Melatonin Improves the Fertilization Capacity of Sex-Sorted Bull Sperm by Inhibiting Apoptosis and Increasing Fertilization Capacitation via MT1

Abstract

Little information is available regarding the effect of melatonin on the quality and fertilization capability of sex-sorted bull sperm, and even less about the associated mechanism. Sex-sorted sperm from three individual bulls were washed twice in wash medium and incubated in a fertilization medium for 1.5 h, and each was supplemented with melatonin (0, 10−3 M, 10−5 M, 10−7 M, and 10−9 M). The reactive oxygen species (ROS) and endogenous antioxidant activity (glutathione peroxidase (GPx); superoxide dismutase (SOD); catalase (CAT)), apoptosis (phosphatidylserine [PS] externalization; mitochondrial membrane potential (Δψm)), acrosomal integrity events (malondialdehyde (MDA) level; acrosomal integrity), capacitation (calcium ion [Ca2+]i level; cyclic adenosine monophosphate (cAMP); capacitation level), and fertilization ability of the sperm were assessed. Melatonin receptor 1 (MT1) and 2 (MT2) expression were examined to investigate the involvement of melatonin receptors on sex-sorted bull sperm capacitation. Our results show that treatment with 10−5 M melatonin significantly decreased the ROS level and increased the GPx, SOD, and CAT activities of sex-sorted bull sperm, which inhibited PS externalization and MDA levels, and improved Δψm, acrosomal integrity, and fertilization ability. Further experiments showed that melatonin regulates sperm capacitation via MT1. These findings contribute to improving the fertilization capacity of sex-sorted bull sperm and exploring the associated mechanism.

Melatonin Non-Linearly Modulates Bull Spermatozoa Motility and Physiology in Capacitating and Non-Capacitating Conditions

“…Indeed, melatonin promotes sperm viability and modifies its physiology, as confirmed in different species [13][14][15][16]. Notably, it appears to modulate capacitation [17].…”

“…We have provided evidence that melatonin, even at the low 1-pM concentration, affects the physiology of bull spermatozoa. Whereas the effect of melatonin on sperm biology has drawn increasing attention [4,10,[14][15][16]32,34,48,49], there is still little information on its relevance regarding this cell type. Most studies have focused on its practical application in artificial reproductive techniques and on its effects as an antioxidant [35,39,[50][51][52], mostly using concentrations well above the nanomolar range.…”

“…Melatonin could affect the spermatozoon at different levels; previous studies have found a variety of effects, sometimes contrary, in different species and concentrations. Some protective and anti-apoptotic effects could be attributed by its antioxidant activity at the micro or millimolar levels, either by direct removal of oxidant species or indirectly by promoting survival signaling pathways [13,14,16]. Moreover, melatonin may have a chemotactic effect during capacitation, contributing to sperm guidance towards the fertilization site [4].…”

“…Our objective in the present study is to clarify the effect of melatonin at different concentrations in the physiology of bull spermatozoa. There is a lack of information on this important farm species, with only a few reports focusing on the antioxidant protection of melatonin in the millimolar-nanomolar range [16,28]. Reports on melatonin in the picomolar range-where only membrane receptors should mediate its effects-are still scarce regarding mammal spermatozoa.…”

“…There is a lack of systematic research on these topics, which would help us to understand sperm physiology better. Whereas many studies have focused on the effects on hyperactivation and capacitation-inducing conditions [15][16][17], they are scarce regarding non-capacitating conditions while using melatonin within the physiological range [14,17]. Moreover, this research would contribute not only with basic knowledge but also with practical applications in the field of animal breeding.…”