Norihiro Nagai

(Pro)renin Receptor–Mediated Signal Transduction and Tissue Renin-Angiotensin System Contribute to Diabetes-Induced Retinal Inflammation

OBJECTIVE The term “receptor-associated prorenin system” (RAPS) refers to the pathogenic mechanisms whereby prorenin binding to its receptor dually activates the tissue renin-angiotensin system (RAS) and RAS-independent intracellular signaling via the receptor. The aim of the present study was to define the association of the RAPS with diabetes-induced retinal inflammation. RESEARCH DESIGN AND METHODS Long-Evans rats, C57BL/6 mice, and angiotensin II type 1 receptor (AT1-R)-deficient mice with streptozotocin-induced diabetes were treated with (pro)renin receptor blocker (PRRB). Retinal mRNA expression of prorenin and the (pro)renin receptor was examined by quantitative RT-PCR. Leukocyte adhesion to the retinal vasculature was evaluated with a concanavalin A lectin perfusion–labeling technique. Retinal protein levels of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule (ICAM)-1 were examined by ELISA. Retinal extracellular signal–regulated kinase (ERK) activation was analyzed by Western blotting. RESULTS Induction of diabetes led to significant increase in retinal expression of prorenin but not the (pro)renin receptor. Retinal adherent leukocytes were significantly suppressed with PRRB. Administration of PRRB inhibited diabetes-induced retinal expression of VEGF and ICAM-1. To clarify the role of signal transduction via the (pro)renin receptor in the diabetic retina, we used AT1-R–deficient mice in which the RAS was deactivated. Retinal adherent leukocytes in AT1-R–deficient diabetic mice were significantly suppressed with PRRB. PRRB suppressed the activation of ERK and the production of VEGF, but not ICAM-1, in AT1-R–deficient diabetic mice. CONCLUSIONS These results indicate a significant contribution of the RAPS to the pathogenesis of diabetes-induced retinal inflammation, suggesting the possibility of the (pro)renin receptor as a novel molecular target for the treatment of diabetic retinopathy.

Angiotensin II Type 1 Receptor–Mediated Inflammation Is Required for Choroidal Neovascularization

Background—Choroidal neovascularization (CNV) is a critical pathogenesis in age-related macular degeneration, the most common cause of blindness in the developed countries. The aim of the current study was to determine the involvement of the renin-angiotensin system (RAS) with the development of CNV, using human surgical samples and the murine model of laser-induced CNV. Methods and Results—In the human and murine CNV tissues, the vascular endothelium expressed angiotensin II type 1 receptor (AT1-R), AT2-R, and angiotensin II. The CNV volume was significantly suppressed by treatment with an AT1-R blocker telmisartan, but not with an AT2-R blocker. AT1-R signaling blockade with telmisartan inhibited various inflammatory mechanisms including macrophage infiltration and upregulation of VEGF, intercellular adhesion molecule-1 (ICAM-1), MCP-1, and IL-6 in the retinal pigment epithelium-choroid complex. A PPAR-&ggr; antagonist partially but significantly reversed the suppressive effect of telmisartan on in vivo induction of CNV and in vitro upregulation of ICAM-1 and MCP-1 in endothelial cells and IL-6 in macrophages, showing the dual contribution of PPAR-&ggr;-agonistic and AT1-R-antagonistic actions in the telmisartan treatment. Conclusions—AT1-R–mediated inflammation plays a pivotal role in the development of CNV, indicating the possibility of AT1-R blockade as a novel therapeutic strategy to inhibit CNV.

Macular Pigment Lutein Is Antiinflammatory in Preventing Choroidal Neovascularization

Background—Choroidal neovascularization (CNV) is a critical pathogenesis in age-related macular degeneration, the most common cause of blindness in the developed countries. The aim of the current study was to investigate the effect of lutein supplementation on the development of the murine model of laser-induced CNV together with underlying molecular mechanisms. Methods and Results—Mice were orally pretreated with lutein daily from 3 days before laser photocoagulation untill the end of the study. The index of CNV volume was significantly suppressed by the treatment with lutein, compared with vehicle-treated animals. Lutein treatment led to significant inhibition of macrophage infiltration into CNV and of the in vivo and in vitro expression of inflammation-related molecules including vascular endothelial growth factor, monocyte chemotactic protein −1, and intercellular adhesion molecule-1. Importantly, lutein suppressed I&kgr;B-α degradation and nuclear translocation of nuclear factor (NF)-&kgr;B p65 both in vivo and in vitro. Additionally, the development of CNV was significantly suppressed by inhibiting NF-&kgr;B p65 nuclear translocation, to the levels seen in the lutein treatment. Conclusions—Lutein treatment led to significant suppression of CNV development together with inflammatory processes including NF-&kgr;B activation and subsequent upregulation of inflammatory molecules, providing molecular evidence of potential validity of lutein supplementation as a therapeutic strategy to suppress CNV.

Angiotensin II Type 1 Receptor Signaling Contributes to Synaptophysin Degradation and Neuronal Dysfunction in the Diabetic Retina

OBJECTIVE—Pathogenic mechanisms underlying diabetes-induced retinal dysfunction are not fully understood. The aim of the present study was to show the relationship of the renin-angiotensin system (RAS) with the synaptic vesicle protein synaptophysin and neuronal activity in the diabetic retina. RESEARCH DESIGN AND METHODS—C57BL/6 mice with streptozotocin-induced diabetes were treated with the angiotensin II type 1 receptor (AT1R) blocker telimsartan or valsartan, and retinal function was analyzed by electroretinography. Retinal production of the RAS components and phosphorylation of ERK (extracellular-signal regulated kinase) were examined by immunoblotting. Retinal mRNA and protein levels of synaptophysin were measured by quantitative RT-PCR and immunoblot analyses, respectively. In vitro, synaptophysin levels were also evaluated using angiotensin II–stimulated PC12D neuronal cells cultured with or without the inhibition of ERK signaling or the ubiquitin-proteasome system (UPS). RESULTS—Induction of diabetes led to a significant increase in retinal production of angiotensin II and AT1R together with ERK activation in the downstream of AT1R. AT1R blockade significantly reversed diabetes-induced electroretinography changes and reduction of synaptophysin protein, but not mRNA, levels in the diabetic retina. In agreement with the AT1R-mediated posttranscriptional downregulation of synaptophysin in vivo, in vitro application of angiotensin II to PC12D neuronal cells caused the UPS–mediated degradation of synaptophysin protein via AT1R, which proved to be induced by ERK activation. CONCLUSIONS—These data indicate the first molecular evidence of the RAS-induced synaptophysin degradation and neuronal dysfunction in the diabetic retina, suggesting the possibility of the AT1R blockade as a novel neuroprotective treatment for diabetic retinopathy.

Inhibition of choroidal neovascularization with an anti-inflammatory carotenoid astaxanthin

PURPOSE Astaxanthin (AST) is a carotenoid found in marine animals and vegetables. The purpose of the present study was to investigate the effect of AST on the development of experimental choroidal neovascularization (CNV) with underlying cellular and molecular mechanisms. METHODS Laser photocoagulation was used to induce CNV in C57BL/6J mice. Mice were pretreated with intraperitoneal injections of AST daily for 3 days before photocoagulation, and treatments were continued daily until the end of the study. CNV response was analyzed by volumetric measurements 1 week after laser injury. Retinal pigment epithelium-choroid levels of IkappaB-alpha, intercellular adhesion molecule (ICAM)-1, monocyte chemotactic protein (MCP)-1, interleukin (IL)-6, vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)-1, and VEGFR-2 were examined by Western blotting or ELISA. AST was applied to capillary endothelial (b-End3) cells, macrophages, and RPE cells to analyze the activation of NF-kappaB and the expression of inflammatory molecules. RESULTS The index of CNV volume was significantly suppressed by treatment with AST compared with that in vehicle-treated animals. AST treatment led to significant inhibition of macrophage infiltration into CNV and of the in vivo and in vitro expression of inflammation-related molecules, including VEGF, IL-6, ICAM-1, MCP-1, VEGFR-1, and VEGFR-2. Importantly, AST suppressed the activation of the NF-kappaB pathway, including IkappaB-alpha degradation and p65 nuclear translocation. CONCLUSIONS AST treatment, together with inflammatory processes including NF-kappaB activation, subsequent upregulation of inflammatory molecules, and macrophage infiltration, led to significant suppression of CNV development. The present study suggests the possibility of AST supplementation as a therapeutic strategy to suppress CNV associated with AMD.

(Pro)renin receptor promotes choroidal neovascularization by activating its signal transduction and tissue renin-angiotensin system

The receptor-associated prorenin system (RAPS) refers to pathogenic mechanisms whereby prorenin binding to its receptor activates both the tissue renin-angiotensin system (RAS) and RAS-independent intracellular signaling pathways. Although we found significant involvement of angiotensin II type 1 receptor (AT1-R)-mediated inflammation in choroidal neovascularization (CNV), a central abnormality of vision-threatening age-related macular degeneration, the association of receptor-associated prorenin system with CNV has not been defined. Here, (pro)renin receptor blockade in a murine model of laser-induced CNV led to the significant suppression of CNV together with macrophage infiltration and the up-regulation of intercellular adhesion molecule-1, (ICAM-1) monocyte chemotactic protein-1, (MCP-1) vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)-1, and VEGFR-2. To clarify the role of signal transduction via the (pro)renin receptor in CNV, we used mice in which renin-angiotensin system was deactivated by either the pharmacological blockade of AT1-R with losartan or the genetic ablation of AT1-R or angiotensinogen. Compared with wild-type controls, these mice exhibited significant reduction of CNV and macrophage infiltration, both of which were further suppressed by (pro)renin receptor blockade. The (pro)renin receptor and phosphorylated extracellular signal-regulated kinases (ERK) were co-localized in vascular endothelial cells and macrophages in CNV. (Pro)renin receptor blockade suppressed ERK activation and the production of MCP-1 and VEGF, but not ICAM-1, VEGFR-1, or VEGFR-2, in AT1-R-deficient mice with CNV and in losartan-treated microvascular endothelial cells and macrophages. These results indicate the significant contribution of RAPS to CNV pathogenesis.

Predictive factors for non-response to intravitreal ranibizumab treatment in age-related macular degeneration

Background/aims To study the initial characteristics and response to intravitreal ranibizumab (IVR) treatment of age-related macular degeneration (AMD). Methods We reviewed the clinical records of 141 eyes in 141 AMD patients who received monthly IVR for 3 months and thereafter pro re nata (PRN) injections for 9 months as the first treatment for AMD. Patients whose best corrected visual acuity (BCVA) worsened at month 12, and those with increased exudative fundus findings after IVR or an increased central retinal thickness of more than 100 μm at month 12, were considered to be non-responders as judged by BCVA and fundus findings, respectively. Non-responders’ initial characteristics were analysed using logistic regression models. Results 14.9% of eyes were non-responders as judged by BCVA, and 17.0% were non-responders as judged by fundus findings. Initial fibrovascular pigment epithelial detachment (PED) (OR 22.9, 95% CI 2.61 to 201) and serous PED (OR 4.12, 95% CI 1.08 to 15.8) were associated with non-response as judged by BCVA. Initial fibrovascular PED (OR 33.5, 95% CI 2.95 to 381) and type 1 choroidal neovascularization (OR 6.46, 95% CI 1.39 to 30.0) were associated with non-response, as judged by fundus findings. Conclusions Although most AMD responded to IVR, non-responders had initial clinical characteristics that might be informative for managing their treatment.

Disruption of Cell-Cell Junctions and Induction of Pathological Cytokines in the Retinal Pigment Epithelium of Light-Exposed Mice

PURPOSE To elucidate the influences of light exposure on the retinal pigment epithelium (RPE) in vivo that may be involved in the pathogenesis of AMD. METHODS Six- to 7-week-old BALB/c mice were exposed to light at 2000 lux for 3 hours. Flat-mount RPE samples were immunostained with anti-ZO-1 antibody for evaluating tight junction, anti-N-cadherin, and anti-β-catenin antibodies for adherens junction, and stained with phalloidin for actin cytoskeleton. The reactive oxygen species (ROS) level was measured using DCFH-DA; Rho-associated coiled-coil forming kinase (ROCK) activity was by ELISA. Cytokine expression was analyzed by real-time RT-PCR and/or ELISA in the RPE-choroid, and macrophage recruitment was by real-time RT-PCR and immunohistochemistry. Either an antioxidant, N-Acetyl-L-cysteine (NAC), or a ROCK inhibitor, Y-27632, were administered to analyze the roles of ROS and ROCK activation, respectively. RESULTS Light exposure disrupted staining patterns of tight junctions, adherens junctions, and actin cytoskeleton in the RPE, where ROS was elevated. However, NAC treatment avoided the RPE changes, reducing ROS. ROCK activity increased after light exposure was suppressed by NAC, and the structural disruptions were suppressed by Y-27632. The levels of MCP-1, CCL11, and IL-6 increased after light exposure were suppressed by NAC. Light-induced MCP-1 and IL-6 were suppressed by Y-27632. Macrophage recruitment after light exposure was also suppressed either by NAC or Y-27632. CONCLUSIONS Light exposure induced ROS and Rho/ROCK activation, which caused disruption of cell-cell junctions (tight junctions and adherens junctions) and actin cytoskeleton, the RPEs barrier structure, and induced AMD-associated pathological changes in the RPE-choroid.

Binding of ADAM28 to P-selectin glycoprotein ligand-1 enhances P-selectin-mediated leukocyte adhesion to endothelial cells

ADAMs (a disintegrin and metalloproteinases) are a recently discovered gene family of multifunctional proteins with the disintegrin-like and metalloproteinase domains. To analyze the biological functions of ADAM28, we screened binding molecules to secreted-type ADAM28 (ADAM28s) by the yeast two-hybrid system and identified P-selectin glycoprotein ligand-1 (PSGL-1). Binding between the disintegrin-like domain of ADAM28s and the extracellular portion of PSGL-1 was determined by yeast two-hybrid assays, binding assays of the domain-specific recombinant ADAM28s species using PSGL-1 stable transfectants and leukocyte cell lines expressing native PSGL-1 (HL-60 cells and Jurkat cells), and co-immunolocalization and co-immunoprecipitation of the molecules in these cells. Incubation of HL-60 cells with recombinant ADAM28s enhanced the binding to P-selectin-coated wells and P-selectin-expressing endothelial cells. In addition, intravenous injection of ADAM28s-treated HL-60 cells increased their accumulation in the pulmonary microcirculation and alveolar spaces in a mouse model of endotoxin-induced inflammation. These data suggest a novel function that ADAM28s promotes PSGL-1/P-selectin-mediated leukocyte rolling adhesion to endothelial cells and subsequent infiltration into tissue spaces through interaction with PSGL-1 on leukocytes under inflammatory conditions.

Suppression of Experimental Autoimmune Uveitis by Angiotensin II Type 1 Receptor Blocker Telmisartan

PURPOSE Angiotensin II type 1 receptor (AT1-R) blockers are used widely for the treatment of patients with hypertension. Recent reports have suggested that AT1-R also plays a key role in various inflammatory conditions. The aim of this study was to examine whether blockade of AT1-R is effective in the suppression of murine experimental autoimmune uveoretinitis (EAU). METHODS C57BL/6 mice were immunized with human interphotoreceptor retinoid binding protein-derived peptide 1-20 (hIRBP-p). Telmisartan, an AT1-R blocker, was administrated daily by intraperitoneal injection. On day 21 after immunization, the severity of EAU was assessed clinically and histopathologically. With the use of flow cytometry, the activation of draining lymph node (LN) cells was assessed by cell proliferation response against hIRBP-p and by the number of CD44(high) activated CD4(+) T cells present. In addition, mRNA expression of ICAM-1, MCP-1, and IFN-gamma in the eye was analyzed by reverse-transcriptase PCR, and the number of retinal adherent leukocytes was counted by retinal perfusion labeling. RESULTS Telmisartan significantly suppressed EAU clinically and histopathologically. Intraocular mRNA expression of ICAM-1 and MCP-1 was downregulated, and the retinal adherent leukocyte counts were significantly decreased in telmisartan-treated mice compared with vehicle-treated mice. LN cell proliferative responses against hIRBP-p and the number of CD44(high)CD4(+) T cells were remarkably reduced in telmisartan-treated mice. CONCLUSIONS Systemic administration of telmisartan significantly suppressed EAU by the inhibition of antigen-specific T-cell activation in the LNs and of leukocyte adhesion in the retina. These results indicate that telmisartan may be a novel therapeutic regimen for patients with endogenous uveitis.