Ultrastructural investigation of extracellular structures in subcapsular white corrugated cataract (anterior capsular cataract)

Dealings between Cataract and Retinal Reattachment Surgery in PVR

Introduction. To evaluate the impact of the eye lens status and oil side effects on the outcome of vitreoretinal surgery in retinal detachment with proliferative vitreoretinopathy (PVR) and a temporary silicone oil tamponade (SOT). Methods. 101 eyes were analyzed retrospectively and 103 eyes prospectively in regard to their retinal reattachment success rate and key factors for the outcome. Subgroup analysis of 27 eyes with Scheimpflug lens photography (SLP) before and after retinal reattachment service with SOT was performed. For SLP (65% phakic eyes) a Pentacam densitometry reference body with 3 mm diameter was chosen and 3 segments (anterior/mid/posterior) were evaluated separately after a quality check. Results. The retinal reattachment rate was highest in the prospective pseudophakic group (p = 0.039). Lens transparency loss occurred earlier in middle aged patients than in younger patients. Besides the nucleus, layers posterior and anterior to it showed specific transparency changes. The emulsification rate was higher when eyes had been operated on in the anterior chamber before retinal reattachment service. Conclusions. Retinal reattachment surgery seems to benefit from preoperative cataract removal. We found significant lens changes in the nucleus as well as in the layers anterior and posterior to it. This corresponds to the histology of the lens epithelium published before.

Elevated tropomyosin expression is associated with epithelial-mesenchymal transition of lens epithelial cells

Injury to lens epithelial cells (LECs) leads to epithelial–mesenchymal transition (EMT) with resultant fibrosis. The tropomyosin (Tpm) family of cytoskeleton proteins is involved in regulating and stabilizing actin microfilaments. Aberrant expression of Tpms leads to abnormal morphological changes with disintegration of epithelial integrity. The EMT of LECs has been proposed as a major cause of posterior capsule opacification (PCO) after cataract surgery. Using in vivo rodent PCO and human cataractous LECs, we demonstrated that the aberrant expression of rat Tpm and human Tpm1α/2β suggested their association in remodelling of the actin cytoskeleton during EMT of LECs. Expression analysis from abnormally growing LECs after lens extraction revealed elevated expression of α-smooth muscle actin (α-SMA), a marker for EMT. Importantly, these cells displayed increased expression of Tpm1α/2β following EMT/PCO formation. Expression of Tpm1α/2β was up-regulated in LECs isolated from cataractous lenses of Shumiya Cataract Rats (SCRs), compared with non-cataractous lenses. Also, LECs from human patients with nuclear cataract and anterior subcapsular fibrosis (ASF) displayed significantly increased expression of Tpm2β mRNA, suggesting that similar signalling invokes the expression of these molecules in LECs of cataractous SCR and human lenses. EMT was observed in LECs overexpressed with Tpm1α/2β, as evidenced by increased expression of α-SMA. These conditions were correlated with remodelling of actin filaments, possibly leading to EMT/PCO and ASF. The present findings may help clarify the condition of the actin cytoskeleton during morphogenetic EMT, and may contribute to development of Tpm-based inhibitors for postponing PCO and cataractogenesis.

Integrins in lens development and disease

Integrins are the major cell surface receptors for proteins in the extracellular matrix. These receptors form major cell signaling centers that are bidirectional, communicating messages between the cell and its environment. They are a large receptor family, with members well-known to regulate cellular processes essential to both development and disease. In this review we examine the literature regarding integrins in the lens. Here we cover integrin function in lens cell differentiation, in the development of the lens and in protection of the lens epithelial cell phenotype. In addition, we analyze the role of integrins in the progression of lens fibrotic diseases, focusing particularly on integrin regulation of TGFbeta signaling pathways in posterior capsule opacification (PCO) and anterior subcapsular cataract (ASC).

Results of cataract extraction after implantable contact lens removal

PURPOSE

To evaluate the visual results following insertion of implantable contact lenses (ICLs) in ametropic eyes and the development of subcapsular opacification with visual loss and to examine the anterior capsule, including the subcapsular tissue alteration, by light microscopy.

SETTING

Department of Ophthalmology, Schlosspark-Klinik, affiliated hospital of the Charité Berlin, Humbold University, Berlin, Germany.

METHODS

A prospective noncomparative interventional case series of anterior subcapsular cataracts in 9 of 127 (7.1%) patient eyes receiving ICLs to correct myopia and hyperopia was studied. The cataracts were phacoemulsified due to visual loss, and an intraocular lens (IOL) was implanted in the bag. After capsulorhexis, the anterior capsule was withdrawn for light microscopy examination. Visual acuity in each eye was measured before and after ICL implantation and before and after cataract extraction. The age range of cataract patients was 39 to 53 years.

RESULTS

Implantable contact lens removal and phacoemulsification with IOL implantation for emmetropia resulted in an increased visual acuity compared to initial vision. Four of 28 hyperopic eyes (14.3%) developed subcapsular central opacification after ICL implantation, whereas 5 of 99 myopic patients (5.1%) developed opacifications.

CONCLUSIONS

Patients should be informed prior to ICL implantation, there is a possibility of secondary subcapsular cataract formation and vision reduction. Although the posterior chamber inlay as well as the cataract can be removed and better acuity can be restored, a possible complication due to the ICL implantation cannot be avoided and the accommodation in young patients lost.

Transforming growth factor-beta-induced epithelial-mesenchymal transition in the lens: a model for cataract formation

The vertebrate lens has a distinct polarity and structure that are regulated by growth factors resident in the ocular media. Fibroblast growth factors, in concert with other growth factors, are key regulators of lens fiber cell differentiation. While members of the transforming growth factor (TGFbeta) superfamily have also been implicated to play a role in lens fiber differentiation, inappropriate TGFbeta signaling in the anterior lens epithelial cells results in an epithelial-mesenchymal transition (EMT) that bears morphological and molecular resemblance to forms of human cataract, including anterior subcapsular (ASC) and posterior capsule opacification (PCO; also known as secondary cataract or after-cataract), which occurs after cataract surgery. Numerous in vitro and in vivo studies indicate that this TGFbeta-induced EMT is part of a wound healing response in lens epithelial cells and is characterized by induced expression of numerous extracellular matrix proteins (laminin, collagens I, III, tenascin, fibronectin, proteoglycans), intermediate filaments (desmin, alpha-smooth muscle actin) and various integrins (alpha2, alpha5, alpha7B), as well as the loss of epithelial genes [Pax6, Cx43, CP49, alpha-crystallin, E-cadherin, zonula occludens-1 protein (ZO-1)]. The signaling pathways involved in initiating the EMT seem to primarily involve the Smad-dependent pathway, whereby TGFbeta binding to specific high affinity cell surface receptors activates the receptor-Smad/Smad4 complex. Recent studies implicate other factors [such as fibroblast growth factor (FGFs), hepatocyte growth factor, integrins], present in the lens and ocular environment, in the pathogenesis of ASC and PCO. For example, FGF signaling can augment many of the effects of TGFbeta, and integrin signaling, possibly via ILK, appears to mediate some of the morphological features of EMT initiated by TGFbeta. Increasing attention is now being directed at the network of signaling pathways that effect the EMT in lens epithelial cells, with the aim of identifying potential therapeutic targets to inhibit cataract, particularly PCO, which remains a significant clinical problem in ophthalmology.

Expression of alphasmooth muscle actin in lens epithelia from human donors and cataract patients

In order to re-evaluate functional implications of alphasmooth muscle actin (alphaSMA) expression in lens epithelial cells (LECs), we assessed its presence in donor lenses without visible opacities (DON), lenses with mature cataract (CAT), and cataractous lenses with posterior subcapsular opacities (PSO) or anterior subcapsular fibrosis (ASF). The levels of alphaSMA and transforming growth factor-beta2 (TGFbeta2) mRNAs were measured by classical and real-time PCR. Expression and structural organisation of alphaSMA protein and beta-catenin were monitored by Western blotting and confocal microscopy. All DON analysed contained measurable amounts of alphaSMA mRNA. In CAT without and with PSO, mRNA expression was increased and, again more than doubled in ASF. TGFbeta2 mRNA expression varied widely between the individual samples but was slightly increased in ASF. No correlation existed between alphaSMA or TGFbeta2 expression and the age of the donors in any of the lens categories. Confocal microscopy revealed that, in DON and CAT, alphaSMA was preferentially expressed in a simple granular pattern in single or small clusters of LECs within a normally shaped cobblestone epithelium. Locally, the granules were merged into short stretches at the cell margin. In CAT, a few abnormally shaped cells contained polygonal alphaSMA structures and short stress fibres. In CAT with PSO and ASF, polygons and stress fibre bundles predominated in spindle-shaped cells. Expression patterns of different complexity were often present in the same epithelium. Apical polygons and basal stress fibres were detected within the same cell and may reflect instability of the interface between epithelium and cortical fibres and changes in adhesion to the capsule, respectively. High levels of betacatenin mRNA and protein were present in all lens types. However, with increasing complexity of alphaSMA organisation, betacatenin staining disappeared from the cell margin and basal infoldings and was shifted towards the cytoplasm and nucleus. The presence of alphaSMA in DON, the absence of any correlation between mRNA level and age, and the modest increase in complexity of alphaSMA-containing structures in CAT argue against an inevitable link between alphaSMA expression and the development of age-related cataract. Low levels of alphaSMA expression may reflect repair of normal wear and tear. In pathologic situations such as PSO and ASF, persisting stimulation and additional incentives may induce increased alphaSMA expression and more elaborate patterning, eventually leading to completion of EMT.

TGFbeta induces morphological and molecular changes similar to human anterior subcapsular cataract

BACKGROUND

Transforming growth factor beta (TGFbeta) has been shown to induce subcapsular plaques in cultured rat lenses as well as in lenses of transgenic mice. In the present study the authors have extended their analysis of these cataract models to determine how closely they mimic human cataract. In particular, they studied the maturation of cataract in the transgenic model to determine if it develops similar features as previously described for anterior subcapsular cataract (ASC) in humans. Furthermore, they investigated whether both of these animal models express the range of molecular markers that have now been shown to be present in human ASC.

METHODS

Histology and periodic acid Schiff staining were used to study the development and maturation of subcapsular plaques in transgenic mice overexpressing TGFbeta1 in the lens. Immunolabelling methods were used to identify the molecular markers for ASC in both the transgenic mouse model and in rat lenses cultured with TGFbeta2.

RESULTS

Histological analysis showed that the subcapsular plaques that develop in adult transgenic mouse lenses bear a striking similarity to mature human ASC, including the formation of a new epithelial-like layer extending between the subcapsular plaque and the underlying fibre mass. All known molecular markers for human ASC were induced in both rodent models, including collagen types I and III, tenascin, and fibronectin. They also identified the presence of desmin in these plaques, a putative novel marker for human cataract.

CONCLUSIONS

In both transgenic mouse and rat lens culture models TGFbeta induces markers similar to those found in human ASC. Atypical expression of these cataract markers is also characteristic of posterior capsular opacification (PCO). The molecular markers expressed are typical of a myofibroblastic/fibroblastic phenotype and suggest that a common feature of ASC and PCO may be induction of an epithelial-mesenchymal transition by TGFbeta.

Degeneration and transdifferentiation of human lens epithelial cells in nuclear and anterior polar cataracts

PURPOSE

To study the possible mechanisms of cataractogenesis by evaluating the characteristics of cataractous lens epithelial cells (LECs) in different types of human cataract.

SETTING

Kangnam St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea.

METHODS

Lens epithelial cells attached to the anterior capsules in eyes with nuclear or anterior subcapsular were analyzed for morphological characteristics by electron microscopy and for cellular characteristics by immunohistochemistry.

RESULTS

Human LECs beneath the anterior capsule were degenerated in nuclear cataracts and were transdifferentiated in anterior polar cataracts. In senile nuclear cataractous lenses, LECs beneath the anterior capsule showed degenerative changes in morphology. In nuclear cataracts, LECs were immunohistochemically positive for cytokeratin and vimentin, while those in anterior polar cataracts were positive for vimentin only. The LECs of anterior subcapsular cataracts were transdifferentiated into spindle-shaped fibroblast-like cells without cellular junctions and embedded within a fibrillar meshwork mass. The extracellular matrixes in the anterior capsule of anterior subcapsular cataracts were immunohistochemically positive for fibronectin, laminin, collagen type I, and collagen type IV.

CONCLUSIONS

Lens epithelial cells in different types of cataracts have distinct cellular characteristics and may possess a bipotential nature with the ability to transdifferentiate into mesenchymal cells. This may be an underlying mechanism for the development of cataract and capsule opacification.

Ultrastructure of the anterior lens capsule after vitrectomy with silicone oil injection. Correlation of clinical and morphological features

To clarify the mechanical difficulties experienced when performing anterior capsulorhexis in vitrectomized eyes filled with silicone oil. Five anterior lens capsules removed from eyes with a silicone oil history were submitted to light and electron microscopic analysis and then compared to two capsules from eyes with trauma history and seven capsules from eyes without silicone oil or trauma history. Comparable abnormalities of the inner and outer surface of the anterior lens capsule were consistently observed after silicone oil fill of the vitreous cavity or after traumatic impact to the lens: patches of multilayer epithelial cells with interspersed capsule material and connective tissue were observed on the posterior surface of the anterior lens capsule. The development of this anterior subcapsular tissue plaque is obviously influenced not only by the PVR process or by side effects of the surgical procedure but also by the silicone oil tamponade or a trauma history. The plaque can be considered primarily responsible for the increased mechanical resistance of the lens capsule in all eyes with silicone oil / trauma history examined in this study.

The lenticular capsule and cellular migration in anterior capsular cataract

A light and electron-microscopical study was performed on six lenses harboring anterior capsular cataract. The cataracts are typically divided by numerous sheets of basement membranes that merge with the lenticular capsule at the edge of the cataract. Basally, the cataract may or may not be bounded by a basement membrane. Myofibroblastlike cells may be observed, apparently traversing the basal border of the capsular cataract. Within the substance of the lens, isolated aggregations of collagenous material are present. Degenerating cells or collagenous aggregations are situated within the lenticular capsule. It is suggested that this configuration arises through the merging of basement membrane systems, surrounding the cells within the cataract, with the lenticular capsule.