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Departments of Physiology (S.B.R., P.A., J.T., M.P., I.H.) and Anatomy (S.M.), Institute of Biomedicine, University of Turku, FIN-20520 Turku, Finland
Address all correspondence and requests for reprints to: Ilpo Huhtaniemi, M.D., Ph.D., Institute of Reproductive and Developmental Biology, Imperial College London, Faculty of Medicine, Du Cane Road, London W12 ONN, United Kingdom. E-mail: ilpo.huhtaniemi{at}imperial.ac.uk.
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-subunit fusion gene. The double-TG mice expressed excessive levels of dimeric hCG, with 2000-fold elevated circulating LH/hCG bioactivity. These male mice were infertile, primarily due to inability to copulate, and they showed enhanced testicular androgen production despite clear down-regulation of LH/hCG receptors. Their intratesticular inhibin B was unaltered, but serum FSH was markedly reduced. Apparently the chronic hCG hyperstimulation led to focal Leydig cell proliferation/hypertrophy at 6 months of age, but failed to promote testicular tumors. Even though full spermatogenesis occurred in most of the seminiferous tubules, progressive tubule degeneration was apparent as the males grew older. The prostate and seminal vesicles were enlarged by distension of glandular lumina. Functional urethral obstruction was indicated by distension and sperm accumulation in distal vas deferens as well as by dilated urinary bladder and enlarged kidneys. The abnormal function of accessory sex glands and/or lower urinary tract as a consequence of the disturbed sex hormone balance or direct action of hCG may be the main cause of infertility in this model. The present study provides in vivo evidence that exposure of male mice to chronically elevated levels of hCG severely affects their urogenital tract function at multiple sites and causes infertility, but, unlike in LH/hCG overexpressing female mice, it is not tumorigenic. |
Introduction |
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- and the hormone-specific ß-subunit (1). Dimerization is obligatory for hormonal activity, as the individual subunits of hCG are devoid of bioactivity (2). Being structurally and biologically closely related to the pituitary-derived LH, hCG binds to the same receptor and acts as a potent LH agonist. The LH/hCG receptor belongs to the seven-transmembrane domain, G protein-coupled receptor family (3). Activation of the receptor by LH/hCG leads to activation of Gs, the G protein coupled to adenylyl cyclase, and to an increase in cAMP. In vitro studies demonstrate that high concentrations of LH/hCG can also activate the inositol phosphate and MAPK signaling cascades (4). In males, LH plays a role in both normal and abnormal reproductive function by modulating testicular Leydig cell differentiation and steroidogenesis. Testosterone secreted by Leydig cells, in turn, promotes male sexual differentiation, pubertal androgenization, and fertility. In the testis, functional LH receptors are expressed in Leydig cells during fetal development, transiently in early postnatal life, and from puberty to adult life (5). Although primarily expressed in gonads, LH receptors are also found in several extragonadal sex organs, including the prostate (6, 7), epididymis (8), and seminal vesicles (9), but the physiological significance of these extratesticular receptors remains unclear.
In man, naturally occurring mutations of the LH/hCG receptor have been associated with disrupted reproductive function (10). Inactivating mutations of the receptor cause pseudohermaphroditism associated with different degrees of Leydig cell hypoplasia, whereas constitutively activating mutations induce gonadotropin-independent, male-limited precocious puberty with autonomous hypersecretion of testosterone (10). In addition, Leydig cell adenomas are associated with a specific activating mutation of the LH receptor (Asp578His) (11, 12). This finding emphasizes the potential role of gonadotropins as tumor promoters, as has also been proposed by recent clinical and experimental findings (10) and in particular in female transgenic (TG) mice overexpressing LH or hCG (13, 14).
Genetically modified animal models are of great importance in corroborating the findings on humans related to disrupted or enhanced gonadotropin function. In fact, the abolition of LH action in mice by targeted disruption of the LH receptor did not affect normal masculinization at birth, but resulted in postnatal blockade of testicular growth, arrest of external genital and accessory sex organ maturation, and azoospermia (15, 16). Animal models harboring activating LH receptor or inactivating LHß mutations have not yet been reported.
Many attempts have been made to elucidate the effects of elevated chronic LH/hCG stimulation on testicular function in vivo. A TG mouse model overexpressing LH has been produced (13), but only female mice produced elevated levels of LH. Nothing is known at the moment about the phenotypic consequences of LH overproduction in males. Findings on long- and short-term hCG treatments in rats are inconsistent and seem to be age, dose, and time dependent (17, 18, 19, 20, 21, 22, 23), and the formation of antibodies against the foreign protein poses a confounding factor. In fetal and neonatal rat testes, the regulation of LH/hCG receptor expression and function appears to differ from that in the adult. Unlike those in adults, fetal and neonatal testes are refractory to gonadotropin-induced receptor down-regulation, and treatment with LH/hCG causes marked up-regulation of the cognate receptors and enhancement of steroidogenesis (20, 24, 25). This finding is intriguing because normally the male is effectively protected from high LH/hCG action through down-regulation of testicular LH/hCG receptors and desensitization of steroidogenesis after prolonged exposure to high levels of LH/hCG.
To study the effects of chronically elevated levels of LH/hCG on male reproductive functions, we generated and characterized two TG mouse models expressing either the hCG ß-subunit alone or together with the common -subunit, both under the same ubiquitin C promoter. TG expression of hCGß produced moderate elevation of circulating LH/hCG bioactivity, whereas the double-TG hCGß mice presented with pharmacological levels of the hormone. We present in this paper the phenotypic characterization of males of the two TG mouse models.
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Materials and Methods |
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minigene was released from the original plasmid pIB [provided by Dr. I. Boime (26)] and subcloned into the BamHI site of pGEM-4Z vector (Promega, Madison, WI). Thereafter, the 1.2-kb BglII-BamHI human ubiquitin C promoter fragment was inserted upstream of the hCG minigene. The 3.6-kb ubiquitin C/hCG fragment was released from the backbone vector by digestion with EcoRI and SphI. The fragments were resolved in a 1% agarose gel and were isolated by electroelution, followed by purification with Elutip-D columns (Schleicher & Schuell, Keene, NH). Finally, the fragments were diluted in TE buffer (10 mM Tris-HCl and 5 mM EDTA, pH 7.5) at a concentration of 2 ng/µl for microinjection. The 2.8-kb ubiquitin C/hCGß transgene was constructed and used for TG mouse generation as described previously (14).
Generation of TG mice
The hCG+ TG mice carrying the ubiquitin C/hCG transgene were generated by microinjecting the transgene into pronuclei of fertilized oocytes from FVB/N mice, and the microinjected embryos were implanted into oviducts of pseudopregnant female mice of the NMRI strain. The generation of ubiquitin C/hCGß TG mice has been described previously (14). PCR analyses of genomic DNA from tail biopsies were used to identify the TG animals. One microgram of genomic DNA was added to the 50-µl PCR containing 10 mM Tris-HCl (pH 8.8), 1.5 mM MgCl2, 50 mM KCl, 200 µM deoxynucleotide triphosphate mix, 0.2 µM primers, and 2.5 U DNA polymerase. A 600-bp DNA fragment of the ubiquitin/hCG transgene was amplified using primers specific for the ubiquitin promoter (5'-CGCGCCCTCGTCGTGTC-3') and the hCG minigene (5'-CCGGCTGGGAGAAGAATGG-3'). An 830-bp DNA fragment of the ubiquitin/hCGß transgene was obtained by using specific primers for the ubiquitin C promoter (see above) and the hCGß-cDNA (5'-AAGCGGGGGTCATCACAGGTC-3'). Genotyping of the double-TG mice (see below) was performed by separate PCRs for the two transgenes. The DNA was denatured at 94 C for 4 min, followed by PCR: 94 C for 0.5 min, 57 C for 1 min, and 72 C for 1.5 min for 32 cycles. The resulting PCR products were analyzed by electrophoresis on 2% agarose gel, and the fragments were UV-visualized with ethidium bromide.
The animals were housed in a specific pathogen-free environment under controlled conditions of temperature and light, and they were provided with tap water and commercial mouse chow ad libitum. All mice were produced and handled in accordance with the institutional animal care policies of the University of Turku.
Fertility studies
Wild-type (wt), hCG+, hCGß+, or hCGß+ male mice were housed individually at 6–8 wk of age with randomly cycling wt female mice for at least 2 months for fertility and fecundity tests (n = 8–10/group). The number of offspring born and frequency of births were recorded. Short-term mating studies were conducted to determine the relative reproductive performance of the males. Six-week-old wt females were superovulated by sc administration of 7.5 IU pregnant mare’s serum gonadotropin (PMSG), followed by 5 IU hCG 47 h later, and immediately housed individually with wt, hCGß+, or hCGß+ male mice. Vaginal plugs were monitored on the following morning to confirm 2mating.
Measurement of hormone levels
Six-month-old male mice were killed by cervical dislocation in the morning, blood was collected from the heart, and serum samples were separated by centrifugation and stored at -20 C until hormone measurements. Serum hCG was measured by an immunofluorometric assay technique (IFMA; Delfia, Wallac Oy, Turku, Finland), adapted to detect specifically the hCG-subunit in mouse serum samples. Briefly, microtitration wells coated with streptavidin and a biotinylated monoclonal antibody against the -subunit were used in combination with a europium-labeled mouse monoclonal antibody against the -subunit from the human FSH Delfia kit. The reference preparation from the NIDDK, NIH (Bethesda, MD), hCG CR-119, was used as the standard. The detection limit was 50 ng/liter. Serum hCGß levels were measured by IFMA, adapted to specifically detect the hCGß-subunit in mouse serum samples, as previously described (14). The reference preparation from NIH, hCGß CR-121, was used as the standard. The detection limit was 40 µg/liter. Serum levels of dimeric hCG were measured by IFMA using the Delfia hCG kit according to the manufacturer’s instructions; the detection limit was 0.5 IU/liter. FSH levels were measured by IFMA as described previously (27); the sensitivity of the assay was 50 ng/liter. Intratesticular testosterone and progesterone were determined by homogenizing one testis in 200 µl PBS. The homogenates or sera were extracted twice with 2 ml diethyl ether and evaporated to dryness. After reconstitution into PBS, testosterone and progesterone were measured by conventional RIAs. The bioactivity of circulating hCG was determined by the mouse interstitial cell in vitro bioassay (28). Testosterone production, determined by RIA, was used as an index of the hCG response. Recombinant hCG (specific activity, 14,800 IU/mg; Organon, Oss, The Netherlands) was used as the standard. The sensitivity of the bioassay was 0.5 IU/liter, and the intra- and interassay coefficients of variation were less than 5% and 10%, respectively. Intratesticular inhibin B was measured with a serum inhibin B kit (Oxford Bio-Innovation Ltd., Oxford, UK) for the human according to the manufacturer’s protocol. Before assay, frozen testis samples were weighed and homogenized in saline phosphate buffer. Samples were centrifuged at 13,000 rpm for 10 min, and supernatants were used for protein and inhibin B measurements.
Histological analysis
Testes and epididymides were fixed overnight in Bouin’s reagent or 4% paraformaldehyde. Seminal vesicles, ventral prostates, and kidneys were fixed overnight in 4% paraformaldehyde. Tissues were dehydrated and embedded in paraffin and 5-µm-thick sections were stained with hematoxylin and eosin.
LH/hCG receptor binding assay
Testicular LH/hCG receptor binding was measured as previously described (29). Highly purified hCG (NIH CR-125; 13,000 IU/mg) was radioiodinated using a solid phase lactoperoxidase method (29). Briefly, one testis was homogenized in 700 µl Dulbecco’s PBS and 0.1% BSA. Thereafter, 100-µl aliquots of testicular homogenate were incubated in triplicate in the presence of saturating concentrations of [125I]iodo-hCG (150,000 cpm/tube; 
3 ng). Nonspecific binding was assessed in the presence of 50 IU unlabeled hCG (Pregnyl, Organon, Oss, The Netherlands). After overnight incubation at room temperature, the homogenates were washed with 4 ml ice-cold Dulbecco’s PBS and 0.1% BSA and centrifuged at 2000 x g for 20 min. The supernatants were aspirated, and pellets were counted in a 
-spectrometer. Protein concentrations were measured using the Bradford method (30), and specific hCG binding was expressed as a percentage of the control, based on counts per minute per milligram of protein.
Statistical analysis
SigmaStat for Windows 2.03 was used for t test or Student-Newman-Keuls test. Significance was set at P < 0.05. The values are presented as the mean ± SEM.
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Results |
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ß+ mouse lines+ and hCGß+ mice were established by mating founders with wt FVB/N counterparts. Double-TG hCGß+ mice were obtained by cross-breeding hCG+ and hCGß+ mice. To succeed in producing double-TG mice, the combination of four different hCG+ lines with one established hCGß+ TG line was attempted (Table 1
). Pregnancy and delivery of double TG offspring were successful only when hCG+ females of line 59 were used, coincident with the lowest levels of transgene expression. As the double TG males and females were infertile, constant cross-breeding of hCGß+ with the hCG+ line mentioned was necessary to obtain hCGß+ mice.
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ß+ mice, circulating levels of dimeric hCG were markedly elevated (hCGß+, 9970 ± 1770 IU/liter; hCGß+, <0.5 IU/liter; wt, <0.5 IU/liter), indicating that the TG hCG- and ß-subunits were properly synthesized, dimerized, and secreted. In the hCGß+ mice, in which hCG/LH bioactivity depends upon the association of hCGß-subunit with endogenously expressed -subunit present in pituitary gonadotrope and thyrotrope cells, the circulating levels of bioactive hCG/LH were 3- to 4-fold higher than those in wt males. In hCGß+ male mice, levels of the bioactive form of hCG was more than 2000-fold the respective levels in wt mice (Fig. 1A).
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ß+ male mice with randomly cycling wt females (Table 2). During the 2-month mating period, wt and hCGß+ males sired an average of eight offspring per litter every 21–22 d, whereas hCGß+ males sired no offspring. In a short-term fertility test in which wt female mice were PMSG/hCG hormone-primed to induce ovulation, hCGß+ male mice mated normally (visible vaginal plugs). However, eight of eight double-TG hCGß+ males failed to mate with superovulated wt females, confirming that these male mice were infertile due to abnormal mating behavior. On the other hand, aggressive behavior against the female was evidenced with these males, resulting in biting and severe injuries, even death, of their female partners when caged for breeding. The fertility and fecundity of both male and female hCG+ mice were normal when bred with wt counterparts (data not shown).
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ß+ mice compared with wt animals (Table 3). The testicular weights of hCGß+ and hCGß+ mice were 75% and 50% of those of wt mice, respectively. Seminal vesicle weights (with coagulating glands) were 3-fold increased in the double-TG males, whereas epididymal weight was slightly decreased in hCGß+ mice and was unaltered in hCGß+ mice compared with wt mice.
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ß+ mice, the serum FSH levels were reduced to 40% and 3% of control levels, respectively (Fig. 1B
). The intratesticular inhibin B contents were decreased by about 50% (P < 0.05; data not shown) in both adult hCGß+ and hCGß+ males, but no significant changes were observed when the inhibin B concentration were adjusted to testis weight (Fig. 1C).
Serum progesterone was significantly increased in adult hCGß+ mice compared with wt or hCGß+ males (Table 3). As serum testosterone levels are normally highly fluctuating in mice (31), the intratesticular concentration of testosterone was determined as a more stable parameter to evaluate testicular hormone production. Both intratesticular testosterone and progesterone levels were significantly increased in adult hCGß+ compared with wt or hCGß+ mice (Fig. 2, A and B).
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ß+ mice (Fig. 2C). hCG binding was reduced to 42% in hCGß+ testes with respect to wt samples, and a more pronounced reduction to 1.4% occurred in the hCGß+ testes, apparently due to receptor occupancy and down-regulation by the very high circulating hCG levels.
Histology of the testes
Histological examination of the adult testes revealed progressive changes in the structure of the seminiferous epithelium according to age (Fig. 3). At the age of 2–4 months, the testes of both hCGß+ and hCGß+ mice showed normal tubular structure and full spermatogenesis. At the age of 6 months, most seminiferous tubules were still normal, and spermatogenesis was complete in both TG lines (Fig. 3, C–E). At this age, incipient tubular degeneration was observed in hCGß+ males, and large vacuoles were also present in the basal compartment of some seminiferous tubules (Fig. 3F). In addition, clear Leydig cell hypertrophy was observed in hCGß+ mice, in particular under the capsule. At the age of 8–9 months, the degeneration of seminiferous tubules had progressed, and a more severe damage was observed (Fig. 3, G and H). At this age, Leydig cell hypertrophy was also evident. No sign of Leydig cell tumor was observed in any of the animals studied.
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ß+ male mice, there were clear signs of infravesical (urethral) obstruction. The kidneys were enlarged (Fig. 4, upper panel), and the renal pelvis, ureters, and urinary bladder were markedly distended (Fig. 5). In renal cortex, tubular lumina were distended, and cortical cells were enlarged (Fig. 4, lower panel). LH receptor expression was undetectable in kidneys from wt and hCGß+ mice. As further signs of infravesical obstruction in hCGß+ mice, the distal parts of vasa deferentia were distended and filled with sperm (Fig. 6, A and B). The epithelium in the posterior wall of the urethra was hyperplastic, and the cells were filled with vacuoles (Fig. 6C). However, open urethral lumen was visible, indicating that the obstruction was functional, rather than anatomical/mechanical.
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ß+ mice appeared greatly enlarged compared with those in age-matched wt controls (Fig. 5). The glandular lumina of seminal vesicles were distended, the epithelium was flattened, mucosal folding was less prominent, and the fibromuscular layer was thickened (Fig. 6, D and E). Enlarged glands with flat single-layer epithelium were frequently seen in the ventral prostates of hCGß+ mice (Fig. 7). In addition, abnormal epithelial structures were present in multiple foci. These included hyperplastic, multilayered epithelium with vacuolated cytoplasm and the presence of structures resembling mucus-filled goblet cells (Fig. 7, E–K).
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ß+ mice at 6 months did not reveal any changes compared with wt mice (Fig. 8, A and B). At the age of 8–9 months, increased connective tissue and smooth muscle cells were observed in cauda epididymis, and these changes were most prominent around the tubules (Fig. 8, C and D). The tubule structure was totally abnormal, resembling that of sperm granulomas. In some cases increased smooth muscle and connective tissue were also observed in the distal part of corpus epididymides. Morphologically normal, motile sperm were present in cauda epididymis at 2–6 months of age in hCGß+ males (Fig. 8, E and G), but abnormal sperm structure associated with bent tails was observed at 8–9 months (Fig. 8H).
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Discussion |
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-subunit, was only moderately elevated in males due to a strong down-regulation of -subunit gene expression at the pituitary level (1). In accordance, hCGß+ males presented with only a mild reproductive phenotype and were fertile. To achieve higher levels of hCG, double-TG hCGß+ mice were generated by cross-breeding TG mice harboring the hCG-subunit with those overexpressing hCGß. In this way excessive pharmacological levels of circulating bioactive hCG were achieved in the double-TG hCGß+ mice, and consequently, these males were infertile and presented significant reproductive disturbances.
Fertility tests demonstrated that the failure of hCGß+ males to produce progeny was primarily due to their inability to copulate. Motile and morphologically normal sperm were observed in cauda epididymis at the ages when fertility was tested, indicating that the problem is at the level of copulatory or ejaculatory function and not in sperm production or maturation at that age. No vaginal plugs were observed when hCGß+ males were mated with PMSG-treated females. This could be due to either altered reproductive behavior or abnormal function or anatomy of the accessory sex glands or urethra. Locally produced estrogens from circulating testosterone mediate the activating effects of testosterone on male copulatory behavior and are crucial for fetal brain masculinization (32, 33). This could explain the behavioral defect, when altered sex steroid profile during specific periods of embryonic and neonatal life may have influenced the sexual development of the brain and imprinted sexual behavior in adulthood. Additional studies should be carried out to investigate whether the reproductive deficit observed in our mice reflects primarily motivational or consummatory aspects of behavior. On the other hand, testosterone has been shown to increase aggressive behavior in both male and female mice (34), which could explain the aggressive behavior of the hCGß+ males toward females. Finally, the possibility that an anatomical impediment resulted in painful coituses cannot be ruled out.
FSH production was clearly reduced in adulthood in both TG models, apparently due to elevated androgen feedback regulation to the hypothalamic-pituitary level (1). The reason why FSH levels were also reduced in hCGß+ mice despite the minimal changes found in testosterone secretion is not clear. The possibility that other androgen metabolites not measured in this study were influencing gonadotropin feedback regulation cannot be ruled out. FSH is known to play a major role in Sertoli cell proliferation in the maturing testis, which, in turn, influences Leydig cell function and vice versa (35). The reduced levels of FSH found in both hCGß+ and hCGß+ mice could be a contributing factor to the abnormal testis growth by reducing the finite number of Sertoli cells, a determinant of total tubular length. Inhibin B, in addition to being a negative feedback regulator of FSH secretion, is a marker of spermatogenesis and Sertoli cell function (36). FSH is recognized to stimulate testicular inhibin secretion, but the possibility that Leydig cells contribute to the synthesis and secretion of inhibin B through LH/hCG action is less clear. mRNAs encoding inhibin and ßB and the subunits themselves have been localized in Sertoli as well as Leydig cells (36, 37). Even though it was suggested that in male Gottingen miniature pigs, Leydig cells are the predominant source of inhibin B (38), studies carried out in normal or hypogonadal men indicate that LH or hCG failed to stimulate inhibin B secretion (39, 40). No evidence was obtained for changes in testicular inhibin B concentration in our model. Whether this is the result of a compensatory effect between reduced FSH-mediated inhibin B production from Sertoli cells and a putative increased hCG-mediated effect remains to be elucidated.
Long-term treatment of prepubertal or adult rats with LH/hCG was shown to produce hyperplasia, hypertrophy, and an increase in the steroidogenic capacity of adult Leydig cells (17, 18, 21, 23). In agreement with these reports, one of the most conspicuous findings in the double-TG mice was Leydig cell hyperplasia/hypertrophy. These results support the concept that LH/hCG is critical for adult Leydig cells to induce proliferation, hypertrophy, and enhanced steroidogenesis. Although LH/hCG signaling plays a major role in Leydig cell proliferation, the prolonged exposure to hCG hyperstimulation failed to induce Leydig cell tumors in hCGß+ mice. In humans, one specific somatic activating mutation of the LH receptor gene (Asp578His) is associated with Leydig cell adenomas (11, 12). Besides the classical cAMP-mediated signaling, this particular mutation activates the phospholipase C pathway. Activation of alternative intracellular signaling pathways of LH receptor action was therefore proposed to be responsible for the neoplastic transformation (11). Whether LH/hCG signaling is altered upon chronic stimulation remains to be studied. The unaltered intratesticular inhibin concentrations in our model are consistent with the concept that missing inhibin action is related to tumor formation in gonads (41).
Exposure to LH/hCG has a biphasic effect on the control of Leydig cell function. Low doses of the hormone maintain the receptors and steroidogenic enzymes, whereas higher doses cause homologous and heterologous (e.g. PRL receptor) receptor down-regulation and uncoupling of signal transduction (25). In the present study chronic hCG overexpression of hCGß+ mice resulted in enhanced testicular steroidogenesis, as demonstrated by elevated intratesticular testosterone and progesterone. Significant LH receptor down-regulation in this system in the face of elevated testicular testosterone synthesis suggests that the small fraction of free LH/hCG receptors is sufficient for the steroidogenic capacity of the Leydig cells, in keeping with the spare receptor concept (42). Activation of alternative signal transduction pathways apart from cAMP, such as phospholipase C and MAPKs, may occur with high doses of LH/hCG.
Seminiferous tubules of the hCG-overexpressing testes first presented with full spermatogenesis and normal sperm quality, but progressive tubular degeneration occurred in hCGß+ mice as the animals grew older. This event correlated with the appearance of epididymal structure abnormalities and altered sperm structure with bent tails. Foci of degenerative seminiferous tubules were characteristic of the hCGß+ phenotype, but were absent in hCGß+ mice. hCG-induced high testicular blood flow (43, 44), precapillary vasoconstriction (45), and inflammatory-type response in the intertubular tissue with localized degeneration of the seminiferous epithelium have been described (46) and would provide the likely explanation for the seminiferous tubular damage observed in our model. On the other hand, the infertility of estrogen receptor -knockout males was caused by abnormal fluid reabsorption in the epididymis, leading to disrupted spermatogenesis and seminiferous tubule organization through a back-pressure effect (47, 48). Because the hCGß+ males presented either obstruction or dysfunction at several levels of the urinary tract, the spermatogenic defect may be a consequence of these, also causing obstruction of the vas deferens. Progressive changes associated with obstruction were seen in the epididymis, resembling granulomas seen in rodents after traumatic injury (49). Obstruction at the level of epididymis has been shown to cause degeneration of seminiferous tubules and vacuolization of seminiferous tubules in rats (50, 51).
The accessory sex organs (prostate and seminal vesicles) were enlarged mainly due to distension of the glandular lumina, indicating either enhanced production of secretory material or impaired emptying of the glands. The former response would be in line with the elevated androgen levels in ERKO mice (47, 48). The distension of vas deferens and accumulation of sperm in distal vas as well as the pronounced distension of urinary bladder and enlarged kidneys clearly indicate infravesical (urethral) obstruction of, to date, unknown cause. No obvious signs of solid tissues blocking the urethral lumen were observed, suggesting that the obstruction was functional, probably due to defects in smooth muscle function or premature coagulation of secretory fluids. The presence of goblet-like cells in the prostatic epithelium may suggest altered secretory function. There was no evidence for LH receptor expression in kidneys from either wt or hCGß+ mice that could explain a direct effect of hCG on this organ. The response is thus more probably a consequence of the severe steroid hormone imbalance in these mice. Although there are receptors of LH/hCG in the epididymis, seminal vesicles, and prostate (6, 7, 8, 9), we still consider most of the changes in the accessory sex glands of the hCGß+ males to be due to hyperandrogenism. In contrast to the epididymis, prostate and seminal vesicle growth respond strongly to androgen excess (52).
In summary, the present study provides in vivo evidence that the exposure of male mice to chronically elevated levels of hCG is not sufficient to promote testicular tumor formation. However, male reproductive function was severely affected at multiple sites, resulting in infertility. Chronic hCG hyperstimulation led to apparent Leydig cell proliferation and hypertrophy and enhanced testicular steroidogenesis, despite dramatic LH receptor down-regulation. Progressive seminiferous tubule degeneration occurred as mice grew older, and their accessory reproductive organs and kidneys were also severely affected. It is possible that the abnormal function and obstructions of accessory sex glands and/or lower urinary tract due to adverse back-pressure are the main cause of the infertility observed.
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Acknowledgments |
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Footnotes |
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Abbreviations: hCG, Human chorionic gonadotropin; IFMA, immunofluorometric assay; PMSG, pregnant mare’s serum gonadotropin; TG, transgenic; wt, wild-type.
Received March 31, 2003.
Accepted for publication July 24, 2003.
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References |
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subunit in the secretion and assembly of human chorionic gonadotrophin. J Cell Biol 106:1049–1059 and ßB subunits and expression of corresponding messenger RNAs in the human adult testis. Biol Reprod 68:230–235-Inhibin is a tumour-suppressor gene with gonadal specificity in mice. Nature 360:313–319[CrossRef][Medline]
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