Bioprinted 3D Model Uncovers Drivers of AMD

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Researchers from the NEI bioprinted a 3D model of the outer-blood-retina barrier (oBRB) to study the role of the retinal pigment epithelium (RPE) and choriocapillaris in the development of age-related macular degeneration (AMD). They found that complement activation in the oBRB induced dry AMD, whereas hypoxia triggered wet AMD.¹

“We believe that 3D-oBRB is a powerful and physiologically relevant model for the identification of genetic and environmental factors contributing to AMD. Understanding the mechanisms of AMD initiation and progression can help us diagnose and treat AMD at an early stage or prevent the progression of dry AMD to wet AMD,” said Kapil Bharti, PhD, at the NEI.

Bioprinted oBRB also will provide “a unique opportunity to test new drugs and gene therapies directly on human eye tissue, study the role of genetics on treatment response, and develop personalized therapies,” he added.

BIOPRINTED MODEL OF WET AMD. Fluorescence image showing choroidal neovascularization in bioprinted 3D human eye tissue (cyan = RPE cells; dark blue = nuclei of RPE cells; magenta = proliferative choroidal capillaries that have migrated into the sub-RPE space).

Study rationale. A key challenge hindering the development of effective therapies for AMD is the limited understanding of the disease owing to the lack of reliable models, said Dr. Bharti. “So far, nobody has been able to replicate true AMD-like macular phenotype in animal models.”

The team developed bioprinted oBRB as an in vitro model to study molecular and morphological changes during AMD initiation and progression. They also used human oBRB tissue to study the interaction between RPE and choriocapillaris.

Producing stable tissue. The bioprinting process deposited human endothelial cells, pericytes, and fibroblasts onto a biodegradable scaffold containing an RPE monolayer. Characterization of the bioprinted 3D-oBRB tissue showed that the polarized RPE monolayer supported the formation of fenestrated capillaries and a Bruch membrane–like structure by promoting gene expression alterations in choroid cells. “This native-like oBRB tissue was stable for weeks, allowing us to perform long-term studies,” Dr. Bharti noted.

Triggers of dry and wet AMD. Results of tissue analyses and genetic and functional testing showed that complement activation promoted sub-RPE drusen deposits and significant RPE loss, which are features of dry AMD. In contrast, stabilization of the transcription factor HIF-a triggered wet AMD and choriocapillaris neovascularization, confirming the role of hypoxia in AMD progression.

Thus far, “people thought that only the endothelial cells and pericytes in the choroid were important in AMD,” Dr. Bharti said. However, the NEI team found, the fibroblasts contributed to a different part of Bruch membrane, suggesting that they are also “important for the formation of a healthy choroid at the back of the eye,” he said.

Looking ahead. “We are working on further improving our human oBRB model by incorporating macrophages and perfused capillaries to mimic the microenvironment and systemic circulation of the human eye,” Dr. Bharti said. The team also plans to use the oBRB model to study the role of metabolism in AMD progression.

—Christos Evangelou, PhD

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1 Song MJ et al. Nat Methods. 2023;20(1):149-162.

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Relevant financial disclosures: Dr. Bharti—None.

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