Optogenetics is a rapidly developing multi-disciplinary bioengineering technology that integrates optics, software control, gene manipulation technology, and electrophysiology. The main principle is to first use gene manipulation techniques to transfer light-sensitive genes (such as ChR2, eBR, NaHR3.0, Arch or OptoXR, etc.) into specific types of cells in the nervous system for expression of specific ion channels or GPCRs. The photo-sensing ion channel will selectively induce the passage of cations or anions under different wavelengths of light stimulation, thereby causing changes in the membrane potential on both sides of the cell membrane to achieve selective excitation or inhibition of the cells.
The optogenetic technology has unique characteristics of high spatial and temporal resolution and cell type specificity. It overcomes many shortcomings of traditional methods to control the activity of cells or organisms, and can completely change the nerves by performing non-invasive precise positioning stimulation operations on neurons. The state of research in the field of science provides a revolutionary approach to neuroscience. In the future, optogenetic techniques may develop a series of new therapies for central nervous system diseases.
The application of optogenetics technology has developed rapidly since 2010. The applied research field covers a number of classical experimental animal species (Drosophila, C. elegans, mice, rats, marmosets, cynomolgus monkeys, etc.) and involves various aspects of neuroscience research areas, including basic research in neural circuits, learning and memory studies, addiction studies, dyskinesias, sleep disorders, Parkinson’s disease models, animal models of depression and anxiety.
In the application of optogenetics technology, scientists must first search for suitable light-sensitive proteins; secondly, carry out corresponding genetic information transmission, that is, through transfection, viral transduction, the establishment of the transgenic animal, etc. Genetic information is passed to the target cells; scientists then use controllable demonstrations to achieve the precise demonstration of cellular activity by controlling the specificity of the light in time and space; and finally reading the results of the study. The electrode can be used to measure the change in the fluorescence efficiency of the light-sensitive protein by detecting the voltage inside and outside the cell membrane during the study process, and the fluorescence biosensor can be used to detect the readout value of different cells, and then the behavioral test can be used to evaluate the effect of adjusting the cell activity on the whole animal.
Based on this, we conducted some recent progress in optogenetics technology to readers.
- Cell: Significant progress! Extend the optogenetics toolkit by turning the rhodopsin
In a new study, researchers from research institutions such as the Howard Hughes Medical Institute in the United States have discovered a new approach to the transformation of a class of light-sensitive proteins called rhodopsin. By flipping such proteins in cell membranes, they are able to produce tools with different properties. Related research results were published online in the Cell Journal, entitled “Expanding the Optogenetics Toolkit by Topological Inversion of Rhodopsins.” The author of the paper is Joshua Dudman and Alla Karpova of the Howard Hughes Medical Institute. This technology can double the number of proteins used in optogenetics, a technique that uses light to manipulate neuronal activity. These newly developed hybrid rhodopsin proteins allow these researchers to conduct new experiments that help analyze brain circuits and study the neuroscience behind Parkinson’s disease.
Inspired by evolution, under the leadership of Jennifer Brown, Reza Behnam, Luke Coddington, and Gowan Tervo, these researchers developed a complementary technology to transform the new rhodopsin. In addition to mutations, recombination—the combination of protein domains with different functions through gene reshuffling—also makes protein diversity appear in nature. Scientists believe that recombination is crucial for the emergence of a small number of proteins—through evolution and orientation in the cell membrane.
When these researchers simulated recombination by adding a new protein to one end of a rhodopsin, it flipped. This is really unexpected. If every existing engineered or newly discovered rhodopsin acquires new functions when flipped, this may lead to a doubling of protein tools used in optogenetics. Not only can they alter the orientation of proteins in the cell membrane, but they also discover that these new, modified rhodopsin have unique and useful new functions. One of the rhodopsin, called FLInChR (Full-Length Inversion of ChR), plays a role in activating neurons at the beginning. When turned over, it becomes a potent and fast inhibitor that can be used to conduct new experiments.
- Science: A major breakthrough in optogenetics! Upconverting nanoparticles helps deep brain stimulation! Or will subvert nerve disease treatment!
Thomas McHugh, research leader at the Institute of Brain Science at the Japan Institute of Physical and Chemical Research (RIKEN), and colleagues now find new ways to introduce light non-invasively into the deep brain. In their article published in Science, they used upconverting nanoparticles (UCNPs) to introduce lasers deep into the skull. Such nanoparticles can absorb near-infrared light and convert them into visible light at depths that are not achievable by conventional optogenetics. This method is used to activate neurons in different regions of the brain, silence epilepsy, and activate memory cells. “Nanoparticles can effectively extend the depth that our fibers can reach, enabling long-range delivery of light for non-invasive treatment,” McHugh said.
In addition to activating neurons, UCNPs can also be used to inhibit the condition of mice with epilepsy. The researchers injected mice with a green light in the hippocampus and then irradiated the surface of the skull with near-infrared light. As a result, epileptic neurons of these mice were effectively silenced. In another area called the medial septum, the light emitted by the nanoparticles promotes the synchronization of the neuron theta cycle, an important brainwave. In mice with fear memory, the researchers succeeded in stimulating the fear memory of mice in the hippocampus using luminescent UCNPs. These neuronal activation, inhibition, and memory arousal effects were only observed in mice injected with nanoparticles.
- Science: Boosting the development of optical genetics! Analyze the three-dimensional structure of rhodopsin 2
Channelrhodopsin 2 (ChR2) is a membrane protein widely used in optogenetics. Optogenetics is a relatively new technology involving the use of light to manipulate neurons and muscle cells in living organisms. A similar approach has been used to partially reverse hearing/visual loss and control muscle contraction.
To reveal the structure of ChR2, researchers from Germany, France, Russia, and the Czech Republic used an analytical technique called X-ray diffraction. This technique is only used to analyze protein samples in the form of crystals. They culture ChR2 protein crystals in a so-called cubic lipid mesophase that allows proteins to move freely without leaving the membrane. They irradiated their cultured ChR2 protein crystals with X-rays with a wavelength of about 1 angstrom, and successfully analyzed the structure of the ChR2 protein by analyzing the diffraction of X-rays in this protein crystal. The results of the study were published in Science, entitled “Structural insights into ion conduction by channelrhodopsin 2”.
- Hippocampus: “Optogenetics” therapy may restore the memory of some people with Alzheimer’s disease
Recently, researchers from Columbia University published an article in the journal Hippocampus to restore the memory of mice with Alzheimer’s disease by optogenetics. This discovery may change our understanding of the disease.
First, the authors performed optogenetic transformations on mice to emit light-colored fluorescence while storing memory, and red fluorescence when re-acquired. Afterward, the authors gave genetically engineered wild-type mice and Alzheimer’s mice stimulation with a lemon scent followed by electrical stimulation to correlate the two memories. A week later, the authors again gave these mice a stimulating smell of lemon. The results showed that wild-type mice were able to simultaneously show yellow and red fluorescence, and there was a manifestation of fear, which indicated that memory re-acquisition occurred at the same time as memory formation. However, the areas of brain luminescence in Alzheimer’s mice are significantly different, indicating that their brains are disrupted during memory reacquisition. Later, the researchers used a blue light to stimulate the brain of the mouse, which enabled it to reactivate the mouse’s memory of lemon odor and electrical stimulation, so that the mouse showed a tremor when it smelled the odor again.
(To Be Continued…)