Fertilization promoting peptide: an important regulator of sperm function in vivo?

Abstract

Fertilization promoting peptide (FPP; pGlu-Glu-ProNH2), a tripeptide structurally related to thyrotrophin releasing hormone, is produced by the prostate gland and released into seminal plasma. Recent studies carried out in vitro have revealed that FPP elicits biologically important responses in both mouse and human spermatozoa. In the presence of physiological concentrations of FPP (50-100 nmol l(-1)), uncapacitated spermatozoa undergo accelerated capacitation and so become potentially fertilizing more quickly, while capacitated spermatozoa are inhibited from undergoing spontaneous acrosomal exocytosis, an event that would make them non-fertilizing. In vivo, these responses would be very important since relatively few spermatozoa reach the site of fertilization; FPP could help to ensure that these were potentially fertilizing cells. A putative receptor (TCP-11) for FPP has been identified in mice. The gene for TCP-11 (which has a human homologue) maps to the t-complex, a region known to contain genes affecting male fertility. Current evidence indicates that FPP and TCP-11 act by modulating the activity of adenylyl cyclase and hence production of cAMP, a signal transduction pathway shown to be important in the acquisition of fertilizing ability. These results suggest that FPP plays an important role in normal fertility and that insufficient FPP could reduce fertility. Prostatic dysfunction can lead to decreased synthesis of FPP and increased synthesis of FPP-related peptides with reduced biological activity, both of which could compromise fertility in vivo. Given that 'male factor' infertility is a common contributor to subfertility in couples, it may prove possible to develop new therapeutic treatments, for at least some males, using FPP. In addition, this ligand-receptor pair could provide a novel target for male contraception.