Unique treatment generates new neurons, kills Parkinson’s disease in mice

Xiang-Dong Fu, Ph.D., has never been more excited about something in his entire career. He has long studied the basic biology of RNA, a genetic cousin of DNA, and the proteins that bind it. But a single discovery has launched Fu into a whole new field: neuroscience.

For decades, Fu and his team at the University of California, San Diego School of Medicine studied a protein called PTB, which is well known for binding to RNA and influencing which genes are turned on or off in a cell. To study the role of a protein like PTB, scientists often manipulate cells to reduce the amount of that protein, and then watch to see what happens.

Several years ago, a postdoctoral researcher working in Fu’s lab was taking that approach, using a technique called siRNA to silence the PTB gene in connective tissue cells known as fibroblasts. But it is a tedious process that must be done over and over again. He got tired of it and convinced Fu that they should use a different technique to create a stable cell line that permanently lacked PTB. At first, the postdoc complained about that too, because it made the cells grow very slowly.

But then he noticed something strange after a couple of weeks: very few fibroblasts remained. Most of the plate was full of neurons.

In this fortuitous way, the team discovered that inhibiting or deleting a single gene, the gene that codes for PTB, transforms various types of mouse cells directly into neurons.

More recently, Fu and Hao Qian, Ph.D., another postdoctoral researcher in their lab, took a major step forward in the search, applying it to what might one day be a new therapeutic approach to Parkinson’s disease and other neurodegenerative diseases. . Only one treatment to inhibit PTB in mice converted the native astrocytes, star-shaped support cells of the brain, into neurons that produce the neurotransmitter dopamine. As a result, the symptoms of the Parkinson’s disease in the mice disappeared.

The study is published on June 24, 2020 in Nature.

“Researchers around the world have tried many ways to generate neurons in the laboratory, using stem cells and other means, so that we can better study them, as well as use them to replace lost neurons in neurodegenerative diseases,” said Fu, who is Distinguished Professor in the Department of Cellular and Molecular Medicine of the UC San Diego School of Medicine. “The fact that we could produce so many neurons in a relatively easy way was a big surprise.”

There are several different ways to mimic Parkinson’s disease in mice. In this case, the researchers applied a dopamine-like molecule to poison dopamine-producing neurons. As a result, the mice lose dopamine-producing neurons and develop symptoms similar to Parkinson’s disease, such as movement deficiencies.

The treatment works like this: The researchers developed a non-infectious virus that carries an antisense oligonucleotide sequence, an artificial piece of DNA designed to specifically bind RNA that encodes PTB, thereby degrading it, preventing it from being translated into a functional protein. and stimulates the neuron. developing.

Antisense oligonucleotides, also known as DNA design drugs, are a proven approach to neurodegenerative and neuromuscular diseases: Study co-author Don Cleveland, Ph.D., was a pioneer in the technology, and now forms the basis of a Food and Drug Administration (FDA approved therapy) for spinal muscular atrophy and various other therapies currently in clinical trials. Cleveland is chairman of the Department of Cellular and Molecular Medicine at UC San Diego School of Medicine and a member of the Ludwig Institute for Cancer Research, San Diego.

The researchers administered PTB antisense oligonucleotide treatment directly to the mouse midbrain, which is responsible for regulating motor control and reward behaviors, and the part of the brain that generally loses dopamine-producing neurons in Parkinson’s disease. A control group of mice received sham treatment with an empty virus or an irrelevant antisense sequence.

In treated mice, a small subset of astrocytes converted to neurons, increasing the number of neurons by approximately 30 percent. Dopamine levels were restored to a level comparable to that of normal mice. Furthermore, neurons grew and sent their processes to other parts of the brain. There were no changes in the control mice.

Using two different limb movement and response measures, the treated mice returned to normal within three months of a single treatment and remained completely symptom-free of Parkinson’s disease for the rest of their lives. In contrast, control mice showed no improvement.

“I was amazed at what I saw,” said study co-author William Mobley, MD, Ph.D., Distinguished Professor of Neuroscience at the University of California, San Diego School of Medicine. “This new strategy for treating neurodegeneration gives hope that it will be possible to help even people with advanced disease.”

What is it about PTB that makes this work? “This protein is present in many cells,” said Fu. “But as neurons start to develop from their precursors, it disappears naturally. What we discovered is that forcing PTB to disappear is the only signal a cell needs to activate the genes necessary to produce a neuron.”

Of course, mice are not people, he warned. The model the team used does not perfectly recapitulate all the essential characteristics of Parkinson’s disease. But the study provides a proof of concept, Fu said.

The team then plans to optimize their methods and test the approach on mouse models that mimic Parkinson’s disease through genetic changes. They have also patented PTB antisense oligonucleotide treatment to advance toward human testing.

“It is my dream to see this through clinical trials, to test this approach as a treatment for Parkinson’s disease, but also for many other diseases where neurons are lost, such as Alzheimer’s and Huntington’s disease, and stroke. Fu said. “And dreaming even more, what if we could target PTB to correct defects in other parts of the brain, to treat things like inherited brain defects?

“I intend to spend the rest of my career answering these questions.”