Activation of the Novel Prothrombinase, fgl2, as a Basis for the Pregnancy Complications Spontaneous Abortion and Pre‐eclampsia
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PROBLEM: Impaired trophoblast invasion during the first trimester of pregnancy is linked to spontaneous abortion, and defective invasion in the second trimester to hypertension+proteinuria (pre‐eclampsia). Hypertension developing during the third trimester of human pregnancy represents, in part, a corrective response in the mother to provide adequate placental perfusion for fetal growth when trophoblast has not to invaded and converted the myometrial porprtion of maternal spiral arteries into to low resistance‐high capacitance conduits. Deportation of vesicles from hypoxemic trophoblast is thought to cause hypertension plus proteinuria, vascular damage and a systemic coagulopathy. Trophoblast invasion may be inhibited by local cytokines, such as TGF‐βs but Th1‐type cytokines associated with pre‐eclapmsia and spontaneous abortions (e.g., IL‐1, TNF‐α, IFN‐γ) are not known to inhibit migration at in situ concentrations. Trophoblast invasion is also inhibited by the binding of surface integrins to fibronectin and fibrin, and fibrin production is stimulated by these Th1 cytokines via up‐regulation of prothrombinases(s) such as fgl2 which directly and via TNF‐α‐facilitated inflamation compromise trophoblast cell integrity. We, therefore, asked if fgl2 expression and TNF‐α are increased in first trimester human miscarriage and in third trimester pre‐eclampsia.
METHODS: fgl2 mRNA was detected using in situ hybridization and fgl2 protein by immunohistochemistry. TNF‐α mRNA and protein were similarly tested. The techniques were validated using uterine sections from day 8.5 of CBA×DBA/2 pregnancies, and then were applied to sections of placentae from normal and pre‐eclamptic pregnancies with and without intrauterine fetal growth restriction (IUGR). Fibrin was detectectd by immunohistochemistry. RESULTS: Expression of fgl2 protein correlated with fgl2 mRNA expression in mouse uteri and in placentae from normal human pregnancies. Increased expression of fgl2 and TNF‐α mRNA and protein, and increased fibrin deposition was detected in placental trophoblast. CONCLUSIONS: Activation of fgl2 prothrombinase by Th1‐type cytokines in pregnancy may lead to spontaneous abortion, or in ongoing pregnancy, to pre‐eclampsia and/or IUGR.
