Immunolocalization of clusterin in the ram testis, rete testis, and excurrent ducts

Comparative high-throughput analysis of sperm membrane proteins from crossbred bulls with contrasting fertility

The aim of the present study was to identify fertility associated sperm membrane proteins in crossbred bulls. Sperm membrane proteins from high- and low-fertile Holstein Friesian crossbred bulls (n = 3 each) were subjected to high-throughput liquid chromatography-mass spectrometry (LC-MS/MS) for comparative proteomic analysis. Proteomic profiling identified a total of 456 proteins in crossbred bull spermatozoa; it was found that 108 proteins were up regulated while 26 proteins were down regulated (>1.5-folds) in spermatozoa from low- compared to high-fertile bulls. Gene ontology classification revealed that upregulated proteins in low-fertile bulls were involved in biological process such as oxidation-reduction process (p = 3.14E-06), fusion of sperm to egg plasma membrane (p = 7.51E-04), sperm motility (p = 0.03), and capacitation (p = 0.09), while down regulated proteins were associated with transport (p = 6.94E-04), superoxide metabolic process (p = 0.02), and tricarboxylic acid cycle (p = 0.04). KEGG pathway analysis revealed that oxidative phosphorylation and tricarboxylic acid cycle pathways are the most significantly affected pathway in low-fertile bulls. It was concluded that expression of proteins associated with oxidative phosphorylation and tricarboxylic acid cycle pathways were altered in low-fertile crossbred bulls, and expression levels of SPATA19, ELSPBP1, ACRBP, CLU, SUCLA2, and SPATC1 could aid in assessing potential fertility of crossbred bulls.

Gross and microanatomy of the male reproductive duct system of the saltwater crocodile Crocodylus porosus

Information on the morphology and histology of the male reproductive system of the Crocodylia species is necessary to determine the role of these tissues in the production of functional spermatozoa. Accordingly, in this study we examined the gross morphology and microanatomy of the testis and the male excurrent duct system through which spermatozoa pass before ejaculation. The data demonstrate that the reproductive system in male saltwater crocodiles comprises paired testes, which convey spermatozoa distally via the rete testis into an excurrent duct system comprising ductuli efferentes, ductuli epididymides, ductus epididymidis and ductus deferens. The epithelium delineating the male tract was dominated by non-ciliated and ciliated cells structured into a simple columnar lining of the ductuli efferentes and ductuli epididymides, through to the high pseudostratified columnar epithelium of the ductus epididymidis and ductus deferens. The morphology and histochemical staining of these ducts suggest their involvement in seminal fluid production and/or its modification, which likely contributes to the nourishment, protection and/or storage of crocodile spermatozoa. As a reflection of their common Archosaurs ancestry, the overall structural characteristics we describe for the crocodile male excurrent duct system share closer similarities to those of the Aves than other clades within the Reptilia class or Mammalia.

Clusterin in the mouse epididymis: possible roles in sperm maturation and capacitation

Clusterin (CLU) is known as an extracellular chaperone for proteins under stress, thus preventing them from aggregation and precipitation. We showed herein that CLU, expressed by principal cells of the mouse caput epididymis, was present in high amounts in the lumen. In the cauda epididymis, CLU bound tightly to the sperm head surface and its amount on total sperm was similar to that in the bathing luminal fluid. In both immotile and motile caudal epididymal sperm, CLU was localized over the entire sperm head except at the convex ridge, although in the motile sperm population, the CLU immunofluorescence pattern was distinctively mottled with a lower intensity. However, when motile sperm became capacitated, CLU was relocalized to the head hook region, with immunofluorescence intensity being higher than that on the non-capacitated counterparts. Under a slightly acidic pH of the epididymal lumen, CLU may chaperone some luminal proteins and deliver them onto the sperm surface. Immunoprecipitation of epididymal fluid proteins indicated that CLU interacted with SED1, an important egg-binding protein present in a high amount in the epididymal lumen. In a number of non-capacitated sperm, fractions of SED1 and CLU co-localized, but after capacitation, SED1 and CLU dissociated from one another. While CLU moved to the sperm head hook, SED1 translocated to the head convex ridge, the egg-binding site. Overall, CLU localization patterns can serve as biomarkers of immotile sperm, and non-capacitated and capacitated sperm in mice. The chaperone role of CLU may also be important for sperm maturation and capacitation.

Proteome of the rete testis fluid from tropically-adapted Morada Nova rams

The rete testis has a close relationship with sperm development and may have other functions besides serving as an intercalated channel. The aim of this study was to identify and characterize the proteins of rete testis fluid (RTF) from tropically-adapted Morada Nova rams. Testicles obtained from six Morada Nova rams were dissected and the head of the epididymis was separated to access the efferent ducts. Rete testis fluid was obtained by gentle massage of the testis. The fluid was centrifuged to remove cell debris and sperm. RTF samples (containing 400μg protein) were separated by 2-D SDS-PAGE and gels, analyzed using PDQuest software (Bio Rad, USA). Proteins were identified using tandem mass spectrometry. Gene ontology and protein network were analyzed using the software tool for searching annotations of proteins (STRAP) and STRING database. Gels had, on average, 227±13.5 spots and 51% of the proteins were found above 40kDa, corresponding to 65% of the intensity of all spots detected. Based on gene ontology analysis, the most common biological processes associated with RTF proteins were regulation (24.3%) and cellular process (23.3%). Binding (27.3%) and catalytic activity (19.3%) corresponded to the most frequent molecular functions. Albumin, clusterin, serotransferrin, immunoglobulin gamma-1 chain and alpha-2-HS-glycoprotein were the most abundant proteins in the ram rete testis fluid. In conclusion, proteins identified in the ram rete testis fluid are linked to several physiological processes associated with sperm protection and spermatogenesis.

Presence, localization, and origin of clusterin in normal human spermatozoa

PURPOSE

Clusterin in mammalian semen is a secretory form of clusterin (sCLU) with the heterodimeric structure. It is secreted by the epididymis and seminal vesicle. It is generally agreed that clusterin mainly exists on the surface of abnormal spermatozoa and is implicated in decreased sperm motility, sperm aggregation and infertility. However, few studies observe clusterin in normal spermatozoa, which is presumed to be a novel form. Up to now, the systematical information about the presence, localization, origin and function of clusterin in normal human spermatozoa has yet not been established. The aim of our current study is to systematically research clusterin in normal human spermatozoa.

METHODS

We detected the presence of clusterin via western blot, explored the localization of clusterin using immunofluorescence, and investigated the origin and distribution of clusterin in human testis by western blot and immunohistochemistry.

RESULTS

We found native clusterin in the inner plasma membrane of normal human spermatozoa. It was derived from the testis and showed similar molecular weight and heterodimeric structure compared with sCLU in semen and on the surface of abnormal spermatozoa.

CONCLUSION

Clusterin in normal spermatozoa should be self-synthesized during the later stage of spermatogenesis. The different localization and origin suggested that the clusterin observed by us may be a novel form compared with conventional sCLU on the surface of abnormal spermatozoa.

Chapter 1: Introduction

Since the beginning, Clusterin (CLU) was revealed not as simple to study, and certainly not a single protein. The growing research interest on CLU soon produced many contributions by independent laboratories working in different systems. Thus, many different names or acronyms have been given to CLU in the early years after its discovery. Now, a general consensus recommend the name Clusterin and the abbreviation CLU. CLU was first described as a glycoprotein found nearly ubiquitous in tissues and body fluids. This early knowledge is mostly related to the secretory form of CLU (sCLU), which is exported from the cell and released in secretions acting as an extracellular chaperone. But CLU can also enter the nucleus. The detection of nCLU (nuclear CLU), which is usually associated to cell death, is now emerging as a very important event making this issue even more complex. This may explain why CLU is still often described as an "enigmatic" protein. The use of the term "enigmatic" is a clear indication that too many aspects related to the biological function(s) of CLU and its possible role in pathogenesis have been obscure, or very difficult to interpret, for long time. Contradictory findings on CLU are also present in the literature, sometimes due to technical biases or alternative interpretation of the same result. The aim of the book is ambitious: through a careful review of old data, in the light of novel information and up to date methods and hypotheses, we will try to simplify the picture for the reader and bring more light in a field still perceived to be too obscure to fully appreciate its importance and potential implementation in the clinical setting. This introduction will provide a brief general history and a critical view of the discovery of CLU with the aim to underline what is new in the field and what is now obsolete. In the rest of the book, conclusions and "take home messages" will also be provided to the reader particularly focusing on possible clinical implementations and how all this knowledge will very likely bring novelty in the fight against cancer.

A reexamination of the role of clusterin as a complement regulator

Clusterin is a highly conserved glycoprotein which has been proposed to protect host cells against complement-mediated cytolysis. We tested the hypothesis that clusterin is a complement regulator using erythrocytes and cells which had been stably transfected with a membrane-anchored form of clusterin as targets for complement-mediated cytolysis. Clusterin gave dose-dependent protection of antibody-coated sheep erythrocytes against complement-mediated lysis by diluted normal human serum. There was a linear relationship between the concentration of clusterin giving 50% protection and the concentration of serum; extrapolation of this to the case of undiluted human serum showed that a clusterin concentration at least two orders of magnitude greater than its physiological plasma concentration would be needed to confer protection against complement-mediated cytolysis under physiological conditions. Physiological concentrations of clusterin did not protect rabbit erythrocytes against alternative complement pathway-mediated lysis using dilute human serum. Exogenous clusterin had no effect on lysis of human erythrocytes triggered by the addition of inulin to autologous human serum. Induction of cell-surface clusterin expression by L929 (murine fibroblast) cells which had been stably transfected with cDNA for human clusterin linked to DNA coding for the 44 C-terminal amino acid residues of CD55 did not protect the cells against complement-mediated lysis by either normal or clusterin-depleted human serum. These data suggest that clusterin may not be a physiologically relevant regulator of complement activation.

Interactions of Sertoli cells with laminin are essential to maintain integrity of the cytoskeleton and barrier functions of cells in culture in the two-chambered assembly

The addition of anti-laminin IgG to the basal surfaces of rat Sertoli cells in culture in a two-chambered assembly results in a perturbation of F-actin arrangements, including disruption of the pericellular circumferal rings, impairments of the Sertoli cell permeability barrier, and subsequently focal defoliation, followed by cell reaggregation. The pentapeptide YIGSR, which competes with the laminin receptor for laminin (Kleinman and Weeks: Curr. Oph. Cell Biol., 1:964-967, 1989; Graf et al.: Biochemistry, 26:6896-6900, 1987) also elicited focal defoliation of Sertoli cells from the extracellular matrix-coated filter in the two-chambered assembly. Addition of YIGSR to Sertoli cell cultures resulted in cell detachment within 2 to 3 h. In contrast, the irrelevant peptide YIGSE had no detectable effects. The anti-laminin IgG was effective only when added to the chamber in which access was readily available to the basal surfaces of Sertoli cells, but YIGSR was effective when added either to the outer chamber or to the inner chamber. These data were interpreted to indicate that the Sertoli cell barrier generated in the two-chambered assembly allowed a relatively rapid diffusion of YIGSR between chambers, but prevented the rapid equilibration of anti-laminin IgG between compartments. Addition of anti-laminin IgG to the basal, but not to the apical surfaces of Sertoli cells, resulted in more rapid rates of equilibration of [3H]-methoxyinulin and [86Rb]Cl across the Sertoli cell monolayer. This evidence of impairment to the integrity of the barrier was detected prior to the disruption of stress fibers and focal defoliation, but after evidence of dissolution of the circumferal F-actin ring, which occurred within 1 h after addition of anti-laminin IgG. We consider the possibility that a transmembrane link exists between extracellular laminin and cytoskeletal elements which modulates the circumferal F-actin ring. We further postulate that this linkage can influence the nature of tight junctional complexes, and thereby the integrity of the Sertoli cell barrier.

Clusterin: the intriguing guises of a widely expressed glycoprotein

The glycoprotein clusterin has recently entered the scientific arena in diverse guises. It forms high-density lipoprotein complexes with apolipoprotein A-I, participates in the terminal complement reaction and serves as a granule constituent in neuronal and endocrine cells. Apically secreted, it is also found in the male reproductive tract and the tubular lumen of epithelial ducts. Thus, it may serve important functions in tissue remodelling, immune defense and transport of biologically active peptides.

The SGP-2 gene is developmentally regulated in the mouse kidney and abnormally expressed in collecting duct cysts in polycystic kidney disease

Sulfated glycoprotein-2 (SGP-2) is a secreted, dimeric, glycosylated protein synthesized by a number of different epithelial cell types. Although its function is not yet understood, SGP-2 has been hypothesized to be involved in such diverse processes as the promotion of cell-cell interactions, spermatogenesis, modulation of the complement system, and programmed cell death. We have now found that the SGP-2 gene is developmentally regulated in the mouse kidney. SGP-2 gene expression is first detected in the condensing nephrogenic mesenchyme and is subsequently down-regulated during the maturation of the glomerular epithelia, proximal tubules, and collecting ducts. SGP-2 continues to be expressed in the mature kidney in distal tubules and in the urothelial lining of the calyx and papilla. We have also examined the expression of the SGP-2 gene in polycystic kidneys of the C57BL/6J-cpk mouse, a model of autosomal recessive polycystic kidney disease in which there is development of epithelial-lined cysts arising primarily from the collecting duct system. Abnormally high levels of SGP-2 mRNA were found in the cyst wall epithelium of polycystic kidneys. The expression of the SGP-2 gene in normal development suggests that it plays a role in differentiating epithelial structures; and the abnormally high levels of SGP-2 gene expression in polycystic kidneys suggests that the cells lining cysts are not fully differentiated. It is possible, therefore, that polycystic kidney disease is caused by a defective developmental process in which there is a delay in terminal differentiation.

Lack of complement activation in the seminal plasma of men with antisperm antibodies associated in vivo on their sperm

A specific and sensitive "sandwich"-type radiolabeled antiglobulin assay (RAA) using monoclonal anti-human C5b-9 neoantigen and polyclonal anti-human C5b-9 was used to evaluate the presence of the in vivo product of human complement (C) activation (SC5b-9) in the seminal plasma (SP) of 19 fertile and 61 infertile men. SP SC5b-9 was detectable in 7 (8.7%; 1 fertile and 6 infertile men) of the 80 men with a range of 10 to 175 ng/ml. Levels of SP SC5b-9 in other men were below the limit of detection (less than 10 ng/ml). Of the 33 infertile men with sperm-associated immunoglobulin (Ig) G and/or IgA, 27 (82%) had undetectable levels of SP SC5b-9 immunoreactivity. There was no correlation between the SP SC5b-9 levels and the degree of sperm-associated IgG (r = 0.086) or IgA (r = 0.23) activity. However, significant deposition of sperm-bound C5b-9 due to autologous C activation was demonstrated by flow cytometry of donor sperm treated with sera from autoimmune men with ASA in their sera and on their sperm. These findings suggest that sperm-bound Ig cannot activate C in SP.

Structural analysis of sulphated glycoprotein 2 from amino acid sequence. Relationship to clusterin and serum protein 40,40

Sulphated glycoprotein 2 (SGP-2) is the major secreted protein product of rat Sertoli cells; likewise, clusterin is a major constituent of ram rete testis fluid. Isolation and sequencing of the intact subunits and peptides derived from clusterin show that it is the ram homologue of rat SGP-2. Human serum protein 40,40 (SP-40,40), a component of the SC5b-9 complex of complement, has recently been reported to be the human homologue of rat SGP-2. Analysis of the amino acid sequences of rat SGP-2 and human SP-40,40 show that both of these proteins have a significant relationship to the heavy chain of myosin. The regions of highest sequence similarity correspond to the major amphipathic domains in SGP-2/SP-40,40 and the long alpha-helical-tail domain of myosin, which forms a rod-like structure. SGP-2 has anomalous sedimentation behaviour which indicates that it probably exists in an extended conformation. A putative dinucleotide-binding structure has been identified in the longest stretch of identity between SGP-2 and SP-40,40. Elucidation of these features of SGP-2 and SP-40,40 may help to direct future studies into the role of these proteins in the reproductive and complement systems.

Human seminal clusterin (SP-40,40). Isolation and characterization

Molecular cloning of the human complement inhibitor SP-40,40, has revealed strong homology to a major rat and ram Sertoli cell product, sulfated glycoprotein-2, known also as clusterin. This study reports the purification and characterization of human seminal clusterin. Two-dimensional gel electrophoresis revealed charge differences between clusterin purified from semen and the serum-derived material. Both preparations demonstrate comparable hemagglutination (clustering) activity and inhibition of C5b-6 initiated hemolysis. The average clusterin concentration in normal seminal plasma is considerably higher than that found in serum. Mean seminal plasma clusterin concentrations were significantly lower in azoospermia caused by obstruction or seminiferous tubule failure than with oligospermia or normospermia. Only men with vasal agenesis had undetectable seminal clusterin, suggesting that some of the seminal clusterin is produced by the seminal vesicles. Immunofluorescence of human spermatozoa revealed that clusterin was detected on 10% of spermatozoa, predominantly those that were immature or had abnormal morphology. A pilot study of 25 patients suggests that seminal clusterin concentration, together with sperm motility and morphology, is correlated with the fertilization rate in vitro. The function of seminal clusterin is unknown. Its extensive distribution in the male genital tract and its high concentration in seminal plasma suggests an important role in male fertility.

Molecular structure and functional characterization of a human complement cytolysis inhibitor found in blood and seminal plasma: identity to sulfated glycoprotein 2, a constituent of rat testis fluid

A component of soluble terminal complement complexes was identified and affinity-purified to homogeneity by using a monoclonal antibody previously developed against the soluble C5b-9 complex. The protein, which we have designated complement cytolysis inhibitor (CLI), has a molecular mass of 70 kDa and consists of two nonidentical, disulfide-linked subunits of 35 kDa. Partial amino acid sequences determined for the amino-termini of the two subunits were identical with those of a recently characterized serum protein called SP-40,40. An almost full-length cDNA clone of 1651 base pairs was isolated from a human liver cDNA library by using long synthetic oligonucleotides as probes. The encoded amino acid sequence of CLI consists of 427 amino acid residues preceded by a 21-residue-long typical signal peptide and shows an overall 75.6% amino acid sequence homology to sulfated glycoprotein 2 (SGP-2), a major Sertoli cell-derived protein of rat testis fluid. As in SGP-2, proteolytic processing between residues 206 and 207 yields the two disulfide-linked subunits of plasma CLI. CLI and SGP-2 were shown to be orthologous single-copy genes in humans and rats by Southern blotting experiments. In addition, CLI was immunologically identified in human seminal plasma. Functional studies with purified terminal complement components showed that CLI suppresses the cytolytic potential of nascent C5b-7 complexes at physiological blood plasma concentrations (approximately 50 micrograms/ml). Its presence on the surface of mature sperm cells and its relative abundance in seminal plasma (approximately 250 micrograms/ml) suggest that CLI protects sperm cells and epithelial tissues against complement attack in the male reproductive tract.

Topography and behavior of Sertoli cells in sparse culture during the transitional remodeling phase

We report observations on the behavior of Sertoli cells in sparse culture during the period from the time of plating to the time of initial confluence (the transitional remodeling phase). Changes in shape, structure, and polarity of cells, as well as changes in migration patterns and cell-cell association patterns, have been followed during the transitional remodeling phase with the aid of topographical markers. These markers are based upon differences between ultrastructural features of the basolateral and apicolateral surfaces. The basolateral surface is characterized by plasmalemmal blebs, whereas the apicolateral surface is characterized by filopodial extensions. Structural differences observed in situ remain evident in Sertoli cells isolated by sequential enzymatic treatments that are described. Another marker is provided by laminin-binding sites, which are detected exclusively on the blebbed, basolateral surfaces of freshly prepared Sertoli cell aggregates. The orientation described is sustained during the initial radial migration of Sertoli cells explanted on uncoated glass coverslips. Under these conditions, blebs are detected only on the dorsal surfaces, and filopodial extensions are evident only on the ventral surfaces. In contrast, Sertoli cells sparsely plated on a reconstituted basement membrane (air-dried Matrigel) migrate rapidly, display an extraordinary capacity to form elaborate cytoplasmic extensions for cell-cell and cell-substratum contacts, and readily retract blebs and filopodial extensions. These cells do not form mosaic borders, whereas cells plated on uncoated glass do form a monolayer with mosaic-like borders. Cells sparsely seeded on gelated Matrigel migrate preferentially at gaps between adjacent cell explants, and develop a compact cell-cell association pattern. These cells display few, if any, cytoplasmic extensions. We compare the behavior of Sertoli cells sparsely plated on Matrigel with the behavior of Sertoli cells in situ during different stages of development.

Protein secretions of Sertoli cells

As was stated in the introduction, many of the functions of the Sertoli cells are apparently carried out by the protein secretions of these cells. The use of Sertoli cell cultures and appropriate biochemical and immunological techniques has allowed the characterization of some of these secretion products. It is likely that many of the functions of the Sertoli cells are necessary because of the presence of the blood-testis barrier. Many growth and nutritive factors which are necessary for cell viability are available to most cells via the serum. The germinal cells within the adluminal compartment do not have access to serum factors and one of the functions of the Sertoli cells is to synthesize serum-like components and secrete them into the adluminal compartment. The historical description of Sertoli cells as "nurse cells" thus appears to have been accurate. The nurse-cell function is most clearly demonstrated by the proposed mechanism by which germinal cells obtain ferric ions. The Sertoli cells have developed a system to move serum-derived iron through their own cytoplasm and to secrete it bound to newly synthesized testicular transferrin molecules which can deliver it to specific receptors on the germinal cell surface (Huggenvik et al., 1984). Functionally, all of the secreted proteins from Sertoli cells which have been characterized or proposed fall into one of five basic classes. First, Sertoli cells secrete a number of transport proteins including transferrin, ceruloplasmin, and ABP. The proposed function of these proteins is the transport of Fe3+, Cu2+, and androgens to the germinal cells or to the epididymis (ABP). Second, Sertoli cells synthesize and secrete a number of proteins which have a hormone-like or growth factor-like activity. AMH is a clear and well-documented example of this type of product while the evidence for inhibin, somatomedin C, EGF-like growth factor, and seminiferous growth factor will require further corroboration. Third, Sertoli cells secrete proteins which have enzymatic activities. Plasminogen activator is the best characterized example of this class of products and the alpha-lactalbumin-like activity is of potential interest. The fourth class of Sertoli cell secretion products includes those proteins which contribute to the basement membrane, namely, type IV collagen and laminin. Finally, there is a very important group of Sertoli cell secretion products for which there is, as yet, no evidence for a defined function. This group includes SGP-1 and SGP-2 which are the major sertoli cell products in rats and which have been well-characterized biochemically.(ABSTRACT TRUNCATED AT 400 WORDS)