Choline acetyltransferase as a marker for Merkel cells in mucosal and skin tissues

To investigate the expression of choline acetyltransferase (ChAT), the enzyme responsible for acetylcholine (ACh) synthesis, in Merkel cells in hairy and glabrous skin, including whiskers, palms, and oral mucosa, and to evaluate whether ChAT is a general molecular marker for Merkel cells that could indicate a potential cholinergic role in mechanosensory signaling.

Immunofluorescence staining was performed on skin and oral epithelial tissues of ChAT-tau-enhanced green fluorescent protein (ChAT-eGFP) transgenic mice. Co-expression of ChAT-eGFP and the Merkel cell marker, keratin 8 (KRT8), was analyzed to identify ChAT⁺ Merkel cells. Their spatial organization and association with nerve endings were examined, and age-related changes in the Merkel cell count in the palate were quantified.

Merkel cells consistently co-expressed ChAT-eGFP and KRT8 in skin and mucosal tissues, and they were organized into characteristic clusters, closely associated with nerve fibers. There was also ChAT expression in taste-related structures and cholinergic epithelial cells. In aged mice, Merkel cell count in the palate was significantly reduced, particularly in anterior rugae.

This study identified ChAT as a novel and general marker for Merkel cells in skin and oral tissues, revealing a previously unrecognized cholinergic component of Merkel cell signaling. These findings suggest a potential role of ACh in mechanotransduction and tactile sensation. By establishing ChAT as a Merkel cell marker, this study provides new insights into somatosensory biology and provides a molecular framework for exploring cholinergic mechanisms in tactile perception. These findings may inform therapeutic strategies for sensory disorders of skin and oral mucosa.