Effect of reduced glutathione supplementation in semen extender on tyrosine phosphorylation and apoptosis like changes in frozen thawed Hariana bull spermatozoa

- First study to show the effects of GSH on DNA integrity of bull semen after freezing and thawing.
- Unique study to report the role of GSH on tyrosine phosphorylation of 30 kDa protein.
- GSH decreases cryocapacitation by reducing tyrosine phosphorylation.

To provide new insights into the mechanisms through which reduced glutathione (GSH) is able to protect spermatozoa, we tested the hypothesis that cryocapacitation and apoptosis like changes can contribute to the negative effect of freezing and thawing on bull spermatozoa, and that GSH prevent this damage. Having known protective effects of GSH in terms of a potent antioxidant, we evaluated capacitation, tyrosine phosphorylation and apoptosis like changes in bull spermatozoa after freezing and thawing in egg yolk tris glycerol extender containing (0.5 m M-GSH-T1 & 1 mM GSH-T2) and without GSH serving as the control (C). Forty ejaculates were collected from four Hariana bulls and were pooled due to non significant variations among the bull ejaculates for the evaluation of sperm attributes. Capacitation like changes, tyrosine phosphorylation, localization of tyrosine phosphorylated proteins, apoptosis like changes in terms of mitochondrial transmembrane potential and DNA fragmentation after final dilution, 4 h of equilibration at 4 °C and 24 h after freezing and thawing were evaluated. GSH supplementation at 0.5 mM showed significant reduction in B- and AR- pattern spermatozoa during all stages of semen freezing and thawing. Immunoblot revealed six proteins which were tyrosine phosphorylated and protein of 30 and 75 kDa (p30, p75) were the major tyrosine phosphorylted proteins. On further analysis, the p30 showed differential variation in intensity in all the three groups after freezing and thawing. Positive immune reactivity for tyrosine phosphorylated proteins was found in neck, middle piece and post-acrosomal regions of spermatozoa. Addition of 0.5 mM GSH decreased percentage of spermatozoa showing fragmented DNA and increased the percentage of spermatozoa having high transmembrane mitochondrial potential (P < 0.05). This study demonstrates that GSH favours survival of bull spermatozoa by interfering with apoptotic and cryocapacitation pathways, and thereby protects the spermatozoa from deleterious effects of cryopreservation. The findings of the study indicated that GSH at 0.5 mM can be effectively used as an additive in bull semen extender for freezing and thawing.