Abstract

Volume.123 Number.3

Novel Development of Diabetic Retinopathy Research by Integrated Approach
Akiyoshi Uemura
Department of Retinal Vascular Biology, Nagoya City University Graduate School of Medical Sciences

Recent advances in the retinal imaging have dramatically improved the diagnosis of microvascular complications in diabetic retinopathy(DR). However, a lot of cellular and molecular abnormalities underlying these complications remain obscure. For basic research to clarify the pathophysiology of DR and develop new therapeutic modalities, we analyzed mouse models reproducing retinal vascular disorders characteristic of DR through multiple experimental approaches, including intravital imaging.
1. Intravital imaging of mouse retina
During the initiation and progression of DR, various types of cells are assumed to dynamically change their morphology and move within the retinal tissue. To capture the retinal cell dynamics, we developed a real-time, intravital imaging technique for mouse retina. We first customized a cataract-preventing contact lens that maintained fundus visibility for more than 6 h in anesthetized mice. Using this contact lens along with confocal laser scanning microscopy or two-photon excitation microscopy, we successfully monitored dynamic movements of microglia, macrophages, circulating leukocytes, and blood flow under physiological and pathological settings. These techniques can further be utilized for the imaging of molecular dynamics in retinal homeostasis and diseases.
2.Vascular abnormalities in pericyte-deficient retina
Based on the histopathological analyses of human eyes reported in the 1960s, loss of pericytes from the retinal capillary walls has been widely suggested to be responsible for various vascular dysfunctions in DR. However, this concept was not fully validated because the pathological changes similar to that of human retinopathy could not be reproduced in animal models with hyperglycemia. To overcome this obstacle, we directly established a mouse model without hyperglycemia with depleted pericyte accumulation in retinal vessels by systemically injecting postnatal mice with a monoclonal antibody for platelet-derived growth factor receptor β. In the absence of pericyte coverage, retinal blood vessels became enlarged and tortuous, forming numerous microaneurysms, and elevated vascular permeability resulted in the progressive exacerbation of retinal edema and hemorrhage. Moreover, endothelial cells and macrophages, which were infiltrating into pericyte-free retina, formed a damaging cycle via vascular endothelial growth factor A, placental growth factor, and angiopoietin-2, leading to the sustained inflammation and irreversible breakdown of the blood-retina barrier. Thus, pericyte depletion from growing retinal vessels was sufficient to sequentially replicate a series of pathological changes in DR.
3. Vascular regeneration in ischemic retina
In proliferative DR, new blood vessels grow toward the vitreous cavity, therefore retinal hypoxia is not resolved at all. To fundamentally treat this condition, it is desirable to re-vascularize ischemic retinas by rectifying the direction of vascular growth. By investigating the mechanisms regulating the intra-retinal vascular development in postnatal mice, we found that binding of neuron-derived semaphorin 3E(Sema3E)to endothelial PlexinD1 receptor activated a small GTPase RhoJ, retracting disoriented angiogenesis. Furthermore, in an ischemic retinopathy mouse model, intravitreal injections of recombinant Sema3E proteins selectively suppressed extra-retinal outgrowth of new blood vessels thorough activating PlexinD1, without affecting retinal re-vascularization. These results suggested Sema3E―PlexinD1-RhoJ signaling as a potential target for retinal vascular regeneration therapy.
Nippon Ganka Gakkai Zasshi(J Jpn Ophthalmol Soc)123:312-336, 2019.

Key words
Diabetic retinopathy, Mouse, Intravital imaging, Pericytes, Endothelial cells
Reprint requests to
Akiyoshi Uemura, M.D., Ph.D. Department of Retinal Vascular Biology, Nagoya City University Graduate School of Medical Sciences. 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan