Rat retinal ganglion cells culture enriched with the magnetic cell sorter

Effect of VCP modulators on gene expression profiles of retinal ganglion cells in an acute injury mouse model

In glaucoma, retinal ganglion cells are damaged, leading to the progressive constriction of the visual field. We have previously shown that the valosin-containing protein (VCP) modulators, Kyoto University Substance (KUS)121 and KUS187, prevent the death of retinal ganglion cells in animal models of glaucoma, including the one generated by N-methyl-D-aspartate (NMDA)-induced neurotoxicity. KUSs appeared to avert endoplasmic reticulum (ER) stress by maintaining ATP levels, resulting in the protection of ganglion cells from cell death. To further elucidate the protective mechanisms of KUSs, we examined gene expression profiles in affected ganglion cells. We first injected KUS-treated mice with NMDA and then isolated the affected retinal ganglion cells using fluorescence-activated cell sorting. Gene expression in the cells was quantified using a next-generation sequencer. Resultantly, we found that KUS121 upregulated several genes involved in energy metabolism. In addition, we observed the upregulation of Zfp667, which has been reported to suppress apoptosis-related genes and prevent cell death. These results further support the suitability of KUS121 as a therapeutic drug in protecting retinal ganglion cells in ophthalmic disorders, such as glaucoma.

[Evaluation of therapeutic sensitivity of retinal ganglion cells to targeted peptide bioregulator in culture]

PURPOSE

To study how therapeutically sensitive retinal cell culture is to the peptide bioregulator isolated from cattle retina (Retinalamin) in models of glaucomatous optic neuropathy (GON).

MATERIAL AND METHODS

The cells were isolated from the retinae separated from newborn mice. Cell sheets were disaggregated and transformed into a suspension. Removal of the off-target cell population was done by adding antibodies to deplete the cells with CD48 marker, and magnetic microbeads that attach to them. Selection of ganglion cells and obtainment of its enriched fraction was done by immunomagnetic separation. To assess the toxicity of Retinalamin, a cytotoxic test was performed on the culture of skin fibroblasts with sequential dilution of the drug into concentrations of 5.0-0.009 mg/mL. The cells were seeded at 5000 per plate well and exposed to the drug for 24 hours. To study the excitotoxic damage, the first group of plate wells with retinal cells had solution of sodium glutamate added in concentration of 20 mM, Retinalamin was added into the second group of wells in concentration of 1.25 mg/mL; both substances were added into the third group of wells. The control group consisted of intact plate wells. The cells were exposed to substances for 24 hours. Cell vitality was then evaluated using colorimetry. Optic density was measured using an automatic photometer with detection wavelength of λ=490 nm.

RESULTS

The cell culture achieved by immunomagnetic separation is mixed and consists of ganglion and glial cells. Retinalamin does not display significant cytotoxicity in any of the studied concentrations. The excitotoxic damage caused significant decrease of the amount of viable cells in the culture (9% of the control wells). The concomitant addition of glutamate and 1.25 mg/mL Retinalamin resulted in a 51.6% increase in the amount of viable cells. The intergroup differences were statistically significant by Student's t-test.

CONCLUSION

Retinalamin is not cytotoxic. The concomitant addition of glutamate and Retinalamin reliably decreases the toxic action of glutamate on isolated retinal cells.

Increased bioavailability of cyclic guanylate monophosphate prevents retinal ganglion cell degeneration

The nitric oxide - guanylyl cyclase-1 - cyclic guanylate monophosphate (NO-GC-1-cGMP) pathway has emerged as a potential pathogenic mechanism for glaucoma, a common intraocular pressure (IOP)-related optic neuropathy characterized by the degeneration of retinal ganglion cells (RGCs) and their axons in the optic nerve. NO activates GC-1 to increase cGMP levels, which are lowered by cGMP-specific phosphodiesterase (PDE) activity. This pathway appears to play a role in both the regulation of IOP, where reduced cGMP levels in mice leads to elevated IOP and subsequent RGC degeneration. Here, we investigated whether potentiation of cGMP signaling could protect RGCs from glaucomatous degeneration. We administered the PDE5 inhibitor tadalafil orally (10 mg/kg/day) in murine models of two forms of glaucoma - primary open angle glaucoma (POAG; GC-1^-/- mice) and primary angle-closure glaucoma (PACG; Microbead Occlusion Model) - and measured RGC viability at both the soma and axon level. To determine the direct effect of increased cGMP on RGCs in vitro, we treated axotomized whole retina and primary RGC cultures with the cGMP analogue 8-Br-cGMP. Tadalafil treatment increased plasma cGMP levels in both models, but did not alter IOP or mean arterial pressure. Nonetheless, tadalafil treatment prevented degeneration of RGC soma and axons in both disease models. Treatment of whole, axotomized retina and primary RGC cultures with 8-Br-cGMP markedly attenuated both necrotic and apoptotic cell death pathways in RGCs. Our findings suggest that enhancement of the NO-GC-1-cGMP pathway protects the RGC body and axon in murine models of POAG and PACG, and that enhanced signaling through this pathway may serve as a novel glaucoma treatment, acting independently of IOP.

A Novel Retinal Ganglion Cell Promoter for Utility in AAV Vectors

Significant advances in gene therapy have enabled exploration of therapies for inherited retinal disorders, many of which are in preclinical development or clinical evaluation. Gene therapy for retinal conditions has led the way in this growing field. The loss of retinal ganglion cells (RGCs) is a hallmark of a number of retinal disorders. As the field matures innovations that aid in refining therapies and optimizing efficacy are in demand. Gene therapies under development for RGC-related disorders, when delivered with recombinant adeno associated vectors (AAV), have typically been expressed from ubiquitous promoter sequences. Here we describe how a novel promoter from the murine Nefh gene was selected to drive transgene expression in RGCs. The Nefh promoter, in an AAV2/2 vector, was shown to drive preferential EGFP expression in murine RGCs in vivo following intravitreal injection. In contrast, EGFP expression from a CMV promoter was observed not only in RGCs, but throughout the inner nuclear layer and in amacrine cells located within the ganglion cell layer (GCL). Of note, the Nefh promoter sequence is sufficiently compact to be readily accommodated in AAV vectors, where transgene size represents a significant constraint. Moreover, this promoter should in principle provide a more targeted and potentially safer alternative for RGC-directed gene therapies.

Isolation of Primary Murine Retinal Ganglion Cells (RGCs) by Flow Cytometry

Neurodegenerative diseases often have a devastating impact on those affected. Retinal ganglion cell (RGC) loss is implicated in an array of diseases, including diabetic retinopathy and glaucoma, in addition to normal aging. Despite their importance, RGCs have been extremely difficult to study until now due in part to the fact that they comprise only a small percentage of the wide variety of cells in the retina. In addition, current isolation methods use intracellular markers to identify RGCs, which produce non-viable cells. These techniques also involve lengthy isolation protocols, so there is a lack of practical, standardized, and dependable methods to obtain and isolate RGCs. This work describes an efficient, comprehensive, and reliable method to isolate primary RGCs from mice retinae using a protocol based on both positive and negative selection criteria. The presented methods allow for the future study of RGCs, with the goal of better understanding the major decline in visual acuity that results from the loss of functional RGCs in neurodegenerative diseases.

Isolation and Molecular Profiling of Primary Mouse Retinal Ganglion Cells: Comparison of Phenotypes from Healthy and Glaucomatous Retinas

Loss of functional retinal ganglion cells (RGC) is an element of retinal degeneration that is poorly understood. This is in part due to the lack of a reliable and validated protocol for the isolation of primary RGCs. Here we optimize a feasible, reproducible, standardized flow cytometry-based protocol for the isolation and enrichment of homogeneous RGC with the Thy1.2(hi)CD48(neg)CD15(neg)CD57(neg) surface phenotype. A three-step validation process was performed by: (1) genomic profiling of 25-genes associated with retinal cells; (2) intracellular labeling of homogeneous sorted cells for the intracellular RGC-markers SNCG, brain-specific homeobox/POU domain protein 3A (BRN3A), TUJ1, and RNA-binding protein with multiple splicing (RBPMS); and (3) by applying the methodology on RGC from a mouse model with elevated intraocular pressure (IOP) and optic nerve damage. Use of primary RGC cultures will allow for future careful assessment of important cell specific pathways in RGC to provide mechanistic insights into the declining of visual acuity in aged populations and those suffering from retinal neurodegenerative diseases.

Thy1 associates with the cation channel subunit HCN4 in adult rat retina

PURPOSE

The membrane expression and gene promoter of the glycosylphosphatidylinositol (GPI)-anchored protein Thy1 have been widely used to examine the morphology and distribution of retinal ganglion cells in normal eyes and disease models. However, it is not known how adult mammalian retinal neurons use Thy1. Because Thy1 is not a membrane-spanning protein and, instead, complexes with structural and signaling proteins in other tissues, the aim of this study was to find protein partners of retinal Thy1.

METHODS

Coimmunoprecipitation, immunohistochemistry, confocal imaging, and patch-clamp recording were used to test for association of Thy1 and HCN4, a cation channel subunit, in adult rat retina.

RESULTS

Hyperpolarization of cells immunopanned by an anti-Thy1 antibody activated HCN channels. Confocal imaging showed that individual somata in the ganglion cell layer bound antibodies against Thy1 and HCN4, that the majority of these bindings colocalized, and that some of the immunopositive cells also bound antibody against a ganglion cell marker (Brn3a). Consistent with these results, Thy1 and HCN4 were coimmunoprecipitated by magnetic beads coated with either anti-Thy1 antibody or anti-HCN4 antibody. In control experiments, beads coated with these antibodies did not immunoprecipitate a photoreceptor rim protein (ABCR) and uncoated beads did not immunoprecipitate either Thy1 or HCN4.

CONCLUSIONS

This is the first report that Thy1 colocalizes and coimmunoprecipitates with a membrane-spanning protein in retina, that Thy1 complexes with an ion channel protein in any tissue, and that a GPI-anchored protein associates with an HCN channel subunit protein.

Accumulation of neurons differentiated from mouse embryonic stem cells in particular areas of culture plate surface

Nanoscale magnetic beads coated with nerve growth factor (NGF) allow us to accumulate neurons differentiated from mouse ES cells in a selected area of the culture plate surface using a magnet. Neurons with neurite outgrowths within a particular area expressed TrkA and incorporated beads in the soma.

Defective cAMP generation underlies the sensitivity of CNS neurons to neurofibromatosis-1 heterozygosity

Individuals with the neurofibromatosis type 1 (NF1) inherited cancer syndrome exhibit neuronal dysfunction that predominantly affects the CNS. In this report, we demonstrate a unique vulnerability of CNS neurons, but not peripheral nervous system (PNS) neurons, to reduced Nf1 gene expression. Unlike dorsal root ganglion neurons, Nf1 heterozygous (Nf1+/-) hippocampal and retinal ganglion cell (RGC) neurons have decreased growth cone areas and neurite lengths, and increased apoptosis compared to their wild-type counterparts. These abnormal Nf1+/- CNS neuronal phenotypes do not reflect Ras pathway hyperactivation, but rather result from impaired neurofibromin-mediated cAMP generation. In this regard, elevating cAMP levels with forskolin or rolipram treatment, but not MEK (MAP kinase kinase) or PI3-K (phosphatidylinositol 3-kinase) inhibition, reverses these abnormalities to wild-type levels in vitro. In addition, Nf1+/- CNS, but not PNS, neurons exhibit increased apoptosis in response to excitotoxic or oxidative stress in vitro. Since children with NF1-associated optic gliomas often develop visual loss and Nf1 genetically engineered mice with optic glioma exhibit RGC neuronal apoptosis in vivo, we further demonstrate that RGC apoptosis resulting from optic glioma in Nf1 genetically engineered mice is attenuated by rolipram treatment in vivo. Similar to optic glioma-induced RGC apoptosis, the increased RGC neuronal death in Nf1+/- mice after optic nerve crush injury is also attenuated by rolipram treatment in vivo. Together, these findings establish a distinctive role for neurofibromin in CNS neurons with respect to vulnerability to injury, define a CNS-specific neurofibromin intracellular signaling pathway responsible for neuronal survival, and lay the foundation for future neuroprotective glioma treatment approaches.

Erythropoiesis-stimulating protein delivery in providing erythropoiesis and neuroprotection

Erythropoietin (EPO), a glycoprotein, plays an important role in erythropoiesis and neuroprotection. EPO therapies for anemia or neurodegenerative diseases require frequent injections or high-dose systemic administration which may cause unwanted side effects. Various strategies for EPO delivery have been investigated for increasing EPO bioavailability and decreasing side effects, including nano/micro particles, PEGylation of EPO and transport-mediated delivery systems. Nano/micro particles provide EPO with long-term effect and protect EPO against proteolytic cleavage. PEGylated EPO prolong circulating time and reduce injection frequency of anemia treatment. A transport-mediated delivery system enables protein to cross biological barriers. Presently, there is no report about an effective delivery system of EPO for neuroprotection. This review focuses on EPO delivery systems for erythropoiesis or neuroprotection with prolonged duration and enhanced bioavailability.

Selective cultivation of N-cadherin expressing cells from the optic tectum of the chick

Dissociated primary cell cultures of the nervous system are usually composed of many different cell types, which makes it difficult to investigate a specific cell type and to describe its development in vitro without direct or indirect influence of other cell types. Although various methods have been published to specifically separate either neurons or glial cells, there is still a need for simple protocols to isolate distinct neuronal subpopulations. Here we describe a method to purify specific neuronal subtypes from the chick embryonic midbrain. Embryonic (E10) optic tecta were dissociated and a cell suspension was produced. Cells were separated by magnetic cell sorting (MACS) based on their specific expression of somatic N-cadherin. After cultivation on poly-D-lysine coated dishes in serum-free culture medium supplemented with B27, cells were fixed and analyzed with immuncytochemistry. Enriched primary cultures contained about 70% of N-cadherin positive cells compared to 46% before sorting. 7 days after cultivation, N-cadherin expression and its co-localization with synapses was demonstrated.

Neuroprotective effects of erythropoietin on glutamate and nitric oxide toxicity in primary cultured retinal ganglion cells

Erythropoietin receptor (EpoR) is expressed in the central nervous system (CNS), however, no clear consensus has been obtained whether Epo acts as a prosurvival factor in neurons. Because retinal ganglion cell (RGC) death is a common cause of reduced visual function in several ocular diseases, we explored whether Epo might potentially be beneficial in protecting RGCs from glutamate and nitric oxide (NO)-induced cytotoxicity, using isolated RGCs by a two-step panning method. Brain-derived neurotrophic factor (BDNF) was used as a positive control. EpoR mRNA was expressed in isolated RGCs, and EpoR protein was expressed on the RGCs in the normal and ischemic retinas. Epo had less potential to improve the survival of primary RGCs in serum-free medium than BDNF. In these cells, BDNF, but not Epo, downregulated the expression of Bim, a proapoptotic Bcl-2 family member that plays a key role in cytokine-mediated cell survival, suggesting a possible mechanism for this difference. When RGCs were cultured with glutamate or an NO-generating reagent, the survival of RGCs was compromised, and Bcl-2 expression was decreased in these cells. Both Epo and BDNF significantly reduced RGC death induced by glutamate and NO. In agreement with this, these factors reversed the Bcl-2 expression. These findings suggest that Epo may be a potent neuroprotective therapeutic agent for the treatment of ocular diseases that are characterized by RGC death.

Neurite outgrowths of neurons using neurotrophin-coated nanoscale magnetic beads

Neurotrophin-coated nanoscale magnetic beads were used to regulate the differentiation and survival of neurons. The beads coated with nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) promoted neurite outgrowths of neurons in the same manner as soluble NGF or soluble BDNF, but beads coated with bovine serum albumin did not promote neurite outgrowths. When the volume of NGF-coated bead solution was increased, the number of neurons with neurite outgrowths increased. The addition of anti-NGF antibodies decreased the numbers of neurons with neurite outgrowths in proportion to the volume of anti-NGF antibodies added. NGF-coated beads appeared to bind to soma with neurite outgrowths as determined using fluorescence. In addition, hybrid beads coated with both NGF and BDNF promoted neurite outgrowths of PC12h cells, although the cells did not produce neurite outgrowths in response to BDNF. Neurons with neurite outgrowths could be concentrated within a particular area when NGF-coated beads were immobilized in a particular area of the culture plate surface using a magnet. The results demonstrate that neurotrophin-coated nanoscale magnetic beads allow us to cultivate neurons in a selected area of the culture plate surface by using a magnet. Thus, neurotrophin-coated nanoscale magnetic beads are applicable to micro-integrated systems and biosensors.

Application of magnetic techniques in the field of drug discovery and biomedicine

Magnetic separation technology, using magnetic particles, is quick and easy method for sensitive and reliable capture of specific proteins, genetic material and other biomolecules. The technique offers an advantage in terms of subjecting the analyte to very little mechanical stress compared to other methods. Secondly, these methods are non-laborious, cheap and often highly scalable. Moreover, techniques employing magnetism are more amenable to automation and miniaturization. Now that the human genome is sequenced and about 30,000 genes are annotated, the next step is to identify the function of these individual genes, carrying out genotyping studies for allelic variation and SNP analysis, ultimately leading to identification of novel drug targets. In this post-genomic era, technologies based on magnetic separation are becoming an integral part of todays biology laboratory. This article briefly reviews the selected applications of magnetic separation techniques in the field of biotechnology, biomedicine and drug discovery.

Existence of ionotropic glutamate receptor subtypes in cultured rat retinal ganglion cells obtained by the magnetic cell sorter method and inhibitory effects of 20-hydroxyecdysone, a neurosteroid, on the glutamate response

Glutamate and neurosteroids are known to exist in retinal ganglion cells (RGC). Therefore, patch clamp studies using the whole-cell recording method were performed to determine whether or not ionotropic glutamate receptor subtypes, i.e., N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate receptors, were present on RGC obtained by the magnetic cell sorter (MACS) method and cultures. In addition, the effects of 20-hydroxyecdysone (20-HE), a neurosteroid, on inward currents induced by NMDA, AMPA and kainate were examined at a holding potential of -60 mV. The current-voltage relationship for NMDA in the presence of glycine and Mg2+-free, as well as those for AMPA and kainate were linear, with a reversal potential of around 0 mV. NMDA-induced currents were blocked by MK-801, while both AMPA- and kainate-induced currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Application of 20-HE in the bath resulted in significant inhibitions on NMDA-, AMPA- and kainate-induced currents. Thus, NMDA, AMPA and kainate receptors were confirmed to exist on MACS-separated cultured RGC. Moreover, 20-HE inhibited NMDA receptor-mediated currents most prominently and AMPA- and kainate-mediated currents moderately, suggesting that neurosteroids may be playing a role in modulating glutamate-mediated transmission in RGC, and 20-HE might be useful for preventing glutamate neurotoxicity.

In situ localization of nitric oxide synthase and direct evidence of NO production in rat retinal ganglion cells

The expression of isoforms of nitric oxide synthase (NOS), enzymes responsible for NO production, and the synthesis of nitric oxide (NO) in rat retinal ganglion cells (RGCs) during synaptogenesis for various phases of the pre- and postnatal developmental periods were investigated. The retinas from prenatal, lactating, young, and adult rats were fixed in paraformaldehyde. The cryosections or paraformaldehyde-fixed ganglion cells purified from rat pups were immunostained for constitutive isoforms of NOS (n and eNOS) and observed with a confocal laser scanning microscope. Synthesis of NO in the RGCs was achieved by in vitro stimulation with glutamate. The intracellular NO levels were measured in real time using diaminofluorescein-2 diacetate, a fluorescence indicator of NO. Immunohistochemical analysis revealed nNOS and eNOS expressed in retinal ganglion cells during the first 2 postnatal weeks. Cultured RGCs also expressed nNOS and eNOS in vitro. Intracellular NO levels in cultured RGCs showed spontaneous fluctuation during a 20-min observation. The presence of both a non-specific NOS inhibitor, L-NAME, and a specific nNOS inhibitor, 7-NI, significantly inhibited (P<0.001) the increase of intracellular NO 6 and 8 min after the introduction of L-arginine and glutamate to the medium. This study revealed that all constitutive NOS isoforms are expressed in RGCs and demonstrated that NO is produced by nNOS mainly through stimulation by glutamate in cultured RGCs.