arah Zhang writes in Wired Magazine that the single-cell green algae Chlamydomonas reinhardtii have an eyespot that makes use of light-sensitive proteins. One of them is called channelrhodopsin-2. This algal protein, transplanted into the human retina, could one day restore sight to the blind. Last month, the FDA approved human clinical trials for the Ann Arbor-based company RetroSense to do just that.
For the past decade, neuroscientists have been using channelrhodopsin-2 to make neurons react to light. By genetically encoding the protein into neurons, scientists can easily probe brain circuits with light, a technique known as optogenetics.
RetroSense is planning to use optogenetics in humans for the first time, recruiting 15 patients blinded by the genetic eye disease retinitis pigmentosa for its clinical trial. “We are looking to get it off the ground this year in the fall,” says CEO Sean Ainsworth.
RetroSense will use a virus to insert copies of the channelrhodopsin-2 gene into neurons of the inner retina, which normally are not sensitive to light. (Rods and cones are the usual light-sensitive cells.)
RetroSense is licensing its technology from Zhuo-Hua Pan, a vision researcher at Wayne State University who studies how to restore sight when the rods and cones of the eye die off. That’s what happens in diseases like retinitis pigmentosa or age-related macular degeneration.
The obvious solution fixes human deficiencies with human genes: encode the light-sensitive proteins from human rods in the other functional cells in the diseased retina. But those proteins are finicky, and they have to work in concert with several other proteins – meaning scientists need to insert several genes. “We thought that would be almost impossible to do,” says Pan.
In 2003, Pan came across a paper on channelrhodopsin-2 from Chlamydomonas reinhardtii. Scientists started putting it into mammalian cells—and all they needed was one gene and one protein. “It worked perfectly, even in the very beginning,” says Pan. “That basically was just really, really lucky.” The hundreds of neuroscience labs relying on optogenetics might say the same.