Sperm DNA fragmentation increases with age but not chromatin decondensation

Abstract

OBJECTIVE: The impact of Sperm DNA damages and chromatin structure (DNA packaging) on reproductive outcome is no longer a matter for debates. The relationship between paternal age and sperm DNA fragmentation is now of common knowledge. We have tried to define here if the chromatin structure follows the same type of variations.DESIGN: We have tested in a retrospective study including 633 patients consulting for hypofertility DNA fragmentation index % (DFI), and DNA decondensation %(SDI).MATERIALS AND METHODS: Sperm DNA fragmentation has been studied by TUNEL assay either coupled with flow cytometry or on slides when sperm concentration was too low (<1 million sperm per ml). The correlation between our 2 techniques has been controlled. DNA decondensation (SDI) was tested using aniline blue. The effect of age and abstinence was analysed using variance covariance analysis (Table 1).Table 1DFI and SDI according to paternal agepaternal ageNfragmentation index % (DFI)decondensation index % (SDI)≥ 3418022,2 ± 9,118,0 ± 9,935-3924523,9 ± 10,217,6 ± 11,140-4916425,8 ± 12,317,5 ± 7,9≥ 504435,1 ± 14,115,0 ± 4,2statistical significancyp<0.001p<0.01 Open table in a new tab CONCLUSIONS: Sperm DNA fragmentation and chromatin structure are not correlated. Increase of DFI with age can be interpreted as a weaker resistance to reactive oxygen species with age. This increase in reactive oxygen species (ROS) in sperm surrounding has a rather positive effect on chromatin structure: DNA packaging needs oxidation of the protamine cystein moieties to cystin in order to lock the DNA. If the impact of DNA fragmentation on ART is rather well documented, poor chromatin structure leads to chromosomal anomalies which are a classical feature in IVF/ICSI embryos. DFI and SDI are independent but complementary: they have a mandatory place in the realisation of a complete male fertility check up especially in relation with paternal age. OBJECTIVE: The impact of Sperm DNA damages and chromatin structure (DNA packaging) on reproductive outcome is no longer a matter for debates. The relationship between paternal age and sperm DNA fragmentation is now of common knowledge. We have tried to define here if the chromatin structure follows the same type of variations. DESIGN: We have tested in a retrospective study including 633 patients consulting for hypofertility DNA fragmentation index % (DFI), and DNA decondensation %(SDI). MATERIALS AND METHODS: Sperm DNA fragmentation has been studied by TUNEL assay either coupled with flow cytometry or on slides when sperm concentration was too low (<1 million sperm per ml). The correlation between our 2 techniques has been controlled. DNA decondensation (SDI) was tested using aniline blue. The effect of age and abstinence was analysed using variance covariance analysis (Table 1). CONCLUSIONS: Sperm DNA fragmentation and chromatin structure are not correlated. Increase of DFI with age can be interpreted as a weaker resistance to reactive oxygen species with age. This increase in reactive oxygen species (ROS) in sperm surrounding has a rather positive effect on chromatin structure: DNA packaging needs oxidation of the protamine cystein moieties to cystin in order to lock the DNA. If the impact of DNA fragmentation on ART is rather well documented, poor chromatin structure leads to chromosomal anomalies which are a classical feature in IVF/ICSI embryos. DFI and SDI are independent but complementary: they have a mandatory place in the realisation of a complete male fertility check up especially in relation with paternal age.