above that observed with IL-1alpha alone. GH was found to increase the level of IGF-I in the cultured Leydig cells, an effect that was potentiated by IL-1alpha. The costimulatory effect of GH on steroidogenesis was abolished by treatment with picropodophyllin, a specific inhibitor of the IGF-I receptor, indicating that the action of GH is mediated via IGF-I. Moreover, cells costimulated with IL-1alpha and GH exhibited a marked decrease in the level of intact IGF-binding protein-3 in the culture medium due to the induction of proteolytic activity toward this binding protein. In contrast, secretion of IGF-binding protein-2 was increased by such costimulation. These findings suggest that the stimulation of steroidogenesis in Leydig cells evoked by GH and IGFs requires cooperation with IL-1alpha. This cooperation may play an important role in connection with postnatal Leydig cell maturation and steroidogenesis.

The Consequences of Altered Somatotropic System on Reproduction1

Although the primary control of gonadotropin secretion is by the hypothalamic GnRH and the gonadal function is controlled by the pituitary gonadotropins and prolactin, the emerging evidence suggests a vital role of the somatotropic axis, growth hormone (GH), and insulin-like growth factor-I (IGF-I) in the control of the pituitary and gonadal functions. It has been shown that GH deficiency, GH resistance, and experimental alterations in IGF-I secretion modify folliculogenesis, ovarian maturation, ovulation, and pregnancy, and in the male, GH/IGF-I plays an important role in spermatogenesis and the Leydig cell function. The primary focus of this review is to examine the role of GH/ IGF-I on the onset of puberty, fertility, pituitary, and gonadal endocrine functions. A number of studies have revealed that fertility is affected in GH-deficient dwarf and in IGF-I gene-ablated mice, possibly due to subnormal function of either the pituitary gland or the gonads. In the female GH receptor gene knockout (GHR-KO) mice, there was impairment in follicular development, ovulation rate, sexual maturation, production of and responsiveness to pheromonal signals, and the corpus luteum function. In IGF-I-deficient male GHR-KO mice, puberty is delayed, spermatogenesis is affected, and neuroendocrine-gonadal function is attenuated. Similarly, in some of the human Laron syndrome patients, puberty is delayed due to GH resistance. These data suggest that, in addition to GnRH and gonadotropins, GH/IGF-I influences the pituitary and gonadal functions in animals and humans.

Reproductive abnormalities in human insulin-like growth factor-binding protein-1 transgenic male mice

Adult transgenic mice overexpressing human insulin-like growth factor-binding protein-1 in the liver present reproductive abnormalities in both sexes. In the present work, we have investigated the mechanisms responsible for limiting breeding capacity in these transgenic male mice. Homozygous adult transgenic male mice (3-6 months old) exhibited irregular copulatory behavior and a reduction of the number of pregnancies per female as well as of litter size per pregnancy. Genital tract weight, more specifically epididymal and seminal vesicle weights, were reduced by 45% in homozygous transgenic vs. nontransgenic mice. Homozygous transgenic mice exhibited a 30% reduction of the length of seminiferous tubules (P = 0.007), a 30% decrease in daily sperm production per testis (P = 0.019), and a 50% decrease in the number of spermatozoa in testis (P = 0.037), associated with morphological abnormalities of the sperm heads leading to an approximately 50% reduction of fertilized two-cell eggs (P = 0.002) and of implanted embryos on d 5.5 after mating (P = 0.004). The round spermatids also appeared altered in their morphology. In addition, Leydig cells in homozygous transgenic mice exhibited an altered appearance, with a 1.8-fold increase in lipid droplets in their cytoplasm (P < 0.001). Moreover, the concentration of 3beta-hydroxysteroid dehydrogenase was 66% lower in testis from transgenics compared with those from normal mice (P = 0.01), leading to a tendency toward lower plasma testosterone levels (P = 0.1). Interestingly, LH concentrations were increased by 40% in transgenic pituitary extracts (P = 0.02), and basal LH secretion by pituitary explants in vitro was increased by 60% in homozygous transgenic vs. normal mice (P = 0.04), suggesting an alteration of LH pulsatile secretion in vivo. In conclusion, these data suggest that the breeding impairment of human insulin-like growth factor-binding protein-1 transgenic males is due at least in part to an alteration of the process of spermatogenesis, leading to a diminution of sperm production and of its quality. Minor impairment of steroidogenesis may also contribute to the reduced reproductive capacity of these animals. Our observations are consistent with the idea that normal spermatogenesis and perhaps also steroidogenesis are dependent on the actions of sufficient concentrations of unbound IGF-I.

Insulin-like growth factors and their binding proteins: Potential relevance to reproductive physiology

Cyclic ovarian follicular development is a complex process that involves proliferation, differentiation, and death of follicle cells. Gonadotropins produced by the pituitary gland have a central role in the regulation of these processes. In addition, a wide range of paracrine and autocrine factors produced in the reproductive organs have been proposed as regulators of reproductive functions. Components of the insulin-like growth factors (IGF) system are widely expressed in the female reproductive tract. The IGFs and their binding proteins play a significant role in several processes of reproductive physiology, including ovarian follicular development, oogenesis and oocyte maturation, ovulation, luteal function, follicular atresia, and testicular function. The majority of these physiological actions of the IGFs are believed to occur via activation of the IGF-I receptor, although the IGF-I effects are modulated by IGF binding proteins (IGFBPs). As much of the data obtained to date have been in the rodent reproductive organs, it may not be possible to directly extrapolate the results to the primate organs. There is a distinct species-difference in the gene expression and functional roles of the IGF-IGFBP system in reproductive organs. However, the disturbance of the IGF-IGFBP system in human reproductive physiology may lead to anovulation, disorders of androgen excess, infertility associated with implantation failure, and male infertility. Further research is needed in domestic animals to determine if manipulation of the IGF-IGFBP system may result in improved reproductive efficiency. As our understanding of the IGF-IGFBP system increases, the uses of human recombinant IGF peptides and IGFBPs as clinical therapy for disease states is becoming a reality. (Reprod Med Biol 2003; 2: 1-24).

Impact of growth hormone resistance on female reproductive function: new insights from growth hormone receptor knockout mice

We examined multiple aspects of reproductive function in growth hormone receptor gene knockout (GHR-KO) and normal mice to clarify the role of growth hormone in female reproduction. In adult animals, estrous cycle duration was comparable in all mice housed individually but was significantly longer in group-housed GHR-KO females. Histological evaluation of ovaries of adult females at estrus showed that the numbers of preovulatory follicles and corpora lutea were significantly reduced in GHR-KO mice, as was the plasma estradiol level. The number of atretic preovulatory follicles was reduced in GHR gene-ablated animals. Although reverse transcription polymerase chain reaction analysis revealed reduced ovarian insulin-like growth factor I (IGF-I) mRNA expression in GHR-KO females, the expression of several steroidogenic enzyme mRNAs did not differ between groups. The numbers of active corpora lutea and uterine implantation sites were reduced in GHR-KO females at Day 7 of gestation. When young females were mated to normal males, latency to first mating and age of the female at first mating were significantly delayed in GHR-KO females, but maternal age at first conception was similar between groups. Significantly fewer virgin GHR-KO females exhibited pseudopregnancies when initially placed with vasectomized normal males than did normal female counterparts. Growth hormone resistance and IGF-I insufficiency negatively impacted 1) follicular development/ovulation rate, 2) sexual maturation, 3) production of and responsiveness to pheromonal signals, and 4) the ability of virgin females to respond to coitus by activation of luteal function. Although GHR-KO female mice are fertile, they exhibit quantitative deficits in various parameters of reproductive function.

Consequences of growth hormone (GH) overexpression and GH resistance

Development of transgenic mice overexpressing GH and GHR-KO mice with GH resistance provided novel animal models for study of the somatotropic axis and for identifying GH actions that may be relevant to its current and contemplated use in medicine and agriculture. Studies of phenotypic characteristics of these animals revealed previously unsuspected actions of GH and IGF-I on neuroendocrine functions related to reproduction and to the release of "stress hormones" (glucocorticoids and prolactin). These studies also provided novel and still-disputed evidence for involvement of somatotropic axis in the control of aging and life span and in mediating the actions of longevity genes.