The role of prosaposin and cathepsin D in male reproduction

SOSA MA; CARVELLI L; OKO R; MORALES CR; O´FLAHERTY C

Villa de Merlo, San Luis

Congreso; XXXV Reunión Científica Anual de la Sociedad de Biología de Cuyo; 2017

Sociedad de Biología de Cuyo

In mammalian epididymis, luminal proteins interact with the surface of in-transit spermatozoa as a requirement for maturation and acquisition of gamete fertilization capacity. The major sulfoglycolipid of the sperm plasma membrane is a sulfogalactosylglycerolipid (SGG), substrate of Arylsulphatase A (ARSA). ARSA modifies SGG in the presence of a sphingolipid activator protein, termed saposin B (SapB). Both the precursor of SapB, Prosaposin (PSAP), and ARSA are secreted by the epididymal epithelium, and they interact with the sperm plasma membrane. Moreover, the intracellular processing of prosaposin into saposins occurs in an acidic pH, and it requires the protease cathepsin D (CatD). Given that CatD is secreted by the epididymal epithelium and that the female genital tract has an acidic environment, we tested whether CatD is active for processing of PSAP at acidic pH and whether an eventual inhibition of PSAP/SapB action results in decreased fertilization. Mice epididymal fluid and spermatozoa were collected with buffers, adjusted to different pHs (5.5-6.3-7.2), with and without the presence of Pepstatin A (CatD inhibitor) or antibodies raised against PSAP/SapB. Luminal epididymal proteins were subjected to immunoblotting. Sperm motility (by CASA) and in vitro fertilization (IVF) were also tested. Acidification did not alter motility parameters; however, PSAP processing by CatD was enhanced at pH 6.3. Moreover, sperm motility and IVF were significantly decreased by a blockade of PSAP/SapB with a specific antibody. These results suggest that PSAP/SapB, and the hydrolases ARSA and CatD, play an important role in modifying the sperm plasma membrane during sperm capacitation and fertilization.