Regulation of keratinocyte differentiation through aryl hydrocarbon receptor signaling involves the transient activation of TFAP2A

Terminal differentiation of keratinocytes is essential for skin barrier development and tightly coordinated by a complex network of interacting transcription factors. Previous work identified the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor and environmental sensor, to orchestrate epidermal differentiation through transient activation of putative downstream transcription factors, amongst others TFAP2A. For proof-of-concept studies on a presumed AHR- TFAP2A axis that is co-opted in epidermal differentiation, we utilized siRNA-mediated TFAP2A knockdown in primary keratinocytes and CRISPR-Cas9 induced TFAP2AKO in N/TERT keratinocytes combined with transcriptomic analysis and organotypic epidermis modeling. Keratinocyte- specific ablation of TFAP2A negatively impacted epidermal development resulting in disorganized stratification, aberrant differentiation and reduced barrier function (by transepithelial resistance) in organotypic TFAP2AKO epidermis. Furthermore, TFAP2A deficiency impeded the AHR ligand- mediated induction of terminal differentiation gene expression (e.g. HRNR, DSC1, S100A8, MMP1). We conclude that TFAP2A is an essential transcription factor for human keratinocyte differentiation and that AHR regulates epidermal differentiation through transient activation of a specific panel of key transcription factors, as herein illustrated by TFAP2A. Identification of this AHR-TFAP2A axis provides further insights into the complex regulatory network driving epidermal differentiation in response to environmental cues and prompts new avenues for the treatment of barrier dysfunction related diseases by targeting AHR’s partners in crime.