Involvement of cAMP efflux, through MRP4 transporter, in the acquisition of fertilization ability of mouse spermatozoa

Abstract

Mammalian spermatozoa must undergo biochemical and structural changes to acquire fertilizing ability, in a process known as capacitation. Activation of PKA is essential for capacitation, and thus cAMP levels are tightly regulated during this process. Previously, we demonstrated that during capacitation, bovine spermatozoa extrude cAMP through the Multidrug Resistance Protein 4 (MRP4) which regulates intracellular levels of the nucleotide and provides cAMP to the extracellular space. Here, we report the presence of a functional MRP4 in murine spermatozoa, since its pharmacological inhibition with MK571 decreased levels of extracellular cAMP. This also produced a sudden increase in PKA activity, with decreased tyrosine phosphorylation (pY) at the end of capacitation. Blockade of MRP4 inhibited induced-acrosome reaction, hyperactivation and in vitro fertilization. Moreover, MRP4 inhibition induced an increase in Ca2+ levels mediated by PKA and depletion of Ca2+ salts from the medium prevented the loss of motility and pY inhibition produced by MK571. These results were supported using spermatozoa from CatSper Ca2+-channel knockout mice. Altogether, these results suggest that cAMP efflux, through MRP4, plays an essential role in mouse sperm capacitation.