744 Role of epithelial stem cells in meibomian gland development, dysfunction, and dry eye disease

Dry eye disease (DED), one of the most common disorders of the ocular surface, affects over 16 million adults in the U.S. DED occurs from insufficient lubrication of the cornea, a consequence of destabilization of the tear film. In the majority of DED cases, this destabilization is caused by Meibomian gland dysfunction (MGD). MGD encompasses various conditions characterized by a defect in the production of meibum, the lipid outer layer of the tear film. MGD results from a variety of causes including loss of the Meibomian gland. In this study, we evaluated the importance of the zinc-finger transcription factor KROX20 and KROX20-expressing cells in Meibomian gland morphogenesis and homeostasis. During our characterization of mice lacking KROX20 protein in epithelial cells, we serendipitously observed that these mice developed squamous metaplasia of the ocular surface, a hallmark of DED. Histological analyses revealed that these mice lacked Meibomian glands. Furthermore, expression analyses showed that while KROX20-expressing cells are restricted to the central duct area of the Meibomian gland, Krox20-lineage cells are spread throughout the entire Meibomian gland, indicating that KROX20 marks a stem/progenitor cell population that gives rise to the whole Meibomian gland structure. Similar to the phenotype observed upon depletion of KROX20 protein, depletion of epithelial KROX20-expressing cells resulted in the failure of Meibomian gland formation, indicating that Krox20-lineage cells are critical for Meibomian gland morphogenesis. Taken together, this study identifies Krox20 as an important driver of Meibomian gland development and homeostasis, and provides a robust stem cell-centric model for studying DED secondary to MGD and for therapeutic testing.