Transcriptome response of granulosa cells to seasonal heat stress in beef cows
Investigation of cellular responses to thermal heat stress can lead to identifying novel targets of intervention to tackle the increasing fertility decline due to climate change-associated seasonal heat stress. We aimed to study the response of granulosa cells to seasonal thermal stress. Dry beef cows (n=11) were kept together during the study and subjected to synchronization and stimulation for follicular dynamics. Ovum pick-up (OPU) was conducted on all animals in the winter and summer. Once OPU-fluid settled, cumulus-oocyte-complexes (COCs) and granulosa cells were isolated from the OPU fluid and stored in a -80 freezer after snap freezing. In addition, blood samples and rectal temperature data were collected on each OPU. Environmental data were collected daily for three weeks before each OPU using the Florida Automated Weather Network. Data were analyzed using SAS. Data are presented as mean ± standard error of the mean. RNA was extracted from five pools of granulosa cells followed by library preparation and sequencing (NovaSeq; Illumina). As expected, environmental conditions were contrasting: average air temperature (11.5°C vs. 27.5°C), average max air temperature (16.9°C vs. 33.7°C), relative humidity (83.5% vs. 82.3%), and temperature-humidity index (53.39 vs. 79.16) for winter and summer, respectively. The average rectal temperature was higher (P = 0.03) in summer (39.2 ± 0.2°C) than in winter (38.8 ± 0.2°C). Of the total differentially expressed genes, granulosa cells during summer showed up and downregulation of 1083 and 1126 transcripts, respectively compared to the winter season (Fold Change = -2 or = 2 and FDR p-value = 0.05). Many of the downregulated transcripts were found to be involved in the inhibition of immunological pathways such as activation of lymphatic system cells and activation of lymphocytes. In conclusion, exposure of cows to thermal stress can induce significant alteration in the transcriptome of granulosa cells which may have a negative impact on follicular physiology. Overall design: Multiparous angus dry beef cows (n?=?11) were kept together during the study and subjected to synchronisation and stimulation of follicular growth using a 5-day CIDR and follicle-stimulating hormone (FSH) protocol. Ovum pick-up (OPU) was conducted on all animals in the winter (January) and summer (August). Granulosa cells (GCs) were isolated from the follicular fluid aspirated during the OPU procedure, snap frozen, and stored at -80?°C until further use for RNA sequencing