In-vitro effects of FSH and testosterone withdrawal on caspase activation and DNA fragmentation in different cell types of human seminiferous epithelium

BACKGROUND: Caspases are downstream elements of apoptosis-mediating pathways initiated by the Fas ligand/Fas receptor system which is supposed to play a central role in the regulation of apoptosis in the human seminiferous epithelium. However, caspase activity in different cell types of this epithelium has never been addressed. METHODS AND RESULTS: We evaluated caspase activity and DNA integrity in Sertoli and germ cells within in-vitro cultured segments of human seminiferous tubules after induction of apoptosis by FSH or testosterone withdrawal. FSH withdrawal increased the incidence of DNA fragmentation in meiotic (primary spermatocytes) and post-meiotic (spermatids) germ cells without producing any detectable effect on caspase activity in these cells and without affecting DNA integrity or caspase activity in Sertoli cells. Testosterone withdrawal stimulated caspase activity and produced DNA fragmentation in Sertoli cells, but showed only a weak effect on DNA fragmentation in germ cells and did not alter germ cell caspase activity. CONCLUSIONS: These findings confirm the central role of caspases in apoptosis of Sertoli cells. However, they also suggest that acute apoptosis of germ cells in the adult human testis occurs in a caspase-independent way and is controlled by Sertoli cells via an as yet undetermined mechanism.     

Germline niche transplantation restores fertility in infertile mice

BACKGROUND: Stem cells interact closely with their microenvironment or niche, and abnormalities in niche compromise the self-renewing tissue. In testis, for example, Sertoli cells interact with germ cells, and defects in Sertoli cells compromises spermatogenesis, leading to male infertility. However, it has not been possible to restore spermatogenesis from endogenous stem cells in infertile testis with environmental defects. METHODS AND RESULTS: When healthy Sertoli cells from infertile white spotting (W) mouse were transplanted into the seminiferous tubules of infertile Steel (Sl) mouse testis that had defective Sertoli cells, spermatogenesis occurred from Sl stem cells in the recipient testis. On average, 1.1% of the recipient tubules showed spermatogenesis. Furthermore, in a microinsemination experiment with germ cells that developed in the testis, we obtained four normal offspring from 114 successfully injected oocytes. CONCLUSIONS: This study demonstrates that defects in male germline microenvironment can be corrected by Sertoli cell transplantation. Although further improvements are required to enhance the low efficiency of spermatogenesis, the ability to correct environmental defect by niche transplantation has important implications in developing new strategies for treating incurable disorders in self-renewing tissues.     

Accelerated germ cell apoptosis in sex chromosome aneuploid fetal human gonads

The purpose of the study was to examine the occurrence of programmed cell death (apoptosis) in normal and chromosomally aneuploid testis and ovaries during the second trimester of human development. Such information may be useful in understanding normal and abnormal germ cell development and disorders associated with infertility in adult life. Apoptosis was studied by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) analysis in human fetal ovaries (n = 16) and testis (n = 14) between 9 and 23 weeks of development, in ovaries of four Turner's syndrome fetuses (45X) and in the gonad of an XO/XY fetus. In normal fetal testis, a small proportion of germ cells, Sertoli cells and Leydig cells undergo apoptosis. In normal fetal ovaries, some developing oocytes and granulosa cells were detected as TUNEL positive. Semiquantitative analysis of fetal ovaries revealed that approximately 3-7% of oocytes were apoptotic. In abnormal fetal testis (XO/XY genotype). TUNEL analysis revealed that only germ cells not enclosed in seminiferous tubules undergo apoptosis. TUNEL analysis of the Turner's syndrome (45X) ovaries studied at 15 and 20 weeks of development revealed massive apoptosis of the oocytes. Nearly 50-70% of the oocytes were TUNEL positive in these ovaries. These results suggest that germ cell apoptosis is a common event occurring during development of human gonads. Chromosomal defects by some means accelerates apoptosis that probably leads to gonadal dysgenesis later in life.     

Maturation phenotype of Sertoli cells in testicular biopsies of azoospermic men

The involvement of Sertoli cells in different spermatogenic impairments has been studied by an immunohistomorphometric technique using cytokeratin-18 (CK-18) as a marker for immature Sertoli cells. CK-18 is known to be expressed in Sertoli cells during prenatal and prepubertal differentiation and is normally lost at puberty. Forty-nine azoospermic men were included in the current study. Quantitative measurements on testicular biopsies revealed the highest CK-18 expression in the mixed atrophy biopsies (22 men), a lower expression in the Sertoli cell-only (SCO) biopsies (12 men), and minimal residual staining in the group considered as representing normal spermatogenesis (six obstructive azoospermia patients). The cytokeratin immunopositive-stained tubules were associated either with arrest in spermatogenesis or with SCO. Examination of sections from nine men with microdeletions in the AZF region of the Y chromosome revealed that these men were either negative for CK-18 expression or showed only weak residual staining. This may suggest that the spermatogenic defect in the AZF-deleted men originates in the germ cell and has no impact on Sertoli cell maturation. The cause that determined the spermatogenic defect in the other cases of male infertility with high CK-18 expression may have damaged both the Sertoli and the germ cells.     

Caspase-dependent and -independent DNA fragmentation in Sertoli and germ cells from men with primary testicular failure: relationship with histological diagnosis

BACKGROUND: Germ cell elimination and sperm DNA fragmentationin men with primary testiculopathies involve apoptosis-relatedprocesses whose mechanisms are poorly understood. This studyexamines the participation of typical (caspase-dependent) andatypical (caspase-independent) pathways in these processes.METHODS: Caspase activity and DNA fragmentation were evaluatedin Sertoli and germ cells from 63 men with non-obstructive azoospermiaand with different histological diagnoses who were undergoingtesticular biopsy for an assisted reproduction attempt. In eightof these men, phosphatidylserine externalization was also examined.RESULTS: The percentage of Sertoli cells showing caspase activityand DNA fragmentation was low and uniform in all diagnoses.In germ cells that remained tightly associated with Sertolicells despite vigorous mechanical treatment, the incidence ofboth caspase activity and DNA fragmentation was high, particularlyin men with maturation arrest. In Sertoli cell-free germ cells,high incidence of DNA fragmentation contrasted with low incidenceof caspase activity and phosphatidylserine externalization.CONCLUSIONS: In men with primary testicular failure, apoptosisof Sertoli cells is insignificant. Some germ cells undergo caspase-dependentapoptosis, show phosphatidylserine externalization and are tightlyassociated with Sertoli cells. Other germ cells show caspase-independentDNA fragmentation, do not externalize phosphatidylserine andlack a tight association with Sertoli cells.     

Lactate inhibits germ cell apoptosis in the human testis

Dysregulation of male germ cell apoptosis has been associated with the pathogenesis of male infertility. Therefore, factors involved in the regulation of germ cell death are being actively investigated. Here, we studied the effects of lactate on human male germ cell death, using as a model a testis tissue culture in which physiological contacts are maintained between the germ cells and the supportive somatic Sertoli cells. Apoptosis of spermatocytes, spermatids and a few spermatogonia was induced by culturing segments of seminiferous tubules under serum-free conditions. This germ cell death was inhibited effectively and dose-dependently by lactate, indicating that it plays a crucial role in controlling cell death cascades of male germ cells. Interestingly, the anti-apoptotic role of lactate was not associated with changes in testicular adenine nucleotide (ATP, ADP and AMP) levels. In the seminiferous tubules, the final site of the death-suppressing action of lactate appeared to be downstream along the cell death pathway activated by the Fas receptor of the germ cells. In conclusion, testicular cell death was effectively regulated by lactate, which may be regarded as a potential compound for optimizing in-vitro methods involving male germ cells for assisted reproduction.     

Misregulation of histone acetylation in Sertoli cell-only syndrome and testicular cancer

In many species, including humans, chromatin remodelling during spermiogenesis is initiated with a marked increase in histone acetylation in elongating spermatids. We have investigated whether this process is disturbed when spermatogenesis is defective or in human testicular tumours. For this purpose, the presence of highly acetylated histone H4 was detected on testicular sections from men with a severe impairment of spermatogenesis of several origins, as well as in different types of testicular tumours. In most tubules devoid of germinal cells (including SCO, Sertoli cell only syndromes) or lacking spermatocytes and spermatids, the Sertoli cells' nuclei showed a global increase in histone H4 acetylation. A similar observation was made in the peritumoral seminiferous tubules of testicular tumour tissues, whenever they were lacking germinal cells, with carcinoma in situ (CIS) cells being hypoacetylated. The global hyperacetylation of elongating spermatids during spermatogenesis could be part of an intercellular signalling pathway involving Sertoli cells and germinal cells, which could be disturbed in cases of severe spermatogenesis impairment, as well as in tubes surrounding germ cells in testicular tumours.     

Expression of carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) in normal human Sertoli cells and its up-regulation in impaired spermatogenesis

Carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1) is usually expressed at the luminal surface of different epithelia and is up-regulated in endothelial cells during angiogenesis. Here, we demonstrate evidence of morphogenetic effects of CEACAM1 in spermatogenesis. CEACAM1 is detectable in normal testicular tissue and seminal fluid. It is present in the adluminal part of Sertoli cells extending only as far as the tight junctions between them. CEACAM1 immunostaining is significantly increased and extends to the basal part of Sertoli cells in the presence of carcinoma in situ. Also, in vitro-induced spermatogenetic disturbance leads to an enhanced CEACAM1 expression in Sertoli cells after 3 days of culture. Remarkably, seminiferous tubules containing exclusively Sertoli cells do not exhibit any CEACAM1 expression. CEACAM1 staining was absent in vascular endothelial cells of normal testicular tissue, but present in small blood vessels of seminomas. These data suggest that CEACAM1 expression in Sertoli cells depends on the presence of germ cells and plays a role in adhesive interactions between Sertoli and differentiating germ cells. Its up-regulation in Sertoli cells accompanying spermatogenic damage may contribute to reconstruction and maintenance of the tubular structure of seminiferous tubules. Additionally, CEACAM1 is apparently involved in the angiogenesis of germ cell tumours.     

Expression patterns of male germ cell markers in cryptorchid pig testes

Male germ cell apoptosis has been described in heat-damaged testes by cryptorchidism. In the present study, wild type pig testes were compared with cryptorchid testes via histological and immunohistological analyses. Spermatozoa were not detected in two cryptorchid testes and the diameters of seminiferous tubules were significantly reduced in cryptorchid pig testes compared with wild type pig testes. Cells expressing marker genes for undifferentiated spermatogonia, such as protein gene product 9.5 was significantly decreased in cryptochid pig testes. In addition, the numbers of cells expressing DEAD-box polypeptide 4 (VASA), synaptonemal complex protein 3, protamine, and acrosin (a biomarker of spermatocyte, spermatid, and spermatozoa) were significantly reduced in cryptochid pig testes. However, the number of vimentin-expressing Sertoli cells was not changed or was significantly increased in cryptorchid pig testes. This result indicates that male germ cells are specifically damaged by heat in cryptorchid pig testes and not Sertoli cells. These findings will facilitate the further study of spermatogenesis and the specific mechanisms by which cryptorchidism causes male infertility.     

Manifestation of Y-chromosomal deletions in the human testis: a morphometrical and immunohistochemical evaluation

BACKGROUND: Deletions of the AZF (azoospermia factor) subregions on the Y chromosome are accompanied by a diverse spectrum of spermatogenic disturbances ranging from hypospermatogenesis to total depletion of germ cells causing infertility. The AZF region encodes gene products which are candidates for the genetic control of spermatogenesis. Although it is known which genes are involved, a general principle of cause and effect cannot yet be deciphered and the deletion type has non-uniform histological phenotypes. METHODS AND RESULTS: We analysed morphological parameters of testicular biopsies from 17 patients diagnosed for Y chromosome microdeletions. As control groups we analysed testes from patients with idiopathic Sertoli cell-only (SCO) syndrome (n = 11), mixed atrophy (n = 10) and complete spermatogenesis (n = 11). A detailed genetic analysis on the extension of the observed microdeletions revealed similar breakpoints in the distal and proximal region of the AZFc region, indicating a common mechanism of homologous recombination for such deletions, as has been suggested before. Morphometric parameters such as the diameter of the tubules, lumen, thickness of the lamina propria and height of the tubule epithelia were investigated. The diameter of the tubules from patients with microdeletions was found to be significantly smaller compared with patients with mixed atrophy. Considering also the size of the tubules, lumen and epithelia, a Y-chromosomal microdeletion represents an intermediate state between an idiopathic SCO and normal spermatogenesis. The immunohistochemical analysis of six different Sertoli cell markers, cytokeratin 18, vimentin, inhibin alpha subunit, 14-3-3 theta, FSH receptor and androgen receptor, revealed no impact of AZF deletion on the specific expression pattern of these genes. CONCLUSIONS: Our results suggest that, notwithstanding the deletion of a common region in the AZFc region, microdeletions of the Y chromosome lead to an intermediate status between idiopathic SCO and complete spermatogenesis, resulting in a heterogeneous histological profile regardless of the seminiferous activity. The Sertoli cell function seems not to be altered.     

The Human Blood-Testis Barrier in Impaired Spermatogenesis

The aim of this study was to explore the competence of the blood-testis barrier (BTB) using electron opaque tracers in diverse human testicular pathologies associated with Sertoli cell only syndrome. Two groups of patients were studied: (1) those with complete depletion (absence) of germ cells, and (2) those with severe germ cell depletion but with some germ cells left in the seminiferous epithelium. The first situation was associated with cryptorchidism with absence of germinal cells, idiopathic cases of aplasia of germ cells, peritumoral areas surrounding small seminomas where the seminiferous tubules were observed to contain a predominant population of Sertoli cells, or long estrogen treatment. The second was found also in cryptorchidism with early germ cells, idiopathic azoospermia, and oligospermia associated with sterility. In the first situation, seminiferous tubules lacked lumen and Sertoli cells had immature morphological characteristics, i.e., oval nuclei with smooth profiles, even heterochromatin distribution and a single, small nucleolus. Inter-Sertoli tight junctions were tortuous, interrupted, and mostly perpendicular to the basal lamina. Lanthanum hydroxide or nickel nitrate permeated most of the inter-Sertoli spaces, indicating disruption of the BTB. In the second situation, seminiferous tubules had a lumen, and Sertoli cells exhibited a mature appearance with large tripartite nucleoli and irregular, highly infolded nucleo-lemma. Only spermatogonia or primary spermatocytes showing diverse degrees of cell involution were found. Numerous inter-Sertoli tight junctions, uninterrupted and parallel to the basal lamina, stopped the electron opaque intercellular tracers close to it; this meant the assembly of a competent BTB. Therefore, a close correlation was found between morphological parameters of Sertoli cell maturity, including their tight junction organization, and BTB integrity.     

Human 'testicular dysgenesis syndrome': a possible model using in-utero exposure of the rat to dibutyl phthalate

BACKGROUND: The disorders comprising human 'testicular dysgenesis syndrome' (TDS) may be increasing in incidence. TDS originates in fetal life but the mechanisms are not known, and discerning them requires an animal model. METHODS AND RESULTS: The study investigated whether male rats exposed in utero to dibutyl phthalate [DBP; 500 mg/kg on gestational days (GD) 13-21] would provide a suitable model for human TDS. DBP induced a high rate (>60%) of cryptorchidism (mainly unilateral), hypospadias, infertility and testis abnormalities, similar to those in human TDS. Cell-specific immunohistochemistry and confocal microscopy were used to track development of Sertoli [anti-Müllerian hormone (AMH), Wilm's tumour (WT-1) protein, p27(kip)], Leydig [3beta-hydroxysteroid dehydrogenase (3beta-HSD)], germ (DAZL protein) and peritubular myoid (smooth muscle actin) cells from fetal life to adulthood. In scrotal and cryptorchid testes of DBP-exposed males, areas of focal dysgenesis were found that contained Sertoli and Leydig cells, and gonocytes and partially formed testicular cords; these dysgenetic areas were associated with Leydig cell hyperplasia at all ages. Suppression ( approximately 90%) of testicular testosterone levels on GD 19 in DBP-exposed males, coincident with delayed peritubular myoid cell differentiation, may have contributed to the dysgenesis. Double immunohistochemistry using WT-1 (expressed in all Sertoli cells) and p27(kip) (expressed only in mature Sertoli cells) revealed immature Sertoli cells in dysgenetic areas. DBP-exposed animals also exhibited Sertoli cell-only (SCO) tubules, sporadically in scrotal and predominantly in cryptorchid, testes, or foci of SCO within normal tubules in scrotal testes. In all SCO areas the Sertoli cells were immature. Intratubular Leydig cells were evident in DBP-exposed animals and, where these occurred, Sertoli cells were immature and spermatogenesis was absent. Abnormal Sertoli cell-gonocyte interaction was evident at GD 19 in DBP-exposed rats coincident with appearance of multinucleated gonocytes, although these disappeared by postnatal day 10 during widespread loss of germ cells. CONCLUSIONS: Abnormal development of Sertoli cells, leading to abnormalities in other cell types, is our hypothesized explanation for the abnormal changes in DBP-exposed animals. As the testicular and other changes in DBP-exposed rats have all been reported in human TDS, DBP exposure in utero may provide a useful model for defining the cellular pathways in TDS.