Rat Sertoli cells acquire a beta-adrenergic response during primary culture

Beta2 adrenergic receptors mediate cAMP, tissue-type plasminogen activator and transferrin production in rat Sertoli cells

FSH is the main regulator of Sertoli cell function. Nevertheless, several other effectors such as catecholamines can also stimulate these cells through the adenylyl cyclase transduction pathway. However, the expression of beta adrenergic receptors in Sertoli cells is a subject of controversy. The aim of the present study was to determine if there are physiologically functional beta adrenergic receptors in Sertoli cells and to which subtype(s) they belong. In freshly isolated Sertoli cells, isoproterenol, a non selective beta-adrenergic agonist, was found to stimulate cAMP production and tissue-type plasminogen activator secretion. Specific transcripts for the beta1 and beta2, but not beta3, subtypes were detected by RT-PCR analysis. Beta2 transcripts were the form expressed predominantly in Sertoli cells. Binding experiments carried out on freshly isolated and on cytospined Sertoli cells indicated that in both conditions, [125I]iodocyanopindolol binding was inhibited by a non-selective and a 2 selective antagonist, whereas a beta1 selective antagonist had no effect. Scatchard analysis of beta2 specific inhibition revealed a dissociation constant of 0.3 nM and a receptor density of 14000 sites per cell. In freshly isolated Sertoli cells, we observed that cAMP and tissue-type plasminogen activator were stimulated by isoproterenol and a beta2 selective agonist, but not by beta1 or beta3 selective agonists. Accordingly, the isoproterenol-stimulated tissue-type plasminogen activator responses were abolished by the beta2 selective antagonist only. In cultured Sertoli cells, the trend was the same: tissue-type plasminogen activator and transferrin secretions were increased by isoproterenol and beta2 but not by beta1 or beta3 selective agonists. We conclude that freshly isolated Sertoli cells express beta2 adrenergic receptors which are functionally coupled to adenylyl cyclase and that these characteristics are preserved in cell culture. For the tested parameters, catecholamines and FSH effects were similar, but response magnitudes were systematically lower with beta agonists than with FSH. As norepinephrine is normally present in physiologically-relevant amounts in the interstitial fluid, it can be suspected to play a role in the regulation of Sertoli cell function.

Changes in the distribution of intermediate filaments in rat Sertoli cells during the seminiferous epithelium cycle and postnatal development

BACKGROUND

Intermediate filaments (IFs) are components of the cytoskeleton. In mammalian Sertoli cell, IFs are formed by vimentin. Previous studies have shown some characteristics of its distribution in Sertoli cells, however, very little is known of its distributional changes during the seminiferous epithelium cycle and during postnatal development.

METHODS

Immunohistochemical and electron microscopic methods were used to determine the distribution of vimentin-type IFs in rat Sertoli cells during the seminiferous epithelium cycle and postnatal development.

RESULTS

The distribution of IFs in adult rat Sertoli cell showed distinct cyclic changes during the seminiferous epithelium cycle. At stages I-VI, bundles of IFs extend from the perinuclear region to the supranuclear and apical regions of the Sertoli cell. These apical extensions became shorter at stage VII, and at stages VIII-X IFs were observed only in the perinuclear region. Short apical extensions reappeared at stages XI-XII; and at stages XIII-XIV, they extended again into the apical region. During this cycle, IFs were always closely associated with the heads of elongate spermatids. IFs were also shown to be in close apposition to some specialized structures on the cell membrane, such as the ectoplasmic specialization between adjacent Sertoli cells. During postnatal (p.n.) development, IFs were mainly observed at the basal nuclear region on p.n. day 7. The IFs in the supranuclear or apical regions first appeared at p.n. day 14 and gradually increased during the development. The perinuclear IFs network was fully established by p.n. day 28 and the adult distribution pattern of the IFs was established by p.n. day 42.

CONCLUSIONS

Vimentin-type IFs in rat Sertoli cells are a delicate endocellular network, which is centered in the perinuclear region and extends to the apical region of the cell. During the seminiferous epithelium cycle, the distribution of IFs changes in a stage-dependent manner and is closely related to the location of the heads of elongate spermatids. During postnatal development, IFs gradually increase in numbers and the main distribution area is transferred from the basal nuclear to the perinuclear and supranuclear regions.

Intermediate filaments in Sertoli cells

Using immunohistochemical techniques both at light and electron microscopic levels, the arrangement and distribution of intermediate filaments in Sertoli cells of normal testis (in rat and human), during pre- and postnatal development (in rabbit, rat, and mouse) and under experimental and pathological conditions (human, rat), have been studied and related to the pertinent literature. Intermediate filaments are centered around the nucleus, where they apparently terminate in the nuclear envelope providing a perinuclear stable core area. From this area they radiate to the plasma membranes; apically often a close association with microtubules is seen. Basally, direct contacts of the filaments with focal adhesions occur, while the relationship to the different junctions of Sertoli cells is only incompletely elucidated. In the rat (not in human) a group of filaments is closely associated with the ectoplasmic specializations surrounding the head of elongating spermatids. Both in rat and human, changes in cell shape during the spermatogenic cycle are associated with a redistribution of intermediate filaments. As inferred from in vitro studies reported in the literature, these changes are at least partly hormone-dependent (vimentin phosphorylation subsequent to FSH stimulation) and influenced by local factors (basal lamina, germ cells). Intermediate filaments, therefore, are suggested to be involved in the hormone-dependent mechanical integration of exogenous and endogenous cell shaping forces. They permit a cycle-dependent compartmentation of the Sertoli cell into a perinuclear stable zone and a peripheral trafficking zone with fluctuating shape. The latter is important with respect to the germ cell-supporting surface of the cell which seems to limit the spermatogenetic potential of the male gonad.

Stage- and cell-specific gene expression and hormone regulation of the seminiferous epithelium

The regulation of spermatogenesis seems to involve complex cell interactions in the testis. Little is known about these cellular communication events. Advances in molecular technology and cell or cell group separation methods have made it possible to analyze function of defined spermatogenic and Sertoli cells, thereby giving some insights into the paracrine regulation of spermatogenesis. In this review we will describe how seminiferous tubule segments with distinct cell associations can be rapidly isolated and how the cell composition can be modified by high-energy X-irradiation. Results of the recent studies performed using these techniques will be briefly summarized. Spermatogenic cells at defined stages of their development can be isolated in living condition for morphological and biochemical studies by the transillumination technique. For accurate identification of the stages of the seminiferous epithelial cycle, phase contrast microscopy of live cell squashes has been used. The criteria described by Leblond and Clermont (Am. NY Acad. Sci., 55:548-573, 1952) can be used for accurate recognition of most of the stages of the cycle. However, stages I and II and substages of VII that are important in several studies are difficult to distinguish. Therefore, in addition to the morphology of early spermatids, development of the flagella at step 16 of spermiogenesis and the changing morphology of the cytoplasmic lobes (residual bodies) at stage VII of the cycle were used as criteria for rapid identification and isolation (preparative) of the seminiferous tubule segments. Expression of nucleoprotein and heat shock protein 70-related protein genes was analyzed with Northern blot, slot blot, and in situ hybridization techniques in accurately staged seminiferous tubules. Accurate stage-dependent timing of the onset of transcription, followed by storage and disappearance of the messages was demonstrated. The chromatoid body (cb) has been proposed to have a specific function in storage of the long-lived mRNAs in the spermatids. It is an actively moving cytoplasmic organelle that interacts with Golgi complex during formation of the acrosomic system. The chromatoid body is apparently also dependent on cytoplasmic microtubules, since its movements are inhibited and its structure becomes abnormal in the presence of vincristin, an inhibitor of tubulin polymerization. Follicle-stimulating hormone (FSH) is an important regulator of Sertoli cell function. Since both basal and FSH-dependent cyclic AMP (cAMP) production by seminiferous tubules showed marked stage dependency, Sertoli cells are apparently influenced by spermatogenic cells. Thus, Sertoli cell function varies cyclically depending on the stage of the seminiferous epithelial cycle to provide an optimal microenvironment for spermatogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of basal and FSH-dependent cyclic AMP production in rat seminiferous tubules staged by an improved transillumination technique

The stage-dependent action of follicle-stimulating hormone (FSH) in the rat seminiferous epithelium was investigated in microdissected 1 mm tubule segments, where the precise stage of the cycle was identified by a rapid screening method of live cell squash preparations. For distinction of stages I and II and the substages of VII, new criteria were used. The step 16 spermatids with rapid assembly of outer dense fibers leading to marked increase of flagellar thickness were used for distinction of stages I and II. The form and density of the cytoplasmic lobes of step 19 spermatids was used for recognition of substages of VII. Highest basal production of cyclic AMP (cAMP, measured by radioimmunoassay) was found in stage II of the cycle and stages XIV-I-VI had higher values than did stages VII-XIII. A decline occurred during stage VII and an increase at stage XIV. When stimulated with FSH, highest cAMP secretion was found in stage IV of the cycle; again, stages XIV-I-VI had higher values than did other stages. A small but significant (P less than .01) stimulation was found at substage VIId. FSH-stimulated and basal cAMP productions of different stages were compared, highest values were found at stages IV and XIII, and lowest, at stages VIIa-c and IX of the cycle. Since the FSH-dependent cAMP production is confined to Sertoli cells, and the number of these cells is constant per unit length of seminiferous tubules, the Sertoli cells are obviously under a stage-specific paracrine control by the surrounding spermatogenic cells. Specific steps in cell differentiation, such as spermatogonial proliferation, final maturation of the spermatids (stages I-VII), onset of meiosis (substage VIId), and completion of meiotic divisions (stage XIV) may be involved in this interaction.

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.

Adenosine triphosphate, bradykinin, and thyrotropin-releasing hormone regulate the intracellular Ca2+ concentration and the 45Ca2+ efflux of human thyrocytes in primary culture

The hormonal stimulation of phospholipase C and the consequent activation of the Ca2+-phosphatidylinositol cascade in eukaryotic cells is associated with modifications of the [Ca2+]i (intracellular Ca2+ concentration) which modulates cellular functions. In this study, these modifications were investigated in primary cultures of human thyroid cells. The mean apparent basal [Ca2+]i of human thyrocytes measured using the intracellularly trapped fluorescent indicator Quin-2 was found to be 89 +/- 16 nM (n = 49). ATP and, to a lesser extent, ADP, but not AMP or adenosine, elicited a concentration-dependent biphasic rise in human thyrocytes [Ca2+]i and increased their 45Ca2+ efflux. The first transient phase of the [Ca2+]i rise induced by ATP was resistant to extracellular Ca2+ depletion, whereas the second sustained phase was abolished in these conditions. This suggests that although the first phase of this response involves a release of Ca2+ from intracellular stores, the second phase requires extracellular Ca2+ influx. The response of human thyrocytes to analogs of ATP is compatible with a P2-purinergic effect of ATP on these cells. Bradykinin and TRH affected the human thyrocyte [Ca2+]i and 45Ca2+ efflux similarly to ATP. The human thyrocyte [Ca2+]i and the 45Ca2+ efflux were not modified by carbachol, a nonhydrolyzable analog of acetylcholine. The present results suggest the presence of P2-purinergic receptors to ATP and of receptors to TRH and bradykinin on human follicular thyroid cells. They also confirm that the Ca2+-phosphatidylinositol cascade is present in these cells and suggest that this cascade is modulated by ATP, TRH, and bradykinin. As this cascade is involved in the regulation of protein iodination, and therefore of thyroid hormones synthesis, these agents might have an important role in the regulation of the thyroid function.

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.

Characterization and localization of beta-adrenergic receptors in control and cryptorchidized rat testis by in vitro autoradiography

beta-adrenergic receptors were localized and characterized in control and cryptorchidized rats to investigate further their role in testicular function. Slide-mounted cryostat sections were incubated with [125I]cyanopindolol, a specific ligand for beta-adrenergic receptors. The subtypes were characterized by the displacement of [125I]cyanopindolol binding by practolol, which binds preferentially to the beta 1 subtype, and zinterol, which is preferential for beta 2 receptors. Labeling was detected by autoradiography, first by exposing sections to Ultrofilm (LKB) and second by dipping slides in NTB-2 Kodak photographic emulsion. The histologic distribution of receptors was analyzed by counting silver grains overlying the testicular structures. It was found that the vast majority of receptors were of the beta 2-subtype. In intact rats, the greatest density of receptors was found in interstitial cells, with some specific labeling over the seminiferous tubules. However, in cryptorchidized animals, the proportion of beta 2 receptors in tubules that contained mainly Sertoli cells appeared to be markedly increased. The results obtained suggest that catecholamines have multiple sites of action in the testis.

A light microscopic and morphometric analysis of the Sertoli cell during the spermatogenic cycle of the rat

Testes from 8 adult rats were perfusion-fixed with buffered glutaraldehyde and semi-thin sections of the seminiferous epithelium at all stages of the spermatogenic cycle were subjected to morphometric analysis at the light microscope level. Methods are presented to derive the volume occupied by the Sertoli cells within the total volume of the seminiferous epithelium at each stage of the cycle for a single testis. The total number of Sertoli cells present in each stage for the whole testis was calculated from a measurement of Sertoli cell numerical density and the total volume of the seminiferous tubule in the testis at each stage of the cycle. Average volume of a single Sertoli cell for each stage was derived by dividing the first set of data by the latter data. Average Sertoli cell volume exhibited a cyclic variation in relation to the stages of the spermatogenic cycle. Sertoli cells were smallest during stages VI-VIII (5300-5500 micron3) increased to maximum volume during stages XII-XIV (7700-8000 micron3) and thereafter during stages I-V, gradually contracted in volume to complete the cycle. Stage-dependent cyclic variations in Sertoli cell volume offers evidence that the morphology of the Sertoli cell undergoes structural modifications to accommodate changes in the shape and volume of the developing germ cells. Furthermore these volume changes implicate the Sertoli cells in cyclic metabolic, absorptive and secretory functions which possibly direct the maturation of germ cells during the spermatogenic cycle.

An automated perifusion system for the study of rat spermatogenesis in vitro

We report details of an automated perifusion system for the study of spermatogenesis in vitro. A potential of this new system is the evaluation of hormone/growth factor effects on the mitotic clonal expansion of spermatogonia and the meiotic and postmeiotic clonal differentiation of spermatogenic cells in coculture with Sertoli cells and in incubated seminiferous tubular segments.

Cholinergic inhibition of cAMP accumulation in Sertoli cells cultured from immature hamsters

Acetylcholine inhibits FSH-induced cAMP accumulation in cultured Sertoli cells from immature hamsters. This action of acetylcholine is mimicked by muscarinic cholinergic agonists with a rank order of carbachol greater than acetylcholine greater than arecoline greater than pilocarpine. The carbachol-induced inhibition of stimulated cAMP accumulation is blocked by atropine greater than pirenzepine but not by d-tubocurarine, indicating an apparent muscarinic receptor similar to that found in other peripheral tissues. The fact that pirenzepine is less effective as an inhibitor of the carbachol effect than atropine further defines the muscarinic effect as of the M2 subtype. The ability of carbachol to inhibit FSH-induced cAMP accumulation is blocked by pertussis toxin, which inhibits the action of the Ni inhibitory transducer of adenylate cyclase. These data indicate that cultured Sertoli cells from immature hamsters contain an M2 type muscarinic cholinergic receptor that is negatively coupled to the adenylate cyclase system through the inhibitory Ni transducer.

The effect of long-term variation in sympathetic activity on testicular morphology in immature rats

In order to investigate the effect of increased and decreased sympathetic activity on testicular development, immature male rats were injected with isoproterenol or 6-hydroxydopamine from birth up to 49 days of age. Isoproterenol treatment resulted in a marked Leydig cell hypertrophy but the development of the spermatogenic epithelium was unaffected compared to that in saline treated controls. 6-hydroxydopamine treatment in a dose inhibiting the development of the parotid gland did not influence testicular development.

Alkaline phosphatase histochemistry discriminates peritubular cells in primary rat testicular cell culture

Histochemical demonstration of alkaline phosphatase activity appears to be useful in identifying rat peritubular cells in primary testicular cell culture. In both frozen sections of rat testis and Mirsky's fixed, methacrylate-embedded rat testis, the reaction product localized primarily in peritubular cells, vascular endothelium and occasionally in interstitial cells, with much smaller amounts of reaction product associated with elongating spermatids in the germinal epithelium. Occasional late-stage tubules (X-XIV) showed weak reactivity in the epithelium, associated with spermatocytes or Sertoli cells. Ultrastructurally, Gomori-method reaction product was localized to peritubular cells, lymphatics, and spermatogonia in stage VII; no staining was found consistently in Sertoli cells. In isolated cell preparations enriched for Sertoli and germ cells, 1 to 8% of the cells demonstrated alkaline phosphatase activity, while greater than 50% of the cells stained positive for alkaline phosphatase activity in peritubular-enriched fractions. The histochemical demonstration of alkaline phosphatase activity can be useful for identifying peritubular cells in primary cultures of testicular cells.

Sertoli-cell prostaglandin synthesis. Effects of (follitropin) differentiation and dietary vitamin E

The synthesis of prostanoids by the Sertoli cell was assessed as part of a study on the role of vitamin E in maintaining spermatogenesis. Analyses of eicosanoid synthesis from endogenous substrate were carried out using freshly isolated Sertoli-cell-enriched preparations from both pre-pubertal and adult rats fed purified diets with and without vitamin E, as well as cells carried in primary culture. Freshly isolated cells from both the immature and fully differentiated adult testes produced PGI2 (prostaglandin I2) and PGE2, but PGF2 alpha was produced only by cells of the adult vitamin E-deficient rat. Cells from adult controls synthesized PGF2 alpha after primary culture. In contrast with other hormone responses of this cell, which are refractory in the adult, FSH (follitropin) potentiated prostaglandin production by freshly isolated cells of both immature and adult rats. The FSH response of Sertoli cells from immature animals did not change after primary culture. Adult cells were refractory to the hormone after culture, but the total amounts of prostaglandins produced by these cells were 10-fold higher than by either freshly isolated or cells of the immature in culture. Analogues of cyclic AMP did not potentiate prostaglandin synthesis. However, mepacrine, a phospholipase inhibitor, blocked the FSH effect. The finding that Sertoli cells synthesize prostaglandins and FSH enhances prostaglandin production implicates a potential role for eicosanoids in spermatogenesis and suggests that vitamin E may affect intratesticular regulators.

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.

Contrasting levels of transferrin gene activity in cultured rat Sertoli cells and intact seminiferous tubules

Two-dimensional polyacrylamide gel electrophoresis of proteins and transfer blot hybridization of RNA have been used to study the activity and expression of the rat transferrin gene in cultured Sertoli cells and in whole testis and isolated seminiferous tubules of sexually immature and mature rats. Although the transferrin gene in cultured Sertoli cells is actively engaged in the transcription of mRNA and the mRNA is translated into a secretory product, little transferrin mRNA and transferrin protein are present in whole testes and isolated seminiferous tubules. Sertoli cells upon culturing show a time-dependent transferrin gene activation, and abundant transferrin mRNA can be detected 6 hr after plating. A similar study using intact seminiferous tubular segments from the same rats failed to show a comparable temporal activation of the transferrin gene. Results of this study, together with previous experimental data, suggest that Sertoli cells in vivo are most likely not actively engaged in the synthesis of a testicular transferrin but, instead, rely mainly on plasma transferrin contributed by the liver. In vitro, Sertoli cells, released from the physiological constraints that operate in vivo, rapidly activate the transferrin gene, resulting in abundant newly synthesized Sertoli cell transferrin product.