Towards the identification of reliable sperm biomarkers for male infertility: A sperm proteomic approach.

Male infertility evaluation is mainly based on semen analysis. Thus, identification of additional diagnostic methods is valuable. The aim of this study was to analyse the sperm proteome of infertile men to identify the underlying mechanisms and reliable diagnostic biomarkers. This cross-sectional study consisted of 16 infertile men and seven proven fertile men. An LC-MS/MS approach was performed in five pooled samples of each group (proven fertile men, primary infertility and secondary infertility). Differentially expressed proteins were used for functional enrichment analyses, and the most central proteins involved in altered functions in both infertile groups and the testis-specific proteins were validated using Western blotting and immunocytochemistry. In total, 1,305 sperm proteins were identified, of which 102 were underexpressed and 15 were overexpressed proteins in both infertile groups. Underexpressed proteins were mostly related to protein post-translational modification and folding, especially BAG6, HSPA2 and SPA17. Validation analysis revealed an underexpression of BAG6 in infertile men, whereas HSPA2 and SPA17 expressions did not differ between the groups. No differences were observed in the sperm localisation of these proteins. An overexpression of HIST1H2BA-a testis-specific protein-was observed in both proteomic approaches. Therefore, BAG6 and HIST1H2BA are potential candidates for male infertility biomarkers.