Lipid Composition and Thermotropic Properties of Meibum of Animal Models and Humans with Meibomian Gland Dysfunction

Meibum-a lipid-rich secretion produced by holocrine Meibomian glands (MG)-plays a central role in maintaining ocular surface homeostasis in humans. Previously, changes in MG lipidomes induced by inactivation of critical genes of meibogenesis, such as Elovl3, Soat1, Awat2, Sdr16c5/Sdr16c6, and others were shown to cause MG dysfunction (MGD) and dry eye in experimental animals. Here, we describe the impact of the changes in the lipid composition of meibum on its protective properties, specifically physiologically relevant thermotropic characteristics, using various mutant and wild-type animal models, and comparing them with healthy human subjects and patients with MGD. Meibum samples were analyzed using liquid chromatography/mass spectrometry (LC/MS) and differential scanning microcalorimetry (DSC). We found that any change in the balance between major lipid classes in meibum-wax esters, cholesteryl esters, triacylglycerols, and free cholesterol-cause detrimental changes in its thermotropic properties, loss of cohesiveness, and abnormal expressibility from MG, resulting in MGD-like phenotypes of the eyes and adnexa. We conclude that tested knockout mice can be valuable models for modeling and studying MGD. A combination of LC/MS and DSC can be a powerful diagnostic tool and may help to diagnose MGD and other pathologies, as well as determine their molecular mechanisms.