A patch-clamp investigation of membrane currents in a novel mammalian retinal ganglion cell line

Light-Induced Retinal Ganglion Cell Damage and the Relevant Mechanisms

While light is the basic element for inducing vision and modulating circadian rhythms, excessive light has been reported to have a negative effect on the survival of various types of retinal cells. Among them photoreceptors and retinal pigment epithelial (RPE) cells degeneration after light exposure is widely observed, but light-induced retinal ganglion cell (RGC) damage achieves relatively little attention. The purpose of this article is to summarize the experimental evidence for the possible negative effects of excessive light on RGCs. By searching the database, twenty-six related articles have been included. Taken together, excessive light may insult RGCs through the three main ways: (i) directly action on RGC mitochondria, as well as DNA, resulting in an upregulation of reactive oxygen species (ROS) and subsequently caspase-dependent or -independent cell death; (ii) mediation in gliotransmitters or relevant receptors of retinal glial cells; and (iii) a secondary event to photoreceptors and RPE cells degeneration and subsequent retinal remodeling. So RGCs can certainly be injured by excessive light, especially when they are already energetically compromised in some diseases. And more attentions should be paid to this topic to take timely measures to protect these frail RGCs from being damaged by excessive light.

Modeling the Mechanical Parameters of Glaucoma

Glaucoma is a major eye disease characterized by a progressive loss of retinal ganglion cells (RGCs). Biomechanical forces as a result of hydrostatic pressure and strain play a role in this disease. Decreasing intraocular pressure is the only available therapy so far, but is not always effective and does not prevent blindness in many cases. There is a need for drugs that protect RGCs from dying in glaucoma; to develop these, we need valid glaucoma and drug screening models. Since in vivo models are unsuitable for screening purposes, we focus on in vitro and ex vivo models in this review. Many groups have studied pressure and strain model systems to mimic glaucoma, to investigate the molecular and cellular events leading to mechanically induced RGC death. Therefore, the focus of this review is on the different mechanical model systems used to mimic the biomechanical forces in glaucoma. Most models use either cell or tissue strain, or fluid- or gas-controlled hydrostatic pressure application and apply it to the relevant cell types such as trabecular meshwork cells, optic nerve head astrocytes, and RGCs, but also to entire eyes. New model systems are warranted to study concepts and test experimental compounds for the development of new drugs to protect vision in glaucoma patients. Impact Statement The outcome of currently developed models to investigate mechanically induced retinal ganglion cell death by applying different mechanical strains varies widely. This suggests that a robust glaucoma model has not been developed yet. However, a comprehensive overview of current developments is not available. In this review, we have therefore assessed what has been done before and summarized the available knowledge in the field, which can be used to develop improved models for glaucoma research.

Dietary Antioxidants, Macular Pigment, and Glaucomatous Neurodegeneration: A Review of the Evidence

Primary open-angle glaucoma (POAG) is a leading cause of irreversible blindness worldwide, and the prevalence is projected to increase to 112 million worldwide by 2040. Intraocular pressure is currently the only proven modifiable risk factor to treat POAG, but recent evidence suggests a link between antioxidant levels and risk for prevalent glaucoma. Studies have found that antioxidant levels are lower in the serum and aqueous humor of glaucoma patients. In this review, we provide a brief overview of the evidence linking oxidative stress to glaucomatous pathology, followed by an in-depth discussion of epidemiological studies and clinical trials of antioxidant consumption and glaucomatous visual field loss. Lastly, we highlight a possible role for antioxidant carotenoids lutein and zeaxanthin, which accumulate in the retina to form macular pigment, as evidence has emerged supporting an association between macular pigment levels and age-related eye disease, including glaucoma. We conclude that the evidence base is inconsistent in showing causal links between dietary antioxidants and glaucoma risk, and that prospective studies are needed to further investigate the possible relationship between macular pigment levels and glaucoma risk specifically.

Early changes in staurosporine-induced differentiated RGC-5 cells indicate cellular injury response to nonlethal blue light exposure

PURPOSE

Blue light has been previously demonstrated to induce injury of retinal cells. The cellular responses to nonlethal blue light exposure for each type of retinal cell are of particular interest but remain undetermined. Based on the doses of blue light reported in previous research to be nonlethal to retinal pigment epithelial cells, here we investigated whether and to what extent such doses of blue light are cytotoxic to staurosporine-differentiated RGC-5 cells.

METHODS

RGC-5 cells were differentiated for 24 hours using 200 nM staurosporine. The resulting cells were cultured and exposed to blue light at three different energy levels (1, 10, and 50 J cm(-2)). Cellular morphologies were investigated with an inverted microscope and cell viability was assessed with a Cell Counting Kit-8 (CCK-8) assay. The generation of intracellular reactive oxygen species (ROS) was evaluated by H2DCFDA. After loading of MitoTracker Green FM dye, the mitochondrial contents were analyzed using flow cytometry. The lactate dehydrogenase (LDH) activities in the media were also measured. The level of lipid peroxidation was determined by measuring the amount of malondialdehyde (MDA).

RESULTS

Treatment of the cells for 24 hours with 200 nM staurosporine successfully induced the differentiation of RGC-5 cells. No morphological changes were observed in the ssdRGC-5 cells exposed to blue light at 50 J cm(-2), which was the highest energy level tested. Exposure of the ssdRGC-5 cells to this energy level of blue light did, however, decrease their numbers by approximately 72.1% compared to the numbers of such cells found after being left in the dark. Remarkably, the levels of ROS generation and mitochondrial contents were, respectively, increased to 142% and 118% of those of the control by a 10 J cm(-2) exposure of blue light. The LDH activities and MDA levels exhibited no obvious changes in the blue light-exposed ssdRGC-5 cells compared to the control cells.

CONCLUSIONS

In vitro nonlethal blue light exposure led to cellular damage of staurosporine-differentiated RGC-5 cells. These increases in oxidative stress and mitochondrial content were the early steps of the cellular response to the exposure of relatively low doses (10 J cm(-2)) of blue light.

Growth hormone and retinal ganglion cell function: QNR/D cells as an experimental model

Retinal ganglion cells (RGCs) have been shown to be sites of growth hormone (GH) production and GH action in the embryonic (embryo day 7, ED7) chick neural retina. Primary RGC cell cultures were previously used to determine autocrine or paracrine actions of GH in the retina, but the antibody used in their immunopanning (anti-Thy-1) is no longer available. We have therefore characterized an immortalized neural retina (QNR/D) cell line derived from ED7 embryonic quail as a replacement experimental model. These cells express the GH gene and have GH receptor (GHR)-immunoreactivity. They are also immunoreactive for RGC markers (islet-1, calretinin, RA4) and neural fibers (neurofilament, GAP 43, vimentin) and they express the genes for Thy-1, neurotrophin 3 (NTF3), neuritin 1 (NRN1) and brn3 (POU4F). These cells are also electrically active and therefore resemble the RGCs in the neural retina. They are also similarly responsive to exogenous GH, which induces overexpression of the neurotrophin 3 and insulin-like growth factor (IGF) 1 genes and stimulates cell survival, as in the chick embryo neural retina. QNR/D cells are therefore a useful experimental model to assess the actions of GH in retinal function.

Impedance-based cell culture platform to assess light-induced stress changes with antagonist drugs using retinal cells

This Article describes an unprecedented, simple, and real-time in vitro analytical tool to measure the luminous effect on the time responses function of retinal ganglion cells (RGC-5) by electric cell substrate impedance sensing (ECIS) system. The ECIS system was used for the continuous measurement of different color light-induced effects on the response of cells that exposed to protective drugs. The measurement suggests that the association of photo-oxidative stress was mediated by reactive oxygen species (ROS), which plays a critical role that leads to cell stress, damages, and retinopathy, resulting in eye degenerative diseases. Continuous light radiation caused time-dependent decline of RGC-5 response and resulted in photodamage within 10 h due to adenosine 5'-triphosphate depletion and increased ROS level, which is similar to in vivo photodamage. The ECIS results were correlated with standard cell viability assay. ECIS is very helpful to determine the protective effects of analyzed drugs such as β-carotene, quercetin, agmatine, and glutathione in RGC-5 cells, and the maximum drug activity of nontoxic safer drug concentrations was found to be 0.25, 0.25, 0.25, and 1.0 mM, respectively. All drugs show protection against light radiation toxicity in a dose-dependent manner; the most effective drug was found to be glutathione. The proposed system identifies the phototoxic effects in RGC-5 and provides high throughput drug screening for photo-oxidative stress during early stages of drug discovery. This study is convenient and potential enough for the direct measurements of the photoprotective effect in vitro and would be of broad interest in the field of therapeutics.

Classification of potassium and chlorine ionic currents in retinal ganglion cell line (RGC-5) by whole-cell patch clamp

Retinal ganglion cell line (RGC-5) has been widely used as a valuable model for studying pathophysiology and physiology of retinal ganglion cells in vitro. However, the electrophysiological characteristics, especially a thorough classification of ionic currents in the cell line, remain to be elucidated in details. In the present study, we determined the resting membrane potential (RMP) in RGC-5 cell line and then identified different types of ionic currents by using the whole-cell patch-clamp technique. The RMP recorded in the cell line was between −30 and −6 mV (−17.6 ± 2.6 mV, n = 10). We observed the following voltage-gated ion channel currents: (1) inwardly rectifying Cl− current (ICl,ir), which could be blocked by Zn2+; (2) Ca2+-activated Cl− current (ICl,Ca), which was sensitive to extracellular Ca2+ and could be inhibited by disodium 4,4’-diisothiocyanatostilbene-2,2’-disulfonate; (3) inwardly rectifying K+ currents (IK1), which could be blocked by Ba2+; (4) a small amount of delayed rectifier K+ current (IK). On the other hand, the voltage-gated sodium channels current (INa) and transient outward potassium channels current (IA) were not observed in this cell line. These results further characterize the ionic currents in the RGC-5 cell line and are beneficial for future studies especially on ion channel (patho)physiology and pharmacology in the RGC-5 cell line.

Expression of novel opsins and intrinsic light responses in the mammalian retinal ganglion cell line RGC-5. Presence of OPN5 in the rat retina

The vertebrate retina is known to contain three classes of photoreceptor cells: cones and rods responsible for vision, and intrinsically photoresponsive retinal ganglion cells (RGCs) involved in diverse non-visual functions such as photic entrainment of daily rhythms and pupillary light responses. In this paper we investigated the potential intrinsic photoresponsiveness of the rat RGC line, RGC-5, by testing for the presence of visual and non-visual opsins and assessing expression of the immediate-early gene protein c-Fos and changes in intracellular Ca²⁺mobilization in response to brief light pulses. Cultured RGC-5 cells express a number of photopigment mRNAs such as retinal G protein coupled receptor (RGR), encephalopsin/panopsin (Opn3), neuropsin (Opn5) and cone opsin (Opn1mw) but not melanopsin (Opn4) or rhodopsin. Opn5 immunoreactivity was observed in RGC-5 cells and in the inner retina of rat, mainly localized in the ganglion cell layer (GCL). Furthermore, white light pulses of different intensities and durations elicited changes both in intracellular Ca²⁺ levels and in the induction of c-Fos protein in RGC-5 cell cultures. The results demonstrate that RGC-5 cells expressing diverse putative functional photopigments display intrinsic photosensitivity which accounts for the photic induction of c-Fos protein and changes in intracellular Ca²⁺ mobilization. The presence of Opn5 in the GCL of the rat retina suggests the existence of a novel type of photoreceptor cell.

Real-Time dynamics of Ca2+, caspase-3/7, and morphological changes in retinal ganglion cell apoptosis under elevated pressure

Quantitative information on the dynamics of multiple molecular processes in individual live cells under controlled stress is central to the understanding of the cell behavior of interest and the establishment of reliable models. Here, the dynamics of the apoptosis regulator intracellular Ca(2+), apoptosis effector caspase-3/7, and morphological changes, as well as temporal correlation between them at the single cell level, are examined in retinal gangling cell line (differentiated RGC-5 cells) undergoing apoptosis at elevated hydrostatic pressure using a custom-designed imaging platform that allows long-term real-time simultaneous imaging of morphological and molecular-level physiological changes in large numbers of live cells (beyond the field-of-view of typical microscopy) under controlled hydrostatic pressure. This examination revealed intracellular Ca(2+) elevation with transient single or multiple peaks of less than 0.5 hour duration appearing at the early stages (typically less than 5 hours after the onset of 100 mmHg pressure) followed by gradual caspase-3/7 activation at late stages (typically later than 5 hours). The data reveal a strong temporal correlation between the Ca(2+) peak occurrence and morphological changes of neurite retraction and cell body shrinkage. This suggests that Ca(2+) elevation, through its impact on ion channel activity and water efflux, is likely responsible for the onset of apoptotic morphological changes. Moreover, the data show a significant cell-to-cell variation in the onset of caspase-3/7 activation, an inevitable consequence of the stochastic nature of the underlying biochemical reactions not captured by conventional assays based on population-averaged cellular responses. This real-time imaging study provides, for the first time, statistically significant data on simultaneous multiple molecular level changes to enable refinements and testing of models of the dynamics of mitochondria-mediated apoptosis. Further, the platform developed and the approach has direct significance to the study of a variety of signaling pathway phenomena.

Lutein protects RGC-5 cells against hypoxia and oxidative stress

Retinal ischemia and oxidative stress lead to neuronal death in many ocular pathologies. Recently, we found that lutein, an oxy-carotenoid, protected the inner retina from ischemia/reperfusion injury. However, it is uncertain whether lutein directly protects retinal ganglion cells (RGCs). Here, an in vitro model of hypoxia and oxidative stress was used to further investigate the neuroprotective role of lutein in RGCs. Cobalt chloride (CoCl₂) and hydrogen peroxide (H₂O₂) were added to a transformed RGC cell line, RGC-5, to induce chemical hypoxia and oxidative stress, respectively. Either lutein or vehicle was added to cultured cells. A higher cell count was observed in the lutein-treated cells compared with the vehicle-treated cells. Our data from this in vitro model revealed that lutein might protect RGC-5 cells from damage when exposed to either CoCl₂-induced chemical hypoxia or H₂O₂-induced oxidative stress. These results suggest that lutein may play a role as a neuroprotectant.

Retinal ganglion cell line apoptosis induced by hydrostatic pressure

Cellular responses to changes in pressure are implicated in numerous disease processes. In glaucoma apoptosis of retinal ganglion cells (RGCs) is associated with elevated intra-ocular pressure, however, the exact cellular mechanisms remain unclear. We have previously shown that pressure can induce apoptosis in B35 and PC12 neuronal cell lines, using an in vitro model for pressure elevation. A novel RGC line allows us to study the effects of pressure on retinal neurons. 'RGC-5' cultures were subjected to elevated ambient hydrostatic pressure conditions in our model. Experimental pressure conditions were 100 mm Hg and 30 mm Hg, representing acute (high) and chronic (lower-pressure) glaucoma, and 15 mm Hg for normal intra-ocular pressure, set above atmospheric pressure for 2 h. Negative controls were treated identically except for the application of pressure, while positive controls were generated by treatment with a known apoptotic stimulus. Apoptosis was determined by a combination of cell morphology and specific TUNEL and Annexin V fluorescent markers. These were assessed simultaneously by laser scanning cytometry (LSC), which also enabled quantitative marker analysis. RGC-5 neurons showed a significantly increased proportion of apoptotic cells compared with controls; maximal at 100 mm Hg, moderate at 30 mm Hg and not statistically significant at 15 mm Hg. This graded response, proportionate to the level of pressure elevation, is representative of the severity of analogous clinical settings (acute, chronic glaucoma and normal). These results complement earlier findings of pressure-induced apoptosis in other neuronal cultures. They suggest the possibility of novel mechanisms of pressure-related mechanotransduction and cell death, relevant to the pathogenesis of diseases such as glaucoma.

Retinal ganglion cell death and neuroprotection: Involvement of the CaMKIIα gene

The purpose of this study is to determine if calcium/calmodulin-dependent protein kinase-II (CaMKII) plays a role in neuronal cell death and if inhibition of this kinase affords some neuroprotection in the RGC-5 retinal ganglion cell line. The RGC-5 cells were treated with glutamate at various concentrations for increasing increments of time. Cytotoxicity was assayed by measuring the lactate dehydrogenase (LDH) leakage from non-viable cells and TUNEL assays. The involvement of caspase-3, Bcl-2 and caspase-8 in glutamate-induced cytotoxicity was determined by immunoblots and/or real time RT-PCR. In addition, the autocamtide-2-related inhibitory peptide (AIP), a specific inhibitor of CaMKII, was used to determine the involvement of CaMKII in glutamate-induced RGC-5 cell death. Application of increasing concentrations of glutamate to RGC-5 cells caused a dose-dependent increase in the level of cell death after 24 h. There was a glutamate-stimulated increase in the expression of caspase-8 and caspase-3 and a corresponding decrease in Bcl-2. The active fragment of caspase-3 increased in glutamate-treated cells. An early transient increase in the expression of CaMKIIalpha(B) gene and a corresponding CaMKIIalpha nuclear translocation was found in glutamate-treated cells. Treatment with AIP blocked the activation of caspase-3 and protected RGC from glutamate-mediated cell death but did not alter the glutamate-enhanced expression levels of caspase-8 or caspase-3. This report shows the likely involvement of a transcript of the CaMKIIalpha gene in the cytotoxicity response of RGC-5 cells similar to previous reports in the neural retina. AIP is shown to be a neuroprotectant for RGC-5 cells as was reported for the neural retina.

The rat retinal ganglion cell in culture: An accessible CNS neurone

Retinal ganglion cells are vital for vision, some have intrinsic light sensing properties and in retinal networks display complex computational abilities. Furthermore they are implicated in a very common form of blindness, glaucoma as well some the symptoms of AIDS. Retinal ganglion cells, unlike many neurones of the central nervous system, have a clearly defined physiological role and can be identified in primary cultures with ease. Here we detail the cell culture and electrophysiological methods required to obtain recordings on the voltage-gated and ligand-gated ion currents and channels expressed by these neurones. Information is given on the range of non-ionotropic receptors that are thought to be present on these cells and what role they may have as model systems in the pharmacological and pharmaceutical research environment.