Controlling cells' environments: A step toward building much-needed tissues and organs

 

With stem cells so fickle and indecisive that they make Shakespeare’s Hamlet pale by comparison, scientists today described an advance in encouraging stem cells to make decisions about their fate. The technology for doing so, reported here at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), is an advance toward using stem cells in “regenerative medicine” -- to grow from scratch organs for transplants and tissues for treating diseases.

“Stem cells have great potential in regenerative medicine, in developing new drugs and in advancing biomedical research,” said Laura L. Kiessling, Ph.D., who presented the report. “To exploit that potential, we need two things: first, reproducible methods to grow human stem cells in the laboratory, and second, the ability to make stem cells grow into heart cells, brain cells or whatever kind of cell. Our technology takes a different approach to both of these problems, and the results are very encouraging.”

Biologically, so-called pluripotent human embryonic stem cells have not made up their minds about what to become. That’s essential because these cells, which are derived from embryos, have the agility to develop into the hundreds of different kinds of cells in a fully-formed human body. But controlling their differentiation has also stood as a major barrier to making the stem cell dream come true and using these all-purpose cells in medicine.

Past approaches to growing and scripting the fate of stem cells have involved adding growth-regulating and other substances to cultures of stem cells growing in the laboratory. These conditions left scientists guessing about exactly what wound up in the stem cells. Kiessling and colleagues are pioneering a new approach that involves using chemically controlled surfaces.

Kiessling previously developed chemically modified plastic and glass surfaces that take much of the guess work out of growing stem cells in laboratory cultures. In the past, scientists grew stem cells on surfaces that contained mouse cells. That left scientists with nagging questions about possible contamination of stem cells with disease-causing animal viruses — a stumbling block for using stem cells in potential medical applications. And that growth system was what scientists term “undefined.” There were variations from batch to batch of mouse cells, and scientists never really knew what the stem cells were coming into contact with and how it might be changing them. The synthetic, chemically-defined, surfaces ended that uncertainty. The approach was inexpensive, simple and a much-needed advance in producing stem cells, Kiessling explained.

With the ability to grow stem cells on the synthetic surfaces under chemically defined, or known, conditions, Kiessling’s group took an additional step in their latest research. It found that chemically defined surfaces can exert control over signaling pathways. “Signaling” is how molecules talk to one another and get things done inside a cell. It’s how an immune cell knows to fight an infection or how a pancreatic cell determines that more insulin is needed in the bloodstream, for example. By controlling how molecules inside a stem cell communicate, researchers could someday in the future nudge them to become one type of cell or tissue over another.

To see whether a new chemically defined surface could change signaling in a pilot experiment, Kiessling tested cancer cells. The research involved use of a signaling substance, transforming growth factor-beta (TGF-beta), which controls a range of activities, from cell growth to self-destruction.

“The new surfaces give scientists much more control over cells, opening up a wide range of possible future applications,” Kiessling explained. Building directly on the results of the pilot study, the surfaces could have applications in wound healing. TGF- beta can help wounds heal, but if it touches healthy skin, inflammation or even a cancerous tumor could develop. “We haven’t done this, but you could imagine a bandage that has a localized concentration of the special peptide surface that would recruit TGF-beta just to the wound site,” said Kiessling.

The surfaces also could make it easier to manufacture organs and tissues in the laboratory someday. “We think that this strategy, with different sets of peptides (building blocks of proteins) bound to the surface, could direct certain human embryonic stem cells on the surface to become one type of cell and other stem cells to become a second cell type, right next to each other. For the tissue engineering involved in growing replacement organs, you need to organize specialized cells in particular ways like this.”

Provided by American Chemical Society (news : web)

Controlling movements with light

German researchers at the Ruhr-Universitaet have succeeded in controlling the activity of certain nerve cells using light, thus influencing the movements of mice. By changing special receptors in nerve cells of the cerebellum such that they can be activated and deactivated by light, the researchers have shown that the signaling pathways, which are activated by the receptors play a crucial role in controlling movement.

Unlike conventional methods, with the so-called optogenetics, the researchers are able to target one cell type. "We are now going to use this method to find out exactly what goes wrong in the nerve cells in movement disorders such as ataxias", said Prof. Dr. Stefan Herlitze (RUB Department for Biology and Biotechnology). The results are reported in the Journal of Biological Chemistry.

The Bochum team examined a specific signalling pathway that is controlled by a so-called G-protein-coupled receptor. This pathway is important for the modulation of activity in complex neuronal networks. Disturbances of the function can, for example, have an effect on emotional and motor behaviours. "We know that the activity pattern of the Purkinje cells in the cerebellum is crucial for the coordination of movements", Herlitze explained. "It is unclear, however, what contribution is made by the individual receptors." In conventional studies, researchers use drugs that inhibit or stimulate specific proteins in nerve cells to investigate the contribution of these proteins to the activity of the cells. However, Herlitze's team was interested in a protein (G-protein-coupled receptor) which occurs in various cell types. Had the researchers administered a drug, they would not only have deactivated the receptor in the Purkinje cells, but in all cell types in which it occurs. The drug method therefore makes it impossible to observe the contribution of the receptor in the Purkinje cells in isolation.

Optogenetics: replacing drugs with light

To avoid this problem, Herlitze's team replaced the drugs with proteins that are activated by light. Using genetic methods, the researchers integrated rhodopsin, the light-sensitive protein of the eye, into the Purkinje cells of mice. They also implanted a laser probe in the cerebellum, with which they illuminated the rhodopsin. The light-activated rhodopsin then activated the G-protein-coupled receptor in the Purkinje cells, while the same receptors in other cell types remained inactive. The RUB Department of General Zoology and Neurobiology has been instrumental in establishing this method worldwide.

Investigated receptor is crucial for movement control

The researchers found that activation of the G-protein-coupled receptor changed the activity pattern of the Purkinje cells. Herlitze's team had to expose the rhodopsin to light for several seconds to achieve these effects. A twenty to thirty percent reduction in cell activity was sufficient to induce visible motor deficits in the behaviour of the mice, such as impaired balance or coordination problems. "We were able to demonstrate for the first time that the modulation of a specific G-protein-coupled receptor in the Purkinje cells is of crucial importance for the control and coordination of movement", summed up Herlitze.

More information: Gutierrez, D.V., Mark, M.D., Masseck, O., Maejima, T., Kuckelsberg, D., Hyde, R.A., Krause, M., Kruse, W., Herlitze, S. Optogenetic control of motor coordination by Gi/o protein-coupled vertebrate rhodopsin in cerebellar Purkinje cells. J. Biol. Chem., doi: 10.1074/jbc.M111.25367 (2011)

Provided by Ruhr-University Bochum