A research team from National Eye Institute (part of the National Institutes of Health) says the technique is a model for studying the genesis of age-related eye diseases.
Researchers have used patient stem cells and 3D Bioprinting to make eye tissue. This will allow scientists to better understand the mechanisms of blinding diseases.
According to a news release, the research team from the National Eye Institute (NEI), part of the National Institutes of Health, printed a combination of cells that form the outer blood-retina barrier—eye tissue that supports the retina’s light-sensing photoreceptors. This technique allows for the study of degenerative retinal diseases like age-related macular disease (AMD) with a theoretically unlimited amount of patient-derived tissue.
Researchers used patient stem cells as well as 3D bioprinting to create eye tissue. This will help advance our understanding of blinding diseases.
Kapil Bharti PhD, heads the NEI Section of Ocular and Stem Cell Translational Research. He noted in the news statement that AMD is a result of damage to the outer blood-retina barrier.
“However, mechanisms of AMD initiation and progression to advanced dry and wet stages remain poorly understood due to the lack of physiologically relevant human models,” Bharti said in the release.
The outer blood-retina barrier consists of the retinal pigment epithelium (RPE), separated by Bruch’s membrane from the blood-vessel rich choriocapillaris. Bruch’s membrane regulates nutrients and waste exchange between the RPE and the choriocapillaris. Bruch’s membrane is impeded by lipoprotein deposits, called drusen, that form in AMD. RPE can eventually break down, leading to photoreceptor loss and degeneration.
Bharti, along with his colleagues, combined three immature types of choroidal cell types into a hydrogel. They were pericytes and endothelial, which are essential components of capillaries, and fibroblasts which give tissues their structure. The scientists printed the gel onto a biodegradable substrate. Within days, the cells had developed into dense capillary networks.
According to the NIH press release, scientists seeded the retinal pigment epithelial (RPE) cells on the opposite side of the scaffold on day 9. On day 42, the printed tissue was fully mature. The printed tissue behaved and looked similar to the native outer blood-retina border, according to tissue analyses and genetic and function testing.
Under stress, printed tissue displayed signs of early AMD. These included drusen deposits under the RPE, and then progressed to dry stage AMD. Low oxygen levels caused wet AMD, which was characterized by hyperproliferation in choroidal vessels and migration into the sub RPE zone. This was due to AMD treatment using anti-VEGF drugs. These drugs suppressed vessel migration and overgrowth, and restored tissue morphology.
“By printing cells, we’re facilitating the exchange of cellular cues that are necessary for normal outer blood-retina barrier anatomy,” Bharti explained in the news release. “For example, presence of RPE cells induces gene expression changes in fibroblasts that contribute to the formation of Bruch’s membrane – something that was suggested many years ago but wasn’t proven until our model.”
Among the technical challenges that Bharti’s team addressed were generating a suitable biodegradable scaffold and achieving a consistent printing pattern through the development of a temperature-sensitive hydrogel that achieved distinct rows when cold but that dissolved when the gel warmed. A good row consistency allowed for a better system of quantifying the tissue structures. They also optimized cell mixture ratios of endothelial and pericytes cells, as well as fibroblasts.
Co-author Marc Ferrer, PhD, director of the 3D Tissue Bioprinting Laboratory at NIH’s National Center for Advancing Translational Sciences, and his team provided expertise for the biofabrication of the outer blood-retina barrier tissues “in-a-well,” along with analytical measurements to enable drug screening.
“Our collaborative efforts have resulted in very relevant retina tissue models of degenerative eye diseases,” Ferrer said in a statement. “Such tissue models have many potential uses in translational applications, including therapeutics development.”
Bharti and his collaborators use blood-retina barrier printed models to study AMD. They are also experimenting with adding other cell types to the printing process such as immune cells to better replicate native tissue.
1. 3D outer retina Barrier reveals RPE dependent choroidal phenotypes in advanced macular damage. Nature uses methods. https://www.nature.com/articles/s41592-022-01701-1. DOI:10.1038/s41592-022-01701-1.