Shoji Notomi

Programmed necrosis, not apoptosis, is a key mediator of cell loss and DAMP-mediated inflammation in dsRNA-induced retinal degeneration

There is no known treatment for the dry form of an age-related macular degeneration (AMD). Cell death and inflammation are important biological processes thought to have central role in AMD. Here we show that receptor-interacting protein (RIP) kinase mediates necrosis and enhances inflammation in a mouse model of retinal degeneration induced by dsRNA, a component of drusen in AMD. In contrast to photoreceptor-induced apoptosis, subretinal injection of the dsRNA analog poly(I : C) caused necrosis of the retinal pigment epithelium (RPE), as well as macrophage infiltration into the outer retinas. In Rip3−/− mice, both necrosis and inflammation were prevented, providing substantial protection against poly(I : C)-induced retinal degeneration. Moreover, after poly(I : C) injection, Rip3−/− mice displayed decreased levels of pro-inflammatory cytokines (such as TNF-α and IL-6) in the retina, and attenuated intravitreal release of high-mobility group box-1 (HMGB1), a major damage-associated molecular pattern (DAMP). In vitro, poly(I : C)-induced necrosis were inhibited in Rip3-deficient RPE cells, which in turn suppressed HMGB1 release and dampened TNF-α and IL-6 induction evoked by necrotic supernatants. On the other hand, Rip3 deficiency did not modulate directly TNF-α and IL-6 production after poly(I : C) stimulation in RPE cells or macrophages. Therefore, programmed necrosis is crucial in dsRNA-induced retinal degeneration and may promote inflammation by regulating the release of intracellular DAMPs, suggesting novel therapeutic targets for diseases such as AMD.

Laboratory Evidence of Sustained Chronic Inflammatory Reaction in Retinitis Pigmentosa

PURPOSE To study the nature of retinal inflammatory response in rd10 mice, an animal model of retinitis pigmentosa (RP), and to investigate the effect of an antioxidant on retinal inflammation and photoreceptor apoptosis. DESIGN Experimental study. PARTICIPANTS AND CONTROLS This study included 42 untreated rd10 mice, 30 N-acetylcysteine (NAC)-treated rd10 mice, and 20 C57BL/6 mice as controls. METHODS Real-time polymerase chain reaction (PCR) was performed to evaluate the expression levels of inflammatory factors (proinflammatory cytokines and chemokines) in rd10 mouse retinas. Rd10 mice were treated with an antioxidant NAC, and its effect on retinal inflammation and photoreceptor apoptosis were examined by immunohistochemistry. MAIN OUTCOME MEASURES Real-time PCR and immunohistochemistry. RESULTS We demonstrated sequential events involving increased expression of proinflammatory cytokines and chemokines, activation of microglia, and photoreceptor apoptosis during retinal degeneration of rd10 mice. Furthermore, antioxidant treatment with NAC prevented the photoreceptor cell death along with suppression of inflammatory factors and microglial activation. CONCLUSIONS Sustained chronic inflammatory reaction may contribute to the pathogenesis of retinal degeneration in rd10 mice, suggesting interventions for ocular inflammatory reaction using antioxidants as a potential treatment for patients with RP. FINANCIAL DISCLOSURE(S) The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Dynamic Increase in Extracellular ATP Accelerates Photoreceptor Cell Apoptosis via Ligation of P2RX7 in Subretinal Hemorrhage

Photoreceptor degeneration is the most critical cause of visual impairment in age-related macular degeneration (AMD). In neovascular form of AMD, severe photoreceptor loss develops with subretinal hemorrhage due to choroidal neovascularization (CNV), growth of abnormal blood vessels from choroidal circulation. However, the detailed mechanisms of this process remain elusive. Here we demonstrate that neovascular AMD with subretinal hemorrhage accompanies a significant increase in extracellular ATP, and that extracellular ATP initiates neurodegenerative processes through specific ligation of Purinergic receptor P2X, ligand-gated ion channel, 7 (P2RX7; P2X7 receptor). Increased extracellular ATP levels were found in the vitreous samples of AMD patients with subretinal hemorrhage compared to control vitreous samples. Extravascular blood induced a massive release of ATP and photoreceptor cell apoptosis in co-culture with primary retinal cells. Photoreceptor cell apoptosis accompanied mitochondrial apoptotic pathways, namely activation of caspase-9 and translocation of apoptosis-inducing factor (AIF) from mitochondria to nuclei, as well as TUNEL-detectable DNA fragmentation. These hallmarks of photoreceptor cell apoptosis were prevented by brilliant blue G (BBG), a selective P2RX7 antagonist, which is an approved adjuvant in ocular surgery. Finally, in a mouse model of subretinal hemorrhage, photoreceptor cells degenerated through BBG-inhibitable apoptosis, suggesting that ligation of P2RX7 by extracellular ATP may accelerate photoreceptor cell apoptosis in AMD with subretinal hemorrhage. Our results indicate a novel mechanism that could involve neuronal cell death not only in AMD but also in hemorrhagic disorders in the CNS and encourage the potential application of BBG as a neuroprotective therapy.

Astrocyte-Mediated Ischemic Tolerance

Preconditioning (PC) using a preceding sublethal ischemic insult is an attractive strategy for protecting neurons by inducing ischemic tolerance in the brain. Although the underlying molecular mechanisms have been extensively studied, almost all studies have focused on neurons. Here, using a middle cerebral artery occlusion model in mice, we show that astrocytes play an essential role in the induction of brain ischemic tolerance. PC caused activation of glial cells without producing any noticeable brain damage. The spatiotemporal pattern of astrocytic, but not microglial, activation correlated well with that of ischemic tolerance. Interestingly, such activation in astrocytes lasted at least 8 weeks. Importantly, inhibiting astrocytes with fluorocitrate abolished the induction of ischemic tolerance. To investigate the underlying mechanisms, we focused on the P2X7 receptor as a key molecule in astrocyte-mediated ischemic tolerance. P2X7 receptors were dramatically upregulated in activated astrocytes. PC-induced ischemic tolerance was abolished in P2X7 receptor knock-out mice. Moreover, our results suggest that hypoxia-inducible factor-1α, a well known mediator of ischemic tolerance, is involved in P2X7 receptor-mediated ischemic tolerance. Unlike previous reports focusing on neuron-based mechanisms, our results show that astrocytes play indispensable roles in inducing ischemic tolerance, and that upregulation of P2X7 receptors in astrocytes is essential.

Therapeutic effect of prolonged treatment with topical dorzolamide for cystoid macular oedema in patients with retinitis pigmentosa

Aim To evaluate the therapeutic effect of continuous treatment with topical dorzolamide (a carbonic anhydrase inhibitor) for cystoid macular oedema (CME) associated with retinitis pigmentosa (RP). Methods 18 eyes in 10 patients with CME secondary to RP were included. Baseline visual acuity, visual field and optical coherence tomography (OCT) measurements were obtained for all patients. All patients used 1% dorzolamide three times daily in each affected eye. Patients underwent follow-up examinations at 1, 3, 6, 12 and 18 months after treatment. The response to treatment was monitored by the Humphrey field analyser (HFA: the central 10-2 program); in addition, foveal thickness was measured by OCT. Evaluation of ‘macular sensitivity’ was calculated by HFA as the average of 12 central points. Results The ‘macular sensitivity’ in 10 eyes in which CME was almost completely resolved was significantly improved (p<0.05). In eight of the nine eyes in which CME was almost completely resolved within 6 months, the therapeutic efficacy persisted through 18 months. Five eyes which were almost completely resolved or showed an initial response within 6 months experienced recurrence of CME. Conclusions The prolonged (longer than 1 year) use of topical dorzolamide is effective for the treatment of CME in patients with RP. Therefore, we propose topical dorzolamide treatment as a first choice.

Establishment of a new animal model of focal subretinal fibrosis that resembles disciform lesion in advanced age-related macular degeneration.

PURPOSE Subretinal fibrosis causes damage to visual acuity, especially if the lesion is in the macula, as is frequently observed in advanced age-related macular degeneration. Exudate leukocytes form abnormal vessels that initiate regional inflammation accompanied with local glial proliferation and matrix production. The purpose of this study was to establish an animal model of focal subretinal fibrosis. METHODS Macrophage-rich peritoneal exudate cells (PECs) were injected into the subretinal space of C57BL/6 or MCP-1 knockout (KO) mice. Seven days later, the size of the subretinal fibrotic tissue was evaluated by the adherent area of glial fibrillary acidic protein (GFAP)-positive retinal glial cells on choroidal flat mounts. Myofibroblastic changes and collagen synthesis were detected by α-smooth muscle actin (α-SMA) and Masson trichrome staining of the histologic section, respectively. α-SMA expression was also examined on retinal pigment epithelium (RPE) cells during co-culture with activated macrophages. RESULTS Subretinal fibrous tissue was observed by funduscopy in PEC-injected mice after 7 days. The tissue consisted of a monotonous, low-cell-density area that expressed α-SMA with collagen synthesis. Both steroid and antioxidant treatment can reduce residual glia. Because PEC-injected MCP-1 KO mice showed less residual glia, not only exogenous macrophages, but also intrinsic macrophages were activated. The macrophages directly induced myofibrotic changes in RPE cells in vitro. CONCLUSIONS Activated macrophages form subretinal fibrosis when they are placed in the subretinal space and induce myofibrotic changes in RPE cells.

The Role of Mislocalized Phototransduction in Photoreceptor Cell Death of Retinitis Pigmentosa

Most of inherited retinal diseases such as retinitis pigmentosa (RP) cause photoreceptor cell death resulting in blindness. RP is a large family of diseases in which the photoreceptor cell death can be caused by a number of pathways. Among them, light exposure has been reported to induce photoreceptor cell death. However, the detailed mechanism by which photoreceptor cell death is caused by light exposure is unclear. In this study, we have shown that even a mild light exposure can induce ectopic phototransduction and result in the acceleration of rod photoreceptor cell death in some vertebrate models. In ovl, a zebrafish model of outer segment deficiency, photoreceptor cell death is associated with light exposure. The ovl larvae show ectopic accumulation of rhodopsin and knockdown of ectopic rhodopsin and transducin rescue rod photoreceptor cell death. However, knockdown of phosphodiesterase, the enzyme that mediates the next step of phototransduction, does not. So, ectopic phototransduction activated by light exposure, which leads to rod photoreceptor cell death, is through the action of transducin. Furthermore, we have demonstrated that forced activation of adenylyl cyclase in the inner segment leads to rod photoreceptor cell death. For further confirmation, we have also generated a transgenic fish which possesses a human rhodopsin mutation, Q344X. This fish and rd10 model mice show photoreceptor cell death caused by adenylyl cyclase. In short, our study indicates that in some RP, adenylyl cyclase is involved in photoreceptor cell death pathway; its inhibition is potentially a logical approach for a novel RP therapy.

Correlation between macular blood flow and central visual sensitivity in retinitis pigmentosa

To investigate the changes in macular blood flow and the correlation between those changes and central visual function in patients with retinitis pigmentosa (RP).

The Regulatory Roles of Apoptosis-Inducing Factor in the Formation and Regression Processes of Ocular Neovascularization

The role of apoptosis in the formation and regression of neovascularization is largely hypothesized, although the detailed mechanism remains unclear. Inflammatory cells and endothelial cells both participate and interact during neovascularization. During the early stage, these cells may migrate into an angiogenic site and form a pro-angiogenic microenvironment. Some angiogenic vessels appear to regress, whereas some vessels mature and remain. The control mechanisms of these processes, however, remain unknown. Previously, we reported that the prevention of mitochondrial apoptosis contributed to cellular survival via the prevention of the release of proapoptotic factors, such as apoptosis-inducing factor (AIF) and cytochrome c. In this study, we investigated the regulatory role of cellular apoptosis in angiogenesis using two models of ocular neovascularization: laser injury choroidal neovascularization and VEGF-induced corneal neovascularization in AIF-deficient mice. Averting apoptosis in AIF-deficient mice decreased apoptosis of leukocytes and endothelial cells compared to wild-type mice and resulted in the persistence of these cells at angiogenic sites in vitro and in vivo. Consequently, AIF deficiency expanded neovascularization and diminished vessel regression in these two models. We also observed that peritoneal macrophages from AIF-deficient mice showed anti-apoptotic survival compared to wild-type mice under conditions of starvation. Our data suggest that AIF-related apoptosis plays an important role in neovascularization and that mitochondria-regulated apoptosis could offer a new target for the treatment of pathological angiogenesis.

Verteporfin-induced formation of protein cross-linked oligomers and high molecular weight complexes is mediated by light and leads to cell toxicity

Verteporfin (VP) was first used in Photodynamic therapy, where a non-thermal laser light (689 nm) in the presence of oxygen activates the drug to produce highly reactive oxygen radicals, resulting in local cell and tissue damage. However, it has also been shown that Verteporfin can have non-photoactivated effects such as interference with the YAP-TEAD complex of the HIPPO pathway, resulting in growth inhibition of several neoplasias. More recently, it was proposed that, another non-light mediated effect of VP is the formation of cross-linked oligomers and high molecular weight protein complexes (HMWC) that are hypothesized to interfere with autophagy and cell growth. Here, in a series of experiments, using human uveal melanoma cells (MEL 270), human embryonic kidney cells (HEK) and breast cancer cells (MCF7) we showed that Verteporfin-induced HMWC require the presence of light. Furthermore, we showed that the mechanism of this cross-linking, which involves both singlet oxygen and radical generation, can occur very efficiently even after lysis of the cells, if the lysate is not protected from ambient light. This work offers a better understanding regarding VP’s mechanisms of action and suggests caution when one studies the non-light mediated actions of this drug.