Tissue specificity of the epididymal androgen dependent phospholipase A

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.

Antioxidant strategies in the epididymis

Spermatozoa are very specialized cells, dedicated to fertilization of the oocyte. The attainment of this biological role is partly due to the fusogenic properties of the sperm plasma membrane, which is particularly rich in polyunsaturated fatty acids (PUFA). This predominance of PUFA renders spermatozoa highly susceptible to lipid peroxidation due to attacks from reactive oxygen species (ROS). These attacks ultimately lead to the impairment of sperm function through oxidative stress. Despite such disruptive effects, it should be also emphasized that these molecules also play an important positive, physiological role in the regulation of sperm physiology through their participation in apoptosis and the signal transduction cascades that control sperm maturation and capacitation. In this article, the different sources of ROS are examined and then the antioxidant strategies that protect these cells during epididymal transit are reviewed. While the major focus is on the involvement of glutathione peroxidase in this process, consideration will also be given to a range of additional antioxidant enzymes (catalase, indolamine dioxygenase and superoxide dismutase) that have evolved to protect spermatozoa during this extremely vulnerable phase in their life history. Besides the classical enzymatic roles of these enzymes in recycling ROS, additional features are discussed in the light of contraceptive development.

Ectopic epididymal expression of guinea pig intestinal phospholipase B. Possible role in sperm maturation and activation by limited proteolytic digestion

Guinea pig intestinal phospholipase B is a calcium-independent phospholipase hydrolyzing sequentially the acyl ester bonds at sn-2 and sn-1 positions of glycerophospholipids, promoting the formation of sn-glycero-3-phosphocholine from phosphatidylcholine. This 140-kDa glycoprotein from the brush border membrane of differentiated enterocytes contributes to lipid digestion as an ectoenzyme. The cDNA coding for guinea pig phospholipase B was revealed to be the homologue of AdRab-B, an mRNA appearing in rabbit upon intestine development. The sequence predicts a polypeptide of 1463 amino acids displaying four homologous repeats, two of them containing the lipase consensus sequence GXSXG. A 5-kilobase transcript was particularly abundant in mature ileal and jejunal enterocytes but was also detected in epididymis, where phospholipase B displayed a higher molecular mass (170 kDa versus 140 kDa in intestine), with no obvious evidence for enzyme activity. Trypsin treatment of phospholipase B immunoprecipitated from epididymal membranes reduced its size to 140 kDa, coinciding with the appearance of a significant phospholipase A2 activity. The same results were obtained in COS cells transfected with phospholipase B cDNA. Since sn-glycero-3-phosphocholine present at high concentrations in seminal plasma mainly stems from epididymis, this suggests a possible role of phospholipase B in male reproduction. This novel localization also unravels a mechanism of phospholipase B activation by limited proteolysis involving either trypsin in the intestinal lumen or a trypsin-like endopeptidase in the male reproductive tract.

Structure and function of the epididymis

Testicular spermatozoa are functionally immature in that they cannot fertilize ova. It was first demonstrated by Young that spermatozoa undergo certain changes as they migrate through the epididymis. He proposed that spermatozoa ripen during epididymal transit. It is now known that specific maturational changes occur in spermatozoa during epididymal transit which result in their developing the ability to fertilize ova. Concomitant with this functional maturity are changes in spermatozoal morphology, motility, chemistry, permeability, density and metabolism. It is apparent that in some way not understood these changes are necessary for sperm to achieve the ability to complete the fertilization process. When these mechanisms are understood, we may be able to effectively treat conditions such as necrospermia or abnormally low sperm motility. Furthermore, with the development of the hamster-egg penetration test a "new" type of male infertility has become evident in recent years; the inability of otherwise normal sperm to penetrate an ovum. It is during epididymal transit that this ability is normally acquired. Thus, any insight into how sperm attain the capacity to penetrate an ovum could lead to an effective treatment of patients whose sperm do not have this ability. In addition, the epididymis holds significant promise as the site of action for a male contraceptive. Thus, it is the purpose of this review to describe the structure and function of the mammalian epididymis with particular emphasis on the factors regulating sperm maturation.

Phosphatidylcholine of blood lipoprotein is the precursor of glycerophosphorylcholine found in seminal plasma

Glycerophosphorylcholine (GPC) concentration of the male reproductive tract increases from under 0.1 mM in the efferent ducts of the testis to 10-50 mM in the cauda epididymidis. It is reasonable to assume that choline-containing phospholipids serve as precursor(s) of GPC but the identity and source of these precursors had not been established. We performed in vivo labeling experiments in rabbits to distinguish between two types of phospholipid metabolism that might account for epididymal GPC formation: (a) addition of phospholipids to sperm during epididymal transit with degradation of these phospholipids by sperm to yield GPC or (b) degradation of phospholipids by epididymal epithelial cells with excretion of GPC into the duct lumen. We concluded that the latter route accounted for most of the GPC accumulation and that the primary source of the choline moiety of GPC was phosphatidylcholine of blood lipoprotein. We believe that these observations established a specific, vectorial metabolism of phospholipids whereby circulating lipoproteins on one side of the epididymal epithelial cell are transferred to the cell, the lipoproteins degraded by the epithelial cell to GPC, and the GPC moved into the lumen.