Developmental expression and androgen regulation of 24 kDa secretory proteins by the murine epididymis

Distinct actions of testicular endocrine and lumicrine signaling on the proximal epididymal transcriptome

The epididymal function and gene expression in mammals are under the control of the testis. Sex steroids are secreted from the testis and act on the epididymis in an endocrine manner. There is another, non-sex steroidal secreted signaling, named lumicrine signaling, in which testis-derived secreted proteins go through the male reproductive tract and act on the epididymis. The effects of such multiple regulations on the epididymis by the testis have been investigated for many genes. The recent development of high-throughput next-generation sequencing now enables us a further comparative survey of endocrine and lumicrine action-dependent gene expression. In the present study, testis-derived endocrine and lumicrine actions on epididymal gene expression were comparatively investigated by RNA-seq transcriptomic analyses. This investigation utilized experimental animal models in which testis-derived endocrine and/or lumicrine actions were interfered with, such as unilateral or bilateral orchidectomy. By bilateral orchidectomy, which interferes with both endocrine and lumicrine actions, 431 genes were downregulated. By unilateral orchidectomy, which also interferes with endocrine and lumicrine actions by the unilateral testis, but the endocrine action was compensated by the contralateral testis, 283 genes were downregulated. The content of such genes downregulated by unilateral orchidectomy was like those of lumicrine action-interfered efferent duct-ligation, W/Wv, and Nell2-/- mice. When genes affected by unilateral and bilateral orchidectomy were compared, 154 genes were commonly downregulated, whereas 217 genes were specifically downregulated only by bilateral orchidectomy, indicating the distinction between endocrine and lumicrine actions on the proximal epididymal transcriptome. Comparative transcriptome analyses also showed that the expressions of genes emerging since Amniota were notably impacted by bilateral orchidectomy, unilateral orchidectomy, and lumicrine action-interfering treatments; the degree of influence from these treatments varied based on the evolutionary stage beyond Amniota. These findings unveil an evolutional transition of regulated gene expression in the proximal epididymis by two different testis-derived signaling mechanisms.

Busulfan administration replicated the characteristics of the epididymal initial segment observed in mice lacking testis-epididymis lumicrine signaling

The physiological functions of the mammalian epididymis are typically regulated by the testes. In addition to sex steroids secreted by testicular Leydig cells, which act on the epididymis in an endocrine manner, there is a non-sex-steroidal signaling pathway known as the lumicrine pathway. This lumicrine signaling pathway involves ligand proteins secreted from germ cells within the testicular seminiferous tubules traversing the male reproductive tract, which induce epithelial differentiation in the epididymis. These findings prompted an inquiry into whether treatments influencing testis physiology can disrupt epididymal function by interfering with testis-epididymis communication. Busulfan, an alkylating agent commonly used to deplete testicular germ cells in reproductive biology, has not been sufficiently explored because of its effects on the epididymis. This study investigated the effects of busulfan administration on the proximal epididymis using histological and transcriptomic analyses. Notably, busulfan, as opposed to the vehicle dimethyl sulfoxide (DMSO), altered the morphology of the initial segment of the epididymis, leading to a reduction in the cell height of the luminal epithelium. RNA sequencing identified 185 significantly downregulated genes in the proximal epididymis of busulfan-administered mice compared to DMSO-administered mice. Comparative transcriptome analyses revealed similarities between the epididymal transcriptome of busulfan-administered mice and lumicrine-deficient mice, such as efferent-duct-ligated W/Wv and Nell2-/- mice. However, this differed from that of bilaterally orchidectomized mice, in which both the endocrine and lumicrine signaling pathways were simultaneously ablated. Collectively, these results suggested that the harmful effects of busulfan on the proximal epididymis are secondary consequences of the ablation of testis-epididymis lumicrine signaling.

Expression of selenium-independent glutathione peroxidase 5 (GPx5) in the epididymis of Small Tail Han sheep

OBJECTIVE

Selenium-independent glutathione peroxidase (GPx5) is specifically expressed in the mammalian epididymis and plays an important role in protecting sperm from reactive oxygen species and lipid peroxidation damage. This study investigates GPx5 expression in the epididymis of Small Tail Han sheep.

METHODS

GPx5 expression was studied in three age groups: lamb (2 to 3 months), young (8 to 10 months), and adult (18 to 24 months). The epididymis of each age group divided into caput, corpus and cauda, respectively. Analysis the expression quantity of GPx5 in epididymis and testis by real-time fluorescent quantitative polymerase chain reaction and Western blot. Finally, GPx5 protein locating in the epididymis by immunohistochemical.

RESULTS

The results demonstrate that in the lamb group, the GPx5 mRNA, but not protein, can be detected. GPx5 mRNA and expressed protein were detected in both the young and adult groups. Moreover, both the mRNA and protein levels of GPx5 were significantly higher in the young group than in other two groups. When the different segments of epididymis were investigated, GPx5 mRNA was expressed in each segment of epididymis regardless of age. Additionally, the mRNA level in the caput was significantly higher than that in corpus and cauda within same age group. The GPx5 protein was in the epithelial cells' cytoplasm. However, GPx5 mRNA and protein were not detected in the testis.

CONCLUSION

These results suggest that GPx5 is mainly expressed in the epididymis of Small Tail Han sheep, and that the expression level of GPx5 is associated with age. Additionally, GPx5 was primarily expressed in the epithelial cells of the caput. Taken together, these studies indicate that GPx5 is expressed in the epididymis in all age grades.

Proteasome activators, PA28γ and PA200, play indispensable roles in male fertility

Protein degradation mediated by the proteasome is important for the protein homeostasis. Various proteasome activators, such as PA28 and PA200, regulate the proteasome function. Here we show double knockout (dKO) mice of Psme3 and Psme4 (genes for PA28γ and PA200), but not each single knockout mice, are completely infertile in male. The dKO sperms exhibited remarkable defects in motility, although most of them showed normal appearance in morphology. The proteasome activity of the mutant sperms decreased notably, and the sperms were strongly positive with ubiquitin staining. Quantitative analyses of proteins expressed in dKO sperms revealed up-regulation of several proteins involved in oxidative stress response. Furthermore, increased 8-OHdG staining was observed in dKO sperms head, suggesting defective response to oxidative damage. This report verified PA28γ and PA200 play indispensable roles in male fertility, and provides a novel insight into the role of proteasome activators in antioxidant response.

Deficient tryptophan catabolism along the kynurenine pathway reveals that the epididymis is in a unique tolerogenic state

Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme of tryptophan catabolism through the kynurenine pathway. Intriguingly, IDO is constitutively and highly expressed in the mammalian epididymis in contrast to most other tissues where IDO is induced by proinflammatory cytokines, such as interferons. To gain insight into the role of IDO in the physiology of the mammalian epididymis, we studied both wild type and Ido1(-/-)-deficient mice. In the caput epididymis of Ido1(-/-) animals, the lack of IDO activity was not compensated by other tryptophan-catabolizing enzymes and led to the loss of kynurenine production. The absence of IDO generated an inflammatory state in the caput epididymis as revealed by an increased accumulation of various inflammation markers. The absence of IDO also increased the tryptophan content of the caput epididymis and generated a parallel increase in caput epididymal protein content as a consequence of deficient proteasomal activity. Surprisingly, the lack of IDO expression had no noticeable impact on overall male fertility but did induce highly significant increases in both the number and the percentage of abnormal spermatozoa. These changes coincided with a significant decrease in white blood cell count in epididymal fluid compared with wild type mice. These data provide support for IDO playing a hitherto unsuspected role in sperm quality control in the epididymis involving the ubiquitination of defective spermatozoa and their subsequent removal.

Dietary magnesium depletion does not promote oxidative stress but targets apical cells within the mouse caput epididymidis

It is well documented that a dietary deficiency in magnesium can induce oxidative stress and an inflammatory response in animal models. In our study, we have investigated these responses in the mouse epididymis after mice had been fed a magnesium-deficient diet for a 2-week duration. The extracellular and intracellular concentrations of magnesium where shown to be depleted on this diet. This was followed, however, only in the liver of the Mg-deficient animals, by an increase in both alpha 2-macroglobulin (alpha-2m), an acute phase marker, and interleukin-6 transcripts suggesting that an inflammatory response had been initiated. These changes were correlated with a decrease in circulating neutrophils. To address the question of whether or not peroxidation was induced in mouse epididymis following hypomagnesia, we have monitored the level of endogenous peroxidation, their ability to respond to induced peroxidation as well as the expression and activity of the enzymatic glutathione peroxidase (GPX) antioxidant family. To evaluate if the epididymis had evolved specific protections against peroxidation, other organs such as the liver and the kidney were monitored in parallel. We detected no evidence for increased peroxidation in any of the mouse organs tested. However, GPX activity was found to be significantly lower in the liver and the kidney of Mg-deficient animals while it was unchanged in the epididymides of the same animals during the deficiency. Histological analysis of the epididymis showed no major difference in the overall cytological aspect of the organ. Segment 2 of the caput, however presented a significant increase in the number of apically located cells or blebbing cells. Immunohistochemical analysis proved that these cells were epididymal apical cells and not infiltrated leukocytes. These observations suggested that the mouse caput epididymidis segment 2 specifically responded to Mg deficiency via the apical cells. Finally, a comparative analysis of stress response genes was conducted in control and magnesium-deficient caput epididymidis samples. It brought forward some genes that might be involved in the peculiar response of the caput epithelium following hypomagnesia.

Delivery of ferric ion to mouse spermatozoa is mediated by lipocalin internalization

The aim of this study was to illustrate the further process of 24p3 protein after association with epididymal spermatozoa. We have previously identified a caput-initiated 24p3 protein, which interacts with the spermatozoa surface in vitro. In the present study, we investigate another role of the 24p3 protein with spermatozoa. Mouse epididymal spermatozoa exhibit the ability to bind spontaneously with exogenous 24p3 protein, a part of which is further internalized into the spermatozoa in epididymal caput. We have now focused on this issue using freshly prepared spermatozoa from caudal region of epididymis. First, the cytosolic fractionation of spermatozoa has revealed that biotinylated 24p3 protein signal could be detected by supplying biotinylated protein under 37 degrees C incubation after 30 min at this experiment. Further, flow cytometric analysis of FITC-protein containing spermatozoa has revealed two distinct types of fluorescent spermatozoa, and microscopical experimentation with fluorescent FITC-24p3 protein has shown that the 24p3 protein did accumulate in the cytosolic portion of spermatozoa. All of these events, which showed protein uptake into the cell, demonstrated time- and temperature-dependence of endocytotic characteristics, these constituting the critical points in the process of endocytosis for spermatozoa as for other cells. Using a fluorometric method, the binding affinities of ferrous ion and ferric ion to 24p3 protein were shown to be (1.5+/-0.2)x10(6) and (3.0+/-0.4)x10(7)M(-1), respectively. We have also determined the internalization of this protein in the transition of iron into spermatozoa. We report here that spermatozoa, from the caudal epididymis, demonstrate the ability to bind with 24p3 protein and further internalize it and deliver the ferric ion to the spermatozoa via protein internalization. We suggest that the 24p3 protein plays a physiological role in spermatozoa in the context of protein-ligand complex internalization.

Expression, immunolocalization and sperm-association of a protein derived from 24p3 gene in mouse epididymis

The cDNA sequence for 24p3 protein in ICR mouse epididymal tissue was determined by PCR using primers designed according to the cDNA sequence derived from 24p3 protein in mouse uterine tissue. In the present study, 24p3 protein was immunolocalized in the epithelial cells and lumen of mouse epididymis. Both immunoblot analysis for protein and northern blot analysis for mRNA level showed a declining gradient of 24p3 expression from the caput to caudal region of the epididymis. The 24p3 protein was undetectable in the testis. These findings suggest that the 24p3 protein is a caput-initiated secretory protein in the mouse epididymis. A postnatal study revealed that 24p3 gene expression occurred in mice at the age of 14 days, before the completion of epididymal differentiation. This expression remained at a constant level until epididymal differentiation was completed. We also found that the secreted 24p3 protein interacted predominantly with the acrosome of caudal spermatozoa. Our findings suggest that the epididymal 24p3 protein is a caput-initiated and sperm-associated gene product and may be important in the reproductive system.

Selenium-independent epididymis-restricted glutathione peroxidase 5 protein (GPX5) can back up failing Se-dependent GPXs in mice subjected to selenium deficiency

We have previously characterized and cloned a secreted sperm-bound selenium-independent glutathione peroxidase protein (GPX5), the expression of which was found to be restricted to the mouse caput epididymidis. Because of the lack of selenium (Se) in the active site of this enzyme, unlike the other animal GPXs characterized to date, it was suspected that GPX5 does not function in the epididymis as a true glutathione peroxidase in vivo. In the present report, following dietary selenium deprivation which is known to reduce antioxidant defenses and favor oxidative stress in relation with depressed Se-dependent GPX activities, we show that the epididymis is still efficiently protected against increasing peroxidative conditions. In this model, the caput epididymides of selenium-deficient animals showed a limited production of lipid peroxides, a total GPX activity which was not dramatically affected by the shortage in selenium availability and an increase in GPX5 mRNA and protein levels. Altogether, these data strongly suggest that the selenium-independent GPX5 could function as a back-up system for Se-dependent GPXs.

Tissue and developmental distribution, dependence upon testicular factors and attachment to spermatozoa of GPX5, a murine epididymis-specific glutathione peroxidase

Using immunohistochemistry and Western blotting analyses, we present a detailed study of the distribution of the glutathione peroxidase protein (GPX5) within the mouse epididymis. We have shown that the expression of the epididymis-specific protein is restricted to the caput and essentially localized to the apical cell border of the caput epithelium. Secretion of the protein was detected as early as the proximal segment of the caput and GPX5 was subsequently found in the lumen of corpus and cauda epididymis duct. Within the caput, Western blot analyses have shown that equivalent quantities of GPX5 protein were found in segments I, II, and III. During ontogenesis, GPX5 appeared at 20 days postnatal, before the completion of the morphological differentiation of the caput and concomitantly with the appearance of spermatozoa within the epididymis, in agreement with what was reported earlier regarding the transcription of its corresponding gene during epididymal ontogenesis (Faure et al., 1991). Hormonal privation by castration abolished the accumulation of the GPX5 protein confirming previous data obtained on GPX5 mRNA levels. Treatments such as testosterone replacement or hemicastration led to the restriction of the protein to the caput epithelium, suggesting that protein secretion partly depends both on the presence of testicular factors and on spermatozoa. Using electron microscopy, we have shown that the secreted protein binds to spermatozoa and is found predominantly on the sperm acrosomic region. Finally, we report here that the GPX5 protein can be detected in fluids recovered from the uterine horns of freshly mated female mice. These results suggest that GPX5 might play an important role in sperm maturation from the early events up to the onset of fertilization and therefore could potentially be used as a tool to monitor sperm quality.

Cloning of the mouse gene encoding plasma glutathione peroxidase: organization, sequence and chromosomal localization

Using a reverse transcription coupled to PCR amplification strategy, with degenerated primers localized in highly conserved domains of known glutathione peroxidase (GPX) proteins, we have generated, from mouse epididymal RNA, a cDNA fragment which was subsequently used to isolate a genomic clone encoding mouse plasma GPX (GPX3). GPX3 is a major enzyme in reducing lipid hydroperoxides and hydrogen peroxide in plasma. We confirm here that the mouse epididymis is a new site of expression of GPX3 and report, together with the sequence, the structural analysis and the chromosomal localization of the mouse GPX3 single-copy gene to chromosome 11.

Synthesis, characterization and hormonal regulation of epididymal proteins during postnatal development of the mouse

Maturation of mammalian spermatozoa depends on their interactions with epididymal proteins. The incorporation of 35S-methionine into these proteins was investigated by in vitro incubation of tissue minces from the mouse epididymis at different ages of postnatal development. The greatest amount of incorporation per wet weight of tissue was seen in 7 to 21-day-old mice. It decreased progressively during development while the rate of proteins released into the medium remained almost constant until the adult state. Separation of labeled proteins on sodium dodecyl sulphate polyacrylamide gels followed by fluorography showed that the great majority of secretory proteins synthesized in adult mouse epididymis could be recovered already from 7-day-old animals. Regional differences appeared at 21 days of age. These were marked by the secretion of proteins characteristic of the proximal (26, 25, 20, 19 kDa) and distal (44, 29 kDa) epididymis. Analysis of cytosol and luminal fluid proteins from prepubertal and adult epididymis revealed a number of proteins of the same mobility as those synthesized and secreted in vitro. Among the luminal proteins which showed variations during development and regional differences, four (29, 26, 20, 19 kDa) were characteristics of the epididymis and three (88, 34, 13 kDa) comigrated with testicular components. Castration or estrogen treatment of prepubertal mice for 4, 3 and 2 weeks inhibited or reduced the synthesis of the luminal proteins which appeared during postnatal development and/or presented regional differences. Testosterone replacement of castrated mice reversed this effect and induced the secretion of new proteins (37, 24 kDa).(ABSTRACT TRUNCATED AT 250 WORDS)