Pyroglutamyl peptidase I and prolyl endopeptidase in human semen: increased activity in necrozoospermia

Necrozoospermia: The tree that hides the forest

BACKGROUND

Necrozoospermia is a condition found in 0.2 to 0.4 % of male infertility cases. The causes of necrozoospermia are multiple: they can be related to testicular and/or post-testicular damage. Additionally, these causes most often involve the production of reactive oxygen species (ROS) and/or sperm DNA fragmentation (SDF) which can reduce the chances of spontaneous pregnancy or affect the outcome of assisted reproductive technologies.

OBJECTIVE

To focus on potential etiologies of necrozoospermia, its diagnosis and its therapeutic management especially before the employment of ICSI.

METHODS

Authors searched PubMed/Medline, Web of Science, Cochrane Library, Google and Institutional websites for medical subheading terms and free text words referred to "necrozoospermia", "sperm vitality", "sperm viability", "sperm DNA fragmentation" and "ICSI".

RESULTS

We identified twelve main etiologies of necrozoospermia responsible for either a decrease of sperm vitality, a mild a moderate or a severe necrozoospermia. In case of a confirmed decreased vitality, a thorough check-up should be conducted and if available, etiological treatment should be proposed. Therapeutic management could also include repeated ejaculations, drug treatments, the use of ICSI with ejaculated or surgically extracted spermatozoa in case of a non-treatable necrozoospermia.

DISCUSSION AND CONCLUSION

The potential causes of necrozoospermia should be investigated because many of them could be corrected, thus avoiding the use of ICSI. Moreover, if ICSI procedure remains necessary, the therapeutic management of necrozoospermia could also improve the chances of success by reducing oxidative stress and/or sperm DNA fragmentation. This article is protected by copyright. All rights reserved.

Study on PREP localization in mouse seminal vesicles and its possible involvement during regulated exocytosis

SummaryProlyl endopeptidase (PREP) is a post-proline cleaving enzyme. It is involved in the regulation of multiple inositol polyphosphate phosphatase activity implicated in the pathway of inositol 1,4,5-trisphosphate, resulting in the modulation of cytosolic Ca2+ levels. Besides its peptidase activity, PREP was identified as a binding partner of tubulin, suggesting that it may participate in microtubule-associate processes. In this paper, we evaluated the expression of PREP mRNA and protein by polymerase chain reaction and western blot analyses and its co-localization with tubulin by immunofluorescence in adult mouse seminal vesicles. We showed that both proteins are cytoplasmic: tubulin is localized at the apical half part of the cell, while PREP has a more diffuse localization, showing a prominent distribution at the apical cytoplasm. These findings support our hypothesis of a specific role for PREP in cytoskeletal rearrangement that occurs during the exocytosis of secretory vesicles, and in particular its association with tubulin filaments. Moreover, it may regulate Ca2+ levels, and promote the final step of vesicular exocytosis, namely the fusion of the vesicles with the plasma membrane. These results strongly suggest that there is a pivotal role for PREP in vesicle exocytosis, as well as in the physiology of mouse seminal vesicles.

Subcellular Localization of Prolyl Endopeptidase During the First Wave of Rat Spermatogenesis and in Rat and Human Sperm

Prolyl endopeptidase (PREP) is an enzyme which cleaves several peptide hormones and neuropeptides on the carboxyl side of proline residues and is involved in many biological processes, including cell proliferation and differentiation, glucose metabolism, learning, memory, and cognitive disorders. PREP has also been identified as a binding partner of tubulin, suggesting the involvement of endopeptidase in microtubule-associate processes, independent of its peptidase activity. Furthermore, several reports have implied PREP participation in both male and female reproduction-associated mechanism. We herein assess a potential association of PREP to the morphogenesis of rat testis, profiling its localization versus tubulin, during the first wave of spermatogenesis and in the adult gonad (from 7 to 60 dpp). We show that, in mitotic phases, PREP shares its localization with tubulin in Sertoli cells, gonocytes, and spermatogonia. Later, during meiosis, both proteins are found in spermatocytes, and in the cytoplasm of Sertoli cells protrusions, surrounding the germ cells, while, during spermiogenesis, they both localize in the cytoplasm of round and elongating spermatids. We also found that this enzyme has a peculiar nuclear localization, in the proliferating cells in all phases of analysis. Finally, they are expressed in the flagellum of mature gametes, as corroborated by additional immunolocalization analysis on both rat and human sperm. Our data support the hypothesis of the fundamental role of PREP in reproduction and in cytoskeletal organization during mammalian testis morphogenesis and gamete progression.

[Necrozoospermia: From etiologic diagnosis to therapeutic management]

This review describes necrospermia, its diagnosis, causes and management. Sperm vitality is commonly assessed in the laboratory of reproductive biology, with the eosin test or with the hypo-osmotic swelling test. Necrospermia is defined by a percentage of living spermatozoa inferior to 58%, and can be related to male infertility. Several pathological mechanisms may be involved and can be classified either in testicular causes (hyperthyroidism, local hyperthermia, varicocele), or post-testicular causes (epididymal necrospermia, dysregulation of seminal plasma, adult polycystic kidney disease, vasectomy reversal, anti-sperm antibodies) or both (infection, toxic, age, spinal cord injury). The first treatment is to correct the underlying cause, if possible. Repetitive ejaculation has demonstrated to be effective as well. Many drugs would also improve the sperm vitality (antioxidants, non-and-steroidal anti-inflammatory drugs) but there is currently no guideline to recommend their use. With necrospermia, fertilization rates are lower but in vitro fertilization (IVF) with Intracytoplasmic sperm injection (ICSI) improves the chances of conception.

Prolyl Endopeptidase (PREP) is Associated With Male Reproductive Functions and Gamete Physiology in Mice

Prolyl endopeptidase (PREP) is a serine protease which has been implicated in many biological processes, such as the maturation and degradation of peptide hormones and neuropeptides, learning and memory, cell proliferation and differentiation, and glucose metabolism. A small number of reports have also suggested PREP participation in both male and female reproduction-associated processes. In the present work, we examined PREP distribution in male germ cells and studied the effects of its knockdown (Prep(gt/gt)) on testis and sperm in adult mice. The protein is expressed and localized in elongating spermatids and luminal spermatozoa of wild type (wt) mice, as well as Sertoli, Leydig, and peritubular cells. PREP is also expressed in the head and midpiece of epididymal spermatozoa, whereas the remaining tail region shows a weaker signal. Furthermore, testis weight, histology of seminiferous tubules, and epididymal sperm parameters were assessed in wt and Prep(gt/gt) mice: wild type testes have larger average tubule and lumen diameter; in addition, lumenal composition of seminiferous tubules is dissimilar between wt and Prep(gt/gt), as the percentage of spermiated tubules is much higher in wt. Finally, total sperm count, sperm motility, and normal morphology are also higher in wt than in Prep(gt/gt). These results show for the first time that the expression of PREP could be necessary for a correct reproductive function, and suggest that the enzyme may play a role in mouse spermatogenesis and sperm physiology.

Evaluation of testicular toxicology of doxorubicin based on microarray analysis of testicular specific gene expression

Testicular toxicity of chemical substances has been generally assessed by sperm properties and histology. However, the methods can provide only a few information of the mechanism of the toxicity. The aim of this study is to show a method that can evaluate an overview of testicular toxic mechanisms using a tissue-specific microarray and classification of genes using Medical Subject Headings (MeSH). Male ICR mice (6 weeks old) were treated with doxorubicin hydrochloride (0, 0.1, 0.3 mg/kg/time, three times per week) by subcutaneous injection for 6 weeks (until 11 weeks old). Six weeks after the final administration, tissue and blood samples were obtained. Testes were subjected to gene expression analysis using quantitative RT-PCR and cDNA microarray (testis2). To interpret the microarray data, genes were classified using MeSH related to the functions of testis and sperm. Doxorubicin (both 0.1 and 0.3 mg/kg group) induced a decrease in sperm normal morphology and mortality, daily sperm production, and the number of Sertoli cells in the seminiferous tubules. Quantitative RT-PCR and microarray analysis showed dysregulation of mRNA expression levels of genes related to Sertoli cells, germ cells and spermatogenesis. Analysis of microarray data showed a significant enrichment of a total of ten MeSH categories including Spermatogenesis, Sertoli cells, Germ cells and Male infertility. This article concluded that analysis using testicular specific microarray combined with MeSH showed a more comprehensive overview of testicular toxic mechanisms than existing methods; i.e., examination of sperm properties and the histological examinations.

Prolyl endopeptidase mRNA expression in the central nervous system during rat development

Prolyl endopeptidase (PEP) is a serine protease that cleaves small peptides at the carboxyl side of L-proline. PEP has been reported to have important functions in the brain being implicated in learning and memory processes, psychological disorders and neurodegenerative diseases. Several PEP substrates have been shown to play a role during brain development and this observation led us to investigate the expression of PEP mRNA in the rat brain and spinal cord, from embryo to adult stages. In situ hybridization revealed that PEP mRNA is expressed early, from embryonic day 15, notably in germinative areas including the neocortical, hippocampal, pallidal, thalamic, anterior hypothalamic, tectal, cerebellar, pontine and medullary neuroepithelia. PEP mRNA was also found in the differentiating fields of the olfactory bulb, the orbital and cingulate cortex, the hippocampal formation, the cortical plate and the subventricular zone of the cortex. Quantitative RT-PCR analysis in various brain areas and the spinal cord showed that PEP mRNA levels are more abundant during the perinatal stages, coinciding with a period of neuronal migration and differentiation. From then on, PEP mRNA expression decreased, reaching its lowest levels at adulthood. Overall, the present data support the possibility that PEP exerts specific functions related to neurodevelopment besides those proposed to date.

Seasonal variation of peptidase activities in the reproductive tract of Crotalus durissus terrificus

Seasonal quantitative patterns of acid (APA), basic (APB), puromycin-sensitive (APN-PS) and puromycin-insensitive neutral (APN-PI), cystyl (CAP), dipeptidyl IV (DPPIV), type-1 pyroglutamyl (PAP-I) and prolyl-imino (PIP) aminopeptidases and prolyl oligopeptidase (POP) activities in soluble (SF) and solubilized membrane-bound (MF) fractions from ductus deferens, vagina and uterus were studied to evaluate their relationships with the reproductive cycle and the extensive long-term spermatozoa storage (LTSS) of the Neotropical rattlesnake Crotalus durissus terrificus. APB, PIP and POP were detected only in SF, while other peptidases were detected in SF and MF. APB, APN-PI and APN-PS were predominant in most tissues in all seasons. Peptidase activities had a common pattern of increment during the dry season (winter/autumn), which coincides with the mating period (autumn) and LTSS in the female (winter), as well as the reduction of spermatozoa motility and maintenance of fertilization capacity of spermatozoa. The high CAP activity in the soluble fraction of the vagina during winter, compared to summer (time of parturition) and spring, coincides with the relaxation of this tissue. In the soluble fraction, the low PAP-I activity of the ductus deferens coincided with its high activity in the vagina during the winter; and the inverse occurred in summer, which is consistent with the physiological process of preserving spermatozoon viability. In conclusion, the studied peptidase activities had seasonal and tissue-specific characteristics, which suggest a relevant role in the reproductive physiology of C. d. terrificus.

Peptidase activities in Crotalus durissus terrificus semen

To understand the role of peptidases in seminal physiology ofCrotalus durissus terrificus, activity levels of representative enzymes in semen and their sensitivities to inhibitors, cofactors, and peptide hormones were evaluated. The existence of seminal fractions and the association of peptidases with these fractions were also characterized for the first time in snakes. The prominent inhibitors of aminopeptidases (APs) were amastatin for acid, basic, and neutral; bestatin for basic; and diprotin A for dipeptidyl-IV. Cystyl and prolyl-imino APs were similarly susceptible to the majority of these inhibitors. The basic and neutral were characterized as metallo-peptidases, acid AP was activated by MnCl2, and cystyl, prolyl-imino, and type I pyroglutamyl were characterized as sulphydryl-dependent APs. Angiotensin II, vasotocin, bradykinin, fertilization-promoting peptide, and TRH altered the majority of these peptidase activities; these peptides are possible substrates and/or modulators of these peptidases. Peptidase activities were found in all seminal fractions: seminal plasma (SP), prostasome-like (PR) structures, and soluble (S-) and membrane-bound fractions (MFs) of spermatozoa. The levels of activity of each peptidase varied among different seminal fractions. In SP, the higher activities were puromycin-insensitive neutral and basic APs. In PR, the higher activity was puromycin-insensitive neutral AP. In spermatozoa, the higher activity in subcellular SF was puromycin-sensitive neutral, while in MF both puromycin-sensitive and -insensitive neutral APs were equally higher than the other examined peptidases. Data suggested that these peptidases, mainly basic and neutral, have a high relevance in regulating seminal functions ofC. d. terrificus.

On the role of prolyl oligopeptidase in health and disease

Prolyl oligopeptidase (POP) is a serine peptidase which digests small peptide-like hormones, neuroactive peptides, and various cellular factors. Therefore, this peptidase has been implicated in many physiological processes as well as in some psychiatric disorders, most probably through interference in inositol cycle. Intense research has been performed to elucidate, on the one hand, the basic structure, ligand binding, and kinetic properties of POP, and on the other, the pharmacology of its inhibitors. There is fairly strong evidence of in vivo importance of POP on substance P, arginine vasopressin, thyroliberin and gonadoliberin metabolism. However, information about the biological relevance of POP is not yet conclusive. Evidence regarding the physiological role of POP is lacking, which is surprising considering that peptidase inhibitors have been exploited for drug development, some of which are currently in clinical trials as memory enhancers for the aged and in a variety of neurological disorders. Here we review the recent progress on POP research and evaluate the relevance of the peptidase in the metabolism of various neuropeptides. The recognition of novel forms and relatives of POP may improve our understanding of how this family of proteins functions in normal and in neuropathological conditions.

Molecular basis of pregnancy-induced breast cancer protection

We have postulated that the lifetime protective effect of an early pregnancy against breast cancer is due to the complete differentiation of the mammary gland characterized by a specific genomic signature imprinted by the physiological process of pregnancy. In the present work, we show evidence that the breast tissue of postmenopausal parous women has had a shifting of stem cell 1 to stem cell 2 with a genomic signature different from similar structures derived from postmenopausal nulliparous women that have stem cell 1. Those genes that are significantly different are grouped in major categories on the basis of their putative functional significance. Among them are those gene transcripts related to immune surveillance, DNA repair, transcription, chromatin structure/activators/co-activators, growth factor and signal transduction pathway, transport and cell trafficking, cell proliferation, differentiation, cell adhesion, protein synthesis and cell metabolism. From these data, it was concluded that during pregnancy there are significant genomic changes that reflect profound alterations in the basic physiology of the mammary gland that explain the protective effect against carcinogenesis. The implication of this knowledge is that when the genomic signature of protection or refractoriness to carcinogenesis is acquired by the shifting of stem cell 1 to stem cell 2, the hormonal milieu induced by pregnancy or pregnancy-like conditions is no longer required. This is a novel concept that challenges the current knowledge that a chemopreventive agent needs to be given for a long period to suppress a metabolic pathway or abrogate the function of an organ.

Transmission electron microscopy, immunocytochemical and fluorescence in situ hybridisation studies in a case of 100% necrozoospermia: case report

We present the ultrastructural, functional and chromosomal analyses of sperm from an infertile man with a normal karyotype and 100% necrozoospermia. Tests for microbial infection showed the presence of Escherichia coli in seminal and urethral fluid. Semen analysis was performed concomitantly with the infection and repeated twice after the therapy, in the absence of infection, to control the possible recovery of necrozoospermia. Morphological sperm evaluation was performed by light, fluorescent and electron microscopy; meiotic segregation was examined by fluorescence in situ hybridisation (FISH) technique. Polymerase chain reaction (PCR) was carried out on DNA from peripheral blood lymphocytes to analyse partial sequences of the Akap4 and Akap3 genes. AKAP3 protein is synthesised in round spermatids, incorporated into the fibrous sheath and is involved in organising the basic structure of the fibrous sheath. AKAP4 protein is incorporated late in spermatid development and plays a major role in completing fibrous sheath assembly. The whole sperm population was immotile and non-viable. The ultrastructural characteristics of sperm necrosis were identified. Immunostaining of tubulin and AKAP4 proteins was negative in sperm tails. PCR did not reveal any deletions in the investigated regions. FISH sperm analysis highlighted an altered meiotic segregation. After recovery from infection, 100% necrozoospermia persisted and chromosomal sperm aneuploidies were still present.

Suggested functions for prolyl oligopeptidase: a puzzling paradox

Prolyl oligopeptidase (PO, E.C. 3.4.21.26) is a post-proline cleaving enzyme with endopeptidase activity towards peptides not longer than 30 amino acids. It has been purified and characterized from various mammalian and bacterial sources, but despite its thorough enzymological and structural characterization, the exact function of PO remains obscure. Many investigations have addressed the physiological role of this enzyme, mainly by the use of specific PO inhibitors, activity measurements in clinical samples and (neuro)peptide degradation studies. From the combined results emerges a puzzling paradox: how can an intracellular, cytoplasmatic oligopeptidase affect not only the amount of extracellular neuropeptides but also signal transduction and secretion? This report provides a review of the literature on the suggested functions for PO, highlighting possible pitfalls and contradictions.