Minireview

Proteolytic Degradation of Insulin-Like Growth Factor Binding Proteins by Ovarian Follicles: A Control Mechanism for Selection of Dominant Follicles

Abstract
This review summarizes evidence for the role of proteolytic enzymes that degrade and inactivate insulin-like growth factor binding proteins (IGFBP) during follicular development in mammals. In some species (e.g., bovine), evidence indicates that decreases in IGFBP-4 and -5 levels in estrogen dominant preovulatory follicles are likely due, in part, to increased protease activity, whereas lower levels of IGFBP-2 are not due to increased proteolysis. Increased IGFBP-4 and -5 protease along with lower amounts of IGFBP-4 binding activity and greater amounts of free IGF-I are some of the earliest developmental changes documented in bovine growing antral follicles. This protease activity has recently been ascribed to serine metalloprotease(s) including pregnancy associated plasma protein-A (PAPP-A), which was first detected in human follicular fluid nearly 20 years ago. Other recent studies verified the presence of PAPP-A mRNA in granulosa cells of humans, monkeys, cattle, mice, and pigs. Increases in the amount of PAPP-A mRNA in granulosa cells during follicular development occurs in some but not all species, indicating that other proteases or protease inhibitors may be involved in IGFBP degradation. Whether the hormonal control of PAPP-A production/activity by the ovary differs between monotocous and polytocous animals will require further study. These protease-induced decreases in IGFBP-4 and -5 likely cause increased levels of bioavailable (or "free") IGFs that stimulate steroidogenesis and mitogenesis in developing dominant follicles which ultimately prepare the follicle(s) and oocyte(s) for successful ovulation and fertilization.

Key words: Ovary • Follicle • Follicular development • Granulosa cells • Growth factors

This article has been cited by other articles:

				J. L. Stevenson, J. C. Dalton, J. E. P. Santos, R. Sartori, A. Ahmadzadeh, and R. C. Chebel Effect of Synchronization Protocols on Follicular Development and Estradiol and Progesterone Concentrations of Dairy Heifers J Dairy Sci, August 1, 2008; 91(8): 3045 - 3056. [Abstract] [Full Text] [PDF]

				K. Tamura, M. Matsushita, A. Endo, M. Kutsukake, and H. Kogo Effect of Insulin-Like Growth Factor-Binding Protein 7 on Steroidogenesis in Granulosa Cells Derived from Equine Chorionic Gonadotropin-Primed Immature Rat Ovaries Biol Reprod, September 1, 2007; 77(3): 485 - 491. [Abstract] [Full Text] [PDF]

				A. T. Grazul-Bilska, C. Navanukraw, M. L. Johnson, K. A. Vonnahme, S. P. Ford, L. P. Reynolds, and D. A. Redmer Vascularity and expression of angiogenic factors in bovine dominant follicles of the first follicular wave J Anim Sci, August 1, 2007; 85(8): 1914 - 1922. [Abstract] [Full Text] [PDF]

				L.J. Spicer and P.Y. Aad Insulin-Like Growth Factor (IGF) 2 Stimulates Steroidogenesis and Mitosis of Bovine Granulosa Cells Through the IGF1 Receptor: Role of Follicle-Stimulating Hormone and IGF2 Receptor Biol Reprod, July 1, 2007; 77(1): 18 - 27. [Abstract] [Full Text] [PDF]

				S Llewellyn, R Fitzpatrick, D A Kenny, J J Murphy, R J Scaramuzzi, and D C Wathes Effect of negative energy balance on the insulin-like growth factor system in pre-recruitment ovarian follicles of post partum dairy cows Reproduction, March 1, 2007; 133(3): 627 - 639. [Abstract] [Full Text] [PDF]

				M. C. Lucy The bovine dominant ovarian follicle J Anim Sci, March 1, 2007; 85(13_suppl): E89 - E99. [Abstract] [Full Text] [PDF]

				K. Miyakoshi, M. J. Murphy, R. R. Yeoman, S. Mitra, C. J. Dubay, and J. D. Hennebold The Identification of Novel Ovarian Proteases Through the Use of Genomic and Bioinformatic Methodologies Biol Reprod, December 1, 2006; 75(6): 823 - 835. [Abstract] [Full Text] [PDF]

				M A Beg and O J Ginther Follicle selection in cattle and horses: role of intrafollicular factors. Reproduction, September 1, 2006; 132(3): 365 - 377. [Abstract] [Full Text] [PDF]

				L J Spicer, P Y Aad, D Allen, S Mazerbourg, and A J Hsueh Growth differentiation factor-9 has divergent effects on proliferation and steroidogenesis of bovine granulosa cells. J. Endocrinol., May 1, 2006; 189(2): 329 - 339. [Abstract] [Full Text] [PDF]

				O J Ginther, E L Gastal, M O Gastal, and M A Beg In vivo effects of pregnancy-associated plasma protein-A, activin-A and vascular endothelial growth factor on other follicular-fluid factors during follicle deviation in mares Reproduction, April 1, 2005; 129(4): 489 - 496. [Abstract] [Full Text] [PDF]

				H. Lopez, R. Sartori, and M. C. Wiltbank Reproductive Hormones and Follicular Growth During Development of One or Multiple Dominant Follicles in Cattle Biol Reprod, April 1, 2005; 72(4): 788 - 795. [Abstract] [Full Text] [PDF]

				B. Nicholas, R. Alberio, A.A. Fouladi-Nashta, and R. Webb Relationship Between Low-Molecular-Weight Insulin-Like Growth Factor-Binding Proteins, Caspase-3 Activity, and Oocyte Quality Biol Reprod, April 1, 2005; 72(4): 796 - 804. [Abstract] [Full Text] [PDF]

				D. C. Woods and A.L. Johnson Regulation of Follicle-Stimulating Hormone-Receptor Messenger RNA in Hen Granulosa Cells Relative to Follicle Selection Biol Reprod, March 1, 2005; 72(3): 643 - 650. [Abstract] [Full Text] [PDF]