Proteomic Analysis Reveals that Topoisomerase 2A is Associated with Defective Sperm Head Morphology

Human spermatogenesis is a far from perfect process and even fertile men produce high numbers of defective spermatozoa. These cells are often characterized by chromatin defects. Following the isolation of normal and abnormal sperm cells, a label free comparison (SWATH) of nuclei from these populations demonstrates a retention of nuclear proteins in abnormal cells. Validation of mass spectrometry results by immuno-analysis reveals Topoisomerase 2A as a promising biomarker of sperm nuclear quality. [Display omitted] Highlights •Human spermatozoa possess cells of poor morphology that lack nuclear integrity.•These cells can be isolated by density separation.•Mass spectrometry reveals their nuclei contain excess protein.•TOP2A is a promising marker of this poor nuclear development. Male infertility is widespread and estimated to affect 1 in 20 men. Although in some cases the etiology of the condition is well understood, for at least 50% of men, the underlying cause is yet to be classified. Male infertility, or subfertility, is often diagnosed by looking at total sperm produced, motility of the cells and overall morphology. Although counting spermatozoa and their associated motility is routine, morphology assessment is highly subjective, mainly because of the procedure being based on microscopic examination. A failure to diagnose male-infertility or sub-fertility has led to a situation where assisted conception is often used unnecessarily. As such, biomarkers of male infertility are needed to help establish a more consistent diagnosis. In the present study, we compared nuclear extracts from both high- and low-quality spermatozoa by LC-MS/MS based proteomic analysis. Our data shows that nuclear retention of specific proteins is a common facet among low-quality sperm cells. We demonstrate that the presence of Topoisomerase 2A in the sperm head is highly correlated to poor head morphology. Topoisomerase 2A is therefore a potential new biomarker for confirming male infertility in clinical practice.