Transforming growth factor-beta isoform proteins in cell and matrix deposits on intraocular lenses

Let-7c-3p suppresses lens epithelial-mesenchymal transition by inhibiting cadherin-11 expression in fibrotic cataract

Fibrotic cataract, including anterior subcapsular cataract (ASC) and posterior capsule opacification, always lead to visual impairment. Epithelial-mesenchymal transition (EMT) is a well-known event that causes phenotypic alterations in lens epithelial cells (LECs) during lens fibrosis. Accumulating studies have demonstrated that microRNAs are important regulators of EMT and fibrosis. However, the evidence explaining how microRNAs modulate the behavior and alter the cellular phenotypes of the lens epithelium in fibrotic cataract is insufficient. In this study, we found that hsa-let-7c-3p is downregulated in LECs in human ASC in vivo as well as in TGFβ2-induced EMT in vitro, indicating that hsa-let-7c-3p may participate in modulating the profibrotic processes in the lens. We then demonstrated that overexpression of hsa-let-7c-3p markedly suppressed human LEC proliferation and migration and attenuated TGFβ2-induced EMT and injury-induced ASC in a mouse model. In addition, hsa-let-7c-3p mediated lens fibrosis by directly targeting the CDH11 gene, which encodes cadherin-11 protein, an important mediator in the EMT signaling pathway. It decreased cadherin-11 protein expression at the posttranscriptional level but not at the transcriptional level by binding to a specific site in the 3-untranslated region (3'-UTR) of CDH11 mRNA. Moreover, blockade of cadherin-11 expression with a specific short hairpin RNA reversed TGFβ2-induced EMT in LECs in vitro. Collectively, these data demonstrated that hsa-let-7c-3p plays a clear role in attenuating ASC development and may be a novel candidate therapeutic for halting fibrosis and maintaining vision.

Genipin suppression of fibrogenic behaviors of the α-TN4 lens epithelial cell line

PURPOSE

To determine in a lens epithelial cell line, alpha-TN4, whether genipin, an intestinal metabolite component of the herbal medicine inchin-ko-to, suppresses profibrogenic myofibroblast generation and upregulation of fibrogenic cytokines and to evaluate the potential benefit of the medicine in preventing posterior capsule opacification (PCO).

SETTING

Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan.

METHODS

In this study, alpha-TN4 cell proliferation, migration, and expression of alpha-smooth muscle actin (alpha-SMA), the hallmark of myofibroblast generation, were assayed with a colorimetric assay, scratch wound assay, immunohistochemistry, and Western blot analysis. Gene expression of transforming growth factor-beta1 (TGF-beta1) and connective tissue growth factor (CTGF) was characterized with real-time reverse transcription-polymerase chain reaction. In addition, p38 mitogen-activated protein kinase (p 38 MAPK), extracellular signal-regulated kinase (ERK) limb, and Smad signalings were evaluated by Western blotting and immunohistochemistry. Cytotoxicity of genipin was evaluated using a commercial colorimetric assay kit for nuclear matrix protein 41/7 (NMP41/7) in culture medium.

RESULTS

Genipin suppressed cell proliferation and migration in association with inhibition of Smad and p38 MAPK phosphorylation, although ERK signaling was enhanced. Genipin suppressed mRNA expression of TGF-beta1 and CTGF. Cytoplasmic fiber formation declined based on less intense alpha-SMA immunocytochemical staining. However, alpha-SMA protein expression was actually not altered. This negative result suggests that genipin attenuated formation of alpha-SMA-containing cytoskeleton. Treatment of the cells with genipin for 48 hours did not increase the release of NMP41/7 to the medium, indicating this compound is not cytotoxic.

CONCLUSION

Because genipin suppressed alpha-TN4 lens cell fibrogenic behaviors, it may be of therapeutic value in preventing PCO.

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.

Relationship between posterior capsule opacification and intraocular lens biocompatibility

The type of healing process that occurs in response to cataract surgery and intraocular lens (IOL) implantation is dependent on a complex set of variables. Their interactions determine whether or not optical clarity is restored as a result of this procedure. In this process, wound healing entails cells undergoing either epithelial-mesenchymal transition, resulting in the generation of fibroblastic cells and accumulation of extracellular matrix, or lenticular structure formation. Such desperate cellular behaviors are regulated by the localized release of different cytokines, including transforming growth factor beta and fibroblast growth factors, which can result in post-operative capsular opacification. Other factors affecting the biological and mechanical outcome of IOL implantation are its composition, surface properties and shape.

TGFbeta-Smad signalling in postoperative human lens epithelial cells

AIMS

To localise Smads3/4 proteins in lens epithelial cells (LECs) of fresh and postoperative human specimens. Smads3/4 are involved in signal transduction between transforming growth factor beta (TGFbeta) cell surface receptors and gene promoters. Nuclear localisation of Smads indicates achievement of endogenous TGFbeta signalling in cells.

METHODS

Three circular sections of the anterior capsule, one lens, and 17 capsules undergoing postoperative healing were studied. Immunohistochemistry was performed for Smads3/4 in paraffin sections of the specimens. The effect of exogenous TGFbeta2 on Smad3 subcellular localisation was examined in explant cultures of extracted human anterior lens epithelium.

RESULTS

The cytoplasm, but not the nuclei, of LECs of uninjured lenses was immunoreactive for Smads3/4. In contrast, nuclear immunoreactivity for Smads3/4 was detected in LECs during capsular healing. Nuclei positive for Smads3/4 were observed in monolayered LECs adjacent to the regenerated lens fibres of Sommerring's ring. Interestingly, the nuclei of LECs that were somewhat elongated, and appeared to be differentiating into fibre-like cells, were negative for Smads3/4. Fibroblast-like, spindle-shaped lens cells with nuclear immunoreactivity for nuclear Smads3/4 were occasionally observed in the extracellular matrix accumulated in capsular opacification. Exogenous TGFbeta induced nuclear translocation of Smad3 in LECs of anterior capsule specimens in explant culture.

CONCLUSIONS

This is consistent with TGFbeta induced Smad signalling being involved in regulating the behaviour of LECs during wound healing after cataract surgery.

Latent TGFbeta binding protein-1 and fibrillin-1 in human capsular opacification and in cultured lens epithelial cells

BACKGROUND/AIM

It was previously reported that collagenous extracellular matrix (ECM) in human capsular opacification contained isoforms of transforming growth factor beta (TGFbeta). In the present study, the authors performed immunohistochemistry to examine whether ECM in human capsular opacification and in cultures of bovine lens epithelial cells (LECs) contained latent TGFbeta binding protein-1 (LTBP-1), TGFbeta1 latency associated peptide (beta1-LAP), and fibrillin-1, a suspected ligand of LTBP-1 as well as a component of the extracellular microfibrillar apparatus. The aim of the study was to further clarify the mechanism of TGFbeta1 deposition in ECM of capsular opacification.

METHODS

Human capsular opacification specimens and uninjured lens capsules, as well as cultured bovine LECs, were processed for immunohistochemistry using antibodies against LTBP-1, beta1-LAP, fibrillin-1, and collagen type I.

RESULTS

LTBP-1, beta1-LAP, and fibrillin-1 all were localised to the ECM in human capsular opacification. Uninjured lens epithelium stained for beta1-LAP, but not for LTBP-1 and fibrillin-1. ECM deposited in confluent LEC cultures stained for LTBP-1, beta1-LAP, and fibrillin-1, while cultures with only sparse cellularity were unstained for LTBP-1 or fibrillin-1.

CONCLUSIONS

LECs upregulate LTBP-1 and fibrillin-1 during postoperative healing. LTBP-1, beta1-LAP, and fibrillin-1 colocalised to the ECM in capsular opacification and in confluent LEC cultures. TGFbeta1 is considered to deposit in ECM in the large latent form. ECM secreted by LEC may function as a scavenger or repository of TGFbeta.

Posterior capsule opacification and anterior capsule opacification

Posterior capsule opacification (PCO) is still the most frequent complication of cataract surgery. A variety of studies has led to a better understanding of the pathogenesis of PCO, and strategies of molecular biology have produced new therapeutic options, such as immunological techniques or gene therapeutic approaches. Surgical strategies and intra-ocular lens-dependent factors also are capable to reduce the rate of PCO. In-the-bag implantation of intra-ocular lenses with a sharp optic edge seems to be effective in inhibiting equatorial lens epithelial cell migration to the center of the posterior capsule. Several PCO documentation systems have been developed that will lead to more exact and better comparable recording of PCO rates. In the year 2000, PCO or secondary cataract is still the most frequent complication after extracapsular cataract surgery. In a 1998 meta-analysis, PCO rates of 11.8% 1 year after extracapsular cataract surgery with intraocular lens implantation, 20.7% after 3 years, and 28.4 % after 5 years have been reported. For the United States, it has been estimated that the overall expenses for treatment of PCO are only exceeded by the costs for cataract treatment itself. In the past decade, a lot of experimental and clinical studies have been performed on this topic. They have led to 1) to a better understanding of the pathogenesis of the development of anterior and posterior capsule opacification; 2) more objective and better comparable systems of documentation and analysis of PCO; and a number of 3) surgical and 4) pharmaceutical strategies to prevent PCO.