PCSK4-null sperm display enhanced protein tyrosine phosphorylation and ADAM2 proteolytic processing during in vitro capacitation

Objective: To study the molecular basis for the accelerated capacitation rate in PCSK4-null sperm. Design: Comparative and controlled experimental research study. Setting: Academic medical institute. Animal(s): Male mice C57BL/6J wild-type or null congenics for the Pcsk4 allele. Intervention(s): Cauda and epididymal sperm were capacitated for varying times. Main Outcome Measure(s): Differences in sperm protein tyrosine phosphorylation and proteolytic processing of sperm-egg ligands ADAM2 and ADAM3. Result(s): The PCSK4-null sperm proteins are hyper-tyrosine phosphorylated during capacitation. This hyper-phosphorylation is dependent on protein kinase A (PKA), albumin, and calcium. There is also more ADAM2 proteolytic processing from a 46-kDa form of ADAM2 to a 27-kDa form in PCSK4-null sperm than in wild-type sperm. This processing is dependent on cholesterol efflux. Conclusion(s): Lack of PCSK4 is associated with quantitative changes in the phosphorylation and proteolysis of sperm proteins during capacitation; therefore, alterations in signal transduction and proteolytic processing during capacitation may underlie the fertilization incompetence of PCSK4-null sperm. More investigation is needed to determine how and to what extent these changes might contribute to the loss of fertilizing ability of PCSK4-null sperm. (Fertil Steril (R) 2010;93:1112-23. (C)2010 by American Society for Reproductive Medicine.)