Cell Division: A Proposed Model for Cell Identity Preservation

While all cells in the human body contain the same DNA (genetic instructions), each cell expresses only the genes needed to become the cell type it is (i.e. neuron, lymphocyte, cardiomyocytes). Each cell’s fate is largely determined by chemical modifications to the histone proteins around the DNA, which control gene expression. Considering that these cells lose half of their modifications when replicating in cell division, a new MIT study suggests that these cells maintain their memory of what cell type they’re supposed to be through the 3D folding pattern of its genome determining which portions will be marked by chemical modifications. Essentially, the way that these chromosomes were folded are like a blueprint to determine where the remaining marks should go. Thus, by juggling between 3D folding and the marks, the epigenetic memory can be preserved over hundreds of divisions.

In general, this proposed model provides valuable insight into how epigenetic markings play a role in establishing cell identity and maintaining this memory after cell division. Through this model, biologists may be able to better understand how this epigenetic memory of cell identity is lost as cells begin to age and potentially better understand the epigenetic mechanisms underlying our genome.

For more information, view the news article linked here and the journal publication of the research study linked here.

The Biological Clock for Some Tissues May Be Ticking Faster than for Others

       Popular Science recently posted an article about Steve Hovarth, a geneticist at UCLA’s medical school, who has developed a new technique for identifying the exact biological age of human tissue. His research suggests that not all tissues of the body follow the same biological clock. The process involves the observation of DNA methylation, which has been suggested to be a biomarker for the age of a cell. As hypothesized, cancerous tissues age far faster than healthy tissue. However, it was also displayed that even some healthy tissues age faster than the rest of the body; in Hovarth’s study, breast tissue was examined. While completely healthy breast tissue is two to three years older than the rest of the female body, it was also shown that tumors aged the tissue an additional 36 years, and healthy breast tissue that was near a tumor was about 12 years older than tissue in other parts of the body.

Hovarth’s study highlighted over 8,000 healthy samples of 51 different types of tissues. He then went even further to study 6,000 samples of cancerous tissue. For each sample, Hovarth examined the DNA methylation levels of the given tissue. Once the biological age of the tissue was determined through the observation of DNA methylation levels, Hovarth compared the biological age of the tissue to the chronological age of the issue donor. His method was virtually completely successful. Not only did Hovarth’s study find a method of effectively calculating the age of various tissues, but he was also able to transform adult human cells into pluripotent stem cells. This transformation essentially rearranges the cells so that they act as if they were embryonic stem cells; Hovarth commented that this transformation “resets the cells’ clock to zero.”

I found this article particularly interesting not only because it explains how some tissues are biologically older than the rest of the body, but also because it proposes a way to essentially reverse that aging process. Looking at this article from a health perspective, it is fascinating how some parts of the body can age faster than others; this increased age of certain tissues definitely makes them more susceptible to acquire different diseases and illnesses. If Hovarth’s method of reprogramming cells to make them act as embryonic stem cells proves to be effective, then not only can the medical community use this method to combat different diseases, but it can also be utilized as a new weapon in the ongoing war against aging. I am a gerontology minor, so I have been learning a lot about the downside of aging as well as the biological aspects of aging. It is exciting to think that in the near future, this method can be perfected and used to improve the health of the population of individuals who are experiencing difficulty or discomfort when aging.

Aging Changes all Tissues

Possibly Reverse Cell Aging by Adopting a Healthy Lifestyle

        

     A study of 35 men with prostate cancer conducted by the University of California may support the fact that a strict diet, meditation, and exercise routine may reverse cell aging. The men who altered their lifestyles had much younger cells. Ten men adopted meditation, yoga, and a vegetarian diet. The telomeres of these men increased by an average of 10% over the five year study period, while the telomeres of the twenty-five men who did not change their lifestyle decreased by an average of 3%.  Telomeres are caps at the end of the chromosome that protest the chromosome end and protect against genetic information loss in cell division. Telomeres shorten as we age due to cell division and indicate when cell death should occur. Many have wondered if the shortening of telomeres can be stopped or reversed. The work done by Professor Dean Ornish suggests that telomere length can be increased.

     Several age-related diseases, such as many cancers and heart disease, are related to telomere length. A possible area of research may be the effect of altered lifestyles and increase in telomere length on cancer outcomes. Professor Ornish suggests that if the study is applied to controlled, randomized trials, lifestyle changes can be proven to decrease the risk of early mortality and many diseases. Yet, some, such as Dr. Lyn Cox and Dr. Tom Vulliamy, believe that the study is too small to draw significant conclusions. Decrease in telomere length is unlikely to be the only explanation for aging.

     Other work supports these findings by suggesting that sedentary lifestyles hasten cell aging. A twin study showed that those who engage in physical activity in their free time were “biologically younger” while those who were inactive had telomeres that shortened faster. The study was conducted at King’s College London using 2,401 white twins. The study focused on white blood cells in the immune system. Individuals who engaged in the least amount of exercise had telomeres 200 nucleotides shorter than those that engaged in the greatest amount of exercise. On average, those who engaged in the most physical activity had telomeres the length of inactive individuals ten years younger. Further, stress may impact telomere length.

     I believe that research on the effect of lifestyle on cell aging holds much significance. Heart disease, diabetes, and other diseases caused by unhealthy lifestyles are on the rise. Giving concrete evidence of the effects of lifestyle on our biology will be more effective in encouraging individuals to adopt healthy lifestyles. Studies should be conducted on individuals of varying races, genders, and ages to, as the studies discussed were conducted using only small or homogenous groups. I hope that further, more extensive studies are conducted to give concrete evidence that healthy lifestyles can help decrease cell aging. 

Sources: http://www.bbc.co.uk/news/health-24111357
              http://news.bbc.co.uk/2/hi/health/7212698.stm