In the Lab with Dr. Samuel Pfaff � The Search for Stem Cell Cures

Developing neurons in laboratory

By Jamie Talan - Neurology Today - Sept..3.2009

More than two decades ago, Samuel Pfaff, PhD, got his first taste of developmental biology when he watched a one-cell frog embryo become a swimming tadpole overnight. Since then, the molecular biologist, now a professor in the Gene Expression Laboratory at the Salk Institute in La Jolla, Ca, has been traveling the developmental road of neurons to figure out how to repopulate damaged cells on the heels of spinal cord injury and amyotrophic lateral sclerosis (ALS). He is trying to recapitulate development in a lab dish. His hope is to generate the right kinds of cell types and figure out how to wire them up to repair the CNS. In his studies, Dr. Pfaff, who is also a Howard Hughes Medical Institute investigator, is targeting astrocytes.

� We have excellent ways to generate motor neurons and even better ways to develop astrocytes,� he told Neurology Today. � If you ask us today what we would do to successfully stop the death of motor neurons in ALS , this is it. We Will target the bad guy in the system and see if we can overwhelm it with healthy astrocytes.�

Dr. Pfaff spoke to Neurology Today about his work, which is providing a new way to grow new neurons in the damaged adult brain.

HOVE DOES UNDERSTANDIG NEURONAL DEVELOPMENT HELP IN CONSIDERING NEW WAYS TO TREAT SEVERE CONDITIONS LIKE ALS?

Only in the last decade have scientists taken embryonic stem cells and used the information we know about normal development to capture in a lab dish what is going on inside the human body. We can lead to a totally different fate. For instance, if embryonic stem cells are exposed to the right concentration of a protein called sonic hedgehog, the cells become motor neurons. Using this model might make it possible to affecting these cells and uncover the pathways that control normal development and function of these cells.

WHAT ARE SOME OF THE HUEDLES TO THIS APPROACH?

There are many hurdles how to make populations of motor neurons and deliver them to sites where they need to be and to make connections. When motor neurons are transplanted into the spinal cord, the environment is much different in the adult than in the embryo. When immature motor neurons are engrafted into an adult CNS, it is out of context, like dropping people into a strange city, where they lack clues for knowing where they are or what they should do. In the embryo, motor neurons grow an axon that seeks a muscle. In the adult, the motor neurons do not naturally regrow through a foreign environment. It may be necessary to use genes to enhance or alter the growth of characteristics of the cells.

WHAT IS POSSIBLE ONCE WE UNDERSTAND HOW TO DELIVER HELTHY MOTOR NEURONS WHERE THEY BELONG?

We know that motor neurons are lost in ALS but we don�t know how this happens. Does the problem originate within the motor neurons? In the SDO [ superoxide dismutase] animal model of ALS, the evidence leads to defects in other cell types. Motor neurons are exposed normally to different neurotrophic factors. Glial cells and astrocytes maintain the motor neurons. When astrocytes carry the mutation in SOD, they secrete an unidentified substance that kills motor neurons. We can watch as they grow and introduce cells and see how changes the structure and function of the cell.

HOW WILL IT WORK?

Once we have healthy astrocytes we will transplant them into the spinal cord of mutant SOD mice, especially cervical regions that regulate breathing. Ultimately, we need to target the entire system. The collaborative effort includes Don Cleveland, PhD, and his colleagues at the University of California � San Diego, who are testing antisense oligonucleotides that are taken up by cells to block the production of SOD.