Sperm were then incubated with mGX for 10 minutes and scored for AR. AR and that this was associated with decreased in vitro fertilization (IVF) efficiency due to a drop in the fertilization potential of the sperm and an increased rate of aborted embryos. Treatment of sperm with sPLA2 inhibitors and antibodies specific for mGX blocked spontaneous AR of wild-type sperm and reduced IVF success. Addition of lysophosphatidylcholine, a catalytic product of mGX, overcame these deficiencies. Finally, recombinant mGX brought on AR and improved IVF outcome. Taken together, our results highlight a paracrine role for mGX during capacitation in which the enzyme primes sperm for efficient fertilization and boosts premature AR of a likely phospholipid-damaged sperm subpopulation to eliminate suboptimal sperm from the pool available for fertilization. Introduction Spermatogenesis within the testis leads to the production of morphologically mature sperm that are still functionally immature, immotile, and incompetent for fertilization. Before fertilization, sperm should undergo two major series of important morphological, biochemical, and functional modifications, one within the epididymis and the other within the female reproductive tract after ejaculation. During their transit through the epididymis, sperm acquire progressive motility and primary the signaling pathways that will eventually orchestrate capacitation. The full fertilization potential of spermatozoa will be reached in vivo only after capacitation, a final maturation process occurring in the female reproductive tract. Capacitation was discovered by Austin and Chang in the early 1950s and is defined as a complex set of molecular events that allow ejaculated sperm to fertilize an egg (1, 2). Fertilization then starts with sperm binding on the zona pellucida (ZP), followed by the physiological acrosome reaction (AR), which is essential for sperm-oocyte fusion. Only fully capacitated spermatozoa can bind to the zona-intact egg and are competent for AR (3). However, during capacitation, a large fraction of sperm (30%C40%) undergoes a premature AR called spontaneous AR (4). This process is currently interpreted as a sperm malfunction and suggests that a subpopulation of ejaculated sperm does not tolerate the above-described final maturation process. The endogenous factors responsible for spontaneous AR and the possible physiological reasons for this process have not been identified. Indeed, the molecular mechanisms of sperm capacitation are still poorly understood, even after 50 years of intensive research (5C10). If capacitation clearly depends on cellular redox activity, ion fluxes, and protein phosphorylations, this process is also characterized by a strong dependence on the lipid membrane composition and lipid metabolism. Indeed, major lipid remodeling events of sperm including reorganization of the plasma membrane and formation of membrane subdomains, have been observed during capacitation at both chemical and biophysical levels (10, 11). During capacitation, the most well-known modification of the plasma membrane is cholesterol efflux, which Hexachlorophene plays a major role in sperm maturation both in vivo and in vitro (5). Other major changes during capacitation include remodeling of lipid rafts, efflux of desmosterol, and changes in sterol sulfates, phospholipids, sphingomyelin, and ceramides, all of them likely contributing to the increase in Hexachlorophene membrane fluidity by changing lipid packing and thereby providing heterogeneity of the sperm population (5, Hexachlorophene 12C14). If several families of lipolytic enzymes are involved in these lipid modifications (15), phospholipases A2 (PLA2s) are likely to be important, because of their abundant expression in male reproductive organs (16C19) and because of their great diversity of action, from phospholipid remodeling and lipid mediator release to inflammation and host defense (20, 21). PLA2s catalyze the hydrolysis of phospholipids at the position to generate free fatty acids and lysophospholipids, which are precursors of different lipid mediators, such as eicosanoids and platelet-activating factor (PAF) (23, 23). PLA2 metabolites either leave the cellular membrane and are involved in different cellular signaling pathways or accumulate in the leaflet of the membrane and change its biophysical properties. PLA2s constitute one of the largest families of lipid-hydrolyzing enzymes and have been classified into several groups (20). Based on their respective structure and cellular localization, PLA2s can be divided into 2 major sets of proteins: a set of 15 distinct Ca2+-dependent and Ca2+-independent intracellular PLA2s and another set of 10 Ca2+-dependent secreted PLA2s (sPLA2s). The PLA2 family also includes a set of intracellular and secreted forms of PAF acetylhydrolase. Deciphering the biological functions of each PLA2 member is Rabbit Polyclonal to TLE4 challenging. Studies over the last decade have shown that intracellular PLA2s and extracellular PLA2s are involved in the production of various lipid mediators in different tissues and cell types, these lipid mediators being important in numerous and diverse physiological and pathophysiological conditions (21C24). Several intracellular and secreted PLA2s in the testis and other male reproductive.