Phosphoproteomic and functional approaches reveal changes in sperm-specific proteins downstream KOR in human spermatozoa

G-protein coupled receptors (GPCRs) belong to the seven transmembrane receptors superfamily that in response to external stimuli, transduce signals via G proteins to initiate different intracellular signaling pathways which culminate in specific cellular responses. Although in somatic cells the GPCR participate in a broad variety of physiological processes, the expression of diverse GPCRs at the plasma membrane of human spermatozoa suggests their involvement in the regulation of sperm fertility. Mature spermatozoa could present unique features in their molecular mechanisms downstream GPCRs due to the fact that they possess sperm-specific proteins and are transcriptionally and translationally silent. In order to decipher the signaling pathways engaged by this receptor superfamily in human spermatozoa, we selected the kappa-opioid receptor (KOR) as a study model and applied, for first time, phosphoproteomic approach based on TMT labeling and LC-MS/MS analyses combined with functional studies using a specific agonist of KOR, U50488H.