Mucin and epithelial surface glycoprotein layer (MUC layer)

The mucin and epithelial surface glycoprotein layer is a specialized biological barrier primarily composed of high-molecular-weight glycoproteins (mucins) and the glycocalyx, which coats the apical surfaces of epithelial cells [1]. This layer is essential for maintaining the physiological integrity of mucosal surfaces, particularly in the eye, respiratory tract, and gastrointestinal system, by providing lubrication, preventing desiccation, and acting as a physical shield against pathogens and mechanical friction [2]. In the context of the ocular surface, this layer converts the hydrophobic corneal epithelium into a hydrophilic surface, allowing for the stable spreading of the tear film; its disruption is a hallmark of dry eye disease [3]. Pharmacologically, this layer is targeted through various modalities: mucolytic agents like N-acetylcysteine reduce the viscosity of pathological mucus in respiratory diseases [4], while secretagogues such as rebamipide and diquafosol are used to enhance mucin production and restore barrier function in ophthalmology [5]. Additionally, specific membrane-bound mucins like MUC1 are significant targets in oncology due to their role in cell signaling and their frequent overexpression in adenocarcinomas [2].

Other names

Mucus layerGlycocalyxMucin-type glycoprotein layerPre-ocular tear film mucin layerMucus-bicarbonate barrier

Mucolytics reduce viscosity by cleaving disulfide bonds in mucin polymers [4]; secretagogues stimulate mucin production from goblet cells via P2Y2 receptor activation or other intracellular pathways [3,5]; monoclonal antibodies target specific mucin epitopes to inhibit oncogenic signaling or induce antibody-dependent cellular cytotoxicity [2].