Mitochondrial aspartate aminotransferase (GOT2) protein as a potential cryodamage biomarker in rooster spermatozoa cryopreservation

Spermatozoa cryopreservation has been widely used for animal genetic conservation. Despite advances in chicken semen cryopreservation, the mechanism of spermatozoa cryodamage remains to be revealed. The cryopreservation process induces motion parameter decreased, structure damaged, proteomic and antioxidant system remodeled in spermatozoa. Mitochondrial glutamate-oxaloacetate transaminase 2 (GOT2) is part of the malate aspartate shuttle, which is ubiquitous in mitochondria and is associated with cellular metabolism regulation. Thus, this study is the first to investigate GOT2 biological role in chicken spermatozoa during freezing process. The results showed that the sperm total motility, straight-line velocity (VSL) and mitochondrial membrane potential (MMP) of the frozen group were significantly lower than these of the fresh group (P < 0.05). The fresh sperm mitochondrial membrane was continuous and mitochondrial matrix was dense and homogeneous. However, after the freezing-thawing, the density of the matrix was reduced, and the mitochondria appeared slightly swollen and membrane damaged. In chicken sperm, the GOT2 protein was localized in the head and the midpiece of spermatozoa where mitochondria are located by immunostaining analysis. This was consistent with the subcellular localization prediction. GOT2 protein was more abundant in the fresh sperm than in the frozen sperm, which indicated that freezing may lead to sperm mitochondrial damage, reduced GOT protein expression, and affected sperm motility and fertility. The protein-protein interaction prediction of GOT2 protein indicated that its ten most confident interactors were predominantly mitochondria-related proteins. The binding ability was higher between GOT2 protein and two mitochondria-targeted antioxidants, SkQ1 and Mito-TEMPO, respectively. In conclusion, GOT2 played an important role in chicken spermatozoa, which was possibly associated with the regulation of mitochondria function and spermatozoa metabolism. Moreover, it may be a potential cryodamage improvement target for spermatozoa. However, the underlying mechanism of GOT2 in spermatozoa cryopreservation needs further exploration.