Expression and activation of mitogen-activated protein kinases in the optic nerve head in a rat model of ocular hypertension

Casein kinase-2 inhibition promotes retinal ganglion cell survival after acute intraocular pressure elevation

Intraocular pressure elevation can induce retinal ganglion cell death and is a clinically reversible risk factor for glaucoma, the leading cause of irreversible blindness. We previously demonstrated that casein kinase-2 inhibition can promote retinal ganglion cell survival and axonal regeneration in rats after optic nerve injury. To investigate the underlying mechanism, in the current study we increased the intraocular pressure of adult rats to 75 mmHg for 2 hours and then administered a casein kinase-2 inhibitor (4,5,6,7-tetrabromo-2-azabenzimidazole or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole) by intravitreal injection. We found that intravitreal injection of 4,5,6,7-tetrabromo-2-azabenzimidazole or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole promoted retinal ganglion cell survival and reduced the number of infiltrating macrophages. Transcriptomic analysis showed that the mitogen activated protein kinase signaling pathway was involved in the response to intraocular pressure elevation but was not modulated by the casein kinase-2 inhibitors. Furthermore, casein kinase-2 inhibition downregulated the expression of genes (Cck, Htrsa, Nef1, Htrlb, Prph, Chat, Slc18a3, Slc5a7, Scn1b, Crybb2, Tsga10ip, and Vstm21) involved in intraocular pressure elevation. Our data indicate that inhibition of casein kinase-2 can enhance retinal ganglion cell survival in rats after acute intraocular pressure elevation via macrophage inactivation.

Targeted Microglial Attenuation through Dendrimer-Drug Conjugates Improves Glaucoma Neuroprotection

Retinal microglial/macrophage activation and optic nerve (ON) microglial/macrophage activation are glaucoma biomarkers and potential therapeutic targets for this blinding disease. We report targeting of activated microglia by PAMAM dendrimers in a rat glaucoma model and neuroprotection by N-acetylcysteine-conjugated dendrimer (D-NAC) conjugates in a post-injury rescue experiment. Intravitreally delivered fluorescently labeled dendrimer (D-Cy5) conjugates targeted and were retained in Iba-1-positive cells (90% at 7 days and 55% after 28 days) in the retina following intraocular pressure (IOP) elevation, while systemically delivered D-Cy5 targeted ON cells. A single intravitreal D-NAC dose given 1 week after IOP elevation significantly reduced transcription of pro-inflammatory (IL-6, MCP-1, IL-1β) and A1 astrocyte (Serping1, Fkbp5, Amigo2) markers and increased survival of retinal ganglion cells (39 ± 12%) versus BSS- (20 ± 15%, p = 0.02) and free NAC-treated (26 ± 14%, p = 0.15) eyes. These results highlight the potential of dendrimer-targeted microglia and macrophages for early glaucoma detection and as a neuroprotective therapeutic target.

MAPK Pathways in Ocular Pathophysiology: Potential Therapeutic Drugs and Challenges

Mitogen-activated protein kinase (MAPK) pathways represent ubiquitous cellular signal transduction pathways that regulate all aspects of life and are frequently altered in disease. Once activated through phosphorylation, these MAPKs in turn phosphorylate and activate transcription factors present either in the cytoplasm or in the nucleus, leading to the expression of target genes and, as a consequence, they elicit various biological responses. The aim of this work is to provide a comprehensive review focusing on the roles of MAPK signaling pathways in ocular pathophysiology and the potential to influence these for the treatment of eye diseases. We summarize the current knowledge of identified MAPK-targeting compounds in the context of ocular diseases such as macular degeneration, cataract, glaucoma and keratopathy, but also in rare ocular diseases where the cell differentiation, proliferation or migration are defective. Potential therapeutic interventions are also discussed. Additionally, we discuss challenges in overcoming the reported eye toxicity of some MAPK inhibitors.

Establishing human lacrimal gland cultures from biopsy-sized tissue specimens

OBJECTIVES

To establish cultures of human lacrimal gland from patient-derived, biopsy-sized, tissue specimens.

METHODS

Tissue was obtained after surgical removal from patients without dry eye disease undergoing routine procedures. Samples were subjected to mechanical and enzymatic digestion and resulting cell suspensions were plated onto collagen-coated glass coverslips and grown for up to 21 days. Cultures were analysed by immunocytochemistry and light microscopy, and resultant cellular distributions were compared to those in sections of fixed human lacrimal gland tissue.

RESULTS

Dissociation of biopsy-sized pieces of human lacrimal gland and seeding onto coated surfaces allowed development of a mixed population of cells in vitro. Within 7-14 days, cellular aggregation was observed and by 21 days many cells had organised themselves into distinct three-dimensional complexes. Immunohistochemistry revealed a heterogeneous population of cells, including epithelial, myoepithelial, mesenchymal and progenitor cells. Some of the epithelia labelled positively for lysozyme and lactoferrin.

CONCLUSIONS

Collection and dissociation of biopsy-sized pieces of human lacrimal gland leads to a cellular preparation that can proliferate in vitro and organise into three-dimensional structures. This is the first report detailing that biopsy-collected specimens of human lacrimal gland can be used to establish cell cultures.

Role of the AMPK signalling pathway in the aetiopathogenesis of ocular diseases

BACKGROUND

AMP-activated protein kinase (AMPK) plays a precise role as a master regulator of cellular energy homeostasis. AMPK is activated in response to the signalling cues that exhaust cellular ATP levels such as hypoxia, ischaemia, glucose depletion and heat shock. As a central regulator of both lipid and glucose metabolism, AMPK is considered to be a potential therapeutic target for the treatment of various diseases, including eye disorders.

OBJECTIVE

To review all the shreds of evidence concerning the role of the AMPK signalling pathway in the pathogenesis of ocular diseases.

METHOD

Scientific data search and review of available information evaluating the influence of AMPK signalling on ocular diseases.

RESULTS

Review highlights the significance of AMPK signalling in the aetiopathogenesis of ocular diseases, including cataract, glaucoma, diabetic retinopathy, retinoblastoma, age-related macular degeneration, corneal diseases, etc. The review also provides the information on the AMPK-associated pathways with reference to ocular disease, which includes mitochondrial biogenesis, autophagy and regulation of inflammatory response.

CONCLUSION

The study concludes the role of AMPK in ocular diseases. There is growing interest in the therapeutic utilization of the AMPK pathway for ocular disease treatment. Furthermore, inhibition of AMPK signalling might represent more pertinent strategy than AMPK activation for ocular disease treatment. Such information will guide the development of more effective AMPK modulators for ocular diseases.[Formula: see text].

Resveratrol acts via the mitogen-activated protein kinase (MAPK) pathway to protect retinal ganglion cells from apoptosis induced by hydrogen peroxide

The current study investigated the ability of resveratrol to protect RGC-5 retinal ganglion cells in culture against H₂O₂-induced apoptosis and the underlying mechanism of protection. RGC-5 cells were pre-exposed to resveratrol (5, 10, or 20 μM), followed by 200 μM H₂O₂. Cell viability and apoptosis were detected to assess the cell growth, and expression levels of apoptosis-related and MAPK cascade-associated proteins were determined using western blotting. Levels of reactive oxygen species and mitochondrial membrane potential were also tested, as well as the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GSH). At a concentration-dependent way, resveratrol reversed H₂O₂-induced increases in expressions of cleaved caspase-3 and cleaved caspase-9, production of ROS, loss of mitochondrial membrane potential and the expressions of p-p38, p-ERK, and p-JNK. It also promoted the activities of SOD, CAT, and GSH. Furthermore, the agonists of p38, ERK, and JNK partially weakened the protective effects of resveratrol against H₂O₂-induced apoptosis in RGC-5 cells. Thus, resveratrol can protect retinal ganglion cells against H₂O₂-induced apoptosis by suppressing MAPK cascades. The drug therefore shows potential for preventing glaucoma.

JNK and p38 Inhibitors Prevent Transforming Growth Factor-β1-Induced Myofibroblast Transdifferentiation in Human Graves' Orbital Fibroblasts

Transforming growth factor-β1 (TGF-β1)-induced myofibroblast transdifferentiation from orbital fibroblasts is known to dominate tissue remodeling and fibrosis in Graves’ ophthalmopathy (GO). However, the signaling pathways through which TGF-β1 activates Graves’ orbital fibroblasts remain unclear. This study investigated the role of the mitogen-activated protein kinase (MAPK) pathway in TGF-β1-induced myofibroblast transdifferentiation in human Graves’ orbital fibroblasts. The MAPK pathway was assessed by measuring the phosphorylation of p38, c-Jun N-terminal kinase (JNK), and extracellular-signal-regulated kinase (ERK) by Western blots. The expression of connective tissue growth factor (CTGF), α-smooth muscle actin (α-SMA), and fibronectin representing fibrogenesis was estimated. The activities of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) responsible for extracellular matrix (ECM) metabolism were analyzed. Specific pharmacologic kinase inhibitors were used to confirm the involvement of the MAPK pathway. After treatment with TGF-β1, the phosphorylation levels of p38 and JNK, but not ERK, were increased. CTGF, α-SMA, and fibronectin, as well as TIMP-1 and TIMP-3, were upregulated, whereas the activities of MMP-2/-9 were inhibited. The effects of TGF-β1 on the expression of these factors were eliminated by p38 and JNK inhibitors. The results suggested that TGF-β1 could induce myofibroblast transdifferentiation in human Graves’ orbital fibroblasts through the p38 and JNK pathways.

Dual Specific Phosphatase 14 Deletion Rescues Retinal Ganglion Cells and Optic Nerve Axons after Experimental Anterior Ischemic Optic Neuropathy

PURPOSE

Understanding molecular changes is essential for designing effective treatments for nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults older than 50 years. We investigated changes in the mitogen-activated protein kinase (MAPK) pathway after experimental AION and focused on dual specificity phosphatase 14 (Dusp14), an atypical MAPK phosphatase that is downstream of Krüppel-like transcription factor (KLF) 9-mediated inhibition of retinal ganglion cell (RGC) survival and axonal regeneration.

MATERIALS AND METHODS

We induced severe AION in a photochemical thrombosis model in adult C57BL/6 wild-type and Dusp14 knockout mice. For comparison, some studies were performed using an optic nerve crush model. We assessed changes in MAPK pathway molecules using Western blot and immunohistochemistry, measured retinal thickness using optical coherence tomography (OCT), and quantified RGCs and axons using histologic methods.

RESULTS

Three days after severe AION, there was no change in the retinal protein levels of MAPK ERK1/2, phosphorylated-ERK1/2 (pERK1/2), downstream effector Elk-1 and phosphatase Dusp14 on Western blot. Western blot analysis of purified RGCs after a more severe model using optic nerve crush also showed no change in Dusp14 protein expression. Because of the known importance of the Dusp14 and MAPK pathway in RGCs, we examined changes after AION in Dusp14 knockout mice. Three days after AION, Dusp14 knockout mice had significantly increased pERK1/2⁺, Brn3A⁺ RGCs on immunohistochemistry. Three weeks after AION, Dusp14 knockout mice had significantly greater preservation of retinal thickness, increased number of Brn3A⁺ RGCs on whole mount preparation, and increased number of optic nerve axons compared with wild-type mice.

CONCLUSIONS

Genetic deletion of Dusp14, a MAPK phosphatase important in KFL9-mediated inhibition of RGC survival, led to increased activation of MAPK ERK1/2 and greater RGC and axonal survival after experimental AION. Inhibiting Dusp14 or activating the MAPK pathway should be examined further as a potential therapeutic approach to treatment of AION.

Abbreviations: AION: anterior ischemic optic neuropathy; Dusp14: dual specific phosphatase 14; ERK1/2: extracellular signal-regulated kinases 1/2; Elk-1: ETS Like-1 protein; GCC: ganglion cell complex; GCL: ganglion cell layer; inner nuclear layer; KO: knockout; MAPK: mitogen-activated phosphokinase; OCT: optical coherence tomography; RGC: retinal ganglion cell; RNFL: retinal nerve fiber layer.

Role of glia in optic nerve

Glial cells are critically important for maintenance of neuronal activity in the central nervous system (CNS), including the optic nerve (ON). However, the ON has several unique characteristics, such as an extremely high myelination level of retinal ganglion cell (RGC) axons throughout the length of the nerve (with virtually all fibers myelinated by 7 months of age in humans), lack of synapses and very narrow geometry. Moreover, the optic nerve head (ONH) - a region where the RGC axons exit the eye - represents an interesting area that is morphologically distinct in different species. In many cases of multiple sclerosis (demyelinating disease of the CNS) vision problems are the first manifestation of the disease, suggesting that RGCs and/or glia in the ON are more sensitive to pathological conditions than cells in other parts of the CNS. Here, we summarize current knowledge on glial organization and function in the ON, focusing on glial support of RGCs. We cover both well-established concepts on the important role of glial cells in ON health and new findings, including novel insights into mechanisms of remyelination, microglia/NG2 cell-cell interaction, astrocyte reactivity and the regulation of reactive astrogliosis by mitochondrial fragmentation in microglia.

Of Mice and Monkeys: Neuroprotective Efficacy of the p38 Inhibitor BIRB 796 Depends on Model Duration in Experimental Glaucoma

Glaucoma is a group of optic neuropathies associated with aging and sensitivity to intraocular pressure (IOP). Early progression involves retinal ganglion cell (RGC) axon dysfunction that precedes frank degeneration. Previously we demonstrated that p38 MAPK inhibition abates axonal dysfunction and slows degeneration in the inducible microbead occlusion model of glaucoma in rat. Here, we assessed the neuroprotective effect of topical eye delivery of the p38 MAPK inhibitor BIRB 796 in three models of glaucoma (microbead occlusion in rat and squirrel monkey and the genetic DBA/2 J mouse model) with distinct durations of IOP elevation. While BIRB 796 did not influence IOP, treatment over four weeks in rats prevented degradation of anterograde axonal transport to the superior colliculus and degeneration in the optic nerve. Treatment over months in the chronic DBA/2 J model and in the squirrel monkey model reduced expression and activation of p38 downstream targets in the retina and brain but did not rescue RGC axon transport or degeneration, suggesting the efficacy of BIRB 796 in preventing associated degeneration of the RGC projection depends on the duration of the experimental model. These results emphasize the importance of evaluating potential therapeutic compounds for neuroprotection in multiple models using elongated treatment paradigms for an accurate assessment of efficacy.

JIP1 Deficiency Protects Retinal Ganglion Cells From Apoptosis in a Rotenone-Induced Injury Model

Retinal ganglion cells (RGCs) undergo apoptosis after injury. c-Jun N-terminal kinase (JNK)-interacting protein 1 (JIP1) is a scaffold protein that is relevant to JNK activation and a key molecule known to regulate neuronal apoptosis. However, the specific role of JIP1 in the apoptosis of RGCs is currently undefined. Here, we used JIP1 gene knockout (KO) mice to investigate the importance of JIP1-JNK signaling in the apoptosis of RGCs in a rotenone-induced injury model. In adult JIP1 KO mice, the number and electrophysiological functions of RGCs were not different from those of wild-type (WT) mice. Ablation of JIP1 attenuated the activation of JNK and the cleavage of caspase-3 in the retina after rotenone injury and contributed to a lower number of TUNEL-positive RGCs, a greater percentage of surviving RGCs, and a significant reduction in the electrophysiological functional loss of RGCs when compared to those in WT controls. We also found that JIP1 was located in the neurites of primary RGCs, but accumulated in soma in response to rotenone treatment. Moreover, the number of TUNEL-positive RGCs, the level of activation of JNK and the rate of cleavage of caspase-3 were reduced in primary JIP1-deficient RGCs after rotenone injury than in WT controls. Together, our results demonstrate that the JIP1-mediated activation of JNK contributes to the apoptosis of RGCs in a rotenone-induced injury model in vitro and in vivo, suggesting that JIP1 may be a potential therapeutic target for RGC degeneration.

Improved immunohistochemical detection of phosphorylated mitogen-activated protein kinases in the injured rat optic nerve head

The activity of mitogen-activated protein kinases (MAPKs) is largely controlled by addition or removal of phosphate groups, which are carried out by kinase or phosphatase enzymes, respectively. Determining the phosphorylation status of MAPK isoenzymes, therefore, aids elucidation of the physiological and pathological roles of this enzyme. In practical terms, however, end-point procurement of appropriate experimental tissues produces conditions where MAPK phosphorylation status can rapidly alter, thus giving rise to aberrant data. We therefore attempted to instigate a means of stabilising end-point MAPK phosphorylation levels when procuring tissues for analysis. We employed a well-described rat model of ocular hypertension in which MAPK isoenzyme activation occurs in the optic nerve head (ONH), but can vary according to the level of resultant tissue pathology. Animals were appropriately treated and after 3 days were perfused in the presence or absence of a cocktail of phosphatase inhibitors (PIs), immediately prior to tissue fixation, in order to prevent dephosphorylation of phosphorylated MAPKs. Immunohistochemical labelling for phosphorylated MAPKs in untreated ONH sections was unaffected by the presence of PIs in the perfusate. MAPK activation was detected by immunohistochemistry in the treated ONH, but findings varied considerably, particularly in animals with less extensive tissue damage. The presence of PIs in the perfusate, however, significantly reduced this variation and enabled consistent changes to be detected, particularly in the animals with less extensive tissue damage. Thus, the addition of PIs to the perfusate is suggested when studying MAPK activation by immunohistochemistry, especially in the ONH.

Kaempferol attenuates retinal ganglion cell death by suppressing NLRP1/NLRP3 inflammasomes and caspase-8 via JNK and NF-κB pathways in acute glaucoma

AIMS OR PURPOSE

Glaucoma is the leading cause of vision loss and blindness in the world. Elucidating the pathogenesis of glaucoma and developing effective treatment should be the priority. Inflammation and oxidative stress play essential roles in glaucoma pathogeneisis. Kaempferol is a natural flavonol and has anti-inflammatory and anti-oxidative activities. In this study, we explored the potential effects of kaempferol on acute glaucoma.

METHODS

We established the retinal ischemia-reperfusion (I/R) mice model and administrated kaempferol to I/R mice. We monitored the retina thickness change, retinal ganglion cell (RGC) death, caspase-8 and caspase-3 activation, NLRP1/NLRP3 inflammasomes activation, pro-inflammatory cytokines production, and activations of NF-κB and MAPKs signaling pathways.

RESULTS

Kaempferol prevented retina thickness change and RGC death in I/R mice. The activations of caspase-8, caspase-3, and NLRP1/NLRP3 inflammasome activation were inhibited by kaempferol. Kaempferol prevented pro-inflammatory cytokines productions in I/R mice. The activation of NF-κB and JNK signaling pathways was also inhibited by Kaempferol in I/R mice.

CONCLUSION

Kaempferol attenuated retinal ganglion cell death by suppressing NLRP1/NLRP3 inflammasomes and caspase-8 via inhibiting NF-κB and JNK pathways in acute glaucoma.

MicroRNA-141-3p inhibits retinal neovascularization and retinal ganglion cell apoptosis in glaucoma mice through the inactivation of Docking protein 5-dependent mitogen-activated protein kinase signaling pathway

Retinal neovascularization occurs in various ocular disorders including proliferative diabetic retinopathy and secondary neovascular glaucoma, resulting in blindness. This paper aims to investigate the effect of microRNA-141-3p (miR-141-3p) on retinal neovascularization and retinal ganglion cells (RGCs) in glaucoma mice through the Docking protein 5 (DOK5)-mediated mitogen-activated protein kinase (MAPK) signaling pathway. Chip retrieval and difference analysis were used for the potential mechanism of miR-141-3p on glaucoma. All modeled mice were transfected with different expression of mimic or inhibitor. The expressions of miR-141-3p, DOK5, and related genes and proteins of the MAPK signaling pathway were detected by Reverse transcription quantitative polymerase chain reaction and western blot analysis. Cell proliferation, lumen formation, and apoptosis in the retinal vascular epithelial cells and RGCs were detected using Matrigel angiogenesis and terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling assays. Moreover, a total of 63 and 294 differentially expressed genes were obtained in GSE2378 and GSE9944 chips, and 4 genes were within the intersection of the chips. In addition, the results showed that miR-141-3p was found to inhibit the DOK5 gene and activate the MAPK pathway. The number of RGCs, the expression of p38, extracellular-signal-regulated kinases (ERK), Jun N-terminal kinase (JNK), IGF-1, VEGF, HIF1-α, Bax, caspase-3, and the extent of p38, ERK, and JNK phosphorylated were decreased with miR-141-3p upregulation. Lastly, the results obtained showed that miR-141-3p inhibited the proliferation of retinal vascular epithelial cells and inhibited angiogenesis, as well as promoted apoptosis of RGCs. The study suggests that miR-141-3p inhibits retinal neovascularization in glaucoma mice by impeding the activation of the DOK5-mediated MAPK signaling pathway.