Molecular markers of human sperm functions

Hexachlorocyclohexane impairs human sperm motility by affecting lysine glutarylation and mitochondrial functions

Decreased sperm motility is a leading cause of male infertility and persistent organic pollutants are known to contribute significantly to the development of this disease. The effects of organochlorine pesticides such as hexachlorocyclohexane (HCH) on human sperm function and their mechanisms of action have received much attention, but are still not fully understood. Herein, we discovered that HCH has a concentration- and time-dependent inhibitory effect on human sperm motility in vitro. Moreover, HCH could reduce the levels of lysine glutarylation (Kglu) and glucose-6-phosphate dehydrogenase activity in sperm. Meanwhile, HCH could increase reactive oxygen species and thereby lead to mitochondrial depolarization and the down-regulation of adenosine triphosphate levels. In particular, we observed that sodium glutarate (Na-glu), the precursor of glutaryl-CoA, could alleviate the inhibitory effect of HCH on sperm Kglu levels, whereas the ROS scavenger N-acetyl-L-cysteine (NAC) had no effect. Intriguingly, both Na-glu and NAC were able to partially inhibit the HCH-induced increase in sperm ROS levels and impaired sperm motility. In conclusion, we propose that HCH inhibits sperm Kglu, leading to the disruption of mitochondrial energy metabolism, which in turn adversely affects sperm motility.

The pair ceramide 1-phosphate/ceramide kinase regulates intracellular calcium and progesterone-induced human sperm acrosomal exocytosis

Before fertilization, spermatozoa must undergo calcium-regulated acrosome exocytosis in response to physiological stimuli such as progesterone and zona pellucida. Our laboratory has elucidated the signaling cascades accomplished by different sphingolipids during human sperm acrosomal exocytosis. Recently, we established that ceramide increases intracellular calcium by activating various channels and stimulating the acrosome reaction. However, whether ceramide induces exocytosis on its own, activation of the ceramide kinase/ceramide 1-phosphate (CERK/C1P) pathway or both is still an unsolved issue. Here, we demonstrate that C1P addition induces exocytosis in intact, capacitated human sperm. Real-time imaging in single-cell and calcium measurements in sperm population showed that C1P needs extracellular calcium to induce [Ca2+]i increase. The sphingolipid triggered the cation influx through voltage-operated calcium (VOC) and store-operated calcium (SOC) channels. However, it requires calcium efflux from internal stores through inositol 3-phosphate receptors (IP3R) and ryanodine receptors (RyR) to achieve calcium rise and the acrosome reaction. We report the presence of the CERK in human spermatozoa, the enzyme that catalyzes C1P synthesis. Furthermore, CERK exhibited calcium-stimulated enzymatic activity during the acrosome reaction. Exocytosis assays using a CERK inhibitor demonstrated that ceramide induces acrosomal exocytosis, mainly due to C1P synthesis. Strikingly, progesterone required CERK activity to induce intracellular calcium increase and acrosome exocytosis. This is the first report, implicating the bioactive sphingolipid C1P in the physiological progesterone pathway leading to the sperm acrosome reaction.

miR-199-5p regulates spermiogenesis at the posttranscriptional level via targeting Tekt1 in allotriploid crucian carp

BACKGROUND

Sperm abnormalities are one of the primary factors leading to male sterility, but their pathogenesis is still unclear. Although miRNAs are suggested to exert important roles in the regulation of spermatogenesis at both transcriptional and posttranscriptional levels, little is currently known regarding the regulation of sperm flagella assembly by microRNAs (miRNAs). The role of miRNAs in the development of sperm abnormalities in sterile triploid fish has not been studied.

RESULTS

In this study, we found that miR-199-5p was widely expressed in all detected tissues of different-ploidy crucian carp. As one of the testis-specific candidate markers, Tekt1 was predominantly expressed in the testis. Quantitative real-time PCR (qRT-PCR) analyses showed that the expression trend of miR-199-5p was exactly opposite to that of Tekt1. Through bioinformatics analysis, we identified a putative miR-199-5p binding site in the Tekt1 mRNA. We further identified Tekt1 as a target of miR-199-5p using luciferase reporter assay. Finally, we confirmed that miR-199-5p was necessary for sperm flagellar assembly and spermatogenesis in vivo via intraperitoneal injection of miR-199-5p antagomir or agomir in diploid red crucian carp. Moreover, miR-199-5p gain-of-function could lead to spermatids apoptosis and abnormal spermatozoa structure, which is similar to that of allotriploid crucian carp.

CONCLUSIONS

Our studies suggested that abnormally elevated miR-199-5p inhibited the sperm flagella formation in spermiogenesis by negatively regulating the expression of Tekt1, thereby causing sperm abnormalities of male allotriploid crucian carp.

The level of secondary messengers and the redox state of NAD+/NADH are associated with sperm quality in infertility

In order to explore the interrelation of Calcium, cAMP, and redox state of pyridine nucleotides in seminal plasma and ejaculate quality in cases of idiopathic infertility we conducted an evaluation of 170 infertile males and 46 fertile males aged 20-43 years. Sperm analysis was undertaken according to WHO protocol. The content of Calcium in the seminal plasma was detected using optical emission spectrometry, cAMP levels were determined via enzymatic immunoassay. The redox state of pyridine nucleotides was evaluated from the ratio of pyruvate to lactate, determined via enzymatic method. Our results show a decrease in Calcium, cAMP, pyruvate and the oxidation-reduction potential of pyridine nucleotides in the seminal plasma of infertile males with pathospermia. This corresponds to anaerobic inversion of oxidative conversions and metabolism inadaptation. Such processes are often seen in inflammatory and autoimmune conditions. cAMP levels reliably correlated with the number of progressively mobile sperm cells, but not with the number of their pathological forms. A positive correlation between the concentration of cAMP and calcium was discovered as well. Pathospermia was characterized by the positive relation between the value of the NAD⁺/NADH coefficient and the spermatozoa concentration that was not present in fertile donors. Our study shows distinct changes in the concentration of secondary messengers and redox state of pyridine nucleotides in the seminal fluid that can act as molecular predictors for the development of idiopathic infertility.

Impact of Cryopreservation on Spermatozoa Freeze-Thawed Traits and Relevance OMICS to Assess Sperm Cryo-Tolerance in Farm Animals

Sperm cryopreservation is a powerful tool for the livestock breeding program. Several technical attempts have been made to enhance the efficiency of spermatozoa cryopreservation in different farm animal species. However, it is well-recognized that mammalian spermatozoa are susceptible to cryo-injury caused by cryopreservation processes. Moreover, the factors leading to cryo-injuries are complicated, and the cryo-damage mechanism has not been methodically explained until now, which directly influences the quality of frozen–thawed spermatozoa. Currently, the various OMICS technologies in sperm cryo-biology have been conducted, particularly proteomics and transcriptomics studies. It has contributed while exploring the molecular alterations caused by cryopreservation, identification of various freezability markers and specific proteins that could be added to semen diluents before cryopreservation to improve sperm cryo-survival. Therefore, understanding the cryo-injury mechanism of spermatozoa is essential for the optimization of current cryopreservation processes. Recently, the application of newly-emerged proteomics and transcriptomics technologies to study the effects of cryopreservation on sperm is becoming a hotspot. This review detailed an updated overview of OMICS elements involved in sperm cryo-tolerance and freeze-thawed quality. While also detailed a mechanism of sperm cryo-injury and utilizing OMICS technology that assesses the sperm freezability potential biomarkers as well as the accurate classification between the excellent and poor freezer breeding candidate.

Progesterone, spermatozoa and reproduction: An updated review

The rapid effects of steroids on spermatozoa have been demonstrated for the first time more than three decades ago. Progesterone (P), which is present throughout the female genital tract with peaks of levels in the cumulus matrix surrounding the oocyte, has been shown to stimulate several sperm functions in vitro, including capacitation, hyperactivation, chemotaxis and acrosome reaction (AR). Besides an increase of intracellular calcium, P has been shown to activate other sperm signalling pathways including tyrosine phosphorylation of several sperm proteins. All these effects are mediated by extra-nuclear pathways likely involving interaction with molecules present on the sperm surface. In particular, the increase in intracellular calcium ([Ca²⁺]_i) in spermatozoa from human and several other mammalian species is mediated by the sperm specific calcium channel CatSper, whose expression and function are required for sperm hyperactive motility. P-mediated CatSper activation is indeed involved in promoting sperm hyperactivation, but the involvement of this channel in other P-stimulated sperm functions, such as AR and chemotaxis, is less clear and further studies are required to disclose all the involved pathways. In human spermatozoa, responsiveness to P in terms of [Ca²⁺]_i increase and AR is highly related to sperm fertilizing ability in vitro, suggesting that the steroid is a physiological inducer of AR during in vitro fertilization. In view of their physiological relevance, P-stimulated sperm functions are currently investigated to develop new tools to select highly performant spermatozoa for assisted reproduction.

Ceramide induces a multicomponent intracellular calcium increase triggering the acrosome secretion in human sperm

Exocytosis of spermatozoon's secretory vesicle, named acrosome reaction (AR), is a regulated event that plays a central role in fertilization. It is coupled to a complex calcium signaling. Ceramide is a multitasking lipid involved in exocytosis. Nevertheless, its effect on secretion is controversial and the underlying cellular and molecular mechanisms remain unknown. Human spermatozoa are useful to dissect the role of ceramide in secretion given that the gamete is not capable to undergo any trafficking mechanisms other than exocytosis. We report for the first time, the presence of sphingolipid metabolism enzymes such as neutral-sphingomyelinase and ceramide synthase in sperm. Ceramidases are also present and active. Both the addition of cell-permeable ceramide and the rise of the endogenous one, increase intracellular calcium acting as potent inducers of exocytosis. Ceramide triggers AR in capacitated spermatozoa and enhances the gamete response to progesterone. The lipid induces physiological ultrastructural changes in the acrosome and triggers an exocytosis-signaling cascade involving protein tyrosine phosphatase 1B and VAMP2. Real-time imaging showed an increment of calcium in the cytosol upon ceramide treatment either in the absence or in the presence of extracellular calcium. Pharmacological experiments demonstrate that at early stages the process involves ryanodine receptors, CatSper (calcium channel of sperm), and store-operated calcium channels. We set out the signaling sequence of events that connect ceramide to internal calcium mobilization and external calcium signals during secretion. These results allow the coordination of lipids and proteins in a pathway that accomplishes secretion. Our findings contribute to the understanding of ceramide's role in regulated exocytosis and fertilization.

Human sperm testicular angiotensin-converting enzyme helps determine human embryo quality

Angiotensin-converting enzyme functions in the male reproductive system, but the extent of its function in reproduction is not fully understood. The primary objective of this work was to investigate the relationship between the testicular isoform of angiotensin-converting enzyme present in human spermatozoa and semen parameters, human embryo quality, and assisted reproduction success. A total of 81 semen samples and 635 embryos from couples undergoing oocyte donation cycles at the IVI Bilbao Clinic were analyzed. Semen parameters, embryos quality, and blastocyst development were examined according to the World Health Organization standards and the Spanish Association of Reproduction Biology Studies criteria. The percentage of testicular angiotensin-converting enzyme-positive spermatozoa and the number of molecules per spermatozoon were analyzed by flow cytometry. Both parameters were inversely correlated with human sperm motility. Higher percentages of testicular angiotensin-converting enzyme-positive spermatozoa together with fewer enzyme molecules per spermatozoon were positively correlated with better embryo quality and development. Our results suggest that embryos with a higher implantation potential come from semen samples with higher percentages of testicular angiotensin-converting enzyme-positive cells and fewer enzyme molecules per spermatozoon. Based on these findings, we propose that testicular angiotensin-converting enzyme could be used to aid embryologists in selecting better semen samples for obtaining high-quality blastocysts during in vitro fertilization procedures.

Comparative analysis of the transcriptome of the Amazonian fish species Colossoma macropomum (tambaqui) and hybrid tambacu by next generation sequencing

Background

The C. macropomum is a characiform fish from the Amazon basin that has been hybridized with other pacu species to produce commercial hybrids, such as the tambacu. However, little is known of the functional genomics of the parental species or these hybrid forms. The transcriptome of C. macropomum and tambacu were sequenced using 454 Roche platform (pyrosequencing) techniques to characterize the domains of Gene Ontology (GO) and to evaluate the levels of gene expression in the two organisms.

Results

The 8,188,945 reads were assembled into 400,845 contigs. A total of 58,322 contigs were annotated with a predominance of biological processes for both organisms, as determined by Gene Ontology (GO). Similar numbers of metabolic pathways were identified in both the C. macropomum and the tambacu, with the metabolism category presenting the largest number of transcripts. The BUSCO analysis indicated that our assembly was more than 40% complete. We identified 21,986 genes for the two fishes. The P and Log2FC values indicated significant differences in the levels of gene expression, with a total of 600 up-regulated genes.

Conclusion

In spite of the lack of a reference genome, the functional annotation was successful, and confirmed a considerable difference in the specificity and levels of gene expression between the two organisms. This report provides a comprehensive baseline for the genetic management of these commercially important fishes, in particular for the identification of specific genes that may represent markers involved in the immunity, growth, and fertility of these organisms, with potential practical applications in aquaculture management.

Sperm lipidic profiles differ significantly between ejaculates resulting in pregnancy or not following intracytoplasmic sperm injection

Although assisted reproduction techniques involve the use of semen samples, there is little scientific methodology applied when selecting sperm. To select the most appropriate spermatozoa, first we need to define the optimal molecular characteristics. Sperm lipids may contribute to sperm function, thus our aim was to compare the lipidic profiles of sperm samples used in intracytoplasmic sperm injection cycles that ultimately led to a pregnancy with those that did not.Spermatozoa from infertile patients after intracytoplasmic sperm injection (group non-pregnant, n = 16; vs. group pregnant, n = 22) were analyzed for lipid composition using ultra-high performance liquid chromatography coupled to mass spectrometry, by means two platforms for measuring fatty acyls, bile-acids, lysoglycerophospholipids, glycerolipids, cholesteryl-esters, sphingolipids, and glycerophospholipids. Lipid levels were compared using a univariate test and multivariate analyses after logarithmic transformation.We detected 151 different lipids in the sperm samples, 10 of which were significantly increased in sperm samples from the NP group, ranging from 1.10- to 1.30-fold change. These were primarily ceramides, sphingomyelins and three glycerophospholipids, a lysophosphatidylcholine, and two plasmalogen species. Additionally, 2-Monoacylglycerophosphocholine were also found in higher levels in non-pregnant group.Our results describe the composition of sperm lipids linked to optimal sperm function, opening new possibilities for the development of male fertility diagnostic tools and culture media formulations to improve sperm quality and enhance reproductive results. Given that lipids compose the majority of the sperm plasma membrane, this information is also useful in designing new sperm selection tools that will allow for the selection of the best spermatozoa.

Mobile phones electromagnetic radiation and NAD+-dependent isocitrate dehydrogenase as a mitochondrial marker in asthenozoospermia

NAD+-dependent Isocitrate Dehydrogenase (NAD+-IDH) could be one of the cell phone radiation targets. Enzyme activity alteration may lead to decline in sperm motility during radio-frequency electromagnetic waves (RF-EMW) exposure. The current case control study aimed to investigate the possible relationship between mitochondrial NAD+-IDH activity in human seminal plasma and sperm motility among asthenozoospermic cellular phone users. A total number of ninety idiopathic infertile males referred from the Department of Dermatology and Andrology, were enrolled in this study. NAD+-IDH activity was measured in human seminal plasma by spectrophotometer. Computer-aided sperm analysis (CASA) following WHO criteria has been used for semen analyses. The results showed that IDH activity was increased in patients with prolonged cell phone daily use ≥4 h/day. Its level, correlated negatively with either the motility ratio percentages (r = -0.46, p < 0.001) or the progressive motility percentages (r = -0.50, p < 0.001) in the study groups. The current study suggests that NAD+-IDH in human seminal plasma could be one of seminal plasma biomarkers reflecting the mitochondrial function of spermatozoa. Alteration of its level could reflect the defective motility of sperms among some cases of cellular phone users.

Mammalian sperm fertility related proteins

Infertility is an important aspect of human and animal reproduction and still presents with much etiological ambiguity. As fifty percent of infertility is related to the male partner, molecular investigations on sperm and seminal plasma can lead to new knowledge on male infertility. Several comparisons between fertile and infertile human and other species sperm proteome have shown the existence of potential fertility markers. These proteins have been categorized into energy related, structural and other functional proteins which play a major role in sperm motility, capacitation and sperm-oocyte binding. The data from these studies show the impact of sperm proteome studies on identifying different valuable markers for fertility screening. In this article, we review recent development in unraveling sperm fertility related proteins.

Comparative analysis of Mafriwal (Bos taurus × Bos indicus) and Kedah Kelantan (Bos indicus) sperm proteome identifies sperm proteins potentially responsible for higher fertility in a tropical climate

The fertility of zebu cattle (Bos indicus) is higher than that of the European purebred (Bos taurus) and crossbred (Bos taurus × Bos indicus) cattle in tropical areas. To identify proteins related to the higher thermo-tolerance and fertility of Zebu cattle, this study was undertaken to identify differences in sperm proteome between the high fertile Malaysian indigenous zebu cattle (Kedah Kelantan) and the sub-fertile crossbred cattle (Mafriwal). Frozen semen from three high performance bulls from each breed were processed to obtain live and pure sperm. Sperm proteins were then extracted, and two-dimensional gel electrophoresis performed to compare proteome profiles. Gel image analysis identified protein spots of interest which were then identified by liquid chromatography mass spectrometry quadrupole time-of-flight (LC MS/MS Q-TOF). STRING network analysis predicted interactions between at least 20 of the identified proteins. Among the identified proteins, a number of motility and energy related proteins were present in greater abundance in Kedah Kelantan. Sperm motility evaluation by Computer Assisted Semen Analysis (CASA) confirmed significantly higher motility in Kedah Kelantan. While results from this study do identify proteins that may be responsible for the higher fertility of Kedah Kelantan, functional characterization of these proteins is warranted to reinforce our understanding of their roles in sperm fertility.

Genetic loss or pharmacological blockade of testes-expressed taste genes causes male sterility

TAS1R taste receptors and their associated heterotrimeric G protein gustducin are involved in sugar and amino acid sensing in taste cells and in the gastrointestinal tract. They are also strongly expressed in testis and sperm, but their functions in these tissues were previously unknown. Using mouse models, we show that the genetic absence of both TAS1R3, a component of sweet and amino acid taste receptors, and the gustducin α-subunit GNAT3 leads to male-specific sterility. To gain further insight into this effect, we generated a mouse model that expressed a humanized form of TAS1R3 susceptible to inhibition by the antilipid medication clofibrate. Sperm formation in animals without functional TAS1R3 and GNAT3 is compromised, with malformed and immotile sperm. Furthermore, clofibrate inhibition of humanized TAS1R3 in the genetic background of Tas1r3(-/-), Gnat3(-/-) doubly null mice led to inducible male sterility. These results indicate a crucial role for these extraoral "taste" molecules in sperm development and maturation. We previously reported that blocking of human TAS1R3, but not mouse TAS1R3, can be achieved by common medications or chemicals in the environment. We hypothesize that even low levels of these compounds can lower sperm count and negatively affect human male fertility, which common mouse toxicology assays would not reveal. Conversely, we speculate that TAS1R3 and GNAT3 activators may help infertile men, particularly those that are affected by some of the mentioned inhibitors and/or are diagnosed with idiopathic infertility involving signaling pathway of these receptors.

Assessment of sperm hyperactivated motility and acrosome reaction can discriminate the use of spermatozoa for conventional in vitro fertilisation or intracytoplasmic sperm injection: preliminary results

Basic semen analysis is insufficient for determining the fertility potential. The aim of this study was to determine if hyperactivated motility (HAM) and acrosome reaction (AR) can be useful tests for evaluating semen quality during male infertility evaluations and to help the clinician decide whether regular insemination or intracytoplasmic sperm injection (ICSI) is preferable during in vitro fertilisation. A prospective study was conducted. Patients with normal sperm according to World Health Organization guidelines who underwent IVF treatment and planned regular insemination were asked to participate. A portion of sperm sample was evaluated for HAM and AR on day of ovum pick up. In HAM assessment, 93.3% of patients with increased HAM had a high fertilisation rate compared with 64% in the group without increased HAM (P = 0.059). For the AR evaluation, 91.7% of samples with a low rate of spontaneous AR had a high fertilisation rate compared with 39.3% in the group with a high rate of spontaneous AR (P = 0.004).

Cellular mechanisms regulating sperm-zona pellucida interaction

For mammalian spermatozoa to exhibit the ability to bind the zona pellucida (ZP) they must undergo three distinct phases of maturation, namely, spermatogenesis (testis), epididymal maturation (epididymis) and capacitation (female reproductive tract). An impressive array of spermatozoa surface remodeling events accompany these phases of maturation and appear critical for recognition and adhesion of the outer vestments of the oocyte, a structure known as the ZP. It is becoming increasingly apparent that species-specific zona adhesion is not mediated by a single receptor. Instead, compelling evidence now points toward models implicating a multiplicity of receptor-ligand interactions. This notion is in keeping with emerging research that has shown that there is a dynamic aggregation of proteins believed to be important in sperm-ZP recognition to the regions of sperm that mediate this binding event. Such remodeling may in turn facilitate the assembly of a multimeric zona recognition complex (MZRC). Though formation of MZRCs raises questions regarding the nature of the block to polyspermy, formation and assembly of such a structure would no doubt explain the strenuous maturation process that sperm endure on their sojourn to functional maturity.

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.

Sphingosine 1-phosphate and sphingosine kinase are involved in a novel signaling pathway leading to acrosomal exocytosis

Regulated secretion is a central issue for the specific function of many cells; for instance, mammalian sperm acrosomal exocytosis is essential for egg fertilization. Sphingosine 1-phosphate is a bioactive sphingolipid that regulates crucial physiological processes. Here we report that this lipid triggers acrosomal exocytosis in human sperm by a mechanism involving a G(i)-coupled receptor. Real-time imaging showed a remarkable increase of cytosolic calcium upon activation with sphingosine 1-phosphate and pharmacological experiments indicate that the process requires extracellular calcium influx through voltage and store-operated calcium channels and efflux from intracellular stores through inositol 1,4,5-trisphosphate-sensitive calcium channels. Sphingosine 1-phosphate-induced exocytosis requires phospholipase C and protein kinase C activation. We investigated possible sources of the lipid. Western blot indicates that sphingosine kinase 1 is present in spermatozoa. Indirect immunofluorescence showed that phorbol ester, a potent protein kinase C activator that can also trigger acrosomal exocytosis, redistributes sphingosine kinase 1 to the acrosomal region. Functional assays showed that phorbol ester-induced exocytosis depends on the activation of sphingosine kinase 1. Furthermore, incorporation of (32)P to sphingosine demonstrates that cells treated with the phorbol ester increase their sphingosine kinase activity that yields sphingosine 1-phosphate. We present here the first evidence indicating that human spermatozoa produce sphingosine 1-phosphate when challenged with an exocytic stimulus. These observations point to a new role of sphingosine 1-phosphate in a signaling cascade that facilitates acrosome reaction providing some clues about novel lipid molecules involved in exocytosis.

Potential biological role of poly (ADP-ribose) polymerase (PARP) in male gametes

Maintaining the integrity of sperm DNA is vital to reproduction and male fertility. Sperm contain a number of molecules and pathways for the repair of base excision, base mismatches and DNA strand breaks. The presence of Poly (ADP-ribose) polymerase (PARP), a DNA repair enzyme, and its homologues has recently been shown in male germ cells, specifically during stage VII of spermatogenesis. High PARP expression has been reported in mature spermatozoa and in proven fertile men. Whenever there are strand breaks in sperm DNA due to oxidative stress, chromatin remodeling or cell death, PARP is activated. However, the cleavage of PARP by caspase-3 inactivates it and inhibits PARP's DNA-repairing abilities. Therefore, cleaved PARP (cPARP) may be considered a marker of apoptosis. The presence of higher levels of cPARP in sperm of infertile men adds a new proof for the correlation between apoptosis and male infertility. This review describes the possible biological significance of PARP in mammalian cells with the focus on male reproduction. The review elaborates on the role played by PARP during spermatogenesis, sperm maturation in ejaculated spermatozoa and the potential role of PARP as new marker of sperm damage. PARP could provide new strategies to preserve fertility in cancer patients subjected to genotoxic stresses and may be a key to better male reproductive health.

Nongenomic activation of spermatozoa by steroid hormones: facts and fictions

The rapid effects of steroids on spermatozoa have been demonstrated for the first time two decades ago. Progesterone (P), which is present throughout the female genital tract with peaks of levels in the cumulus matrix surrounding the oocyte, stimulates several sperm functions, including hyperactivation and acrosome reaction. These effects are mediated by an extranuclear pathway, as P stimulates an influx of calcium, the tyrosine phosphorylation of sperm proteins and other signalling cascades in a rapid manner. Whether these effects are receptor mediated and which receptors mediate these effects are still a matter of discussion despite all the efforts of the scientific community aimed at identifying them during the last 20 years. Although responsiveness to P is related to sperm fertilizing ability, the physiological role of P during the process of fertilization is discussed, and recent evidence points for a role of the steroid as a chemotactic agent for sperm. A similar situation applies for estrogens (E), which have been shown to induce direct effects on sperm by an extranuclear pathway. In particular, E appear to decrease acrosome reaction in response to P, exerting a role in ensuring an appropriate timing for sperm exocytosis during the process of fertilization.