Germ Cell Apoptosis in Undescended Testis: The Origin of its Impaired Spermatogenesis in the TS Inbred Rat

Testicular heat stress, a historical perspective and two postulates for why male germ cells are heat sensitive

Herein, we compare the different experimental regimes used to induce testicular heat stress and summarise their impact on sperm production and male fertility. Irrespective of the protocol used, scrotal heat stress causes loss of sperm production. This is first seen 1-2 weeks post heat stress, peaking 4-5 weeks thereafter. The higher the temperature, or the longer the duration of heat, the more pronounced germ cell loss becomes, within extreme cases this leads to azoospermia. The second, and often underappreciated impact of testicular hyperthermia is the production of poor-quality spermatozoa. Typically, those cells that survive hyperthermia develop into morphologically abnormal and poorly motile spermatozoa. While both apoptotic and non-apoptotic pathways are known to contribute to hyperthermic germ cell loss, the mechanisms leading to formation of poor-quality sperm remain unclear. Mechanistically, it is unlikely that testicular hyperthermia affects messenger RNA (mRNA) abundance, as a comparison of four different mammalian studies shows no consistent single gene changes. Using available evidence, we propose two novel models to explain how testicular hyperthermia impairs sperm formation. Our first model suggests aberrant alternative splicing, while the second model proposes a loss of RNA repression. Importantly, neither model requires consistent changes in RNA species.

Cryptorchidism, gonocyte development, and the risks of germ cell malignancy and infertility: A systematic review

BACKGROUND/AIM

Cryptorchidism, or undescended testis (UDT) occurs in 1%-4% of newborn males and leads to a risk of infertility and testicular malignancy. Recent research suggests that infertility and malignancy in UDT may be caused by abnormal development of the neonatal germ cells, or gonocytes, which normally transform into spermatogonial stem cells (SSC) or undergo apoptosis during minipuberty at 2-6 months in humans (2-6 days in mice). We aimed to identify the current knowledge on how UDT is linked to infertility and malignancy.

METHODS

Here we review the literature from 1995 to the present to assess the possible causes of infertility and malignancy in UDT, from both human studies and animal models.

RESULTS

Both the morphological steps and many of the genes involved in germ cell development are now characterized, but the factors involved in gonocyte transformation and apoptosis in both normal and cryptorchid testes are not fully identified. During minipuberty there is evidence for the hypothalamic-pituitary axis stimulating gonocyte transformation, but without known direct control by LH and androgen, although FSH may have a role. An arrested gonocyte maybe the origin of later malignancy at least in syndromic cryptorchid testes in humans, which is consistent with the recent finding that gonocytes are normally absent in a rodent model of congenital cryptorchidism, where malignancy has not been reported.

CONCLUSION

The results of this review strengthen the view that malignancy and infertility in men with previous UDT may be caused by abnormalities in germ cell development during minipuberty.

TYPE OF STUDY

Systematic review (secondary, filtered) LEVEL OF EVIDENCE: Level I.

Stereological and morphological analysis of the effects of aging on spermatogenesis in rat testis 1

PURPOSE

To quantify, through stereological and morphometric analysis, spermatogenesis in rats undergoing the natural aging process.

METHODS

Seventy-two male Wistar rats were divided into 6 equal groups according to age at the time of killing: 3, 6, 9, 12, 18, and 24 months. All the rats were subjected orchiectomy and collection of testicular parenchymal fragments for histological and morphometric analysis. The numerical density of spermatids was calculated using a stereological study, and morphometric analysis was conducted to measure the height of the germinal epithelium and the area of the seminiferous tubules.

RESULTS

We found that the 18 and 24 months groups showed a significant reduction in the number of round spermatids. However, the height of the germinal epithelium was not significantly different between the groups. The area of seminiferous tubules was also significantly reduced in the elderly rats compared to that in the young ones.

CONCLUSION

Aging of rats showed a significant reduction in the number of round spermatids and the area of the seminiferous tubules, more pronounced in the rats at 18 and 24 months of life.

Ghrelin regulates Bax and PCNA but not Bcl-2 expressions following scrotal hyperthermia in the rat

More recently, we have reported the beneficial effects of ghrelin in improvement of histopathological features of the rat testis following local heat exposure. However, the exact mechanism and the precise role of apoptosis- and proliferation-specific proteins in this regeneration process remained to be explored. Thus, thirty adult male Wistar rats were allotted for the experiment and subdivided equally into three groups: control-saline (CS), heat-saline (HS) and heat-ghrelin (HG). The scrota of HS and HG groups were immersed once in water bath at 43°C for 15 min. HG animals received 2 nmol of ghrelin subcutaneously immediately after heating every other day until day 60 and the other groups were given physiological saline using the same method. The testes of all groups were taken after rat killing on days 30 and 60 after heat treatment for immunocytochemical detection of pro-apoptotic factor Bax, anti-apoptotic protein Bcl-2 and proliferation-associated peptide PCNA in the germ cells. Ghrelin could significantly suppress the Bax expression in spermatocytes compared to the HS group at day 30 (P<0.05). Likewise, the mean percentages of spermatogonia containing Bax substance were lower in ghrelin-exposed animals, however the differences were not statistically significant. There were immunoreactive cells against Bcl-2 in each germ cell neither in the control nor in the heated animals of experimental groups. In contrast, the number of PCNA immunolabeling cells were higher in HG group in compared to HS or CS animals on both experimental days (P<0.001). Down-regulation of Bax expression concurrent with overexpression of PCNA in HG group indicates the ability of ghrelin in acceleration of testicular germ cells regeneration following heat stress. These findings indicate that ghrelin may be used as a novel and efficient antioxidant agent to induce resumption of spermatogenesis upon environmental heat exposure.

A ROLE FOR APOPTOSIS INDUCED BY ACUTE HERPES SIMPLEX VIRUS INFECTION IN MICE

Acute herpes simplex virus (HSV) infection causes apoptosis in the adrenal cortex and myenteric plexus of the gut, ovary, pituitary gland, and liver of mice. Apoptosis of infected cells is increased in immunosuppressed regions of the adrenal cortex and liver of macrophage-depleted mice. HSV carries the US3 gene which interferes with host cell apoptosis. When the livers of macrophage-depleted mice are infected with a US3-null virus, apoptosis occurs in the narrow areas of inflammatory cell infiltration, restricting viral replication and spread. Thus, these data suggest that apoptosis may function as a primitive immune response to HSV infection in mice.

Effect of allopurinol on damage caused by free radicals to cryptorchid testes

Cryptorchidism causes apoptosis of germ cells. It has been suggested that the redox regulatory system is involved in this process. The free radicals produced are thought to be generated during the production of uric acid, a reaction catalyzed by xanthine oxidase. This enzyme is inhibited by allopurinol; however, the role of allopurinol in neonate rats with inguinal cryptorchidism has not been assessed yet. Sixty male Wistar rats were used and five groups were formed: a control, a sham, a sham group with allopurinol administration and two groups with surgical unilateral cryptorchidism, which either did not receive, or received, allopurinol. The rats were assessed at 40 days post-partum. Reactive oxygen species concentration and epithelial area were measured and the histopathological, apoptotic and cellular proliferation indexes were determined. We found a decrease in reactive oxygen species, histopathological and apoptotic indexes and an increase in proliferation index and epithelial area in rats with cryptorchidism treated with allopurinol in comparison with rats with untreated cryptorchidism. We suggest that the over-production of reactive oxygen species plays an important role in the damage of the cryptorchid testes. Allopurinol administration decreases reactive oxygen species concentrations as well as the damage to the germ epithelium.

Early orchiopexy improves subsequent testicular development and spermatogenesis in the experimental cryptorchid rat model

PURPOSE

The most appropriate period for orchiopexy is controversial. We performed histological analyses of undescended testes to evaluate the influence of orchiopexy timing in an experimental cryptorchid rat model. Furthermore, we extrapolated the timing of orchiopexy in humans from our results.

MATERIALS AND METHODS

Experimental cryptorchid rats were induced with androgen blocker by injecting flutamide into the abdomen of pregnant Sprague-Dawley rats (Chubu Kagaku Shizai, Nagoya, Japan) for 7 days from days 14 to 20 of gestation. Approximately 90% of male newborns had undescended testes and we performed orchiopexy on them 4, 5 and 7 weeks after birth. The testes were removed 10 weeks after birth in all groups, and weight and histological findings were assessed. A modified Johnsen score was used to determine spermatogenesis maturity and germ cell apoptosis was also evaluated.

RESULTS

Nonoperated undescended testes showed atrophic and hypospermatogenesis with germ cell apoptosis, whereas treated undescended testes showed the development of early elongated spermatids. In addition, performing orchiopexy 4 weeks after birth decreased the degeneration of undescended testes compared with that in other groups.

CONCLUSIONS

From the point of view of only testicular development 4-week-old rats reportedly correspond to 1-year-old humans. While we should be cautious when extrapolating our findings to the clinical setting, our current study provides evidence in support of early orchiopexy during the first year of life.

Effect of dexamethasone on germ cell apoptosis in the contralateral testis after testicular ischemia-reperfusion injury in the rat

OBJECTIVE

To evaluate the effect of dexamethasone on spermatogenesis and germ cell apoptosis in the ipsilateral and contralateral testis after testicular ischemia-reperfusion (IR) in rats.

DESIGN

Laboratory study.

SETTING

Medical research laboratory in a university setting.

ANIMAL(S)

Forty adult Sprague-Dawley rats weighing 250-280 g.

INTERVENTION(S)

Testicular IR, treatment with dexamethasone (10 mg per kilogram of body weight).

MAIN OUTCOME MEASURE(S)

Testicular germ cell apoptosis was assessed by deoxyuridine nick-end labeling immunohistochemical assay.

RESULT(S)

Testicular ischemia in rats led to histological damage in the ipsilateral testis. In the contralateral testis, minimal damage was observed. Germ cell apoptosis in both the ischemic and the contralateral testis increased significantly after IR. Treatment with dexamethasone did not change germ cell apoptosis in ischemic testis but decreased germ cell apoptosis in the contralateral testis.

CONCLUSION(S)

Glucocorticoids may be beneficial for spermatogenesis after testicular IR by decreasing germ cell apoptosis in the contralateral testis.

HtrA2 is up-regulated in the rat testis after experimental cryptorchidism

AIM

The aim of the present study was to elucidate the role of high temperature requirement A2 (HtrA2) in germ cell loss in the heat-stressed testis.

METHODS

We examined the expression of HtrA2, caspase-9 activity and proteolytic activity of HtrA2 in the rat testis, and their in vivo responses to experimental cryptorchid treatment.

RESULTS

Northern analysis revealed the expression of HtrA2 mRNA peaked at days 1 and 7 after cryptorchid treatment. While expression of HtrA2 mRNA was seen in the spermatogonium, spermatocytes and some spermatids in normal adult rat testis, experimental cryptorchidism treatment resulted in a marked increase in its signal intensity in spermatocytes and some spermatids, and the layers of spermatogonium and early primary spermatocytes became negative at days 1 and 7 after the treatment. However, the spermatogonium, Sertoli cells and interstitial cells appeared to have strong intensities at days 14, 28 and 56 after the treatment. Western analysis revealed the expression of HtrA2 protein peaked at day 2 coinciding with the increase of positive spermatogonium, the appearance of protein-positive interstitial cells, and day 28 coinciding with the reappearance of protein-positive interstitial cells. Caspase-9 activity peaked at day 2 and HtrA2 proteolytic activity peaked at day 28. Consequently, the first peak of HtrA2 mRNA expression was followed by the peak of caspase-9 activity and the second peak was followed by the peak of proteolytic activity; however, the second peak of mRNA expression had considerable chronological difference from that of the protein.

CONCLUSION

These findings suggest the probabilities that the heat stress results in germ cell death by a caspase-independent manner with the elevation of HtrA2 proteolytic activity, as well as a caspase-dependent manner with the elevation of caspase-9 activity.

Expression of stress inducible protein 1 (Stip1) in the mouse testis

Phthalate esters are considered endocrine disruptors that interfere with the endocrine balance and development of the mammalian testis. Mono-2-ethylhexyl phthalate (MEHP), the active metabolite of the ubiquitously used plasticizer di-2-ethylhexyl phthalate (DEHP), acts upon Sertoli cells as initial target. By subtractive cDNA libraries we identified genes deregulated as response to MEHP in primary cultures of mouse Sertoli cells. The expression of mouse stress inducible protein 1 (Stip1) was detected as upregulated as a result of MEHP exposure. Stip1 is a cochaperone protein that is homologous to the human heat shock cognate protein 70 (hsc70)/heat shock protein 90 (hsp90)-organizing protein (Hop). To assess the presence and localization of Stip1 in mouse testis and its potential role in stress defense, we studied the expression pattern of the Stip1 protein by immunohistochemistry and of the mRNA by in situ hybridization. Both the protein and the mRNA of Stip1 were mainly found in the cytoplasm of all types of spermatogonia and spermatocytes up till zygotene, the expression decreased during late pachytene and was very weak in diplotene spermatocytes and round spermatids. Interestingly, this expression pattern resembled the pattern of stress sensitivity of spermatogenic cells in that the most sensitive cell types show the weakest expression of Stip1. This suggests an important role for Stip1 in the ability of germ cells to survive in stress conditions including high temperatures.

Effect of diclofenac on germ cell apoptosis following testicular ischemia-reperfusion injury in a rat

Recent evidence suggests that enhanced cell apoptosis is responsible for germ cell loss following testicular ischemia-reperfusion (IR) injury. A nonsteroidal anti-inflammatory drug diclofenac sodium (Voltaren) is a prostaglandin-synthesis inhibitor, which is widely used in many testicular disorders. The purpose of the present study was to examine the effect of diclofenac (DIC) on germ cell apoptosis in the ischemic and contralateral testes following testicular IR in a rat. Forty rats were divided randomly into four experimental groups of ten rats each: group A (Sham)-Sham operated animals; group B (Sham-DIC)-Sham operated rats that were treated with DIC given subcutaneously at a dose of 10 mg/kg, once daily, 24, 48 and 72 h following operation; group C (IR) underwent 90 min of unilateral testicular IR; group D (IR-DIC)-rats underwent 90 min of unilateral testicular IR and were treated with DIC similarly to group B. Ninety-six hours following operation, the rats were sacrificed and testes were harvested. Johnsen's criteria and the number of germinal cell layers were used to categorize the spermatogenesis. TUNEL assay was used to determine germ cell apoptosis in both the ischemic and contralateral testes. Statistical analysis was performed using the non-parametric Kruskal-Wallis ANOVA test, with P less than 0.05 considered statistically significant. Testicular ischemia in rats led to histological damage in the ipsilateral testis. In the contralateral testis, minimal damage was observed. Germ cell apoptosis in both the ischemic and the contralateral testes increased significantly after IR. Treatment with DIC did not change histologic parameters of spermatogenesis in both the ischemic and contralateral testes, but decreased germ cell apoptosis in both testes following testicular IR. We conclude that testicular ischemia causes an increase in germ cell apoptosis in the contralateral testis. Diclofenac may be beneficial for spermatogenesis following testicular IR by decreasing germ cell apoptosis.

EFFECT OF EPIDERMAL GROWTH FACTOR ON SPERMATOGENESIS IN THE CRYPTORCHID RAT

PURPOSE

Epidermal growth factor (EGF) is secreted mainly from the submandibular glands. Submandibular gland ablation causes a marked decrease in male fertility, which suggests that EGF influences spermatogenesis. We investigated the effect of EGF in combination with orchiopexy on cryptorchid rat testes in which tubular deterioration had become partially irreversible.

MATERIALS AND METHODS

Unilaterally cryptorchid rats were obtained by daily administration of 7.5 mg flutamide (Nihonkayaku, Tokyo, Japan), an androgen receptor antagonist, to pregnant rats. At age 10 weeks the unilaterally cryptorchid rats underwent orchiopexy with or without EGF administered into the cryptorchid testis. EGF solution (10 microg/ml) was delivered into the seminiferous tubules by retrograde perfusion through the rete testis. At 14 days testicular recovery was assessed based on the maturity of spermatogenesis using a modified Johnsen score and from the number of apoptotic germ cells per seminiferous tubule.

RESULTS

Mean Johnsen score +/- SEM was significantly higher in the orchiopexy with EGF than in the orchiopexy without EGF group (7.85 +/- 0.12 vs 7.12 +/- 0.13, p <0.001). The number of apoptotic germ cells tended to be smaller in the orchiopexy with EGF group than in the orchiopexy without EGF group (0.16 +/- 0.05 vs 0.28 +/- 0.08).

CONCLUSIONS

Although orchiopexy for cryptorchidism partly improved spermatogenesis, recovery was limited. EGF administered in combination with orchiopexy was more effective for spermatogenesis than orchiopexy alone. This may be applicable in patients with cryptorchidism.

Effect of testicular biopsy in childhood on spermatogenesis, fertility, and paternity in adulthood--a mouse model study

OBJECTIVES

To study the effect of testicular biopsy in childhood on spermatogenesis, fertility, and paternity in subsequent adulthood using an animal model. Considerable controversy exists as to whether testicular biopsy should be performed in children.

METHODS

Four-week-old male ICR mice were subjected to unilateral testicular biopsy (group 1), bilateral biopsy (group 2), or a sham operation (group 3). At 8 weeks of age, the testicular weight, seminiferous tubular diameter, and manifestation of apoptosis were examined. The motility of sperm obtained from the epididymides of the same testes was also examined. Fertility and paternity was assessed in each mouse by housing it with 2 age-matched females for 2 weeks.

RESULTS

No significant differences were found in the testicular weight, mean seminiferous tubular diameter, or number of apoptotic germ cells between the biopsied and unbiopsied side in group 1 or between groups 2 and 3. No significant differences were noted in the average sperm motility rate between the biopsied (30.5% +/- 14.5%) and unbiopsied side (35.8% +/- 19.2%) in group 1, or between groups 2 (37.6% +/- 18.0%) and 3 (39.3% +/- 10.0%). All females who coupled with the male mice in all groups became pregnant. The average number of offspring from the 2 female mice was not significantly different among the three groups (group 1, 13.1 +/- 2.3; group 2, 12.3 +/- 2.0; and group 3, 11.3 +/- 3.0).

CONCLUSIONS

The spermatogenesis, fertility, and paternity of mature mice were unaffected by testicular biopsy in childhood.

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.

Determination of apoptosis through bax expression in cryptorchid testis: an experimental study

The aim was to determine the expression of Bax in germ cells of rats with unilateral experimental cryptorchidism, and to evaluate the role of apoptosis in germ cell loss. Twenty-one prepubertal rats were randomly subdivided into three groups after the execution of the left cryptorchidism model. Group 1 (n=8), group 2 (n=6) and group 3 (n=7) rats were killed at the end of the first, second and third month, respectively. Bax expression was assessed in Sertoli cells, spermatogonia and spermatocytes by immunohistochemistry. Percentages of Bax expression in spermatocytes and spermatogonia were decreased in the left testicles in the 2nd and 3rd months compared to results obtained in the 1st month (p<0.05). Percentage of Bax expression in the left testicles of group 1, at the level of both spermatogonia and spermatocytes was higher than that in the right one (p<0.05). However, in groups 2 and 3, the higher Bax expression on the left side was only seen in the spermatocytes (p<0.05). In all groups, the mean weight of the left testicle was lower than that of the scrotal counterpart where the difference was significant only in groups 1 and 3 (p<0.05). The weight of the left and right testicles was increasing with time. In this model of cryptorchidism, the affected testis had a decreased weight compared to the normal one. Based on the increased Bax expression, we think that apoptosis may play a role in the germ cell loss.

MODULATION OF GERM CELL APOPTOSIS WITH A NITRIC OXIDE SYNTHASE INHIBITOR IN A MURINE MODEL OF CONGENITAL CRYPTORCHIDISM

PURPOSE

Apoptosis has been implicated in testicular germ cell loss in experimental models of cryptorchidism. Nitric oxide synthase (NOS) has been shown to have a role in apoptosis in many cell types. The Hoxa 11 knockout mouse has congenital bilateral cryptorchidism and is uniformly sterile. We examined the time course of apoptosis in this model and attempted to attenuate this response in vivo by inhibition of NOS.

MATERIALS AND METHODS

The offspring of heterozygous Hoxa 11 knockout mice were genotyped by polymerase chain reaction. Homozygous knockout mice treated with the NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) and untreated controls were sacrificed at weekly intervals at 3 to 13 weeks of age. Spermatogenesis was evaluated with hematoxylin and eosin staining. Germ cell apoptosis was assessed with a TUNEL assay and DNA staining. Co-localization of NOS activity was measured with a polyclonal antibody to endothelial NOS.

RESULTS

Impaired spermatogenesis was observed in Hoxa 11 knockout mice. Testis/body weight ratios were decreased in this group at weeks 6 and 7, while body weights were unchanged. Germ cell apoptosis was significantly higher in the knockout group compared to wild-type controls. Co-localization was observed between endothelial NOS activity and apoptotic cells, while mice treated with L-NAME demonstrated improved spermatogenesis and attenuated apoptosis.

CONCLUSIONS

Apoptosis and NOS reactivity appeared to co-localize in the seminiferous tubules in the Hoxa 11 knockout mouse model. Treatment with the NOS inhibitor L-NAME attenuated apoptosis and improved spermatogenesis. This finding suggests that early treatment might serve as an adjunct to early surgical intervention to reduce testicular atrophy, although any impact on long-term fertility remains to be determined.