Isolation and characterization of a protein with homology to angiotensin converting enzyme from the periacrosomal plasma membrane of equine spermatozoa

Regulation of Male Fertility by the Renin-Angiotensin System

The renin-angiotensin system (RAS) is a peptidic system known mainly for its roles in the maintenance of blood pressure and electrolyte and fluid homeostasis. However, several tissues and cells have been described to possess an intrinsic RAS that acts locally through different paracrine and autocrine mechanisms. In the male reproductive system, several components of this system have been observed in various organs and tissues, such as the testes, spermatozoa and seminal fluid. Some functions attributed to this local RAS are maintenance of seminal plasma electrolytes, regulation of steroidogenesis and spermatogenesis, and sperm functions. However, their specific actions in these locations are not fully understood. Therefore, a deep knowledge of the functions of the RAS at both the testicular and seminal levels could clarify its roles in male infertility and sperm physiology, and the different RAS elements could be used to design tools enabling the diagnosis and/or treatment of male infertility.

Zinc: A Necessary Ion for Mammalian Sperm Fertilization Competency

The importance of zinc for male fertility only emerged recently, being propelled in part by consumer interest in nutritional supplements containing ionic trace minerals. Here, we review the properties, biological roles and cellular mechanisms that are relevant to zinc function in the male reproductive system, survey available peer-reviewed data on nutritional zinc supplementation for fertility improvement in livestock animals and infertility therapy in men, and discuss the recently discovered signaling pathways involving zinc in sperm maturation and fertilization. Emphasis is on the zinc-interacting sperm proteome and its involvement in the regulation of sperm structure and function, from spermatogenesis and epididymal sperm maturation to sperm interactions with the female reproductive tract, capacitation, fertilization, and embryo development. Merits of dietary zinc supplementation and zinc inclusion into semen processing media are considered with livestock artificial insemination (AI) and human assisted reproductive therapy (ART) in mind. Collectively, the currently available data underline the importance of zinc ions for male fertility, which could be harnessed to improve human reproductive health and reproductive efficiency in agriculturally important livestock species. Further research will advance the field of sperm and fertilization biology, provide new research tools, and ultimately optimize semen processing procedures for human infertility therapy and livestock AI.

Testis-specific isoform of angiotensin-converting enzyme (tACE) is involved in the regulation of bovine sperm capacitation

We hypothesized that the testis-specific isoform of angiotensin-converting enzyme (tACE) is released during bovine sperm capacitation, and its peptidase activity is required for capacitation. Specific objectives of this study were to (i) develop an anti-tACE antibody; (ii) characterize expression of tACE in bovine testes and sperm; and (iii) determine the role of tACE in capacitation. A 110-kDa protein, consistent with the mass of tACE, was detected in sperm extract by our anti-tACE immunoserum. This immunotarget localized at the acrosomal region and principal piece, but was only expressed in testis of mature bulls. When bull sperm were incubated in Sp-TALP (0 and 4 hr) plus 10 µg/ml heparin (capacitation group) or 10 µg/ml heparin + 10 µM captopril (an ACE inhibitor) for 4 hr, the number of acrosome-reacted (40.1 vs. 24.0%, respectively) and hyperactivated (15.0 vs. 9.7%) sperm increased, and tyrosine phosphoprotein content were higher (p < 0.05) for sperm in heparin alone. tACE activity was also higher (0.04 U/ml; p < 0.01) in incubation medium of sperm exposed to heparin compared to 0- and 4-hr incubation controls or heparin + captopril conditions (0, 0.005, and 0.009 U/ml, respectively). Furthermore, capacitation-associated shedding of a portion of tACE into the medium decreased sperm content of the 110-kDa tACE, but concurrently increased the abundance of a 60-kDa tACE variant. Thus, a portion of the extracellular region of tACE (containing its catalytic site) is released from bovine sperm during capacitation, and tACE activity may be required for sperm capacitation.

Characterization and activity of angiotensin-converting enzyme in Holstein semen

The study was designed to perform immunodetection in spermatozoa and seminal plasma, immunolocalization in spermatozoa, and evaluation of the enzymatic activity of angiotensin-converting enzyme (ACE) in the semen of Holstein bulls. We used ejaculates from five bulls as part of a regular collection of semen. The monoclonal anti-ACE antibody recognized a single protein band with 100 kDa in detergent extract prepared from sperm and in seminal plasma. ACE enzymatic activity in sperm was 43.7, 21.3, 45.6, 60.0, and 57.7 mU/mL in bulls 1, 2, 3, 4, and 5, respectively, and 0.3, 2.3, 3.0, 2.3, and 2.6 mU/mL in seminal plasma of the same bulls, respectively. The average percentages of sperm with acrosome reactions after treatment with heparin were 28.3%, 28.6%, 35.2%, 25.0%, and 32.3%, respectively. These values were higher than the percentages of acrosome reactions in controls and the captopril group (P<0.05), although no difference was seen between the captopril and control groups (P>0.05). After 4h of incubation, motility in the control group (32.9%) was significantly higher than that in the heparin (15.7%) and captopril (12.1%) groups. No difference was found in motility after the capacitation assay in the heparin and captopril groups (P>0.05). In conclusion, ACE was immunologically localized in the acrosome of the spermatozoa of Holstein bull, the specific enzymatic activity of ACE in detergent-extracted spermatozoa and seminal plasma was inhibited by captopril, and this ACE inhibitor reduced the percentage of sperm with progressive motility and acrosome reactions after capacitation in vitro.

Fertilisation in the horse and paracrine signalling in the oviduct

The mammalian oviduct plays a crucial role in the preparation of gametes for fertilisation (transport and final maturation) and fertilisation itself. An increasing number of studies offers a comprehensive overview of the functions of the oviduct and its secretions, but this topic has had limited investigation in the horse. Limited data are available on the final oocyte maturation in the equine oviduct. However, in vitro and in vivo systems have been established to analyse the influence of equine oviduct epithelial cells (OEC) during maturation on the potential of oocytes for fertilisation and development. Most studies focus on the role of the oviduct in equine sperm function, such as spermatozoa transport, attachment to oviduct epithelium, viability, motility and capacitation. Moreover, some possible candidate molecules for sperm-oviducal interactions have been identified in the horse. Finally, the low efficiency of conventional in vitro fertilisation and the in vivo fertilisation of equine oocytes transferred into the oviduct of an inseminated mare predicted an influence of oviduct in equine fertilisation. Actually, in vivo and in vitro experiments demonstrated a role of the oviduct in equine fertilisation. Moreover, recent studies showed a beneficial effect of homologous and heterologous OEC on equine in vitro fertilisation, and some candidate molecules have been studied.

Testicular Isoform of Angiotensin I-Converting Enzyme (ACE, CD143) on the Surface of Human Spermatozoa: Revelation and Quantification Using Monoclonal Antibodies

PROBLEM

The elucidation of the role of angiotensin-converting enzyme (ACE, CD143) in the male fertility has been hampered by the absence of highly specific antibodies to the native testicular isoform (tACE). The quantification of tACE expression on human-ejaculated spermatozoa was performed using a novel panel of monoclonal antibodies (mAbs).

METHOD OF STUDY

The expression of tACE on the surface of live and fixed human spermatozoa was analyzed by flow cytometry and immunocytochemistry using new mAbs to human tACE.

RESULTS

Monoclonal antibodies 1E10 and 4E3 similarly revealed tACE on the surface of live and fixed spermatozoa. The high percentage of tACE-positive spermatozoa (median 81%) was revealed in the swim-up fraction of sperm. Antibody-induced tACE shedding occurs preferentially from live sperm with defective function and/or morphology. Testicular ACE is located on the plasma membrane of the post-acrosomal region, the neck and midpiece of normal spermatozoa, but showed a variable distribution on the defective cells.

CONCLUSIONS

The new mAbs recognizing the C-terminal domain of human ACE are useful tools for quantification of tACE expression on human live and fixed spermatozoa and further adequate analysis of the tACE role in reproduction.

Activity of angiotensin-converting enzyme (ACE) in reproductive tissues of the stallion and effects of angiotensin II on sperm motility

A testis-specific isoform of angiotensin-converting enzyme (ACE) has been identified in a number of mammalian species. The purpose of this study was to characterize the activity of ACE in equine spermatozoa, seminal plasma, and testis. Activity of ACE was determined in seminal plasma, ejaculated and epididymal spermatozoa from mature stallions as well as from pre- and postpubertal testis. The effect of addition of angiotensin II on equine sperm motility was also evaluated. The activity of ACE in detergent extracted sperm plasma membrane was approximately 13-fold higher than that detected in seminal plasma (93.7 mU/mg versus 7.0 mU/mg protein, respectively). Activity of ACE in equine testis was significantly higher in postpubertal than in prepubertal males (3.0 mU/mg versus 0.4 mU/mg protein, respectively), and ACE activity was reduced (P<0.001) in a dose-dependent fashion by the addition of captopril. The effect of angiotensin II on sperm motility was evaluated by computer-assisted semen analysis in sperm incubated with angiotensin II (0, 1, 10, 100 nM) at 38.5 degrees C. There was no significant effect of angiotensin II on the percent motile sperm; however, there was a significant main effect of angiotensin II (P<0.01) on the kinematic parameters beat cross frequency (BCF), average path velocity (VAP), and curvilinear velocity (VCL), respectively. In addition, there were significant stallionxconcentration interactions for amplitude lateral movement (ALH), BCF, linearity (LIN), straightness (STR), and VCL. This study demonstrates that ACE activity is present in sperm membrane from ejaculated and epididymal spermatozoa and in postpubertal testis. Further studies are required to determine the role of this testis-specific enzyme.

Angiotensin I-converting enzyme and potential substrates in human testis and testicular tumours

The angiotensin I-converting enzyme (ACE, kininase II, CD143) shows a broad specificity for various oligopeptides. Besides the well-known conversion of angiotensin I to II, ACE degrades efficiently kinins and the tetrapeptide AcSDKP (goralatide) and thus equally participates in the renin-angiotensin system, the kallikrein-kinin system, and the regulation of stem cell proliferation. In the mammalian testis, ACE occurs in two isoforms. The testicular isoform (tACE) is exclusively expressed during spermatogenesis and is generally thought to represent the germ cell-specific isozyme. However, we have previously demonstrated that, in addition to tACE, the somatic isoform (sACE) is also present in human germ cells. Similar to other oncofoetal markers, sACE exhibits a transient expression during foetal germ cell development and appears to be a constant feature of intratubular germ cell neoplasm, the so-called carcinoma-in-situ (CIS) and, in particular, of classic seminoma. This demands the existence of specific paracrine functions during male germ cell differentiation and development of male germ cell tumours, which are mediated by either of the two ACE isoforms. Considering the complexity of current data about ACE, a logical connection is required between (I) the precise localisation of ACE isoforms, (I) the local access to potential substrates and (II) functional data obtained by knockout mice models. The present article summarises the current knowledge about ACE and its potential substrates with special emphasis on the differentiation-restricted ACE expression during human spermatogenesis and prespermatogenesis, the latter being closely linked to the pathogenesis of human germ cell tumours.

Germinal angiotensin I-converting enzyme is totally shed from the rodent sperm membrane during epididymal maturation

Acquisition of sperm fertilizing ability is due, in part, to the reorganization of plasma membrane proteins that occurs during epididymal sperm transit. Using polyclonal antibodies against angiotensin I-converting enzyme (ACE), we showed that this enzyme is immunolocalized mainly on the middle piece of rat and mouse testicular sperm and with less intensity along the initial part of the principal piece of the flagellum. In both species, only some sperm from the caput epididymis were still reactive, whereas no labeling was observed on cauda epididymal sperm. The 105- to 110-kDa germinal ACE was absent from the rat testicular fluid but appeared in the fluid of the anterior epididymis. Thereafter, its molecular weight shifted to 94 kDa in the corpus epididymal fluid and remained at this weight in the caudal region. The 105- to 110-kDa immunoreactive protein was present in testicular rat sperm extract but was completely absent from epididymal sperm extracts. Western blot analysis of testicular and epididymal tissue extracts from the rat and mouse also confirmed that the germinal enzyme was absent from the epididymal sperm cell. Our results demonstrated that the rodent germinal ACE is released from the testicular sperm membrane when sperm enter the epididymis, a process similar to that observed in domestic mammals. This result is discussed in view of the suggested role for this enzyme in sperm fertility.

Physiological and enzymatic properties of the ram epididymal soluble form of germinal angiotensin I-converting enzyme

The 94-kDa ram epididymal fluid form of the sperm membrane-derived germinal angiotensin I-converting enzyme (ACE) was purified by chromatography, and some of its enzymatic properties were studied. For the artificial substrate furanacryloyl-L-phenylalanylglycylglycine (FAPGG), the enzyme exhibited a Michaelis constant (K(m)) of 0.18 mM and a V(max) of 34 micromoles/(min x mg) and for hippuryl-L-histidyl-L-leucine a K(m) of 2.65 mM and a V(max) of 163 micromoles/(min x mg) under the defined standard conditions (300 mM NaCl and 50 mM Tris; pH 7.5 and 8.3, respectively). The FAPGG hydrolysis was decreased by 82.5% and 67.5% by EDTA and dithioerythritol, respectively, and was totally inhibited by specific ACE inhibitors such as captopril, P-Glu-Trp-Pro-Arg-Pro-Glu-Ile-Pro-Pro, and lisinopril. Optimum activity for FAPGG was with pH 6.0, 50 mM chloride, and 500 microM zinc. Under the various conditions tested, bradykinin, angiotensin (Ang) I, Ang II, and LHRH were competitors for FAPGG. Bradykinin and angiotensin I were the best competitors. The enzyme cleaved Ang I into Ang II, and the optimal conditions were with pH 7.5 and 300 mM chloride. The relationship between the carboxypeptidase activity in seminal plasma and the prediction of fertility of young rams was also studied. These results indicated a correlation between sperm concentration and ACE activity in semen but showed no statistically significant correlation between such activity and fertility of the animal. Finally, we tested the role of ACE in fertilization; no difference in the in vitro fertilization rate was observed in the presence of 10(-4) M captopril.

A 105- to 94-kilodalton protein in the epididymal fluids of domestic mammals is angiotensin I-converting enzyme (ACE); evidence that sperm are the source of this ACE

SDS-PAGE analysis of luminal fluid from the ram testis and epididymis revealed a protein of about 105 kDa in the fluid in the caput epididymal region. The molecular mass of this fluid protein shifted from 105 kDa to 94 kDa in the distal caput epididymidis and remained at 94 kDa in the lower regions of the epididymis. The possible sperm origin of this protein was suggested by the decrease in intensity of a 105-kDa compound on the sperm plasma membrane extract and by its total disappearance from the fluid of animals with impaired sperm production caused by scrotal heating. The 94-kDa protein was purified from ram cauda epididymal fluid, and a rabbit polyclonal antiserum was obtained. This antiserum showed that membranes of testicular sperm and sperm from the initial caput were positive for the presence of an immunologically related antigen. The protein was immunolocalized mainly on the flagellar intermediate piece, whereas in some corpus and caudal sperm, only the apical ridge of the acrosomal vesicle was labeled. The purified protein was microsequenced: its N-terminal was not found in the sequence database, but its tryptic fragments matched the sequence of the angiotensin I-converting enzyme (ACE). Indeed, the purified 94-kDa protein exhibited a carboxypeptidase activity inhibited by specific blockers of ACE. All the soluble seminal plasma ACE activity in the ram was attributable to the 94-kDa epididymal fluid ACE. The polyclonal antiserum also showed that a soluble form of ACE appeared specifically in the caput epididymal fluid of the boar, stallion, and bull. This soluble form was responsible for all the ACE activity observed in the fluid from the distal caput to the cauda epididymidis in these species. Our results strongly suggest that the epididymal fluid ACE derives from the germinal form of ACE that is liberated from the testicular sperm in a specific epididymal area.

Angiotensin II: a reproductive hormone too?

It has long been known that angiotensin II (Ang II) can affect reproductive tissues such as the uterus. However, the existence of a local renin-angiotensin system (RAS) in female as well as male reproductive tissues is a relatively recent observation. Of great interest is the discovery that all components of the RAS are present in the ovary, that the ovary secretes components of the RAS into the bloodstream, and that the ovary itself is responsive to Ang II. Recent studies suggest that the primary role of Ang II in the ovary is to cause atresia in non-ovulatory follicles; however, there is also compelling data to suggest that Ang II facilitates ovulation. Male reproductive structures also contain all of the components of the RAS, gonadotropins regulate the activity of these components, and these tissues have Ang II receptors. Of great interest is the expression of testis-specific angiotensin-converting enzyme (ACE), which is located on germ cells. Recent studies using gene knock-out techniques indicate that testis ACE plays an important role in male fertility. However, the overall significance of the RAS for normal reproductive function remains questionable. There is now a body of evidence implicating the RAS in pathophysiologies associated with reproductive function, which gives rise to the possibility that drugs acting on the RAS might ameliorate some of these disorders. Considerable work remains to determine the role of Ang II in reproductive functions.

Effect of angiotensin converting enzyme (ACE) and angiotensins on human sperm functions

The presence of components of the renin angiotensin system (RAS) and specific receptors of angiotensin II in the female and male reproductive tract supports the hypothesis that reproductive functions may be controlled by RAS. Therefore, the present study investigated the influence of ACE and angiotensins on sperm functions and the sperm-egg interaction. The experiments did not indicate direct effects of ACE on the capacitation process or acrosome reaction. Release of ACE from human spermatozoa during capacitation was not related to their ability to undergo acrosome reaction after stimulation with ionophore. Therefore, ACE release does not seem to be a useful clinical marker for human sperm capacitation. However, decreased binding of human spermatozoa to the oolemma of zonafree hamster oocytes after inhibition of ACE by captopril indicates that kininase II is involved in sperm-egg interactions. In contrast to other studies, incubation with captopril had no influence on sperm binding to the zona pellucida. Because effects of ACE on sperm-egg interactions but not on capacitation or acrosome reaction were observed, several experiments were performed to study the influence of substrates and products on the acrosome reaction. Angiotensin II induced the acrosome reaction dose-dependently, whereas angiotensin I had no effect on the acrosome reaction. The effect of angiotensin II on acrosome reaction seems to be calcium-dependent and mediated by protein kinases. Since a specific type 2 angiotensin II receptor inhibits the acrosome reaction induced by angiotensin II, this subtype of receptors may be present at the surface of sperm heads. Another clue for the presence of type 2 receptors on human spermatozoa is the finding that pertussis toxin did not inhibit the angiotensin II induced acrosome reaction. In contrast to type 1 angiotensin II receptors, type 2 receptors are known to be G-protein independent.

Angiotensin-converting enzyme and male fertility

The angiotensin-converting enzyme (ACE; EC 3.4.15.1) gene (Ace) encodes both a somatic isozyme found in blood and several other tissues, including the epididymis, and a testis-specific isozyme (testis ACE) found only in developing spermatids and mature sperm. We recently used gene targeting to disrupt the gene coding for both ACE isozymes in mice and reported that male homozygous mutants mate normally but have reduced fertility; the mutant females are fertile. Here we explore the male fertility defect. We demonstrate that ACE is important for achieving in vivo fertilization and that sperm from mice lacking both ACE isozymes show defects in transport within the oviducts and in binding to zonae pellucidae. Males generated by gene targeting that lack somatic ACE but retain testis ACE are normally fertile, establishing that somatic ACE in males is not essential for their fertility. Furthermore, male and female mice lacking angiotensinogen have normal fertility, indicating that angiotensin I is not a necessary substrate for testis ACE. Males heterozygous for the mutation inactivating both ACE isozymes sire wild-type and heterozygous offspring at an indistinguishable frequency, indicating no selection against sperm carrying the mutation.