AHR-TFAP2A regulates epidermal differentiation in response to environmental cues [RNA-seq]
The Aryl Hydrocarbon Receptor (AHR) is an environmental sensor and an indispensable regulator of epithelial homeostasis. To investigate AHR-mediated gene regulation, we performed a comprehensive transcriptomic and epigenomic analysis using human primary epidermal keratinocytes. Our results showed that AHR activation led to the induction of canonical transcription factors involved in epidermal differentiation as an early response, i.e. Transcription Factor AP-2a (TFAP2A), while epidermal differentiation-related genes, such as filaggrin and keratins, were activated as late responsive genes. The identified AHR-TFAP2A axis and its role in keratinocyte terminal differentiation was confirmed through AHR and TFAP2A knockout using CRISPR/Cas9. Our findings demonstrate that AHR regulates epidermal differentiation through the transient activation of specific transcription factors, such as TFAP2A, in response to environmental cues. The herein identified AHR-TFAP2A axis provides a promising target for the treatment of diseases related to skin barrier dysfunction. Overall design: To characterize the gene expression pattern upon AHR activation in keratinocytes, we performed RNA-seq on either TCDD or CT treated keratinocytes. In addition, to identify AHR-responsive enhancers, we performed ChIP-seq of AHR and H3K27ac that marks active enhancers in the genome of keratinocytes after TCDD treatment for 30 and 90 minutes. With integrated analyses of  RNA-seq, AHR, and H3K27ac ChIP-seq data, we identified that TFAP2A is a direct AHR target and is an important transcription factor involved in epidermal differentiation. To further test our hypothesis that AHR controls epidermal differentiation via TFAP2A expression, we knocked down TFAP2A in monolayer primary keratinocyte cultures and performed RNA-seq analysis.