ABSTRACT
BACKGROUND: The excessive reactive oxygen species produced during semen-freezing and -thawing damage the macromolecules resulting in impairment of cellular functions. Proteins are the primary targets of oxidative damage, wherein methionine residues are more prone to oxidation and get converted into methionine sulfoxide, thus affecting the protein function. The methionine sulfoxide reductase A (MsrA) catalyzes the conversion of methionine sulfoxide to methionine and restores the functionality of defective proteins. OBJECTIVES: To establish the expression of MsrA in male reproductive organs, including semen and its effect on quality of cryopreserved semen upon exogenous supplementation, taking buffalo semen as a model. MATERIALS AND METHODS: The expression of MsrA was established by immunohistochemistry, PCR, and Western blots. Further, the effect of recombinant MsrA (rMsrA) supplementation on the quality of cryopreserved spermatozoa was assessed in three treatment groups containing 1.0, 1.5, and 2.0 µg of rMsrA/50 million spermatozoa in egg yolk glycerol extender along with a control group; wherein the post-thaw progressive motility, viability, membrane integrity, and zona binding ability of cryopreserved spermatozoa were studied. RESULTS: The MsrA was expressed in buffalo testis, epididymis, accessory sex glands, and spermatozoa except in seminal plasma. In group 2, the supplementation has resulted in a significant (p < 0.05) improvement as compared to the control group in mean progressive motility (47.50 ± 2.50 vs. 36.25 ± 2.63), viability (56.47 ± 1.85 vs. 48.05 ± 2.42), HOST (50.76 ± 1.73 vs. 44.29 ± 1.29), and zona binding ability of spermatozoa (149.50 ± 8.39 vs. 29.50 ± 2.85). DISCUSSION AND CONCLUSION: In the absence of native MsrA of seminal plasma, the supplementations of rMsrA may repair the oxidatively damaged seminal plasma proteins and exposed sperm plasma membrane proteins resulting in better quality with a fivefold increase in fertilizability of frozen-thawed spermatozoa. The findings can be extended to other species to improve the semen quality with the variation in the amounts of rMsrA supplementation.
