Scientists have engineered mammalian cells to be activated using ultrasound. The method paves the way toward non-invasive versions of deep brain stimulation, pacemakers and insulin pumps.
«Going wireless is the future for just about everything,» says senior author Sreekanth Chalasani, an associate professor in Salk’s Molecular Neurobiology Laboratory. «We already know that ultrasound is safe, and that it can go through bone, muscle and other tissues, making it the ultimate tool for manipulating cells deep in the body.»
About a decade ago, Chalasani pioneered the idea of using ultrasonic waves to stimulate specific groups of genetically marked cells, and coined the term «sonogenetics» to describe it. In 2015, his group showed that, in the roundworm Caenorhabditis elegans, a protein called TRP-4 makes cells sensitive to low-frequency ultrasound. When the researchers added TRP-4 to C. elegans neurons that didn’t usually have it, they could activate these cells with a burst of ultrasound — the same sound waves used in medical sonograms.
When the researchers tried adding TRP-4 to mammalian cells, however, the protein was not able to make the cells respond to ultrasound. A few mammalian proteins were reported to be ultrasound-sensitive, but none seemed ideal for clinical use. So Chalasani and his colleagues set out to search for a new mammalian protein that made cells highly ultrasound sensitive at 7 MHz, considered an optimal and safe frequency.
«Our approach was different than previous screens because we set out to look for ultrasound-sensitive channels in a comprehensive way,» says Yusuf Tufail, a former project scientist at Salk and a co-first author of the new paper.
The researchers added hundreds of different proteins, one at a time, to a common human research cell line (HEK), which does not usually respond to ultrasound. Then, they put each cell culture under a setup that let them monitor changes to the cells upon ultrasound stimulation.
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