title: Comparative study of biomarker expression and composition of secretions from human and murine meibomian glands, free sebaceous glands, and hair-associated sebaceous glands
title: Vergleichende Untersuchung der Expression von Biomarkern und der Zusammensetzung der Sekrete humaner und muriner Meibomdrüsen, freier Talgdrüsen und haarassoziierter Talgdrüsen
Creators: name: Liu, Yuqiuhe
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 0
Subjects: subject: DDC Classification::6 Technik, Medizin, angewandte Wissenschaften :: 61 Medizin und Gesundheit :: 610 Medizin und Gesundheit

description: Dry eye disease (DED) is one of the most common ocular surface diseases, affecting millions of individuals over the world. Patients with DED often have symptoms such as dryness, irritation, and loss of vision, leading to a reduced quality of life and even blindness. DED has received increasing attention in recent years, and its pathogenesis has been studied and validated. Hot compress with massage, artificial tears, and anti-inflammatory eye drops are currently the conventional treatment, and since multiple factors may all contribute to DED, there is no definitive causal treatment. Therefore, it is crucial to identify new treatment strategies. Meibomian gland dysfunction (MGD) is the most common reason for DED. The lipids produced by the meibomian gland (MG) secretion pass through the central duct and then form the outermost lipid layer on the ocular surface, thereby preventing the evaporation of tears. Any qualitative/quantitative changes that may result in terminal duct obstruction and/or glandular secretion can lead to MGD. The sebaceous gland (SG) can be divided into two types, one is not related to hair which is called “free” SG, and the other one is called hair-associated SG. The structure of “free” SGs is similar to MGs, they consist of a single acinus or a bunch of acini that connect to the central duct by short ductules and a terminal end of the central duct that opens directly onto the skin’s surface. MG is a kind of free SG. Both MG and SG follow a holocrine secretory mechanism: basal cells located at the periphery of the acini differentiate over mature cells to overmature cells that eventually die by apoptosis and become an oily secretion (meibum or sebum) that is transported through the lumen of the ducts to the ocular surface or skin. No comprehensive comparative study has been performed between MGs, free SGs, and hair- associated SGs in humans and mice. Therefore, this project will be the first to gain deeper insights into the expression of various biomarkers, including cytokeratins (CK), stem cell markers, and cell-cell contact markers, as well as the secretion composition of MGs, free SGs and hair-associated SGs in humans and mice. Moreover, the composition of human sebum and meibum are analyzed and compared. A detailed comparison of these three types of glands is expected to provide some new clues for developing future treatment strategies for DED. The following tissues were examined for the expression of CK1, 8, 10, 14; stem cell markers keratin (KRT) 15, N-cadherin; cell-cell contact markers desmoglein 1 (Dsg1), desmocollin 3 (Dsc3), plakoglobin (Pg), desmoplakin (Dp), E-cadherin and tight junction Claudin 5 by immunohistochemical methods: human MGs from the eyelids, free SGs from the nasal wings, the lips, the external auditory canals, and hair-associated SGs from the scalps; mouse MGs from the eyelids, free SGs from the lips, the external auditory canals, and hair-associated SGs from the skin. Oil red O (ORO) staining was used to detect the lipid distribution on human MGs, free SGs, and hair-associated SGs. Consequently, analyzing the composition of secretions from healthy human volunteers’ MGs, free SGs, and hair-associated SGs by liquid chromatography (LC) - mass spectrometry (MS) and processing the data by Progenesis QI software. A partial least squares discriminant analysis (PLS-DA) model was used to compare the composition of secretion from human MGs, free SGs, and hair-associated SGs by EZinfo software. In human tissue, CK1 was expressed in hair-associated SGs differently than in MG and other free SGs. CK8, CK10, and CK14 expressions in MG were different from hair-associated SGs and other free SGs. KRT15 was expressed differently in hair-associated SGs, while N-cadherin expressed the same in three kinds of glands. Cell-cell contact markers, like Dsg1, Dp, Dsc3, Pg, and E-cadherin, were expressed identically in MG, free SG, and hair-associated SG. In mouse tissue, since the presence of hairs was also observed in hematoxylin and eosin staining sections of lip and external auditory canal tissues, these glands cannot be considered as free SGs unrelated to hairs (See chapter 3.1.2 for details). They will be considered hair-associated SGs in this section. Expression of CK8, CK10, and CK14 was different in MGs than in hair- associated SG. KRT15 and N-cadherin expressed differently between MGs and hair-associated SGs. Dsg1 and E-cadherin were expressed differently between MGs and hair-associated SGs. Lipids were observed to be more distributed in human MG by ORO staining with larger lipid droplets, while lipids were less distributed in free SGs and hair-associated SGs. It was found that the score distribution of meibum was far away from the scores of sebum from nasal wings, external auditory canals, and scalps in score plot. The score distribution of sebum from nasal wings and scalps was quite close, while the score of the external auditory canals was far away from them. This study concludes that the MGs differs from other free and hair-associated SGs in terms of histology and lipids. MGs can be considered a highly specialized type of SGs. In human tissues, cytokeratins such as CK10 and CK14 were expressed differently in MG than in other SG; stem cell markers, KRT15 was only expressed in ductules of MG. Cell-cell contact markers were expressed equally in MGs, free SGs, and hair-associated SGs. The composition of meibum from human MGs was different from sebum from human free SGs and hair-associated SGs. Biomarker expression was also significantly different between the human body donor and the mouse. This implies that there are still differences in histological features between humans and mice, which means that caution must be considered when using mice as a disease model for MGD for strategies for human DED treatment.