Downregulation of p53 drives autophagy during human trophoblast differentiation

The placental barrier is crucial for the supply of nutrients and oxygen to the developing fetus and is maintained by differentiation and fusion of mononucleated cytotrophoblasts into the syncytiotrophoblast, a process only partially understood. Here transcriptome and pathway analyses during differentiation and fusion of cultured trophoblasts yielded p53 signaling as negative upstream regulator and indicated an upregulation of autophagy-related genes. We further showed p53 mRNA and protein levels decreased during trophoblast differentiation. Reciprocally, autophagic flux increased and cytoplasmic LC3B-GFP puncta became more abundant, indicating enhanced autophagic activity. In line, in human first trimester placenta p53 protein mainly localized to the cytotrophoblast, while autophagy marker LC3B as well as late autophagic compartments were predominantly detectable in the syncytiotrophoblast. Importantly, ectopic overexpression of p53 reduced levels of LC3B-II, supporting a negative regulatory role on autophagy in differentiating trophoblasts. This was also shown in primary trophoblasts and human first trimester placental explants, where pharmacological stabilization of p53 decreased LC3B-II levels. In summary our data suggest that differentiation-dependent downregulation of p53 is a prerequisite for activating autophagy in the syncytiotrophoblast

Placental fractalkine mediates adhesion of THP-1 monocytes to villous trophoblast

The chemokine fractalkine (CX3CL1) recently attracted increasing attention in the field of placenta research due to its dual nature, acting both as membrane-bound and soluble forms. While the membrane-bound form mediates flow-resistant adhesion of leukocytes to endothelial and epithelial cells via its corresponding receptor CX3CR1, the soluble form arises from metalloprotease-dependent shedding and bears chemoattractive activity for monocytes, natural killer cells and T cells. In human placenta, fractalkine is expressed at the apical microvillous plasma membrane of the syncytiotrophoblast, which may enable close physical contact with circulating maternal leukocytes. Based on these observations, we tested the hypothesis that fractalkine mediates adhesion of monocytes to the villous trophoblast. Forskolin-induced differentiation and syncytialization of the trophoblast cell line BeWo was accompanied with a substantial upregulation in fractalkine expression and led to increased adhesion of the monocyte cell line THP-1, which preferentially bound to syncytia. Blocking as well as silencing of the fractalkine receptor CX3CR1 proved involvement of the fractalkine/CX3CR1 system in adherence of THP-1 monocytes to villous trophoblast. Pre-incubation of THP-1 monocytes with human recombinant fractalkine as well as silencing of CX3CR1 expression in THP-1 monocytes significantly impaired their adherence to BeWo cells and primary term trophoblasts. The present study suggests fractalkine as another candidate among the panel of adhesion molecules enabling stable interaction between leukocytes and the syncytiotrophoblast

Human placental transthyretin in fetal growth restriction in combination with preeclampsia and the HELLP syndrome

Fetal growth restriction is a serious, still poorly understood pregnancy-related pathology often associated with preeclampsia. Recent studies speculate on the role of human transthyretin, a carrier protein for thyroxin and retinol binding protein, in the etiology of both pregnancy pathologies. Objective was to investigate the localization and abundance of transthyretin (TTR) in placentas of pregnancies suffering from fetal growth restriction with and without preeclampsia and HELLP. This was a retrospective case control study on human paraffin-embedded placentas from pregnancies with a gestational age at delivery between the 24th and 34th week of gestation. 16 placentas were included in this study, 11 cases and 5 from normotensive pregnancies as controls. Cases were divided into three groups: four from early onset idiopathic intrauterine growth restriction (IUGR), four from early-onset severe preeclampsia (PE), and three from early-onset IUGR with preeclampsia plus HELLP syndrome. Distribution and abundance of TTR were investigated by means of immunohistochemistry. Semi quantitative analysis of TTR staining of placental sections revealed that TTR was mostly expressed in the villous trophoblast covering placental villi. Only weak staining of TTR in villous stroma could be detected. The comparison of placentas revealed that in pure IUGR and severe PE there is a much stronger TTR reactivity compared to controls and cases with IUGR + PE + HELLP. Concluding, the study showed that TTR is dysregulated in cases of IUGR and severe early onset preeclampsia. Interestingly, TTR expression is not affected in cases with HELLP syndrome that reveal the same staining intensities as age-matched controls. © Springer-Verlag 2012

Placental fractalkine is up-regulated in severe early-onset preeclampsia

The pathogenesis of preeclampsia (PE) includes the release of placental factors into the maternal circulation, inducing an inflammatory environment in the mother. One of the factors may be the proinflammatory chemokine fractalkine, which is expressed in the syncytiotrophoblast of human placenta, from where it is released into the maternal circulation by constitutive shedding. We examined whether placental fractalkine is up-regulated in severe early-onset PE and whether the proinflammatory cytokines tumor necrosis factor (TNF)-{alpha} and IL-6 are able to increase the expression of fractalkine. Gene expression analysis, enzyme-linked immunosorbent assay, and immunohistochemistry consistently showed increased fractalkine expression in placentas from severe early-onset PE, compared to gestational age-matched controls. Expression of a disintegrin and metalloproteinases 10 and 17, which convert transmembrane fractalkine into the soluble form, was significantly increased in these cases. Incubation of first-trimester placental explants with TNF-{alpha} provoked a significant increase in fractalkine expression and release of the soluble form, whereas IL-6 had no effect. TNF-{alpha}-mediated up-regulation of placental fractalkine was reversed in the presence of the aspirin-derivative salicylate, which impaired activation of NF-{kappa}B p65 in TNF-{alpha}-treated explants. On the basis of data from placental explants, we suggest that increased maternal TNF-{alpha} may up-regulate the expression and release of placental fractalkine, which, in turn, may contribute to an exaggerated systemic inflammatory response in PE

Placental expression of sFlt-1 and PlGF in early preeclampsia vs. early IUGR vs. age-matched healthy pregnancies

Objective: To investigate whether differences between early preeclampsia and early fetal growth restriction can be explained by differential placental expression patterns of sFlt-1, Flt-1, and PlGF. Methods: Placental tissues and maternal blood samples from six cases of preeclampsia, seven IUGR, and six age-matched controls were studied for mRNA and protein levels as well as protein localization and expression intensity. Results: Neither placental PlGF mRNA and protein expression nor placental villous trophoblast expression intensity of PlGF was altered by placental dysfunction. Conclusion: High sFlt-1 concentrations may account for diminished maternal serum PlGF levels