Functional significance of non-neuronal acetylcholine in skin epithelia

In recent years, the physiological role of non-neuronal acetylcholine (ACh) and its receptors (AChR) in epidermal physiology has been under intense investigation. However, little is known about the role of the non-neuronal cholinergic system in inflammatory skin diseases. We chose the clinically nicotine-dependent skin disease hidradenitis suppurativa (HS) as model to study the influence of long term nicotine ingestion on epidermal morphology and AChR expression. HS is a chronic inflammatory, disabling disease of unknown pathogenesis emerging from the pilosebaceous unit of the intertriginous areas. In order to correlate our findings to specific nicotine effects, we used the organotypical coculture system (OTC) and raised artificial epidermis in the presence of nicotine. After 12 days in culture control OTC showed a mature epithelium, while nicotine treated OTCs were significantly thicker. Using immunofluorescence analysis, nicotine treated OTCs produced significantly stronger immunoreactivity (IR) for the α3, M₃ and M₅ AChR antisera than control. In contrast, the α7 nAChR antiserum showed a slightly reduced IR in the granular layer and the α9 nAChR IR retracted to the lower suprabasal layers. In HS epidermis we found the strongest IR for all AChR around the follicular infundibulum while in the sinus epithelia it was only weak. In contrast to the nicotine treated OTC, the α7 nAChR IR in the hyperplastic HS epidermis was clearly extended to all living layers. Altogether we provide first hints for a causative role of the non-neuronal cholinergic system in the pathogenesis of HS by promoting infundibular epithelial hyperplasia and thus follicular plugging.