Antibodies against neurofilament subunits label retinal ganglion cells but not displaced amacrine cells of hamsters

Pan-retinal ganglion cell markers in mice, rats, and rhesus macaques

Univocal identification of retinal ganglion cells (RGCs) is an essential prerequisite for studying their degeneration and neuroprotection. Before the advent of phenotypic markers, RGCs were normally identified using retrograde tracing of retinorecipient areas. This is an invasive technique, and its use is precluded in higher mammals such as monkeys. In the past decade, several RGC markers have been described. Here, we reviewed and analyzed the specificity of nine markers used to identify all or most RGCs, i.e., pan-RGC markers, in rats, mice, and macaques. The best markers in the three species in terms of specificity, proportion of RGCs labeled, and indicators of viability were BRN3A, expressed by vision-forming RGCs, and RBPMS, expressed by vision- and non-vision-forming RGCs. NEUN, often used to identify RGCs, was expressed by non-RGCs in the ganglion cell layer, and therefore was not RGC-specific. γ-SYN, TUJ1, and NF-L labeled the RGC axons, which impaired the detection of their somas in the central retina but would be good for studying RGC morphology. In rats, TUJ1 and NF-L were also expressed by non-RGCs. BM88, ERRβ, and PGP9.5 are rarely used as markers, but they identified most RGCs in the rats and macaques and ERRβ in mice. However, PGP9.5 was also expressed by non-RGCs in rats and macaques and BM88 and ERRβ were not suitable markers of viability.

Distribution of prototypical primary cilia markers in subtypes of retinal ganglion cells

Loss of retinal ganglion cells (RGCs) underlies several forms of retinal disease including glaucomatous optic neuropathy, a leading cause of irreversible blindness. Several rare genetic disorders associated with cilia dysfunction have retinal degeneration as a clinical hallmark. Much of the focus of ciliopathy associated blindness is on the connecting cilium of photoreceptors; however, RGCs also possess primary cilia. It is unclear what roles RGC cilia play, what proteins and signaling machinery localize to RGC cilia, or how RGC cilia are differentiated across the subtypes of RGCs. To better understand these questions, we assessed the presence or absence of a prototypical cilia marker Arl13b and a widely distributed neuronal cilia marker AC3 in different subtypes of mouse RGCs. Interestingly, not all RGC subtype cilia are the same and there are significant differences even among these standard cilia markers. Alpha-RGCs positive for osteopontin, calretinin, and SMI32 primarily possess AC3-positive cilia. Directionally selective RGCs that are CART positive or Trhr positive localize either Arl13b or AC3, respectively, in cilia. Intrinsically photosensitive RGCs differentially localize Arl13b and AC3 based on melanopsin expression. Taken together, we characterized the localization of gold standard cilia markers in different subtypes of RGCs and conclude that cilia within RGC subtypes may be differentially organized. Future studies aimed at understanding RGC cilia function will require a fundamental ability to observe the cilia across subtypes as their signaling protein composition is elucidated. A comprehensive understanding of RGC cilia may reveal opportunities to understanding how their dysfunction leads to retinal degeneration.

OTX2 stimulates adult retinal ganglion cell regeneration

Retinal ganglion cell (RGC) axons provide the only link between the light sensitive and photon transducing neural retina and visual centers of the brain. RGC axon degeneration occurs in a number of blinding diseases and the ability to stimulate axon regeneration from surviving ganglion cells could provide the anatomic substrate for restoration of vision. OTX2 is a homeoprotein transcription factor expressed in the retina and previous studies showed that, in response to stress, exogenous OTX2 increases the in vitro and in vivo survival of RGCs. Here we examined and quantified the effects of OTX2 on adult RGC axon regeneration in vitro and in vivo. The results show that exogenous OTX2 stimulates the regrowth of axons from RGCs in cultures of dissociated adult retinal cells and from explants of adult retinal tissue and that RGCs respond directly to OTX2 as regrowth is observed in cultures of purified adult rat RGCs. Importantly, after nerve crush in vivo, we observed a positive effect of OTX2 on the number of regenerating axons up to the optic chiasm within 14 days post crush and a very modest level of acuity absent in control mice. The effect of OTX2 on RGC survival and regeneration is of potential interest for degenerative diseases affecting this cell type. All animal procedures were approved by the local “Comié d’éιthique en expérimentation animale n°59” and authorization n° 00702.01 delivered March 28, 2014 by the French “Ministére de l’enseignement supérieur et de la recherche”.

The RNA binding protein RBPMS is a selective marker of ganglion cells in the mammalian retina

There are few neurochemical markers that reliably identify retinal ganglion cells (RGCs), which are a heterogeneous population of cells that integrate and transmit the visual signal from the retina to the central visual nuclei. We have developed and characterized a new set of affinity-purified guinea pig and rabbit antibodies against RNA-binding protein with multiple splicing (RBPMS). On western blots these antibodies recognize a single band at 〜24 kDa, corresponding to RBPMS, and they strongly label RGC and displaced RGC (dRGC) somata in mouse, rat, guinea pig, rabbit, and monkey retina. RBPMS-immunoreactive cells and RGCs identified by other techniques have a similar range of somal diameters and areas. The density of RBPMS cells in mouse and rat retina is comparable to earlier semiquantitative estimates of RGCs. RBPMS is mainly expressed in medium and large DAPI-, DRAQ5-, NeuroTrace- and NeuN-stained cells in the ganglion cell layer (GCL), and RBPMS is not expressed in syntaxin (HPC-1)-immunoreactive cells in the inner nuclear layer (INL) and GCL, consistent with their identity as RGCs, and not displaced amacrine cells. In mouse and rat retina, most RBPMS cells are lost following optic nerve crush or transection at 3 weeks, and all Brn3a-, SMI-32-, and melanopsin-immunoreactive RGCs also express RBPMS immunoreactivity. RBPMS immunoreactivity is localized to cyan fluorescent protein (CFP)-fluorescent RGCs in the B6.Cg-Tg(Thy1-CFP)23Jrs/J mouse line. These findings show that antibodies against RBPMS are robust reagents that exclusively identify RGCs and dRGCs in multiple mammalian species, and they will be especially useful for quantification of RGCs.

Targeted CNS Delivery Using Human MiniPromoters and Demonstrated Compatibility with Adeno-Associated Viral Vectors

Critical for human gene therapy is the availability of small promoter tools to drive gene expression in a highly specific and reproducible manner. We tackled this challenge by developing human DNA MiniPromoters using computational biology and phylogenetic conservation. MiniPromoters were tested in mouse as single-copy knock-ins at the Hprt locus on the X Chromosome, and evaluated for lacZ reporter expression in CNS and non-CNS tissue. Eighteen novel MiniPromoters driving expression in mouse brain were identified, two MiniPromoters for driving pan-neuronal expression, and 17 MiniPromoters for the mouse eye. Key areas of therapeutic interest were represented in this set: the cerebral cortex, embryonic hypothalamus, spinal cord, bipolar and ganglion cells of the retina, and skeletal muscle. We also demonstrated that three retinal ganglion cell MiniPromoters exhibit similar cell-type specificity when delivered via adeno-associated virus (AAV) vectors intravitreally. We conclude that our methodology and characterization has resulted in desirable expression characteristics that are intrinsic to the MiniPromoter, not dictated by copy number effects or genomic location, and results in constructs predisposed to success in AAV. These MiniPromoters are immediately applicable for pre-clinical studies towards gene therapy in humans, and are publicly available to facilitate basic and clinical research, and human gene therapy.

Differential calcium signaling mediated by voltage-gated calcium channels in rat retinal ganglion cells and their unmyelinated axons

Aberrant calcium regulation has been implicated as a causative factor in the degeneration of retinal ganglion cells (RGCs) in numerous injury models of optic neuropathy. Since calcium has dual roles in maintaining homeostasis and triggering apoptotic pathways in healthy and injured cells, respectively, investigation of voltage-gated Ca channel (VGCC) regulation as a potential strategy to reduce the loss of RGCs is warranted. The accessibility and structure of the retina provide advantages for the investigation of the mechanisms of calcium signalling in both the somata of ganglion cells as well as their unmyelinated axons. The goal of the present study was to determine the distribution of VGCC subtypes in the cell bodies and axons of ganglion cells in the normal retina and to define their contribution to calcium signals in these cellular compartments. We report L-type Ca channel α1C and α1D subunit immunoreactivity in rat RGC somata and axons. The N-type Ca channel α1B subunit was in RGC somata and axons, while the P/Q-type Ca channel α1A subunit was only in the RGC somata. We patch clamped isolated ganglion cells and biophysically identified T-type Ca channels. Calcium imaging studies of RGCs in wholemounted retinas showed that selective Ca channel antagonists reduced depolarization-evoked calcium signals mediated by L-, N-, P/Q- and T-type Ca channels in the cell bodies but only by L-type Ca channels in the axons. This differential contribution of VGCC subtypes to calcium signals in RGC somata and their axons may provide insight into the development of target-specific strategies to spare the loss of RGCs and their axons following injury.

Heterogeneity of intrinsically photosensitive retinal ganglion cells in the mouse revealed by molecular phenotyping

Intrinsically photosensitive retinal ganglion cell (ipRGC) types can be distinguished by their dendritic tree stratification and intensity of melanopsin staining. We identified heavily stained melanopsin-positive M1 cells branching in the outermost part of the inner plexiform layer (IPL) and weakly melanopsin-positive M2 cells branching in the innermost layer of the IPL. A third type can be distinguished by the displacement of the soma to the inner nuclear layer and has morphological similarities with either M1 cells or M2 cells, and is termed here displaced or M-d cells. The aim of the present study was to examine the phenotypic traits of ipRGC types. Using whole retinae from adult mice, we performed immunohistochemistry using melanopsin immunostaining and a number of antibodies directed against proteins typically expressed in retinal ganglion cells. The majority of M1 and M2 ipRGCs expressed Isl-1, microtubule associated protein-2 (MAP2), γ-synuclein, and NeuN, whereas Brn3 transcription factor and the different neurofilaments (NF68, NF160, NF200) were able to discriminate between ipRGC subtypes. Brn3 was expressed preferentially in M2 cells and in a small subpopulation of weakly melanopsin-positive M-d cells with similarities to M2 cells. All three neurofilaments were primarily expressed in large M2 cells with similarities to the recently described alpha-like M4 cells, but not in M1 cells. Expression of NF68 and NF160 was also observed in a few large M-d ipRGCs. These findings show that ipRGCs are not a phenotypically homogenous population and that specific neuronal markers (Brn3 and neurofilament) can partly distinguish between different ipRGC subtypes.

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.

Severe neurologic impairment in mice with targeted disruption of the electrogenic sodium bicarbonate cotransporter NBCe2 (Slc4a5 gene)

The choroid plexus lining the four ventricles in the brain is where the majority of cerebrospinal fluid (CSF) is produced. The secretory function of the choroid plexus is mediated by specific transport systems that allow the directional flux of nutrients and ions into the CSF and the removal of toxins. Normal CSF dynamics and chemistry ensure that the environment for neural function is optimal. Here, we report that targeted disruption of the Slc4a5 gene encoding the electrogenic sodium bicarbonate cotransporter NBCe2 results in significant remodeling of choroid plexus epithelial cells, including abnormal mitochondrial distribution, cytoskeletal protein expression, and ion transporter polarity. These changes are accompanied by very significant abnormalities in intracerebral ventricle volume, intracranial pressure, and CSF electrolyte levels. The Slc4a5(-/-) mice are significantly more resistant to induction of seizure behavior than wild-type controls. In the retina of Slc4a5(-/-) mice, loss of photoreceptors, ganglion cells, and retinal detachment results in visual impairment assessed by abnormal electroretinogram waveforms. Our findings are the first demonstration of the fundamental importance of NBCe2 in the biology of the nervous system.

Otx2 promotes the survival of damaged adult retinal ganglion cells and protects against excitotoxic loss of visual acuity in vivo

Retinal ganglion cells (RGCs) are the projection neurons from the eye to the brain and their loss results in visual impairment in a number of diseases. Transcription factors with a homeodomain can translocate between cells and, in at least one reported case, can stimulate neuronal survival. Otx2 is a homeoprotein transcription factor expressed in the retina that is taken up by RGCs. We thus hypothesized that Otx2 capture could regulate the survival of adult RGCs. We report that Otx2 stimulates the survival of adult mouse and rat RGCs in vitro and protects RGCs against NMDA-induced toxicity in vivo in mice. In the latter model, Otx2 also preserves visual acuity.

RNA binding protein with multiple splicing: a new marker for retinal ganglion cells

PURPOSE

To characterize expression of the RNA binding protein (RBPMS) in the retina as a specific marker for retinal ganglion cells (RGCs).

METHODS

Optic nerve transection (ONT) was performed on adult male Wistar rats. Retrograde RGC labeling was performed with FluoroGold (FG) applied to the cut surface of the optic nerve. RBPMS mRNA and protein expression in the retina was analyzed by in situ hybridization and immunohistochemistry, respectively. The expression of RBPMS in various rat tissues was analyzed with semiquantitative RT-PCR.

RESULTS

RBPMS mRNA and protein expression was localized primarily to irregularly shaped cells in the ganglion cell layer of the retina. Quantitative analysis showed that almost 100% of RGCs labeled by FG were also RBPMS-positive, irrespective of their location relative to the optic nerve head. Approximately 94% to 97% of RBPMS-positive cells were also positive for Thy-1, neurofilament H, and III beta-tubulin. In 2-week ONT retinas, the remaining few RGCs were weakly stained with RBPMS compared with intact RGCs in control retinas. Outside the retina, expression of RBPMS was observed in the heart, kidney, liver, and lungs. No expression was detected in any neuronal tissues except the retina.

CONCLUSIONS

The data indicate that in the retina RBPMS is selectively expressed in RGCs and therefore could serve as a marker for RGC quantification in normal retinas and for estimation of RGC loss in ocular neuropathies.

A Thy1-CFP DBA/2J mouse line with cyan fluorescent protein expression in retinal ganglion cells

A DBA/2J (D2) transgenic mouse line with cyan fluorescent protein (CFP) reporter expression in ganglion cells was developed for the analysis of ganglion cells during progressive glaucoma. The Thy1-CFP D2 (CFP-D2) line was created by congenically breeding the D2 line, which develops pigmentary glaucoma, and the Thy1-CFP line, which expresses CFP in ganglion cells. Microsatellite marker analysis of CFP-D2 progeny verified the genetic inclusion of the D2 isa and ipd loci. Specific mutations within these loci lead to dysfunctional melanosomal proteins and glaucomatous phenotype in D2 mice. Polymerase chain reaction analysis confirmed the inclusion of the Thy1-CFP transgene. CFP-fluorescent ganglion cells, 6-20 microm in diameter, were distributed in all retinal regions, CFP processes were throughout the inner plexiform layer, and CFP-fluorescent axons were in the fiber layer and optic nerve head. Immunohistochemistry with antibodies to ganglion cell markers NF-L, NeuN, Brn3a, and SMI32 was used to confirm CFP expression in ganglion cells. Immunohistochemistry with antibodies to amacrine cell markers HPC-1 and ChAT was used to confirm weak CFP expression in cholinergic amacrine cells. CFP-D2 mice developed a glaucomatous phenotype, including iris disease, ganglion cell loss, attrition of the fiber layer, and elevated intraocular pressure. A CFP-D2 transgenic line with CFP-expressing ganglion cells was developed, which has (1) a predominantly D2 genetic background, (2) CFP-expressing ganglion cells, and (3) age-related progressive glaucoma. This line will be of value for experimental studies investigating ganglion cells and their axons in vivo and in vitro during the progressive development of glaucoma.

Immunohistochemical localization of sortilin and p75(NTR) in normal and ischemic rat retina

In our previous study, we found the increased expression of p75(NTR) and sortilin by Western blotting in ischemic retina induced by elevated intraocular pressure (IOP). Cell specific expression of sortilin and p75 neurotrophin receptor (p75(NTR)) was now characterized in normal and ischemic rat retina induced by elevated IOP by double-labeling immunochemistry. Two patterns of sortilin staining in normal retina were identified: punctate and consistent. The former was seen in the retinal ganglion cell (RGC) bodies, probably in Golgi apparatus. The latter was found in astrocytes and Müller glial cells (MGCs). The expression pattern of sortilin did not change in ischemic state induced by elevated IOP. p75(NTR) was not found in RGCs, but in MGCs of most of the retinal layers, especially the inner plexiform layer (IPL), and outer plexiform layer (OPL) of normal retina. Taken together, the enhanced expression of sortilin in MGCs might be involved in the neuro-glial interactions in ischemic retina, but may not directly contribute to RGCs death through proNGF binding to complex receptor composed of sortilin and p75(NTR) in ischemic retina.

Differential enhancement of neural and photoreceptor cell differentiation of cultured pineal cells by FGF-1, IGF-1, and EGF

There are several common features between the pineal organ and the lateral eye in their developmental and evolutionary aspects. The avian pineal is a photoendocrine organ that originates from the diencephalon roof and represents a transitional type between the photosensory organ of lower vertebrates and the endocrine gland of mammals. Previous cell culture studies have shown that embryonic avian pineal cells retain a wide spectrum of differentiative capacities, although little is known about the mechanisms involved in their fate determination. In the present study, we investigated the effects of various cell growth factors on the differentiation of photoreceptor and neural cell types using pineal cell cultures from quail embryos. The results show that IGF-1 promotes differentiation of rhodopsin-immunoreactive cells, but had no effect on neural cell differentiation. Simultaneous administration of EGF and IGF-1 further enhanced differentiation of rhodopsin-immunoreactive cells, although the mechanism of the synergistic effect is unknown. FGF-1 did not stimulate proliferation of neural progenitor cells, but intensively promoted and maintained expression of a neural cell phenotype. FGF-1 appeared to lead to the conversion from an epithelial (endocrinal) to a neuronal type. It also enhanced phenotypic expression of retinal ganglion cell markers but rather suppressed expression of an amacrine cell marker. These results indicate that growth factors are important regulatory cues for pineal cell differentiation and suggest that they play roles in determining the fate of the pineal organ and the eye. It can be speculated that the differences in environmental cues between the retina and pineal may result in the transition of the pineal primordium from a potentially ocular (retinal) organ to a photoendocrine organ.

Microarray analysis of gene expression in adult retinal ganglion cells

Retinal ganglion cells (RGCs) transfer visual information to the brain and are known to be susceptible to selective degeneration in various neuropathies such as glaucoma. This selective vulnerability suggests that these highly specialized neurons possess a distinct gene expression profile that becomes altered by neuropathy-associated stresses, which lead to the RGC death. In this study, to identify genes expressed predominantly in adult RGCs, a global transcriptional profile of purified primary RGCs has been compared to that of the whole retina. To avoid alterations of the original gene expression profile by cell culture conditions, we isolated RNA directly from adult RGCs purified by immunopanning without prior sub-cultivation. Genes expressed predominantly in RGCs included: Nrg1, Rgn, 14-3-3 family (Ywhah, Ywhaz, Ywhab), Nrn1, Gap43, Vsnl1, Rgs4. Some of these genes may serve as novel markers for these neurons. Our analysis revealed enrichment in genes controlling the pro-survival pathways in RGCs as compared to other retinal cells.

Rat retinal ganglion cell loss caused by kainate, NMDA and ischemia correlates with a reduction in mRNA and protein of Thy-1 and neurofilament light

Quantification of retinal ganglion cell (RGC) loss/survival following a defined insult to the retina is a prerequisite in order to allow a comparison to be made between the effectiveness of potential neuroprotective drugs. The purpose of the present study was to extend the characterisation of our previously published semiquantitative RT-PCR assay to assess RGC loss/survival. Comparisons were made between the total mRNA levels of the ganglion cell-specific markers Thy-1 and neurofilament light (NF-L) in the retina at specific times after an intravitreal injection of N-methyl-D-aspartate (NMDA) or kainate or after 45 min of ischemia/reperfusion and also between the levels of NF-L mRNA and protein at various times after NMDA injection. Changes in Thy-1 and NF-L immunoreactivities were also observed. NMDA, kainate and ischemia/reperfusion all caused a reduction in the retinal content of Thy-1 and NF-L mRNAs and immunoreactivities. An excellent correlation was observed between the levels of the two mRNAs after these treatments. After NMDA, loss of NF-L mRNA was shown to precede loss of NF-L protein but total loss of each marker was similar after 7 days. The results of the study demonstrate that injury and subsequent death of RGCs, which occurs after ischemia/reperfusion and after intraocular injection of NMDA or kainate, can be followed by measurement of total retinal levels of Thy-1 and NF-L mRNAs and NF-L protein. The assays provides accurate, practical and complementary methods for assessing the potential benefits of neuroprotective drugs on RGCs which have been injured by a variety of experimental modalities.

Neurotrophic factors and depolarization do not enhance viability and process regrowth on a purified set of chick embryo retinal ganglion cells

As retinal ganglion cells (RGCs) develop, the amount of membrane glycoprotein Thy-1 increases, consequently, the RGC binding to Thy-1 antibody enlarges. This phenomenon sustained Thy-1 panning purification of two sets: loose bound cells (LBCs); and tight bound cells (TBCs). Thy-1, neurofilament and growth associated protein-43 characterized both sets as RGCs, but the expression of RA4 antigen and gangliotetraosylgangliosides distinguished LBCs as immature and TBCs as mature. The cell composition in 4-day TBC cultures remained unchanged as immunocharacterization indicated. These cells survived and regrew their processes in plain medium, however, trophic factors (TFs) and depolarization did not enhance their development. This peculiar behavior might be due to their neural maturity, whereas in LBC cultures, TFs produced positive effects.

Partial regeneration and long-term survival of rat retinal ganglion cells after optic nerve crush is accompanied by altered expression, phosphorylation and distribution of cytoskeletal proteins

In a screen to identify genes that are expressed differentially in the retina after partial optic nerve crush, we identified MAP1B as an up-regulated transcript. Western blot analysis of inner retina protein preparations confirmed changes in the protein composition of the microtubule-associated cytoskeleton of crushed vs. uncrushed nerve. MAP1B immunoreactivity and transcript levels were elevated for two weeks after crush. Immunostaining and Western blots with monoclonal antibodies directed against developmentally regulated phosphorylation sites on MAP1B revealed a gradient of MAP1B phosphorylation from the proximal optic nerve stump to the soma of retinal ganglion cells. Most interestingly, using antibodies directed against developmentally regulated phosphorylation sites on MAP1B, we observed that a significant number of crushed optic nerve axons develop MAP1B-immunopositive growth cones, which cross the crush site and migrate along the distal nerve fragment. In parallel, an abnormal distribution of highly phosphorylated neurofilament protein (pNF-H) in the cell soma and dendrites of presumably axotomized retinal ganglion cells was observed following partial nerve crush. This redistribution is present for the period between day 7 and 28 postcrush and is not seen in cells that stay connected to the superior colliculus. Axotomized ganglion cells, which contain pNF-H in soma and dendrites appear to have been disconnected from the colliculus at an early stage but survive axonal trauma for long periods.