iTRAQ-based comparative proteomics reveal an enhancing role of PRDX6 in the freezability of Mediterranean buffalo sperm.

BACKGROUND: Semen cryopreservation is a critical tool for breed improvement and preservation of biodiversity. However, instability of sperm freezability affects its application. The Mediterranean buffalo is one of the river-type buffaloes with the capacity for high milk production. Until now, there is no specific cryopreservation system for Mediterranean buffalo, which influences the promotion of excellent cultivars. To improve the semen freezing extender used in cryopreservation of Mediterranean buffalo, different protein datasets relating to freezability sperm were analyzed by iTRAQ-based proteomics. This study will be beneficial for further understanding the sperm freezability mechanism and developing new cryopreservation strategy for buffalo semen.

RESULTS: 2652 quantified proteins were identified, including 248 significantly differentially expressed proteins (DEP). Gene Ontology (GO) analysis indicated that many these were mitochondrial proteins, enriched in the molecular function of phospholipase A2 activity and enzyme binding, and biological processes of regulation of protein kinase A signaling and motile cilium assembly. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis identified 17 significant pathways, including oxidative phosphorylation (OXPHOS). Furthermore, 7 DEPs were verified using parallel reaction monitoring or western blot, which confirmed the accuracy of the iTRAQ data. Peroxiredoxin 6 (PRDX6), which expressed 1.72-fold higher in good freezability ejaculate (GFE) compared to poor freezability ejaculate (PFE) sperms, was selected to explore the function in sperm freezability by adding recombinant PRDX6 protein into the semen freezing extender. The results showed that the motility, mitochondrial function and in vitro fertilization capacity of frozen-thawed sperm were significantly increased, while the oxidation level was significantly decreased when 0.1 mg/L PRDX6 was added compared with blank control.

CONCLUSIONS: Above results revealed the metabolic pattern of freezability of Mediterranean buffalo sperms was negatively associated with OXPHOS, and PRDX6 had protective effect on cryo-damage of frozen-thawed sperms.