Effect of lysoplatelet-activating factor on human sperm fertilizing ability**Supported by a grant from the Institut de Médecine de la Reproduction de Montreal, Montréal, Quebec, Canada

Lipidomics profiles of human spermatozoa: insights into capacitation and acrosome reaction using UPLC-MS-based approach

Introduction

Lipidomics elucidates the roles of lipids in both physiological and pathological processes, intersecting with many diseases and cellular functions. The maintenance of lipid homeostasis, essential for cell health, significantly influences the survival, maturation, and functionality of sperm during fertilization. While capacitation and the acrosome reaction, key processes before fertilization, involve substantial lipidomic alterations, a comprehensive understanding of the changes in human spermatozoa's lipidomic profiles during these processes remains unknown. This study aims to explicate global lipidomic changes during capacitation and the acrosome reaction in human sperm, employing an untargeted lipidomic strategy using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS).

Methods

Twelve semen specimens, exceeding the WHO reference values for semen parameters, were collected. After discontinuous density gradient separation, sperm concentration was adjusted to 2 x 106 cells/ml and divided into three groups: uncapacitated, capacitated, and acrosome-reacted. UPLC-MS analysis was performed after lipid extraction from these groups. Spectral peak alignment and statistical analysis, using unsupervised principal component analysis (PCA), bidirectional orthogonal partial least squares discriminant analysis (O2PLS-DA) analysis, and supervised partial least-squares-latent structure discriminate analysis (PLS-DA), were employed to identify the most discriminative lipids.

Results

The 1176 lipid peaks overlapped across the twelve individuals in the uncapacitated, capacitated, and acrosome-reacted groups: 1180 peaks between the uncapacitated and capacitated groups, 1184 peaks between the uncapacitated and acrosome-reacted groups, and 1178 peaks between the capacitated and acrosome-reacted groups. The count of overlapping peaks varied among individuals, ranging from 739 to 963 across sperm samples. Moreover, 137 lipids had VIP values > 1.0 and twenty-two lipids had VIP > 1.5, based on the O2PLS-DA model. Furthermore, the identified twelve lipids encompassed increases in PI 44:10, LPS 20:4, LPA 20:5, and LPE 20:4, and decreases in 16-phenyl-tetranor-PGE2, PC 40:6, PS 35:4, PA 29:1, 20-carboxy-LTB4, and 2-oxo-4-methylthio-butanoic acid.

Discussion

This study has been the first time to investigate the lipidomics profiles associated with acrosome reaction and capacitation in human sperm, utilizing UPLC-MS in conjunction with multivariate data analysis. These findings corroborate earlier discoveries on lipids during the acrosome reaction and unveil new metabolites. Furthermore, this research highlights the effective utility of UPLC-MS-based lipidomics for exploring diverse physiological states in sperm. This study offers novel insights into lipidomic changes associated with capacitation and the acrosome reaction in human sperm, which are closely related to male reproduction.

Platelet-activating factor induces acrosome reaction via the activation of extracellular signal-regulated kinase in human spermatozoa

Platelet-activating factor (PAF) affects capacitation, acrosome reaction and fertilisation potential of spermatozoa. This study investigated the underlying mechanism(s) through which PAF regulated sperm function. Our data demonstrated that PAF dose-dependently induced, whilst lyso-PAF (PAF precursor) showed no effect on acrosome reaction of capacitated human spermatozoa. Treatment with PAF for 90 min enhanced tyrosine phosphorylation and expression of extracellular signal-regulated protein kinases (ERK) 1 and 2 in human spermatozoa. Moreover, pre-treatment with the ERK inhibitor U0126 significantly and dose-dependently suppressed PAF-induced acrosome reaction. Therefore, PAF may be actively involved in the modulation of sperm acrosome reaction by interacting with ERK. The role of PAF in fertilisation warrants further investigation.

1-O-alkylglycerols improve boar sperm motility and fertility

1-O-alkylglycerols are naturally occurring ether lipids with potent biological activities. They may interfere with lipidic signaling, and they amplify platelet-activating factor (PAF) biosynthesis in a monocyte cell line. The PAF is produced by mammalian sperm and is an important activator of sperm motility. The aim of this study was to evaluate the effect of in vitro treatment of boar spermatozoa with natural 1-O-alkylglycerols (10 microM) on 1) boar sperm motility; 2) production of PAF and its metabolite, lyso-PAF, by spermatozoa; and 3) fertility in artificial inseminations of breeding sows. Using a computer-assisted spermatozoa analyzer, we found that 1-O-alkylglycerols increased percentage motility as well as velocity parameters after 24 h. These effects were partially or totally reversed by the PAF receptor-antagonist SR 27417. After [3H]-1-O-alkylglycerol incubation with boar spermatozoa, we identified [3H]lyso-PAF by high-performance liquid chromatography. Production of PAF and lyso-PAF was measured with a biological assay using [3H]serotonin release from rabbit platelets. 1-O-alkylglycerols significantly increased lyso-PAF production but had no effect on PAF production. The effect of 1-O-alkylglycerols on fertilization was also evaluated in industrial breedings: 1-O-alkylglycerol-treated or untreated semen dilutions were alternately used for artificial inseminations of sows on 12 farms. 1-O-alkylglycerol treatment increased the number of farrows but had no effect on the mean size of the litters. This study demonstrates that 1-O-alkylglycerol treatment of boar spermatozoa in vitro improves their motility and fertility, and it suggests that this effect is related to PAF metabolism and function in boar spermatozoa.

Effects of platelet activating factor on capacitation and acrosome reaction in mouse spermatozoa

Platelet activating factor (PAF) plays an important role in mammalian reproduction. The aim of this study was to investigate the effects of PAF on capacitation and acrosome reaction of mouse spermatozoa by chlortetracycline (CTC) fluorescence assay and coomassie blue staining. The percentage of capacitated mouse spermatozoa was increased (P < 0.05) by incubation with 50 ng/ml PAF for 20-120 min. The peak response occurred between 80 to 100 min of exposure to PAF. In contrast, the effects of PAF on acrosome reaction may be not receptor-mediated since lyso-PAF had the same effects. Ionophore A23187 stimulated an increase in acrosome-reacted spermatozoa of PAF-treated spermatozoa, but not of lyso-PAF-treated ones. These results suggest that PAF mainly acts on sperm capacitation.