Conditional knockdown of tubedown-1 in endothelial cells leads to neovascular retinopathy.

PURPOSE: Identification of novel proteins involved in retinal neovascularization may facilitate new and more effective molecular-based treatments for proliferative retinopathy. Tubedown-1 (Tbdn-1) is a novel protein that shows homology to the yeast acetyltransferase subunit NAT1 and copurifies with an acetyltransferase activity. Tbdn-1 is expressed in normal retinal endothelium but is specifically suppressed in retinal endothelial cells from patients with proliferative diabetic retinopathy. The purpose of this study was to investigate the importance of Tbdn-1 expression in retinal blood vessels in vivo. METHODS: A bitransgenic mouse model that enables conditional knockdown of Tbdn-1 specifically in endothelial cells was produced and studied using molecular, histologic, and immunohistochemical techniques and morphometric analysis. RESULTS: Tbdn-1-suppressed mice exhibited retinal and choroidal neovascularization with intra- and preretinal fibrovascular lesions similar to human proliferative retinopathies. Retinal lesions observed in Tbdn-1-suppressed mice increased in severity with prolonged suppression of Tbdn-1. In comparison to normal retina, the retinal lesions displayed alterations in the basement membrane of blood vessels and in the distribution of glial and myofibroblastic cells. Moreover, the pathologic consequences of Tbdn-1 knockdown in endothelium were restricted to the retina and the choroid. CONCLUSIONS: These results indicate that the maintenance of Tbdn-1 expression is important for retinal blood vessel homeostasis and for controlling retinal neovascularization in adults. Restoration of Tbdn-1 protein expression and/or activity may provide a novel approach for treating proliferative retinopathies.

Progenitor cell proliferation in the retina is dependent on Notch-independent Sonic hedgehog/Hes1 activity.

Sonic hedgehog (Shh) is an indispensable, extrinsic cue that regulates progenitor and stem cell behavior in the developing and adult mammalian central nervous system. Here, we investigate the link between the Shh signaling pathway and Hes1, a classical Notch target. We show that Shh-driven stabilization of Hes1 is independent of Notch signaling and requires the Shh effector Gli2. We identify Gli2 as a primary mediator of this response by showing that Gli2 is required for Hh (Hedgehog)-dependent up-regulation of Hes1. We also show using chromatin immunoprecipitation that Gli2 binds to the Hes1 promoter, which suggests that Hes1 is a Hh-dependent direct target of Gli2 signaling. Finally, we show that Shh stimulation of progenitor proliferation and cell diversification requires Gli2 and Hes1 activity. This paper is the first demonstration of the mechanistic and functional link between Shh, Gli, and Hes1 in the regulation of progenitor cell behavior.