The release of neurotransmitters allows for everything that we do and everything we see and feel. It was back in the 1950s when Bernard Katz, MD, PhD, working at University of College London, discovered how the junctions across nerve cells — the synapses — transmit information. Dr. Katz observed that synapses use a calcium signal to trigger release of a chemical neurotransmitter from one neuron, and the neurotransmitter is then recognized by another neuron.
His findings set the stage for Richard H. Scheller, PhD, and Thomas C. Südhof, MD, scientists who independently went after the molecular events that underlie the regulation of the release of neurotransmitters at the synapse. They began their work in the late 1980s, almost two decades after Dr. Katz accepted the Nobel Prize for Physiology and Medicine (1970) for his game-changing studies.
Dr. Scheller's work at Stanford in the late 1980s led to the isolation of proteins in the synaptic vesicle. In 2001, he joined Genentech, where he is now executive vice president of research and early development. Dr. Südhof performed his experiments at the University of Texas Southwestern, and moved to Stanford in 2008, where he is the Avram Goldstein professor of molecular and cellular physiology at Stanford University School of Medicine and a Howard Hughes Medical Institute Investigator. He continues to work at the synapse.
In September, Dr. Südhof and Dr. Scheller were awarded the 2013 Albert Lasker Basic Medical Research Award for their work. In interviews with Neurology Today, the awardees spoke about the ideas and events that inspired and propelled their work.
SÜDHOF: FROM GERMANY TO THE US
Dr. Südhof said that he grew up in “an academic household with a strong religious bent.” Early on, he said, he began questioning his parents' beliefs and “this desire to question what is actually true” is deeply ingrained in his nature.
Dr. Südhof was 27 years old when he finished a postdoctoral fellowship at the Max Planck Institute for Biophysical Chemistry in Germany, where he was born and where he would later complete his medical studies
“My greatest pleasure has always been to discover facts, to figure out how something works, to identify the relationships and connections that explain an observation.”
“After finishing my postdoc, I merged my earlier love of synaptic vesicles with my new knowledge of how to purify and clone membrane proteins, with the ultimate goal of pursuing something entirely new — to identify all the membrane proteins that make up a synaptic vesicle, and to figure out how these vesicle proteins mediate release of neurotransmitters,” he said.
In 1983, with his medical degree in hand, Dr. Südhof settled into another postdoctoral training position at the University of Texas Health Science Center. It was there that he worked for Michael Brown, MD, and Joseph Goldstein, MD, who would share a Nobel Prize in Physiology and Medicine (1985) for their work in unraveling the role of LDL receptors in cholesterol metabolism. Their work would lead to new ways to treat high cholesterol and reduce the risk for heart disease.
A year after Drs. Goldstein and Brown accepted their Nobel award, their protégé realized that he was more interested in the molecular underpinnings of tissue in the brain. At the University of Göttingen, he was doing research on organelles and proteins in the laboratory of Victor Whittaker, PhD. Dr. Whittaker isolated synaptic vesicles in the 1960s. Two decades later, when Dr. Südhof wanted to study the synapse, neuroscientists were working on life on the post-synaptic side of the neuron. Dr. Südhof's interest was in the events on the pre-synaptic side. He was fascinated by the synapse, a career choice that has kept him busy for three decades.
“It was 1986. At the time, nothing was known about the molecular underpinnings that allow a synapse to operate as precisely and quickly as it does. Bernard Katz's work 50 years earlier had beautifully illustrated that calcium influx into the presynaptic nerve terminals trigger neurotransmitter release, which then leads to post-synaptic receptor activation. But how calcium triggers that release was unknown,” Dr. Südhof explained.
“We cloned the first synaptic vesicle protein in 1987. Two more followed in our lab and the field took off. But unraveling the whole mechanism took much longer. It took years to understand how precisely the pre-synaptic terminal operates. We figured out how the fusion mechanism works but also how calcium triggering operates and how calcium influx in a pre-synaptic nerve terminal closely localizes to synaptic vesicles and the tight coupling of the action potential.”
His work in the Brown/Goldstein lab gave him the tools to go after the events at the synapse. “We showed how synapses are organized by active zone proteins, and described the first synaptic cell-adhesion molecules that guide synapse formation.” He left UT Southwestern for Stanford in 2008.
SCHELLER: FROM STANFORD TO GENENTECH
In the mid-1980s, Richard Scheller, PhD, was already making a name for himself at Stanford. He too was intrigued by the events that take place when nerve cells communicate through the synapse. He left Stanford in 2001 to head research at Genentech. In 2008, he was appointed the company's chief scientific officer.
Born and raised in Milwaukee, Wisconsin, Dr. Scheller said he always saw himself as a scientist. His parents always kept him well-stocked in microscopes and test-tubes. His mother loved to refer to him as her “little scientist.”
By high school, while his intentions still revolved around science — biochemistry to be more precise — the young man was more interested in music than schoolwork. But his scientific ambitions were ignited full-tilt when he started his undergraduate career at the University of Wisconsin. At the University of Wisconsin, he read a chemistry textbook by X-ray crystallographer Richard Dickerson, PhD, and heard him present his studies. Soon after, Dr. Scheller sought a position in his lab. He was interested, he said, “in the way structure determines the function of the molecules.”
The Dickerson laboratory was intent on isolating proteins to study their structure and function. Cloning was in its infancy and the lab was producing novel synthetic DNA to help them advance their work. The young Scheller was in his element. He was figuring out novel ways to clone DNA to study unsolved problems in molecular genetics. It was the late 1970s and recombinant DNA techniques were taking off.
The grad student wanted to understand how DNA gives rise to a complex organism. He conducted research in X-ray crystallography and that shaped his decision to go to graduate school at the California Institute of Technology. At Caltech, he worked on actin genes involved in the development of the cytoskeleton.
His interest in neuroscience was piqued during a postdoctoral fellowship at Columbia University. There, he would study with Richard Axel, MD, and Eric Kandel, MD, scientists who won independent Nobel Prizes in Physiology and Medicine in 2000 (Kandel) and 2004 (Axel). They were interested in understanding behavior by studying neural circuits and then seeing how experience altered the expression of the cells.
Dr. Scheller cloned the gene for the egg-laying hormone in Aplysia, a sea slug. What they learned was that one single protein can then be cut up into multiple chemical messengers that are used to orchestrate a complex behavior such as egg-laying. At Columbia, Dr. Scheller would become a molecular neurobiologist.
It was with these new tools that he returned to California and took an academic position at Stanford. Drs. Kandel and Axel had been working to understand learning and memory and Dr. Scheller decided that he would tackle this problem across the country. He believed that insights into learning and memory would come from studying the molecular biology of the synapse.
And that is what he did. He began cloning DNA encoding proteins of the synaptic vesicle and then he pieced together the events that were unfolding at the synapse during neurotransmitter release.
“It was known that neurotransmitters are contained within small organelles called synaptic vesicles. When action potentials travel down nerve terminals the vesicles fuse with the pre-synaptic plasma membrane to release neurotransmitter. It was known that this was triggered by the influx of calcium into the nerve terminal. However, beyond that little was known about the molecular events that underlie calcium signaling and fusion of the vesicle membrane with the plasma membrane. Our work uncovered the molecular mechanisms of the fusion process,” Dr. Scheller recalled.
“Our first experiments were aimed at isolating the proteins that were present and localized to the synaptic vesicle with the idea that these proteins were likely to be to be important in the transmission release process. Having isolated these proteins, we used biochemical, molecular biology and cell biology techniques to understand their function. The proteins are generally known as SNARE proteins, short for soluble N-ethylmaleimide-sensitive factor attachment protein receptor. One is called vesicle-associated membrane protein (VAMP) and another is syntaxin. VAMP-1 turned out to be on the synaptic vesicle. Syntaxin was present on the plasma membrane. That led us to believe that there was a link between the synaptic vesicle and plasma membrane. These are two of the three proteins that catalyzed the membrane fusion reaction.”
Both Dr. Scheller and Dr. Südhof believe that problems at the synapse can trigger many neurological problems.
“Many of us believed that synapse malfunction at some level had to underlie most of the diseases of the brain because the brain works via synaptic connections. Now we understand some of the proteins that are dysregulated, which results in neuronal degeneration,” said Dr. Dr. Südhof. “Disruption of neural circuitry then leads to disease.”
Dr. Südhof went on to identify synapse alterations in autism that could one day lead to novel treatments.
“I believe that we have a number of insights that provide those of us interested in therapeutic intervention reason to be optimistic about our progress working with diseases of neuronal degeneration, such as Alzheimer's, amyotrophic lateral sclerosis, and Parkinson's,” said Dr. Scheller. “The genetics of these conditions has uncovered pathways that are likely important in causing the diseases, at least in certain subsets of patients. The ability to dissect the pathways with molecular and cellular techniques has pointed us toward mechanism and in some cases suggested ways one might intervene with therapeutics.”
TUNE IN: In September, Richard H. Scheller, PhD, and Thomas C. Südhof, MD, were awarded with the 2013 Lasker Award for Basic Medical Research for their independent efforts to unravel the molecular events that underlie the regulation of the release of neurotransmitters at the synapse. In a podcast interview with Neurology Today, they describe their research and what their basic findings could mean for neurological diseases and disorders: http://bit.ly/rCBryX.
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