Neuronal Sirtuin1 mediates retinal vascular regeneration in retinopathy

Abstract

Purpose: Regeneration of blood vessels in ischemic neuronal tissue is critical to reduce neuronal damage after ischemic injury in diseases. In ischemic proliferative retinopathy, initial vessel loss leads to retinal ischemia, followed by either regrowth of blood vessels to restore normal metabolism and minimize ischemic damage, or hypoxia-induced blinding pathologic retinal vessel proliferation. This project aims to explore the role of Sirtuin1 (Sirt1), a metabolically regulated protein deacetylase and a sensor of cellular ischemic stress, in ischemic retinopathy.

Methods: Ischemic proliferative retinopathy is induced in mice with an oxygen-induced retinopathy (OIR) model, in which neonatal mice were exposed to 75% oxygen from postnatal day (P) 7 to 12 to induce vessel loss and tissue ischemia, with maximal neovascular response observed at P17. Neuronal specific Sirt1 knockout mice were generated by crossing conditional Sirt1 knockout mice with Nestin-Cre mice. An in vitro cell culture model (RGC5) of retinal ganglion cell and an aortic ring vascular sprouting assay were used to explore the effect of specific inhibition of Sirt1 in retinal neurons on vascular growth.

Results: We found that Sirt1 is highly induced in avascular ischemic retina in OIR. Conditional knockout of neuronal Sirt1 leads to significantly decreased vascular regeneration in OIR and thereby precipitates hypoxia-induced pathologic neovascularization. This effect is independent of PGC-1α, a known Sirt1 substrate, as PGC-1α knockout mice do not exhibit similar vascular phenotype in OIR. We found that neuronal Sirt1 controls vascular regrowth in part through modulating deacetylation of hypoxia-induced factors (HIF) and expression of angiogenic factor erythropoietin. Conditioned medium collected from RGC5 cell culture treated with Sirt1 inhibitor Ex527 resulted in significantly decreased vascular growth in an aortic ring sprouting assay.

Conclusions: These results suggest a novel role of Sirt1, as a metabolically regulated stress sensor, in mediating retinal vascular regeneration in ischemic retinopathy.

Keywords: 572 ischemia • 657 protein modifications-post translational • 706 retinopathy of prematurity