Age-related macular degeneration: Study finds surprising culprit
A new study suggests that a molecule that always suppresses harmful blood vessel growth can do the opposite in a kind of sight loss called age-related macular degeneration (AMD). If confirmed in future studies, the discovery could result in more effective treatments.
More than 1.8 million Americans aged 40 years and over have AMD, according to the Centers for Disease Control and Prevention (CDC).
According to 1 source, 10-15% of folks with AMD have a far more severe form of the condition known as “wet” AMD that progresses more rapidly.
Wet AMD involves inflammation and excessive growth of fragile arteries beneath the macular. It is the central part of the retina that allows the attention to see details. These vessels leak blood and fluid, which damages photoreceptors in the macular and results in loss of central vision.
Research into other conditions involving nerve damage, such as for example Alzheimer’s and Parkinson’s disease, suggests that an immune-signaling molecule called interleukin-4 (IL-4) may play an anti-inflammatory, protective role.
IL-4 is also recognized to suppress blood vessel growth, which might assist in preventing the growth of tumors.
In addition, bone marrow cells usually help the body repair damaged tissues, including blood vessels.
Aqueous humor
Researchers in the Division of Ophthalmology and Visual Science at Tottori University in Japan set out to discover whether IL-4 and bone marrow cells protect the photoreceptors of folks with wet AMD.
The team published their finding in the journal eLife.
First, they measured levels of IL-4 in the aqueous humor - the watery fluid in the eyes - of 234 people with wet AMD at their first treatment session. They also collected samples of aqueous humor from 104 older persons undergoing surgery for cataracts, who served as controls.
People who have wet AMD had higher degrees of IL-4 than those in the control group.
The researchers also discovered that mice with a condition that mimics AMD had raised degrees of IL-4 to them. To determine whether the molecule is protective or harmful, they injected IL-4 into the bloodstream of the mice and found it increased excessive blood vessel growth to them.
Injecting the mice with an antibody that blocks IL-4 production had the contrary effect, reducing blood vessel growth.
The researchers continued to use cell culture experiments to show that IL-4 really helps to control the response of mice bone marrow cells and the growth of new retinal arteries. In its absence, the fragile arteries that characterize AMD were unable to grow.
Crucial role
“Our results show that IL-4 plays a crucial role in excessive blood-vessel growth by recruiting bone marrow cells that aid this growth to the lesion in the eye,” says Takashi Baba, co-first author of the study.
The researchers conclude that far from protecting photoreceptors by inhibiting the growth of new arteries - which is what they expected - IL-4 promotes the growth of more arteries.
“These results were surprising and advise that normally helpful immune responses can instead cause more harm,” says co-first author Dai Miyazaki.
Within their paper, the authors write that while IL-4 may reduce inflammation, prevent the growth of new arteries, and protect nerve cells, these functions appear to be dependent on the context.
Nonetheless, they think that their surprise finding offers new possibilities for treating AMD.
“As IL-4 plays an integral disease-promoting role in AMD, it may serve as a target for new treatments to take care of this problem,” says Miyazaki.
These treatments could block either IL-4 itself or the receptors to which it binds.
For now, however, the findings remain preliminary and will should be investigated further to verify the researchers’ conclusions.
Source: www.medicalnewstoday.com
