Thyroid hormone and anti-Mullerian hormone (AMH) on Leydig cell differentiation: studies using C57BL/6 mice and AMH over expressing mice

Although the thyroid hormone has stimulatory effects and anti-Mullerian hormone (AMH) has inhibitory effects on prepubertal Leydig cell (LC) differentiation, it is important to find out whether the stimulatory effect of thyroid hormone could overcome the inhibitory effect of AMH on postnatal LC differentiation. Therefore, the objective of the present study was to use the anti-Mullerian hormone overexpressing mouse (AMH++) model to understand the simultaneous effects of AMH and thyroid hormone on postnatal LC differentiation, proliferation, maturation and function and to test whether the inhibitory effect of AMH could be overcome by the stimulatory effect of the thyroid hormone. Four age groups (7, 21, 40, 90 days) of control (C57BL/6; C) and AMH++ were used. Mice received either saline or triiodothyronine (T3) SC injections daily from birth to 21days. The four experimental groups were C, C+T3, AMH++ and AMH+T3. Body and testis weights of both C+T3 and AMH+T3 mice were significantly reduced at days 21, 40 and 90, compared to their age-matched saline-treated mice (C and AMH++). BrdU studies revealed the absence of LC proliferation in AMH++ mice at day7, however, same-aged mice of C+T3 and AMH+T3 mice showed increased LC proliferation; the rate was highest in C+T3 at day21. C+T3 mice of day 21 had more LC than C mice as well as AMH+T3 and AMH++ mice. At days 40 and 90, LC number/testis in C+T3 was lower than C, however, AMH+T3 had higher LC numbers than AMH++ mice. Cellular apoptosis was not seen as the cause of reduced LC numbers. Serum testosterone was not different among groups at day 21, but significantly higher levels were seen in AMH+T3 compared to AMH++ mice at days 40 and 90. Similar pattern was seen for luteinizing hormone (LH)-stimulated testicular testosterone and androstenedione production in vitro. Findings suggest that T3-treatment for the first postnatal 21 days was able to partially counteract the inhibitory effect of AMH on prepubertal LC differentiation. Whether continuation of the T3-treatment beyond 21 days would have resulted in complete removal of this inhibition, is a question that needs to be addressed.

Spermatogenetic but not immunological defects in mice lacking the τCstF-64 polyadenylation protein

Alternative polyadenylation controls expression of genes in many tissues including immune cells and male germ cells. The τCstF-64 polyadenylation protein is expressed in both cell types, and we previously showed that Cstf2t, the gene encoding τCstF-64 was necessary for spermatogenesis and fertilization. Here we examine consequences of τCstF-64 loss in both germ cells and immune cells. Spermatozoa from Cstf2t null mutant (Cstf2t(-/-)) mice of ages ranging from 60 to 108 days postpartum exhibited severe defects in motility and morphology that were correlated with a decrease in numbers of round spermatids. Spermatozoa in these mice also displayed severe morphological defects at every age, especially in the head and midpiece. In the testicular epithelium, we saw normal numbers of cells in earlier stages of spermatogenesis, but reduced numbers of round spermatids in Cstf2t(-/-) mice. Although Leydig cell numbers were normal, we did observe reduced levels of plasma testosterone in the knockout animals, suggesting that reduced androgen might also be contributing to the Cstf2t(-/-) phenotype. Finally, while τCstF-64 was expressed in a variety of immune cell types in wild type mice, we did not find differences in secreted IgG or IgM or changes in immune cell populations in Cstf2t(-/-) mice, suggesting that τCstF-64 function in immune cells is either redundant or vestigial. Together, these data show that τCstF-64 function is primarily to support spermatogenesis, but only incidentally to support immune cell function.

Alteration in testicular cell components following transiently induced ischaemia in prepubertal bulls

The aim of the present study was to evaluate transient testicular ischaemia (induced using elastrator bands) in Jersey calves on testicular morphology and development. Treatments (at 27 +/- 5 days of age) consisted of control (0 h banding) and banding for 2, 4 or 8 h (n = 4 in each group). After castration (at 60 +/- 5 days of age), the right testis was used for calculation of cell components per testis according to the point-counting method. Bodyweight (59.8 +/- 6.2 kg) and scrotal circumference (SC) at banding (9.1 +/- 0.2 cm) did not differ between groups. Fresh testis weight, scrotal temperature immediately before band removal and daily SC growth were decreased in ischaemic (4 and 8 h) testes compared with controls (P < 0.05). In addition, the number of Sertoli and Leydig cells was significantly reduced in the 8 h ischaemic treatment group (P < 0.05). Transiently induced ischaemia significantly decreased the number of germ cells in the 8 h ischaemic treatment group (13 +/- 5 x 10(6) cells) compared with the 0, 2 and 4 h ischaemic treatment groups (38 +/- 6, 32 +/- 6 and 33 +/- 5 x 10(6) cells, respectively; P < 0.05). These results suggest that transiently induced ischaemia for 8 h significantly decreases the number of germ, Sertoli and Leydig cells in prepubertal testis.

228 RECIPIENT PREPARATION FOR SPERMATOGONIAL STEM CELL TRANSPLANTATION: ALTERATION IN TESTICULAR CELL COMPONENTS FOLLOWING TRANSIENTLY INDUCED ISCHEMIA

Depletion of endogenous spermatogonial stem cells using busulfan (Brinster et al. 2003 Biol. Reprod. 69, 412–420) or irradiation (Izadyar et al. 2003 Reproduction 126, 765–774) have been used in preparation of recipient animals prior to transplantation; however, both techniques are not without compromises (severe bone marrow depression or specialized radiotherapy equipment required). Induced testicular ischemia in rams altered spermatic epithelium with germ cell-depleted seminiferous tubules (Markey et al. 1994 Reprod. Fertil. 101, 643–650). The objective was to evaluate testicular transiently induced ischemia (using elastrator bands) in Jersey calves on testicular morphology and development. Treatments (at 27 ± 5 days of age) consisted of control (0, n = 4), banding for periods of 2 h (2, n = 4), 4 h (4, n = 4), and 8 h (8, n = 4). After castration (age: 60 ± 5 days), the right testis of each animal was used for calculation of cell components per testis according to the point counting method. Data were analyzed using the MIXED procedure of SAS (SAS Institute, Inc., Cary, NC, USA). Body weight (59.8 ± 6.2 kg) and scrotal circumference (SC) at banding (9.1 ± 0.2 cm) did not differ between treatments. Fresh testis weight (TW), scrotal temperature immediately before banding removal (ST), and daily scrotal circumference growth (SC) were decreased (4 and 8 h) in ischemic testes compared to controls (Table 1: P < 0.05). In addition, Sertoli and Leydig cells were severely reduced in the 8-h ischemic treatment (Table 1: P < 0.05). Transiently induced ischemia significantly decreased the number of germ cells in the 8-h group, compared to the 0-, 2-, and 4-h groups (Table 1: P < 0.05). These results suggest that transiently induced ischemia significantly decreases the number of germ, Sertoli, and Leydig cells in the testis. Therefore, these present findings could be applicable for preparation of recipient animals through depletion of endogenous germ cells within the seminiferous tubules. This procedure may provide a suitable environment for transplanted donor germ cell colonization in prepubertal recipient bulls. Table 1. Parameters evaluated under transient-induced ischemia treatments

Expression of insulin-like peptide 3 in the postnatal rat Leydig cell lineage: timing and effects of triiodothyronine-treatment

Fetal (FLC) and adult Leydig cells (ALC) secrete insulin-like peptide 3 (INSL3), which is linked to cryptorchidism in the newborn rat. Its gene regulation appears to be independent of that for most steroidogenic enzymes, and may thus be a marker for other aspects of ALC differentiation. Our study examined the following on INSL3 peptide expression in ALC lineage (i) timing, (ii) which cell stage, and (iii) effects of triiodothyronine (T3). Male Sprague-Dawley (SD) rats of postnatal days (pd) 1, 5, 7-21, 28, 40, 60, and 90 were used for the objectives (i) and (ii). For the objective (iii), control and T3-treated (daily T3 SC, 50 mug/kg bw) SD rats of pd7-16 and 21 were used. INSL3 was immunolocalized in Bouin's-fixed testes. FLC were positive and mesenchymal and Leydig progenitor cells were negative for INSL3 at tested ages. INSL3 in ALC lineage was first detected in newly formed ALC on pd16, although they were present from pd10. The intensity of INSL3 label was greater in ALC of pd40-90. ALC were present in T3-treated testes at pd9, but INSL3 first detected in them was on pd12. While INSL3 in FLC regulates testicular descent, INSL3 in ALC still has no well-defined function. However, its pattern of expression correlates temporally with the development of steroidogenic function and spermatogenesis. Thus, the delay between ALC differentiation and INSL3 expression in them implies that INSL3 in ALC is associated with maturation. The advancement of INSL3 expression in the ALC of T3-treated rats implies that this function is established earlier with T3-treatment.

Changes in the testis seminiferous tubules and interstitium in prepubertal bull calves immunised against inhibin at the time of gonadotropin administration

The aim of the present study was to evaluate the effects of gonadotropin administration at initiation of inhibin passive immunisation in Jersey bull calves (age 27 � 5 days) on testicular morphology and development. Primary treatments consisted of control (keyhole limpet haemocyanin, KLH; n = 9) or immunisation against inhibin (INH; n = 9). Subsets of calves were randomly assigned within primary treatments (TRT) to receive saline ( n = 3 per TRT), follicle-stimulating hormone (FSH; n = 3 per TRT) or gonadotrophin-releasing hormone (GnRH, n = 3 per TRT). The right testis was removed (age 118 � 5 days) to determine volumes of testicular components and cell numbers per testis using stereology. Data were analysed using the MIXED procedure of the SAS program. Antibody titres against inhibin were increased in INH bulls compared with KLH bulls (P < 0.05). In addition, a significant immunisation � hormone treatment interaction was noted for the number of germ cells. Administration of FSH at the time of initial immunisation against inhibin significantly increased the number of germ cells (92.2 � 9 � 106 cells) compared with INH+saline bulls (54.9 � 10 � 106 cells), with INH+GnRH bulls having an intermediate number of cells (64.5 � 9 � 106 cells; P < 0.05). These results suggest that gonadotropin administration at the time of inhibin immunisation increases the number of germ cells in the testis.

Detection of platelet-derived growth factor-alpha (PDGF-A) protein in cells of Leydig lineage in the postnatal rat testis

Platelet-derived growth factor-A (PDGF-A) is a locally produced growth factor in the rat testis secreted by both Sertoli cells and Leydig cells. It has been suggested that PDGF-A may be involved in modulation of testosterone production and may be essential to Leydig cell differentiation, however it is not known at what stage of differentiation PDGF-A begins to be expressed in the cells of Leydig lineage in the postnatal rat testis. Therefore, the objectives of this research were to determine at what postnatal age and in which cell type is PDGF-A first expressed in cells of the adult Leydig cell lineage, and does PDGF-A expression coincide with expression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), an indicator of steroid hormone synthesis. Male Sprague Dawley rats of postnatal day 1, 7, 9-14, 21, 28, 40, 60, and 90 were used (n=6). Animals were euthanized and their testicles removed, fixed in Bouin's solution, embedded in paraffin, and 5 micrometers sections were prepared. Immunolocalization of PDGF-A and 3beta-HSD was carried out using a peroxidase-streptavidin-biotin method. PDGF-A was first detected in cells of the Leydig cell lineage at postnatal day 10 in progenitor cells, which were surrounding the seminiferous tubules (peritubular). These cells were confirmed to be the progenitor cells and not the mesenchymal or any other spindle-shaped cells in the testis interstitium by immunolocalization of 3beta-HSD and PDGF-A in the cells in adjacent sections of testis tissue from rats of postnatal days 10-14. After postnatal day 10, PDGF-A was continued to be expressed in subsequent cells of the Leydig lineage through day 90 (adult), however, was not present in peritubular mesenchymal precursor cells of the Leydig cell lineage or any other spindle-shaped cells in the testis interstitium at any tested age. These results revealed that PDGF-A first appears in Leydig progenitor cells in the postnatal rat testis at the onset of mesenchymal cell differentiation into progenitor cells at postnatal day 10 and suggest that a functional role(s) of PDGF-A in postnatally differentiated Leydig cells in the rat testis is established at the time of the onset of postnatal Leydig stem cell differentiation. It is suggested that the significance of the first expression of PDGF-A in the Leydig progenitor cells may be associated with inducing cell proliferation and migration of this cell away from the peritubular region during Leydig cell differentiation.

Detection of anti-Mullerian hormone receptor II protein in the postnatal rat testis from birth to sexual maturity

Anti-Mullerian hormone (AMH) produced by the immature Sertoli cells negatively regulates the postnatal Leydig cell (i.e. adult Leydig cells/ALC) differentiation, however, the mechanism is sparsely understood. AMH negatively regulates the steroidogenic function of fetal Leydig cells (FLC) and ALC. However, when this function is established in the ALC lineage and whether AMH has a function in FLC in the postnatal testis are not known. Therefore, the objectives of this study were to examine the presence of AMH receptor type II (AMHR-II) in FLC and cells in the ALC lineage in the postnatal mammalian testis using the rat model Male Sprague Dawley rats of days 1, 5, 7-21, 28, 40, 60 and 90 were used. AMHR-II in testicular interstitial cells was detected in testis tissue using immunocytochemistry. Findings showed that the mesenchymal and the progenitor cells of the ALC lineage, were negative for AMHR-II. The newly formed ALC were the first cell type of the ALC lineage to show positive labeling for AMHR-II, and the first detection was on postnatal day 13, although they were present in the testis from day 10. From days 13-28, labeling intensity for AMHR-II in the ALC was much weaker than those at days 40-90. FLC were also positive. The time lag between the first detection of the newly formed ALC in the testis and the first detection of AMHR-II in them suggests that the establishment of the negative regulatory role of AMH on ALC steroidogenesis does not take place immediately upon their differentiation; no change in cell size occurs during this period. The absence of AMHR-II in mesenchymal cells suggests that it is unlikely that the negative regulatory effect of AMH on ALC differentiation in the postnatal testis is achieved via a direct action of AMH on mesenchymal cells. The presence of AMHR-II in postnatal FLC suggests a possible role by AMH on FLC, which warrants future investigations.

308 TESTICULAR DEVELOPMENT IN PREPUBERTAL JERSEY BULL CALVES IMMUNIZED AGAINST INHIBIN

Previous studies have shown that immunization against inhibin (INH) in bull calves increased subsequent sperm production (Martin et al. 1991 Biol. Reprod. 45, 73; Bame et al. 1996 Biol. Reprod. 54, 328). The objective of the current study was to evaluate the effectiveness of gonadotropin administration at initiation of inhibin immunization in bull calves on testicular morphology. The study was performed using the inhibin peptide (bovine inhibin α1–26) conjugated to keyhole limpet hemocyanin (KLH). Primary treatments administered to Jersey bull calves (initial immunization at 27 ± 5 days of age; Day 1 of the experimental period) consisted of control (KLH, 250 µg, n = 9) or immunization (INH; 500 μg INH: 250 µg KLH, n = 9) with each emulsified in 2 mL of Freund's complete adjuvant (FCA). Booster immunizations (identical preparation in FCA) occurred every 21 days with the last administration on Day 84 of the trial. Subsets of calves were randomly assigned within primary treatments (TRT) to receive saline (1 mL, n = 3/TRT), FSH (20 mg, n = 3/TRT), or GnRH (50 μg, n = 3/TRT) every 8 h (0600, 1400, and 2200 h) from Day 1 to Day 3 of the study. Blood samples were obtained daily from Days 0–14 and weekly until testes collection (Day 91) for FSH, LH, testosterone (T), and determination of antibody titers. Body weight and scrotal circumference (SC) were measured at each immunization and immediately before testes removal. The right testis was weighed and used for absolute volume calculation of cell components per testis. Tissue sections were examined using a light microscope (400×). For each cell type, absolute volume of Sertoli, Leydig, and germ cells were counted according to the point counting method. Data were analyzed using MIXED procedure of SAS (SaS Institute, Inc., Cary, NC, USA). Antibody titers were increased in INH bulls compared to KLH bulls (P < 0.05) during the experimental period. Body weight (89.8 ± 14.2 kg), SC (14.6 ± 1.3 cm), and single testicular weight (19.2 ± 6.2 g) recorded at the end of the experimental period did not differ between treatments. Neither serum concentrations of FSH, LH, and T nor population of Leydig and Sertoli cells differed between treatment groups. However, a significant immunization X hormone treatment interaction was noted for germ cell volume per testis (P < 0.008). Administration of FSH at the time of initial immunization against inhibin significantly increased germ cell population (1.22 ± 0.1 cm3) compared to INH-saline bulls (0.64 ± 0.1 cm3) with INH-GnRH bulls intermediate (0.84 ± 0.1 cm3; P < 0.05). In contrast, germ cell volume was not increased following hormone administration in KLH bulls. These results suggest that gonadotropin administration at the time of inhibin immunization increases germ cell volume in the testis without altering Sertoli and Leydig cell volume.

Effects of thyroid hormones on Leydig cells in the postnatal testis

Thyroid hormones (TH) stimulate oxidative metabolism in many tissues in the body, but testis is not one of them. Therefore, in this sense, testis is not considered as a target organ for TH. However, recent findings clearly show that TH have significant functions on the testis in general, and Leydig cells in particular; this begins from the onset of their differentiation through aging. Some of these functions include triggering the Leydig stem cells to differentiate, producing increased numbers of Leydig cells during differentiation by causing proliferation of Leydig stem cells and progenitors, stimulation of the Leydig cell steroidogenic function and cellular maintenance. The mechanism of action of TH on Leydig cell differentiation is still not clear and needs to be determined in future studies. However, some information on the mechanisms of TH action on Leydig cell steroidogenesis is available. TH acutely stimulate testosterone production by the Leydig cells in vitro via stimulating the production of steroidogenic acute regulatory protein (StAR) and StAR mRNA in Leydig cells; StAR is associated with intracellular trafficking of cholesterol into the mitochondria during steroid hormone synthesis. However, the presence and/or the types of TH receptors in Leydig cells and other cell types of the Leydig cell lineage is still to be resolved. Additionally, it has been shown that thyrotropin-releasing hormone (TRH), TRH receptor and TRH mRNA in the testis in many mammalian species are seen exclusively in Leydig cells. Although the significance of the latter observations are yet to be determined, these findings prompt whether hypothalamo-pituitary-thyroid axis and hypothalamo-pituitary-testis axis are short-looped through Leydig cells.