Ever since the cloning of channelrhodopsin-2 (ChR2), there has been an explosion of interest in applying optogenetic methods to all aspects of neuroscience¹. Initially, ChR2 was used to control neuronal activity in vitro^2,3, and shortly thereafter in animal models⁴. More recently, light-activated systems have even made their way to human clinical trials. Scientists and clinicians continue to develop and brainstorm new uses for this powerful set of tools. Here are a few of the interesting applications of optogenetics that may soon directly impact human health, and in some cases already have.

Restoring sight to the blind

Probably the first proposed use of optogenetics to treat a disease was by Zhuo-Hua Pan, who hypothesized that ectopic expression of light-gated channels in patients with retinal degeneration could restore light-sensitivity to the eye. This approach proved successful in mouse models when adeno-associated virus (AAV) was used to express ChR2 in inner retinal neurons⁵, and is currently being used in clinical trials to treat human patients with retinal degeneration^6,7.

Optical pacemakers

A group of Israeli researchers have developed an optogenetic pacemaker system in rat hearts. After using AAV to introduce ChR2 directly to cardiac cells, and were able to control heart beat frequency and timing using blue-light illumination⁸. The use of optical stimulation along with gene therapy, rather than electrical stimulation, allows for more precise control of the location and intensity of cardiac excitation.

Stopping seizures with light

Scientists at Stamford University have applied optogenetics to controlling seizures in a rat model of brain injury-related epilepsy⁹. The group first identified that thalamocortical (TC) neurons played an important role in inducing the seizures that often follow cerebrocortical injuries, such as stroke. They then used an AAV vector to introduce eNpHR, a light-sensitive inhibitory halorhodopsin, to rat TC neurons, and implanted an illumination system to selectively inhibit this circuit during seizures. Their tests showed that optoggenetically inhibiting the activity of these neurons was sufficient to immediately interrupt seizures.

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References

1. Nagel G, Szellas T, Huhn W, Kateriya S, Adeishvili N, Berthold P, Ollig D, Hegemann P, Bamberg E. Channelrhodopsin-2, a directly light-gated cation-selective membrane channel. Proc Natl Acad Sci U S A. 2003 Nov 25;100(24):13940-5.
2. Boyden ES, Zhang F, Bamberg E, Nagel G, Deisseroth K. Millisecond-timescale, genetically targeted optical control of neural activity. Nat Neurosci. 2005 Sep;8(9):1263-8.
3. Li X, Gutierrez DV, Hanson MG, Han J, Mark MD, Chiel H, Hegemann P, Landmesser LT, Herlitze S. Fast noninvasive activation and inhibition of neural and network activity by vertebrate rhodopsin and green algae channelrhodopsin. Proc Natl Acad Sci U S A. 2005 Dec 6;102(49):17816-21.
4. Nagel G, Brauner M, Liewald JF, Adeishvili N, Bamberg E, Gottschalk A. Light activation of channelrhodopsin-2 in excitable cells of Caenorhabditis elegans triggers rapid behavioral responses. Curr Biol. 2005 Dec 20;15(24):2279-84.
5. Bi A, Cui J, Ma YP, Olshevskaya E, Pu M, Dizhoor AM, Pan ZH. Ectopic expression of a microbial-type rhodopsin restores visual responses in mice with photoreceptor degeneration. Neuron. 2006 Apr 6;50(1):23-33
6. RST-001 Phase I/II Trial for Advanced Retinitis Pigmentosa. Allergan. ClinicalTrials.gov Identifier: NCT02556736.
7. Dose-escalation Study to Evaluate the Safety and Tolerability of GS030 in Subjects With Retinitis Pigmentosa (PIONEER). GenSight Biologics. ClinicalTrials.gov Identifier: NCT03326336.
8. Nussinovitch U, Gepstein L. Optogenetics for in vivo cardiac pacing and resynchronization therapies. Nat Biotechnol. 2015 Jul;33(7):750-4.
9. Paz JT, Davidson TJ, Frechette ES, Delord B, Parada I, Peng K, Deisseroth K, Huguenard JR. Closed-loop optogenetic control of thalamus as a tool for interrupting seizures after cortical injury. Nat Neurosci. 2013 Jan;16(1):64-70