Epigenetics is the study of heritable factors which are not directly based on the genetic code. In addition to non-genetic “cellular memory,” which records developmental and environmental cues for DNA and RNA expression, epigenetics also covers heredity in molecules other than DNA and RNA. For example, some hereditary traits are carried in prions, an infectious form of protein.
Cell differentiation and stem cells
Epigenetics is especially relevant to the human race when it comes to stem cells. These undifferentiated cells may hold the clue to healing the unhealable, longer healthy lifespans and maybe even immortality.
This is possible because stem cells are the only undifferentiated cells in the human body. They are totipotent, capable of producing any other kind of human cell.
In contrast, every other human cell is differentiated to perform its specific task, and is no longer capable of performing any tasks other than the task for which it has been differentiated. With the exception of meiosis to produce reproductive cells, every differentiated cell always reproduces into more of the same kind of cell. Once differentiation has occurred, it is absolute.
For example, a pancreatic alpha cell in the islets of Langerhans cannot change into a pancreatic beta cell, even if every other pancreatic beta cell has been destroyed and the body can no longer produce insulin. As long as differentiation is absolute, a diabetic’s only hope for a real cure is successful transplantation of pancreatic islets from a donor. As of the time of writing, this kind of transplant is only effective for roughly five years. In addition, all forms of organ transplantation from a donor require immunosuppressive drugs for life to prevent graft-versus-host disease. This preventive regime must continue even after the transplanted islets have stopped working.
Differentiation cannot be explained through conventional genetics. Although they all carry the same genetic code, cells express differently in different parts of the human body. Some other factor must be at work. This is where epigenetics comes in.
Unlocking the differentiation code
If epigenetics can explain cell differentiation, it is also possible that epigenetics may hold the key to reversing cell differentiation. This could result in the ability to produce stem cells from any cell in the human body. These stem cells could then be differentiated into whatever type of tissue is needed.
This approach would have several advantages. There would be no chance of graft-versus-host disease from transplanted tissues which were grown from a person’s own cells. In theory, healthy tissue of any kind could be grown whenever it is needed, without the difficult wait for a suitable donor. These stem cell applications could potentially cure most non-infectious diseases.
Stem cells which are preserved early in life could also be used later in life to produce tissues with longer telomeres. Because telomeres are pieces of genetic code at the end of each chromosome which protect them from age-related damage, this approach could result in “younger” tissue. In turn, replacing parts of the human body with “younger” tissue could potentially increase human lifespans. How far this could go is still unknown.
Epigenetics and human society
At present, the only known natural sources of totipotent human stem cells are embryos and, to a lesser extent, umbilical cord blood. In addition to being an extremely limited resource, this has led to many ethical debates about acceptable limits of research. Stem cells can also be extracted from bone marrow, fat, and blood, but these types of stem cells only have limited pluripotency.
In contrast, the epigenetic approach could potentially turn any cell in the human body into a source for any other type of human tissue. This completely eliminates ethical questions about sacrificing human embryos for research, because there would be many other much more acceptable sources for totipotent stem cells.
However, if the full medical potential of epigenetics is achieved, these kinds of cures and lifespan prolongation would also have serious effects on human society. If past history is any indication, these new cures and lifespan prolongation will not be available equally to all people. In addition, current pension structures and other economic policies are not equipped to handle the implications of increased human longevity. In all these ways, the medical potential of epigenetics will have an effect on everyone in the human race.