Group X phospholipase A2 is released during sperm acrosome reaction and controls fertility outcome in mice

Abstract

Ejaculated mammalian sperm must undergo a maturation process called capacitation before they are able to fertilize an egg. Several studies have suggested a role for members of the secreted phospholipase A 2 (sPLA 2 ) family in capacitation, acrosome reaction (AR), and fertilization, but the molecular nature of these enzymes and their specific roles have remained elusive. Here, we have demonstrated that mouse group X sPLA 2 (mGX) is the major enzyme present in the acrosome of spermatozoa and that it is released in an active form during capacitation through spontaneous AR. mGX-deficient male mice produced smaller litters than wild-type male siblings when crossed with mGX-deficient females. Further analysis revealed that spermatozoa from mGX-deficient mice exhibited lower rates of spontaneous 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 sPLA 2 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 triggered 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.

A new era of secreted phospholipase A2

“…1 and 2 ) ( 64,70,74,112,121,132,134,135 ). It is now obvious that individual sPLA 2 s play unique and tissue-specifi c roles by acting on extracellular phospholipids, which include adjacent cell membranes, noncellular lipid components, and foreign phospholipids, such as those in microbes and food.…”

“…Thus, sPLA 2 -X, a "reproductive sPLA 2 ," plays a specifi c role in sperm activation, boosting the acrosome reaction probably through production of some lipid products from sperm membranes in a paracrine or autocrine manner. LPC is a candidate product responsible for the action of sPLA 2 -X, because it can partially restore the defective fertilization of wild-type sperm treated with anti-sPLA 2 -X antibody ( 132 ). Lastly, a striking skin phenotype characterized by alopecia in Pla2g10 -transgenic mice points to a unique role of sPLA 2 -X in hair homeostasis ( 36 ).…”

Flow cytometry analysis reveals a decrease in intracellular sodium during sperm capacitation

“…In mouse sperm, capacitation depends on lipid remodeling of the plasma membrane (Trevino et al, 2001;Visconti et al, 1999a;Visconti et al, 1999b), increase of intracellular pH (Nakanishi et al, 2001;Zeng et al, 1996), increase in protein tyrosine phosphorylation (Arcelay et al, 2008;Krapf et al, 2010;Visconti et al, 1995a;Visconti et al, 1995b) and changes in fluxes of ions such as Ca 2+ , HCO 3 2 , K + and Na + (Arnoult et al, 1997;Demarco et al, 2003;Felix et al, 2002;Munoz-Garay et al, 2001). These events are associated with functional sperm parameters such as hyperactivated motility (Yanagimachi, 1994), the ability to undergo a physiological stimulated acrosome reaction (Buffone et al, 2008;Escoffier et al, 2010b;Tomes, 2007) and the ability to penetrate the egg. Among ion fluxes occurring during capacitation, transport of HCO 3 2 (Demarco et al, 2003) constitutes one essential step in the initiation of capacitation.…”

Les phospholipases, enzymes clés de la physiologie spermatique

“…Curieusement, seule une sous-population de spermatozoïdes est sensible à l'activité de la sPLA 2 -GX. L'inhibition pharmacologique ou génétique de la sPLA 2 -GX entraîne une diminution du taux de fécondation et a un effet délétère sur le développement embryonnaire précoce, alors que le traitement de spermatozoïdes avec de la sPLA 2 -GX exogène conduit à l'effet inverse [27]. Ces résultats suggèrent que les modifications lipidiques induites par la sPLA 2 -GX au cours de la capacitation sont importantes pour insérer dans le spermatozoïde des messagers lipidiques secondaires favorisant le déve-loppement embryonnaire précoce.…”

“…Ces spermatozoïdes ne peuvent plus participer à la fécondation, car ils sont incapables de traverser la zone pellucide et sont donc éliminés du processus de fécondation. Voie 2 : la sPLA 2 -GX change la composition lipidique des spermatozoïdes insensibles à l'effet de la sPLA 2 sur la réac-tion acrosomique, et ces modifications sont nécessaires pour optimiser la fécondation (d'après [27] [33]. La PLC est la plus petite des PLC connues à ce jour, et elle est dépourvue des domaines habituellement présents comme les domaines SH2 (Src homology 2), SH3 ou PH (pleckstrin homology).…”