Prostaglandins alter expression of select long-chain cholesteryl esters produced by human meibomian gland epithelial cells in culture

Abstract

Purpose : Ocular surface disease is a common comorbidity in glaucoma patients treated with prostaglandin analogs. To date, however, there is little understanding of the physiologic roles that prostaglandins have on the meibomian glands. Therefore, human meibomian gland epithelial cells (HMGECs) were treated with two common prostaglandins (PGE₂ and PGF_2α) to evaluate their effects on cell viability and lipid expression.

Methods : Differentiated HMGECs were stained with antibodies against PGE₂ (EP1, EP2, EP3, EP4) and PGF_2α (FP) receptors and imaged with the Zeiss Axioplan-2 Microscope (Jena, Germany). For cell viability and lipidomic analyses, differentiated HMGECs were cultured with PGE₂ or PGF_2α (1 to 1000 nM) for three hours. Following culture, cell viability was assessed with the Cell Titer Glo Assay (Promega, Madison, WI). Lipid extracts were concentrated two-fold and directly infused into a Triple TOF 5600 mass spectrometer (SCIEX, Framingham, MA) with electrospray ionization in the positive ion mode. Meibum-relevant lipids were defined to be wax esters (WE) with carbon number (n_c) ≥ 32 and cholesteryl esters (CE) with n_c ≥ 16. Lipids are labeled as n_c: # double bonds.

Results : Differentiated HMGECs express three receptors for PGE₂ (EP1, EP2, and EP4) and the only receptor for PGF_2α (FP). None of the concentrations of PGE₂ (p > 0.73 for all) or PGF_2α (p > 0.99 for all) affected cell viability. When evaluating the lipidome, there were 26 CEs and 0 WEs that met the criteria for inclusion. Increasing concentrations of PGE₂ were associated with a dose-dependent decrease in CE 22:1 (mean fold change [FC] = 0.89 per ten-fold change in dose, p = 0.03). Both the 1000 and 100 nM concentrations of PGE₂ significantly reduced CE 24:0 relative to control (mean FC = 0.47, p < 0.03 for both). For PGF_2α, the 10 nM concentration upregulated CE 16:0 relative to control (FC = 1.31, p = 0.01). All other CEs remained unchanged across all concentrations of prostaglandins.

Conclusions : Receptors for both PGE₂ and PGF_2α are expressed on HMGECs. Neither PGE₂ or PGF_2α affects cell viability; however, both molecules are capable of altering the expression of select cholesteryl esters. It is possible that prostaglandin analogs elicit molecular changes to human meibum and the tear film, which may represent one possible explanation for the concurrence of glaucoma and ocular surface disease.

This is a 2020 ARVO Annual Meeting abstract.