Effects of Chymase on the Macular Region in Monkeys and Porcine Müller Cells: Probable Involvement of Chymase in the Onset of Idiopathic Macular Holes

Etiology of Idiopathic Macular Holes in the Light of Estrogen Hormone

The aim of this review was to identify a new potential explanation for the development of macular holes in relation to the female sex and to explain the possible underlying pathways. This approach was based on the evaluation of anatomical, physiological, and morphological analyses currently available in the literature. The findings showed that estrogen exerts a protective effect on the neuroretina and may influence Müller and cone cells. Both cell types are responsible for the building of the fovea structure. However, this protection may be lost due to the sudden decrease in estrogen levels during menopause. In conclusion, the fovea cones, through its sensitivity to estrogen and high energy consumption, may be very vulnerable to damage caused by a sudden changes in the concentration of estrogen in menopausal females. Such changes may result in cone degeneration, and thus a destroyed structure of the fovea, and may lead to the development of a hole in the fovea, as in the case of macular holes. This review revealed that under the decreasing influence of estrogen may cones play a key role with regard to the etiology of the development of macular holes. This aspect may be of strategic importance in prophylactic therapy for the prevention of the development of macular holes in premenopausal females or after ocular trauma.

Internalization of Angiotensin-(1-12) in Adult Retinal Pigment Epithelial-19 Cells

Purpose: Angiotensin-(1-12) [Ang-(1-12)] serves as a primary substrate to generate angiotensin II (Ang II) by angiotensin-converting enzyme and/or chymase suggests it may be an unrecognized source of Ang II-mediated microvascular complication in hypertension-mediated retinopathy. We investigated Ang-(1-12) expression and internalization in adult retinal pigment epithelial-19 (ARPE-19) cultured cells. We performed the internalization of Ang-(1-12) in ARPE-19 cells in the presence of a highly specific monoclonal antibody (mAb) developed against the C-terminal end of the Ang-(1-12) sequence. Methods: All experiments were performed in confluent ARPE-19 cells (passage 28-35). We employed high-performance liquid chromatography to purify radiolabeled, 125I-Ang-(1-12) and immuno-neutralization with Ang-(1-12) mAb to demonstrate Ang-(1-12)'s internalization in ARPE-19 cells. Internalization was also demonstrated by immunofluorescence (IF) method. Results: These procedures revealed internalization of an intact 125I-Ang-(1-12) in ARPE-19 cells. A significant reduction (∼53%, P < 0.0001) in 125I-Ang-(1-12) internalization was detected in APRE-19 cells in the presence of the mAb. IF staining experiments further confirms internalization of Ang-(1-12) into the cells from the extracellular culture medium. No endogenous expression was detected in the ARPE-19 cells. An increased intensity of IF staining was detected in cells exposed to 1.0 μM Ang-(1-12) compared with 0.1 μM. Furthermore, we found hydrolysis of Ang-(1-12) into Ang II by ARPE-19 cells' plasma membranes. Conclusions: Intact Ang-(1-12) peptide is internalized from the extracellular spaces in ARPE-19 cells and metabolized into Ang II. The finding that a selective mAb blocks cellular internalization of Ang-(1-12) suggests alternate therapeutic approaches to prevent/reduce the RPE cells Ang II burden.

Spontaneous disappearance and recurrence of impending macular hole: a case report

Background

There have been several reports of spontaneous closure and reopening of a macular hole, however, in most of those cases, it was observed in eyes post vitrectomy. Here, we report a case of multiple episodes of spontaneous disappearance and recurrence of impending macular hole (stage 1B macular hole) with no history of previous surgery.

Case presentation

A 76-year-old Japanese man presented with a primary complaint of reduced visual acuity in his right eye. On initial examination, the visual acuity in his right and left eye was 0.4 and 0.01, respectively. He had previously been diagnosed as having macular degeneration of unknown origin in his left eye. Optical coherence tomography imaging confirmed vitreomacular traction and impending macular hole in his right eye. After a 1-week follow-up period, posterior vitreous detachment was detected, and the impending macular hole appeared to be resolved. Two months later, the impending macular hole had completely disappeared and his visual acuity had improved to 0.9. Six months later, he again noticed decreased vision in his right eye. An examination revealed that his visual acuity had dropped to 0.4, and there was a recurrence of impending macular hole. An optical coherence tomography examination showed no definitive findings of vitreous traction, and, 1 month later, spontaneous disappearance was observed again and his visual acuity improved to 0.7.

Conclusions

In this case, both the initial onset and the recurrence involved impending macular hole, however, the optical coherence tomography findings differed at each examination. These findings suggest that some causes other than vitreous traction were responsible for both the spontaneous disappearance and recurrence of the impending macular hole in this present case.

Immunohistological Study of Monkey Foveal Retina

The fovea centralis, an anatomically concave pit located at the center of the macula, is avascular, hypoxic, and characteristic of stem-cell niches of other tissues. We hypothesized that in the fovea, undifferentiated retinal-stem-cell-like cells may exist, and that neurogenesis may occur. Hence, we performed an immunohistological study using cynomolgus monkey retinas. After preparing frozen tissue sections of the retina including the foveal pit, immunostaining was performed for glial fibrillary acidic protein (GFAP), nestin, vimentin, neuron-specific class III β-tubulin (Tuj-1), arrestin 4, neurofilament, CD117, CD44, Ki67, and cellular retinaldehyde-binding protein (CRALBP), followed by fluorescence and/or confocal microscopy examinations. Immunostaining of the tissue sections enabled clear observation of strongly GFAP-positive cells that corresponded to the inner-half layer of the foveolar Müller cell cone. The surface layer of the foveal slope was partially costained with GFAP and vimentin. Tuj-1-positive cells were observed in the innermost layer of the foveolar retina, which spanned to the surrounding ganglion cell layer. Moreover, colocalization of Tuj-1 and GFAP was observed at the foveal pit. The coexpression of CD117 and CD44 was found in the interphotoreceptor matrix of the fovea. The foveolar cone stained positive for both nestin and arrestin 4, however, the photoreceptor layer outside of the foveola displayed weak staining for nestin. Colocalization of nestin and vimentin was observed in the inner half of the Henle layer, while colocalization of nestin and neurofilament was observed in the outer half, predominantly. Scattered Ki67-positive cells were observed in the cellular processes of the outer plexiform layer and the ganglion cell layer around the foveola. Immunostaining for CRALBP was negative in most parts of the GFAP-positive area. The Müller cell cone was divided into GFAP-strongly positive cells, presumably astrocytes, in the inner layer and nestin-positive/GFAP-weakly positive radial glia-like cells in the outer layer. These findings indicated that groups of such undifferentiated cells in the foveola might be involved in maintaining morphology and regeneration.

Involvement of premacular mast cells in the pathogenesis of macular diseases

We previously reported on the elevated intravitreal activities of tryptase and chymase in association with idiopathic epiretinal membrane (ERM) and idiopathic macular hole (MH). In this present study, we investigated the potential intraocular production of these serine proteases, and measured and compared tryptase and chymase activities in the vitreous body and serum in ERM, MH, proliferative diabetic retinopathy (PDR), and rhegmatogenous retinal detachment (RRD) patients. In addition, nuclear staining with hematoxylin and eosin (H&E) and mast-cell staining with toluidine blue were performed on samples of the vitreous core and bursa premacularis (BPM) of MH. We also performed immunostaining on the above two regions of vitreous samples for MH with anti-tryptase antibody, anti-chymase antibody, anti-podoplanin antibody, anti-lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) antibody, and anti-fibroblast antibody. Moreover, we performed immunostaining with anti-tryptase antibody and anti-chymase antibody on ERMs collected intraoperatively. Tryptase activity in the vitreous body was significantly higher in ERM and MH than in PDR. However, no significant differences were observed in the tryptase activity in the serum among these four diseases. Chymase activity in the vitreous body was significantly higher in MH than in the other three diseases, yet chymase activity in the serum was below detection limit in any of the diseases. Nuclear staining with H&E revealed an abundance of nuclei in the BPM region, but few in the surrounding area. Mast-cell staining with toluidine blue revealed that the BPM showed metachromatic staining. In immunostaining with anti-fibroblasts antibody, anti-tryptase antibody, anti-chymase antibody, anti-podoplanin antibody, and anti-LYVE-1 antibody, the BPM stained more strongly than the vitreous core. Tryptase and chymase-positive cells were also observed in ERM. These findings revealed that the presence of mast cells in the BPM potentially represent the source of these serine proteases. Moreover, the BPM, as a lymphatic tissue, may play an important role in the pathogenesis of macular disease.

Role of Tissue Renin-angiotensin System and the Chymase/angiotensin-( 1-12) Axis in the Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy (DR) is a major diabetes complication and the leading cause for vision loss and blindness in the adult human population. Diabetes, being an endocrinological disorder dysregulates a number of hormonal systems including the renin angiotensin system (RAS), which thereby may damage both vascular and neuronal cells in the retina. Angiotensin II (Ang II), an active component of the RAS is increased in diabetic retina, and may play a significant role in neurovascular damage leading to the progression of DR. In this review article, we highlight the role of Ang II in the pathogenesis of retinal damage in diabetes and discuss a newly identified mechanism involving tissue chymase and angiotensin-(1-12) [Ang-(1-12)] pathways. We also discuss the therapeutic effects of potential RAS inhibitors targeting blockade of cellular Ang II formation to prevent/ protect the retinal damage. Thus, a better understanding of Ang II formation pathways in the diabetic retina will elucidate early molecular mechanism of vision loss. These concepts may provide a novel strategy for preventing and/or treating diabetic retinopathy, a leading cause of blindness worldwide.

Expression of a hyaluronic acid-binding proteoglycan (versican) in the cynomolgus monkey eye

The expression of versican, a hyaluronic acid (HA)-binding protein, during the development and differentiation of the retina has been reported. In this study, we performed histochemical and immunohistological analysis of HA and versican from the ciliary body to the retina in cynomolgus monkey eyes. Paraffin-embedded sections of cynomolgus monkey eyes, including from the ciliary body to the macular region, were prepared. The distribution of versican and HA was examined by histochemical and immunohistochemical methods. The sites of HA expression and versican expression in the eye specimens were similar. Expression of HA and versican was observed in the peripheral retina and ciliary body, but not from the macular region to the mid-periphery of the retina. Versican was strongly expressed in the ciliary body, particularly in the non-pigmented ciliary epithelium. Expression in the retina from the periphery to posterior pole gradually decreased. Versican is expressed from the ciliary body to the peripheral retina, but this expression decreases toward the posterior pole. This suggests a physiological function for versican in the peripheral retina.

The role of tryptase and anti-type II collagen antibodies in the pathogenesis of idiopathic epiretinal membranes

Purpose

To investigate the pathogenesis of idiopathic epiretinal membrane (ERM) from a biochemical perspective, the relationships between ERM and tryptase activity, a serine protease, and the levels of anti-type II collagen (anti-IIC) antibodies in the serum.

Patients and methods

Vitreous samples for measurement of tryptase activity were obtained from 54 eyes of 54 patients who underwent a vitrectomy for vitreoretinal disease, ie, 14 eyes of 14 patients with idiopathic macular hole, 14 eyes of 14 patients with proliferative diabetic retinopathy (PDR), 13 eyes of 13 patients with ERM, and 13 eyes of 13 patients with rhegmatogenous retinal detachment (RRD). Tryptase activity was measured by spectrophotometry. Anti-IIC antibodies were measured in the serum obtained from 17 patients with ERM, eight patients who underwent cataract surgery, 12 patients with PDR, and nine patients with RRD. In these 46 patients, the anti-IIC antibodies were measured using a Human/Monkey Anti-Type I and Type II Collagen IgG Assay Kit.

Results

Vitreal tryptase activity (mean ± standard deviation [SD]) in macular hole, PDR, ERM, and RRD was 0.0146±0.0053, 0.0018±0.0018, 0.0166±0.0046, and 0.0117±0.0029 mU/mg protein, respectively. Vitreal tryptase activity was significantly higher in macular hole and ERM than in PDR and RRD (P<0.05, Fisher’s protected least significant difference). The serum levels of anti-IIC immunoglobulin G (IgG) antibody (mean ± SD) in ERM, cataract surgery, PDR, and RRD were 58.222±30.986, 34.890±18.165, 55.760±26.008, and 35.453±12.769 units/mL, respectively. The serum levels of anti-IIC IgG antibody were significantly higher in ERM and PDR than in cataract surgery and RRD (P<0.05, Fisher’s protected least significant difference, two-sided).

Conclusion

In the pathogenesis of ERM, increased vitreal tryptase activity may be involved in tissue fibrosis, and elevated serum anti-IIC antibodies may lead to an immune response at the vitreoretinal interface, thus resulting in membrane formation.

En face optical coherence tomography of foveal microstructure in full-thickness macular hole: a model to study perifoveal Müller cells

PURPOSE

To characterize perifoveal intraretinal cavities observed around full-thickness macular holes (MH) using en face optical coherence tomography and to establish correlations with histology of human and primate maculae.

DESIGN

Retrospective nonconsecutive observational case series.

METHODS

Macular en face scans of 8 patients with MH were analyzed to quantify the areas of hyporeflective spaces, and were compared with macular flat mounts and sections from 1 normal human donor eye and 2 normal primate eyes (Macaca fascicularis). Immunohistochemistry was used to study the distribution of glutamine synthetase, expressed by Müller cells, and zonula occludens-1, a tight-junction protein.

RESULTS

The mean area of hyporeflective spaces was lower in the inner nuclear layer (INL) than in the complex formed by the outer plexiform (OPL) and the Henle fiber layers (HFL): 5.0 × 10(-3) mm(2) vs 15.9 × 10(-3) mm(2), respectively (P < .0001, Kruskal-Wallis test). In the OPL and HFL, cavities were elongated with a stellate pattern, whereas in the INL they were rounded and formed vertical cylinders. Immunohistochemistry confirmed that Müller cells followed a radial distribution around the fovea in the frontal plane and a "Z-shaped" course in the axial plane, running obliquely in the OPL and HFL and vertically in the inner layers. In addition, zonula occludens-1 co-localized with Müller cells within the complex of OPL and HFL, indicating junctions in between Müller cells and cone axons.

CONCLUSION

The dual profile of cavities around MHs correlates with Müller cell morphology and is consistent with the hypothesis of intra- or extracellular fluid accumulation along these cells.

Vitreous estrogen levels in patients with an idiopathic macular hole

Purpose

Estrogen, a female hormone, activates collagenase and might be associated with the pathogenesis of vitreoretinal collagen fiber disease. The purpose of the present study was to investigate the vitreous levels of estrone (E1) and estradiol (E2) in subjects with an idiopathic macular hole (IMH).

Methods

Vitreous samples were obtained from ten female patients with an IMH and from nine female patients with other retinal diseases (six with rhegmatogenous retinal detachment and three with age-related macular degeneration) as a control at the time of vitreous surgery. E1 and E2 levels in the vitreous samples were then determined using the Coat-A-Count^® Estradiol Radioimmunoassay (RIA) Kit and the DSL-70 Estrone RIA Kit, respectively.

Results

The mean vitreous levels of E1 and E2 in the subjects with IMH were 1.83±2.00 pg/mL and 7.03±2.97 pg/mL, respectively, whereas in the control subjects they were 2.42±1.25 pg/mL and 4.90±2.90 pg/mL, respectively. Thus, the vitreous E2 levels in the subjects with IMH were significantly higher than in the controls (P<0.05).

Conclusion

The findings of this study suggest that E2 might be associated with the pathogenesis of IMH, but further investigation is needed to elucidate that association.

Multimodal imaging and multifocal electroretinography demonstrate autosomal recessive Stargardt disease may present like occult macular dystrophy

PURPOSE

To describe multimodal imaging and electrophysiologic characteristics of an unusual subset of patients with genetically confirmed autosomal recessive Stargardt disease (STGD1) who exhibited a central form of cone dysfunction resembling occult macular dystrophy that preceded the development of lipofuscin flecks, atrophy of retinal pigment epithelium (RPE), or full-field electroretinography abnormalities.

METHODS

Retrospective, observational descriptive case series.

RESULTS

Five patients with compound heterozygous ABCA4 mutations presented with bilateral visual acuity reduction, normal-appearing fundi, and blocked choroidal fluorescence on fluorescein angiography. One sibling each of two probands with identical genotypes was also included for analysis. Full-field electroretinography testing was normal in all patients, but multifocal electroretinography demonstrated centripetally depressed amplitudes exceeding areas of fundus autofluorescence, infrared imaging, and spectral domain optical coherence tomography abnormalities. Spectral domain optical coherence tomography initially revealed disruption of the inner segment ellipsoid band accompanying an ovoid hypofluorescent foveolar lesion. Progression to later stages was accompanied by the loss of the foveal photoreceptor outer segments, creating foveal cavitation with preservation of the RPE. Fundus autofluorescence and infrared imaging demonstrated corresponding bull's eye lesions. Over time, the foveal potential space on spectral domain optical coherence tomography collapsed, and three patients developed RPE atrophy and visible lipofuscin flecks. The flecks were detectable by fundus autofluorescence and infrared imaging earlier than by biomicroscopy. From these findings, a staging system for this subset of Stargardt disease presenting with central cone dysfunction was developed and presented herein.

CONCLUSION

Autosomal recessive Stargardt disease may present as a central cone dysfunction syndrome before the development of lipofuscin flecks, atrophy of RPE, or full-field electroretinography abnormalities. If emerging therapies for Stargardt disease succeed, early recognition and treatment of patients with preserved foveal photoreceptor and RPE cell bodies may yield a more favorable visual prognosis.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.