Identification and regulation of the IGFBP-4 protease and its physiological inhibitor in human trophoblasts and endometrial stroma: evidence for paracrine regulation of IGF-II bioavailability in the placental bed during human implantation.
The IGF family plays an important role in implantation and placental physiology. IGF-II is abundantly expressed by placental trophoblasts, and IGF binding protein (IGFBP)-4, a potent inhibitor of IGF actions, is the second most abundant IGFBP in the placental bed, expressed exclusively by the maternal decidua. Proteolysis of IGFBP-4 results in decreased affinity for IGF peptides, thereby enhancing IGF actions. In the current study, we have identified the IGFBP-4 protease and its inhibitor in human trophoblast and decidualized endometrial stromal cell cultures, and we have investigated their regulation in an effort to understand control of IGF-II bioavailability at the placental-decidual interface in human implantation. IGFBP-4 protease activity was detected in conditioned media (CM) from human trophoblasts and decidualized endometrial stromal cells using (125)I-IGFBP-4 substrate. Identification of the IGFBP-4 protease as pregnancy-associated plasma protein-A (PAPP-A) was confirmed by specific immunoinhibition and immunodepletion of the IGFBP-4 protease activity with specific PAPP-A antibodies. The IGFBP-4 protease activity was IGF-II-dependent in trophoblast CM. In decidualized stromal CM, PAPP-A/IGFBP-4 protease activity was also IGF-II-dependent, but was evident only when IGF-II was added in molar excess of the predominant IGFBP in decidualized stromal cell CM, IGFBP-1, supporting bioavailable IGF-II as a key cofactor of IGFBP-4 proteolysis by PAPP-A. Cultured first and second trimester human trophoblasts (n = 5) secreted PAPP-A into CM with mean +/- SEM levels of 172.4 +/- 32.8 mIU/liter.10(5) cells, determined by specific ELISA. PAPP-A in trophoblast CM (n = 3) and did not change in the presence of IGF-II (1-100 ng/ml). Cultured human endometrial stromal cells (n = 4) secreted low levels of PAPP-A (6.25 +/- 3.6 mIU/liter.10(5) cells). A physiological inhibitor of PAPP-A, the proform of eosinophil major basic protein (proMBP), was detected in trophoblast CM at levels of 1853 +/- 308 mIU/liter.10(5) cells, determined by specific ELISA, and was nearly undetectable in CM of human endometrial stromal cells. Upon in vitro decidualization of endometrial stromal cells with progesterone, PAPP-A levels in CM increased nearly 9-fold without a concomitant change in proMBP. In contrast to the experiments with trophoblasts, IGF-II and the IGF analogues, Leu(27) IGF-II, and Des (1-6) IGF-II, resulted in a dose-dependent decrease of PAPP-A levels in decidualized endometrial stromal CM by 70-90%, and a dose-dependent increase in proMBP of 14- to 41-fold. The data demonstrate conclusively that the IGF-II-dependent IGFBP-4 protease of human trophoblast and decidual origin is PAPP-A. Furthermore, the differential regulation of decidual PAPP-A and proMBP by insulin-like peptides supports a role for trophoblast-derived IGF-II as a paracrine regulator of these maternal decidual products that have the potential to regulate IGF-II bioavailability at the trophoblast-decidual interface. Overall, the data underscore potential roles for a complex family of enzyme (PAPP-A), substrate (IGFBP-4), inhibitor (proMBP), and cofactor (IGF-II) in the placental bed during human implantation.
Giudice
L C
LC
Department of Gynecology and Obstetrics, Stanford University Medical Center, Stanford, California 94305, USA. giudice@stanford.edu
Conover
C A
CA
Bale
L
L
Faessen
G H
GH
Ilg
K
K
Sun
I
I
Imani
B
B
Suen
L-F
LF
Irwin
J C
JC
Christiansen
M
M
Overgaard
M T
MT
Oxvig
C
C
D001798:Blood Proteins / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media / Q000737:chemistry; D003656:Decidua / Q000502:physiology; D010064:Embryo Implantation / Q000502:physiology; D004717:Endometrium / Q000166:cytology / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism*; D047091:Eosinophil Granule Proteins; D005260:Female; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology; D019899:Paracrine Communication / Q000502:physiology; D010920:Placenta / Q000502:physiology; D011247:Pregnancy; D011266:Pregnancy-Associated Plasma Protein-A / Q000378:metabolism; D012260:Ribonucleases; D013002:Somatomedins / Q000494:pharmacology; D017154:Stromal Cells / Q000378:metabolism*; D014327:Trophoblasts / Q000378:metabolism*
D001798:Blood Proteins; D003470:Culture Media; D004791:Enzyme Inhibitors; D047091:Eosinophil Granule Proteins; D018974:Insulin-Like Growth Factor Binding Protein 4; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II; D012260:Ribonucleases; D010450:Endopeptidases; D011266:Pregnancy-Associated Plasma Protein-A