Signaling pathways involved in tubedown regulation of retinal endothelial permeability

Ho, Nhu Phan Minh (2012) Signaling pathways involved in tubedown regulation of retinal endothelial permeability. Masters thesis, Memorial University of Newfoundland.

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Abstract

Increased vascular permeability is the early physical manifestation of diseases such as diabetic retinopathy (PDR) and age-related macular degeneration (AMD), which are the leading causes of blindness. Previous studies in Drs. Gendron-Paradis lab have suggested that Tubedown (Tbdn) is an important regulator of endothelial permeability in the retina. Tbdn is a member of the Natl family of proteins that associate with the acetyltransferase Ardl. Tbdn protein expression is suppressed in eye specimens from patients with PDR and AMD. Moreover, the conditional endothelial specific Tbdn knockdown mouse model (TIE2/rtTA/Enh-TREIASTBDN-1) was found to mimic the pathological features of PDR and AMD and to have increased extravasation of Albumin. Previously, we found that Tbdn co-immunoprecipitated with the actin binding protein Cortactin and co-localized with Cortactin and F -actin in endothelial cytoplasmic and cortex regions. Cortactin plays an essential role in the Albumin permeability pathway and is a well-known substrate of c-Src. Tyrosine kinase c-Src not only phosphorylates Cortactin but also takes part in signaling to increase the permeability of endothelial cells. Based on this knowledge, we hypothesized that Tbdn knockdown would lead to an increase in phospho-Cortactin and phospho-Src. Tbdn knockdown in vitro by siRNA and stable transfection of an antisense Tbdn eDNA construct significantly increased phospho-Cortactin and phospho-Src levels. In vivo, using the Tbdn knockdown mouse model, we confirmed the increase in phospho-Src. Furthermore, human PD R specimens, known for downregulation of Tbdn, also revealed robust levels of phospho-Src. These results support the hypothesis that Tbdn regulates signaling pathways mediating retinal endothelial cell permeability to Albumin by influencing Cortactin and c-Src. Future therapies for neovascular retinopathies could target Tbdn with the hope of preventing, and not simply treating, these devastating causes of blindness.

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