Electron microscopic immunolocalization of the 18 and 29 kilodalton secretory proteins in the mouse epididymis: evidence for differential uptake by clear cells

Are the basal cells of the mammalian epididymis still an enigma?

Basal cells are present in the columnar pseudostratified epithelium covering the epididymis of all mammalian species, which regulates the microenvironment where the functionally incompetent germ cells produced by the testis are matured and stored. Striking novelties have come from investigations on epididymal basal cells in the past 30–40 years. In addition to an earlier hypothesised scavenger role for basal cells, linked to their proven extratubular origin and the expression of macrophage antigens, basal cells have been shown to be involved in cell–cell cross-talk, as well as functioning as luminal sensors to regulate the activity of principal and clear cells. Involvement of basal cells in the regulation of electrolyte and water transport by principal cells was hypothesised. This control is suggested to be mediated by the local formation of prostaglandins. Members of the aquaporin (AQP) and/or aquaglyceroporin family (AQP3, AQP7 and AQP8) are also specifically expressed in the rat epididymal basal cells. Transport of glycerol and glycerylphosphorylcholine from the epithelium of the epididymis to the lumen in relation to sperm maturation may be mediated by AQP. Most probably basal cells collaborate to the building up of the blood–epididymis barrier through cell adhesion molecules, implying an involvement in immune control exerted towards sperm cells, which are foreigners in the environment in which they were produced.

Estrogen, efferent ductules, and the epididymis

Estrogen's presence in the male reproductive system has been known for over 60 years, but its potential function in the epididymis remains an important area of investigation. Estrogen is synthesized by germ cells, producing a relatively high concentration in rete testis fluid. There are two estrogen receptors (ESR), the presence of which in the head of the epididymis is well documented and consistent between species; however, in other regions of the epididymis, their expression appears to be isotype, species, and cell specific. ESR1 is expressed constitutively in the epididymis; however, its presence is downregulated by high doses of estrogen, making the design of experiments complicated, as the phenotype of the Cyp19a1(-/-) mouse does not resemble that of the Esr1(-/-) mouse. Ligand-independent and DNA-binding Esr1 mutant models further demonstrate the complexity and importance of both signaling pathways in maintenance of efferent ductules and epididymis. Data now reveal the presence of not only classical nuclear receptors, but also cytoplasmic ESR and rapid responding membrane receptors; however, their importance in the epididymis remains undetermined. ESR1 regulates ion transport and water reabsorption in the efferent ducts and epididymis, and its regulation of other associated genes is continually being uncovered. In the male, some genes, such as Aqp9 and Slc9a3, contain both androgen and estrogen response elements and are dually regulated by these hormones. While estrogen pathways are a necessity for fertility in the male, future studies are needed to understand the interplay between androgens and estrogens in epididymal tissues, particularly in cell types that contain both receptors and their cofactors.

Functional studies of acid transporter in cultured rat epididymal cell

OBJECTIVE

To explore the functional role of vacuolar H(+)-ATPase in the pH regulation of epididymal fluid and its effect on sperm motility.

DESIGN

Experimental study.

SETTING

Physiology laboratory in a university.

ANIMAL(S)

Immature male Sprague-Dawley rats.

INTERVENTION(S)

The H(+)-ATPase inhibitor was applied to the primary culture of epididymal cells.

MAIN OUTCOME MEASURE(S)

The intracellular luminal fluid pH and sperm percent motility were recorded.

RESULT(S)

Double immunofluorescence of H(+)-ATPase and carbonic anhydrase II in primary culture of cauda epididymal epithelial cells showed that the system was a suitable model for investigation of acid secretion by clear cells. Clear cells were pharmacologically distinct from principal cells in acid/base transportation. The intracellular pH recovery from cellular acidification was suppressed by the H(+)-ATPase inhibitor bafilomycin A1(100 nM) and the Na(+)/H(+) exchanger inhibitor amiloride (1 mM) by 85% and 54%, respectively. These results suggest that, in addition to Na(+)/H(+) exchanger, clear cells actively pump proton from cytoplasm into extracellular space through H(+)-ATPase. In addition, inhibition of H(+)-ATPase by bafilomycin A1 blocked the acidification of luminal fluid with IC(50) values of 12 nM, which supports that H(+)-ATPase acidifies the luminal fluid. We also confirm that the acid fluid regulates rat cauda sperm motility.

CONCLUSION(S)

The present work shows that clear cells, the minority cell type of epididymal cell population, play an important role in the pH regulation of epididymal fluid by H(+)-ATPase.

Absence of estrogen receptor alpha leads to physiological alterations in the mouse epididymis and consequent defects in sperm function

Male mice deficient in ESR1 (ERalpha) (Esr1KO mice) are infertile, and sperm recovered from the cauda epididymis exhibit reduced motility and fail to fertilize eggs in vitro. These effects on sperm appear to result from defective epididymal function and not a direct effect on spermatogenesis, as Esr1KO germ cells transplanted into wild-type testes yield normal offspring. We hypothesized that the previously described defect in efferent duct fluid reabsorption would lead to alterations in the epididymal fluid milieu, which would negatively impact sperm function. Analysis of the epididymal fluid revealed that the Esr1KO maintains a higher luminal pH throughout the epididymis, confirming an inability of the efferent ducts and/or epididymis to properly acidify the luminal contents. Subsequent studies showed that these abnormalities were not the result of global defects in epididymal function since protein secretion by the Esr1KO epididymis appeared normal as judged by SDS-PAGE of total secreted proteins and by immunoblotting of candidate secreted proteins. To gain insight into the basis of the aberrant fluid homeostasis in the Esr1KO epididymis, the expression of several enzymes and transporters known to be involved in acid/base regulation were analyzed. The levels of SLC9A3 (NHE3) as well as carbonic anhydrase XIV and SLC4A4 (NBC1) were all reduced in the proximal portion of the Esr1KO epididymis, while other components appeared unaffected, including other ion transporters and ATP6V0A1 (V-ATPase). The altered luminal milieu of the Esr1KO epididymis was shown to lead to a corresponding increase in the intracellular pH of Esr1KO sperm, relative to sperm from control animals. Since pH and bicarbonate ions are critical regulators of sperm cAMP levels and motility, we attempted to bypass the abnormal luminal and intracellular environment by supplementing sperm with exogenous cAMP. This treatment rescued all defective motility parameters, as assayed by CASA, further showing that motility defects are not intrinsic to the sperm but, rather, result from the abnormal epididymal milieu.

GPX5 orthologs of the mouse epididymis-restricted and sperm-bound selenium-independent glutathione peroxidase are not expressed with the same quantitative and spatial characteristics in large domestic animals

We report here on the cloning of cDNAs coding bovine and equine orthologs of mouse epididymis-restricted and sperm-bound glutathione peroxidase 5 (GPX5), a selenium-independent member of the multigenic GPX family in mammals. The complete sequence of bovine GPX5 as well as a partial sequence of the equine GPX5 were characterized, conceptually translated and aligned with other known mammalian GPX5 proteins. Using Northern blotting assays, we show that the level of expression of GPX5 is high in bovine but low in equine and that in both species the regionalization of GPX5 expression in epididymis is not totally identical to what was reported for rodent mouse GPX5. An antibody was produced against GPX5 and used in Western blot assays as well as in immunohistochemistry assays on bovine epididymis sections. It shows that the protein is essentially present in the cytoplasmic compartment of the caput segment 2 epithelium of the bovine epididymis. Unlike in the mouse model, bovine GPX5 seems to be poorly secreted and does not seem to be present on cauda epididymal spermatozoa.

Immortalization by large T-antigen of the adult epididymal duct epithelium

The SV40 large T-antigen has been widely used to convert various cell types to a transformed phenotype, and also to induce progressive tumours in transgenic animals. The objectives of this review are to compare and discuss three different approaches to generate epididymal epithelial cell lines using the large T-antigen. In the first approach, retroviral transfection of primary cultures was used to immortalize canine epididymal cells in vitro; the other two approaches used transgenic mice expressing the large T-antigen. In one of these in vivo approaches, a construct consisting of the coding sequence of a temperature sensitive (ts) SV40 large T-antigen was inserted in a mouse genome. When the cells are exposed to the permissive temperature of 33 degrees C, functional expression of the large T-antigen occurs and cells start to proliferate. In the second in vivo approach a tissue-specific promoter, the 5kb GPX5 promoter, was used to direct expression of the large T-antigen to the epididymal duct epithelium.

Expression and regulation of H+K+ATPase in lysosomes of epithelial cells of the adult rat epididymis

Endocytosis is an important event in the epididymis as it contributes to a luminal environment conducive for sperm maturation. Principal and clear cells contain numerous lysosomes which degrade many substances internalized by endocytosis from the epididymal lumen. The interior of the lysosomes depends on low pH to activate the release of their enzymes and to activate their acid hydrolases. In the present study, H+K+ATPase was localized by light microscopy in the adult rat epididymis of intact and of orchidectomized animals supplemented with testosterone or not. In normal animals, numerous lysosomes of nonciliated cells of the efferent ducts were intensely reactive for anti-H+K+ATPase antibody. In the initial segment, only a few lysosomes of principal cells were reactive. In the intermediate zone of the epididymis, numerous lysosomes of principal cells were intensely reactive, while the number of intensely reactive lysosomes decreased progressively from the proximal caput to the distal caput with none being seen in the proximal corpus region. In the distal corpus and cauda regions, only a few lysosomes of some principal cells were reactive. In contrast, clear cells of all regions showed intense reactivity. Orchidectomy resulted in the abolishion of H+K+ATPase in lysosomes of principal cells of all regions except the initial segment. However, while clear cells of the caput and corpus regions also became unreactive, those of the cauda region remained as reactive as in controls. Orchidectomized animals supplemented with testosterone maintained a staining pattern similar to controls for both cell types. These observations demonstrate the presence in principal and clear cells of H+K+ ATPase which may have an important role in acidifying the interior of their lysosomes. However, there is a region-specific expression of H+K+ATPase in lysosomes of principal cells, unlike that for clear cells. In addition, H+K+ATPase expression in lysosomes of principal cells depends on testosterone in all regions except the initial segment. However, in the case of clear cells, only those of the caput and the corpus regions are dependent on testosterone, while those of the cauda region appear to be regulated by some other factor.

Cathepsin A is expressed in a cell- and region-specific manner in the testis and epididymis and is not regulated by testicular or pituitary factors

The epithelial cells of the testis are involved in the production, differentiation, and sustenance of sperm, and those of the epididymis play a major role in sperm maturation, protection, and storage. These tissues express various proteins that respond differently to androgens. Cathepsin A is a multifunctional lysosomal carboxypeptidase that also functions as a protective and an activator protein for neuraminidase and beta-galactosidase. In this study, cathepsin A was immunolocalized by light and electron microscopy using a polyclonal affinity-purified antibody on the testis and epididymis of normal, orchidectomized with or without testosterone supplementation, efferent duct-ligated, and hypophysectomized adult rats. In normal rats, cathepsin A expression was noted in lysosomes of Sertoli and Leydig cells but not in germ cells of the testis, as well as nonciliated cells of the efferent ducts. In the epididymis, a cell- and region-specific distribution of cathepsin A was noted. In experimentally treated animals, no changes were noted in the expression of cathepsin A. Immunolabeling of tissues examined at the electron microscopic level revealed that lysosomes were reactive. These data indicate cell- and region-specific expression of cathepsin A in cells of the testis and epididymis and also indicate that cathepsin A expression is not regulated by testicular or pituitary factors.

Distribution of immune cells in the epididymis of the aging Brown Norway rat is segment-specific and related to the luminal content

Remarkable changes occur during aging in the testis and epididymis of the Brown Norway rat. A dramatic increase in the number of halo cells, which are present in the epididymal epithelium and originate from the immune system, is found in animals of increasing age. Halo cells have been postulated to be either lymphocytes or monocytes. We hypothesized that halo cells are a mixture of different immune cells and that their relative composition changes with age. To verify this hypothesis, markers for helper T lymphocytes, cytotoxic T lymphocytes, B lymphocytes, and monocytes-macrophages were used to identify the major categories of immune cells in the epididymides of Brown Norway rats ranging in age from 3 to 24 mo. The numbers of immunocompetent cells in the epididymis were determined in relation to age, epididymal segment, and luminal content. We found that monocytes, helper T lymphocytes, and cytotoxic T lymphocytes belong to the population of halo cells. In addition, a segment-specific increase with age in the number of these immune cells was noted. Finally, we report a segment-specific recruitment of cytotoxic T lymphocytes and monocytes-macrophages in the epididymal epithelium of aged rats whose epididymal lumen contained few spermatozoa. We postulate that accumulation of damaged epithelial cells and antigens of germ cell origin, leaking through a dysfunctional blood-epididymis barrier, may contribute to the active recruitment of immune cells with age.

Expression and regulation of LRP-2/megalin in epithelial cells lining the efferent ducts and epididymis during postnatal development

Low density lipoprotein receptor-related protein-2/megalin (LRP-2) is a receptor belonging to the low density lipoprotein receptor family that mediates endocytosis and lysosomal degradation of a variety of ligands including apolipoprotein J (Apo J)/clusterin/SGP-2. LRP-2 has been shown to be expressed regionally in the adult rat epididymis. In this study, we describe the pattern of expression of LRP-2 in the efferent ducts and epididymis during postnatal development of the rat and examine the role of testicular luminally derived substances on its expression. The expression of LRP-2 was analyzed immunocytochemically in tissues of normal animals ranging in age from postnatal day 7-90 and in 15-day-old efferent-duct-ligated animals sacrificed at later ages. In the efferent ducts, LRP-2 expression, appearing as a dense band on the apical surface of the nonciliated epithelial cells, was noted as early as day 7, well before the entry of sperm, Sertoli-cell-derived secretory products, and high levels of androgens. Efferent duct ligation studies further revealed that expression under this condition was comparable to controls at all later ages examined, suggesting that the factor regulating its expression was not a luminally derived testicular substance. In normal untreated animals, LRP-2 expression was not apparent at any of the ages examined in the proximal initial segment of the epididymis. By comparison, the distal initial segment, although having no LRP-2 expression from 7-15 days, showed expression in principal cells by day 21 which intensified at days 29 and 39. However, by day 49 and at later ages (56 and 90), LRP-2 immunoreactivity over principal cells became spotty or with weak or moderate reactivity in some cells and none in others. LRP-2 expression in the intermediate zone, proximal caput, corpus, and cauda regions also appeared in principal cells by day 21, intensified at days 29 and 39 and persisted as such at all later ages examined, correlating with high levels of androgens shown to occur by day 39. Although LRP-2 expression in the distal caput region was evident in principal cells at days 21 and 29, it became spotty with weak, moderate, or absent reactivity over principal cells at all later ages. These data suggest that LRP-2 expression is under the influence of both stimulatory and region-specific inhibitory factors. Analysis of 15-day-old efferent-duct-ligated animals at all later ages examined revealed that there was no change in LRP-2 expression along the entire epididymis, suggesting that both the stimulatory and inhibitory factors are not luminally derived testicular substances. The observed pattern of LRP-2 expression in all regions of the epididymis, except the distal caput region, was similar to that described for Apo J internalization by principal cells during postnatal development, showing a correlation between LRP-2 expression and its ligand, Apo J. In summary, LRP-2 expression in the epididymis undergoes region-specific changes during postnatal development and appears to be influenced by both stimulatory and inhibitory factors.

Molecular cloning and hormonal regulation of a murine epididymal retinoic acid-binding protein messenger ribonucleic acid

A complementary DNA encoding the mouse epididymal secretory protein MEP 10 (mouse epididymal protein 10) was cloned and is now renamed murine epididymal retinoic acid binding protein (mE-RABP). The analysis of the predicted primary amino acid sequence showed that mE-RABP has a 75% identity with rat ESP I (epididymal secretory protein I), another epididymal retinoic acid-binding protein. The homology strongly suggests that mE-RABP is the mouse orthologue of rat ESP I. A computer analysis of the predicted three-dimensional structure confirmed that mE-RABP can accommodate retinoic acid as ligand. In the rat, ESP I messenger RNA (mRNA) is expressed in the efferent ducts and in the entire caput epididymidis. However, in the mouse, the expression of a 950-bp mE-RABP mRNA was detected only in principal cells of the mid/distal caput epididymidis, suggesting that the regulation of region-specific expression is different in rat and mouse. Northern blot analyses showed that mE-RABP gene expression is no longer detected 10 days after castration but progressively rebounds between days 15 and 60. However, mE-RABP protein could not be detected by Western blot 30 days after castration. Androgen replacement, begun 5 days after castration and continued for 4 days restored significant expression of mE-RABP mRNA. Efferent duct ligation for 10 days did not affect gene expression. Taken together, these results indicate that mE-RABP mRNA expression is regulated by androgens but not by testicular factors. The overall similarity in the primary amino acid sequence of mE-RABP with ESP I and other members of the lipocalin superfamily suggests that they are evolutionarily related.

Binding of rat and ovine epididymis-specific prealbumins (PES) to rat spermatozoa without effect of heterologous immunization on rat fertility

The epididymis, under control of testosterone, secretes proteins which bind to the membrane of the spermatozoa during their passage through the lumen. One such class is termed PES (prealbumin epididymal specific). Injection of heterologous oPES (ovine PES) into male rats caused antibody production but failed to induce sterility, unlike results previously obtained when rat PES was injected into male rats. This suggests that only very restricted species-specific epitopes of PES might be useful for causing immunocontraception. Despite this, the sperm binding properties of PES purified from the rat (rat PES) and from the ram (oPES) were shown to be similar. When either rat PES or oPES, conjugated with a fluorescent probe (dimethylamino-fluorescein), was incubated with washed rat spermatozoa originating from the caput, corpus or cauda epididymis, results of flow cytometric analysis showed: (1) the number of spermatozoa bound to isologous or heterologous fluorescent PES, and (2) the binding-affinity of spermatozoa for PES was greater for sperm collected from more distal sites in the epididymis.

Isolation and characterization of the androgen-dependent mouse cysteine-rich secretory protein-1 (CRISP-1) gene

In mice, cysteine-rich secretory protein-1 (CRISP-1) is mainly found in the epididymis and also, to a lesser extent, in the salivary gland of males, where androgens control its expression. We have now isolated and characterized overlapping phage clones covering the entire length of the CRISP-1 gene. DNA sequencing revealed that the gene is organized into eight exons, ranging between 55 and 748 bp in size, and seven introns. All exon-intron junctions conformed to the GT/AG rule established for eukaryotic genes. The intron length, as determined by PCR, varied between 1.05 and 4.0 kb so that the CRISP-1 gene spans over 20 kb of the mouse genome. The transcription-initiation site was determined by primer extension and localized at the expected distance downstream of a consensus TATA box. Approximately 3.7 kb of the CRISP-1 promoter region were isolated and sequenced, and several stretches fitting the androgen-responsive element consensus were found. Those that most resembled the consensus were analysed by electrophoretic mobility-shift assay and found to form specific complexes with the liganded androgen receptor in vitro, but with different affinities. Putative binding elements for the transcription factors Oct, GATA, PEA3, CF1. AP-1 and AP-3 were also found in the promoter region.

The human cysteine-rich secretory protein (CRISP) family. Primary structure and tissue distribution of CRISP-1, CRISP-2 and CRISP-3

We report the isolation and characterisation of cDNAs encoding three different, human members of the cysteine-rich secretory protein (CRISP) family. The novel CRISP-1 exists in five cDNA subtypes differing by the presence or absence of a stretch coding for a C-terminal cysteine-rich domain so far found in all members of the family, and by the length of their 3'-untranslated region. CRISP-2 cDNA corresponds to the previously described TPX1 form, with so far unreported 5'-untranslated sequence heterogeneities while CRISP-3 cDNA codes for a new, unique protein. Northern blot analysis of various human organs indicates that CRISP-1 transcripts are epididymis-specific whereas CRISP-2/TPX1 transcripts are detected mainly in the testis and also in the epididymis. CRISP-3 transcripts are more widely distributed and found predominantly in the salivary gland, pancreas and prostate, and in less abundance in the epididymis, ovary, thymus and colon. A protein reacting with an anti-mouse CRISP-1 antibody was isolated from human epididymal extracts and N-terminal sequencing revealed that it corresponded to the CRISP-1 cDNA we have isolated. In contrast to findings on its rat counterpart epididymal protein DE/acidic epididymal glycoprotein (AEG), no significant association of CRISP-1 with human spermatozoa was observed.