A key issue in the Masters in Bioethics taught at our Catholic University is the “biological status of the human embryo”, because demonstrating that the early human embryo (from the blastocyst phase) is a biological being of our species and not a uniform cluster of cells is crucial to be able to argue in its defence, and thus establish that any technique that involves destroying that embryo is bioethically unacceptable. These techniques include obtaining embryonic stem cells, so their use for biomedical experimentation is ethically very negative.
In order to support our contention that the early embryo is a living being of our species, one argument that we use is the so-called “dialogue between the human embryo and its mother”, i.e. the communication that is established between the early embryo, as early as its passage through the Fallopian tube until it implants in the maternal uterus.
As far as we are aware, this dialogue has hitherto been considered fundamentally biochemical and immunological (enlace), but now, following the publication of an interesting paper in Development (142;3210-3221,2015), which includes some experiments conducted by investigators at the Valencian Institute of Infertility (IVI), this dialogue has been extended to the genetic area.
The fact that the early human embryo can establish this biological dialogue with the uterine endometrium (in other words, with its mother) is very strong evidence for claiming that the early embryo is not a cell cluster with no organisation, but an organised biological entity capable of establishing the “embryo-maternal dialogue” that we mentioned, which is further proof that an early embryo is a living being of our species.
The maternal-foetal dialogue
What, though, does this dialogue between the human embryo and its mother consist of?
During the passage through the Fallopian tube and its implantation in the maternal endometrium, the blastocyst — the early embryo — produces and secretes a series of biochemical compounds, messengers that act on the endometrium to facilitate its implantation; it is like saying that the embryo tells its mother that it is nearing the nesting place in her uterus so that it can be prepared, i.e. so it can adapt or tailor the environment where her child is to be implanted.
In turn, the maternal endometrium produces and secretes other compounds in the endometrial fluid in which the embryo is contained, which are fundamental for its implantation; these include several integrins (β3, α4 and α1) and interleukins (such as interleukin-1), as well as cytokines (IL8, MCP-1), leptin and human chorionic gonadotrophin (hCG).
Another biological event also occurs in that maternal dialogue, which equally supports the early embryo’s nature of organised living being. In effect, when a foreign body is introduced into our body, the body reacts by rejecting it. This is what happens sometimes with transplants. It is a biological mechanism to defend oneself against possible external dangers.
The embryo is a biological being that is foreign to the mother, since half its genomic content comes from the father. On this occasion however, and to facilitate implantation of the embryo — her child — the mother suppresses the immune reaction that would reject her child, to thus facilitate its implantation. This is another important facet of that embryo-maternal dialogue, as we described in a recent article (link inmunidad materno-fetal).
Now however, with the publication of the aforementioned article in Development, that biochemical and immunological dialogue has been extended to the genetic field, after investigators showed that elements in the fluid secreted by the endometrium, and which the child absorbs during the implantation process, may modify the genetic expression of the child.
This has major biomedical and bioethical consequences. From a biomedical point of view, this genetic interrelation could predispose the embryo to both metabolic and genetic disorders, i.e. it could increase the child’s risk of some diseases, such as type 2 diabetes, or biological conditions that could increase the risk of having certain diseases, such as obesity.
This interrelationship between mother and child could also occur in in-vitro fertilisation (IVF) when donor eggs (i.e. not from the mother) or surrogate mothers are used. In the first case, in the implanted embryos from fertilisation of donor eggs, the gene expression of their genome could be modified by the influence of the maternal messages. In other words, information would be incorporated in the child’s genome from the maternal endometrium so that somehow, and very partially, would constitute an embryo that was genetically modified by the influence of the biological mother.
Moreover, in the case of surrogacy, the surrogate mother could also influence the child’s genome, i.e. biological links could be established with the child gestated, beyond those fostered by the pregnancy.
In both circumstances, by modifying the expression of the child’s genome, the relationship between the egg donor or surrogate mother and the child born would be substantially implemented, which could undoubtedly create more biological and social problems than these practices currently entail.
This is therefore a very interesting paper which, in our opinion, supports the human nature of that biological entity that is the early human embryo, and which adds fresh insights, especially in the field of IVF and surrogate motherhood.
Justo Aznar and Julio Tudela
Catholic University of Valencia