Role of prosaposin and cathepsin D in male reproduction

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

Montreal

Conferencia; 7th International conference on the epididymis; 2018

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 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 processes PSAP at an acidic pH and whether the inhibition of PSAP/SapB 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 (Figure 1). Moreover, sperm motility and IVF were significantly decreased by a blockade of PSAP/SapB with a specific antibody (Figures 2 and 3). These results suggest that PSAP/SapB, and CatD, play an important role in modifying the sperm plasma membrane during sperm capacitation and fertilization.