Quantitative ex vivo detection of rodent retinal ganglion cells by immunolabeling Brn-3b

Differential Distribution of RBPMS in Pig, Rat, and Human Retina after Damage

RNA binding protein with multiple splicing (RBPMS) is expressed exclusively in retinal ganglion cells (RGCs) in the retina and can label all RGCs in normal retinas of mice, rats, guinea pigs, rabbits, cats, and monkeys, but its function in these cells is not known. As a result of the limited knowledge regarding RBPMS, we analyzed the expression of RBPMS in the retina of different mammalian species (humans, pigs, and rats), in various stages of development (neonatal and adult) and with different levels of injury (control, hypoxia, and organotypic culture or explants). In control conditions, RBPMS was localized in the RGCs somas in the ganglion cell layer, whereas in hypoxic conditions, it was localized in the RGCs dendrites in the inner plexiform layer. Such differential distributions of RBPMS occurred in all analyzed species, and in adult and neonatal retinas. Furthermore, we demonstrate RBPMS localization in the degenerating RGCs axons in the nerve fiber layer of retinal explants. This is the first evidence regarding the possible transport of RBPMS in response to physiological damage in a mammalian retina. Therefore, RBPMS should be further investigated in relation to its role in axonal and dendritic degeneration.

An open-source computational tool to automatically quantify immunolabeled retinal ganglion cells

A fully automated and robust method was developed to quantify β-III-tubulin-stained retinal ganglion cells, combining computational recognition of individual cells by CellProfiler and a machine-learning tool to teach phenotypic classification of the retinal ganglion cells by CellProfiler Analyst. In animal models of glaucoma, quantification of immunolabeled retinal ganglion cells is currently performed manually and remains time-consuming. Using this automated method, quantifications of retinal ganglion cell images were accelerated tenfold: 1800 images were counted in 3 h using our automated method, while manual counting of the same images took 72 h. This new method was validated in an established murine model of microbead-induced optic neuropathy. The use of the publicly available software and the method's user-friendly design allows this technique to be easily implemented in any laboratory.

Neuroprotective effect of water-dispersible hesperetin in retinal ischemia reperfusion injury

PURPOSE

To determine whether water-dispersible hesperetin (WD-Hpt) can prevent degeneration of ganglion cell neurons in the ischemic retina.

METHODS

Ischemia reperfusion (I/R) injury was induced by increasing the intraocular pressure of mice to 110 mmHg for 40 min. Mice received daily intraperitoneal injections with either normal saline (NS, 0.3 ml/day) or WD-Hpt (0.3 ml, 200 mg/kg/day). Reactive oxygen species (ROS) was assessed by dihydroethidium and nitrotyrosine formation. Inflammation was estimated by microglial morphology in the retina. Lipopolysaccharide (LPS)-stimulated BV-2 cells were used to explore the anti-inflammatory effect of WD-Hpt on activated microglia by quantifying the expression of IL-1β using real-time quantitative reverse transcription-polymerase chain reaction. Ganglion cell loss was assessed by immunohistochemistry of NeuN. Glial activation was quantified with glial fibrillary acidic protein (GFAP) immunoreactivity. Apoptosis was evaluated with a terminal deoxynucleotidyl transferase (TUNEL) assay and immunohistochemistry of cleaved caspase-3. Phosphorylation of extracellular signal-regulated kinase (p-ERK) was surveyed by western blotting.

RESULTS

WD-Hpt decreased I/R-induced ROS formation. WD-Hpt alleviated microglial activation induced by I/R and reduced mRNA levels of IL-1β in LPS-stimulated BV-2. I/R resulted in a 37% reduction in the number of ganglion cells in the NS-treated mice, whereas the reduction was only 5% in the WD-Hpt-treated mice. In addition, WD-Hpt mitigated the immunoreactivity of GFAP, increased expression of cleaved caspase-3, increased number of TUNEL positive cells and p-ERK after I/R.

CONCLUSIONS

WD-Hpt protected ganglion cells from I/R injury by inhibiting oxidative stress and modulating cell death signaling. Moreover, WD-Hpt had an anti-inflammatory effect through the suppression of activated microglia.

Melanopsin-expressing retinal ganglion cell loss and behavioral analysis in the Thy1-CFP-DBA/2J mouse model of glaucoma

In this study, the role of melanopsin-expressing retinal ganglion cells (mRGCs) in the glaucoma-induced depressive behavioral response pattern was investigated. The CFP-D2 transgenic glaucoma animal model from five age groups was used in this study. Immunohistochemical labeling, quantitative analysis of mRGC morphology, open field test (OFT), and statistical analysis were used. In comparison with C57 BL/6 mice, the age-matched CFP-D2 mice had significantly elevated intraocular pressure (IOP). We observed parallel morphological changes in the retina, including a reduction in the density of cyan fluorescent protein-(CFP) expressing cells (cells mm(-2) at 2 months of age, 1309±26; 14 months, 878±30, P<0.001), mRGCs (2 months, 48±3; 14 months, 19±4, P<0.001), Brn3b-expressing RGCs (2 months, 1283±80; 14 months, 950±31, P <0.001), Brn-3b expressing mRGCs (5 months, 50.17%±5.5%; 14 months, 12.61%±3.8%, P<0.001), and reduction in the dendritic field size of mRGCs (mm(2) at 2 months, 0.077±0.015; 14 months, 0.065±0.015, P<0.05). CFP-D2 mice had hyperactive locomotor activity patterns based on OFT findings of the total distance traveled, number of entries into the center, and time spent in the center of the testing apparatus. The glaucoma induced hyperactive response pattern could be associated with dysfunctional mRGCs, most likely Brn-3b-positive mRGCs in CFP-D2 mice.

Whole number, distribution and co-expression of brn3 transcription factors in retinal ganglion cells of adult albino and pigmented rats

The three members of the Pou4f family of transcription factors: Pou4f1, Pou4f2, Pou4f3 (Brn3a, Brn3b and Brn3c, respectively) play, during development, essential roles in the differentiation and survival of sensory neurons. The purpose of this work is to study the expression of the three Brn3 factors in the albino and pigmented adult rat. Animals were divided into these groups: i) untouched; ii) fluorogold (FG) tracing from both superior colliculli; iii) FG-tracing from one superior colliculus; iv) intraorbital optic nerve transection or crush. All retinas were dissected as flat-mounts and subjected to single, double or triple immunohistofluorescence The total number of FG-traced, Brn3a, Brn3b, Brn3c or Brn3 expressing RGCs was automatically quantified and their spatial distribution assessed using specific routines. Brn3 factors were studied in the general RGC population, and in the intrinsically photosensitive (ip-RGCs) and ipsilateral RGC sub-populations. Our results show that: i) 70% of RGCs co- express two or three Brn3s and the remaining 30% express only Brn3a (26%) or Brn3b; ii) the most abundant Brn3 member is Brn3a followed by Brn3b and finally Brn3c; iii) Brn3 a-, b- or c- expressing RGCs are similarly distributed in the retina; iv) The vast majority of ip-RGCs do not express Brn3; v) The main difference between both rat strains was found in the population of ipsilateral-RGCs, which accounts for 4.2% and 2.5% of the total RGC population in the pigmented and albino strain, respectively. However, more ipsilateral-RGCs express Brn3 factors in the albino than in the pigmented rat; vi) RGCs that express only Brn3b and RGCs that co-express the three Brn3 members have the biggest nuclei; vii) After axonal injury the level of Brn3a expression in the surviving RGCs decreases compared to control retinas. Finally, this work strengthens the validity of Brn3a as a marker to identify and quantify rat RGCs.

Glaucoma-induced degeneration of retinal ganglion cells prevented by hypoxic preconditioning: a model of glaucoma tolerance

Like all cells, neurons adapt to stress by transient alterations in phenotype, an epigenetic response that forms the basis for preconditioning against acute ischemic injury in the central nervous system. We recently showed that a modified repetitive hypoxic preconditioning (RHP) regimen significantly extends the window of ischemic tolerance to acute retinal ischemic injury from days to months. The present study was undertaken to determine if this uniquely protracted neuroprotective phenotype would also confer resistance to glaucomatous neurodegeneration. Retinal ganglion cell death at somatic and axonal levels was assessed after both 3 and 10 wks of sustained intraocular hypertension in an adult mouse model of inducible, open-angle glaucoma, with or without RHP before intraocular pressure elevation. Loss of brn3-positive ganglion cell soma after 3 wks of experimental glaucoma, along with increases in several apoptotic endpoints, were all significantly and robustly attenuated in mice subjected to RHP. Soma protection by RHP was also confirmed after 10 wks of intraocular hypertension by brn3 and SMI32 immunostaining. In addition, quantification of axon density in the postlaminar optic nerve documented robust preservation in RHP-treated mice, and neurofilament immunostaining also revealed preconditioning-induced improvements in axon integrity/survival in both retina and optic nerve after 10 wks of experimental glaucoma. This uniquely protracted period of phenotypic change, established in retinal ganglion cells by the activation of latent antiapoptotic, prosurvival mechanisms at both somatic and axonal levels, reflects a novel form of inducible neuronal plasticity that may provide innovative therapeutic targets for preventing and treating glaucoma and other neurodegenerative diseases.

Quantitative analysis of retinal ganglion cell survival with Rbpms immunolabeling in animal models of optic neuropathies

PURPOSE

To investigate whether a recently described retinal ganglion cell (RGC) marker Rbpms (RNA binding protein with multiple splicing) could be used for RGC quantification in various models of RGC degeneration.

METHODS

Optic nerve crush, excitotoxicity, and elevated intraocular pressure (IOP) rat models were used. Topographic analysis of Rbpms immunolabeling was performed on retinal wholemounts. Retrograde labelings with Fluorogold (FG) and III β-tubulin immunohistochemistry were compared.

RESULTS

In the optic nerve crush model, 37%, 87%, and 93% of Rbpms-positive cells were lost 1, 2, and 4 weeks, respectively. Significant loss of Rbpms-positive cells was noted 1 week after intravitreal injection of 12, 30, and 120 nmol N-methyl-d-aspartate (NMDA), whereas coinjection of 120 nmol of NMDA along with MK-801 increased the cell number from 10% to 59%. Over 95% of Rbpms-positive cells were FG- and III β-tubulin-positive after injury caused by optic nerve crush and NMDA injection. In rats with elevated IOP, induced by trabecular laser photocoagulation, there was a significant loss of Rbpms-positive cells compared with that of contralateral controls (P = 0.0004), and cumulative IOP elevation showed a strong linear relationship with the quantification of RGCs by Rbpms immunolabeling and retrograde labeling with FG. More than 99% of the remaining Rbpms-positive cells were double-labeled with FG.

CONCLUSIONS

Rbpms can reliably be used as an RGC marker for quantitative evaluation in rat models of RGC degeneration, regardless of the nature and the location of the primary site of the injury and the extent of neurodegeneration.

Neuroprotection from retinal ischemia/reperfusion injury by NOX2 NADPH oxidase deletion

PURPOSE

The aim of this study was to determine whether NOX2, one of the homologs of NADPH oxidase, plays a role in neuronal cell death during retinal ischemia.

METHODS

Ischemia reperfusion (I/R) injury was generated in C57/BL6 and NOX2(-/-) mice by increasing the intraocular pressure (IOP) to 110 mm Hg for 40 minutes followed by reperfusion. Quantitative PCR and Western blot analysis were performed to measure NOX2 expression. Reactive oxygen species (ROS) formation was assessed by dihydroethidium imaging of superoxide formation and Western blot analysis for tyrosine nitration. TUNEL assay was performed to determine cell death at 3 days after I/R. Survival of neurons within the ganglion cell layer (GCL) was assessed at 7 days after I/R by confocal morphometric imaging of retinal wholemounts immunostained with NeuN antibody. Activation of mitogen-activated protein kinases and nuclear factor κB (NF-κΒ) was measured by Western blot analysis.

RESULTS

NOX2 mRNA and protein and ROS were significantly increased in wild-type I/R retinas. This effect was associated with a 60% decrease in the number of GCL neurons and a 10-fold increase in TUNEL-positive cells compared with the fellow sham control eyes. Phosphorylation of ERK and NF-κB was significantly increased in wild-type I/R retinas. Each of these effects was markedly attenuated in the NOX2(-/-) retina (P < 0.01).

CONCLUSIONS

These data demonstrate that the deletion of NOX2 can reduce I/R-induced cell death and preserve retinal GCL neurons after I/R injury. The neuronal cell injury caused by I/R is associated with the activation of ERK and NF-κB signaling mechanisms.

Histological observation of RGCs and optic nerve injury in acute ocular hypertension rats

AIM

To explore the injury of retinal ganglion cells (RGCs) and optic nerves in acute ocular hypertension (OHT) rats.

METHODS

We retrogradely labeled RGCs and optic nerves of Sprague-Dawley rats by injecting 20g/L fluorogold (FG) into bilateral superior colliculi. Twenty-four hours after the injection, the right eyes were performed physiological saline anterior chamber perfusion with intraocular pressure maintained at 100mmHg for 60 minutes, while the contralateral eyes were performed sham procedure as control group without elevation of the saline bottle. Retinal hematoxylin and eosin (HE) sections, retinal whole mounts and frozen sections were made 14 days later to observe the morphology and survival of RGCs. Frozen sections and transmission electron microscopy were utilized to investigate the histological manifestations of optic nerves at the same time.

RESULTS

A larger number of RGCs presented in control group. It had an average density of 1995±125/mm(2) and distributed uniformly, while RGCs in OHT eyes reduced significantly to 1505±43/mm(2) compared with control group (P<0.05). The optic nerves in control group showed stronger and more uniform fluorescence on the frozen sections, and the auxiliary fibers as well as myelin sheaths were in even and intact organization by transmission electron microscopy. However, exiguous fluorescence signals, vesicular dissociation and disintegration of myelin sheaths were found in OHT group.

CONCLUSION

The present study suggested that fluorogold retrograde tracing is a feasible, convenient method for quantitative and qualitative study of neuronal populations and axonal injury in acute ocular hypertension rats.

Laser-induced ocular hypertension in albino CD-1 mice

PURPOSE

To establish a laser-induced model of ocular hypertension (LIOH) in albino CD-1 mice and to characterize the sequence of pathologic events triggered by intraocular pressure (IOP) elevation.

METHODS

LIOH was induced unilaterally in CD-1 mice by laser photocoagulation of limbal and episcleral veins 270 degrees to 300 degrees circumferentially, sparing the nasal aspect and the long ciliary arteries. IOP was measured with a rebound tonometer. Hematoxylin and eosin-stained plastic sections were used for morphometric analysis of retinal layers, and retinal whole-mounts were immunostained with anti-Brn-3b to quantify retinal ganglion cell (RGC) gene expression ion and density. Axonal and myelin morphologies were characterized using appropriate antibodies, and axon counts were obtained from paraphenylenediamine-stained optic nerve sections.

RESULTS

LIOH resulted in IOP doubling within 4 hours after laser treatment, which returned to normal by 7 days. Axon degenerative changes, reactive plasticity, and aberrant regrowth were detected at the optic nerve head (ONH) as early as 4 days after treatment. By 7 days, axon number was significantly reduced in the myelinated optic nerve, with concurrent signs of myelin degradation. At 14 days, Brn-3b(+) RGC density was reduced, with neuronal loss confined to the RGC layer and no apparent effects on other retinal layers.

CONCLUSIONS

Laser photocoagulation of limbal and episcleral veins induces transient ocular hypertension in albino CD-1 mice. The ensuing retinal and optic nerve pathologic events recapitulated key features of glaucoma and placed ONH RGC axon responses as an early manifestation of damage. LIOH in albino mice may be useful as a mouse model to examine mechanisms of RGC and axon glaucomatous injury.

Evaluation of Fluoro-Jade C as a marker of degenerating neurons in the rat retina and optic nerve

Detection of neuronal death is an essential requirement for researchers investigating retinal degeneration. Fluoro-Jade C (FJC) is a novel, fluorescent dye that has been successfully used to label degenerating neurons in the brain, but its effectiveness in the eye has not been ascertained. In the current study, we determined the efficacy of FJC for detection of neuronal degeneration in the retina and optic nerve in various paradigms of injury. N-methyl-D-aspartate (NMDA) and kainic acid-induced excitotoxicity, optic nerve transection, and bilateral occlusion of the common carotid arteries (BCCAO) were performed using standard techniques. Rats were killed at various time points and the retinas with optic nerves attached were removed for tissue processing prior to labelling for FJC, for DNA fragmentation by TUNEL or for immunohistochemical analysis. Retinas from RCS rats of different ages were also analysed. After excitotoxicity-induced injury, cell bodies and dendrites within the ganglion cell and inner plexiform layers were specifically labelled by FJC within 6h, a time point comparable to the appearance of TUNEL-positive nuclei and to reductions in mRNA levels of retinal ganglion cell-specific proteins, but in advance of alterations in some immunohistochemical markers. The number of FJC-labelled cell bodies in the retina declined over time as cell loss proceeded, although dendritic staining remained prominent. Colocalisation of FJC with TUNEL and with immunohistochemical neuronal markers was achieved. FJC was successful at identifying somato-dendritic degeneration following ischemia induced by BCCAO, but surprisingly, not after optic nerve transection. FJC visualised photoreceptor degeneration in the RCS rat, albeit less effectively than with the TUNEL assay, and was also effective for imaging and quantifying degenerating axons in the optic nerve after multiple injuries. In addition to labelling degenerating neurons, however, FJC also bound non-specifically to astrocytes and to blood cells in unperfused rats. Since the ganglion cell layer is adjacent to astrocytes within the nerve fibre layer, caution is needed when using FJC as a quantitative tool for detecting ganglion cell death.

The neuropeptide NAP provides neuroprotection against retinal ganglion cell damage after retinal ischemia and optic nerve crush

BACKGROUND

NAP, an 8-amino acid peptide (NAPVSIPQ=Asn-Ala-Pro-Val-Ser-Ile-Pro-Gln) derived from activity-dependent neuroprotective protein (ADNP), plays an important role in neuronal differentiation and the survival of neurons in different pathological situations. We already discovered that NAP increases the survival of retinal ganglion cells (RGC) in vitro, and supports neurite outgrowth in retinal explants at femtomolar concentrations. The aim of this study was to investigate the effects of NAP on RGC survival after transient retinal ischemia and optic nerve crush.

METHODS

RGC of male Wistar rats were labelled retrogradely with 6 l FluoroGold injected stereotactically into both superior colliculi. Seven days later, retinal ischemia was induced by elevating the intraocular pressure to 120 mm Hg for 60 minutes or by crushing one optic nerve for 10 s after a partial orbitotomy. NAP was either injected intraperitoneally in the concentration of 100 microg/kg [corrected] 1 day before, directly after, and on the first and the second days after damage, or intravitreally (0.05 or 0.5 microg/eye) [corrected] directly after the optic nerve crush. Controls received the same concentrations of a control peptide. Densities of surviving RGC and activated microglial cells (AMC) were quantified in a masked fashion 10 days after damage by counting FluoroGold-labelled cells.

RESULTS

After retinal ischemia, intraperitoneal injections of NAP increased the number of surviving RGC by 40% (p < 0.005) compared to the control group. After optic nerve crush, NAP raised the number of surviving RGC by 31% (p = 0.07) when injected intraperitoneally and by 54% (p < 0.05) when administered intravitreally.

CONCLUSIONS

NAP acts neuroprotectively in vivo after retinal ischemia and optic nerve crush, and may have potential in treating optic nerve diseases.

Rodent models for glaucoma retinopathy and optic neuropathy

Animal models are useful to elucidate the etiology and pathology of glaucoma and to develop novel and more effective therapies for the disease. Because of the substantial similarities between the rodent and primate eyes, and the advances of relevant study techniques, rat and mouse models of glaucoma have recently become popular as research tools. This review surveys research techniques used in the measurement of rodent intraocular pressure, and also the evaluation of pertinent morphologic, biochemical, and functional changes in the retina, optic nerve head, and optic nerve. This review further describes in detail the individual rodent models, some of which serve as surrogate models and do not entail ocular hypertension, whereas others involve transient or chronic increases of intraocular pressure. The technical considerations and theoretical concerns of these models, their advantages, and limitations, are also discussed.

Complex neurodegeneration in retina following moderate ischemia induced by bilateral common carotid artery occlusion in Wistar rats

Bilateral common carotid artery occlusion (BCCAO) produces moderate levels of ischemia in the retina of rats, which may simulate the inflow disturbances in severe carotid artery disease. ERG changes following acute BCCAO have been well described, but the effects of chronic BCCAO on the histopathology of the retina remain to be characterized in a reproducible model. Chronic BCCAO was induced in halothane-anaesthetized male Wistar rats and the retina fixed after 3, 6, or 24 hr, 1 week, and 2, 4, or 6 months. Cell counts and measurements of retinal layers were performed in H&E stained paraffin sections. Immunohistochemistry with a panel of fourteen antibodies served to examine the survival of different retinal cell class, astrocytic reactions and the expression of acute stress response proteins. A lectin method was used to label activated microglial cells. Microglial activation, heme oxygenase-1 upregulation and caspase-3 cleavage occurred during the first 24hr in the absence of overt cell death of retinal ganglion cells (RGC). Three waves of neurodegeneration followed. RGCs were affected after 1 week, followed by neurons in the inner nuclear layer at 2 months, and finally photoreceptors at 4 months. Immunomarkers indicated acute damage to horizontal cells and prolonged survival of amacrine cells. In conclusion, chronic BCCAO produced delayed neuronal death in the retina of adult male Wistar rats. The window of moderate changes of at least 1 day may facilitate molecular studies on retinal ganglion cell loss.

Retinal neurospheres prepared as tissue for transplantation

The present work was conducted to study the cellular composition and developmental capacity of retinal neurospheres. Furthermore, the ability of grafted neurospheres to integrate into adult retinal tissue was studied in an in vitro model. Retinal progenitor cells isolated from rat embryos were expanded into neurospheres in vitro in the presence of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and leukemia inhibitory factor (LIF). Neurospheres labeled with a lipophilic dye were placed onto explants, and tissue interactions were analyzed after 2-6 days of culture. Immunocytochemical analysis of neurospheres revealed the presence of neuronal and glial cells. Proliferating neuronal and glial cells were observed after 2 weeks, whereas the neuronal cell proliferation declined considerably after 4 weeks. Few apoptotic cells were observed in the neurospheres. Neurospheres cultured on explanted adult retina engrafted with the surrounding tissue, but progenitor cell migration into the explants was low. However, the grafted neurospheres appeared to limit the experimentally induced photoreceptor apoptosis in the surrounding explant tissue.

Retinal ganglion cells and supporting elements in culture

Elucidating the pathophysiology of glaucoma has traditionally relied on animal models of intraocular hypertension and optic nerve injury, which are closely related to the human disease with respect to tissue damage. However, cell culture models of retinal neurons (particularly retinal ganglion cells) and supporting cells (particularly retinal glia and lamina cribrosa cells), although less closely related to glaucoma pathophysiology, have particular advantages in understanding intracellular processes associated with glaucomatous optic neuropathy. Examples of studies which are more readily achievable with cultured cells include: 1) Isolation and separation of purified cells to help define the role of classes of cell types; 2) Transfection of genetic material to over-express or knockdown specific genes; 3) Fluorescent imaging of calcium concentrations, reactive oxygen species concentrations, mitochondrial membrane potential, cellular pH, and other measures of cellular physiology.