The role of leucine-rich alpha-2-gycoprotein 1 (Lrg1) in retinal vascular development and disease

The uncontrolled growth of new blood vessels and damaging changes to existing blood vessels in the retina, the light sensitive part of the eye, is a major cause of blindness. These harmful changes occur in a number of different eye diseases but the most common is diabetes where loss of vision can affect up to 40% of patients. Although some advances have been made in the treatment of these conditions they still remain very difficult to control. There is therefore an urgent need to understand in much greater detail the biological mechanisms that cause these changes so that we can identify new therapeutic targets, especially during the early stages of disease, to which drugs can be developed. Our objective in this project is to investigate the role of a newly discovered molecule called Lrg1, which our preliminary data have shown to be produced at high levels by abnormal retinal blood vessels and to cause blood vessel cell proliferation. In this project we will investigate in detail how Lrg1 regulates the growth of blood vessels in the retina during normal development and how it may contribute to the development of harmful blood vessels that occur in many eye diseases. By gaining insight into the biology of this molecule we aim to validate it as a potential therapeutic target for the treatment of sight-threatening retinal vascular disease.

Vascular remodelling of the retina in diseases such as diabetic retinopathy (DR), retinal vein occlusion, retinopathy of prematurity and macular telangiectasia contributes to loss of vision and, despite advances in treatment, remains a significant and debilitating clinical problem. Although there is a growing understanding of the role of certain key mediators of angiogenesis, such as VEGF, the biology underpinning retinal vascular remodelling, especially pre-angiogenic changes, is complex and our knowledge is inadequate. In order to gain insight into the biological basis of retinal vascular remodeling, we previously conducted a genome-wide transcriptomic study to identify candidate genes that contribute to vascular changes observed in various rodent models of retinal disease. This study revealed a significant increase in the expression of a novel secreted glycoprotein, leucine-rich alpha-2-glycoprotein-1 (Lrg1), the expression of which is largely restricted to the retinal vasculature. In subsequent preliminary studies we have shown that Lrg1 interacts with the TGFbeta1 receptors TGbetaRII and ALK1, causing a switch in TGFbeta1 signaling away from the predominantly homeostatic ALK5 pathway, towards a proliferative, pro-angiogenic pathway. In this project we will undertake in vivo approaches to investigate how Lrg1 regulates the growth of blood vessels in the retina during developmental angiogenesis and how it contributes to neoangiogenesis and vascular remodeling in animal models of retinal angiogenesis. We will define the factors that control Lrg1 expression in endothelial cells and examine how Lrg1 mediates pro-angiogenic TGFbeta signalling. The effects of Lrg1 on endothelial cell function, such as proliferation, migration, sprouting and tube formation will be determined using in vitro and ex vivo assays. These studies will define the role of Lrg1 as a modulator of angiogenesis and help to validate Lrg1 as a potentially novel and highly promising therapeutic target.