l-arginine alters the proteome of frozen-thawed bovine sperm during in vitro capacitation

The aim of this work was to evaluate the proteomic changes that occurred in the frozen-thawed bovine spermatozoa after the addition of l-arginine (L-arg) during in vitro sperm capacitation. Aspects related to the sperm capacitation pattern like membrane integrity, mitochondrial activity, sperm motility and vigor, and the sperm proteome were determined. These were respectively assessed by chlortetracycline staining, H342/PI, JC-1, light microscopy, and the proteomic abundance by nUPLC-MS/MS analysis. Frozen-thawed sperm from three Nellore bulls were capacitated in vitro for 3 h in sp-TALP medium supplemented with 20 μg/mL heparin (Control) or with 20 μg/mL heparin plus 1 mM L-arg (L-arg group). Data were subjected to analysis of variance and means compared by SNK test at 5% probability. When compared to Control, the percentage of sperm motility was higher in the L-arg group (P < 0.05). For test data after 3 h of incubation, sperm capacitated with L-arg showed higher membrane integrity and mitochondrial potential when compared to Control (P < 0.05). Moreover, we observed an increase in the percentage of capacitated sperm pattern (P < 0.05). Protein abundance analysis identified 367 proteins. Forty proteins were differentially abundant between Control and L-arg group (P < 0.05), of which 11 were up-regulated, and 29 were down-regulated in L-arg group. In addition, we observed that one protein was uniquely abundant in the L-arg group. Our findings indicate that the addition of L-arg to the culture medium presented a differential protein abundance pattern and increased the bovine frozen-thawed sperm quality and the percentage of capacitated sperm. The proteomic changes observed may be linked to the molecular mechanisms involved in the action of L-arg on the in vitro sperm capacitation of cattle.