The placenta is a transient organ that supports the growth and development of the fetus. Although the placenta is a normal tissue, its constituent cells, the trophoblastic cells, share several common features with tumour cells such as a modest inhibition by contact, high proliferation index, the ability to escape to effectors of the immune system and their migratory, invasive and fusogenic properties. In both cellular systems, these properties are modulated by various stimuli as the levels of glucose, lipid metabolism, oxygen tension, and oxidative stress. However, unlike tumours, in normal placentation cell proliferation, migration, invasion and cell differentiation are strictly controlled.

Failures in these processes produce an alteration of placental function with a direct impact on fetal and maternal health. In this context it becomes critically important to understand, at the molecular level, the mechanisms that control the cellular differentiation processes that take place in placenta development. Among the molecules whose function emerges as relevant for placental development and whose expression is altered in tumour cells are the KLF6 transcription factor and the StarD7 lipid binding protein. On the basis of these considerations, our working hypotheses are:

1. KLF6 and StarD7 are required in proliferation, migration/invasion, adhesion and differentiation of trophoblasts as well as in tumour cells;

2. The expression and/or localization of KLF6 and StarD7 are regulated by stimuli capable of generating endoplasmic reticulum stress response such as: an increase in glucose concentration, changes in oxygen tension and oxidative stress. Therefore they might contribute to trophoblast and tumour cells deregulation that characterize pathological stages.

3. The delicate balance of interactions among endogenous programs of gene expression and external signals, responsible for the development and differentiation of the placenta, can be altered by exposure to low levels of environmental pollutants.

Research projects

StarD7 role in the molecular mechanism s involved in proliferation, migration, invasion, adhesion and cell differentiation.

StarD7, identified in our laboratory, belongs to the superfamily of lipid transfer proteins related to the StAR protein, characterized by having a START domain involved in the transport of lipids and sterols. In previous work we have reported some biochemical characteristics of StarD7, its expression levels in various cell lines and placental tissue, as well as certain mechanisms that regulate its expression. Recently, we showed that StarD7silencing leads to a decrease in cell proliferation and migration and an increase in differentiation of the trophoblastic tumour JEG-3 cell model. These phenotypic changes are associated with a decrease in the synthesis of phospholipids and the expression of the efflux transporter ABCG2. Currently, we are trying to define StarD7 participation in the mechanisms that regulate the processes of migration, proliferation and cellular differentiation.

Effect of the organophosphate chlorpyrifos (CPF) in the biology of trophoblast

We have previously demonstrated that the βhCG, GCM1, and ABCG2 mRNA levels were increased in placental cells exposed to CPF in micromolar concentrations that did not alter cell viability. Interestingly, CPF lead to morphological alterations in the chorionic villi of placental explants exposed in vitro. Also, we reported that CPF induces an increase in the production of ROS, a reduction in intracellular glutathione content and an increase in the activity of the enzyme catalase, and also the induction of the via Nrf2/ARE accompanied by an increase in phase II detoxification genes: hemoxigenase1 and glutathione reductase. These results indicate that CPF modifies the expression of functionally relevant genes on human placental cells, activating defense mechanisms to protect its functionality and thereby preserve pregnancy. Currently, we are trying to establish whether the imbalance of redox status induced by CPF promotes an endoplasmic reticulum stress response and which mechanisms are involved in this response.

Role of KLF6 in the differentiation of trophoblast cells

KLF6 was originally isolated in our laboratory due to its ability to bind and regulate the promoter of genes encoding the pregnancy-specific glycoproteins (PSG) in human placenta. Many authors later showed that KLF6 plays a crucial role in differentiation, angiogenesis, cell cycle control and proliferation, primarily in different types of cancer where it functions as a tumour suppressor gene. Significantly, klf6 knock-out mice die at day E12.5 showing a defective placenta among other developmental defects. Recently, we have demonstrated that KLF6 is required in villous trophoblast differentiation, both in the biochemical and cell fusion processes, regulating the expression of proteins critically involved. In addition, we showed that epigenetic mechanisms modulate the nuclear localization and activity of KLF6 on PSG5 promoter. KLF6 expression is early and transiently activated in cells and explants of normal term placentas cultivated under hypoxic conditions and in JEG-3 cells exposed in vitro to CPF. We are currently studying the role of KLF6 in the migration, invasion, and proliferation of the invasive extravillous trophoblast cells as well as the genes regulated by KLF6 in hypoxic and stress conditions.