Metabolomic fingerprinting of bull spermatozoa for identification of fertility signature metabolites.

The objective of the study was to identify the fertility-associated metabolites in bovine spermatozoa using liquid chromatography-mass spectrometry (LC-MS). Six Holstein Friesian crossbred bulls (three high-fertile and three low-fertile bulls) were the experimental animals. Sperm proteins were isolated and protein-normalized samples were processed for metabolite extraction and subjected to LC-MS/MS analysis. Mass spectrometry data were processed using iMETQ software and metabolites were identified using Human Metabolome DataBase while, Metaboanalyst 4.0 tool was used for statistical and pathway analysis. A total of 3,704 metabolites belonging to various chemical classes were identified in bull spermatozoa. After sorting out exogenous metabolites, 56 metabolites were observed common to both the groups while 44 and 35 metabolites were found unique to high- and low-fertile spermatozoa, respectively. Among the common metabolites, concentrations of 19 metabolites were higher in high-fertile compared to low-fertile spermatozoa (fold change > 1.00). Spermatozoa metabolites with variable importance in projections score of more than 1.5 included hypotaurine, d-cysteine, selenocystine. In addition, metabolites such as spermine and l-cysteine were identified exclusively in high-fertile spermatozoa. Collectively, the present study established the metabolic profile of bovine spermatozoa and identified the metabolomic differences between spermatozoa from high- and low-fertile bulls. Among the sperm metabolites, hypotaurine, selenocysteine, l-malic acid, d-cysteine, and chondroitin 4-sulfate hold the potential to be recognized as fertility-associated metabolites.