Sterol O-acyltransferase 1 (Soat1) is critical for cholesteryl ester production in mouse Meibomian glands

Abstract

Purpose : Cholesteryl esters (CE) are the second most abundant class of lipids produced by the Meibomian glands (MG). The Soat1 gene is encoding a SOAT1 enzyme that is responsible for the formation of cholesteryl esters (CE) from cholesterol (Chl) and fatty acids, and is highly expressed in MG of humans and mice. The purpose of this study was to determine the impact of Soat1 ablation on meibum composition and the homeostasis of the ocular surface and adnexa in mice.

Methods : The ocular surface of 2- to 4-month old male and female knockout (Soat1^-/-) and wild-type (WT) mice was assessed via a slit lamp. Their eye geometry was evaluated. Phenol red thread test was used to assess tear production. Tarsal plate (TP) anatomy was evaluated by hematoxylin and eosin staining. Lipid profiling was conducted by liquid chromatography and mass spectrometry (LC/MS). Melting temperature of meibum (T_m) was measured by hot stage cross-polarized light microscopy (HSPLM).

Results : Soat1^-/- had noticeably smaller, slit-eye openings (p= <0.001) when compared with WT mice. Slit lamp examination of Soat1^-/- mice revealed thick meibum accumulations and meibum protrusions from the MG orifices. Tear production was increased in Soat1^-/- mice (p=0.002). Excised TP of Soat1^-/- mice had visible MG, central ducts and connecting ductules, but lacked discernible acini. The histology displayed abnormal acini and dilated central ducts. Lipid profiling of Soat1^-/- meibum revealed an upsurge of free Chl (reaching 30% of all MG lipids) and an almost complete loss of CE. HSPLM experiments revealed that Soat1^-/- meibum had highly elevated T_m : only half of lipids melted at 50°C, requiring temperatures in excess of 100°C to be completely melted. WT meibum melts 50% at 34°C and 100% at 50°C.

Conclusions : Soat1 is essential for the conversion of free Chl into CE in the MG. The increased Chl and lack of CE had detrimental effects on the physical and biochemical properties of meibum leading to an abnormal ocular phenotype. The changes in meibum and the ocular phenotype resemble characteristic signs of MG dysfunction in humans and demonstrate the importance of Soat1 in MG lipid homeostasis.

This is a 2021 ARVO Annual Meeting abstract.