Transmembrane mucin 1 is a polarity protein in the organization of apical surface microplicae in oral epithelium

This study aims to provide a new insight into the oral mucosal defense, and to investigate the oral microbial attachment to the oral mucosa. A total of 68 oral mucosal samples were prepared for light microscopy, immunohistochemistry (IHC), and both scanning and transmission electron microscopy. Tissue samples were IHC stained for transmembrane mucin 1 (tMUC1), which was also examined with immuno-scanning electron microscopy (iSEM). The scanning electron microscopy (SEM) images were procured to analyze the attachment of microbes on different parts of the oral mucosa. The IHC for tMUC1 presented its localization in the apical portion of the superficial surface of non-keratinized epithelial cells, whereas no such expression was observed in keratinized epithelium. In SEM images, the microplicae (MPL) structure organized in non-keratinized epithelial cells, and iSEM showed tMUC1 localized at the tips of MPLs. Microbial attachment was low in the areas showing tMUC1-MPL-structures, whereas more abundant in the areas that lack tMUC1 attachment with MPL. The superficial MPL and the attachment of tMUC1 form a complex that functionally prevents the attachment of microbes. The iSEM confirms that tMUC1 is a polarity protein, which generates the apical MPL structure in oral epithelial surface cells and together provides protection against microbial colonization and invasion.