Abstract
Earlier we have reported mercury-induced alterations in functional dynamics of buck spermatozoa through free radicals-mediated oxidative stress and spontaneous acrosome reaction. Based on our earlier findings, we aimed to investigate the effect of mercury exposure on motility, kinematic patterns, DNA damage, apoptosis and ultra-structural alterations in goat spermatozoa following in vitro exposure to different concentrations (0.031–1.25 µg/ml) of mercuric chloride for 15 min and 3 h. Following exposure of sperm cells to 0.031 µg/ml of mercuric chloride for 3 h, livability and motility of sperms was significantly reduced along with altered kinematic patterns, significant increase in per cent necrotic sperm cells and number of cells showing DNA damage; and this effect was dose- and time-dependent. Contrary to up-regulation of Bax gene after 3 h in control group, there was significant increase in expression of Bcl-2 in mercury-treated groups. Transmission electron microscopy studies revealed rifts and nicks in plasma and acrosomal membrane, mitochondrial sheath, and collapsed mitochondria with loss of helical organization of mitochondria in the middle piece of spermatozoa. Our findings evidently suggest that mercury induces necrosis instead of apoptosis and targets the membrane, acrosome, mid piece of sperms; and the damage to mitochondria seems to be responsible for alterations in functional and kinematic attributes of spermatozoa.
Highlights
Earlier we have reported mercury-induced alterations in functional dynamics of buck spermatozoa through free radicals-mediated oxidative stress and spontaneous acrosome reaction
Intrinsic variability of semen samples as well as individual variations or differences arising as a result of treatments can be better studied by using computer-assisted sperm analysis (CASA) system that allows simultaneous generation of huge data-sets consisting of kinematic trajectories from thousands of spermatozoa[21]
United Nations Environment Programme’s (UNEP) Chemicals Working Group has pointed out that mercury contamination in India is reaching at alarming levels largely due to the discharge of mercury-bearing industrial effluents ranging from 0.058 to 0.268 mg/l31; and this is several times more than the prescribed Indian and WHO standards for drinking water and for industrial effluents
Summary
Earlier we have reported mercury-induced alterations in functional dynamics of buck spermatozoa through free radicals-mediated oxidative stress and spontaneous acrosome reaction. Based on our earlier findings, we aimed to investigate the effect of mercury exposure on motility, kinematic patterns, DNA damage, apoptosis and ultra-structural alterations in goat spermatozoa following in vitro exposure to different concentrations (0.031–1.25 μg/ml) of mercuric chloride for 15 min and 3 h. We too have recently reported mercury-induced significant alterations in functional dynamics of goat spermatozoa following in vitro exposure due to significant decrease in total antioxidant defense, increase in intracellular calcium and cAMP levels along with spontaneous acrosomal reaction, inhibition of tyrosine phosphorylation and capacitation like events in sperm c ells[13]. The present study was undertaken to investigate mercury-induced alterations in motility and motion kinematics of goat spermatozoa along with ultra-structural changes and mechanism(s) of sperm cell death. Effect of mercury on motility and kinematic patterns will help us in determining the quality and its suitability for cryopreservation, and delineating the molecular mechanism(s) of its toxic effects apart from providing some insights in evolving suitable cyto-protective measures to counter mercury-induced cell damage, and improve sperm competence for successful fertilization
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