RNAs as effectors and sensors of pluripotency and differentiation
Human embryonic stem cells (ESCs) have the unique property of being pluripotent: they have the capacity to develop, or ‘differentiate,’ into most of the body's cell types in the petri dish, which makes them an immensely powerful tool for studying how certain diseases arise and for finding drug candidates that might combat these diseases. They also hold the promise to one day enable cell replacement therapies, in which the function of tissues that have been lost or damaged due to disease or injury is restored by transplantation of stem cell-derived differentiated cells. A few years ago, researchers discovered how to derive such pluripotent stem cells from non-pluripotent cells, for example from a person's skin cell. The method of, in effect, de-differentiating an adult cell back to a pluripotent state is called reprogramming, and the resulting cells are so-called induced pluripotent stem cells, or iPSCs. By obtaining iPSCs from patients, researchers have already begun to study the molecular mechanisms responsible for the development of some diseases.
iPSCs are generated by forcing non-pluripotent cells to produce several proteins known as reprogramming or pluripotency factors, usually by infecting the cells with viruses that have been engineered to integrate the DNA encoding these factors into the genome of the cells. As one might imagine, this process can lead to mutations. What is more, these factors must eventually be turned off completely for the pluripotent cell to differentiate, a process that is not always efficient. When the factors remain turned on, the cells can become cancerous, and grafting virus-derived iPSCs carries certain risks. Our research aims to develop a new tool for virus-free derivation of iPSCs, namely by introducing into cells artificial messenger RNAs encoding the pluripotency factors . These RNAs do not incorporate into the cells’ genomes and are eventually degraded by the cells once reprogramming is complete. If we succeed, researchers and clinicians can more safely reprogram cells, bringing iPSC-based cell replacement therapies a major step closer to implementation.
Differentiating ESCs or iPSCs into particular cell types in the petri dish – say, into a so-called dopaminergic neuron, the type of neuron that is lost in patients with Parkinson’s disease – requires the carefully timed and dosed application of growth factors and the manual isolation of cells with the desired properties. Often even our best protocols yield cell populations with only a small fraction of the desired cells. In what is another application of our RNA-based approach, we have developed RNA molecules that can sense the presence of so-called microRNAs, whose presence marks particular cell types, and we aim to show that these RNA sensors can be used to sort out the desired cells from the unwanted ones. Thus, both of our goals promise to help bring stem cells a significant step closer to their clinical use in patients.
Our proposed research ultimately aims to establish new procedures for the safer and more efficient derivation of stem cell-based cell preparations for use in cell replacement therapies. The California Institute for Regenerative Medicine has recognized the urgent need for technologies that accelerate the translation of basic stem cell research into clinical application, and our proposed research is addressing this need.
The technology we seek to launch will benefit California in several ways. Our methods represent an enabling technology that has the potential to accelerate both basic and translational stem cell research conducted in California, thus reinforcing and expanding California’s eminence in the field. Since its utility is not limited to a particular disease area, our technology holds the promise to find widespread application in stem cell laboratories across the state. In addition, the tools, methods and reagents we seek to develop will lower the barrier of entry into stem cell research for scientists from neighboring areas of expertise, thereby leveraging California’s existing stem cell infrastructure.
More importantly, however, by promising to make the derivation of patient-specific induced pluripotent stem cells more efficient, our proposed research promises to speed up the development of stem cell-based disease models, thus facilitating the establishment of drug screens and accelerating drug development. Our innovative non-genetic method to purify desired types of cells from mixed populations without the need to raise cell-type specific antibodies has the potential to become widely used as a routine quality control step in the derivation of purified cell preparations for grafting. Given that a growing number of Californians are afflicted by degenerative diseases for which cell replacement therapy might be of therapeutic benefit, our proposed research may have a direct positive impact on the quality of life of millions of Californians.