Noninvasive, ultrasound-mediated viral delivery of genes for optogenetic study of brain function

Optogenetics - genetically modifying cells to make them light-sensitive, in order to read and write signals into the brain - has revolutionised neuroscience. The ability to imprint particular patterns of neural activity into the brain, and to observe signalling in networks of brain cells during behaviour, is already bringing substantial new understanding of topics such as memory, perception and movement. In the longer term, it also offers us new ways to interface with the brain, to repair or enhance brain function. However, at the moment, the use of optogenetic techniques requires a highly invasive procedure: direct injection of viral vectors into the nervous system. In this project, we will develop and optimise a technology which promises to replace this intracerebral injection with a much less invasive approach: intravenous injection of the vector, followed by delivery of the genes across the blood-brain barrier by using specially tailored sequences of fast ultrasound pulses. If successful, this will mean that many neuroscience experiments that currently require surgical intervention will be able to be carried out almost entirely non-invasively. It will also result in new neuroscience techniques being much more translatable to human studies, as ultrasound can be safely carried out in human subjects.

Optogenetics - genetically modifying cells to make them light-sensitive, in order to observe and perturb physiological processes - has revolutionised systems neuroscience. However, current optogenetic techniques require either highly invasive procedures such as intracerebral infusion of viral constructs, or extensive transgenic breeding programmes. The development of non-, or less, invasive procedures for gene delivery into targeted brain regions would enhance scientific outcomes and improve prospects for long-term translation towards human therapeutic applications.

Focused ultrasound, which has been used successfully to deliver small molecule drugs across the blood-brain barrier (BBB), provides a new approach for noninvasive delivery of optogenetic constructs into targeted brain regions. To effectively deliver large molecular weight compounds such as adeno-associated viruses (AAVs) across the BBB, without inflammatory response in the brain, new pulse sequences must be devised. The development of a successful and highly reproducible protocol for noninvasive delivery of genetically encoded sensors such as GCaMP6 would allow in vivo calcium imaging experiments to be performed with no procedure more invasive than a standard tail vein injection.

The aim of this project is to develop a novel device for noninvasive delivery of genes into targeted brain regions, and to demonstrate its use by noninvasively labelling cerebral cortex with the calcium sensor GCaMP6s, and imaging neuronal activity through the skull with a two photon microscope.

UK society will benefit from the research that our new technique makes possible. The aging demographic of UK society makes neurodegenerative disorders a substantial upcoming problem, which neuroscience research is necessary to solve. The advances in basic neuroscience research made possible by this research project offer the prospect of substantially enhancing society's ability to deal with this impending problem.

The technique developed here substantially refines our ability to deliver optogenetic constructs into animals, by rendering the procedure almost entirely noninvasive (requiring only a simple i.v. injection). This research thus benefits animals used for scientific experiments (whose welfare is directly enhanced), and also those members of UK society who are concerned for animal welfare.

There is substantial prospect for commercialisation of the technology that will be developed in this project - there is likely to be a substantial commercial market for a noninvasive gene delivery device. The UK life sciences instrumentation sector, which is likely to be in a very good position to capitalise upon this commercial opportunity, will thus be a strong beneficiary from the research project.