Adapted from Sessler, and others.
A new form of optogenetics activates or suppresses neurons longer than previous versions, according to a December study. scientific progress. The technology could be used in the laboratory to permanently increase or decrease the activity of neurons involved in brain signaling imbalances thought to underlie autism, or involved in seizures. says the researchers.
In conventional optogenetics, neurons are turned on or off with flashes of light that open and close light-sensitive ion channels. Opening channels that add positive charge to the interior of the neuron promotes cell firing, whereas opening channels that increase negative charge suppresses firing. By manipulating conductivity in this way in animal models of autism, we were able to identify cells responsible for some of the hallmarks of autism.
However, the effect of this technique is short-lived. [their charge] Jia Liu, an assistant professor of engineering and applied sciences at Harvard University who co-led the new study, said, “We’re back at baseline levels.” “It forces the cells to excite or depress. But none of the intrinsic properties of the circuit are being manipulated,” he says.
To promote lasting change, Liu and his colleagues created a new light-sensitive enzyme that modulates another component of neural excitability: membrane capacity, the amount of charge cell membranes can hold. Once activated, the enzyme initiates the assembly of synthetic polymer layers on and within the neuronal membrane. Depending on the type of polymer used, the newly deposited layer can either insulate neurons, decreasing membrane capacitance and increasing excitability, or increase neuronal conductance, increasing membrane capacitance and decreasing excitability. I can.
Because the polymer stays in place and maintains the membrane’s new capacitance even after the light is shut off, it could theoretically encourage the rest of the cellular network to adapt to new functional patterns. There is, says Liu. “The properties of cells have changed fundamentally.”
L.iu and his colleagues used a harmless virus to deliver genes for light-sensitive enzymes into cultured human kidney cells. Cells were then treated with one of two amine-based monomer solutions, depending on whether the purpose was insulating or conductive. Using light to activate the enzyme, each monomer was oxidized and polymerized on and within the cell membrane.
The researchers next tested the polymer on cultured rat cortical neurons. There, too, light led to the formation of polymers that altered the electrical properties of cell membranes. Insulating polymers decreased membrane capacitance and increased neuronal excitability, while conducting polymers had the opposite effect.
The team also observed that the longer the cells were exposed to light, the more polymer accumulated in the cell membrane. Liu and his team didn’t test how long the polymer lasted, but in their experiment the change in membrane capacitance remained after his three days, the most recent time point they measured. was
The technique builds on work Liu did as a postdoctoral researcher in Zhenan Bao’s lab at Stanford University in California, where he used similar enzymes to build synthetic polymers on neurons and membranes on them. Changed capacity. But the enzyme wasn’t sensitive to light and produced a toxic byproduct, hydrogen peroxide.The amount of hydrogen peroxide released was enough to kill the cells, Liu says.
A new light-sensitive enzyme produces toxic byproducts called reactive oxygen species. But the enzyme’s photosensitivity allows the growth of synthetic polymers to be carefully guided by altering the timing of the cell’s exposure to light, he says. By having neurons express only small amounts of new enzymes and more precisely controlling the amount of polymers produced using light, the amount of toxic byproducts appears to be minimized. and untreated cells revealed cell staining regardless of which polymer was produced. Still, the level of dead cells was slightly elevated in the treatment group. More work is needed to mitigate this toxicity, he said.
“This work represents a significant improvement [over] Their previous technique may lead to better in vivo studies, especially in terms of toxicity,” said Longzhi Tan, an assistant professor of neurobiology at Stanford University, who said he believes the study not involved in This new technique could help examine transcriptional and epigenetic changes after optogenetic manipulation in both wild-type mice and mice that model the human condition, he says.
Liu and his colleagues are now testing whether the optogenetic technique works in living mouse brains. They also screen various enzymes, looking for those that do not produce toxic byproducts, especially during prolonged illumination.
