Comparative sperm protein profiling in bulls differing in fertility and identification of phosphatidylethanolamine-binding protein 4, a potential fertility marker

This study aimed to identify sperm proteomic signatures regulating sperm functions and fertility by: (i) comparing the sperm electrophoretic protein profiles and identifying the differentially abundant proteins among breeding bulls differing in fertility status and (ii) elucidating the possible role of one of the identified novel proteins, PEBP4 on sperm function and fertility. The grouping of bulls as fertile (n = 6) and low fertile (n = 6) was performed based on bull fertility index and infertile (n = 6) based on semen rejection rate (>33%). The sperm motility, fructolysis index, acrosomal reaction, intracellular calcium levels, and seminal plasma fructose and calcium levels were studied among fertility groups. The differentially expressed sperm proteins observed in single-and two-dimensional gel electrophoresis (2DE) were identified using Nano-LC-MS/MS. In the fertile bulls, the expression levels of calmodulin (CALM1), spermadhesinZ13 (SPADH2), and phosphatidylethanolamine-binding protein 4 (PEBP4) were significantly (p < 0.05) higher than in other fertility groups. In bovine, expression of PEBP4 a novel seminal protein was not observed in spermatozoa of infertile bulls. When the bulls were grouped based on the presence (n = 8) or absence (n = 10) of PEBP4 protein in spermatozoa, a positive significant (p < 0.05) association of this protein with the percentage of motile, type-A spermatozoa, and sperm fructose uptake was observed. Further, PEBP4 was localized in elongated spermatids, Leydig cells, excurrent duct system, and principal piece of spermatozoa. These findings suggest a crucial role for the PEBP4 protein in spermiogenesis, epididymal sperm maturation, and sperm motility. This first study in bovine indicates the positive association of PEBP4 in regulating sperm maturation, functions, and fertility and could be a potential marker for predicting semen quality and fertility.