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Anne McMahon, Seher Yuksel, Nita Bhat, Hai Pham, Amber Wilkerson, Igor A Butovich; Inactivation of Awat2 in mice causes loss of wax ester lipids from meibum.. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2632.
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© ARVO (1962-2015); The Authors (2016-present)
Meibomian glands (MG), embedded in the eyelid tarsal plates (TP), secrete an oily mix called meibum on to the eyelid lid margin from where it spreads across the surface of the tear film. The most abundant class of lipids in meibum are wax esters (WE), accounting for 30-48% of lipid in humans. Towards understanding the functional roles of WE in ocular physiology we studied mice carrying an inactivating mutation in Awat2, coding for one of two rate limiting AWAT enzymes that catalyzes the formation of the ester bond between the fatty alcohols and fatty acyl-CoAs in WE.
The Awat2 gene is present on the X chromosome so animals studied were hemizygous male (Hemi) and homozygous female (Hom) from a mutant line carrying an inactivating mutation in the Awat2 gene. Study animals were older than 2 months and were age, and sex matched to wild types (WT) from the same colony. Evaluation of ocular features was performed with a slit lamp. Total TP lipids were characterized by liquid chromatography-mass spectrometric analysis (LC-MS). Eyelids were both evaluated following H&E staining and used to study the melting temperature (Tm) of lipids within the MG ducts by hot stage cross-polarized light microscopy (HSPM).
Awat2 mutant mice of all genotypes were viable and fertile. In mixed genotype litters, Hemi and Hom mice were, pre wean, smaller than littermates and displayed a dry skin phenotype. Adults of all genotypes were indistinguishable. Slit Lamp exams of Hemi and Hom eyes revealed accumulation of solid lipid material on the eyelid margins and the presence of particulate material on the corneal surface. LC-MS analysis of the eyelid deposits identified the MG as the source. In the TP of mutants, MG central duct lipid deposits appeared as a solid column of material protruding through the lid margin ducts. HSPM of this material identified a ~10oC increase in the Tm. H&E staining revealed a widening of the central ducts in mutant glands. LC-MS profiling revealed very little WE lipids in the meibum of mutant mice.
In the absence of a functional Awat2 gene MG in mice synthesize meibum lacking significant levels of WE. Loss of WE altered the Tm of meibum such that it remained a solid when secreted onto the eyelid margin. Ongoing studies will further define the ocular long-term consequences of these changes.
This is a 2020 ARVO Annual Meeting abstract.
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