Granulosa Cells from Emerged Antral Follicles of the Bovine Ovary Initiate Inflammation in Response to Bacterial Pathogen-Associated Molecular Patterns via Toll-Like Receptor Pathways

Bacterial infections of the uterus or mammary gland commonly perturb ovarian antral follicle growth and function, causing infertility in cattle. Cells of the innate immune system use Toll-like receptors (TLRs) TLR2, TLR4, and TLR5 to recognize pathogen-associated molecular patterns (PAMPs) of bacteria, leading to production of inflammatory mediators, such as IL-1beta, IL-6, and IL-8. The present study examined whether granulosa cells from emerged antral follicles have functional responses to typical bacterial PAMPs. Granulosa cells from emerged bovine antral follicles expressed mRNA for all 10 TLRs. Cellular expression of mRNA for the cytokines IL1B, IL6, IL10, and TNF, and chemokines IL8 and CCL5, increased after treatment with synthetic bacterial lipoprotein binding TLR2, lipopolysaccharide binding TLR4, or flagellin binding TLR5. Supernatants of granulosa cells accumulated IL-1beta, IL-6, and IL-8 protein in a concentration-dependent manner when treated with lipoprotein or lipopolysaccharide, but not flagellin. Accumulation of IL6 in response to lipoprotein and lipopolysaccharide was attenuated using siRNA targeting TLR2 and TLR4, respectively. Granulosa cells increased phosphorylation of mitogen-activated protein kinase (MAPK) 14 and MAPK3/1 within 30 min of treatment with lipopolysaccharide or lipoprotein, and inhibitors targeting MAPK14 reduced the accumulation of IL-6 in response to the PAMPs. Treatment with hormones follicle-stimulating hormone, luteinizing hormone, estradiol, or progesterone did not significantly affect granulosa cell responses to PAMPs. However, epidermal growth factor enhanced IL-6 accumulation in response to lipoprotein and inhibiting epidermal growth factor receptor (EGFR) abrogated the effect, whereas lipoprotein increased granulosa cell EGFR mRNA expression. In conclusion, bovine granulosa cells from emerged follicles sense bacterial PAMPs and initiate inflammatory responses via TLR2 and TLR4 pathways.