Effects of bone morphogenetic protein 4, gremlin, and connective tissue growth factor on estradiol and progesterone production by bovine granulosa cells
Abstract Bone morphogenetic proteins (BMP) are members of the transforming growth factor β (TGFβ) family of proteins that have been implicated in the paracrine regulation of granulosa cell (GC) function, but whether responses to BMPs change with follicular size or interact with connective tissue growth factor (CTGF) or BMP antagonists (e.g., gremlin) to directly affect GC function of cattle is unknown. Therefore, to determine the effects of BMP4 on proliferation and steroidogenesis of GC and its interaction with gremlin or CTGF, experiments were conducted using bovine GC cultures. In vitro, BMP4 (30 ng/mL) inhibited (P < 0.05) follicle-stimulating hormone (FSH) plus insulin-like growth factor 1 (IGF1)-induced progesterone and estradiol production by large- and small-follicle GC but the inhibitory effect of BMP4 on estradiol production was much more pronounced in large-follicle GC. In small-follicle GC, BMP4 had no effect (P > 0.10) on IGF1-induced proliferation, but gremlin inhibited (P < 0.05) cell proliferation and estradiol and progesterone production in IGF1 plus FSH-treated GC. In large-follicle GC, BMP4 (10-30 ng/mL) increased (P < 0.05) GC numbers and gremlin (100 ng/mL) blocked this effect. In large-follicle GC, CTGF inhibited (P < 0.05) FSH plus IGF1-induced progesterone and estradiol production, and CTGF blocked the stimulatory effect of BMP4 on GC proliferation. These results indicate that BMP4, gremlin, and CTGF inhibit GC aromatase activity and progesterone production. Also, the stimulatory effect of BMP4 on GC proliferation and the inhibitory effects of BMP4 on GC steroidogenesis are more pronounced in large versus small follicles.