Duke engineers grow retinal blood vessel cells from pluripotent stem cells

Biomedical engineers at Duke University have used induced pluripotent stem cells (iPSCs) to grow specialized blood vessel cells critical to retinal health for the first time.

When injected into mouse models of retinal disease, these "retinal endothelial cells" integrated into the damaged tissue to regenerate blood vessels and restore retinal function. Researchers also demonstrated these cells' ability to form functional retinal vascular tissue in a lab-grown environment, providing a pathway to model and research various eye diseases.

The results, published online June 30 in the journal Nature Biomedical Engineering and federally funded through the National Eye Institute and NASA, point toward the potential of using these retinal cells and models to develop new methods of impactful vision loss treatments and eye disorder research.

Retinal vascular diseases affect millions of people in the US, but our understanding remains limited, hindering our ability to discover and develop new therapeutics. Using human stem cells, we generated the cells found in retinal blood vessels, paving the way for new therapeutic approaches."

Sharon Gerecht, the Paul M. Gross Distinguished Professor and Chair of Biomedical Engineering at Duke

The old saying that the eyes are windows into the soul is more accurate than one might think. Neurons from the retina-the back part of the eye that detects light-extend directly to the brain, technically making the eyes part of the central nervous system.

Also like the brain, the retina has a blood barrier that strictly controls what gets in and out such as oxygen, nutrients, water-and pharmaceuticals. While this barrier keeps the retina healthy and relatively protected from disease-causing agents, it also makes treating the retina difficult.

This barrier is formed by blood vessel tissue comprising a tight network of retinal endothelial cells, which form the inner layer of blood vessels, in concert with other specialized cells called pericytes and astrocytes. The specificity of these cells and the fact that they do not form in other areas of the body make the complex tissue difficult to heal or to grow from scratch.

"When this specialized blood vessel tissue begins to break down, it can cause a lot of different diseases that lead to vision loss," said Parker Esswein, a PhD student working in the Gerecht laboratory and first co-author of the paper. "While there are sources of retinal endothelial cells, being able to grow a continuous supply from scratch could offer many advantages for those working in the field."

These retinal endothelial cells are currently collected and grown from real patients, making them relatively expensive with a limited supply. To expand access, reduce cost and control variability, the Gerecht lab wanted to see if they could grow them from iPSCs. These are essentially mature adult cells reprogrammed to become primal versions of themselves that can then grow into a wide variety of other cell types.

To do this, Ying-Yu Lin, a former PhD student in Gerecht's lab, and Esswein took commercial iPSCs and used a well-established procedure to get them to grow into common endothelial cells that form the inner layer of most of the body's blood vessels. The researchers then used a specialized cocktail of growth factors to coax the cells into becoming the specific type of endothelial cells found in the retina.

Once successful, the researchers put their new creations to the test.

In benchtop experiments, the team was able to get the cells to form the same networks and structures that they do within the body. They then subjected these lab-grown tissues to low oxygen and high glucose levels, which are detrimental conditions often seen within real people. These conditions are fundamental causes of diabetic retinopathy, the leading cause of vision loss in working-age people in the United States, and caused the tissue barrier to break down just like it does in patients.

The researchers then tried their lab-grown cells as a therapy for mouse models with weak, unstructured retinal blood vessels. When injected into the mice before any actual vision loss occurred, these cells successfully integrated into the existing tissue and helped develop strong blood vessels with strong barriers.

"The tests showed that these lab-grown cells have promise for preventative treatments, especially since they should be easier and cheaper to obtain using our technique," Esswein said. "And while our benchtop experiments did not attempt to model a wide variety of specific eye diseases in these studies, we're confident we can create excellent human tissue models in the lab to help better understand these diseases and uncover therapies."

Moving forward, the researchers are planning to explore these potential uses for their retinal endothelial cells both in their laboratory and through emerging industry partnerships. The group also has a patent pending that covers both the stem cell-based therapeutics and in vitro modeling for drug discovery and testing.

This work was supported by the National Institutes of Health (EY035853), the SNT0101 from the Translational Research Institute through NASA Cooperative Agreement NNX16AO69A, the National Science Foundation Research Fellowship Program, and the National Defense Science & Engineering Graduate Fellowship Program.