Retinal ganglion cell survival after severe optic nerve injury is modulated by crosstalk between Jak/Stat signaling and innate immune responses in the zebrafish retina.

Visual information is transmitted from the eye to the brain along the optic nerve, a structure composed of retinal ganglion cell (RGC) axons. The optic nerve is highly vulnerable to damage in neurodegenerative diseases, such as glaucoma, and there are currently no FDA-approved drugs or therapies to protect RGCs from death. Zebrafish possess remarkable neuroprotective and regenerative abilities. Here, utilizing an optic nerve transection (ONT) injury and an RNA-seq-based approach, we identify genes and pathways active in RGCs that may modulate their survival. Through pharmacological perturbation, we demonstrate that Jak/Stat pathway activity is required for RGC survival after ONT. Furthermore, we show that immune responses directly contribute to RGC death after ONT; macrophages/microglia are recruited to the retina and blocking neuroinflammation or depleting these cells after ONT rescues survival of RGCs. Taken together, these data support a model in which crosstalk between macrophages/microglia and RGCs, mediated by Jak/Stat pathway activity, regulates RGC survival after optic nerve injury.

Microglia/Macrophages and CD4+CD25+ T Cells Enhance the Ability of Injury-Activated Lymphocytes to Reduce Traumatic Optic Neuropathy In Vitro.

Inflammation after acute CNS injury plays a dual role. The interplay between immune cells and inflammatory mediators is critical to the outcome of injured neurons. Microglia/macrophages are the first sensors and regulators of the immune response. We previously found that the enhancement of macrophages on neuron survival does not persist in thymectomized rats. How T lymphocytes and macrophages interact and benefit neuron survival is not fully elucidated. To this point, we introduce and characterize a cell-retina co-culture model that mimics the recruitment of peripheral lymphocytes at the injury site. Three-day post-optic nerve transection (ONT) in Fischer 344 rats, transected retinas were co-cultured with either peripheral lymph node-derived lymphocytes (injury-activated) or from intact rats as the control. The injury-activated lymphocytes preserved retinal ganglion cells (RGCs) and caused extensive retina microglial/macrophage infiltration. CD4+CD25+ T cells were upregulated in the injury-activated lymphocytes and increased RGC survival, suggesting that CD4+CD25+ T cells suppressed the cytotoxicity of control lymphocytes. When microglia/macrophages were depleted by clodronate, neuron loss was more extensive, the cytotoxicity of control lymphocytes on RGCs was alleviated, and the neuroprotective effect of injury-activated lymphocytes remain unchanged Cytokine detection showed an increase in IL-6 and TNF-α levels that were reduced with microglia/macrophage depletion. Our results suggest that microglial/macrophage infiltration into axotomized retinas promotes RGC survival by secreting cytokines to induce CD4+CD25+ T cells and suppress T cell-mediated RGC toxicity. These findings reveal a specific role for microglia/macrophage and CD4+CD25+ T cells in inflammation after CNS injury, thereby adding to the mechanistic basis for the development of microglial/macrophage modulation therapy for traumatic CNS injury.

Retinal Ganglion Cell Axon Regeneration Requires Complement and Myeloid Cell Activity within the Optic Nerve.

Axon regenerative failure in the mature CNS contributes to functional deficits following many traumatic injuries, ischemic injuries, and neurodegenerative diseases. The complement cascade of the innate immune system responds to pathogen threat through inflammatory cell activation, pathogen opsonization, and pathogen lysis, and complement is also involved in CNS development, neuroplasticity, injury, and disease. Here, we investigated the involvement of the classical complement cascade and microglia/monocytes in CNS repair using the mouse optic nerve injury (ONI) model, in which axons arising from retinal ganglion cells (RGCs) are disrupted. We report that central complement C3 protein and mRNA, classical complement C1q protein and mRNA, and microglia/monocyte phagocytic complement receptor CR3 all increase in response to ONI, especially within the optic nerve itself. Importantly, genetic deletion of C1q, C3, or CR3 attenuates RGC axon regeneration induced by several distinct methods, with minimal effects on RGC survival. Local injections of C1q function-blocking antibody revealed that complement acts primarily within the optic nerve, not retina, to support regeneration. Moreover, C1q opsonizes and CR3+ microglia/monocytes phagocytose growth-inhibitory myelin debris after ONI, a likely mechanism through which complement and myeloid cells support axon regeneration. Collectively, these results indicate that local optic nerve complement-myeloid phagocytic signaling is required for CNS axon regrowth, emphasizing the axonal compartment and highlighting a beneficial neuroimmune role for complement and microglia/monocytes in CNS repair.SIGNIFICANCE STATEMENT Despite the importance of achieving axon regeneration after CNS injury and the inevitability of inflammation after such injury, the contributions of complement and microglia to CNS axon regeneration are largely unknown. Whereas inflammation is commonly thought to exacerbate the effects of CNS injury, we find that complement proteins C1q and C3 and microglia/monocyte phagocytic complement receptor CR3 are each required for retinal ganglion cell axon regeneration through the injured mouse optic nerve. Also, whereas studies of optic nerve regeneration generally focus on the retina, we show that the regeneration-relevant role of complement and microglia/monocytes likely involves myelin phagocytosis within the optic nerve. Thus, our results point to the importance of the innate immune response for CNS repair.

MMP2 Modulates Inflammatory Response during Axonal Regeneration in the Murine Visual System.

Neuroinflammation has been put forward as a mechanism triggering axonal regrowth in the mammalian central nervous system (CNS), yet little is known about the underlying cellular and molecular players connecting these two processes. In this study, we provide evidence that MMP2 is an essential factor linking inflammation to axonal regeneration by using an in vivo mouse model of inflammation-induced axonal regeneration in the optic nerve. We show that infiltrating myeloid cells abundantly express MMP2 and that MMP2 deficiency results in reduced long-distance axonal regeneration. However, this phenotype can be rescued by restoring MMP2 expression in myeloid cells via a heterologous bone marrow transplantation. Furthermore, while MMP2 deficiency does not affect the number of infiltrating myeloid cells, it does determine the coordinated expression of pro- and anti-inflammatory molecules. Altogether, in addition to its role in axonal regeneration via resolution of the glial scar, here, we reveal a new mechanism via which MMP2 facilitates axonal regeneration, namely orchestrating the expression of pro- and anti-inflammatory molecules by infiltrating innate immune cells.

Protection against experimental cisplatin-induced optic nerve toxicity using resveratrol: A rat model study.

AIM: To investigate the effects of resveratrol on oxidative stress and inflammation parameters and histological alterations in cisplatin-induced optic nerve damage in a mouse model. MATERIAL AND METHOD: Thirty-six albino Wistar male rats were divided into three groups as control, 5 mg/kg cisplatin-administered (Cis) and 5 mg/kg cisplatin + 25 mg/kg resveratrol-administered (Cis + Res) animals. At the end of the experimental period, the rats were sacrificed with high-dose (50 mg/kg) thiopental sodium, and their optic nerves were dissected. Malondialdehyde (MDA), total glutathione (tGSH), total oxidant status (TOS), total antioxidant status (TAS), tumour necrosis factor alpha (TNF-α), nuclear factor kappa B (NF-KB) levels, and histopathological findings were assessed using the optic nerve tissues. RESULTS: In the Cis + Res group, the MDA, TOS, OSI, TNF-a and NFK-B levels were significantly lower and the tGSH and TAS levels were significantly higher compared with the Cis group (P = 0.001). In histological evaluations, there were dilated and congested blood vessels, destruction, oedema, degeneration, haemorrhage, and proliferating capillaries indicating the presence of inflammation and damage only in the Cis-administered group. However, in the Cis + Res group, the histological findings were very similar to the healthy controls. CONCLUSION: Resveratrol is a promising neuroprotective agent for cisplatin-induced optic nerve toxicity with its anti-oxidant and anti-inflammatory effects. Further investigations are needed to evaluate the possible therapeutic effects on other optic nerve toxicities.

Visual recovery following optic nerve crush in male and female wild-type and TRIF-deficient mice.

BACKGROUND: There is growing evidence that the TIR-domain-containing adapter-inducing interferon-ß (TRIF) pathway is implicated in the modulation of neuroinflammation following injuries to the brain and retina. After exposure to injury or to excitotoxic pathogens, toll-like receptors (TLR) activate the innate immune system signaling cascade and stimulate the release of inflammatory cytokines. Inhibition of the TLR4 receptor has been shown to enhance retinal ganglion cell (RGC) survival in optic nerve crush (ONC) and in ischemic injury to other parts of the brain. OBJECTIVE: Based on this evidence, we tested the hypothesis that mice with the TRIF gene knocked out (TKO) will demonstrate decreased inflammatory responses and greater functional recovery after ONC. METHODS: Four experimental groups -TKO ONC (12 males and 8 females), WT ONC (10 males and 8 females), TKO sham (9 males and 5 females), and WT sham (7 males and 5 females) -were used as subjects. Visual evoked potentials (VEP) were recorded in the left and right primary visual cortices and optomotor response were assessed in all mice at 14, 30, and 80 days after ONC. GFAP and Iba-1 were used as markers for astrocytes and microglial cells respectively at 7 days after ONC, along with NF-kB to measure inflammatory effects downstream of TRIF activation; RMPBS marker was used to visualize RGC survival and GAP-43 was used as a marker of regenerating optic nerve axons at 30 days after ONC. RESULTS: We found reduced inflammatory response in the retina at 7 days post-ONC, less RGC loss and greater axonal regeneration 30 days post-ONC, and better recovery of visual function 80 days post-ONC in TKO mice compared to WT mice. CONCLUSIONS: Our study showed that the TRIF pathway is involved in post-ONC inflammatory response and gliosis and that deletion of TRIF induces better RGC survival and regeneration and better functional recovery in mice. Our results suggest the TRIF pathway as a potential therapeutic target for reducing the inflammatory damage caused by nervous system injury.

Anterior chamber associated immune deviation to cytosolic neural antigens avoids self-reactivity after optic nerve injury and polarizes the retinal environment to an anti-inflammatory profile.

It has been hypothesized that anterior chamber-associated immune deviation (ACAID) to neural antigens induced prior to central nervous system injury can inhibit self-reactivity and lessen secondary degeneration. This work evaluated the effect of ACAID induced to three neural tissue-derived extracts (whole extract, cytosolic extract, CE; or organelle-membrane extract) prior to optic nerve injury on retinal ganglion cell (RGC) survival. The results show that only ACAID to the CE increased RGC survival at 7 and14 days post-injury (dpi). This effect was achieved by retinal polarization towards an anti-inflammatory profile, driven by regulatory T cells and M2-type macrophages at 7 dpi.

The levels and significance of inflammasomes in the mouse retina following optic nerve crush.

Inflammasomes play an important role in neuroinflammation. However, their function during the secondary death of retinal cells after traumatic optic neuropathy and their dependence on pathogen stimuli remains unclear. Therefore, we evaluated the expression profiles of 10 different inflammasome-related mRNAs in the retina following an optic nerve crush (OPC) injury under both conventional sterile as well as non-sterile conditions, and validated two significantly varied ones on a protein level. While most factors were much more highly elevated in non-sterile conditions, both Nlrp1b and Nlrp3 inflammasome mRNAs were increased significantly on postoperative day 1 to day 7 in the mouse sterile OPC injury model. While production of the inflammation-associated cytokines IL-1ß and IL-18 could be continuously detected on an mRNA level postoperatively, a clear peak could be seen on day 7 that coincided with maximal expression of caspase-1 mRNA and with observation of retinal ganglion cells death, despite the mice being held in specific-pathogen free conditions. As such, the pro-inflammatory cytokines activated by inflammasome activation during OPC injury may drive secondary cell death through pyroptosis, and inhibition of these delayed responses may be an important means of preventing worsened injury and loss of vision in trauma patients.

Microglia Regulate Neuroglia Remodeling in Various Ocular and Retinal Injuries.

Reactive microglia and infiltrating peripheral monocytes have been implicated in many neurodegenerative diseases of the retina and CNS. However, their specific contribution in retinal degeneration remains unclear. We recently showed that peripheral monocytes that infiltrate the retina after ocular injury in mice become permanently engrafted into the tissue, establishing a proinflammatory phenotype that promotes neurodegeneration. In this study, we show that microglia regulate the process of neuroglia remodeling during ocular injury, and their depletion results in marked upregulation of inflammatory markers, such as Il17f, Tnfsf11, Ccl4, Il1a, Ccr2, Il4, Il5, and Csf2 in the retina, and abnormal engraftment of peripheral CCR2+ CX3CR1+ monocytes into the retina, which is associated with increased retinal ganglion cell loss, retinal nerve fiber layer thinning, and pigmentation onto the retinal surface. Furthermore, we show that other types of ocular injuries, such as penetrating corneal trauma and ocular hypertension also cause similar changes. However, optic nerve crush injury-mediated retinal ganglion cell loss evokes neither peripheral monocyte response in the retina nor pigmentation, although peripheral CX3CR1+ and CCR2+ monocytes infiltrate the optic nerve injury site and remain present for months. Our study suggests that microglia are key regulators of peripheral monocyte infiltration and retinal pigment epithelium migration, and their depletion results in abnormal neuroglia remodeling that exacerbates neuroretinal tissue damage. This mechanism of retinal damage through neuroglia remodeling may be clinically important for the treatment of patients with ocular injuries, including surgical traumas.

The effects of immune protein CD3ζ development and degeneration of retinal neurons after optic nerve injury.

Major histocompatibility complex (MHC) class I molecules and their receptors play fundamental roles in neuronal death during diseases. T-cell receptors (TCR) function as MHCI receptor on T-cells and both MHCI and a key component of TCR, CD3ζ, are expressed by mouse retinal ganglion cells (RGCs) and displaced amacrine cells. Mutation of these molecules compromises the development of RGCs. We investigated whether CD3ζ regulates the development and degeneration of amacrine cells after RGC death. Surprisingly, mutation of CD3ζ not only impairs the proper development of amacrine cells expressing CD3ζ but also those not expressing CD3ζ. In contrast to effects of MHCI and its receptor, PirB, on other neurons, mutation of CD3ζ has no effect on RGC death and starburst amacrine cells degeneration after optic nerve crush. Thus, unlike MHCI and PirB, CD3ζ regulates the development of RGCs and amacrine cells but not their degeneration after optic nerve crush.

The retinal pigment epithelium as a gateway for monocyte trafficking into the eye.

The choroid plexus epithelium within the brain ventricles orchestrates blood-derived monocyte entry to the central nervous system under injurious conditions, including when the primary injury site is remote from the brain. Here, we hypothesized that the retinal pigment epithelium (RPE) serves a parallel role, as a gateway for monocyte trafficking to the retina following direct or remote injury. We found elevated expression of genes encoding leukocyte trafficking determinants in mouse RPE as a consequence of retinal glutamate intoxication or optic nerve crush (ONC). Blocking VCAM-1 after ONC interfered with monocyte infiltration into the retina and resulted in a local pro-inflammatory cytokine bias. Live imaging of the injured eye showed monocyte accumulation first in the RPE, and subsequently in the retina, and peripheral leukocytes formed close contact with the RPE Our findings further implied that the ocular milieu can confer monocytes a phenotype advantageous for neuroprotection. These results suggest that the eye utilizes a mechanism of crosstalk with the immune system similar to that of the brain, whereby epithelial barriers serve as gateways for leukocyte entry.

Immune protective mechanism of rMOMP protein ophthalmic vaccine regarding intraocular hypertension and retinal optic nerve injury in rats.

The aim of this study was to explore the immune protective mechanism of rMOMP protein vaccine in intraocular hypertension and retinal optic nerve injury in rats. The rMOMP protein ophthalmic vaccine was prepared and quality-controlled. Sixty normal adult SD rats were randomly divided into two groups to establish a chronic ocular hypertension model and an optic nerve injury model. The model rats were vaccinated with rMOMP-CS ophthalmic vaccine. Fluorogold retrograde tracing was used to observe retinal ganglion cells, and an immunofluorescence method to determine the expression of retinal GAP43, CD3, BDNF, and GDNF. rMOMP protein ophthalmic vaccine met the requirements for medicinal use. The number of retinal ganglion cells (RGCs) of the rMOMP-CS group in the chronic ocular hypertension model was significantly higher than that of the CS group (P < 0.05). The count of RGCs of the rMOMP-CS group in the optic nerve clamping injury model was significantly higher than that of the CS group (P < 0.01). Thus, rMOMP protein ophthalmic vaccine can induce an increase in the expression of retinal neurotrophic factors, thereby exerting a protective effect on damaged retinal optic nerve.

Regulatory T cells in central nervous system injury: a double-edged sword.

Previous research investigating the roles of T effector (T(eff)) and T regulatory (T(reg)) cells after injury to the CNS has yielded contradictory conclusions, with both protective and destructive functions being ascribed to each of these T cell subpopulations. In this work, we study this dichotomy by examining how regulation of the immune system affects the response to CNS trauma. We show that, in response to CNS injury, T(eff) and T(reg) subsets in the CNS-draining deep cervical lymph nodes are activated, and surgical resection of these lymph nodes results in impaired neuronal survival. Depletion of T(reg), not surprisingly, induces a robust T(eff) response in the draining lymph nodes and is associated with impaired neuronal survival. Interestingly, however, injection of exogenous T(reg) cells, which limits the spontaneous beneficial immune response after CNS injury, also impairs neuronal survival. We found that no T(reg) accumulate at the site of CNS injury, and that changes in T(reg) numbers do not alter the amount of infiltration by other immune cells into the site of injury. The phenotype of macrophages at the site, however, is affected: both addition and removal of T(reg) negatively impact the numbers of macrophages with alternatively activated (tissue-building) phenotype. Our data demonstrate that neuronal survival after CNS injury is impaired when T(reg) cells are either removed or added. With this exacerbation of neurodegeneration seen with both addition and depletion of T(reg), we recommend exercising extreme caution when considering the therapeutic targeting of T(reg) cells after CNS injury, and possibly in chronic neurodegenerative conditions.

Effect of RSCs combined with COP-1 on optic nerve damage in glaucoma rat model.

OBJECTIVE: To explore effect of retinal stem cells (RSCs) combined with copolymer-1 (COP-1) immunotherapy on optic nerve damage in glaucoma rat model. METHODS: A total of 40 SD rats were selected for glaucoma model and were randomly divided into 4 groups to observe protective effects of RSCs transplantation combined with COP-1. RESULTS: Brain-derived neurotrophic factor (BDNF) and insulin like growth factor-1 (IGF-1) were either positive in retina of RSCs transplanted or COP-1 immunological treated rat. Positive rate of BDNF and IGF-1 and expression of mRNA and protein were significantly higher in RSCs transplantation combined with COP-1 immunotherapy treated rats compared with the other 3 groups, in which amount of apoptotic RGCs was lowest. CONCLUSIONS: RSCs transplantation combined with COP-1 immunotherapy can promote the secretion of BDNF and IGF-1. They protect RGCs in glaucoma rats in coordination, significantly reduce the number of apoptosis RGCs so as to alleviate the optic nerve damage. It ponits a new research direction for treatment of glaucoma.

Innate immune network in the retina activated by optic nerve crush.

PURPOSE: Innate immunity plays a role in many diseases, including glaucoma and AMD. We have used transcriptome profiling in the mouse to identify a network of genes involved in innate immunity that is present in the normal retina and that is activated by optic nerve crush (ONC). METHODS: Using a recombinant inbred (RI) mouse strain set (BXD, C57BL/6 crossed with DBA/2J mice), we generate expression datasets (Illumina WG 6.2 arrays) in the normal mouse retina and 2 days after ONC. The normal dataset is constructed from retinas from 80 mouse strains and the ONC dataset is constructed from 62 strains. These large datasets are hosted by GeneNetwork.org, along with a series of powerful bioinformatic tools. RESULTS: In the retina datasets, one intriguing network involves transcripts associated with the innate immunity. Using C4b to interrogate the normal dataset, we can identify a group of genes that are coregulated across the BXD RI strains. Many of the genes in this network are associated with the innate immune system, including Serping1, Casp1, C3, Icam1, Tgfbr2, Cfi, Clu, C1qg, Aif1, and Cd74. Following ONC, the expression of these genes is upregulated, along with an increase in coordinated expression across the BXD strains. Many of the genes in this network are risk factors for AMD, including C3, EFEMP1, MCDR2, CFB, TLR4, HTA1, and C1QTNF5. CONCLUSIONS: We found a retina-intrinsic innate immunity network that is activated by injury including ONC. Many of the genes in this network are risk factors for retinal disease.

Sciatic nerve conditioning lesion increases macrophage response but it does not promote the regeneration of injured optic nerves.

UNLABELLED: Injured optic nerves in the matured central nervous system (CNS), alike injured neurons in other CNS regions, fail to regenerate. Interestingly, activation of inflammatory cells (macrophages) following optic lens injury or implantation of peripheral nerve fragments into the vitreous body, have been previously reported to stimulate retinal ganglion cells (RGCs) to regenerate axons across the injury site and into the distal optic nerve. In addition, the beneficial role of macrophage cells has also been demonstrated in the regeneration of lesioned spinal neurons following sciatic nerve injury. However, it is not known whether these locally activated macrophage cells also contribute to the regeneration of remotely injured neurons within the CNS. Adult Sprague Dawley rats received a conditioning sciatic nerve injury followed by an optic nerve crush (ONC). Retrograde and anterograde tracing results revealed that injured optic axons did not regenerate after peripheral dorsal root ganglion (DRG) lesion, as the beneficial effects of this injury extended only locally. However, a greater inflammatory infiltration/activation was found in injury-combined animals compared to controls, although this was not sufficient to trigger a systemic regenerative response. Proximity of cell body response to injury, accompanied by a timely macrophage activation are critical factors for regeneration of injured CNS neurons to occur. Immune cell surveillance into the CNS compartment was enhanced following peripheral nerve injury. SCOPE: nervous system development, regeneration and aging.

Early events of secondary degeneration after partial optic nerve transection: an immunohistochemical study.

Secondary degeneration in the central nervous system involves indirect damage to neurons and glia away from the initial injury. Partial transection of the dorsal optic nerve (ON) results in precise spatial separation of the primary trauma from delayed degenerative events in ventrally placed axons and parent somata. Here we conduct an immunohistochemical survey of secondary cellular changes in and around axons and their parent retinal ganglion cell (RGC) somata during the first 3 days after a restricted, dorsal ON transection. This is before the secondary loss of RGCs and axons projecting through the uninjured, ventral portion of the ON. Within 5 min, manganese superoxide dismutase (MnSOD; a marker of oxidative stress) co-localizes within the astrocytic network across the entire profile of the ON. Secondary astrocyte hypertrophy of immunofluorescent labeling was evident from 3 h, with sustained increases in myelin basic protein immunoreactivity across the nerve by 24 h. Increases in NG-2-positive oligodendrocyte precursor cells, ED-1-positive activated microglia/macrophages, and Iba1-positive reactive resident microglia/macrophage numbers were only seen in ON vulnerable to secondary degeneration by 3 days. Changes within RGC somata exclusively vulnerable to secondary degeneration were detected at 24 h, as evidenced by increases in MnSOD immunoreactivity, followed by increases in c-jun immunoreactivity at 3 days. Treatment with the voltage-gated calcium channel blocker lomerizine did not alter any measured outcome. We conclude that oxidative stress spreading via the astrocytic network and from injured axons to parent RGC somata is an early event during secondary degeneration, and containment is likely to be required in order to prevent further damage to the nerve.

Neuroprotective and axon growth-promoting effects following inflammatory stimulation on mature retinal ganglion cells in mice depend on ciliary neurotrophic factor and leukemia inhibitory factor.

After optic nerve injury retinal ganglion cells (RGCs) normally fail to regenerate axons in the optic nerve and undergo apoptosis. However, lens injury (LI) or intravitreal application of zymosan switch RGCs into an active regenerative state, enabling these neurons to survive axotomy and to regenerate axons into the injured optic nerve. Several factors have been proposed to mediate the beneficial effects of LI. Here, we investigated the contribution of glial-derived ciliary neurotrophic factor (CNTF) to LI-mediated regeneration and neuroprotection using wild-type and CNTF-deficient mice. In wild-type mice, CNTF expression was strongly upregulated in retinal astrocytes, the JAK/STAT3 pathway was activated in RGCs, and RGCs were transformed into an active regenerative state after LI. Interestingly, retinal LIF expression was correlated with CNTF expression after LI. In CNTF-deficient mice, the neuroprotective and axon growth-promoting effects of LI were significantly reduced compared with wild-type animals, despite an observed compensatory upregulation of LIF expression in CNTF-deficient mice. The positive effects of LI and also zymosan were completely abolished in CNTF/LIF double knock-out mice, whereas LI-induced glial and macrophage activation was not compromised. In culture CNTF and LIF markedly stimulated neurite outgrowth of mature RGCs. These data confirm a key role for CNTF in directly mediating the neuroprotective and axon regenerative effects of inflammatory stimulation in the eye and identify LIF as an additional contributing factor.

Different factors promote axonal regeneration of adult rat retinal ganglion cells after lens injury and intravitreal peripheral nerve grafting.

We have investigated the differential mediators of the neurotrophic effects of intravitreal peripheral nerve grafting and lens injury on adult rat retinal ganglion cells (RGC). Lens injury and intravitreal peripheral nerve grafting both stimulated RGC neurite growth in vitro and axon regeneration past the optic nerve lesion site in vivo concomitant with activation of retinal glia and invasion of macrophages into the eye. These observations, together with the results of coculture studies using a macrophage-free intact peripheral nerve segment, a macrophage-free intact lens, a macrophage-rich peripheral nerve segment, or a macrophage-rich injured lens in retinal cultures suggest that the stimulation of RGC axon regeneration by lens injury and intravitreal peripheral nerve grafting share a common macrophage-derived component overlain by distinct lens-derived and peripheral nerve-derived neurotrophic factors, respectively. RGC axon regeneration following lens injury and intravitreal peripheral nerve grafting was similar in vivo, correlating with similar retinal glia activation whereas, in vitro, the level of RGC neurite outgrowth was significantly higher following intravitreal peripheral nerve grafting compared with lens injury, concomitant with the presence of increased numbers of activated retinal glia. This suggests that in vivo RGC axon regeneration induced by lens injury and peripheral nerve grafting may be limited, in part, by factors derived from activated retinal glia.