Secretion of inhibin B by human prepubertal testicular cells in culture

Experimental models of testicular development and function using human tissue and cells

The mammalian testis has two main roles, production of gametes for reproduction and synthesis of steroid- and peptide hormones for masculinization. These processes are tightly regulated and involve complex interactions between a number of germ and somatic cell-types that comprise a unique microenvironment known as the germ stem cell niche. In humans, failure of normal testicular development or function is associated with susceptibility to a variety of male reproductive disorders including disorders of sex development, infertility and testicular cancer. Whilst studies in rodent models have provided detailed insight into the signaling pathways and molecular mechanisms that regulate the testis, there are important species differences in testicular development, function and reproductive disorders that highlight the need for suitable experimental models utilising human testicular tissues or cells. In this review, we outline experimental approaches used to sustain cells and tissue from human testis at different developmental time-points and discuss relevant end-points. These include survival, proliferation and differentiation of cell lineages within the testis as well as autocrine, paracrine and endocrine function. We also highlight the utility of these experimental approaches for modelling the effects of environmental exposures on testicular development and function.

Cancer treatment in childhood and testicular function: the importance of the somatic environment

Testicular function and future fertility may be affected by cancer treatment during childhood. Whilst survival of the germ (stem) cells is critical for ensuring the potential for fertility in these patients, the somatic cell populations also play a crucial role in providing a suitable environment to support germ cell maintenance and subsequent development. Regulation of the spermatogonial germ-stem cell niche involves many signalling pathways with hormonal influence from the hypothalamo-pituitary-gonadal axis. In this review, we describe the somatic cell populations that comprise the testicular germ-stem cell niche in humans and how they may be affected by cancer treatment during childhood. We also discuss the experimental models that may be utilized to manipulate the somatic environment and report the results of studies that investigate the potential role of somatic cells in the protection of the germ cells in the testis from cancer treatment.

Primary Human Testicular Cells Self-Organize into Organoids with Testicular Properties

So far, successful de novo formation of testicular tissue followed by complete spermatogenesis in vitro has been achieved only in rodents. Our findings reveal that primary human testicular cells are able to self-organize into human testicular organoids (TOs), i.e., multi-cellular tissue surrogates, either with or without support of a biological scaffold. Despite lacking testis-specific topography, these mini-tissues harbored spermatogonia and their important niche cells, which retained specific functionalities during long-term culture. These observations indicate the posibility of in vitro re-engineering of a human testicular microenvironment from primary cells. Human TOs might help in the development of a biomimetic testicular model that would exert a tremendous impact on research and development, clinical treatment of infertility, and screening in connection with drug discovery and toxicology.

Establishment of long-term monolayer cultures of somatic cells from human fetal testes and expansion of peritubular myoid cells in the presence of androgen

The somatic (Sertoli cell (SC), Leydig cell (LC), and peritubular myoid (PTM) cell) cells play key roles in development of the fetal testis. We established monolayer cultures from second trimester human testes and investigated the pattern of expression of cell-lineage characteristic mRNAs. Expression of some SC-associated genes (SRY, SOX9, WT1, GATA4, and SF1) was detectable up to and including passage 3 (P3), while others (anti-Müllerian hormone; desert hedgehog) present prior to dissociation were not expressed in the cultured cells. Transcripts encoding the androgen receptor were expressed but addition of dihydrotestosterone (DHT) had no impact on expression of mRNAs expressed in SC or LC. Total concentrations of mRNAs encoding smooth muscle actin (ACTA2) and desmin increased from P1 to P3; an increasing proportion of the cells in the cultures were immunopositive for ACTA2 consistent with proliferation/differentiation of PTM cells. In conclusion, somatic cell monolayer cultures were established from human fetal testes; these cultures could form the basis for future studies based on isolation of purified populations of somatic cells and manipulation of gene expression that is difficult to achieve with organ culture systems. Our results suggest that fetal SC do not maintain a fully differentiated phenotype in vitro, yet PTM (ACTA2 positive) cells readily adapt to monolayer culture conditions in the presence of DHT. This culture system provides an opportunity to study the impact of regulatory factors on gene expression in PTM cells, a population thought to play a key role in mediating androgen action within the developing testis.

Role of IGFs and insulin in the human testis during postnatal activation: differentiation of steroidogenic cells

Immunoexpression of IGF-I, IGF-II, type 1 IGF receptor (IGFR), insulin receptor (IR), and GH receptor (GHR) was analyzed in human testis, in three age groups (Gr): Gr1 (neonates), Gr2 (postnatal testicular activation), and Gr3 (early prepuberty). In interstitial cells, low IGF-I and GHR, but moderate IR immunoexpression was observed in all Grs. However, high expression of IGF-II in Gr1, and moderate expression of IGFR in Gr1 and Gr2 were found. In Leydig cell (LC), high expression of IGF-II, moderate expression of IGFR and GHR, and undetectable IGF-I was found. Moreover, IR was highly expressed in Gr2. The effect of IGF-I on cell proliferation (PI) and apoptosis (AI), induction of cytochrome P450 side chain cleavage (cP450scc) immunoexpression, 3beta-hydroxysteroid dehydrogenase mRNA and testosterone (T) secretion was evaluated in human testis cell cultures. IGF-I increased P450scc immunoexpression, 3beta-hydroxysteroid dehydrogenase mRNA, T secretion, and PI, but decreased AI. We propose that IGF-II, mainly through IR, is involved in functional LC differentiation. In some interstitial cells, probably in LC precursors, IGF-II/IR could be involved, among other factors, in the stimulation of PI and/or inhibition of AI, and in LC differentiation.

Prepubertal serum inhibin B in cryptorchid infants and in monorchid boys with compensatory testicular hypertrophy

OBJECTIVE

To investigate the prepubertal serum inhibin B levels in monorchid boys with compensatory testicular hypertrophy (CTH) and in surgically treated cryptorchid boys with normal testicular volume.

DESIGN

Prospective study.

SETTING

Pediatric Division, University of Verona, Italy.

PATIENT(S)

Thirty-two prepubertal boys: 11 monorchids with CTH and 21 cryptorchids. For comparison we analyzed 15 healthy boys.

MAIN OUTCOME MEASURE(S)

All patients underwent a GnRH agonist test. Inhibin B measurement was performed at basal time.

RESULT(S)

There was a significant difference in mean testicular volume between monorchid and cryptorchid or healthy children, with boys with CTH evidencing larger testicle volume. There was no significant difference in inhibin B levels between boys with CTH and cryptorchid, but the levels were significantly lower in both groups than in the control group. Boys with CTH had significantly higher serum levels of basal FSH than children with cryptorchid. The FSH peak response to GnRH agonist stimulation was significantly higher in boys with CTH than in those with cryptorchid.

CONCLUSION(S)

Monorchid infants with CTH showed low inhibin B and high FSH levels. Our finding may confirm the hypothesis that CTH is unable to prevent testicular insufficiency in adulthood. We suggest an early hormonal evaluation of boys with CTH at puberty, together with early sperm analysis.

Larger testes and higher inhibin B levels in Finnish than in Danish newborn boys

CONTEXT

Recent studies showed that male reproductive health problems, such as cryptorchidism, hypospadias, testicular cancer, and low sperm quality, are more prevalent in Denmark than in Finland.

OBJECTIVES

We hypothesized that, if fetal testicular dysgenesis contributed to these observations, differences in gonadal development and the hypothalamus-pituitary-testis axis would already be detectable perinatally. Thus, we investigated healthy newborn boys in both countries.

DESIGN

This was a prospective, longitudinal population-based study.

SETTING

Two primary obstetric centers were included at the University Hospitals of Copenhagen, Denmark, and Turku, Finland.

PARTICIPANTS

The participants of the study included 633 Danish and 1044 Finnish boys, born at term with appropriate weight for gestational age.

INTERVENTIONS

Ultrasound determination of testis size at 0, 3, and 18 months and blood sampling (n = 727) at 3 months were analyzed.

MAIN OUTCOME MEASURES

Testicular volume and reproductive hormones were measured.

RESULTS

Testis volume was significantly higher at all ages in Finnish than in Danish boys (medians, 98 vs. 95, 185 vs. 119, and 188 vs. 136 mm(3), respectively; P < 0.00001). Testis growth from birth to 3 months was larger in Finnish than in Danish boys (mean, 75 vs. 26 mm(3); P < 0.0001). Serum hormone levels were higher in Finnish than Danish boys for inhibin B (median, 456 vs. 385 pg/ml; P < 0.0001), FSH (1.33 vs. 1.21 IU/liter; P < 0.036), and SHBG (143 vs. 136 nmol/liter; P < 0.022). Inhibin B was significantly positively correlated to testicular volume (r = 0.25; P < 0.006).

CONCLUSIONS

The larger testes and higher inhibin B levels most likely represent a bigger volume of seminiferous tubules in Finnish compared with Danish boys. Although this phenomenon may be attributable to a genetic difference between the two countries, it may also reflect environmental factors influencing testicular development.

Macroorchidism in two unrelated prepubertal boys with a normal FSH receptor

BACKGROUND

Macroorchidism in prepuberty is an uncommon condition which we hypothesised might reflect constitutive activation of the FSH receptor (FSHR).

PATIENTS AND METHODS

Patient 1 was found to have macroorchidism (15 ml testicular volume) at the time of orchidopexy when 3.7 years of age. A gonadal biopsy was obtained at the time of surgery. Patient 2 developed macroorchidism (5 ml) when 8.8 years old. Despite a testicular volume >4 ml, morning testosterone levels were unrecordable with no measurable gonadotrophin production in either patient. Patient 2 had prepubertal gonadotrophin levels 3 years later despite a testicular volume that was 8 ml bilaterally. Inhibin B was measured and the FSHR sequenced in both patients.

RESULTS

Inhibin B levels were age and pubertal stage appropriate. Gonadal biopsy (patient 1) demonstrated areas of Sertoli cell hyperplasia. Sequence analysis of all 10 exons of the FSHR was normal. There was significant, presumed gonadotrophin-dependent testosterone production in both boys by 15 years of age.

CONCLUSIONS

The cause of prepubertal macroorchidism in our patients is unclear but the pronounced difference in phenotype suggests that there may be more than one underlying mechanism. This mechanism was not constitutive activation of a mutated FSHR.

Inhibins in female and male reproductive physiology: role in gametogenesis, conception, implantation and early pregnancy

A great deal of new information has arisen in the recent years concerning inhibin physiology and clinical relevance in reproductive medicine. It is now recognized that the two inhibin isoforms, named inhibin A and inhibin B, are produced by the gonads in the course of gamete maturation and in women have a different pattern of secretion throughout the menstrual cycle. Since inhibins are also produced by placenta and fetal membranes, it has been suggested that there is an involvement in physiological adaptation of pregnancy. Evidence from several sources has underlined the clinical usefulness of the measurement of inhibin-related proteins in the diagnosis and follow-up of different fertility disturbances and early pregnancy viability. In the male, inhibin B is produced in the testis, principally by the Sertoli cells. Inhibin B expression and secretion are positively correlated with Sertoli cell function, sperm number, and spermatogenic status and are negatively correlated with FSH. This review covers the most recent advances on the role of inhibins in human reproductive function. Considerable progress in the understanding of inhibin physiology has resulted from selective measurement of the two inhibin molecular forms, named inhibin A and B. Newly recognized alterations of inhibin levels in gynaecological diseases as well as in normal and pathological pregnancy are discussed, with particular emphasis on the potential clinical usefulness of assessing inhibin levels in serum and other biological fluids.

Apoptosis and proliferation of human testicular somatic and germ cells during prepuberty: high rate of testicular growth in newborns mediated by decreased apoptosis

Programmed cell death and proliferation are evolutionary conserved processes that play a major role during normal development and homeostasis. In the testis, during the fetal and newborn periods, they might determine final adult size and fertility potential. In the present study, we have measured the relative number of testicular cells in apoptosis and in active proliferation in the seminiferous cords and in the interstitium, at different age periods of prepubertal testicular development in humans. Testes from 44 prepubertal subjects without endocrine and metabolic abnormalities were collected at necropsy. They were divided in three age groups (Gr): Gr 1, newborn (1- to 21-d-old neonates), n = 18, mean (+/-SD) age 0.3 +/- 0.23 months; Gr 2, post natal activation (1- to 6-month-old infants), n = 13, mean age 3.93 +/- 1.90 months; and Gr 3, early childhood period (1- to <6-yr-old boys), n = 13, mean age 31.5 +/- 18.9 months. Apoptosis was detected in 5- microm tissue sections using a modified terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay and cell proliferation was assessed by Ki-67 immunohistochemistry. Evaluation of apoptosis was confirmed by estimation of active caspase-3. Mean (+/-SD) testicular weight was 0.38 +/- 0.20, 0.54 +/- 0.35, and 0.51 +/- 0.11 g in Gr 1, Gr 2, and Gr 3, respectively. In Gr 1, there was a significant positive correlation between age and testis weight (P = 0.02). Mean (+/-SD) germ cell apoptotic index, AI, (% of apoptotic cells out of total cell number) was 15.0 +/- 6.60, 27.0 +/- 8.80 and 33.4 +/- 11.4 in Gr 1, Gr 2, and Gr 3, respectively. In Sertoli cells, it was 6.60 +/- 4.07, 22.0 +/- 14.0 and 27.5 +/- 19.8, respectively. In interstitial cells, it was 10.2 +/- 6.38, 18.0 +/- 6.70 and 25.7 +/- 15.5, respectively. In the three types of cells, AI in Gr 1 was significantly lower than in Gr 2 or Gr 3 (P < 0.05). Mean (+/-SD) germ cell proliferation index, PI, was 18.6 +/- 13.0, 10.0 +/- 6.50 and 10.9 +/- 6.24% in Gr 1, Gr 2, and Gr 3, respectively. In Sertoli cells and in interstitial cells PI was similar in the three age groups. The PI/AI ratio was used to compare relative differences among age groups. The PI/AI ratio of germ cells, Sertoli cells and interstitial cells in Gr 1 was significantly higher than in Gr 2 or Gr 3 (P < 0.05). It is concluded that, in normal subjects, there is a vigorous growth of the testis during the newborn period with subsequent stabilization during the first years of prepuberty. This cell growth seems to be mainly mediated by decreased apoptosis. The factors that modulate apoptosis of testicular cells are not known, but it is remarkable that this change takes place before the testosterone peak of the post natal gonadal activation of the first trimester of life. These changes taking place during the newborn period might be important to define testicular function in adults.

Inhibins in childhood and puberty

Inhibin is a heterodimeric glycoprotein that consists of an alpha-subunit linked to either a betaA subunit (inhibin A) or to a betaB subunit (inhibin B) and it exists in at least six different isoforms. These isoforms can not be measured separately by immunoassays. In boys, serum inhibin B levels change in concert with the increase in gonadotrophins. Associated with the postnatal activation of gonadotrophin secretion, the early inhibin B secretion is sustained until the age of 18-24 months; thereafter serum concentrations subside. In boys, between Tanner stages G1 and G2, serum inhibin B concentration again increases, but then plateaus. Inhibin A levels in human males are below the detection limit, but in girls, during the postnatal activation of gonadotrophin secretion, both serum inhibin A and inhibin B concentrations are measurable. Serum inhibin B levels correlate positively with age several years before the clinical onset of puberty, suggesting increasing follicular activity in late prepuberty. During female puberty, the inhibin B level increases from Tanner stage B1 through stage B3, suggesting high follicular activity before the development of ovulatory menstrual cycles, but serum inhibin A levels become measurable later in puberty, in agreement with the idea that inhibin A is mainly produced by the corpus luteum.

Somatostatin inhibits stem cell factor messenger RNA expression by Sertoli cells and stem cell factor-induced DNA synthesis in isolated seminiferous tubules

Immature porcine Sertoli cells have been reported to be targets for the regulatory peptide somatostatin (SRIF), which inhibits the basal and FSH-induced proliferation of Sertoli cells through a decrease of cAMP production. In the present study, we show that SRIF inhibits both basal and FSH-stimulated expression of the stem cell factor (SCF), a Sertoli cell-specific gene. The SRIF-mediated inhibition of forskolin-triggered, but not of 8-bromoadenosine-cAMP-triggered, SCF mRNA expression demonstrates the involvement of adenylyl cyclase in underlying peptide actions. Moreover, these effects require functional coupling of specific plasma membrane receptors to adenylyl cyclase via inhibitory G proteins, because pertussis toxin prevents SRIF-mediated inhibition of SCF mRNA expression. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assays suggest the involvement of sst2 receptors in SRIF actions on Sertoli cells. The biological relevance of these data is supported by an SRIF-mediated decrease in SCF-induced incorporation of [(3)H]thymidine in isolated seminiferous tubules. In situ hybridization and confocal microscopy show that, in seminiferous tubules only, spermatogonia display both c-kit and sst2 receptors. Taken together, these results suggest that SCF-stimulated DNA synthesis can be inhibited by SRIF in spermatogonia, but not in Sertoli and peritubular cells. Combined RT-PCR and immunohistochemical approaches point toward spermatogonia and Leydig cells as the source of testicular SRIF. These data argue in favor of paracrine/autocrine SRIF actions in testis.