News Release, National Institutes of Health
NIH researchers discover that TGF signaling governs immune cell function in the eye.
A signaling pathway controlled by transforming growth factor beta (TGF) could be involved in the progression of age-related macular degeneration (AMD). Researchers at the National Eye Institute (NEI), part of the National Institutes of Health, have found that interrupting TGF signals to immune cells called microglia causes the cells to enter an activated, inflammatory state. These activated microglia damage the retina, the light-sensitive tissue at the back of the eye. This damage is similar to cellular effects observed in AMD, a common cause of vision loss among older Americans. The study was published today in the journal eLife.
Scientists have known for years that people with certain variations in genes in the TGF pathway may be more at risk for advanced AMD, which suggests that TGF might contribute to disease progression. In a healthy retina, neurons continuously emit a variety of signaling molecules, including TGF, which communicate to neighboring cells that all is well, or conversely, let those cells know if something is wrong. When microglia sense normal levels of these molecules, they adopt a branched shape connected with and maintaining the health of their neuron neighbors. But when the signals change, microglia can enter an activated state, where they move to sites of injury to remove damaged or dead cells.
“Communication between neurons and microglia in the retina is going on all the time. Neurons tell the microglia how to behave and how to be of service to the rest of the retina,” said Wai Wong, M.D., Ph.D., chief of the NEI section on neuron-glia interactions in retinal disease, who led the study. “We wanted to know whether there was a connection between this genetic risk involving TGF and abnormal retinal microglia, which are often found in AMD.”
To study this connection, Wong and his team created genetically-modified mice where the researchers could turn off the microglial cells’ ability to sense TGF. When cells stopped sensing TGF, they immediately changed shape, moved to incorrect locations, and began to proliferate. The microglia also decreased their expression of their “sensome,” a collection of proteins that the microglia use to sense their environment. Instead, they started expressing proteins used in their activated state.
While microglia are critical for maintaining healthy neurons, decreased TGF activity switches microglia to a pro-inflammatory mode, which is worse than having no microglia at all, said Wong.
The activation of microglia, and the corresponding loss of microglial support of retinal cells, has cascading effects on the retina. In their mice, Wong and colleagues found that another group of retinal support cells, called Müller glia, began to show signs of distress, and retinal neurons began to fail and die. Additionally, abnormal microglia drastically exacerbated the growth of new blood vessels in a model of AMD. All these pathological changes are similar to what happens in the progression to late AMD, indicating that microglia and TGF signaling may help drive disease progression in humans.
Wong doesn’t believe that TGF signals are completely missing in AMD. Instead, small changes in the strength of the TGF signal could be disrupting the fine balance in signaling that immune cells like microglia require for optimal function. An imbalance in these signals over time can lead to a slow progression towards disease.
TGF may represent an important therapeutic target for treating AMD, according to Wong. “The TGF pathway may be one of the buttons on immune cells that one can tweak, in order to move the immune system in the retina one way or the other, in ways that are beneficial to disease outcome,” he said.
The Southern Maryland Chronicle is a local, small business entrusted to provide factual, unbiased reporting to the Southern Maryland Community. While we look to local businesses for advertising, we hope to keep that cost as low as possible in order to attract even the smallest of local businesses and help them get out to the public. We must also be able to pay employees(part-time and full-time), along with equipment, and website related things. We never want to make the Chronicle a “pay-wall” style news site.
To that end, we are looking to the community to offer donations. Whether it’s a one-time donation or you set up a reoccurring monthly donation. It is all appreciated. All donations at this time will be going to furthering the Chronicle through hiring individuals that have the same goals of providing fair, and unbiased news to the community. For now, donations will be going to a business PayPal account I have set-up for the Southern Maryland Chronicle, KDC Designs. All business transactions currently occur within this PayPal account. If you have any questions regarding this you can email me at firstname.lastname@example.org
Thank you for all of your support and I hope to continue bringing Southern Maryland the best news possible for a very long time. — David M. Higgins II