Central to Das's development are the brain cells known as astrocytes. Named for their star-like shape, they fill in the spaces between neurons—the brain cells responsible for transmitting information—to form a chemically balanced network that helps neurons thrive. Brain damage can make these astrocytes go a little haywire in a phenomenon called astrogliosis, where they stop taking in neurotransmitter chemicals like glutamate. Too much glutamate overstimulates neurons and can make them die off.
To keep that from happening, Das put a specific chain of microRNA—something prized for its ability to alter the expression of certain genes—into an exosome. Exosomes are essentially tiny natural balloons that scientists use to deliver drugs and other therapies across the blood-brain barrier. Das hoped that her microRNA would work to mimic the signals that healthy astrocytes send to neurons and help them take in the right amount of glutamate. It worked. "When I found the protein moving away from the cell membrane, that was a pretty good day," Das says in a NowThis video. "Neurons are surviving. This is pretty decent."