Examination of brain activity has recently been made easier with the discovery by MIT bio-engineers of the properties of a protein known as “Jaws”. This discovery could in the long term enable neurons to be manipulated non-invasively, using a light source outside the skull.
A discovery by researchers at the Massachusetts Institute of Technology (MIT) in the United States looks set to revolutionise optogenetics, a technology that allows scientists to monitor, model and control some brain functionality by shining light on neurons. Up to now the technique has required a light source to be implanted in the brain, where it can reach the cells to be manipulated. Now however the MIT team have engineered a protein which allows the light source to be diffused from outside the skull. In addition to being non-invasive, thus avoiding potential problems arising from an implant, the technique also allows a larger volume of tissue to be influenced at the same time. Optogenetics, which basically uses light-sensitive proteins that can suppress or stimulate electrical signals within cells, helps to advance neurologists’ understanding of the various functions of the neurons and enables them to map neural networks.
Revealing the potential of ‘Jaws’
Optogenetics provides a means of silencing or stimulating specific types of neurons in the brain, allowing neuroscientists to learn more about their functions. The neurons to be studied must first be genetically engineered to produce light-sensitive proteins known as opsins. The researchers then insert a light source, usually an optical fibre, into the brain to manipulate the selected neurons. Ph.D student Amy Chuong and her fellow-researchers in a team led by Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT, observed that many microbes and other organisms use opsins to detect light and react to their environment. However, while most of the natural opsins currently being used for optogenetics respond best to blue or green light, the deepest penetration into living tissue is achieved by red light. Chuong engineered one of the relatives of a red light sensitive protein and tested its electrical activity. The result of her work is a mutant strain known as ‘Jaws’, which retains its red light sensitivity but has a much stronger photocurrent – sufficiently powerful to shut down neural activity.
Using optogenetics to treat disorders
At the moment the Jaws opsin is being tested on mice, but the US researchers believe that being able to diffuse light from outside the skull means that the technique could be used on animals with larger brains. Further down the road this non-invasive approach could lead to the development of optogenetic treatment for brain disorders such as epilepsy and other neurological conditions. It might even be feasible to stimulate and improve the mental capabilities of people who do not suffer from any cerebral abnormalities. Another possible field of application is to treat people suffering from retinitis pigmentosa, an eye condition whereby vital light-sensitive cells called ‘cones’ slowly atrophy, eventually leading to blindness. The MIT team have demonstrated Jaws' ability to restore some light sensitivity to retinal cones in mice. The next step will be to test the protein’s compatibility and efficacy with human eyes.