PPARγ Regulates Mouse Meibocyte Differentiation and Lipid Synthesis

Purpose: Previous reports suggest that agerelated meibomian gland atrophy is associated with decreased expression of the lipid-sensitive nuclear receptor, PPAR gamma. The purpose of this study was to identify the role of PPARg in modulating meibocyte lipid synthesis. Methods: Cytoplasmic and nuclear fractions from meibomian glands of young (2M) and old (2Y) C57Bl6 mice were probed using antibodies specific for PPARg. Mouse meibocytes were cultured, immortalized using a SV40 lentiviral vector, and evaluated for lipid synthesis using LipidTox staining and CARS/Raman microspectroscopy. Lipid synthesizing clones were tested for effects of PPAR gamma agonist, rosiglitazone, on lipid synthesis and PPAR gamma localization, post-translational modification and induction of PPAR gamma response genes. Results: The cytoplasmic fraction in young mice contained both 50 and 72 kDa PPAR gamma bands that were absent or reduced by 75% in older mice, respectively. Cultured meibocytes produced neutral lipid containing equal amounts of wax and cholesterol esters, similar to mouse meibum. Addition of rosiglitazone (10-50 mu M) significantly increased lipid production (P<.05) in meibocytes, associated with SUMO1 sumoylation and cytoplasmic accumulation of the 72 kDa PPAR gamma. Rosiglitazone also increased the localization of PPAR gamma to the cytoplasm and up-regulated of PPAR gamma, ADP and ADFP mRNA. Conclusions: This study confirms the loss of cytoplasmic/vesicular PPAR gamma localization in older, atrophic mouse meibomian glands. Furthermore, PPAR gamma stimulates lipid synthesis in mouse meibocytes, associated with PPAR gamma sumoylation and translocation to the cytoplasm. Taken together these data suggest that lipid synthesis in older mice is down regulated by a PPAR gamma mediated pathway.