Inhibition of nitric oxide synthetase at mid-gestation in rats is associated with increases in arterial pressure, serum tumor necrosis factor-alpha, and placental apoptosis

BACKGROUND

Reduced uteroplacental perfusion and maternal cardiovascular dysfunction have been considered to be the main pathophysiological features of preeclampsia. In order to determine whether inhibition of nitric oxide synthetase (NOS) during the initial stage of placentation is associated with impaired placental development and maternal cardiovascular dysfunction, we studied the effect of N-nitro-arginine methyl ester (L-NAME), a NOS inhibitor, on morphological changes in the placenta, maternal blood pressure, and serum tumor necrosis factor-alpha (TNF-alpha) in pregnant rats during the initial stage of placentation.

METHODS

Pregnant Wister rats were treated during mid-gestation (days 8-14) with either L-NAME or saline. On day 20 of pregnancy the rats were killed, and maternal blood and placentas were extracted and examined.

RESULTS

In comparison with pregnant saline-treated control rats (blood pressure 119 +/- 9 mm Hg), pregnant rats treated with L-NAME displayed significant hypertension (blood pressure 178 +/- 7 mm Hg), which continued even after the withdrawal of L-NAME administration (P < 0.01). In L-NAME-treated pregnant rats, morphological examination showed decreased populations of placental trophoblast lineages, and a significant increase in placental trophoblast apoptosis. Serum TNF-alpha levels at day 20 of pregnancy were significantly higher in treated pregnant rats (21.2 +/- 9.6 pg/ml) than in control pregnant rats (3.3 +/- 2.8 pg/ml) (P < 0.01).

CONCLUSIONS

Inhibition of NOS at mid-gestation in pregnant rats is associated with increases in arterial pressure, placental apoptosis, and serum TNF-alpha, all of which have been implicated as being pathophysiological features of preeclampsia.

Hypoxia Represses the Differentiation of Rcho-1 Rat Trophoblast Giant Cells

BACKGROUND

A hypoxic environment is known to be essential for early placentation. A low oxygen tension induces hypoxia-inducible factor-1 (HIF-1alpha) which may play an important role as a transcription factor in maintaining the proliferative and undifferentiated phenotype in human trophoblasts.

METHODS

We analyzed the effect of a low oxygen tension on the rat trophoblast giant cell differentiation pathway using Rcho-1 cells which were derived from rat choriocarcinomas and consist of trophoblast stem cells.

RESULTS

We found that a low oxygen tension suppressed the morphological changes and steroidogenesis during differentiation. The anticipated downregulation of the Id-1 transcription factor, a negative regulator of trophoblast giant cell differentiation, was not observed in the hypoxic environment. On the other hand, deferoxamine, which mimics hypoxia and induces HIF-1alpha, caused downregulation of Id-1 transcription factor and trophoblast giant cell differentiation.

CONCLUSION

These results indicate that hypoxia represses rat trophoblast giant cell differentiation via an HIF-1alpha-independent pathway.

E-selectin expression and function in a unique placental trophoblast population at the fetal-maternal interface: regulation by a trophoblast-restricted transcriptional mechanism conserved between humans and mice

Trophoblast are the earliest differentiated cells to emerge during mammalian ontogeny. Proper differentiation and maturation of trophoblast contributes to the fetal-maternal vascular interface of the mature placenta and is required for all subsequent stages of embryogenesis. Although lineage commitment and early differentiation of trophoblast have been investigated experimentally, molecular markers and regulatory mechanisms operating later in trophoblast development remain uncertain. We now report that E-selectin is expressed in a unique pattern in secondary trophoblast giant cells, trophoblast lining the central artery, and a subpopulation of labyrinthine trophoblast all located at the fetal-maternal interface of the murine placenta. These cells line vascular channels but express a unique profile of gene products not displayed by vascular endothelium. Placentae lacking E-selectin show increased trophoblast glycogen cells and fewer labyrinthine neutrophils compared with normal placentae, suggesting that recognition of E-selectin on trophoblast by counter-receptors on other cells contributes to placental development. Novel, distant first exons direct E-selectin expression in both murine and human placentae, suggesting that evolutionarily conserved and lineage-restricted transcriptional mechanisms regulate expression in homologous trophoblast populations in both species. These results define, at molecular and anatomic levels, a unique population of trophoblast located at the physiologically critical fetal-maternal vascular interface in mice. We also present initial functional characterization of E-selectin in placenta. These results support the general hypothesis that endothelial-leukocyte adhesion molecules performing specialized functions in adults may also function in development of human and murine hemochorial placentae.

The HAND1 basic helix-loop-helix transcription factor regulates trophoblast differentiation via multiple mechanisms

The basic helix-loop-helix (bHLH) transcription factor genes Hand1 and Mash2 are essential for placental development in mice. Hand1 promotes differentiation of trophoblast giant cells, whereas Mash2 is required for the maintenance of giant cell precursors, and its overexpression prevents giant cell differentiation. We found that Hand1 expression and Mash2 expression overlap in the ectoplacental cone and spongiotrophoblast, layers of the placenta that contain the giant cell precursors, indicating that the antagonistic activities of Hand1 and Mash2 must be coordinated. MASH2 and HAND1 both heterodimerize with E factors, bHLH proteins that are the DNA-binding partners for most class B bHLH factors and which are also expressed in the ectoplacental cone and spongiotrophoblast. In vitro, HAND1 could antagonize MASH2 function by competing for E-factor binding. However, the Hand1 mutant phenotype cannot be solely explained by ectopic activity of MASH2, as the Hand1 mutant phenotype was not altered by further mutation of Mash2. Interestingly, expression of E-factor genes (ITF2 and ALF1) was down-regulated in the trophoblast lineage prior to giant cell differentiation. Therefore, suppression of MASH2 function, required to allow giant cell differentiation, may occur in vivo by loss of its E-factor partner due to loss of its expression and/or competition from HAND1. In giant cells, where E-factor expression was not detected, HAND1 presumably associates with a different bHLH partner. This may account for the distinct functions of HAND1 in giant cells and their precursors. We conclude that development of the trophoblast lineage is regulated by the interacting functions of HAND1, MASH2, and their cofactors.

A Null Mutation in the Inflammation-Associated S100 Protein S100A8 Causes Early Resorption of the Mouse Embryo

S100A8 (also known as CP10 or MRP8) was the first member of the S100 family of calcium-binding proteins shown to be chemotactic for myeloid cells. The gene is expressed together with its dimerization partner S100A9 during myelopoiesis in the fetal liver and in adult bone marrow as well as in mature granulocytes. In this paper we show that S100A8 mRNA is expressed without S100A9 mRNA between 6.5 and 8.5 days postcoitum within fetal cells infiltrating the deciduum in the vicinity of the ectoplacental cone. Targeted disruption of the S100A8 gene caused rapid and synchronous embryo resorption by day 9.5 of development in 100% of homozygous null embryos. Until this point there was no evidence of developmental delay in S100A8−/− embryos and decidualization was normal. The results of PCR genotyping around 7.5–8.5 days postcoitum suggest that the null embryos are infiltrated with maternal cells before overt signs of resorption. This work is the first evidence for nonredundant function of a member of the S100 gene family and implies a role in prevention of maternal rejection of the implanting embryo. The S100A8 null provides a new model for studying fetal-maternal interactions during implantation.

PL48: a novel gene associated with cytotrophoblast and lineage-specific HL-60 cell differentiation

The cDNA for a novel gene, PL48, isolated by subtractive hybridization between undifferentiated human term cytotrophoblast and differentiating cytotrophoblast, has been cloned and sequenced. PL48 contains an open reading frame coding for a 537-amino acid protein, has multiple potential PKC, casein kinase II, and cAMP/cGMP-dependent kinase phosphorylation sites, and N-linked glycosylation sites. It is not present in a wide variety of proliferating cancer cells, but PL48 mRNA shows marked expression during cytotrophoblast and granulocyte lineage-specific HL-60 promyelocytic cell differentiation induced by DMSO.