Germ cell apoptosis and its molecular trigger in mouse testes

Short and long-term 2100 MHz radiofrequency radiation causes endoplasmic reticulum stress in rat testis

Long-term radiofrequency radiation (RFR) exposure, which adversely affects organisms, deteriorates testicular functions. Misfolding or unfolding protein accumulation in the endoplasmic reticulum (ER) initiates an intracellular reaction known as ER stress (ERS), which activates the unfolded protein response (UPR) for proteostasis. Since both RFR exposure and ERS can cause male infertility, we hypothesized that RFR exposure causes ERS to adversely affect testicular functions in rats. To investigate role of ERS in mediating RFR effects on rat testis, we established five experimental groups in male rats: control, short-term 2100-megahertz (MHz) RFR (1-week), short-term sham (sham/1-week), long-term 2100-MHz RFR (10-week), and long-term sham (sham/10-week). ERS markers Grp78 and phosphorylated PERK (p-Perk) levels and ERS-related apoptosis markers Chop and caspase 12 were investigated by immunohistochemistry, immunoblotting, and quantitative real-time polymerase chain reaction (qPCR). Long-term RFR exposure increased Grp78, p-Perk, and Chop levels, while short-term RFR exposure elevated Chop and caspase 12 levels. Chop expression was not observed in spermatogonia and primary spermatocytes, which may protect spermatogonia and primary spermatocytes against RFR-induced ERS-mediated apoptosis, thereby allowing transmission of genetic material to next generations. While short and long-term RFR exposures trigger ERS and ERS-related apoptotic pathways, further functional analyses are needed to elucidate whether this RFR-induced apoptosis has long-term male infertility effects.

Heat Shock Related Protein Expression in Abdominal Testes of Asian Elephant (Elephas maximus)

The abdominal testes of Asian elephants show normal spermatogenesis. Heat shock in cryptorchid testes elevates heat shock factor (HSF) expression, leading to germ cell apoptosis, while increased heat shock proteins (HSPs) levels provide protection. To investigate how heat shock affects elephant spermatogenic cells, focusing on heat shock-related molecules and the cell death mechanism, immunohistochemistry and TUNEL staining were employed to assess the immunoexpression of several heat shock-related molecules and the status of apoptosis in elephant fibroblasts (EF) induced by heat shock stimulus. Additionally, the immunoexpression of heat shock-related molecules and cell proliferation status in the elephant spermatogenic cells. Our finding indicated that heat shock-induced HSF1 immunoexpression in EF leads to apoptosis mediated by T-cell death-associated gene 51 (TDAG51) while also upregulating HSP70 to protect damaged cells. In elephant spermatogenic cells, immunostaining revealed a predominance of proliferating cell nuclear antigen (PCNA)-positive cells with minimal TDAG51- and TUNEL-positive cells, suggesting active proliferation and apoptosis suppression during normal spermatogenesis in the abdominal testis. Interestingly, spermatogonia co-immunoexpressed HSF1 and HSP90, potentially reducing apoptosis through protective mechanisms different from those observed in other mammals. Spermatogenic cells did not show immunolocalisation of HSP70, and hence, it may not contribute to protecting the spermatogonia from heat shock because the transcriptional activity of HSF1 is suppressed by HSP90A binding. This study provides insight into the specific heat shock response and defence mechanisms in elephant spermatogenic cells and may contribute to our understanding of species-specific adaptation to environmental stresses of the testis.

Insights into Canine Infertility: Apoptosis in Chronic Asymptomatic Orchitis

Chronic asymptomatic orchitis (CAO) is a common cause of acquired non-obstructive azoospermia in dogs. To understand the impact and mode of action of apoptosis, we investigated TUNEL, Bax, Bcl-2, Fas/Fas ligand, and caspase 3/8/9 in testicular biopsies of CAO-affected dogs and compared the results to undisturbed spermatogenesis in healthy males (CG). TUNEL⁺ cells were significantly increased in CAO, correlating with the disturbance of spermatogenesis. Bcl-2, Bax (p < 0.01 each), caspase 9 (p < 0.05), Fas, caspase 8 (p < 0.01 each), and caspase 3 (p < 0.05) were significantly increased at the mRNA level, whereas FasL expression was downregulated. Cleaved caspase 3 staining was sporadic in CAO but not in CG. Sertoli cells, some peritubular (CAO/CG) and interstitial immune cells (CAO) stained Bcl-2⁺, with significantly more immunopositive cells in both compartments in CAO compared to CG. Bcl-2 and CD20 co-expressing B lymphocytes were encountered interstitially and in CAO occasionally also found intratubally, underlining their contribution to the maintenance of CAO. Our results support the crucial role of the intrinsic and extrinsic apoptotic pathways in the pathophysiology of canine CAO. Autoprotective Bcl-2 expression in Sertoli cells and B lymphocytes seems to be functional, however, thereby also maintaining and promoting the disease by immune cell activation.

An in vitro system for experimentally induced cryptorchidism

Cryptorchidism is one of the most common abnormalities of male sexual development, and is characterized by the failure of the testis to descend into the scrotum. Despite extensive studies of cryptorchidism over the past century, the mechanisms for temperature-induced germ-cell loss are not well understood. All of the main cell types in the testis are believed to be affected by the elevated testis temperature induced by cryptorchidism. The cooler temperature in the special environment of the scrotum is required for maintaining optional conditions for normal spermatogenesis. Many studies reported that experimentally induced cryptorchidism caused germ cell apoptosis and suppressed spermatogenesis. However, other factors including hormones must also be examined for cryptorchidism. To explore the mechanism for cryptorchidism, in vitro cultures of testes have been used, but complete spermatogenesis using in vitro methods was not accomplished until 2011. In 2011, Sato et al. (Nature, 471, 504-507) reported the in vitro production of functional sperm in cultured neonatal mouse testes. Using this in vitro system, for the first time, we report that spermatogenesis was abrogated at 37 °C, in accordance with in vivo surgery-mediated cryptorchidism, while spermatogenesis proceeded at 34 °C in cultured testes. This result clearly showed that temperature is the sole determinant of cryptorchidism. Moreover, we found that spermatogenesis was arrested before early spermatocytes at 37 °C. In conclusion, using our in vitro system, we have demonstrated that (1) temperature is the determining factor for cryptorchidism, and (2) higher temperature (37 °C) suppresses DNA synthesis in spermatogenesis.

Effect of gallic acid on the reproduction of adolescent male Brandt’s voles (Lasiopodomys brandtii)

Gallic acid (GA), a phenol that is present in various plants, potentially contains antioxidant properties. This study aimed to investigate the effects of GA on the reproduction of adolescent male Brandt’s voles (Lasiopodomys brandtii (Radde, 1861)). Antioxidant levels and apoptosis in the testis, as well as reproductive physiology, were evaluated in adolescent males treated with GA. The results showed that a low dose of GA enhanced relative epididymis mass and the sperm density in the epididymis, increased the mRNA levels of steroidogenic acute regulatory protein in the testis, and reduced the percentages of abnormal and dead sperm. In addition, a low dose of GA significantly increased the levels of superoxide dismutase, catalase, and glutathione peroxidase, and decreased the level of malondialdehyde in the testis, as well as the mRNA and protein levels of the apoptosis-related gene, caspase-3. However, a high dose of GA sharply reduced the mean diameter of the seminiferous tubules compared with a low dose. Collectively, these findings demonstrate that GA treatment during puberty affects the reproductive responses of male Brandt’s voles in a dose-dependent manner by regulating antioxidant levels and apoptosis.

Vitamin K-Dependent γ-Glutamyl Carboxylase in Sertoli Cells Is Essential for Male Fertility in Mice

γ-Glutamyl carboxylase (GGCX) is a vitamin K (VK)-dependent enzyme that catalyzes the γ-carboxylation of glutamic acid residues in VK-dependent proteins. The anticoagulant warfarin is known to reduce GGCX activity by inhibiting the VK cycle and was recently shown to disrupt spermatogenesis. To explore GGCX function in the testis, here, we generated Sertoli cell-specific Ggcx conditional knockout (Ggcx scKO) mice and investigated their testicular phenotype. Ggcx scKO mice exhibited late-onset male infertility. They possessed morphologically abnormal seminiferous tubules containing multinucleated and apoptotic germ cells, and their sperm concentration and motility were substantially reduced. The localization of connexin 43 (Cx43), a gap junction protein abundantly expressed in Sertoli cells and required for spermatogenesis, was distorted in Ggcx scKO testes, and Cx43 overexpression in Sertoli cells rescued the infertility of Ggcx scKO mice. These results highlight GGCX activity within Sertoli cells, which promotes spermatogenesis by regulating the intercellular connection between Sertoli cells and germ cells.

Global changes in epigenomes during mouse spermatogenesis: possible relation to germ cell apoptosis

Mammalian spermatogenesis is characterized by disproportionate germ cell apoptosis. The high frequency of apoptosis is considered a safety mechanism that serves to avoid unfavorable transmission of paternal aberrant genetic information to the offspring as well as elimination mechanism for removal of overproduced immature or damaged spermatogenic cells. The molecular mechanisms involved in the induction of germ cell apoptosis include both intrinsic mitochondrial Bcl-2/Bax and extrinsic Fas/FasL pathways. However, little is known about the nuclear trigger of those systems. Recent studies indicate that epigenomes are essential in the regulation of gene expression through remodeling of the chromatin structure, and are genome-like transmission materials that reflect the effects of various environmental factors. In spermatogenesis, epigenetic errors can act as the trigger for elimination of germ cells with abnormal chromatin structure, abnormal gene expression and/or morphological defects (disordered differentiation). In this review, we focus on the relationship between global changes in epigenetic parameters and germ cell apoptosis in mice and other mammals.

Research Progress on the Biological Effects of Low-Dose Radiation in China

Human are exposed to ionizing radiation from natural and artificial sources, which consequently poses a possible risk to human health. However, accumulating evidence indicates that the biological effects of low-dose radiation (LDR) are different from those of high-dose radiation (HDR). Low-dose radiation–induced hormesis has been extensively observed in different biological systems, including immunological and hematopoietic systems. Adaptive responses in response to LDR that can induce cellular resistance to genotoxic effects from subsequent exposure to HDR have also been described and researched. Bystander effects, another type of biological effect induced by LDR, have been shown to widely occur in many cell types. Furthermore, the influence of LDR-induced biological effects on certain diseases, such as cancer and diabetes, has also attracted the interest of researchers. Many studies have suggested that LDR has the potential antitumor and antidiabetic complications effects. In addition, the researches on whether LDR could induce stochastic effects were also debated. Studies on the biological effects of LDR in China started in 1970s and considerable progress has been made since. In the present article, we provide an overview of the research progress on the biological effects of LDR in China.

The DNA double-strand "breakome" of mouse spermatids

De novo germline mutations arise preferentially in male owing to fundamental differences between spermatogenesis and oogenesis. Post-meiotic chromatin remodeling in spermatids results in the elimination of most of the nucleosomal supercoiling and is characterized by transient DNA fragmentation. Using three alternative methods, DNA from sorted populations of mouse spermatids was used to confirm that double-strand breaks (DSB) are created in elongating spermatids and repaired at later steps. Specific capture of DSB was used for whole-genome mapping of DSB hotspots (breakome) for each population of differentiating spermatids. Hotspots are observed preferentially within introns and repeated sequences hence are more prevalent in the Y chromosome. When hotspots arise within genes, those involved in neurodevelopmental pathways become preferentially targeted reaching a high level of significance. Given the non-templated DNA repair in haploid spermatids, transient DSBs formation may, therefore, represent an important component of the male mutation bias and the etiology of neurological disorders, adding to the genetic variation provided by meiosis.

Alterations in chromosomal synapses and DNA repair in apoptotic spermatocytes of Mus m. domesticus

We investigated whether apoptotic spermatocytes from the mouse Mus m. domesticus presented alterations in chromosomal synapses and DNA repair. To enrich for apoptotic spermatocytes, the scrotum's temperature was raised by partially exposing animals for 15 min to a 42ºC water bath. Spermatocytes in initial apoptosis were identified in situ by detecting activated Caspase-9.  SYCP1 and SYCP3 were markers for evaluating synapses or the structure of synaptonemal complexes and Rad51 and γH2AX for detecting DNA repair and chromatin remodeling. Apoptotic spermatocytes were concentrated in spermatogenic cycle stages III-IV (50.3%), XI-XII (44.1%) and IX-X (4.2%). Among apoptotic spermatocytes, 48% were in middle pachytene, 44% in metaphase and 6% in diplotene. Moreover, apoptotic spermatocytes showed several structural anomalies in autosomal bivalents, including splitting of chromosomal axes and partial asynapses between homologous chromosomes. gH2AX and Rad51 were atypically distributed during pachytene and as late as diplotene and associated with asynaptic chromatin, single chromosome axes or discontinuous chromosome axes. Among apoptotic spermatocytes at pachytene, 70% showed changes in the structure of synapses, 67% showed changes in gH2AX and Rad51 distribution and 50% shared alterations in both synapses and DNA repair. Our results showed that apoptotic spermatocytes from Mus m. domesticus contain a high frequency of alterations in chromosomal synapses and in the recruitment and distribution of DNA repair proteins. Together, these observations suggest that these alterations may have been detected by meiotic checkpoints triggering apoptosis.

Effects of dietary selenium on apoptosis of germ cells in the testis during spermatogenesis in roosters

The aim of this study was to determine the effects of dietary selenium (Se) supplementation on apoptosis of germ cells in the testis during spermatogenesis in roosters. Eighty 12-week-old Hy-Line Variety white roosters with an averaged body weight of 1.38 ± 0.2 kg were selected and randomly divided into four experimental groups. They were fed the basal diet (0.044 mg/kg Se dry matter) supplemented with 0 (control), 0.5, 1.0, or 2.0 mg/kg of Se dry matter (from sodium selenite). After the 45-day feeding experiment, testis samples were collected from the roosters of each treatment group to detect the population of apoptotic germ cells using the terminal deoxynucleotidy1 transferase dUTP nick end labeling assay. The protein expression of cell cycle-related genes and the messenger RNA (mRNA) expression of apoptosis and cell cycle-related genes had also been detected. The results show that the population of apoptotic germ cells in the control and 2.0 mg/kg groups was increased (P < 0.05) compared with that in the 0.5 mg/kg and 1.0 mg/kg groups. Expressions of CDC2 and CCNB1 protein in the control and 2.0 mg/kg groups were lower (P < 0.05) than those in the 0.5 mg/kg and 1.0 mg/kg groups. The mRNA level of CDC2 in the 0.5 mg/kg group was higher (P < 0.05) than that in other groups. The lowest (P < 0.05) mRNA expressions of apoptosis-related genes (BCL-2, CASPASE 3, CASPASE 8) were also obtained in the 0.5 mg/kg group. These results show that dietary Se of roosters can affect apoptosis of germ cells by regulating the mRNA expressions of apoptosis- and cell cycle-related genes in the testis during spermatogenesis.

Malathion-induced testicular toxicity is associated with spermatogenic apoptosis and alterations in testicular enzymes and hormone levels in male Wistar rats

Malathion has a broad range of toxicities while its reproductive effects have not been fully elucidated. In this study, we treated animals with malathion by gavage at doses of 0, 33.75, 54, and 108 mg/kg for 60 days and evaluated the alterations in histology, biochemistry and serology. Malathion caused the reduction in the sperm counts and motility. The reduced body and testis weights were coupled with mild to severe degenerative changes in seminiferous tubules. We found malathion at 54 mg/kg increased spermatogenic apoptosis rate which was confirmed by changes in protein expression of Bax and Bcl-2. The activities of testicular enzymes including ACP, LDH and γ-GT were significantly altered with the reduced level of reproductive hormones such as LH, FSH and T. These results indicate that malathion can elicit deleterious effects on reproductive system of rats. The abnormal levels of hormones and apoptotic proteins induced by malathion may play important roles.

Disruption of Sertoli cell vimentin filaments in prepubertal rats: an acute effect of butylparaben in vivo and in vitro

Parabens are p-hydroxybenzoic acid ester compounds widely used as preservatives in foods, cosmetics, toiletries and pharmaceuticals. We have recently shown that butylparaben induces spermatogenic cell apoptosis in prepubertal rats. We have conducted the present study for further information. Three-week-old male Sprague-Dawley rats (n=8) were given a single oral dose of 1,000 mg/kg butylparaben. The rats were sacrificed under anesthesia at 3, 6 and 24h after administration and their testes were collected for histopathological and immunohistochemical examination. Results showed a gradual collapse of Sertoli cell vimentin filaments and decreased actin staining intensity without accompanying changes in the pattern of tubulin expression, while spermatogenic cells became separated from the basement membrane and sloughed into the lumen in the butylparaben-treated rats, compared to the controls. To determine the direct effects of butylparaben on Sertoli cells, primary Sertoli cell cultures with and without butylparaben treatment were examined. Toluidine blue staining in butylparaben treated-cultured Sertoli cells showed an increased number and size of vacuoles in their cytoplasm. In agreement with the in vivo experiment, the in vitro study also clearly demonstrated disruption of vimentin filaments in Sertoli cells after butylparaben treatment. Considering both our present and previous reports, we can speculate that butylparaben-induced disruption of Sertoli cell vimentin filaments may lead to precocious release of spermatogenic cells from underlying Sertoli cells, and the released cells may undergo apoptosis owing to loss of support provided by the Sertoli cells.

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.

Single administration of butylparaben induces spermatogenic cell apoptosis in prepubertal rats

Parabens are p-hydroxybenzoic acid ester compounds widely used as preservatives in foods, cosmetics, toiletries and pharmaceuticals. Some parabens, including butylparaben, exert an estrogenic activity as determined by in vitro estrogen receptor assay and in vivo uterotrophic assay, and adversely affect endocrine secretion and male reproductive function. We conducted a research study to evaluate the acute effects of butylparaben on testicular tissues of prepubertal rats. Three-week-old male rats (n=8) were given a single dose of 1000mg/kg butylparaben. The rats were sacrificed under anesthesia at 3, 6 and 24h after administration, and their testes were collected for histopathological examination. The study revealed progressive detachment and sloughing of spermatogenic cells into the lumen of the seminiferous tubules at 3h, and this effect was enhanced at 6h after administration. Thin seminiferous epithelia and wide tubular lumina were seen at 24h in the butylparaben-treated group, compared to the control. In order to clarify whether sloughed spermatogenic cells underwent apoptosis, TUNEL assay was carried out. We found a significant increase in the number of apoptotic spermatogenic cells in all the treated groups, compared to the controls and a maximal number of apoptotic cells were detected at 6h after administration. In semithin sections, apoptotic cells were easily detected by their prominent basophilia and condensed chromatin, mainly found in spermatocytes. Ultrastructurally, the condensed chromatin and shrunken cytoplasm and nucleus, hallmarks of apoptotic cell death, were observed in butylparaben-treated groups. These observations lead us to postulate that butylparaben, similar to other estrogenic compounds, also induces spermatogenic cell apoptosis.

Acute testicular toxicity induced by melamine alone or a mixture of melamine and cyanuric acid in mice

Eight-week-old male Kunming mice were administered either melamine (MA, 30, 140, or 700 mg/kg/day), a melamine and cyanuric acid mixture (MC, each at 15, 70, or 350 mg/kg/day), or vehicle (control) for 3 consecutive days. Testicular toxicity was evaluated on days 1 and 5 after the final exposure. The testicular and epididymal weights and serum testosterone level were significantly decreased in the highest MC group (350 mg/kg/day). Histopathologically, both MA and MC caused obvious lesions in the testis and epididymis, with significant increases in sperm abnormalities. By TEM, the blood-testis barrier was damaged dose dependently. TUNEL staining showed that both MA and MC induced increases in germ cell apoptosis. The Sertoli cell vimentin was collapsed in the treated animals as detected by immunohistochemical staining and Western blotting. This study demonstrated that both MA and MC treatments could disrupt the blood-testis barrier and cause a clear testicular toxicity.

Roles of epigenome in mammalian spermatogenesis

Mammalian spermatogenesis is a successive process consisting of spermatogonial proliferation, spermatocytic meiosis, and spermiogenesis, representing the maturation of haploid spermatids. During the process, 25-75 % of the expected sperm yield is thought to be lost through apoptosis. In addition, spermatogenesis is considered to be a process undergoing successive heterochromatinization, finally reaching a complete condensed form in the sperm head. Thus, cell proliferation, differentiation and death may be strictly regulated by epigenetic factors in this process. This review describes the current understanding of the role of epigenome in spermatogenesis, especially focusing on the following aspects; DNA methylation, modification of histones, and small RNA function. These epigenetic factors affect each other and play a central role in events essential for spermatogenesis, fertilization and embryogenesis, through the regulation of gene expression, transposon activities, meiotic sex chromosome inactivation, histone remodeling and genome imprinting. Finally, a brief discussion of future avenues of study is highlighted.

Involvement of endoplasmic reticulum stress in apoptosis of testicular cells induced by low-dose radiation

The study examined the role of endoplasmic reticulum stress (ERS) and signaling pathways of inositol-requiring enzyme-1 (IRE1), RNA-activated protein kinase-like ER kinase (PERK) and activating transcription factor-6 (ATF6) in apoptosis of mouse testicular cells treated with low-dose radiation (LDR). In the dose-dependent experiment, the mice were treated with whole-body X-ray irradiation at different doses (25, 50, 75, 100 or 200 mGy) and sacrificed 12 h later. In the time-dependent experiment, the mice were exposed to 75 mGy X-ray irradiation and killed at different time points (3, 6, 12, 18 or 24 h). Testicular cells were harvested for experiments. H(2)O(2) and NO concentrations, and Ca(2+)-ATPase activity were detected by biochemical assays, the calcium ion concentration ([Ca(2+)]i) by flow cytometry using fluo-3 probe, and GRP78 mRNA and protein expressions by quantitative real-time RT-PCR (qRT-PCR) and Western blotting, respectively. The mRNA expressions of S-XBP1, JNK, caspase-12 and CHOP were measured by qRT-PCR, and the protein expressions of IRE1α, S-XBP1, p-PERK, p-eIF2α, ATF6 p50, p-JNK, pro-caspase-12, cleaved caspase-12 and CHOP by Western blotting. The results showed that the concentrations of H2O2 and NO, the mRNA expressions of GRP78, S-XBP1, JNK, caspase-12 and CHOP, and the protein expressions of GRP78, S-XBP1, IRE1α, p-PERK, p-eIF2α, ATF6 p50, p-JNK, pro-caspase-12, cleaved caspase-12 and CHOP were significantly increased in a time- and dose-dependent manner after LDR. But the [Ca(2+)]i and Ca(2+)-ATPase activities were significantly decreased in a time- and dose-dependent manner. It was concluded that the ERS, regulated by IRE1, PERK and ATF6 pathways, is involved in the apoptosis of testicular cells in LDR mice, which is associated with ERS-apoptotic signaling molecules of JNK, caspase-12 and CHOP.

Low dose bisphenol A impairs spermatogenesis by suppressing reproductive hormone production and promoting germ cell apoptosis in adult rats

Bisphenol A (BPA), an estrogenic chemical, has been shown to reduce sperm count; however, the underlying mechanisms remain unknown. Herein, we show that oral administration of BPA (2 µg/kg) for consecutive 14 days in adult rats (BPA rats) significantly reduced the sperm count and the number of germ cells compared to controls. The serum levels of testosterone and follicle-stimulating hormone (FSH), as well as the level of GnRH mRNA in BPA rats were lower than those of control rats. Testosterone treatment could partially rescue the reduction of germ cells in BPA rats. Notably, the number of apoptotic germ cells was significantly increased in BPA rats, which was insensitive to testosterone. Furthermore, the levels of Fas, FasL and caspase-3 mRNA in the testicle of BPA rats were increased in comparison with controls. These results indicate that exposure to a low dose of BPA impairs spermatogenesis through decreasing reproductive hormones and activating the Fas/FasL signaling pathway.

Germ cell differentiation and proliferation in the developing testis of the South American plains viscacha, Lagostomus maximus (Mammalia, Rodentia)

Cell proliferation and cell death are essential processes in the physiology of the developing testis that strongly influence the normal adult spermatogenesis. We analysed in this study the morphometry, the expression of the proliferation cell nuclear antigen (PCNA), cell pluripotency marker OCT-4, germ cell marker VASA and apoptosis in the developing testes of Lagostomus maximus, a rodent in which female germ line develops through abolished apoptosis and unrestricted proliferation. Morphometry revealed an increment in the size of the seminiferous cords with increasing developmental age, arising from a significant increase of PCNA-positive germ cells and a stable proportion of PCNA-positive Sertoli cells. VASA showed a widespread cytoplasmic distribution in a great proportion of proliferating gonocytes that increased significantly at late development. In the somatic compartment, Leydig cells increased at mid-development, whereas peritubular cells showed a stable rate of proliferation. In contrast to other mammals, OCT-4 positive gonocytes increased throughout development reaching 90% of germ cells in late-developing testis, associated with a conspicuous increase in circulating FSH from mid- to late-gestation. TUNEL analysis was remarkable negative, and only a few positive cells were detected in the somatic compartment. These results show that the South American plains viscacha displays a distinctive pattern of testis development characterized by a sustained proliferation of germ cells throughout development, with no signs of apoptosis cell demise, in a peculiar endocrine in utero ambiance that seems to promote the increase of spermatogonial number as a primary direct effect of FSH.

Involvement of the Fas and Fas ligand in testicular germ cell apoptosis by zearalenone in rat

Zearalenone (ZEA), a nonsteroidal estrogenic mycotoxin, is known to cause testicular toxicity in animals. In the present study, the effects of ZEA on spermatogenesis and possible mechanisms involved in germ cell injury were examined in rats. Ten-week-old Sprague-Dawley rats were treated with 5 mg/kg i.p. of ZEA and euthanized 3, 6, 12, 24 or 48 h after treatment. Histopathologically, spermatogonia and spermatocytes were found to be affected selectively. They were TUNEL-positive and found to be primarily in spermatogenic stages I-VI tubules from 6 h after dosing, increasing gradually until 12 h and then gradually decreasing. Western blot analysis revealed an increase in Fas and Fas ligand (Fas-L) protein levels in the ZEAtreated rats. However, the estrogen receptor (ER)alpha expression was not changed during the study. Collectively, our data suggest that acute exposure of ZEA induces apoptosis in germ cells of male rats and that this toxicity of ZEA is partially mediated through modulation of Fas and Fas-L systems, though ERalpha may not play a significant role.

Methylphenidate has dose-dependent negative effects on rat spermatogenesis: decreased round spermatids and testicular weight and increased p53 expression and apoptosis

In the present study, we aimed to evaluate the possible effects of methylphenidate on rat testes. Forty-two Wistar rats were randomly distributed into three experimental groups of 14 rats each. For 90 days, each group via gavage received the following: group 1 = tap water (control group), group 2 = 5 mg/kg/day of ritalin (methylphenidate, MPH), and group 3 = 10 mg/kg/day of ritalin. After sacrificing the animals, the body weights as well as the absolute and relative testicular weights were measured. Testes were sampled, fixed, and processed and, by histopathological examination, quantitative morphometric analysis of Sertoli cells, spermatocytes, and spermatids was performed in stages II, V, and XII. Immunohistochemistry was performed for transforming growth factor (TGF)-β1 and p53, and the apoptotic index was assessed through the TUNEL method. Group 2 had a reduction of round spermatids in stage II. Group 3 had reduction in both stage II and stage V spermatids, as well as lower testicular weight. The p53 expression was increased in group 3. In groups 2 and 3, the TGF-β1 expression was reduced and the apoptotic index by TUNEL was increased. Body weights remained stable on either group. Our results showed that methylphenidate might negatively affect spermatogenesis not only by reducing testicular weight and amount of round spermatids but also by increasing apoptotic death and p53 activation. The findings of the study, however, must be cautiously interpreted.

Male germ cell-specific protein Trs4 binds to multiple proteins

Temperature-related sequence 4 (Trs4) has been identified as a testis-specific gene with expression sensitive to the abdominal temperature changes induced by artificial cryptorchidism. In murine testes, Trs4 mRNA was detected in round spermatids and its protein was localized mainly in the elongating spermatids as well as in the acrosomes and tails of mature spermatozoa. Using a yeast two-hybrid screening system, we identified Rshl-2, Gstmu1, and Ddc8 as putative binding partners of the Trs4 protein in mouse testes. Their interactions were confirmed by in vivo and in vitro binding assays. Further studies demonstrated that Ddc8, a newly identified gene with unknown functions, displayed a similar expression pattern with Trs4 in mouse testes. In particular, Trs4, Ddc8, and Rshl-2 proteins were co-localized to the tails of mature spermatozoa. These results suggested that Trs4 might be involved in diverse processes of spermiogenesis and/or fertilization through interactions with its multiple binding partners.

FAS and FASLG polymorphisms and susceptibility to idiopathic azoospermia or severe oligozoospermia

FAS, together with FASLG, triggers germ cell apoptosis, which occurs in various stages of mammalian testicular development. Single nucleotide polymorphisms (SNP) in the promoter regions of these two genes can influence their transcriptional activities and result in abnormal cell apoptosis, thus leading to spermatogenesis impairment. Therefore, it is reasonable to postulate that FAS and FASLG SNP may be associated with idiopathic azoospermia or severe oligozoospermia. To test this hypothesis, the distributions of FAS -1377G/A and -670A/G SNP and FASLG -844C/T SNP were studied in Han Chinese men. These SNP were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 203 infertile men with idiopathic azoospermia or severe oligozoospermia and in 246 proven fertile controls. Frequencies of FASLG -844CC, CT and TT genotypes among infertile men were significantly different from those among controls (P = 0.024). Men with FASLG -844TT genotype had an increased risk of idiopathic azoospermia or severe oligozoospermia compared with those with CC and CT genotype (odds ratio 2.72, 95% confidence interval 1.25-5.93). The results suggest that FASLG -844C/T SNP may be a genetic predisposing factor of idiopathic azoospermia or severe oligozoospermia among Han Chinese men.

Hypogonadal Mouse, a Model to Study the Effects of the Endogenous Lack of Gonadotropins on Apoptosis1

Testicular apoptosis is involved in the regulation of germ cell numbers, allowing optimal sperm production. Apoptosis has been described to occur in response to the absence of hormonal stimulation of the testis. Here we investigate the effect of the physiological lack of gonadotropins from birth using the hypogonadal (homozygous for the mutant allele Gnrh1(hpg)) mouse as a model. We pursued a concerted strategy using microarray analysis and RT-PCR to assess transcript levels, TUNEL to quantify the incidence of apoptosis, and Western blotting to assess the respective contribution of the extrinsic and intrinsic apoptotic pathways. Our results indicate a large increase in apoptosis of both somatic and germ cell compartments in the hpg testis, affecting Sertoli cells as well as germ cells of all ages. We confirmed our observations of Sertoli cell apoptosis using anti-Mullerian inhibiting substance staining and staining for cleaved fodrin alpha. In the somatic compartment, apoptosis is primarily regulated via the membrane receptor (extrinsic) apoptotic pathway, while in the germ cell compartment, regulation occurs via both the mitochondrial (intrinsic) and membrane receptor (extrinsic) apoptotic pathways, the latter potentially in a stage-specific manner. This study is the first report of spermatogonial apoptosis in response to gonadotropin deficiency as well as the first report of Sertoli cell apoptosis in response to gonadotropin deficiency in the mouse.

Spermatocyte responses in vitro to induced DNA damage

Spermatocytes normally sustain many meiotically induced double-strand DNA breaks (DSBs) early in meiotic prophase; in autosomal chromatin, these are repaired by initiation of meiotic homologous-recombination processes. Little is known about how spermatocytes respond to environmentally induced DNA damage after recombination-related DSBs have been repaired. The experiments described here tested the hypothesis that, even though actively completing meiotic recombination, pachytene spermatocytes cultured in the absence of testicular somatic cells initiate appropriate chromatin remodeling and cell-cycle responses to environmentally induced DNA damage. Two DNA-damaging agents were employed for in vitro treatment of pachytene spermatocytes: gamma-irradiation and etoposide, a topoisomerase II (TOP2) inhibitor that results in persistent unligated DSBs. Chromatin modifications associated with DSBs were monitored after exposure by labeling surface-spread chromatin with antibodies against RAD51 (which recognizes DSBs) and the phosphorylated variant of histone H2AFX (herein designated by its commonly used symbol, H2AX), gammaH2AX (which modifies chromatin associated with DSBs). Both gammaH2AX and RAD51 were rapidly recruited to irradiation- or etoposide-damaged chromatin. These chromatin modifications imply that spermatocytes recruit active DNA damage responses, even after recombination is substantially completed. Furthermore, irradiation-induced DNA damage inhibited okadaic acid-induced progression of spermatocytes from meiotic prophase to metaphase I (MI), implying efficacy of DNA damage checkpoint mechanisms. Apoptotic responses of spermatocytes with DNA damage differed, with an increase in frequency of early apoptotic spermatocytes after etoposide treatment, but not following irradiation. Taken together, these results demonstrate modification of pachytene spermatocyte chromatin and inhibition of meiotic progress after DNA damage by mechanisms that may ensure gametic genetic integrity.

Apoptotic cell death induced by low-dose radiation in male germ cells: hormesis and adaptation

Biological effects of low-dose radiation (LDR) in somatic cells have captured the interest of radiobiologists for the last two decades. Apoptosis of germ cells is required for normal spermatogenesis and often occurs through highly conserved events, including the transfer of vital cellular materials to the growing gametes following death of neighboring cells. Apoptosis of germ cells also functions in diverse processes, including removal of abnormal or superfluous cells at specific checkpoints, establishment of caste differentiation, and individualization of gametes. Moreover, germ cells are very sensitive to radiation-induced genomic and cytological effects. Therefore, induction of germ-cell apoptosis has been observed in the testis of animals exposed to both high-dose radiation (HDR) and LDR. Exposure of male germ cells to LDR induces a stimulating effect, while exposure to HDR causes an inhibitory effect on the metabolism, antioxidant capacity, and proliferation and maturation of cells, a phenomenon termed hormesis. Preexposure to LDR also protects cells from subsequently HDR-induced genomic and cytological effects, a phenomenon termed adaptive response. This review describes the features of male germ-cell apoptosis. It reviews the evidence that LDR induces the hormesis and adaptive responses in the male germ cells in terms of apoptosis. This review also discusses the possible effects of LDR-induced apoptotic hormesis and adaptive response on the modulation of inheritable genomic damage caused by subsequent radiation exposure to male germ cells.

Transcriptional regulation of FasL expression and participation of sTNF-alpha in response to sertoli cell injury

The Fas/FasL signaling pathway has previously been demonstrated to be critical for triggering germ cell apoptosis in response to mono-(2-ethylhexyl)phthalate (MEHP)-induced Sertoli cell injury. Although Sertoli cells ubiquitously express the FasL protein, MEHP-induced germ cell apoptosis appears to tightly correlate with increased levels of Sertoli cell FasL. Here we characterize the transcriptional regulation of the murine FasL gene in Sertoli cells after MEHP exposure. A serial deletion strategy for 1.5 kb of the 5'-upstream activating sequence of the FasL promoter was used to determine transcriptional activity in response to MEHP. Luciferase activity of the FasL promoter in the rat Sertoli cell line ASC-17D revealed that two regions, -500 to -324 and -1250 to -1000, were necessary to drive the inducible transcription of FasL. Sequence analysis of these two regions revealed two cis-regulatory elements, NF-kappaB and Sp-1. By site-directed mutagenesis, electrophoretic mobility shift and chromatin immunoprecipitation assays, it was confirmed that MEHP-induced FasL expression is enhanced through the transcriptional regulation of both NF-kappaB and Sp-1. Experiments performed both in vitro and in vivo revealed that MEHP exposure results in an increased production of sTNF-alpha and that sTNF-alpha-mediated NF-kappaB activation causes robust increases in FasL levels in both the ASC-17D Sertoli cell line and in primary rat Sertoli cell/germ cell co-cultures. In the seminiferous epithelium, Sertoli cells express TNFR1, whereas germ cells produce TNF-alpha. Therefore, sTNF-alpha released by germ cells after MEHP-induced Sertoli cell injury acts upon Sertoli cell TNFR1 and activates NF-kappaB and Sp-1 that consequently causes a robust induction of FasL expression. These novel findings point to a potential "feed-forward" signaling mechanism by which germ cells prompt Sertoli cells to trigger their apoptotic elimination.

The preventive effects of thiopental and propofol on testicular ischemia-reperfusion injury

BACKGROUND

Testicular torsion is a urological emergency that requires immediate surgical intervention to prevent testicular damage. The aim of the study was to investigate the preventive effects of thiopental and propofol as anesthetics on testicular ischemia-reperfusion injury.

METHODS

Forty male Wistar Albino rats were randomly assigned to four groups of 10 rats each. During 5 h, anesthesia was induced and maintained with thiopental in groups 1 and 2 and with propofol in groups 3 and 4. Groups 2 and 4 received left testicular ischemia (torsion) during 1 h and reperfusion (detorsion) during 4 h. Groups 1 and 3 (control groups) had no testicular torsion and detorsion. At the end of 5 h, animals were killed and both ipsilateral and contralateral testes were removed for histopathologic examination and measurement of tissue MDA (malondialdehyde) and NO (nitric oxide) levels.

RESULTS

In the contralateral testes of all the groups, MDA and NO measurements were not different from ipsilateral testes of the control groups. Between the groups 1 and 3, there were no differences in MDA and NO levels. Although torsion/detorsion of testes in group 4 caused significantly increased levels of tissue MDA and NO values compared with group 3, ischemia-reperfusion in group 2 caused a further increase in these levels compared with group 4. The ipsilateral testes in the control groups did not show any morphological changes. Testicular torsion/detorsion in rats with thiopental anesthesia (group 2) caused significantly greater histopathologic injury levels than rats with propofol anesthesia (group 4).

CONCLUSION

Our results suggest that propofol as an anesthetic agent may prevent testicular damage by scavenging reactive oxygen and nitrogen species and inhibiting lipid peroxidation in an animal model of testicular torsion and detorsion.

Fas ligand in bull ejaculated spermatozoa:A quantitative immunocytochemical study

Apoptosis, or programmed cell death, provides a way to remove redundant cells at the end of their lifespan and thus acts as a homeostatic mechanism, maintaining the correct number of cells in the body by balancing their production and death. In the testis, this process seemed to play a pivotal role in spermatogenesis. It is generally accepted that Sertoli cells control the germ cell population through one of the best-known apoptotic pathways, the Fas/Fas L paracrine signal transduction system, in which a Fas ligand (Fas L) expressed by Sertoli cells induces apoptosis when it binds with its receptor, Fas, expressed by the germ cells. Recently, we demonstrated the presence of Fas antigen in normal ejaculated spermatozoa from fertile bulls and suggested that this molecule might have a non-apoptotic, defensive role against injuries, especially oxidative stress. We have now investigated whether bull mature, fertile spermatozoa express not only the Fas receptor but also its natural ligand Fas L. Our results indicate that the whole sperm population expresses Fas L. We suggest that Fas L in bull spermatozoa, like in murine spermatozoa, might be able to kill activated lymphocytes and protect the male gamete from damage by the self-immune system or the cytotoxic activity of leukocytes in the female genital tract.

Death receptor and mitochondrial pathways are involved in germ cell apoptosis in an experimental model of autoimmune orchitis

BACKGROUND

Studies on experimental autoimmune orchitis (EAO) have helped to elucidate immunological mechanisms involved in testicular damage. We previously demonstrated that EAO is characterized by lymphomononuclear cell infiltrates and apoptosis of spermatocytes and spermatids expressing Fas and TNFR1. The aim of this work was to characterize the pathways involved in germ cell apoptosis in EAO and to determine the involvement of the Bcl-2 protein family in this process.

METHODS AND RESULTS

EAO was induced in rats by immunization with testicular homogenate (TH) and adjuvants, whereas control (C) rats were injected with saline solution and adjuvants. Testis of EAO rats showed procaspase 8 cleavage products (western blot) with high caspase 8 activity. Cytochrome c content increased in the cytosol and decreased in the mitochondrial fraction of testis from EAO rats compared with C, concomitant with increased caspase 9 activity. Bax was mainly expressed in spermatocytes and spermatids and Bcl-2 in basal germ cells (immunohistochemistry). Baxbeta isoform content increased in EAO rat testis compared with C, whereas content of Baxalpha remained unchanged (western blot). However, Baxalpha content decreased in the cytosol and increased in the mitochondrial and endoplasmic reticulum (ER)-enriched fractions of testis from EAO rats compared with C (western blot). Bcl-2 content also increased in the testes of EAO rats.

CONCLUSIONS

Our results demonstrated that extrinsic, mitochondrial and possibly ER pathways are inducers of germ cell apoptosis in EAO and that Bax and Bcl-2 proteins modulate this process.

Expression and identification of a novel apoptosis gene Spata17 (MSRG-11) in mouse spermatogenic cells

In this study, anti-spermatogenesis-associated 17 (Spata17) polyclonal antibody was prepared by immunizing New Zealand white rabbits with a synthesized peptide corresponding to the amino acid sequence 7-23 of the mouse Spata17 protein. Immunohistochemical analysis revealed that Spata17 protein was most abundant in the cytoplasm of round spermatids and elongating spermatids within seminiferous tubules of the adult testis. The expression of Spata17 mRNA in cultured mouse spermatogonia (GC-1) cells was almost undetectable. In an experimental unilateral cryptorchidism model of an adult mouse, the expression of Spata17 mRNA had no obvious difference with the normal testis until postoperation day 1, but gradually decreased from day 3 and was almost undetectable on day 17. Immunohistochemical analysis revealed that the protein was almost undetectable within seminiferous tubules of an experimental unilateral cryptorchidism model of the adult testis on postoperation day 8. Flow cytometry analysis showed that the expression of Spata17 protein in the GC-1 cell line could accelerate GC-1 cell apoptosis. The effect increases with the increasing of the transfected dose of pcDNA3.1(-)/Spata17. By Hoechst 33258 staining, a classical way of identifying apoptotic cells, we further confirmed that the apoptosis was induced by expression of Spata17 in transfected GC-1 cells.

A possible role of Fas antigen in ejaculated spermatozoa of fertile bulls: an immunocytochemical quantitative approach

The Fas/Fas L system is a widely recognized apoptosis signal transduction pathway in which transmembrane receptor protein (Fas) triggers a programmed cell death when bound by the Fas ligand (Fas L). This system in the testis is believed to be a paracrine signaling system by which Sertoli cells expressing Fas L can initiate killing of Fas-expressing germ cells during spermatogenesis. So far, the presence of Fas antigen in ejaculated spermatozoa was related only to subfertility or infertility conditions. We demonstrated for the first time that normal ejaculated spermatozoa also express Fas antigen. Our data showed that a large percentage of normal ejaculated spermatozoa of fertile bulls are immunocytochemically positive for Fas. Our observations provide further evidence of the "regionalization" of sperm membrane antigens. Furthermore, we suggest that in mature fertile ejaculated spermatozoa the Fas antigen may also provide resistance to programmed cell death, like in some other cells expressing molecules that inhibit the signals induced by Fas or the death program itself. In addition, we suggest that Fas antigen can partly protect the spermatozoa against apoptosis induced by lipoperoxidative damage that can occur spontaneously in the male gamete at various stages in its lifetime.

Spermatocyte-specific expression of constitutively active heat shock factor 1 induces HSP70i-resistant apoptosis in male germ cells

Spermatocytes, the most sensitive male germ cells to heat-induced apoptosis, do not respond to hyperthermia by inducing heat shock proteins (HSPs), including HSP70i, which has been previously shown to confer resistance to apoptosis in somatic cells. To dissect the mechanism of heat-induced apoptosis and to determine if we could protect spermatocytes by expressing HSP70i, we engineered transgenic mice that express in spermatocytes constitutively active heat shock transcription factor (HSF)1. Such HSF1 expression did not lead to transcription of inducible Hsp70 genes, but instead induced caspase-dependent apoptosis that mimicked heat shock-induced death of spermatogenic cells. Both mitochondria-dependent and death receptor-dependent pathways appear to be involved in such HSF1-induced apoptosis: the levels of Bcl-2 family proteins became increased, p53 protein accumulated and expression levels of caspase-8 and death-receptor-interacting proteins (including Fas-associated death domain protein and TNF receptor associated death domain protein) became elevated. Surprisingly, the constitutive spermatocyte-specific expression of HSP70i in double-transgenic males did not protect against such HSF1-induced apoptosis.

Expression of keratinocyte growth factor and its receptor in human breast cancer: its inhibitory role in the induction of apoptosis possibly through the overexpression of Bcl-2

Keratinocyte growth factor (KGF), a mesenchymal cell derived paracrine growth factor that regulates normal epithelial cell proliferation, appears to be an essential mediator of steroids in various reproductive organs. The present study was designed to determine the expression and role of KGF and its receptor (KGFR) in human breast carcinoma tissues by immunohistochemistry. We also compared the results with the expression of estrogen receptor alpha(ERalpha), ERbeta, the proliferative activity assessed by the labeling index (LI) for the Ki-67 antigen, apoptotic frequency assessed by terminal dUTP nick end-labeling (TUNEL) index, and the expression of Bcl-2. All of KGF-positive cases were ERalpha- positive (p<0.05), but not that of ERbeta, while all of KGFR-positive cases were ERbeta-positive (p<0.05), but not that of ERalpha. The specimens with the coexpression of KGF and KGFR significantly correlated with a lower TUNEL index (p<0.05), but not with Ki-67 LI in breast cancer tissues. Further analysis at the cellular level revealed that Bcl-2 was colocalized in KGFR-positive cells, and these cells were almost negative for TUNEL staining. Bcl-2-positive cells were also associated with ERbeta, as expected. Therefore, the results indicate that ERalpha may be involved in KGF expression, and that the coexpression of KGF and KGFR may play an inhibitory role in the induction of apoptosis possibly through the up-regulation of Bcl-2 expression in human breast cancer.

Overexpression of anti-apoptotic Mcl-1 in testicular germ cell tumours

AIMS

To determine the expression of Mcl-1 in testicular germ cell tumours in order to clarify the role of this anti-apoptotic factor in these tumours. Various members of the Bcl-2 family have been implicated in the apoptotic mechanisms regulating germ cell apoptosis. Mcl-1 is an anti-apoptotic Bcl-2 family member and has recently been reported to be related to the progression of malignancy; however, the involvement of Mcl-1 in the development of germ cell tumours is still unknown.

METHODS AND RESULTS

Mcl-1 expression in testicular germ cell tumours was investigated by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR). By immunohistochemistry, overexpression of Mcl-1 was present in all germ cell tumours that were studied, including embryonal carcinoma and yolk sac tumour, as well as choriocarcinoma and teratoma. In teratomas, Mcl-1 was widely distributed in the epithelial, myogenic, neural and mesenchymal components. RT-PCR analysis after microdissection revealed high levels of Mcl-1 mRNA in all tumour variants compared with non-neoplastic germ cells.

CONCLUSION

Overexpression of anti-apoptotic Mcl-1 may function to enhance the viability of testicular germ cells, thereby leading to tumorigenesis.