Lipopolysaccharide (LPS) inhibits steroid production in theca cells of bovine follicles in vitro: distinct effect of LPS on theca cell function in pre- and post-selection follicles.

In postpartum dairy cows, lipopolysaccharide (LPS) derived from gram-negative bacteria such as Escherichia coli causes uterine inflammation and leads to ovarian dysfunction. The aim of this study was to determine the effect of LPS on steroid production in bovine theca cells at different stages of follicular development. Theca cells isolated from pre- and post-selection follicles (PRFs, <8.5 mm in diameter, and POFs, >8.5 mm in diameter, respectively) of bovine ovaries were exposed to LPS under luteinizing hormone (LH) conditions, estradiol (E2) conditions or both conditions in vitro. Bovine theca cells expressed the LPS receptor gene complex: Toll-like receptor 4 (TLR4), CD14 and MD2. LPS suppressed progesterone (P4) and androstenedione (A4) production with downregulation of steroidogenic enzyme transcripts when theca cells were stimulated with LH. By contrast, LPS did not affect P4 or A4 production when theca cells were stimulated with E2. P4 and A4 production in theca cells from PRFs was suppressed by LPS as early as at 48 h of culture, whereas the effect of LPS on theca cells from POFs was observed at 96 h of culture. The results demonstrate that LPS inhibits steroid production in theca cells under LH conditions. Moreover, theca cells from POFs showed a slower response to LPS compared with that of theca cells from PRFs, which might imply a distinct effect of LPS on follicles at different developmental stages. These findings suggest a possible mechanism of ovarian dysfunction and subsequent infertility in cows with endometritis.

Lipopolysaccharide in ovarian follicular fluid influences the steroid production in large follicles of dairy cows.

In postpartum dairy cows, various inflammatory diseases depress reproductive performance. Lipopolysaccharide (LPS) derived from infections of the uterus or mammary gland with Gram-negative bacteria was shown to suppress steroid production in the granulosa cells of follicles in vitro. The aim of the study was to investigate the relationship between LPS in ovarian follicular fluid and steroidogenesis by the theca and granulosa cells of the large follicles in vivo. Bovine ovaries were collected from a slaughterhouse, and the largest (F1) and the second largest (F2) follicles were used (>8 mm in diameter, n=38). LPS concentration in the follicular fluid was measured using quantitative kinetic assay. Follicular steroidogenesis was evaluated by measuring the estradiol (E2) and progesterone (P4) concentration in follicular fluid and by analysing transcription levels of steroidogenesis-related genes in theca and granulosa cells. LPS concentration detected in follicular fluid ranged from 0.2 to 2.0 EU/mL. In follicles with a high level of LPS (>0.5 EU/mL, n=15), the concentration of E2 was lower and that of P4 was higher when compared to those in follicles with a low level of LPS (<0.5 EU/mL, n=23), which was observed both in F1 and F2 follicles. Furthermore, in follicles with a high level of LPS, transcripts of steroidogenic enzymes such as CYP17 and P450arom were lower. In those follicles, the expression of caspase-3 was high, suggesting an association with follicular atresia. These findings indicate that LPS present in follicular fluid may cause ovarian dysfunction by inhibiting follicular activity.