Optimization of a novel in situ hybridization technology on 3D organotypic cell cultures

Introduction: Developed by Advanced Cell Diagnostics, RNAscope® in situ hybridization technology enables detection of a target RNA in a cell-specific manner on formalin-fixed paraffin-embedded tissue sections and represents a good alternative to immunohistochemistry. The goal of this work is to illustrate an optimized protocol of the RNAscope technology to detect target genes in various human organotypic culture models (nasal, small airway, and gingival). These culture models retain the three-dimensional structure of native epithelium, mimic in vivo morphology and human physiology, and can be used as alternative sources to animal testing. Materials and Methods: After fixation and processing of five replicates of the three different organotypic cell cultures, the tissue morphology was checked by hematoxylin and eosin staining. The RNAscope protocols were optimized based on three crucial parameters: heat pretreatment, enzymatic digestion, and signal amplification. Digital images of the RNAscope stained slides were generated using the Hamamatsu NanoZoomer 2.0 slide scanner, and images were quantified using a custom-made plugin on Definiens Tissue Studio software (Definiens AG, Munich, Germany). Results: The tissue morphology demonstrates optimum fixation and processing for samples, while the optimized protocol for RNAscope shows preserved RNA with staining on the positive control probe with score ≥2 and no staining on the negative control probe with score <1. Discussion and Conclusion: RNAscope combined with organotypic cell cultures is a promising tool to better understand cell-specific RNA expression while implementing 3R (replace, reduce, and refine animal testing) principles.