Isorhamnetin protects porcine oocytes from heat stress by maintaining cumulus cells-oocyte communications.

Because of the increased global warming, heat stress (HS) damage to animals reproduction has become an inevitable and urgent problem to be solved. The disruption of oocyte maturation caused by HS is considered the main cause of impaired reproductive ability. Particularly, porcine oocytes are more susceptible to HS damage due to their sensitivity to temperature changes and physiological characteristics of high lipid droplet content. At present, there is no effective antidote for HS damage. In mammalian ovaries, maintaining cumulus cells-oocyte communications promotes oocyte development. Isorhamnetin has various pharmacological activities. However, the effect of isorhamnetin in HS-induced oocyte damage and cumulus cells-oocyte communications are still unclear. Oocytes were cultured at 39 °C (control group) or 41.5 °C (HS group) for 44 h. Oocytes were treated with different concentrations isorhamnetin (5, 10, 20 and 30 μM) respectively, during heat stress. Nuclear maturation, blastocyst development, cumulus cells-oocyte communications, COCs function, ROS levels, mitochondrial function, apoptosis, calcium ion level, and endoplasmic reticulum distribution of oocytes were detected. Our study showed that isorhamnetin therapy prevented HS-damaged oocyte development. Isorhamnetin enhanced nuclear maturation and blastocyst development inhibited by HS. Meanwhile, isorhamnetin prevented cumulus cells-oocyte communications and cumulus cell proliferation damaged by HS. Isorhamnetin alleviated HS-induced mitochondrial dysfunction in porcine oocytes by maintaining cumulus cells-oocyte communications, thereby reducing ROS accumulation and enhancing mitochondrial function. Isorhamnetin inhibited HS-induced endoplasmic reticulum (ER) stress by decreasing Ca2+ levels and increasing normal ER distribution, which was blocked by carbenoxolone. These results suggest that maintaining cumulus cells-oocyte communications is an important mechanism by which isorhamnetin protects oocytes from HS-damage. Collectively, our data indicate that isorhamnetin enhances HS-damaged oocyte development by maintaining cumulus cells-oocyte communications to inhibit oxidative stress, apoptosis, mitochondrial dysregulation and ER stress, providing a new strategy to solve the threat of HS to animal and human reproduction.