Abstract
There is a critical need to develop high-throughput assays to identify compounds that offer therapy for individuals suffering from neurodegenerative diseases. Most brain disorders, including neurodegenerative diseases, share the common neuropathology of mitochondria dysfunction, which can lead to apoptosis of neurons, overproduction of reactive oxygen species (ROS), and other cellular neuropathologies characteristic of these diseases. Human induced pluripotent stem cells (iPSCs) with a stable genomic insertion of the neurogenin-2 transcription factor under the control of the TetOn promoter can be differentiated into excitatory human neurons (i3Neurons) within 3 days of exposure to doxycycline. These neurons have been used to develop and validate a live-cell assay for parameters of mitochondrial dynamics and function using two compounds known to promote mitochondrial elongation in mouse neurons, 4-hydroxychalcone and 2,4-dihyrdroxychalcone. The assay involves plating the neurons in 384-well microtiter plates, treating them with known or unknown substances, and then capturing morphological information for the neuronal mitochondria using a lentivirus vector to express a mitochondrial-targeted fluorescence reporter. The i3Neuron cultures exposed to these two compounds for 24 h exhibit significantly decreased circularity and significantly increased length compared to controls, two morphological parameters correlated with increased mitochondrial health. The assay is rapid, with results obtained after a one-week-long i3Neuron culture or one month if neurons are co-cultured with astrocytes. This live-cell, mitochondrial phenotypic assay can be used for high-throughput screening or as an orthogonal assay for compounds obtained via other high-throughput screening campaigns.