Spindle transfer can restore developmental capability of mammalian oocytes damaged by oxidative stress

Abstract

Oxidative stress is suggested responsible for the dysfunctional mitochondria and the abnormal meiotic spindle in aged oocytes. The objective of this study was to investigate the effect of oxidative stress on cellular organelles and developmental potency of mammalian mature oocytes, and also to assess whether spindle transfer (ST) can restore the damage induced by oxidative stress. Changes in the meiotic spindles, mitochondrial function and developmental potency of the oxidatively damaged oocytes were studied. The ability of ST on restoring the developmental potential of the damaged oocytes was assessed. Mouse MII oocytes were treated with 50 or 100 μM H2O2 for 15 and 30 min. Morphology of the spindle chromosome complex was studied immunohistochemically, while mitochondrial membrane potential was evaluated with JC-1 dye. The spindle of a damaged oocyte was isolated and inserted subzonally into an enucleated intact oocyte with inactivated Sendai virus. The reconstituted oocytes were ICSI fertilized and cultured for 4 days. The length of the H2O2 damaged spindle was remarkably shorter than the control (21.8±0.5 μm vs. 24.4±0.6 μm). In addition, diamond shaped spindle was frequently observed in the damaged oocytes in comparison to the typical barrel shaped control spindle. These changes were dose dependent, such as the exposure time and the concentration of H2O2. JC-1 staining revealed the immediate and sustained reduction in the mitochondrial membrane potential after the damage. When the damaged oocytes were ICSI inseminated, the first cleavage rate was only 40%, and none reached to the blastocyst stage. Following ST of the damaged spindle into intact ooplasm, all cleaved and 16.7% formed blastocyst. The H2O2 exposure affected the spindle morphology, impaired the mitochondrial function, and compromised the development of mouse oocytes. ST was able to restore the developmental ability of the oxidatively stressed oocytes.