Butovich Igor A
Department of Ophthalmology and the Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9057, United States.
Exp Eye Res. 2017 Oct;163:2-16. doi: 10.1016/j.exer.2017.06.020. Epub 2017 Jun 29.
Meibum is a lipid-rich secretion that is produced by fully differentiated meibocytes in the holocrine Meibomian glands (MG) of humans and most mammals. The secretion is a part of a defense mechanism that protects the ocular surface from hazardous environmental factors, and from desiccation. Meibomian lipids that have been identified in meibum are very diverse and unique in nature. The lipid composition of meibum is different from virtually any other lipid pool found in the human body. In fact, meibum is quite different from sebum, which is the closest secretion that is produced by anatomically, physiologically, and biochemically related sebaceous glands. However, meibum of mice have been shown to closely resemble that of humans, implying similar biosynthetic mechanisms in MG of both species. By analyzing available genomic, immunohistochemical, and lipidomic data, we have envisioned a unifying network of enzymatic reactions that are responsible for biosynthesis of meibum, which we call meibogenesis. Our current theory is based on an assumption that most of the biosynthetic reactions of meibogenesis are catalyzed by known enzymes. However, the main features that make meibum unique - the ratio of identified classes of lipids, the extreme length of its components, extensive ω-hydroxylation of fatty acids and alcohols, iso- and anteiso-branching of meibomian lipids (e.g. waxes), and the presence of rather unique complex lipids with several ester bonds - make it possible that either the activity of known enzymes is altered in MG, or some unknown enzymes contribute to the processes of meibogenesis, or both. Studies are in progress to elucidate meibogenesis on molecular level.
睑脂是一种富含脂质的分泌物，由人类和大多数哺乳动物全浆分泌型睑板腺（MG）中完全分化的睑板细胞产生。这种分泌物是一种防御机制的一部分，可保护眼表免受有害环境因素和干燥的影响。在睑脂中鉴定出的睑板脂质在性质上非常多样且独特。睑脂的脂质组成与人体中发现的几乎任何其他脂质库都不同。事实上，睑脂与皮脂有很大不同，皮脂是由解剖学、生理学和生物化学相关的皮脂腺产生的最接近的分泌物。然而，已证明小鼠的睑脂与人类的睑脂非常相似，这意味着这两个物种的睑板腺中存在相似的生物合成机制。通过分析现有的基因组、免疫组织化学和脂质组学数据，我们设想了一个负责睑脂生物合成的统一酶促反应网络，我们称之为睑脂生成。我们目前的理论基于这样一个假设，即睑脂生成的大多数生物合成反应是由已知酶催化的。然而，使睑脂独特的主要特征——已鉴定的脂质类别比例、其成分的极长长度、脂肪酸和醇的广泛ω-羟基化、睑板脂质（如蜡）的异支链和前异支链，以及存在具有多个酯键的相当独特的复合脂质——使得已知酶的活性在睑板腺中可能发生改变，或者一些未知酶参与睑脂生成过程，或者两者皆有。目前正在进行研究以在分子水平上阐明睑脂生成。
