Researchers from the laboratory of Yosef (Yossi) Buganim at Hebrew University of Jerusalem have used genetic engineering techniques to directly reprogram mouse skin cells into stable, and fully functional placenta-generating cells called induced trophoblast stem cells (iTSCs).
The placenta forms a vital link between a mother and her baby. When the placenta does not work as well as it should, the baby will receive less oxygen and nutrients from the mother. Consequently, the baby might show signs of fetal stress (that is the baby’s heart does not work properly), not grow nearly as well, and have a more difficult time during labor. Such a condition is called “placental insufficiency” and it can cause recurrent miscarriages, low birth weight, and birth defects.
Placental dysfunction has also been linked to a condition called fetal growth restriction (AKA Intrauterine growth restriction). Intrauterine growth restriction or IUGR is a condition characterized by poor growth of a baby while in the mother’s womb during pregnancy.
How can scientists study the placenta? Virtually all attempts to grow placental cells in culture have been largely unsuccessful.
Buganim and his colleagues have solved this problem. A screen for genes that support the development of the placenta yielded three genes: GATA3, Eomes, and Tfap2c. Next the Buganim team took mouse skin fibroblasts and forced the expression of these three placenta-specific genes in them. This initiated a cascade of events in the cells that converted them into stable and fully functional placenta-generating cells.
These skin-derived TSCs behave and look like native TSCs and they also function and contribute to developing placenta. The Bugamin laboratory used mouse cells for these experiments, but they want to expand their experiments to include human cells to make human iTSCs.
The success of this study could potentially give women who suffer from recurrent miscarriage and placental dysfunction diseases the ability to have healthy babies. The embryo is not at risk from such cells, since iTSCs integrate into the placenta and not into the embryos itself.
Soon after the publication of this paper that adult mouse cells could be reprogrammed into embryonic-like stem cells simply by exposing them to acidic environments or other stresses , Charles Vacanti at Harvard Medical School has reported that he and his colleagues have demonstrated that this procedure works with human cells.
STAP cells or stimulus-triggered acquisition of pluripotency cells were derived by Vacanti and his Japanese collaborators last year. These new findings show that adult cells can be reprogrammed into embryonic-like stem cells without genetic engineering. However, this technique worked well in mouse cells, but it was not clear that it would work with human adult cells.
Vacanti and others shocked the world when they published their paper in the journal Nature earlier this year when they announced that adult cells in mice could be reprogrammed through exposure to stresses and proper culture conditions.
“If they can do this in human cells, it changes everything, said Robert Lanza of Advanced Cell Technologies in Marlborough, Massachusetts. Such a procedure promises cheaper, faster, and potentially more flexible cells for regenerative medicine, cancer therapy and cell and tissue cloning.
Vacanti and his colleagues say they have taken human fibroblast cells and tested several environmental stressors on them to recreate human STAP cells. He will not presently disclose which particular stressors were applied, he says the resulting cells appear similar in form to the mouse STAP cells. His team is in the process of testing to see just how stem-cell-like these cells are.
According to Vacanti, the human cells took about a week to resemble STAP cells, and formed spherical clusters just like their mouse counterparts. Vacanti and his Harvard colleague Koji Kojima emphasized that these results are only preliminary and further analysis and validation is required.
Bioethical problems potentially emerge with STAP cells despite their obvious potential. The mouse cells that were derived and characterized by Vacanti’s group and his collaborators were capable of making placenta as well as adult cell types. This is different from embryonic stem cells, which can potentially form all adult cell types, but typically do not form placenta. Embryonic stem cells, therefore, are pluripotent, which means that they can form all adult cell types. However, the mouse STAP cells can form all embryonic and adult cell types and are, therefore, totipotent. Mouse STAP cells could form an entirely new mouse. While it is now clear if human STAP cells, if they in fact exist, have this capability, but if they do, they could potentially lead to human cloning.
Sally Cowley, who heads the James Martin Stem Cell Facility at the University of Oxford, said of Vacanti’s present experiments: “Even if these are STAP cells they may not necessarily have the same potential as mouse ones – they may not have the totipotency – which is one of the most interesting features of the mouse cells.”
However the only cells known to be naturally totipotent are in embryos that have only undergone the first couple of cell divisions immediately after fertilization. According to Cowley, any research that utilizes totipotent cells would have to be under very strict regulatory surveillance. “It would actually be ideal if the human cells could be pluripotent and not totipotent – it would make everyone’s life a lot easier,” she opined.
Cowley continued: “However, the whole idea that adult cells are so plastic is incredibly fascinating,” she says. “Using stem cells has been technically incredibly challenging up to now and if this is feasible in human cells it would make working with them cheaper, faster and technically a lot more feasible.”
This is all true, but Robert Lanza from Advanced Cell Technology in Marlborough, Massachusetts, a scientist with whom I have often deeply disagreed, noted: “The word totipotent brings up all kinds of issues,” says Robert Lanza of Advanced Cell Technology in Marlborough, Massachusetts. “If these cells are truly totipotent, and they are reproducible in humans then they can implant in a uterus and have the potential to be turned into a human being. At that point you’re entering into a right-to-life quagmire”
A quagmire indeed, for Vacanti has already talked about using these STAP cells to clone human embryos. Think of it: the creation of very young human beings just for the purpose of ripping them apart and using their cells for research or medicine. Would we allow this if the embryo were older; say the age of a toddler? No we would rightly condemn it as murder, but because the embryo is very young, that somehow counts against it. This is little more than morally grading the embryo according to astrology.
Therefore, whole Vacanti’s experiments are exciting and novel, they hold chilling possibilities. Lanza is right, and it is doubtful that scientists would show the same deference or sensitivities to the moral exigencies he has shown.
Preeclampsia occurs during pregnancy, and is characterized by a gradual rise in blood pressure to dangerous levels. It usually presents after the 20th week of pregnancy, and can even persist after delivery.
How common is preeclampsia? In the United States, preeclampsia affects 5-8% of all births. Among the women of Canada, the United States, and Western Europe, the births affected by preeclampsia range from 2-5%. (5,6) In the developing world, the percentage of births affected by preeclampsia range from 4% of all deliveries to as high as 18% in parts of Africa. In Latin America, preeclampsia is the number one cause of maternal death.
Globally, ten million women develop preeclampsia each year, and 76,000 pregnant women die each year from preeclampsia and related disorders. The number of babies who die from these disorders is thought to be on the order of 500,000 per year.
In developing countries, a woman is seven times more likely to develop preeclampsia than a woman in a developed country, and between 10-25% of those cases will result in the death of the mother.
Now that I’ve hopefully convinced you that preeclampsia is a problem, how do we address it? Research in laboratory mice have told us a great deal about preeclampsia and other disorders that arise during pregnancy, but finding a sound model system that can be used to develop effective and safe treatments requires something closer to humans.
Work in laboratory mice has shown that preeclamsia often arises because of a malformed placenta. This poorly-formed placenta does not provide enough oxygen and nutrients for the growth needs of the baby at the fetal stages of development, and the mother’s body responds by increasing the mother’s blood pressure in order to increase blood flow through the placenta.
The work by Mikkola and her colleagues have provided physicians and developmental biologists with a new “tool box” for understanding the development of the placenta and the different cell types that compose it. Hopefully, various complications during pregnancy might be due to malfunctions of these particular cell types and the progenitor cells that produce them.
Mikkola and others started with laboratory mice, since it is possible to label single cells in mouse embryos and track exactly where those cells and their progeny go and what they do. The powerful genetic tools available in laboratory mice also allows scientists to identify the various biochemical signaling pathways that cells use to communicate with other cells during placental development. Also, if something goes wrong with particular cell signaling pathways, the mouse model allows scientists to precisely characterize the developmental consequences of much dysfunction.
Through their work in the mouse, Mikkola and her co-workers identified a placental progenitor cells called the Epcamhi labyrinth trophoblast progenitor or LaTP. The LaTP is like a multipotent adult of tissue-specific stem cell that can become many of the cells required to make the placenta.
Mikkola and her group also showed that the “c-Met” signaling pathway was required to sustain the growth of LaTPs during placental development and that this same signaling pathway was required to form a specific group of cells (syncytiotrophoblasts) that form the interface between the placenta and the mother’s endometrium. Elimination of c-Met signaling completely compromised the growth of the fetus and its development.
This new cell type should provide a wealth of opportunities to examine complications during pregnancy like preeclampsia and others and design treatments that can save the lives of mothers and their babies.
The placenta does more than provide yet unborn babies with oxygen from the mother’s blood supply; they are also a rich source of stem cells. Vladamir Serikov from the Children’s Hospital Oakland Research Institute in Oakland, California first isolated and characterized “chorionic mesenchymal stem cells” from human placenta in 2009 (see Exp Biol Med 2009 234:813-23), and since that time, his work has been conformed by several other research labs (Cell Stem Cell 2009 5:385-95 & Dev Biol 2009 327:24-33). Now Serikov and his research team have used his hCMSCs to repair damaged lungs in laboratory animals.
In this present publication, the Serikov team grew placenta-derived hCMSCs in culture and discovered that these grew like gangbusters. After 100 doublings, the cells showed no signs of giving up and their chromosomes show no signs of shortening, which is a symptom of aging when cells are grown in culture. Stem cells, have the ability to properly maintain the ends of their chromosomes and not show these signs of aging. Serikov’s hCMSCs have this definitive stem cell ability.
Next, the Oakland-based team tried to get these hCMSCs to differentiate into various cell types using published protocols. The hCMScs formed fat cells, bone cells, blood vessel-like cells, and liver cells in culture. When treated with a molecule called nerve growth factor, hCMSCs even sprouted nerve cell-like extensions and expressed genes common found in neurons (the cells that make a propagate nerve impulses).
To determine if these cells had the capacity to heal damaged tissue, Serikov and co-workers treated human lungs that were donated by a deceased individual but were denied for transplantation with a bacterial toxin that tends to really screw up the lungs. One lobe of the lung was treated with toxin only but the other side was treated with the toxin and five million hCMSCs. The side that received only the toxin showed damage to the lining of the lungs that was reflected in poor gas exchange and high fluid uptake by the lung tissue, but the side that received the hCMSCs was able to properly pump out the liquid and maintain the structure of the lung. When this same assay was applied to cultured lung tissue from humans, it was clear that the hCMSCs helped repair the columns of lung cells through the modicum of growth factors that they secrete. Certainly, hCMSCs have the capacity to heal the lungs after they are ravaged by a deadly bacterial toxin.
Two other experiments underscored the therapeutic capacity of these cells. When hCMSCs were infused into mice after the animals have been hit with high doses of radiation, they took up residence in multiple tissues, including the intestine, lungs, brain, and liver. Therefore, hCMSCs can not help heal tissues by means of what they secrete (so-called paracrine mechanisms), but by incorporating into tissues and becoming an integral part of it. Finally, when hCMSCs were implanted into mice and examined one year later, none of the mice showed any signs of tumors. There were also no signs of pain, heart problems, distress, fever, or weight loss. Therefore, these cells seem to be well tolerated, and do not have a high capacity for tumor formation.
These preclinical studies should give way to studies in larger animals, and if those are successful, hopefully, the first human clinical trials with these amazing stem cells that come from an abundant source, the human afterbirth.
See Igor Nazarov et al., “Multipotential Stromal Stem Cells from Human Placenta Demonstrate High Therapeutic Potential,” Stem Cells Translational Medicine 2012 1:359-72.