Chemical anoxia delays germ cell apoptosis in the human testis

Influence of open testicular biopsy in prepubertal rats on rats' adulthood fertility with correlation to serum levels of inhibin B and follicle stimulating hormone

OBJECTIVE

Open testicular biopsy (OTB) is one of the options to accurately assess fertility potential of the undescended testis. The aim of the study was to investigate consequences of OTB in prepubertal rats on their adulthood fertility.

METHODS

Thirty-eight prepubertal male rats were divided into three groups depending on day 20 procedure. The first group was the control group, the second sham operated and the third has left OTB. Bilateral orchiectomy was performed on day 70 to all groups, with determination of serum inhibin B and follicle stimulating hormone (FSH). Removed testes were compared according to the weight, volume, spermatogenesis, histological and apoptotic changes in both testes with differences in serum levels of inhibin B and FSH.

RESULTS

Ipsilateral testicular weight, volume, and spermatogenesis reduction with a reduction of tubular number, diameter and germinative epithelium was found in OTB group. Significant increase in apoptotic index was found in biopsied testis without compensatory hypertrophy of contralateral testis. Differences of inhibin B and FSH were not statistically significant among three groups.

CONCLUSION

OTB in prepubertal rats has detrimental effects on fertility in adulthood. It does not cause compensatory hypertrophy of the contralateral testis nor does it disturb serum levels of inhibin B and FSH.

Testicular effect of a mixture of 2-methoxyethanol and 2-ethoxyethanol in rats

BACKGROUND

2-Methoxyethanol (ME) and 2-ethoxyethanol (EE) represent a large group of chemicals which are used separately or as mixtures. These compounds exert multidirectional toxic effects. The present studies aimed to demonstrate the effects of ME and EE alone and their mixture on the reproductive organs in the rats.

METHODS

Male Wistar rats were treated subcutaneously with ME and EE alone (1.25-5.0mM/kg/day) or with their mixture (1:1) for 4 weeks. After completion of the experiment, the testes, epididymides, and prostate were weighed. In post-mitochondrial supernatant of the testes, the level of total protein, non-protein and protein sulfhydryl groups, malondialdehyde, total antioxidant status, and glutathione peroxidase and glutathione reductase activities were determined.

RESULTS

Exposure to ME alone resulted in a dose-dependent decrease in the organ weights, the total protein, non-protein and protein sulfhydryl groups. EE alone led to less marked alterations. Co-exposure to ME and EE caused alterations similar as in the rats treated with ME alone.

CONCLUSIONS

Marked testicular atrophy, decrease in epididymis and prostate weights are predominant effects of the repeated exposure to relatively low doses of ME and EE. A decrease in the total protein level, and protein sulfhydryl groups may be responsible for testicular atrophy. A significant depletion of non-protein sulfhydryl groups and occasionally elevated glutathione peroxidase activity may indicate that ME and EE resulted in disturbances of pro-oxidant/antioxidant balance. The study suggests that testicular toxicity in male rats co-exposed to ME and EE is mainly caused by the former compound.

Toxicity of ethylene glycol monomethyl ether: impact on testicular gene expression

Methoxyacetic acid (MAA), the active biological oxidation product of the industrial solvent ethylene glycol monomethyl ether (EGME), causes acute toxicity in several species including humans. MAA primarily affects tissues with rapidly dividing cells and high rates of energy metabolism, including testes, thymus and the fetus. Testicular toxicity, one of the most prominent consequences of EGME, and MAA, exposure, results from apoptosis of primary spermatocytes and is associated with changes in the expression of various genes and signalling pathways. This review of EGME metabolism and its organ-specific toxicities emphasizes genes and signalling pathways that are modulated by EGME exposure and their relevance to the molecular mechanisms underlying EGME and MAA toxicity. Of particular importance are the genes that code for oxidative stress response factors, protein kinases, and nuclear hormone receptors. Nuclear receptors and protein kinases regulate multiple cellular processes and are critical for signalling events required for spermatogenesis. De-regulation of their activity by EGME or MAA leads to inappropriate signalling in testicular cells. Oxidative stress in spermatocytes exposed to MAA triggers mitochondrial release of cytochrome C, activation of caspases and ultimately apoptosis. Detailed investigation of the molecular responses to MAA exposure may help elucidate the overall impact and extent of toxicity seen following EGME exposure. Finally, given the effects of EGME on multiple genes and signalling pathways in the testis, mixture studies combining EGME, or MAA, with other testicular toxicants may help identify toxicities that are aggravated by EGME exposure.

Superoxide dismutase, catalase, and glutathione peroxidase in the testis of the Mexican big-eared bat (Corynorhinus mexicanus) during its annual reproductive cycle

The reproductive physiology of Corynorhinus mexicanus includes a testes growth-involution cycle. Testis recrudescence begins in May-June, peaks in August and then undergoes a profound involution being totally regressed in November. Adult, male individuals were captured monthly during one year and ROS scavenging enzyme activities were measured in testes and expressed per total wet-weight and per mg protein. SOD total activity is very low from October to February; increases sharply one full month before testes recrudescence starts, and in August, when testis activity was at its peak, SOD is 3-4 times lower than in July. Catalase total activity is bimodal. The main peak of activity occurs during testicular recrudescence with an additional smaller peak, two months before the onset of recrudescence. Glutathione peroxidase total activity parallels almost exactly the testis growth cycle, increases in July, reaches a peak in August and decreases through September to almost disappear in October. SOD specific activity shows a pre-testicular increase of activity, maintains its activity from March to July and then descends drastically to almost nil in August, maintaining these low values until February. Catalase specific activity is particularly important during the period of testicular regression. GPX specific activity is low from March to July, months of testicular recrudescence; whereas its activity increases in August and peaks in November, when testes regression occurs. Our data show that ROS-scavenging enzymes may play a very important role during testes involution-recrudescence in C. mexicanus, and we believe their participation could be equally important in all seasonally breeding mammals.

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.

Spermatogonial stem cells: characteristics and experimental possibilities

The continuation of the spermatogenic process throughout life relies on a proper regulation of self-renewal and differentiation of the spermatogonial stem cells. These are single cells situated on the basal membrane of the seminiferous epithelium. Only 0.03% of all germ cells are spermatogonial stem cells. They are the only cell type that can repopulate and restore fertility to congenitally infertile recipient mice following transplantation. Although numerous expression markers have been helpful in isolating and enriching spermatogonial stem cells, such as expression of THY-1 and GFRalpha-1 and absence of c-kit, no specific marker for this cell type has yet been identified. Much effort has been put into developing a protocol for the maintenance of spermatogonial cells in vitro. Recently, coculture systems of testicular cells on various feeder cells have made it possible to culture spermatogonial stem cells for a long period of time, as was demonstrated by the transplantation assay. Even expansion of testicular cells, including the spermatogonial stem cells, has been achieved. In these culture systems, hormones and growth factors are investigated for their role in the process of proliferation of spermatogonial stem cells. At the moment the best culture system known still consists of a mixture of testicular cells with about 1.33% spermatogonial stem cells. Recently pure SV40 large T immortalized spermatogonial stem cell lines have been established. These c-kit-negative cell lines did not show any differentiation in vitro or in vivo. A telomerase immortalized c-kit-positive spermatogonial cell line has been established that was able to differentiate in vitro. Spermatocytes and even spermatids were formed. However, spermatogonial stem cell activity by means of the transplantation assay was not tested for this cell line. Both the primary long-term cultures and immortalized cell lines have represented a major step forward in investigating the regulation of spermatogonial self-renewal and differentiation, and will be useful for identifying specific molecular markers.

The time relationship between ipsilateral testicular ischemia and germ cell apoptosis in the contralateral testis in rat

Unilateral testicular ischemia-reperfusion (IR) in the rat is followed by histologic damage in the contralateral testis, which has been previously explained on immunologic grounds. There is evidence to suggest that apoptosis in the contralateral testis is involved in germ cell loss following IR injury to the testis. We examined the time-dependent effect of testicular ischemia on germ cell apoptosis in the contralateral testis in a rat. Adult Sprague-Dawley rats weighing 250-280 g, were subjected to testicular ischemia for 1, 2, 3 or 24 h. Twenty-four hours following onset of the ischemic insult, testes were harvested for immunohistochemical studies. Apoptosis was detected using TUNEL immunohistochemical assay. Testicular ischemia in rats led to histological damage, which was related to the duration of the ischemia. In the contralateral testis, the minimal damage included a decrease in number of germ cell layers, mild disorganization, and single cell apoptosis. Apoptosis in the contralateral testes increased significantly after 2, 3, and 24 h of ischemia and showed direct, time-related correlation with the duration of ischemia. We conclude that testicular ischemia causes an increase in germ cell apoptosis in the contralateral testis. The extent of apoptosis increases with the duration of the ischemia.

Sphingosine-1-phosphate inhibits nuclear factor kappaB activation and germ cell apoptosis in the human testis independently of its receptors

Early apoptosis-inducing events are potentially important targets for preventing germ cell loss caused by external stress. The sphingolipid sphingosine-1-phosphate (S1P) is an important regulator of stress-induced apoptosis. It affects the cell as an intracellular signaling molecule or as a ligand to its cell membrane-bound S1P(1-5) receptors. We previously demonstrated that S1P inhibits stress-induced male germ cell death in vitro and in vivo. Here, we further define the mechanisms of S1P-mediated inhibition of male germ cell death. Using immunohistochemistry, we detected expression of the S1P(1) and S1P(2) receptors in the somatic Sertoli cells of the human testis. In a culture of human seminiferous tubules, S1P inhibited germ cell apoptosis, suppressed both nuclear factor kappaB (NF-kappaB) DNA-binding activity and expression of phosphorylated Akt, but did not affect activator protein-1 (AP-1) DNA-binding activity. Dihydro-S1P, which binds to and activates S1P receptors but has no direct intracellular effect, suppressed neither apoptosis nor NF-kappaB activity. These results suggest that S1P inhibits male germ cell apoptosis independently of its receptors, possibly by inhibiting the transcription factor NF-kappaB and Akt phosphorylation.

Effects of Acid Sphingomyelinase Deficiency on Male Germ Cell Development and Programmed Cell Death1

Deficiency of acid sphingomyelinase (ASM), an enzyme responsible for producing a pro-apoptotic second messenger ceramide, has previously been shown to promote the survival of fetal mouse oocytes in vivo and to protect oocytes from chemotherapy-induced apoptosis in vitro. Here we investigated the effects of ASM deficiency on testicular germ cell development and on the ability of germ cells to undergo apoptosis. At the age of 20 weeks, ASM knock-out (ASMKO) sperm concentrations were comparable with wild-type (WT) sperm concentrations, whereas sperm motility was seriously affected. ASMKO testes contained significantly elevated levels of sphingomyelin at the age of 8 weeks as detected by high-performance, thin-layer chromatography. Electron microscopy revealed that the testes started to accumulate pathological vesicles in Sertoli cells and in the interstitium at the age of 21 days. Irradiation of WT and ASMKO mice did not elevate intratesticular ceramide levels at 16 h after irradiation. In situ end labeling of apoptotic cells also showed a similar degree of cell death in both groups. After a 21-day recovery period, the numbers of primary spermatocytes and spermatogonia at G2 as well as spermatids were essentially the same in the WT and ASMKO testes, as detected by flow cytometry. In serum-free cultures both ASMKO and WT germ cells showed a significant increase in the level of ceramide, as well as massive apoptosis. In conclusion, ASM is required for maintenance of normal sphingomyelin levels in the testis and for normal sperm motility, but not for testicular ceramide production or for the ability of the germ cells to undergo apoptosis.

Germ cell apoptosis in the testes of normal stallions

Apoptosis in testicular germ cells has been demonstrated in many mammalian species. However, little is known about the stallion (Equus caballus) and rates of apoptosis during spermatogenesis. Morphological and biochemical features of apoptosis reported in other species were used to confirm that the TdT-mediated dUTP Nick end labeling (TUNEL) assay is an acceptable method for identification and quantification of apoptotic germ cells in histological tissue sections from stallion testis. Seminiferous tubules from eight stallions with normal testis size and semen quality were evaluated according to stage of seminiferous epithelium to determine the germ cell types and stages where apoptosis most commonly occurs. Spermatogonia and spermatocytes were the most common germ cell types labeled by the TUNEL assay. A low rate of round and elongated spermatids were labeled by the TUNEL assay. Mean numbers of TUNEL-positive germ cells per 100 Sertoli cell nuclei were highest in stages IV (15.5 +/- 1.0) and V (13.5 +/- 1.1) of the seminiferous epithelial cycle (P < 0.001). An intermediate level of apoptosis was detected in stage VI (P < 0.02). These stages (IV-VI) correspond to meiotic divisions of primary spermatocytes and mitotic proliferation of B1 and B2 spermatogonia. Establishing basal levels of germ cell apoptosis is a critical step towards understanding fertility and the role of apoptosis in regulating germ cell numbers during spermatogenesis.