Abstract
Hyperosmotic stress may induce apoptosis of different cells. However, oocytes show tolerance to osmotic stress during cryopreservation by vitrification, which is an assisted reproductive technique. The underlying mechanism is still not understood. Here, we demonstrated that hyperosmosis produced by high concentrations of cryoprotectants, including DMSO, ethylene glycol and sucrose, significantly upregulated the protein levels of aquaporin (AQP) 7, but not AQP3 and AQP9, in mouse oocytes. Knockdown of AQP7 expression by siRNA-injection significantly reduced the survival of oocytes after vitrification. In oocytes, AQP7 was shown to bind with F-actin, a protein involved in almost all biological events. Moreover, we found that hyperosmosis could upregulate the phosphorylation levels of CPE-binding protein (CPEB) and Aurora A. Inhibition of the PI3K and PKC pathways blocked the hyperosmosis-induced upregulation of AQP7 and the phosphorylation of CPEB and Aurora A in oocytes. In conclusion, hyperosmosis could upregulate the expression of AQP7 via Aurora A/CPEB phosphorylation mediated by the PI3K and PKC pathways, and upregulation of AQP7 plays an important role in improving of tolerance to hyperosmotic stress and survival of oocytes during cryopreservation by vitrification.
Highlights
Hyperosmotic stress may induce apoptosis of different cells
We found that a hyperosmotic cryoprotectant solution containing Ethylene glycol (EG), DMSO and sucrose, respectively, increase expression of AQP7 in oocytes, but not the expression of AQP3 and AQP9, which are the same subtype as AQP7
The results suggest that hyperosmotic stress may selectively upregulate AQP7 expression in mouse oocytes, and AQP7 may play a main function in water and cryoprotectant transport during oocyte cryopreservation
Summary
Hyperosmotic stress may induce apoptosis of different cells. oocytes show tolerance to osmotic stress during cryopreservation by vitrification, which is an assisted reproductive technique. We demonstrated that hyperosmosis produced by high concentrations of cryoprotectants, including DMSO, ethylene glycol and sucrose, significantly upregulated the protein levels of aquaporin (AQP) 7, but not AQP3 and AQP9, in mouse oocytes. Hyperosmosis could upregulate the expression of AQP7 via Aurora A/CPEB phosphorylation mediated by the PI3K and PKC pathways, and upregulation of AQP7 plays an important role in improving of tolerance to hyperosmotic stress and survival of oocytes during cryopreservation by vitrification. Human oocyte cryopreservation is an important technology in assisted reproduction, and may help to preserve the future fertility of women who face cancer/extirpative therapy or who want to extend their childbearing years. Our previous study demonstrated that cryoprotectants, including DMSO and EG, might upregulate AQP7 protein expression in mouse oocytes during cryopreservation[12].
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