Transforming growth factor-beta2 mediates mesenchymal-epithelial interactions of testicular somatic cells

Sertoli and Germ Cells Within Atrophic Seminiferous Tubules of Men With Non-Obstructive Azoospermia

BACKGROUND

Infertile men with non-obstructive azoospermia (NOA) have impaired spermatogenesis. Dilated and un-dilated atrophic seminiferous tubules are often present in the testes of these patients, with the highest likelihood of active spermatogenesis in the dilated tubules. Little is known about the un-dilated tubules, which in NOA patients constitute the majority. To advance therapeutic strategies for men with NOA who fail surgical sperm retrieval we aimed to characterize the spermatogonial stem cell microenvironment in atrophic un-dilated tubules.

METHODS

Testis biopsies approximately 3x3x3 mm³ were obtained from un-dilated areas from 34 patients. They were classified as hypospermatogenesis (HS) (n=5), maturation arrest (MA) (n=14), and Sertoli cell only (SCO) (n= 15). Testis samples from five fertile men were included as controls. Biopsies were used for histological analysis, RT-PCR analysis and immunofluorescence of germ and Sertoli cell markers.

RESULTS

Anti-Müllerian hormone mRNA and protein expression was increased in un-dilated tubules in all three NOA subtypes, compared to the control, showing an immature state of Sertoli cells (p<0.05). The GDNF mRNA expression was significantly increased in MA (P=0.0003). The BMP4 mRNA expression showed a significant increase in HS, MA, and SCO (P=0.02, P=0.0005, P=0.02, respectively). The thickness of the tubule wall was increased 2.2-fold in the SCO-NOA compared to the control (p<0.05). In germ cells, we found the DEAD-box helicase 4 (DDX4) and melanoma-associated antigen A4 (MAGE-A4) mRNA and protein expression reduced in NOA (MAGE-A: 46% decrease in HS, 53% decrease in MA, absent in SCO). In HS-NOA, the number of androgen receptor positive Sertoli cells was reduced 30% with a similar pattern in mRNA expression. The γH2AX expression was increased in SCO as compared to HS and MA. However, none of these differences reached statistical significance probably due to low number of samples.

CONCLUSIONS

Sertoli cells were shown to be immature in un-dilated tubules of three NOA subtypes. The increased DNA damage in Sertoli cells and thicker tubule wall in SCO suggested a different mechanism for the absence of spermatogenesis from SCO to HS and MA. These results expand insight into the differences in un-dilated tubules from the different types of NOA patients.

Betaglycan (TβRIII) is a Key Factor in TGF-β2 Signaling in Prepubertal Rat Sertoli Cells

Transforming growth factor-βs (TGF-βs) signal after binding to the TGF-β receptors TβRI and TβRII. Recently, however, betaglycan (BG) was identified as an important co-receptor, especially for TGF-β2. Both proteins are involved in several testicular functions. Thus, we analyzed the importance of BG for TGF-β1/2 signaling in Sertoli cells with ELISAs, qRT-PCR, siRNA silencing and BrdU assays. TGF-β1 as well as TGF-β2 reduced shedding of membrane-bound BG (mBG), thus reducing the amount of soluble BG (sBG), which is often an antagonist to TGF-β signaling. Treatment of Sertoli cells with GM6001, a matrix metalloproteinases (MMP) inhibitor, also counteracted BG shedding, thus suggesting MMPs to be mainly involved in shedding. Interestingly, TGF-β2 but not TGF-β1 enhanced secretion of tissue inhibitor of metalloproteinases 3 (TIMP3), a potent inhibitor of MMPs. Furthermore, recombinant TIMP3 attenuated BG shedding. Co-stimulation with TIMP3 and TGF-β1 reduced phosphorylation of Smad3, while a combination of TIMP3/TGF-β2 increased it. Silencing of BG as well as TIMP3 reduced TGF-β2-induced phosphorylation of Smad2 and Smad3 significantly, once more highlighting the importance of BG for TGF-β2 signaling. In contrast, this effect was not observed with TIMP3/TGF-β1. Silencing of BG and TIMP3 decreased significantly Sertoli cell proliferation. Taken together, BG shedding serves a major role in TGF-β2 signaling in Sertoli cells.

Expression and function of scleraxis in the developing auditory system

A study of genes expressed in the developing inner ear identified the bHLH transcription factor Scleraxis (Scx) in the developing cochlea. Previous work has demonstrated an essential role for Scx in the differentiation and development of tendons, ligaments and cells of chondrogenic lineage. Expression in the cochlea has been shown previously, however the functional role for Scx in the cochlea is unknown. Using a Scx-GFP reporter mouse line we examined the spatial and temporal patterns of Scx expression in the developing cochlea between embryonic day 13.5 and postnatal day 25. Embryonically, Scx is expressed broadly throughout the cochlear duct and surrounding mesenchyme and at postnatal ages becomes restricted to the inner hair cells and the interdental cells of the spiral limbus. Deletion of Scx results in hearing impairment indicated by elevated auditory brainstem response (ABR) thresholds and diminished distortion product otoacoustic emission (DPOAE) amplitudes, across a range of frequencies. No changes in either gross cochlear morphology or expression of the Scx target genes Col2A, Bmp4 or Sox9 were observed in Scx(-/-) mutants, suggesting that the auditory defects observed in these animals may be a result of unidentified Scx-dependent processes within the cochlea.

Production and characterization of engineered alginate-based microparticles containing ECM powder for cell/tissue engineering applications

A method for the production of engineered alginate-based microparticles, containing extracellular matrix and neonatal porcine Sertoli cells (SCs), is described. As a source for extracellular matrix, a powder form of isolated and purified urinary bladder matrix (UBM) was employed. We demonstrated that the incorporation of UBM does not significantly alter the morphological and dimensional characteristics of the microparticles. The alginate microparticles were used for SC encapsulation as an immunoprotective barrier for transplant purposes, while the co-entrapped UBM promoted retention of cell viability and function. These engineered microparticles could represent a novel approach to enhancing immunological acceptance and increasing the functional life-span of the entrapped cells for cell/tissue engineering applications. In this respect, it is noteworthy that isolated neonatal porcine SCs, administered alone in highly biocompatible microparticles, led to diabetes prevention and reversion in nonobese diabetic (NOD) mice.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Fetal testis dysgenesis and compromised Leydig cell function in Tgfbr3 (beta glycan) knockout mice

Betaglycan (Tgfbr3) is a coreceptor for transforming growth factor-beta (TGFB) superfamily ligands. In the current study, a defect in seminiferous cord formation was detected in 12.5-13.5 days postcoitum (dpc) beta glycan null murine testis. Immunohistochemistry with antibodies against cell-specific markers revealed defects in somatic cell populations. To confirm these data, quantitative real-time PCR was performed to determine changes in the expression levels of genes involved in fetal testis cell differentiation and function. The expression levels of the Leydig cell markers Insl3, Cyp17a1, Cyp11a1, Star, and Hsd3b1 were reduced in knockout testis compared to wild-type testis, beginning at 12.5 dpc. Whole mount in situ hybridization confirmed that Cyp11a1 expression was reduced in the null testis, but its distribution pattern was unchanged. Apoptosis was not affected by the loss of beta glycan, but proliferation within the interstitium was reduced at 14.5 dpc. However, morphometric analysis showed no changes in Leydig cell counts between the wild-type and the knockout testes at 14.5 dpc, indicating that fetal Leydig function, rather than number, was affected by the loss of beta glycan. The expression levels of Sertoli cell markers Dhh, Sox9, and Amh were also reduced in the knockout testis at 14.5 dpc. However, the expression of fetal germ cell markers Pou5f1 and DDX4 were not changed across the genotypes at any age examined. Our data show that the presence of beta glycan is required for normal cord formation, normal fetal Leydig cell development, and the establishment of fetal testis endocrine function, thus implicating TGFB superfamily members as regulators of early fetal testis structure and function.

Differential expression of TGFBR3 (betaglycan) in mouse ovary and testis during gonadogenesis

TGFBR3 is an accessory receptor that binds to and modulates the activities of both transforming growth factor-beta (TGFbeta) and inhibin, two members of the TGFbeta superfamily of growth factors that regulate many aspects of reproductive biology. Tgfbr3 is known to be expressed in adult testis and ovary, but little is known about this receptor during gonadogenesis. Herein, we describe Tgfbr3 expression in the male and female fetal and neonatal murine gonad. Real-time PCR analysis revealed that Tgfbr3 mRNA was expressed at higher levels in the developing testis compared to ovary. TGFBR3 was expressed within the fetal testis interstitium, predominantly by Leydig cells, but expression shifted inside the seminiferous cords at birth. In contrast, TGFBR3 was detected in both the somatic and germ cell lineages in the fetal and neonatal ovary. This differential expression pattern suggests divergent roles for this TGFBR3 in developing testis and ovary.

Analysis of the mRNA expression of the TGF-Beta family in testicular cells and localization of the splice variant TGF-beta2B in testis

The transforming growth factors (TGF)-beta, TGF-beta1, TGF-beta2, and TGF-beta3, and their receptors [TbetaRI, TbetaRII, TbetaRIII (betaglycan)] elicit many functions in the testis, for example, they perturb the blood testis barrier (BTB). Although expression of the ligands and receptors have been investigated, the alternative splice variants are incompletely examined. We therefore have analyzed all ligands, the receptors, and the splice variants TbetaRIB, TbetaRIIB, and TGF-beta2B in testicular cells from rat and mouse. In mouse, the novel transcript variant TGF-beta2B was identified and was found in Leydig cells, spermatogonia, pachytene spermatocytes, and in the apical regions of the Sertoli cells in adult testis. Even though expression of the splice variant TbetaRIB could be shown in mouse and rat, we never found the isoform TbetaRIIB in the rat cell lines studied. Whereas in all testicular cells expression of all TGF-beta ligands could be shown, receptor mRNA expression was slightly more diverse. Furthermore, expression pattern of the splice variants was more heterogeneous, for example, TbetaRIB was not detectable in adult Sertoli cells, primary peritubular cells, and immortalized peritubular cells. The heterogeneous expression of the receptors and especially of the splice variants might provide possible clues for the different functions of the TGF-beta ligands in testicular cells.

Effects of TGF-betas and a specific antagonist on apoptosis of immature rat male germ cells in vitro

Massive apoptosis of pubertal male germ cells is important for the development of functional spermatogenesis in the adult testis. Although the trigger(s) for male germ cell loss at puberty remain undefined, we have hypothesized that transforming growth factor-betas (TGF-betas) play an active role. Here we demonstrate that the three mammalian TGF-beta isoforms, TGF-beta1, TGF-beta2 and TGF-beta3, induce distinct apoptosis of pubertal spermatogonia and spermatocytes in a dose-dependent manner. Induction of male germ cell death by activation of caspase-3 was most pronounced with TGF-beta2 compared to TGF-beta1 and TGF-beta3. Furthermore, we found colocalization of activated caspase-3 with apoptotic protease-activating factor-1 (Apaf-1) in apoptotic germ cells, thus indicating the importance of the intrinsic mitochondrial pathway in TGF-beta-induced apoptosis. The specificity of the TGF-beta effects was proven by addition of recombinant latency-associated peptide against TGF-beta1 (rLAP-TGF-beta1) which completely abolished TGF-beta1-induced and TGF-beta3-induced germ cell apoptosis. Although TGF-beta2-triggered germ cell death also was significantly reduced by rLAP-TGF-beta1, inhibition was not maximal. Our results suggest that the three TGF-beta isoforms induce apoptosis of pubertal male germ cells via the mitochondrial pathway in vitro and are thus likely candidates involved in the excessive first wave of apoptosis of male germ cells during puberty.

Development of testicular inflammation in the rat involves activation of proteinase-activated receptor-2

Mast cells are involved in early events crucial to inflammation and autoimmune disease. Recently, proteinase-activated receptor-2 (PAR(2)), a G-protein coupled receptor important to injury responses, was shown to be activated by mast cell tryptase. To investigate whether mast cells and PAR(2) are involved in the development and/or aggravation of testicular inflammation, we studied acute and chronic inflammatory models in the rat. In normal testes, PAR(2) was detected immunohistochemically in macrophages, in peritubular cells (PTCs) and in spermatid acrosomes. In experimentally induced autoimmune orchitis (EAO), PAR(2) was strongly upregulated in macrophages and peritubular-like cells, forming concentric layers around granulomas. Mast cells increased 10-fold in number, were more widely distributed throughout the interstitial tissue, and were partially degranulated. Isolated PTCs expressed functional PAR(2), responded to PAR(2) activation by phosphorylating extracellular signal-regulated kinases 1/2 (ERK1/2) and activating protein kinase c, and increased intracellular Ca(2+) concentrations as well as monocyte chemoattractant protein-1 (MCP-1), transforming growth factor beta(2) (TGFbeta(2)), and cyclooxygenase-2 (COX-2) mRNA expression. Expression of these inflammatory mediators, together with iNOS, also increased significantly in testes 50 days after EAO. In vivo, expression of cytokines and inflammatory mediators was upregulated after injection of recombinant tryptase (MCP-1, TGFbeta(2), and COX-2) and a specific PAR(2) peptide agonist (MCP-1, TGFbeta(2)) in the testis after 5 h. These results suggest that PAR(2) activation elicited on PTCs by mast cell tryptase contributes to acute testicular inflammation and that this pathogenetic mechanism may also play a role in autoimmune orchitis.

Effects of glial cell line-derived neurotrophic factor on isolated developing mouse Sertoli cells in vitro

Cell proliferation is a key factor in sex determination where a size increase relative to the XX gonad is one of the first signs of testis differentiation. Moreover, proliferation of Sertoli cells during development is important in building up the stock of supporting cells necessary for subsequent successful fertility. Because proliferation is such an essential part of testis development, the hypothesis under long-term investigation is that it is under fail-safe control by multiple alternative growth factors. This study was undertaken to investigate the role of glial cell-derived neurotrophic factor (GDNF) on developing mouse Sertoli cells in vitro. Sertoli cells, isolated from mouse embryos at three stages of testis development, were maintained for 2-7 days in vitro (div) in the presence or absence of GDNF at 1, 10 and 100 ng mL(-1). Overall the presence of extracellular matrix gel had little effect on proliferative activity, but encouraged expression of the epithelial phenotype. A statistically significant difference in proliferation, assessed by immunocytochemical staining for proliferating cell nuclear antigen, was seen with GDNF at embryonic day (E)12.5 after 2 div (at both 10 and 100 ng mL(-1), P < 0.001) and 7 div (at both 10 and 100 ng mL(-1), P < 0.05); at E13.5 after 3 div (at both 10 and 100 ng mL(-1), P < 0.05) and at E14.5 after 7 div (100 ng mL(-1), P < 0.01), compared with controls cultured without growth factor. In conclusion, GDNF stimulates mitosis throughout this critical developmental window. The in vitro approach used here is a useful adjunct to the knockout mouse model and has been applied to show that GDNF exerts a proliferative effect on developing mouse Sertoli cells.

Macrophage migration inhibitory factor suppresses transforming growth factor-β2 secretion in cultured rat testicular peritubular cells

Cytokines have direct effects on testicular cell functions and a number of cytokines are produced constitutively within the testis, even in the absence of immune-activation events. There is clear evidence that cytokines play a dual role as important regulatory factors in the normal function of the testis, as well as in testicular inflammation. The pro-inflammatory cytokine macrophage migration inhibitory factor (MIF) is expressed locally in the testis and has direct effects on peritubular cells, which, in turn, produce anti-inflammatory mediators, including transforming growth factor (TGF)-β2. In the present study, we investigated the function of MIF by examining its effect on the secretion of TGF-β2 in peritubular cells. Expression of TGF-β2 mRNA was shown by reverse transcription–polymerase chain reaction in peritubular cells isolated from 19-day-old rat testis. The addition of recombinant MIF to cultured peritubular cells resulted in a dose-dependent decrease in TGF-β2 secretion up to 52% of control levels after 48 h, which was significant for all doses investigated (10–100 ng mL−1 MIF). Inhibition of TGF-β2 secretion was sustained for 72 h for the highest dose of MIF used (100 ng mL−1). No effect of MIF was observed on TGF-β2 mRNA expression levels, as shown by real-time polymerase chain reaction. These results suggest that the pro-inflammatory cytokine MIF can shift the cytokine balance from the immunosuppressive state towards an inflammatory reaction, potentially through the inhibition of TGF-β2 secretion by peritubular cells.

Bioengineered human bone tissue using autogenous osteoblasts cultured on different biomatrices

Surgical treatment of critical-size posttraumatic bone defects is still a challenging problem, even in modern bone and joint surgery. Progress in cellular and molecular biology during the last decade now permits novel approaches in bone engineering. Recent conceptual and technical advances have enabled the use of mitotically expanded, bone-derived cells as a therapeutic approach for tissue repair. Using three different tissue carrier systems, we successfully cultivated human osteoblasts in a newly developed perfusion chamber. We studied cell proliferation and the expression of osteocalcin, osteopontin, bone morphogenetic protein-2A, alkaline phosphatase, and vascular endothelial growth factor as parameters for osteoblast function and viability. Adherence of highly enriched human osteoblasts had already started after 1 h and resulted in completely overgrown human bone pieces after 10 days. Expression analysis of bone-specific alkaline phosphatase indicated differentiating osteoblasts, whereas the high mRNA expression of osteocalcin and osteopontin revealed terminally differentiated osteoblasts and the process of mineralization. Additionally, gene expression was significantly higher when demineralized bone was used as biomatrix, compared to autoclaved bone and hydroxyapatite ceramics. We conclude that with our newly developed perfusion culture system, vital autogenous bone implants of clinically applicable size can be generated within 17 days in order to manage critical-size bone defects.

TGF-betas: their role in testicular function and Sertoli cell tight junction dynamics

Transforming growth factor-betas (TGF-betas) are known to regulate multiple physiological functions in the testis, which include spermatogenesis, Leydig cell steroidogenesis, extracellular matrix synthesis and testis development. More recent studies have shown that TGF-beta3 also regulates Sertoli cell tight junction (TJ) dynamics in vitro via the p38 mitogen-activated protein (MAP) kinase pathway, suggesting that this cytokine plays a crucial role in regulating the opening and closing of the blood-testis barrier (BTB). This in turn regulates the passage of pre-leptotene and leptotene spermatocytes across the BTB at stages VIII-XI of the seminiferous epithelial cycle. This review summarizes recent advances of studies on TGF-betas in the testis, highlighting their regulatory role in TJ dynamics.

Defining the actions of transforming growth factor beta in reproduction

Members of the transforming growth factor beta (TGFbeta) family are pleiotropic cytokines with key roles in tissue morphogenesis and growth. TGFbeta1, TGFbeta2 and TGFbeta3 are abundant in mammalian reproductive tissues, where development and cyclic remodelling continue in post-natal and adult life. Potential roles for TGFbeta have been identified in gonad and secondary sex organ development, spermatogenesis and ovarian function, immunoregulation of pregnancy, embryo implantation and placental development. However, better tools must now be employed to map more precisely essential functions and the regulatory networks governing their activity. Gene ablation and transgenic models are expected to provide novel insights into distinct physiological activities for each TGFbeta isoform in normal reproductive function and reproductive pathologies. It is also necessary to consider the mechanisms controlling TGFbeta activation from latent precursor forms, and receptor and binding protein expression. Smad intracellular signalling circuitry and modulation by environmental stimuli through cross-talk with other signal transduction pathways will further constrain TGFbeta action. This review examines existing evidence for TGFbeta1, TGFbeta2 and TGFbeta3 regulation of male and female reproductive biology, and highlights prospects for future research.

Expression of differentially expressed nucleolar transforming growth factor-beta1 target (DENTT) in adult mouse tissues

Differentially expressed nucleolar TGF-beta1 target (DENTT) is a novel member of the TSPY/TSPY-L/SET/NAP-1 (TTSN) superfamily that we have previously identified in human lung cancer cells. Here, we have investigated the expression of this protein in the adult mouse. By Western analysis, DENTT is highly expressed in the pituitary gland and moderately in the adrenals, brain, testis, and ovary. Immunohistochemical staining analysis for DENTT showed differential cytoplasmic and nuclear staining patterns in several cell types. The pituitary gland showed the highest level of immunostaining for DENTT, with strong cytoplasmic immunoreactivity in the anterior lobe, moderate levels in the posterior lobe, and a few cells showing nuclear staining in the intermediate lobe. In contrast, the intermediate lobe of the pituitary showed intense cytoplasmic staining for TGF-beta1. Nuclear and cytoplasmic staining for DENTT was present in the islets of Langerhans in the pancreas. Cytoplasmic staining for DENTT was particularly intense in the cortex of the adrenal gland, whereas the medulla showed weak nuclear staining. In the nervous system, the choroid plexus showed the highest immunoreactivity, with cortical motoneurons and Purkinje cells having relatively high levels of staining for DENTT as well. DENTT immunoreactivity was found in Leydig interstitial cells, Sertoli cells, and primary spermatocytes in the testis. In the female reproductive system, DENTT immunoreactivity was present in oocytes, thecal cells, and corpora lutea. The bronchial epithelium of the lung showed moderate levels of staining for DENTT localized to the cell nucleus. Additionally, three rodent pituitary cell lines (AtT20, GH3, and alphaT3-1, representing corticotropes, lactotropes, and gonadotropes, respectively) showed expression of DENTT. Addition of TGF-beta1 or serum to AtT20 cells increased DENTT protein production by 4 hr and, after reaching maximal levels at 2.4-fold above basal level by 8 hr, decreased, whereas no more than a 1.5-fold increase in DENTT protein occurred in GH3 or alphaT3-1 cells. Transient transfection studies showed that ectopic DENTT expression significantly increased the level of p3TP-Lux reporter transcription in AtT20 cells, but not in GH3 or alphaT3-1 cells. Interestingly, addition of TGF-beta1 had no significant effect on the ability of DENTT expression to influence p3TP-Lux reporter transcription in AtT20 cells. This report is the first detailed immunohistochemical examination of a member of the TTSN superfamily in the adult mouse. Expression of DENTT in endocrine tissues, nervous system, lung, oocytes, and thecal cells, in addition to the testis, suggests new roles for the TTSN superfamily. The differential patterns of expression of DENTT and TGF-beta1 in some tissues, including the pituitary, suggest that other factors are likely to be regulators of DENTT besides TGF-beta1.