Researchers from Johns Hopkins Medicine have successfully used stem cells to repair diabetic damage to retinal blood vessels. The researchers believe that their findings will advance regenerative approaches that seek to reverse conditions such as diabetic retinopathy and other eye diseases that lead to blindness.
Induced pluripotent stem cells (iPSCs) have been around for well over a decade now, and they have become familiar to the rejuvenation community in the context of stem cell therapies. iPSCs are created from adult cells that have been genetically reprogrammed into an embryonic stem cell–like state by exposing them to specific protein factors.
Cells that have been reverted to iPSCs have the potential to become any other type of cell in the body and can be further guided towards a desired cell type by using additional chemical stimuli. Resetting a cell’s identity also has the side effect of resetting its cellular age, causing it to function like a young cell once again.
Normally, the body can fix wear and tear itself, but these maintenance systems are not as efficient in older people, and their tissues are often poorly repaired. This is why the use of iPSCs has been steadily growing in the past decade or so to bolster repair as a treatment for arthritis and similar degenerative conditions.
However, there have been considerable hurdles to overcome to get such therapies working. There are many studies that have tested stem cell therapies and shown that some individuals respond well while others do not respond to the same treatment. Unraveling why stem cell therapies are somewhat erratic has been, and continues to be, a challenge.
In a new study published in Nature Communications, researchers experimented with fibroblasts, a common connective tissue cell, collected from type 1 diabetics . They then used reprogramming factors on the cells, but they went further than normal iPSCs, reverting the cells back to an even more primitive and flexible state.
These new cells closely resemble the state of embryonic cells around six days or so following fertilization, which are are very early on developmentally. According to the researchers, it is during this phase that the cells are the most “naive”, or flexible enough to become any other type of cell in the body, and have a far greater level of efficiency than iPSCs, which can often have high failure rates and are not programmed successfully.
To create these early naive stem cells, the research team used a cocktail of drugs known to reprogram cells, namely the GSK3β inhibitor CHIR99021, which inhibits carbohydrate storage in cells, the MEK inhibitor PD0325901, an anti-cancer drug that inhibits cell growth, and, finally, a PARP inhibitor, which has been used to treat cancers. They named this combination of drugs 3i, due to the three inhibitor drugs that are used.
During the study, the researchers charted changes to various biomarkers, including proteins NANOG, NR5A2, DPPA3 and E-cadherin, which facilitate cell differentiation. They found that the levels of these proteins resembled those found in naive epiblast cells, the primitive cells that are found in six-day-old human embryos.
The good news is that the 3i cocktail also appeared to reprogram the cells without making harmful alterations to DNA or causing abnormal epigenetic alterations. Past attempts to create similar naive stem cells have tended to suffer from problems with epigenetic changes, so the new approach appears to mitigate this.
Finally, the researchers injected the mice with vascular progenitors, cells that can build new blood vessels, that were created from a basis of 3i naive stem cells. The mice were suffering from a form of diabetic retinopathy in which the tiny blood vessels in the eye are damaged, eventually leading to blindness.
They discovered that once injected into the eye, the vascular progenitor cells moved into the deeper tissue layer of the retina with greater efficiency than the same types of cells created using an iPSC approach.
The vascular progenitors successfully took root in the tissue there, and the majority of these cells were still alive at least four weeks later when examined during the study. The cells also had their disease-associated epigenetic makers erased, which returned them to a healthy, non-diabetic, functional state.
Here, we report that the functionality of vascular progenitors (VP) generated from normal and disease-primed conventional human induced pluripotent stem cells (hiPSC) can be significantly improved by reversion to a tankyrase inhibitor-regulated human naïve epiblast-like pluripotent state. Naïve diabetic vascular progenitors (N-DVP) differentiated from patient-specific naïve diabetic hiPSC (N-DhiPSC) possessed higher vascular functionality, maintained greater genomic stability, harbored decreased lineage-primed gene expression, and were more efficient in migrating to and re-vascularizing the deep neural layers of the ischemic retina than isogenic diabetic vascular progenitors (DVP). These findings suggest that reprogramming to a stable naïve human pluripotent stem cell state may effectively erase dysfunctional epigenetic donor cell memory or disease-associated aberrations in patient-specific hiPSC. More broadly, tankyrase inhibitor-regulated naïve hiPSC (N-hiPSC) represent a class of human stem cells with high epigenetic plasticity, improved multi-lineage functionality, and potentially high impact for regenerative medicine.
The team will now be following up this initial success with further studies to refine the 3i cocktail approach. The arrival of a more efficient stem cell type and reprogramming process is very welcome indeed, given that stem cell exhaustion is a hallmark of aging.
 Park, T. S., Zimmerlin, L., Evans-Moses, R., Thomas, J., Huo, J. S., Kanherkar, R., … & Barbato, M. (2020). Vascular progenitors generated from tankyrase inhibitor-regulated naïve diabetic human iPSC potentiate efficient revascularization of ischemic retina. Nature Communications, 11(1), 1-20.