Up-regulation of CD95 (Apo-1/Fas) is associated with spermatocyte apoptosis during the first round of spermatogenesis in the rat

Somatic-Immune Cells Crosstalk In-The-Making of Testicular Immune Privilege

Immunological infertility contributes significantly to the etiology of idiopathic male infertility. Shielding the spermatogenic cells from systemic immune responses is fundamental to secure normal production of spermatozoa. The body's immune system is tuned with the host self-components since the early postnatal period, while sperm first develops during puberty, thus rendering spermatogenic proteins as 'non-self' or 'antigenic.' Development of antibodies to these antigens elicits autoimmune responses affecting sperm motility, functions, and fertility. Therefore, the testes need to establish a specialized immune-privileged microenvironment to protect the allogenic germ cells by orchestration of various testicular cells and resident immune cells. This is achieved through sequestration of antigenic germ cells by blood-testis barrier and actions of various endocrine, paracrine, immune-suppressive, and immunomodulatory mechanisms. The various mechanisms are very complex and need conceptual integration to disclose the exact physiological scenario, and to facilitate detection and management of immunogenic infertility caused by disruption of testicular immune regulation. The present review aims to (a) discuss the components of testicular immune privilege; (b) explain testicular somatic and immune cell interactions in establishing and maintaining the testicular immune micro-environment; and (c) illustrate the integration of multiple mechanisms involved in the control of immune privilege of the testis.

Physiological Adaptation to Simultaneous Chronic Exposure to High-Fat Diet and Dichlorodipheniletylhene (DDE) in Wistar Rat Testis

Environmental chemicals can be introduced by consuming contaminated foods. The environmental chemical dichlorodiphenyldichloroethylene (DDE), a persistent metabolite of dichlorodiphenyltrichloroethane (DDT), can affect spermatogenesis. Our study aims to evaluate, by using spectrophotometric analyses, western blot, and immunohistochemistry, the adaptive responses in testis of adult rats treated with a non-toxic dose of DDE, alone or in association with a high-fat diet (HFD). Four experimental groups were performed: N (normal diet); D (HFD); D + DDE (HFD + DDE); N + DDE (normal diet + DDE). D group showed a reduction in antioxidant capacity, and increases in lipid peroxidation, apoptosis, and proliferation associated with morphological impairment. A reduction in androgen receptor (AR) and serum testosterone levels were also found. DDE-treated groups exhibited higher lipid peroxidation levels compared to N and D, associated with pronounced defect in antioxidant capacity, apoptosis, cellular proliferation, as well as with tissue damage. Moreover, decreases in AR and serum testosterone levels were found in DDE-treated groups vs. N and D. In conclusion, HFD and DDE produced cellular stress leading to antioxidant impairment, apoptosis, and decreases in AR and serum testosterone levels associated with tissue damage. Cellular proliferation could be used as an adaptation to counterbalance the occurred damage, maintaining a pool of tubules that follow physiological maturation.

Possible Mechanisms for The Effects of Calcium Deficiency on Male Infertility

Calcium (Ca) is a significant element that acts as an intracellular second messenger. It is necessary for many physi- ological processes in spermatozoa including spermatogenesis, sperm motility, capacitation, acrosome reaction and fertilization. Although influences of Ca deficiency on sperm function and male infertility have been widely studied, mechanisms for these abnormalities are not well considered. Poor sperm motility, impairment of chemotaxis, capaci- tation, acrosome reaction and steroidogenesis are the major mechanisms by which Ca deficiency induces male infertil- ity. Therefore, an optimal seminal Ca concentration is required to strengthen sperm function and all steps leading to successful fertilization. Furthermore, identification of these mechanisms provides valuable information regarding the mechanisms of Ca deficiency on male reproductive system and the way for developing a better clinical approach. In this review, we aim to discuss the proposed cellular and molecular mechanisms of Ca deficiency on male reproductive system, sperm function and male fertility. Also we will discuss the valuable information currently available for the roles of Ca in male reproduction.

Lead induces apoptosis in mouse TM3 Leydig cells through the Fas/FasL death receptor pathway

The study was aimed to investigate the effect of Pb toxicity on mouse Leydig cells and its molecular mechanism. The TM3 cells were cultured in vitro and exposed to Pb at different concentrations for 24h. The effects of Pb on cell proliferation and apoptosis were analyzed with MTT and Annexin V-FITC/PI via flow cytometry, respectively. Expression levels of Fas, Fas-L and caspase-8 in TM3 cells were determined by western blot. As well as the inhibitory effect of the caspase-8 inhibitor Z-IETD-FMK on cell apoptosis. We found that Pb treatment significantly decreased the cellar viability (P<0.05), increased the apoptosis (P<0.01) and the Fas, FasL, and caspase-8 expression levels in Pb-treated cells as compared to the control cells (P<0.05 or P<0.01). Furthermore, the caspase-8 inhibitor effectively block the Pb-induced cell apoptosis. Taken together, our data suggest that Pb-induced TM3 cell toxic effect may involve in the Fas/FasL death receptor signaling pathway.

The contribution of p53 and Y chromosome long arm genes to regulation of apoptosis in mouse testis

Apoptosis of excessive or defective germ cells is a natural process occurring in mammalian testes. Tumour suppressor protein p53 is involved in this process both in developing and adult male gonads. Its contribution to testicular physiology is known to be modified by genetic background. The aim of this study was to evaluate the combined influence of the p53 and Y chromosome long arm genes on male germ cell apoptosis. Knockout of the transformation related protein 53 (Trp53) gene was introduced into congenic strains: B10.BR (intact Y chromosome) and B10.BR-Ydel (Y chromosome with a deletion in the long arm). The level of apoptosis in the testes of 19-day-old and 3-month-old male mice was determined using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick-end labelling (TUNEL) method. The study revealed that although p53 is involved in germ cell apoptosis in peripubertal testes, this process can also be mediated by p53-independent mechanisms. However, activation of p53-independent apoptotic pathways in the absence of the p53 protein requires engagement of the multicopy Yq genes and was not observed in gonads of B10.BR-Ydel-p53-/- males. The role of Yq genes in the regulation of testicular apoptosis seems to be restricted to the initial wave of spermatogenesis and is not evident in adult gonads. The study confirmed, instead, that p53 does participate in spontaneous apoptosis in mature testes.

Arachidonic acid triggers [Ca2+]i increases in rat round spermatids by a likely GPR activation, ERK signalling and ER/acidic compartments Ca2+ release

Arachidonic acid (AA), a compound secreted by Sertoli cells (SC) in a FSH-dependent manner, is able to induce the release of Ca²⁺ from internal stores in round spermatids and pachytene spermatocytes. In this study, the possible site(s) of action of AA in round spermatids, the signalling pathways associated and the intracellular Ca²⁺ stores targeted by AA-induced signalling were pharmacologically characterized by measuring intracellular Ca²⁺ using fluorescent Ca²⁺ probes. Our results suggest that AA acts by interacting with a fatty acid G protein coupled receptor, initiating a G protein signalling cascade that may involve PLA2 and ERK activation, which in turn opens intracellular ryanodine-sensitive channels as well as NAADP-sensitive channels in acidic intracellular Ca²⁺ stores. The results presented here also suggest that AMPK and PKA modulate this AA-induced Ca²⁺ release from intracellular Ca²⁺ stores in round spermatids. We propose that unsaturated free fatty acid lipid signalling in the seminiferous tubule is a novel regulatory component of rat spermatogenesis.

Ultrastructural Localization of Intracellular Calcium During Spermatogenesis of Sterlet (Acipenser ruthenus)

Calcium regulates many intracellular events such as growth and differentiation during different stages of gamete development. The aim of this study was to localize and quantify the intracellular distribution of calcium during different developmental stages of spermatogenesis in sterlet, Acipenser ruthenus, using a combined oxalate-pyroantimonate technique. The distribution of calcium was described in spermatogonium, spermatocyte, spermatid, and spermatozoon stages. In the spermatogonium and spermatocyte, calcium deposits were mainly localized in the nucleus and cytoplasm. The spermatid had calcium in the nucleus, developing acrosomal vesicle, and cytoplasm. Intracellular calcium transformed from scattered deposits in spermatogonia and spermatocyte stages into an unbound form in spermatid and the spermatozoon. The proportion of area covered by calcium increased significantly (p<0.05) from early to late stages of spermatogenesis. The largest proportion of area covered by calcium was observed in the nucleus of the spermatozoon. In conclusion, although most of the intracellular calcium is deposited in limited areas of the spermatogonium and spermatocyte, it is present an unbound form in the larger area of spermatids and spermatozoa which probably reflects changes in its physiological function and homeostasis during the process of male gamete production in spermatogenesis.

Effects of Fatty Acids on Intracellular [Ca2+], Mitochondrial Uncoupling and Apoptosis in Rat Pachytene Spermatocytes and Round Spermatids

The aim of this work was to explore the ability of free arachidonic acid, palmitic acid and the unsaturated fatty acids oleic acid and docosahexaenoic acid to modify calcium homeostasis and mitochondrial function in rat pachytene spermatocytes and round spermatids. In contrast to palmitic acid, unsaturated fatty acids produced significant increases in intracellular calcium concentrations ([Ca²⁺]_i) in both cell types. Increases were fatty acid specific, dose-dependent and different for each cell type. The arachidonic acid effects on [Ca²⁺]_i were higher in spermatids than in spermatocytes and persisted when residual extracellular Ca²⁺ was chelated by EGTA, indicating that the increase in [Ca²⁺]_i originated from release of intracellular calcium stores. At the concentrations required for these increases, unsaturated fatty acids produced no significant changes in the plasma membrane potential of or non-specific permeability in spermatogenic cells. For the case of arachidonic acid, the [Ca²⁺]_i increases were not caused by its metabolic conversion to eicosanoids or anandamide; thus we attribute this effect to the fatty acid itself. As estimated with fluorescent probes, unsaturated fatty acids did not affect the intracellular pH but were able to induce a progressive decrease in the mitochondrial membrane potential. The association of this decrease with reduced reactive oxygen species (ROS) production strongly suggests that unsaturated fatty acids induced mitochondrial uncoupling. This effect was stronger in spermatids than in spermatocytes. As a late event, arachidonic acid induced caspase 3 activation in a dose-dependent manner both in the absence and presence of external Ca²⁺. The concurrent but differential effects of unsaturated fatty acids on [Ca²⁺]_i and mitochondrial functions are additional manifestations of the metabolic changes that germ cells undergo during their differentiation.

Left-Biased Spermatogenic Failure in 129/SvJ Dnd1Ter/+ Mice Correlates with Differences in Vascular Architecture, Oxygen Availability, and Metabolites

Homozygosity for the Ter mutation in the RNA-binding protein Dead end 1 (Dnd1(Ter/Ter)) sensitizes germ cells to degeneration in all mouse strains. In 129/SvJ mice, approximately 10% of Dnd1(Ter/+) heterozygotes develop spermatogenic failure, and 95% of unilateral cases occur in the left testis. The first differences between right and left testes were detected at Postnatal Day 15 when many more spermatogonial stem cells (SSCs) were undergoing apoptosis in the left testis compared to the right. As we detected no significant left/right differences in the molecular pathway associated with body axis asymmetry or in the expression of signals known to promote proliferation, differentiation, and survival of germ cells, we investigated whether physiological differences might account for asymmetry of the degeneration phenotype. We show that left/right differences in vascular architecture are associated with a decrease in hemoglobin saturation and increased levels of HIF-1alpha in the left testis compared to the right. In Dnd1 heterozygotes, lower oxygen availability was associated with metabolic differences, including lower levels of ATP and NADH in the left testis. These experiments suggest a dependence on oxygen availability and metabolic substrates for SSC survival and suggest that Dnd1(Ter/+) SSCs may act as efficient sensors to detect subtle environmental changes that alter SSC fate.

Dual role of immune cells in the testis: Protective or pathogenic for germ cells?

The purpose of this review is to describe how the immune cells present in the testis interact with the germinal epithelium contributing to survival or apoptosis of germ cells (GCs). Physiologically, the immunosuppressor testicular microenvironment protects GCs from immune attack, whereas in inflammatory conditions, tolerance is disrupted and immune cells and their mediators respond to GC self antigens, inducing damage of the germinal epithelium. Considering that experimental models of autoimmune orchitis have clarified the local immune mechanisms by which protection of the testis is compromised, we described the following topics in the testis of normal and orchitic rats: (1) cell adhesion molecule expression of seminiferous tubule specialized junctions and modulation of blood-testis barrier permeability by cytokines (2) phenotypic and functional characteristics of testicular dendritic cells, macrophages, effector and regulatory T cells and mast cells and (3) effects of pro-inflammatory cytokines (TNF-α, IL-6 and FasL) and the nitric oxide-nitric oxide synthase system on GC apoptosis.

Protective effect of beta-carotene against titanium dioxide nanoparticles induced apoptosis in mouse testicular tissue

In this study, the effects of beta-carotene (BC) on testicular germ cell apoptosis arising from titanium dioxide nanoparticles (NTiO2 ) have been evaluated. In NTiO2 -treated mice, expression of apoptotic related genes including Bid, FasL, caspase-3 and p38MAPK was significantly increased. Measurement apoptosis using TUNEL method showed significant increase in apoptotic index of germ cells in NTiO2 -treated mice (P < 0.05). TUNEL assessments showed that the increase of apoptotic index of testicular germ cells in NTiO2 -treated mice was reversed by BC. Beta-carotene pre-treatment could also effectively attenuate the expression of apoptotic related genes. The application of BC may serve as a beneficial medication to protect germ cells against apoptosis induced by nanoparticles and be helpful for male fertility.

Differential expression and localization of ADAM10 and ADAM17 during rat spermatogenesis suggest a role in germ cell differentiation

Background

Extracellular metolloproteases have been implied in different process such as cell death, differentiation and migration. Membrane-bound metalloproteases of the ADAM family shed the extracellular domain of many cytokines and receptor controlling auto and para/juxtacrine cell signaling in different tissues. ADAM17 and ADAM10 are two members of this family surface metalloproteases involved in germ cell apoptosis during the first wave of spermatogenesis in the rat, but they have other signaling functions in somatic tissues.

Results

In an attempt to further study these two enzymes, we describe the presence and localization in adult male rats. Results showed that both enzymes are detected in germ and Sertoli cells during all the stages of spermatogenesis. Interestingly their protein levels and cell surface localization in adult rats were stage-specific, suggesting activation of these enzymes at particular events of rat spermatogenesis.

Conclusions

Therefore, these results show that ADAM10 and ADAM17 protein levels and subcellular (cell surface) localization are regulated during rat spermatogenesis.

Characterization of the role of tumor necrosis factor apoptosis inducing ligand (TRAIL) in spermatogenesis through the evaluation of trail gene-deficient mice

TRAIL (TNFSF10/Apo2L) is a member of the tumor necrosis factor (TNF) superfamily of proteins and is expressed in human and rodent testis. Although the functional role of TRAIL in spermatogenesis is not known, TRAIL is recognized to induce apoptosis via binding to its cognate receptors; DR4 (TRAIL-R1/TNFRSF10A) and DR5 (TRAIL-R2/TNFRSF10B). Here, we utilize Trail gene-deficient (Trail-/-) mice to evaluate the role of TRAIL in spermatogenesis by measuring testis weight, germ cell apoptosis, and spermatid head count at postnatal day (PND) 28 (pubertal) and PND 56 (adult). Trail-/- mice have significantly reduced testis to body weight ratios as compared to wild-type C57BL/6J at both ages. Also, Trail-/- mice (PND 28) show a dramatic increase in basal germ cell apoptotic index (AI, 16.77) as compared to C57BL/6J (3.5). In the testis of adult C57BL/6J mice, the AI was lower than in PND 28 C57BL/6J mice (2.2). However, in adult Trail-/- mice, the AI was still higher than that of controls (9.0); indicating a relative high incidence of germ cell apoptosis. Expression of cleaved caspase-8 (CC8) and cleaved caspase-9 (CC9) (markers of the extrinsic and intrinsic apoptotic pathway, respectively) revealed a two-fold increase in the activity of both pathways in adult Trail-/- mice compared to C57BL/6J. Spermatid head counts in adult Trail-/- mice were dramatically reduced by 54% compared to C57BL/6J, indicating these animals suffer a marked decline in the production of mature spermatozoa. Taken together, these findings indicate that TRAIL is an important signaling molecule for maintaining germ cell homeostasis and functional spermatogenesis in the testis.

Propolis attenuates doxorubicin-induced testicular toxicity in rats

Doxorubicin (Dox), an effective anticancer agent, can impair testicular function leading to infertility. The present study aimed to explore the protective effect of propolis extract on Dox-induced testicular injury. Rats were divided into four groups (n=10). Group I (normal control), group II received propolis extract (200 mg kg(-1); p.o.), for 3 weeks. Group III received 18 mg kg(-1) total cumulative dose of Dox i.p. Group IV received Dox and propolis extract. Serum and testicular samples were collected 48 h after the last treatment. In addition, the effects of propolis extract and Dox on the growth of solid Ehrlich carcinoma in mice were investigated. Dox reduced sperm count, markers of testicular function, steroidogenesis and gene expression of testicular 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD) and steroidogenic acute regulatory protein (StAR). In addition, it increased testicular oxidative stress, inflammatory and apoptotic markers. Morphometric and histopathologic studies supported the biochemical findings. Treatment with propolis extract prevented Dox-induced changes without reducing its antitumor activity. Besides, administration of propolis extract to normal rats increased serum testosterone level coupled by increased activities and gene expression of 3ß-HSD and 17ß-HSD. Propolis extract may protect the testis from Dox-induced toxicity without reducing its anticancer potential.

Differential effects of temperature on reactive oxygen/nitrogen species production in rat pachytene spermatocytes and round spermatids

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) like superoxide and nitric oxide are produced by testis and spermatogenic cells in response to heat stress. However, the magnitude and mechanisms of this production in spermatogenic cells have not been described. In this work, we evaluated ROS/RNS production, its pharmacology, mitochondrial oxidative metabolism, membrane potential and antioxidant capacity at different temperatures in isolated rat pachytene spermatocytes and round spermatids. Our results showed an increment in ROS/RNS production by pachytene spermatocytes when increasing the temperature to 40 °C. Instead, ROS/RNS production by round spermatids did not change at temperatures higher than 33 °C. ROS/RNS production was sensitive to NADPH oxidase inhibitor diphenylene iodonium or the mitochondrial complex I inhibitor rotenone. No additive effects were observed for these two compounds. Our results suggest an important mitochondrial ROS/RNS production in spermatogenic cells. Oligomycin-insensitive oxygen consumption (uncoupled oxygen consumption) increased with temperature and was significantly larger in round spermatids than pachytene spermatocytes, indicating a likely round spermatid mitochondrial uncoupling at high temperatures. A similar conclusion can be reached by measuring the mitochondrial membrane potential using rhodamine 123 fluorescence in permeabilized cells or JC-1 fluorescence in intact cells. The antioxidant capacity was higher in round spermatids than pachytene spermatocytes at 40 °C. Our results strongly suggest that at high temperatures (40 °C) pachytene spermatocytes are more susceptible to oxidative stress, but round spermatids are more protected because of a temperature-induced mitochondrial uncoupling together with a larger antioxidant capacity.

Apoptosis, necrosis and autophagy are influenced by metabolic energy sources in cultured rat spermatocytes

Apoptosis, necrosis and autophagy are mechanistically related processes that control tissue homeostasis and cell survival. In the testis, germ cell death is important for controlling sperm output, but it is unknown whether or not germ cells can switch from apoptosis to necrosis, as has been reported in other tissues. Furthermore, autophagy has not been reported in spermatogenesis. Spermatocytes (meiotic cells) and spermatids (haploid cells) use lactate rather than glucose as their primary substrate for producing ATP. The metabolism of glucose, but not lactate, reduces ATP levels and increases intracellular [H(+)] and [Ca(2+)], both of which are associated with apoptosis and/or necrosis in somatic cells. In this work, we evaluated whether different energy sources, such as lactate or glucose, can influence spermatocyte death type and/or survival in primary cultures. Spermatocytes cultured for 12 h without an energy source died by necrosis, while spermatocytes cultured with 5 mM glucose showed a significant increase in apoptosis, as evidenced by caspase activity, TUNEL assay and phosphatidylserine exposure. Apoptosis was not observed in spermatocytes cultured with 5 mM lactate or deoxyglucose. Autophagy markers, such as LC3-II and autophagosomes, were detected after 12 h of culture, regardless the culture conditions. These results suggest that the availability of glucose and/or lactate affect the type of death or the survival of primary spermatocytes, where glucose can induce apoptosis, while lactate is a protective factor.

The hypoxic testicle: physiology and pathophysiology

Mammalian spermatogenesis is a complex biological process occurring in the seminiferous tubules in the testis. This process represents a delicate balance between cell proliferation, differentiation, and apoptosis. In most mammals, the testicles are kept in the scrotum 2 to 7°C below body core temperature, and the spermatogenic process proceeds with a blood and oxygen supply that is fairly independent of changes in other vascular beds in the body. Despite this apparently well-controlled local environment, pathologies such as varicocele or testicular torsion and environmental exposure to low oxygen (hypoxia) can result in changes in blood flow, nutrients, and oxygen supply along with an increased local temperature that may induce adverse effects on Leydig cell function and spermatogenesis. These conditions may lead to male subfertility or infertility. Our literature analyses and our own results suggest that conditions such as germ cell apoptosis and DNA damage are common features in hypoxia and varicocele and testicular torsion. Furthermore, oxidative damage seems to be present in these conditions during the initiation stages of germ cell damage and apoptosis. Other mechanisms like membrane-bound metalloproteinases and phospholipase A2 activation could also be part of the pathophysiological consequences of testicular hypoxia.

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.

Involvement of TACE/ADAM17 and ADAM10 in etoposide-induced apoptosis of germ cells in rat spermatogenesis

Germ cell apoptosis is important to regulate sperm production in the mammalian testis, but the molecular mechanisms underlying apoptosis are still poorly understood. We have recently shown that in vitro, etoposide induces upregulation of TACE/ADAM17 and ADAM10, two membrane-bound extracellular metalloproteases. Here we show that in vivo these enzymes are involved in etoposide-, but not in heat shock-, induced apoptosis in rat spermatogenesis. Germ cell apoptosis induced by DNA damage was associated with an increase in protein levels and cell surface localization of TACE/ADAM17 and ADAM10. On the contrary, apoptosis of germ cells induced by heat stress, another cell death stimulus, did not change levels or localization of these proteins. Pharmacological in vivo inhibition of TACE/ADAM17 and ADAM10 prevents etoposide-induced germ cell apoptosis. Finally, Gleevec (STI571) a pharmacological inhibitor of p73, a master gene controlling apoptosis induced by etoposide, prevented the increase of TACE/ADAM17 levels. Our results strongly suggest that TACE/ADAM17 participates in in vivo apoptosis of male germ cells induced by DNA damage.

Microinjection manipulation resulted in the increased apoptosis of spermatocytes in testes from intracytoplasmic sperm injection (ICSI) derived mice

The invention of intracytoplasmic sperm injection (ICSI) has possibly been the most important development in reproductive medicine, one that has given hope to thousands of infertile couples worldwide. However, concerns remain regarding the safety of this method since it is a more invasive procedure than in vitro fertilization (IVF), since a spermatozoon is injected into the oocyte cytoplasm. Using mice derived from IVF technology as a control, we assessed the influence of invasive microinjection in the process of transferring sperm into oocyte cytoplasm in ICSI procedure on the development and physiologic function of resultant offspring. Our results demonstrated that mice produced from ICSI and IVF had no significant difference in phenotypic indices including body weight, forelimb physiology, and learning and memory ability. However, increased spermatocyte apoptosis was observed in the testis of adult ICSI mice, when compared with IVF mice. And, decreased testis weight and marked damage of spermatogenic epithelia were found in aged ICSI mice. Furthermore, proteomic analysis verified that most of the differentiated proteins in testes between adult ICSI and IVF mice were those involved in regulation of apoptosis pathways. Our results demonstrated that the microinjection manipulation used in the ICSI procedure might pose potential risks to the fertility of male offspring. The changed expression of a series of proteins relating to apoptosis or proliferation might contribute to it. Further studies are necessary to better understand all the risks of ICSI.

The emerging role of matrix metalloproteases of the ADAM family in male germ cell apoptosis

Constitutive germ cell apoptosis during mammalian spermatogenesis is a key process for controlling sperm output and to eliminate damaged or unwanted cells. An increase or decrease in the apoptosis rate has deleterious consequences and leads to low sperm production. Apoptosis in spermatogenesis has been widely studied, but the mechanism by which it is induced under physiological or pathological conditions has not been clarified. We have recently identified the metalloprotease ADAM17 (TACE) as a putative physiological inducer of germ cell apoptosis. The mechanisms involved in regulating the shedding of the ADAM17 extracellular domain are still far from being understood, although they are important in order to understand cell-cell communications. Here, we review the available data regarding apoptosis during mammalian spermatogenesis and the localization of ADAM proteins in the male reproductive tract. We propose an integrative working model where ADAM17, p38 MAPK, protein kinase C (PKC) and the tyrosine kinase c-Abl participate in the physiological signalling cascade inducing apoptosis in germ cells. In our model, we also propose a role for the Sertoli cell in regulating the Fas/FasL system in order to induce the extrinsic pathway of apoptosis in germ cells. This working model could be applied to further understand constitutive apoptosis in spermatogenesis and in pathological conditions (e.g., varicocele) or following environmental toxicants exposure (e.g., genotoxicity or xenoestrogens).

Male germ cell apoptosis: regulation and biology

Cellular apoptosis appears to be a constant feature in the adult testis and during early development. This is essential because mammalian spermatogenesis is a complex process that requires precise homeostasis of different cell types. This review discusses the latest information available on male germ cell apoptosis induced by hormones, toxins and temperature in the context of the type of apoptotic pathway either the intrinsic or the extrinsic that may be used under a variety of stimuli. The review also discusses the importance of mechanisms pertaining to cellular apoptosis during testicular development, which is independent of exogenous stimuli. Since instances of germ cell carcinoma have increased over the past few decades, the current status of research on apoptotic pathways in teratocarcinoma cells is included. One other important aspect that is covered in this review is microRNA-mediated control of germ cell apoptosis, a field of research that is going to see intense activity in near future. Since knockout models of various kinds have been used to study many aspects of germ cell development, a comprehensive summary of literature on knockout mice used in reproduction studies is also provided.

Ehd4 is required to attain normal prepubertal testis size but dispensable for fertility in male mice

The four highly homologous members of the C-terminal EH domain-containing (EHD) protein family (EHD1-4) regulate endocytic recycling. To delineate the role of EHD4 in normal physiology and development, mice with a conditional knockout of the Ehd4 gene were generated. PCR of genomic DNA and Western blotting of organ lysates from Ehd4(-/-) mice confirmed EHD4 deletion. Ehd4(-/-) mice were viable and born at expected Mendelian ratios; however, males showed a 50% reduction in testis weight, obvious from postnatal day 31. An early (Day 10) increase in germ cell proliferation and apoptosis and a later increase in apoptosis (Day 31) were seen in the Ehd4(-/-) testis. Other defects included a progressive reduction in seminiferous tubule diameter, dysregulation of seminiferous epithelium, and head abnormalities in elongated spermatids. As a consequence, lower sperm counts and reduced fertility were observed in Ehd4(-/-) males. Interestingly, EHD protein expression was seen to be temporally regulated in the testis and EHD4 levels peaked between days 10 and 15. In the adult testis, EHD4 was highly expressed in primary spermatocytes and EHD4 deletion altered the levels of other EHD proteins in an age-dependent manner. We conclude that high levels of EHD1 in the adult Ehd4(-/-) testis functionally compensate for lack of EHD4 and prevents the development of severe fertility defects. Our results suggest a role for EHD4 in the proper development of postmitotic and postmeiotic germ cells and implicate EHD protein-mediated endocytic recycling as an important process in germ cell development and testis function.

TACE/ADAM17 is involved in germ cell apoptosis during rat spermatogenesis

The pathways leading to male germ cell apoptosis in vivo are poorly understood, but are highly relevant for the comprehension of sperm production regulation by the testis. In this work, we show the evidence of a mechanism where germ cell apoptosis is induced through the inactivation and shedding of the extracellular domain of KIT (c-kit) by the protease TACE/a disintegrin and metalloprotease 17 (ADAM17) during the first wave of spermatogenesis in the rat. We show that germ cells undergoing apoptosis lacked the extracellular domain of the KIT receptor. TACE/ADAM17, a membrane-bound metalloprotease, was highly expressed in germ cells undergoing apoptosis as well. On the contrary, cell surface presence of ADAM10, a closely related metalloprotease isoform, was not associated with apoptotic germ cells. Pharmacological inhibition of TACE/ADAM17, but not ADAM10, significantly prevented germ cell apoptosis in the male pubertal rat. Induction of TACE/ADAM17 by the phorbol-ester phorbol 12-myristate 13-acetate (PMA) induced germ cell apoptosis, which was prevented when an inhibitor of TACE/ADAM17 was present in the assay. Ex-vivo rat testis culture showed that PMA induced the cleavage of the KIT extracellular domain. Isolation of apoptotic germ cells showed that even though protein levels of TACE/ADAM17 were higher in apoptotic germ cells than in nonapoptotic cells, the contrary was observed for ADAM10. These results suggest that TACE/ADAM17 is one of the elements triggering physiological germ cell apoptosis during the first wave of spermatogenesis.

Spermatocyte apoptosis, which involves both intrinsic and extrinsic pathways, explains the sterility of Graomys griseoflavus x Graomys centralis male hybrids

Spermatogenic impairment and the apoptotic pathways involved in establishing sterility of male hybrids obtained from crossing Graomys griseoflavus females with Graomys centralis males were studied. Testes from G. centralis, G. griseoflavus and hybrids were compared at different ages. Terminal transferase-mediated dUTP nick-end labelling assay (TUNEL), Fas, Bax and cytochrome c labelling were used for apoptosis evaluation, and calbindin D(28k) staining as an anti-apoptotic molecule. In 1-month-old animals, spermatocytes were positive for all apoptotic markers, but moderate TUNEL (+) spermatocyte frequency was only found in G. centralis. At subsequent ages, the apoptotic markers were downregulated in testes from parental cytotypes, but not in hybrid testes. TUNEL (+) spermatocytes were present at 78% and 44% per tubule cross-section in 2- and 3-month-old hybrid animals, respectively. Pachytene spermatocyte death in adult hybrids occurs via apoptosis, as revealed by high caspase-3 expression. Calbindin was highly expressed in spermatocytes of adult hybrids, in which massive cell death occurs via apoptosis. Calbindin co-localisation with TUNEL or Fas, Bax and cytochrome c was very limited, suggesting an inverse regulation of calbindin and apoptotic markers. Hybrid sterility is due to breakdown of spermatogenesis at the pachytene spermatocyte stage. Both extrinsic and intrinsic pathways are involved in apoptosis of spermatocytes, which are the most sensitive cell type to apoptotic stimuli.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

A critical role of PUMA in maintenance of genomic integrity of murine spermatogonial stem cell precursors after genotoxic stress

Neonatal gonocytes are precursors of spermatogonial stem cells. Preserving their integrity by elimination of damaged germ cells may be crucial to avoid the transmission of genetic alterations to progeny. Using gamma-irradiation, we investigated by immunohistochemistry, flow cytometry and real-time PCR components of the death machinery in neonatal gonocytes. Their death was correlated with caspase 3 activation but not with AIF translocation into the nucleus. The in vivo contribution of both the extrinsic and the intrinsic pathways was then investigated. We focused on the roles of TRAIL/Death Receptor 5 (DR5) and PUMA. Our results were validated using knockout mice. Whereas DR5 expression was upregulated at the cell surface after radiation, caspase 8 was not activated. However, we detected caspase 9 cleavage associated with cytochrome c release. In mice deficient for PUMA, radiation-induced gonocyte apoptosis was reduced, whereas invalidation of TRAIL had no effect. Overall, our results show that genotoxic stress-induced apoptosis of gonocytes is caspase-dependent and involves almost exclusively the intrinsic pathway. Furthermore, PUMA plays a critical role in the maintenance of genomic integrity of spermatogonial stem cell precursors.

A molecular evaluation of germ cell death induced by etoposide in pubertal rat testes

Etoposide is widely used in the treatment of patients with testicular cancer. The mechanism underlying apoptosis induction in cancer cells has been studied in different cell types, but it is not known whether the same factors participate in viable germ cells undergoing programmed cell death. Since testicular cancer primarily affects young males, we used pubertal rats (21 days old) as a model to determine different apoptotic parameters after etoposide treatment in healthy testes. We found that one intratesticular injection of etoposide (1.2 microg/testis) induced a significant increase in spermatocytes undergoing apoptosis, along with activation of caspase-9, -8 and -3 after 24 h of treatment. Spermatocyte apoptosis was inhibited when a general caspase inhibitor was added along with etoposide. Etoposide induces a significant stabilization/activation of p53, resulting in an increase level of this protein. The mRNA of Bcl-2 antagonist of cell death (BAD), a pro-apoptotic gene and a transcriptional target of p53, was significantly increased after etoposide treatment. Thus, our results suggest a single injection of etoposide induces apoptosis in healthy pachytene spermatocytes mediated by p53 and caspase activation. These findings will assist the search for new therapies to prevent the deleterious effect of cancer drugs upon normal cells.

A mitochondrial mechanism is involved in apoptosis of Robertsonian mouse male germ cells

The aim of this study was to determine whether the intrinsic mechanism of apoptosis is involved in the death of germ cells in Robertsonian (Rb) heterozygous adult male mice. Testes from 5-month-old Rb heterozygous CD1 x Milano II mice were obtained and compared with those from homozygous CD1 (2n=40) and Milano II (2n=24) mice. For histological evaluation of apoptosis, TUNEL labelling and immunohistochemistry were used to localise Bax and cytochrome c. Expression of calbindin D(28k) (CB), an anti-apoptotic molecule, was also analysed by immunohistochemistry and immunoblotting. Testicular ultrastructure was visualised by electron microscopy. Morphology and cell associations were abnormal in the Rb heterozygous seminiferous epithelium. An intense apoptotic process was observed in tubules at stage XII, mainly in metaphase spermatocytes. Metaphase spermatocytes also showed Bax and cytochrome c redistributions. Mitochondria relocated close to the paranuclear region of spermatocytes. CB was mainly expressed in metaphase spermatocytes, but also in pachytene spermatocytes, spermatids and Sertoli cells at stage XII. The co-localisation of CB and TUNEL labelling was very limited. Sixty per cent of metaphase spermatocytes were apoptotic and calbindin negative, while 40% were calbindin positive without signs of apoptosis. Ten per cent of the Bax- and cytochrome c-positive cells were also calbindin positive. These data suggest that apoptosis of the germ cells in heterozygous mice occurs, at least in part, through a mitochondrial-dependent mechanism. Calbindin overexpression might prevent or reduce the apoptosis of germ cells caused by Rb heterozygosity, which could partially explain the subfertility of these mice.

Relevance of caspase activity during apoptosis in pubertal rat spermatogenesis

Caspases are a family of cysteine-proteases, activated upon several different stimuli, which execute apoptosis in many cell death models. Previous work of our group has shown rats have the highest rate of apoptosis during the first wave of spermatogenesis (between 20 and 25 days after birth), as evaluated by TUNEL and caspase activity. However, the hierarchical order of caspase activation and the relevance of each caspase during germ cell apoptosis are not clear. Thus, the goal of this work is to take a pharmacological approach to dissect the apoptosis pathway of caspase activation. Results showed that intratesticular injection of a caspase-8 inhibitor (z-IETD-fmk), or a pan-caspase inhibitor (z-VAD- fmk), significantly decreased the cleavage of p115 and PARP, two endogenous substrates of caspases, in 22-day-old rats. Additionally, these inhibitors promoted a significant reduction in the number of apoptotic germ cells. On the other hand, intratesticular injection of two different inhibitors of the intrinsic pathway (z-LEHD-fmk and minocycline) did not have any effect upon caspase substrates cleavage (p115 and PARP) or the number of apoptotic germ cells. Therefore, we conclude that the extrinsic pathway of apoptosis plays an important role in physiological germ cell apoptosis during the first round of spermatogenesis in the rat.

Follicle-stimulating hormone affects spermatogonial survival by regulating the intrinsic apoptotic pathway in adult rats

Follicle-stimulating hormone plays a key role in spermatogonial development in adult rats via poorly understood mechanisms. We aimed to identify the role of this hormone in the regulation of germ cell apoptosis and proliferation in adult rats by suppression of FSH action following passive immunoneutralization with a rat FSH antibody for 4 and 7 days. Apoptosis and proliferation were identified by TUNEL and proliferating cell nuclear antigen labeling methods, respectively. Intrinsic and extrinsic apoptotic pathways were identified by immunohistochemistry, stereological techniques, and RT-PCR by assessing pathway-specific proteins and genes. Following FSH suppression for 4 and 7 days, we have previously reported a 30% decrease in spermatogonial number, with increased apoptosis in a stage-specific manner. The present study also shows stage-specific increases in apoptosis with no changes in proliferation. This increase in apoptosis was attributable to an increase in spermatogonial apoptosis via the intrinsic rather than extrinsic pathway, as shown by increased activated caspase 9-positive spermatogonia. The concomitant suppression of FSH and LH/testosterone showed that testosterone alone or together with FSH was more important in spermatocyte and spermatid survival by regulating both apoptotic pathways. A reduction in the level of the intrinsic pathway transcript Bcl2l2 (apoptosis suppressor gene) following FSH suppression for 4 days shows that FSH regulates some components of the intrinsic pathway. This study reveals that FSH predominantly acts as a survival factor for spermatogonia by regulating the intrinsic pathway while having no affect on germ cell proliferation in rats in vivo.