Reduction Of Retinal Ganglion Cells Research Articles

Intravitreal MPTP drives retinal ganglion cell loss with oral nicotinamide treatment providing robust neuroprotection

Neurodegenerative diseases have common underlying pathological mechanisms including progressive neuronal dysfunction, axonal and dendritic retraction, and mitochondrial dysfunction resulting in neuronal death. The retina is often affected in common neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. Studies have demonstrated that the retina in patients with Parkinson’s disease undergoes changes that parallel the dysfunction in the brain. These changes classically include decreased levels of dopamine, accumulation of alpha-synuclein in the brain and retina, and death of dopaminergic nigral neurons and retinal amacrine cells leading to gross neuronal loss. Exploring this disease's retinal phenotype and vision-related symptoms is an important window for elucidating its pathophysiology and progression, and identifying novel ways to diagnose and treat Parkinson’s disease. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is commonly used to model Parkinson’s disease in animal models. MPTP is a neurotoxin converted to its toxic form by astrocytes, transported to neurons through the dopamine transporter, where it causes mitochondrial Complex I inhibition and neuron degeneration. Systemic administration of MPTP induces retinal changes in different animal models. In this study, we assessed the effects of MPTP on the retina directly via intravitreal injection in mice (5 mg/mL and 50 mg/mL to 7, 14 and 21 days post-injection). MPTP treatment induced the reduction of retinal ganglion cells—a sensitive neuron in the retina—at all time points investigated. This occurred without a concomitant loss of dopaminergic amacrine cells or neuroinflammation at any of the time points or concentrations tested. The observed neurodegeneration which initially affected retinal ganglion cells indicated that this method of MPTP administration could yield a fast and straightforward model of retinal ganglion cell neurodegeneration. To assess whether this model could be amenable to neuroprotection, mice were treated orally with nicotinamide (a nicotinamide adenine dinucleotide precursor) which has been demonstrated to be neuroprotective in several retinal ganglion cell injury models. Nicotinamide was strongly protective following intravitreal MPTP administration, further supporting intravitreal MPTP use as a model of retinal ganglion cell injury. As such, this model could be utilized for testing neuroprotective treatments in the context of Parkinson’s disease and retinal ganglion cell injury.

Retinal hypoxia after experimental subarachnoid hemorrhage

Background and PurposeThe patients who survive subarachnoid hemorrhage (SAH) often have long-term neurological complications. There are no reports about the pathological change of retina after SAH. MethodsAn experimental model of SAH was established by injecting autologous blood into the prechiasmatic cistern of Sprague-Dawley rats. Hematoxylin and eosin (HE) staining was performed to show the alternation of morphology in retina after SAH. To detect the retinal new vessels (NVs), CD31 was labelled by immunofluorescence and immunohistochemistry. The time-course expressions of vascular endothelial growth factor (VEGF)-A and hypoxia-inducible factor-1α (HIF-1 α) was also revealed by Western blot analysis. ResultsA clear reduction of retinal ganglion cells (RGCs) was noticed after SAH. The immunofluorescence and immunohistochemical staining of CD31 reveals a large number of NVs in RGC layer after SAH compared with the normal controls. The level of VEGF-A in the retina after SAH was increased and peaked at 12h and 14 d. The expression of HIF-1α in the retina increased as early as 3 h after SAH, reached a peak at 12 h after SAH. ConclusionsThe results showed that SAH induced the retina hypoxia resulting in the reduction of RGCs, increase of NVs and activation of NVs related HIF-1α/VEGF-A pathway.

Mutation in Bmpr1b Leads to Optic Disc Coloboma and Ventral Retinal Gliosis in Mice.

PurposeThe clinical phenotype of retinal gliosis occurs in different forms; here, we characterize one novel genetic feature, (i.e., signaling via BMP-receptor 1b).MethodsMouse mutants were generated within a recessive ENU mutagenesis screen; the underlying mutation was identified by linkage analysis and Sanger sequencing. The eye phenotype was characterized by fundoscopy, optical coherence tomography, optokinetic drum, electroretinography, and visual evoked potentials, by histology, immunohistology, and electron-microscopy.ResultsThe mutation affects intron 10 of the Bmpr1b gene, which is causative for skipping of exon 10. The expression levels of pSMAD1/5/8 were reduced in the mutant retina. The loss of BMPR1B-mediated signaling leads to optic nerve coloboma, gliosis in the optic nerve head and ventral retina, defective optic nerve axons, and irregular retinal vessels. The ventral retinal gliosis is proliferative and hypertrophic, which is concomitant with neuronal delamination and the reduction of retinal ganglion cells (RGCs); it is dominated by activated astrocytes overexpressing PAX2 and SOX2 but not PAX6, indicating that they may retain properties of gliogenic precursor cells. The expression pattern of PAX2 in the optic nerve head and ventral retina is altered during embryonic development. These events finally result in reduced electrical transmission of the retina and optic nerve and significantly reduced visual acuity.ConclusionsOur study demonstrates that BMPR1B is necessary for the development of the optic nerve and ventral retina. This study could also indicate a new mechanism in the formation of retinal gliosis; it opens new routes for its treatment eventually preventing scar formation in the retina.

Transfer of the Experimental Autoimmune Glaucoma Model from Rats to Mice-New Options to Study Glaucoma Disease.

Studies have suggested an involvement of the immune system in glaucoma. Hence, a rat experimental autoimmune glaucoma model (EAG) was developed to investigate the role of the immune response. Here, we transferred this model into mice. Either 0.8 mg/mL of the optic nerve antigen homogenate (ONA; ONA 0.8) or 1.0 mg/mL ONA (ONA 1.0) were injected in 129/Sv mice. Controls received sodium chloride. Before and 6 weeks after immunization, the intraocular pressure (IOP) was measured. At 6 weeks, retinal neurons, glia cells, and synapses were analyzed via immunohistology and quantitative real-time PCR (RT-qPCR). Additionally, optic nerves were examined. The IOP stayed in the normal physiological range throughout the study (p > 0.05). A significant reduction of retinal ganglion cells (RGCs) was noted in both immunized groups (p < 0.001). Remodeling of glutamatergic and GABAergic synapses was seen in ONA 1.0 retinas. Furthermore, both ONA groups revealed optic nerve degeneration and macrogliosis (all: p < 0.001). An increase of activated microglia was noted in ONA retinas and optic nerves (p < 0.05). Both ONA concentrations led to RGC loss and optic nerve degeneration. Therefore, the EAG model was successfully transferred from rats to mice. In further studies, transgenic knockout mice can be used to investigate the pathomechanisms of glaucoma more precisely.

Modeling activity and target-dependent developmental cell death of mouse retinal ganglion cells ex vivo.

Programmed cell death is widespread during the development of the central nervous system and serves multiple purposes including the establishment of neural connections. In the mouse retina a substantial reduction of retinal ganglion cells (RGCs) occurs during the first postnatal week, coinciding with the formation of retinotopic maps in the superior colliculus (SC). We previously established a retino-collicular culture preparation which recapitulates the progressive topographic ordering of RGC projections during early post-natal life. Here, we questioned whether this model could also be suitable to examine the mechanisms underlying developmental cell death of RGCs. Brn3a was used as a marker of the RGCs. A developmental decline in the number of Brn3a-immunolabelled neurons was found in the retinal explant with a timing that paralleled that observed in vivo. In contrast, the density of photoreceptors or of starburst amacrine cells increased, mimicking the evolution of these cell populations in vivo. Blockade of neural activity with tetrodotoxin increased the number of surviving Brn3a-labelled neurons in the retinal explant, as did the increase in target availability when one retinal explant was confronted with 2 or 4 collicular slices. Thus, this ex vivo model reproduces the developmental reduction of RGCs and recapitulates its regulation by neural activity and target availability. It therefore offers a simple way to analyze developmental cell death in this classic system. Using this model, we show that ephrin-A signaling does not participate to the regulation of the Brn3a population size in the retina, indicating that eprhin-A-mediated elimination of exuberant projections does not involve developmental cell death.

PTEN regulates retinal interneuron morphogenesis and synaptic layer formation

The lipid phosphatase PTEN is a critical negative regulator of extracellular signal-induced PI3K activities, yet the roles of PTEN in the neural retina remain poorly understood. Here, we investigate the function of PTEN during retinal development. Deletion of Pten at the onset of neurogenesis in retinal progenitors results in the reduction of retinal ganglion cells and rod photoreceptors, but increased Müller glial genesis. In addition, PTEN deficiency leads to elevated phosphorylation of Akt, especially in the developing inner plexiform layer, where high levels of PTEN are normally expressed. In Pten mutant retinas, various subtypes of amacrine cells show severe dendritic overgrowth, causing specific expansion of the inner plexiform layer. However, the outer plexiform layer remains relatively undisturbed in the Pten deficient retina. Physiological analysis detects reduced rod function and augmented oscillatory potentials originating from amacrine cells in Pten mutants. Furthermore, deleting Pten or elevating Akt activity in individual amacrine cells is sufficient to disrupt dendritic arborization, indicating that Pten activity is required cell autonomously to control neuronal morphology. Moreover, inhibiting endogenous Akt activity attenuates inner plexiform layer formation in vitro. Together, these findings demonstrate that suppression of PI3K/Akt signaling by PTEN is crucial for proper neuronal differentiation and normal retinal network formation.

Age-Related Losses of Retinal Ganglion Cells and Axons

Age-related losses in retinal nerve fiber layer (RNFL) thickness have been assumed to be the result of an age-dependent reduction of retinal ganglion cells (RGCs), but the published rates differ: age-related losses of RGCs of approximately 0.6%/year compared to 0.2%/year for thinning of the RNFL. An analysis of normative data for standard automated perimetry (SAP) sensitivities and optical coherence tomography (OCT) measures of RNFL thickness showed that the apparent disagreement in age-dependent losses of RGCs and axons in the RNFL can be reconciled by an age-dependent decrease in the proportion of the RNFL thickness that is composed of axons. The purpose of the present study was to determine whether the mechanisms of age-related losses that were suggested by the normative data can be confirmed with data from healthy, normal eyes. Data were obtained from visual fields (normal results in a Glaucoma Hemifield Test [GHT] on standard automated perimetry [SAP] 24-2 fields) and RNFL thickness measurements (standard OCT scan) of 55 patients (age range, 18-80 years; mean, 44.5 +/- 17.3). The SAP measures of visual sensitivity and OCT measures of RNFL thickness for one eye of each patient were used to estimate neuron counts by each procedure. The age-related thinning of RNFL was 0.27%/year when a constant axon density was used to derive axon counts from RNFL thickness, compared with 0.50%/year for the age-related loss of RGCs from SAP. In agreement with the model developed with normative clinical data, concordance between losses of axons and soma was achieved by an age-dependent reduction of 0.46%/year in the density of axons in the RNFL. The results suggest that the proportion of RNFL that is composed of RGC axons is not constant with age; rather, the proportion of the total thickness from non-neuronal tissue increases with age. If a similar compensation occurs in the RNFL thickness with axon loss from glaucoma, then a stage-dependent correction to translate OCT measurements to neuronal components is needed, in addition to the age-dependent correction.

Apoptosis in retinal ganglion cell decrease in human glaucomatous eyes

Hematoxylin-eosin staining, the TUNEL method for in situ detection of the intranuclear DNA fragmentation, which indicates apoptosis, and electron microscopy were used to study the morphologic changes in specimens from the eyes of 8 patients with secondary glaucoma and 2 normal control eyes to evaluate our hypothesis that apoptosis causes a decrease in retinal ganglion cells in human glaucomatous eyes. The TUNEL method permits identification of intranuclear DNA fragmentation. Apoptosis was found in the ganglion cells of 2 glaucomatous eyes with recent sight loss, and in the ganglion cells of a control eye from a 95-year-old subject, taken at autopsy. Results of our study indicate that a decrease in retinal ganglion cells in glaucomatous eyes is caused by apoptosis. In addition, apoptosis resulting from aging must be considered in order to understand the reduction of retinal ganglion cells in the glaucomatous eyes of elderly patients.