Hydroxyapatite nanoparticle improves ovine oocyte developmental capacity by alleviating oxidative stress in response to vitrification stimuli

The wide application of ovine oocyte vitrification is limited by its relatively low efficiency. Nanoparticle is potentially to be used in cryopreservation technology for its unique characteristics with high biocompatibility, potent antioxidant property as well as superiority in membrane permeation and heat transduction. However, the effect of nanoparticle on ovine oocyte cryopreservation as well as the underlying mechanism has not been systematically evaluated. The objective of this study was to investigate the impact of nanoparticles on ovine oocytes cryopreservation and further identify the underlying mechanism. Firstly, the effects of Hydroxyapatite (HA) and Fe₃O₄ nanoparticles on the developmental potential of vitrified ovine oocytes were determined, and the results showed that neither HA (VC = 85.95 ± 6.23 % vs. VH = 92.47 ± 8.11 %, P > 0.05) nor Fe₃O₄ (VC = 85.95 ± 6.23 % vs. VF = 89.39 ± 6.32 %, P > 0.05) had adverse effect on the survival rate of vitrified-thawed oocytes. Notably, both HA (VC = 77.78 ± 0.09 % vs. VH = 44.00 ± 0.09 %, P＜0.01) and Fe₃O₄ (VC = 77.78 ± 0.09 % vs. VF = 51.67 ± 0.15 %, P＜0.01) nanoparticles effectively reduced the level of oocyte apoptosis after freezing and thawing. What's more, HA could significantly improve the cleavage rate of frozen oocytes (VC = 33.79 ± 2.83 % vs. VH = 59.54 ± 4.13 %, P＜0.05). Moreover, reduced reactive oxygen species (ROS) level (VC = 13.66 ± 0.47 vs. VH = 12.61 ± 0.53, P < 0.05), increased glutathione (GSH) content (VC = 60.69 ± 7.89 vs. VH = 87.92 ± 1.05, P < 0.05) and elevated mitochondrial membrane potential (MMP) level (VC = 1.43 ± 0.04 vs. VH = 1.63 ± 0.01，P＜0.01) were observed in oocytes treated with HA nanoparticles when compared with that of the control group. Furthermore, Smart-RNA sequence technology was utilized to identify differentially expressed mRNAs (DEMs) induced by nanoparticles during cryopreservation. When compared with the control counterparts, a total of 721 DEMs (309 up-regulated and 412 down-regulated mRNAs) were identified in oocytes treated with HA, while 702 DEMs (480 up-regulated and 222 down-regulated mRNAs) were identified in oocytes treated with Fe₃O₄. A comparison of DEMs showed that total 692 mRNAs were expressed in oocytes treated with HA and Fe₃O₄. Notably, we discovered that 15 mRNAs were specially highly expressed in oocytes treated with HA, and Focal adhesion signaling pathway mainly contributed to the improved ovine oocyte quality after vitrification by alleviating oxidative stress.