Toll-Like Receptor 4 Inhibits Estradiol Secretion via NF-κB Signaling in Human Granulosa Cells

Area of Science:

• Reproductive Biology
• Immunology
• Endocrinology

Background:

• Toll-like receptor 4 (TLR4) is implicated in follicular development, but its specific role in granulosa cells is not well-defined.
• Limited data exist on TLR4's function within the ovarian follicle, necessitating further investigation into its impact on steroidogenesis.

Purpose of the Study:

• To investigate the effects of TLR4 activation and inhibition on steroidogenesis in human granulosa cells.
• To elucidate the signaling pathways involved in TLR4-mediated regulation of steroidogenesis and follicular function.

Main Methods:

• Immunohistochemistry and immunofluorescence were used to detect TLR4 expression in mouse ovaries and human granulosa-like tumor cells (KGN).
• TLR4 activation using lipopolysaccharides (LPS) and inhibition were performed in KGN cells to assess effects on steroidogenic gene expression (CYP19A1, FSHR, StAR) and estradiol (E2) secretion.
• Signaling pathway activation (p38, JNK, NF-κB) was analyzed, and the role of NF-κB was confirmed using an antagonist.

Main Results:

• TLR4 expression was observed in mouse ovarian follicles and human KGN cells.
• LPS treatment inhibited follicular development and E2 synthesis in mice.
• In KGN cells, TLR4 activation suppressed CYP19A1, FSHR, and StAR expression and E2 secretion, while TLR4 inhibition reversed these effects.
• TLR4 activation induced p38, JNK, and NF-κB signaling, and NF-κB inhibition prevented the suppression of CYP19A1 and E2 secretion.

Conclusions:

• TLR4 activation suppresses CYP19A1 expression and estradiol secretion in human granulosa cells, primarily through the NF-κB signaling pathway.
• These findings highlight a significant role for TLR4 in regulating ovarian steroidogenesis and have implications for understanding ovarian pathophysiology.