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National Natural Science Foundation of China (No. 31400996); Natural Science Foundation of Jiangxi, China (No. 20161BAB204167 and No. 20142BAB215050); open project of National Population and Family Planning Key Laboratory of Contraceptives and Devices Research (No. 2016KF07) to T. Luo; National Natural Science Foundation of China (No. 81300539) to L.P. Zheng. The authors have no conflicts of interest to declare.

It is well known that there has been a worldwide decrease in human male fertility in recent years. One of the main factors affecting this is environmental pollution. Lead is one of the major heavy metal contaminants that threaten the health of animals and human beings in China. It preferentially accumulates in male reproductive organs and can be up to 10 µM in human seminal plasma. Lead impairs mammalian spermatogenesis and sperm quality in vivo. It also inhibits sperm functions in vitro but the underlying mechanisms remain unclear. Therefore, we aimed to investigate the in vitro toxicity of lead on human sperm functions and to elucidate the underlying mechanisms. Semen samples were collected from 20 healthy volunteers with different careers and backgrounds living in Nanchang, Jiangxi. Human sperm suspensions were treated with different concentrations of lead acetate (0, 0.5, 2.5, 10, 50, and 100 µM) and the viability, motility, capacitation and progesterone-induced acrosome reaction were examined. Treatment with 10-100 µ M lead acetate dose-dependently inhibited total and progressive motility measures, capacitation and progesterone-induced acrosome reaction. It also dose-dependently decreased the intracellular concentrations of cyclic adenosine monophosphate (cAMP) and calcium ([Ca 2+ ] i ), and reduced the tyrosine phosphorylation of sperm proteins, all of which are thought to be key factors in the regulation of sperm function. Our findings suggest that lead inhibits human sperm functions by reducing the levels of sperm intracellular cAMP, [Ca 2+ ] i and tyrosine phosphorylation of sperm proteins in vitro.

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Background: Matrine is a bioactive alkaloid that has a variety of pharmacological effects and is widely used in Chinese medicine. However, its effects on male reproduction are not well known. In this study, we aimed to investigate the in vitro toxicity of matrine on mature mouse sperm. Methods: Mouse cauda epididymal sperm were exposed to matrine (10-200 µM) in vitro. The viability, motility, capacitation, acrosome reaction and fertilization ability of the mouse sperm were examined. Furthermore, the intracellular calcium concentration ([Ca²⁺]_i), calcium (Catsper) and potassium (Ksper) currents, and phosphorylation of extracellular signal regulated kinases 1/2 (p-ERK1/2) of the sperm were analyzed. Results: After exposure to 100 µM or more of matrine, mouse cauda epididymal sperm exhibited a significant reduction in total motility, progressive motility, linear velocity and acrosome reaction rate induced by Ca²⁺ ionophore A23187. As a result, the fertilization ability of mouse sperm was remarkably decreased by matrine. Our data further demonstrated that matrine significantly reduced sperm [Ca²⁺]_i and [Ca²⁺]_i-related p-ERK1/2; however, both the CatSper and KSper currents, which are thought to interactively regulate Ca²⁺ influx in sperm, were not affected by matrine. Conclusion: Our findings indicate that matrine inhibits mouse sperm function by reducing sperm [Ca²⁺]_i and suppressing the phosphorylation of ERK1/2.

Testis-specific proteins, synthesized during spermatogenesis and spermiogenesis, are necessary for spermatid differentiation and/or for mature sperm function during fertilization. However, majority of these genes have neither been identified nor fully characterized. Testis developmental related gene 1 (TDRG1), a newly identified human testis-specific gene, encodes a 100-amino-acid protein without any characterized protein domains, and it may play a role in spermatogenesis. However, whether this human-specific protein is important for mature sperm function remains unclear. As an initial effort, in this study, we aimed to systematically investigate the expression and localization of TDRG1 in normal human spermatozoa. Thus, immunohistochemistry was used to analyze the distribution of TDRG1 in human testis. Reverse transcription-polymerase chain reaction, western blot analysis and indirect immunofluorescence were used to determine the expression and localization of TDRG1 in normal human spermatozoa. The immunohistochemistry results showed that the TDRG1 protein was expressed in spermatogenic cells in the seminiferous tubules of human testis. Interestingly, the TDRG1 was more abundant in spermatogenic cells at the late stages of spermatogenesis. The TDRG1 antibody specifically recognized an 11-kDa protein only in soluble extracts from normal human spermatozoa. Indirect immunofluorescence assays indicated that TDRG1 located in the midpiece, principal piece and flagellum of normal human spermatozoa. In conclusion, TDRG1 was found not only in spermatogonia, but also in spermatozoa. The localization of TDRG1 in human normal spermatozoa implies its potential regulatory role in sperm motility.