PSX-A-19 - Late-Breaking: Potential application of granulosa cell derived extracellular vesicles to mitigate the effects of heat stress in bovine oocytes

Environmental heat stress negatively affects reproductive efficiency by disrupting follicular development, ultimately compromising gamete competency in cattle. Recently, outlined through the bystander effect, granulosa cell derived extracellular vesicles (EVs) were found to suppress negative effects of recurrent heat stress in recipient bovine granulosa cells. Here, we aimed to assess the effects of supplementing granulosa cell derived EVs during bovine in vitro maturation (IVM) on developmental competence following thermal stress. For this, we modeled a cell culture protocol to generate EVs from bovine granulosa cells subjected to differing ambient temperatures, 38.5°C (body temperature) vs. 42°C (heat stress). At the time of IVM, experimental cumulus oocyte complexes (COCs) were arranged in a 2 x 3 factorial design for temperature (38.5°C or 41°C) versus EV supplementation (normal EVs, stressed EVs and non-supplemented controls) at 20% of the IVM media. Following an initial 8h priming period, half the COCs were subjected to heat shock, the others remained at normal temperature to complete IVM. Results indicate that EV supplementation increased cumulus expansion and the expression of cumulus expansion genes (PTX3, PTGS2 and EGFR). Cleavage rates were increased when supplemented with normal (90.2±1.4%; P = 0.023) or stressed (89.8±2.9%; P = 0.029) EVs, compared to the non-supplemented control (80.5±1.5%) under non-thermal conditions. Similarly, exposure to recurrent thermal stress, cleavage rates were (91±0.9%) and (89±0.6%) when supplemented with normal and stressed EVs respectively, compared to the non-supplemented control (88.5±2.5%). In the absence of exposure to recurrent heat stress, blastocysts rates were (32.4±3.5%) and (31.3±2.9%) when COCs were supplemented with normal and stressed EVs, compared to the control (20.7±4.4%). Blastocysts rates were (23.3±4.7%) and (22.5±3.2%) when COCs were supplemented with normal and stressed EVs, compared to the control (15.5±4.5%) when exposed to recurrent thermal stress. In conclusion, granulosa cell derived EVs have potential to induce oocyte tolerance against recurrent thermal stress.