I have heard of genetics, but what is epigenetics?
Blog vol 6.10. I have heard of genetics, but what is epigenetics?
Epigenetics plays a big role in the aging of the eye.
Genetics is the study of genes and of their component parts particularly deoxyribonucleic acid, DNA. Epigenetics studies changes to DNA through environmental stress, chemical changes from diet, or aging. These changes are usually reversible. Using the analogy of a computer, the DNA is like the fixed hardware, and the changes to the DNA (epigenetics) are like software which is continually “updating”.
A recent paper in Nature (read here) uses a meta-analysis of 17 different tissues in humans over a lifetime and comes up with some interesting findings. We are focussing on the eyes.
It has been known for some time that surface changes to our DNA affect the retina in aging. Macular degeneration, which is the number one cause of vision loss in North America, is a prime example.
As we age, the DNA in our genes gets methylated: a small chemical tag, most likely a cytosine base, changes the structure of the DNA and alters its expression. At the most extreme, the tag can actually turn off the gene so that it does not get expressed in the tissue. In the “atlas” of epigenetics, retinal tissue is the most likely to be affected as we age. The theory is that the eyes’ high oxidative demands make it more susceptible to this tagging.
That is the hard reality. From changing light photons into neural impulses then into visual images in the cortex, the metabolic requirements of the visual system are staggering. The photoreceptors are constantly being absorbed and replaced as they are used in this all-consuming process. It should not surprise us that all this activity can make the retina very vulnerable to any tweaks in the DNA. Of course, there are the regular genetics of macular degeneration, the ones you inherit, where there are a number of alleles that are directly linked to the disease, like ARMS2 and HTRA1, on chromosome 10. Add the methylation of DNA to pre-existing genetics and the odds are not in your favour.
What to do about methylation? Prevention is key. Our modifiables are cardiovascular fitness, diet, possible therapeutic helps like statins, eliminating smoking, and blocking ultraviolet, along with limiting blue light exposure (jury still out on this, but would not be surprised). On the positive side, use longer wavelengths like red light to boost mitochondria (think oxidation cellular powerhouses), include in your diet leafy greens, blueberries, anything rich in antioxidants, and get some omega 3 fatty acid (fish oils).
Do note that we can do everything right and still end up with macular degeneration. Aging is not preventable or reversible. All we can do is work to minimize our risk factors.
Please have regular eye visits, check-ups with your family doctor, get out for a walk and enjoy the beautiful fall weather, and be deliberate about what you eat.
‘til next week,
The good doctor
