Photoreceptor cells are major contributors to diabetes-induced oxidative stress and local inflammation in the retina

Abstract

Accumulating evidence suggests that photoreceptor cells play a previously unappreciated role in the development of early stages of diabetic retinopathy, but the mechanism by which this occurs is not clear. Inhibition of oxidative stress is known to inhibit the vascular lesions of early diabetic retinopathy, and we investigated whether the diabetes-induced oxidative stress in the retina emanates from photoreceptors. Superoxide generation was assessed in retinas of male C57BL/6J mice made diabetic for 2 mo (4 mo of age when killed) using histochemical (dichlorofluorescein and dihydroethidine) and bioluminescence (lucigenin) methods. Photoreceptors were eliminated in vivo by genetic (opsin −/− ) and chemical (iodoacetic acid) techniques. Immunoblots were used to measure expression of intercellular adhesion molecule 1 and the inducible form of nitric oxide synthase. Diabetes increased the generation of superoxide by diabetic mouse retina more at night than during the day. Photoreceptors were the major source of reactive oxygen species in the retina, and their deletion (either genetically in opsin −/− mice or acutely with iodoacetic acid) inhibited the expected diabetes-induced increase in superoxide and inflammatory proteins in the remaining retina. Both mitochondria and NADPH oxidase contributed to the observed retinal superoxide generation, which could be inhibited in vivo with either methylene blue or apocynin. Photoreceptors are the major source of superoxide generated by retinas of diabetic mice. Pharmaceuticals targeting photoreceptor oxidative stress could offer a unique therapy for diabetic retinopathy.T he pathogenesis of diabetic retinopathy remains unclear, but prior work by us and others has provided strong evidence in animal models that oxidative stress and inflammatory processes play important roles in the development of the vascular lesions characteristic of early stages of this retinopathy (1, 2). Inhibition of oxidative stress by feeding antioxidants or overexpressing antioxidant enzymes has reduced diabetes-induced degeneration of retinal capillaries (3-7). Moreover, oxidative stress has been reported to regulate expression of proinflammatory proteins (8-10), which also have been shown to play a critical role in the pathogenesis of this early retinopathy (2). However, which cells of the retina are the major sources of such oxidative stress in diabetes is unclear. In vitro studies of retinal endothelial cells or Müller cells incubated in elevated levels of glucose have demonstrated that these cells can contribute to oxidative stress (11, 12), but the contribution of other cell types and their relative importance has not been studied.Rod and cone photoreceptor cells are the most prevalent cells in the retina. These postmitotic cells have a very high metabolic rate, using more oxygen than other cells throughout the body. They are also considered as likely contributors to the eventual development of retinal hypoxia and subsequent neovascularization in advanced stages of diabetic retinopathy (13,14). Th...

Mechanistic Insights into Pathological Changes in the Diabetic Retina

“…33 Diabetes causes a significant increase in leukocyte adhesion to the retinal microvasculature (leukostasis), and selective antagonism of that adhesion by expression of neutrophil inhibitory factor has been shown to inhibit the diabetes-induced degeneration of retinal capillaries. 60 Leukocytes normally play an important role in immune function, so it is significant that the study also provided evidence that neutrophil inhibitory factor did not inhibit normal immune surveillance. Thus, inhibition of leukocyte adhesion to retinal endothelial cells is a potential therapeutic target to inhibit DR.…”

“…58,60,61 Several recent lines of evidence have also identified potential new targets for inhibition of DR, and several Food and Drug Administrationeapproved drugs (against other diseases) have been found to inhibit the diabetes-induced degeneration of retinal capillaries characteristic of DR in diabetic rodents. Some of these repurposed drugs were initially identified as protective against DR in clinical trials, whereas others are being tested now only in animals.…”

“…We recently confirmed this using opsindeficient mice and in mice having a P23H mutant opsin knocked in, and extended this observation by showing that the stress in photoreceptors undergoing degeneration greatly exacerbated capillary degeneration, but that this stress is reduced after the photoreceptors have degenerated. Photoreceptors do not characteristically degenerate because of diabetes, 78 so they manifest a continuous stress that includes increased oxidative stress 60 and affects the vasculature. Hypotheses that might help explain how photoreceptors influence the development of DR include hypoxia 79,80 and oxidative stress.…”

“…Hypotheses that might help explain how photoreceptors influence the development of DR include hypoxia 79,80 and oxidative stress. 60 These hypotheses are not mutually exclusive.…”

Avaliação das vias do sistema visual por eletrorretinograma e testes psicofísicos na Distrofia Muscular de Duchenne e na Diabetes Mellitus tipo 1

“…Há neurodegeneração na camada interna da retina tanto em pesquisas com modelos animais de DM quanto em seres humanos com DM (Barber et al 1998, El-Asar, Dralands, Missotten, Al-Jadaan, & Geboes, 2004, van Dijk et al, 2010. Esses indícios também relacionam o estresse oxidativo como causa do dano neural e que essa pode ser uma fase inicial da retinopatia diabética, ou 39 seja, esse dano neural pode anteceder os danos vasculares (Du et al, 2013).…”