05 July 2017

Gene delivery to neurons

Evolution has turned viruses into highly efficient carriers for delivering genes inside cells. Researchers are actively using these abilities, reprogramming viruses so that they act as vectors that deliver therapeutic genes to the nuclei of cells of a living organism. However, in the process of creating such vectors, viruses lose their own genes, which deprives them of the ability to reproduce and, accordingly, to spread independently in the body. The most inaccessible regions include the brain, which can only be accessed by overcoming the so-called blood-brain barrier, and the peripheral nervous system, whose neurons are dispersed throughout the body.

Researchers at the California Institute of Technology, working under the guidance of Associate Professor Viviana Gradinaru, have developed two new viral vectors that solve the problem of delivering therapeutic genes to cells of the central and peripheral nervous systems. Both vectors are derivatives of a vector based on an adeno-associated virus (AAV) developed in 2016. Due to modifications of the capsid (the outer shell of the virus), one of them – AAV-PHP.eB – gained the ability to carry its cargo through the blood-brain barrier, while the other – AAV-PHP.S – is effectively absorbed by peripheral nerve cells located outside the brain and spinal cord, including neurons responsible for the sensation of pain, regulation of heart rate, respiration and digestion.

Both vectors hit their targets after being injected into the bloodstream. They can also be modified depending on the need and used both in gene therapy of neurodegenerative diseases affecting the entire nervous system, such as Huntington's disease, and for mapping or modulating neural circuits, as well as studying their changes accompanying the progression of the disease.

The new adenoviral vectors can deliver genes encoding colored fluorescent proteins used for cell identification and labeling to cells. To do this, vectors that are carriers of fluorescent proteins of different colors are mixed and injected into the bloodstream. When they reach their targets, each neuron acquires a unique color combination, which makes it possible to differentiate it from neighboring neurons and conduct a detailed study.


In addition, the authors have developed a technology for controlling the number of neurons absorbing the label. Tagging too many neurons makes it difficult to recognize individual cells, so limiting the number of tags allows you to visualize the shape of individual neurons and track the nerve fibers connecting them in intact tissues using a technology known as tissue enlightenment.


The authors note that usually in order for a mouse or other animal model to express fluorescent proteins in certain cells, researchers have to develop genetically modified animals, which take months or even years to create and study the characteristics of. The new technique allows using a single injection for several weeks to mark specific cells with different colors.

Article by Ken Y Chan et al. Engineered AAVs for efficient noninvasive gene delivery to the central and peripheral nervous systems is published in the journal Nature Neuroscience.

Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru Based on the materials of the California Institute of Technology: Novel Viral Vectors Deliver Useful Cargo to Neurons Throughout the Brain and Body.


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