A novel primary culture technique for adult retina allows for evaluation of CNS axon regeneration in rodents

Adenosine A2AR blockade prevents neuroinflammation-induced death of retinal ganglion cells caused by elevated pressure

BACKGROUND

Elevated intraocular pressure (IOP) is a major risk factor for glaucoma, a degenerative disease characterized by the loss of retinal ganglion cells (RGCs). There is clinical and experimental evidence that neuroinflammation is involved in the pathogenesis of glaucoma. Since the blockade of adenosine A2A receptor (A2AR) confers robust neuroprotection and controls microglia reactivity in the brain, we now investigated the ability of A2AR blockade to control the reactivity of microglia and neuroinflammation as well as RGC loss in retinal organotypic cultures exposed to elevated hydrostatic pressure (EHP) or lipopolysaccharide (LPS).

METHODS

Retinal organotypic cultures were either incubated with LPS (3 μg/mL), to elicit a pro-inflammatory response, or exposed to EHP (+70 mmHg), to mimic increased IOP, for 4 or 24 h, in the presence or absence of the A2AR antagonist SCH 58261 (50 nM). A2AR expression, microglial reactivity and neuroinflammatory response were evaluated by immunohistochemistry, quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). RGC loss was assessed by immunohistochemistry. In order to investigate the contribution of pro-inflammatory mediators to RGC loss, the organotypic retinal cultures were incubated with rabbit anti-tumour necrosis factor (TNF) (2 μg/mL) and goat anti-interleukin-1β (IL-1β) (1 μg/mL) antibodies.

RESULTS

We report that the A2AR antagonist (SCH 58261) prevented microglia reactivity, increase in pro-inflammatory mediators as well as RGC loss upon exposure to either LPS or EHP. Additionally, neutralization of TNF and IL-1β prevented RGC loss induced by LPS or EHP.

CONCLUSIONS

This work demonstrates that A2AR blockade confers neuroprotection to RGCs by controlling microglia-mediated retinal neuroinflammation and prompts the hypothesis that A2AR antagonists may be a novel therapeutic option to manage glaucomatous disorders.

Expression of insulin-like growth factor 1 receptor in rat retina following optic nerve injury

PURPOSE

To investigate the apoptosis in retinal ganglion cells (RGCs) and insulin-like growth factor 1 receptor (IGF-1R) in the retina following optic nerve crush.

METHODS

Healthy Wistar rats (N = 70) were divided into two groups: a normal control group and an optic nerve injury group. Immunohistochemistry and flow cytometry were performed to detect the expression of IGF-1R and to measure the apoptosis of RGCs, respectively.

RESULTS

Immunohistochemistry revealed that at 1 hr after optic nerve injury, IGF-1R immunoreactivity began to increase and reached a maximal level at 24 hr (p < 0.05), where it remained elevated up to 14 days after injury. RGC apoptosis in the normal control group was 0.53%, while the apoptosis rate in the optic nerve injury group increased over time. The apoptosis rate in the optic nerve injury group was 1.4% at 1 hr, 4.4% at 6 hr, 5.2% at 12 hr and reached a maximal level (8.5%) at 24 hr. Subsequently, the rate declined to 1.9% 7 days after injury and 0.9% 2 weeks after injury.

CONCLUSION

The IGF-1R immunereactivity in the retina increased after optic nerve injury. IGF-1R may regulate the apoptosis and regeneration of RGCs at different stages after optic nerve injury.

Organotypic tissue culture of adult rodent retina followed by particle-mediated acute gene transfer in vitro

Background

Organotypic tissue culture of adult rodent retina with an acute gene transfer that enables the efficient introduction of variable transgenes would greatly facilitate studies into retinas of adult rodents as animal models. However, it has been a difficult challenge to culture adult rodent retina. The purpose of this present study was to develop organotypic tissue culture of adult rodent retina followed by particle-mediated acute gene transfer in vitro.

Methodology/Principal Findings

We established an interphase organotypic tissue culture for adult rat retinas (>P35 of age) which was optimized from that used for adult rabbit retinas. We implemented three optimizations: a greater volume of Ames' medium (>26 mL) per retina, a higher speed (constant 55 rpm) of agitation by rotary shaker, and a greater concentration (10%) of horse serum in the medium. We also successfully applied this method to adult mouse retina (>P35 of age). The organotypic tissue culture allowed us to keep adult rodent retina morphologically and structurally intact for at least 4 days. However, mouse retinas showed less viability after 4-day culture. Electrophysiologically, ganglion cells in cultured rat retina were able to generate action potentials, but exhibited less reliable light responses. After transfection of EGFP plasmids by particle-mediated acute gene transfer, we observed EGFP-expressing retinal ganglion cells as early as 1 day of culture. We also introduced polarized-targeting fusion proteins such as PSD95-GFP and melanopsin-EYFP (hOPN4-EYFP) into rat retinal ganglion cells. These fusion proteins were successfully transferred into appropriate locations on individual retinal neurons.

Conclusions/Significance

This organotypic culture method is largely applicable to rat retinas, but it can be also applied to mouse retinas with a caveat regarding cell viability. This method is quite flexible for use in acute gene transfection in adult rodent retina, replacing molecular biological bioassays that used to be conducted in isolated cultured cells.

Trophic responsiveness of purified postnatal and adult rat retinal ganglion cells

Central neurons lose the ability for axonal re-growth during development and typically do not regenerate their axons following axotomy once they become mature unless given a growth-permissive environment i.e. peripheral nerve graft. In the present study, the growth responsiveness of purified retinal ganglion cells (RGCs) at different ages to neurotrophic factors and Schwann cell (SC)-secreted factors were examined directly. The purity of adult RGCs was 97% as assessed by retrograde labelling with 4,6-diamidino-2-phenylindole. The stability of cultures were demonstrated by long-term survival (30 days) in medium contained brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and forskolin (F) (BCF). RGCs from postnatal (P) (P0, P4, P8, P21) and adult (P90) rats showed decreasing levels of survival and neuritogenesis when grown in BCF. In contrast, the opposite was observed in SC-conditioned medium (CM)-treated P0-P8 RGCs which were increasingly responsive. SCCM induced maximal neurite outgrowth in P8 RGCs via the activation of extracellular regulated kinase 1/2 (Erk1/2). Inhibition of mitogen-activated protein kinase-Erk1/2 signaling using an Erk1/2-specific inhibitor (UO126) abolished SCCM-induced Erk1/2 phosphorylation and neuritogenesis completely. Although both SCCM and BCF failed to sustain the same levels of growth in P21 or P90 cultures as observed in P8 cultures, SCCM promoted higher survival and neuritogenesis than BCF-treated adult RGCs. This study is the first report of adult rat RGC purification and demonstrates that mature RGCs need multiple factors for survival and neurite outgrowth.

Adult retinal neuronal cell culture

Despite a relatively long history, general knowledge is not widespread that adult neurons can be maintained in cell culture for fairly extended periods of time. Within the central nervous system, this capacity seems to be particularly well developed in the retina, although it is still not clear whether this property is due to physical reasons (spatial configuration, simple connections) or to more fundamental differences (molecular composition, physiological function). Irrespective of the reasons, in vitro model systems are useful for investigating physiological and pathological processes occurring in mature retina. The authors argue that the numerous molecular changes undergone during maturation (modifications in ion channels and receptors, apoptotic pathways and growth factor effects) should be taken into account when using in vitro approaches to study processes involved in photoreceptor and ganglion cell degeneration, and hence that more classical methods relying on embryonic or newborn tissue should be interpreted with caution. A number of examples are given where the use of adult retinal neuronal culture may be especially informative: neurite regeneration, neuroprotection assays and pathogenic mechanisms; and areas of further research that should be explored: cell transplantation.

A primary culture technique of adult retina for regeneration studies on adult CNS neurons

This protocol details a tissue culture technique that allows for quantified regeneration studies on adult retinal ganglion cells (RGCs), that is, CNS neurons. The method may also allow for elucidation of molecular cues, for example of signals relevant in neuronal survival and axon regeneration. The procedure relies on fractioned stripe culture of previously injured retina in defined culture media. Naive dendritic cell contacts of RGCs are preserved, and the system is independent of growth factors. In contrast to other techniques, the protocol is based on tissue grown from adult animals; it dispenses immature co-cultures and evaluates the outgrowth of unmyelinated neurites in a milieu lacking CNS myelin. The technique is suitable for rodent retina from mouse or rat. A growth-conditioning injury of the optic nerve is set 10 days before retinal explantation. Explants are cultured for 5-7 days. Mere preparation of a single retina should be completed within 20 min.

Roller Culture of Free-Floating Retinal Slices: A New System of Organotypic Cultures of Adult Rat Retina

No experimental system exists to date for the in vitro study of retinal ganglion cell populations in a three-dimensional organotypic tissue environment. Here, we describe such a novel method for roller cultivation of adult retinas. Retinas of adult (1-3 months old) rats were cut into rectangular slices of approximately 1 mm(2). Free-floating slices were cultured on a horizontal rotating roller drum (50-60 rpm) in a dry incubator at 36.5 degrees C. During the first days of cultivation, primary flat retinal slices changed their configuration and transformed into ball-shaped tissue spheres (retinal bodies). Histological and immunocytochemical studies showed that the outer wall of the retinal bodies was formed by cell and fibre layers typical of mature retina with photoreceptors located on the outside. Initially, retinal bodies contained an inner cavity which later was completely obliterated and filled with glial cells, sprouting nerve fibres, and vascular structures. This culture system was further developed into a robust model of glutamate-induced neurotoxicity. Using a novel culture method of adult rat retina, preservation of the three-dimensional organotypic retinal cytoarchitecture was achieved, including survival of neurons in the ganglion cell layer and sprouting of nerve fibres of the axotomized retinal ganglion cells. This novel culture model promises to facilitate studies of retinal physiology and pathology.

A novel organotypic culture model of the postnatal mouse retina allows the study of glutamate-mediated excitotoxicity

A novel organotypic culture method of mouse retina explants is being introduced and characterized to evaluate its usefulness in studying glutamate excitotoxicity. Retinal whole-mounts were dissected from eyes of C57BL/6 mice aged P10-14 and transferred to poly-D-lysine/laminin coated round coverslips. After 7 days in vitro, retina explants were treated with varying concentrations of L-glutamate and cell death was accessed with TUNEL histochemistry. Neurofilament-68 kDa immunoreactivity was used to identify retinal ganglion cells (RGC) with immunohistochemistry. Additional cell markers were used to further characterize the cytoarchitecture of the organotypic retina cultures. Retina explants attached very well to the coated coverslips allowing for experimental manipulation and pharmacological access to the tissue. Hematoxylin-Eosin (HE) staining of vertical cryostat sections of retina explants demonstrated well preserved intact cytoarchitecture under organotypic culture conditions and PKCalpha, Calbindin, GABA, Rhodopsin, GFAP and neurofilament immunoreactivities identifying rod bipolar, horizontal, amacrine, photoreceptor, glial, and retinal ganglion cells, respectively, were not different from freshly isolated mouse retina. Dose dependent glutamate toxicity and accompanying RGC apoptotic cell death were determined by TUNEL histochemistry. In contrast to previously published methods using slice or floating whole-mount cultures, the ex vivo culture system presented here combines accessibility to experimental manipulation, and adherence of whole-mount cultures to a substrate with a significant preservation of retinal cell types, numbers and morphology. The described retina explant culture on glass coverslips allows for effective pharmacological manipulation including the study of neuronal cell death and RGC physiology.

Excess Bcl-XL increases the intrinsic growth potential of adult CNS neurons in vitro

The regenerative potential of adult mammalian CNS neurons is limited. Recent data suggest that inactivation of major growth inhibitors may not suffice to induce robust regeneration from mature neurons unless the intrinsic growth state is modulated. To investigate a possible role of Bcl-XL for axon regeneration in the adult mammalian CNS, Bcl-XL was adenovirally overexpressed in severed rat RGCs. Bcl-XL overexpression in mature axotomized RGCs in vivo increased both numbers [3.10-fold (+/-0.20)] and cumulative length [6.72-fold (+/-0.47)] of neurites regenerated from retinal explants, and this effect was further pronounced in the central retina where specific and dense axoplasmatic transduction occurs. Similarly, delayed Bcl-XL gene transfer to explanted retinae 12-13 days after lesion increased the numbers and length of emanating neurites by a factor of 5.22 (+/-0.41) and 8.29 (+/-0.69), respectively. In vivo, intraretinal sprouting of unmyelinated RGC axons into the nerve fiber layer was increased. However, fiber ingrowth into the optic nerve remained sparse, likely due to myelin inhibitors and scar components. Therefore, Bcl-XL overexpression may enhance, but may not be sufficient to, restitute functional regeneration in the adult CNS. As assessed by cell quantification analysis, Bcl-XL overexpression rescued a higher proportion of RGCs in vivo than in vitro. Therefore, Bcl-XL is capable to induce both neuronal survival and axon regeneration, but these two processes appear to be differentially modified by distinct pathways in vivo.