The effects of ethylene dimethane sulphonate (EDS) on rat Leydig cells: evidence to support a connective tissue origin of Leydig cells

Testicular toxicity in mice exposed to terephthalic acid in utero and during lactation

Terephthalic acid (TPA) is a worldwide aromatic compound widely used to manufacture resins and the raw material for the polymerization reaction with ethylene glycol to produce polyethylene terephthalate, known as PET. The use of TPA extends to the synthesis of phthalates, plasticizers used in various industrialized products such as toys and cosmetics. The present study aimed to evaluate the testicular toxicity of terephthalic acid on male mice exposed in utero and during lactation to TPA in different developmental windows. The animals were treated intragastric with TPA at stock dispersal dosages corresponding to 0.0014 g/ml and 0.56 g/ml of TPA in 0.5% v/v carboxymethylcellulose as well as the control dose, composed solely of dispersion of carboxymethylcellulose (0.5% v/v). Four experimental windows were established: group I-treatment in utero, in the fetal period (gestational day-GD 10.5-18.5), with euthanasia at GD 18.5; group II-treatment in utero, in the fetal period (GD 10.5-18.5) and the lactational period (postnatal day (PND-15)), with euthanasia at 15 days; group III-treatment in utero in the fetal period (DG 10.5-18.5) with euthanasia at 70 days (age of sexual maturity, PND 70); group IV-treatment in utero, in the fetal period (GD 10.5-18.5) and the lactational period (PND-15), with euthanasia at 70 days (PND70). The results indicate that TPA changes the reproductive parameters (testicular weight, GI, penis size, and anogenital index) only at the dose of 0.56 g/ml in the fetal period. Data on the volumetric ratio of the testis elements show that the dispersion with the highest concentration of TPA significantly altered the blood vessel/capillary, lymphatic vessel, and connective tissue percentages. Only at the dose of 0.56 g/ml TPA was it effective in decreasing the Leydig and Sertoli cell numbers of the euthanized animals at GD 18.5. In group II, TPA increased the diameter and lumen of seminiferous tubules, which indicates that TPA accelerated the maturation process of Sertoli cells without changing the number and the nuclear volume of these cells. The Sertoli and Leydig cell numbers of the 70-day animals exposed to TPA in the gestational and lactational period were similar to the control. Therefore, the present study is the first in the literature to show that TPA presents a testicular toxicity during fetal (DG18.5) and postnatal life (PND15), without repercussion in adulthood (70 days).

Emerging concepts on Leydig cell development in fetal and adult testis

Leydig cells (Lc) reside in the interstitial compartment of the testis and are the target of Luteinising hormone (LH) for Testosterone (T) production, thus critically regulates male fertility. Classical histological studies have identified two morphologically different populations of Lc during testicular development [fetal (FLc) and adult (ALc)]. Recent progress in ex vivo cell/organ culture, genome-wide analysis, genetically manipulated mouse models, lineage tracing, and single-cell RNA-seq experiments have revealed the diverse cellular origins with differential transcriptomic and distinct steroidogenic outputs of these populations. FLc originates from both coelomic epithelium and notch-active Nestin-positive perivascular cells located at the gonad-mesonephros borders, and get specified as Nr5a1 (previously known as Ad4BP/SF-1) expressing cells by embryonic age (E) 12.5 days in fetal mouse testes. These cells produce androstenedione (precursor of T, due to lack of HSD17β3 enzyme) and play critical a role in initial virilization and patterning of the male external genitalia. However, in neonatal testis, FLc undergoes massive regression/dedifferentiation and gradually gets replaced by T-producing ALc. Very recent studies suggest a small fraction (5-20%) of FLc still persists in adult testis. Both Nestin-positive perivascular cells and FLc are considered to be the progenitor populations for ALc. This minireview article summarizes the current understanding of Lc development in fetal and adult testes highlighting their common or diverse cellular (progenitor/stem) origins with respective functional significance in both rodents and primates. (227 words).

Bisphenol AF blocks Leydig cell regeneration from stem cells in male rats

Bisphenol A (BPA) is a ubiquitous environmental pollutant, mainly from the manufacture and use of plastics. The use of BPA is restricted, and its new analogs (including bisphenol AF, BPAF) are being produced to replace it. However, the effect of BPAF on the male reproductive system remains unclear. Here, we report the effect of BPAF on Leydig cell regeneration in rats. Leydig cells were eliminated by ethane dimethane sulfonate (EDS, i.p., 75 mg/kg) and the regeneration began 14 days after its treatment. We gavaged 0, 10, 100, and 200 mg/kg BPAF to rats on post-EDS day 7-28. BPAF significantly reduced serum testosterone and progesterone levels at ≧10 mg/kg. It markedly reduced serum levels of estradiol, luteinizing hormone, and follicle-stimulating hormone at 100 and 200 mg/kg. BPAF significantly reduced Leydig cell number at 200 mg/kg. BPAF significantly down-regulated the expression of Cyp17a1 at doses of 10 mg/kg and higher and the expression of Insl3, Star, Hsd17b3, Hsd11b1 in Leydig cells at 100 and 200 mg/kg, while it induced a significant up-regulation of Fshr, Dhh, and Sox9 in Sertoli cells at 200 mg/kg. BPAF induced oxidative stress and reduced the level of SOD2 at 200 mg/kg. It induced apoptosis and autophagy by increasing the levels of BAX, LC3B, and BECLIN1 and lowering the levels of BCL2 and p62 at 100 and 200 mg/kg. It induced autophagy possibly via decreasing the phosphorylation of AKT1 and mTOR. BPAF also significantly induced ROS production and apoptosis at a concentration of 10 μM, and reduced testosterone synthesis in rat R2C Leydig cells at a concentration of 10 μM in vitro, but did not affect cell viability after 24 h of treatment. In conclusion, BPAF is a novel endocrine disruptor, inhibiting the regeneration of Leydig cells.

Mast Cells in the Mammalian Testis and Epididymis-Animal Models and Detection Methods

Mast cells (MCs) are an evolutionary well-conserved type of cells, mediating and modulating allergic responses in innate immunity and tissue remodeling after chronic inflammation. Among other tissues, they inhabit both the testis and epididymis. In the testis, MCs usually appear in the interstitial compartment in humans, but not in other standard experimental models, like rats and mice. MCs seem to be responsible for testicular tissue fibrosis in different causes of infertility. Although experimental animal models follow the effect on MC activation or penetration to the interstitial tissue like in humans to some extent, there is an inconsistency in the available literature regarding experimental design, animal strain, and detection methods used. This comprehensive review offers an insight into the literature on MCs in mammalian testes and epididymides. We aimed to find the most suitable model for research on MC and offer recommendations for future experimental designs. When using in vivo animal models, tunica albuginea incorporation and standard histological assessment need to be included. Domesticated boar strains kept in modified controlled conditions exhibit the highest similarity to the MC distribution in the human testis. 3D testicular models are promising but need further fine-tuning to become a valid model for MC investigation.

Short-term exposure to perfluorotetradecanoic acid affects the late-stage regeneration of Leydig cells in adult male rats

Perfluorotetradecanoic acid (PFTeDA) is one of perfluoroalkyl substances widely found in the environment. PFTeDA may cause the dysfunction of male reproductive system. However, whether PFTeDA affects the regeneration of Leydig cells remains unclear. The objective of this study was to examine the effects of short-term exposure of PFTeDA on the late-stage maturation of Leydig cells. Fifty-four adult Sprague-Dawley male rats were daily gavaged with PFTeDA (0, 10, or 20 mg/kg body weight) for 10 days, and then were injected intraperitoneally with ethylene dimethane sulfonate (EDS, 75 mg/kg body weight/once) to ablate Leydig cells to induce their regeneration. On day 21 (early stage) and 56 (late stage) after EDS, hormone levels, gene expression, and protein levels were measured. PFTeDA did not affect the early stage of Leydig cell regeneration, because it had no effect on serum testosterone, luteinizing hormone, and follicle-stimulating hormone levels, Leydig cell number, and its gene and protein expression. PFTeDA significantly reduced serum testosterone level and down-regulated the expression of Leydig cell genes (Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Hsd11b1, and Insl3) and their proteins (CYP11A1, HSD3B1, CYP17A1, HSD17B3, and INSL3), decreased the phosphorylation of AKT1 and ERK1/2, as well as lowered sperm count in the epididymis at 20 mg/kg. In conclusion, short-term exposure to PFTeDA blocks the late-stage maturation of Leydig cells.

Neurotrophin-3 stimulates stem Leydig cell proliferation during regeneration in rats

Neurotrophin‐3 (NT‐3) acts as an important growth factor to stimulate and control tissue development. The NT‐3 receptor, TRKC, is expressed in rat testis. Its function in regulation of stem Leydig cell development and its underlying mechanism remain unknown. Here, we reported the role of NT‐3 to regulate stem Leydig cell development in vivo and in vitro. Ethane dimethane sulphonate was used to kill all Leydig cells in adult testis, and NT‐3 (10 and 100 ng/testis) was injected intratesticularly from the 14th day after ethane dimethane sulphonate injection for 14 days. NT‐3 significantly reduced serum testosterone levels at doses of 10 and 100 ng/testis without affecting serum luteinizing hormone and follicle‐stimulating hormone levels. NT‐3 increased CYP11A1‐positive Leydig cell number at 100 ng/testis and lowered Leydig cell size and cytoplasmic size at doses of 10 and 100 ng/testis. After adjustment by the Leydig cell number, NT‐3 significantly down‐regulated the expression of Leydig cell genes (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Hsd11b1, Insl3, Trkc and Nr5a1) and the proteins. NT‐3 increased the phosphorylation of AKT1 and mTOR, decreased the phosphorylation of 4EBP, thereby increasing ATP5O. In vitro study showed that NT‐3 dose‐dependently stimulated EdU incorporation into stem Leydig cells and inhibited stem Leydig cell differentiation into Leydig cells, thus leading to lower medium testosterone levels and lower expression of Lhcgr, Scarb1, Trkc and Nr5a1 and their protein levels. NT‐3 antagonist Celitinib can antagonize NT‐3 action in vitro. In conclusion, the present study demonstrates that NT‐3 stimulates stem Leydig cell proliferation but blocks the differentiation via TRKC receptor.

Development of fetal and adult Leydig cells

BACKGROUND

In mammals, two distinct Leydig cell populations, fetal Leydig cells (FLCs) and adult Leydig cells (ALCs), appear in the prenatal and postnatal testis, respectively. Although the functional differences between these cell types have been well described, the developmental relationship between FLCs and ALCs has not been fully understood. In this review, I focus on the cellular origins of FLCs and ALCs as well as the developmental and functional links between them.

METHODS

I surveyed previous reports about FLC and/or ALC development and summarized the findings.

MAIN FINDINGS

Fetal Leydig cells and ALCs were identified to have separate origins in the fetal and neonatal testis, respectively. However, several studies suggested that FLCs and ALCs share a common progenitor pool. Moreover, perturbation of FLC development at the fetal stage induces ALC dysfunction in adults, suggesting a functional link between FLCs and ALCs. Although the lineage relationship between FLCs and ALCs remains controversial, a recent study suggested that some FLCs dedifferentiate at the fetal stage, and that these cells serve as ALC stem cells.

CONCLUSION

Findings obtained from animal studies might provide clues to the causative mechanisms of male reproductive dysfunctions such as testicular dysgenesis syndrome in humans.

Histological Changes of the Testicular Interstitium during Postnatal Development in Microminipigs

Microminipigs have become an attractive animal model for the toxicology- and pharmacology-related studies because of their manageable size. In this study, the development of the testicular interstitium and steroidogenesis in microminipigs, from 0 to 12 months of age, were investigated. Testicular interstitium was mostly composed of two types of Leydig cells (large and small Leydig cells) and a few macrophages and mast cells. Large Leydig cells were observed in the peritubular area throughout all the ages. Small Leydig cells were present in the interlobular and subcapsular areas at an early age and then gradually converted into large Leydig cells. Testicular composition of the Leydig cells began to increase after 3 months of age, when spermatogenesis was completed, and reached approximately 35% at 12 months. Steroidogenic enzymes in Leydig cells were detected by immunohistochemistry from 0 month of age. Serum testosterone levels increased substantially from 1.5 to 4.5 months of age, which coincided well with the age of sexual development previously reported in microminipigs. Because the interstitial space of the testis has dramatic variations between species, the basic information obtained in the present study will be a useful reference for all the future toxicity evaluations in microminipigs.

Effects of spermatogenic cycle on Stem Leydig cell proliferation and differentiation

We reported previously that stem Leydig cells (SLC) on the surfaces of rat testicular seminiferous tubules are able to differentiate into Leydig cells. The proliferation and differentiation of SLCs seem likely to be regulated by niche cells, including nearby germ and Sertoli cells. Due to the cyclical nature of spermatogenesis, we hypothesized that the changes in the germ cell composition of the seminiferous tubules as spermatogenesis proceeds may affect tubule-associated SLC functions. To test this hypothesis, we compared the ability of SLCs associated with tubules at different stages of the cycle to differentiate into Leydig cells in vitro. SLCs associated with stages IX-XI were more active in proliferation and differentiation than SLCs associated with stages VII-VIII. However, when the SLCs were isolated from each of the two groups of tubules and cultured in vitro, no differences were seen in their ability to proliferate or differentiate. These results suggested that the stage-dependent local factors, not the SLCs themselves, explain the stage-dependent differences in SLC function. TGFB, produced in stage-specific fashion by Sertoli cells, is among the factors shown in previous studies to affect SLC function in vitro. When TGFB inhibitors were included in the cultures of stages IX-XI and VII-VIII tubules, stage-dependent differences in SLC development were reduced, suggesting that TGFB may be among the paracrine factors involved in the stage-dependent differences in SLC function. Taken together, the findings suggest that there is dynamic interaction between SLCs and germ/Sertoli cells within the seminiferous tubules that may affect SLC proliferation and differentiation.

The risk of TESE-induced hypogonadism: a systematic review and meta-analysis

BACKGROUND

Testicular sperm extraction (TESE) is a surgical procedure to retrieve spermatozoa from the testes of men with azoospermia to help them achieve biological parenthood. Although effective, the surgical procedure is not without complications and haematoma, devascularization, inflammation and a decrease in testosterone levels have been described as such. The prevalence and duration of hypogonadism and associated symptoms after TESE have not been studied systematically.

OBJECTIVE AND RATIONALE

In this systematic review we addressed the following research questions: Are serum testosterone levels decreased after TESE and, if so, do these levels recover over time? What is the prevalence of symptoms and signs related to hypogonadism after TESE and are they related to testosterone levels?

SEARCH METHODS

We searched the databases Pubmed and Embase from 1 January 1993 to 26 June 2017. We combined subject headings with terms in title and/or abstract for participants, intervention and outcomes. We included all studies that reported on TESE, regardless of the specific technique used, that measured testosterone and/or LH, and/or had information on signs or symptoms related to hypogonadism as defined by hypogonadism guidelines. An additional inclusion criterion was that studies described these measurements both before and after TESE. The quality of the included studies was assessed using the Risk Of Bias In Non-randomized Studies-of Interventions tool.

OUTCOMES

We identified 15 studies reporting on total testosterone levels of which five studies also reported on testicular volume and one study on erectile dysfunction. Men with Klinefelter syndrome and men with non-obstructive azoospermia had the strongest decrease in total testosterone levels 6 months after TESE, with a mean decrease of 4.1 and 2.7 nmol/l, respectively, which recovered again to baseline levels 26 and 18 months after TESE, respectively. At 6 months after TESE, some studies reported serum total testosterone concentrations below a cut-off value of 12 nmol/l, where symptoms and signs related to hypogonadism may appear. Furthermore, an increased prevalence of erectile dysfunction related to decreased total testosterone levels 6 months after TESE was reported. Also, in some men a decrease in testicular volume was reported. However, it is not clear if this is related to low testosterone levels.

WIDER IMPLICATIONS

The transient, but statistically significant, decrease in total testosterone levels indicates that men are at risk of developing a temporary hypogonadism after TESE, but there is insufficient evidence for whether patients actually experience clinical symptoms in case of decreased serum testosterone levels. To be able to properly counsel TESE patients, more large-scale monitoring on signs and symptoms of hypogonadism, in combination with testosterone measurements, needs to be performed in men undergoing TESE.

Recent progress in understanding the mechanisms of Leydig cell differentiation

Leydig cells in fetal and adult testes play pivotal roles in eliciting male characteristics by producing androgen. Although numerous studies of Leydig cells have been performed, the mechanisms for differentiation of the two cell types (fetal Leydig and adult Leydig cells), their developmental and functional relationship, and their differential characteristics remain largely unclear. Based on recent technical progress in genome-wide analysis and in vitro investigation, novel and fascinating observations concerning the issues above have been obtained. Focusing on fetal and adult Leydig cells, this review summarizes the recent progress that has advanced our understanding of the cells.

Influence of fetal Leydig cells on the development of adult Leydig cell population in rats

Leydig cells are the main endogenous testosterone synthesis cells in the body. Testosterone is an essential hormone in males that affects metabolism, emotion, and pubertal development. However, little is known about the development of Leydig cells and relationship between fetal Leydig cells (FLCs) and adult Leydig cells (ALCs). The aims of this study were to investigate the effect of (FLCs) on ALC development. Our study showed that FLCs in neonatal rat testis can be eliminated by 100 mg/kg ethane dimethane sulfonate (EDS) treatment without affecting the health of newborn rats. Immunohistological results showed that eliminating FLCs led to early re-generation of the ALC population (progenitor Leydig cells [PLCs] and ALCs) accompanied at first by increased and then by decreased serum testosterone, indicating that ALCs which appeared after neonatal EDS treatment were degenerated or had attenuated functions. Our results showed that FLCs were eliminated 4 days after EDS treatment, the ALC population regenerated by 21 days, and serum testosterone levels dramatically decreased at 56 days. Collectively, our results indicate that the ablation of FLCs in neonatal rat results in abnormal development of ALCs. Our study further indicates that abnormal development of Leydig cells in the fetal stage leads to steroid hormone disorders, such as testosterone deficiency, in the adult stage. Therefore, studies of Leydig cell development are important for understanding the pathogenesis of testosterone deficiency or pubertas praecox.

In utero single low-dose exposure of cadmium induces rat fetal Leydig cell dysfunction

Cadmium chloride (Cd) is a potent endocrine disruptor and may cause the malformation in the male reproductive tract. However, the effects of a single in utero exposure to low doses of Cd on fetal Leydig cell development are still unknown. The objective of this study is to investigate the effects of a single in utero exposure to low doses of Cd on rat fetal Leydig cell development. Adult 64-day-old Sprague-Dawley dams received a single intraperitoneal injection of 0, 0.25, 0.5, and 1.0 mg/kg Cd on gestational day 12. Cd dose-dependently reduced testosterone production of fetal testis, lowered fetal Leydig cell numbers, downregulated protein expression levels of Leydig (LHCGR, SCARB1, STAR, CYP11A1, HSD3B1, and CYP17A1), and Sertoli cells (HSD17B3, DHH, and FSHR). In conclusion, our results demonstrated that a single in utero exposure to low doses of Cd blocked fetal Leydig cell development.

A brief exposure to cadmium impairs Leydig cell regeneration in the adult rat testis

Cadmium is an endocrine disruptor, impairing male reproduction. The objective of this study is to investigate whether cadmium affects rat Leydig cell regeneration and to dissect the underlying mechanism. Adult male Sprague-Dawley rats received a single intraperitoneal injection (i.p.) of 0, 0.5 or 1.0 mg/kg of cadmium chloride, followed by ethane dimethane sulfonate (EDS) treatment to eliminate adult Leydig cells 20 days later. Compared to control (0 dose), cadmium treatment reduced serum testosterone levels by days 21, 35, and 56 after EDS treatment. Serum luteinizing hormone (LH) levels were also affected by day 56, the only time point examined. There were fewer regenerated Leydig cells in the cadmium-treated testis on days 35 and 56 after EDS treatment. Further studies demonstrated that the mRNA or protein levels of Leydig (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, and Hsd11b1), non-Leydig (Fshr and Dhh), and gonadotroph (Lhb) cells were also significantly lower in cadmium-treated animals. Since LH and desert hedgehog (DHH) are critical factors for Leydig cell differentiation, our result demonstrated that the lower doses of cadmium exposure, even briefly, may permanently damage Leydig cell regeneration.

Leydig progenitor cells in fetal testis

Testicular Leydig cells play pivotal roles in masculinization of organisms by producing androgens. At least two distinct Leydig cell populations sequentially emerge in the mammalian testis. Leydig cells in the fetal testis (fetal Leydig cells) appear just after initial sex differentiation and induce masculinization of male fetuses. Although there has been a debate on the fate of fetal Leydig cells in the postnatal testis, it has been generally believed that fetal Leydig cells regress and are completely replaced by another Leydig cell population, adult Leydig cells. Recent studies revealed that gene expression patterns are different between fetal and adult Leydig cells and that the androgens produced in fetal Leydig cells are different from those in adult Leydig cells in mice. Although these results suggested that fetal and adult Leydig cells have distinct origins, several recent studies of mouse models support the hypothesis that fetal and adult Leydig cells arise from a common progenitor pool. In this review, we first provide an overview of previous knowledge, mainly from mouse studies, focusing on the cellular origins of fetal Leydig cells and the regulatory mechanisms underlying fetal Leydig cell differentiation. In addition, we will briefly discuss the functional differences of fetal Leydig cells between human and rodents. We will also discuss recent studies with mouse models that give clues for understanding how the progenitor cells in the fetal testis are subsequently destined to become fetal or adult Leydig cells.

Leydig cell stem cells: Identification, proliferation and differentiation

Adult Leydig cells develop from undifferentiated mesenchymal-like stem cells (stem Leydig cells, SLCs) present in the interstitial compartment of the early postnatal testis. Putative SLCs also have been identified in peritubular and perivascular locations of the adult testis. The latter cells, which normally are quiescent, are capable of regenerating new Leydig cells upon the loss of the adult cells. Recent studies have identified several protein markers to identify these cells, including nestin, PDGFRα, COUP-TFII, CD51 and CD90. We have shown that the proliferation of the SLCs is stimulated by DHH, FGF2, PDGFBB, activin and PDGFAA. Suppression of proliferation occurred with TGFβ, androgen and PKA signaling. The differentiation of the SLCs into testosterone-producing Leydig cells was found to be regulated positively by DHH (Desert hedgehog), lithium-induced signaling and activin; and negatively by TGFβ, PDGFBB, FGF2, Notch and Wnt signaling. DHH, by itself, was found to induce SLC differentiation into LH-responsive steroidogenic cells, suggesting that DHH plays a critical role in the commitment of SLC into the Leydig lineage. These studies, taken together, address the function and regulation of low turnover stem cells in a complex, adult organ, and also have potential application to the treatment of androgen deficiency.

A role of KIT receptor signaling for proliferation and differentiation of rat stem Leydig cells in vitro

In the testis, KIT ligand (KITL, also called stem cell factor) is expressed by Sertoli cells and its receptor (c-kit, KIT) is expressed by spermatogonia and Leydig cells. Although KITL-KIT signaling is critical for the spermatogenesis, its roles in Leydig cell development during puberty are not clear. In the present study, we investigated effects of KITL on stem Leydig cell proliferation and differentiation. Using an in vitro culture system of seminiferous tubules from Leydig cell-depleted testis, we found that KITL increased the proliferation activity of putative stem Leydig cells at higher concentration (10 and 100 ng/ml). Low concentration (1 ng/ml) of KITL significantly induced the differentiation of stem Leydig cells via increasing the expression level of steroidogenic acute regulatory protein (Star). In contrast, higher concentration (100 ng/ml) of KITL inhibited the differentiation of stem Leydig cells via inhibiting the steroidogenic enzyme (Cyp11a1, Cyp17a1, and Hsd17b3) expression levels. We cultured rat progenitor Leydig cells with KITL for 48 h and did not find any influence of KITL on the proliferation and androgen production of these cells. In conclusion, KITL is a growth factor that regulates the development of the stem Leydig cell.

Transplantation of alginate-encapsulated seminiferous tubules and interstitial tissue into adult rats: Leydig stem cell differentiation in vivo?

In vivo and in vitro studies were conducted to determine whether testosterone-producing Leydig cells are able to develop from cells associated with rat seminiferous tubules, interstitium, or both. Adult rat seminiferous tubules and interstitium were isolated, encapsulated separately in alginate, and implanted subcutaneously into castrated rats. With implanted tubules, serum testosterone increased through two months. Tubules removed from the implanted rats and incubated with LH produced testosterone, and cells on the tubule surfaces expressed steroidogenic enzymes. With implanted interstitial tissue, serum levels of testosterone remained undetectable. However, co-culture of interstitium plus tubules in vitro resulted in the formation of Leydig cells by both compartments. These results indicate that seminiferous tubules contain both cellular and paracrine factors necessary for the differentiation of Leydig cells, and that the interstitial compartment contains precursor cells capable of forming testosterone-producing Leydig cells but requires stimulation by paracrine factors from the seminiferous tubules to do so.

Regulation of development of rat stem and progenitor Leydig cells by activin

Stem Leydig cells have been demonstrated to differentiate into adult Leydig cells via intermediate stages of progenitor and immature Leydig cells. However, the exact regulatory mechanisms are unclear. We hypothesized that the development of stem or progenitor Leydig cells depends upon locally produced growth factors. Microarray analysis revealed that the expression levels of activin type I receptor (Acvr1) and activin A receptor type II-like 1 (Acvrl1) were stem > progenitor = immature = adult Leydig cells. This indicates that their ligand activin might play an important role in stem and progenitor Leydig cell proliferation and differentiation. When seminiferous tubules were incubated with 1 or 10 ng/mL activin A for 3 days, it concentration-dependently increased EdU incorporation into stem Leydig cells by up to 20-fold. When progenitor Leydig cells were incubated with 1 or 10 ng/mL activin A for 2 days, it concentration-dependently increased ³ H-thymidine incorporation into progenitor Leydig cells by up to 200%. Real-time PCR analysis showed that activin A primarily increased Pcna expression but reduced Star, Hsd3b1, and Cyp17a1 expression levels. Activin A also significantly inhibited the basal and luteinizing hormone-stimulated androgen production. In conclusion, activin A primarily stimulates the proliferation of stem and progenitor Leydig cells, but inhibits the differentiation of stem and progenitor Leydig cells into the Leydig cell lineage in rat testis.

Cell-specific ablation in the testis: what have we learned?

Testicular development and function is the culmination of a complex process of autocrine, paracrine and endocrine interactions between multiple cell types. Dissecting this has classically involved the use of systemic treatments to perturb endocrine function, or more recently, transgenic models to knockout individual genes. However, targeting genes one at a time does not capture the more wide‐ranging role of each cell type in its entirety. An often overlooked, but extremely powerful approach to elucidate cellular function is the use of cell ablation strategies, specifically removing one cellular population and examining the resultant impacts on development and function. Cell ablation studies reveal a more holistic overview of cell–cell interactions. This not only identifies important roles for the ablated cell type, which warrant further downstream study, but also, and importantly, reveals functions within the tissue that occur completely independently of the ablated cell type. To date, cell ablation studies in the testis have specifically removed germ cells, Leydig cells, macrophages and recently Sertoli cells. These studies have provided great leaps in understanding not possible via other approaches; as such, cell ablation represents an essential component in the researchers’ tool‐kit, and should be viewed as a complement to the more mainstream approaches to advancing our understanding of testis biology. In this review, we summarise the cell ablation models used in the testis, and discuss what each of these have taught us about testis development and function.

Steroidogenic fate of the Leydig cells that repopulate the testes of young and aged Brown Norway rats after elimination of the preexisting Leydig cells

The capacity of Brown Norway rat Leydig cells to produce testosterone (T) decreases with aging. In a previous study, we reported that a new generation of Leydig cells can be restored in both young and old rat testes after a single injection of ethane dimethanesulfonate (EDS), and that the abilities of the new Leydig cells in young and old rats to produce T were equivalent. Our objective herein was to compare the steroidogenic fate of the new Leydig cells over time. Young (3 month-old) and old (18 month-old) rats were injected with EDS to eliminate the existing Leydig cells. Ten weeks after EDS, Leydig cells had been restored and T production by the new Leydig cells isolated from young and old rat testes was equivalent. Thirty weeks after EDS treatment of young rats, the ability of the new Leydig cells to produce T had not diminished from 10 weeks post-EDS. In contrast, at 30 weeks post-EDS, T production by new cells in old rat testes was reduced significantly from the 10-week level. Serum T levels at 10 and 30 weeks were consistent with Leydig cell T production. Serum LH levels did not differ in any group. Thus, although the Leydig cells restored to both young and old rats after EDS initially produced T at high, equivalent levels, the cells in the old testes did not maintain this ability. These results suggest that: 1) the cells from which new populations of Leydig cells are derived may differ depending upon the age of the rat; and/or 2) factors extrinsic to the new Leydig cells in young and old testes differ, and it is these differences that are responsible for reductions in T by the newly formed Leydig cells in the testes of old rats.

Regulation of the proliferation and differentiation of Leydig stem cells in the adult testis

We reported previously that stem cells associated with adult rat testis seminiferous tubules are able to give rise to differentiated Leydig cells in vitro. The regulatory mechanisms by which they do so, however, are uncertain. Herein, we hypothesized that the proliferation and differentiation of Leydig cell stem cells (stem Leydig cells, SLCs) depend upon locally produced factors from the seminiferous tubules. Microarray analysis revealed that platelet-derived growth factor receptor alpha (PDGFRalpha) is up-regulated and PDGFRbeta is down-regulated with postnatal differentiation of SLCs. This suggested that their ligands, PDGF-AA and PDGF-BB, respectively, might have important roles in SLC proliferation and differentiation. To test this, we developed a unique in vitro culture system in which SLCs proliferate on the surfaces of cultured seminiferous tubules largely during Week 1 of culture and their progeny subsequently differentiate to testosterone-forming Leydig cells during Weeks 2 through 4. Using this system, seminiferous tubules from adult rat testes were cultured with PDGF-AA or PDGF-BB for up to 4 wk. Both ligands stimulated SLC proliferation during the first week of culture, with PDGF-BB significantly more potent than PDGF-AA. Furthermore, PDGF-AA had a stimulatory effect on SLC differentiation from Weeks 2 through 4 of culture. In contrast, PDGF-BB, which stimulated cell proliferation during Week 1, had a significant inhibitory effect on differentiation during Weeks 2 through 4. These findings, made possible by the development of the seminiferous tubule culture system, reveal distinct roles by locally produced PDGFs in SLC regulation.

Proliferative and nonproliferative lesions of the rat and mouse male reproductive system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and differential diagnosis for classifying microscopic lesions observed in the male reproductive system of laboratory rats and mice, with color microphotographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available for society members electronically on the Internet (http://goreni.org). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for lesions of the male reproductive system in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Identification, proliferation, and differentiation of adult Leydig stem cells

Leydig cells, the testosterone-producing cells of the adult testis, rarely turn over. However, their elimination with ethane dimethanesulfonate (EDS) is followed by the appearance of new, fully functional adult Leydig cells. The cells that give rise to the new Leydig cells have not been well characterized, and little is known about the mechanism by which they are regulated. We isolated cells expressing platelet-derived growth factor receptor-α, but not 3β-hydroxysteroid dehydrogenase (3β-HSD(neg)) from the testes of EDS-treated adult rats. Depending on conditions, these cells proliferated indefinitely or differentiated and produced testosterone. To localize these cells and to determine the effect of the testicular environment on their function, the seminiferous tubules and testicular interstitium were physically separated and cultured. During the first 72 h in culture, 3β-HSD(neg) cells on the tubule surfaces underwent divisions. Some of these cells later expressed 3β-HSD and produced testosterone. Removal of the newly formed 3β-HSD(pos) cells from the tubule surfaces with EDS, followed by further culture of the stripped tubules, resulted in the reappearance of testosterone-producing cells. These results, taken together, suggest that the precursors for newly formed Leydig cells are stem cells, with many if not all situated on the surfaces of the seminiferous tubules. Although normally quiescent, the stem cells are capable of self-renewal and differentiation. The development of the tubule culture system should provide a valuable in vitro approach to assess the role(s) of niche components on the function of adult Leydig stem cells despite their residing in a complex mammalian tissue.

Stem Leydig cells: from fetal to aged animals

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell (ALC) population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Distinct stages of ALC development have been identified and characterized. These include stem Leydig cells (SLCs), progenitor Leydig cells, immature Leydig cells, and ALCs. This review describes our current understanding of the SLCs in the fetal, prenatal, peripubertal, adult, and aged rat testis, as well as recent studies of the differentiation of steroidogenic cells from the stem cells of other organs.

Ontogeny of gonadal sex steroids

Sex steroids are crucial hormones for the proper development and function of the body; they regulate sexual differentiation, the secondary sex characteristics, and sexual behaviour patterns. Gonads are the major sources of sex steroids, although adrenal cortex, placenta, and to a lesser extent other tissues contribute to their production in adult life and at various phases of development. Steroidogenesis of gonadal sex hormones is by definition sexually dimorphic, and involves differences not only in hormonal action but also in regulation and temporal patterns of production. This review focuses on the ontogeny and developmental regulation of steroid hormones in the gonads, with an attempt to detail these processes in humans.

Differential expression and regulation of integral membrane protein 2b in rat male reproductive tissues

AIM

To examine the expression and regulation of integral membrane protein 2b (Itm2b) in rat male reproductive tissues during sexual maturation and under different treatments by in situ hybridization.

METHODS

Testis, epididymis, and vas deferens were collected on days 1-70 to examine Itm2b expression during sexual maturation. To further examine the regulation of Itm2b, adult rats underwent surgical castration and cryptorchidism. Ethylene dimethane sulfonate and busulfan treatments were carried out to test the regulation of Itm2b after destruction of Leydig cells and germ cells.

RESULTS

In testis, Itm2b expression was moderately detected in the adluminal area of seminiferous cords on days 1-10, and detected at a low level in the spermatogonia on days 20 and 30. The Itm2b level was markedly increased in Leydig cells from day 20 to day 70. In epididymis and vas deferens, Itm2b was detected from neonate to adults, and the signal gradually increased in accordance with sexual maturation. Itm2b expression was significantly downregulated in epididymis and vas deferens of castrated rats, and strongly stimulated when castrated rats were treated with testosterone. Cryptorchidism led to a significant decline of Itm2b expression in testis and caput epididymis. Itm2b expression in epididymis and vas deferens was significantly decreased after the Leydig cells were destroyed by ethylene dimethane sulfonate. Busulfan treatment produced no obvious change in Itm2b expression in epididymis or vas deferens.

CONCLUSION

Our data suggested that Itm2b expression is upregulated by testosterone and might play a role in rat male reproduction.

Histological changes of the testis and epididymis in adult rats as a result of Ley dig cell destruction after ethane dimethane sulfonate treatment: a morphometric study

AIM

To quantitatively study the histological changes of the testis and epididymis as a result of a drastic reduction of testosterone secretion.

METHODS

Fourteen adult Sprague-Dawley rats were injected intraperitoneally with ethane dimethane sulfonate (EDS, 75 mg/kg) and the same number of animals were injected with normal saline as a control. At days 7 and 12 (after treatment), respectively, half of the animals from each group were killed. The testes and epididymides were removed and tissue blocks embedded in methacrylate resin. The cell number per testis was estimated using the stereological optical disector and some other parameters were obtained using other morphometric methods.

RESULTS

The EDS treatment resulted in an almost complete elimination of Leydig cells but had no effect on the numbers of Sertoli cells per testis. At day 7 after EDS treatment, many elongated spermatids were retained in the seminiferous epithelium and many round spermatids could be seen in the epididymal ducts. At day 12, a looser arrangement of spermatids and spermatocytes became evident, with apparent narrow empty spaces being formed between germ cells in an approximately radial direction towards the tubule lumen; the numbers (per testis) of non-type B spermatogonia and spermatocytes were similar to controls, whereas that of type B spermatogonia increased by 59%, and that of early round, elongating and late elongated spermatids decreased by 37%, 72% and 52%, respectively.

CONCLUSION

The primary spermatogenic lesions following EDS administration were (i) spermiation failure and (ii) detachment of spermatids and spermatocytes associated with impairment in spermiogenesis and meiosis.

Morphometric Studies on the Testis of Korean Ring-necked Pheasant (Phasianus colchicus karpowi) during the Breeding and Non-breeding Seasons

The purpose of this study was to obtain detailed quantitative information on all cell types in the testis interstitium of Korean ring-necked pheasants and to combine these data with changes in the steroidogenic function of the testis during the breeding and non-breeding seasons. For animals collected during the breeding season, their testis weights, sperm production, serum testosterone levels and leuteinizing hormone (LH)-stimulated testosterone secretion were significantly (p < 0.01) increased compared to the non-breeding season. Testes of the pheasants during the non-breeding season displayed a 98% reduction in testis volume that was associated with a decrease in the absolute volume of seminiferous tubules (98% reduction), tubular lumen (100%), interstitium (90%), blood vessels (84%), lymphatic spaces (97%), Leydig cells (79%), mesenchymal cells (51%) and myoid cells (61%) compared to the breeding season. The numbers of Leydig cells, mesenchymal cells and myoid cells per testis in the breeding season were much higher than in the non-breeding season. Although the mean volume of a Leydig cell was 74% lower in the non-breeding season, the mean volumes of myoid and mesenchymal cells remained unchanged. These results demonstrate that there are striking differences in the testicular structure of the Korean ring-necked pheasant during the breeding and non-breeding seasons. Every structural parameter of the Leydig cell was positively correlated with both testosterone serum levels and LH-stimulated testosterone secretion. The correlation of changes in hormonal status with the morphometric alterations of Leydig cells suggests that the Korean-ring necked pheasant may be used as a model to study structure-function relationships in the avian testis.

Gestational exposure to ethane dimethanesulfonate permanently alters reproductive competence in the CD-1 mouse

Although the adult mouse Leydig cell (LC) has been considered refractory to cytotoxic destruction by ethane dimethanesulfonate (EDS), the potential consequences of exposure during reproductive development in this species are unknown. Herein pregnant CD-1 mice were treated with 160 mg/kg on Gestation Days 11-17, and reproductive development in male offspring was evaluated. Prenatal administration of EDS compromised fetal testosterone (T) levels, compared with controls. EDS-exposed pups recovered their steroidogenic capacities after birth because T production by hCG-stimulated testis parenchyma from prepubertal male offspring was unchanged. However, prepubertal testes from prenatally exposed males contained seminiferous tubules (STs) devoid of germ cells, indicating a delay in spermatogenesis. In adults, some STs in exposed males still contained incomplete germ cell associations corroborating observed reductions in epididymal sperm reserves, fertility ratios, and litter size. Morphometry revealed an EDS-induced increase in interstitial area and a concomitant decrease in ST area, but stereology revealed an unexpected decrease in the number and size of the LCs per testis in exposed males. Paradoxically, there was an increase in both serum LH and T production by adult testis parenchyma, indicating that the LCs were hyperstimulated. These data demonstrate permanent lesions in LC development and spermatogenesis caused by prenatal exposure in mice. Thus, although adult mouse LCs are insensitive to EDS, EDS appears to have direct action on fetal LCs, resulting in abnormal testis development.

Spermatotoxic effect of aflatoxin B(1) in the albino mouse

With the background that the foodborne mycotoxin aflatoxin B(1) (AFB(1)) could be toxic to the male reproductive mechanism in man as well as wild and domestic animals, the present study was aimed at finding the effect of AFB(1) on sperm. The Swiss albino mouse was the test animal. AFB(1,) suspended in corn oil and ethanol (95:5, v/v), was administered intraperitoneally to 90-day-old mice at a daily dose of 50 microg/kg body weight for 7, 15, 35 and 45 days. The analysis consisted of fertility testing and counts, motility and abnormalities of the cauda epididymidal sperm, adopting light- as well as electron-microscopy. The fertility of the treated mice was reduced drastically. Sperm concentration in the epididymis and sperm motility decreased whereas sperm abnormalities increased. In particular, sperm abnormalities like two axonemes in a common cytoplasm, sticking together of heads/tails, etc., were noted. A higher percentage of cauda epididymidal spermatozoa than in the control mice retained the cytoplasmic droplet (CD) and such retention was dependent on the duration of the treatment. Spermatozoa retaining the CD were inhibited in motility. Sperm CD of AFB(1)-treated mice contained electron-dense spherical inclusions, which are hypothesized as lipid inclusions produced from the lamellae through the spherical vesicles of the CD. The results indicate disruption of the spermatogenic as well as androgenic compartments of the testis by AFB(1). The results also reflect an alteration of epididymal function towards the post-testicular sperm maturation process by AFB(1).

Expression of amphiphysin I in Sertoli cells and its implication in spermatogenesis

Amphiphysin I is a protein concentrated in nerve terminals and involved in the endocytosis of synaptic vesicle membrane. We show here that amphiphysin I is expressed in the rat testis, localized exclusively in the Sertoli cells. In the postnatal testicular development, expression of amphiphysin I was not evident at birth, but became significant at postnatal day 15 (P15), coinciding with the onset of spermatogenesis. The expression level of amphiphysin I increased 10-fold between P15 and P25 to reach the adult level. In adult testes reversibly damaged by ethane dimethane sulphonate administration, expression of amphiphysin I did not change following the damage, whereas the protein was transiently converted into its phosphorylated form. The increase in levels of phosphorylated amphiphysin I was closely associated with the severe histological damage to germ cells. The present findings suggest that amphiphysin I in Sertoli cells is involved in spermatogenesis, probably through endocytic processes.

Ultrastructural, morphometric, and hormonal analysis of the effects of testosterone treatment on Leydig cells and other interstitial cells in young adult rats

Early effects of testosterone (T) treatment on the ultrastructure of testicular interstitium were analyzed by morphometry. In T-treated young adult rats the T-LH feed-back loop functioned as expected and the marked increase in peripheral T caused almost complete depletion of peripheral LH. Even though the peripheral LH concentration was almost undetectably low, the Leydig cells maintained regulatory interactions with macrophages, peritubular myoid cells and with the seminiferous epithelium lining the tubular lumina as indicated by the high correlations of morphometric parameters between the Leydig and other cell types. The morphometric alterations in the ultrastructure of Leydig cells suggest that the seminiferous tubules may signal by releasing inhibitory paracrine factors affecting the morphology and function of Leydig cells in T-treated young adult rats. The morphometry of Leydig cells in T-treated young adult rats showed a significant quantifiable reduction in nuclei and organelles involved in steroid synthesis and this analysis also offers a good basis for elucidation of the early effects of testosterone in terms of its contraceptive function as well as of different toxic compounds on reproductive functions.

Expression of neurotrophin receptors in rat testis. Upregulation of TrkA mRNA with hCG treatment

We report the expression of TrkA, TrkB and TrkC mRNAs in adult rat testis. With in situ hybridisation a low signal for TrkB and TrkC could be seen in postmeiotic cells of the seminiferous epithelium, whereas no signal for TrkA could be observed in untreated animals. Animals treated with hCG showed an induction of TrkA mRNA in premeiotic cells 12 h after the treatment, whereas an injection with EDS had no effect on the expression of Trk mRNAs. With the RNAse protection assay a low signal for TrkA was seen in whole testis of hCG treated animals. In staged tubules low expression was seen at stages VII-XI of untreated animals. Animals injected with hCG revealed that TrkA induction was highest during stages VIIcd and VIII of the cycle. The distinct expression pattern of these high-affinity neurotrophin receptors suggests different roles for neurotrophins during spermatogenesis. Induction of TrkA mRNA by hCG suggests that high-affinity binding of NGF during stages VIIcd-VIII in premeiotic cells is under control of the hypothalamic-pituitary-testicular axis.

Effects of thyroid hormone on Leydig cell regeneration in the adult rat following ethane dimethane sulphonate treatment

We tested the effects of thyroid hormone on Leydig cell (LC) regeneration in the adult rat testis after ethane dimethyl sulphonate (EDS) treatment. Ninety-day-old, thyroid-intact (n = 96) and thyroidectomized (n = 5) male Sprague-Dawley rats were injected intraperitoneally (single injection) with EDS (75 mg/kg) to destroy LC. Thyroid-intact, EDS-treated rats were equally divided into three groups (n = 32 per group) and treated as follows: control (saline-injected), hypothyroid (provided 0.1% propyl thiouracil in drinking water), and hyperthyroid (received daily subcutaneous injections of tri-iodothyronine, 100 microg/kg). Testing was done at Days 2, 7, 14, and 21 for thyroid-intact rats and at Day 21 for thyroidectomized rats after the EDS treatment. Leydig cells were absent in control and hyperthyroid rats at Days 2, 7, and 14; in hypothyroid rats at all ages; and in thyroidectomized rats at Day 21. The LC number per testis in hyperthyroid rats was twice as those of controls at Day 21. 3beta-Hydroxysteroid dehydrogenase (LC marker) immunocytochemistry results agreed with these findings. Mesenchymal cell number per testis was similar in the three treatment groups of thyroid-intact rats on Days 2 and 7, but it was different on Days 14 and 21. The highest number was in the hypothyroid rats, and the lowest was in the hyperthyroid rats. Serum testosterone levels could be measured in control rats only on Day 21, were undetectable in hypothyroid rats at all stages, and were detected in hyperthyroid rats on Days 14 and 21. These levels in hyperthyroid rats were twofold greater than those of controls on Day 21. Serum androstenedione levels could be measured only in the hyperthyroid rats on Day 21. Testosterone and androstenedione levels in the incubation media showed similar patterns to those in serum, but with larger values. These findings indicate that hypothyroidism inhibits LC regeneration and hyperthyroidism results in accelerated differentiation of more mesenchymal cells into LC following the EDS treatment. The observations of the EDS-treated, thyroidectomized rats confirmed that the findings in hypothyroid rats were, indeed, due to the deficiency of thyroid hormone.

The potential roles of estrogens in regulating Leydig cell development and function: a review

It is generally agreed that estrogens, principally estradiol-17beta, are synthesized by and act in the testis of mammals, including humans. The site of estradiol synthesis in the testis is generally believed to begin in the Sertoli cell and switch to the Leydig cell during neonatal development where a gonadotropin-regulated aromatase is present. Numerous studies suggest that the primary target cell of estradiol in the testis at all ages is the Leydig cell. In fact, the Leydig cell is known to possess an estrogen receptor that binds estradiol in the classic manner. The mechanism of estradiol action and the role of its receptor in the testis, however, remain unresolved. In Leydig cells, estradiol appears to induce several alterations that are dependent in large part on the developmental stage of the Leydig cell. In the fetal and neonatal testes, estradiol appears to block the ontogenic development of Leydig cells from precursor cells. There is also evidence that estradiol similarly blocks the regeneration of Leydig cells in the testis of mature, ethane dimethylsulfonate-treated animals. Evidence indicates that the precursor cell possesses high levels of estrogen receptors relative to that of the Leydig cell. It is postulated that estradiol is a paracrine factor involved in regulating the interstitial population of Leydig cells. Evidence also indicates that estradiol acts directly in the mature testis to block androgen production. It appears to do so by inhibiting the activities of several steroidogenic enzymes involved in testosterone synthesis. Although the more conventional receptor-mediated mode of action is feasible, several studies have suggested that this action might entail direct competitive inhibition of key steroidogenic enzymes by estradiol. In summary, the net biologic effect of estradiol in the testis appears to be inhibition of androgen production, either by limiting development and growth of the Leydig cell population or through direct action in the Leydig cell.

Identification of markers for precursor and leydig cell differentiation in the adult rat testis following ethane dimethyl sulphonate administration

Administration of ethane dimethane sulphonate (EDS) to adult rats results in the destruction of all Leydig cells, followed by a complete regeneration. We investigated this regeneration process in more detail, using different markers for precursor and developing Leydig cells: the LH receptor, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), transforming growth factor alpha (TGFalpha), and a new marker for Leydig cell maturation, relaxin-like factor (RLF). LH receptor immunoreactivity was found in Leydig cell-depleted testes at 3 and 8 days after EDS administration. The positive (precursor) cells had a mesenchymal-like morphology. The number of LH receptor-positive cells 8 days after EDS administration was 15 +/- 4 per 500 Sertoli cell nuclei. Fifteen days after EDS administration, the first new Leydig cells could be observed. These cells stained positively with both the antibodies against the LH receptor and 3beta-HSD, while some cells also stained positively for TGFalpha. After EDS administration, RLF mRNA disappeared from the testis and reappeared again at the time of the appearance of the first Leydig cells. Concomitant with the increase in the number of Leydig cells, the number of RLF-expressing cells increased. The observations of the present study give further support to the hypothesis that Leydig cell development in the prepubertal testis, and in the adult testis following EDS administration, takes place along the same cell lineage and suggest, therefore, that the adult EDS-treated rat can serve as a model for studying the adult-type Leydig cell development that normally occurs in the prepubertal rat testis.

A switch in the cellular localization of macrophage migration inhibitory factor in the rat testis after ethane dimethane sulfonate treatment

Macrophage migration inhibitory factor (MIF), one of the first cytokines to be discovered, has recently been localized to the Leydig cells in adult rat testes. In the following study, the response of MIF to Leydig cell ablation by the Leydig cell-specific toxin ethane dimethane sulfonate (EDS) was examined in adult male rats. Testicular MIF mRNA and protein in testicular interstitial fluid measured by ELISA and western blot were only marginally reduced by EDS treatment, in spite of the fact that the Leydig cells were completely destroyed within 7 days. Immunohistochemistry using an affinity-purified anti-mouse MIF antibody localized MIF exclusively to the Leydig cells in control testes. At 7 days post-EDS treatment, there were no MIF immunopositive Leydig cells in the interstitium, although distinct MIF immunostaining was observed in the seminiferous tubules, principally in Sertoli cells and residual cytoplasm, and some spermatogonia. A few peritubular and perivascular cells were also labelled at this time, which possibly represented mesenchymal Leydig cell precursors. At 14 and 21 days, Sertoli cell MIF immunoreactivity was observed in only a few tubule cross-sections, while some peritubular and perivascular mesenchymal cells and the re-populating immature Leydig cells were intensely labeled. At 28 days after EDS-treatment, the MIF immunostaining pattern was identical to that of untreated and control testes. The switch in the compartmentalization of MIF protein at 7 days after EDS-treatment was confirmed by western blot analysis of interstitial tissue and seminiferous tubules separated by mechanical dissection. These data establish that Leydig cell-depleted testes continue to produce MIF, and suggest the existence of a mechanism of compensatory cytokine production involving the Sertoli cells. This represents the first demonstration of a hitherto unsuspected pattern of cellular interaction between the Leydig cells and the seminiferous tubules which is consistent with an essential role for MIF in male testicular function.

Intratesticular serotonin affects steroidogenesis in the rat testis

The effect of intratesticular administration of serotonin (5-HT), ketanserin (5-HT2 receptor antagonist), and 5,7-dihydroxytryptamine (5,7-DHT) (the neurotoxin that destroys serotoninergic neural elements) on steroidogenesis was studied in immature and adult rats. In adults, bilateral intratesticular injection of 5-HT resulted in a significant decrease in basal but not in hCG-stimulated testosterone secretion and in serum testosterone concentration, whereas ketanserin induced a significant rise in steroidogenesis 1 h post-treatment. There was no effect 1 day after administration of 5-HT or ketanserin, and 7 days after the injection of 5,7-DHT. In immature rats 1 day after bilateral testicular administration of ketanserin, basal testosterone secretion in vitro was significantly suppressed. In immature hemicastrates, local injection of 5-HT resulted (1 day post-treatment) in a significant rise in steroidogenesis while administration of 5,7-DHT decreased testosterone secretion 7 days after the injection of the neurotoxin. The results indicate that in adult rats 5-HT exerts a suppressive, whereas in immature rats, a stimulatory action on steroidogenesis occurs. Data also suggest that, in both age groups, the effect of 5-HT is mediated through 5-HT2 receptors. The observation that in immatures administration of the neurotoxin resulted in an effect similar to that found following the treatment with the receptor antagonist suggests that, in this age group, 5-HT derived from local neural elements might also be involved in the control of 5-HT on Leydig cell steroidogenesis.

Restoration of Leydig cells after repeated administration of ethane dimethanesulfonate in adult rats

Adult male rats were repeatedly treated with ethane dimethanesulfonate (EDS), an agent known to destroy Leydig cells selectively. Following a second injection, changes in serum testosterone levels and histological and morphometric changes of Leydig cells showed the time course to be similar to those after the first treatment. The number and volume of Leydig cells markedly decreased at day 2, began to increase from day 7, and recovered to the values of the control rats at day 30, concomitant with the changes of serum testosterone levels. Cells in the interstitial tissue labeled with bromodeoxyuridine markedly increased in number at day 2, gradually decreased thereafter, and returned to the values of the controls at day 14. During this period, cells undergoing mitosis were seen, their type unable to be determined, but were presumed to be regenerating Leydig cells. Even 30 days following four treatments with intervals of 30 days each, serum testosterone levels were the same as those in the controls. Also the numerical and volume densities of Leydig cells and the volume of an average Leydig cell were the same as those of the controls. Mitosis was observed in mature Leydig cells at this period, if any. It appears that new Leydig cells began to proliferate by division earlier than 14 days after EDS, allowing that there were several stages of proliferation, and that the source of reappearing Leydig cells may not be a limited number of precursor cells, implying the presence of stem cells for Leydig cells.

The transcriptional and translational control of diazepam binding inhibitor expression in rat male germ-line cells

The diazepam binding inhibitor [DBI, also known as acyl-CoA-binding protein, (ACBP), or endozepine] is a 10-kD protein that has been suggested to be involved in the regulation of several biological processes such as acyl-CoA metabolism, steroidogenesis, insulin secretion, and gamma-aminobutyric acid type A (GABA(A))/benzodiazepine receptor modulation. DBI has been cloned from vertebrates, insects, plants, and yeasts. In mammals, DBI is expressed in almost all the tissues studied. Nevertheless, DBI expression is restricted to specific cell types. Here we have studied DBI gene expression in the germ-line cells of rat testis. The DBI gene was intensively transcribed in postmeiotic round spermatids from stages VI to VIII of the seminiferous epithelial cycle. A prominent, spermatid-specific upstream transcription initiation site was identified in addition to the multiple common transcriptional initiation sites found in the somatic tissues. However, no DBI protein was detected in round spermatids, suggesting that the DBI transcripts were translationally arrested. The DBI protein was detected in the late spermatogenic stages starting from elongating spermatids from step 18 (stage VI) onward. The DBI protein was also detected in mature spermatozoa and in ejaculated human sperms. The majority of DBI was located at the middle piece of the spermatozoons tail enriched with mitochondria. On the basis of this observation and the well-established role of DBI in acyl-CoA metabolism, we propose that DBI expression in spermatozoa reflects the usage of fatty acids as a primary energy source by spermatozoa. The biological function of DBI in spermatozoa could thus be related to the motility function of sperm.

Morphometric study of the testicular interstitial tissue of the monkey Cebus apella during postnatal development

The purpose of this study was to evaluate the developmental changes of the Leydig cells and their precursors during postnatal development in the monkey Cebus apella. Four groups of monkeys were studied: neonatal, infantile, early pubertal and late pubertal. Light microscopy, immunocytochemistry, electron microscopy and stereological studies were performed to determine cytologic and cytochemical characteristics, volume density, absolute volume and cell counts of Leydig cells. In the interstitial tissue two components were recognized: specific interstitium comprising mature and immature Leydig cells and differentiating Leydig cell precursors, and non-specific interstitium including connective tissue and blood vessels. Mature Leydig cells were polygonal with a round, euchromatic nucleus and abundant cytoplasm. Immature Leydig cells were more elongated and the nucleus showed more heterochromatin. Mature and immature Leydig cells showed either a pale- or a dark-stained cytoplasm. Pale Leydig cells showed abundant smooth endoplasmic reticulum (SER), mitochondria with tubular cristae and glycogen granules. The SER of dark Leydig cells consisted of abundant flat cisternae, only few glycogen inclusions and abundant lipid droplets. All Leydig cells were intensely reactive for 3beta-hydrohysteroid dehydrogenase (3beta-HSD). Some peritubular cells acquired nuclear and cytoplasmic characteristics that indicated that they were differentiating to Leydig cells, as evidenced by the strong 3beta-HSD positivity found in scattered elongated cells of the peritubular tissue. Absolute interstitial volume increased from birth to the end of puberty due to an increment in Leydig cells numbers and size. The mature and immature Leydig cell populations showed a different evolution during postnatal development. While immature Leydig cells increased 7-fold from the neonatal to the early pubertal period and increased at a lower rate during puberty, mature Leydig cells remained stable until early puberty and increased significantly during late pubertal development.

Signs of aging are apparent in the testis interstitium of Sprague Dawley rats at 6 months of age

The present study investigated the effects of aging in the testis interstitium in Sprague Dawley rats. Rats of 3, 6 and 24 months of age were used. Testes of rats (n = 5) were fixed by whole body perfusion using a fixative containing 2.5% glutaraldehyde in cacodylate buffer, processed and embedded in eponaraldite. Using 1 microns sections stained with methylene blue, qualitative and quantitative morphological studies were performed. Purified Leydig cell preparations, obtained by collagenase digestion followed by elutriation and density gradient centrifugation, were used to determine luteinizing hormone (LH; 100 ng/ml) stimulated testosterone secretory capacity per Leydig cell in vitro. Testosterone levels in the incubation medium, and testosterone and luteinizing hormone levels in serum of these three groups of rats were determined via radioimmunoassay. Morphological studies revealed that Leydig cells were more abundant in the testis interstitium at 6 and 24 months when compared to 3 months. Moreover, collagen fiber bundles were more frequently observed in the testis interstitium at older ages. Blood vessels of the testis interstitium in 24-month-old rats frequently showed partial and complete occlusion of their lumen and thickening of vessel walls. This feature was also present at 6 months, but less frequently. The results of the stereological studies revealed that the volumes of seminiferous tubules, interstitium and Leydig cells per testis was significantly higher (P < 0.05), at 6 and 24 months of age than those at 3 months. Moreover, volume of macrophages per testis was observed to be significantly higher (P < 0.05) at 6 months when compared to 3 and 24 months, and volume of connective tissue cells per testis was observed to be significantly lower (P < 0.05) at 6 and 24 months when compared to 3 months of age. No significant difference (P > 0.05) was observed for the volume of lymphatic space per testis in the three age groups studied. Volume of interstitial blood vessels per testis was not significantly different at 3 and 6 months of age, but a significantly greater (P < 0.05) volume was observed at 24 months. However, at 6 and 24 months, only 71% and 31% of the total blood vessel volumes respectively had completely open lumen in them; the rest of the blood vessels were either partially (12.5% at 6 months and 17% at 24 months) or completely (16.5% at 6 months and 52% at 24 months) occluded. The number of Leydig cells per testis was doubled at 6 and 24 months of age compared to 3 months. The average volume of a Leydig cell was not significantly different between 3 and 6 months of age, however, at 24 months a significantly lower (P < 0.05) value was observed. LH stimulated testosterone secretory capacity per Leydig cell in vitro was reduced by 50% at 6 months of age compared to 3 months; a further significant (P < 0.05) reduction was observed at 24 months. Serum testosterone and LH levels were not significantly different between 3 and 6 months of age but at 24 months a significantly lower (P < 0.05) value was observed for both of these hormones. In summary, the present study demonstrated many changes in the components of the testis interstitium in the aged Sprague Dawley rat. Modifications in the blood vessels and the occurrence of abundant collagen fibers in the interstitial space could possibly contribute to the reduced testosterone secretory capacity per Leydig cell with advancing in age. The observed Leydig cell hyperplasia could be suggested as a compensatory effort to maintain the normal androgen status of the aged rat, which is rather successful at 6 months but unsuccessful at 24 months. This investigation further revealed that these characteristic changes in the aged testis interstitium at 24 months are also present to some extent at 6 months of age in Sprague Dawley rats, suggesting that aging of the testis in this strain of rats commences early in life.