Selective gene delivery modifies diseased cells.

Scientists have demonstrated for the first time that it is possible to specifically modify gene expression in diseased upper motor neurons, brain cells that break down in ALS.

The new Northwestern Medicine study, published in Nature Gene Therapy, provides evidence that lays a foundation for developing future gene replacement therapies to treat patients with the fatal neuromuscular disorder.

Using a nontoxic virus injected directly into the motor cortex of mouse models with ALS, the scientists showed they can deliver new genes to damaged upper motor neurons. This process of transferring DNA from a virus to neurons is called transduction.

To test the feasibility of transduction, the research team had the virus deliver a gene that expresses a green fluorescent protein – the color helped the scientists visualize how the neurons worked. Now that they know the transduction strategy is effective, they’ll use it in future research to deliver genes that correct mutations in ALS cells.

Importantly, the scientists were able to specifically modify the gene expression in diseased upper motor neurons without disturbing other neurons in the motor cortex. Inadvertently manipulating other cells could set off a cascade of unknown effects.

“The brain is very complex, with many different cells, but in ALS only a distinct neuron population shows initial vulnerability and undergoes progressive degeneration,” said lead study author Hande Ozdinler, assistant professor of neurology at Northwestern University Feinberg School of Medicine. “To develop effective treatment strategies, we must deliver genes only to the neurons in need. This is not easy to accomplish – previous studies have managed to induce a broad but non-specific transduction of many different neurons.”

ALS, or amyotrophic lateral sclerosis, is marked by the deterioration of motor neurons, which causes muscle weakness and impaired speaking, swallowing and breathing, eventually leading to paralysis and death. In previous research, Ozdinler showed that defects in upper motor neurons (also known as corticospinal motor neurons), which send messages from the brain to the spinal cord to activate voluntary movement, may be a starting point for the disease.

In the recent study, Ozdinler’s team tested seven different strains of the adeno-associated virus. They found that a nontoxic strain called AAV2-2, already used in clinical studies for diseases such as Parkinson’s, was able to deliver genes to damaged upper motor neurons at rates higher than ever seen before.

“With just a one-time injection into the motor cortex, genes were very specifically delivered to the upper motor neurons,” Ozdinler said. “Among all cells transduced, about 70 percent were upper motor neurons. Without selectivity, this would be about 1 percent.”

The investigators showed that the AAV2-2 virus transduced upper motor neurons in models of both pre-symptomatic and symptomatic stages of ALS, suggesting patients could eventually benefit from therapy based on this work even after they’ve started experiencing symptoms.

“This new study has very important clinical implications, especially for patients with familial ALS who display upper motor neuron defects,” Ozdinler said.

An upper motor neuron projects information to the spinal cord through its axon, a long, branch-like part of the cell that sends impulses to other cells. The fluorescent protein that was transferred to the neurons made this process visible.

“We saw that during ALS, damaged upper motor neurons stop talking to spinal neurons,” Ozdinler said. “In further research, we will examine how we can modulate gene expression to introduce correct versions of mutated genes and improve that connectivity and motor functions.”

About this ALS research

Others authors of the study include Javier Jara, Macdonell Stanford, Yongling Zhu, Michael Tu, William Hauswirth, Martha Bohn, and Dr. Steven DeVries.

Funding: The research was funded by the Les Turner ALS Foundation, Herbert C Wenske Foundation, Northwestern University Clinical and Translational Sciences Institute, an ALSA Safenowitz fellowship and the Weinberg College of Arts and Sciences at Northwestern University.

Source: Marla Paul – Northwestern University

Image Source: The image is credited to Iamozy and is licensed CC BY-SA 3.0

Original Research: Full open access research for “Healthy and diseased corticospinal motor neurons are selectively transduced upon direct AAV2-2 injection into the motor cortex by J H Jara, M J Stanford, Y Zhu, M Tu, W W Hauswirth, M C Bohn, S H DeVries and P H Özdinler in Nature Gene Therapy. Published online January 21 2016 doi:10.1038/gt.2015.112

Abstract

Healthy and diseased corticospinal motor neurons are selectively transduced upon direct AAV2-2 injection into the motor cortex

Direct gene delivery to the neurons of interest, without affecting other neuron populations in the cerebral cortex, represent a challenge owing to the heterogeneity and cellular complexity of the brain. Genetic modulation of corticospinal motor neurons (CSMN) is required for developing effective and long-term treatment strategies for motor neuron diseases, in which voluntary movement is impaired. Adeno-associated viruses (AAV) have been widely used for neuronal transduction studies owing to long-term and stable gene expression as well as low immunoreactivity in humans. Here we report that AAV2-2 transduces CSMN with high efficiency upon direct cortex injection and that transduction efficiencies are similar during presymptomatic and symptomatic stages in hSOD1G93A transgenic amyotrophic lateral sclerosis (ALS) mice. Our findings reveal that choice of promoter improves selectivity as AAV2-2 chicken β-actin promoter injection results in about 70% CSMN transduction, the highest percentage reported to date. CSMN transduction in both wild-type and transgenic ALS mice allows detailed analysis of single axon fibers within the corticospinal tract in both cervical and lumbar spinal cord and reveals circuitry defects, which mainly occur between CSMN and spinal motor neurons in hSOD1G93A transgenic ALS mice. Our findings set the stage for CSMN gene therapy in ALS and related motor neuron diseases.

“Healthy and diseased corticospinal motor neurons are selectively transduced upon direct AAV2-2 injection into the motor cortex by J H Jara, M J Stanford, Y Zhu, M Tu, W W Hauswirth, M C Bohn, S H DeVries and P H Özdinler in Nature Gene Therapy. Published online January 21 2016 doi:10.1038/gt.2015.112

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