Age-related macular degeneration (AMD) is the number one cause of vision loss, which can contribute to blindness among seniors. Nearly 20 percent of seniors aged 65 to 75 suffer from AMD and yet much is still unknown about the condition.
In age-related macular degeneration, abnormal blood vessels invade the retina, and the macula – located in the retina – begins to deteriorate. The retina senses light and is located in the back of the eye. The name age-related macular degeneration accurately describes the condition as it occurs with aging, so you will not see this vision problem in younger people.
A new study carried out by researchers from Montreal and Boston aimed to uncover the mechanisms behind age-related macular degeneration to find out what causes the vision disorder to contribute to blindness.
Starving eye cells contribute to AMD
Jean-Sébastien Joyal from the University of Montreal explained, “In a murine model of AMD, we found that the inability of photoreceptors – nerve cells that capture light and generate vision – to produce energy may drive abnormal blood vessels to invade the retina. We also discovered that photoreceptors do not rely exclusively on glucose to produce energy as previously thought, but also use lipids as a fuel substrate (like the heart, for example).”
The researchers found that when the blood vessels covering the retina are deprived of oxygen, they start abnormally overgrowing to compensate for the lack of oxygen and deficient energy production. Dr. Joyal explained, “To our surprise, we found that photoreceptors also feed on fatty acids. It was previously believed that these specialized nerve cells, which are energy-intensive, rely primarily on glucose.” Photoreceptors’ propensity for using different fuel sources indicates an evolutionary survival technique that’s advantageous during times of feast and famine.
To test their theory, the researchers used murine models that were incapable of using fat properly and observed abnormal blood vessels in the retina similar to those found in AMD. The researchers found the models developed far more lesions on the retina when raised in darkness, which is a factor known to rise the retina’s energy consumption. The findings suggest a link between energy needs and vascular supply of the retina.
The researchers then asked the question whether blood vessels that are deprived of fat can use glucose. Dr. Joyal explained, “Probably in normal conditions, but paradoxically not in our lipid-uptake deficient model. These have elevated circulating blood levels of fatty acids. To explain this puzzling observation, we found the presence of lipid sensors on the surface of photoreceptors. We think these receptors help match available fuel substrate in circulation with the energy production of photoreceptors. When lipid sensors detect excess fatty acids in the blood, it considers the available lipid fuel to be sufficient and suppresses glucose absorption.”
“In lipid-uptake deficient models, photoreceptors end up being starved for both fatty acids and glucose. Starved photoreceptors secrete signals that attract new blood vessels in order to increase nutrient supply. By proliferating behind the retina however, these vessels cause a decline in eyesight, leading to blindness.”
So, at the end of the day, what’s the take-home message? “Well, there are three based on our in vivo findings”, recaps Dr. Joyal. “AMD may be caused in part by an energy deficiency. Fat is also a source of energy for photoreceptors. And lipid sensors may control glucose entry in the retina,” Dr. Joyal summarized.
Additional research is required to develop new treatment therapies for age-related macular degeneration.
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