Gut Bacteria Slip into the Eye

A gene mutation causes porous gut and retinal barriers, allowing bacteria to travel from one to the other, triggering retinal degeneration in mice.

Rachael Gorman in The Scientist: The retina is layered with photoreceptors, a variety of other neurons, and protective and structural membranes, but retinal disorders can tamper with this delicate system. Mutations in the Crumbs homolog 1 (CRB1) gene disrupt the integrity of retinal membranes, leading to the gradual loss of photoreceptors. CRB1 mutations associate with multiple retinal diseases, including Leber congenital amaurosis and retinitis pigmentosa. However, since each patient’s disease presents differently, with various types, numbers, and locations of retinal lesions, some scientists suspect that environmental factors interact with the CRB1 gene to influence how disease manifests.

new study published in Cell demonstrated one way that the environment modifies the phenotype of mice with a CRB1 mutation.1 Researchers showed that CRB1 degradation triggers both a leaky colon epithelial barrier and a leaky retinal pigment epithelium (RPE) barrier in the mice, allowing bacteria to pass from the gut into the bloodstream, and then into the eye, damaging the retina.

Converting photons into electrical signals requires an intricate retinal anatomy. The retina’s inner limiting membrane separates the vitreous cavity of the eye from the axons of the first layer of neurons. Deeper in, the outer limiting membrane, the membrane compromised in CRB1 mutants, divides photoreceptor nuclei from their light-absorbing outer and inner segments. Finally, the RPE separates photoreceptor outer segments from a tissue called the choroid, which has high blood flow.

“The gut part is a new finding,” said Peter Quinn, a Columbia University retinal disease researcher not involved in this study. “The finding that the retinal pigment epithelium is also broken down is a completely new finding.”

More here.