Efficient Revascularization of the Retina Using Primitive Stem Cells

Efficient Revascularization of the Retina Using Primitive Stem Cells

Image: Elias Zambidis, Johns Hopkins Medicine – Human vascular progenitor cells (green) created from naïve stem cells

Researchers at Johns Hopkins Medicine have used advanced regenerative medicine techniques to reverse diabetic retinopathy in mice. Their technique could also be used to treat other eye diseases that cause blindness.

Diabetic retinopathy is the leading cause of blindness in adults in the United States. It is a complication of diabetes caused by high blood sugar levels. High blood sugar causes blockages in the blood vessels in the retina where light is processed and converted into neural signals that are sent to the brain. When the blood vessels get blocked, new blood vessels are formed, but they fail to develop properly and leak causing vision problems. Diabetic retinopathy can also lead to glaucoma and retinal detachment. It has been estimated that by 2050, 14.6 million Americans will suffer from diabetic retinopathy.

The researchers harvested connective tissues cells – fibroblasts – from patients with type 1 diabetes and reprogrammed the cells in the lab to revert them to a primitive state where they function as stem cells – cells that have the ability to differentiate into all other cell types in the body, such as blood vessels.

Human cells were first reprogrammed into induced pluripotent stem cell (IPSCs) in 2007, but the Johns Hopkins researchers say the stem cells they created are much more primitive than standard IPSCs. Their primitive stem cells more closely resemble embryonic stem cells 6 days after fertilization – a time when the stem cells are more naïve and can differentiate into any cell type with greater efficiency.

To achieve this, the researchers bathed the fibroblasts in a solution of two drugs commonly used to reprogram cells into IPSCs: GSK3β inhibitor CHIR99021 and MEK inhibitor PD0325901. The former blocks carbohydrate storage in cells and the latter is an experimental drug for blocking cancer cell growth. The researchers added a third drug to the mix, a PARP inhibitor, which is a drug used to treat breast and ovarian cancer. The drug cocktail, named 3i by the researchers, was much more effective at winding back the clock and reprogramming the fibroblasts into a very primitive stem cell state.

Reprogramming stem cells is just the first stage. The researchers then need to get the cells to differentiate, and historically there have been problems at this stage. While IPSCs can be converted into a range of different cell types, they often become cancerous.

The researchers differentiated their primitive stem cells into vascular progenitor cells, from which blood vessels are formed, using proteins such as NANOG, NR5A2, DPPA3 and E-cadherin in similar concentrations to those found in epiblast cells in 6-day-old human embryos.

The vascular progenitor cells were then injected into the eyes of mice bred to have a form of diabetic retinopathy. Another group of mice were treated with vascular progenitor cells created from standard IPSCs. The researchers found the vascular progenitor cells created from their naïve stem cells migrated to the innermost tissue layer in the retina with greater efficiency than those created from standard IPSCs and most survived for the duration of the four-week study and regenerated blood vessels in the retina. The cells created from standard IPSCs failed to migrate as deeply or did not survive for the duration of the study.

“Interestingly, the 3i ‘naive reprogramming’ cocktail appeared to erase disease-associated epigenetics in the donor cells, and brought them back to a healthy, pristine non-diabetic stem cell state,” said Elias Zambidis, M.D., Ph.D., associate professor of oncology at the Johns Hopkins Kimmel Cancer Center and a member of Johns Hopkins’ Institute for Cell Engineering. “Our study results bring us a step closer to using stem cells more widely in regenerative medicine, without the historical problems our field has encountered in getting such cells to differentiate and avoid becoming cancerous.”

The researchers are now refining their 3i cocktail and are performing further studies to assess the regenerative capabilities of their naïve stem cells.

You can read more about the study in the paper – Vascular progenitors generated from tankyrase inhibitor-regulated naïve diabetic human iPSC potentiate efficient revascularization of ischemic retina – which was recently published in the journal Nature Communications. DOI: 10.1038/s41467-020-14764-5

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