Functional Characterization of the Epidermal Cholinergic System In Vitro

The aim of this study was to analyze the influence of cholinergic and anticholinergic drugs on epidermal physiology using organotypic cocultures (OTCs). Blocking of all acetylcholine receptors (AChRs) by combined treatment with mecamylamine and atropine or treatment with strychnine (blocking alpha9nAChR) for 7-14 days resulted in a complete inhibition of epidermal differentiation and proliferation. Blockage of nicotinic (n)AChR with mecamylamine led to a less pronounced delay in epidermal differentiation and proliferation than blockage of muscarinic (m)AChR with atropine, evidenced by reduced epithelial thickness and expression of terminal differentiation markers like cytokeratin 2e or filaggrin. In OTCs treated with atropine, mecamylamine, or strychnine, we could demonstrate intracellular lipid accumulation in the lower epidermal layers, indicating a severely disturbed epidermal barrier. In addition, we observed prominent acantholysis in the basal and lower suprabasal layers in mecamylamine-, atropine-, and strychnine-treated cultures, accompanied by a decreased expression of cell adhesion proteins. This globally reduced cell adhesion led to cell death via intrinsic activation of apoptosis. In contrast, stimulation of nAChR and mAChR with cholinergic drugs resulted in a significantly thickened epithelium, accompanied by an improved epithelial maturation. In summary, we show that epidermal AChR are crucially involved in the regulation of epidermal homeostasis.