Sertoli cell and germ cell cystatin C: stage-dependent expression of two distinct messenger ribonucleic acid transcripts in rat testes

Functional amyloids in the mouse sperm acrosome

The acrosomal matrix (AM) is an insoluble structure within the sperm acrosome that serves as a scaffold controlling the release of AM-associated proteins during the sperm acrosome reaction. The AM also interacts with the zona pellucida (ZP) that surrounds the oocyte, suggesting a remarkable stability that allows its survival despite being surrounded by proteolytic and hydrolytic enzymes released during the acrosome reaction. To date, the mechanism responsible for the stability of the AM is not known. Our studies demonstrate that amyloids are present within the sperm AM and contribute to the formation of an SDS- and formic-acid-resistant core. The AM core contained several known amyloidogenic proteins, as well as many proteins predicted to form amyloid, including several ZP binding proteins, suggesting a functional role for the amyloid core in sperm-ZP interactions. While stable at pH 3, at pH 7, the sperm AM rapidly destabilized. The pH-dependent dispersion of the AM correlated with a change in amyloid structure leading to a loss of mature forms and a gain of immature forms, suggesting that the reversal of amyloid is integral to AM dispersion.

Epididymal protease inhibitor (EPPIN) is differentially expressed in the male rat reproductive tract and immunolocalized in maturing spermatozoa

EPPIN (epididymal protease inhibitor; SPINLW1), an antimicrobial cysteine-rich protein containing both Kunitz and whey acidic protein (WAP)-type four disulfide core protease inhibitor consensus sequences, is a target for male contraception because of its critical role in sperm motility. Here, we characterized EPPIN's expression and cellular distribution in rat tissues and its in vivo regulation by androgens in the epididymis. EPPIN (mRNA and protein) was abundantly expressed in the rat testis and epididymis; we also found that the vas deferens, seminal vesicles, and brain were novel sites of EPPIN expression. PCR studies demonstrated that in addition to Sertoli cells, spermatogenic cells expressed Eppin mRNA. EPPIN was immunolocalized in Sertoli cells and spermatogenic cells (pachytene spermatocytes and round and elongated spermatids) and in epithelial cells and spermatozoa from efferent ductules and epididymis. EPPIN staining was observed on the middle and principal pieces of the flagellum of testicular spermatozoa. Epididymal spermatozoa had more intense EPPIN staining on the flagellum, and the EPPIN staining became apparent on the head and neck regions. This suggested that the EPPIN found on maturing spermatozoa was secreted primarily by the epithelial cells of the epididymis. Surgical castration down-regulated EPPIN expression levels (mRNA and protein) in the caput and cauda epididymis, an effect reversed by testosterone replacement. Altogether, our data suggested that EPPIN expression in rats is more widespread than in humans and mice, and is androgen-dependent in the epididymis. This species could be used as an experimental model to further study EPPIN's role in male fertility.

Cystatin C in macular and neuronal degenerations: implications for mechanism(s) of age-related macular degeneration

Cystatin C is a strong inhibitor of cysteine proteinases expressed by diverse cells. Variant B cystatin C, which was associated with increased risk of developing age-related macular degeneration, differs from the wild type protein by a single amino acid (A25T) in the signal sequence responsible for its targeting to the secretory pathway. The same variant conveys susceptibility to Alzheimer disease. Our investigations of the trafficking and processing of variant B cystatin C in living RPE cells highlight impaired secretion of extracellular modulators and inappropriate protein retention in RPE cells as potential molecular mechanisms underpinning macular, and possibly neuronal, degeneration.

Extracellular quality control in the epididymis

The epididymal lumen represents a unique extracellular environment because of the active sperm maturation process that takes place within its confines. Although much focus has been placed on the interaction of epididymal secretory proteins with spermatozoa in the lumen, very little is known regarding how the complex epididymal milieu as a whole is maintained, including mechanisms to prevent or control proteins that may not stay in their native folded state following secretion. Because some misfolded proteins can form cytotoxic aggregate structures known as amyloid, it is likely that control/surveillance mechanisms exist within the epididymis to protect against this process and allow sperm maturation to occur. To study protein aggregation and to identify extracellular quality control mechanisms in the epididymis, we used the cystatin family of cysteine protease inhibitors, including cystatin-related epididymal spermatogenic and cystatin C as molecular models because both proteins have inherent properties to aggregate and form amyloid. In this chapter, we present a brief summary of protein aggregation by the amyloid pathway based on what is known from other organ systems and describe quality control mechanisms that exist intracellularly to control protein misfolding and aggregation. We then present a summary of our studies of cystatin-related epididymal spermatogenic (CRES) oligomerization within the epididymal lumen, including studies suggesting that transglutaminase cross-linking may be one mechanism of extracellular quality control within the epididymis.

Antimicrobial Actions of Human and Macaque Sperm Associated Antigen (SPAG) 11 Isoforms: influence of the N-terminal peptide

In addition to their role in sperm maturation, recent evidence has indicated that epididymal proteins have a role in male reproductive tract innate immunity. Herein we demonstrate that human and macaque epididymal protein isoforms in the SPAG (sperm associated antigen) 11 family, full length SPAG11C, K and L exhibit potent antibacterial activity against E. coli. Analysis of activities of the N- and C-terminal domains revealed that the human N-terminal peptide is bactericidal, while the C-terminal domains that contain the defensin-like 6 cysteine array in SPAG11C and partial arrays in SPAG11K and SPAG11L, lack antibacterial activity. The N-terminal peptide does not appear to contain all the determinants of activity since full-length human SPAG11C is more active than the isolated N-terminal peptide and since sulfhydryl reduction and alkylation, which would affect primarily the C-terminal peptides, completely abolished activities of the whole proteins. These results suggest that the structure conferred by the disulfide bonds in human SPAG11C contributes to the antibacterial activity of the whole molecule. The activities of the N-terminal peptide and of full length human SPAG11C were somewhat reduced in increasing NaCl concentrations. In contrast, the antibacterial activities of full length macaque SPAG11C, K and L were unaffected by the presence of NaCl suggesting a mechanism in the macaque that is less dependent upon electrostatic interactions. SPAG11C, K and L disrupted E. coli membranes but had no effect on erythrocyte membranes. Inhibition of E. coli RNA, DNA and protein synthesis by nonlethal concentrations of SPAG11 isoforms indicated an additional mechanism of bacterial killing.

The Blood‐Testis Barrier: Its Biology, Regulation, and Physiological Role in Spermatogenesis

The blood-testis barrier (BTB) in mammals, such as rats, is composed of the tight junction (TJ), the basal ectoplasmic specialization (basal ES), the basal tubulobulbar complex (basal TBC) (both are testis-specific actin-based adherens junction [AJ] types), and the desmosome-like junction that are present side-by-side in the seminiferous epithelium. The BTB physically divides the seminiferous epithelium into basal and apical (or adluminal) compartments, and is pivotal to spermatogenesis. Besides its function as an immunological barrier to segregate the postmeiotic germ-cell antigens from the systemic circulation, it creates a unique microenvironment for germ-cell development and confers cell polarity. During spermatogenesis, the BTB in rodents must physically disassemble to permit the passage of preleptotene and leptotene spermatocytes. This occurs at late stage VII through early stage VIII of the epithelial cycle. Studies have shown that this dynamic BTB restructuring to facilitate germ-cell migration is regulated by two cytokines, namely transforming growth factor-beta3 (TGF-beta3) and tumor necrosis factor-alpha (TNFalpha), via downstream mitogen-activated protein kinases. These cytokines determine the homeostasis of TJ- and basal ES-structural proteins, proteases, protease inhibitors, and other extracellular matrix (ECM) proteins (e.g., collagen) in the seminiferous epithelium. Some of these molecules are known regulators of focal contacts between the ECM and other actively migrating cells, such as macrophages, fibroblasts, or malignant cells. These findings also illustrate that cell-cell junction restructuring at the BTB is regulated by mechanisms involved in the junction turnover at the cell-matrix interface. This review critically discusses these latest findings in the field in light of their significance in the biology and regulation of the BTB pertinent to spermatogenesis.

Expression of cathepsin L in human testis under diverse infertility conditions

The cathepsin family of proteolytic enzymes play an important role in the remodeling seminiferous epithelia in rodent testis. In an effort to uncover the cathepsin L expression in diverse pathological conditions in human testis, the immunohistochemical localization of cathepsin L was conducted in human testis under diverse male infertility condition including spermatogenic hypoplasia and testis cancer. In seminiferous tubule of normal, non-obstructive azoospermic, decreased spermatogenesis, and maturation arrest conditions, cathepsin L was found in both germ cells and Sertoli cells. In contrast, there was no visible expression of cathepsin L in seminiferous tubule tissues from Sertoli cell-only syndrome, spermatogenic hypoplasia, and testicular cancer. Our result suggests that the cross-talk between germ cells and Sertoli cells is crucial for the control of cathepsin L expression in human testis. The absence of expression of cathepsin L in germ cell cancer emphasizes that cathepsin L expression in Sertoli cells is regulated by functional germ cells in human testis.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Characterization of mouse Eppin and a gene cluster of similar protease inhibitors on mouse chromosome 2

We have recently described a novel gene on human chromosome 20q 12-13.2 called Eppin (Epididymal protease inhibitor) that expresses three mRNAs encoding two isoforms of a cysteine-rich protein containing both Kunitz-type and WAP-type (four disulfide core) consensus sequences (Richardson et al., 2001). To further our studies on Eppin, we have cloned, sequenced and characterized mouse Eppin and report that it lies within a 200 Kb cluster of putative Eppin-like genes on mouse chromosome 2. Analysis of the homologies between the genes in the human and mouse Eppin clusters indicates that the first part of the cluster immediately surrounding Eppin represents a conserved linkage because the order of homologous genes is conserved. Sequencing of reverse transcription polymerase chain reaction (RT-PCR) products confirmed the expression of five of these novel Eppin-like genes in the mouse, which include the mouse homologue of HE-4. These genes are characterized by having either one or both of the Kunitz-type and WAP-type consensus sequences. Additional RT-PCR experiments revealed that expression of some of the Eppin-like genes is restricted to epididymis and testis while others are expressed in several somatic tissues. Northern blot analysis of 22 different mouse tissues identified Eppin transcripts only in the epididymis and testis. Immunostaining of Eppin with anti-recombinant mouse Eppin demonstrated Eppin predominantly on the postacrosomal region of mouse spermatozoa, in Sertoli cells, Leydig cells, and round spermatids in the testis, and in the principal cells of the cauda epididymidis epithelium. Eppin is first expressed by Sertoli cells of 12-day-old mice and subsequently in round spermatids, which is consistent with androgen regulation. Our results demonstrate that mouse chromosome 2 contains a conserved linkage of Eppin-like protease inhibitor genes that are expressed in the epididymis.

Identification and characterization of testis- and epididymis-specific genes: cystatin SC and cystatin TE-1

Differential display-reverse transcriptase-polymerase chain reaction was used to examine Sertoli cell gene expression. As a result, two new members of the mouse cystatin multigene family were isolated and named cystatin SC (cystatin-related gene expressed in Sertoli cells) and cystatin TE-1 (cystatin-related gene highly expressed in testis and epididymis). The full-length cDNA sequence of cystatin SC contains an open reading frame that encodes a putative signal peptide of 20 amino acids and a mature protein of 110 amino acids, whereas that of cystatin TE-1 encodes a 128 amino acid protein with a predicted signal peptide of 21 amino acids. Both of the deduced amino acid sequences contain four highly conserved cysteine residues in precise alignment with other cystatin family members. The derived cystatin SC and TE-1 amino acid sequences lack some of the specific, highly conserved motifs believed to be necessary for cysteine proteinase inhibition activity. Northern blot analysis revealed that cystatin SC mRNA was detected only in the testis, whereas the cystatin TE-1 gene was highly expressed in testis and epididymis with very low expression in ovary and prostate. In situ hybridization showed that cystatin SC mRNA was localized mainly to Sertoli cells with an obvious stage-dependent expression, and that cystatin TE-1 mRNA was predominantly expressed in Sertoli cells without apparent stage-dependent expression. Cystatin TE-1 mRNA, as displayed by in situ hybridization, was expressed only in the epithelial cells of the proximal caput region of the epididymis. The unusual amino acid sequence and highly restricted expression suggests that cystatins SC and TE-1 play a very specialized role in the testis and epididymis.

Cystatin 11: a new member of the cystatin type 2 family

Cystatin (CST)11, a novel member of the CST type 2 family of cysteine protease inhibitors, was identified in Macaca mulatta epididymis by subtractive hybridization cloning. The human CST11 gene on chromosome 20p11.2 is located near three other CST genes expressed predominantly in the male reproductive tract. The CST11 gene spans three exons, a structure similar to that of other CST family 2 genes. An exon 2-deleted alternative transcript (CST11Delta2) was also identified. CST11 mRNA is expressed only in the epididymis as judged by Northern blot hybridization and is androgen regulated. The protein is most abundant in the initial segment, but is detected throughout the epididymis and on ejaculated human sperm. The calculated tertiary structure of CST11 reveals that the three regions corresponding to the protease inhibitory wedge of CST3 are similarly juxtaposed in CST11, consistent with protease inhibitor function. Intact and exon 2-deleted CST11 recombinant proteins were tested for antibacterial activity. After a 2-h incubation of Escherichia coli with 50 microg/ml recombinant CST11 or CST11Delta2, bacterial colony-forming units were reduced to 30% of control, indicating that both forms have antimicrobial activity.

Cystatin-related epididymal spermatogenic protein colocalizes with luteinizing hormone-beta protein in mouse anterior pituitary gonadotropes

The CRES (cystatin-related epididymal spermatogenic) protein, a member of the cystatin superfamily of cysteine protease inhibitors, exhibits highly restricted expression in the mouse testis and epididymis, suggesting roles in reproduction. Considering the well-established relationship that exists between the gonads and the neuroendocrine system, the present studies were undertaken to determine whether the CRES messenger RNA and protein are expressed in the anterior pituitary gland and, if so, whether the expression is regulated by hormones. RT-PCR analysis of whole pituitary gland RNA preparations, and Northern blot analyses of pituitary gland cell lines, demonstrated that the CRES gene is expressed in the male and female anterior pituitary gland gonadotropes. Furthermore, Western blot analysis demonstrated that CRES protein was present in whole mouse pituitary glands and was synthesized and secreted by the LbetaT2 gonadotrope cell line. Interestingly, whereas the predominant CRES proteins present in epididymal lysates, LbetaT2 secretory granules, and whole pituitary gland lysates were 19 and 14 kDa, the predominant CRES proteins present in the cell culture conditioned media were 17 and 12 kDa. Deglycosylation studies revealed that the higher-molecular-mass CRES proteins (19 and 17 kDa) were the result of N-linked glycosylation, caused by the presence of high mannose residues. Double-label immunofluorescence and confocal microscopic analysis of male and female mouse pituitary gland tissue confirmed the RNA studies and showed that CRES protein colocalized with LHbeta protein in the gonadotropes. Finally, gonadectomy and hormone replacement studies suggest that CRES protein in the gonadotropes is hormonally regulated. These studies suggest that CRES protein may perform a role in the gonadotrope-mediated control of reproduction.

Possible involvement of proteases in the regulation of spermatogenesis

Proteolytic enzymes, which are synthesized and secreted by cells of the seminiferous tubule of the testis, have important functions in spermatogenesis. We performed metabolic studies using small peptide hormones as a substrate to investigate the activity of proteases in cultured Sertoli cells of the rat. High-performance liquid chromatographic analysis of the cell culture supernatants showed cleavage of met- and leu-enkephalin, substance P, and bradykinin. No peptidolysis was observed for the cyclic peptide oxytocin. The hormone cleavage pattern and the use of specific protease inhibitors in peptide degradation experiments demonstrated activities of several proteases in Sertoli cells. These are mainly metalloproteinases including neutral metalloendopeptidases, angiotensin-converting enzyme and aminopeptidases. In addition, activities of serine and aspartic proteases were detected. Only marginal proteolytic activities were observed in Sertoli cell conditioned supernatants, indicating that the investigated proteases are mainly located on Sertoli cell membranes. The peptide hormones used in this study have been found to play a potential role in the endocrine, paracrine or autocrine regulation of testicular cells. The membrane-associated proteases reported here may therefore be involved in the metabolism and inactivation of these peptides.

Protease-protease inhibitor interactions in Sertoli cell-germ cell crosstalk

Peritubular cells, Sertoli cells, and germ cells of the seminiferous tubule synthesize and secrete several proteases and protease inhibitors. Experimental evidence suggests that the complex network of proteolytic enzyme activity and their regulation by protease inhibitors play an important role in male reproduction. Interaction between protease and protease inhibitors seems to play an important role in remodeling and restructuring of the seminiferous tubule during spermatogenesis. Controlled proteolytic activity is also involved in the migration of germ cells from the basal compartment to the lumen of the seminiferous epithelium, and in the release of spermatids during spermiation. The recently reported occurrence of Sertoli cell membrane-associated proteases indicate the possible involvement of regulatory peptide systems within the testis. This view is supported by the detection of all components of one of these paracrine systems, the kallikrein-kinin system, in cells of the seminiferous tubule.

Interactions between ovine cathepsin L, cystatin C and alpha 2-macroglobulin. Potential role in the genital tract

The specific inhibitor of cysteine proteinases, cystatin C, was purified from ram rete testis fluid and the conditioned medium of Sertoli cells. This molecule associated with sheep liver cathepsin L at one of the fastest rates ever described for a proteinase/inhibitor interaction (1.75 +/- 0.20 x 10(8) M-1.s-1). But the association rate constant for the interaction of cathepsin L with alpha 2-macroglobulin, a non-specific inhibitor of proteinases, was also extremely high (8.8 +/- 0.75 x 10(6) M-1.s-1). Cathepsin L complexed with alpha 2-macroglobulin was protected from inhibition by type 2 and type 3 cystatins. The data indicate that cystatin C is the most potent inhibitor of cathepsin L in mammalian male genital tract fluids, whereas alpha 2-macroglobulin may act as a terminal acceptor of this enzyme. These inhibitors could therefore inhibit the activated form of procathepsin L which may appear during the complex process of spermatozoa production and maturation in the testis and epididymis.

Metabolism and testicular toxicity of 1,3-dinitrobenzene in the rat: evaluation of the stage-synchrony model

Because many testicular toxicants cause damage to specific stages of spermatogenesis, the present study has investigated the utility of a model in which the testis is synchronized to contain only a few closely related spermatogenic stages. The susceptibility of different stages to 1,3-dinitrobenzene (1,3-DNB) toxicity was investigated in rats, the testes of which had been stage synchronized by a vitamin A depletion/repletion (VADR) procedure. 1,3-DNB (25 mg/kg, IP) or vehicle was injected 58, 61, or 78 d after vitamin A readministration, and testicular histopathology was evaluated 48 h later. At the time of sacrifice, testes in the three groups were synchronized to stages I-VI, VII-IX, or X-XIV+I. The data indicated that tubules in all stages of spermatogenesis, in both synchronized and unsynchronized animals, demonstrated histopathologic changes in response to 1,3-DNB. However, the lesion seen in synchronized animals was more severe and less stage specific than that seen in weight-matched, unsynchronized animals. This increase in degree of susceptibility could be partially explained by differences in toxicokinetics. Stage-synchronized testes could provide unique insights into stage-specific cellular and molecular events, especially for in vitro studies where the stage enrichment could be maximally exploited. However, results obtained from in vivo toxicity studies using animals subjected to VADR should be interpreted carefully in light of the confounding physiologic/metabolic perturbations potentially induced by the VADR procedure.