Optogenetics: What you see is what you think

Syeda Anika Imam, Amandeep Taank, Dana Zaitoun, Seo Hyun Lee

http://www.livescience.com/29340-optogenetics-brain-research-breakthrough-nsf-bts.html

PHM142 Fall 2015Coordinator: Dr. Jeffrey HendersonInstructor: Dr. David Hampson

What is Optogenetics?• Optogenetics is a branch of biotechnology which combines genetic engineering with optical methods

• Research tool to obtain insights into complex tissue function such as Parkinson’s disease

• Optogenetics is subdivided into:

• Sensors: monitor neural circuits

• Effectors: manipulate neural circuits

• Basic concept: expressing a light activated ion channel in a specific group of cells such as neurons then illuminating the cells to control activity

http://web.stanford.edu/group/dlab/optogenetics/

How it works: Neurons

•Every neuron has a pump and channel proteins that control the flow of ions across the membrane

•Resting membrane potential is negative

•When a signal arrives, an influx of Na+ ions causes depolarization

http://antranik.org/synaptic-transmission-by-somatic-motorneurons/

Photosensory Molecules

•Molecules that convert light into electricity

•Can be naturally occurring or chemically modified Channelrhodopsin (ChR2) - found in algae Chlamydomonas reinhardtii Halorhodopsin (NpHR) – found in archaeon Natronomonas pharaonic

•Genes that code for these molecules can be delivered by:- Transfection (introducing nucleic acids into cells, non-viral methods in eukaryotic cells)- Viral transduction- Creation of transgenic animal lines

Channelrhodopsin•Cation channel

•Activated by blue light (470nm)

•Allows Na+ influx across the membrane and depolarizes the neuron, thus activating it

•Acts as the on switch

Halorhodopsin•Chloride pump

•Activated by yellow light (580 nm)

•Triggers influx of Cl- which hyperpolarizes the cell and inhibits the neuron

•Acts as the Off switch

Pastrana, E. (2011). Optogenetics: Controlling cell function with light. Nature Methods, 8(1), 24-25. DOI:10.1038/nmeth.f.323

Deisseroth, K. (2011). Optogenetics. Nature Methods, 8(1), 26-29.

Parkinson’s Disease (PD)

• Neurological disorder due to degeneration of neurons that produce dopamine (dopaminergic neurons)

• Decrease in dopamine leads to abnormal brain activity, and diseases such as PD• Symptoms include:

• tremors• bradykinesia• stiff muscles• loss of involuntary movements• speech problems• other motor problems

Optogenetic Application to PD Treatment

• Cell replacement therapy: integrating engineered dopamine releasing (DA) neurons into the brain network

• Engineered DA neurons express halorhodopsin• in vitro conditions, release of dopamine in DA neurons inhibited when exposed to light• after grafting the DA neurons into lesion-induced PD mice, the subjects showed substantial

recovery of motor symptoms, but when yellow light shines on DA neurons, motor recovery of mice was lost

Deep Brain Stimulation (DBS)

Deisseroth, K., & Tye, K. (2012). Optogenetic investigation of neural circuits underlying brain disease in animal models. Neuroscience Nat. Rev., 13, 251-266.

Currently used to investigate…

• Schizophrenia• Anxiety and Mood Disorders• Addiction• Autism

Pros and Cons

Pros of Optogenetics Cons of OptogeneticsExcellent spatial and temporal solution Viral infections and exogenous proteins can lead to

structural abnormalities/toxicity

Significant experimental control Damage to surrounding tissue

Can be applied to many fields

Can be used as disease models

References(2010). Optogenetics. Research Papers of the Max Planck Society, 24-25.

Butler, J. (2012). Optogenetics: Shining a light on the brain. Bioscience Horizons, 5, 1-8. doi: 10.1093/biohorizons/hzr020

Deisseroth, K. (2011). Optogenetics. Nature Methods, 8(1), 26-29.

Deisseroth, K., & Tye, K. (2012). Optogenetic investigation of neural circuits underlying brain disease in animal models. Neuroscience Nat. Rev., 13, 251-266.

Dugue, G.P. et., al. (2012). A comprehensive concept of optogenetics. Progress in brain research, 196, 1-28.

Fowler, C.D., et., al. (2014). Using Optogenetics and Designer Receptors Exclusively Activated by Designer Drugs (DREADDS). 1-3.

Lamballais, S. (2013). Optogenetics and its Applications in Psychology: Manipulating the Brain Using Light. Journal of European Psychology Students, 4, 87-100.

Liu, X., Tonegawa, S. (2010). Optogenetics 3.0. Cell, 141, 22-24.

Steinbeck, J.A., Choi, S.J., Mrejeru, A., Ganat, Y., Deisseroth, K., Sulzer, D., Mosharov, E.V., Studer, L. (2015). Optogenetics enables functional analysis of human embryonic stem cell-derived grafts in a Parkinson’s disease model. Nature Biotechnology, 33 (2): 204-209. doi: 10.1038/nbt.3124.

Pastrana, E. (2011). Optogenetics: Controlling cell function with light. Nature Methods, 8(1), 24-25. DOI:10.1038/nmeth.f.323

Summary• Optogenetics is a branch of biotechnology which combines genetic engineering with optical methods

to observe and control the function of genetically targeted groups of cells with light

• Channelrhodopsin = ion channel that is activated by blue light and depolarizes a neuron

• Halorhodopsin = Chloride channel that is activated by yellow light and inhibits neuronal action

• Parkinson’s disease (PD): neurological disorder due to degeneration of neurons that produce

dopamine

• Cell replacement therapy uses halorhodopsin to test validity

• Deep Brain Stimulation (DBS) is a current therapy used for PD, where you have a pace maker that

stimulates the brain

• Optogenetics is used to determine the mechanism of DBS

• Pros: excellent spatial and temporal resolution

• Cons: can lead to structural abnormalities and toxicity