Retinal Neuronal Injury Research Articles

Neuroprotective and Anti-Inflammatory Activities of Hybrid Small-Molecule SA-10 in Ischemia/Reperfusion-Induced Retinal Neuronal Injury Models.

To induce I/R injury and inflammation, we subjected R28 and primary microglial cells to oxygen glucose deprivation (OGD) for 6 h in vitro or treated these cells with a cocktail of TNF-α, IL-1β and IFN-γ for 1 h, followed by the addition of SA-10 (10 µM). Inhibition of microglial activation, ROS scavenging, cytoprotective and anti-inflammatory activities were measured. In vivo I/R-injured mouse retinas were treated with either PBS or SA-10 (2%) intravitreally, and pattern electroretinogram (ERG), spectral-domain optical coherence tomography, flash ERG and retinal immunocytochemistry were performed. SA-10 significantly inhibited microglial activation and inflammation in vitro. Compared to the control, the compound SA-10 significantly attenuated cell death in both microglia (43% vs. 13%) and R28 cells (52% vs. 17%), decreased ROS (38% vs. 68%) production in retinal microglia cells, preserved neural retinal function and increased SOD1 in mouse eyes. SA-10 is protective to retinal neurons by decreasing oxidative stress and inflammatory cytokines.

GSK840 Alleviates Retinal Neuronal Injury by Inhibiting RIPK3/MLKL-Mediated RGC Necroptosis After Ischemia/Reperfusion.

This study aimed to explore the impact of GSK840 on retinal neuronal injury after retinal ischemia/reperfusion (IR) and its associated mechanism. We established an in vivo mouse model of IR and an in vitro model of oxygen and glucose deprivation/reoxygenation (OGDR) in primary mouse retinal ganglion cells (RGCs). GSK840, a small-molecule compound, was used to specifically inhibit RIPK3/MLKL-dependent necroptosis. Retinal structure and function evaluation was performed by using hematoxylin and eosin staining, optical coherence tomography, and electroretinography. Propidium Iodide (PI) staining was used for detection of necroptotic cell death, whereas Western blot analysis and immunofluorescence were used to assess necroptosis-related proteins and inner retinal neurons. RIPK3/MLKL-dependent necroptosis was rapidly activated in RGCs following retinal IR or OGDR. GSK840 helped maintain relatively normal inner retinal structure and thickness by preserving inner retinal neurons, particularly RGCs. Meanwhile, GSK840 ameliorated IR-induced visual dysfunction, as evidenced by the improved amplitudes of photopic negative response, a-wave, b-wave, and oscillatory potentials. And GSK840 treatment significantly reduced the population of PI+ RGCs after injury. Mechanistically, GSK840 ameliorated RGC necroptosis by inhibiting the RIPK3/MLKL pathway. GSK840 exerts protective effects against retinal neuronal injury after IR by inhibiting RIPK3/MLKL-mediated RGC necroptosis. GSK840 may represent a protective strategy for RGC degeneration in ischemic retinopathy.

Blue Light-Induced Retinal Neuronal Injury and Amelioration by Commercially Available Blue Light-Blocking Lenses.

Blue light exposure-induced retinal damage has been extensively studied. Although many in vitro studies have shown the benefits of blue light-blocking lenses (BBL) there have been few comprehensive in vivo studies to assess the effects of BBL. We investigated the influence of blue light exposure using light-emitting diodes on retinal histology and visual cortex neurons in rodents. We also considered whether retinal and cortical changes induced by blue light could be ameliorated with blue light-blocking lenses. A total of n = 24 (n = 6 in each group; control, light exposure without lenses, two different BBLs)) male Wistar rats were subjected to blue light exposure (LEDs, 450–500 lux) without or with BBLs (400–490 nm) for 28 days on a 12:12 h light–dark cycle. Histological analysis of retinae revealed apoptosis and necrosis of the retinal pigment epithelium (RPE), photoreceptors, and inner retina in the light exposure (LE) group, along with increase caspase-3 immunostaining in the ganglion cell layer (p < 0.001). BBL groups showed less caspase-3 immunostaining compared with the LE group (p < 0.001). V1-L5PNs (primary visual cortex layer 5 pyramidal neurons) demonstrated reduced branching and intersections points for apical (p < 0.001) and basal (p < 0.05) dendrites following blue light exposure. Blue light-blocking lenses significantly improved the number of basal branching points compared with the LE group. Our study shows that prolonged exposure to high levels of blue light pose a significant hazard to the visual system resulting in damage to the retina with the associated remodeling of visual cortex neurons. BBL may offer moderate protection against exposure to high levels of blue light.

2/15-Lipoxygenase Contributes to Retinal Neuronal Injury in Diabetic Retinopathy

2/15-Lipoxygenase Contributes to Retinal Neuronal Injury in Diabetic Retinopathy

Deletion of Arginase 2 Ameliorates Retinal Neurodegeneration in a Mouse Model of Multiple Sclerosis.

Optic neuritis is a major clinical feature of multiple sclerosis (MS) and can lead to temporary or permanent vision loss. Previous studies from our laboratory have demonstrated the critical involvement of arginase 2 (A2) in retinal neurodegeneration in models of ischemic retinopathy. The current study was undertaken to investigate the role of A2 in MS-mediated retinal neuronal damage and degeneration. Experimental autoimmune encephalomyelitis (EAE) was induced in wild-type (WT) and A2 knockout (A2-/-) mice. EAE-induced motor deficits, loss of retinal ganglion cells, retinal thinning, inflammatory signaling, and glial activation were studied in EAE-treated WT and A2-/- mice and their respective controls. Increased expression of A2 was observed in WT retinas in response to EAE induction. EAE-induced motor deficits were markedly reduced in A2-/- mice compared with WT controls. Retinal flat mount studies demonstrated a significant reduction in the number of RGCs in WT EAE retinas in comparison with normal control mice. A significant improvement in neuronal survival was evident in retinas of EAE-induced A2-/- mice compared with WT. RNA levels of the proinflammatory molecules CCL2, COX2, IL-1α, and IL-12α were significantly reduced in the A2-/- EAE retinas compared with WT EAE. EAE-induced activation of glia (microglia and Müller cells) was markedly reduced in A2-/- retinas compared with WT. Western blot analyses showed increased levels of phospho-ERK1/2 and reduced levels of phospho-BAD in the WT EAE retina, while these changes were prevented in A2-/- mice. In conclusion, our studies establish EAE as an excellent model to study MS-mediated retinal neuronal damage and suggest the potential value of targeting A2 as a therapy to prevent MS-mediated retinal neuronal injury.

Loss of XBP1 Leads to Early-Onset Retinal Neurodegeneration in a Mouse Model of Type I Diabetes.

Retinal neuronal injury and degeneration is one of the primary manifestations of diabetic retinopathy, a leading cause of vision loss in working age adults. In pathological conditions, including diabetes and some physiological conditions such as aging, protein homeostasis can become disrupted, leading to endoplasmic reticulum (ER) stress. Severe or unmitigated ER stress can lead to cell death, which in retinal neurons results in irreversible loss of visual function. X-box binding protein 1 (XBP1) is a major transcription factor responsible for the adaptive unfolded protein response (UPR) to maintain protein homeostasis in cells undergoing ER stress. The purpose of this study is to determine the role of XBP1-mediated UPR in retinal neuronal survival and function in a mouse model of type 1 diabetes. Using a conditional retina-specific XBP1 knockout mouse line, we demonstrate that depletion of XBP1 in retinal neurons results in early onset retinal function decline, loss of retinal ganglion cells and photoreceptors, disrupted photoreceptor ribbon synapses, and Müller cell activation after induction of diabetes. Our findings suggest an important role of XBP1-mediated adaptive UPR in retinal neuronal survival and function in diabetes.

Neuroprotective Effects of HSF1 in Retinal Ischemia-Reperfusion Injury.

PurposeRetinal ischemia, a common cause of several vision-threatening diseases, contributes to the death of retinal neurons, particularly retinal ganglion cells (RGCs). Heat shock transcription factor 1 (HSF1), a stress-responsive protein, has been shown to be important in response to cellular stress stimuli, including ischemia. This study is to investigate whether HSF1 has a role in retinal neuronal injury in a mouse model of retinal ischemia-reperfusion (IR).MethodsIR was induced by inserting an infusion needle into the anterior chamber of the right eye and elevating a saline reservoir connected to the needle to raise the intraocular pressure to 110 mm Hg for 45 minutes. HSF1, Hsp70, molecules in the endoplasmic reticulum (ER) stress branches, tau phosphorylation, inflammatory molecules, and RGC injury were determined by immunohistochemistry, Western blot, or quantitative PCR.ResultsHSF1 expression was significantly increased in the retina 6 hours after IR. Using our novel transgenic mice carrying full-length human HSF gene, we demonstrated that IR-induced retinal neuronal apoptosis and necroptosis were abrogated 12 hours after IR. RGCs and their function were preserved in the HSF1 transgenic mice 7 days after IR. Mechanistically, the beneficial effects of HSF1 may be mediated by its induction of chaperone protein Hsp70 and alleviation of ER stress, leading to decreased tau phosphorylation and attenuated inflammatory response 12 to 24 hours after IR.ConclusionsThese data provide compelling evidence that HSF1 is neuroprotective against retinal IR injury, and boosting HSF1 expression may be a beneficial strategy to limit neuronal degeneration in retinal diseases.

AAV2-mediated GRP78 Transfer Alleviates Retinal Neuronal Injury by Downregulating ER Stress and Tau Oligomer Formation.

PurposeRetinal ganglion cell (RGC) death following axonal injury occurring in traumatic optic neuropathy (TON) causes irreversible vision loss. GRP78 is a molecular chaperone that enhances protein folding and controls activation of endoplasmic reticulum (ER) stress pathways. This study determined whether adeno-associated virus (AAV)-mediated gene transfer of GRP78 protected RGCs from death in a mouse model of TON induced by optic nerve crush (ONC).MethodsONC was induced by a transient crush of optic nerve behind the eye globe. AAV was used to deliver genes into retina. Molecules in the ER stress branches, tau oligomers, and RGC injury were determined by immunohistochemistry or Western blot.ResultsAmong tested AAV serotypes, AAV2 was the most efficient for delivering genes to RGCs. Intravitreal delivery of AAV2-GRP78 markedly attenuated ER stress and RGC death 3 days after ONC, and significantly improved RGC survival and function 7 days after ONC. Protein aggregation is increased during ER stress and aggregated proteins such as tau oligomers are key players in neurodegenerative diseases. AAV2-GRP78 alleviated ONC-induced increases in tau phosphorylation and oligomerization. Furthermore, tau oligomers directly induced RGC death, and blocking tau oligomers with tau oligomer monoclonal antibody (TOMA) attenuated ONC-induced RGC loss.ConclusionThese data indicate that the beneficial effect of AAV2-GRP78 is partially mediated by the reduction of misfolded tau, and provide compelling evidence that gene therapy with AAV2-GRP78 or immunotherapy with TOMA offers novel therapeutic approaches to alleviate RGC loss in TON.

L-Satropane Prevents Retinal Neuron Damage by Attenuating Cell Apoptosis and Aβ Production via Activation of M1 Muscarinic Acetylcholine Receptor

ABSTRACTMuscarinic acetylcholine receptor (mAChR) agonists have been used to treat glaucoma due to their intraocular pressure-lowering effects. Recently, it has been reported that retinal mAChRs activation can also stimulate neuroprotective pathways.Purpose: In our study, we evaluated the potential neuroprotective effect of L-satropane, a novel mAChR agonist, on retinal neuronal injury induced by cobalt chloride (CoCl2) and ischemia/reperfusion (I/R).Methods: CoCl2-induced hypoxia injury in cultured cell models and I/R-induced retinal neuronal damage in rats in vivo were used to evaluate the abilities of L-satropane. In detail, we measured the occurrence of retinal pathological changes including molecular markers of neuronal apoptosis and Aβ expression.Results: Pretreatment with L-satropane protects against CoCl2-induced neurotoxicity in PC12 and primary retinal neuron (PRN) cells in a dose-dependent manner by increasing retinal neuron survival. CoCl2 or I/R-induced cell apoptosis by upregulating Bax expression and downregulating Bcl-2 expression, which resulted in an increased Bax/Bcl-2 ratio, and upregulating caspase-3 expression/activity was significantly reversed by L-satropane treatment. In addition, L-satropane significantly inhibited the upregulation of Aβ production in both retinal neurons and tissue. We also found that I/R-induced histopathological retinal changes including cell loss in the retinal ganglion cell layer (GCL) and increased TUNEL positive retinal ganglion cells in GCL and thinning of the inner plexiform layer (IPL) and inner nuclear layer (INL) were markedly improved by L-satropane. The effects of L-satropane were largely abolished by the nonselective mAChRs antagonist atropine and M1-selective mAChR antagonist pirenzepine.Conclusion: These results demonstrated that L-satropane might be effective in preventing retinal neuron damage caused by CoCl2 or I/R. The neuroprotective effects of L-satropane may be attributed to decreasing cell apoptosis and Aβ production through activation of M1 mAChR.

Hypertension management: Old drug revisited - Cilnidipine

Cilnidipine is a promising fourth-generation calcium channel blocker which along with inhibition of the L-type Ca 2+ channels in vascular smooth muscle cells, also inhibits the N-type Ca 2+ channels in sympathetic neurons. As a result, in addition to hypotensive action secondary to vascular relaxation, it also demonstrates significant sympatholytic action, whereby it attenuates platelet activation (and consequent arterial thrombosis), tachycardia, oxidative stress, and also inhibits activation of renin-angiotensin system in blood vessels. By virtue of the latter effect, they relieve constriction of postglomerular vessels and thereby ameliorate glomerular hypertension and render renoprotective effect. Besides these, cilnidipine also improves insulin resistance, nitric oxide production, and protects against retinal neuronal injury. Thus, it is expected to be a very useful addition in the current armamentarium for the treatment of hypertension.

MTOR inhibition attenuates glucose deprivation-induced death in photoreceptors via suppressing a mitochondria-dependent apoptotic pathway

Acute energy depletion contributes to ischemia-induced retinal neuronal injury, causing photoreceptor death and subsequent vision loss. The mTOR pathway is a crucial cellular signaling hub modulating RNA transcription, protein synthesis, and metabolic balance. Thus, we mimicked acute energy depletion in photoreceptor cells (661W cells) with glucose deprivation and investigated neuroprotective mechanisms of mTOR inhibition. We found that treatment with rapamycin, an mTOR-specific inhibitor, reduced intracellular ROS, maintained the mitochondrial membrane potential and restored mitochondrial dysfunction. In addition, inhibiting the mTOR signal suppressed DRP1 translocation to the mitochondria, pro-apoptotic mitochondrial protein release, and caspase 3 activation when glucose was deprived. Inhibition of mTOR offers significant neuroprotection against glucose deprivation-induced injury in 661W cells, chiefly via suppressing mitochondrial-dependent pathways. These observations may shed light on treating ischemia-related retinal diseases.

Endoplasmic reticulum stress-regulated CXCR3 pathway mediates inflammation and neuronal injury in acute glaucoma.

Acute glaucoma is a leading cause of irreversible blindness in East Asia. The mechanisms underlying retinal neuronal injury induced by a sudden rise in intraocular pressure (IOP) remain obscure. Here we demonstrate that the activation of CXCL10/CXCR3 axis, which mediates the recruitment and activation of inflammatory cells, has a critical role in a mouse model of acute glaucoma. The mRNA and protein expression levels of CXCL10 and CXCR3 were significantly increased after IOP-induced retinal ischemia. Blockade of the CXCR3 pathway by deleting CXCR3 gene significantly attenuated ischemic injury-induced upregulation of inflammatory molecules (interleukin-1β and E-selectin), inhibited the recruitment of microglia/monocyte to the superficial retina, reduced peroxynitrite formation, and prevented the loss of neurons within the ganglion cell layer. In contrast, intravitreal delivery of CXCL10 increased leukocyte recruitment and retinal cell apoptosis. Inhibition of endoplasmic reticulum (ER) stress with chemical chaperones partially blocked ischemic injury-induced CXCL10 upregulation, whereas induction of ER stress with tunicamycin enhanced CXCL10 expression in retina and primary retinal ganglion cells. Interestingly, deleting CXCR3 attenuated ER stress-induced retinal cell death. In conclusion, these results indicate that ER stress-medicated activation of CXCL10/CXCR3 pathway has an important role in retinal inflammation and neuronal injury after high IOP-induced ischemia.

Differential Gene Expression Profiling after Conditional Müller-Cell Ablation in a Novel Transgenic Model

Müller cells, the principal glial cells in the mammalian retina, play an important role in the maintenance of retinal homeostasis. Recent reports suggest that Müller-cell dysfunction may contribute to the pathogenesis of retinal diseases such as idiopathic macular telangiectasia type 2. In the present study, we used microarray to compare retinae isolated from transgenic mice in which the Müller cells of adult mice retinae can be selectively ablated with control mice. Retinae were isolated 1 week, 1 month, and 3 months after tamoxifen-induced selective Müller-cell ablation and microarray were performed with Affymatrix microarrays. Differentially expressed (DE) genes, temporal trends of DE genes, and pathway analysis were conducted. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to validate the results. Strong upregulation of mRNA of proteins involved in gliosis, apoptosis, and neurotrophism was found 1 week after ablation and their related pathways such as the apoptotic and Jak/Stat pathways were identified. Three months after induced Müller-cell ablation, Müller-cell metabolic pathways and vasculopathy-related pathways such as genes involved in glycolysis and tight junctions were downregulated. qRT-PCR analysis showed consistent expression trends of selected genes. The results were generally consistent with the previous morphologic findings in this model, in which photoreceptor degeneration soon after Müller-cell ablation, accompanied by blood-retinal barrier breakdown and subsequent retinal neovascularization were reported. These results are consistent with a significant contribution of Müller-cell dysfunction on retinal neuronal injury and vascular pathology at the mRNA level.

Spatial frequency threshold and contrast sensitivity of an optomotor behavior are impaired in the Ins2 Akita mouse model of diabetes

Diabetic retinopathy can lead to progressive loss of vision and is a leading cause of blindness. The Ins2 Akita mouse model of diabetes develops significant retinal and systemic pathology, but how these affect visual behavior is unknown. Here, we show that Ins2 Akita mice have progressive, quantifiable vision deficits in an optomotor behavior. This mouse line is a promising model in which to understand the contribution of retinal neuronal injury during the chronic hyperglycemia and hypoinsulinemia of diabetes to deficits in vision.

Antioxidant Effect of Melatonin in Human Retinal Neuron Cultures

This study investigates whether the neurohormone melatonin can prevent the retinal neuronal injury caused by reactive oxygen species (ROS) in cultured human retinal neuronal cells. Cultures of human retinal neuronal cells established from a variety of donors were grown to 14 days and then subjected to experimental hypoxanthine/xanthine oxidase (HX/XO)-induced injury. Intracellular production of ROS by administration of HX/XO was confirmed by flow cytometry; the ROS resulted in both apoptotic and necrotic pattern of cell death in the retinal neuron cultures. The efficacy of melatonin against ROS injury was quantitated by MTT assay, enzyme immunoassay, and immunocytochemistry for neurofilament protein. The antioxidative effect of melatonin was compared with that of α-tocopherol. Retinal neuronal injury significantly reduced in a dose–response manner by a treatment of 1.0–8.0 mM α-tocopherol. Melatonin, in concentrations of more than 2.0 mM, also significantly reduced the injury. About 70% of cells are rescued by pretreatment with 1.0 mM α-tocopherol and 8.0 mM melatonin in the MTT assay. Our observations suggest that melatonin can rescue retinal neurons from ROS injury in human retinal cell cultures.