Evidence from human placenta, ER-stressed trophoblasts and transgenic mice links transthyretin proteinopathy to preeclampsia

We have demonstrated that protein aggregation plays a pivotal role in the pathophysiology of preeclampsia (PE) and identified several aggregated proteins in the circulation of PE patients, most significantly the serum protein transthyretin (TTR). Here we show robust accumulation of TTR aggregates in the placentas of women with early-onset PE (e-PE). TTR aggregation was inducible in primary human trophoblasts (PHTs) and the TCL-1 trophoblast cell line by ER stress inducers or autophagy-lysosomal disruptors. Hypoxia/reoxygenation (H/R) of cultured PHTs increased intracellular BiP, phosphorylated IRE1alpha, PDI and Ero-1, all markers of the UPR, and the apoptosis mediator caspase-3. Blockade of IRE1alpha inhibited H/R-induced upregulation of Ero-1 in PHTs. Excessive UPR was observed in the PE placenta. Further, pregnant mice, overexpressing transgene encoded wild type human TTR, displayed aggregated TTR in the junctional zone of the placenta and PE-like features including hypertension, proteinuria, intrauterine growth restriction, kidney injury, and elevated levels of the PE biomarkers serum sFlt-1 and endoglin. High Resolution Ultrasound analysis revealed low blood flow in uterine and umbilical arteries compared to that found in wild type pregnant mice. On the other hand, loss of mouse TTR function did not cause any pregnancy abnormalities in Ttr-/- mice. These observations in the PE placenta, cultured trophoblast cells and TTR transgenic mice indicate that TTR aggregation is an important causal contributor to PE pathophysiology.