259 The Role of Extracellular Vesicles in Mitigating the Effect of Heat Stress

Abstract

Abstract Environmental heat stress negatively affects the fertility of dairy cows by disrupting reproductive processes spanning from follicular development to maternal recognition of pregnancy. Investigation of cellular level responses to stress would contribute to the understanding of the mechanism behind survival responses. Extracellular vesicles (EVs), which carry biologically active signaling molecules, are reported to play a significant role in the cellular response to stress. They are produced by almost all types of cells and abundantly present in various biological fluids including follicular fluid, oviductal fluid, uterine fluids in vivo, and in spent culture media in vitro. Those EV-coupled molecular signals in biological fluids are indicative of the physiological status of the cells of their origin. This has been evidenced by the presence of EV-mediated miRNA signals in follicular fluid associated with the metabolic status of cows. Recent studies revealed the potential role of follicular fluid EVs in carrying molecular signals which can reverse or protect the damage incurred by heat stress in bovine oocytes. In addition to cellular defense responses (activation of HSP70 and HSP90, NRF2 and GRP78 & 94), bovine granulosa cells exposed to heat stress in vitro released EVs enriched with selected mRNA (HSP90 and SOD1) and miRNAs. Among others, miR-1246, miR-374a, and miR-2904 were found to be enriched in EVs released from granulosa cells exposed to thermal stress. Those miRNAs were found to regulate pathways related to heat and endoplasmic reticulum stress responses. The priming of recipient bovine granulosa cells by EVs derived from heat-stressed granulosa cells induced tolerance against recurrent heat stress. Collectively, EV-mediated molecular signals would provide another layer of cell-to-cell communication and deliver protective signals against oxidative stress to recipient cells. This would provide opportunities for future potential application of EVs in tackling oxidative stress-associated fertility problems in humans and animals.