Abstract/Summary

Pro-inflammatory cytokines secreted by macrophages and other cell-types are implicated as intra-ovarian factors affecting different aspects of ovarian function including follicle and corpus luteum 'turnover', steroidogenesis and angiogenesis. Here, we compared granulosal (GC) and thecal (TC) expression of TNF, IL6 and their receptors (TNFR1, TNFRSF1B, IL6R) during bovine antral follicle development; all five mRNA transcripts were detected in both GC and TC and statistically significant cell-type and follicle stage-related differences were evident. Since few studies have examined cytokine actions on TC steroidogenesis, we cultured TC under conditions that retain a non-luteinized 'follicular' phenotype and treated them with TNFα and IL6 under basal and LH-stimulated conditions. Both TNFα and IL6 suppressed androgen secretion concomitantly with CYP17A1 and LHCGR mRNA expression. In addition, TNFα reduced INSL3, HSD3B1 and NOS3 expression but increased NOS2 expression. IL6 also reduced LHCGR and STAR expression but did not affect HSD3B1, INSL3, NOS2 or NOS3 expression. Since macrophages are a prominent source of these cytokines in vivo we next co-cultured TC with macrophages and observed an abolition of LH-induced androgen production accompanied by a reduction in CYP17A1, INSL3, LHCGR, STAR, CYP11A1 and HSD3B1 expression. Exposure of TC to bacterial lipopolysaccharide also blocked LH-induced androgen secretion, an effect reduced by a toll-like receptor blocker (TAK242). Collectively, the results support an inhibitory action of macrophages on thecal androgen production, likely mediated by their secretion of pro-inflammatory cytokines that downregulate expression of LHCGR, CYP17A1 and INSL3. Bovine theca interna cells can also detect and respond directly to lipopolysaccharide.