The C5b-9 Membrane Attack Complex of Complement Activation Localizes to Villous Trophoblast Injury in vivo and Modulates Human Trophoblast Function in vitro

Abstract

The complement system plays an important role in normal human pregnancy. Uncontrolled activation of this system has been associated with many disease states. We tested the hypothesis that the C5b-9 membrane attack complex (MAC) localizes to sites of villous injury and modulates trophoblast function. Placental sections from pregnancies with no complications, intrauterine growth restriction, or preeclampsia were immunostained and the surface density for MAC and fibrin was determined by morphometric analysis. Primary cytotrophoblasts from term placentas were cultured in a FiO2 of < 1%, 8% and 20% with 10% human serum containing active MAC or heat-inactivated control serum. Immunofluorescent MAC binding to trophoblast was quantified, and the neoepitopes formed in cytokeratin 18 filaments and poly-ADP-ribose polymerase during apoptosis were used to measure cell death. Trophoblast differentiation was assessed by HCG secretion, formation of syncytia, and expression of syncytin. MAC localized to fibrin deposits in normal placentas, and especially in placentas from IUGR and preeclampsia. MAC binding to cytotrophoblasts was inversely proportional to FiO2 and enhanced apoptosis. MAC increased markers of differentiation in cultures at 72h (medium HCG, syncytia and syncytin expression). Our findings demonstrate that MAC associates with fibrin deposits at sites of villous injury in vivo. Hypoxia also enhances MAC deposition in cultured trophoblasts and MAC alters trophoblast function in a phenotype specific manner.

Biomarkers of coagulation, inflammation and angiogenesis are independently associated with preeclampsia

“…Since the first step in the generation of sC5b-9 is the cleavage of C5 to C5a and C5b, this observation is in agreement with others who have suggested that C5a-dependent mechanisms might be of interest in placental pathology in preeclampsia (35,36). In the stratified analysis the activation of the complement system could only be demonstrated for nulliparous women.…”

Complement Activation and Kidney Injury Molecule-1–Associated Proximal Tubule Injury in Severe Preeclampsia

“…Complement activation likely begins early in pregnancy with local effects at the placental interface, 60,61 but may ultimately become a systemic process 62 because of shedding of apoptotic or aponecrotic fetoplacental debris into the maternal circulation 63,64 with resulting systemic inflammation and endothelial activation. 14,15,17,18 Complement proteins may be filtered through an injured glomerulus and basement membrane 65 or may propagate terminal complement activation locally at the proximal tubule, 66 contributing directly to tubular inflammation (C3a, C5a) and cell death (C5b-9).…”

Urinary Excretion of C5b-9 in Severe Preeclampsia

“…[13][14][15][16] C5a propagates a potent proinflammatory response, 13,24-26 whereas C5b-9 incorporates into cell membranes, including villous trophoblast, 27 and contributes to platelet activation, procoagulant effects, and lytic cell death. [28][29][30][31] In addition, C5a stimulates monocytes to release soluble fmslike tyrosine kinase 1, 32 which sequesters vascular endothelial growth factor and PlGF, contributing to hypertension and glomerular endotheliosis.…”