Role of Structure and Glycosylation of Adsorbed Protein Films in Biolubrication

Water forms the basis of lubrication in the human body, but is unable to provide sufficient lubrication without additives. The importance of biolubrication becomes evident upon aging and disease, particularly under conditions that affect secretion or composition of body fluids. Insufficient biolubrication, may impede proper speech, mastication and swallowing, underlie excessive friction and wear of articulating cartilage surfaces in hips and knees, cause vaginal dryness, and result in dry, irritated eyes. Currently, our understanding of biolubrication is insufficient to design effective therapeutics to restore biolubrication. Aim of this study was to establish the role of structure and glycosylation of adsorbed protein films in biolubrication, taking the oral cavity as a model and making use of its dynamics with daily perturbations due to different glandular secretions, speech, drinking and eating, and tooth brushing. Using different surface analytical techniques (a quartz crystal microbalance with dissipation monitoring, colloidal probe atomic force microscopy, contact angle measurements and X-ray photo-electron spectroscopy), we demonstrated that adsorbed salivary conditioning films in vitro are more lubricious when their hydrophilicity and degree of glycosylation increase, meanwhile decreasing their structural softness. High-molecular-weight, glycosylated proteins adsorbing in loops and trains, are described as necessary scaffolds impeding removal of water during loading of articulating surfaces. Comparing in vitro and in vivo water contact angles measured intra-orally, these findings were extrapolated to the in vivo situation. Accordingly, lubricating properties of teeth, as perceived in 20 volunteers comprising of equal numbers of male and female subjects, could be related with structural softness and glycosylation of adsorbed protein films on tooth surfaces. Summarizing, biolubrication is due to a combination of structure and glycosylation of adsorbed protein films, providing an important clue to design effective therapeutics to restore biolubrication in patients with insufficient biolubrication.水是人体润滑功能的核心物质基础，但缺乏添加剂辅助时，无法提供充足的润滑效果。生物润滑（biolubrication）的重要性在衰老与疾病状态下尤为凸显，尤其是在影响体液分泌或组分的病理生理条件中。生物润滑不足可阻碍正常言语、咀嚼与吞咽功能，引发髋、膝关节软骨关节面的过度摩擦与磨损，导致阴道干涩，还会引发眼部干燥与刺激症状。目前，学界对生物润滑的认知仍不足以设计出可有效恢复润滑功能的治疗方案。本研究旨在明确吸附态蛋白膜的结构与糖基化（glycosylation）修饰在生物润滑中的作用，以口腔作为模型体系，并利用其因不同腺体分泌、言语、进食饮水及刷牙等日常活动所产生的动态扰动特征。本研究采用多种表面分析技术，包括耗散型石英晶体微天平（quartz crystal microbalance with dissipation monitoring）、胶体探针原子力显微镜（colloidal probe atomic force microscopy）、接触角测量法及X射线光电子能谱（X-ray photo-electron spectroscopy），证明体外构建的唾液吸附调理膜（salivary conditioning films）的亲水性与糖基化程度越高，其润滑性能越佳，同时结构柔软性会随之降低。以环式与链式构型吸附的高分子量糖基化蛋白，被认为是维持关节加载过程中水分不易流失的必要骨架结构。通过对比体外与口腔内原位测得的水接触角，本研究将体外实验结果外推至体内生理环境。据此，在20名性别比例均等的志愿者中所感知的牙齿润滑特性，可与牙面吸附蛋白膜的结构柔软性及糖基化程度建立关联。综上，生物润滑功能由吸附态蛋白膜的结构与糖基化修饰共同决定，这一结论为设计针对生物润滑不足患者的有效治疗方案提供了重要思路。