Effects of cryopreservation on sperm quality, nuclear DNA integrity, in vitro fertilization, and in vitro embryo development in the mouse

Efficient freezing, archiving, and thawing of sperm are essential techniques to support large scale research programs using mouse models of human disease. The purpose of this study was to investigate the effects of variable combinations and concentrations of cryoprotectants on sperm-assessment parameters of frozen-thawed mouse sperm in order to optimize cryopreservation protocols. Sperm was frozen using combinations of 3% skim milk + 0.2 or 0.3 M nonpermeating raffinose with either permeating glucose, fructose, propylene glycol, ethylene glycol, glycerol, or sodium pyruvate in CD-1, C3FeB6F1/J, B6129SF1, C57BL/6NCrIBR, 129S/SvPaslco, and DBA/2NCrIBR mice. Sperm-assessment parameters included progressive motility, plasma membrane integrity (SYBR-14 + Pl), in vitro fertilization rate, and in vitro embryo development rate to blastocyst. DNA content analysis of sperm was measured by the sperm chromatin structure assay (SCSA). 0.3 M raffinose with 0.1 M fructose significantly improved post-thaw sperm-assessment parameters for CD-1, C3B6F1, B6129SF1 mice (P < 0.05-0.01), whereas 0.2 M raffinose with 0.1 M glycerol or 0.1 M fructose enhanced sperm assessment values for C57BL/6 and 129S mice (P < 0.01), compared to 0.3 M raffinose alone. DNA fragmentation during cryopreservation was significantly increased in all strains evaluated when compared with fresh control sperm in a strain- dependent manner (P < 0.01). Supplementation with permeating glycerol or fructose to the cryoprotectant(CPA) solution showed a significant protective effect to DNA integrity when cryopreserving sperm from C57BL/6 and 129S mice. Damage to sperm DNA significantly decreased the rate of in vitro embryo development to blastocyst in C57BL/6 mice. The type of monosaccharide sugar or polyols, CPA molarity, and combination of permeating and nonpermeating cryoprotectant are significant factors for improving progressive motility, plasma membrane integrity, DNA integrity, in vitro fertilization rate, and in vitro embryo development rate to blastocyst in cryopreserved mouse sperm.