Type I IGF receptors of Leydig cells are upregulated by human chorionic gonadotropin

Advances in stem cell research for the treatment of primary hypogonadism

In Leydig cell dysfunction, cells respond weakly to stimulation by pituitary luteinizing hormone, and, therefore, produce less testosterone, leading to primary hypogonadism. The most widely used treatment for primary hypogonadism is testosterone replacement therapy (TRT). However, TRT causes infertility and has been associated with other adverse effects, such as causing erythrocytosis and gynaecomastia, worsening obstructive sleep apnoea and increasing cardiovascular morbidity and mortality risks. Stem-cell-based therapy that re-establishes testosterone-producing cell lineages in the body has, therefore, become a promising prospect for treating primary hypogonadism. Over the past two decades, substantial advances have been made in the identification of Leydig cell sources for use in transplantation surgery, including the artificial induction of Leydig-like cells from different types of stem cells, for example, stem Leydig cells, mesenchymal stem cells, and pluripotent stem cells (PSCs). PSC-derived Leydig-like cells have already provided a powerful in vitro model to study the molecular mechanisms underlying Leydig cell differentiation and could be used to treat men with primary hypogonadism in a more specific and personalized approach.

Chemerin Impairs In Vitro Testosterone Production, Sperm Motility, and Fertility in Chicken: Possible Involvement of Its Receptor CMKLR1

The chemokine chemerin is a novel adipokine involved in the regulation of energy metabolism but also female reproductive functions in mammals. Its effects on male fertility are less studied. Here, we investigated the involvement of chemerin in chicken male reproduction. Indeed, the improvement of the sperm of roosters is a challenge for the breeders since the sperm quantity and quality have largely decreased for several years. By using specific chicken antibodies, here we show that chemerin and its main receptor CMKLR1 (chemokine-like receptor 1) are expressed within the chicken testis with the lowest expression in adults as compared to the embryo or postnatal stages. Chemerin and CMKLR1 are present in all testicular cells, including Leydig, Sertoli, and germinal cells. Using in vitro testis explants, we observed that recombinant chicken chemerin through CMKLR1 inhibits hCG (human chorionic gonadotropin) stimulated testosterone production and this was associated to lower 3βHSD (3beta-hydroxysteroid dehydrogenase) and StAR (steroidogenic acute regulatory protein) expression and MAPK ERK2 (Mitogen-Activated Protein Kinase Extracellular signal-regulated kinase 2) phosphorylation. Furthermore, we demonstrate that chemerin in seminal plasma is lower than in blood plasma, but it is negatively correlated with the percentage of motility and the spermatozoa concentration in vivo in roosters. In vitro, we show that recombinant chicken chemerin reduces sperm mass and individual motility in roosters, and this effect is abolished when sperm is pre-incubated with an anti-CMKLR1 antibody. Moreover, we demonstrate that fresh chicken sperm treated with chemerin and used for artificial insemination (AI) in hen presented a lower efficiency in terms of eggs fertility for the four first days after AI. Taken together, seminal chemerin levels are negatively associated with the rooster fertility, and chemerin produced locally by the testis or male tract could negatively affect in vivo sperm quality and testosterone production through CMKLR1.

Growth Hormone and Insulin-Like Growth Factor Action in Reproductive Tissues

The role of growth hormone (GH) in human fertility is widely debated with some studies demonstrating improvements in oocyte yield, enhanced embryo quality, and in some cases increased live births with concomitant decreases in miscarriage rates. However, the basic biological mechanisms leading to these clinical differences are not well-understood. GH and the closely-related insulin-like growth factor (IGF) promote body growth and development via action on key metabolic organs including the liver, skeletal muscle, and bone. In addition, their expression and that of their complementary receptors have also been detected in various reproductive tissues including the oocyte, granulosa, and testicular cells. Therefore, the GH/IGF axis may directly regulate female and male gamete development, their quality, and ultimately competence for implantation. The ability of GH and IGF to modulate key signal transduction pathways such as the MAP kinase/ERK, Jak/STAT, and the PI3K/Akt pathway along with the subsequent effects on cell division and steroidogenesis indicates that these growth factors are centrally located to alter cell fate during proliferation and survival. In this review, we will explore the function of GH and IGF in regulating normal ovarian and testicular physiology, while also investigating the effects on cell signal transduction pathways with subsequent changes in cell proliferation and steroidogenesis. The aim is to clarify the role of GH in human fertility from a molecular and biochemical point of view.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Expression and localization of growth factors and their receptors in the mammalian testis. Part I: Fibroblast growth factors and insulin-like growth factors

It is now well established that normal development and function of testis are mediated by endocrine and paracrine pathways including hormones, growth factors and cytokines as well as by direct cell-to-cell contacts depending on tight, adhering and gap junctions. In the last two decades, several growth factors were identified in the testis of various mammalian species. Growth factors are shown to promote cell proliferation, regulate tissue differentiation, and modulate organogenesis. Interestingly, most of these peptides are expressed not only in the adult mammalian testis during spermatogenesis but also during testicular morphogenesis in prenatal and postnatal life. Our study was launched to provide an overview of the expression, localization, and putative physiological roles of growth factors and their receptors in the mammalian testis. The growth factors considered in this part of our review are fibroblast growth factors and insulin-like growth factors. These factors are found in testicular cells in prenatal, postnatal, and adult animals and are implicated in the regulation of important testicular activities including testicular cord morphogenesis, modulation of testicular hormone secretion and control of spermatogenesis.

Differentiation of adult Leydig cells

Adult Leydig cells originate within the testis postnatally. Their formation is a continuous process involving gradual transformation of progenitors into the mature cell type. Despite the gradual nature of these changes, studies of proliferation, differentiation and steroidogenic function in the rat Leydig cell led to the recognition of three distinct developmental stages in the adult Leydig cell lineage: Leydig cell progenitors, immature Leydig cells and adult Leydig cells. In the first stage, Leydig cell progenitors arise from active proliferation of mesenchymal-like stem cells in the testicular interstitium during the third week of postnatal life and are recognizable by the presence of Leydig cell markers such as histochemical staining for 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and the present of luteinizing hormone (LH) receptors. They proliferate actively and by day 28 postpartum differentiate into immature Leydig cells. In the second stage, immature Leydig cells are morphologically recognizable as Leydig cells. They have an abundant smooth endoplasmic reticulum and are steroidogenically active, but primarily produce 5 alpha-reduced androgens rather than testosterone. Immature Leydig cells divide only once, giving rise to the total adult Leydig cell population. In the third and final stage, adult Leydig cells are fully differentiated, primarily produce testosterone and rarely divide. LH and androgen act together to stimulate differentiation of Leydig cell progenitors into immature Leydig cells. Preliminary data indicate that insulin like growth factor-1 (IGF-1) acts subsequently in the transformation of immature Leydig cells into adult Leydig cells.

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

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

Growth factors as mediators of testicular cell-cell interactions

The development of testicular function may require local cell-cell interactions to regulate tissue growth and differentiation. Locally produced growth factors may mediate the differential growth of mesenchymal, epithelial and germinal cells that occurs during fetal, prepubertal and postpubertal testis development. The complex co-ordination of differential and temporal cellular growth suggests that a variety of locally produced factors may be involved. Presently, a number of growth factors have been identified in the testis, including IGF-I, TGF-alpha, TGF-beta, NGF, IL-1, FGF, SGF and SCSGF. These factors may mediate interactions involving growth stimulation, growth inhibition and differentiation in this tissue (Table 2 and Figure 1). Endocrine agents are also necessary for testis development and function. In many organs, endocrine hormones appear to alter local cell-cell interactions. Similarly, gonadotrophins may modulate growth factor interactions within the testis. Understanding testicular cell-cell interactions involving growth factors requires evaluation of the cellular site of factor expression, production, secretion, target cell action and in vivo significance. Presently, none of the proposed cell-cell interactions involving growth factors have evaluated all these criteria. Further cellular and molecular analysis of these intercellular interactions are necessary to clarify the role of growth factors in the development and maintenance of testicular function.

Insulin-like growth factor receptors in testicular vascular tissue from normal and diabetic rats

Testicular blood vessels contain IGF-I and IGF-II/M6P receptors. Binding to these receptors was altered following treatment with streptozotocin to induce diabetes. Intensity of labelling and size of receptors were examined using SDS-gel electrophoresis and autoradiography. The IGF-I and IGF-II/M6P receptor of the diabetic rat testicular microvessels appear to have a lower molecular weight as compared to controls. Macro- and microvascular tissues from diabetic rats apparently contain more IGF-I receptors than normal Sprague-Dawley rats. Using immunohistochemical techniques, the IGF-II/M6P receptor appears to dissociate easier from diabetic rat testicular arteries than from control animal blood vessels. M6P appears to increase both IGF-I and IGF-II binding to the rat IGF-II/M6P receptor, at least as visualized using affinity crosslinking analysis. Whether these differences in the IGF receptors are involved in the development of diabetic vascular disease is not yet known.

Regulation of insulin-like growth factor-I messenger ribonucleic acid expression in Leydig cells

In the present study, we evaluated insulin-like growth factor-I (IGF-I) messenger RNA expression in the rat testis. Crude interstitial cells were separated into three distinct bands on 15-60% Percoll density gradients. IGF-I mRNA was mainly localized in the Leydig cell-enriched fraction (band 3), while band 1 and band 2 cells did not contain significant amounts of IGF-I mRNA. Leydig cell IGF-I mRNA consisted of multiple species varying from 0.8 to 7.5 kb and was present in rat Leydig cells all ages examined, from 25 to 55 days old. To further document that IGF-I mRNAs are present in Leydig cells, the method of Klinefelter et al. (Biol. Reprod. (1987) 36, 769-783) was used to isolate highly purified (greater than 98% pure) Leydig cells. Most of the IGF-I mRNA was localized in these Leydig cells, while there was no detectable IGF-I mRNA in the whole testis or other interstitial cells. Furthermore, IGF-I mRNA in Leydig cells was increased more than 2-fold by growth hormone (GH) administration in vivo. This suggests that IGF-I mRNA in Leydig cells is also GH dependent. Interstitial IGF-I produced in Leydig cells may have both autocrine and paracrine effects in the testis.

The albumin fraction of rat testicular fluid stimulates steroid production by isolated Leydig cells

Rat testicular fluid (rTF), but not rat serum (rS) or plasma (rP) can further increase within 4 h maximally luteinizing hormone (LH)-stimulated or 22 R-hydroxycholesterol-supported pregnenolone production by immature rat Leydig cells in vitro. This effect of rTF is dose dependent (0.05-1.2% protein, w/v) with an increase up to 4-fold. The objective of the present study was to isolate and characterize the bioactive factor(s) in rTF. After sequential ammonium sulfate fractionation, gel filtration chromatography on Superose 12 and affinity chromatography on concanavalin A-Sepharose it was shown that the albumin fraction was a major biologically active fraction in rTF. The relative specific activity in these fractions was never greater than 1.3-1.4, which is in agreement with the purification factor required to obtain pure albumin from rTF. Commercially obtained albumin fractions from human, bovine and rat sera, up to 99% purity, also increased Leydig cell steroid production more than 3-fold when added in concentrations between 0.1 and 1% w/v in combination with LH or 22R-hydroxycholesterol. Other proteins such as hemoglobin and ovalbumin were not effective in stimulation of steroid production. Bovine serum albumin (bSA, fraction V) at concentrations of 0.25 and 1.0% (w/v), had no or minor effects on LH-stimulated steroid production by rat granulosa cells or adrenocorticotrophic hormone (ACTH)-stimulated steroid production by rat adrenal cells. These findings indicate that albumin itself or minor compounds copurified with albumin represent the main biologically active component in rTF for short-term stimulation of Leydig cell steroid production. Since bioactivity could not be demonstrated in serum which contains similar amounts of albumin as rTF, inhibitory compounds may be present in rat serum.