Prosaposin is involved in male fertility

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

Mendoza

Congreso; XXXVI Reunión Científica Anual de la Sociedad de Biología de Cuyo; 2018

Sociedad de Biología de Cuyo

Luminal proteins of mammalian epididymis interact with the surface of in-transit spermatozoa as a requirement for gamete maturation and acquisition of fertilizing ability. The major sulfoglycolipid of the sperm plasma membrane is a sulfogalactosylglycerolipid (SGG), which is a substrate for 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 PSAP into saposins occurs at acidic pH, and 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 can process PSAP at acidic pH and whether the fertilization rate is affected under these conditions. Additionally, we evaluated whether the inhibition of PSAP/SapB results in altered motility and/or fertilization. Mouse epididymal fluid and spermatozoa were collected with buffers adjusted to pH 5.5, 6.3 or 7.2, without or with pepstatin A (CatD inhibitor) or with antibody raised against PSAP/SapB. Luminal epididymal proteins were then subjected to immunoblotting. Sperm motility (by CASA) and in vitro fertilization (IVF) were also tested. Although PSAP processing by CatD was enhanced at pH 6.3, with subsequent increasing of fertilization rate, the acidification did not alter sperm motility parameters. Moreover, sperm motility and IVF were significantly decreased by blockade of PSAP/SapB with a specific antibody. These results suggest that PSAP/SapB play an important role in modifying the sperm plasma membrane during sperm capacitation and fertilization.