Retinal pigment epithelial (RPE) cell dysfunction plays a central role in various retinal degenerative diseases, but knowledge is limited regarding the pathways responsible for adult RPE stress responses in vivo. RPE mitochondrial dysfunction has been implicated in the pathogenesis of several forms of retinal degeneration. Here we have shown that postnatal ablation of RPE mitochondrial oxidative phosphorylation in mice triggers gradual epithelium dedifferentiation, typified by reduction of RPE-characteristic proteins and cellular hypertrophy. The electrical response of the retina to light decreased and photoreceptors eventually degenerated. Abnormal RPE cell behavior was associated with increased glycolysis and activation of, and dependence upon, the hepatocyte growth factor/met proto-oncogene pathway. RPE dedifferentiation and hypertrophy arose through stimulation of the AKT/mammalian target of rapamycin (AKT/mTOR) pathway. Administration of an oxidant to wild-type mice also caused RPE dedifferentiation and mTOR activation. Importantly, treatment with the mTOR inhibitor rapamycin blunted key aspects of dedifferentiation and preserved photoreceptor function for both insults. These results reveal an in vivo response of the mature RPE to diverse stressors that prolongs RPE cell survival at the expense of epithelial attributes and photoreceptor function. Our findings provide a rationale for mTOR pathway inhibition as a therapeutic strategy for retinal degenerative diseases involving RPE stress.
Chen Zhao, Douglas Yasumura, Xiyan Li, Michael Matthes, Marcia Lloyd, Gregory Nielsen, Kelly Ahern, Michael Snyder, Dean Bok, Joshua L. Dunaief, Matthew M. LaVail, Douglas Vollrath
Usher syndrome is a genetically heterogeneous recessive disease characterized by hearing loss and retinitis pigmentosa (RP). It frequently presents with unexplained, often intrafamilial, variability of the visual phenotype. Although 9 genes have been linked with Usher syndrome, many patients do not have mutations in any of these genes, suggesting that there are still unidentified genes involved in the syndrome. Here, we have determined that mutations in PDZ domain–containing 7 (PDZD7), which encodes a homolog of proteins mutated in Usher syndrome subtype 1C (USH1C) and USH2D, contribute to Usher syndrome. Mutations in PDZD7 were identified only in patients with mutations in other known Usher genes. In a set of sisters, each with a homozygous mutation in USH2A, a frame-shift mutation in PDZD7 was present in the sister with more severe RP and earlier disease onset. Further, heterozygous PDZD7 mutations were present in patients with truncating mutations in USH2A, G protein–coupled receptor 98 (GPR98; also known as USH2C), and an unidentified locus. We validated the human genotypes using zebrafish, and our findings were consistent with digenic inheritance of PDZD7 and GPR98, and with PDZD7 as a retinal disease modifier in patients with USH2A. Pdzd7 knockdown produced an Usher-like phenotype in zebrafish, exacerbated retinal cell death in combination with ush2a or gpr98, and reduced Gpr98 localization in the region of the photoreceptor connecting cilium. Our data challenge the view of Usher syndrome as a traditional Mendelian disorder and support the reclassification of Usher syndrome as an oligogenic disease.
Inga Ebermann, Jennifer B. Phillips, Max C. Liebau, Robert K. Koenekoop, Bernhard Schermer, Irma Lopez, Ellen Schäfer, Anne-Francoise Roux, Claudia Dafinger, Antje Bernd, Eberhart Zrenner, Mireille Claustres, Bernardo Blanco, Gudrun Nürnberg, Peter Nürnberg, Rebecca Ruland, Monte Westerfield, Thomas Benzing, Hanno J. Bolz
During human embryogenesis, neural crest cells migrate to the anterior chamber of the eye and then differentiate into the inner layers of the cornea, the iridocorneal angle, and the anterior portion of the iris. When proper development does not occur, this causes iridocorneal angle dysgenesis and intraocular pressure (IOP) elevation, which ultimately results in developmental glaucoma. Here, we show that heparan sulfate (HS) deficiency in mouse neural crest cells causes anterior chamber dysgenesis, including corneal endothelium defects, corneal stroma hypoplasia, and iridocorneal angle dysgenesis. These dysfunctions are phenotypes of the human developmental glaucoma, Peters anomaly. In the neural crest cells of mice embryos, disruption of the gene encoding exostosin 1 (Ext1), which is an indispensable enzyme for HS synthesis, resulted in disturbed TGF-β2 signaling. This led to reduced phosphorylation of Smad2 and downregulated expression of forkhead box C1 (Foxc1) and paired-like homeodomain transcription factor 2 (Pitx2), transcription factors that have been identified as the causative genes for developmental glaucoma. Furthermore, impaired interactions between HS and TGF-β2 induced developmental glaucoma, which was manifested as an IOP elevation caused by iridocorneal angle dysgenesis. These findings suggest that HS is necessary for neural crest cells to form the anterior chamber via TGF-β2 signaling. Disturbances of HS synthesis might therefore contribute to the pathology of developmental glaucoma.
Keiichiro Iwao, Masaru Inatani, Yoshihiro Matsumoto, Minako Ogata-Iwao, Yuji Takihara, Fumitoshi Irie, Yu Yamaguchi, Satoshi Okinami, Hidenobu Tanihara
Zhenglin Yang, Yali Chen, Concepcion Lillo, Jeremy Chien, Zhengya Yu, Michel Michaelides, Martin Klein, Kim A. Howes, Yang Li, Yuuki Kaminoh, Haoyu Chen, Chao Zhao, Yuhong Chen, Youssef Tawfik Al-Sheikh, Goutam Karan, Denis Corbeil, Pascal Escher, Shin Kamaya, Chunmei Li, Samantha Johnson, Jeanne M. Frederick, Yu Zhao, Changguan Wang, D. Joshua Cameron, Wieland B. Huttner, Daniel F. Schorderet, Frances L. Munier, Anthony T. Moore, David G. Birch, Wolfgang Baehr, David M. Hunt, David S. Williams, Kang Zhang
In several disease states, abnormal growth of blood vessels is associated with local neuronal degeneration. This is particularly true in ocular diseases such as retinal angiomatous proliferation (RAP) and macular telangiectasia (MacTel), in which, despite the absence of large-scale leakage or hemorrhage, abnormal neovascularization (NV) is associated with local neuronal dysfunction. We describe here a retinal phenotype in mice with dysfunctional receptors for VLDL (Vldlr–/– mice) that closely resembles human retinal diseases in which abnormal intra- and subretinal NV is associated with photoreceptor cell death. Such cell death was evidenced by decreased cone and, to a lesser extent, rod opsin expression and abnormal electroretinograms. Cell death in the region of intraretinal vascular abnormalities was associated with an increased presence of markers associated with oxidative stress. Oral antioxidant supplementation protected against photoreceptor degeneration and preserved retinal function, despite the continued presence of abnormal intra- and subretinal vessels. What we believe to be novel, Müller cell–based, virally mediated delivery of neurotrophic compounds specifically to sites of NV was also neuroprotective. These observations demonstrate that neuronal loss secondary to NV can be prevented by the use of simple antioxidant dietary measures or cell-based delivery of neurotrophic factors, even when the underlying vascular phenotype is not altered.
Michael I. Dorrell, Edith Aguilar, Ruth Jacobson, Oscar Yanes, Ray Gariano, John Heckenlively, Eyal Banin, G. Anthony Ramirez, Mehdi Gasmi, Alan Bird, Gary Siuzdak, Martin Friedlander
Increased retinal vasopermeability contributes to diabetic retinopathy, the leading cause of blindness in working-age adults. Despite clinical progress, effective therapy remains a major need. Vasoinhibins, a family of peptides derived from the protein hormone prolactin (and inclusive of the 16-kDa fragment of prolactin), antagonize the proangiogenic effects of VEGF, a primary mediator of retinal vasopermeability. Here, we demonstrate what we believe to be a novel function of vasoinhibins as inhibitors of the increased retinal vasopermeability associated with diabetic retinopathy. Vasoinhibins inhibited VEGF-induced vasopermeability in bovine aortic and rat retinal capillary endothelial cells in vitro. In vivo, vasoinhibins blocked retinal vasopermeability in diabetic rats and in response to intravitreous injection of VEGF or of vitreous from patients with diabetic retinopathy. Inhibition by vasoinhibins was similar to that achieved following immunodepletion of VEGF from human diabetic retinopathy vitreous or blockage of NO synthesis, suggesting that vasoinhibins inhibit VEGF-induced NOS activation. We further showed that vasoinhibins activate protein phosphatase 2A (PP2A), leading to eNOS dephosphorylation at Ser1179 and, thereby, eNOS inactivation. Moreover, intravitreous injection of okadaic acid, a PP2A inhibitor, blocked the vasoinhibin effect on endothelial cell permeability and retinal vasopermeability. These results suggest that vasoinhibins have the potential to be developed as new therapeutic agents to control the excessive retinal vasopermeability observed in diabetic retinopathy and other vasoproliferative retinopathies.
Celina García, Jorge Aranda, Edith Arnold, Stéphanie Thébault, Yazmín Macotela, Fernando López-Casillas, Valentín Mendoza, Hugo Quiroz-Mercado, Hebert Luis Hernández-Montiel, Sue-Hwa Lin, Gonzalo Martínez de la Escalera, Carmen Clapp
Williams-Beuren syndrome (WBS), a neurodevelopmental genetic disorder whose manifestations include visuospatial impairment, provides a unique model to link genetically determined loss of neural cell populations at different levels of the nervous system with neural circuits and visual behavior. Given that several of the genes deleted in WBS are also involved in eye development and the differentiation of retinal layers, we examined the retinal phenotype in WBS patients and its functional relation to global motion perception. We discovered a low-level visual phenotype characterized by decreased retinal thickness, abnormal optic disk concavity, and impaired visual responses in WBS patients compared with age-matched controls by using electrophysiology, confocal and coherence in vivo imaging with cellular resolution, and psychophysics. These mechanisms of impairment are related to the magnocellular pathway, which is involved in the detection of temporal changes in the visual scene. Low-level magnocellular performance did not predict high-level deficits in the integration of motion and 3D information at higher levels, thereby demonstrating independent mechanisms of dysfunction in WBS that will require remediation strategies different from those used in other visuospatial disorders. These findings challenge neurodevelopmental theories that explain cortical deficits based on low-level magnocellular impairment, such as regarding dyslexia.
Miguel Castelo-Branco, Mafalda Mendes, Ana Raquel Sebastião, Aldina Reis, Mário Soares, Jorge Saraiva, Rui Bernardes, Raquel Flores, Luis Pérez-Jurado, Eduardo Silva
Sphingosine 1–phosphate (S1P), a multifunctional lipid mediator that signals via the S1P family of G protein–coupled receptors (S1PR), regulates vascular maturation, permeability, and angiogenesis. In this study, we explored the role of S1P 2 receptor (S1P2R) in normal vascularization and hypoxia-triggered pathological angiogenesis of the mouse retina. S1P2R is strongly induced in ECs during hypoxic stress. When neonatal mice were subjected to ischemia-driven retinopathy, pathologic neovascularization in the vitreous chamber was suppressed in S1p2–/– mice concomitant with reduction in endothelial gaps and inflammatory cell infiltration. In addition, EC patterning and normal revascularization into the avascular zones of the retina were augmented. Reduced expression of the proinflammatory enzyme cyclooxygenase-2 (COX-2) and increased expression of eNOS were observed in the S1p2–/– mouse retina. S1P2R activation in ECs induced COX-2 expression and suppressed the expression of eNOS. These data identify the S1P2R-driven inflammatory process as an important molecular event in pathological retinal angiogenesis. We propose that antagonism of the S1P2R may be a novel therapeutic approach for the prevention and/or treatment of pathologic ocular neovascularization.
Athanasia Skoura, Teresa Sanchez, Kevin Claffey, Suzanne M. Mandala, Richard L. Proia, Timothy Hla
Glaucoma, a progressive optic neuropathy due to retinal ganglion cell (RGC) degeneration, is one of the leading causes of irreversible blindness. Although glaucoma is often associated with elevated intraocular pressure (IOP), IOP elevation is not detected in a significant subset of glaucomas, such as normal tension glaucoma (NTG). Moreover, in some glaucoma patients, significant IOP reduction does not prevent progression of the disease. Thus, understanding IOP-independent mechanisms of RGC loss is important. Here, we show that mice deficient in the glutamate transporters GLAST or EAAC1 demonstrate spontaneous RGC and optic nerve degeneration without elevated IOP. In GLAST-deficient mice, the glutathione level in Müller glia was decreased; administration of glutamate receptor blocker prevented RGC loss. In EAAC1-deficient mice, RGCs were more vulnerable to oxidative stress. These findings suggest that glutamate transporters are necessary both to prevent excitotoxic retinal damage and to synthesize glutathione, a major cellular antioxidant and tripeptide of glutamate, cysteine, and glycine. We believe these mice are the first animal models of NTG that offer a powerful system for investigating mechanisms of neurodegeneration in NTG and developing therapies directed at IOP-independent mechanisms of RGC loss.
Takayuki Harada, Chikako Harada, Kazuaki Nakamura, Hun-Meng A. Quah, Akinori Okumura, Kazuhiko Namekata, Tadashiro Saeki, Makoto Aihara, Hiroshi Yoshida, Akira Mitani, Kohichi Tanaka
Choroideremia (CHM) is an X-linked degeneration of the retinal pigment epithelium (RPE), photoreceptors, and choroid, caused by loss of function of the CHM/REP1 gene. REP1 is involved in lipid modification (prenylation) of Rab GTPases, key regulators of intracellular vesicular transport and organelle dynamics. To study the pathogenesis of CHM and to develop a model for assessing gene therapy, we have created a conditional mouse knockout of the Chm gene. Heterozygous-null females exhibit characteristic hallmarks of CHM: progressive degeneration of the photoreceptors, patchy depigmentation of the RPE, and Rab prenylation defects. Using tamoxifen-inducible and tissue-specific Cre expression in combination with floxed Chm alleles, we show that CHM pathogenesis involves independently triggered degeneration of photoreceptors and the RPE, associated with different subsets of defective Rabs.
Tanya Tolmachova, Ross Anders, Magnus Abrink, Laurence Bugeon, Margaret J. Dallman, Clare E. Futter, José S. Ramalho, Felix Tonagel, Naoyuki Tanimoto, Mathias W. Seeliger, Clare Huxley, Miguel C. Seabra