Role of calcium channels in the development of diabetic retinopathy

Wayne State University, Detroit MI

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Abstract

DESCRIPTION (provided by applicant): There remains an urgent need to prevent vision loss from diabetic retinopathy (DR), a common and significant problem in patients with diabetes. Preclinical studies have highlighted retinal oxidative stress in the pathogenesis of DR. We reason that identifying the retinal mechanisms mediating pathogenic oxidative stress in diabetes will be important in the development of new and effective treatments. In neurons, oxidative stress and L-type calcium channels (LTCCs) activity are closely linked: increased LTCC activity elevates intracellular calcium content which must then be removed against a steep inter/extracellular calcium concentration gradient via ATP-dependent mechanisms which generate oxygen free radicals. We have discovered that diabetes profoundly changes the overall activity of photoreceptor LTCCs. Remarkably, a non-anti-oxidant and photoreceptor-specific treatment that corrected the abnormal outer retinal LTCC phenotype in vivo concurrently eliminated diabetic retinal oxidative stress. These experiments, using a validated and analytical tool (MEMRI), provide the first evidence for an unexpected and potentially very important discovery linking abnormal photoreceptor LTCCs and oxidative stress in diabetes. In the retina there are 3 major LTCC subtypes (Cav): Cav1.2 (located in inner retina), Cav1.3 (in inner retina, photoreceptor, and retinal pigment epithelium layers), and Cav1.4 (only in photoreceptors. How diabetes alters photoreceptor subtype channels are not yet known. We hypothesized that diabetes induces reproducible abnormalities in photoreceptor Cav1.3 and 1.4 expression and activity, and these changes actively contribute to oxidative stress and diabetic retinopathy. To begin to evaluate our new working hypothesis, we propose the following specific aim, which will take full advantage of our expertise in blending high resolution and analytical in vivo imaging of photoreceptor pathophysiology (manganese-enhanced MRI) with biochemistry (reactive oxygen species, western blot analysis (channel expression)) and histopathology (trypsin digest) in models of DR. SA 1: Test that diabetic alterations in photoreceptor Cav1.3, and 1.4 LTCC activity are required for oxidative stress and DR. The proposed experiments will open up a new line of scientific inquiry that is expected to improve our understanding about the origins of oxidative stress in DR. Because Cav1.3 and 1.4 subtypes are relatively insensitive to commonly used calcium channel blockers, our specific genetic and pharmacological approaches in concert with a novel imaging technique make these studies highly significant. These experiments will be crucial in the identification of new molecular targets for prevention and treatment of DR. The proposed research is highly innovative because it investigates a previously unsuspected but key role of photoreceptor LTCC subtype abnormalities in diabetes-induced oxidative stress, and will thus establish a firm scientific basis for changing current thinking regarding the origins of, and therapeutic options for, pathogenic oxidative stress in DR.