Channelrhodopsin: Potential Applications in Vision Restoration


Channelrhodopsins, the directly light‐gated ion channels from green algae, provide a powerful tool for basic research in neuroscience as well as potential applications for treating neurological diseases and disorders. One of the promising clinical applications is to cure blindness caused by the death of rod and cone photoreceptors. Retinitis pigmentosa (RP) is one of diseases that causes blindness. Although photoreceptor cells are degenerated in the retina of RP patients, other retinal neurons such as retinal ganglion cells and on bipolar cells still survive. Owing to the inherent characteristics of chlamydomonas‐derived channelrhodopsin‐2 (ChR2), photosensitive neurons can be produced in the retina by the transfer of the ChR2 gene into survived retinal neurons. A single injection of a virus vector into the eye can achieve the vision restoration in rodent model that will be a useful treatment for the patients with blindness. Herein, we introduce the molecular properties of ChR2 and a potential as a new strategy for restoring vision in humans.

Key Concepts

  • Channelrhodopsins, microbial retinal binding proteins, transiently induce photo currents by light stimuli.
  • Photocycle of channelrhodopsins remains preserved when they are heterologously expressed in animal and human cells.
  • Channelrhodoposins functions as a directly light‐gated cation channels with million second activation and deactivation kinetics.
  • Artificial photoreceptor cells can be produced in various types of animal neurons by transducing a single gene.
  • Converting surviving inner retinal neurons into directly photosensitive cells is a new strategy to treating blindness after the death of rod and cone photoreceptors.
  • Using delivery by adeno‐associated viral vectors, long‐term expression of channelrhodopsin‐2 can be achieved in rodent inner retinal neurons in vivo.
  • ChR2 can be expressed without immunologically harmful reactions in vivo.

Keywords: channelrhodopsins; directly light‐gated ion channels; retinal blinding diseases; vision restoration

Figure 1. Photocycle of ChR2. The D470 dark state is converted by a light‐induced retinal isomerisation into an early intermediate, P500. Thermal relaxation accompanied by transient Schiff base deprotonation (P390) and conformational changes of the protein creates the putative conducting state, P520. The D470 dark state recovers via the two P480 intermediates, P480a and P480b. The latter, via a major backbone rearrangement in P480b, leads to restoration of the original dark state. Like P520, the P480b intermediate is photoreactive and can be converted by light to the early P500 intermediate, but at lower quantum efficiency. Modified from Ritter et al. 2008 ©American Society for Biochemistry and Molecular Biology.
Figure 2. Expression of a Chop2‐GFP fusion construct in HEK 293 cells. (a) pCMV‐Chop2‐GFP expression cassette. (b) Chop2‐GFP expression in HEK 293 cells with pCMV‐Chop2‐GFP viewed under a fluorescence microscope. Scale bar: 15 µm. (c) and (d) Representative recordings of light responses from Chop2‐GFP fusion protein‐expressing HEK 293 cells. The current was recorded from a HEK cell, preincubated in the presence of 1 μM all‐trans retinal (c). The current was also observed in HEK cells in the absence of exogenous all‐trans retinal. (e) The average currents recorded from HEK cells in the absence or presence of 0.1 and 1 μM all‐trans retinal.
Figure 3. Properties of light‐evoked currents of the ChR2‐expressing retinal neurons (modified from Bi et al., ). (a) A recording of a Chop2‐expressing retinal cell response to light stimuli of wavelengths ranging from 420 to 580 nm. (b) A representative recording of the currents elicited by light stimuli at a wavelength of 460 nm with light intensities ranging from 2.2 × 1015 to 1.8 × 1018 photons cm−2 s−1. (c) Light‐intensity response curve. The data points were fitted with a single logistic function curve. Reproduced from Bi et al., 2006 © Elsevier.
Figure 4. Expression and light‐response properties of ChR2 in retinal neurons of rd1/rd1 mice (modified from Bi et al., ). Chop2‐GFP fluorescence viewed in flat retinal whole‐mount (a) and vertical sections (b). (c) Light microscope image of a semi‐thin vertical retinal section. Scale bar: 50 µm in (a) and 30 µm in (b) and (c). (d) Representative recordings of a Chop2‐GFP‐positive neuron in four incremental intensities at a wavelength of 460 nm. The relationship between the light intensity and the current amplitude (e), membrane depolarisation (f) and the number of spikes (g). Reproduced from Bi et al., 2006 © Elsevier.
Figure 5. Central projections of Chop2‐GFP‐expressing retinal ganglion cells and visual‐evoked potentials in rd1/rd1 mice (modified from Bi et al., ). GFP‐labelled terminal arbours of retinal ganglion cells in ventral lateral geniculate nucleus and dorsal lateral geniculate nucleus (a) and in superior colliculus (b). OT, optical track; vLGN, ventral lateral geniculate nucleus; dLGN, dorsal lateral geniculate nucleus; SC, superior colliculus. Scale bar: 200 µm in (a), 100 µm in (b). (c) VEPs recorded from a wild‐type mouse. The responses were observed at both wavelengths of 460 and 580 nm. (d) VEPs recorded from an rd1/rd1 mouse injected with Chop2‐GFP viral vectors. The responses were elicited only by light at the wavelength of 460 nm but not at the wavelength of 580 nm. (e) No detectable VEPs were observed from rd1/rd1 mice injected with viral vectors carrying GFP alone. Reproduced from Bi et al., 2006 © Elsevier.
Figure 6. Immune responses to the long‐term expression of ChR2 in rat retinas (modified from Sugano et al., ). Lymphocytes were isolated from the peripheral blood at the indicated time points and T‐cell ratio of CD4+CD25+ was calculated (a). Representative data of flow cytometric analysis at pre‐injection and 7 days post‐injection are indicated. An AAV‐Venus was injected into the eyes as a control. Production levels of the antibody to ChR2 were measured by the ELISA (b). At 64 weeks post‐injection, paraffin‐embedded retinal sections were stained with haematoxylin and eosin (c; left: control, right: ChR2, bar = 20μm). There is no difference between the ChR2‐injected and the age‐matched untreated RCS (rdy/rdy) rats. No inflammatory cells were observed in both retinas. Reproduced from Sugano et al., 2010 © Nature Publishing Group.


Adamantidis AR , Zhang F , Aravanis AM , et al. (2007) Neural substrates of awakening probed with optogenetic control of hypocretin neurons. Nature 450: 420–424.

Alilain WJ , Li X , Horn KP , et al. (2008) Light‐induced rescue of breathing after spinal cord injury. Journal of Neuroscience 28: 11862–11870.

Arenkiel BR , Peca J , Davison IG , et al. (2007) In vivo light‐induced activation of neural circuitry in transgenic mice expressing channelrhodopsin‐2. Neuron 54: 205–218.

Atasoy D , Aponte Y and Su HH (2008) A FLEX switch targets Channelrhodopsin‐2 to multiple cell types for imaging and long‐range circuit mapping. Journal of Neuroscience 28: 7025–7030.

Berthold P , Tsunoda SP and Ernst OP (2008) Channelrhodopsin‐1 initiates phototaxis and photophobic responses in Chlamydomonas by immediate light‐induced depolarization. Plant Cell 20: 1665–1677.

Bi A , Cui J , Ma Y , et al. (2006) Ectopic expression of a microbial‐type rhodopsin restores visual responses in mice with photoreceptor degeneration. Neuron 50: 23–33.

Boyden ES , Zhang F , Bamberg E , et al. (2005) Millisecond‐timescale, genetically targeted optical control of neural activity. Nature Neuroscience 8: 1263–1268.

Caldwell JH , Herin GA , Nagel G , et al. (2008) Increases in intracellular calcium triggered by channelrhodopsin‐2 potentiate the response of metabotropic glutamate receptor mGluR7. Journal of Biological Chemistry 283: 24300–24307.

Chang B , Hawes NL , Hurd RE , et al. (2002) Retinal degeneration mutants in the mouse. Vision Research 42: 517–525.

D'Cruz PM , Yasumura D , Weir J , et al. (2000) Mutation of the receptor tyrosine kinase gene Mertk in the retinal dystrophic RCS rat. Human Molecular Genetics 9: 645–651.

Douglass AD , Kraves S , Deisseroth K , et al. (2008) Escape behavior elicited by single, channelrhodopsin‐2‐evoked spikes in zebrafish somatosensory neurons. Current Biology 18: 1133–1137.

Ernst OP , Sanchez Murcia PA , Daldrop P , et al. (2008) Photoactivation of channelrhodopsin. Journal of Biological Chemistry 283: 1637–1643.

Flannery JG , Zolotukhin S , Vaquero MI , et al. (1997) Efficient photoreceptor‐targeted gene expression in vivo by recombinant adeno‐associated virus. Proceedings of the National Academy of Sciences of the United States of America 94: 6916–6921.

Harvey AR , Kamphuis W , Eggers R , et al. (2002) Intravitreal injection of adeno‐associated viral vectors results in the transduction of different types of retinal neurons in neonatal and adult rats: a comparison with lentiviral vectors. Molecular and Cellular Neuroscience 21: 141–157.

Hegemann P , Ehlenbeck S and Gradmann D (2005) Multiple photocycles of channelrhodopsin. Biophysical Journal 89: 3911–3918.

Huber D , Petreanu L , Ghitani N , et al. (2008) Sparse optical microstimulation in barrel cortex drives learned behaviour in freely moving mice. Nature 451: 61–64.

Ishizuka T , Kakuda M , Araki R , et al. (2006) Kinetic evaluation of photosensitivity in genetically engineered neurons expressing green algae light‐gated channels. Neuroscience Research 54: 85–94.

Lagali PS , Balya D , Awatramani GB , et al. (2008) Light‐activated channels targeted to ON bipolar cells restore visual function in retinal degeneration. Nature Neuroscience 11: 667–675.

Li X , Gutierrez DV , Hanson MG , et al. (2005) Fast noninvasive activation and inhibition of neural and network activity by vertebrate rhodopsin and green algae channelrhodopsin. Proceedings of the National Academy of Sciences of the United States of America 102: 17816–17821.

Lin B , Koizumi A , Tanaka N , et al. (2008) Restoration of visual function in retinal degeneration mice by ectopic expression of melanopsin. Proceedings of the National Academy of Sciences of the United States of America 105: 16009–16014.

Mace E , Caplette R , Marre O , et al. (2014) Targeting channelrhodopsin‐2 to ON‐bipolar cells with vitreally administered AAV Restores ON and OFF visual responses in blind mice. Molecular Therapy 23: 7–16.

Mahoney TR , Luo S , Round EK , et al. (2008) Intestinal signaling to GABAergic neurons regulates a rhythmic behavior in Caenorhabditis elegans . Proceedings of the National Academy of Sciences of the United States of America 105: 16350–16355.

Martin KR , Quigley HA , Zack DJ , et al. (2003) Gene therapy with brain‐derived neurotrophic factor as a protection: retinal ganglion cells in a rat glaucoma model. Investigative Ophthalmology and Visual Science 44: 4357–4365.

McLaughlin ME , Sandberg MA , Berson EL , et al. (1993) Recessive mutations in the gene encoding the beta‐subunit of rod phosphodiesterase in patients with retinitis pigmentosa. Nature Genetics 4: 130–134.

Milam AH , Li ZY and Fariss RN (1998) Histopathology of the human retina in retinitis pigmentosa. Progress in Retinal and Eye Research 17: 175–205.

Nagel G , Brauner M , Liewald JF , et al. (2005) Light activation of channelrhodopsin‐2 in excitable cells of Caenorhabditis elegans triggers rapid behavioral responses. Current Biology 15: 2279–2284.

Nagel G , Ollig D , Fuhrmann M , et al. (2002) Channelrhodopsin‐1: a light‐gated proton channel in green algae. Science 296: 2395–2398.

Nagel G , Szellas T , Huhn W , et al. (2003) Channelrhodopsin‐2, a directly light‐gated cation‐selective membrane channel. Proceedings of the National Academy of Sciences of the United Sates of America 100: 13940–13945.

Oesterhelt D (1998) The structure and mechanism of the family of retinal proteins from Halophilic archaea. Current Opinion in Structural Biology 8: 489–500.

Oesterhelt D and Stoeckenius W (1973) Functions of a new photoreceptor membrane. Proceedings of the National Academy of Sciences of the United States of America 70: 2853–2857.

Petreanu L , Huber D , Sobczyk A , et al. (2007) Channelrhodopsin‐2‐assisted circuit mapping of long‐range callosal projections. Nature Neuroscience 10: 663–668.

Rauschecker JP and Shannon RV (2002) Sending sound to the brain. Science 295: 1025–1029.

Ritter E , Stehfest K , Berndt A , et al. (2008) Monitoring light‐induced structural changes of channelrhodopsin‐2 by UV‐visible and fourier transform infrared spectroscopy. Journal of Biological Chemistry 283: 35033–35041.

Santos A , Humayun MS , de Juan E Jr , et al (1997) Preservation of the inner retina in retinitis pigmentosa. A morphometric analysis. Archives of Ophthalmology 115: 511–515.

Schroll C , Riemensperger T , Bucher D , et al. (2006) Light‐induced activation of distinct modulatory neurons triggers appetitive or aversive learning in Drosophila larvae. Current Biology 16: 1741–1747.

Sineshchekov OA , Jung KH and Spudich JL (2002) Two rhodopsins mediate phototaxis to low‐ and high‐intensity light in Chlamydomonas reinhardtii . Proceedings of the National Academy of Sciences of the United States of America 99: 8689–8694.

Sineshchekov OA , Govorunova EG , Wang J , et al. (2012) Enhancement of the long‐wavelength sensitivity of optogenetic microbial rhodopsins by 3,4‐dehydroretinal. Biochemistry 51: 4499–4506.

Sugano E , Isago H , Wang Z , et al. (2010) Immune responses to adeno‐associated virus type 2 encoding channelrhodopsin‐2 in a genetically blind rat model for gene therapy. Gene Therapy 18: 266–274.

Tomita H , Sugano E , Murayama N , et al. (2014) Restoration of the majority of the visual spectrum by using modified Volvox channelrhodopsin‐1. Molecular Therapy 22 (8): 1434–1440.

Tomita H , Sugano E , Yawo H , et al. (2007) Restoration of visual response in aged dystrophic RCS rats using AAV‐mediated channelopsin‐2 gene transfer. Investigative Ophthalmology and Visual Science 48: 3821–3826.

Toni N , Laplagne DA , Zhao C , et al. (2008) Neurons born in the adult dentate gyrus form functional synapses with target cells. Nature Neuroscience 11: 901–907.

Wang H , Sugiyama Y , Hikima T , et al. (2009) Molecular determinants differentiating photocurrent properties of two channelrhodopsins from chlamydomonas. Journal of Biological Chemistry 284: 5685–5696.

Wang H , Peca J , Matsuzaki M , et al. (2007) High‐speed mapping of synaptic connectivity using photostimulation in Channelrhodopsin‐2 transgenic mice. Proceedings of the National Academy of Sciences of the United States of America 104: 8143–8148.

Wässle H (2004) Parallel processing in the mammalian retina. Nature Reviews Neuroscience 5: 747–757.

Weleber RG (1994) Retinitis pigmentosa and allied disorders. In: Ryan SJ (ed) Retina, pp. 335–466. St. Louis, MO: Mosby.

Zemelman BV , Lee GA , Ng M , et al. (2002) Selective photostimulation of genetically chARGed neurons. Neuron 33: 15–22.

Zhang W , Ge W and Wang Z (2007a) A toolbox for light control of Drosophila behaviors through Channelrhodopsin 2‐mediated photoactivation of targeted neurons. European Journal of Neuroscience 26: 2405–2416.

Zhang F , Aravanis AM , Adamantidis A , et al. (2007b) Circuit‐breakers: optical technologies for probing neural signals and systems. Nature Reviews Neuroscience 8: 577–581.

Zhang F , Prigge M , Beyrière F , et al. (2008) Red‐shifted optogenetic excitation: a tool for fast neural control derived from Volvox carteri. Nature Neuroscience 11: 631–633.

Further Reading

Flannery JG and Greenberg KP (2006) Looking within for vision. Neuron 50: 1–3.

Francis PJ , Mansfield B , Rose S (2013) Proceedings of the First International Optogenetic Therapies for Vision Symposium. Translational Vision Science & Technology 2:1–15 (doi/full/10.1167/tvst.2.7.4).

Hegemann P (2008) Algal sensory photoreceptors. Annual Review of Plant Biology 59: 167–189.

Herlitze S and Landmesser SL (2007) New optical tools for controlling neuronal activity. Current Opinion in Neurobiology 17: 87–94.

Liewald JF , Brauner M , Stephens GJ , et al. (2008) Optogenetic analysis of synaptic function. Nature Methods 5: 895–902.

Zhang F , Wang LP , Boyden ES , et al. (2006) Channelrhodopsin‐2 and optical control of excitable cells. Nature Methods 3: 785–792.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Tomita, Hiroshi(Aug 2015) Channelrhodopsin: Potential Applications in Vision Restoration. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0021388.pub2]