Clusterin Facilitates Exchange of Glycosyl Phosphatidylinositol-Linked SPAM1 Between Reproductive Luminal Fluids and Mouse and Human Sperm Membranes1

Abstract

Glycosyl phosphatidylinositol (GPI)-linked proteins, which are involved in post-testicular maturation of sperm and have a role in fertilization, are acquired on the sperm surface from both vesicular and membrane-free soluble fractions of epididymal luminal fluid (LF) and uterine LF. Herein, we investigate the mechanism of uptake of these proteins from the soluble fraction of LFs using sperm adhesion molecule 1 (SPAM1) as a model. Ultracentrifugation and native Western blot analysis of the soluble fraction revealed that SPAM1 is present in low-molecular-weight (monomeric) and high-molecular-weight (oligomeric) complexes. The latter are incapable of transferring SPAM1 and may serve to produce monomers. Monomers are stabilized by hydrophobic interactions with clusterin (CLU), a lipid carrier that is abundantly expressed in LFs. We show that CLU is involved in the transfer of SPAM1 monomers, whose delivery was decreased by anti-CLU antibody under normal and apolipoprotein-enhanced conditions. Coimmunoprecipitation revealed an intimate association of CLU with SPAM1. Both plasma and recombinant CLU had a dose-related effect on transfer efficiency: high concentrations reduced and low concentrations enhanced delivery of SPAM1 to human and mouse sperm membranes, reflecting physiological states in the epididymal tract. We propose a lipid exchange model (akin to the lipid-poor model for cholesterol efflux) for the delivery of GPI-linked proteins to sperm membranes via CLU. Our investigation defines specific conditions for membrane-free GPI-linked protein transfer in vitro and could lead to technology for improving fertility or treating sperm pathology by the addition of relevant GPI-linked proteins critical for successful fertilization in humans and domestic animals.

Oviductosome-Sperm Membrane Interaction in Cargo Delivery

“…microvesicles, and exosomes, which serve as vehicles for the transfer of proteins to the sperm surface (1)(2)(3). This protein transfer during the interaction of sperm with the microenvironment in the female tract is essential for their maturation and fertilizing ability.…”

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

“…Immunohistochemical analysis showed that clusterin was present in spermatogenic cells besides Sertoli cells in the lumen of seminiferous tubules. As mentioned in the introduction, clusterin derived from Sertoli cells bound to the surface of testicular spermatozoa in the rete testis fluid and would be replaced by clusterin from the epididymis or seminal vesicle during sperm migration [3,8,9,32]. Therefore the clusterin observed by us in the inner membrane of normal spermatozoa may have been synthesized by the spermatogenic cells.…”

“…Most previous studies have shown that clusterin is secreted into semen by the epididymis and seminal vesicle, and mainly adheres to the surfaces of abnormal spermatozoa [3,8,9,25,32]. Only a few researchers observed clusterin in normal human spermatozoa [2,26,35].…”

“…Animal experiments have indicated that clusterin in the rete testis fluid is synthesized by Sertoli cells and adheres to the surface of testicular spermatozoa. When spermatozoa move through the rete testis and efferent duct, testis-derived clusterin is replaced by clusterin from the epididymis or seminal vesicle [3,8,9,32]. Clusterin on abnormal spermatozoa is implicated in decreased sperm motility, sperm aggregation and infertility [7,12,13,26].…”

Influence of reproductive tract obstruction on expression of epididymal proteins and their restoration after patency

“…The protein expression levels of HE2, FA-1, clusterin and PH20 were selected for verification by Western blot and RT-PCR because they play important roles in sperm maturation and fertilization process. [21][22][23][24][25][26][27][28][29] Western blot demonstrated that the content of HE2 was downregulated after reproductive tract obstruction and the downward trend was more obvious with increasing time of obstruction. Another study by Légaré et al 21 showed that vasectomy did not influence expression of HE2 in the human epididymis .…”