Arkady Turchinsky, Shoshana Savion, Masha Berengauz-Breitman, Elena Friedman, Amos Fine Vladimir Toder. Department of Cell and Developmental Biology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
Pregnancy loss and the appearance of birth defects are often accompanied by cell death in an apoptotic process in intra- and extra-fetal tissues. The processes leading to cell death or survival are mediated by molecules capable of inducing or inhibiting apoptosis and the interrelationships between these molecules will determine the fate of the embryonic cells. Further to this, the goal of our work is to understand the mechanisms leading to the formation of birth defects in fetuses exposed to teratogenic factors that harm the fetus.
For this purpose, we tested the activity of molecules that control the induction or inhibition of apoptosis as part of the processes leading to the formation of defects, using methods of molecular and cellular biology that allow quantifying the expression of these molecules and identifying the embryonic cells that produce them. Indeed, we were able to show that exposing embryos to cyclophosphamide, a drug given to humans to treat cancer, caused embryo absorption and the appearance of head and limb malformations (target organs for the teratogen), which were accompanied by a high level of apoptosis in these organs. The increase in the level of apoptosis was also found to be accompanied by changes in the expression of molecules involved in the induction, inhibition and execution of the process.
Thus, an increase in the expression of molecules such as the caspase enzymes and the transcription factor p53, which are known to have the ability to induce apoptosis, was demonstrated, and in contrast, the level of molecules that inhibit apoptosis such as the transcription factors NF B and bcl-2 was found to be lower in the affected fetal organs.
Similar results were also obtained after exposing the pregnant mice to heat stroke or after inducing diabetes that caused the maternal blood sugar level to rise. In addition, cells from mouse embryos lacking the gene that codes for the p65 unit of the transcription factor NF B demonstrated a higher sensitivity to exposure to methotrexate, which is also used as a chemotherapeutic drug, compared to normal cells, when following the exposure a decrease in the number of cells and their proliferation, an increase in the percentage of dead cells and the appearance of markers suggesting The beginning of an apoptotic process.
At the same time, boosting the maternal immune system (immunopotentiation) by injecting rat lymphocytes or the cytokine GM-CSF, known to support pregnancy, caused a reduction in the effect of the various teratogens, which was manifested in a decrease in the percentage of absorptions and the percentage of fetuses with defects. The reduction of the teratogenic effect is also accompanied by a decrease in the level of apoptosis in the target organs for teratogens and a normalization of the expression of the molecules involved in the process such as p53 and bcl-2.
In conclusion, the results of our study emphasize the importance of understanding the mechanisms leading to the creation of birth defects as a result of exposure to teratogens. The identification of the molecules involved in the cell death processes that precede the formation of defects may serve as a basis for developing methods to reduce and prevent these phenomena.
