LAUSR

ABSTRACT We recently discovered that the anti‐glaucoma pharmaceuticals timolol, a &bgr; adrenergic antagonist, and pilocarpine, a cholinergic compound, negatively influence the morphology, proliferative capacity and survival of human meibomian gland epithelial cells (HMGECs). We hypothesize that another class of anti‐glaucoma drugs, the &agr;2 adrenergic agonists, also acts directly on HMGECs to affect their structure and function. We tested this hypothesis. Immortalized (i) HMGECs were cultured with brimonidine, as well as clonidine (&agr;2 agonist), phenylephrine (&agr;1 agonist), RX821002 (inverse &agr;2 agonist) and MK912 (neutral &agr;2 agonist) for up to 7 days. Cells were counted with a hemocytometer, and evaluated for morphology, signaling pathway activity, protein biomarker expression, and the accumulation of neutral lipids, phospholipids and lysosomes. Our findings demonstrate that brimondine treatment induces a dose‐dependent decrease in Akt signaling and proliferation of iHMGECs. In contrast, brimonidine also promotes a dose‐dependent differentiation of iHMGECs, including an increase in neutral lipid, phospholipid and lysosome levels. These effects were paralleled by an inhibition of p38 signaling, and duplicated by cellular exposure to clonidine, but not phenylephrine. Brimonidine also enhanced the cellular content of sterol regulatory binding protein‐1, a master regulator of lipid synthesis. Of particular interest, the putative &agr;2 antagonists, RX821002 and MK912, did not interfere with brimonidine action, but rather stimulated IHMGEC differentiation. Our results support our hypothesis and demonstrate that &agr;2 adrenergic agonists act directly on iHMGECs. However, these compounds do not elicit an overall negative effect. Rather, the &agr;2 agonists promote the differentiation of iHMGECs. HighlightsBrimonidine stimulates the differentiation of human meibomian gland epithelial cells.Brimonidine decreases the proliferation of, and Akt and p38 signaling in, these cells.Brimonidine's cellular effects are duplicated by clonidine, but not by phenylephrine.Brimonidine enhances the cellular content of sterol regulatory binding protein‐1.