NEJM: Optogenetics, let blind patients re-perceive light

"I don't believe your experimental results, although I hope you are right
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" This is Dieter Oesterhelt's report to his mentor, Feodor Lynen, winner of the Nobel Prize in Physiology or Medicine in 1964, that he discovered the sight in a salt lake archaea.
The feedback you get when you are yellow aldehyde
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As the name suggests, retinal is photosensitive
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However, it was such an initially overlooked discovery that opened the prelude to optogenetics, an essential tool of modern neuroscience, and optogenetics-based therapy also allowed a blind patient to restore part of his vision
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Dieter Oesterhelt and two other scientists, Peter Hegemann and Karl Deisseroth, who have made key contributions in the field, were awarded the 2021 Lasker Basic Medical Research Award for optogenetics last month
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They are also strong contenders for the Nobel Prize in the future
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The New England Journal of Medicine (NEJM) published a review article describing to us how this important advancement in the field of medicine has emerged from the most bizarre corners of basic research
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We publish the full text translation of this article here
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Optogenetics-the power of light Optogenetics-The Might of LightHäusser MDOI: 10.
1056/NEJMcibr2111915 The use of light to control neuronal activity has been the dream of neuroscientists for decades
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Light does not interfere with the normal function of the brain, and can achieve extremely high time and space accuracy.
Scientists have long believed that compared with traditional electrophysiological or pharmacological methods, light has the potential to become a stronger and more powerful influence on brain activity.
A selective approach
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This hope is realized by a revolutionary method called "optogenetics," which uses light-sensitive proteins expressed in specific neurons under genetic control
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The 2021 Lasker Basic Medical Research Award recognizes Karl Deisseroth, Peter Hegemann, and Dr.
Dieter Oesterhelt for their contributions to this field: they discovered light-sensitive microbial proteins and developed this initial discovery into an essential tool for neuroscience research
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The road to this achievement has taken decades, and includes the collaborative efforts of many scientists from different disciplines
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The whole story is extraordinary.
It shows how important advances in the field of medicine have emerged from the most bizarre corners of basic research
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The story begins with the single-celled prokaryotic organism Halobacterium salinarum, which lives in extreme ecologic niche (ecologic niche) such as the pink lagoon (the color of the lake is derived from this extraordinary archaea)
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Halobacterium has a "purple membrane", which is the power plant of this simple microorganism.
Its role is to convert light into a proton gradient, which can be used to synthesize ATP
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In the early 1970s, Dieter Oesterhelt collaborated with Walter Stoeckenius of the University of California, San Francisco, and discovered that the purple membrane passes through the protein bacterial rhodopsin that acts as a light-gated proton pump [1] (a molecular machine that converts light into electrochemical signals).
(A molecule with close structural homology to vertebrate rhodopsin) achieved this feat
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The subsequent cloning of the bacterial rhodopsin-encoding gene and its heterologous expression in Xenopus laevis oocytes proved that it can generate light-activated currents, which established the basic principle of the current field of optogenetics: using a single gene to drive A single protein is expressed, and the protein can respond to light and activate the transmembrane current
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The discovery of bacterial rhodopsin has encouraged people to search for other light-activated transmembrane proteins in more microorganisms (Figure 1)
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Oesterhelt and colleagues discovered a light-gated pump that is selective for chloride ions in Halobacterium salina and named it the halophilic bacterium rhodopsin
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An archaeal bacterium Natronomonas pharaonis found in alkaline lakes can produce another halophilic bacterium rhodopsin.
Later structural analysis showed that archaeal rhodopsin constitutes a family, and they have A similar domain that can transport protons and other ions
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Figure 1.
The source and potential of extremophilic microbial opsin
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Optogenetic tools were originally discovered by studying single-celled organisms that usually live in extreme habitats, such as archaea and algae (Figure A)
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The bacterial rhodopsin (green light-gated proton pump) is found in Salina bacillus (living in saltwater lakes)
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Channel rhodopsin (mixed cation conductance that produces blue light gating) is found in Chlamydomonas reinhardtii (living in lakes and soil)
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The halophilic bacterium rhodopsin (a yellow light-gated chloride pump) is found in Salinamonas pharaohs (living in alkaline lakes)
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When expressed in neurons (Figure B), these proteins can activate and inhibit action potentials with millisecond precision
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The combined application of optogenetic activator and silencer can achieve bimodal control of neural activity, while step opsin can achieve long-term activation or inhibition of neurons
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The next chapter of the story is about a completely different single-celled organism, Chlamydomonas reinhardtii
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This is a kind of green algae that often lives in freshwater lakes and has phototaxis: it can move towards light, thereby maximizing photosynthesis (its energy source)
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Peter Hegemann and colleagues demonstrated that Chlamydomonas exhibits extremely fast light-gated currents mediated by rhodopsin-like proteins [2]
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In the fruitful collaboration of Peter Hegemann, Georg Nagel, and Ernst Bamberg [3], sequence mining of the Chlamydomonas genome identified the genes encoding two light-activated proteins.
These two proteins are channel rhodopsin 1 ( ChR1) and channel rhodopsin 2 (ChR2), which produce direct light-gated proton conductance and mixed cation conductance, respectively
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This series of microbial proteins constitutes a molecular toolbox, ready for its application in neurons
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The pioneering work of Gero Miesenböck and colleagues in 2002 proved that the expression of the Drosophila phototransduction cascade consisting of three genes can produce light-induced responses in mammalian neurons [4], which indicates that optogenetics The strategy is feasible in principle
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In 2005, Karl Deisseroth and colleagues published a landmark study, which proved that a simple single-molecule microbial opsin can be used as an optogenetic tool [5]: the expression of ChR2 in cultured hippocampal neurons Enables light to trigger action potentials with millisecond precision
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Crucially, they proved that ChR2 can function normally without externally providing additional cofactor retinal (vitamin A's aldehyde)
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After the research was published, many teams followed up soon.
Their research proved that ChR2 can be used for optogenetic activation in different systems (including in vivo models)
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The next key development is the use of microbial opsin to silence neurons
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The laboratories of Karl Deisseroth [6] and Edward Boyden [7] proved that the expression of halophilic rhodopsin in Salmonella pharaoh can silence neuronal activity with millisecond precision
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Importantly, both studies have shown that the co-expression of channel rhodopsin and halophilic rhodopsin in the same cell can achieve bidirectional, dual-wavelength control of neuronal activity, so that we can develop in neural circuits Important function gain and inactivation experiments
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After the miracle year in 2005, the field of optogenetics has made great progress
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We now have a series of microbial opsins, some of which are of natural origin, and some have been optimized by site-directed mutagenesis
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With these opsins, we can not only activate and silence neurons quickly through a series of wavelengths and dynamics, but also genetically engineer opsins to redesign the channel holes (promoting chloride ion flux to achieve Step activation and triggering cascade activation) to achieve more potent optogenetic inhibition [8]
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Strategies involving virus expression (mainly using adeno-associated virus vectors) and transgene expression have been developed to achieve in vivo expression in specific cell types
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Using the fiber-coupled diode technology pioneered by the Deisseroth research team, we can activate specific neurons in the deep brains of freely moving animals
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After the successful development of opsins that can be activated by two-photon irradiation, we can target specific neurons in physiological spatial and temporal patterns, and the simultaneous expression of genetically encoded calcium indicators and opsins provides access to and control of neural circuits The "all-optical" strategy was adopted (Figure 2)
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This makes us hopeful that we can implement closed-loop control of neuronal activity [9], which will lay the foundation for a new brain-computer interface
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Figure 2.
Opsin in behavior
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The combined expression of opsin and gene-encoded activity sensors allows us to read and write activity in the neural circuit at the same time
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By reading activity, neurons related to behavior can be identified, which in turn allows optogenetic manipulation of "correct" neurons to manipulate animal behavior
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This powerful "optogenetic toolbox" has become part of the standard scientific research methods of thousands of neuroscience teams, and has largely replaced the traditional electrical stimulation electrodes used to activate neural pathways
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The advantage of this method is obvious: it can manipulate a genetically defined subset of neurons with millisecond resolution without directly interfering with neighboring neurons
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It can detect functional connections in the body with unprecedented precision and establish causal relationships between specific neuron activity and behavior
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Similarly, the application of optogenetic tools in disease models to probe the dysfunction mechanisms of neural circuits can reveal how specific pathways contribute to Parkinson's disease, epilepsy, anxiety, depression, and other neurological and psychiatric diseases
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What is the application prospect of optogenetic tools in humans? To be applied to the human body, a series of challenges must be solved first, such as the safe and efficient delivery of exogenous genes to the neurons of interest, ensuring that there is no immunogenicity and genotoxicity for a long time, and the delivery of sufficient light to relevant brain regions
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A large number of attempts and verifications in non-human primates have yielded encouraging results, indicating that these challenges may soon be resolved [10]
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Among the many medical applications of optogenetics, scientists have always believed that restoring vision is an easy goal because the human retina is accessible
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This potential has recently been demonstrated strikingly.
After a blind patient received optogenetic therapy using microbial opsin, his vision function was partially restored (Figure 3) [11]
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Figure 3.
Strategies for applying optogenetics to restore vision
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The expression of microbial opsin in retinal ganglion cells (targeting ganglion cells by injecting adeno-associated virus vectors into the eye) enabled a patient with congenital blindness to activate the visual mode through light stimulation of special glasses [11]
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The work of Deisseroth, Hegemann, Oesterhelt, and other scientists produced optogenetic tools and strategies for controlling neural activity
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These microbial proteins, originally discovered in humble single-celled organisms, may provide a means to understand and treat the most complex brain diseases, and we look forward to a more exciting chapter in the optogenetics story
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 References 1.
Oesterhelt D, Stoeckenius W.
Functions of a new photoreceptor membrane.
Proc Natl Acad Sci USA 1973;70:2853-7.
2.
Harz H, Hegemann P.
Rhodopsin-regulated calcium currents in Chlamydomonas.
Nature 1991;351:489 -91.
3.
Nagel G, Szellas T, Huhn W, et al.
Channelrhodopsin-2, a directly light-gated cation-selective membrane channel.
Proc Natl Acad Sci USA 2003;100:13940-5.
4.
Zemelman BV, Lee GA, Ng M, Miesenböck G.
Selective photostimulation of genetically chARGed neurons.
Neuron 2002;33:15-22.
5.
Boyden ES, Zhang F, Bamberg E, Nagel G, Deisseroth K.
Millisecond-timescale, genetically targeted optical control of neural activity.
Nat Neurosci 2005;8:1263-8.
6.
Zhang F, Wang LP, Brauner M, et al.
Multimodal fast optical interrogation of neural circuitry.
Nature 2007;446:633-9.
7.
Han X, Boyden ES.
Multiple-color optical activation, silencing ,and desynchronization of neural activity, with single-spike temporal resolution.
PLoS One 2007;2(3):e299-e299.
8.
Zhang F, Vierock J, Yizhar O, et al.
The microbial opsin family of optogenetic tools.
Cell 2011 ;147:1446-57.
9.
Zhang Z, Russell LE, Packer AM, Gauld OM, Häusser M.
Closed-loop all-optical interrogation of neural circuits in vivo.
Nat Methods 2018;15:1037-40.
10.
Tremblay S, Acker L , Afraz A, et al.
An open resource for non-human primate optogenetics.
Neuron 2020;108(6):1075-1090.
e6.
11.
Sahel JA, Boulanger-Scemama E, Pagot C, et al.
Partial recovery of visual function in a blind patient after optogenetic therapy.
Nat Med 2021;27:1223-9.
Copyright information NEJM Medical Frontiers" translation, writing or manuscriptet al.
The microbial opsin family of optogenetic tools.
Cell 2011;147:1446-57.
9.
Zhang Z, Russell LE, Packer AM, Gauld OM, Häusser M.
Closed-loop all-optical interrogation of neural circuits in vivo.
Nat Methods 2018;15:1037-40.
10.
Tremblay S, Acker L, Afraz A, et al.
An open resource for non-human primate optogenetics.
Neuron 2020;108(6):1075-1090.
e6.
11.
Sahel JA, Boulanger -Scemama E, Pagot C, et al.
Partial recovery of visual function in a blind patient after optogenetic therapy.
Nat Med 2021;27:1223-9.
Copyright information Translation, writing or commissioning of "NEJM Frontiers in Medicine" jointly created by "New England Journal of Medicine" (NEJM)et al.
The microbial opsin family of optogenetic tools.
Cell 2011;147:1446-57.
9.
Zhang Z, Russell LE, Packer AM, Gauld OM, Häusser M.
Closed-loop all-optical interrogation of neural circuits in vivo.
Nat Methods 2018;15:1037-40.
10.
Tremblay S, Acker L, Afraz A, et al.
An open resource for non-human primate optogenetics.
Neuron 2020;108(6):1075-1090.
e6.
11.
Sahel JA, Boulanger -Scemama E, Pagot C, et al.
Partial recovery of visual function in a blind patient after optogenetic therapy.
Nat Med 2021;27:1223-9.
Copyright information Translation, writing or commissioning of "NEJM Frontiers in Medicine" jointly created by "New England Journal of Medicine" (NEJM)An open resource for non-human primate optogenetics.
Neuron 2020;108(6):1075-1090.
e6.
11.
Sahel JA, Boulanger-Scemama E, Pagot C, et al.
Partial recovery of visual function in a blind patient after optogenetic therapy.
Nat Med 2021;27:1223-9.
Copyright information Or commissionAn open resource for non-human primate optogenetics.
Neuron 2020;108(6):1075-1090.
e6.
11.
Sahel JA, Boulanger-Scemama E, Pagot C, et al.
Partial recovery of visual function in a blind patient after optogenetic therapy.
Nat Med 2021;27:1223-9.
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.

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