Human testicular protein NYD-SP16 is involved in sperm capacitation and the acrosome reaction

Loss of histone reader Phf7 leads to immune pathways activation via endogenous retroviruses during spermiogenesis

Genetic studies have elucidated the critical roles of Phf7 in germline development in animals; however, the exact etiology of Phf7 mutations leading to male infertility and the possibility of mechanism-based therapy are still unclear and warrant further investigation. Using the Phf7 knockout mouse model, we verified that genetic defects were responsible for male infertility by preventing histone-to-protamine exchange, as previously reported. The deficiency of spermatogenesis caused by Phf7 deletion through the endogenous retrovirus-mediated activation of the immune pathway is a common mechanism of infertility. Furthermore, we identified PPARα as a promising target of immunity and inflammation in the testis, where endogenous retroviruses are suppressed, and Phf7 as a crucial regulator of endogenous retrovirus-mediated immune regulation and revealed its role as an epigenetic reader. The loss of Phf7 activates immune pathways, which can be rescued by the PPARα agonist astaxanthin. These results showed that astaxanthin is a potential therapeutic agent for treating male infertility. The findings in our study provide insights into the molecular mechanisms underlying male infertility and suggest potential targets for future research and therapeutic development.

Curcumin improves asthenozoospermia by inhibiting reactive oxygen species reproduction through nuclear factor erythroid 2-related factor 2 activation

We conducted this study for the purpose of evaluating the protective mechanisms of curcumin against oxidative stress in asthenozoospermic individuals. Asthenozoospermic individuals were grouped into AS group, curcumin treatment group and brusatol + curcumin treatment group. The sperm motility was measured by computer-aided sperm analysis. We conducted flow cytometry and spectrophotometry to assess the levels of reactive oxygen species (ROS) and malondialdehyde (MDA). Chlortetracycline (CTC) was used to examine the acrosomal reaction of spermatozoa. Also, Western blotting was carried to measure antioxidant gene Nrf2 (nuclear factor erythroid 2-related factor) expression level. As our results shown, treatment with curcumin significantly decreased ROS formation and MDA production, compared with spermatozoa of AS group; however, Nrf2 inhibitor, Brusatol, inhibited Nrf2 expression and sperm function. Our results have shown that curcumin might protect spermatozoa by regulating Nrf2 level.

C-type natriuretic peptide regulates sperm capacitation by the cGMP/PKG signalling pathway via Ca2+ influx and tyrosine phosphorylation

RESEARCH QUESTION

What is the effect of C-type natriuretic peptide (CNP) on human sperm capacitation in vitro and what is the mechanism of this effect?

DESIGN

CNP/NPR-B expression in the female rat genital tract was examined by immunohistochemistry and western blot assay, and then the role of CNP in human sperm capacitation was determined. The signal transduction pathway of CNP in the process was determined to elucidate the regulation mechanism of CNP by enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

Both CNP and NPR-B were expressed in the genital tract of female rats, especially in the mucosa epithelium cell of the oviduct; the CNP level in the rat oviduct was higher than that in the cervix. Both CNP and NPR-B level in the rat oviduct varied during the oestrus cycle, maximal expression being observed at proestrus. Furthermore, intracellular cGMP level in spermatozoa was significantly enhanced by CNP (P < 0.01). PKG activity was detected in the spermatozoa, and it can be activated by the CNP and 8-Br-cGMP (cGMP analogue). The PKG inhibitor KT5823 inhibited the effect of CNP on sperm hyperactivation and the acrosome reaction. Finally, Ca²⁺ and tyrosine phosphorylation levels in spermatozoa were markedly improved by CNP and 8-Br-cGMP but significantly inhibited by the addition of KT5823 (P < 0.05).

CONCLUSIONS

CNP secreted by the female genital tract might bind to NPR-B on the spermatozoa. It successively stimulated intracellular cGMP/PKG signalling, increased Ca²⁺ and tyrosine-phosphorylated proteins, promoted hyperactivation and induced the acrosome reaction, which ultimately facilitated sperm capacitation.

Capacitation in the presence of methyl-β-cyclodextrin results in enhanced zona pellucida-binding ability of stallion spermatozoa

While IVF has been widely successful in many domesticated species, the development of a robust IVF system for the horse remains an elusive and highly valued goal. A major impediment to the development of equine IVF is the fact that optimised conditions for the capacitation of equine spermatozoa are yet to be developed. Conversely, it is known that stallion spermatozoa are particularly susceptible to damage arising as a consequence of capacitation-like changes induced prematurely in response to semen handling and transport conditions. To address these limitations, this study sought to develop an effective system to both suppress and promote thein vitrocapacitation of stallion spermatozoa. Our data indicated that the latter could be achieved in a bicarbonate-rich medium supplemented with a phosphodiesterase inhibitor, a cyclic AMP analogue, and methyl-β-cyclodextrin, an efficient cholesterol-withdrawing agent. The populations of spermatozoa generated under these conditions displayed a number of hallmarks of capacitation, including elevated levels of tyrosine phosphorylation, a reorganisation of the plasma membrane leading to lipid raft coalescence in the peri-acrosomal region of the sperm head, and a dramatic increase in their ability to interact with heterologous bovine zona pellucida (ZP) and undergo agonist-induced acrosomal exocytosis. Furthermore, this functional transformation was effectively suppressed in media devoid of bicarbonate. Collectively, these results highlight the importance of efficient cholesterol removal in priming stallion spermatozoa for ZP bindingin vitro.

Regulation of rat tetratricopeptide repeat domain 29 gene expression by follicle-stimulating hormone

We screened the gene that encodes tetratricopeptide repeat domain 29 (Ttc29) in the maturing rat testis. Gene expression was determined by Northern blotting of 7-week-old rat testes, and a strong signal was detected close to the 18S rRNA band in addition to two weak high-molecular-weight signals. In situ hybridization revealed that Ttc29 was expressed primarily in the spermatocytes. We evaluated the effect of gonadotropin on Ttc29 expression using hypophysectomized rats. The pituitary was removed from 3-week-old rats, gonadotropin was injected at 5 weeks, and Ttc29 expression was determined at 7 weeks. Although testicular development and hyperplasia of interstitial cells were observed following chorionic gonadotropin treatment after hypophysectomy, Ttc29 expression was upregulated by treatment with follicle-stimulating hormone. Ttc29 encodes axonemal dynein, a component of sperm flagella. Taken together, these data indicate that axonemal dynein expression starts in the spermatocytes and is regulated by follicle-stimulating hormone.

Key functional genes of spermatogenesis identified by microarray analysis

At present many couples face difficulties when trying to conceive that may have a genetic basis. The male factor is the cause of infertility as often as the female. Therefore it is important to identify key genes involved in spermatogenesis which may be linked to male infertility. This review discusses the identification of a range of genes associated with male fertility using microarrays. Based on differences in gene expression profiles between fertile and infertile male subgroups or between fetal and adult male gonads, many genes important for spermatogenesis have been discovered. Genes that are critical at particular stages of spermatogenesis were defined and can be considered as potential male fertility biomarkers. The studies described showed that microarrays may be potentially used as a diagnostic platform to increase the efficacy of diagnosis and perhaps treatment of infertile males.

A defined medium supports changes consistent with capacitation in stallion sperm, as evidenced by increases in protein tyrosine phosphorylation and high rates of acrosomal exocytosis

Efficient in vitro capacitation of stallion sperm has not yet been achieved, as suggested by low sperm penetration rates reported in in vitro fertilization (IVF) studies. Our objectives were to evaluate defined incubation conditions that would support changes consistent with capacitation in stallion sperm. Protein tyrosine phosphorylation events and the ability of sperm to undergo acrosomal exocytosis under various incubation conditions were used as end points for capacitation. Sperm incubated 4-6h in modified Whitten's (MW) with the addition of 25 mM NaHCO3 and 7 mg/mL BSA (capacitating medium) yielded high rates of protein tyrosine phosphorylation. Either HCO3(-) or BSA was required to support these changes, with the combination of both providing the most intense results. When a membrane-permeable form of cAMP and a phosphodiesterase inhibitor (IBMX) were added to MW in the absence of HCO3(-) and BSA, the tyrosine phosphorylation results obtained in our capacitating conditions could not be replicated, suggesting either effects apart from cAMP were responsible for tyrosine phosphorylation, or that stallion sperm might respond differently to these reagents as compared to sperm from other mammals. Sperm incubation in capacitating conditions was also associated with high percentages (P<or=0.001) of acrosomal exocytosis upon exposure to progesterone (44.6%) or calcium ionophore (51.6%), as compared to sperm incubated in medium devoid of BSA and NaHCO3. Our results were novel in that we report protein tyrosine phosphorylation in stallion sperm incubated in defined conditions, coupled with significant percentages of acrosome reacted sperm. The continuation of these studies might help to elucidate the conditions and pathways supporting sperm capacitation in the horse.