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Many diseases and health conditions are linked to one another. In a new study, researchers from the Gladstone Institutes and University of California, San Francisco examined the link between the eye and the brain. They discovered that early signs of cell loss in the retina were linked to early signs of changes associated with frontotemporal dementia (FTD) in patients with an increased risk of the brain disease due to genetics.

For this study, the researchers recruited adults who carried a genetic mutation that was linked to an increased risk of FTD and analyzed the health of the participants' retina. The retina, which is a part of the eye, is made up of neurons that are directly tied to the brain. They discovered that the people with early signs of cell loss in their retinas also had signs of FTD even before physical symptoms showed up.

"The retina may be used as a model to study the development of FTD in neurons. If we follow these patients over time, we may be able to correlate a decline in retinal thickness with disease progression. In addition, we may be able to track the effectiveness of a treatment through a simple eye examination," lead author Michael Ward, MD, PhD, a postdoctoral fellow at the Gladstone Institutes and assistant professor of neurology at UCSF, explained according to the press release.

More specifically, the team found a relationship between neurodegeneration, protein, progranulin, and protein, TDP-43. When progranulin was depleted, TDP-43 move from the cell's nucleus into the cytoplasm. The mislocalization of TDP-43 was then linked to neurodegeneration. The team used mice models of FTD in order to regulate the levels of TDP-43 through another protein called Ran. When the researchers increased Ran's expression, TDP-43 levels increased as well in the nucleus of neurons that were depleted of progranulin. This ultimately prevented the death of the cells.

"This finding suggests that the retina acts as a type of 'window to the brain,'" said Gladstone investigator Li Gan, PhD. "Retinal degeneration was detectable in mutation carriers prior to the onset of cognitive symptoms, establishing retinal thinning as one of the earliest observable signs of familial FTD. This means that retinal thinning could be an easily measured outcome for clinical trials."

The study was published in the Journal of Experimental Medicine.