Endocrine Abstracts

Growth in utero depends on adequate development and function of the fetal / maternal interface. During pregnancy, the insulin-like growth factors (IGFs), which are known to be critically involved in placental development, are controlled by a binding protein - IGFBP-1 - produced by maternal decidualised endometrium. We have recently found that decidua also produces a protease which cleaves IGFBP-1 into fragments that are unable to bind ligand. This study aimed to identify and characterise the IGFBP-1 protease responsible for increasing IGF bioavailabilty at the maternal / fetal interface.

Medium conditioned by decidualised endometrial cells from tissue obtained at termination of first trimester pregnancy contained 55 and 90kDa enzymes which cleaved IGFBP-1 and gelatin when analysed by zymography. These data together with inhibitor profile studies suggested matrix metalloproteases (MMPs) as candidate enzymes. A subsequent screen of medium by Western immunoblotting demonstrated immunoreactivity for MMP-3 and MMP-9. Immunocytochemistry verified the production of these enzymes by decidual cells.

Incubation of IGFBP-1 with either MMP-3 or MMP-9 produced an identical fragment profile (5 and 21 kDa) to that obtained with decidual conditioned medium. Sequence analysis revealed that the enzymes cleave IGFBP-1 at 144Lys / Lys145 resulting in a small (5kDa) C-terminal peptide of IGFBP-1 which retains the RGD site.

MMP activity is inhibited by TIMPs and we have previously shown that alpha₂-macroglobulin inhibits IGFBP-1 proteolysis. Western immunoblotting and immunocytochemistry demonstrated that decidual cells produced TIMP-1, TIMP-2 and alpha₂-macroglobulin and all three inhibitors attenuated the proteolysis of IGFBP-1 by MMP-3.

We hypothesise that in addition to releasing IGF, MMP proteolysis of IGFBP-1 at the fetal / maternal interface is a mechanism for producing IGFBP-1 fragments which have independent effects