Estrogen: Roles in Spermatogenesis

Effects of single and combined exposure to zinc and two tetracycline antibiotics on zebrafish at the early stage

Tetracycline antibiotics (TCs) and heavy metals are commonly used in livestock and poultry farming, leading to their coexistence in the aquatic environment. This coexistence causes combined toxicity to aquatic organisms. Here, zebrafish embryos were exposed to chlortetracycline (CTC), oxytetracycline (OTC), zinc chloride (ZnCl₂), and their combinations for 120 h to evaluate their adverse effects on the growth, antioxidant system, immune system, and endocrine system during the early stage of life. OTC/ZnCl₂ combined exposure significantly reduced the body weight, whereas the TCs/ZnCl₂ combination significantly increased the heart rate of zebrafish larvae, suggesting growth impairment induced by TCs and ZnCl₂. Further, combined groups showed more prominent toxicity to the antioxidant system than single groups, as revealed by related levels of enzyme activity and gene expression. In addition, the levels of most pro-inflammatory genes were downregulated, and those of NF-κB-related genes were upregulated in all treatment groups, indicating an immunosuppressive response and the potential role of NF-κB signaling, while the combined treatment was not more toxic than TCs or ZnCl₂ alone. Similarly, hormone and endocrine related gene levels were determined. Although both single and combined exposures caused certain endocrine-disrupting effects, the combined exposure did not result in higher toxicity than a single exposure. Our findings showed that a mixture of TCs and ZnCl₂ might exert greater toxic effects as compared to a single compound on some systems, providing fundamental data on the toxic effects of single and combined TC and ZnCl₂ exposure on aquatic organisms, although studies are needed to explore the underlying mechanisms.

Effect of Letrozole, a selective aromatase inhibitor, on testicular activities in adult mice: Both in vivo and in vitro study

The aim of present study was to evaluate the significance of estradiol (E2) in testicular activities and to find out the mechanism by which E2 regulates spermatogenesis in mice. To achieve this, both in vivo and in vitro effect of Letrozole on testis of adult mice was investigated. Letrozole-induced changes in testicular histology, cell proliferation (proliferating cell nuclear antigen; PCNA), cell survival (B cell lymphoma factor-2; Bcl2), apoptotic (cysteine-aspartic proteases; caspase-3), steroidogenic (side chain cleavage; SCC, 3β-hydroxy steroid dehydrogenase enzyme; 3β HSD, steroidogenic acute regulatory protein; StAR, aromatase and luteinizing hormone receptor; LH-R) markers, glucose level, and rate of expression of glucose transporter (GLUT) 8 and insulin receptor (IR) proteins in the testis along with changes in serum E2 and testosterone (T) levels were evaluated. Letrozole acts on testis and caused significant decrease in E2 synthesis, but increase in testosterone level and showed regressive changes in the spermatogenesis. Letrozole-induced changes in various testicular markers were compared with the changes in serum E2 level. The correlation study showed that decreased circulating E2 level may be responsible for decreased insulin receptor (IR) level in the testis. The decreased effects of insulin inhibited the glucose transport in the testis by suppressing GLUT8. The decreased level of testicular glucose may produce less lactate as energy support to developing germ cells consequently resulting in decreased cell proliferation and cell survival, but increased apoptosis. Thus, Letrozole suppresses spermatogenesis by reducing insulin sensitivity and glucose transport in the testis, but significantly increased testosterone level by promoting gonadotrophin release by decreased E2.

Role of non-receptor protein tyrosine kinases in spermatid transport during spermatogenesis

Non-receptor protein tyrosine kinases are cytoplasmic kinases that activate proteins by phosphorylating tyrosine residues, which in turn affect multiple functions in eukaryotic cells. Herein, we focus on the role of non-receptor protein tyrosine kinases, most notably, FAK, c-Yes and c-Src, in the transport of spermatids across the seminiferous epithelium during spermatogenesis. Since spermatids, which are formed from spermatocytes via meiosis, are immotile haploid cells, they must be transported by Sertoli cells across the seminiferous epithelium during the epithelial cycle of spermatogenesis. Without the timely transport of spermatids across the epithelium, the release of sperms at spermiation fails to occur, leading to infertility. Thus, the molecular event pertinent to spermatid transport is crucial to spermatogenesis. We provide a critical discussion based on recent findings in this review. We also provide a hypothetical model on spermatid transport, and the role of non-receptor protein tyrosine kinases in this event. We also highlight areas of research that deserve attention by investigators in the field.

Estrogens: new players in spermatogenesis

Aromatase that irreversibly transforms androgens into estrogens is present in the smooth endoplasmic reticulum of nearly all cell types in the mammalian testis. In rodents, all testicular cells except for myoid cells express aromatase activity. We have demonstrated the presence of the functional aromatase (transcript or protein, and biological activity) in adult rat germ cells including pachytene spermatocytes and round spermatids. We have also demonstrated estrogen output from these cells equivalent to that of Leydig cells. Unlike androgen receptors, which are localized mainly in testicular somatic cells, estrogen receptors are present in both somatic and germ cells in the testis. Moreover, we have recently described the rapid membrane effects of estrogens (via G protein-coupled receptor [GPER]) in purified rat germ cells. On the basis of various experimental models, in vitro studies and clinical data, it can be concluded that estrogens play an essential role in male reproduction, specifically in the development of spermatozoa.

Regulation of aromatase expression by 1α,25(OH)2 vitamin D3 in rat testicular cells

It is well known that the vitamin D endocrine system is involved in physiological and biochemical events in numerous tissues, especially gut, bone and kidney but also testis. Therefore, in this study the effect and mechanisms of action of 1α,25(OH)2 vitamin D3 (1,25D) on aromatase gene expression in immature rat Sertoli cells were evaluated. Vitamin D receptor transcripts were present in immature Sertoli cells as well as in adult testicular germ cells and somatic cells. The treatment of immature Sertoli cells with 100 nM 1,25D increased the amount of aromatase transcript, mainly in 30-day-old rats. The protein kinase A (PKA) blocker, H89, partially inhibited the 1,25D effect. The stimulation of aromatase gene expression in 30-day-old Sertoli cells by the agonist 1α,25(OH)2 lumisterol3, and the suppression of the 1,25D effect by the antagonists 1β,25(OH)2 vitamin D3 and (23S)-25-dehydro-1α (OH)-vitamin D3-26,23-lactone suggested, besides a genomic effect of 1,25D, the existence of non-genomic activation of the membrane-bound vitamin D receptor involving the PKA pathway.

A local autocrine axis in the testes that regulates spermatogenesis

Spermiation--the release of mature spermatozoa from Sertoli cells into the seminiferous tubule lumen--occurs by the disruption of an anchoring device known as the apical ectoplasmic specialization (apical ES). At the same time, the blood-testis barrier (BTB) undergoes extensive restructuring to facilitate the transit of preleptotene spermatocytes. While these two cellular events take place at opposite ends of the Sertoli cell epithelium, the events are in fact tightly coordinated, as any disruption in either process will lead to infertility. A local regulatory axis exists between the apical ES and the BTB in which biologically active laminin fragments produced at the apical ES by the action of matrix metalloproteinase 2 can regulate BTB restructuring directly or indirectly via the hemidesmosome. Equally important, polarity proteins play a crucial part in coordinating cellular events within this apical ES-BTB-hemidesmosome axis. Additionally, testosterone and cytokines work in concert to facilitate BTB restructuring, which enables the transit of spermatocytes while maintaining immunological barrier function. Herein, we will discuss this important autocrine-based cellular axis that parallels the hormonal-based hypothalamic-pituitary-testicular axis that regulates spermatogenesis. This local regulatory axis is the emerging target for male contraception.

Aromatase, oestrogens and human male reproduction

In most mammalian species aromatase is encoded by a single gene (Cyp19), which contains 18 exons, nine of them being translated. In man, the presence of a biologically active aromatase and oestrogen receptors (ERalpha and ERbeta) has been reported in Leydig cells, and also in immature germ cells and ejaculated spermatozoa. Concerning aromatase, the amount of transcript and enzymatic activity are decreased in immotile compared with motile sperm. We have amplified aromatase mRNA by real-time polymerase chain reaction in spermatozoa from asthenospermic, teratospermic and asthenoteratospermic men and recorded, respectively, 44, 52 and 67 per cent decreases of the amount of transcripts compared with fertile donors. A high degree of correlation (r = -0.64) between the abnormal spermatozoa (especially microcephaly and acrosome malformations) and aromatase/GAPDH transcript ratio has been observed. Idiopathic infertility is a wide health problem and no treatment is currently available. In humans, even if the role of oestrogens in spermatogenesis is still a matter of debate, the observations of decreased sperm number and motility in men genetically deficient in aromatase, together with our data and those reported in the literature, may suggest a role for aromatase/oestrogens not only during the development and maintenance of spermatogenesis but also in the final maturation of spermatozoa.

Regulation of spermatogenesis in the microenvironment of the seminiferous epithelium: new insights and advances

Spermatogenesis is a complex biochemical event, involving the participation of the hypothalamus and the pituitary gland via secretion of the hypothalamus hormone GnRH, and two pituitary hormones FSH and LH. Thus, the hypothalamic-pituitary-testicular axis is a crucial regulatory axis for testicular function. Recent studies have shown that in the microenvironment of the seminiferous epithelium, wherein each Sertoli cell supports approximately 30-50 germ cells at different stages of development, locally produced autocrine and paracrine factors are also involved in spermatogenesis, in particular at the level of cell junctions. These cell junctions at the Sertoli-Sertoli and Sertoli-germ cell interface are crucial for coordinating different events of spermatogenesis by sending signals back-and-forth between Sertoli and germ cells, in order to precisely regulate spermatogonial cell renewal by mitosis, cell cycle progression, meiosis, spermiogenesis, germ cell movement across the epithelium, spermiation and germ cell apoptosis. In this minireview, we provide an update on these latest findings for an emerging new concept regarding the presence of a local "apical ectoplasmic specialization-blood-testis barrier-hemidesmosome/basement membrane" functional axis that regulates the events of spermiation and blood-testis barrier (BTB) restructuring via paracrine/autocrine factors and polarity proteins produced locally in the seminiferous epithelium. These findings provide a new window of research for investigators in the field to tackle the functional regulation of spermatogenesis.

Medicinal plants as potential male anti-infertility agents: a review

For millions of couples, the inability to have a child is a personal tragedy and a large proportion of childless people are confronted with social stigmatization (blame) and personal frustration. Formerly assigned to women, infertility of a couple is nowadays equitably distributed between the two sexes. Among the methods used to treat male infertility problems, medicinal plants have been used empirically as extracts, decoctions, fractions or semi-purified compounds. These herbal products are used in the treatment of a dysfunctioning of the libido, sexual asthenia, erection, and sperm disorders. Pharmacological activities of many of these plants have been shown in vitro using cells, in vivo (on laboratory animals) and human studies. For instance, extracts of Panax ginseng, Panax quinquefolius and Lepidium meyenii have shown positive effects on sexual desire; while extracts of Astragalus membranaceus, Asparagus racemous, Withania somnifera, Andrographis paniculata and Acanthopanax senticosus improved sperm parameters. Plants provide a treatment option that is affordable and available for infertile couples, and phytotherapy is an essential form of treatment in our health system. However, herbal products are still anarchically used in many regions and countries, and a great proportion of medicinal plants used traditionally to solve male reproductive disorders have not yet been scientifically evaluated. Therefore in this review, we have summarized most of the data dealing with the effects of plant extracts on mammalian reproductive functions.

Protective effects of estrogens and caloric restriction during aging on various rat testis parameters

AIM

To investigate the effects of 17beta-estradiol (E2), Peganum harmala extract (PHE) and caloric restriction (CR) on various testis parameters during aging.

METHODS

Twelve month-old male rats were treated for 6 months with either E2 or PHE, or submitted to CR (40%).

RESULTS

Our results show that estrogens and CR are able to protect the male gonad by preventing the decrease of testosterone and E2 levels as well as the decrease of aromatase and estrogen receptor gene expressions. Indeed, E2, PHE and CR treatments induced an increase in the superoxide dismutase activities and decreased the activity of testicular enzymes: gamma-glutamyl transferase, alkaline phosphatase, lactate deshydrogenase as well as the aspartate and lactate transaminases in aged animals. In addition, the testicular catalase and gluthatione peroxidase activities were enhanced in E2, PHE and CR-treated rats compared to untreated animals at 18 months of age. Moreover, the positive effects of estradiol, PHE and CR were further supported by a lower level of lipid peroxidation. Recovery of spermatogenesis was recorded in treated rats.

CONCLUSION

Besides a low caloric diet which is beneficial for spermatogenesis, a protective antioxydant role of estrogens is suggested. Estrogens delay testicular cell damage, which leads to functional senescence and, therefore, estrogens are helpful in protecting the reproductive functions from the adverse effects exerted by reactive oxygen species (ROS) produced in large quantities in the aged testis.

Anchoring junctions as drug targets: role in contraceptive development

In multicellular organisms, cell-cell interactions are mediated in part by cell junctions, which underlie tissue architecture. Throughout spermatogenesis, for instance, preleptotene leptotene spermatocytes residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier to enter the adluminal compartment for continued development. At the same time, germ cells must also remain attached to Sertoli cells, and numerous studies have reported extensive restructuring at the Sertoli-Sertoli and Sertoli-germ cell interface during germ cell movement across the seminiferous epithelium. Furthermore, the proteins and signaling cascades that regulate adhesion between testicular cells have been largely delineated. These findings have unveiled a number of potential "druggable" targets that can be used to induce premature release of germ cells from the seminiferous epithelium, resulting in transient infertility. Herein, we discuss a novel approach with the aim of developing a nonhormonal male contraceptive for future human use, one that involves perturbing adhesion between Sertoli and germ cells in the testis.