Scientists used patient stem cells and 3D bioprinting to create eye tissue that will advance understanding of the mechanisms of blinding diseases. The research team from the National Eye Institute (NEI), part of the National Institutes of Health, printed a combination of cells that make up the outer blood-retinal barrier – eye tissue that supports the retina’s light-sensitive photoreceptors. The technique offers a theoretically unlimited supply of patient-derived tissue to study degenerative retinal diseases such as age-related macular degeneration (AMD).
“We know that AMD starts in the outer blood-retinal barrier,” said Kapil Bharti, Ph.D., who directs the NEI’s Section for Ocular and Stem Cell Translational Research. “However, the mechanisms of AMD initiation and progression to advanced dry and wet stages are still poorly understood due to the lack of physiologically relevant human models.”
The outer blood-retina barrier consists of the retinal pigment epithelium (RPE), which is separated from the blood-vessel-rich choriocapillaris by Bruch’s membrane. Bruch’s membrane regulates the exchange of nutrients and waste between the choriocapillaris and the RPE. In AMD, deposits of lipoproteins called drusen build up outside Bruch’s membrane, impairing its function. Over time, the RPE breaks down, leading to photoreceptor degeneration and vision loss.
Bharti and colleagues combined three immature choroidal cell types in one hydrogel: pericytes and endothelial cells, which are key components of capillaries; and fibroblasts, which provide structure to tissue. The scientists then printed the gel onto a biodegradable scaffold. Within a few days, the cells began to mature into a dense capillary network.
On the ninth day, the scientists implanted retinal pigment epithelial cells on the back of the scaffold. The printed web reached full maturity by day 42. Tissue analysis, genetic and functional testing showed that the printed tissue looked and behaved similar to the native outer blood-retina barrier. Under induced stress, the printed tissue showed patterns of early AMD such as drusen deposits under the RPE and progression to late dry AMD where tissue degradation was observed. Low oxygen resulted in a wet AMD-like appearance with hyperproliferation of choroidal vessels migrating to the sub-RPE zone. Anti-VEGF drugs used to treat AMD suppressed this vessel overgrowth and migration and restored tissue morphology.
“By printing cells, we facilitate the exchange of cellular cues that are necessary for normal anatomy of the outer blood-retinal barrier,” Bharti said. “For example, the presence of RPE cells induces changes in gene expression in fibroblasts that contribute to Bruch’s membrane formation – something that was proposed many years ago but was not proven until our model.”
Among the technical challenges Bharti’s team faced was generating a suitable biodegradable scaffold and achieving a consistent print pattern by developing a temperature-sensitive hydrogel that rows distinctly when cold but disintegrates when the gel is heated. Good row consistency allowed for a more accurate system for quantifying tissue structures. They also optimized the cell mixing ratio of pericytes, endothelial cells and fibroblasts.
Co-author Marc Ferrer, Ph.D., director of the 3D Tissue Bioprinting Laboratory at the NIH’s National Center for Advancing Translational Sciences, and his team provided expertise in biofabricating the outer blood-retinal barrier tissue “in-a-well.” Disposal. ” along with analytical measurements to enable drug screening.
“Our combined efforts have resulted in very relevant retinal tissue models of degenerative eye diseases,” Ferrer said. “Such tissue models have many potential uses in translational applications, including therapeutics development.”
Bharti and his collaborators use printed models of the blood-retina barrier to study AMD, and they are experimenting with adding additional cell types to the printing process, such as: B. Immune cells to better recapitulate native tissue.
Materials provided by NIH/National Eye Institute. Note: Content can be edited for style and length.