Microscopical studies of necrotising scleritis. II. Collagen degradation in the scleral stroma

Scleral Proteome in Noninfectious Scleritis Unravels Upregulation of Filaggrin-2 and Signs of Neovascularization

Purpose

Scleritis is a severe inflammatory ocular disorder with unknown pathogenesis. We investigated healthy sclera as well as sclera affected by noninfectious scleritis for differentially expressed proteins using a mass spectrometry approach.

Methods

We collected scleral samples of enucleated eyes due to severe noninfectious scleritis (n = 3), and control scleral tissues (n = 5), all exenterated eyes for eyelid carcinomas (n = 4), or choroidal melanoma (n = 1) without scleral invasion. Samples were prepared for the nano liquid-chromatography mass spectrometer (LC-MS), data were analyzed using proteomics software (Scaffold), and is available via ProteomeXchange (identifier PXD038727). Samples were also stained for immuno-histopathological evaluation.

Results

Mass spectrometry identified 629 proteins within the healthy and diseased scleral tissues, whereof collagen type XII, VI, and I were the most abundantly expressed protein. Collagen type II-XII was also present. Filaggrin-2, a protein that plays a crucial role in epidermal barrier function, was found upregulated in all scleritis cases. In addition, other epithelial associated proteins were upregulated (such as keratin 33b, 34, and 85, epiplakin, transglutaminase-3, galectin 7, and caspase-14) in scleritis. Further, upregulated proteins involved in regulation of the cytoskeleton (vinculin and myosin 9), and housekeeping proteins were found (elongation factor-2 and cytoplasmic dynein 1) in our study. Upregulation of filaggrin-2 and myosin-9 was confirmed with immunohistochemistry, the latter protein showing co-localization with the endothelial cell marker ETC-related gene (ERG), indicating neovascularization in scleral tissue affected by scleritis.

Conclusions

We found upregulation of filaggrin-2 and signs of neovascularization in scleral tissue of patients with noninfectious scleritis. Further research, ideally including more scleritis cases, is needed to validate our findings.

Current insights in the pathogenesis of scleritis

Scleritis is a sight-threatening inflammation characterized by severe pain and redness of the eye. It can cause blindness by severe complications like scleral and corneal necrosis, keratitis, and uveitis. The pathogenesis of scleritis is largely unknown due to a combination of the rarity of the disease, the little available human tissue-based research material, and the lack of animal models. The immune system is assumed to play a crucial role in the pathogenesis of scleritis. Multiple clues indicate probable antigenic stimuli in scleritis, and the involvement of matrix metalloproteinases in the destruction of scleral tissue. In this article we review the current insights into the pathogenesis of scleritis, and we suggest new hypotheses by implementing knowledge of systemic autoimmune disease pathogenesis. Understanding the pathogenesis of scleritis is crucial to improve the clinical management, as well as to find novel treatment modalities.

The ultrastructure of rabbit sclera after scleral crosslinking with riboflavin and blue light of different intensities

PURPOSE

We aimed to determine the ultrastructural changes of collagen fibrils and cells in the rabbit sclera after scleral crosslinking using riboflavin and blue light of different intensities. Scleral crosslinking is known to increase scleral stiffness and may inhibit the axial elongation of progressive myopic eyes.

METHODS

The equatorial parts of the sclera of one eye of six adult albino rabbits were treated with topical riboflavin solution (0.5 %) followed by irradiation with blue light (200, 400, 650 mW/cm(2)) for 20 min. After 3 weeks, the ultrastructure of scleral cells and the abundance of small- (10-100 nm) and large-diameter (>100 nm) collagen fibrils in fibril bundles of different scleral layers were examined with electron microscopy.

RESULTS

In the scleral stroma of control eyes, the thickness of collagen fibrils showed a bimodal distribution. The abundance of small-diameter collagen fibrils decreased from the inner towards the outer sclera, while the amount of large-diameter fibrils and the scleral collagen content did not differ between different stroma layers. Treatment with riboflavin and blue light at 200 mW/cm(2) did not induce ultrastructural changes of cells and collagen fibrils in the scleral stroma. Treatment with blue light of higher intensities induced scleral cell activation in a scleral layer-dependent manner. In addition, outer scleral layers contained phagocytes that engulfed collagen fibrils and erythrocytes. Blue light of the highest intensity induced a reduction of the scleral collagen content, a decreased abundance of large-diameter collagen fibrils, and an increased amount of small-diameter fibrils in the whole scleral stroma.

CONCLUSIONS

The data indicate that in rabbits, scleral crosslinking with riboflavin and blue light of 200 mW/cm(2) for 20 min is relatively safe and does not induce ultrastructural alterations of scleral cells and of the collagen composition of the scleral stroma. Irradiation with blue light of intensities between 200 and 400 mW/cm(2) induces scleral cell activation, which may contribute to scleral scarring and stiffening. Higher intensities cause scleritis.

Observations on the ultrastructure of equatorial scleral collagen fibrils in sheep eyes

OBJECTIVE

To investigate collagen fibrils of the equatorial sclera in relation to the age-related changes in eye size in sheep.

ANIMALS STUDIED

Lambs and outbred ewes.

PROCEDURES

Sheep eyes (three lamb and three from adult outbred ewes), presumed disease-free, were processed for transmission electron microscopy (TEM) immediately postmortem. Tissue blocks from the equatorial region were sectioned across fibril bundles orientated along the equator. Micrographs including at least 500 fibrils were projected at 22,000× magnification for measures of fibril diameters (FDs).

RESULTS

Lamb eyes were smaller than those of adult ewes but equatorial scleral thickness was only marginally less at 0.232±0.013 vs. 0.254±0.012 mm (P value not significant). Scleral tissue was composed of compacted bundles of collagen fibers that tended to be rounder in outer compared to being flatter in inner regions. In typical (normal) appearing regions, FDs were distinctly larger (68-410 nm) in outer sclera compared to inner sclera (63-281 nm). Outer sclera FDs were bimodal averaging 192±58 nm, compared to unimodal distributions at inner locations averaging 156±48 nm (P<0.001). Some atypical regions, especially at outer-mid sclera locations, were also noted where the FD distribution was bimodal but also included numerous microfibrils (<50 nm diameter), with similar appearances being found for both lamb and adult ewe eyes.

CONCLUSIONS

The equatorial sclera is a mixture of rounder versus flatter collagen fiber bundles, the former being more likely to be made up of a mixture of both smaller and larger fibrils, as compared to slightly smaller fibrils.

Therapy Insight: scleritis and its relationship to systemic autoimmune disease

The term scleritis describes a chronic inflammation that involves the outermost coat and skeleton of the eye. Disease can be isolated to the eye, but in up to half of affected individuals it occurs in the context of an immune-mediated systemic inflammatory condition, such as rheumatoid arthritis or Wegener's granulomatosis. Although uncommon, scleritis is often extremely painful, can lead to vision-threatening complications (and involvement of other ocular tissues), and is considered to confer an increased risk of mortality in patients with rheumatoid arthritis. Pathogenic mechanisms in scleritis are poorly understood, but enzymatic degradation of collagen fibrils by resident cells and infiltrating leukocytes seems to be a key feature. Several forms of inflammation can be distinguished histologically; interestingly, although the disease typically presents with engorgement of scleral vessels, vasculitis is not universally present at the microscopic level. Although some patients with scleritis respond well to treatment with NSAIDs, aggressive systemic therapy is often required to obtain a favorable outcome, particularly when systemic disease coexists. The mainstay of treatment is oral prednisone, but this agent is usually combined with a steroid-sparing immunosuppressive drug. New therapies presently under investigation for scleritis include local corticosteroid injections and various biologic agents.

Anterior scleritis: three case reports and a review of the literature

BACKGROUND

Scleritis is a rare ocular condition involving vasculitis. It can result in severe ocular morbidity and has a high association with underlying systemic disease and mortality. Management can be challenging and under-diagnosis is a concern. Treatment usually requires systemic medications and co-management with a medical specialist in the appropriate field to manage any underlying systemic etiology.

METHODS

Three cases are presented: idiopathic nodular scleritis with complete recovery; bilateral, diffuse anterior scleritis with rheumatoid arthritis; and scleromalacia perforans treated with chemotherapeutic agents and co-managed with a rheumatologist. A search of the English language literature is reported, also.

RESULTS

The reported cases exemplify much of our knowledge regarding scleritis. The literature review focuses on the challenges of an accurate diagnosis and management. Management is challenging and, although standards exist, controversy remains. The literature discusses the relationship of scleritis to underlying systemic disease and the significant implication of this association.

CONCLUSION

Knowledge of scleritis may aid in determining a timely and accurate diagnosis and treatment of both the ocular and any underlying systemic conditions, thus decreasing morbidity and mortality.

Scleral structure, organisation and disease. A review

Although disease of the sclera is unusual, when it occurs it can rapidly destroy both the eye and vision. However, normally the sclera provides an opaque protective coat for the intraocular tissues and a stable support during variations in internal pressure and eye movements, which would otherwise perturb the visual process through distortion of the retina and the lens/iris diaphragm. This stability, which is vital for clear vision is made possible by the organisation and viscoelastic properties of scleral connective tissue. Microscopically, the sclera displays distinct concentric layers including, from outside, Tenon's capsule, episclera, the scleral stroma proper and lamina fusca, melding into underlying choroid. Two sites exhibit specialised structure and function: the perilimbal trabecular meshwork, through which aqueous filters into Schlemm's canal, and the lamina cribrosa, which permits axons of the optic nerve to exit the posterior sclera. Throughout, sclera is densely collagenous, the stroma consisting of fibrils with various diameters combining into either interlacing fibre bundles or defined lamellae in outer zones. Scleral fibrils are heterotypic structures made of collagen types I and III, with small amounts of types V and VI also present. Scleral elastic fibres are especially abundant in lamina fusca and trabecular meshwork. The interfibrillar matrix is occupied by small leucine-rich proteoglycans, decorin and biglycan, containing dermatan and dermatan/chondroitin sulphate glycosaminoglycans, together with the large proteoglycan, aggrecan, which also carries keratan sulphate sidechains. Decorin is closely associated with the collagen fibrils at specific binding sites situated close to the C-terminus of the collagen molecules. Proteoglycans influence hydration, solute diffusion and fluid movement through the sclera, both from the uvea and via the trabecular meshwork. As the sclera is avascular, nutrients come from the choroid and vascular plexi in Tenon's capsule and episclera, where there is an artery to artery anastomosis in which blood oscillates, rather than flows rapidly. This predisposes to the development of vasculitis causing a spectrum of inflammatory conditions of varying intensity which, in the most severe form, necrotising scleritis, may destroy all of the structural and cellular components of the sclera. Scleral cells become fibroblastic and the stroma is infiltrated with inflammatory cells dominated by macrophages and T-lymphocytes. This process resembles, and may be concurrent with, systemic disease affecting other connective tissues, particularly the synovial joints in rheumatoid arthritis. Current views support an autoimmune aetiology for scleritis. Whilst the role of immune complexes and the nature of initial pro-inflammatory antigen(s) remain unknown, the latter may reside in scleral tissue components which are released or modified by viral infection, injury or surgical trauma.

Ultrasound biomicroscopy in scleritis

OBJECTIVE

This study aimed to investigate the usefulness of ultrasound biomicroscopy (UBM) for detecting and following up scleritis and episcleritis.

DESIGN

The study design was a case series.

PARTICIPANTS

Patients with scleral inflammatory diseases (n = 16) were examined.

INTERVENTION

Patient-reported problems and slit-lamp and UBM (50-MHz transducer) findings were compared retrospectively for signs of scleral inflammation.

MAIN OUTCOME MEASURES

Thickness, reflectivity, and homogeneity of the sclera and episclera were the criteria for discriminating between the different types of scleritis with the UBM technique.

RESULTS

Scleral disease was associated with Wegener disease (n = 3), Cogan disease (n = 1), Hashimoto thyroiditis (n = 1), myositis (n = 1), or panuveitis (n = 1). Initial slit-lamp evaluation showed episcleritis (n = 3), diffuse scleritis (n = 9), nodular scleritis (n = 3), or necrotizing scleritis (n = 1). By means of UBM analysis, the diagnosis of episcleritis or scleritis was in agreement with the slit-lamp findings in 2 of 3 and 6 of 13 cases, respectively. In contrast to the slit-lamp diagnosis, UBM studies excluded scleritis in one patient, disclosed necrosis in four patients with scleritis, and detected nodular scleritis patterns in two further patients with diffuse scleritis. The determination of complete remission, improvement, or progression of disease by slit-lamp and UBM evaluation was in agreement in 11 of the 14 patients examined. However, UBM was superior to slit-lamp examination with respect to detecting scleral necrosis, scleral thinning, or the nodular type of scleritis.

CONCLUSIONS

The findings indicate that UBM is helpful in rapidly differentiating scleritis from severe episcleritis, detecting the diverse scleritis types with high accuracy, disclosing minimal disease progression, and judging treatment efficacy.

Increased expression of matrix metalloproteinases in vivo in scleritis tissue and in vitro in cultured human scleral fibroblasts

Scleritis is a sight-threatening inflammatory disorder of the eye characterized by the degradation of scleral matrix. Matrix metalloproteinases (MMPs) are ubiquitous proteolytic enzymes important in physiological and pathological processes, the activity of which is stringently controlled by the action of a family of natural antagonists, the tissue inhibitors of matrix metalloproteinases (TIMPs). We hypothesized that enhanced expression of MMPs, without the negative regulatory influence of TIMPs, may be a key feature of tissue destruction in inflammatory eye diseases, such as scleritis. The aim of this study was to localize and characterize cells expressing MMPs and TIMPs in sclera affected by necrotizing scleritis and, in a parallel study, to establish whether cytokines modulate MMP expression in cultured human scleral fibroblasts. In situ hybridization and immunohistochemical analyses indicated that resident scleral fibroblasts as well as inflammatory cells such as macrophages and T lymphocytes express stromelysin, gelatinase B, and TIMP-1 in necrotizing scleritis tissue. In addition, cytoplasmic immunoreactivity for tumor necrosis factor-alpha, an inducer of MMPs, was detected in infiltrating inflammatory cells. Cultured scleral fibroblasts stimulated with the combination of interleukin-1 alpha plus tumor necrosis factor-alpha increased TIMP-1 mRNA twofold above constitutive levels. By contrast, these cytokines induced a sevenfold increase in the steady-state levels of stromelysin mRNA. Using Western blotting, stromelysin and TIMP-1 protein production paralleled mRNA induction in cytokine-stimulated human scleral fibroblasts. Culture supernatants harvested from cytokine-stimulated human scleral fibroblasts were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis gelatin substrate zymography. Our results revealed a prominent 92-kd gelatinolytic band corresponding to gelatinase B, which was inducible with interleukin-1 alpha. These data provide evidence for our hypothesis, that an imbalance between enzyme/inhibitor ratios may be the underlying mechanism of the tissue destruction characteristic of scleritis. Our results demonstrate the potential involvement of MMPs and their modulation by cytokines produced by infiltrating inflammatory cells in destructive ocular inflammation.

Ultrasound biomicroscopy in the assessment of anterior scleral disease

High-frequency ultrasound biomicroscopy is a new method of examining subsurface anterior segment structures of the eye at microscopic resolution. The sclera has a high internal reflectivity and can be differentiated from the cornea, and overlying and underlying tissue. Using this modality, we examined 18 patients with various manifestations of scleral disease. Localized anterior staphyloma could be differentiated from other causes of a black spot on the scleral surface. Episcleral thickening could be differentiated from involvement of the sclera itself. Different patterns of scleral involvement could be imaged including diffuse low-reflective mottling, low-reflective nodules extending into the scleral substance, and scleral thinning. Scleral thinning could be assessed and quantified. Underlying changes in the vitreous could be detected. Ultrasound biomicroscopy was a useful adjunct to clinical examination in the assessment of anterior scleral disease.

Posterior scleritis: a clinical and histological survey

The clinical course of 47 patients with posterior scleritis is reviewed. Though clinical presentation varied widely, 73% of the patients presented with a visual acuity of 6/18 or less. Because the posterior scleritis was not always associated with pain or with anterior scleritis, the diagnosis was often not considered when the patient was first seen. The most common findings in the fundus were disc swelling, retinal detachment, and macular oedema and the most useful investigation was B scan ultrasound. No common aetiology was found, although 60% had a systemic disorder which was accompanied by a vasculitis. Those who were diagnosed and treated with the minimum delay had the most satisfactory visual outcome. However, there appears to be a group of patients with no underlying systemic disease who fail to respond to intensive therapy, and lose vision. A new sub-group of West Indians with the disease is described. The histopathology of 7 cases confirmed the presence of scleral vasculitis of the vessels in and around the sclera in all the specimens. Other significant findings include inflammatory swelling and focal loss of pigment epithelium together with choroidal vascular closure. This could account for the fluorescein angiographic findings.

Posterior scleritis

Posterior scleritis must be considered in the differential diagnosis of many ocular conditions, including angle closure glaucoma, choroidal folds, optic disk edema, circumscribed fundus mass, choroidal detachment, and exudative retinal detachment. Because it is rare, a high index of suspicion is necessary. Anterior scleritis, pain, or a history of collagen-vascular disease, when present, help to alert the clinician to the correct diagnosis. Posterior scleritis affects women more often than men, but annular ciliochoroidal effusion and choroidal folds are more common in men. Exudative macular detachment and a circumscribed fundus mass are more common in women. This paper reviews the world literature on posterior scleritis and describes findings in a series of 43 patients seen at Wills Eye Hospital. It stresses the clinical features and ancillary diagnostic tests that help to establish the diagnosis.

Ultrastructural changes in scleral proteoglycans precede destruction of the collagen fibril matrix in necrotizing scleritis

Proteoglycans were localized using cuprolinic blue and visualized by electron microscopy in sclera from the eye of a 58-year-old woman with necrotizing scleritis. Samples of sclera taken from clinically normal anterior and posterior sclera and from sites involved in anterior necrotizing scleritis with ulceration and posterior scleritis showed markedly different patterns of proteoglycan distribution. Proteoglycans appeared as stain-positive filaments associated regularly with the 'd/e' bands of the collagen fibrils in normal anterior sclera, but were absent from intact collagen fibrils in the zone of anterior ulcerative scleritis. In posterior sclera including a site of posterior scleritis, proteoglycans were reduced in number with more heterogeneous associations with collagen fibrils. Depletion of scleral proteoglycans therefore precedes the degradation of scleral collagen in necrotizing scleritis, which may also involve the synthesis of atypical proteoglycan types in pathological sclera.

Changes at the periphery of a lesion in necrotising scleritis: anterior segment fluorescein angiography correlated with electron microscopy

Anterior segment fluorescein angiography in scleral disease reveals highly characteristic changes in the vasculature of the anterior segment associated with necrotising scleritis. The vaso-obliterative changes discovered in this investigation have been correlated with the histopathology in a patient who had to have tissue replaced. Light and electron microscopy of scleral tissue excised from sites of vascular closure detected by fluorescein angiography peripheral to the scleral defect revealed pathological changes in the absence of inflammatory cell infiltration. These changes included vascular stasis, partial vaso-obliteration, and fibroblastic transformation of scleral fibrocytes in association with intra- and extracellular degradation of the collagenous component of the matrix.

Microscopical studies of necrotising scleritis. I. Cellular aspects

Light and electron microscopy were used to examine tissue excised during surgery from eight patients with advanced destructive scleral disease. These comprised two cases of scleromalacia perforans, three cases of anterior necrotising scleritis alone or in conjunction with other systemic diseases, and three cases in which scleritis developed following ocular surgery. It was not possible to distinguish between these three categories by histological or cytopathological criteria. All showed extensive granulomatous infiltration of the conjunctiva, episclera, and sclera by plasma cells and lymphocytes. Mast cells were abundant throughout these inflamed tissues. Examination of scleral stroma from sites in advance of the granuloma revealed active fibroblastic cells in the absence of other inflammatory cells. Fibroblastic transformation of scleral cells may be one of the earliest events in scleral degradation during necrotising disease.