Reproduction Abstracts

Introduction: A common defect encountered in the spermatozoa of male infertility patients is an idiopathic failure of sperm–egg recognition. The aim of this study was to investigate the molecular basis of this condition.

Materials and methods: For the purpose of this study we compared the proteomic profiles of spermatozoa from male infertility patients exhibiting an impaired capacity for sperm–egg recognition with that of sperm from males of proven fertility using label free mass spectrometry-based quantification. The dominant protein identified as being differentially expressed between these sperm samples was characterized to determine its role in fertilization.

Results and discussion: Our analysis indicated that impaired human sperm–zona pellucida binding was associated with reduced expression of the molecular chaperone, HSPA2, from the sperm proteome. This defect did not extend to other members of the HSP70 family. HSPA2 was present in the acrosomal domain of human spermatozoa as a major component of five large molecular mass complexes, the most dominant of which was found to contain just two other molecules, SPAM1 and ARSA, both of which that have previously been implicated in sperm–egg interaction. Furthermore, we demonstrated that HSPA2 regulates the expression of SPAM1 and ARSA on the surface of human spermatozoa. The close association between SPAM1, ARSA and HSPA2 in a multimeric complex mediating sperm–egg interaction, coupled with the complete failure of this process when HSPA2 is depleted in infertile patients, provides new insights into the mechanisms by which sperm function is impaired in cases of idiopathic male infertility.