Analysis of the Sperm Head Protein Profiles in Normozoospermic Men: Consistency Across Time in the Levels of Expression of Heat Shock Proteins and Peroxiredoxins.

Abstract

The delivery of a genetically intact sperm nucleus during fertilization is required for normal embryo development. The condensed sperm DNA is closely associated with the proteinaceous sperm nuclear matrix. Although there is still little known about the functions of the nuclear matrix or its protein component, some nuclear proteins have been shown to have a role in normal sperm function. The objectives of this study were to identify the proteins in the head of human spermatozoa using a 1D Gel-MS label-free quantitative proteomics approach and to investigate quantitative and qualitative variations in the proteins extracted from human sperm heads. Sperm samples were obtained from each of three men (n=3) having high sperm counts at three different time points. This design allowed us to analyse intra-individual variations across time and inter-individual variations in the human sperm head proteome. To determine the background of the method used we analysed technical triplicates for each of the nine samples. The distribution of the coefficient of variation associated with the corresponding average of the triplicates was analysed. Intra-individual analysis from spectral counting methods reviewed that nearly 85% of the identified proteins had a low variation of expression level (< 2-fold) at various time points in each man. Across individuals, more than 30% of proteins were found to have a variation more than 2-fold with 10% considered highly variable (>3 fold). Interestingly, we found that 65 proteins did not vary across time or among men. This finding was confirmed both by ion profiling and spectral counting methods. Among these uniformly expressed proteins were chaperones, peroxiredoxins, isomerases, and cytoskeletal proteins. Our results suggest that there is a significant level of inter-individual variation in the protein profiles of human sperm heads. This highlights the importance of the effects of sample size and clinical characteristics of subjects when interpreting proteomic results with human sperm. The consistency in the levels of expression the various proteins suggests that they are essential and tightly regulated during spermatogenesis. Further investigations are required to elucidate their potential biological roles in sperm physiology. (Supported by the Canadian Institutes of Health Research - CIHR MOP86636).