We finally know how Botox infiltrates neurons. The finding could aid efforts to develop an antidote to the molecule’s neurotoxic effects, which can lead to paralysis or even death.
Botox uses a type of botulinum neurotoxin, a highly toxic substance produced by bacteria. The toxin disrupts communication between neurons, leading to muscle paralysis. In small therapeutic doses, it can relieve muscle spasms, treat migraines or, most famously, reduce wrinkles. However, in high doses, the molecule causes botulism, a potentially fatal disease with few treatments.
Frederic Meunier at the University of Queensland in Australia and his colleagues analyzed how botulinum neurotoxin type A enters neurons using a technique called single molecule imaging. This allowed them to capture the movement of molecules labeled with a fluorescent dye.
The researchers placed the toxin in a dish with rat neurons. They trained one camera on the neurotoxin and another on receptors in neuronal membranes, also marked with different colored dyes.
Previously, only two receptors, called polysialoganglioside (PSG) and synaptic vesicle glycoprotein 2 (SV2), were thought to be essential for toxin entry into cells. But as they tracked SV2’s response to the toxin, they saw that it moved in tandem with another receptor known as synaptotagmin 1 (Syt1).
“We basically started thinking, ‘oh, that’s weird,'” Meunier says. The researchers genetically modified rat neurons to prevent Syt1 from binding to SV2 and repeated the experiment. If you inhibit the binding between these two receptors, the toxin can no longer enter the cell, explains Meunier.
The same was true when they genetically engineered neurons to lack PSG, indicating that all three receptors are needed for botulinum neurotoxin type A to infiltrate cells. Future drugs that prevent the three receptors from binding together could prevent the toxin from infecting neurons, Meunier says.
“By better understanding the mechanism of cell entry, we are one step closer to preventing cell entry and preventing botulism,” says Sabine Pellet at the University of Wisconsin-Madison.