Optogenetic control of iPS cell-derived neurons in 2D and 3D culture systems using channelrhodopsin-2 expressed by the SYN1 and CaMKII promoters

Abstract

Development of optogenetically controllable human neural network model in three-dimensional (3D) can provide an investigative system that is physiologically relevant or mimic to the human brain. Light-sensitive neurons were generated by transducing channelrhodopsin-2 (ChR2) into human induced pluripotent stem cells (hiPSCs) derived neural progenitor cells (Axol) using lentiviruses and cell-type specific promoters. A mixed population of human iPSC-derived cortical neurons, astrocytes and progenitor cells was obtained (Axol-ChR2) upon neural differentiation. Pan-neuronal promoter synapsin-1 (SYN1) and excitatory neuron-specific promoter calcium-calmodulin kinase II (CaMKII) were used to drive reporter gene expression in order to assess the differentiation status of the targeted cells. Expression of ChR2 and characterisation of sub-populations in differentiated Axol-ChR2 cells were evaluated using flow cytometry and immunofluorescent staining. These cells were transferred from 2D culture to 3D alginate hydrogel functionalised with arginine-glycine-aspartate (RGD) and small molecules (Y-27632). Improved RGD-alginate hydrogel was physically characterised and assessed for cell viability to serve as a generic 3D culture system for hPSCs and neuronal cells. Prior to cell encapsulation, neural network activities of Axol-ChR2 cells and primary neurons were investigated using calcium imaging. Results demonstrate that functional activities were successfully achieved through expression of ChR2- by both the CaMKII and SYN1 promoters. The RGD-alginate hydrogel system supports the growth of differentiated Axol-ChR2 cells whilst allowing detection of ChR2 expression upon light stimulation. This allows precise and non-invasive control of human neural networks in 3D.