Toll-like receptor signaling in hen ovarian granulosa cells is dependent on stage of follicle maturation

Abstract

The recent identification of toll-like receptor (TLR) signaling within ovarian granulosa cells has broad implications for ovarian physiology. Functions of TLRs within granulosa cells of the laying hen are of particular interest due to the method of transovarian transmission of Salmonella enteritidis, which results in egg contamination. This study utilized hen granulosa cells to evaluate the expression and function of Gallus TLR-signaling at distinct stages of follicular maturity. Data presented herein demonstrate the presence of TLR2, TLR4, and TLR15 mRNAs in undifferentiated granulosa cells from prehierarchal follicles and differentiated granulosa cells from preovulatory follicles, together with mRNAs encoding adaptor proteins and signaling components required for TLR signaling gene. Treatment with lipopolysaccharide (LPS) or LH, in vitro, led to the differential regulation of TLRs based on the stage of follicle maturation, with the largest (F1) follicle granulosa cells having the most rapid response. Furthermore, treatment with LPS resulted in attenuation of agonist-induced progesterone synthesis in undifferentiated, but not differentiated, granulosa cells. Additionally, undifferentiated granulosa cells were significantly more sensitive to LPS-induced apoptosis than differentiated granulosa cells from the F1 follicle. Together, these data provide evidence for a complete and functional TLR signaling pathway in hen granulosa cells, with effects on steroidogenesis and cell viability dependent upon stage of maturation. These differences may reflect the susceptibility of granulosa cells at early stages of maturation to undergo apoptosis in response to select pathogenic stimuli, thus attenuating transovarian transmission, whereas granulosa cells from preovulatory follicles are comparably resistant to LPS-mediated apoptosis.