Defining parameters of specificity for bioluminescent optogenetic activation of neurons using in vitro multi electrode arrays (MEA)

Abstract

In Bioluminescent Optogenetics (BL-OG) a biological, rather than a physical, light source is used to activate light-sensing opsins, such as channelrhodopsins or pumps. This is commonly achieved by utilizing a luminopsin (LMO), a fusion protein of a light-emitting luciferase tethered to a light-sensing opsin. Light of the wavelength matching the activation peak of the opsin is emitted by the luciferase upon application of its small molecule luciferin, resulting in activation of the fused opsin and subsequent effects on membrane potential. Using optimized protocols for culturing, transforming, and testing primary neurons in multi electrode arrays, we systematically defined parameters under which changes in neuronal activity are specific to bioluminescent activation of opsins, rather than due to off-target effects of either the luciferin or its solvent on neurons directly, or on opsins directly. We further tested if there is a direct effect of bioluminescence on neurons. Critical for assuring specific BL-OG effects are testing the concentration and formulation of the luciferin against proper controls, including testing effects of vehicle on LMO expressing and of luciferin on nonLMO expressing targets.

Restoring Function After Severe Spinal Cord Injury Through Bioluminescence-Driven Optogenetics

“…Here we use LMO3 which consists of slow burn Gaussia luciferase fused to Volvox channelrhodopsin 1. This system has been demonstrated to consistently activate expressing neuronal cells with little to no off target effects caused by the substrate and bioluminescent reaction that takes place (16,17,MGR). Moreover, bioluminescence is light emitted without heat ("cold light") and thus does not approach the damaging levels encountered for traditional optogenetics (18).…”

The BioLuminescent-OptoGenetic in vivo Response to Coelenterazine is Proportional, Sensitive and Specific in Neocortex

“…BioLuminescent OptoGenetics ('BL-OG') is an emerging dual strategy that provides both optogenetic and chemogenetic capabilities. In this approach, binding of an oxidative enzyme (luciferase) to a small light-emitting molecule (luciferin) drives bioluminescence that, in turn, regulates a neighboring opsin (Berglund et al, 2013;Birkner et al, 2014;Tung et al, 2015;Berglund et al, 2016b;Berglund et al, 2016a;Park et al, 2017;Prakash et al, 2018;Tung et al, 2018;Zenchak et al, 2018;Berglund et al, 2019). To ensure proximity of the bioluminescent reaction to the recipient opsin, the luminopsin (LMO) construct was invented, in which a luciferase is linked to the optogenetic element by a short 15 amino acids linker (Berglund et al, 2016a).…”

“…Here, we systematically tested the relationship between BL-OG neural modulation and photon production, and the possibility that non-specific components of its bioluminescent reaction modulate neuronal spiking. To this end, we expressed LMO3 in mice, a BL-OG construct previously demonstrated to robustly activate neurons (Berglund et al, 2016b;Berglund et al, 2016a;Prakash et al, 2018), and drive behavioral responses when activated by CTZ (Berglund et al, 2016a;Zenchak et al, 2018). We tested whether the neural response in LMO3expressing mice was proportional to CTZ dose and photon production.…”

Opto‐chemogenetics with luminopsins: A novel avenue for targeted control of neuronal activity

“…The same molecule can be activated by external light, similar to conventional optogenetics (right). Prakash et al () and Berglund et al () capitalized on this unique property of bimodal activation in vitro and in vivo…”

“…Although CTZ is expected to exert no significant off‐target effects in the brain except for potential antioxidative effects (Dubuisson et al, ), the solvent may affect the physiology of brain cells. Using neuronal firing recorded in a multielectrode array in vitro as a readout, Prakash, Medendorp, and Hochgeschwender () systematically examined the effect of different preparations of CTZ in different solvents for different LMOs. Their thorough study is a convenient guide for new luminopsin users to choose from different preparations of CTZ to avoid potential artifacts.…”