Conjunctival goblet cells are the major cell type that synthesize and secrete mucins for the maintenance of ocular surface integrity. Lack of mucins in the tear film due to goblet cells abnormality causes dry eye syndrome (DES) and affects millions of people's vision and life. The lack of knowledge regarding the regulatory mechanisms by which conjunctival epithelial cells differentiate to form goblet cells hampers the development of treatment regimens for DES. We found that inhibition of Notch via conditional expression of a dominant negative transcriptional coactivator mastermind-like 1 (dnMAML1) in the ocular surface epithelia (OSdnMAML1) suppressed goblet cell differentiation in mouse model. Compared to the wild-type mouse (OSWt), the ocular surface of the OSdnMAML1 exhibited conjunctival epithelial hyperplasia, aberrant desquamation, and impaired goblet cell formation. Moreover, OSdnMAML1 inhibited Krppel-like transcriptional factor 4 and 5 genes (Klf4 and Klf5) expression and Muc5/ac synthesis. In contrast, conjunctival epithelium was expanded and differentiated into goblet cells in entire eyelid stroma of the TGFRII conditional knockout (cKO) mice. The expanded TGFRIIcKO conjunctival epithelium strongly expressed SAM-pointed domain containing ETS transcription factor (SPDEF), which plays a critical role in goblet cell differentiation in multiple organs. We hypothesize that intrinsic canonical Notch and TGF signaling pathways and their interaction(s) play pivotal roles in conjunctival goblet cell differentiation. We propose three aims to test this hypothesis.
Aim 1 : To elucidate that Jagged1/Notch1 N1-ICD/Rbp-j?MAML1 Klf4/5 Muc5/ac axis is critical for the conjunctival goblet cell differentiation.
Aim 2 : To elucidate that TGFRII Smads SPDEF Muc5/ac axis has a role in goblet cell differentiation.
Aim 3 : To delineate how Notch and TGF pathways interact to come up with a physiological output for balanced goblet cell differentiation.
The goal of the proposed research entitled 'Ocular Surface in Health and Disease' is to understand the cellular signaling pathway(s) network in controlling normal ocular surface morphogenesis and the pathogenesis of Keratoconjunctivitis sicca (KCS or dry eye). Specifically, we focus on two important cellular signaling pathways: 1) Notch signaling activates Klf4/5 transcription factor which in turn regulates goblet cell differentiation and mucin synthesis; 2) TGF signaling in regulating goblet cell differentiation by negative regulation of transcription factor Spdef in conjunctival epithelium. Moreover, we also found that inhibition of Notch dampened Klf4/5 expression and diminished Spdef and Muc5/ac synthesis in the conjunctival epithelium, suggesting that there is interaction between Notch and TGF signaling pathways to control goblet cell differentiation in conjunctival epithelium. Based on these data, we set out to investigate in-depth molecular mechanisms by which Notch and TGF pathways cross-talk to come up with a physiological output for balanced goblet cell differentiation. Genetic and/or epigenetic alteration of Notch and TGF signaling network can lead to severe KCS in the transgenic mouse model as well as in human. Therefore, fine-tune Notch activation to control Klf4/5 expression and/or TGF to control Spdef can be a potential strategy to treat KCS with mucins deficient dry eye.
