Structural characterization of proteoglycans produced by testicular peritubular cells and Sertoli cells

Regulation of spermatogenesis by a local functional axis in the testis: role of the basement membrane-derived noncollagenous 1 domain peptide

Spermatogenesis takes place in the epithelium of the seminiferous tubules of the testes, producing millions of spermatozoa per day in an adult male in rodents and humans. Thus, multiple cellular events that are regulated by an array of signaling molecules and pathways are tightly coordinated to support spermatogenesis. Here, we report findings of a local regulatory axis between the basement membrane (BM), the blood-testis barrier (BTB), and the apical ectoplasmic specialization (apical ES; a testis-specific, actin-rich adherens junction at the Sertoli cell-spermatid interface) to coordinate cellular events across the seminiferous epithelium during the epithelial cycle. In short, a biologically active fragment, noncollagenous 1 (NC1) domain that is derived from collagen chains in the BM, was found to modulate cell junction dynamics at the BTB and apical ES. NC1 domain from the collagen α3(IV) chain was cloned into a mammalian expression vector, pCI-neo, with and without a collagen signal peptide. We also prepared a specific Ab against the purified recombinant NC1 domain peptide. These reagents were used to examine whether overexpression of NC1 domain with high transfection efficacy would perturb spermatogenesis, in particular, spermatid adhesion (i.e., inducing apical ES degeneration) and BTB function (i.e., basal ES and tight junction disruption, making the barrier leaky), in the testis in vivo We report our findings that NC1 domain derived from collagen α3(IV) chain-a major structural component of the BM-was capable of inducing BTB remodeling, making the BTB leaky in studies in vivo Furthermore, NC1 domain peptide was transported across the epithelium via a microtubule-dependent mechanism and is capable of inducing apical ES degeneration, which leads to germ cell exfoliation from the seminiferous epithelium. Of more importance, we show that NC1 domain peptide exerted its regulatory effect by disorganizing actin microfilaments and microtubules in Sertoli cells so that they failed to support cell adhesion and transport of germ cells and organelles (e.g., residual bodies, phagosomes) across the seminiferous epithelium. This local regulatory axis between the BM, BTB, and the apical ES thus coordinates cellular events that take place across the seminiferous epithelium during the epithelial cycle of spermatogenesis.-Chen, H., Mruk, D. D., Lee, W. M., Cheng, C. Y. Regulation of spermatogenesis by a local functional axis in the testis: role of the basement membrane-derived noncollagenous 1 domain peptide.

Biology of the Sertoli Cell in the Fetal, Pubertal, and Adult Mammalian Testis

A healthy man typically produces between 50 × 10(6) and 200 × 10(6) spermatozoa per day by spermatogenesis; in the absence of Sertoli cells in the male gonad, this individual would be infertile. In the adult testis, Sertoli cells are sustentacular cells that support germ cell development by secreting proteins and other important biomolecules that are essential for germ cell survival and maturation, establishing the blood-testis barrier, and facilitating spermatozoa detachment at spermiation. In the fetal testis, on the other hand, pre-Sertoli cells form the testis cords, the future seminiferous tubules. However, the role of pre-Sertoli cells in this process is much less clear than the function of Sertoli cells in the adult testis. Within this framework, we provide an overview of the biology of the fetal, pubertal, and adult Sertoli cell, highlighting relevant cell biology studies that have expanded our understanding of mammalian spermatogenesis.

Forty-four novel protein-coding loci discovered using a proteomics informed by transcriptomics (PIT) approach in rat male germ cells

Spermatogenesis is a complex process, dependent upon the successive activation and/or repression of thousands of gene products, and ends with the production of haploid male gametes. RNA sequencing of male germ cells in the rat identified thousands of novel testicular unannotated transcripts (TUTs). Although such RNAs are usually annotated as long noncoding RNAs (lncRNAs), it is possible that some of these TUTs code for protein. To test this possibility, we used a "proteomics informed by transcriptomics" (PIT) strategy combining RNA sequencing data with shotgun proteomics analyses of spermatocytes and spermatids in the rat. Among 3559 TUTs and 506 lncRNAs found in meiotic and postmeiotic germ cells, 44 encoded at least one peptide. We showed that these novel high-confidence protein-coding loci exhibit several genomic features intermediate between those of lncRNAs and mRNAs. We experimentally validated the testicular expression pattern of two of these novel protein-coding gene candidates, both highly conserved in mammals: one for a vesicle-associated membrane protein we named VAMP-9, and the other for an enolase domain-containing protein. This study confirms the potential of PIT approaches for the discovery of protein-coding transcripts initially thought to be untranslated or unknown transcripts. Our results contribute to the understanding of spermatogenesis by characterizing two novel proteins, implicated by their strong expression in germ cells. The mass spectrometry proteomics data have been deposited with the ProteomeXchange Consortium under the data set identifier PXD000872.

Building the mammalian testis: origins, differentiation, and assembly of the component cell populations

Development of testes in the mammalian embryo requires the formation and assembly of several cell types that allow these organs to achieve their roles in male reproduction and endocrine regulation. Testis development is unusual in that several cell types such as Sertoli, Leydig, and spermatogonial cells arise from bipotential precursors present in the precursor tissue, the genital ridge. These cell types do not differentiate independently but depend on signals from Sertoli cells that differentiate under the influence of transcription factors SRY and SOX9. While these steps are becoming better understood, the origins and roles of many testicular cell types and structures-including peritubular myoid cells, the tunica albuginea, the arterial and venous blood vasculature, lymphatic vessels, macrophages, and nerve cells-have remained unclear. This review synthesizes current knowledge of how the architecture of the testis unfolds and highlights the questions that remain to be explored, thus providing a roadmap for future studies that may help illuminate the causes of XY disorders of sex development, infertility, and testicular cancers.

Evidence for the Presence of Angiogenin in Human Testis

We have reported the expression and possible roles of angiogenin, a potent angiogenic factor, in human female reproductive organs. In this study, we investigated the expression of angiogenin in the human testis, a male reproductive organ. Western blot analysis showed the presence of angiogenin in the human testis, with a single band of the same size as recombinant human angiogenin. Immunohistochemical study and in situ hybridization showed that the angiogenin protein and messenger RNA (mRNA) localized in peritubular myoid cells (PTMCs) and vascular endothelial and smooth muscle cells. PTMCs are known to play various roles in the testes concerned with spermatogenesis, transport of spermatozoa, structural support to the seminiferous tubules, and mediation of Sertoli cell function. The specific localization of angiogenin in PTMCs suggests that angiogenin plays physiologic roles in the human testis.

Stereological analysis of age-related changes of testicular peritubular cells in men

This work aimed to analyze quantitative changes of peritubular cells in testes of aged men. Testicular tissues were obtained from 42 aged men with advanced prostate cancer and 16 young men with biopsy, quantitatively investigated with stereological techniques with quadrate mask grid, measured the parameters volume density (V(V)), numerical density on area (N(A)), and numerical density (N(V)) with grid test points. No significant differences were found in cell ratio, peritubular cell number per tubule, diameter of seminiferous tubules between young and old men (p>0.05). Aged men had higher pathologic assignment score than that of young men, which demonstrated more severe pathologic changes (p<0.05). Peritubular cell V(V) and pachytene germ cell V(V) increased significantly in old men compared to young men (p<0.05). Sertoli cell (SC) number per tubule in two-dimensional was significantly less in aged men than that of young men, p<0.01. Peritubular cell N(A), N(V) decreased significantly in aged men compared to young one, p<0.05. It is concluded that the stereological data of peritubular cells from three-dimensional level in testes of aged men suggest a significant decrease when compared with young men, indicating age-related changes.

Heparan sulphate proteoglycan as mediator of some adhesive responses and cytoskeletal reorganization of cells on fibronectin matrices: independent versus cooperative functions

Fibronectin is a multifunctional glycoprotein which promotes the adhesion of a variety of cell types to extracellular matrices, including artificial tissue culture substrata. Biochemical analyses of substratum adhesion sites indicated important functions for cell-surface heparan sulphate proteoglycan (HS-PG) in directly mediating adhesive responses by the binding of heparan sulphate sequences to fibronectin. In addition, fibronectin has a binding domain for a cell surface 'receptor' (possibly a 140K glycoprotein) important in these responses. To differentiate the relative importance of these two binding activities, a proteolytically generated cell-binding fragment of fibronectin has been isolated which binds to the 140K 'receptor' but not to HS or to collagen. Platelet factor 4 (PF4), a tetravalent HS-binding protein, provides a model of the tetravalent HS-binding activity of fibronectin, as supported by affinity chromatography studies (these studies also reveal the complexity of HS-PG metabolism in adhesion sites). Responses are measured on substrata coated with the cell-binding fragment of fibronectin, intact fibronectin, or PF4, singly or in combination. Fibroblast-like BALB/c 3T3 cells form both close and tight-focal adhesive contacts with associated microfilament stress fibres on intact fibronectin. Whereas HS-PG binding appears to mediate the formation of close contacts and linear microfilament bundles, a cooperative relationship exists between the HS- and the cell-binding activities of the intact fibronectin molecule in the formation of focal contacts and stress fibres. Human dermal fibroblasts generate different adhesive responses on HS-binding or cell-binding substrata, which are dependent on whether cells have been grown in medium with ascorbate to maximize production of their own collagenous matrix. As with 3T3 cells, focal contact and stress fibre formations of dermal cells require both binding activities in the intact fibronectin molecule. A third system consists of neuroblastoma tumour cells which adhere and extend neurites on fibronectin. Cell-body adherence, but not neurite extension, occurs on HS-binding matrices whereas neurite extension requires only fibronectin's cell-binding activity; the responses of primary peripheral neurons were exactly the opposite and CNS neurons did not respond at all. These studies indicate the diversity of molecular mechanisms by which various cells interact with the multifunctional fibronectin molecule in order to perform specialized functions, as well as the independent or cooperative functions of heparan sulphate proteoglycan on the cell surface in mediating these responses.

Use of Sertoli cell transplants to provide local immunoprotection for tissue grafts

The recent success of allogeneic islet transplantation for the treatment of type I diabetes has renewed interest in cell therapy for diseases of secretory cell dysfunction. Unfortunately, widespread clinical use of cell transplantation is limited by tissue availability and the need for long-term immunosuppresion. Testicular Sertoli cells can confer local immunoprotection for co-transplanted cells and may provide a means of overcoming the obstacles associated with cell transplantation. Sertoli cell grafts protect islets in animal models of diabetes and can be transplanted into the brain to enhance regeneration and promote the survival of co-grafted tissues. This review describes the role that Sertoli cells normally play in testicular immunology, details the preclinical data using transplanted Sertoli cells in models of diabetes and Parkinson's disease and discusses some of the possible mechanisms involved in this phenomena, as well as the future of this technology.

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.

Regulation of glypican-1, syndecan-1 and syndecan-4 mRNAs expression by follicle-stimulating hormone, cAMP increase and calcium influx during rat Sertoli cell development

In seminiferous tubules, Sertoli cells provide structural and nutritional support for the developing germinal cells. Cell- to-cell signaling and cell adhesion require proteoglycans expressed at the cell membrane. A preliminary biochemical and structural approach indicated that cell surface proteoglycans are mostly heparan sulfate proteoglycans (HSPG). Glypican-1, syndecans-1 and -4 were identified using a molecular approach. Their differential regulation was demonstrated in immature rat Sertoli cells. Follicle-stimulating hormone (FSH) is the main regulator of Sertoli cell function. Signal transduction triggered by FSH involves both an increased intracellular cAMP synthesis and a calcium influx. This study demonstrates that FSH, through its second messengers (increase in intracellular cAMP and intracellular calcium), downregulated the glypican-1 mRNA expression in Sertoli cells from 20-day-old rats. On the other hand, syndecan-1 mRNA expression is not modulated by FSH as it would result from the antagonistic effects of increased intracellular cAMP and intracellular calcium levels. Finally, syndecan-4 mRNA expression is not regulated by this pathway. The present study was extended during Sertoli cell development. Indeed, Sertoli cells undergo extensive changes during the postnatal period both in structure and function. These important transformations are critical for the establishment of spermatogenesis and development of the adult pattern of testicular function. Our data indicated that the regulation of HSPG mRNA expression is HSPG-specific and depends on the Sertoli cell developmental stage.

Biochemical characterization of integral membrane heparan sulfate proteoglycans in Sertoli cells from immature rat testis

(35)S-Radiolabeled cultured Sertoli cells from immature rat testis were extracted with detergent and the different proteoheparan sulfate (HSPG) forms of the extract were discriminated and quantified on the basis of their high anionic charge, hydrodynamic size, lipophilic properties, susceptibility to trypsin and phosphatidylinositol phospholipase C (PI-PLC). Trypsin released 50% of total cellular HSPG corresponding to 80% of total hydrophobic HSPG. Trypsin-accessible HSPG were presumed to be integral membrane species. Trypsin-resistant HSPG, probably intracellular, distributed into non-lipophilic (37.5%) and lipophilic (12.5%) populations. Biochemical analysis of PG copurified with plasma membrane confirmed the existence of hydrophobic HSPG integrated into this structure. Among hydrophobic HSPG accessible to trypsin, 35% were PI-PLC released and radiolabeled by [(3)H]inositol indicating that about one third of integral membrane HSPG were intercalated into the plasma membrane through a phosphatidylinositol anchor (glypican type). PI-PLC-resistant forms represented HSPG inserted into the membrane through a hydrophobic segment of the core protein (syndecan type). No lipophilic PG was present in other cell compartments (culture medium, cell periphery, extracellular matrix). (125)I-Iodinated hydrophobic HSPG were deglycanated and submitted to SDS-polyacrylamide gel electrophoresis. In the glypican family, a core protein (64--65 kDa) was detected, whereas in the syndecan family, bands of 60 and 68 kDa were observed which may correspond to self-association of different core proteins. In Sertoli cell, specific functional attributes of different integral membrane HSPG forms remain to be investigated.

Mesenchymal entactin-1 (nidogen-1) is required for adhesion of peritubular cells of the rat testis in vitro

Epithelial-like Sertoli cells isolated from immature rat testis aggregate to form tubule-like structures when cultured on a monolayer of mesenchyme-derived peritubular cells. At the end of this morphogenetic process both cell types are separated by a basement membrane. In this study the gene expression of monocultures and direct cocultures of peritubular cells and Sertoli cells was examined using DD-RT-PCR. One of the isolated cDNA clones showed high homology to the cDNA encoding the basement membrane component entactin-1 (nidogen-1). Even though the entactin-1 (nidogen-1) gene is transcribed in peritubular cells, Sertoli cells, and in direct cocultures, the mRNA is translated only by the peritubular cells. No entactin-1 (nidogen-1) was detected in the Sertoli cells by Western blotting. Moreover, peritubular cell monocultures and cocultures showed the presence of one single band at 152 kDa in the supernatant, whereas in cell lysates two bands were detectable at 152 kDa and 150 kDa. Perturbation experiments using monoclonal antibodies directed against entactin-1 (nidogen-1) were performed with peritubular cells and Sertoli cells, respectively, and demonstrated loss of cell adhesion of the peritubular cells, while the Sertoli cells remained adherent. From these data we conclude that entactin-1 is exclusively produced and secreted by mesenchymal peritubular cells, and affects adhesion of peritubular cells in an autocrine manner.

Activation of protein kinase C increases proteoglycan synthesis in immature rat Sertoli cells

In order to determine the signal transduction pathways involved in the regulation of proteoglycan (PG) synthesis in immature rat Sertoli cells (SC), we have examined the effect of the tumor promoter phorbol ester PMA (phorbol myristate acetate) on [35S]sulfate and [3H]glucosamine incorporation into PG molecules neosynthesized by cultured rat SC. PMA induced a dose- and time-dependent stimulation of labeled cell-associated PG as determined by quantitative solid phase assay. The overall effect of PMA resulted from enhancement of both glycosylation and catabolism of cell PG, this latter effect leading to a drastic decrease of their residence time in the membrane. Besides these quantitative effects, activation of protein kinase C by PMA induced qualitative changes as reflected by increase in relative proportion of heparan sulfate PG (HSPG) in cell membrane PG. In light of our previous results suggesting an inverse relationship between PG synthesis and FSH responsiveness in immature rat Sertoli cells, the PMA-induced upregulation of cell membrane PG, and particularly HSPG, could constitute one mechanism involved in the repression of FSH-stimulated steroidogenesis induced by PKC activation.

Gelatinase A secretion and its control in peritubular and Sertoli cell cultures: effects of hormones, second messengers and inducers of cytokine production

Extracellular matrix components as well as enzymes and enzyme-inhibitors controlling the turn-over of these components play an important role in the local control of testicular function. Zymographic analysis was used to study the secretion and the control of the secretion of gelatinase A (MMP-2) and B (MMP-9) by primary cultures of rat Sertoli cells and by subcultures of peritubular cells. Data on gelatinase A were complemented by measurement of the corresponding mRNA by Northern blot analysis. The agonists investigated included hormones (FSH, testosterone), second messengers (dbcAMP, phorbolester and a Ca(2+)- ionophore), interleukin-1 beta (IL-1 beta) and inducers of cytokine production (Concanavalin A: ConA; lipopolysaccharide: LPS; double stranded RNA: PIC). It is demonstrated that Sertoli cells originally secrete both gelatinase A and B. When maintained in serum-free medium, however, they rapidly lose the ability to secrete gelatinase B. After 3 days of culture gelatinase A remains the only measurable gelatinase in both Sertoli and peritubular cell cultures. The production in peritubular cells, however, exceeds that in Sertoli cells some 25-fold. This was confirmed by a 30-fold difference in the level of steady-state gelatinase A mRNA levels. Gelatinase A secretion and gelatinase A mRNA were stimulated by ovine FSH in Sertoli cells and by dbcAMP and ConA in both Sertoli and peritubular cells. IL-1 beta displayed measurable but limited stimulatory effects in both cell types. Interestingly, in peritubular cells but not in Sertoli cells, ConA stimulated the production of a lower MW species probably representing an activated form of gelatinase A. It is concluded that both the amounts of gelatinase A produced, the levels of the corresponding mRNA and the regulation differ in cultured peritubular cells and Sertoli cells. The lectin concanavalin A is a novel and potent inducer of gelatinase A. It resembles cytochalasin D in selectively inducing an activated form of gelatinase A in peritubular cells. The mechanism responsible for this selective effect warrants further investigation.

Inhibition of proteoglycan synthesis induces an increase in follicle stimulating hormone (FSH)-stimulated estradiol production by immature rat Sertoli cells

In order to define the possible involvement of proteoglycans (PG) in the regulation of Sertoli cell functions, we have examined the effect of para-nitrophenyl-beta-D-xyloside (PNPX), a specific inhibitor of PG synthesis, on follicle stimulating hormone (FSH)-dependent estradiol production by immature rat Sertoli cells. Addition of PNPX to the culture medium induced a dose-dependent inhibition of 35S-labeled PG synthesis in Sertoli cells both in the medium and the cell layer. Simultaneously there was a drastic increase in 35S-labeled secreted glycosaminoglycans. By 1 mM PNPX, syntheses of chondroitin sulfate proteoglycans released into culture medium and of heparan sulfate proteoglycans associated with the cell layer were 35% of values from untreated cells. Simultaneously, PNPX induced a twofold (mean of seven experiments, range 17-250%) enhancement of FSH (100 ng/ml)-stimulated estradiol production. In each individual experiment, there was an inverse relationship between the amplitude of PNPX-induced increase in FSH responsiveness and the FSH capability to stimulate basal estradiol production in cultured rat Sertoli cells. The effect of PNPX on FSH-stimulated aromatase activity was not mimicked by para-nitrophenyl-beta-D-galactoside, a structural analog of PNPX that has no effect on PG synthesis. The (Bu)2cAMP-stimulated estradiol synthesis was not modified in the presence of PNPX. Moreover, PNPX enhancement of FSH-stimulated estradiol synthesis disappeared when Sertoli cells were cultured in the presence of 1-methyl-3-isobutylxanthine, an inhibitor of phosphodiesterase activity. These findings suggest that inhibition of PG synthesis under PNPX conditions did not affect signal transduction steps distal to cAMP but rather decreased the phosphodiesterase activity in Sertoli cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the sulfation extent of membrane-associated proteoglycans produced by Sertoli cells in culture

Sertoli cells in culture synthesize two different membrane-associated proteoglycans (MA-PG): a proteoglycan containing heparan sulfate (HS) and chondroitin sulfate (CS) glycosaminoglycan (GAG) chains and a CS-PG containing only CS-GAG chains. The structure of these molecules is regulated by the presence of fetal calf serum (FCS) in the culture medium. Changes in the concentration of FCS resulted in changes in the total 35SO4 incorporation into MA-PG and a shift in the elution profile of each component subjected to ion-exchange chromatography. Thus, without FCS, the incorporation was low, while in 1% and 10% FCS, the uptake of the precursor was 1.7 and 4.5 times higher, respectively. MA-PG synthesized by Sertoli cells cultured in 10% FCS eluted from DEAE-Sephacel columns at higher salt concentration than the MA-PG synthesized by cells cultured in 0% or 1% FCS. Double-labeled experiments showed that the 35SO4/3H-glucosamine ratio incorporated into MA-PG produced by Sertoli cells, increased from 17.6 to 23.6 and 50.9 in cells cultured at 0, 1, and 10% FCS, respectively. However, the presence of FCS affected neither the hydrodynamic size nor the chemical nature of GAG chains of MA-PG. These results show that changes in the FCS concentration promote changes in the sulfation extent of MA-PG molecules produced by Sertoli cells.

Membrane associated proteoglycans in rat testicular peritubular cells

Confluent testicular peritubular cells derived from immature rats were used to study membrane associated proteoglycans (PG). Peripheral material (heparin releasable), membrane and intracellular material (Triton X-100 releasable) were collected, purified by anion exchange chromatography then characterized by gel filtration and by hydrophobic interaction chromatography, followed by enzymatic digestion and chemical treatment. The peripheral material was constituted of two populations of PG (Kav = 0 and 0.10 on Superose 6 column), each containing both heparan sulfate proteoglycans (HSPG) and chondroitin proteoglycans (CSPG) and perhaps a hybrid PG (HSCSPG). These PG being not retained on an octyl Sepharose column, they were devoided of hydrophobic properties. The integral membrane proteoglycans isolated on the basis of their hydrophobic properties represented 20% of the Triton X-100 releasable material, and were exclusively constituted of proteoheparan sulfate. There were no relationships between this membrane HSPG and the peripheral HSPG as evidenced by pulse chase experiments. The mode of intercalation of the hydrophobic HSPG in the cell membrane was studied. The majority of these macromolecules (80%) were sensitive to trypsin and only a minor proportion (20%) were sensitive to phosphatidylinositol specific phospholipase C. Thus, about 80% of the hydrophobic HSPG were intercalated in the cell membrane by a hydrophobic segment of the core protein whereas about 20% were associated with the cell membrane via a phosphatidylinositol residue covalently bound to the core protein of the PG.

Proteoglycans in male reproductive tract

Proteoglycans in male reproductive tract have been mainly characterized in testicular extracellular matrix and somatic cells. Heparan sulfate, chondroitin sulfate and hybrid chondroitin/heparan sulfate proteoglycans coexist within the testes. Their biological roles are not currently established, however, the molecular characterization of some of them is indicative that they might be involved in various regulatory processes during spermatogenesis.

Rat Sertoli cell extracellular matrix regulates glycosaminoglycan synthesis by peritubular myoid cells in vitro

We have previously reported metabolic cooperation between Sertoli and peritubular myoid cells in terms of synthesis of one of the main testicular extracellular matrix (ECM) constituents, glycosaminoglycans (GAG). This study concerns Sertoli cell ECM-peritubular myoid cell interactions in terms of GAG synthesis. We have examined the responses of hormones and other regulatory agents such as a combination of follicle-stimulating hormone (FSH), insulin, retinol, and testosterone (FIRT) on peritubular myoid cells, and tested if Sertoli cell ECM or serum factor substitute for the stimulation by FIRT. Testicular peritubular myoid cells cultured on Sertoli cell ECM showed significant increases in the levels of cell- and ECM-associated GAG over that when cultured on uncoated plastic. This indicates a specific cell-substratum interaction between Sertoli cell ECM and peritubular myoid cells in the testis in terms of GAG synthesis. Moreover, in terms of cell-associated GAG synthesis, peritubular myoid cell cultured on Sertoli cell ECM or on plastic in the presence of serum substituted for the stimulatory response of FIRT on peritubular myoid cells cultured on uncoated plastic. The data are discussed in relation to the possible role of cell-substratum interaction in maintaining peritubular myoid cell functions.

Testican, a multidomain testicular proteoglycan resembling modulators of cell social behaviour

The molecular characterization of a human testicular proteoglycan, the progenitor of a seminal plasma glycosaminoglycan-bearing peptide, was achieved by cDNA cloning. Its protein core encompasses several domains encountered in various proteins associated with adhesion, migration and cell proliferation. An osteonectin-like domain, a Kazal-like sequence and a 46-amino-acid motif around a Cys-Trp-Cys-Val peptide encountered in cell-surface antigens, cell-adhesion molecules and growth-factor-binding proteins are distributed within the testican protein core. Testican is the progenitor of the unique heparan/chondroitin-sulfate-bearing peptide present in human seminal plasma, a feature which might confer additional potentialities to this hybrid proteoglycan.

Collagen increases the synthesis of membrane-associated proteoglycans produced by Sertoli cells

Sertoli cells in culture produce two isoforms of proteoglycans which are found in the culture medium and associated with the cell membrane. The amount of both types of proteoglycans increased when Sertoli cells were plated on type I collagen-coated dishes as compared to uncoated dishes. The effect is due to an increase in the synthesis of proteoglycans rather than a diminished rate of degradation of these molecules. The collagen substrate also affects the distribution of these macromolecules; an increase in the amount of membrane-associated proteoglycans occurs at the expense of the proteoglycans released to the culture medium.

Detergent-solubilized proteoglycans in rat testicular Sertoli cells

Rat Sertoli cells were cultured for 48 h in the presence of [35S]sulfate and extracted with 4 M guanidine chloride. In this extract, a Sepharose CL-2B Kav 0.10 proteoheparan appeared lipid associated, since after addition of detergent it emerged at Kav = 0.65 on Sepharose CL-2B. Treatment of cells with 0.2% Triton X-100 released 35S-labeled material which was purified by ion-exchange chromatography and hydrophobic interaction chromatography on octyl-Sepharose. Proteoglycan with affinity for octyl-Sepharose (Kav = 0.30 and 0.12 on Sepharose CL-4B and CL-6B, respectively) mostly carried heparan sulfate chains with Kav = 0.38 and minor proportion of heparan chains with Kav = 0.77 on Sepharose CL-6B. An association with lipids was confirmed by intercalation into liposomes of this proteoheparan which might be anchored in the plasma membrane, via an hydrophobic segment and/or covalently linked to an inositol-containing phospholipid. Non-hydrophobic material consisted of: (i) proteoheparan slightly smaller in size than lipophilic proteoheparan and possibly deriving from this one and (ii) two heparan sulfate glycosaminoglycan populations (Kav = 0.38 and 0.86 on Sepharose CL-6B) corresponding to single glycosaminoglycan chains and their degradation products.

Sertoli cells in culture secrete paracrine factor(s) that inhibit peritubular myoid cell proliferation: identification of heparinoids as likely candidates

Conditioned medium from Sertoli cells, prepared from testes of 20-day-old rats, contains component(s) that inhibit the incorporation of [3H]-thymidine into DNA of peritubular myoid cells (PMC) and inhibit the proliferation of PMC. These components are trypsin-resistant, heat-stable compounds having a molecular weight less than 30,000. The active inhibitory components in Sertoli cell conditioned medium are inactivated by treatment with heparinase, but not by treatment with hyaluronidase or chondroitin sulfate lyases. Addition of heparin or heparan sulfate results in inhibition of DNA synthesis by PMC in a dose-dependent manner, whereas other glycosaminoglycans (GAGs) examined (hyaluronic acid, keratan sulfate, and chondroitin sulfate) have no detectable effects. Heparin and heparan sulfate are unique among GAGs tested in inhibiting the characteristic multilayer growth pattern of PMC following the attainment of confluence in serum-rich medium. On the basis of these and other data presented, it is concluded that heparin and other heparin-like GAGs synthesized by Sertoli cells are implicated in the modulation of growth of PMC in vitro during co-culture. It is postulated that heparin may play a similar role in maintaining the quiescent peritubular myoid cell phenotype in vivo.

Fibroblast growth factor modulates the release of transferrin from cultured Sertoli cells

The acute and chronic effects of basic fibroblast growth factor (bFGF) on transferrin (TF) secretion from Sertoli cells were investigated by using reverse hemolytic plaque assays which enabled the visualization of release from individual cells in culture. We found that acute treatment with bFGF stimulates the release of TF from some but not al Sertoli cells in cultures obtained from 20-day-old rats. Chronic treatment with this growth factor resulted in increases in overall cell number in cultures from animals of each age tested (8-20 days of age). In contrast, this long-term treatment decreased markedly the proportions of Sertoli cells that secreted TF but only in cultures from 10-day-old animals. When taken together, these findings of acute and chronic influences of bFGF on TF secreting cells support the possibility that bFGF not only contributes to the modulation of the day-to-day release of certain substances from Sertoli cells, but may also influence development of the portions of the cell population that secrete these substances.

Golden hamster myoid cells during active and inactive states of spermatogenesis: correlation of testosterone levels with structure

Myoid cells were examined quantitatively in adult golden hamsters with active spermatogenesis and compared with hamsters in which the testes were regressed due to a modification in the light-dark cycle. A detailed morphometric study was undertaken utilizing animals previously examined. The cell-surface area and volumes of most organelles were not significantly different in animals which were gonadally active as compared with regressed animals. A slight, but significant, increase in nuclear volume (31%) and a slight, but significant, decrease (28%) in cell volume were recorded for regressed animals. The total volume of pinocytotic vesicles was increased dramatically (approximately threefold) in active animals in comparison with inactive animals (P less than 0.01), indicating that an increase in non-specific transport across the myoid cell is associated with spermatogenic activity. Intravascularly injected horseradish peroxidase was capable of entering pinocytotic vesicles in both active and inactive animals. Plasma luteinizing hormone (LH) as well as plasma and testicular testosterone levels were weakly (r = 0.64, 0.68, and 0.65, respectively), but significantly (P less than 0.05), correlated with cell size. Plasma and testicular testosterone were correlated with the total volume of pinocytotic vesicles (r = 0.74 and 0.68, respectively). The data indicate that although the rat myoid cell possesses receptors for testosterone, there are few structural manifestations of the hamster myoid cell that correlate well with testosterone levels. Thus, the hamster myoid cell differs from two other hormone-responsive somatic cells in the testis, the Sertoli cell and the Leydig cell, that show dramatic structural alterations with changes in gonadal activity and striking correlations of structural features with functional measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Viability of meiotic prophase spermatocytes of rats is facilitated in primary culture of dispersed testicular cells on collagen gel by supplementing epinephrine or norepinephrine: evidence that meiotic prophase spermatocytes complete meiotic divisions in vitro

Dispersed testicular cells prepared from 14-d-old rats were cultured on type 1 collagen gels using a medium composed of a 1:1 mixture of Ham's F12 medium and Leibovitz's L15 medium (F12-L15 medium) containing 10% (vol/vol) fetal bovine serum. The viability of the spermatogenic cells was facilitated by supplementing a rat adrenal extract into the medium. The effective substance(s) (the survival factor) was purified from acid extracts of adrenals by molecular sieve high performance liquid chromatography and identified as epinephrine and norepinephrine. Both epinephrine and norepinephrine promoted the survival of the spermatogenic cells with a half saturating dose of 10 ng/ml. The spermatogenic cells, which could be cultured for 2 wk on a collagen gel by supplementing with the survival factor (epinephrine or norepinephrine), were subjected to Giemsa staining and to DNA flow cytometry. The following results were obtained: a) The spermatogenic cells from 14-d-old rats did not contain spermiogenic cells (1c-cells). b) During a culture period of 2 to 7 d the ratio of meiotic prophase spermatocytes (4c-cells) to premeiotic cells (2c-cells) increased. On Day 7, more than 90% of the surviving cells were meiotic prophase spermatocytes. c) On Day 10, spermatids (1c-cells) appeared for the first time. The time of the first appearance of spermatids in the culture was consistent with that in vivo. These results suggest that both epinephrine and norepinephrine facilitated the viability of meiotic prophase spermatocytes and that a part of the meiotic prophase spermatocytes completed the meiotic divisions in the testicular cell culture.

Synthesis of proteoglycans and hyaluronic acid by long-term cultures of testicular cells from immature and pubertal rats

Long-term cultures of somatic testicular cells derived from immature and pubertal rats were used to study the synthesis of proteoglycans (PG) and hyaluronic acid (HA). Labelled PG and HA in the culture medium, membrane-associated and intracellular pools were characterized by gel filtration, ion exchange chromatography and selected enzymatic and chemical treatments. Somatic cells synthesize a PG containing both heparan and chondroitin/dermatan sulfate (CS/DS) chains and a PG containing only CS/DS chains. No major qualitative changes in the type of PG were observed in cells derived from immature and pubertal animals. However, significant age-dependent differences in the cell distribution pattern of PG and HA were determined. This may have implications in the regulation of spermatogenesis.

Cellular localization of fibronectin gene expression in the seminiferous tubule

The cellular location of fibronectin expression within the seminiferous tubule was investigated in order to better understand testicular cell functions and cell-cell interactions. Peritubular cells were shown to actively synthesize and secrete fibronectin in culture by the detection of a radiolabeled 220 kDa secreted protein that is immunologically similar to fibronectin and by the quantitation of fibronectin in peritubular cell conditioned medium with a fibronectin enzyme-linked immunosorbent assay. Sertoli cells did not produce detectable levels of fibronectin when assayed by either of these procedures. A 6.5 kb fibronectin messenger RNA was detected in freshly isolated or cultured peritubular cells, but no fibronectin gene expression was detected in Sertoli cells or developing germinal cells. Combined results imply that the peritubular cells are the only apparent site of fibronectin expression within the seminiferous tubule. During the development of the testis the levels of fibronectin expression increased to a maximum at early puberty (15-day-old rats) and then slowly declined. The results demonstrate that fibronectin can be utilized as a unique functional and biochemical marker for peritubular cells when compared to other cell types in the seminiferous tubule. Production of fibronectin by peritubular cells provides an example of the ability of peritubular cells and Sertoli cells to cooperate in the production of individual components of the basement membrane of the seminiferous tubule. This cellular interaction is an example of a mesenchymal/stromal-epithelial interaction which is postulated to be important for the physiology of many tissues.

Synthesis of extracellular matrix components by somatic testicular cells from immature and pubertal rats

Total testicular cells derived from immature and pubertal rats were cultured under long-term conditions. Somatic adherent cells proliferated in culture and produced collagen and proteoglycans. Collagen synthesis accounted for 25% and 5% of total protein synthesized by adherent cells derived from immature, and pubertal rats, respectively. Proteoglycan synthesis was higher in cells from immature than from pubertal rats. The proportion of different types of glycosaminoglycan chains (particularly hyaluronic acid and chondroitin sulphate) also varied according to the age of the donor. The results suggest that the synthesis of extracellular matrix components by somatic testicular cells is an age-related process which probably plays an active role in spermatogenesis.

Physiology of the male reproductive system: endocrine, paracrine and autocrine regulation

This presentation reviews the male reproductive system, concentrating on newer advances in our knowledge of its physiology, biochemistry, and regulation, and introduces the topic of male reproductive toxicology. GnRH is the hypothalamic peptide responsible for the stimulation of LH and FSH release from the pituitary. It is synthesized as a pro-hormone, processed in the hypothalamus and released into the portal system in a pulsatile fashion. The timing of these pulses is critical to the release of LH and FSH into the general circulation. While LH and FSH are the main trophic hormones for the testis, we now realize the importance of not only endocrine control, but also of paracrine and autocrine regulation. Specifically, the local control of Leydig cells, Sertoli cells, and germ cells appears to be modulated by numerous growth factors and local regulators arising from within the testis. This point is emphasized both during a discussion of the interaction of the various cell types in the testis and during a discussion of spermatogenesis, where techniques which show stage-specific secretions are highlighted. Newest advances in the mechanism of action of steroidal and peptide hormones are also emphasized with special reference to the possible interaction between toxicants and endocrine control of the reproductive system. This update of the reproductive system "sets the stage" for an in-depth examination of the site and mechanism of action of reproductive toxicants.

Cell-cell interactions in the testis

In conclusion, the information available indicates that the interactions between different cell types in the testis play an important role in the control and maintenance of testicular functions. Further characterization of these interactions will clearly provide insight into the cell biology of the testis and into the regulation of cellular differentiation, function, and growth. It is apparent that no testicular cell type is autonomous, but that there is communication and cooperation between all cell types in the testis.

Vectorial secretion of transferrin and androgen binding protein in Sertoli cell cultures: effect of extracellular matrix, peritubular myoid cells and medium composition

We examined the effect of various culture conditions on the polarized secretion of androgen binding protein (ABP) and transferrin (Trf) by Sertoli cells (Sc) in vitro. Sc from 18-day-old rats were cultured as confluent monolayers on permeable membranes in two-compartment chambers for up to 11 days. Coating of the membranes with extracellular matrix (ECM) components: collagen IV + laminin (CL) or reconstituted basement membrane (RBM) enhanced ABP and Trf secretion (200% and 150%, respectively), with RBM being more effective than CL in stimulating ABP but not Trf secretion. Neither CL nor RBM significantly influenced the relative amounts of ABP and Trf secreted into the outer (OC) and inner (IC) compartments of the culture chamber (OC/IC ratio). All of these effects were not significantly influenced by the presence of testosterone and serum. Co-culture of Sc with peritubular myoid cells (Pc) significantly increased the secretion of both ABP and Trf, although the magnitude of stimulation and the time-response patterns were different for each protein. Co-culture with Pc also dramatically increased the OC/IC ratios for ABP and Trf. Testosterone (10(-6) M) enhanced the Pc effects. In cultures of Sc alone, presence of 2% fetal bovine serum increased the OC/IC ratios, whereas testosterone had no effect. Based on these results, we suggest a possible role of Pc in the regulation of Sc polarized secretions.

Morphogenetic restructuring and formation of basement membranes by Sertoli cells and testis peritubular cells in co-culture: inhibition of the morphogenetic cascade by cyclic AMP derivatives and by blocking direct cell contact

Addition of dibutyryl cyclic AMP (dbcAMP), methylisobutylxanthine (MIX), or cytochalasin D to co-cultures of Sertoli cells and testicular peritubular myoid cells blocks a series of morphogenetic changes which otherwise occur during culture. When Sertoli cells are plated directly onto preexisting layers of peritubular cells maintained under basal conditions, structures form which display many of the characteristics of germ cell-depleted seminiferous tubules. The presence of dbcAMP, MIX, or cytochalasin D, added at varying times after plating Sertoli cells, results in the inhibition of each successive stage of in vitro remodeling: the inhibition of migration of Sertoli cells, the inhibition of initial ridge formation, the blockage of subsequent formation of mounds and nodules of compacted Sertoli cell aggregates, the prevention of the formation of basal lamina and associated layers of extracellular matrix between Sertoli cell aggregates and surrounding peritubular cells, and the inhibition of tubule formation. The presence of dbcAMP also inhibits the migration of peritubular cells, contractions by these cells, and compaction of Sertoli cell aggregates. When intimate cell apposition is prevented by plating the two cell types on either side of a membrane filter, the morphogenetic cascade is blocked, and no formation of a germ cell-depleted seminiferous tubule-like structure occurs. Other effects of dbcAMP on cell shape, cell movement, and cell association patterns during co-culture are described. Possible mechanisms by which dbcAMP, MIX, or cytochalasin D blocks restructuring are discussed. Since each elicits perturbations of the cytoskeleton, we offer the interpretation that cytoskeletal changes may be correlated with the prevention of closely apposing cell compact and the inhibition of basement membrane formation. Interactions observed between Sertoli cells and peritubular cells during co-culture are postulated to be analogous to those occurring in other types of mesenchymal cell-epithelial cell interactions during organogenesis and during tubulogenesis in the fetal testis. Speculatively, the blockage by dbcAMP of the morphogenetic cascade in the co-cultured system may be related to the inhibition by dbcAMP of testis cord formation in organ cultures of fetal gonads reported by others.

Intragonadal control mechanisms

On the weight of the evidence presented above, it is concluded that regulation at a local, intragonadal level is an integral part of the overall regulation of gonadal function in both sexes. The interaction between cells within a gonad extends beyond the same cell type to include germ cell-somatic cell interactions as well. We believe this local interaction between cell types facilitates the differing requirements of the various developmental stages of germ cells within the gonad, which would not be possible by simply varying the afferent pituitary hormone supply. We re-emphasize that the local factors responsible for these interactions are acting in conjunction with the pituitary hormones, and, in some cases, may be their proximate regulators. A more controversial phenomenon is the possibility of an interaction between the gonads which does not involve the hypothalamic-pituitary axis. The little evidence which is available to support this hypothesis comes mainly from studies on ovarian function, particularly recruitment and selection of follicles. More research on this phenomenon is warranted. Not surprisingly there are many parallels between the testes and ovaries with respect to the nature and action of local regulators. For example, the intragonadal action of steroids, the local modulation of the response of target cells to FSH, the influence of macrophages on steroidogenesis and the presence of mitotic and meiotic regulators are common to both sexes. It would not be surprising if the chemical nature of these factors in the ovary and testes are similar. If the ever-increasing list of factors and activities being discovered in the gonads is any guide, the phenomena outlined in this review are just the beginning of an extensive list of cell-cell interactions occurring within and between the gonads. No doubt the gonads will share with other organs the same interactions between cells which are required for normal cellular function. The uniqueness of the gonads lies in their protection and production of germ cells. The challenge of the future for reproductive biologists will be to discover and describe the interactions within and between germ cells which are obligatory for normal reproductive function, and to apply that information to devising ways of overcoming infertility and regulating fertility.

Hormonal regulation of Sertoli cell function

The Sertoli cell is clearly influenced, directly and indirectly, by hormones. Among these are FSH, T, insulin and Vitamin A, but others may also be involved. Mechanisms are still not well understood. The biochemical effects of these hormones can be divided into quantitative and qualitative influences, with the former predominating. Specific cellular and secretory proteins and metabolites are affected, in many cases by more than one hormone. Often these same functions are influenced by other factors in the environment of the testis as well. Hormonal responsiveness of the Sertoli cell is determined in part by the maturational state of the cell. Some secreted products bind to specific cell types in the testis and epididymis and may influence the process of spermatogenesis. However, detailed mechanisms are not known at the present time. Understanding Sertoli cell function at the biochemical level and its control by hormones is clearly of key importance in understanding the control of the spermatogenic process.

Cell-substratum and cell-cell interactions promote testicular peritubular myoid cell histotypic expression in vitro

Peritubular cells, prepared from seminiferous tubules from testes of 20-day-old-rats, were seeded onto different substrata and cultured under varying conditions. When plated onto polystyrene or glass surfaces, peritubular cells assumed a typical fibroblast-like cell shape and cell association pattern, together with a fibroblast-like migration behavior. They maintained high rates of proliferation even after achieving confluency. In contrast, when peritubular cells were plated onto a seminiferous tubule biomatrix (ST-biomatrix) surface, they spread to form a continuous cell layer having a myoepithelioid histotype similar to that of peritubular myoid cells in the intact seminiferous tubule. The characteristics of the myoepithelioid histotype described include a squamous, polyhedral cell shape; a cobblestone-like cell association pattern, with closely apposing or slightly overlapping cell borders, and a very low mitotic index. When peritubular cells were plated onto laminin, collagen, fibronectin, heparin, or a liver biomatrix, a fibroblast-like pattern resulted, indicating that ECM components listed and liver biomatrix are unable to substitute for ST-biomatrix in maintaining normal myoepithelioid characteristics in vitro. In cocultures of Sertoli cells plated on top of peritubular cells, the peritubular cells directly in contact with Sertoli cell aggregates developed a myoepithelioid histotype, whereas peritubular cells in regions not in direct contact had a fibroblast-like histotype. The data are discussed in relation to the possible role of cell-cell interactions, and cell-substratum interactions, in the acquisition and stabilization of the histotype of peritubular cells in the seminiferous tubule during development.

Extracellular matrix components and testicular peritubular cells influence the rate and pattern of Sertoli cell migration in vitro

We report the patterns of migration of Sertoli cells plated on specific substrata, and the influences of testicular peritubular cells on these processes. Data presented indicate that while peritubular cells readily spread when explanted onto Type I collagen, Sertoli cells do not. A delay of 4 to 6 days occurs after Sertoli cells are plated before they begin to migrate randomly to form plaque-like monolayers on Type I collagen. These processes are dependent upon the synthesis and subsequent deposition of laminin and/or Type IV collagen by Sertoli cells, and are independent of fibronectin. A different behavior occurs when reconstituted mixtures of purified Sertoli cells and pertiubular cells are sparsely plated onto Type I collagen. Peritubular cells rapidly spread to form chains of cells between Sertoli cell aggregates. Sertoli cells then migrate on the surfaces of the peritubular cells, culminating in the formation of cable-like structures between aggregates. Evidence is presented that the Sertoli cell migration to form "cables" under these conditions is dependent upon fibronectin synthesized by peritubular cells, and is independent of the presence of laminin or Type IV collagen. We discuss the possible relevance of these data to the role which precursors of peritubular cells may play in determining the behavior of Sertoli cell precursors in vivo during tubulogenesis, or in the remodelling of the seminiferous tubule which occurs during different stages of the cycle of the seminiferous epithelium in spermatogenesis.