Elongases of very long chain fatty acids-3 and 4 (ELOVL3 and ELOVL4) are essential for biosynthesis of meibum in mice

Abstract

Purpose : We previously found that the Meibomian glands (MG) in tarsal plates (TP) of humans and mice express similar lipid metabolism-related genes. Elovl3/ELOVL3 and Elovl4/ELOVL4 are highly expressed in MGs and are responsible for the elongation of saturated and monounsaturated very long chain fatty acids (VLC FA). The purpose of this study was to elucidate the interactions of Elovl3 and Elovl4 within the MG and their impact on lipid composition and ocular phenotype.

Methods : Two to four months old male and female Elovl3 knockout/Elovl4 heterozygous (E3k/E4h) and matching wild-type (WT) mice were evaluated using a slit lamp, and the phenol red thread test. Lipid profiling of TP was conducted by means of liquid chromatography and mass spectrometry (LC/MS). Melting temperature of meibum (T_m) was measured by hot stage cross-polarized light microscopy. Structural changes in TP were examined by H&E staining. The blink rates and the geometry of the eye opening were measured.

Results : E3k/E4h mice had abnormal eye phenotypes such as delayed eye opening, gooey eyes, crusty eyelids, ulceration of the eyelid, eyelid edema, and slit eye appearance. The T_m of meibum in E3k/E4h was reduced by ~10°C compared to WT mice. Slit lamp evaluation revealed cornea neovascularization. Tear production increased in E3k/E4h mice (p>0.001), and so did the eccentricity of the eye openings (p>0.001). LC/MS analysis of E3k/E4h meibum revealed an even larger accumulation of lipids with C₁₆-C₁₉ FA than in E3k-only mice. Moreover, there was a strong reduction in longer chain CE with >C₂₈ FA, which clearly accentuates the role of ELOVL4 in making VLC FA in MG.

Conclusions : Elovl3 and Elovl4 are vital for producing normal meibomian lipids (ML) and the preservation of the ocular surface. Simultaneous inactivation of Elovl3 and Elovl4 led to an even more dramatic change in the chemical composition and properties of meibum, and abnormal ocular phenotypes, when compared to E3k or E4h alone. The partial loss of Elovl4 had an additive effect, altering the FA balance even more. Changes in the biochemical makeup of meibum may be responsible for increased fluidity of meibum in E3k/E4h mice. Many of the abnormal ocular features noted in the E3k/E4h mice are similar to those found in human subjects with various forms of dry eye, MG dysfunction and blepharitis.

This is a 2020 ARVO Annual Meeting abstract.