Elongase of Very Long Chain Fatty Acids-3 (Elovl3) Is Critical for Meibum Biosynthesis in Mice

Abstract

Purpose : We previously found that tarsal plates (TP) of humans and mice express similar lipid metabolizing genes. In order to better understand the biosynthesis of meibum (meibogenesis), we decided to alter expression levels of selected lipid metabolism-related genes to determine their effects on the lipid composition of meibum and ocular surface physiology. One of those genes –ELOVL3/Elovl3– is highly expressed in the Meibomian glands of humans and mice. This gene catalyzes the elongation of C₁₆, C₁₈, and C₂₀ saturated and monounsaturated very long-chain fatty acids (VLCFAs). The purpose of this study was to determine the role of Elovl3 in meibogenesis and the impact of its inactivation on the physiology of the ocular surface.

Methods : Two to four month old male and female Elovl3 knockout (E3-KO) and matching WT mice were evaluated by slit lamp, and phenol red thread test. Lipid profiling of TP were conducted using chromatography and mass spectrometry. Structural changes in TP of E3-KO mice were examined by H& E staining. Mice in relaxed state were recorded to determine blink rates and to measure eye geometry.

Results : E3-KO mice had abnormal eye phenotypes such as delayed eye opening, weeping eyes, crusty eyelids, eyelid edema, highly vascularized TP, and slit eye appearance. It was noticed that meibum of E3-KO had a much higher fluidity than that of WT mice. Slit lamp evaluation revealed cornea neovascularization in 40% of E3-KO mice. Tear production increased in E3-KO mice (p<0.001) as well as the eccentricity of the eye openings (p<0.001). Mass spectrometric analysis revealed a large increase in shorter chain cholesteryl esters (CE, C₁₆-C₁₉), and a decrease in VLC-CE (C₂₀-C₂₇), with almost complete ablation of the C₂₃ product.

Conclusions : Elovl3 is important for producing normal meibomian lipids and the maintenance of the ocular surface. Inactivating Elovl3 leads to dramatic changes in the chemical composition and properties of meibum, and abnormal ocular phenotype. The altered ratio of VLCFA to shorter chain fatty acids in meibomian lipids, leading to preferential accumulation of shorter chain lipids with lower melting points, may be responsible for increased fluidity of meibum and lipid accumulation around the eye. Many of the abnormal ocular features noted in the E3-KO mice are similar to those found in human subjects with various forms of dry eye, Meibomian gland dysfunction and blepharitis.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.