Fas regulates germ cell apoptosis in the human testis in vitro

Role of sperm apoptosis and oxidative stress in male infertility: A narrative review

Activation of caspase, externalization of phosphatidyl serine, change in the mitochondrial membrane potential, and DNA fragmentation are apoptosis markers found in human ejaculated spermatozoa. Also, reactive oxygen species (ROS) play a vital role in the different types of male infertility. In this review, data sources including Google Scholar, Scopus, PubMed, and Science Direct were searched for publications with no particular time restriction to get a holistic and comprehensive view of the research. Apoptosis regulates the male germ cells, correct function and development from the early embryonic stages of gonadal differentiation to fertilization. In addition to maintaining a reasonable ratio between the Sertoli and germ cells, apoptosis is one of the well-known quality control mechanisms in the testis. Also, high ROS levels cause a heightened and dysregulated apoptotic response. Apoptosis is one of the well-known mechanisms of quality control in the testis. Nevertheless, increased apoptosis may have adverse effects on sperm production. Recent studies have shown that ROS and the consequent oxidative stress play a crucial role in apoptosis. This review aims to assimilate and summarize recent findings on the apoptosis in male reproduction and fertility. Also, this review discusses the update on the role of ROS in normal sperm function to guide future research in this area.

Apoptosis of germ cells in the normal testis of the Japanese quail (Coturnix coturnix japonica)

It has been established that excess germ cells in normal and in pathological conditions are removed from testicular tissue by the mechanism of apoptosis. Studies on germ cell apoptosis in avian species are grossly lacking, and there are only a few reports on induced germ cell degenerations in the testis tissue of birds. This study was designed to investigate the process of apoptosis of germ cells in the Japanese quail (Coturnix coturnix japonica). Germ cell degenerations were investigated in birds of all age groups, namely pre-pubertal, pubertal, adult, and aged. Apoptosis of germ cells in the quails, as shown by hematoxylin & eosin (H&E), TdT dUTP Nick End Labeling (TUNEL) assay and electron microscopy, was similar to that observed in previous studies of germ cells and somatic cells of mammalian species. The observed morphological features of these apoptotic cells ranged from irregular plasma and nuclear membranes in the early stage of apoptosis to rupture of the nuclear membrane, condensation of nuclear material, as well as fragments of apoptotic bodies, in later stages of apoptosis. In the TUNEL-positive cell counts, there was a significant difference between the mean cell counts for the four age groups (P < 0.05). Post hoc analysis revealed a highly significant difference in the aged group relative to the pubertal and adult age groups, while the cell counts of the pre-pubertal group were significantly higher than those of the pubertal group. However, there was no significant difference between cell counts of the pre-pubertal and the adult, and between the pre-pubertal and the aged groups.

Reactive oxygen species in male reproduction: A boon or a bane?

Reactive oxygen species (ROS) are free radicals derived from oxygen during normal cellular metabolism. ROS play a crucial role in the physiological processes and signalling pathways associated with male fertility. At physiological concentrations, ROS act as molecular mediators of signal transduction pathways involved in the regulation of the hypothalamic-pituitary-gonadal axis, spermatogenesis and steroidogenesis. They also trigger the morphological changes required for sperm maturation, such as DNA compaction and flagellar modification. Furthermore, ROS modulate crucial processes involved in the attainment of sperm fertilising ability such as capacitation, hyperactivation, acrosome reaction and sperm-oocyte fusion. Conversely, oxidative stress prevails when the concentration of ROS overwhelms the body's antioxidant defence. Various endogenous and exogenous factors enhance the synthesis of ROS resulting in the disruption of structural and functional integrity of spermatozoa through the induction of apoptotic pathway and oxidation of molecules, such as lipids, proteins and DNA. Therefore, maintenance of a balanced redox state is critical for normal male reproductive functions. This article discusses the dual role of ROS in male reproduction, highlighting the physiological role as well as their pathological implications on male fertility.

Mammalian sperm nuclear organization: resiliencies and vulnerabilities

Sperm cells are remarkably complex and highly specialized compared to somatic cells. Their function is to deliver to the oocyte the paternal genomic blueprint along with a pool of proteins and RNAs so a new generation can begin. Reproductive success, including optimal embryonic development and healthy offspring, greatly depends on the integrity of the sperm chromatin structure. It is now well documented that DNA damage in sperm is linked to reproductive failures both in natural and assisted conception (Assisted Reproductive Technologies [ART]). This manuscript reviews recent important findings concerning - the unusual organization of mammalian sperm chromatin and its impact on reproductive success when modified. This review is focused on sperm chromatin damage and their impact on embryonic development and transgenerational inheritance.

Oestrogens as apoptosis regulators in mammalian testis: angels or devils?

In the mammalian testis, spermatogenesis is a highly coordinated process of germ cell development, which ends with the release of ‘mature’ spermatozoa. The fine regulation of spermatogenesis is strictly dependent on sex steroid hormones, which orchestrate the cellular and molecular events underlying normal development of germ cells. Sex steroids actions also rely on the control of germ cell survival, and the programmed cell death by apoptosis has been indicated as a critical process in regulating the size and quality of the germ line. Recently, oestrogens have emerged as important regulators of germ cell fate. However, the beneficial or detrimental effects of oestrogens in spermatogenesis are controversial, with independent reports arguing for their role as cell survival factors or as apoptosis-inducers. The dual behaviour of oestrogens, shifting from ‘angels to devils’ is supported by the clinical findings of increased oestrogens levels in serum and intratesticular milieu of idiopathic infertile men. This review aims to discuss the available information concerning the role of oestrogens in the control of germ cell death and summarises the signalling mechanisms driven oestrogen-induced apoptosis. The present data represent a valuable basis for the clinical management of hyperoestrogenism-related infertility and provide a rationale for the use of oestrogen-target therapies in male infertility.

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.

The role of E3 ligases in the ubiquitin-dependent regulation of spermatogenesis

The ubiquitination of proteins is a post-translational modification that was first described as a means to target misfolded or unwanted proteins for degradation by the proteasome. It is now appreciated that the ubiquitination of proteins also serves as a mechanism to modify protein function and cellular functions such as protein trafficking, cell signaling, DNA repair, chromatin modifications, cell-cycle progression and cell death. The ubiquitination of proteins occurs through the hierarchal transfer of ubiquitin from an E1 ubiquitin-activating enzyme to an E2 ubiquitin-conjugating enzyme and finally to an E3 ubiquitin ligase that transfers the ubiquitin to its target protein. It is the final E3 ubiquitin ligase that confers the substrate specificity for ubiquitination and is the focus of this review. Spermatogenesis is a complex and highly regulated process by which spermatogonial stem cells undergo mitotic proliferation and expansion of the diploid spermatogonial population, differentiate into spermatocytes and progress through two meiotic divisions to produce haploid spermatids that proceed through a final morphogenesis to generate mature spermatozoa. The ubiquitination of proteins in the cells of the testis occurs in many of the processes required for the progression of mature spermatozoa. Since it is the E3 ubiquitin ligase that recognizes the target protein and provides the specificity and selectivity for ubiquitination, this review highlights known examples of E3 ligases in the testis and the differing roles that they play in maintaining functional spermatogenesis.

Caspase signalling pathways in human spermatogenesis

PURPOSE

Little is known about the apoptotic mechanisms involved in abnormal spermatogenesis. In order to describe the significance of apoptosis in azoospermia, testicular tissue from abnormal spermatogenesis was analysed.

METHODS

Testicular treatment biopsies were obtained from 27 men. Five presented oligozoospermia, 9 obstructive azoospermia (4 congenital bilateral absence of the vas deferens; 5 secondary azoospermia) and 13 non-obstructive azoospermia (5 hypospermatogenis; 3 maturation arrest; 5 Sertoli-cell-only syndrome). Immunohistochemical staining was performed for active caspases-3, -8 and -9. The presence of active caspases in Sertoli cells and germ cells was analyzed using stereological tools.

RESULTS

Increased active caspase-3 was found in Sertoli-cell-only syndrome. No significant differences were found in maturation arrest. In hypospermatogenesis, primary spermatocytes were the germ cells with higher active caspases. Oligozoospermia and secondary obstruction showed significant differences among germ cells for the presence of all active caspases. In oligozoospermia, spermatogonia presented significant increased active caspase-9 in relation to active caspase-8. In primary obstruction and hypospermatogenesis, germ cells presented significant increased active caspases-3 and -9.

CONCLUSIONS

Results suggest that increased active caspase-3 might be involved in Sertoli-cell-only syndrome etiology. In cases of hypospermatogenesis, intrinsic lesions at the meiotic stage seem to be related to the pathology. In secondary obstruction apoptosis is suggested to be initiated due to extrinsic and intrinsic lesions, whereas in primary obstruction only the intrinsic apoptotic pathway seems to be present. Finally, in oligozoospermic patients spermatogonia death by mitochondrial damage additionally to meiosis malfunctioning, might be on the origin of the decreased sperm output.

Complete sperm suppression in rats with dienogest plus testosterone undecanoate is facilitated through apoptosis in testicular cells

Complete suppression of the production of sperm in rats with dienogest (DNG, 40 mg/kg body weight [bw]) plus testosterone undecanoate (TU, 25 mg/kg bw), every 45 days, was found to be associated with a significant increase in germ cell apoptosis. Caspase 3 activity and expression in testis were simultaneously upregulated. Rise in the activities of caspase 8 and 9 was associated with overexpression of upstream marker proteins from extrinsic (Fas [Fatty acid synthase], FasL [Fatty acid synthase ligand], and caspase 8) and intrinsic (Bax [Bcl2-associated-x protein], Bcl2 [B-cell lymphoma 2], and caspase 9) pathways of apoptosis. Apart from the germ cells, interstitial cell apoptosis was also observed along with a decline in the number of functional Leydig cells. It is therefore concluded that complete suppression of the production of sperm with DNG + TU is facilitated mainly through the removal of precursor germ cells through apoptosis. The process is largely modulated by upregulation of upstream and downstream marker proteins from intrinsic as well as extrinsic pathway of metazoan apoptosis.

LM23 is a novel member of the Speedy/Ringo family at the crossroads of life and death of spermatogenic cell

LM23 is a gene specifically expressed in the testis of Rattus norvegicus, as previously reported by our laboratory. The aim of the study is to further investigate the biological function of LM23. Several bioinformatic tools were utilized, including PROSITE and BLAST. To determine the subcellullar localization of LM23, a polyclonal antibody specific for LM23 was generated via the immunization of rabbits. The LM23 gene was cloned from rat testis tissue, and LM23 protein was expressed in Escherichia coli. The biological function of LM23 was analyzed with microarray analysis and immunohistochemistry, using a rat model of LM23 gene knockdown. The results suggested that LM23 belongs to the Speedy/Ringo family. LM23 regulated the G₁/S and G₂/M transitions of the cell cycle during spermatogenesis. Downregulation of the LM23 gene during spermatogenesis could lead to the activation of both the Fas-FasL pathway and the mitochondrial pathway. These novel findings indicate that LM23 has a diverse array of functions that are important in both the life and death of the spermatogenic cell.

Evaluation of Fas positive sperm and complement mediated lysis in subfertile individuals

PURPOSE

Evaluation of Fas receptor on surface of sperm, as an apoptotic marker, using flow cytometry and confirming the results using an antibody-antigen complex through the classic complement pathway.

MATERIALS AND METHODS

Semen samples were obtained from 10 fertile and 73 infertile individuals with diagnoses of male factor infertility. Expressions of Fas receptor and phosphatidyl serine on sperm were assessed by flow cytometry. Fas expression was further assessed by antibody-antigen complex through the complement pathway. Lysis was detected via PI (propidium iodide) staining.

RESULTS

The mean Fas expression was considerably lower than previously reported values. No significant differences in the percentage of PI were detected before and after activation of the classic complement pathway. Annexin V positive samples showed low Fas expression.

CONCLUSION

Our results have confirmed the presence of selected apoptotic markers such as Fas or phosphatidyl serine on ejaculate sperm, but suggest that Fas expression is low. Further studies are required to investigate the "abortive apoptosis" mechanism through Fas/Fas L.

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.

FasL gene-deficient mice display a limited disruption in spermatogenesis and inhibition of mono-(2-ethylhexyl) phthalate-induced germ cell apoptosis

FasL (TNFSF6, CD95L) is hypothesized to trigger testicular germ cell apoptosis that normally occurs during a distinct peripubertal period as well as in response to toxicant-induced Sertoli cell injury. To test this hypothesis, we evaluated the testis of FasL gene–deficient mice (FasL^−/−) at two distinct developmental ages (postnatal day [PND] 28 and 44) and after toxicant-induced Sertoli cell injury. Testicular cross sections from peripubertal (PND 28) FasL^−/− mice showed significant increases in the basal germ cell apoptotic index (AI; 20.58 ± 4.59) as compared to the testis of C57BL/6J wild-type mice (5.16 ± 0.08) and closely correlated with increased expression of TRAIL protein in the testis of FasL^−/− mice. A limited, but significant, number of seminiferous tubules in the testis of PND 28 FasL^−/− mice showed a severe loss of germ cells with only Sertoli cells present. In contrast, no apparent gross histological changes were observed in the testis of adult (PND 44) FasL^−/− mice. However, PND 44 FasL^−/− mice did show a 51% reduction in homogenization-resistant elongate spermatids as compared to age-matched C57BL/6J mice. Exposure of PND 28 FasL^−/− mice to mono-(2-ethylhexyl) phthalate (MEHP), a well-described Sertoli cell toxicant, unexpectedly caused a rapid decrease in the germ cell AI that paralleled increased levels of the CFLAR (c-FLIP) protein, a known inhibitor of death receptor signaling. In contrast, MEHP treatment did not decrease c-FLIP levels in PND 28 C57BL/6J mice. Taken together, these findings indicate that FasL protein expression is required during the peripubertal period for the proper regulation of germ cell apoptosis that occurs normally during this period. The influence of FasL on the cellular regulation of c-FLIP protein levels appears to be a unique mechanism for modulating germ cell apoptosis after toxicant-induced Sertoli cell injury.

Positive selection on apoptosis related genes

Apoptosis is a form of programmed cell death crucial for development, homeostasis, immunity, spermatogenesis, and prevention of cancer. Positive selection acting on mammalian apoptosis related genes targets protein interfaces that interact with pathogens and also elements of signaling complexes. Selection appears primarily to be driven by the immune/defense related function of these genes. Moreover, competitive interactions could be driving positive selection among sperm cells, as well as the need for protection against female anti-sperm immune responses. Trade-offs in fitness are expected out of these selective pressures, which could explain the involvement of these genes in various diseases, including cancer.

Defects in the regulatory clearance mechanisms favor the breakdown of self-tolerance during spontaneous autoimmune orchitis

We identified aberrations leading to spontaneous autoimmune orchitis (AIO) in mink, a seasonal breeder and natural model for autoimmunity. This study provides evidence favoring the view that a malfunction of the clearance mechanisms for apoptotic cell debris arising from imbalances in phagocyte receptors or cytokines acting on Sertoli cells constitutes a major factor leading to breakdown of self-tolerance during spontaneous AIO. Serum anti-sperm antibody titers measured by ELISA reflected spermatogenic activity without causing immune inflammatory responses. Orchitic mink showed excess antibody production accompanied by spermatogenic arrest, testicular leukocyte infiltration, and infertility. AIO serum labeled the postacrosomal region, the mid and end piece of mink sperm, whereas normal mink serum did not. Normal serum labeled plasma membranes, whereas AIO serum reacted with germ cell nuclei. Western blot analyses revealed that AIO serum reacted specifically to a 23- and 50-kDa protein. The number of apostain-labeled apoptotic cells was significantly higher in orchitic compared with normal tubules. However, apoptosis levels measured by ELISA in seminiferous tubular fractions (STf) were not significantly different in normal and orchitic tubules. The levels of CD36, TNF-alpha, TNF-alpha RI, IL-6, and Fas but not Fas-ligand (L), and ATP-binding cassette transporter ABCA1 were changed in AIO STf. TNF-alpha and IL-6 serum levels were increased during AIO. Fas localized to germ cells, Sertoli cells, and the lamina propria of the tubules and Fas-L, to germ cells. Fas colocalized with Fas-L in residual bodies in normal testis and in giant cells and infiltrating leukocytes in orchitic tubules.

[Value of targeted treatment for testicular cancer: from molecular approaches to clinical possibilities]

Due to the introduction of tyrosine kinase-inhibitors in the treatment of metastatic renal cell cancer, targeted therapy raises hopes for other urological tumors as well. Even if excellent cure rates, achieved by standardization of diagnosis und therapy, have made testicular cancer a curable disease, up to 6% of young patients still die from tumors refractory to therapy. The quality of life of patients in advanced stages needing aggressive treatment should be improved by new therapies with reduced side effects. The role of tyrosine kinase inhibitors and angiogenesis inhibitors as well as intervention in the cell cycle and induction of apoptosis are discussed.

Simulated microgravity activates apoptosis and NF-kappaB in mice testis

Microgravity is known to have significant effect on all aspects of reproductive function in animal models. Recent studies have also shown that microgravity induces changes at the cellular level, including apoptosis. Our effort here was to study the effect of simulated microgravity on caspase-8 and the caspase-3 activities, the effectors of the apoptotic pathway and on the transcription factor NF-kappaB a signaling molecule in mouse testis. Morey-Holton hind limb suspension model was used to simulate microgravity. Caspase-8 and 3 fluorometric assays were carried out and HLS mice testis exhibited a 51% increase in caspase-8 and caspase-3 compared to the controls. A sandwich ELISA-based immunoassay was carried out for detection of NF-kappaB which again significantly increased in the test mice. Testosterone levels were measured using an ELISA kit and in HLS mice the decrease was significant. There was also a significant decrease in testis weight in the test mice. Simulated microgravity activates caspase 8, 3 and NF-kappaB necessary to stimulate the apoptotic pathway in mice testis. This may account for the drop in testis weight and testosterone level further affecting testicular physiology and function.

Regulation of human male germ cell death by modulators of ATP production

The understanding of testicular physiology, pathology, and male fertility issues requires knowledge of male germ cell death and energy production. Here, we induced human male germ cell apoptosis (detected by Southern blot analysis of DNA fragmentation, TUNEL, activation of caspases-3 and -9, and electron microscopy) by incubating seminiferous tubule segments under hormone- and serum-free conditions. Inhibitors of complexes I to IV of mitochondrial respiration, exposure to anoxia, and inhibition of F0F1-ATPase (with oligomycin) decreased the ATP levels (analyzed by HPLC) and suppressed apoptosis at 4 h. Uncoupler 2,4-dinitrophenol (DNP) and oligomycin combination also suppressed death at 4 h, as did the DNP alone. Inhibition of glycolysis by 2-deoxyglucose neither suppressed nor further induced apoptosis nor altered the antiapoptotic effects of the mitochondrial inhibitors. Furthermore, Fas system activation did not modify the effects of mitochondrial modulators. After 24 h, delayed male germ cell apoptosis was observed despite the presence of the mitochondrial inhibitors. We conclude that the mitochondrial ATP production machinery plays an important role in regulating in vitro-induced primary pathways of human male germ apoptosis. The ATP synthesized by the F0F1-ATPase seems to be the crucial death regulator, rather than any of the complexes (I-IV) alone, the functional electron transport chain, or the membrane potential. We also conclude that there seem to be secondary pathways of human testicular cell apoptosis that do not require mitochondrial ATP production. The present study emphasizes the role of the main catabolic pathways in the complex network of regulating events of male germ cell life and death.

The significance of sperm nuclear DNA strand breaks on reproductive outcome

PURPOSE OF REVIEW

A growing body of evidence indicates that ejaculated spermatozoa from men being treated with intracytoplasmic sperm injection contain nuclear abnormalities. Many of these nuclear anomalies manifest themselves as breaks in the sperm nuclear DNA. This review examines the mechanisms involved in generating DNA strand breaks during spermatogenesis in the human, the main techniques used to assess the sperm nucleus and the evidence, in relation to assisted reproduction, showing that sperm nuclear DNA strand breaks may impact on reproductive outcome.

RECENT FINDINGS

Techniques such as the TUNEL assay and the sperm chromatin structure assay both show increased levels of DNA abnormalities in spermatozoa from men who have poor semen parameters. The reproductive parameters affected by an increased presence of DNA abnormalities in ejaculated spermatozoa include fertilization, blastocyst development, and pregnancy rates.

SUMMARY

There is accumulating evidence linking sperm nuclear DNA anomalies to poor reproductive outcome in relation to assisted reproduction technologies. The tests currently available only provide an inkling of the impact of sperm nuclear DNA abnormalities on reproductive outcomes. Although the impact an abnormal paternal genome may have on reproductive outcome is unquestionably less than that of its female counterpart, it cannot be ignored.

Somatic cell apoptosis markers and pathways in human ejaculated sperm: potential utility as indicators of sperm quality

In this study we extended earlier work to determine whether sperm respond to somatic cell apoptotic stimuli and whether apoptotic phenotypes are significant indicators of human sperm quality. We evaluated ejaculated sperm from fertile donors and subfertile patients following purification of fractions of high and low motility. In unstimulated conditions, caspase enzymatic activity was higher in motile fractions from subfertile patients than in donors, and was higher in low motility fractions from both groups. Staurosporine, but not a Fas ligand or H2O2, significantly increased caspase activity, but only in high motility fractions. Procaspase-3, -7 and -9 and low levels of active caspase-3, -7 and -9 were identified by immunoblot analysis. Apoptosis-inducing factor (AIF) was present in all samples but poly ADP-ribose polymerase-1 (PARP-1) was not detected. Phosphatidylserine translocation was significantly increased only with H2O2 treatment. In ejaculates of both subfertile and fertile men, we demonstrated the presence and activation of several proteins that are key constituents of apoptosis-related pathways in somatic cells, which may serve as markers for sperm quality.

Activator protein-1 in human male germ cell apoptosis

Apoptosis limits germ cell number in the testis, and its dysregulation is associated with male infertility. Here, we evaluated the role of the transcription factor activator protein 1 (AP-1) in male germ cell apoptosis in a culture of human seminiferous tubules. AP-1 DNA-binding activity increased in cultured tubules within 2.5 h, which was earlier than the onset of apoptosis as detected by caspase 3 activation and apoptotic DNA fragmentation. The c-Jun, c-Fos and JunD proteins were detected in the Sertoli cell nuclei, whereas apoptosis occurred in the germ cells. Follicle-stimulating hormone (FSH), whose receptors are expressed in the Sertoli cells, inhibited germ cell apoptosis and concomitantly suppressed AP-1 DNA-binding activity, but had no effect on nuclear factor kappaB (NF-kappaB) activation. These results suggest that AP-1 transcription factors are involved in the Sertoli cell-mediated control of germ cell apoptosis, and that inhibition of germ cell apoptosis by FSH appears to involve suppression of AP-1 activation.

Frequent Fas gene mutations in testicular germ cell tumors

The Fas (Apo-1/CD95)/Fas ligand (L) system is involved in cell death signaling, and has been suggested to be important for the regulation of germ cell apoptosis in the testis. Mutations of the Fas gene may result in accumulation of germ cells and thus might contribute to testicular carcinogenesis. The open reading frame of Fas cDNA was examined in 24 cases of testicular germ cell tumors (TGCTs), comprised of 19 pure histological type (15 seminomas, 3 embryonal carcinomas, 1 immature teratoma) and 5 mixed-type tumors. Mutations of the Fas gene were found in nine (37.5%) of these cases. Each lesion with a homogeneous histological picture was selectively microdissected using a laser capture microdissection method: samples consisted of 18 lesions from seminomas, 7 embryonal carcinomas, 4 immature teratomas, 2 choriocarcinomas, and 1 from a yolk sac tumor. Microdissected genomic DNA was examined to determine which mutations were derived from which kind of histological lesion. Eleven mutations were detected in 10 TGCT lesions from nine cases, but none were found in benign lesions. All were point mutations, and eight missense mutations occurred in exon 9 encoding the core protein of the death domain essential for apoptotic signal transduction. Three were silent mutations. Mutations were found in the seminoma (27.8%) and embryonal carcinoma lesions (62.5%), but none were found in the one yolk sac tumor, two choriocarcinomas, or four immature teratoma lesions. Each seminoma and embryonal carcinoma lesion found in the same case had a different type of Fas mutation from the others. Mouse T-cell lymphoma cells transfected with missense mutated genes were resistant to apoptosis induced by anti-Fas antibody, indicating these to be loss-of-function mutations. These findings suggested a role of Fas gene mutations in the pathogenesis of TGCTs.

Nuclear factor-kappa B activation in human testicular apoptosis

Apoptotic cell death plays an important role in limiting testicular germ cell population during spermatogenesis and its dysregulation has been shown to be associated with male infertility. The growing evidence on the role of the transcription factor nuclear factor (NF)-kappa B in controlling apoptosis prompted us to investigate NF-kappa B activity in the normal human testis and its role in testis tissue undergoing excessive apoptosis in vitro. In electrophoretic mobility shift assays, low-level constitutive NF-kappa B DNA-binding activity was found and, by immunostaining of the RelA and p50 NF-kappa B subunits, was localized to Sertoli cell nuclei. During in vitro-induced testicular apoptosis, the Sertoli cell nuclear NF-kappa B levels and whole seminiferous tubule NF-kappa B DNA-binding activity increased previous detection of germ cells undergoing apoptosis. The anti-inflammatory drug sulfasalazine effectively suppressed stress-induced NF-kappa B DNA binding and NF-kappa B-mediated I kappa B alpha gene expression. Importantly, concomitantly with inhibiting NF-kappa B, sulfasalazine blocked germ cell apoptosis. These results suggest that during testicular stress Sertoli cell NF-kappa B proteins exert proapoptotic effects on germ cells, which raises the possibility that pharmacological inhibition of NF-kappa B could be a therapeutic target in transient stress situations involving excessive germ cell death.

Characterization of subsets of human spermatozoa at different stages of maturation: implications in the diagnosis and treatment of male infertility

BACKGROUND

Reactive oxygen species (ROS)-induced damage of membrane phospholipids and DNA in human spermatozoa has been implicated in the pathogenesis of male infertility. In this study, variations in ROS production, DNA structure (as measured by the sperm chromatin structure assay) and lipid composition, were studied in human spermatozoa at different stages of maturation.

METHODS

Sperm subsets were isolated by discontinuous density gradient centrifugation of semen samples obtained from healthy donors and from infertility patients.

RESULTS

DNA damage and ROS production were highest in immature spermatozoa with cytoplasmic retention and abnormal head morphology, and lowest in mature spermatozoa. Docosahexaenoic acid and sterol content were highest in immature germ cells and immature spermatozoa, and lowest in mature spermatozoa. The relative proportion of ROS-producing immature spermatozoa in the sample was directly correlated with DNA damage in mature spermatozoa, and inversely correlated with the recovery of motile spermatozoa. There was no correlation between DNA damage and sperm morphology in mature spermatozoa.

CONCLUSIONS

The high levels of ROS production and DNA damage observed in immature spermatozoa may be indicative of derangements in the regulation of spermiogenesis. DNA damage in mature spermatozoa may be the result of oxidative damage by ROS-producing immature spermatozoa during sperm migration from the seminiferous tubules to the epididymis.

Expression of Bcl-2 family proteins and spontaneous apoptosis in normal human testis

We investigated the frequency of spontaneous apoptosis and expression of the Bcl-2 family of proteins during normal spermatogenesis in man. Testicular tissue with both normal morphology and DNA content was obtained from necro-donors and fixed in Bouin's solution. A TdT-mediated dUTP end-labelling method (TUNEL) was used for the detection of apoptotic cells. Expression of apoptosis regulatory Bcl-2 family proteins and of p53 and p21(Waf1) was assessed by immunohistochemistry. Germ cell apoptosis was detected in all testes and was mainly seen in primary spermatocytes and spermatids and in a few spermatogonia. Bcl-2 and Bak were preferentially expressed in the compartments of spermatocytes and differentiating spermatids, while Bcl-x was preferentially expressed in spermatogonia. Bax showed a preferential expression in nuclei of round spermatids, whereas Bad was only seen in the acrosome region of various stages of spermatids. Mcl-1 staining was weak without a particular pattern, whereas expression of Bcl-w, p53 and p21(Waf1) proteins was not detected by immunohistochemistry. The results show that spontaneous apoptosis occurs in all male germ cell compartments in humans. Bcl-2 family proteins are distributed preferentially within distinct germ cell compartments suggesting a specific role for these proteins in the processes of differentiation and maturation during human spermatogenesis.

Testicular FasL is expressed by sperm cells

The testis is the main source of Fas ligand (FasL) mRNA in rodents; it is generally believed that this molecule, expressed on bordering somatic Sertoli cells, bestows an immune-privileged status in the testis by eliminating infiltrating inflammatory Fas-bearing leukocytes. Our results demonstrate that the attribution of testicular expression of FasL to Sertoli cells is erroneous and that FasL transcription instead occurs in meiotic and postmeiotic germ cells, whereas the protein is only displayed on mature spermatozoa. These findings point to a significant role of the Fas system in the biology of mammalian reproduction.

Apoptosis of testicular germ cells induced by exogenous glucocorticoid in rats

The influence of exogenous glucocorticoid, dexamethasone (Dex), on testicular germ cell apoptosis was investigated in rats. The percentages of apoptotic tubules and apoptotic germ cells in the Dex-treated group of rats were about seven-fold and 10-fold higher respectively than in either the control group, or in rats treated with glucocorticoid receptor agonist (GR-A), or in rats treated with both Dex and GR-A. These results suggest that, in rats, apoptosis of testicular germ cells is mediated by glucocorticoid receptors.

Hormonal regulation of physiological cell turnover and apoptosis

Physiological cell turnover plays an important role in maintaining normal tissue function and architecture. This is achieved by the dynamic balance of cellular regeneration and elimination, occurring periodically in tissues such as the uterus and mammary gland, or at constant rates in tissues such as the gastrointestinal tract and adipose tissue. Apoptosis has been identified as the prevalent mode of physiological cell loss in most tissues. Cell turnover is precisely regulated by the interplay of various endocrine and paracrine factors, which modulate tissue and cell-specific responses on proliferation and apoptosis, either directly, or by altering expression and function of key cell proliferative and/or death genes. Although recent studies have provided significant information on specific tissue systems, a clearly defined pathway that mediates cell turnover has not yet emerged for any tissue. Several similarities exist among the various tissues with regard to the intermediates that regulate tissue homeostatis, enabling a better understanding of the general mechanisms involved in the process. Here we review the mechanisms by which hormonal and cytokine factors mediate cell turnover in various tissues, emphasizing common themes and tissue-specific differences.

An Mn2+-stimulated neutral-sphingomyelinase in seminiferous tubules of immature Wistar rats

Mammalian sphingomyelinases have been implicated in many important physiological and pathophysiological processes. The seminiferous tubules of immature (19 day-old) Wistar rats have at least three types of sphingomyelinases, a lysosomal one and two microsomal ones. One of the microsomal sphingomyelinases is active at pH 6.5 and is stimulated by Mn2+ > Co2+ > Mg2+, and the other is active at pH 7.4 and is stimulated by Mn2+ > Mg2+ and inhibited by Co2+. The two microsomal enzymes are only slightly inhibited by EDTA and at pH 7.4 the stimulatory effects of Mn2+ and Mg2+ are additive. These data characterize the existence of two different membrane-bound sphingomyelinases in the seminiferous tubules of the rat.

The role of apoptosis in normal and abnormal embryonic development

Programmed cell death or apoptosis is a widespread biological phenomenon. Apoptosis is characterized by typical cell features such as membrane blebbing, chromatin condensation, and DNA fragmentation. It involves a number of membrane receptors (e.g., Fas, TNFR) and a cascade of signal transduction steps resulting in the activation of a number of cysteine proteases known as caspases. Disordered apoptosis may lead to carcinogenesis and participates in the pathogenesis of Alzheimer disease, Parkinson disease, or AIDS. Programmed cell death plays an important role in the processes of gamete maturation as well as in embryo development, contributing to the appropriate formation of various organs and structures. Apoptosis is one of the mechanisms of action of various cytotoxic agents and teratogens. Teratogen-induced excessive death of embryonic cells is undoubtedly one of the most important events preceding the occurrence of structural abnormalities, regardless of their nature. Therefore understanding the mechanisms involved in physiological as well as in disturbed or dysregulated apoptosis may lead to the development of new methods of preventive treatment of various developmental abnormalities. The present review summarizes data on the mechanisms of programmed cell death and concentrates on apoptosis involved in normal or disturbed gametogenesis and in normal and abnormal embryonic development.