Organ regeneration, a phrase usually found only in science fiction movies, is closer to reality thanks to a new generation of bioengineering scientists. They are investigating how stem cells develop into tissues or organs and mimic the growth process in the lab environment.
Randy Ashton, an assistant professor at the Wisconsin Institute for Discovery and the biomedical engineering department at the University of Wisconsin-Madison, recently reported his group is close to generating two-dimensional tissues of the central nervous system (such as a slice of a spinal cord) and expects to be able to regenerate such tissues within five years.
The secret of Ashton’s work is to start with a specific sort of stem cell, called pluripotent stem cells (PS cells). These cells are a normal component of embryos and have the ability to develop into any type of cells of the human body. Not all kinds of stem cells can do this: For example, some stem cells are only able to evolve into closely related families of cell types. PS cells now can be derived from adult skin cells.
According to Ashton, PS cells can “sense” their environment, and, depending on different factors in the environment, can become different kinds of organ cells. For several years, Ashton has been working to uncover those environmental factors so that he can direct PS cells to evolve into the specific cell types he needs.
An example of such a factor is something called cellular communication molecules. Ashton says these molecules exist in every kind of human organs. They are called “communication molecules” because they can send biological signals to stem cells and direct those cells to morph into a specific type of organ cells. Understanding exactly how communication molecules instruct stem cells could enable scientists to replicate the signal and, thus, direct stem cells to develop into the desired organ cells.
But this is just the first step to achieving organ regeneration. Since real tissue is made up of multiple types of cells, scientists not only need to understand which factors can be used to generate a specific cell type but also how to generate these multiple cell types in a proper spatial orientation to obtain a functional tissue or organ.
Thus, according to Ashton, the group is now working to build an artificial environment, called a 3-D biological scaffold. The artificial environment could mimic the biological cues that help scientists control the development of stem cells into complex tissues or organs.
Engineering the scaffold for cells’ growth is like building a particular house. “When you build a house [for cells’ development],” Ashton said, “how do you decorate the house so that as the tissue grows into the house, it gets exposed to the right type of cues at the right time frame to generate a heart or a liver?”
The idea of engineering a cell growth environment outside the body also avoids the complexity of environmental disturbance inside a living body and makes it easier for scientists to control the development of higher orders of tissues.
Ashton’s group mainly focuses on tissue or organ growth in the central nervous system, spinal cord and brain. Their work may create new platforms for biological or medical researchers to model the mechanism of diseases, Ashton notes.
“If I could create a spinal cord and I want to look at a disease like ALS [amyotrophic lateral sclerosis] that affects the spinal cord tissue, then I could essentially get the pluripotent stem cell from patients that have ALS, [and] make my spinal cord tissue from that, and then see what goes wrong in the diseases,” Ashton said.
So far, Ashton’s group has been able to generate different types of neurons, which they call one-dimensional tissues. But the team is now close to generating two-dimensional tissues of the central nervous system and nerve tubes, such as a slice of a spinal cord. Ashton says he expects to successfully regenerate such neural tissues within five years.
Regenerating human tissues or organs has potential for treating and possibly curing a number of injuries and diseases, for example spinal cord injuries or brain diseases, by replacing the damaged parts. Regenerative medicine is described in a government report (“2020: A New Vision-A Future for Regenerative Medicine” by U.S. Department of Health and Human Services, 2005) as the next evolution of healthcare. Officials have also implemented the Federal Initiative for Regenerative Medicine with an ambitious goal of offering tissues and organs for Americans in need by as early as 2020.
Building up a complete, three-dimensional functional human tissue or organ is definitely a complicated task. Yet considering the remarkably fast development in stem cell technology in the past decade, Ashton is optimistic about the future. “It is definitely not unreasonable that in the next 20 years you will be able to regenerate a heart or a liver or a portion of spinal cord or a portion of the brain,” he said.
