Prepubertal rat Sertoli cells secrete a mitogenic factor(s) that stimulates germ and somatic cell proliferation

Xenotransplantation of canine spermatogonial stem cells (cSSCs) regulated by FSH promotes spermatogenesis in infertile mice

Background

Xenotransplantation of spermatogonial stem cells (SSCs) has become a popular topic in various research fields because manipulating these cells can provide insights into the mechanisms associated with germ cell lines and the entire spermatogenesis process; moreover, these cells can be used in several biotechnology applications. To achieve successful xenotransplantation, the in vitro microenvironment in which SSCs are cultured should be an ideal microenvironment for self-renewal and similar to the in vivo testicular microenvironment. The age of the donor, the correct spermatogenesis cycle, and the quality of the donor tissue are also important. Although cell culture-related factors, such as the in vitro supplementation of hormonal factors, are known to promote successful xenotransplantation in mice, little is known about the influence of these factors on SSCs in vitro or in vivo in other mammalian species, such as dogs (Canis lupus familiaris). In this context, the goals of this study were to test the effect of follicle-stimulating hormone (FSH) on canine spermatogonial stem cell (cSSC) cultures since this hormone is related to the glial cell-derived neurotrophic factor (GDNF) signaling pathway, which is responsible for the self-renewal and maintenance of these cells in vivo, and to investigate the microenvironment of the SSC culture after FSH supplementation. Additionally, in vivo analyses of transplanted FSH-supplemented cSSCs in the testes of infertile mice were performed to assess the capacity of cSSCs to develop, maintain, and restore spermatogenesis.

Methods

SSCs from canine prepubertal testes (aged 3 months) were cultured in vitro in the presence of FSH (10 IU L⁻¹). GFRA1 transcript expression was detected to confirm the spermatogonia population in culture and the effect of FSH on these cells. The protein and transcript levels of late germ cell markers (GFRA1, DAZL, STRA8, PLZF, and CD49f) and a pluripotency marker (OCT4) were detected at 72 and 120 h to confirm the cSSC phenotype. In vivo experiments were performed by transplanting GFP+ cSSCs into infertile mice, and a 10-week follow-up was performed. Histological and immunofluorescence analyses were performed to confirm the repopulation capacity after cSSC xenotransplantation in the testis.

Results

Supplementation with FSH in cell culture increased the number of cSSCs positive for GFRA1. The cSSCs were also positive for the pluripotency and early germline marker OCT4 and the late germline markers PLZF, DAZL, C-kit, and GFRA-1. The in vivo experiments showed that the cSSCs xenotransplanted into infertile mouse testes were able to repopulate germline cells in the seminiferous tubules of mice.

Conclusions

In conclusion, our results showed for the first time that the treatment of cSSC cultures with FSH can promote in vitro self-renewal, increase the population of germline cells, and possibly influence the success of spermatogenesis in infertile mice in vivo.

B2 bradykinin receptor mediates the stimulatory effect of bradykinin on rat germ cell proliferation in vitro

The contribution of B1 and B2 bradykinin receptors to germ cell proliferation was studied by using in vitro organ cultures of testicular fragments of 3.5-day-old rats in the presence of 3H thymidine. Different combinations of agonists and antagonists of B1 and B2 receptors exerted differential mitogenic effect on pro-spermatogonial cells. Application of bradykinin (B2 receptor agonist) alone induced a threefold increase in germ cell labelling index compared with the control, whereas des-Arg9-bradykinin (B1 receptor agonist) caused weak stimulation (24%) on spermatogonial mitotic activity. The bradykinin-induced germ cell proliferation was significantly affected by B2 receptor antagonist (HOE-140) but not by B1 receptor antagonist. When B1 or B2 receptor antagonists were applied with des-Arg9-bradykinin, the germ cell labelling indices were nonsignificantly different compared with those of B1 receptor agonist only. The present findings suggest that B2 receptor is involved in mediating the stimulatory effect of bradykinin on germ cell proliferation and therefore bradykinin might be an important local testicular factor in the regulation of spermatogonial division and germ cell number.

Are germ cell factors essential in the testicular enlargement after neonatal hypothyroidism recovery? A study using W/Wv mutant mice model

We examined the issue of whether germ cell factors are required for testicular enlargement that occurs after recovery from neonatal hypothyroidism. Experiments were performed using W/Wv mutant mice (lacking germ cells) and normal mice (ICR). The pups in experimental group (neonatal hypothyroid) received 6 propyl 2-thio-uracil (PTU) treatment, administered by adding 0.1% (w/v) to the water provided to the mother from day 1 of birth through day 25 postpartum, while the pups of control group received drinking water only. Mice were sacrificed at the age of day 25, 50 and 90, in the case of ICR mice, or at day 25 and 90 in the case of W/Wv mutant mice. In both groups, early hypothyroidism caused a partial recoverable decrease in body growth and testicular development. Both ICR and W/Wv mutant mice, those recovered from neonatal hypothyroidism showed an increase in testis weights, the number of Sertoli cells, and the diameter of the semniferous tubules. This study demonstrates that neonatal hypothyroidism led recovery caused testicular enlargement not only in ICR mice but also in germ cell depleted W/Wv mutant mice. Hence these findings deny direct involvement of the germ cell factors in the process of testicular enlargement in recovered mice even in vivo, and reaffirm the notion that thyroid hormone directly regulates the dynamics of Sertoli cell maturation.

Stage-specific nuclear antigen is expressed in rat male germ cells during early meiotic prophase

A germ cell nuclear antigen with approximately 44-kDa molecular weight was identified by a novel monoclonal antibody designated as Mab 2F2 from the library we have accumulated against rat testicular cells. In immature 20-day-old and adult rat testis the recognized antigen was expressed in the nuclei of early meiotic cells from preleptotene to early pachytene spermatocytes exhibiting a stage-specific appearance in the cycle of the seminiferous epithelium. The immunoreactivity was clearly associated with the meiotic chromosomes. The antigen was not detected in the late pachytene spermatocytes and more advanced stages of spermatogenesis. No labeling was observed in spermatogonia and somatic Sertoli and Leydig cells. The pattern of expression of the recognized antigen during early meiotic stages of spermatogenesis but not in mitotically dividing spermatogonia could strengthen its possible role in meiotic division.

Bradykinin stimulates prepubertal rat germ cell proliferation in vitro

The effect of bradykinin on germ cell proliferation was studied by using in vitro organ cultures of testicular fragments from 3.5- and 4.5-day-old rats in the presence of 3H-thymidine. Bradykinin in tested concentrations of 10(-8), 10(-6) and 10(-4) M manifested a significant stimulation of rat prespermatogonial cell proliferation. The percentage of labeled germ cells increased up to 3-fold in comparison with the control value especially in 3.5-day-old rat testicular explants. Two kininase inhibitors: phosphoramidon and captopril were also used in combination with bradykinin. The percentage of labeled germ cells was slightly increased as compared to the samples treated with bradykinin only. Experiments with two agonists and two antagonists of B1 and B2 receptors for kinins showed that the rat prespermatogonial cell proliferation response to bradykinin is probably mediated via B2 receptors. The present findings suggest that bradykinin may be an important local testicular factor with paracrine or autocrine role in the regulation of spermatogonial cell proliferation and germ cell number.

Localization of follicle-stimulating hormone (FSH) immunoreactivity and hormone receptor mRNA in testicular tissue of infertile men

Testicular biopsies from 82 oligo- or azoo-spermic male patients were subjected to immunostaining using anti-human FSH antibodies. Histological evaluation showed normal spermatogenesis (nspg) in 7 (FSH: (2.7 +/- 0.7), mixed atrophy (ma) in 63 (FSH:L 5.3 +/- 0.5), and bilateral or unilateral Sertoli Cell Only syndrome (SCO) in 12 (FSH: 21.7 +/- 3.5) patients. For the relationship between FSH values and testicular histology, see Bergmann et al. (1994). FSH immunoreactivity was found exclusively in Sertoli cells and in some interstitial cells. Seminiferous epithelium showing normal or impaired spermatogenesis displayed only weak immunoreactivity compared to intense immunoreaction, i.e. large and numerous vesicles in Sertoli cells of SCO tubules in biopsies showing mixed atrophy or SCO. In addition, h-FSH receptor mRNA was demonstrated by in situ hybridization using biotinylated cDNA antisense oligonucleotides. Hybridization signals were found within the seminiferous epithelium exclusively in Sertoli cell cytoplasm associated with normal spermatogenesis and in epithelia showing different signs of impairment, including SCO. It is concluded that: (1) Sertoli cells are the only cells within the seminiferous epithelium expressing FSH receptors; (2) the accumulation of FSH immunoreactivity in Sertoli cells of SCO tubules appears to be a sign of impaired Sertoli cell function.

Differential effects of prepubertal rat Sertoli cell secreted proteins on somatic testicular and nontesticular cells

There is little information on the mitogenic and immunoregulatory activities of proteins, secreted by prepubertal Sertoli cells during the stage of meiosis initiation and before creation of the blood-testis barrier. We have previously demonstrated dose-dependent and age-related stimulation of BALB/c 3T3 fibroblasts and quiescent rat prespermatogonia (Kancheva et al., 1990) as well as inhibition of natural killer cell activity of mice, guinea pigs and human lymphocytes (Nikolova et al., 1992) by Sertoli cell-conditioned medium derived from 12-day-old rats. In the current study, using splenic lymphocytes stimulated by PHA, LPS and Con A, we have shown a dose-dependent inhibition of T and B lymphocyte proliferation by prepubertal Sertoli cell-secreted proteins (pSCSP). These results suggest that by the time the blood-testis barrier had been formed, Sertoli cell in rat testis had already synthesized immunoregulatory proteins. In addition we have found that pSCSP stimulate the proliferation of TM3 Leydig but not TM4 Sertoli cells. The differential effect of pSCSP is an expression of the different balance between growth factors secreted by Sertoli cells, which in turn is dependent on the requirements of the cell types at each stage of testicular development.

Survival and proliferation of rat gonocytes in vitro

Quiescent gonocytes were isolated from fetal testes of rat 18-day post coitum and cultured alone or on monolayers of somatic cells from different origins. The gonocytes specifically adhered to Sertoli cells, isolated from 21 to 23-day-old rat testes; this adherence was necessary for their survival in vitro. Addition of follicle-stimulating hormone and testosterone to these cultures did not increase the viability of the gonocytes. Serum was found to be deleterious to the germ cells. Electron-microscopic examination of Sertoli-cell-gonocyte co-cultures revealed the presence of numerous adhesion plaques between these cells, indicating that Sertoli cells and gonocytes are able to communicate in vitro. Gonocytes, in co-culture with Sertoli cells, were viable for at least 9 days. The gonocytes did not spontaneously resume proliferation. The simple culture system described in the present paper should be useful in studying the nature of the factors that are responsible for sending the quiescent gonocytes into the cell cycle and for stimulating the formation of A spermatogonia, a process characterizing the start of spermatogenesis.

Reinitiation of gonocyte mitosis and movement of gonocytes to the basement membrane in testes of newborn rats in vivo and in vitro

Movement of postnatal gonocytes to the periphery of the seminiferous cord, where they contact the basement membrane, and resumption of mitosis by these previously quiescent cells are likely to be critically important in establishing spermatogenesis in neonatal rats. We used several approaches both in vivo and in vitro to determine precisely when each of these two events begins, to study their temporal relationship to each other, to determine whether gonocyte division is a prerequisite for relocation or vice versa, and to probe the source of factors initiating and/or regulating these events. Both light and electron microscopy were used to determine that the first gonocytes make contact with the basement membrane on postnatal day 4, while quantitative autoradiography following 3H-thymidine administration in vivo indicated that the first gonocytes to re-initiate cell division do so one day earlier, on day 3, and that the percentage of gonocytes dividing remains at a stable level through day 5. Moreover, we organ-cultured neonatal testes from birth onwards in the presence of defined, serum- and hormone-free medium and determined that both proliferation and relocation of gonocytes begin and continue in vitro as in vivo. This observation argues against involvement of extratesticular factors in stimulating gonocyte relocation and division, and points to the testis itself as the most likely source of agent(s) regulating postnatal maturation of these cells. In other, similar incubations we included 3H-thymidine for varying periods of time to label either those gonocytes that are the first to divide or all gonocytes that divide during the first 48 hr of culture. From these studies, we confirmed that the first gonocytes to divide do so while separated from the basement membrane and found that, although some cells divide before moving peripherally, others do not.

Sulfhydryl oxidase immunoreactivity in seminiferous tubules of infertile men

Sulfhydryl oxidase (SOx) immunoreactivity was investigated in the seminiferous epithelium of human biopsy material from the testes of 33 adult men with disturbed fertility. SOx immunoreactivity was expressed in normal seminiferous epithelium in type-A spermatogonia (27 +/- 4% of all spermatogonia) (n = 4), in spermatocytes and round spermatids. Mature spermatozoa as well as Sertoli cells were unlabelled. Within the interstitium, Leydig cells were immunopositive. In biopsies of oligozoospermic men showing hypospermatogenesis (n = 24), an increase in labelled spermatogonia up to more than 90% was observed in biopsies, where seminiferous epithelia revealed only spermatogonia and Sertoli cells. Within the group of oligozoospermic patients there was a significant increase of labelled spermatogonia from 43 +/- 13% (greater than 20 mill/ejaculate) (n = 7) to 55 +/- 16% (less than 20 and greater than 10 mill/ejaculate) (n = 6) to 68 +/- 8% (less than 5 mill/ejaculate) (n = 11) and a significant (P = 0.01) decrease of score count from 7.0 +/- 2.7 to 2.0 +/- 1.8. In this group the increase of labelled spermatogonia was correlated with sperm concentrations in the ejaculate (correlation coefficient: r = -0.6). In biopsies of azoospermic patients showing maturation arrest at the level of spermatocytes or spermatids (n = 5) the percentage of labelled spermatogonia was within the range of 24% to 59%.(ABSTRACT TRUNCATED AT 250 WORDS)

Species-specific effect of proteins secreted by cultured pre-pubertal rat Sertoli cells on natural killer cell activity

The effect of proteins secreted by cultured pre-pubertal rat Sertoli cells (pSCP) on natural killer (NK) cell activity of rat, mice and guinea pig splenocytes and human peripheral blood lymphocytes was estimated. The results indicate that pSCP inhibited, in a dose-dependent manner, NK cell activity of mice, guinea pig and human lymphocytes but did not suppress lysis of YAC-1 target cells by rat NK cells. Species-specific differences in the effect of pSCP on NK cell activity probably result from differences in the binding of proteins within the effector cells. These data indicate that in the pre-pubertal period of gonadal development immature Sertoli cells synthesize a factor/s which might contribute to the maintenance of specific testis immunological environment.

Germ cell mitogenic activity is associated with nerve growth factor-like protein(s)

The mitogenicity of germ cell proteins released from round spermatids (RS) and pachytene spermatocytes (PS) was investigated. Germ cells were isolated by centrifugal elutriation from 90-day-old rat testes and incubated in a supplement enriched culture media that lacked exogenous proteins. The conditioned culture media of RS and PS were dialysed/concentrated and lyophilized to prepare RS protein (RSP) and PS protein (PSP). Mitogenic activity of RSP and PSP was determined by 3H-thymidine incorporation into Swiss 3T3 fibroblasts. RSP and PSP stimulated 3H-thymidine incorporation by fibroblasts in a dose-dependent manner. At a higher concentration of RSP (300 micrograms/ml), fibroblast proliferation was stimulated from 6- to 20-fold of control cultures, whereas PSP (300 micrograms/ml) stimulated fibroblast proliferation 2.5-fold of control cultures. Since RSP exhibited substantially greater mitogenic activity than PSP we further investigated the RSP mitogenic substance(s) by immunoneutralization with antibodies against several growth factors. The mitogenic activity of RSP was significantly reduced by treatment with nerve growth factor (NGF) antibody, while neither the treatment of RSP with acidic fibroblast growth factor (aFGF) antibody, nor basic fibroblast growth factor (bFGF) antibody significantly modified the mitogenic activity of RSP. Interestingly, murine NGF-beta, recombinant human NGF-beta, and bovine serum albumin (BSA) did not exhibit mitogenic activity on 3T3 fibroblasts. Nevertheless, the presence of a NGF-like protein in RS and PS was confirmed by indirect immunofluorescence staining with a murine NGF antibody. Subsequently, a Western blot analysis with the NGF antibody identified two immunoreactive bands of 41 +/- 2 kDa and 51 +/- 1 kDa in both RSP and PSP under reduced conditions. These germ cell NGF-like proteins were apparently different from similarly prepared murine and human NGFs (13 kDa) in their molecular weight. Furthermore, neurite outgrowth from pheochromocytoma cells (PC-12), a functional bioassay for NGF-like activity, was stimulated by addition of RSP and PSP to the culture media of the PC-12 cells. These results demonstrate mitogenic activity in germ cell proteins (RSP and PSP) and identify a NGF-like protein(s) which is associated with most of this activity.