Complexity in Disease: Cancer and the New Science of Epigenetics
1. Do you think it is useful to compare suburban sprawl and cancer metastasis? Can such a strategy be useful in helping us to understand the spread of cancer? Why or why not?
Based on the lecture on how cancer cells metastasize into the other body systems, using the suburban sprawl phenomena as a metaphor is not a far stretch. There are similarities between the two phenomena. In terms of involved components, the cell can be likened to the residents of an urban city. Recalling the pathophysiology of cancer, cancerous cells are the result of mutation wherein the “wires” become crossed and the cell fails to follow its pre-programmed course (proliferation, cell maturation, performance of function then programmed death) and instead becomes stuck on the proliferation gear. Over time, this continued growth forms a tumor and occasionally some mutated cells break off and find their way into other areas. In the suburban sprawl phenomena, the city can be considered as an organ and its residents are the cells that make up the organ. When urban populations become over populated, a “mutation” occurs in the “cell” and these residents leave for the suburbs lending to the suburban sprawl phenomena.
Another similarity between suburban sprawl and cancer metastasis is that both are damaging. When cancer cells invade other organ systems, the affected organ is damaged, its functions are (fatally) altered or disrupted and the body’s homeostasis is thrown off balance. Similarly, the suburban sprawl is said to be ecologically and economically damaging by developing land resources that are better left as farming grounds or nature reserves. The phenomenon lends itself to increased vehicle use thus contributing to fossil fuel pollution. Consequently, reliance on private transportation also breeds laziness and reliance on fast food – effectively adding to the growing incidence of obesity, heart disease and other diseases.
The above mentioned are some of the facts that justifies the use of the two phenomena, though of different nature and subjects, as a means to explain the other.
2. a. In your own words describe a person’s epigenome compared to their genome and how this relates to differences we see between identical twins with the same DNA.
The epigenome literally translated means “before” or “above” (prefix epi-) the genome. This implies that, like the genes or genome inherited by every person, the epigenome is also an inherited trait. However as its prefix connotes, it functions differently from genes. Genes can be seen as computer hardware while the epigenome is the software – Windows for example – that dictates how the hardware will run. However, unlike genes which are unchangeable, the epigenome can be influenced. When methylated they deactivate certain genes causing them to “turn-off” and mask any associated traits. For example, in the agouti mice, exposure to bisphenol A causes the retained activation of the agouti gene which predisposes the mice to obesity, diabetes and cancer and results in a yellow coat. DNA identical twins from the same litter can exhibit this difference with the agouti-activated mice coated yellow and obese while the one with a deactivated agouti gene is coated dark brown and leaner. This is how scientist studying epigenome explain subtle differences in human twins such as one acquiring a certain disease while the other doesn’t (but is still at risk for) (Jirtle, 2007).
b. When comparing the epigenomes of younger and older sets of identical twins, which ones have more differences in gene expression between them?
Adult twins demonstrate higher gene expression differences compared to younger twins. Scientists attribute this to the fact that as twins mature, each becomes exposed to different environmental stimuli that can affect their epigenome. Younger twins pretty much share the same exposure and experiences when relatively young and dependent of their caretakers. However as they grow up and become independent either one may acquire or be exposed to habits (such as smoking and drinking) that may affect their latent epigenomic traits (Jirtle, 2007).
c. How may epigenetics be related to cancer? What does this mean for the potential treatment of cancer? Do you think this is a good idea?
Cancer is said to be primarily a genetic disease and, by nature of its pathophysiology, originates at the cellular level. Scientist studying the epigenome hypothesized that perhaps the mutation a cell undergoes to become a cancerous cell is triggered by either an activation or deactivation of certain genes by the epigenome. If the hypothesis is proven to be true, then epigenetics can be a source of a new treatment method not only for cancer but also for other genetic diseases as well. In fact an experimental treatment using epigenetics is already under clinical trial and results are promising for MDS Leukemia patients participating in the trial (Jirtle, 2007).
d. Increased levels of what chemical in a pregnant mother’s diet led to more yellow, obese mice? Where is the chemical found? What is your level of exposure?
The chemical in question is what is commercially known as bisphenol A or BPA. It is a plastic polymer used in the manufacture of most plastic containers such as those used for soda, baby bottles and food packaging. On the average, Americans have detectable levels of BPA in the body plasma but this chemical is excreted through urine. It is still unknown whether BPA has the same effect on the human body as it does with agouti mice. For the experiment, the mice were exposed to “five times lower than the maximum nontoxic threshold dose in rodents” (cited in Jirtle, 2007).
e. Based on our current knowledge of the epigenome, are a person’s genetics or the environment more important in determining who they are? Did viewing this video and slide show change the way you perceive your lifestyle? Why or why not?
With the new science of epigenetics, it is now evident that both the person’s inherited genes and his environment determine how a person turns out. Until further studies are finished, it is quite safe to assume that though we all have predetermined genetic predispositions, our behaviors and habits also play a significant role in how we turn out. It is now my opinion that we should watch what we eat, drink and expose ourselves to as it may affect our epigenome in many ways and we risk passing any of the negative effects onto future generations.
Jirtle, R. (2007). “Ask the Expert”. NOVA Science Now. Retrieved on February 16, 2009 from http://www.pbs.org/wgbh/nova/sciencenow/3411/02.html