Expression and localisation of RXFP3 in human spermatozoa and impact of INSL7 on sperm functions

Insulin-like peptide 7 (INSL7) or relaxin-3 is a member of the insulin superfamily that is recently discovered. This hormone interacts with relaxin family peptide receptor 3 (RXFP3). Although recent studies of INSL7 have focused on its function in the brain as a neuropeptide, spermatozoa may be a candidate target of INSL7 due to its detection in testes and contains binding sites. Therefore, this study aims to analyse the expression and localisation of RXFP3 on human spermatozoa and to assess the effect of INSL7 on human sperm motility. We have incubated normal semen samples in different doses of INSL7. Sperm motility was analysed by Computer Assisted Sperm Analysis. Moreover, localisation and expression of RXFP3 were assessed in human spermatozoa by immunofluorescence and RT-PCR respectively. This study indicated that RXFP3 mainly localised in the post-acrosomal region of sperm head and neck. However, we did not observe expression of RXFP3 mRNA in human spermatozoa. This study showed that INSL7 alleviated the natural decline in sperm motility after a 4-hr incubation period. This was particularly observed in the 1.8 pmol/L treated samples. These data suggested that most likely expression of RXFP3 arrested in spermiogenesis, but the RXFP3 peptide existed on the surface of mature spermatozoa.