Cloning and characterization of a complementary DNA encoding a human epididymis-associated disintegrin and metalloprotease 7 protein

Inactive metallopeptidase homologs: the secret lives of pseudopeptidases

Inactive enzyme homologs, or pseudoenzymes, are proteins, found within most enzyme families, that are incapable of performing catalysis. Rather than catalysis, they are involved in protein-protein interactions, sometimes regulating the activity of their active enzyme cousins, or scaffolding protein complexes. Pseudoenzymes found within metallopeptidase families likewise perform these functions. Pseudoenzymes within the M14 carboxypeptidase family interact with collagens within the extracellular space, while pseudopeptidase members of the M12 "a disintegrin and metalloprotease" (ADAM) family either discard their pseudopeptidase domains as unnecessary for their roles in sperm maturation or utilize surface loops to enable assembly of key complexes at neuronal synapses. Other metallopeptidase families contain pseudopeptidases involved in protein synthesis at the ribosome and protein import into organelles, sometimes using their pseudo-active sites for these interactions. Although the functions of these pseudopeptidases have been challenging to study, ongoing work is teasing out the secret lives of these proteins.

Characterization of primary cultures of adult human epididymis epithelial cells

OBJECTIVE

To establish cultures of epithelial cells from all regions of the human epididymis to provide reagents for molecular approaches to functional studies of this epithelium.

DESIGN

Experimental laboratory study.

SETTING

University research institute.

PATIENT(S)

Epididymis from seven patients undergoing orchiectomy for suspected testicular cancer without epididymal involvement.

INTERVENTION(S)

Human epididymis epithelial cells harvested from adult epididymis tissue.

MAIN OUTCOME MEASURE(S)

Establishment of a robust culture protocol for adult human epididymal epithelial cells.

RESULT(S)

Cultures of caput, corpus, and cauda epithelial cells were established from epididymis tissue of seven donors. Cells were passaged up to eight times and maintained differentiation markers. They were also cryopreserved and recovered successfully. Androgen receptor, clusterin, and cysteine-rich secretory protein 1 were expressed in cultured cells, as shown by means of immunofluorescence, Western blot, and quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The distribution of other epididymis markers was also shown by means of qRT-PCR. Cultures developed transepithelial resistance (TER), which was androgen responsive in the caput but androgen insensitive in the corpus and cauda, where unstimulated TER values were much higher.

CONCLUSION(S)

The results demonstrate a robust in vitro culture system for differentiated epithelial cell types in the caput, corpus, and cauda of the human epididymis. These cells will be a valuable resource for molecular analysis of epididymis epithelial function, which has a pivotal role in male fertility.

The emerging role of matrix metalloproteases of the ADAM family in male germ cell apoptosis

Constitutive germ cell apoptosis during mammalian spermatogenesis is a key process for controlling sperm output and to eliminate damaged or unwanted cells. An increase or decrease in the apoptosis rate has deleterious consequences and leads to low sperm production. Apoptosis in spermatogenesis has been widely studied, but the mechanism by which it is induced under physiological or pathological conditions has not been clarified. We have recently identified the metalloprotease ADAM17 (TACE) as a putative physiological inducer of germ cell apoptosis. The mechanisms involved in regulating the shedding of the ADAM17 extracellular domain are still far from being understood, although they are important in order to understand cell-cell communications. Here, we review the available data regarding apoptosis during mammalian spermatogenesis and the localization of ADAM proteins in the male reproductive tract. We propose an integrative working model where ADAM17, p38 MAPK, protein kinase C (PKC) and the tyrosine kinase c-Abl participate in the physiological signalling cascade inducing apoptosis in germ cells. In our model, we also propose a role for the Sertoli cell in regulating the Fas/FasL system in order to induce the extrinsic pathway of apoptosis in germ cells. This working model could be applied to further understand constitutive apoptosis in spermatogenesis and in pathological conditions (e.g., varicocele) or following environmental toxicants exposure (e.g., genotoxicity or xenoestrogens).

ADAM7 is associated with epididymosomes and integrated into sperm plasma membrane

During epididymal transit, mammalian sperm acquire selected proteins secreted by the epididymis. We previously showed that a disintegrin and metalloprotease (ADAM) 7 is expressed specifically in the epididymis and transferred to the sperm surface during epididymal transit. Here, we show that mouse ADAM7 secreted to the epididymal lumen is associated with membranous vesicles known as epididymosomes. Furthermore, we found that ADAM7 can be transferred directly from epididymal vesicles to sperm and that it is an integral plasma membrane protein in sperm. Thus, our study provides new information regarding the unique mode of secretion and interaction of ADAM7 during the epididymis-to-sperm transfer process.

Novel epididymal proteins as targets for the development of post-testicular male contraception

Apart from condoms and vasectomy, modern contraceptive methods for men are still not available. Besides hormonal approaches to stop testicular sperm production, the post-meiotic blockage of epididymal sperm maturation carries lots of promise. Microarray and proteomics techniques and libraries of expressed sequence tags, in combination with digital differential display tools and publicly available gene expression databases, are being currently used to identify and characterize novel epididymal proteins as putative targets for male contraception. The data reported indicate that these technologies provide complementary information for the identification of novel highly expressed genes in the epididymis. Deleting the gene of interest by targeted ablation technology in mice or using immunization against the cognate protein are the two preferred methods to functionally validate the function of novel genesin vivo. In this review, we summarize the current knowledge of several epididymal proteins shown eitherin vivoorin vitroto be involved in the epididymal sperm maturation. These proteins include CRISP1, SPAG11e, DEFB126, carbonyl reductase P34H, CD52, and GPR64. In addition, we introduce novel proteinases and protease inhibitor gene families with potentially important roles in regulating the sperm maturation process. Furthermore, potential contraceptive strategies as well as delivery methods will be discussed. Despite the progress made in recent years, further studies are needed to reveal further details in the epididymal sperm maturation process and the factors involved, in order to facilitate the development of new epididymal contraceptives.

(Make) stick and cut loose--disintegrin metalloproteases in development and disease

"A disintegrin and metalloprotease" (ADAM) proteases form a still growing family of about 40 type 1 transmembrane proteins. They are defined by a common modular ectodomain architecture that combines cell deadhesion/adhesion and fusion motifs (disintegrin and cysteine-rich domains), with a Zn-protease domain capped by a large prodomain. Their ectodomain thus strikingly resembles snake venom disintegrin proteases, which by combined integrin blocking and extracellular proteolysis, can cause extensive tissue damage after snake bites. A surprisingly large proportion (13 ADAMs) is exclusively expressed in the male gonads, and only a minority can be found throughout all tissues. As predicted by their amino acid sequence, a major proportion of this family has not maintained a functional protease domain, most probably rendering them into pure adhesion and/or fusion proteins. For most ADAMs, the respective key function has remained elusive. Despite their overall conserved ectodomain structure, ADAMs appear to be subdivided into those with a predominant role in direct adhesion (e.g., ADAMs 1, 2, and 3) and those mainly acting as proteases (e.g., ADAMs 10 and 17). Only for a few of them are functions of more than one domain documented (e.g., ADAM9 in cell fusion and proteolysis). Several ADAMs exist in both membrane-resident and secreted isoforms; the functional significance of this dichotomy is in most cases still unclear. Knockout phenotypes have been informative only in a few cases (ADAMs 1, 2, 10, 12, 15, 17, and 19) and are mainly related to their protease function. A common denominator of ADAM-mediated proteolysis is the ectodomain shedding of a broad spectrum of substrates, including paracrine growth factors like epidermal growth factor receptor (EGFR) ligands, cell adhesion molecules like CD44 or cadherins, and the initiation of regulated intramembrane proteolysis (RIP), whereby the transmembrane fragment of the respective substrate is further cleaved by an intramembrane cleaving protease to release an intracellular domain acting as a nuclear transcription regulator. Most ADAMs feature a significant overlap of substrate specificities, explaining why an inactivation of individual ADAMs only rarely causes major phenotypes.

New approaches for male fertility control: HE6 as an example of a putative target

Reversible contraceptive methods for males are still not available. During the last few years several marketing studies have clearly shown that men and women would welcome a situation where men could assume responsibility for family planning. Schering AG and Organon are currently collaborating to develop a hormonal method for male fertility control based on the combination of etonogestrel as gestagenic component and testosterone undecanoate. To further optimize male contraceptives in terms of improved efficiency, rapid onset, reversibility, fewer side effects and a convenient method of application, a search for innovative non-hormonal approaches was started. During the last few years, numerous proteins were identified which play a specific role in male fertility. These proteins have first to fulfil a set of indication-specific criteria before a drug discovery process can be initiated. The most important criteria for a putative target protein are tissue-selective expression, crucial biological function in fertility, drugable properties and feasibility of assay development for high-throughput-screening and lead optimization. The G-protein-coupled receptor HE6 was selected as target and the above selection criteria were applied. HE6 displays a preferred epididymis-specific expression pattern and belongs to the superfamily of GPCRs, which are well known to be drugable with small molecules. A knockout mouse was generated which revealed an infertility phenotype with the onset occurring 6 weeks after initiation of spermatogenesis at the latest. Surprisingly, no epididymis-specific phenotype was observed. Instead, the reabsorption of testicular fluid along the efferent ducts was strongly affected. No further obvious side effects were observed in male or female mice. This study with HE6 exemplifies how targets for male contraception have to be validated before drug development can start.

Genome-wide profiling of segmental-regulated transcriptomes in human epididymis using oligo microarray

Sperm maturation during passage through the epididymis depends on regionalized gene expression which maintains the progressively changing environment within the epididymal tubule. Towards defining the genes that drive the sequential maturation of spermatozoa, we profiled regionally regulated gene expression pattern in the epididymis of a fertile young male donor using Affymetrix human genome U133 plus 2.0 microarray representing approximately the whole human genome. Over 15000 transcripts, almost one-third of the total on the array were identified in whole epididymis. Among them, 65% were detected in all three regions of the epididymis, 410 or 2.6% were present only in one region and the remaining 32.4% were distributed in two regions. Region-specific transcripts observed in caput (264), corpus (61) and cauda (81) epididymides were further classified as empirically determined reported genes or ESTs. This study revealed for the first time, the expression in human epididymis of a number of region-specific genes. The original data will be made publicly available on the Shanghai Science and Technology Database (http://www.scbit.org/human_epididymis_transcriptomes).

Molecular, biochemical, and cellular characterization of epididymal ADAMs, ADAM7 and ADAM28

The mammalian epididymis is critical for sperm to acquire motility and fertilizing capacity. This maturation process involves the interaction of epididymal secretory proteins with sperm. We analyzed mouse a disintegrin and metalloprotease (ADAMs) 7 and 28 expressed specifically or predominantly in the epididymis. We found that these ADAM genes are expressed in an epididymal region-specific manner and their gene expression is regulated by both androgen and testicular factors (ADAM7) or only testicular factors (ADAM28). We identified an ADAM28 transcript isoform that lacks the transmembrane domain. Protein analysis revealed that ADAM7, but not ADAM28, is transferred from the epididymis to the sperm surface and redistributed in the sperm head during acrosome reaction. These processes were shown to occur without processing of the protein. Taken together, our results indicate that the two epididymal ADAMs closely related in phylogeny are differential in various characteristics and ADAM7 has unique secretory feature and interactive relationship with sperm.

Gene and protein expression in the epididymis of infertile c-ros receptor tyrosine kinase-deficient mice

Transgenic male mice bearing inactive mutations of the receptor tyrosine kinase c-ros lack the initial segment of the epididymis and are infertile. Several techniques were applied to determine differences in gene expression in the epididymal caput of heterozygous fertile (HET) and infertile homozygous knockout (KO) males that may explain the infertility. Complementary DNA arrays, gene chips, Northern and Western blots, and immunohistochemistry indicated that some proteins were downregulated, including the initial segment/proximal caput-specific genes c-ros, cystatin-related epididymal-spermatogenic (CRES), and lipocalin mouse epididymal protein 17 (MEP17), whereas other caput-enriched genes (glutathione peroxidase 5, a disintegrin and metalloproteinase [ADAM7], bone morphogenetic proteins 7 and 8a, A-raf, CCAAT/enhancer binding protein beta, PEA3) were unchanged. Genes normally absent from the initial segment (gamma-glutamyltranspeptidase, prostaglandin D2 synthetase, alkaline phosphatase) were expressed in the undifferentiated proximal caput of the KO. More distally, lipocalin 2 (24p3), CRISP1 (formerly MEP7), PEBP (MEP9), and mE-RABP (MEP10) were unchanged in expression. Immunohistochemistry and Western blots confirmed the absence of CRES in epididymal tissue and fluid and the continued presence of CRES in spermatozoa of the KO mouse. The glutamate transporters EAAC1 (EAAT3) and EAAT5 were downregulated and upregulated, respectively. The genes of over 70 transporters, channels, and pores were detected in the caput epididymidis, but in the KO, only three were downregulated and six upregulated. The changes in these genes could affect sperm function by modifying the composition of epididymal fluid and explain the infertility of the KO males. These genes may be targets for a posttesticular contraceptive.

ADAM7 (a disintegrin and metalloprotease 7) mRNA is suppressed in mouse epididymis by neonatal exposure to Diethylstilbestrol

We investigated whether neonatal exposure to diethylstilbestrol (DES) induces the alteration of mRNA expression in adult mouse epididymis, which plays an important role in sperm maturation. Using a cDNA subtraction method, we isolated 15 changed gene clones in neonatally DES-treated mouse epididymides, and we found a clone homologous with a disintegrin and metalloprotease (ADAM) 7 in the epididymis, as a suppressed gene, by means of neonatal DES treatment in 8-week-old mice. Indeed, it was confirmed by Northern blot analysis that the ADAM7 mRNA expression in the epididymis was at a lower level in neonatally DES-treated mice than in non-treated mice. Moreover, in situ hybridization analysis and real-time reverse transcription and polymerase chain reaction (real-time RT-PCR) revealed that ADAM7 expression was markedly reduced in the corpus region of the epididymis of DES-treated mice as compared with non-treated mice. Our results suggest that neonatal exposure to DES leads to the suppression of ADAM7 expression in the epididymis in the long term. ADAM7 gene expression might be a biological marker of fetal or neonatal exposure to estrogenic compounds, including endocrine disruptors.

Identification and characterization of ADAM32 with testis-predominant gene expression

Members of the ADAM (A Disintegrin And Metalloprotease) family of cell surface proteins have been discovered in a variety of tissues and species. We have cloned and sequenced a mouse cDNA encoding a novel member of the ADAM family. This mouse ADAM gene was named ADAM32 after an human homologue previously sequenced but not characterized. The cDNA sequence of ADAM32 has an open reading frame which encodes 750 (mouse ADAM32) and 787 (human ADAM32) amino acids, sharing 69% homology between the two species. The deduced amino acid sequences of mouse and human ADAM32 cDNAs contain all of the domains common to ADAM family members. Comparison of amino acid sequences showed that ADAM32 is highly homologous to ADAM2 and ADAM3, sperm surface proteins required for fertilization. We found that the ADAM32 gene is expressed predominantly in the testis. Examination of transcription in pre-pubertal and adult mouse testes revealed that expression of ADAM32 begins during meiotic prophase, in pachytene spermatocytes. These results suggest a potential role for ADAM32 in sperm development or fertilization. Genome database searches revealed that the mouse and human ADAM32 genes are located on chromosomes 8 and 8q11, respectively. The ADAM32 gene covers a relatively large region of the genome (120 kb for mouse ADAM32 and 180 kb for human ADAM32) and consists of multiple small exons (at least 22 exons in mouse ADAM32 and 25 exons in human ADAM32).