A positive feedback loop between alpha1-adrenoceptors and inflammatory cytokines in keratinocytes

Abstract

A positive feedback loop between inflammatory cytokines and alpha1-adrenoceptors (α1-AR) (a target of the sympathetic nervous system neurotransmitter norepinephrine) influences inflammatory responses in immune cells. This cross-talk between the sympathetic nervous system and immune system may play a role in promoting chronic inflammation. Emerging evidence shows that α1-AR interact with inflammatory cytokines in keratinocytes, and this epidermal adrenergic signalling may contribute to skin inflammatory responses following injury, disease or stress. In this study, utilizing an in vitro approach, we hypothesized that α1-AR interact in a positive feedback loop with inflammatory mediators in keratinocytes. The pro-inflammatory cytokine tumor necrosis factor α (TNFα) was used to induce an inflammatory state in cultured keratinocytes. TNFα increased interleukin (IL)-1β, IL-6, IL-8 and nerve growth factor (NGF) production and gene expression levels of α1-AR subtype B (α1B-AR). Additional stimulation of α1-AR further increased IL-6 levels, while maintaining high levels of IL-8 and decreasing levels of IL-1β and NGF. Our results suggest that reciprocal influences between α1-ARs and inflammatory cytokines may play a role in normal inflammatory responses. However, if unchecked, this cycle could contribute to pathology (e.g. chronic inflammatory diseases, chronic pain conditions, and stress-induced cancer progression).