42: Fetuses with fetal growth restriction (FGR) have elevated proteasome levels and activity

Abstract

To increase lean body mass, the rate of fetal protein synthesis must exceed that of protein breakdown. The ubiquitin-proteasome system is an assembly of enzymatic activities with a key role in protein degradation and homeostasis. Environmental stressors switch the constitutive proteasome (cPROT) to immunoproteasome (iPROT), a quality control proteolytic machinery effective also in the absence of inflammation. Our hypothesis was that FGR fetuses have upregulated levels and enzymatic activity of the proteasome. We analyzed maternal blood, cord blood, and placenta of 70 singleton pregnancies of which 37 were complicated by FGR (EFW< 10%, Table). FGR occurred in the context of preeclampsia with severe features (sPE, n=23), identifiable causes (n=2: CMV infection, true cord knot) or idiopathic factors (n=12). Proteasome levels were measured using ELISA for cPROT and iPROT 20S subunit. Lytic activity was analyzed with fluorogenic substrates for caspase-like (CAS-L), chemotrypsin-like (CHE-L) and trypsin-like (TRY-L) activities. Specificity was confirmed with proteasome inhibitors MG132 and ONX. Placenta was stained for β5 (cPROT) and β5i (iPROT) subunits. Controls were idiopathic preterm births (iPTB) without fetal or placental inflammation. Data was adjusted for gestational age (GA) at birth. 1) The highest maternal cPROT levels were seen in sPE, independent of FGR (sPE p=.003, FGR p=.259, 2-way ANOVA, Fig A); 2) There was no correlation between cord blood and maternal proteasome levels (r=-.009, p=.96); 3) Fetuses with FGR had heightened CHE-L enzymatic activity independent of maternal proteasome levels or activity, sPE status or GA (adjusted p=.04, Fig B); 4) Cord blood proteasome activity of FGR fetuses was inhibited by MG132 and ONX with maximal effect on CHE-L activity which was reduced to 1.7% and 0.6%, respectively; 5) FGR placenta displayed intense β5i staining in trophoblasts and stromal cells suggestive of upregulated iPROT (Fig C). FGR fetuses display a significant upregulation in proteasome enzymatic activity independent of maternal compartment and etiology.View Large Image Figure ViewerDownload Hi-res image Download (PPT)