Effects of tamoxifen citrate on gene expression during nuclear chromatin condensation in male rats

Effects of different doses of tamoxifen on the sperm parameters and chromatin quality in mice: An experimental model

Background

Tamoxifen (TX) is widely used for the treatment of male factor and idiopathic infertility. It has been shown that TX induces sperm production and so improves male fertility.

Objective

This study evaluated the effects of different doses of TX on the sperm parameters and chromatin quality in mice.

Materials and Methods

In this research, 24 male NMRI mice were divided into three groups including group A: control animal receiving vehicle; group B: the group receiving basal diet and TX 0.4 mg/kg/day; and group C: the group receiving basal diet and TX 0.6 mg/kg/day for 35 days. Thereafter, epididymal spermatozoa were analyzed for standard parameters and nuclear chromatin quality using Aniline Blue (AB) and Toluidine Blue (TB) staining.

Results

The results indicated that although the TX did not affect the sperm count, motility, and viability parameters, it could elevate the percentage of sperm cells with abnormal morphology and abnormal chromatin at both doses. In addition, in comparison with the control mice, a significant elevation was observed in spermatozoa with residual histones (assessed by AB staining) at high doses of TX.

Conclusion

Our experimental data in mice suggested that the use of TX for treating male infertility might increase the rates of spermatozoa with abnormal chromatin in a dose-dependent manner.

Genetically Inherited Obesity and High-Fat Diet-Induced Obesity Differentially Alter Spermatogenesis in Adult Male Rats

Obesity is a multifactorial disorder with predominantly genetic and/or environmental causes. Our aim was to delineate effects of genetically inherited and high-fat diet-induced obesity on fertility and spermatogenesis using two Wistar rat models: genetically inherited obese (GIO) WNIN/Ob rats and diet-induced obese (DIO) rats, which received a high-fat diet. The terminal body weights were similar in both groups, but there was a significant difference in metabolic and hormone profiles between the groups. Fertility assessment revealed a significant decrease in the litter size due to increased pre- and postimplantation loss in the DIO group, whereas the rats in the GIO group were infertile due to lack of libido. Significantly decreased sperm counts were observed in the GIO group compared with the DIO group. Enumeration of testicular cells on the basis of ploidy and cell type-specific expression markers, to study the effect of obesity on spermatogenesis, demonstrated that the GIO and DIO states affected mitosis: spermatogonia and S-phase population were increased. However, distinctive effects were observed on meiosis and spermiogenesis in both the groups. Differential effects of GIO and DIO on fertility and spermatogenesis could be due to the significant difference in white adipose tissue accumulation between the groups and not due to high body weights. The differential effects of obesity suggest male obesity-induced infertility observed in humans could be a combination of genetic and environmental factors.

Testosterone Retention Mechanism in Sertoli Cells: A Biochemical Perspective

Mechanism(s) involved in regulating Intratesticular Testosterone levels (iT) have assumed importance in recent years, from the point of view of hormonal contraception. Contraceptives using Testosterone (T) in combination with Progestins (P), for more effective suppression of pituitary gonadotropins thereby iT, are not 100% effective in suppressing spermatogenesis in human males, likely due to pesrsistence of Intratesticular Dihydrotestosterone (iD) in poor-responders. Several lacunae pertaining to the mechanism of action of principal male hormone T during spermatogenesis remain to be resolved. Notably, the mechanism through which T brings about the stage-specific differentiation of germ cells lacking Androgen Receptors (AR). Testosterone is a highly anabolic steroid with a rapid tissue clearance rate. T is intratesticular substrate for synthesis of Dihydrotestosterone (DHT) and Estradiol (E2) involved in spermtaogenesis. Therefore, it is important to delineate the mechanism(s) for retention of iT, in order to understand regulation of its bioavailability in testis. In depth studies, pertaining to the role of androgen-binding protein(s) in sequestration, retention and bioavailability of T/DHT are required to understand male fertility regulation. The appropriate approach to overcome this lacuna would be development of mice lacking functional testicular Androgen-Binding Protein (ABPKO), but not deficient T/DHT, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), in order to understand its physiological functions. Insights gained about androgen retention mechanism(s) from the ABPKO murine model will be of immense help in improving the efficacy of male hormonal contraceptives and infertility management.

Effect of estrogen receptor-subtype-specific ligands on fertility in adult male rats

Maintenance of normal male fertility relies on the process of spermatogenesis which is under complex endocrine control by mechanisms involving gonadotropin and steroid hormones. Although testosterone is the primary sex steroid in males, estrogen is locally produced in the testis and plays a very crucial role in male fertility. This is evident from presence of both the estrogen receptors alpha (ERα) and beta (ERβ) in the testis and their absence, as in the case of knockout mice models, leads to sterility. The present study was undertaken to understand individual roles of the two ERs in spermatogenesis and their direct contribution towards the maintenance of male fertility using receptor-subtype-specific ligands. Administration of ERα and β agonists to adult male rats for 60 days results in a significant decrease in fertility, mainly due to an increase in pre- and post-implantation loss and a concomitant decrease in litter size and sperm counts. Our results indicate that ERα is mainly involved in negative feedback regulation of gonadotropin hormones, whereas both ERs are involved in regulation of prolactin and testosterone production. Histological examinations of the testis reveal that ERβ could be involved in the process of spermiation since many failed spermatids were observed in stages IX-XI following ERβ agonist treatment. Our results indicate that overactivation of estrogen signaling through either of its receptors can have detrimental effects on the fertility parameters and that the two ERs have both overlapping and distinct roles in maintenance of male fertility.

Estradiol affects androgen-binding protein expression and fertilizing ability of spermatozoa in adult male rats

The estrogenicity of certain environmental pollutants is being increasingly correlated to decline in sperm counts and fertility of the males. Qualitative effects, if any, of estrogen(s) on terminal differentiation of spermatids have been less reported. The present study suggests that exposure to estrogen(s) can also alter the status of condensed chromatin in testicular spermatozoa and reduce their fertilizing potential. A significant reduction was evident in the serum gonadotropins, testosterone, weights of reproductive organs, sperm counts and litters sired by male rats after 10 days of estradiol exposure to a dose of 0.1mg/kg/day. Estradiol treatment led to retardation of in vitro decondensation rates of sperm chromatin, reduction in the uptake of acridine orange dye by chromatin, reduction in susceptibility of chromatin to acid denaturation in vitro, reduced uptake of thiol reactive monobromobimane dye and reduced levels of immunoreactive protamine 1 in caput epididymal sperms. Concomitantly, testicular levels of immunoreactive protamine 1, transition proteins 1/2 and cyclic adenosyl response element modulator-tau (CREMtau) were significantly reduced whilst their mRNA levels were unaffected after estradiol treatment. A significant increase was observed in the testicular mRNA levels of androgen-binding protein (ABP) in estradiol treated sires. An inverse correlation was observed between ABP mRNA levels and uptake of acridine orange by estradiol treated caput sperm chromatin. The results suggest that estradiol-induced increase in ABP mRNA underlies the mechanism(s) involved in the reduction in levels of certain proteins involved in nuclear chromatin condensation during spermiogenesis.

Protamines and male infertility

Protamines are the major nuclear sperm proteins. The human sperm nucleus contains two types of protamine: protamine 1 (P1) encoded by a single-copy gene and the family of protamine 2 (P2) proteins (P2, P3 and P4), all also encoded by a single gene that is transcribed and translated into a precursor protein. The protamines were discovered more than a century ago, but their function is not yet fully understood. In fact, different hypotheses have been proposed: condensation of the sperm nucleus into a compact hydrodynamic shape, protection of the genetic message delivered by the spermatozoa, involvement in the processes maintaining the integrity and repair of DNA during or after the nucleohistone-nucleoprotamine transition and involvement in the epigenetic imprinting of the spermatozoa. Protamines are also one of the most variable proteins found in nature, with data supporting a positive Darwinian selection. Changes in the expression of P1 and P2 protamines have been found to be associated with infertility in man. Mutations in the protamine genes have also been found in some infertile patients. Transgenic mice defective in the expression of protamines also present several structural defects in the sperm nucleus and have variable degrees of infertility. There is also evidence that altered levels of protamines may result in an increased susceptibility to injury in the spermatozoan DNA causing infertility or poor outcomes in assisted reproduction. The present work reviews the articles published to date on the relationship between protamines and infertility.