Vision loss from ischemic retinopathies commonly results from the accumulation of fluid in the inner retina [macular edema (ME)]. Although the precise events that lead to the development of ME remain under debate, growing evidence supports a role for an ischemia-induced hyperpermeability state regulated, in part, by VEGF. Monthly treatment with anti-VEGF therapies is effective for the treatment of ME but results in a major improvement in vision in a minority of patients, underscoring the need to identify additional therapeutic targets. Using the oxygen-induced retinopathy mouse model for ischemic retinopathy, we provide evidence showing that hypoxic Müller cells promote vascular permeability by stabilizing hypoxia-inducible factor-1α (HIF-1α) and secreting angiogenic cytokines. Blocking HIF-1α translation with digoxin inhibits the promotion of endothelial cell permeability in vitro and retinal edema in vivo. Interestingly, Müller cells require HIF-but not VEGF-to promote vascular permeability, suggesting that other HIF-dependent factors may contribute to the development of ME. Using gene expression analysis, we identify angiopoietinlike 4 (ANGPTL4) as a cytokine up-regulated by HIF-1 in hypoxic Müller cells in vitro and the ischemic inner retina in vivo. ANGPTL4 is critical and sufficient to promote vessel permeability by hypoxic Müller cells. Immunohistochemical analysis of retinal tissue from patients with diabetic eye disease shows that HIF-1α and ANGPTL4 localize to ischemic Müller cells. Our results suggest that ANGPTL4 may play an important role in promoting vessel permeability in ischemic retinopathies and could be an important target for the treatment of ME.diabetes | retinal vein occlusion | angiogenesis | transcription factor I schemic retinopathies include a diverse group of retinal diseases, in which immature retinal vasculature (e.g., retinopathy of prematurity or incontinentia pigmenti) or damage to mature retinal vessels (e.g., diabetic retinopathy, retinal vein occlusion, or sickle cell retinopathy) leads to retinal ischemia (1). Although diverse (and poorly understood) etiologies may lead to insufficient perfusion of the retina, all lead to a common sequelae: the formation of abnormal leaky blood vessels that can manifest clinically with the accumulation of fluid in the inner retina [i.e., macular edema (ME)] and often, a profound loss of vision (2). Indeed, ME in patients with ischemia-induced retinopathies remains the leading cause of vision loss in the working age population in the developed world (3).The concept that ischemic retinopathies are driven by ischemia-induced angiogenic factors was proposed over half a century ago (4). A single transcriptional activator, hypoxia-inducible factor-1 (HIF-1), has recently emerged as the master regulator of these angiogenic mediators. HIF-1 is a heterodimeric protein composed of an exquisitely oxygen-sensitive α-subunit and a ubiquitous β-subunit. Under hypoxic conditions, degradation of the oxygensensitive HIF-1α subunit is reduced, whereas its trans...

Increased protein O -GlcNAcylation (OGN) is a common feature of failing heart muscle. However, it is unknown if excessive OGN contributes to cardiomyopathy and heart failure. OGN levels are determined by the net activity of two enzymes: OGT ( O -GlcNAc transferase, adds OGN) and OGA ( O -GlcNAcase, removes OGN). We hypothesized that excessive myocardial OGN is a cause of cardiomyopathy. To test for a role of OGN in cardiomyopathy we developed new transgenic (TG) mouse models with myocardial overexpression of OGT or OGA. The OGT-TG hearts showed progressive decline in left ventricular (LV) systolic function, dilation, increased mass (Figure A, B) (Statistical Analysis ANOVA - *** = p<0.001) and increased OGN (Figure C) . OGT-TG mice showed premature mortality compared to WT littermates (Figure D). In contrast, OGA-TG mice exhibit normal contractility, do not have significantly different OGN and have normal lifespan compared to WT littermates. Hearts from OGT-TG and OGA-TG interbred mice have marked improvement of LV systolic function, lower OGN and normal lifespan. We next tested if attenuation of myocardial OGN was beneficial in acquired cardiomyopathy by performing transverse aortic constriction surgery (TAC) on OGA-TG and WT littermates. The OGA-TG hearts had lower OGN, improved LV systolic function, less hypertrophy, and lower expression of heart failure genes compared to WT littermates after TAC. Our data identify excessive OGN as an independent mechanism for cardiomyopathy, and suggest attenuation of OGN may be an effective therapy for heart failure.