Table 4.
Major features of meibomian lipids and key enzymes responsible for their appearance. Predictions about sub-cellular localization of enzymes are based on previous studies of other organs and tissues.
| Feature | Relevant Enzymes And Their Predicted Localization in Meibocytes |
|---|---|
| Low degree of unsaturation of fatty chains (mostly, n-1 to n-3) | Δ9-SCD1, Δ5-FADS2 and Δ6-FADS1 (ER, NU) |
| Branching (“iso” and “anteiso”) | BCKA (MC), FASN (CP, MC) |
| High levels of odd-numbered FA in lipids | unknown |
| ω-Hydroxylation of FA and FAL | Various CYP (ER, MS) |
| High levels of VLC and ELC FA in lipids | ELOVL1-7 (ER) |
| High levels of ELC FAL in WE and DiAD | FAR1/FAR2 (PS) |
| High levels of sterols and their esters | HMGR (ER, PS), LSS (ER), Δ7-DHCR (ER, NU) ACAT (MC), LCAT (SEC), SOAT (ER, PM, MC) |
| High levels of WE | AWAT2/WES (ER, GA) |
| High levels of OAHFA and CHL-OAHFA | unknown |
CP – cytoplasm; GA – Golgi apparatus; ER – endoplasmic reticulum; MC – mitochondrium; MS – microsome; NU – nucleus; PS – peroxisome; SEC – secreted (e.g., blood plasma)