Is the proAKAP4 a suitable biomarker of X-sorted sperm quality from Nelore and Gir bulls?

ProAKAP4 is a protein precursor of AKAP4 present in the principal piece of the flagellum, associated with sperm motility. It has been described in several species, but its concentration has never been measured in sex-sorted sperm. Thus, the study aimed to test the proAKAP4 as a suitable sperm quality biomarker for Bos indicus X-sorted sperm. To achieve the study’s goal, 14 semen straws from different bulls were evaluated, six X-sorted and eight non-sorted. Sperm kinetics and morpho-functional evaluations were carried out, in addition to the concentration of proAKAP4. The characteristics evaluated were compared by the t-test and correlated by the Pearson’s correlation. A difference was found for total motility (P = 0.014), rapid sperm (P = 0.020), and sperm area (P = 0.013) between the non-sorted and X-sorted sperm. The proAKAP4 concentration was higher in the X-sorted sperm (X-sorted sperm: 67.54 ng/106 spermatozoa; non-sorted sperm: 29.76 ng/106 spermatozoa), but it was not correlated to the kinetics or morpho-functional characteristics evaluated. However, the proAKAP4 in non-sorted sperm showed a correlation to sperm total and progressive motility, rapid sperm, and sperm membrane integrity. The study concluded on the unreliability of the proAKAP4 as a biomarker to indicate sperm quality in the X-sorted sperm.