194 Electrical Impedance Spectroscopy Analysis to Evaluate Organotypic Epidermis Formation and Barrier Function in Vitro

For research into skin biology, diseases and drug or chemical interactions, organotypic 3D human epidermal equivalents (HEEs) are frequently utilized, but studies heavily rely on end-points analysis for which HEEs are harvested to study cellular responses. Non-intrusive methods that enable longitudinal analysis by repetitive measurements can minimize batch effects, increase study reproducibility and maximize experimental throughput. Here we used a novel 12-well format electrical impedance spectroscopy (EIS) device, customized to fit with a 24-transwell cell culture system to replace conventional static and labor-intensive transepidermal electrical resistance (TEER) analysis using voltohmmeters. EIS applied for seven consecutive days during epidermal development did not impact epidermal morphology and read-outs were similar to HEEs measured only once at time of harvesting. To explore the utility of EIS to identify defects in tissue formation or barrier function, HEEs were generated from CRISPR/Cas9 engineered N/TERT keratinocyte lines with a proven knockout for genes involved in terminal differentiation (e.g. FLG, TFAP2A, CLDN4 and AHR). Herein, impedance spectra only reached 35-65% to that of wildtype HEEs. In addition, exposure to Th2 cytokines (which affect epidermal differentiation) reduced impedance by 35%. This defect could be rescued by known therapeutic ligands (e.g. therapeutic AHR modulating agents) that stimulate keratinocyte terminal differentiation and interfere with Th2 cytokine signaling. In conclusion, EIS provides a high-throughput standardized system in which barrier function formation of human epidermal equivalents can easily be monitored and followed in time. Other potential applications include the screening of barrier defects as well as therapeutic efficacy skin barrier-promoting agents in organotypic epidermal models.