Sperm Ubiquitination Correlation with Human Semen Quality

Abstract

Background: Ubiquitin, an 8.5 kDa peptide that marks other proteins for proteasomal degradation, tags defective sperm dur­ing epididymal passage. Thus, sperm ubiquitination is a universal marker for sperm defects and can be used as a sperm func­tion test. The objective of the present study was to examine the relationships between sperm ubiquiti­nation and clinical se­men parameters, using simplified immunofluorescence assays in order to establish ubiq­uitin as a biomarker of male infertil­ity.

Methods: Semen samples from 100 couples attending Avicenna Infertility Clinic, Tehran, Iran, were collected and ana­lyzed ac­cording to WHO criteria. Each sample was washed and adjusted at 10⁶ sperm/ml concentration. Sperm were coated on slides, using cytospin centrifugation and were fixed in buffered formaldehyde. Subsequently ubiq­uiti­nated spermatozoa were evaluated by direct immunofluorescence microscopy using FITC-labeled anti-ubiq­uitin antibodies. After counting at least 200 sperm per sample, while employing light microscopy, the percentage of ubiq­uitinated spermatozoa was recorded on the same fields through epifluorescence microscopy.

Results: Negative correlations were obtained between sperm ubiquitination and sperm count (r=-0.278, P< 0.001), sperm concen­tration (r=-0.37, P< 0.001), viability (r=-0.407, P< 0.001), sperm morphology (r=-0.509, P< 0.001), rapid progres­sive motility (a) (r=-0.246, P< 0.001) and slow progressive motility (b) (r=-0.474, P< 0.001). There was a positive correla­tion between ubiquitinated sperm and the percentage of immotile spermatozoa (r=0.486, P< 0.000).

Conclusion: Increased sperm ubiquitination is inversely associated with good semen quality parameters, supporting the use of ubiquitin as a biomarker for evaluation of human sperm quality.