Sperm Ubiquitination Correlation with Human Semen Quality

Ubiquitin, an 8.5 kDa peptide that marks other proteins for proteasomal degradation, tags defective sperm dur ing epididymal passage. Thus, sperm ubiquitination is a universal marker for sperm defects and can be used as a sperm func tion test. The objective of the present study was to examine the relationships between sperm ubiquiti nation and clinical se men parameters, using simplified immunofluorescence assays in order to establish ubiq uitin as a biomarker of male infertil ity. Semen samples from 100 couples attending Avicenna Infertility Clinic, Tehran, Iran, were collected and ana lyzed ac cording 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 ubiq uiti nated spermatozoa were evaluated by direct immunofluorescence microscopy using FITC-labeled anti-ubiq uitin antibodies. After counting at least 200 sperm per sample, while employing light microscopy, the percentage of ubiq uitinated spermatozoa was recorded on the same fields through epifluorescence microscopy. Negative correlations were obtained between sperm ubiquitination and sperm count (r=-0.278, P< 0.001), sperm concen tration (r=-0.37, P< 0.001), viability (r=-0.407, P< 0.001), sperm morphology (r=-0.509, P< 0.001), rapid progres sive motility (a) (r=-0.246, P< 0.001) and slow progressive motility (b) (r=-0.474, P< 0.001). There was a positive correla tion between ubiquitinated sperm and the percentage of immotile spermatozoa (r=0.486, P< 0.000). 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.