Introduction Dry eye is a condition in which there are insufficient tears to lubricate and nourish the eye. An estimated 25 million Americans are affected by dry eye with an increased prevalence among the elderly. The primary cause of dry eye is a lipid deficiency, responsible for 64% of all cases.

Meibomian Gland Dysfunction The meibomian glands are responsible for the secretion of meibum, the oily substance that prevents evaporation of the eye’s tear film. Meibomian gland dysfunction (MGD) leads to alteration in the tear film and dry eye.

PPAR  Peroxisome proliferator activated receptor  (PPAR  ) PPAR  maintains maturation of meibocytes and is key to lipid synthesis. Correlated to decreased lipid production with aging.

Hypothesis Aim 1: Loss of PPAR  will result in abnormalities in meibomian gland formation and lipid production, resulting in dry eye symptoms. Aim 2: Molecular mechanism regulating PPAR  expression and regulation of lipid synthesis is Notch signaling.

Notch Signaling Pathway

Transgenic Mouse Models Two types: Inducible – Tissue Specific –Removal of gene can be controlled Conditional Knockout –Works during the embryonic phase by binding to Pax-6 –More severe phenotype

Loss of PPAR  - Phenotype

Removal of Notch-1 Sign Improper formation of gland, absence of notch signaling is necessary for lipid production Removal of Notch-1 Signaling: Control: Notch-1 Signaling present, normal gland formation, lipids present (Oil Red O Staining). Mutant: Notch-1 Signaling absent, improper gland formation, lipids absent.

Loss of PPARγ – Increased Lining Thickness

Loss of PPAR  - A.Increased protein concentration in tears of mice. B.Eye lid of a control mouse C.Eye lid of a mutant mouse, displaying lymphatic vessel intrusion into the central cornea

Human Meibomian Gland (hMG) cells - Subjected to two different growth mediums: keratinocyte serum-free medium (KSFM) and our differentiation medium (DMEM/FBS/EGF) that contains more growth factors. Picture: hMG cells in KSFM Medium

PPAR  Presence in Differentiation Medium Lipid Presence in Differentiation Medium

PPAR  Presence in KSFM Medium Lipid Presence in KSFM Medium

Conclusion Loss of PPARγ results in malformed meibomian glands with MGD-like attributes. PPARγ is essential to the formation and function of the meibomian glands. Notch signaling is an important regulator of PPARγ.