Marisol Cano

Complement factor H binds malondialdehyde epitopes and protects from oxidative stress.

Oxidative stress and enhanced lipid peroxidation are linked to many chronic inflammatory diseases, including age-related macular degeneration (AMD). AMD is the leading cause of blindness in Western societies, but its aetiology remains largely unknown. Malondialdehyde (MDA) is a common lipid peroxidation product that accumulates in many pathophysiological processes, including AMD. Here we identify complement factor H (CFH) as a major MDA-binding protein that can block both the uptake of MDA-modified proteins by macrophages and MDA-induced proinflammatory effects in vivo in mice. The CFH polymorphism H402, which is strongly associated with AMD, markedly reduces the ability of CFH to bind MDA, indicating a causal link to disease aetiology. Our findings provide important mechanistic insights into innate immune responses to oxidative stress, which may be exploited in the prevention of and therapy for AMD and other chronic inflammatory diseases.

Cigarette smoking, oxidative stress, the anti-oxidant response through Nrf2 signaling, and Age-related Macular Degeneration.

Age-related Macular Degeneration (AMD) is the leading cause of blindness among the elderly. While excellent treatment has emerged for neovascular disease, treatment for early AMD is lacking due to an incomplete understanding of the early molecular events. Cigarette smoking is the strongest epidemiologic risk factor, yet we do not understand how smoking contributes to AMD. Smoking related oxidative damage during the early phases of AMD may play an important role. This review explores how cigarette smoking and oxidative stress to the retinal pigmented epithelium (RPE) might contribute to AMD, and how the transcription factor Nrf2 can activate a cytoprotective response.

Decreased membrane complement regulators in the retinal pigmented epithelium contributes to age-related macular degeneration

Dysregulated complement is thought to play a central role in age‐related macular degeneration (AMD) pathogenesis, but the specific mechanisms have yet to be determined. In maculae of AMD specimens, we found that the complement regulatory protein, CD59, was increased in regions of uninvolved retinal pigmented epithelium (RPE) of early AMD, but decreased in the RPE overlying drusen and in geographic atrophy, an advanced form of AMD. While CD46 immunostaining was basolaterally distributed in the RPE of unaffected controls, it was decreased in diseased areas of early AMD samples. Since oxidized low‐density lipoproteins (oxLDL) collect in drusen of AMD and are a known complement trigger, we treated ARPE‐19 cells with oxLDL and found that cellular CD46 and CD59 proteins were decreased by 2.9‐ and nine‐fold (p < 0.01), respectively. OxLDLs increased complement factor B mRNA and Bb protein, but not factor D, I or H. OxLDLs increased C3b, but not C3a, C5 or C5b‐9. C5b‐9 was increased by 27% (p < 0.01) when the medium was supplemented with human serum, which was sufficient to induce poly(ADP‐ribose) polymerase cleavage, a marker of apoptosis. The decreased levels of CD46 and CD59 were in part explained by their release in exosomal and apoptotic membranous particles. In addition, CD59 was partially degraded through activation of IRE1α. Collectively, these results suggest that a combination of impaired complement regulators results in inadequately controlled complement by the RPE in AMD that induces RPE damage. Copyright

Lysosomal-mediated waste clearance in retinal pigment epithelial cells is regulated by CRYBA1/βA3/A1-crystallin via V-ATPase-MTORC1 signaling

In phagocytic cells, including the retinal pigment epithelium (RPE), acidic compartments of the endolysosomal system are regulators of both phagocytosis and autophagy, thereby helping to maintain cellular homeostasis. The acidification of the endolysosomal system is modulated by a proton pump, the V-ATPase, but the mechanisms that direct the activity of the V-ATPase remain elusive. We found that in RPE cells, CRYBA1/βA3/A1-crystallin, a lens protein also expressed in RPE, is localized to lysosomes, where it regulates endolysosomal acidification by modulating the V-ATPase, thereby controlling both phagocytosis and autophagy. We demonstrated that CRYBA1 coimmunoprecipitates with the ATP6V0A1/V0-ATPase a1 subunit. Interestingly, in mice when Cryba1 (the gene encoding both the βA3- and βA1-crystallin forms) is knocked out specifically in RPE, V-ATPase activity is decreased and lysosomal pH is elevated, while cathepsin D (CTSD) activity is decreased. Fundus photographs of these Cryba1 conditional knockout (cKO) mice showed scattered lesions by 4 months of age that increased in older mice, with accumulation of lipid-droplets as determined by immunohistochemistry. Transmission electron microscopy (TEM) of cryba1 cKO mice revealed vacuole-like structures with partially degraded cellular organelles, undigested photoreceptor outer segments and accumulation of autophagosomes. Further, following autophagy induction both in vivo and in vitro, phospho-AKT and phospho-RPTOR/Raptor decrease, while pMTOR increases in RPE cells, inhibiting autophagy and AKT-MTORC1 signaling. Impaired lysosomal clearance in the RPE of the cryba1 cKO mice also resulted in abnormalities in retinal function that increased with age, as demonstrated by electroretinography. Our findings suggest that loss of CRYBA1 causes lysosomal dysregulation leading to the impairment of both autophagy and phagocytosis.

Nrf2 is a Critical Modulator of the Innate Immune Response in a Model of Uveitis

Uveitis is an inflammatory condition that can lead to blindness. It is therefore important to understand the pathophysiology against which to develop targeted therapy. Herein, we tested whether the oxidant-responsive transcription factor Nrf2 is involved in regulating the innate immune response and oxidative damage in the LPS uveitis model. As shown by dihydroethidium staining, intraperitoneally injected LPS increased reactive oxygen species in the retina and iris-ciliary body of Nrf2+/+ and Nrf2-/- mice. After LPS injection, ICAM-1, IL-6, TNF-alpha, COX-2, iNOS, and MCP-1 mRNAs were increased more in the retina and iris-ciliary body of Nrf2-/- than in those of Nrf2+/+ mice. NQO-1 and GCLM, two Nrf2-responsive antioxidant enzymes, had reduced expression in Nrf2+/+ retinas after LPS injection, but no change in expression in Nrf2-/- mice. The number of FITC-Con A-labeled leukocytes adherent to the retinal vascular endothelium increased after LPS treatment in both Nrf2+/+ and Nrf2-/- mice compared to control injections, with more adherent leukocytes in Nrf2-/- than in Nrf2+/+ mice. Pretreatment with the Nrf2 activator 1-(2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl)imidazole increased antioxidant gene expression in the retina, reduced inflammatory mediator expression, and reduced leukocyte adherence to retinal vasculature after LPS treatment in Nrf2+/+ mice, but had no effect on Nrf2-/- mice. Treatment targeting the Nrf2 pathway may be a new therapy for uveitis.

Decreased Membrane Complement Regulators in the RPE Contributes to AMD

Dysregulated complement is thought to play a central role in age‐related macular degeneration (AMD) pathogenesis, but the specific mechanisms have yet to be determined. In maculae of AMD specimens, we found that the complement regulatory protein, CD59, was increased in regions of uninvolved retinal pigmented epithelium (RPE) of early AMD, but decreased in the RPE overlying drusen and in geographic atrophy, an advanced form of AMD. While CD46 immunostaining was basolaterally distributed in the RPE of unaffected controls, it was decreased in diseased areas of early AMD samples. Since oxidized low‐density lipoproteins (oxLDL) collect in drusen of AMD and are a known complement trigger, we treated ARPE‐19 cells with oxLDL and found that cellular CD46 and CD59 proteins were decreased by 2.9‐ and nine‐fold (p < 0.01), respectively. OxLDLs increased complement factor B mRNA and Bb protein, but not factor D, I or H. OxLDLs increased C3b, but not C3a, C5 or C5b‐9. C5b‐9 was increased by 27% (p < 0.01) when the medium was supplemented with human serum, which was sufficient to induce poly(ADP‐ribose) polymerase cleavage, a marker of apoptosis. The decreased levels of CD46 and CD59 were in part explained by their release in exosomal and apoptotic membranous particles. In addition, CD59 was partially degraded through activation of IRE1α. Collectively, these results suggest that a combination of impaired complement regulators results in inadequately controlled complement by the RPE in AMD that induces RPE damage. Copyright

A potential role for β- and γ-crystallins in the vascular remodeling of the eye

We demonstrate that expression of β‐ and γ‐crystallins is associated with intraocular vessels during normal vascular development of the eye and also in the Nuc1 rat, a mutant in which the hyaloid vascular system fails to regress normally. Real‐Time RT PCR, Western blot and metabolic labeling studies indicate an increased expression of β‐ and γ‐crystallins in Nuc1 retina. The increased expression of crystallins was localized to the astrocytes surrounding the intraocular vessels. A similar pattern of crystallin expression was also observed in the retinal vessels during normal development. Cultured human astrocytes exposed to 3‐nitropropionic acid, an established model of neuronal hypoxia, increased VEGF expression, as expected, but also increased expression of crystallins. Our data suggest that crystallins may function together with VEGF during vascular remodeling. Interestingly, in human PFV (persistent fetal vasculature) disease, where the hyaloid vasculature abnormally persists after birth, we show that astrocytes express both VEGF and crystallins. Developmental Dynamics 234:36–47, 2005.

Nrf2 signaling is impaired in the aging RPE given an oxidative insult.

Age-related macular degeneration (AMD) represents the leading cause of blindness in the elderly, yet no definitive therapy exists for early, dry disease. Several lines of evidence have implicated oxidative stress-induced damage to the retinal pigment epithelium (RPE) in the pathogenesis of AMD, suggesting that the aging RPE may exhibit increased susceptibility to cell damage induced by exogenous stressors. The transcription factor Nrf2 serves as the master regulator of a highly coordinated antioxidant response in virtually all cell types. We compared Nrf2 signaling in the RPE of young (2 months) and old (15 months) mice under unstressed and stressed (sodium iodate) conditions. The aging RPE expressed higher levels of the Nrf2 target genes NQO1, GCLM, and HO1 compared with the RPE of younger mice under unstressed conditions, suggesting an age-related increase in basal oxidative stress. Moreover, the RPE of older mice demonstrated impaired induction of the protective Nrf2 pathway following oxidative stress induced with sodium iodate. The RPE of old mice exposed to sodium iodate also exhibited higher levels of superoxide anion and malondialdehyde than young mice, suggesting inadequate protection against oxidative damage. Induction of Nrf2 signaling in response to sodium iodate was partially restored in the RPE of aging mice with genetic rescue, using conditional knockdown of the Nrf2 negative regulator Keap1 (Tam-Cre; Keap1loxP) compared to Keap1loxP mice. These data indicate that the aging RPE is vulnerable to oxidative damage due to impaired Nrf2 signaling, and that Nrf2 signaling is a promising target for novel pharmacologic or genetic therapeutic strategies.

Oxidative Stress Induces Mitochondrial Dysfunction and a Protective Unfolded Protein Response in RPE cells

How cells degenerate from oxidative stress in aging-related disease is incompletely understood. This studys intent was to identify key cytoprotective pathways activated by oxidative stress and determine the extent of their protection. Using an unbiased strategy with microarray analysis, we found that retinal pigmented epithelial (RPE) cells treated with cigarette smoke extract (CSE) had overrepresented genes involved in the antioxidant and unfolded protein response (UPR). Differentially expressed antioxidant genes were predominantly located in the cytoplasm, with no induction of genes that neutralize superoxide and H2O2 in the mitochondria, resulting in accumulation of superoxide and decreased ATP production. Simultaneously, CSE induced the UPR sensors IRE1α, p-PERK, and ATP6, including CHOP, which was cytoprotective because CHOP knockdown decreased cell viability. In mice given intravitreal CSE, the RPE had increased IRE1α and decreased ATP and developed epithelial-mesenchymal transition, as suggested by decreased LRAT abundance, altered ZO-1 immunolabeling, and dysmorphic cell shape. Mildly degenerated RPE from early age-related macular degeneration (AMD) samples had prominent IRE1α, but minimal mitochondrial TOM20 immunolabeling. Although oxidative stress is thought to induce an antioxidant response with cooperation between the mitochondria and the ER, herein we show that mitochondria become impaired sufficiently to induce epithelial-mesenchymal transition despite a protective UPR. With similar responses in early AMD samples, these results suggest that mitochondria are vulnerable to oxidative stress despite a protective UPR during the early phases of aging-related disease.

p62 provides dual cytoprotection against oxidative stress in the retinal pigment epithelium.

As a signaling hub, p62/sequestosome plays important roles in cell signaling and degradation of misfolded proteins. p62 has been implicated as an adaptor protein to mediate autophagic clearance of insoluble protein aggregates in age-related diseases, including age-related macular degeneration (AMD), which is characterized by dysfunction of the retinal pigment epithelium (RPE). Our previous studies have shown that cigarette smoke (CS) induces oxidative stress and inhibits the proteasome pathway in cultured human RPE cells, suggesting that p62-mediated autophagy may become the major route to remove impaired proteins under such circumstances. In the present studies, we found that all p62 mRNA variants are abundantly expressed and upregulated by CS induced stress in cultured human RPE cells, yet isoform1 is the major translated form. We also show that p62 silencing exacerbated the CS induced accumulation of damaged proteins, both by suppressing autophagy and by inhibiting the Nrf2 antioxidant response, which in turn, increased protein oxidation. These effects of CS and p62 reduction were further confirmed in mice exposed to CS. We found that over-expression of p62 isoform1, but not its S403A mutant, which lacks affinity for ubiquitinated proteins, reduced misfolded proteins, yet simultaneously promoted an Nrf2-mediated antioxidant response. Thus, p62 provides dual, reciprocal enhancing protection to RPE cells from environmental stress induced protein misfolding and aggregation, by facilitating autophagy and the Nrf2 mediated antioxidant response, which might be a potential therapeutic target against AMD.