Abstract
Mechanisms for post-maturation oocyte aging (PMOA) are not fully understood, and whether autophagy plays any role in PMOA is unknown. To explore the role of autophagy in PMOA, expression of autophagosomes and effects of the autophagy (macro-autophagy) activity on PMOA were observed in mouse oocytes. Oocyte activation rates and active caspase-3 levels increased continuously from 0 to 18 h of in vitro aging. While levels of microtubule-associated protein light chain 3 (LC3)-II increased up to 12 h and decreased thereafter, contents of p62 decreased from 0 to 12 h and then elevated to basal level by 18 h. However, the LC3-II/I ratio remained unchanged following aging in different media or for different times. During in vitro aging up to 12 h, upregulating autophagy with rapamycin or lithium chloride decreased activation susceptibility, cytoplasmic calcium, p62 contents, oxidative stress, caspase-3 activation and cytoplasmic fragmentation while increasing developmental competence, LC3-II contents, LC3-II/I ratio, mitochondrial membrane potential, spindle/chromosome integrity and normal cortical granule distribution. Downregulating autophagy with 3-methyladenine (3-MA) produced opposite effects on all these parameters except cytoplasmic fragmentation. After 12 h of aging culture, however, regulating autophagy with either rapamycin/lithium chloride or 3-MA had no impact on oocyte activation susceptibility. It is concluded that autophagy plays an important role in regulating PMOA. Thus, during the early stage of PMOA, autophagy increases as an adaptive response to prevent further apoptosis, but by the late stage of PMOA, the activation of more caspases blocks the autophagic process leading to severer apoptosis.
Highlights
If not fertilized or activated in time, mature oocytes undergo a time-dependent process of post-maturation oocyte aging (PMOA)[1,2,3,4,5,6]
While the highest activation rate was observed in oocytes aging in the FasL-rich conditioned medium (FCM), the lowest was in the newly ovulated control oocytes and in oocytes aging in CZB medium supplemented with MG132, with that in oocytes aging in CZB alone in between (Fig. 1a)
The highest level of light chain 3 (LC3)-II was detected in oocytes aging in FCM, the lowest was in control oocytes, with that in oocytes aging in CZB alone and in CZB + MG132 in between (Fig. 1b)
Summary
If not fertilized or activated in time, mature oocytes undergo a time-dependent process of post-maturation oocyte aging (PMOA)[1,2,3,4,5,6]. The term PMOA is used instead of post-ovulatory oocyte aging because it covers both in vivo and in vitro matured oocytes. Studies have shown that PMOA leads to apoptosis. The expression of the antiapoptotic protein BCL2 was gradually reduced during postovulatory oocyte aging[12,13,14]. Fertilization-like Ca2+ responses induced by injection of sperm cytosolic factor triggered cell death, rather than activation, in aged oocytes[15]. The aged oocytes exhibited extensive cytoplasmic and DNA fragmentation and activation of protein caspases[15,16]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
