Role of fertilization promoting peptide (FPP) in modulating mammalian sperm function

Fertilization promoting peptide (FPP), structurally similar to thyrotrophin releasing hormone, is produced by the prostate gland and secreted into seminal plasma. Recent in vitro studies have provided evidence that FPP elicits biologically relevant responses in mouse, human and boar spermatozoa. In the presence of nanomolar concentrations of FPP, spermatozoa become fertilizing more quickly and then are inhibited from undergoing spontaneous acrosome loss, an event that would make them non-fertilizing. In vivo, these responses would be very important in maximizing the availability of potentially fertilizing spermatozoa. Adenosine, which can elicit the same responses as FPP, is known to modulate the adenylyl cyclase(AC)/cAMP signal transduction pathway; current evidence indicates that FPP and adenosine act via separate receptors on the same signal transduction pathway. Mouse spermatozoa are known to have adenosine receptors and a putative receptor for FPP (TCP-11) has been identified. Unlike many surface receptors, TCP-11 has no obvious transmembrane regions whereby modulation of AC could occur. Recent evidence suggests that FPP receptors may dimerize with adenosine receptors to activate the signaling pathway, with stimulatory adenosine receptors involved in the stimulation of capacitation, but inhibitory receptors involved in inhibition of spontaneous acrosome loss. These results indicate that FPP plays an important role in normal sperm function and that it might be used in new therapeutic strategies designed to alleviate some causes of sperm dysfunction.