A research effort led by Dr. Sheng Ding from the Gladstone Institute and scientists from the Roddenberry Center for Stem Cell Biology and Medicine has successfully transformed skin cells into heart cells and brain cells using little more than a cocktail of chemicals. Previous work that sought to transdifferentiate mature, adult cells into another cell type used gene vectors (such as viruses) that genetically engineered the cells to express new genes at high levels. Because this new protocol uses no genetic engineering techniques, these results are nothing short of unprecedented. This work lays the foundation for, hopefully, being able to regenerate lost or damaged cells with pharmaceutical agents.
In two publications that appeared in the journals Science and Cell Stem Cell, Ding and his collaborators utilized chemical cocktails to drive skin cells to differentiate into organ-specific stem cell-like cells and, then into terminally differentiated heart or brain cells. These results were achieved without genetically engineering cells.
Ding, who was the senior author on both studies, said: “This method brings us closer to being able to generate new cells at the site of injury in patients. Our hope is to one day treat diseases like heart failure or Parkinson’s disease with drugs that help the heart and brain regenerate damaged areas from their own existing tissue cells. This process is much closer to the natural regeneration that happens in animals like newts and salamanders, which has long fascinated us.”
Mature heart muscle cells have very little regenerative ability. Once a patient has suffered a heart attack, the cells that have died are, for the most part, not replaced. Therefore, stem cell scientists have left no stone unturned to find a way to replace dead and dying heart muscle cells. Several clinical trials have transplanted mature adult heart cells or various types of stem cells into the damaged heart. However, such procedures have either not improved heart function or have only modestly improved heart function (with a few exceptions). Typically, transplanted cells do not survive in the hostile environment of the heart after a heart attack and even those cells that do survive fail to properly integrate into the heart. Also, the ability of transplanted cells to differentiate into heart cells is not stellar. Alternatively, Deepak Srivastava, director of cardiovascular and stem cell research at the Gladstone Institute, and his team pioneered a distinctly novel approach in which scar-forming cells in the heart of animals were genetically engineered to differentiate into heart new muscle that greatly improved heart function. Genetic engineering brings its own safety issues to the table and, for these reasons, chemical reprogramming protocols that can do the same thing might provide an easier way to drive heart muscle to regenerate local lesions.
In the Science study, Dr. Nan Cao (a postdoctoral research fellow at Gladstone, and others applied a cocktail of nine chemicals to reprogram human skin cells into beating heart cells. By using a kind of trial-and-error strategy, they discovered the best combination of chemicals to transdifferentiate skin cells into multipotent stem cells. Multipotent stem cells have the ability to differentiate into several distinct cell types from several different types of organs. A second-growth factor/small molecule cocktail drove the multipotent stem cells to differentiate into heart muscle cells.
Perhaps the most surprising result of this protocol is its efficiency. Typically, chemically-induced differentiation is relatively inefficient, but with Ding’s method, over 97% of the cells began beating. These chemically-derived heart muscle cells also responded appropriately to hormones, and they also molecularly resembled heart muscle cells (and not skin cells). Upon transplantation into a mouse heart, these cells developed into healthy-looking heart muscle cells within the heart of the laboratory animal.
“The ultimate goal in treating heart failure is a robust, reliable way for the heart to create new muscle cells,” said Srivastava, co-senior author on the Science paper. “Reprogramming a patient’s own cells could provide the safest and most efficient way to regenerate dying or diseased heart muscle.”
In the second study, published in Cell Stem Cell, which was authored by Gladstone postdoctoral scholar Dr. Mingliang Zhang, PhD, the Gladstone team created neural stem cells from mouse skin cells using a similar approach.
Once again, the chemical cocktail that transdifferentiated skin cells into neural stem cells contained nine different chemicals. Some of the molecules used in the neural stem cell experiment overlapped with those employed in the heart muscle study. Treatment of the skin cells for about ten days with the cocktail transdifferentiated the skins cells into neural-like cells. Virtually all the skin cell-specific genes were shut off and the neural stem cell-specific genes were gradually activated. When these chemical-differentiated cells were transplanted into mice, the cells spontaneously differentiated into neurons, oligodendrocytes, and astrocytes (three basic nerve cells). The neural stem cells were also able to self-replicate, which makes them ideal for treating neurodegenerative diseases or brain injury.
“With their improved safety, these neural stem cells could one day be used for cell replacement therapy in neurodegenerative diseases like Parkinson’s disease and Alzheimer’s disease,” said co-senior author Dr. Yadong Huang, who is a senior investigator at Gladstone. “In the future, we could even imagine treating patients with a drug cocktail that acts on the brain or spinal cord, rejuvenating cells in the brain in real-time.”