A low level of the MMP-2 inhibitor TIMP-2 was observed in all ovarian cell types of normal and miniature pigs, except in the theca externa. In the theca interna of the developing follicles, TIMP-2 expression was higher in miniature pigs, whereas in the granulosa cells of the Graafian follicles, it was higher in normal pigs. After ovulation, TIMP-2 expression was relatively lower in the ovulated follicles of normal pigs than in those of miniature pigs. In miniature pigs, TIMP-2 was strongly expressed in theca lutein cells, while expression was lower in granulosa lutein cells (Fig. 4b).
Although MMP-9 was expressed in the granulosa cells of the developmental follicles of normal pigs, its expression was lower in the theca interna and externa. MMP-9 was highly expressed in all cells of the Graafian follicle, especially in the granulosa cells. Expression was low in the granulosa after ovulation but was high in the theca lutein and theca externa. MMP-9 was also highly expressed in the Graafian follicles of normal pigs. Overall, during follicular development MMP-9 expression was lower in all examined tissues of miniature pigs compared to those of normal pigs. In the granulosa lutein of ovulated follicles, the expression pattern was similar in both breeds, while in the theca lutein cells, a slightly higher expression was noted in miniature pigs (Fig. 4c).
The expression of the MMP-9 inhibitor TIMP-3 was not as strong as that of TIMP-2 in both breeds. Nevertheless, TIMP-3 expression in the theca interna of the developing follicles was higher in miniature pigs than in normal pigs, whereas in the Graafian follicles, it was similar for both groups. After ovulation, TIMP-3 expression was higher in all types of follicular cells (theca externa, theca lutein, and granulosa lutein) in miniature pigs. Overall, TIMP-3 was more prominently expressed in miniature pigs than in normal pigs (Fig. 4d).