Abstract
BACKGROUND: Elevated levels of reactive oxygen species (ROS) are detected in 25% to 80% of infertile men. They are involved in the pathology of male infertility. Understanding the effect of increasing levels of ROS on the differential expression of sperm proteins is important to understand the cellular processes and or/pathways that may be implicated in male infertility. The aim of this study was to examine differentially expressed proteins (DEPs) in spermatozoa from patients with low, medium and high ROS levels. METHODS: A total of 42 infertile men presenting for infertility and 17 proven fertile men were enrolled in the study. ROS levels were measured by chemiluminescence assay. Infertile men were divided into Low (0- < 93 RLU/s/10(6) sperm) (n = 11), Medium (>93-500 RLU/s/10(6) sperm) (n = 17) and High ROS (>500 RLU/s/10(6) sperm) group (n = 14). All fertile men had ROS levels between 4-50 RLU/s/10(6) sperm. 4 subjects from fertile group and 4 each from the Low, Medium and High ROS were pooled. Protein extraction, protein estimation, gel separation of the proteins, in-gel digestion, LTQ-orbitrap elite hybrid mass spectrometry system was conducted. The DEPs, the cellular localization and pathways of DEPs involved were examined utilizing bioinformatics tools. RESULTS: 1035 proteins were identified in the 3 groups by global proteomic analysis. Of these, 305 were DEPs. 51 were unique to the Low ROS group, 47 Medium ROS group and 104 were unique to the High ROS group. 6 DEPs were identified by Uniprot and DAVID that had distinct reproductive functions and they were expressed only in 3 ROS groups but not in the control. CONCLUSIONS: We have for the first time demonstrated the presence of 6 DEPs with distinct reproductive functions only in men with low, medium or high ROS levels. These DEPs can serve as potential biomarkers of oxidative stress induced male infertility.