Abstract
Autophagy is a physiological mechanism that can be activated under stress conditions. However, the role of autophagy during oocyte maturation has been poorly investigated. Therefore, this study characterized the role of autophagy on developmental competence and gene expression of bovine oocytes exposed to heat shock (HS). Cumulus-oocyte-complexes (COCs) were matured at Control (38.5 °C) and HS (41 °C) temperatures in the presence of 0 and 10 mM 3-methyladenine (3MA; autophagy inhibitor). Western blotting analysis revealed that HS increased autophagy marker LC3-II/LC3-I ratio in oocytes. However, there was no effect of temperature for oocytes matured with 3MA. On cumulus cells, 3MA reduced LC3-II/LC3-I ratio regardless of temperature. Inhibition of autophagy during IVM of heat-shocked oocytes (3MA-41 °C) reduced cleavage and blastocyst rates compared to standard in vitro matured heat-shocked oocytes (IVM-41 °C). Therefore, the magnitude of HS detrimental effects was greater in the presence of autophagy inhibitor. Oocyte maturation under 3MA-41 °C reduced mRNA abundance for genes related to energy metabolism (MTIF3), heat shock response (HSF1), and oocyte maturation (HAS2 and GREM1). In conclusion, autophagy is a stress response induced on heat shocked oocytes. Inhibition of autophagy modulated key functional processes rendering the oocyte more susceptible to the deleterious effects of heat shock.
Highlights
Autophagy is a physiological mechanism that can be activated under stress conditions
Experiment 1: Autophagy induction on bovine oocytes and cumulus cells exposed to heat shock during in vitro maturation (IVM)
Autophagy acted as a pro-survival response during oocyte maturation as the developmental capacity of heat-shocked oocytes was markedly reduced in the presence of the autophagy inhibitor
Summary
Autophagy is a physiological mechanism that can be activated under stress conditions. Autophagy is a stress response induced on heat shocked oocytes. Inhibition of autophagy modulated key functional processes rendering the oocyte more susceptible to the deleterious effects of heat shock. Autophagy is a programmed lysosomal process that degrades damaged or unnecessary cellular proteins, lipids, DNA, RNA, and organelles for recycling amino acids, fatty acids, and nucleosides to act as cellular building blocks for anabolic processes[1,2,3]. This event is involved in development, differentiation, immunity, aging, and cell death[2]. The same treatments had no effect from the four-cell to the blastocyst stage[23], demonstrating that autophagy is only required for early stages of preimplantation development
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