Participation of the Fas-signaling system in the initiation of germ cell apoptosis in young rat testes after exposure to mono-(2-ethylhexyl) phthalate

Responses of peritubular macrophages and the testis transcriptome profiles of peripubertal and adult rodents exposed to an acute dose of MEHP

Exposure of rodents to mono-(2-ethylhexyl) phthalate (MEHP) is known to disrupt the blood-testis barrier and cause testicular germ cell apoptosis. Peritubular macrophages (PTMφ) are a newly identified type of testicular macrophage that aggregates near the spermatogonial stem cell niche. We have previously reported that MEHP exposure increased the numbers of PTMφs by 6-fold within the testis of peripubertal rats. The underlying mechanism(s) accounting for this change in PTMφs and its biological significance is unknown. This study investigates if MEHP-induced alterations in PTMφs occur in rodents (PND 75 adult rats and PND 26 peripubertal mice) that are known to be less sensitive to MEHP-induced testicular toxicity. Results show that adult rats have a 2-fold higher basal level of PTMφ numbers than species-matched peripubertal animals, but there was no significant increase in PTMφ numbers after MEHP exposure. Peripubertal mice have a 5-fold higher basal level of PTMφ compared with peripubertal rats but did not exhibit increases in number after MEHP exposure. Further, the interrogation of the testis transcriptome was profiled from both the MEHP-responsive peripubertal rats and the less sensitive rodents via 3' Tag sequencing. Significant changes in gene expression were observed in peripubertal rats after MEHP exposure. However, adult rats showed lesser changes in gene expression, and peripubertal mice showed only minor changes. Collectively, the data show that PTMφ numbers are associated with the sensitivity of rodents to MEHP in an age- and species-dependent manner.

Mono-(2-ethylhexyl) phthalate (MEHP) reversibly disrupts the blood-testis barrier (BTB) in pubertal rats

The blood-testis barrier (BTB) is constituted by tight junctions between adjacent Sertoli cells (SC) that create a specialized adluminal microenvironment to foster the development of spermatocytes and spermatids. The BTB is a well-studied target of numerous environmental toxicants, including di-(2-ethylhexyl) phthalate (DEHP), a compound widely used in various consumer products. MEHP is the active toxic metabolite of DEHP that has long been recognized in postnatal rodents to disrupt SC function. This study evaluates the impact of MEHP on the integrity of the BTB in both pubertal and adult rats and the signal transduction pathways known to be involved in the disruption of the BTB. Treatment of prepubertal rats with 700 mg/kg MEHP for 24 hours functionally disrupted the BTB integrity. A similar treatment of adult rats with MEHP did not disrupt the integrity of the BTB. The observed disruption of the BTB integrity in the MEHP-treated prepubertal rats occurred concomitantly with a decreased expression and mislocalization of both the ZO1 and occludin tight junction-associated proteins, as well as sloughing of spermatocytes and spermatids. At this same time, MEHP treatment induced a transient surge of p44/42 mitogen-activated protein kinase (MAPK) pathway. Interestingly, after a recovery period of 5 weeks, the BTB recovered and was functionally intact. This is the first report to indicate that acute MEHP exposure of prepubertal rats, but not adult rats, disrupts the functional integrity of the BTB and that this effect on the BTB is reversible.

Peritubular Macrophages Are Recruited to the Testis of Peripubertal Rats After Mono-(2-Ethylhexyl) Phthalate Exposure and Is Associated With Increases in the Numbers of Spermatogonia

Peripubertal exposure of male rodents to the phthalate metabolite mono-(2-ethylhexyl) phthalate (MEHP) causes testicular inflammation, spermatocyte apoptosis, and disruption of the blood-testis barrier. The MEHP-induced inflammatory response in the testis includes an infiltration of macrophages and neutrophils, although the cause and purpose of this response is unknown. Recently, a population of testicular macrophages known as peritubular macrophages that are phenotypically distinct from those resident in interstitium was described in mice. Peritubular macrophages aggregate near the spermatogonial stem cell niche and are believed to stimulate their differentiation. We hypothesized that if testicular peritubular macrophages do indeed stimulate spermatogonial differentiation, MEHP exposure would result in an increase of peritubular macrophages to stimulate the replacement of lost spermatocytes. Male rats were exposed to 700 mg/kg MEHP or corn oil (vehicle control) via oral gavage at postnatal day 28 and euthanized at 48 h, 1 or 2 weeks later. Seminiferous tubules were stained with immunofluorescent markers for macrophages (major histocompatibility complex class II [MHC-II+]) and undifferentiated spermatogonia (PLZF). Peritubular macrophages were observed in rat testis: MHC-II+ cells on the surface of seminiferous tubules with heterogeneous morphology. Quantification of MHC-II+ cells revealed that, unlike in the mouse, their numbers did not increase through puberty (2-week period). MEHP increased macrophage presence by 6-fold 48 h after exposure and remained elevated by 2-fold 2 weeks after exposure. An increase of differentiating spermatogonia occurred 2 weeks after MEHP exposure. Taken together, our results suggest that peritubular macrophages play a crucial role in the testis response to acute injury and the subsequent recovery of spermatogenesis.

Di-n-butyl phthalate diminishes testicular steroidogenesis by blocking the hypothalamic-pituitary-testicular axis: relationship with germ cell apoptosis in Japanese quail

Although di-n-butyl phthalate (DBP) induces germ cell apoptosis, the underlying mechanism is not yet clear in quail. In this study, prepubertal quails were given a single dose of 500mg kg-1 DBP by gavage and were then killed 3, 6 and 24h after treatment. There was a significant reduction in intratesticular testosterone (ITT) concentrations and testicular steroidogenic enzyme mRNA expression and a significant increase in germ cell apoptosis in DBP-treated compared with control quails at all time points. Maximum apoptosis was detected 6h after treatment and the maximum reduction in testosterone concentrations was at 3h. To investigate whether DBP suppressed testicular steroidogenesis by affecting the hypothalamic-pituitary-testicular axis, we analysed pituitary LH subunit β (Lhb) mRNA expression and serum LH concentrations. At all time points, pituitary Lhb expression and serum LH concentrations were significantly decreased following DBP treatment. The present observations suggest the possibility that DBP blocked LH secretion from the hypothalamus and/or pituitary, thereby decreasing LH stimulation of Leydig cells and reducing ITT concentrations. DBP-induced decreases in ITT concentrations may cause changes to the physical structure of Sertoli cells, which, in turn, may induce germ cell apoptosis.

Maternal exposure to Di-(2-ethylhexyl) phthalate (DEHP) activates the PI3K/Akt/mTOR signaling pathway in F1 and F2 generation adult mouse testis

Di-(2-ethylhexyl) phthalate (diethylhexyl phthalate, DEHP) can cause male reproductive damage in rodents and human. Moreover, DEHP is known to promote transgenerational inheritance of adult-onset disease in subsequent generations after maternal exposure during fetal gonadal development. The PI3K/Akt/mTOR signaling pathway has been implicated in germ cell survival following testicular damage. In this study, a F0 gestation DEHP exposure and transgenerational inheritance testis injury model was established to study the testis injury phenotype and the expression and activation of members of PI3K/Akt/mTOR signaling pathway in the testis of F1-F3 generation mice. We found that the bodyweight and the anogenital distance (AGD) are reduced only in F1 mice, the sperm motility and deformity decreased in F1-F3 mice, and the testicular histomorphology damagedin F1-F3 mice; however the sperm motility and deformity rates are increased and the histomorphological injury is repaired during the transgenerational process. We also found the activation of PI3K/Akt/mTOR signaling pathway is enhanced in F1 and F2, and the number of apoptotic cells is decreased in F3 generation mice compared to the control group. These results suggest that the PI3K/Akt/mTOR signaling pathway may be activated to promote the proliferation and differentiation and protect testicular cells from apoptosis in the F1 and F2 generation mice after direct exposure to DEHP.

Maternal Exposure to T-2 Toxin Induces Changes in Antioxidant System and Testosterone Synthesis in the Testes of Mice Offspring

Simple Summary

This study investigated the effects of maternal T-2 toxin exposure on the development of testis in the mice offspring. The detrimental effects were assessed by testicular weight, antioxidant capacity, and testosterone synthesis and secretion. Studies have shown that the toxin carried by the mother has bad effects on the testicular development of offspring at puberty, affecting the antioxidant system and testosterone synthesis in the testis, but the maternal exposure of T-2 toxin had no significant impact on the testes of offspring after sexual maturity, suggesting the recovery of reproductive function.

Abstract

T-2 toxin, the most toxic member of trichothecene mycotoxin, is widely distributed in cereals, and has been extensively studied, but few studies focus on the toxicity of maternal exposure to offspring. This study focused on the effects of maternal exposure to T-2 toxin (during gestation and lactation) on the testicular development of mice offspring. Dams were orally administered with T-2 toxin at 0, 0.005, or 0.05 mg/kg body weight from the late stage of gestation to the end of lactation. Testicular samples of the mice offspring were collected on the postnatal day 21, 28, and 56. The results showed significant decreases in body weight and testicular weight on the postnatal day 28. Moreover, significant inhibition of antioxidant system and testosterone synthesis was detected on the postnatal day 28. Furthermore, there were significant decreases in the gene expression levels of StAR and 3β-HSD, which are involved in testosterone synthesis. In general, present results demonstrated that maternal exposure to T-2 toxin during gestation and lactation led to bad effects on the capacity of antioxidant system and inhibited testosterone synthesis in testes during pre-puberty with no significant effects on post-puberty.

Reproductive toxicity of perchlorate in rats

Perchlorate, as an oxidizer, has many applications such as explosives and pyrotechnics, especially in rocket propellants and missile motors. Because it was found in water including wells and drinking water in the US, its effect on human health was being noted. However, the reproductive toxic effect on perchlorate is still unclear. In present study, the effects of repeated exposure to perchlorate on reproductive toxicity were evaluated in Wistar rats. The rats were treated orally with perchlorate at doses of 0.05, 1.00 or 10.00 mg/kg body weight (b.w.) daily for 8 weeks. The levels of T₃ and T₄ hormones in the rat serum were detected by radioimmunoassay kit. The indexes of reproduction, percentage of organ in body weight (%) and frequency of abnormal sperm cells were also analyzed in this study. DNA damage in testicular cells was evaluated by Comet assay. The levels of MDA, GSH and SOD were examined in testicle tissues of rats by ELISA. The expression of c-fos and fas protein was examined in testicle tissues by immunohistochemistry. The results showed that perchlorate did not affect the body weight of rats. Perchlorate also significantly decreased indexes of live birth and weaning in the groups of 1.00 and 10.00 mg/kg, and viability index only in the 10.00 mg/kg group (P < 0.05). Perchlorate also significantly decreased the serum level of T₃ in male rats of 1.00 and 10.00 mg/kg groups, increased the rate of sperm abnormality (10.00 mg/kg), potentially caused DNA damage in testicular cells and altered the status of oxidative stress in male rats. In addition, because of the increase in the expression of fas and c-fos protein in testicle tissues, perchlorate could induce apoptosis in spermatogenesis. Thus, these findings indicate that perchlorate could cause DNA damage in testicular tissues and reduce testicular spermatogenic ability, resulting in reproductive toxicity.

Zearalenone induces apoptosis of rat Sertoli cells through Fas-Fas ligand and mitochondrial pathway

Zearalenone (ZEA) is an estrogen-like toxin produced by Fusarium that is widely found in cereals worldwide. In recent years, ZEA has been found to cause reproductive dysfunction in male animals, but the underlying mechanism remains unclear. This study examined the apoptosis of rat Sertoli cells induced by different concentrations (0, 5, 10, and 20 μmol/L) of ZEA via Fas-Fas ligand and mitochondrial signaling pathway in vitro. Apoptosis rate was detected by flow cytometry. The mitochondrial membrane potential was detected by immunofluorescence assay and flow cytometry. Western Blot and qRT-PCR were used to identify the signaling pathway. The results revealed that ZEA induced apoptosis of rat Sertoli cells, significantly reduced the transcription and expression of the anti-apoptotic protein Bcl-2, increased the transcription and expression of pro-apoptotic proteins Bax and tBID, and Fas, FasL, FADD, and caspase-8. ZEA also increased the activation of caspase-8 and caspase-9, and promoted the release of cytochrome C from mitochondria to cytoplasm. Moreover, addition of caspase-8 inhibitor Z-IETD-FMK led to significant decrease in the mitochondrial membrane potential and apoptosis rate of the ZEA + Z-IETD-FMK group as compared to the ZEA treatment group. The release of cytochrome C from mitochondria to cytoplasm and the activation of caspase-9 and caspase-3 were significantly decreased in the ZEA + Z-IETD-FMK group. These results suggested that ZEA can induce apoptosis of rat Sertoli cells, activate the Fas-Fas ligand signaling pathway and participate in the regulation of mitochondrial apoptosis pathway.

Ocimum gratissimum leaf extract may precipitate infertility in male diabetic Wistar rats

Objective:

This study was designed to investigate the Ocimum gratissimum (OG) effects on sperm quality and testicular cytoarchitecture in alloxan-induced diabetic rats.

Method:

Twenty male Wistar rats (150-200 g) were assigned into 4 groups (n=5) as A (control), B (OG), C (Dia) and D (Dia+OG). Groups A and B were normal animals receiving distilled water or OG (400 mg/kg), respectively while diabetes was induced by alloxan monohydrate (100 mg/kg) in groups C and D, followed by the administration of distilled water or OG, respectively for 28 days. Blood samples were obtained for fasting blood glucose (FBG) and fructosamine determination while, epididymis and testes were obtained for sperm quality assessment using computer-assisted sperm analyzer and testicular histomorphometry, respectively. Seminiferous tubule diameter and interstitial space distance were quantified in hematoxylin and eosin stained slides. Statistical analysis was done using ANOVA and student t-test at α0.05.

Results:

Fructosamine and FBG were reduced in Dia+OG (80.11±3.80µmol/L and 132.0±8.41mg/dl, respectively) compared with Dia (139.66±4.29µmol/L and 285.6±26.69mg/dl, respectively). Sperm count was unchanged in Dia, but decreased in OG and Dia+OG; abnormal sperm cells increased in OG, Dia and Dia+OG. Mild vacuolation in the seminiferous tubule, disorganized germinal cells layer, arrested sperm maturation with empty spermatozoa in lumen, decreased seminiferous tubule diameter and increased interstitial space were found in the testes of OG, Dia and Dia+OG compared with control.

Conclusion:

Diabetes induces sperm impairments and distortions in testicular cytoarchitecture, which were aggravated by OG leaf extract in male Wistar rats.

Sequential testicular atrophy involves changes in cellular proliferation and apoptosis associated with variations in aromatase P450 expression levels in Irs-2-deficient mice

Insulin receptor substrate 2 (Irs-2) is an intracellular protein susceptible to phosphorylation after activation of the insulin receptor. Its suppression affects testis development and its absence induces peripheral resistance to insulin. The aim of this study was to identify changes induced by the deletion of Irs-2 in the testicular structure and by the altered expression of cytochrome P450 aromatase, a protein necessary for the development and maturation of germ cells. Adult knockout (KO) mice (Irs-2^-/- , 6 and 12 weeks old) and age-matched wild-type (WT) mice were used in this study. Immunohistochemistry and Western blot analyses were performed to study proliferation (PCNA), apoptosis (active caspase-3) and P450 aromatase expression in testicular histological sections. Deletion of Irs-2 decreased the number of epithelial cells in the seminiferous tubule and rete testis. Aberrant cells were frequently detected in the epithelia of Irs-2^-/- mice, accompanied by variations in spermatogonia, which were shown to exhibit small hyperchromatic nuclei as well as polynuclear and anuclear structures. The amount of cell proliferation was significantly lower in Irs-2^-/- mice than in WT mice, whereas apoptotic processes were more common in Irs-2^-/- mice. Aromatase P450 reactivity was higher in 6-week-old KO mice than in WT mice of the same age and was even higher at 12 weeks. Our results suggest that Irs-2 is a key element in spermatogenesis because silencing Irs-2 induces the sequential development of testicular atrophy. The effects are observed mainly in germ cells present in the seminiferous tubule, which may be due to changes in cytochrome P450 aromatase expression.

Effect modification by apoptosis-related gene polymorphisms on the associations of phthalate exposure with spermatozoa apoptosis and semen quality

BACKGROUND

Human studies indicate that phthalate exposure is associated with adverse male reproductive health, and this association may be modified by genetic polymorphisms.

OBJECTIVES

We investigated whether apoptosis-related gene polymorphisms modified the associations of phthalate exposure with spermatozoa apoptosis and semen quality.

METHODS

In this Chinese population who sought for semen examination in an infertility clinic, we measured 8 phthalate metabolites in two urine samples to assess the individual's exposure levels. Apoptosis-related gene (Fas, FasL, and caspase3) polymorphisms were performed by real-time PCR. Spermatozoa apoptosis and semen quality parameters were evaluated by Annexin V/PI assay and computer-aided semen analysis, respectively.

RESULTS

We found that Fas rs2234767, FasL rs763110, and caspase3 rs12108497 gene polymorphisms significantly modified the associations between urinary phthalate metabolites and spermatozoa apoptosis. For example, urinary monobutyl phthalate (MBP) associated with an increased percentage of Annexin V⁺/PI^- spermatozoa of 25.11% (95% CI: 4.08%, 50.53%) were only observed among men with CT/TT genotype of FasL rs763110. In addition, we found that caspase3 rs12108497 gene polymorphisms significantly modified the associations of urinary mono (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) with decreased sperm concentration and sperm count (both p-values for interactions = 0.02).

CONCLUSION

Our results provided the first evidence that apoptosis-related gene polymorphisms might contribute to the effects of phthalate exposure on male reproductive health.

Review on crosstalk and common mechanisms of endocrine disruptors: Scaffolding to improve PBPK/PD model of EDC mixture

Endocrine disruptor compounds (EDCs) are environment chemicals that cause harmful effects through multiple mechanisms, interfering with hormone system resulting in alteration of homeostasis, reproduction and developmental effect. Many of these EDCs have concurrent exposure with crosstalk and common mechanisms which may lead to dynamic interactions. To carry out risk assessment of EDCs' mixture, it is important to know the detailed toxic pathway, crosstalk of receptor and other factors like critical window of exposure. In this review, we summarize the major mechanism of actions of EDCs with the different/same target organs interfering with the same/different class of hormone by altering their synthesis, metabolism, binding and cellular action. To show the impact of EDCs on life stage development, a case study on female fertility affecting germ cell is illustrated. Based on this summarized discussion, major groups of EDCs are classified based on their target organ, mode of action and potential risk. Finally, a conceptual model of pharmacodynamic interaction is proposed to integrate the crosstalk and common mechanisms that modulate estrogen into the predictive mixture dosimetry model with dynamic interaction of mixture. This review will provide new insight for EDCs' risk assessment and can be used to develop next generation PBPK/PD models for EDCs' mixture analysis.

A crossover-crossback prospective study of dibutyl-phthalate exposure from mesalamine medications and semen quality in men with inflammatory bowel disease

BACKGROUND

Phthalates are widely used chemicals with ubiquitous exposure. Dibutyl-phthalate (DBP), a male reproductive toxicant in animals, is understudied in humans. Some mesalamine medications used to treat inflammatory bowel disease (IBD) have DBP in their coating, whereas other mesalamine formulations do not.

OBJECTIVES

Taking advantage of differences in mesalamine formulations, we investigated whether high-DBP exposure from mesalamine medications was associated with decreased semen parameters.

METHODS

73 men with IBD taking mesalamine participated in a crossover-crossback prospective study. Men taking non-DBP containing mesalamine at baseline i.e., background exposure, crossed-over for four months to high-DBP mesalamine and then crossed-back for four months to their non-DBP mesalamine (B1HB2-arm;Background1-High-Background2) and vice versa for men taking high-DBP mesalamine at baseline (H1BH2-arm;High1-Background-High2). Men provided up to six semen samples (2: baseline, 2: crossover and 2: crossback).

RESULTS

We estimated crossover, crossback and carryover effects using linear mixed models adjusted for abstinence time, age, season and duration on high-DBP mesalamine at baseline. Semen parameters in B1HB2-arm (26 men, 133 samples) decreased after high-DBP mesalamine exposure (crossover versus baseline), especially motility parameters, and continued to decrease further even after crossback to non-DBP mesalamine (crossback versus crossover). The cumulative carryover effect of high-DBP (crossback versus baseline) was a decrease of % total sperm motility by 7.61(CI:-13.1, -2.15), % progressive sperm motility by 4.23(CI:-8.05, -0.4) and motile sperm count by 26.0% (CI:-46.2%, 1.7%). However, H1BH2-arm (47 men, 199 samples) had no significant change during crossover or crossback.

CONCLUSIONS

Men newly exposed to high-DBP mesalamine for four months had a cumulative reduction in several semen parameters, primarily sperm motility, that was more pronounced and statistically significant even after exposure ended for four months.

The presence of macrophages and inflammatory responses in an in vitro testicular co-culture model of male reproductive development enhance relevance to in vivo conditions

Our 3-dimensional testis co-culture system (3D-TCS) represents a promising model of male reproductive toxicity which captures sensitive processes of male reproductive development and contains the main testes cell types (germ, Leydig and Sertoli cells). Macrophages are another cell type important for testicular function and help to modulate immuno-endocrine processes during testes development. Chemicals such as phthalate esters (PE's) affect macrophage function and testosterone production in the testes in vivo. The aim of this study was to determine whether macrophages were present in the 3D-TCS and investigate responses in our model that may be related to immuno-endocrine functions. We observed consistent expression of the resident macrophage marker ED2 as well as increases in inflammatory cytokines produced by macrophages and testes cells (IL-6, TNF-α and KC/GRO) after exposure to toxic PE's. Pathway analysis of gene expression changes after exposure to PE's showed that IL-6 and TNF-α signaling pathways were enriched after treatment with reproductively toxic, but not non-reproductively toxic phthalates. These results indicate that macrophages and inflammatory processes are captured in the 3D-TCS and that these processes are impacted by exposure to reproductive toxicants. These processes represent a major mode of action for in vivo testis toxicity for a variety of compounds and our novel in vitro model is able to capture toxicant perturbation of immune function.

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

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

Reduced hippocampal dendritic spine density and BDNF expression following acute postnatal exposure to di(2-ethylhexyl) phthalate in male Long Evans rats

Early developmental exposure to di(2-ethylhexyl) phthalate (DEHP) has been linked to a variety of neurodevelopmental changes, particularly in rodents. The primary goal of this work was to establish whether acute postnatal exposure to a low dose of DEHP would alter hippocampal dendritic morphology and BDNF and caspase-3 mRNA expression in male and female Long Evans rats. Treatment with DEHP in male rats led to a reduction in spine density on basal and apical dendrites of neurons in the CA3 dorsal hippocampal region compared to vehicle-treated male controls. Dorsal hippocampal BDNF mRNA expression was also down-regulated in male rats exposed to DEHP. No differences in hippocampal spine density or BDNF mRNA expression were observed in female rats treated with DEHP compared to controls. DEHP treatment did not affect hippocampal caspase-3 mRNA expression in male or female rats. These results suggest a gender-specific vulnerability to early developmental DEHP exposure in male rats whereby postnatal DEHP exposure may interfere with normal synaptogenesis and connectivity in the hippocampus. Decreased expression of BDNF mRNA may represent a molecular mechanism underlying the reduction in dendritic spine density observed in hippocampal CA3 neurons. These findings provide initial evidence for a link between developmental exposure to DEHP, reduced levels of BDNF and hippocampal atrophy in male rats.

Age- and species-dependent infiltration of macrophages into the testis of rats and mice exposed to mono-(2-Ethylhexyl) phthalate (MEHP)

The mechanism by which noninfectious testicular inflammation results in infertility is poorly understood. Here the infiltration of CD11b+ immunoreactive testicular interstitial cells (neutrophil, macrophages, dendritic cells) in immature (Postnatal Day [PND] 21, 28, and 35) and adult (PND 56) Fischer rats is described at 12, 24, and 48 h after an oral dose of 1 g/kg mono-(2-ethylhexyl) phthalate (MEHP), a well-described Sertoli cell toxicant. Increases of CD11b+ cells are evident 12 h after MEHP exposure in PND 21 and 28 rats. In PND 28 rats, CD11b+ cells remained significantly elevated at 48 h, while in PND 21 rats, it returned to control levels by 24 h. The peak number of CD11b+ cells in PND 35 rat testis is delayed until 24 h, but remains significantly elevated at 48 h. In PND 56 rats, no increase in CD11b+ cells occurs after MEHP exposure. In PND 21, 28, and 35 rats, a significant increase in monocyte chemoattractant protein-1 (MCP-1) by peritubular myoid cells occurs 12 h after MEHP. Interestingly, MEHP treatment of C57BL/6J mice did not incite an infiltration of CD11b+ cells at either PND 21 or 28. The peak level of germ cell apoptosis observed 24 h after MEHP exposure in young rats is not seen in mice at any age or in PND 56 rats. Taken together, these findings implicate MCP-1 released by peritubular myoid cells in provoking the migration of CD11b+ cells into the immature rat testis early after MEHP exposure and point to a role for CD11b+ cells in triggering germ cell apoptosis in an age- and species-dependent manner.

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

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

Effects of red ginseng extract on zearalenone induced spermatogenesis impairment in rat

Zearalenone (ZEA) is a phenolic resorcylic acid lactone compound produced by several species of Fusarium. ZEA has toxic effects in the testes of domestic and laboratory animals. Korean red ginseng (KRG), the steamed root of Panax ginseng Meyer, has multiple pharmacological effects such as vasorelaxation, anti-thrombosis, anti-hypertension, etc. In this study, we investigated the effects of KRG extract on testicular toxicity induced by ZEA. Rats were treated with 300 mg/kg oral doses of KRG for 4 weeks every other day. The rats were then treated with a single dose of 5 mg/kg ZEA delivered intraperitoneally, whereas control rats received only doses of the vehicle. As a result, germ cell apoptosis induced by ZEA was decreased by KRG pre-treatment. In addition, Fas and Fas-L expression was reduced in rats that received KRG pre-treatment compared to ones treated with ZEA alone. In conclusion, impaired spermatogenesis resulting from ZEA treatment was prevented by KRG through Fas-Fas L modulating.

Involvement of soluble Fas Ligand in germ cell apoptosis in testis of rats undergoing autoimmune orchitis

Experimental autoimmune orchitis (EAO) is a model of chronic inflammation and infertility useful for studying immune and germ cell (GC) interactions. EAO is characterized by severe damage of seminiferous tubules (STs) with GCs that undergo apoptosis and sloughing. Based on previous results showing that Fas-Fas Ligand (L) system is one of the main mediators of apoptosis in EAO, in the present work we studied the involvement of Fas and the soluble form of FasL (sFasL) in GC death induction. EAO was induced in rats by immunization with testis homogenate and adjuvants; control (C) rats were injected with adjuvants; a group of non-immunized normal (N) rats was also studied. Activation of Fas employing an anti-Fas antibody decreased viability (trypan blue exclusion test) and induced apoptosis (TUNEL) of GCs from STs of N and EAO rats, an effect more pronounced on GCs from EAO STs. By Western blot we detected an increase in sFasL content in the testicular fluid of rats with severe EAO compared to N and C rats. By intratesticular injection of FasL conjugated to Strep-Tag molecule (FasL-Strep, BioTAGnology) and its immunofluorescent localization, we demonstrated that sFasL is able to enter the adluminal compartment of the STs. Moreover, FasL-Strep induced GC apoptosis in testicular fragments of N rats. By flow cytometry, we detected an increase in the number of membrane FasL-expressing CD4+ and CD8+ T cells in testis during EAO development but no expression of FasL by macrophages. Our results demonstrate that sFasL is locally produced in the chronically inflamed testis and that this molecule is able to enter the adluminal compartment of STs and induce apoptosis of Fas-bearing GCs.

Mono-(2-ethylhexyl)-phthalate (MEHP) affects ERK-dependent GDNF signalling in mouse stem-progenitor spermatogonia

Many commercial and household products such as lubricants, cosmetics, plastics, and paint contain phthalates, in particular bis-(2-ethyhexyl)-phthalate (DEHP). As a consequence, phthalates have been found in a number of locations and foods (streambeds, household dust, bottled water and dairy products). Epidemiological and animal studies analysing phthalate exposure in males provide evidence of degradation in sperm quality, associated to an increase in the incidence of genital birth defects and testicular cancers. In the testis, spermatogenesis is maintained throughout life by a small number of spermatogonial stem cells (SSCs) that self-renew or differentiate to produce adequate numbers of spermatozoa. Disruption or alteration of SSC self-renewal induce decreased sperm count and sperm quality, or may potentially lead to testicular cancer. GDNF, or glial cell-line-derived neurotrophic factor, is a growth factor that is essential for the self-renewal of SSCs and continuous spermatogenesis. In the present study, the SSC-derived cell line C18-4 was used as a model for preliminary assessment of the effects of mono-(2-ethylhexyl)-phthalate (MEHP, main metabolite of DEHP) on spermatogonial stem cells. Our data demonstrate that MEHP disrupts one of the known GDNF signalling pathways in these cells. MEHP induced a decrease of C18-4 cell viability in a time- and dose-dependent manner, as well as a disruption of ERK1/2 activation but not of SRC signalling. As a result, we observed a decrease of expression of the transcription factor FOS, which is downstream of the GDNF/ERK1/2 axis in these cells. Taken together, our data suggest that MEHP exposure affects SSC proliferation through inhibition of specific signalling molecules.

The effects of di(2-ethylhexyl)phthalate exposure and selenium nutrition on sertoli cell vimentin structure and germ-cell apoptosis in rat testis

This study aimed to investigate the effects of di(2-ethylhexyl)phthalate (DEHP) on Sertoli-cell vimentin filaments and germ-cell apoptosis in testes of pubertal rats at different selenium (Se) status. Se deficiency was produced in 3-weeks old Sprague-Dawley rats by feeding them ≤ 0.05 Se mg/kg diet for 5 weeks, Se supplementation group was on 1 mg Se/kg diet, and DEHP was applied at 1000 mg/kg dose by gavage during the last 10 days of the feeding period. The diet with excess Se did not cause any appreciable alteration in vimentin staining and apoptosis of germ cells, but Se deficiency caused a mild decrease in the intensity of vimentin immunoreactivity and enhanced germ-cell apoptosis significantly (approximately 3-fold, p <0.0033). DEHP exposure caused disruption and collapse of vimentin filaments and significantly induced apoptotic death of germ cells (approximately 8-fold, p <0.0033). In DEHP-exposed Se-deficient animals, compared with the control, collapse of vimentin filaments was more prominent; there was serious damage to the seminiferous epithelium; and a high increment (approximately 25-fold, p <0.0033) in apoptotic germ cells was observed. Thus, Se deficiency exacerbated the toxicity of DEHP on Sertoli cells and spermatogenesis, whereas Se supplementation provided protection. These results put forward the critical role of Se in the modulation of redox status of testicular cells and emphasize the importance of Se status for reproductive health.

Transcriptional suppression of Sertoli cell Timp2 in rodents following mono-(2-ethylhexyl) phthalate exposure is regulated by CEBPA and MYC

Our previous studies showed that the prototypical testicular toxic phthalate monoester, mono-(2-ethylhexyl) phthalate (MEHP), suppresses Sertoli cell TIMP2 levels and allows for the activation of MMP2 in seminiferous epithelium. Activation of MMP2 is important for triggering germ cell apoptosis and instigating germ cell detachment from Sertoli cells. These novel findings led us to examine the transcriptional regulation of the Timp2 gene that accounts for the decrease in Sertoli cell TIMP2 levels following MEHP exposure. Sequential deletion of the Timp2 5'-upstream activating sequence (1200 bp) was used to survey transcriptional activation in the Timp2 promoter region in response to MEHP. Results indicate that under control conditions in rat Sertoli cells, CCAAT enhancer-binding protein alpha (CEBPA) acts as a transactivator to initiate Timp2 gene transcription, and its action is deactivated by exposure to MEHP. By contrast, MYC protein acts as an inhibitor of Timp2 gene transcription, and its activity is increased after MEHP treatment. Addition of follicle-stimulating hormone (FSH) to cells causes translocation of CEBPA into the Sertoli cell nucleus and rescues MEHP-suppressed TIMP2 levels. Down-regulation of TIMP2 expression by MEHP exposure is blocked by forskolin (a cAMP-elevating agent), suggesting that the decrease in Sertoli cell TIMP2 expression following MEHP exposure is cAMP-dependent. Taken together, these data indicate that MEHP both disrupts the FSH-stimulated cAMP signaling pathway and activates the inhibitory signaling mediated by MYC protein, to ultimately account for the cellular mechanism underlying the decreased expression of TIMP2 in Sertoli cells.

Influence of persistent thyroxine reduction on spermatogenesis in rats neonatally exposed to 2,2',4,4',5,5'-hexa-chlorobiphenyl

BACKGROUND

The aim of the present study is to determine the long-term testicular effects of neonatal exposure to PCB153.

METHODS

Sprague-Dawley (SD) rats were treated by oral gavage with PCB153 in corn oil at doses of 0, 0.025, and 2.5 mg/kg per day from postnatal day 3 (PND 3) to PND7. The rats were sacrificed on PND 8 and PND 77. TUNEL in situ detection for testis apoptosis, immunohistochemical staining of thyroid gland for thyroxine (T4), semi-quantitative RT-PCR for mRNA expression, and radioimmunoassay (RIA) for serum hormone levels were performed.

RESULTS

Neonatal treatment with PCB153 at both doses had no obvious effects on body weight, testis weight, testis histology, and germ cell apoptosis, but decreased T4 staining in thyroid gland was observed on PND 8. On PND 77, neonatal treatment with 2.5 mg/kg per day of PCB153 significantly reduced daily sperm product (DSP). Serum levels of thyroxine (T4) and free thyroxine (FT4) decreased, but there were no differences in thyroid-stimulating hormone (TSH) level between the control and exposed groups. Gap junction connexin43 (CX43) and cyclin-dependent kinase inhibitor (CDKI) P27kip1 mRNA expression, which was associated with Sertoli cell differentiation, was significantly reduced after PCB153 treatment on PND 8 but not on PND 77. Androgen-binding protein (ABP) and androgen receptor (AR) mRNA expression, which indicates Sertoli cell maturation, was suppressed on PND 77 after neonatal PCB153 exposure.

CONCLUSIONS

The findings in this study suggest that neonatal exposure to PCB153 induces persistent T4 reduction, which disturbs Sertoli cell function, and subsequently results in alterations in adult spermatogenesis. Birth Defects Res (Part B) 89:18-25, 2010. (c) 2009 Wiley-Liss, Inc.

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

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

Transplantation of Sertoli-Islet Cell Aggregates Formed by Microgravity: Prolonged Survival in Diabetic Rats

Transplantation of pancreatic islets is a potentially attractive treatment for type I diabetes. We generated the transplantable, tissue-like aggregates composed of Sertoli cells and islets in rotating wall vessel bioreactors, SICA (Sertoli-islet cell aggregates), to improve their biological function in vitro and in vivo. The isolated islet equivalent and Sertoli cells were purified from Wistar rats and cocultured for 5 days in bioreactor to generate SICA. The SICA, islets aggregates, and fresh isolated islets were transplanted under the kidney capsule of diabetic Sprague-Dawley (SD) rats, respectively. The functions of different grafts were ascertained by blood glucose level measurements and an in vivo glucose tolerance test. In response to elevated glucose, insulin secretion from SICA was 1.4-fold higher ( P < 0.05, n = 5) than islet aggregates cultured alone. Of the rats that received SICA, 90% (9/10) remained normoglycemic at 60 days post-transplantation, and the survival significantly increased compared with recipients bearing homotypic islets aggregates or freshly isolated islets. The former responded similarly with healthy rats to the glucose tolerance test. Our results support the usefulness of SICA for the treatment of type 1 diabetes without any immunosuppressive agents.

Structural alterations in the seminiferous tubules of rats treated with immunosuppressor tacrolimus

BACKGROUND

Tacrolimus (FK-506) is an immunosuppressant that binds to a specific immunophilin, resulting in the suppression of the cellular immune response during transplant rejection. Except for some alterations in the spermatozoa, testicular morphological alterations have not been described in rats treated with tacrolimus. In the present study, we purpose to evaluate if the treatment with tacrolimus at long term of follow-up interferes in the integrity of the seminiferous tubules.

METHODS

Rats aging 42-day-old received daily subcutaneous injections of 1 mg/kg/day of tacrolimus during 30 (T-30) and 60 (T-60) days; the rats from control groups (C-30 and C-60) received saline solution. The left testes were fixed in 4% formaldehyde and embedded in glycol methacrylate for morphological and morphometric analyses while right testes were fixed in Bouin's liquid and embedded in paraffin for detection of cell death by the TUNEL method. The epithelial and total tubular areas as well as the stages of the seminiferous epithelium and the number of spermatocytes, spermatids and Sertoli cells (SC) per tubule were obtained.

RESULTS

In the treated groups, seminiferous tubules irregularly outlined showed disarranged cellular layers and loss of germ cells probably due to cell death, which was revealed by TUNEL method. In addition to germ cells, structural alterations in the SC and folding of the peritubular tissue were usually observed. The morphometric results revealed significant decrease in the number of SC, spermatocytes, spermatids and significant reduction in the epithelial and total tubular areas.

CONCLUSION

Tacrolimus induces significant histopathological disorders in the seminiferous tubules, resulting in spermatogenic damage and reduction in the number of Sertoli cells. A careful evaluation of the peritubular components will be necessary to clarify if these alterations are related to the effect of FK-506 on the peritubular tissue.

Mono-(2-ethylhexyl) phthalate targets glycogen debranching enzyme and affects glycogen metabolism in rat testis

Phthalate esters are commonly used plasticizers; however, some are suspected to cause reproductive toxicity. Administration of high doses of di-(2-ethylhexyl) phthalate (DEHP) induces germ cell death in male rodents. Mono-(2-ethylhexyl) phthalate (MEHP), a hydrolyzed metabolite of DEHP, appears to be responsible for this testicular toxicity; however, the underlying mechanism of this chemical's action remains unknown. Here, using a one-step affinity purification procedure, we identified glycogen debranching enzyme (GDE) as a phthalate-binding protein. GDE has oligo-1,4-1,4-glucanotransferase and amylo-1,6-glucosidase activities, which are responsible for the complete degradation of glycogen to glucose. Our findings demonstrate that MEHP inhibits the activity of oligo-1,4-1,4-glucanotransferase, but not of amylo-1,6-glucosidase. Among various phthalate esters tested, MEHP specifically binds to and inhibits GDE. We also show that DEHP administration affects glycogen metabolism in rat testis. Thus, inhibition of GDE by MEHP may play a role in germ cell apoptosis in the testis.

TNF alpha-mediated disruption of spermatogenesis in response to Sertoli cell injury in rodents is partially regulated by MMP2

Mono-(2-ethylhexyl) phthalate (MEHP)-induced Sertoli cell injury in peripubertal rodents results in the stimulation of germ cell apoptosis through an interaction of FAS/FASL between these two cell types. During this peripubertal period, an early spike in the incidence of germ cell apoptosis occurs during the first wave of spermatogenesis and is essential for the development of functional spermatogenesis in adults. Our previous observations revealed that soluble tumor necrosis factor alpha (sTNFA) released by germ cells after MEHP exposure consequently resulted in a robust induction of FASL by Sertoli cells. Metalloproteinases (MPs) are essential for processing the TNFA precursor to its soluble form and its ability to bind to TNFRSF1A. The activity of MPs is regulated by the tissue inhibitors of MPs (TIMPs) family. Herein we report that TIMP2 is predominately expressed in Sertoli cells and that protein levels decrease in a time-dependent manner after MEHP exposure. The secretion of matrix MP 2 (MMP2) in primary rat Sertoli cell-germ cell cocultures is induced after MEHP exposure, and its activity increases in a time-dependent manner. The addition of SB-3CT, a specific gelatinase inhibitor, decreases the activity of MMP2 and significantly reduces MEHP-enhanced sTNFA production in primary cocultures. In vivo challenges with SB-3CT decrease sTNFA and reduce MEHP-induced testicular germ cell apoptosis. In primary cocultures, MEHP exposure causes a 9.46-fold increase in sTNFA, while the addition of recombinant MMP2 protein results in a 5.4-fold increase in sTNFA, suggesting that MEHP-induced MMP2 is in part responsible for the activation of TNFA in the testis. Taken together, these observations indicate the distinct role of specific MPs in response to toxicant-induced Sertoli cell injury, providing further insights into the mechanism by which Sertoli cells control the sensitivity of germ cells to undergo apoptosis.

Cross-talk between the Akt and NF-kappaB signaling pathways inhibits MEHP-induced germ cell apoptosis

Phthalates are ubiquitous contaminants that target the testis during in utero and postnatal development. The PI3K/Akt and nuclear factor kappa B (NF-kappaB) signaling pathways have been implicated in germ cell survival following testicular injury. Here we observe that Akt kinase activity increases in the testes of postnatal day 28 wild-type mice following exposure to 500 mg/kg mono-(2-ethylhexyl) phthalate (MEHP), and that loss of Akt1 results in the premature onset of germ cell apoptosis. To further determine the basis for this sensitivity, we investigated the potential for cross-talk between the PI3K/Akt and NF-kappaB signaling pathways. We found a twofold increase in Akt1-dependent phosphorylation of the I kappaB alpha subunit following exposure to 500 mg/kg MEHP and decreased levels of the total I kappaB alpha protein. Examination of the expression of the NF-kappaB subunits, p50 and p65, in Akt1 wild-type testes following MEHP exposure revealed a twofold increase in p50 mRNA at 6 h. Interestingly, in Akt1-deficient testes, basal expression of both the p50 and p65 subunits was elevated 1.6- and 4-fold, respectively. This was due, at least in part, to increased levels of oxidative stress as measured by both superoxide anion formation and increased expression of SMAC/DIABLO, a proapoptotic mitochondrial protein. In wild-type testes, MEHP-induced Akt1-dependent transcription of the antiapoptotic mitochondrial target gene, Bcl-xL. Together, these results indicate that Akt1 plays a role in the initial protection of germ cells following MEHP-induced germ cell apoptosis and that this response is partially mediated by cross-talk with the NF-kappaB signaling pathway and an increased sensitivity to oxidative stress.

Relevance of caspase activity during apoptosis in pubertal rat spermatogenesis

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

Sertoli cell morphological alterations in albino rats treated with etoposide during prepubertal phase

Sertoli cells are very important to spermatogenesis homeostasis because they control germ cell proliferation, differentiation, and death. Damages to Sertoli cells cause germ cell death and affect fertility. Etoposide is a potent chemotherapeutic drug largely used against a variety of cancers. However, this drug also kills normal cells, especially those undergoing rapid proliferation. In the testis, etoposide acts predominantly on intermediate and type B spermatogonia. Etoposide was shown to permanently alter Sertoli cell function when administered to prepubertal rats. Based on this, we decided to investigate whether etoposide can affect Sertoli cell morphology. For this, 25-day-old rats were treated with etoposide during 8 consecutive days and killed at 32, 45, 64, 127, and 180 days old. Testes were fixed in Bouin's liquid or in a mixture of 2.5% glutaraldehyde and 2% formaldehyde for analysis under light and electron microscopes, respectively. Sertoli cells showed morphological alterations such as the presence of chromatin clumps close to the nuclear membrane, nucleus displacement, and cytoplasmic vacuolization. Some Sertoli cells also showed nuclear and cytoplasmic degenerative characteristics, suggesting that etoposide causes severe damages to Sertoli cell.

Disappearance of vimentin in Sertoli cells: a mono(2-ethylhexyl) phthalate effect

The effects of mono(2-ethylhexyl) phthalate (MEHP) on 21-day-old C57Bl/6N mice and their Sertoli cell cultures were studied. Mice were given a single dose of 800 mg/kg MEHP by oral gavage and sacrificed 24 h later. At the same time, testes were harvested from another batch of mice for Sertoli cell cultures. Cultures were subsequently exposed to 0, 1, and 100 nmol/ml MEHP for 0, 3, 6, 12, and 24 h. An antivimentin antibody was used to detect intermediate filament changes in Sertoli cells. Meanwhile, detection of preapoptotic signals and presence of apoptotic cells were done using annexin V-FITC (fluorescein isothiocyanate) and TUNEL (deoxynucleotidyltransferase-mediated dUTP nick end labeling) analyses, respectively. In vivo results showed a correlation between the increase in TUNEL-positive cells and the vimentin disruption in treated mice. Toluidine blue staining of the Sertoli cell cultures showed the increased number and size of vacuoles in Sertoli cell cytoplasm. Vimentin immunohistochemistry showed gradual disappearance of vimentin in Sertoli cell cultures as time and dose increased. Some Sertoli cells were found to be annexin V-FITC positive, but no TUNEL-positive cells were found. Taken together, these results show that the appearance of vacuoles and the vimentin disappearance caused by MEHP in the Sertoli cells are related with each other and can be observed in relation to time. This can be used as an indicator of the loss of mechanical support for spermatogenic cells, which in the end causes apoptosis of spermatogenic cells.

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

Apoptosis plays a major role in controlling both the rate of sperm production and chromosomal abnormalities in adult male testes. However, little is known on the mechanisms controlling induction and execution of apoptosis under physiological conditions. In this work we have uncovered a major role for the cell death receptor Fas in both the extrinsic and intrinsic pathways in normal germ cell apoptosis. We show here that Fas levels increased significantly in a group of germ cell in 25 d old rats, which were identified as spermatocytes and only a few spermatogonia. In addition, we show that isolated spermatocytes expressing high levels of Fas display activation of caspase-8, -9, -3, -6 and -2, as well as increased levels of intracellular calcium and decreased pH, which coincides with stabilization of p53, and transcriptional activation of PUMA and Fas. Therefore, our data strongly suggests that transcriptional up regulation of Fas could predispose a group of spermatocytes to Fas ligand triggering apoptosis by the extrinsic and intrinsic pathway.

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.

Expression of apoptotic genes in testicular germ cells and their modulation by luteinizing hormone

Gonadotropins regulate spermatogenesis by promoting survival and differentiation of germ cells. The molecular markers that are modulated by these hormones to ensure survival however have not been described in great detail. Immunoneutralization of LH in particular leads to apoptotic cell death of the spermatocytes and the round spermatids. In the present study, the expression pattern and regulation of apoptotic markers after specific immunoneutralization of LH in germ cells purified from rats has been investigated at the RNA and protein level. Of the several markers tested, Bax, caspases 1 and 2 and Fadd exhibit differential expression, with the round spermatids expressing higher levels of caspases 1 and 2, and the spermatocytes expressing higher levels of Bax and Fadd. The two cell types therefore exhibit differential expression of apoptotic markers. The cell types also differ with respect to their response to LH antiserum treatment. Fas and Bax both are up-regulated in the round spermatids after 24h of antiserum treatment. In the spermatocytes, Fas was up-regulated as early as 12h after antiserum treatment while Bax was up-regulated after 2 days. These results demonstrate that LH regulates survival of germ cells by modulating the levels of pro and anti-apoptotic proteins.

Influence of TRP53 Status on FAS Membrane Localization, CFLAR (c-FLIP) Ubiquitinylation, and Sensitivity of GC-2spd (ts) Cells to Undergo FAS-Mediated Apoptosis1

Previously we reported that testicular germ cells undergo FAS-mediated apoptosis after exposure of mice to the Sertoli cell toxicant mono-(2-ethylhexyl) phthalate (MEHP) and that this process is partially dependent on the TRP53 protein (p53). Recent reports have suggested that TRP53 may influence the ubiquitinylation and consequent proteosomal degradation of a negative regulator of FAS, CFLAR (L) (c-FLIP [L]), in human colon cancer cells. To further characterize the relationship between CFLAR and TRP53, we used the transformed germ cell line GC-2spd (ts), which harbors a temperature-sensitive Trp53 mutation that allows for TRP53 activation at 32 degrees C. We report here that GC-2 cells expressed a 10-fold increase in basal cell membrane FAS levels and an increased sensitivity to FAS agonistic antibody (JO2)-triggered apoptosis only when they were maintained at the permissive TRP53 temperature. After JO2 exposure, CFLAR (L) protein levels were enhanced only at the nonpermissive TRP53 temperature (37 degrees C) while real-time PCR results indicated an absence of Cflar (L) mRNA changes in GC-2 cells regardless of the temperature. Furthermore, transfection of GC-2 cells at 37 degrees C with siRNA against Cflar resulted in reduction of CFLAR (L) protein levels and increased sensitivity to JO2-mediated apoptosis. The CFLAR (L) protein was also more strongly ubiquitinylated in response to JO2 treatment at the permissive TRP53 temperature. Taken together, these data suggest that the TRP53 protein influences the sensitivity of GC-2 cells to undergo FAS-mediated apoptosis by modulating the expression of FAS on their cell membranes and subsequently influencing the degradation of the antiapoptotic protein CFLAR (L).

Disruption of reproductive development in male rat offspring following in utero exposure to phthalate esters

Certain Phthalate esters have been shown to produce reproductive toxicity in male rodents with an age dependent sensitivity in effects with foetal animals being more sensitive than neonates which are in turn more sensitive than pubertal and adult animals. While the testicular effects of phthalates in rats have been known for more than 30 years, recent attention has been focused on the ability of these agents to produce effects on reproductive development in male offspring after in utero exposure. These esters and in particular di-butyl, di-(2-ethylhexyl) and butyl benzyl phthalates have been shown to produce a syndrome of reproductive abnormalities characterized by malformations of the epididymis, vas deferens, seminal vesicles, prostate, external genitalia (hypospadias), cryptorchidism and testicular injury together with permanent changes (feminization) in the retention of nipples/areolae (sexually dimorphic structures in rodents) and demasculinization of the growth of the perineum resulting in a reduced anogenital distance (AGD). Critical to the induction of these effects is a marked reduction in foetal testicular testosterone production at the critical window for the development of the reproductive tract normally under androgen control. A second Leydig cell product, insl3, is also significantly down regulated and is likely responsible for the cryptorchidism commonly seen in these phthalate-treated animals. The testosterone decrease is mediated by changes in gene expression of a number of enzymes and transport proteins involved in normal testosterone biosynthesis and transport in the foetal Leydig cell. Alterations in the foetal seminiferous cords are also noted after in utero phthalate treatment with the induction of multinucleate gonocytes that contribute to lowered spermatocyte numbers in postnatal animals. The phthalate syndrome of effects on reproductive development has parallels with the reported human testicular dysgenesis syndrome, although no cause and effect relationship exists after exposure of humans to phthalate esters. However humans are exposed to and produce the critical phthalate metabolites that have been detected in blood of the general population, in children and also human amniotic fluid.

The p53 Protein Influences the Sensitivity of Testicular Germ Cells to Mono-(2-Ethylhexyl) Phthalate-Induced Apoptosis by Increasing the Membrane Levels of Fas and DR5 and Decreasing the Intracellular Amount of c-FLIP1

The consequence of mono-(2-ethylhexyl) phthalate (MEHP)-induced injury of testicular Sertoli cells is the Fas-dependent apoptotic elimination of germ cells. In addition to the well-known ability of p53 to regulate the transcription of various apoptosis-associated proteins, p53 also has been implicated in mediating the localization of Fas to the plasma membrane of various cell types in a transcription-independent manner. To resolve the role of p53 in MEHP-mediated testicular toxicity, we used wild-type (p53(+/+)) and p53 knockout (p53(-/-)) mice. A significantly lower incidence of TUNEL-positive germ cells was observed in p53(-/-) mice compared to p53(+/+) mice at 1, 1.5, and 24 h after MEHP exposure. In these same mice, an induction of Fas and death receptor-5 (DR5) in testicular membrane preparations was observed only in p53(+/+) mice. Analyses of mRNA levels in testes of p53(+/+) and p53(-/-) mice by reverse transcription-polymerase chain reaction revealed that increases in membrane levels of Fas occurred in the absence of their transcriptional up-regulation. Processing of procaspase-8 was observed only in MEHP-treated p53(+/+) mice, and this correlated with the observed incidence of germ cell apoptosis. Interestingly, the p53 status of mice also influenced the stability of c-FLIP (L), a caspase-8 inhibitory protein, that was measured at levels approximately two- to fivefold higher in p53(-/-) mice after MEHP-exposure compared to those in p53(+/+) mice. Taken together, these data suggest that MEHP-induced germ cell apoptosis is dependent, in part, on the p53 protein and on its abilities to increase the localization of Fas and DR5 on the germ cell membrane as well as to decrease the cellular levels of c-FLIP (L).

Apoptosis and testicular alterations in albino rats treated with etoposide during the prepubertal phase

Etoposide is a podophyllotoxin semiderivative that is used in a variety of chemotherapy treatments, including therapy for children tumors. This drug promotes the formation of a ternary DNA-topoisomerase II-etoposide complex that triggers apoptosis. The purpose of this work was to analyze the occurrence of apoptosis in the seminiferous epithelium of prepubertal, pubertal, and adult rats treated with 10, 20, and 40 mg/Kg of etoposide during the prepubertal phase, as well as the role of apoptosis in etoposide-induced testicular damage. The rat testes were fixed in Bouin's liquid, and the apoptotic cells were quantified by means of the hematoxylin and eosin (H&E) technique (all groups) and the terminal dUTP nick end labeling (TUNEL) method (prepubertal groups only). The results obtained from both the H&E and TUNEL methods showed an increased frequency of apoptosis in the seminiferous epithelium of treated animals, except for the subgroup that received the 10-mg/Kg dose and was sacrificed 12 hr after the treatment and for the etoposide-treated pubertal group, that did not show cells suggesting apoptosis during H&E analysis. The labeled cells were mainly primary spermatocytes and differentiated spermatogonia. The prepubertal rats showed an etoposide-dose-dependent diminution of differentiated spermatogonia. Etoposide treatment during the prepubertal phase increases the frequency of apoptosis in the seminiferous epithelium, and causes serious harm to male fertility. 2004.

Alterations of Activities of Cytosolic Phospholipase A2 and Arachidonic Acid-Metabolizing Enzymes in Di-(2-Ethylhexyl)Phthalate-Induced Testicular Atrophy

Di-(2-ethylhexyl) phthalate (DEHP), a peroxisome proliferator-activated receptor alpha (PPARalpha) ligand, alters the lipid composition of rat testis, yet the mechanism is unclear. In this study, we investigated the effect of DEHP on the synthesis and metabolism of arachidonic acid (AA), a precursor of eicosanoids, in the testis of prepubertal rats. DEHP (100 and 1,000 mg/kg, 5 days) administration caused a significant reduction in activity of cytosolic phospholipase A2 (cPLA2), the rate-limiting enzyme in the AA and eicosanoid synthesis pathways. DEHP increased the expression of 12-lipoxygenase (12-LOX) in rat testis, whereas cyclooxygenase-2 (COX-2) expression was not altered. Cytochrome P450 4A1 (CYP4A1), a product of a PPARalpha-regulated gene, was markedly increased in the testis by DEHP administration. Taken together, DEHP suppresses cPLA2 activity and induces the AA metabolizing enzymes such as 12-LOX and CYP4A1, resulting in the reduction of AA level. These data suggest that altered AA metabolic cascades may be related to the decrease of testosterone concentration in DEHP-induced testicular atrophy.