Depletion of Cholesteryl Esters Causes Meibomian Gland Dysfunction-Like Symptoms in a Soat1-Null Mouse Model

Abstract

Previous studies on ablation of several key genes of meibogenesis related to fatty acid elongation, omega oxidation, and esterification into wax esters have demonstrated that inactivation of any of them led to predicted changes in the meibum lipid profiles and caused severe abnormalities in the ocular surface and Meibomian gland (MG) physiology and morphology. In this study, we evaluated the effects of Soat1 ablation that were expected to cause depletion of the second largest class of Meibomian lipids (ML)—cholesteryl esters (CE)—in a mouse model. ML of the Soat1-null mice were examined using liquid chromatography high-resolution mass spectrometry and compared with those of Soat1+/− and wild-type mice. Complete suppression of CE biosynthesis and simultaneous accumulation of free cholesterol (Chl) were observed in Soat1-null mice, while Soat1+/− mutants had normal Chl and CE profiles. The total arrest of the CE biosynthesis in response to Soat1 ablation transformed Chl into the dominant lipid in meibum accounting for at least 30% of all ML. The Soat1-null mice had clear manifestations of dry eye and MG dysfunction. Enrichment of meibum with Chl and depletion of CE caused plugging of MG orifices, increased meibum rigidity and melting temperature, and led to a massive accumulation of lipid deposits around the eyes of Soat1-null mice. These findings illustrate the role of Soat1/SOAT1 in the lipid homeostasis and pathophysiology of MG.

Hyperglycemia Induces Meibomian Gland Dysfunction

“…2 D). As the important participants involved in the process of cholesterol production, 21 sterol O-acyltransferase-1(SOAT1) expression significantly decreased in the 2-month and 4-month DM groups ( Fig. 2 E), other lipid synthesis related genes 3β-Hydroxysteroid-Δ24 reductase (DHCR24; Fig.…”

Dynamic Changes in the Gene Expression Patterns and Lipid Profiles in the Developing and Maturing Meibomian Glands

“…Other house-keeping genes (e.g., those that encode ribosomal proteins of the S family, Emc7 , Hprt , and others) were evaluated as internal references as well, but did not provide any advantages over Gapdh. Due to the very distinctive chemical nature of meibum, whose biosynthesis requires a unique combination of lipid-metabolism related enzymes that is not duplicated in other tissues [ 4 ], the functional enrichment analysis of the MG transcriptome using available tools proved to have limited informativity, while the choice of meibogenesis-related genes was based on recent advances in studying meibogenesis [ 4 , 6 ] using various animal models, such as Elovl1 −/−- [ 7 ], Elovl3 −/− [ 9 , 12 ], Elovl4 +/− [ 8 ], Elovl 6 −/−- [ 17 ], Awat1 −/− and Awat2 −/− [ 13 , 14 , 24 , 25 ], Far1 −/− and Far2 −/− [ 15 , 26 ], Soat1 −/− [ 27 ], Cyp4f39 −/− [ 16 ] gene knockout mice, the human MG epithelial cell line (evaluated for the expression of Hmgcr [ 28 ]), and Elovl7 -transfected cell lines [ 11 ].…”

“…Mice were euthanized with a ketamine/xylazine cocktail and the mouse TPs were immediately excised from the eyelids using a Zeiss Stemi 508 dissecting microscope equipped with a Zeiss CL 6000 LED light source (both from Zeiss, White Plains, NY, USA). Four TPs from each mouse were collected and dissected free from other ocular tissues as described recently on several occasions [ 2 , 9 , 12 , 27 ]. The specimens were kept chilled during the procedure using ice.…”

Candidate Molecular Compounds as Potential Indicators for Meibomian Gland Dysfunction

“…There is considerable evidence of cholesterol ester-depleted meibum losing its integrity in the formation of thin and continuous lipid devoid of high fragmentation in mice ( 105 ). These observed manifestations can be interpreted as evidence of its lost ability to form the tear film lipid layer and as a result not able to mitigate corneal nociceptors’ firing ( 105 ). However, the mechanism of these observed changes in mice needs further clarification requiring additional work in future experiments.…”

“…This change in meibum caused by sterol O-acyltransferase 1-ablated mice mirrored many exact characteristics of human MGD. Ablating sterol O-acyltransferase 1 resulted in almost all loss of cholesterol esters in meibum and gradual mass gathering of their precursor—free cholesterol—in large quantities, virtually replacing very, extremely, and ultra-long cholesterol esters and becoming the main components of abnormal meibum ( 105 ).…”