Changes in Select Redox Proteins of the Retinal Pigment Epithelium in Age-related Macular Degeneration

Abstract

PURPOSE-To examine changes of select reduction-oxidation (redox) sensitive proteins from human donor retinal pigment epithelium (RPE) at four stages of age-related macular degeneration (AMD). DESIGN-Experimental study.METHODS-Human donor eyes were obtained from the Minnesota Lions Eye Bank and graded using the Minnesota Grading System (MGS) into four stages that correspond to stages defined by the age-related eye disease study (AREDS). Protein content in RPE homogenates was measured using Western immunoblotting with protein-specific antibodies.RESULTS-The content of several antioxidant enzymes and specific proteins that facilitate refolding or degradation of oxidatively damaged proteins increased significantly in MGS stage 3. These proteins are involved in the primary (copper-zinc superoxide dismutase [CuZnSOD], manganese superoxide dismutase [MnSOD], and catalase) and secondary (heat shock protein [HSP] 27, HSP 90, and proteasome) defense against oxidative damage. Additionally, the insulin prosurvival receptor exhibited disease-related upregulation.CONCLUSIONS-The pattern of protein changes identified in human donor tissue graded using the MGS support the role of oxidative mechanisms in the pathogenesis and progression of AMD. The MGS uses nearly identical clinical definitions and grading criteria of AMD that are used in the AREDS, so our results apply to clinical and epidemiologic studies using similar definitions. Results from our protein analysis of human donor tissue helps to explain altered oxidative stress regulation and cell-survival pathways that occur in progressive stages of AMD.Age-related macular degeneration (amd) is the leading cause of blindness in developed countries 1-9 . The number of affected individuals in the United States alone is expected to increase nearly twofold, to approximately three million by the year 2020. 10 Fortunately, therapeutic options are improving. The use of antioxidant vitamins has been shown to delay disease progression at an intermediate stage, 11 and rapid innovation in the use of antiangiogenic therapies has resulted in new clinical methods to treat the exudative phase of AMD. 12-18 However, developing new treatment and prevention strategies targeting earlier stages of the disease requires a better understanding of the underlying disease mechanisms.Findings from the Age-Related Eye Disease Study (AREDS) clearly support the hypothesis that oxidative mechanisms play a significant role in the progression of AMD. Although several studies have shown that the intake of antioxidant-rich foods lowers the risk of AMD, 19-24 others have not supported this conclusion. 25-27 Cigarette smoking, a pro-oxidant, NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript significantly increases the risk of AMD, and this association is well supported in numerous, well-designed studies. 28-35The retinal pigment epithelium (RPE) is subject to a particularly high level of oxidative stress because of locally elevated oxygen tension, high polyunsaturated lipid con...

Cigarette Smoke-Related Hydroquinone Induces Filamentous Actin Reorganization and Heat Shock Protein 27 Phosphorylation through p38 and Extracellular Signal-Regulated Kinase 1/2 in Retinal Pigment Epithelium

“…Increased Hsp27 protein content along with evidence of cellular oxidative stress was reported in human eyes with AMD, but Hsp27 phosphorylation was not investigated. 50 Our findings provide novel evidence that phosphorylated Hsp27 may play a major role in the pathogenesis of AMD. In response to stress, phosphorylated Hsp27 undergoes conformational changes and reorganizes into dimeric units.…”

Looking beyond Lucentis on the management of macular degeneration

“…15 Hence, there is only weak epidemiologic evidence that excessive exposure to light is associated with AMD. 16,17 Furthermore, chronic excessive exposure to light increases the risk of cataract formation, 18 this might be a form of natural protection for the retina. With the advances in cataract surgery, surgery is often preformed at an earlier age.…”

“…A direct correlation with upregulation of this antioxidant pathway is seen with the different stages of AMD. 18 There is currently no therapeutic application for the enzymes themselves, however, they are reliant upon enzyme cofactors such as zinc and copper.…”

Unfolding the therapeutic potential of chemical chaperones for age-related macular degeneration

“…Recently, Shen et al reported a direct demonstration of increased oxidative stress in the retinas of AMD eyes with geographic RPE atrophy [39]. Additionally, changes in select RPE redox proteins have been reported in AMD eyes and oxidized phospholipids in the macula have been reported to increase with age and in eyes with AMD [40,41]. Moreover, isolation of microgram quantities of drusen identified a high concentration of oxidatively-modified proteins in AMD eyes [42].…”

“…Among these were several molecular chaperones whose expression decreased with AMD progression, including Hsp60 and HOP [16]. Additionally, several antioxidant enzymes and chaperones that facilitate refolding or degradation of oxidatively damaged proteins decreased in AMD eyes: copper-zinc superoxide dismutase, manganese superoxide dismutase, catalase, and Hsp27, Hsp 90, and proteasome [40]. Moreover, human AMD lesions and retina from the Ccl2/Cx3cr1 deficient murine model of AMD were reported to exhibit decreased mRNA and protein expression of ERp29, a protein escort and folding chaperone [18].…”