Transforming growth factor-β (TGFβ) and its signaling components in peri-ovulatory pig follicles

The present studies investigated the hypothesis that TGFβ plays a role in mediating LH/hCG-induced maturation, ovulation and/or luteinization of follicles in the pig. In Experiment 1, the temporal and spatial gene expression patterns of TGFβ signaling components were examined in pig follicles which had been induced to ovulate and luteinize in vivo by hCG treatment, or by the LH-surge. Pre-pubertal pigs were injected with PG-600 followed by hCG, and ovaries were collected surgically at 0, 1, 12, 24 and 48 h post-hCG. Post-ovulatory follicles were also collected from cycling gilts on Day 4 (D4) of the estrous cycle. Pre- and post-ovulatory follicles were used for the measurement of mRNA (PCR) and protein (Western blots) abundance and for protein localization by immunohistochemistry (IHC). Steady state amounts of mRNA for TGFβ3 and TGFβR2 were increased (P < 0.05, as compared to 0 h) at 12 h and on D4, respectively, while TGFβ2 protein showed a tendency to increase on D4. TGFβ signaling components did not change significantly. By IHC, the localization of TGFβ components was as follows: pre-ovulatory follicles; TGFβ1 – granulosa cells (GC), TGFβ2 – theca cells (TC), TGFβR1 and 2 – GC and TC: post-ovulatory follicles; TGFβ1 and 2 and TGFβR1 and 2 – luteinizing TC and GC. In Experiment 2, TGFβ1 (1–100 ng/ml) alone had no significant effect on progesterone (P4) secretion by pig GC in culture. Furthermore, while LH + IGF-1 (positive control) stimulated P4 ∼10-fold, TGFβ at 10 and 100 ng/ml added in combination with LH + IGF-1, had no effect on P4 accumulation. In conclusion, data from the present study on temporal and spatial patterns of expression of the TGFβ-system suggest that TGFβ may play a role in the overall process of luteinization, but it appears not to influence steroidogenesis in luteinizing pig follicles.