The presence of a C1-inhibitor-like molecule (C1-INH-L) on human sperm: its involvement in sperm motility

C1, MBL-MASPs and C1-inhibitor: novel approaches for targeting complement-mediated inflammation

Complement activation is initiated by the pattern-recognition molecules complement component C1q, mannose-binding lectin (MBL) and ficolins (H-, L-, M-ficolin), which typically recognize antibody-antigen complexes or foreign polysaccharides. The associated proteases (C1r, C1s, MASP-1 and MASP-2) then activate the complement system. The serpin C1-inhibitor (C1-inh) blocks activity of all these complexes and has been successfully used in models of disease. Many structures of these components became available recently, including that of C1-inh, facilitating the structure-guided design of drugs targeting complement activation. Here, we propose an approach in which therapeutic proteins are made up of natural protein domains and C1-inh to allow targeting to the site of inflammation and more specific inhibition of complement activation. In particular, engineering a fast-acting C1-inh or fusing it to an 'aiming module' has been shown to be feasible and economical using a humanized yeast expression system. Complement-mediated inflammation has been linked to ischemia-reperfusion injury, organ graft rejection and even neurodegeneration, so targeting this process has direct clinical implications.

The sequential cleavage of membrane anchored pro-EGF requires a membrane serine protease other than kallikrein in rat kidney

Epidermal growth factor (EGF) is present in kidney membranes as an integral type I precursor protein, enzymatically processed to release immunoreactive materials in urine or incubation medium. The aim of this work was the elucidation of both the anchor of the serine protease activity that processes pro-EGF, and the determination of the steps of the enzymatic processing. Quantification of EGF containing molecules by RIA following gel filtration analysis demonstrated that the membrane precursor is first shed from the kidney membrane principally into a 170-kDa soluble precursor. This entire ectodomain is further processed into a 70-kDa precursor and finally into the mature 5.9 kDa urinary EGF. These species correspond to the ones found in urines. Both shedding and maturation events are clearly realized by membrane anchored serine protease activity, which remains active in detergent. By use of wild-type and knockout mice urines, we found that tissue kallikrein (TK) was not involved in the regulation of this processing.

C1-inhibitor: an anti-inflammatory reagent with therapeutic potential

Excessive activation of the protein cascade systems often leads to severe inflammatory tissue destruction with potential life-threatening outcome. These include clinical disorders, such as capillary leak syndrome, septic shock, myocardial infarction and other ischaemia/reperfusion injuries, trauma, burns, multiple organ failure, as well as graft rejection. A therapeutic substitution of appropriate regulators appears to be a reasonable approach to reduce undesirable inflammatory reactions. C1-inhibitor, a multifunctional regulator of the various kinin-generating cascade systems, is frequently reduced in patients suffering from severe inflammation. C1-inhibitor concentrate has been used for decades as a substitution therapy to treat acute attacks in patients with hereditary angioedema. Studies including pathophysiologically relevant animal models now provide sufficient evidence that C1-inhibitor may also serve as an effective means to protect against inflammatory tissue injury. Promising clinical results are emerging which support C1-inhibitor as a candidate for therapy in severe inflammatory disorders. Although treatment with C1-inhibitor is regarded as safe, recent reports on possible side effects in certain clinical situations emphasise the importance of controlled clinical studies. The following review will focus on the impact of C1-inhibitor treatment on diseases, where complement contributes to the pathogenesis.

Complement component 1 inhibitor (C1-INH) like protein on murine spermatozoa: anti-C1-INH inhibits in vitro fertilization

We investigated if complement component 1 inhibitor-like (C1-INH-L) protein found on human spermatozoa exists on mouse spermatozoa and is relevant to reproduction. We used Western blot analysis and immunofluorescence assays to detect C1-INH on murine sperm and tested the effects of the antibodies to C1-INH and albumin (negative control) on in vitro mouse sperm motility and fertilization. C1-INH-L, with molecular weight similar to human C1-INH (100 kDa), was present on the surface of spermatozoan head and midpiece. Treating mouse sperm with anti-C1-INH reduced the mouse sperm motility (P < 0.01), in vitro fertilization (P < 0.01) and embryo development rates (P < 0.01). Anti-albumin failed to do so. We conclude that C1-inhibitor-like protein is present on mouse sperm surface and appears to be relevant to reproduction.

Quantification of C3 and C4 in infertile men with antisperm antibody in their seminal plasma

PROBLEM

Previous studies showed that some infertilities are caused by antisperm antibodies (ASAs). It was shown that some major complement (C) components are present in seminal fluid. Due to the role of C in the pathogenesis of ASAs, the existence and amount of two key C components (C3 and C4) were investigated in seminal plasma (SP).

METHOD OF STUDY

Single radial immunodiffusion assay and a sandwich-type enzyme-linked immunosorbent assay (ELISA) were used for C3 and/or C4 quantification, respectively, in serum and SP, and the tray agglutination test was used for ASA detection in 12 fertile and 53 infertile men (18 ASA-positive [ASA+] and 35 ASA-negative [ASA-] men).

RESULTS

Of the 18 ASA + infertile men, 61.11% had positive C3, whereas 27.77% showed positive C4 levels. ASA + infertile men showed significant differences in seminal plasma C3 mean values compared with ASA- infertile (P < 0.01) and fertile (P < 0.05) men, but the seminal plasma C4 values only showed differences compared with ASA- infertile men (P < 0.05). No significant differences were observed in serum C3 and/or C4 levels of ASA+ infertile men compared with other groups. No significant correlation was found between ASA titer and C3 and C4 levels in SP. A significant correlation existed between SP and serum C3 levels of ASA+ (r = 0.522, P < 0.01) and ASA- (r = 0.451, P < 0.01) infertile men, but no correlation was observed between C4 levels.

CONCLUSIONS

In the presence of ASAs, the C system has no definitive activity in blood serum or outside the male genital tract. In SP, and in association with ASAs, C has no lytic activity by the classical pathway. The excess of C3 in SP of ASA+ infertile men may participate in other C-mediated activities in the male reproductive tract.

Complement regulatory proteins on the sperm surface: relevance to sperm motility

PROBLEM

To determine whether complement regulatory proteins are present on human spermatozoa and whether antibodies to these proteins adversely affect sperm motility.

METHOD OF STUDY

Human sperm membrane proteins were solubilized and subjected to polyacrylamide gel electrophoresis followed by Western blot analysis against antibodies to complement component 1 inhibitor (C1-INH), decay-activating factor (DAF; CD55), membrane cofactor protein (MCP; CD46), and homologous restriction factor (HRF; CD59). Spermatozoa, obtained by a swim-up technique, were incubated in medium (control 1) and medium supplemented with antibodies to human albumin (control 2) and antibodies to these complement regulatory proteins. We used a computerized sperm motion analysis to determine the effect of these antibodies on sperm motion characteristics.

RESULTS

Complement regulatory proteins such as C1-INH, CD55, CD46, and CD59 were found in the sperm extracts as shown by Western blot analysis. The heat-treated (56 degrees C, 30 min) IgG fraction of antibodies to these proteins significantly reduced sperm motility in general and other motion parameters. Addition of complement did not affect these results except in the antibodies to CD46 in which the reducing action was further amplified.

CONCLUSIONS

Our data suggest that C1-INH, CD55, CD46, and CD59 are present on the sperm surface. These proteins may have biological functions, such as affecting sperm motility, besides the complement regulatory functions. In infertile men and women with antibodies that recognize one or more of these complement regulatory proteins, there may be problems related to poor sperm motility and survival in the reproductive tracts.