Asthma and inflammation transcriptionally up-regulate the aryl hydrocarbon receptor in airway smooth muscle via p38/JNK-AP1 signalling.

Background And Purpose: The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that maintains cellular homeostasis. AhR in airway fibroblasts, epithelial and immune cells inhibit inflammatory responses. Nevertheless, its expression and role in airway smooth muscle (ASM), an airway structural cell indispensable in asthma pathophysiology, are obscure. This study uncovers AhR expression, underlying mechanisms, and activity in ASM during inflammation and asthma.

Experimental Approach: Cultured primary human nonasthmatic and asthmatic ASM cells were treated with TNFα/IL-13, with/without pharmacological inhibitors targeting PI3K, p38MAPK, JNK, NFkB, and AP1. AhR expression was analysed using RNA-sequencing, confocal microscopy, qPCR, and immunoblotting. AP1 specific role was confirmed using c-JUN (AP1) siRNA and ChIP-qPCR. AhR activity was determined by Nano luciferase in AhR agonist-treated cells.

Key Results: We found ubiquitous expression of AhR in ASM with up-regulation in asthmatic ASM. TNFα increased AhR expression, whereas IL-13 did not. Furthermore, p38 and JNK inhibition significantly reduced AhR expression with TNFα exposure, whereas PI3K inhibition had no effect. AP1 inhibition and c-JUN knockdown significantly down-regulated AhR expression, whereas NFkB inhibition showed no effect. TNFα promoted c-JUN binding to AhR promoter and increased AhR mRNA expression. Additionally, AhR agonists significantly increased the xenobiotic response element (XRE) activity, CYP1B1, and AhR nuclear expression. TNFα exposure reduced XRE activity and AhR nuclear expression.

Conclusion And Implications: Our findings suggest inflammation and asthma transcriptionally up-regulates AhR through the p38/JNK-AP1 pathway in ASM, identifying a potential therapeutic target for modulating AhR and its downstream effects in asthma.