Retina

Kasaoka M, Ma J, Lashkari K. c-Met modulates RPE migratory response to laser-induced retinal injury. PLoS One 2012;7(7):e40771.Abstract
Retinal laser injuries are often associated with aberrant migration of the retinal pigment epithelium (RPE), which can cause expansion of the scar beyond the confines of the original laser burn. In this study, we devised a novel method of laser-induced injury to the RPE layer in mouse models and began to dissect the mechanisms associated with pathogenesis and progression of laser-induced RPE injury. We have hypothesized that the proto-oncogene receptor, c-Met, is intimately involved with migration of RPE cells, and may be an early responder to injury. Using transgenic mouse models, we show that constitutive activation of c-Met induces more robust RPE migration into the outer retina of laser-injured eyes, while abrogation of the receptor using a cre-lox method reduces these responses. We also demonstrate that retinal laser injury increases expression of both HGF and c-Met, and activation of c-Met after injury is correlated with RPE cell migration. RPE migration may be responsible for clinically significant anatomic changes observed after laser injury. Abrogation of c-Met activity may be a therapeutic target to minimize retinal damage from aberrant RPE cell migration.
Wen X-H, Duda T, Pertzev A, Venkataraman V, Makino CL, Sharma RK. S100B serves as a Ca(2+) sensor for ROS-GC1 guanylate cyclase in cones but not in rods of the murine retina. Cell Physiol Biochem 2012;29(3-4):417-30.Abstract
Rod outer segment membrane guanylate cyclase (ROS-GC1) is a bimodal Ca(2+) signal transduction switch. Lowering [Ca(2+)](i) from 200 to 20 nM progressively turns it "ON" as does raising [Ca(2+)](i) from 500 to 5000 nM. The mode operating at lower [Ca(2+)](i) plays a vital role in phototransduction in both rods and cones. The physiological function of the mode operating at elevated [Ca(2+)](i) is not known. Through comprehensive studies on mice involving gene deletions, biochemistry, immunohistochemistry, electroretinograms and single cell recordings, the present study demonstrates that the Ca(2+)-sensor S100B coexists with and is physiologically linked to ROS-GC1 in cones but not in rods. It up-regulates ROS-GC1 activity with a K(1/2) for Ca(2+) greater than 500 nM and modulates the transmission of neural signals to cone ON-bipolar cells. Furthermore, a possibility is raised that under pathological conditions where [Ca(2+)](i) levels rise to and perhaps even enter the micromolar range, the S100B signaling switch will be turned "ON" causing an explosive production of CNG channel opening and further rise in [Ca(2+)](i) in cone outer segments. The findings define a new cone-specific Ca(2+)-dependent feature of photoreceptors and expand our understanding of the operational principles of phototransduction machinery.
Yonekawa Y, Kim IK. Pseudophakic cystoid macular edema. Curr Opin Ophthalmol 2012;23(1):26-32.Abstract
PURPOSE OF REVIEW: Pseudophakic cystoid macular edema (PCME) is a common cause of visual impairment after cataract surgery. This article systematically reviews and discusses the epidemiology, risk factors, diagnosis, and treatment of PCME, with a focus on advances in the past 1-2 years. RECENT FINDINGS: The incidence of PCME has declined with the advent of modern surgical techniques. Optical coherence tomography (OCT) has become an important adjunct to biomicroscopy and fluorescein angiography. PCME prophylaxis with topical nonsteroidal anti-inflammatory drugs remains unproven because long-term visual outcomes and comparative effectiveness studies are lacking. Chronic, refractory CME remains a therapeutic challenge, but investigational therapies with potential include corticosteroid intravitreal injections and implants, and intravitreal anti-vascular endothelial growth factor treatments. Few studies have assessed surgical options. SUMMARY: There is currently a lack of well designed randomized clinical trials to guide the treatment of PCME.
Trese M, Regatieri CV, Young MJ. Advances in Retinal Tissue Engineering. Materials (Basel) 2012;5(1):108-120.Abstract
Retinal degenerations cause permanent visual loss and affect millions world-wide. Current treatment strategies, such as gene therapy and anti-angiogenic drugs, merely delay disease progression. Research is underway which aims to regenerate the diseased retina by transplanting a variety of cell types, including embryonic stem cells, fetal cells, progenitor cells and induced pluripotent stem cells. Initial retinal transplantation studies injected stem and progenitor cells into the vitreous or subretinal space with the hope that these donor cells would migrate to the site of retinal degeneration, integrate within the host retina and restore functional vision. Despite promising outcomes, these studies showed that the bolus injection technique gave rise to poorly localized tissue grafts. Subsequently, retinal tissue engineers have drawn upon the success of bone, cartilage and vasculature tissue engineering by employing a polymeric tissue engineering approach. This review will describe the evolution of retinal tissue engineering to date, with particular emphasis on the types of polymers that have routinely been used in recent investigations. Further, this review will show that the field of retinal tissue engineering will require new types of materials and fabrication techniques that optimize the survival, differentiation and delivery of retinal transplant cells.
Yanai R, Thanos A, Connor KM. Complement involvement in neovascular ocular diseases. Adv Exp Med Biol 2012;946:161-83.Abstract
Pathological neovascularization (NV) is a hallmark of late stage neovascular age-related macular degeneration (AMD), diabetic retinopathy (DR), and retinopathy of prematurity (ROP). There is accumulating evidence that alterations in inflammatory and immune system pathways that arise from genetic differences, injury, and disease can predispose individuals to retinal neovascular eye diseases. Yet the mechanism of disease progression with respect to the complement system in these maladies is not fully understood. Recent studies have implicated the complement system as an emerging player in the etiology of several retinal diseases. We will summarize herein several of the complement system pathways known to be involved in ocular neovascular pathologies. Current treatment for many neovascular eye diseases focuses on suppression of NV with laser ablation, photodynamic therapy, or anti-VEGF angiogenic inhibitors. However, these treatments do not address the underlying cause of many of these diseases. A clear understanding of the cellular and molecular mechanisms could bring a major shift in our approach to disease treatment and prevention.
Zhang Q, Liu Q, Austin C, Drummond I, Pierce EA. Knockdown of ttc26 disrupts ciliogenesis of the photoreceptor cells and the pronephros in zebrafish. Mol Biol Cell 2012;23(16):3069-78.Abstract
In our effort to understand genetic disorders of the photoreceptor cells of the retina, we have focused on intraflagellar transport in photoreceptor sensory cilia. From previous mouse proteomic data we identified a cilia protein Ttc26, orthologue of dyf-13 in Caenorhabditis elegans, as a target. We localized Ttc26 to the transition zone of photoreceptor and to the transition zone of cilia in cultured murine inner medullary collecting duct 3 (mIMCD3) renal cells. Knockdown of Ttc26 in mIMCD3 cells produced shortened and defective primary cilia, as revealed by immunofluorescence and scanning electron microscopy. To study Ttc26 function in sensory cilia in vivo, we utilized a zebrafish vertebrate model system. Morpholino knockdown of ttc26 in zebrafish embryos caused ciliary defects in the pronephric kidney at 27 h postfertilization and distension/dilation of pronephros at 5 d postfertilization (dpf). In the eyes, the outer segments of photoreceptor cells appeared shortened or absent, whereas cellular lamination appeared normal in retinas at 5 dpf. This suggests that loss of ttc26 function prevents normal ciliogenesis and differentiation in the photoreceptor cells, and that ttc26 is required for normal development and differentiation in retina and pronephros. Our studies support the importance of Ttc26 function in ciliogenesis and suggest that screening for TTC26 mutations in human ciliopathies is justified.
Thanos A, Morizane Y, Murakami Y, Giani A, Mantopoulos D, Kayama M, Roh M, Michaud N, Pawlyk B, Sandberg M, Young LH, Miller JW, Vavvas DG. Evidence for baseline retinal pigment epithelium pathology in the Trp1-Cre mouse. Am J Pathol 2012;180(5):1917-27.Abstract
The increasing popularity of the Cre/loxP recombination system has led to the generation of numerous transgenic mouse lines in which Cre recombinase is expressed under the control of organ- or cell-specific promoters. Alterations in retinal pigment epithelium (RPE), a multifunctional cell monolayer that separates the retinal photoreceptors from the choroid, are prevalent in the pathogenesis of a number of ocular disorders, including age-related macular degeneration. To date, six transgenic mouse lines have been developed that target Cre to the RPE under the control of various gene promoters. However, multiple lines of evidence indicate that high levels of Cre expression can be toxic to mammalian cells. In this study, we report that in the Trp1-Cre mouse, a commonly used transgenic Cre strain for RPE gene function studies, Cre recombinase expression alone leads to RPE dysfunction and concomitant disorganization of RPE layer morphology, large areas of RPE atrophy, retinal photoreceptor dysfunction, and microglial cell activation in the affected areas. The phenotype described herein is similar to previously published reports of conditional gene knockouts that used the Trp1-Cre mouse, suggesting that Cre toxicity alone could account for some of the reported phenotypes and highlighting the importance of the inclusion of Cre-expressing mice as controls in conditional gene targeting studies.
Lucas K, Karamichos D, Mathew R, Zieske JD, Stein-Streilein J. Retinal laser burn-induced neuropathy leads to substance P-dependent loss of ocular immune privilege. J Immunol 2012;189(3):1237-42.Abstract
Inflammation in the eye is tightly regulated by multiple mechanisms that together contribute to ocular immune privilege. Many studies have shown that it is very difficult to abrogate the immune privileged mechanism called anterior chamber-associated immune deviation (ACAID). Previously, we showed that retinal laser burn (RLB) to one eye abrogated immune privilege (ACAID) bilaterally for an extended period of time. In an effort to explain the inflammation in the nonburned eye, we postulated that neuronal signals initiated inflammation in the contralateral eye. In this study, we test the role of substance P, a neuroinflamatory peptide, in RLB-induced loss of ACAID. Histological examination of the retina with and without RLB revealed an increase of the substance P-inducible neurokinin 1 receptor (NK1-R) in the retina of first, the burned eye, and then the contralateral eye. Specific antagonists for NK1-R, given locally with Ag within 24 h, but not 3, 5, or 7 d post-RLB treatment, prevented the bilateral loss of ACAID. Substance P knockout (KO) mice retained their ability to develop ACAID post-RLB. These data support the postulate that substance P transmits early inflammatory signals from the RLB eye to the contralateral eye to induce changes to ocular immune privilege and has a central role in the bilateral loss of ACAID. The possibility is raised that blocking of the substance P pathway with NK1-R antagonists postocular trauma may prevent unwanted and perhaps extended consequences of trauma-induced inflammation in the eye.
Pennock S, Kazlauskas A. Vascular endothelial growth factor A competitively inhibits platelet-derived growth factor (PDGF)-dependent activation of PDGF receptor and subsequent signaling events and cellular responses. Mol Cell Biol 2012;32(10):1955-66.Abstract
Certain platelet-derived growth factor (PDGF) isoforms are associated with proliferative vitreoretinopathy (PVR), a sight-threatening complication that develops in a subset of patients recovering from retinal reattachment surgery. Although these PDGF isoforms are abundant in the vitreous of patients and experimental animals with PVR, they make only a minor contribution to activating PDGF receptor α (PDGFRα) and driving experimental PVR. Rather, growth factors outside of the PDGF family are the primary (and indirect) agonists of PDGFRα. These observations beg the question of why vitreal PDGFs fail to activate PDGFRα. We report here that vitreous contains an inhibitor of PDGF-dependent activation of PDGFRα and that a major portion of this inhibitory activity is due to vascular endothelial cell growth factor A (VEGF-A). Furthermore, recombinant VEGF-A competitively blocks PDGF-dependent binding and activation of PDGFR, signaling events, and cellular responses. These findings unveil a previously unappreciated relationship between distant members of the PDGF/VEGF family that may contribute to pathogenesis of a blinding eye disease.
Makino CL, Wen X-H, Olshevskaya EV, Peshenko IV, Savchenko AB, Dizhoor AM. Enzymatic relay mechanism stimulates cyclic GMP synthesis in rod photoresponse: biochemical and physiological study in guanylyl cyclase activating protein 1 knockout mice. PLoS One 2012;7(10):e47637.Abstract
Regulation of cGMP synthesis by retinal membrane guanylyl cyclase isozymes (RetGC1 and RetGC2) in rod and cone photoreceptors by calcium-sensitive guanylyl cyclase activating proteins (GCAP1 and GCAP2) is one of the key molecular mechanisms affecting the response to light and is involved in congenital retinal diseases. The objective of this study was to identify the physiological sequence of events underlying RetGC activation in vivo, by studying the electrophysiological and biochemical properties of mouse rods in a new genetic model lacking GCAP1. The GCAP1(-/-) retinas expressed normal levels of RetGC isozymes and other phototransduction proteins, with the exception of GCAP2, whose expression was elevated in a compensatory fashion. RetGC activity in GCAP1(-/-) retinas became more sensitive to Ca(2+) and slightly increased. The bright flash response in electroretinogram (ERG) recordings recovered quickly in GCAP1(-/-), as well as in RetGC1(-/-)GCAP1(-/-), and RetGC2(-/-)GCAP1(-/-) hybrid rods, indicating that GCAP2 activates both RetGC isozymes in vivo. Individual GCAP1(-/-) rod responses varied in size and shape, likely reflecting variable endogenous GCAP2 levels between different cells, but single-photon response (SPR) amplitude and time-to-peak were typically increased, while recovery kinetics remained faster than in wild type. Recovery from bright flashes in GCAP1(-/-) was prominently biphasic, because rare, aberrant SPRs producing the slower tail component were magnified. These data provide strong physiological evidence that rod photoresponse recovery is shaped by the sequential recruitment of RetGC isozyme activation by GCAPs according to the different GCAP sensitivities for Ca(2+) and specificities toward RetGC isozymes. GCAP1 is the 'first-response' sensor protein that stimulates RetGC1 early in the response and thus limits the SPR amplitude, followed by activation of GCAP2 that adds stimulation of both RetGC1 and RetGC2 to speed-up photoreceptor recovery.
Sadaka A, Giuliari GP. Proliferative vitreoretinopathy: current and emerging treatments. Clin Ophthalmol 2012;6:1325-33.Abstract
Proliferative vitreoretinopathy is a disease process that follows the proliferation of ectopic cell sheets in the vitreous and/or periretinal area, causing periretinal membrane formation and traction, in patients with rhegmatogenous retinal detachments. Currently, vitreous surgery is the standard treatment; however, the results aren't satisfactory given the vision loss that ensues and that redetachment is relatively common. It is becoming clearer that there exists an interplay between various cytokines/growth factors, matrix proteins, and the different cell types that drive the undesirable formation of periretinal membranes. This fundamental understanding is aiding in identifying different adjunct agents that can block the cellular events intrinsic to proliferative vitreoretinopathy. In this review, we describe the current understanding on the pathogenesis and discuss how the fundamental understanding of the biochemical/molecular events is instrumental in developing the novel treatment strategies that are also highlighted.
Moysidis SN, Thanos A, Vavvas DG. Mechanisms of inflammation in proliferative vitreoretinopathy: from bench to bedside. Mediators Inflamm 2012;2012:815937.Abstract
Proliferative vitreoretinopathy (PVR) is a vision-threatening disease and a common complication of surgery to correct rhegmatogenous retinal detachment (RRD). Several models of the pathogenesis of this disease have been described with some of these models focusing on the role of inflammatory cells and other models focusing on the role of growth factors and cytokines in the vitreous which come into contact with intraretinal and retinal pigment epithelial cells. New experiments have shed light on the pathogenesis of PVR and offer promising avenues for clinical intervention before PVR develops. One such target is the indirect pathway of activation of platelet-derived growth factor receptor alpha (PDGRα), which plays an important role in PVR. Clinical trials assessing the efficacy of 5-fluorouracil (5-FU) and low-molecular-weight heparin (LMWH), daunorubicin, and 13-cis-retinoic acid, among other therapies, have yielded mixed results. Here we review inflammatory and other mechanisms involved in the pathogenesis of PVR, we highlight important clinical trials, and we discuss how findings at the bench have the potential to be translated to the bedside.
Oliveira C, Cestari DM, Rizzo JF. The use of fourth-generation optical coherence tomography in multiple sclerosis: a review. Semin Ophthalmol 2012;27(5-6):187-91.Abstract
Optical coherence tomography (OCT) has been routinely used to obtain high spatial resolution images of the retina and choroid non-invasively. Within the past decade, a fourth-generation OCT device using Fourier domain (FD) analysis has been developed that provides higher velocity and higher axial resolution images with better reproducibility than the previous generation time domain (TD) OCT technology. This review addresses the use of fourth-generation, FD ocular OCT in patients with multiple sclerosis.

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