Role of follitropin receptor signaling in nuclear protein transitions and chromatin condensation during spermatogenesis

Follicle-stimulating hormone treatment for male factor infertility

Follicle-stimulating hormone (FSH) treatment has been proven effective in stimulating spermatogenesis and improving the reproductive ability of men with hypogonadotropic hypogonadism, while the usefulness of such a treatment in infertile patients with normal pituitary function is restricted to a subgroup of responders that, however, cannot be identified by the current diagnostic tools before treatment. In this review we summarize the role played by FSH in the modulation of spermatogenesis, the effect of FSH treatment at a standard replacement dose and at higher dose on sperm parameters, spontaneous and in vitro fertilization pregnancy rates, and the efforts made to identify possible responders to FSH treatment.

Intracytoplasmic sperm injection: state of the art in humans

Among infertile couples, 25% involve both male and female factors, while male factor alone accounts for another 25% due to oligo-, astheno-, teratozoospermia, a combination of the three, or even a complete absence of sperm cells in the ejaculate and can lead to a poor prognosis even with the help of assisted reproductive technology (ART). Intracytoplasmic sperm injection (ICSI) has been with us now for a quarter of a century and in spite of the controversy generated since its inception, it remains in the forefront of the techniques utilized in ART. The development of ICSI in 1992 has drastically decreased the impact of male factor, resulting in millions of pregnancies worldwide for couples who, without ICSI, would have had little chance of having their own biological child. This review focuses on the state of the art of ICSI regarding utility of bioassays that evaluate male factor infertility beyond the standard semen analysis and describes the current application and advances in regard to ICSI, particularly the genetic and epigenetic characteristics of spermatozoa and their impact on reproductive outcome.

Understanding the spermatozoon

The former perception of the spermatozoon as a delivery device of the male genome has been expanded to include a new understanding of the cell's complex role in fertilization. Once the spermatozoon reaches the oocyte, it triggers egg activation and orchestrates the stages of pre- and post-fertilization in a preprogrammed pattern while tapping the oocyte's resources in an effort to generate a new life.

Age-dependent inhibin B concentration in relation to FSH and semen sample qualities: a study in 2448 men

Inhibin B is an important serum marker of spermatogenesis, whereas sensitivity and predicting power for the spermatogenic situation at several ages are under debate. We performed a retrospective analysis of data from 2448 men who attended our University-based male infertility clinic to evaluate inhibin B in relation to age and semen sample qualities in comparison with FSH. Moreover, the range of inhibin B in 82 nonobstructive azoospermic patients was correlated with the sperm retrieval in testicular sperm extraction procedures. Inhibin B correlated with FSH (Spearman rank correlation (R)=−0.50; P<0.00001). Inhibin B and inhibin B/FSH ratio (IFR) showed an inverse U-shaped dependence on age, whereas FSH showed a U-shaped dependence on age (optimum 20–40 years). However, in men with normal spermiograms inhibin B concentrations did not differ between age groups. Their levels of inhibin B amounted to 130.5, 54.5–247 ng/l (median, 10th–90th precentile), and of IFR to 38.3, 12.5–104.8 (median, 10th–90th percentile), which might be taken as the reference range. Using the 10th percentile of IFR, correct classification in normal or pathological semen groups was achieved in 99.1%. The percentage of aniline blue-negative spermatozoa, i.e. mature spermatozoa with protamines, did not correlate with FSH (P>0.05) but with inhibin B (R=0.15, P<0.001). The probability of retrieving testicular spermatozoa decreased with declining inhibin B: <20 ng/l sperm could never be found. Our results from a large group of men with a wide spectrum of semen qualities allow estimating reference values for inhibin B and IFR. Inhibin B and especially the IFR are more sensitive markers of male infertility than FSH alone.

Estrogens and spermiogenesis: new insights from type 1 cannabinoid receptor knockout mice

Spermatogenesis is a complex mechanism which allows the production of male gametes; it consists of mitotic, meiotic, and differentiation phases. Spermiogenesis is the terminal differentiation process during which haploid round spermatids undergo several biochemical and morphological changes, including extensive remodelling of chromatin and nuclear shape. Spermiogenesis is under control of endocrine, paracrine, and autocrine factors, like gonadotropins and testosterone. More recently, emerging pieces of evidence are suggesting that, among these factors, estrogens may have a role. To date, this is a matter of debate and concern because of the agonistic and antagonistic estrogenic effects that environmental chemicals may have on animal and human with damaging outcome on fertility. In this review, we summarize data which fuel this debate, with a particular attention to our recent results, obtained using type 1 cannabinoid receptor knockout male mice as animal model.

Putative molecular mechanism underlying sperm chromatin remodelling is regulated by reproductive hormones

Background

The putative regulatory role of the male reproductive hormones in the molecular mechanism underlying chromatin condensation remains poorly understood. In the past decade, we developed two adult male rat models wherein functional deficits of testosterone or FSH, produced after treatments with 20 mg/Kg/d of cyproterone acetate (CPA) per os, for a period of 15 days or 3 mg/Kg/d of fluphenazine decanoate (FD) subcutaneously, for a period of 60 days, respectively, affected the rate of sperm chromatin decondensation in vitro. These rat models have been used in the current study in order to delineate the putative roles of testosterone and FSH in the molecular mechanism underlying remodelling of sperm chromatin.

Results

We report that deficits of both testosterone and FSH affected the turnover of polyubiquitylated histones and led to their accumulation in the testis. Functional deficits of testosterone reduced expression of MIWI, the 5-methyl cap binding RNA-binding protein (PIWIlike murine homologue of the Drosophila protein PIWI/P-element induced wimpy testis) containing a PAZ/Piwi-Argonaut-Zwille domain and levels of histone deacetylase1 (HDAC1), ubiquitin ligating enzyme (URE-B1/E3), 20S proteasome α1 concomitant with reduced expression of ubiquitin activating enzyme (ube1), conjugating enzyme (ube2d2), chromodomain Y like protein (cdyl), bromodomain testis specific protein (brdt), hdac6 (histone deacetylase6), androgen-dependent homeobox placentae embryonic protein (pem/RhoX5), histones h2b and th3 (testis-specific h3). Functional deficits of FSH reduced the expression of cdyl and brdt genes in the testis, affected turnover of ubiquitylated histones, stalled the physiological DNA repair mechanism and culminated in spermiation of DNA damaged sperm.

Conclusions

We aver that deficits of both testosterone and FSH differentially affected the process of sperm chromatin remodelling through subtle changes in the ‘chromatin condensation transcriptome and proteome’, thereby stalling the replacement of ‘dynamic’ histones with ‘inert’ protamines, and altering the epigenetic state of condensed sperm chromatin. The inappropriately condensed chromatin affected the sperm chromatin cytoarchitecture, evident from subtle ultrastructural changes in the nuclei of immature caput epididymal sperm of CPA- or FD-treated rats, incubated in vitro with dithiothreitol.

Animal models for aberrations of gonadotropin action

During the last two decades a large number of genetically modified mouse lines with altered gonadotropin action have been generated. These mouse lines fall into three categories: the lack-of-function mice, gain-of-function mice, and the mice generated by breeding the abovementioned lines with other disease model lines. The mouse strains lacking gonadotropin action have elucidated the necessity of the pituitary hormones in pubertal development and function of gonads, and revealed the processes from the original genetic defect to the pathological phenotype such as hypo- or hypergonadotropic hypogonadism. Conversely, the strains of the second group depict consequences of chronic gonadotropin action. The lines vary from those expressing constitutively active receptors and those secreting follicle-stimulating hormone (FSH) with slowly increasing amounts to those producing human choriogonadotropin (hCG), amount of which corresponds to 2000-fold luteinizing hormone (LH)/hCG biological activity. Accordingly, the phenotypes diverge from mild anomalies and enhanced fertility to disrupted gametogenesis, but eventually chronic, enhanced and non-pulsatile action of both FSH and LH leads to female and male infertility and/or hyper- and neoplasias in most of the gonadotropin gain-of-function mice. Elevated gonadotropin levels also alter the function of several extra-gonadal tissues either directly or indirectly via increased sex steroid production. These effects include promotion of tumorigenesis in tissues such as the pituitary, mammary and adrenal glands. Finally, the crossbreedings of the current mouse strains with other disease models are likely to uncover the contribution of gonadotropins in novel biological systems, as exemplified by the recent crossbreed of LHCG receptor deficient mice with Alzheimer disease mice.

Retinoic acid induces myoblasts transdifferentiation into premeiotic Stra8-positive cells

Spermatogonia and sperm-like cells can be derived in vitro via the addition of RA (retinoic acid) to pluripotent ES and EG cells. At present, however, these cells have not been derived from unipotent cells. Here, we have generated premeiotic Stra8-positive cells from C2C12 myoblasts following treatment with 10 μM all-trans-RA for 8 days. The differentiated C2C12 cells exhibited spherical morphology similar to spermatogonia, and they expressed gene markers of premeiosis, meiosis and postmeiosis. In addition, some of the transdifferentiated Stra8-positive cells had a tail-like phenotype. Flow cytometry results indicated that up to 20% of RA-induced C2C12 cells were Stra8-positive. Mvh (mouse vasa homologue) protein, a germ cell-specific ATP-dependent RNA helicase and Prm1 (protamine 1) were detected in transdifferentiated cells. The DNA content in induced C2C12 cells showed that Stra8-positive cells were diploid, suggesting that the myoblast transdifferentiation was in the premeiotic stage of spermatogenesis. The derivation of Stra8-positive cells from C2C12 myoblasts has important implications for studying unipotent cell differentiation. Furthermore, C2C12 myoblasts may provide a useful in vitro cell model to study signal transduction and transdifferentiation during RA treatments.

The clinical utility of sperm DNA integrity testing

Sperm DNA damage is more common in infertile men and may contribute to poor reproductive performance. However, current methods for evaluating sperm DNA integrity do not reliably predict treatment outcomes, and no treatment for abnormal DNA integrity has proven clinical value.

The clinical utility of sperm DNA integrity testing

Sperm DNA damage is more common in infertile men and may contribute to poor reproductive performance. However, current methods for evaluating sperm DNA integrity do not reliably predict treatment outcomes, and no treatment for abnormal DNA integrity has proven clinical value.

Sperm DNA damage: importance in the era of assisted reproduction

PURPOSE OF REVIEW

With the proliferation of assisted reproductive technologies, there is an increasing awareness of the importance of sperm DNA damage. With the recent advent of in-vitro fertilization/intracytoplasmic sperm injection, we are bypassing the normal natural selection barriers and potentially introducing sperm with damaged DNA. To date, these consequences are still largely unknown.

RECENT FINDINGS

Infertile men possess substantially more DNA-damaged sperm than fertile men, and this DNA damage may adversely affect reproductive outcomes. There may be a threshold level of DNA damage beyond which embryo development and subsequent pregnancy are impaired. Protamine deficiency and the effect of reactive oxygen species have been implicated in the etiology of sperm DNA damage. Assays of DNA damage are being used clinically to quantify objectively the degree of DNA damage in the sperm of infertile men in the hope of identifying more accurate ways of gauging fertility potential.

SUMMARY

There now exists clinical evidence to show that sperm DNA damage is detrimental to reproductive outcomes. Tests for DNA damage may provide better prognostic information and may allow for better decision-making than standard semen parameters when evaluating the infertile couple. The etiology of the DNA damage and the full extent of the damage on reproductive outcomes need further study.

Sperm DNA damage: clinical significance in the era of assisted reproduction

Evidence suggests that damage to human sperm DNA might adversely affect reproductive outcomes and that the spermatozoa of infertile men possess substantially more sperm DNA damage than do the spermatozoa of fertile men. This is particularly relevant in an era where advanced forms of assisted reproductive technologies are commonly used (technologies that often bypass the barriers to natural selection), because there is some uncertainty regarding the safety of using DNA-damaged spermatozoa. In this review, we outline our current understanding of how sperm DNA is organized, what causes sperm DNA damage, what impact this damage may have on reproductive capacity and whether tests of sperm DNA damage are clinically useful.

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.

What have we learned about gonadotropin function from gonadotropin subunit and receptor knockout mice?

A number of biochemical and physiological studies elucidated the roles of pituitary and placental glycoprotein hormones. Advances in the past two decades in manipulating the mouse genome by random or site-specific mutagenesis have heralded a new dimension to our understanding of the biology of gonadotropins. It is now possible to model many human reproductive disorders involving gonadotropins/gonadotropin-signaling in the mouse. Mutant mice selectively lacking either FSH or LH or their cognate receptors have been generated. The gonadotropin ligand and the corresponding receptor knockout mice mostly phenocopy each other. Analyses with these genetic models confirmed earlier physiological studies; in addition they also revealed novel roles for gonadotropins previously unrecognized. While FSH action seems dispensable for male but not female fertility, absence of LH causes infertility in both the sexes. While Sertoli cell number and germ cell carrying capacity of the Sertoli cells in compromised in FSH mutants, both somatic and germ cell lineages are affected in the LH mutants resulting in complete male infertility. FSH mutant females demonstrate a preantral stage block in folliculogenesis and FSH alone is not sufficient to promote full folliculogenesis in the absence of LH. Pre-ovulatory stage follicles do not form and most of the follicles undergo apoptosis in the absence of LH. Many extra-gonadal phenotypes have been described for the receptor knockout mice and whether these bear any resemblances to those in patients with similar inactivating mutations in the receptors for FSH and LH remains an open question. Thus the in vivo models will continue to have a significant impact in understanding gonadotropin physiology and pathophysiology and serve as novel genetic tools to study signaling mechanisms in the gonads.