Abstract
BackgroundPreeclampsia (PE) is characterized by exaggerated apoptosis of the villous trophoblast of placental villi. Since p53 is a critical regulator of apoptosis we hypothesized that excessive apoptosis in PE is mediated by abnormal expression of proteins participating in the p53 pathway and that modulation of the p53 pathway alters trophoblast apoptosis in vitro.MethodsFresh placental villous tissue was collected from normal pregnancies and pregnancies complicated by PE; Western blotting and real-time PCR were performed on tissue lysate for protein and mRNA expression of p53 and downstream effector proteins, p21, Bax and caspases 3 and 8. To further assess the ability of p53 to modulate apoptosis within trophoblast, BeWo cells and placental villous tissue were exposed to the p53-activator, Nutlin-3, alone or in combination with the p53-inhibitor, Pifithrin-α (PFT- α). Equally, Mdm2 was knocked-down with siRNA.ResultsProtein expression of p53, p21 and Bax was significantly increased in pregnancies complicated by PE. Conversely, Mdm2 protein levels were significantly depleted in PE; immunohistochemistry showed these changes to be confined to trophoblast. Reduction in the negative feedback of p53 by Mdm2, using siRNA and Nutlin-3, caused an imbalance between p53 and Mdm2 that triggered apoptosis in term villous explants. In the case of Nutlin, this was attenuated by Pifithrin-α.ConclusionsThese data illustrate the potential for an imbalance in p53 and Mdm2 expression to promote excessive apoptosis in villous trophoblast. The upstream regulation of p53 and Mdm2, with regard to exaggerated apoptosis and autophagy in PE, merits further investigation.
Highlights
Preeclampsia (PE), defined as new onset hypertension and proteinuria, is a severe multi-system disorder affecting 3–6% of human pregnancies [1,2]
Over time syncytial nuclei gather in structures, more recently termed syncytial nuclear aggregates (SNAs) [8] but recently it has been observed that apoptosis may not be a significant mechanism in this decline [9]
We have investigated the effects of its deregulation using two approaches: i) RNA interference to reduce p53 and Mdm2 expression in normal term villous trophoblast, and ii) pharmacological modulation of the p53 pathway, using Nutlin-3 and Pifithrin-a
Summary
Preeclampsia (PE), defined as new onset hypertension and proteinuria, is a severe multi-system disorder affecting 3–6% of human pregnancies [1,2]. There is profound cellular dysfunction with increased unfolded protein response, apoptosis, autophagy and necrosis of villous trophoblast [3,4,5] These processes may promote the release of factors from the placenta which trigger maternal endothelial activation and/or systemic inflammation [6,7]. In severe PE, cell turnover is dysregulated, resulting in decreased syncytiotrophoblast area [11,12], increased apoptosis [4,13,14], autophagy [3] and increased density of SNAs [15,16] The role that this exaggerated apoptosis plays in placental pathology in PE is unclear, but it may prevent replenishment of syncytiotrophoblast, promote syncytial degeneration and release vasoactive or inflammatory factors into the maternal circulation [17]. Since p53 is a critical regulator of apoptosis we hypothesized that excessive apoptosis in PE is mediated by abnormal expression of proteins participating in the p53 pathway and that modulation of the p53 pathway alters trophoblast apoptosis in vitro
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