Biosynthesis and secretion of clusterin by ram rete testis cell-enriched preparations in culture

The Association between Clusterin Sialylation Degree and Levels of Oxidative–Antioxidant Balance Markers in Seminal Plasmas and Blood Sera of Male Partners with Abnormal Sperm Parameters

Nearly 30% of infertility cases are caused by male factor. This study aimed at checking the associations between the sialylation degree of glycoprotein clusterin (CLU) and levels of oxidative–antioxidant balance markers in infertile men. Using lectin-ELISA with biotinylated lectins specific to α2,6-linked (Sambucus nigra agglutinin, SNA) and α2,3-linked (Maackia amurensis agglutinin, MAA) sialic acid (SA), the CLU sialylation in 132 seminal plasmas (SP) and 91 blood sera (BS) were analyzed. Oxidative–antioxidant status was measured by determining Sirtuin-3 (SIRT3), Sirtuin-5 (SIRT5), total antioxidant status (TAS), and ferric reducing antioxidant power (FRAP) levels. We indicate that multiple sperm disorders are associated with decreased expression of MAA-reactive SA in SP. Decreased SP SIRT3 concentrations may be associated with teratozoospermia and oligoasthenoteratozoospermia. ROC curve and cluster analysis revealed that SP relative reactivity of CLU glycans with MAA, the value of MAA/SNA ratio, and SIRT3 and SIRT5 concentrations may constitute an additional set of markers differentiating infertile oligoasthenoteratozoospermic patients (OAT) from normozoospermic (N), asthenoteratozoospermic (AT) and teratozoospermic (T). The multinomial logistic regression analysis confirmed the potential utility of SIRT3 determinations for differentiation between N and OAT groups as well as between N and T groups for SIRT3 and SIRT5. For BS, based on ROC curve and cluster analysis, relative reactivities of CLU glycans with SNA, MAA, SIRT3 and FRAP concentrations may be useful in the differentiation of normozoospermic patients from those with sperm disorders. The multinomial logistic regression analysis showed that the SNA relative reactivity with CLU glycans significantly differentiated the N group from AT, OAT and T groups, and FRAP concentrations significantly differed between N and AT groups, which additionally confirms the potential utility of these biomarkers in the differentiation of infertile patients with abnormal sperm parameters. The knowledge about associations between examined parameters may also influence future research aimed at seeking new male infertility therapies.

Transforming growth factor beta regulates clusterin gene expression via modulation of transcription factor c-Fos

Transforming growth factor-beta (TGFbeta) induces gene expression of the glycoprotein clusterin in a variety of cell types via a consensus AP-1 binding site. Here, we demonstrate, by supershift analysis, that JunB, JunD, Fra1, Fra2, and c-Fos bound to AP-1 but that prior treatment of the cells with TGFbeta reduced dramatically c-Fos binding, suggesting that c-Fos might be playing a negative regulatory role in clusterin gene expression. Transient cotransfection assays in mink lung epithelial (CCL64) cells, using a human c-Fos expressing plasmid together with a clusterin promoter/reporter construct or the artificial TGFbeta-inducible reporter construct 3TPLux, revealed that c-Fos was indeed repressive for TGFbeta-induced promoter transactivation. Further, we demonstrate that in stable c-Fos-overexpressing cell lines, TGFbeta induction of endogenous clusterin mRNA, as well as clusterin promoter transactivation are blocked. Co-transfection with c-Fos deletion constructs revealed that the C-terminal region, including the homologue box 2 motif and the extreme C-terminal serine phosphorylation sites (Ser362 and Ser374) are required for repression of clusterin and 3TPLux transactivation. TGFbeta treatment of CCL64 cells resulted in the induction of c-Fos mRNA but caused no alternation in total c-Fos protein levels. The results suggest that the c-Fos represses clusterin gene expression, maintaining a low basal level in the absence of TGFbeta, and that TGFbeta, presumably through its effects on c-Fos protein synthesis and/or stability, abrogates the repression of c-Fos, thereby resulting in gene expression.

Role of apoptosis in mediating phosphoramide mustard-induced rat embryo malformations in vitro

Phosphoramide mustard, an active metabolite of the anticancer drug cyclophosphamide, causes malformations in rat embryos undergoing organogenesis in vitro. The purpose of the present study was to investigate the hypothesis that apoptosis plays an important role in mediating the teratogenicity of phosphoramide mustard. Apoptosis is a process of active or programmed cell death which is characterized by internucleosomal DNA fragmentation and de novo RNA and protein synthesis. Sulphated glycoprotein-2 (SGP-2) or clusterin is induced in some models of apoptosis and is one of the proteins likely to be involved in the maintenance of cell integrity. In the present study, day 10 rat embryos were cultured for 6, 12, 24, and 45 hr, with or without the addition of 10 microM phosphoramide mustard. After culture for 24 or 45 hr with exposure to 10 microM phosphoramide mustard, the embryos were both growth-retarded and malformed. Exposure to phosphoramide mustard for 6 or 12 hr did not significantly alter the relative amounts of either the mRNA or protein for SGP-2; this treatment also had no effect on DNA fragmentation in embryos or their yolk sacs. After 24 hr in culture, the relative amounts of SGP-2 protein, but not mRNA, were increased 2-fold in the yolk sacs of the phosphoramide mustard-exposed embryos, but not in the embryos themselves. At this time, DNA fragmentation was detected in phosphoramide mustard-exposed embryos, but not in their yolk sacs or in control embryos. After 45 hr in culture, SGP-2 protein and mRNA levels were increased 2-4-fold above the controls in the phosphoramide mustard-exposed embryos and their yolk sacs. Immunohistochemical analysis revealed that in control embryos cultured for 45 hr, the SGP-2 reaction product was localized in the heart, hindgut, and yolk sac. In contrast, in phosphoramide mustard-treated embryos cultured for 45 hr, SGP-2 immunostaining was found throughout the embryo, with a strong immunoreaction in the mesenchyme and ectoplacental cone. DNA fragmentation in the embryos exposed to phosphoramide mustard for 45 hr was more extensive than that found after 24 hr, but fragmentation was still not detected in the yolk sac. Thus exposure in vitro to a teratogenic concentration of phosphoramide mustard resulted in DNA fragmentation and an increased expression of SGP-2 in the embryo. These data suggest that apoptosis is involved in mediating the teratogenicity of phosphoramide mustard.

Developmental expression of the S35-S45/SGP-2/TRPM-2 gene in rat testis and epididymis

Testosterone-repressed prostate message-2 (TRPM-2) was originally isolated and cloned from the regressing ventral prostate of the rat. In this tissue, and in other hormone-dependent tissues such as the mammary gland, this gene is induced in the absence of the appropriate trophic hormone. Sequence analysis of the cDNA and genomic clones of TRPM-2 have demonstrated that the coding sequence of this gene is identical to S35-S45 (also known as SGP-2 and clusterin), which is constitutively expressed by the Sertoli cells of the adult testis. Using Northern, slot blot, S1-nuclease analysis, and in situ hybridization, we have investigated the regulation of TRPM-2 expression in the testis and epididymis during development. Slot blot analysis of RNA extracted from the testis and epididymis of 7-, 14-, 28-, 35-, and 91-day-old rats demonstrates that the gene is induced to detectable levels between days 7 and 14 and that the relative level of expression does not change significantly after day 14. In situ hybridization using frozen sections of testis from day 2-, 7-, 14-, 28-, 35-, and 91-day-old rats confirms that there is little expression of TPRM-2 in the seminiferous epithelium of 7-day-old rats, but this increases considerably after 14 days, primarily in Sertoli cells but also in association with meiotic developing spermatogenic cells. However, TRPM-2 mRNA is expressed in the rete testis at 2 days of age, reaches a peak at 35 days of age, and continues to be expressed in the adult. Slot blot analysis demonstrates that TRPM-2 is also induced in the epididymis between 7 and 14 days of age, although, as has been demonstrated by in situ hybridization, TRPM-2 mRNA is detectable in the epithelial cells in the head of the epididymis but is barely detectable in the midportion or tail regions. Northern analysis suggests that the size of the TRPM-2 transcript in the testis also changes during development. In the early stages of testicular development, the TRPM-2 transcript appears to be a broad band of approximately 1.5 kb, while the transcript in the adult appears to be approximately 1.8 kb in length. S1-nuclease protection assays suggest that this increase in size is not due to differential splicing of the first exon of TRPM-2/SGP-2 and most probably reflects a difference in the polyadenylation of the mRNA in the testis at different times during development.

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.

Novel action of carnitine: inhibition of aggregation of dispersed cells elicited by clusterin in vitro

A novel effect of carnitine and O-acylcarnitine derivatives has been described. The presence of these compounds has been shown to inhibit the aggregation of erythrocytes otherwise elicited by the addition of clusterin or fetuin. The specificity of carnitine action has been investigated by comparing influences of chemically related compounds. The concentrations required for inhibition by approximately 50% of aggregation of erythrocytes by clusterin under in vitro conditions defined were determined to be 1.5 mM for L(-) or D(+) enantiomers of carnitine; 0.5 mM for decanoyl(-)- or (+)-carnitine; 0.13 mM for lauroyl(-)- or (+)-carnitine, and 0.05 mM for myristoyl(-)- or (+)-carnitine. In contrast, concentrations up to 12.5 mM of dimethylcarnitine, deoxycarnitine, acetylcholine, acetyl-beta-methylcholine, or inositol had no detectable inhibitory effect on aggregation elicited by clusterin. Clusterin addition also resulted in the aggregation of three other cell types examined (guinea pig spermatozoa, a cell line derived from testes of neonatal mice called TM4 cells, and Sertoli cells from testes of 20 day-old rats). As in the case with erythrocytes, the presence of carnitine inhibited aggregation of spermatozoa, TM4 cells, and Sertoli cells in suspension. We consider possible mechanisms by which carnitine inhibits aggregation of erythrocytes and other populations of dispersed cells incubated in the presence of clusterin.