PURPOSE. The aim of the present study was to identify candidate genes for mediating daily adjustment of vision. METHODS. Genes important for vision and genetically associated with severe retinal diseases were tested for 24-hour rhythms in transcript levels in neuronal retina, microdissected photoreceptors, photoreceptor-related pinealocytes, and retinal pigment epithelium-choroid (RPE-choroid) complex by using quantitative PCR. RESULTS. Photoreceptors of wildtype mice display circadian clock-dependent regulation of visual arrestins (Arr1, Arr4) and the visual cycle gene Rdh12, whereas cells of the RPE-choroid exhibit light-dependent regulation of the visual cycle key genes Lrat, Rpe65, and Rdh5. Clock-driven rhythmicity of Arr1, Arr4, and Rdh12 was observed also in rat pinealocytes, to persist in a mouse model of diabetic retinopathy (db/db) and, in the case of Arr1, to be abolished in retinae of mice deficient for dopamine D4receptors. Therefore, the expression rhythms appear to be evolutionary conserved, to be unaffected in diabetic retinopathy, and, for Arr1, to require dopamine signaling via dopamine D4 receptors. CONCLUSIONS. The data of the present study suggest that daily adjustment of retinal function combines clock-dependent regulation of genes responsible for phototransduction termination (Arr1, Arr4) and detoxification (Rdh12) in photoreceptors with light-dependent regulation of genes responsible for retinoid recycling (Lrat, Rpe65, and Rdh5) in RPE. Furthermore, they indicate circadian and light-dependent regulation of genes genetically associated with severe retinal diseases.
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Shuo Zhang;
Paul Lyuboslavsky;
Jendayi Azeezah Dixon;
Micah A. Chrenek;
Jana T. Sellers;
Jessica M. Hamm;
P Michael Iuvone;
Christophe P. Ribelayga;
Zhijing Zhang;
Yun Z. Le
PURPOSE. The present study tested the hypothesis that connexin-36 (Cx36) and gap junctions between photoreceptor cells contribute to the circadian rhythm of the photopic electroretinogram (ERG) b-wave amplitude. METHODS. Cone-specific disruption of Cx36 was obtained in mice with a floxed Gjd2 gene and human red/green pigment promoter (HRGP)-driven Cre recombinase. Standard ERG, spectral-domain optical coherence tomography (SD-OCT) and histochemical methods were used. RESULTS. HRGPcreGjd2fl/fl mice had a selective reduction in Cx36 protein in the outer plexiform layer; no reduction in Cx36 was observed in the inner plexiform layer. Cx36 disruption had no effect on the number of cones, the thickness of the photoreceptor layer, or the scotopic ERG responses. However, there was a reduction of the photopic ERG circadian rhythm, with b-wave amplitudes in the day and the night locked in the daytime, light-adapted state. In HRGPcreGjd2+/+ and Gjd2fl/fl controls, the circadian rhythm of light-adapted ERG persisted, similar to that in wild type mice. CONCLUSIONS. Cx36 regulation contributes to the circadian rhythm of light-adapted ERG; in the absence of photoreceptor gap junctions, mice appear to be in a fully light-adapted state regardless of the time of day. The higher amplitudes and reduced circadian regulation of the b-wave of HRGPcreGjd2fl/fl mice may be due to increased synaptic strength at the cone to ON bipolar cell synapse due to electrotonic isolation of the terminals lacking gap junctions.
Purpose: Bevacizumab, a humanized monoclonal antibody to vascular endothelial growth factor-A (VEGF-A), was originally developed as an anti-tumor treatment. In ocular oncology, it is being used to treat macular edema due to radiation retinopathy, but it may also be useful for the treatment of primary uveal melanoma (UM) or its metastases. We determined the effect of bevacizumab on the growth of B16F10 cells inside the eye and on B16F10 and UM cells cultured in vitro.
Methods: B16F10 melanoma cells were placed into the anterior chamber of the eye of C57Bl/6 mice and tumor growth was monitored after injection of different doses of bevacizumab or mock injection. In addition, the effect of bevacizumab on in vitro growth of B16F10 and human UM cells and on the expression of VEGF-A, GLUT-1, and HIF-1α was evaluated.
Results: Following intraocular injection of bevacizumab into murine B16 tumor-containing eyes, an acceleration of tumor growth was observed, with the occurrence of anterior chamber hemorrhages. Bevacizumab did not affect proliferation of B16F10 cells in vitro, while it inhibited UM cell proliferation. Expression analysis demonstrated that addition of bevacizumab under hypoxic conditions induced VEGF-A, GLUT-1 and HIF-1α in B16F10 cells as well as in UM cell lines and two of four primary UM tumor cultures.
Conclusions: In contrast with expectations, intraocular injection of bevacizumab stimulated B16F10 melanoma growth in murine eyes. In vitro exposure of B16 and human UM cells to bevacizumab led to paradoxical VEGF-A upregulation. The use of VEGF inhibitors for treatment of macular edema (due to radiation retinopathy) after irradiation of UM should be considered carefully, because of the possible adverse effects on residual UM cells.
Purpose: The purpose of this study is to report a case of microsporidial endophthalmitis after penetrating keratoplasty in a healthy patient and discuss the management.
Methods: This is a case report.
Results: A 69-year-old healthy male underwent penetrating keratoplasty for corneal scar secondary to herpes stromal keratitis. He presented with features of acute graft rejection 3 years later. After failure of medical management, a repeat full thickness keratoplasty was performed. Pathologic examination of the corneal specimen showed microsporidia. The patient then developed a chronic endophthalmitis, and a vitreous tap and injection followed by pars plana vitrectomy were performed. Pathologic examination of tissue showed microsporidia.
Conclusions: Microsporidia are being increasingly identified as the cause of stromal keratitis. This is the first report of microsporidial endophthalmitis in a patient without underlying systemic illness.
We illustrate the growing power of the BXD family of mice (recombinant inbred strains from a cross of C57BL/6J and DBA/2J mice) and companion bioinformatic tools to study complex genome-phenome relations related to glaucoma. Over the past 16 years, our group has integrated powerful murine resources and web-accessible tools to identify networks modulating visual system traits—from photoreceptors to the visual cortex. Recent studies focused on retinal ganglion cells and glaucoma risk factors, including intraocular pressure (IOP), central corneal thickness (CCT), and susceptibility of cellular stress. The BXD family was exploited to define key gene variants and then establish linkage to glaucoma in human cohorts. The power of this experimental approach to precision medicine is highlighted by recent studies that defined cadherin 11 (Cdh11) and a calcium channel (Cacna2d1) as genes modulating IOP, Pou6f2 as a genetic link between CCT and retinal ganglion cell (RGC) death, and Aldh7a1 as a gene that modulates the susceptibility of RGCs to death after elevated IOP. The role of three of these gene variants in glaucoma is discussed, along with the pathways activated in the disease process.
Treatment of many posterior-segment ocular indications would benefit from improved targeting of drug delivery to the back of the eye. Here, we propose the use of iontophoresis to direct delivery of negatively charged nanoparticles through the suprachoroidal space (SCS) toward the posterior pole of the eye. Injection of nanoparticles into the SCS of the rabbit eye ex vivo without iontophoresis led to a nanoparticle distribution mostly localized at the site of injection near the limbus and <15% of nanoparticles delivered to the most posterior region of SCS (>9 mm from the limbus). Iontophoresis using a novel microneedle-based device increased posterior targeting with >30% of nanoparticles in the most posterior region of SCS. Posterior targeting increased with increasing iontophoresis current and increasing application time up to 3 min, but further increasing to 5 min was not better, probably due to the observed collapse of the SCS within 5 min after injection ex vivo. Reversing the direction of iontophoretic flow inhibited posterior targeting, with just ~5% of nanoparticles reaching the most posterior region of SCS. In the rabbit eye in vivo, iontophoresis at 0.14 mA for 3 min after injection of a 100 μL suspension of nanoparticles resulted in ~30% of nanoparticles delivered to the most posterior region of the SCS, which was consistent with ex vivo findings. The procedure was well tolerated, with only mild, transient tissue effects at the site of injection. We conclude that iontophoresis in the SCS using a microneedle has promise as a method to target ocular drug delivery within the eye, especially toward the posterior pole.
Ocular fundus examination is a critical part of the physical examination in patients with severely elevated blood pressure (BP), which is defined by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC7) as a BP exceeding 180/120 mm Hg. Indeed, the presence or absence of severe, grade III/IV hypertensive retinopathy helps differentiate hypertensive emergencies requiring intensive care from less severe hypertensive urgencies. As a secondary analysis in the Fundus photography versus Ophthalmoscopy Trial Outcomes in the Emergency Department (FOTO-ED) study, we sought to explore potential risk factors, in particular BP, for the presence of ocular fundus abnormalities relevant to the care of emergency department (ED) patients. We found evidence of acute end-organ ocular damage at lower blood pressures than the JNC7 criteria.
Diseases that affect the eye, including photoreceptor degeneration, diabetic retinopathy, and glaucoma, affect 11.8 million people in the US, resulting in vision loss and blindness. Loss of sight affects patient quality of life and puts an economic burden both on individuals and the greater healthcare system. Despite the urgent need for treatments, few effective options currently exist in the clinic. Here, we review research on promising neuroprotective strategies that promote neuronal survival with the potential to protect against vision loss and retinal cell death. Due to the large number of neuroprotective strategies, we restricted our review to approaches that we had direct experience with in the laboratory. We focus on drugs that target survival pathways, including bile acids like UDCA and TUDCA, steroid hormones like progesterone, therapies that target retinal dopamine, and neurotrophic factors. In addition, we review rehabilitative methods that increase endogenous repair mechanisms, including exercise and electrical stimulation therapies. For each approach, we provide background on the neuroprotective strategy, including history of use in other diseases; describe potential mechanisms of action; review the body of research performed in the retina thus far, both in animals and in humans; and discuss considerations when translating each treatment to the clinic and to the retina, including which therapies show the most promise for each retinal disease. Despite the high incidence of retinal diseases and the complexity of mechanisms involved, several promising neuroprotective treatments provide hope to prevent blindness. We discuss attractive candidates here with the goal of furthering retinal research in critical areas to rapidly translate neuroprotective strategies into the clinic.
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Minh-Thanh T. Nguyen;
Shruti Vemaraju;
Gowri Nayak;
Yoshinobu Odaka;
Ethan D. Buhr;
Nuria Alonzo;
Uyen Tran;
Mathew Batie;
Brian A. Upton;
Martin Darvas;
Zbynek Kozmik;
Sujata Rao;
Rashmi S. Hegde;
P Michael Iuvone;
Russell N. Van Gelder;
Richard A. Lang
During mouse postnatal eye development, the embryonic hyaloid vascular network regresses from the vitreous as an adaption for high-acuity vision. This process occurs with precisely controlled timing. Here, we show that opsin 5 (OPN5; also known as neuropsin)-dependent retinal light responses regulate vascular development in the postnatal eye. In Opn5-null mice, hyaloid vessels regress precociously. We demonstrate that 380-nm light stimulation via OPN5 and VGAT (the vesicular GABA/glycine transporter) in retinal ganglion cells enhances the activity of inner retinal DAT (also known as SLC6A3; a dopamine reuptake transporter) and thus suppresses vitreal dopamine. In turn, dopamine acts directly on hyaloid vascular endothelial cells to suppress the activity of vascular endothelial growth factor receptor 2 (VEGFR2) and promote hyaloid vessel regression. With OPN5 loss of function, the vitreous dopamine level is elevated and results in premature hyaloid regression. These investigations identify violet light as a developmental timing cue that, via an OPN5–dopamine pathway, regulates optic axis clearance in preparation for visual function.
Purpose: Despite extensive research, mechanisms regulating postnatal eye growth and those responsible for ametropias are poorly understood. With the marked recent increases in myopia prevalence, robust and biologically-based clinical therapies to normalize refractive development in childhood are needed. Here, we review classic and contemporary literature about how circadian biology might provide clues to develop a framework to improve the understanding of myopia etiology, and possibly lead to rational approaches to ameliorate refractive errors developing in children.
Recent findings: Increasing evidence implicates diurnal and circadian rhythms in eye growth and refractive error development. In both humans and animals, ocular length and other anatomical and physiological features of the eye undergo diurnal oscillations. Systemically, such rhythms are primarily generated by the ‘master clock’ in the surpachiasmatic nucleus, which receives input from the intrinsically photosensitive retinal ganglion cells (ipRGCs) through the activation of the photopigment melanopsin. The retina also has an endogenous circadian clock. In laboratory animals developing experimental myopia, oscillations of ocular parameters are perturbed. Retinal signaling is now believed to influence refractive development; dopamine, an important neurotransmitter found in the retina, not only entrains intrinsic retinal rhythms to the light:dark cycle, but it also modulates refractive development. Circadian clocks comprise a transcription/translation feedback control mechanism utilizing so-called clock genes that have now been associated with experimental ametropias. Contemporary clinical research is also reviving ideas first proposed in the nineteenth century that light exposures might impact refraction in children. As a result, properties of ambient lighting are being investigated in refractive development. In other areas of medical science, circadian dysregulation is now thought to impact many non-ocular disorders, likely because the patterns of modern artificial lighting exert adverse physiological effects on circadian pacemakers. How, or if, such modern light exposures and circadian dysregulation contribute to refractive development is not known.
Summary: The premise of this review is that circadian biology could be a productive area worthy of increased investigation, which might lead to the improved understanding of refractive development and improved therapeutic interventions.