Neurodegenerative diseases represent one of the greatest challenges in our aging society. Yet research into these illnesses is difficult because of the limited availability of human brain tissue. Fortunately, scientists at the Life & Brain Research Center and the Clinic for Neurology at the University of Bonn have discovered a way to work around the problem. By taking skin cells from patients with a genetic movement disorder and reprogramming them into so-called induced pluripotent stem cells, researchers were able to create functional neurons that allowed them to investigate the causes of the disease. Their results will be published in the journal Nature.
The focus of the Bonn study is Machado-Joseph disease, which affects people’s ability to coordinate movement. First identified among Portuguese descendants living on the Azores, today it represents the most frequent dominantly inherited cerebellar ataxia in Germany. Most patients first develop symptoms, which include difficulty walking and other neurological difficulties, between the ages of 20 and 40. The cause of the disorder is a repeating sequence in the ATXN3 gene, which causes build-up of the Ataxin protein, damaging neurons in the brain. Before the study, no one knew why the disease affected only nerve cells and what triggered the abnormal protein build-up.
“Master Cells” derived from patient skin samples
To study the disease process on a molecular level, the stem cell researcher Dr. Oliver Brüstle and his team at the University of Bonn’s Institute for Reconstructive Neurobiology derived induced pluripotent stem cells (iPS cells) from small samples of patient skin. iPS cells are cells restored to their early, undifferentiated state. Once “reprogrammed,” these “master” cells divide continuously and can transform into any cell of the body. In a subsequent step, Brüstle and his team converted iPS cells into brain stem cells, creating an ever-ready supply of neurons for their investigations.
A special feature of the neurons is that they stem from affected patients. Carrying the same genetic mutations as the patients, these neurons can serve as a cellular model for Machado-Joseph disease. “This method allows us to investigate diseased cells which we otherwise couldn’t access, almost as if we had put the patient’s brain in a Petri dish,” says Dr. Philipp Koch, a long-time colleague of Brüstle’s and one of the study’s primary authors. Together with Dr. Peter Breuer of the Clinic for Neurology at Bonn’s University Hospital, Koch sent electrical currents through the cultured neurons. The researchers showed that the formation of protein aggregate has a direct relationship with a neuron’s electrical activity. “Playing a key role is the enzyme calpain, which is activated by the increased calcium levels in stimulated neurons,” says Breuer. “This newly discovered mechanism explains why Machado-Joseph disease only affects neurons,” Brüstle explains.
Reprogramed neurons as test objects for new drugs
“The study shows the potential of this special class of stem cells for neurological research,” says Prof. Dr. Thomas Klockgether, the clinical director of the German Center for Neurodegenerative Diseases (DZNE) and director of the Clinic for Neurology at the Bonn’s University Hospital. Klockgether’s team closely collaborated with Brüstle and his researchers. For Brüstle, this was reason enough to start thinking about new organizational structures: “We need interdisciplinary departments in which scientists from stem cell biology and from molecular pathology work side by side.” Prof. Dr. Dr. Pierluigi Nicotera, the scientific director and chairman of the executive board of DZNE, endorses this view. “Cooperative structures are of great interest to DZNE,” he stresses. “Reprogramed stem cells show enormous potential for our understanding of the pathology of neurodegenerative diseases.”
In the future, Brüstle and his colleagues from the Life & Brain Research Center plan to use reprogrammed neurons to develop treatments for neurological diseases.
Koch, P., P. Breuer, M. Peitz, J. Jungverdorben, J. Kesavan, D. Poppe, J. Doerr, J. Ladewig, J. Mertens, T. Tüting, P. Hoffmann, T. Klockgether, B. O. Evert, U. Wüllner, O. Brüstle (2011): Excitation-induced ataxin-3 aggregation in neurons from patients with Machado-Joseph disease. Nature DOI: 10.1038/nature10671