Abstract
This study sought to identify sources of the reduced fertility of men with type 2 diabetes mellitus. Significant reductions in semen volume, sperm concentration, and total sperm count were observed in diabetic individuals, while transmission electron microscopy revealed that the structure of mitochondria in the tail of sperm from diabetic patients was damaged. Proteins potentially associated with these sperm defects were identified using proteomics. Isobaric tagging for relative and absolute quantitation labeling and high-performance liquid chromatography-tandem mass spectrometry allowed us to identify 357 proteins significantly differentially expressed in diabetic versus control semen (>1.2 or <0.83). According to gene ontology enrichment and pathway analyses, many of these differentially expressed proteins are associated with sperm function, including binding of sperm to the zona pellucida and proteasome function; of particular interest, half of these proteins were related to mitochondrial metabolism. Protein-interaction networks revealed that a decrease in Cystatin C and Dipeptidyl peptidase 4 in the mitochondria may be sources of the decreased motility of sperm from diabetic patients.