PPARγ regulates meibocyte differentiation and lipid synthesis of cultured human meibomian gland epithelial cells (hMGEC).

To evaluate the role of PPARγ in regulating meibocyte differentiation and lipid synthesis in a human meibomian gland epithelial cell line (hMGEC). HMGEC were exposed to the PPARγ agonist, Rosiglitazone, from 10-50 μM. Cultures were also exposed to specific PPARγ antagonist, T0070907, to block PPARγ receptor signaling. Cells were then stained with Ki-67 and LipidTox to determine the effects on cell cycling and lipid synthesis, respectively. Expression of meibocyte differentiation related proteins, ADFP, PPARγ, ELOVL4, and FABP4, were evaluated by quantitative PCR and western blotting. A human corneal epithelial cell line (hTCEpi) was used as a control. Rosiglitazone significantly decreased Ki-67 staining within 2 days in a dose-dependent manner (P = 0.003) and increased lipid accumulation in hMGEC in a dose dependent manner. T0070907 suppressed both lipid droplet synthesis and cell cycle exit. Rosiglitazone significantly upregulated expression of ADFP, PPARγ, ELOVL4, and FABP4 by 9.6, 2.7, 2.6, and 3.3 fold on average (all P < 0.05 except for FABP4, P = 0.057) in hMGEC. T0070907 significantly abrogated rosiglitazone-induced upregulation of these genes when treated prior to rosiglitazone treatment (all P < 0.05). The observed lipogenic differentiation response was not duplicated in hTCEpi after exposure to rosiglitazone. Rosiglitazone induced cell cycle exit and upregulation of lipogenic gene expression leading to lipid accumulation in hMGEC. These effects were suppressed by PPARγ antagonist indicating that PPARγ signaling specifically directs lipogenesis in hMGEC. These findings suggest that PPARγ plays a critical role in meibocyte differentiation.