The Wnt1 ligand/Frizzled 3 receptor system plays a regulatory role in the achievement of the 'in vitro' capacitation and subsequent 'in vitro' acrosome exocytosis of porcine spermatozoa.

Abstract

The aim of this work was to determine the existence of a functional Wnt/β-catenin signaling pathway in boar spermatozoa, which would be linked with the already well-known GSK-3 signaling pathway. This was first confirmed by detecting the presence of the specific Frizzled 3 receptor in these cells. Furthermore, this signaling pathway was activated in boar spermatozoa subjected to 'in vitro' capacitation (IVC) and subsequent progesterone-induced 'in vitro' acrosome exocytosis (IVAE) by incubating cells with separate concentrations of Wnt1 ligand, the Wnt/β-catenin signaling pathway-specific effector. Incubation with the Wnt1 ligand increased the rhythm of the time-dependent reduction in sperm viability during the achievement of both IVC and IVAE. This finding was concomitant with an increase in the percentage of spermatozoa with altered membrane fluidity and permeability determined through both merocyanine-540 and YO-PRO-1 stains. While the Wnt1 ligand did not affect total sperm motility during the achievement of the IVC, it induced a fast and transient increase in the overall motility patterns in spermatozoa subjected to IVAE. This IVAE-linked action was related to a decrease in the percentage of cells with high mitochondrial membrane potential and an increase in the percentage of cells with high intracellular Fluo-3-marked Ca(2+) content. In conclusion, our results suggest that the Wnt1 ligand-modulated Wnt/β-catenin signaling pathway plays a relevant role in the modulation of both IVC and subsequent, progesterone-induced IVAE. Furthermore, our data indicate that the transduction pathways by which the Wnt1 ligand acts on IVC and IVAE are different, and that the Wnt/β-catenin pathway is independent from GSK-3 activity in the achievement of IVC.