Growth factors and testicular development

Testicular niche repair after gonadotoxic treatments: Current knowledge and future directions

The testicular niche, which includes the germ cells, somatic cells, and extracellular matrix, plays a crucial role in maintaining the proper functions of the testis. Gonadotoxic treatments, such as chemotherapy and radiation therapy, have significantly improved the survival rates of cancer patients but have also been shown to have adverse effects on the testicular microenvironment. Therefore, repairing the testicular niche after gonadotoxic treatments is essential to restore its function. In recent years, several approaches, such as stem cell transplantation, gene therapy, growth factor therapy, and pharmacological interventions have been proposed as potential therapeutic strategies to repair the testicular niche. This comprehensive review aims to provide an overview of the current understanding of testis damage and repair mechanisms. We will cover a range of topics, including the mechanism of gonadotoxic action, repair mechanisms, and treatment approaches. Overall, this review highlights the importance of repairing the testicular niche after gonadotoxic treatments and identifies potential avenues for future research to improve the outcomes for cancer survivors.

Using a testis regeneration model, FGF9, LIF, and SCF improve testis cord formation while RA enhances gonocyte survival

Implantation of testis cell aggregates from various donors under the back skin of recipient mice results in de novo formation of testis tissue. We used this implantation model to study the putative in vivo effects of six different growth factors on testis cord development. Recipient mice (n = 7/group) were implanted with eight neonatal porcine testis cell aggregates that were first exposed to a designated growth factor: FGF2 at 1 µg/mL, FGF9 at 5 µg/mL, VEGF at 3.5 µg/mL, LIF at 5 µg/mL, SCF at 3.5 µg/mL, retinoic acid (RA) at 3.5 × 10^-5 M, or no growth factors (control). The newly developed seminiferous cords (SC) were classified based on their morphology into regular, irregular, enlarged, or aberrant. Certain treatments enhanced implant weight (LIF), implant cross-sectional area (SCF) or the relative cross-sectional area covered by SC within implants (FGF2). RA promoted the formation of enlarged SC and FGF2 led to the highest ratio of regular SC and the lowest ratio of aberrant SC. Rete testis-like structures appeared earlier in implants treated with FGF2, FGF9, or LIF. These results show that even brief pre-implantation exposure of testis cells to these growth factors can have profound effects on morphogenesis of testis cords using this implantation model.

Effective cryopreservation protocol for preservation of male primate (Macaca fascicularis) prepubertal fertility

RESEARCH QUESTION

Can specimen types (cells versus tissues) and additive cryoprotectant agents contribute to efficient cryopreservation of primate spermatogonial stem cells (SSC)?

DESIGN

Testicular tissues or cells from four prepubertal monkeys were used in this study. The freezing efficacy of testicular tissue was compared with cell suspensions using conventional freezing media (1.4 mol/l dimethyl sulfoxide [DMSO]) and the efficacy of cryoprotectant additives (1.4 mol/l DMSO combined with trehalose 200 mmol/l, hypotaurine 14 mmol/l, necrostatin-1 50 µmol/l or melatonin 100 µmol/l) was evaluated in testicular tissue freezing.

RESULTS

The survival rate (46.0 ± 4.8% versus 33.7 ± 6.0%; P = 0.0286) and number of recovered cells (5.0 ± 1.5 × 10⁶ cells/g versus 0.7 ± 0.8 × 10⁶ cells/g; P = 0.0286) were significantly higher in frozen tissues than in frozen cell suspensions. After tissue freezing, a higher number of recovered PGP9.5⁺ cells were observed with 200 mmol/l trehalose treatment than in DMSO controls (2.4 ± 0.6 × 10⁶ cells/g versus 1.1 ± 0.3 × 10⁶ cells/g; P = 0.0164). Normal establishment of donor-derived colony was observed in SSC after tissue freezing with 200 mmol/l trehalose.

CONCLUSIONS

Testicular tissue freezing is more effective than single cell suspension freezing for higher recovery of undifferentiated spermatogonia. Moreover, it was verified that slow freezing using 200 mmol/l trehalose, 1.4 mol/l DMSO and 10% KnockOut™ Serum Replacement in Dulbecco's phosphate-buffered saline is an effective cryopreservation protocol for primate testicular tissue.

Growth Factors, and Cytokines; Understanding the Role of Tyrosine Phosphatase SHP2 in Gametogenesis and Early Embryo Development

Growth factors and cytokines have vital roles in germ cell development, gamete maturation, and early embryo development. Cell surface receptors are present for growth factors and cytokines to integrate with and trigger protein signaling in the germ and embryo intracellular milieu. Src-homology-2-containing phosphotyrosine phosphatase (SHP2) is a ubiquitously expressed, multifunctional protein that plays a central role in the signaling pathways involved in growth factor receptors, cytokine receptors, integrins, and G protein-coupled receptors. Over recent decades, researchers have recapitulated the protein signaling networks that influence gamete progenitor specification as well as gamete differentiation and maturation. SHP2 plays an indispensable role in cellular growth, survival, proliferation, differentiation, and migration, as well as the basic events in gametogenesis and early embryo development. SHP2, a classic cytosolic protein and a key regulator of signal transduction, displays unconventional nuclear expression in the genital organs. Several observations provided shreds of evidence that this behavior is essential for fertility. The growth factor and cytokine-dependent roles of SHP2 and its nuclear/cytoplasmic presence during gamete maturation, early embryonic development and embryo implantation are fascinating and complex subjects. This review is intended to summarize the previous and recent knowledge about the SHP2 functions in gametogenesis and early embryo development.

Vascular endothelial growth factor (VEGF-A) and fibroblast growth factor (FGF-2) as potential regulators of seasonal reproductive processes in male European bison (Bison bonasus, Linnaeus 1758)

Growth factors: vascular endothelial growth factor A (VEGF-A) and fibroblast growth factor (FGF-2) were reported to affect normal physiological reproductive processes in human, domestic and free living animals. Moreover, some reports suggest that VEGF-A and FGF-2 may be directly involved in the control of the annual reproductive cycle of seasonally breeding animals but detailed knowledge is still missing. Our study aimed to demonstrate the expression of mRNA and protein for both factors in the tissues of testis and epididymis (caput, corpus, cauda) at different periods of the year (March, June, November, December) in European bison as a model of seasonally breeding animal. Results suggest, that VEGF-A expression was more pronounced in testis than in epididymis and the highest expression was noted in December and June. Surprisingly, the highest protein accumulation was observed in June at the same level in all tissues analyzed. On the other hand, the highest FGF-2 mRNA expression was noted in testis in June and in epididymis in March. However, no differences in protein expression of FGF-2 were found between analyzed groups. The results indicate that both factors are necessary for proper functioning of the reproductive system and their levels differ seasonally. Perhaps, it is linked to increased need of these factors in the testis as well as epididymis during preparation for the reproductive functions. Moreover, VEGF-A and FGF-2 not only may regulate reproductive functions by affecting vascularization and cell nutrition, but it also may be possible that they possess protective functions by stabilizing the reproductive cells. Therefore, obtained results provide new insight into mechanisms underlying seasonal breeding of the male European bison.

Pediatric germ cell tumors

Pediatric germ cell tumors represent a diverse group of tumors that present from in utero through adolescence at many nongonadal locations, from the neck to the sacrococcygeal region. Surgical resection remains the central element of management, and accurate surgical staging is essential to properly ascertain the correct risk-based treatment. The management for all benign tumors (mature and immature teratomas) and select completely resectable malignant tumors is surgery alone. Modern-day chemotherapy is extremely effective in infants and children with unresectable and metastatic disease and these children have a very high survival rate. The use of neoadjuvant chemotherapy allows vital organ preservation and there is no role for resection of vital structures at the time of initial presentation.

Childhood primary mesenteric seminoma

We report an 11-year-old child who presented with an abdominal lump and was diagnosed as having an extragonal primary mesenteric seminoma. Patient was treated with 4 cycles of combination chemotherapy cisplatin, etoposide and bleomycin; he is now disease free for 2 years. We discuss and review extragonadal germ cell tumors arising from the mesentery and their management.

Expression and localization of growth factors and their receptors in the mammalian testis. Part I: Fibroblast growth factors and insulin-like growth factors

It is now well established that normal development and function of testis are mediated by endocrine and paracrine pathways including hormones, growth factors and cytokines as well as by direct cell-to-cell contacts depending on tight, adhering and gap junctions. In the last two decades, several growth factors were identified in the testis of various mammalian species. Growth factors are shown to promote cell proliferation, regulate tissue differentiation, and modulate organogenesis. Interestingly, most of these peptides are expressed not only in the adult mammalian testis during spermatogenesis but also during testicular morphogenesis in prenatal and postnatal life. Our study was launched to provide an overview of the expression, localization, and putative physiological roles of growth factors and their receptors in the mammalian testis. The growth factors considered in this part of our review are fibroblast growth factors and insulin-like growth factors. These factors are found in testicular cells in prenatal, postnatal, and adult animals and are implicated in the regulation of important testicular activities including testicular cord morphogenesis, modulation of testicular hormone secretion and control of spermatogenesis.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Fgf9induces proliferation and nuclear localization of FGFR2 in Sertoli precursors during male sex determination

Recently, we demonstrated that loss of Fgf9 results in a block of testis development and a male to female sex-reversed phenotype; however, the function of Fgf9 in sex determination was unknown. We now show that Fgf9 is necessary for two steps of testis development just downstream of the male sex-determining gene, Sry: (1) for the proliferation of a population of cells that give rise to Sertoli progenitors; and (2) for the nuclear localization of an FGF receptor (FGFR2) in Sertoli cell precursors. The nuclear localization of FGFR2 coincides with the initiation of Sry expression and the nuclear localization of SOX9 during the early differentiation of Sertoli cells and the determination of male fate.

Protein phosphatase 1cgamma is required in germ cells in murine testis

The protein phosphatase 1cgamma (PP1cgamma) gene is required for spermatogenesis. Males homozygous for a null mutation are sterile, and display both germ cell and Sertoli cell defects. As these two cell types are physically and functionally intimately connected in the testis, the question arises as to whether the primary site of PP1cgamma action is in Sertoli cells, germ cells, or both. We generated chimeric males by embryo aggregation to test whether wild type Sertoli cells are capable of rescuing mutant germ cells. To distinguish between the desired XY-XY chimeras and uninformative XX-XY chimeras, we designed an adaptation of the single nucleotide primer extension (SNuPE) assay. None of the XY-XY chimeras sired pups derived from mutant germ cells, indicating that the protein is required in germ cells for production of functional sperm. Analysis of a chimeric testis revealed intermediate phenotypes when compared with PP1cgamma-/- testes, suggestive of cell nonautonomous effects. We conclude that PP1cgamma is required in a cell autonomous fashion in germ cells. There may be an additional cell nonautonomous role played by this gene in testes, possibly mediated by defective signaling between germ cells and Sertoli cells.

Cell Junction Dynamics in the Testis: Sertoli-Germ Cell Interactions and Male Contraceptive Development

Spermatogenesis is an intriguing but complicated biological process. However, many studies since the 1960s have focused either on the hormonal events of the hypothalamus-pituitary-testicular axis or morphological events that take place in the seminiferous epithelium. Recent advances in biochemistry, cell biology, and molecular biology have shifted attention to understanding some of the key events that regulate spermatogenesis, such as germ cell apoptosis, cell cycle regulation, Sertoli-germ cell communication, and junction dynamics. In this review, we discuss the physiology and biology of junction dynamics in the testis, in particular how these events affect interactions of Sertoli and germ cells in the seminiferous epithelium behind the blood-testis barrier. We also discuss how these events regulate the opening and closing of the blood-testis barrier to permit the timely passage of preleptotene and leptotene spermatocytes across the blood-testis barrier. This is physiologically important since developing germ cells must translocate across the blood-testis barrier as well as traverse the seminiferous epithelium during their development. We also discuss several available in vitro and in vivo models that can be used to study Sertoli-germ cell anchoring junctions and Sertoli-Sertoli tight junctions. An in-depth survey in this subject has also identified several potential targets to be tackled to perturb spermatogenesis, which will likely lead to the development of novel male contraceptives.

Detection of growth factors in the testis of roe deer (Capreolus capreolus)

Roe deer is a seasonal breeder characterised by a short rutting season in summer. Mature males show synchronised cycles of testicular involution and recrudescence. Therefore, this species is a valuable model to study seasonal regulation of spermatogenesis in ruminants. It is hypothesised that a time-dependent production of testicular growth factors is required to regulate seasonal changes in testis growth and spermatogenesis. To identify potential candidates, total RNA from roe deer testis tissue was extracted at three different seasonal periods (April, August, December), and using RT-PCR the presence of several growth factors (aFGF, bFGF, IGF-I, IGF-II, TGF-alpha, TGF-beta1, TGF-beta3 and two isoforms of VEGF) was detected. Sequencing of the growth factor PCR fragments revealed a high sequence homology between cattle and roe deer. To further explore the expression patterns of the identified growth factors in roe deer their expression levels were standardised using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression. The study demonstrates the expression of several growth factors in roe deer testis and supports the assumption of their seasonally diverse regulation. These results provide the basis to investigate the role of growth factors in the regulation of circannual changes of testicular activity.

The influence of protein malnutrition on the antifertility action of gossypol in the Trypanosoma brucei-infected rat: some ultrastructural observations from the testis

The testes of adult male Wistar rats that were variously protein malnourished, gossypol treated, and/or trypanosome infected (Trypanosoma brucei) were evaluated ultrastructurally. The findings included several necrotic germ cells in the seminiferous epithelium and focal degeneration of Sertoli cells. Leydig cells showed a remarkable paucity of smooth endoplasmic reticulum, and aggregation of mitochondria. These observations were prevalent in those animals that were simultaneously protein-malnourished/gossypol treated/ trypanosome infected, and were either absent or markedly reduced in the other groups. These structural alterations are probably related to increased gossypol availability to the testis and/or represent the additive effects of gossypol and trypanosomes. Such tissue changes could compromise spermatogenesis in affected animals, and suggest that trypanosome infections may exacerbate testicular lesions in the gossypol-treated rat.

Distinct expression of cytokines and mitogenic inhibitory factors in semen of fertile and infertile men

PROBLEM

To assess the effect of seminal plasma (SP) of fertile and infertile men on leukocyte mitogenic response, and the capability of sperm cells to produce IL-1.

METHODS

This study included four groups: fertile men (donors, normal), infertile men with azoospermia (azoo), oligo-terato-asthenozoospermia (OTA), and OTA with genital infection (OTA-inf). Mouse spleen cell proliferation in response to lipopolysaccharide (LPS) or Concanavalin-A (Con-A) was examined in the presence of SP from the above four groups. Supernatants (sup) and lysates (lys) of sperm cells from fertile and oligoteratoasthenospermic (OTA) men were evaluated for IL-1 bioactivity by specific bioassay.

RESULTS

Seminal plasma (SP) of the four groups were shown to inhibit the mitogenic response of mouse spleen cells to LPS and Con-A. SP of fertile men was significantly more inhibitory than SP from infertile men. Sperm cells from fertile and OTA infertile men constitutively produced IL-1. Sperm cells of both groups produced similar levels of IL-1 as examined in the supernatants and lysates.

CONCLUSIONS

Seminal plasma of fertile men had more inhibitory mitogenic activity than that of OTA. Sperm cells constitutively produce IL-1. It is possible that the factors involved in this inhibition are not only anti-proliferative immune factors. Cytokines and inhibitory factors of mitogenesis in the seminal plasma may be involved in the physiology and pathophysiology of sperm functions and thus affect male fertility.

Detection of keratinocyte growth factor (KGF) messenger ribonucleic acid and immunolocalization of KGF in the canine testis

Keratinocyte growth factor (KGF) was originally discovered in human embryonic lung fibroblasts and is a member of the fibroblast growth factor (FGF) family. Members of the FGF family have been shown to regulate testicular function. However, the recently discovered KGF has not been studied in the testis. KGF has been detected in many other tissues, including the prostate, an organ whose development and function have been associated with presence of the testis. In this study, KGF mRNA was detected in the whole testis using reverse transcription polymerase chain reaction (RT-PCR). The 575-bp KGF-specific product was detected along with a 594-bp β-actin-specific product. To identify the cell types in which KGF mRNA was predominantly expressed, interstitial cells were physically separated from seminiferous tubules. The interstitial cells were then sorted on a discontinuous Percoll gradient and total cellular mRNAs isolated. Using RT-PCR and Southern hybridization with specific cDNA probes, the KGF mRNA was detected in interstitial cells. KGF expression levels were then evaluated semiquantitatively with a competitive RT-PCR assay. KGF expression levels were highest in interstitial cells that equilibrated between 20 and 30% Percoll. Enriched Leydig cells and seminiferous tubules expressed low levels of KGF. Finally, immunohistochemical analysis was performed on canine testes using a rabbit anti-KGF polyclonal antibody. The KGF protein was localized predominantly to peritubular cells of the canine testis. These results suggest that KGF is synthesized in the canine testis.

Molecular mechanisms of testicular carcinogenesis

Molecular investigations into the neoplastic transformation of a normal spermatogenic precursor cell into a germ-cell malignancy have implicated a wide array of DNA and RNA alterations. Previous epidemiologic and familial patterns of cancer presentation had suggested that testicular cancer developed from one or more genetic alterations. In particular, mutations in cellular oncogenes such as c-kit and tumor-suppressor genes such as the retinoblastoma gene product have been identified as putative etiologic agents in the development and progression of testicular germ-cell tumors. Additionally, alterations in the transcription of RNA that are regulated through a process of genomic imprinting have been identified in human testis cancers. This report provides a framework for integrating this growing literature on the molecular biology of testicular germ-cell tumors into a potential etiologic hypothesis.

Testicular development involves the spatiotemporal control of PDGFs and PDGF receptors gene expression and action

Platelet-derived growth factors (PDGFs) are growth-regulatory molecules that stimulate chemotaxis, proliferation and metabolism primarily of cells of mesenchymal origin. In this study, we found high levels of PDGFs and PDGFs receptors (PDGFRs) mRNAs, and specific immunostaining for the corresponding proteins in the rat testis. PDGFs and PDGFRs expression was shown to be developmentally regulated and tissue specific. Expression of PDGFs and PDGFRs genes was observed in whole testis RNA 2 d before birth, increased through postnatal day 5 and fell to low levels in adult. The predominant cell population expressing transcripts of the PDGFs and PDGFRs genes during prenatal and early postnatal periods were Sertoli cells and peritubular myoid cells (PMC) or their precursors, respectively, while in adult animals PDGFs and PDGFRs were confined in Leydig cells. We also found that early postnatal Sertoli cells produce PDGF-like substances and that this production is inhibited dose dependently by follicle-stimulating hormone (FSH). The expression of PDGFRs by PMC and of PDGFs by Sertoli cells corresponds in temporal sequence to the developmental period of PMC proliferation and migration from the interstitium to the peritubulum. Moreover, we observed that all the PDGF isoforms and the medium conditioned by early postnatal Sertoli cells show a strong chemotactic activity for PMC which is inhibited by anti-PDGF antibodies. These data indicate that, through the spatiotemporal pattern of PDGF ligands and receptors expression, PDGF may play a role in testicular development and homeostasis.

Testicular dysfunction in human immunodeficiency virus-infected men

This review pertains to gonadal function in men with human immunodeficiency virus (HIV) infection, who often exhibit clinical and biochemical evidence of hypogonadism. Hypogonadotropic hypogonadism appears to be the most commonly encountered abnormality, although complete anterior pituitary insufficiency and primary gonadal failure have been reported. Levels of sex hormone-binding globulin (SHBG) are either unchanged or increased. Plasma levels of estrogens, progesterone, androstenedione, dehydroepiandrosterone sulfate (DHEA-S), and prolactin vary. Pathologically, except for involvement by opportunistic infections, no significant abnormality in the hypothalamic-pituitary area has been described, but evidence of orchitis is commonly present. The cause(s) of these abnormalities remains unclear. The possible factors leading to hypogonadism in HIV-infected men include HIV infection itself, opportunistic infections, chronic debilitating illness, and effects of cytokines on the hypothalamic-pituitary-gonadal axis. Further studies are needed to clarify the cause(s) of testicular dysfunction in HIV-infected men and its clinical significance, treatment, relevance to the progression of HIV infection, and influence on the immune system.

Expression of the c-kit proto-oncogene and its ligand stem cell factor (SCF) in normal and malignant human testicular tissue

Recent findings suggest an important role of the proto-oncogene c-kit, a surface membrane receptor of the tyrosine kinase family, and its ligand stem cell factor (SCF) in normal spermatogenesis and possibly in the pathogenesis of certain testicular germ cell tumors. To further investigate this potential role, the expression of c-kit and SCF was studied in normal and malignant human testicular tissue specimens at the mRNA and protein level by Northern blot analysis and immunohistochemistry, respectively. The detection of the c-kit receptor in normal human germ cells and its natural ligand SCF in Sertoli cells suggests the presence of a local trophic regulatory system that may be active in human spermatogenesis. Additionally, c-kit expression was detected in the seminoma but not in the nonseminoma subtype of human testicular germ cell tumors (GCT). Stem cell factor was not expressed at the mRNA level in tissue from either subtype of GCT as determined by Northern blot analysis; however, the protein was detected immunohistochemically in the cytoplasm of rare tumor cells.

Gonadal function in galactosemics and in galactose-intoxicated animals

Gonadal dysfunction, specifically hypergonadotropic hypogonadism, in female galactosemics is an almost universal finding. Minimal transferase activity may modulate ovarian function and the time of menopause. In contrast, male galactosemics have a relatively low risk of gonadal dysfunction. Animal models have variously suggested prenatal and postnatal insults which may play a role in the gonadal pathology. Several candidate toxic states may be involved. Current dietary restrictions are inadequate to prevent ovarian failure. Until such time as the pathophysiology is better understood, therapy will remain palliative and supportive. Exogenous estrogen and progesterone have roles in assisting pubertal changes and in prevention of the sequelae of a post-menopausal state.