Reduced cytochrome oxidase activity and increased protein tyrosine phosphorylation of mitochondria-rich fractions of buffalo (Bubalus bubalis) spermatozoa after a cycle of freezing and thawing

The Proteomic Modification of Buck Ejaculated Sperm Induced by the Cryopreservation Process

Using two-dimensional electrophoresis along with mass spectroscopy, we have investigated how the cryopreservation process affected the protein profile of goat ejaculated sperm. In this study, five bucks were used for semen collection. After removal of seminal plasma, the Tris-based extender containing glycerol and egg yolk was used to freeze semen. The results indicated that the post-thaw sperm quality showed a significant reduction compared with fresh sperm. The numbers of protein spots acquired in fresh and post-thaw sperm were 2926 ± 57 and 3061 ± 81, respectively. Twenty-two different abundant proteins (DAPs) were identified between fresh sperm and frozen-thawed sperm (≥3.0-folds, p < 0.05). The abundances of 19 proteins were significantly higher in the fresh sperm than the post-thaw sperm. The results of the gene ontology annotation showed the primary location of the DAPs on sperm cytoskeleton, protein complex, cytoplasm, and mitochondria. In addition, these proteins were mainly involved in ion binding, small molecular metabolic processes, structure molecule activity, guanosine triphosphatase activity, oxidoreductase activity, and protein complex assembly. The interaction networks among these DAPs demonstrated that they may play roles in oxidoreductase activity, structure, acrosomal function, and motility of sperm. Collectively, the proteome of goat sperm was altered during the cryopreservation process, demonstrating that protein modification induced by cryopreservation may be associated with the reduced quality of goat sperm after thawing.

Proteomic profiling of stallion spermatozoa suggests changes in sperm metabolism and compromised redox regulation after cryopreservation

Proteomic technologies allow the detection of thousands of proteins at the same time, being a powerful technique to reveal molecular regulatory mechanisms in spermatozoa and also sperm damage linked to low fertility or specific biotechnologies. Modifications induced by the cryopreservation in the stallion sperm proteome were studied using UHPLC/MS/MS. Ejaculates from fertile stallions were collected and split in two subsamples, one was investigated as fresh (control) samples, and the other aliquot frozen and thawed using standard procedures and investigated as frozen thawed subsamples. UHPLC/MS/MS was used to study the sperm proteome under these two distinct conditions and bioinformatic enrichment analysis conducted. Gene Ontology (GO) and pathway enrichment analysis were performed revealing dramatic changes as consequence of cryopreservation. The terms oxidative phosphorylation, mitochondrial ATP synthesis coupled electron transport and electron transport chain were significantly enriched in fresh samples (P = 5.50 × 10^-12, 4.26 × 10^-8 and 7.26 × 10^-8, respectively), while were not significantly enriched in frozen thawed samples (P = 1). The GO terms oxidation reduction process and oxidoreductase activity were enriched in fresh samples and the enrichment was reduced in frozen thawed samples (1.40 × 10^-8, 1.69 × 10^-6 versus 1.13 × 10^-2 and 2-86 × 10^-2 respectively). Reactome pathways (using human orthologs) significantly enriched in fresh sperm were TCA cycle and respiratory electron transport (P = 1.867 × 10^-8), Respiratory electron transport ATP synthesis by chemiosmosis coupling (P = 2.124 × 10^-5), Citric acid cycle (TCA cycle)(P = 8.395 × 10^-4) Pyruvate metabolism and TCA cycle (P = 3.380 × 10^-3), Respiratory electron transport (P = 2.764 × 10^-2) and Beta oxidation of laurolyl-CoA to decanoyl CoA-CoA (P = 1.854 × 10^-2) none of these pathways were enriched in thawed samples (P = 1). We have provided the first detailed study on how the cryopreservation process impacts the stallion sperm proteome. Our findings identify the metabolic proteome and redoxome as the two key groups of proteins affected by the procedure. SIGNIFICANCE: In the present manuscript we investigated how the cryopreservation of stallion spermatozoa impacts the proteome of these cells. This procedure is routinely used in horse breeding and has a major impact in the industry, facilitating the trade of genetic material. This is still a suboptimal biotechnology, with numerous unresolved problems. The limited knowledge of the molecular insults occurring during cryopreservation is behind these problems. The application and development of proteomics to the spermatozoa, allow to obtain valuable information of the specific mechanisms affected by the procedure. In this paper, we report that cryopreservation impacts numerous proteins involved in metabolism regulation (mainly mitochondrial proteins involved in the TCA cycle, and oxidative phosphorylation) and also affects proteins with oxidoreductase activity. Moreover, specific proteins involved in the sperm-oocyte interaction are also affected by the procedure. The information gathered in this study, opens interesting questions and offer new lines of research for the improvement of the technology focusing the targets here identified, and the specific steps in the procedure (cooling, toxicity of antioxidants etc.) to be modified to reduce the damage.