Optogenetics: What you see is what you think PHM142 Fall 2015 Coordinator: Dr. Jeffrey Henderson Instructor: Dr. David Hampson http://www.livescience.com/29340-optogenetics-brain-research-breakthrough-nsf-bts.html Syeda Anika Imam, Amandeep Taank, Dana Zaitoun, Seo Hyun Lee

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 Halorhodopsin •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 Optogenetics Excellent 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