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

Myo/Nog cells: targets for preventing the accumulation of skeletal muscle-like cells in the human lens

Posterior capsule opacification (PCO) is a vision impairing condition that arises in some patients following cataract surgery. The fibrotic form of PCO is caused by myofibroblasts that may emerge in the lens years after surgery. In the chick embryo lens, myofibroblasts are derived from Myo/Nog cells that are identified by their expression of the skeletal muscle specific transcription factor MyoD, the bone morphogenetic protein inhibitor Noggin, and the epitope recognized by the G8 monoclonal antibody. The goal of this study was to test the hypothesis that depletion of Myo/Nog cells will prevent the accumulation of myofibroblasts in human lens tissue. Myo/Nog cells were present in anterior, equatorial and bow regions of the human lens, cornea and ciliary processes. In anterior lens tissue removed by capsulorhexis, Myo/Nog cells had synthesized myofibroblast and skeletal muscle proteins, including vimentin, MyoD and sarcomeric myosin. Alpha smooth muscle actin (α-SMA) was detected in a subpopulation of Myo/Nog cells. Areas of the capsule denuded of epithelial cells were surrounded by Myo/Nog cells. Some of these cell free areas contained a wrinkle in the capsule. Depletion of Myo/Nog cells eliminated cells expressing skeletal muscle proteins in 5-day cultures but did not affect cells immunoreactive for beaded filament proteins that accumulate in differentiating lens epithelial cells. Transforming growth factor-betas 1 and 2 that mediate an epithelial-mesenchymal transition, did not induce the expression of skeletal muscle proteins in lens cells following Myo/Nog cell depletion. This study demonstrates that Myo/Nog cells in anterior lens tissue removed from cataract patients have undergone a partial differentiation to skeletal muscle. Myo/Nog cells appear to be the source of skeletal muscle-like cells in explants of human lens tissue. Targeting Myo/Nog cells with the G8 antibody during cataract surgery may reduce the incidence of PCO.

ERK1/2 pathway mediates epithelial-mesenchymal transition by cross-interacting with TGFβ/Smad and Jagged/Notch signaling pathways in lens epithelial cells

Epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) is the major pathological mechanism in anterior subcapsular cataract (ASC) and posterior capsule opacification (PCO), which are important causes of visual impairment. Extracellular signal-regulated kinase (ERK)1/2 pathway has been reported to play a major role in carcinogenesis, cancer metastasis and various fibrotic diseases. We hypothesized that ERK1/2 signaling can cross-interact with canonical transforming growth factor β (TGFβ)/Smad signaling and the Notch pathway, which subsequently contributes to LECs EMT. In this study, we demonstrated that ERK1/2 signaling was activated in TGFβ2-induced EMT in human LECs, whereas the blockade of TGFβ2/Smad2/3 signaling with SB431542 did not inhibit the activation of ERK1/2 induced by TGFβ2. In addition, inactivation of ERK1/2 signaling with a specific MEK/ERK1/2 inhibitor, U0126, completely prevented the TGFβ2-induced upregulation of α-SMA, collagen type I, collagen type IV and fibronectin. We also demonstrated that inactivation of ERK1/2 signaling inhibited canonical TGFβ/Smad signaling, as well as the Jagged/Notch pathway. By contrast, blockade of the Notch pathway by DAPT inhibited the TGFβ2‑induced activation of ERK1/2 pathway in LECs. Thus, results of this study provide evidence for the complex interplay between ERK1/2, TGFβ/Smad, and Jagged/Notch signaling pathways in the regulation of EMT in LECs. Inhibition of the ERK1/2 pathway may therefore have therapeutic value in the prevention and treatment of ASC and PCO.

The roles of αV integrins in lens EMT and posterior capsular opacification

Posterior capsular opacification (PCO) is the major complication arising after cataract treatment. PCO occurs when the lens epithelial cells remaining following surgery (LCs) undergo a wound healing response producing a mixture of α-smooth muscle actin (α-SMA)-expressing myofibroblasts and lens fibre cells, which impair vision. Prior investigations have proposed that integrins play a central role in PCO and we found that, in a mouse fibre cell removal model of cataract surgery, expression of αV integrin and its interacting β-subunits β1, β5, β6, β8 are up-regulated concomitant with α-SMA in LCs following surgery. To test the hypothesis that αV integrins are functionally important in PCO pathogenesis, we created mice lacking the αV integrin subunit in all lens cells. Adult lenses lacking αV integrins are transparent and show no apparent morphological abnormalities when compared with control lenses. However, following surgical fibre cell removal, the LCs in control eyes increased cell proliferation, and up-regulated the expression of α-SMA, β1-integrin, fibronectin, tenascin-C and transforming growth factor beta (TGF-β)-induced protein within 48 hrs, while LCs lacking αV integrins exhibited much less cell proliferation and little to no up-regulation of any of the fibrotic markers tested. This effect appears to result from the known roles of αV integrins in latent TGF-β activation as αV integrin null lenses do not exhibit detectable SMAD-3 phosphorylation after surgery, while this occurs robustly in control lenses, consistent with the known roles for TGF-β in fibrotic PCO. These data suggest that therapeutics antagonizing αV integrin function could be used to prevent fibrotic PCO following cataract surgery.

Integrin linked kinase (ILK) is required for lens epithelial cell survival, proliferation and differentiation

While the role of growth factors in lens development has been investigated extensively, the role of extracellular matrix signalling is less well understood. The developing lens expresses predominantly laminin-binding integrins (such as α3β1, α6β1), which are cooperatively required in the lens epithelium during development. We investigated the role of ILK, a downstream mediator of integrin signalling in mice conditionally null for Ilk. Mutant lenses showed epithelial thinning at E17.5 with reduced proliferation and epithelial cell number and aberrant fibre differentiation. There was complete loss of the central epithelium from postnatal day (P) 2 due to cell death followed by fibre cell degeneration and death by P10 as well as rupture of the lens capsule between P10 and P21. At E17.5 there was significant inhibition (∼50%) of epithelial cell cycle progression, as shown by BrdU incorporation, cyclin D1/D2 and phospho-histone H3 immunostaining. The epithelial marker, E-cadherin, was decreased progressively from E17.5 to P2, in the central epithelium, but there was no significant change in Pax6 expression. Analyses of ERK and Akt phosphorylation indicated marked depression of MAPK and PI3K-Akt signalling, which correlated with decreased phosphorylation of FRS2α and Shp2, indicating altered activation of FGF receptors. At later postnatal stages there was reduced or delayed expression of fibre cell markers (β-crystallin and p57(kip2)). Loss of Ilk also affected deposition of extracellular matrix, with marked retention of collagen IV within differentiating fibre cells. By quantitative RT-PCR array there was significantly decreased expression of 19 genes associated with focal adhesions, actin filament stability and MAPK and PI3K/Akt signalling. Overall, these data indicate that ILK is required for complete activation of signalling cascades downstream of the FGF receptor in lens epithelium and fibre cells during development and thus is involved in epithelial proliferation, survival and subsequent fibre differentiation.

Attenuation of human lens epithelial cell spreading, migration and contraction via downregulation of the PI3K/Akt pathway

BACKGROUND

Posterior capsule opacification (PCO) represents a major challenge in the postoperative management of cataract patients. Spreading, migration and contraction of residual human lens epithelial cells play a pivotal role in the pathogenesis of PCO. Therefore, we analyzed the effect of the alkylphosphocholine (APC) erufosine on these cellular features as well as on PI3K/Akt, a crucial pathway in PCO pathogenesis.

METHODS

Human lens epithelial cells were cultured under standard cell culture conditions. Cell spreading was analyzed on fibronectin-coated wells and chemokinetic migration was assessed by time-lapse microscopy. For evaluation of cell-mediated collagen matrix contraction, the cells were seeded into collagen gels and incubated with an APC in different non-toxic concentrations before the surface area was measured on day 6. The activity of PI3K/Akt was assessed by an ELISA kit after incubation of the cells with different APC concentrations.

RESULTS

Human lens epithelial cell spreading and migration were attenuated by APCs as follows: 7 % spreading, 48 % migration (0.1 μM APC), and 32 % spreading, 68 % migration (1.0 μM APC). APC concentrations of 0.1 μM reduced collagen gel diameter by 5 %, and 1.0 μM by less than 1 %, compared to untreated, cell-populated gels that resulted in a cell diameter contraction of 36 %. PI3K was downregulated in a concentration-dependent manner.

CONCLUSIONS

The crucial cellular features of PCO pathogenesis are attenuated by the APC erufosine via downregulation of the PI3K pathway. Thus, erufosine might become a valuable tool for pharmacologic PCO prophylaxis in the future.

The epigenetic modifier trichostatin A, a histone deacetylase inhibitor, suppresses proliferation and epithelial-mesenchymal transition of lens epithelial cells

Proliferation and epithelial-mesenchymal transition (EMT) of lens epithelium cells (LECs) may contribute to anterior subcapsular cataract (ASC) and posterior capsule opacification (PCO), which are important causes of visual impairment. Histone deacetylases (HDACs)-mediated epigenetic mechanism has a central role in controlling cell cycle regulation, cell proliferation and differentiation in a variety of cells and the pathogenesis of some diseases. However, whether HDACs are involved in the regulation of proliferation and EMT in LECs remain unknown. In this study, we evaluated the expression profile of HDAC family (18 genes) and found that class I and II HDACs were upregulated in transforming growth factor β2 (TGFβ2)-induced EMT in human LEC lines SRA01/04 and HLEB3. Tricostatin A (TSA), a class I and II HDAC inhibitor, suppressed the proliferation of LECs by G1 phase cell cycle arrest not only through inhibition of cyclin/CDK complexes and induction of p21 and p27, but also inactivation of the phosphatidylinositol-3-kinase/Akt, p38MAPK and ERK1/2 pathways. Meanwhile, TSA strongly prevented TGFβ2-induced upregulation of fibronectin, collagen type I, collagen type IV, N-cadherin, Snail and Slug. We also demonstrated that the underlying mechanism of TSA affects EMT in LECs through inhibiting the canonical TGFβ/Smad2 and the Jagged/Notch signaling pathways. Finally, we found that TSA completely prevented TGFβ2-induced ASC in the whole lens culture semi-in vivo model. Therefore, this study may provide a new insight into the pathogenesis of ASC and PCO, and suggests that epigenetic treatment with HDAC inhibitors may be a novel therapeutic approach for the prevention and treatment of ASC, PCO and other fibrotic diseases.

Scrib is required for epithelial cell identity and prevents epithelial to mesenchymal transition in the mouse

The integrity and function of epithelial tissues depend on the establishment and maintenance of defining characteristics of epithelial cells, cell-cell adhesion and cell polarity. Disruption of these characteristics can lead to the loss of epithelial identity through a process called epithelial to mesenchymal transition (EMT), which can contribute to pathological conditions such as tissue fibrosis and invasive cancer. In invertebrates, the epithelial polarity gene scrib plays a critical role in establishing and maintaining cell adhesion and polarity. In this study we asked if the mouse homolog, Scrib, is required for establishment and/or maintenance of epithelial identity in vivo. To do so, we conditionally deleted Scrib in the head ectoderm tissue that gives rise to both the ocular lens and the corneal epithelium. Deletion of Scrib in the lens resulted in a change in epithelial cell shape from cuboidal to flattened and elongated. Early in the process, the cell adhesion protein, E-cadherin, and apical polarity protein, ZO-1, were downregulated and the myofibroblast protein, αSMA, was upregulated, suggesting EMT was occurring in the Scrib deficient lenses. Correlating temporally with the upregulation of αSMA, Smad3 and Smad4, TGFβ signaling intermediates, accumulated in the nucleus and Snail, a TGFβ target and transcriptional repressor of the gene encoding E-cadherin, was upregulated. Pax6, a lens epithelial transcription factor required to maintain lens epithelial cell identity also was downregulated. Loss of Scrib in the corneal epithelium also led to molecular changes consistent with EMT, suggesting that the effect of Scrib deficiency was not unique to the lens. Together, these data indicate that mammalian Scrib is required to maintain epithelial identity and that loss of Scrib can culminate in EMT, mediated, at least in part, through TGFβ signaling.

RNA Interference Targeting Snail Inhibits the Transforming Growth Factor β 2-Induced Epithelial-Mesenchymal Transition in Human Lens Epithelial Cells

Epithelial-msenchymal transition (EMT) contributes to posterior capsule opacification (PCO) type of cataract. Transcription factors Snail is a key trigger of EMT activated by transforming growth factor β (TGFβ). This study was done to investigate the effect of Snail targeting siRNA on TGFβ2-induced EMT in human lens epithelial cells. TGFβ2 treatment of cultured human epithelial cell line (HLEB3) upregulated the expression of Snail and the EMT relevant molecules such as vimentin and α-SMA but downregulated the expression of keratin and E-cadherin. After the stimulation of TGFβ2, the HLEB3 cells became fibroblast-like in morphology, and the junctions of cell-cell disappeared. TGFβ2 treatment also enhanced migration ability of HLEB3 cells. TGFβ2-induced Snail expression and EMT were significantly inhibited by Snail siRNA. By analyzing the response characteristics of HLEB3 in TGFβ2-induced EMT model with/without Snail-specific siRNA, we concluded that Snail is an element in the EMT of HLEB3 cells induced by TGFβ2. Snail siRNA targeting can block the induced EMT and therefore has the potential to suppress the development of PCO.

What do mechanotransduction, Hippo, Wnt, and TGFβ have in common? YAP and TAZ as key orchestrating molecules in ocular health and disease

Cells in vivo are exposed to a complex signaling environment. Biochemical signaling modalities, such as secreted proteins, specific extracellular matrix domains and ion fluxes certainly compose an important set of regulatory signals to cells. However, these signals are not exerted in isolation, but rather in concert with biophysical cues of the surrounding tissue, such as stiffness and topography. In this review, we attempt to highlight the biophysical attributes of ocular tissues and their influence on cellular behavior. Additionally, we introduce the proteins YAP and TAZ as targets of biophysical and biochemical signaling and important agonists and antagonists of numerous signaling pathways, including TGFβ and Wnt. We frame the discussion around this extensive signaling crosstalk, which allows YAP and TAZ to act as orchestrating molecules, capable of integrating biophysical and biochemical cues into a broad cellular response. Finally, while we draw on research from various fields to provide a full picture of YAP and TAZ, we attempt to highlight the intersections with vision science and the exciting work that has already been performed.

Pax6 regulates gene expression in the vertebrate lens through miR-204

During development, tissue-specific transcription factors regulate both protein-coding and non-coding genes to control differentiation. Recent studies have established a dual role for the transcription factor Pax6 as both an activator and repressor of gene expression in the eye, central nervous system, and pancreas. However, the molecular mechanism underlying the inhibitory activity of Pax6 is not fully understood. Here, we reveal that Trpm3 and the intronic microRNA gene miR-204 are co-regulated by Pax6 during eye development. miR-204 is probably the best known microRNA to function as a negative modulator of gene expression during eye development in vertebrates. Analysis of genes altered in mouse Pax6 mutants during lens development revealed significant over-representation of miR-204 targets among the genes up-regulated in the Pax6 mutant lens. A number of new targets of miR-204 were revealed, among them Sox11, a member of the SoxC family of pro-neuronal transcription factors, and an important regulator of eye development. Expression of Trpm/miR-204 and a few of its targets are also Pax6-dependent in medaka fish eyes. Collectively, this study identifies a novel evolutionarily conserved mechanism by which Pax6 controls the down-regulation of multiple genes through direct up-regulation of miR-204.

The transcription factor Pax6 is reiteratively employed in space and time for the establishment of progenitor pools and the differentiation of neuronal and non-neuronal lineages of the CNS, pancreas, and eye. Execution of these diverse developmental programs depends on simultaneous activation and repression of gene networks functioning downstream of Pax6. MicroRNAs function as inhibitors of gene expression. Many microRNA genes are transcribed through common promoters of host genes. In this study, using wide-scale analysis of changes in gene expression following Pax6 deletion in the lens, we discover that Pax6 regulates the gene Trpm3 and its hosted microRNA, miR-204. We then show that miR-204 suppresses several target genes in the lens, notably the neuronal gene Sox11. Lastly, by conducting parallel experiments in the medaka fish, we show that Pax6 control of miR-204 and its target genes is evolutionarily conserved between mammals and fish, stressing the biological importance of this pathway. Pax6 regulation of miR-204 explains part of the complex, divergent inhibitory activity of Pax6 in ocular progenitor cells, which is required to establish and maintain the identity and function of ocular tissues.

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.

Cataracts and Dupuytren disease: a case report and review of the literature

Purpose. Dupuytren disease is an inherited proliferative and progressive connective disease. Ectopic disease may, however, be located distant from the palmar fascia. 
Methods. Case report and review of the literature. 
Results. We describe a case of symmetric bilateral posterior subcapsular cataracts associated with symmetric bilateral Dupuytren disease and symmetric bilateral Ledderhose disease in a 56-year-old Caucasian man. His medical history was negative for glucocorticoids intake, diabetes, and exposure to radiation. Serum transforming growth factor β (TGF-β)1 concentration has been evaluated and was found to be almost double compared to the controls. 
Conclusions. We speculate that the TGF-β plays an important role for ocular and connective tissue disorders.

Patterns of gene expression in microarrays and expressed sequence tags from normal and cataractous lenses

In this contribution, we have examined the patterns of gene expression in normal and cataractous lenses as presented in five different papers using microarrays and expressed sequence tags. The purpose was to evaluate unique and common patterns of gene expression during development, aging and cataracts.

Osmotic stress, not aldose reductase activity, directly induces growth factors and MAPK signaling changes during sugar cataract formation

In sugar cataract formation in rats, aldose reductase (AR) activity is not only linked to lenticular sorbitol (diabetic) or galactitol (galactosemic) formation but also to signal transduction changes, cytotoxic signals and activation of apoptosis. Using both in vitro and in vivo techniques, the interrelationship between AR activity, polyol (sorbitol and galactitol) formation, osmotic stress, growth factor induction, and cell signaling changes have been investigated. For in vitro studies, lenses from Sprague Dawley rats were cultured for up to 48 h in TC-199-bicarbonate media containing either 30 mM fructose (control), or 30 mM glucose or galactose with/without the aldose reductase inhibitors AL1576 or tolrestat, the sorbitol dehydrogenase inhibitor (SDI) CP-470,711, or 15 mM mannitol (osmotic-compensated media). For in vivo studies, lenses were obtained from streptozotocin-induced diabetic Sprague Dawley rats fed diet with/without the ARIs AL1576 or tolrestat for 10 weeks. As expected, lenses cultured in high glucose/galactose media or from untreated diabetic rats all showed a decrease in the GSH pool that was lessened by ARI treatment. Lenses either from diabetic rats or from glucose/galactose culture conditions showed increased expression of basic-FGF, TGF-β, and increased signaling through P-Akt, P-ERK1/2 and P-SAPK/JNK which were also normalized by ARIs to the expression levels observed in non-diabetic controls. Culturing rat lenses in osmotically compensated media containing 30 mM glucose or galactose did not lead to increased growth factor expression or altered signaling. These studies indicate that it is the biophysical response of the lens to osmotic stress that results in an increased intralenticular production of basic-FGF and TGF-β and the altered cytotoxic signaling that is observed during sugar cataract formation.

Integrin-linked kinase deletion in the developing lens leads to capsule rupture, impaired fiber migration and non-apoptotic epithelial cell death

PURPOSE

The lens is a powerful model system to study integrin-mediated cell-matrix interaction in an in vivo context, as it is surrounded by a true basement membrane, the lens capsule. To characterize better the function of integrin-linked kinase (ILK), we examined the phenotypic consequences of its deletion in the developing mouse lens.

METHODS

ILK was deleted from the embryonic lens either at the time of placode invagination using the Le-Cre line or after initial lens formation using the Nestin-Cre line.

RESULTS

Early deletion of ILK leads to defects in extracellular matrix deposition that result in lens capsule rupture at the lens vesicle stage (E13.5). If ILK was deleted at a later time-point after initial establishment of the lens capsule, rupture was prevented. Instead, ILK deletion resulted in secondary fiber migration defects and, most notably, in cell death of the anterior epithelium (E18.5-P0). Remarkably, dying cells did not stain positively for terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) or activated-caspase 3, suggesting that they were dying from a non-apoptotic mechanism. Moreover, cross to a Bax(fl/fl)/Bak⁻/⁻ mouse line that is resistant to most forms of apoptosis failed to promote cell survival in the ILK-deleted lens epithelium. Electron microscopy revealed the presence of numerous membranous vacuoles containing degrading cellular material. CONCLUSIONS. Our study reveals a role for ILK in extracellular matrix organization, fiber migration, and cell survival. Furthermore, to our knowledge we show for the first time that ILK disruption results in non-apoptotic cell death in vivo.

Pleiotropic effects of miR-183~96~182 converge to regulate cell survival, proliferation and migration in medulloblastoma

Medulloblastomas are the most common malignant brain tumors in children. Several large-scale genomic studies have detailed their heterogeneity, defining multiple subtypes with unique molecular profiles and clinical behavior. Increased expression of the miR-183~96~182 cluster of microRNAs has been noted in several subgroups, including the most clinically aggressive subgroup associated with genetic amplification of MYC. To understand the contribution of miR-183~96~182 to the pathogenesis of this aggressive subtype of medulloblastoma, we analyzed global gene expression and proteomic changes that occur upon modulation of miRNAs in this cluster individually and as a group in MYC-amplified medulloblastoma cells. Knockdown of the full miR-183~96~182 cluster results in enrichment of genes associated with apoptosis and dysregulation of the PI3K/AKT/mTOR signaling axis. Conversely, there is a relative enrichment of pathways associated with migration, metastasis and epithelial to mesenchymal transition, as well as pathways associated with dysfunction of DNA repair in cells with preserved miR-183 cluster expression. Immunocytochemistry and FACS analysis confirm induction of apoptosis upon knockdown of the miR-183 cluster. Importantly, cell-based migration and invasion assays verify the positive regulation of cell motility/migration by the miR-183 cluster, which is largely mediated by miR-182. We show that the effects on cell migration induced by the miR-183 cluster are coupled to the PI3K/AKT/mTOR pathway through differential regulation of AKT1 and AKT2 isoforms. Furthermore, we show that rapamycin inhibits cell motility/migration in medulloblastoma cells and phenocopies miR-183 cluster knockdown. Thus, the miR-183 cluster regulates multiple biological programs that converge to support the maintenance and metastatic potential of medulloblastoma.

Sustained-release celecoxib from incubated acrylic intraocular lenses suppresses lens epithelial cell growth in an ex vivo model of posterior capsule opacity

PURPOSE

To determine whether celecoxib (CXB) can be released from incubated intraocular lenses (IOLs) sufficiently to inhibit lens epithelial cell (LEC) growth in an ex vivo model of posterior capsule opacification (PCO).

MATERIALS

LEC growth was evaluated for 14 days in canine lens capsules (LCs) that had been exposed to media containing 20 μM CXB for 1-5 days. After the incubation of hydrophilic and hydrophobic IOLs in CXB solution, the determination of the in vitro release of CXB from the IOLs was performed for up to 28 days. The incubated and nonincubated IOLs were evaluated in the ex vivo model of PCO, and the rate of LEC growth was evaluated over 28 days.

RESULTS

The treatment of LCs with 20 μM CXB for 4 and 5 days completely inhibited LEC growth. LEC repopulation did not occur after the removal of CXB. IOLs incubated in CXB for 24 h resulted in a sustained release of CXB in vitro at levels theoretically sufficient to inhibit PCO. LCs in the ex vivo model of PCO treated with acrylic IOLs incubated in CXB had significantly suppressed LEC ingrowth compared with untreated and IOL-only LCs.

CONCLUSIONS

A 4-day treatment of LCs with a concentration of 20 μM CXB may effectively prevent PCO. IOLs incubated in CXB for 24 h resulted in a sustained release of CXB in vitro at levels sufficient to inhibit LEC growth in the ex vivo model of PCO. Further studies are needed to determine whether CXB-incubated IOLs can effectively prevent the development of PCO in vivo.

The Roles of Mitogen-Activated Protein Kinase Pathways in TGF-β-Induced Epithelial-Mesenchymal Transition

The mitogen-activated protein kinase (MAPK) pathway allows cells to interpret external signals and respond appropriately, especially during the epithelial-mesenchymal transition (EMT). EMT is an important process during embryonic development, fibrosis, and tumor progression in which epithelial cells acquire mesenchymal, fibroblast-like properties and show reduced intercellular adhesion and increased motility. TGF-β signaling is the first pathway to be described as an inducer of EMT, and its relationship with the Smad family is already well characterized. Studies of four members of the MAPK family in different biological systems have shown that the MAPK and TGF-β signaling pathways interact with each other and have a synergistic effect on the secretion of additional growth factors and cytokines that in turn promote EMT. In this paper, we present background on the regulation and function of MAPKs and their cascades, highlight the mechanisms of MAPK crosstalk with TGF-β signaling, and discuss the roles of MAPKs in EMT.

Ultrastructure of the anterior lens capsule and epithelium in cataracts associated with uveitis

AIMS

To study the ultrastructure of the anterior lens capsule and epithelium, and capsular thickness in uveitic cataracts.

METHODS

Capsulorhexis samples from 20 uveitic cataracts were compared to 20 nuclear cataracts using the semi- and ultra-thin techniques.

RESULTS

Extensive epithelial and capsular-epithelial border changes and epithelial-mesenchymal transition in some fibrotic capsules were found only in the uveitic group. All these changes were observed predominately in white uveitic cataracts. Mild and moderate ultrastructural changes were seen in both groups. Surface deposition of amorphous material was also found only in uveitic cataracts. Capsular thickness was not different between the two groups.

CONCLUSIONS

Uveitic capsules showed more extensive and different ultrastructural changes that probably occurred because of inflammation in the eye and epithelial-mesenchymal transition. These changes might be an additional reason for altered behavior of the lens capsule at capsulorhexis.

Phosphatidylinositol synthase is required for lens structural integrity and photoreceptor cell survival in the zebrafish eye

The zebrafish lens opaque (lop) mutant was previously isolated in a genetic screen and shown to lack rod and cone photoreceptors and exhibit lens opacity, or cataract, at 7 days post-fertilization (dpf). In this manuscript, we provide four different lines of evidence demonstrating that the lop phenotype results from a defect in the cdipt (phosphatidylinositol (PI) synthase; CDP-diacylglycerol-inositol 3-phosphatidyltransferase) gene. First, DNA sequence analysis revealed that the lop mutant contained a missense mutation in the lop open reading frame, which yields a nonconservative amino acid substitution (Ser-111-Cys) within the PI synthase catalytic domain. Second, morpholino-mediated knockdown of the cdipt-encoded PI synthase protein phenocopied the cdipt(lop/lop) mutant, with abnormal lens epithelial and secondary fiber cell morphologies and reduced numbers of photoreceptors. Third, microinjection of in vitro transcribed, wild-type cdipt mRNA into 1-4 cell stage cdipt(lop/lop) embryos significantly reduced the percentage of larvae displaying lens opacity at 7 dpf. Fourth, a cdipt retroviral-insertion allele, cdipt(hi559), exhibited similar lens and retinal abnormalities and failed to complement the cdipt(lop) mutant phenotype. To determine the initial cellular defects associated with the cdipt mutant, we examined homozygous cdipt(hi559/hi559) mutants prior to gross lens opacification at 6 dpf. The cdipt(hi559/hi559) mutants first exhibited photoreceptor layer disruption and photoreceptor cell death at 3 and 4 dpf, respectively, followed by lens dismorphogenesis by 5 dpf. RT-PCR revealed that the cdipt gene is maternally expressed and continues to be transcribed throughout development and into adulthood, in a wide variety of tissues. Using an anti-zebrafish PI synthase polyclonal antiserum, we localized the protein throughout the developing eye, including the photoreceptor layer and lens cortical secondary fiber cells. As expected, the polyclonal antiserum revealed that the PI synthase protein was reduced in amount in both the cdipt(lop/lop) and cdipt(hi559/hi559) mutants. Furthermore, we used a heterologous yeast phenotypic complementation assay to confirm that the wild-type zebrafish cdipt allele encodes functional PI synthase activity. Taken together, the cdipt-encoded PI synthase is required for survival of photoreceptor cells and lens epithelial and secondary cortical fiber cells. These zebrafish cdipt alleles represent excellent in vivo genetic tools to study the role of phosphatidylinositol and its phosphorylated derivatives in lens and photoreceptor development and maintenance.

The lens in focus: a comparison of lens development in Drosophila and vertebrates

The evolution of the eye has been a major subject of study dating back centuries. The advent of molecular genetics offered the surprising finding that morphologically distinct eyes rely on conserved regulatory gene networks for their formation. While many of these advances often stemmed from studies of the compound eye of the fruit fly, Drosophila melanogaster, and later translated to discoveries in vertebrate systems, studies on vertebrate lens development far outnumber those in Drosophila. This may be largely historical, since Spemann and Mangold's paradigm of tissue induction was discovered in the amphibian lens. Recent studies on lens development in Drosophila have begun to define molecular commonalities with the vertebrate lens. Here, we provide an overview of Drosophila lens development, discussing intrinsic and extrinsic factors controlling lens cell specification and differentiation. We then summarize key morphological and molecular events in vertebrate lens development, emphasizing regulatory factors and networks strongly associated with both systems. Finally, we provide a comparative analysis that highlights areas of research that would help further clarify the degree of conservation between the formation of dioptric systems in invertebrates and vertebrates.

The lens as a model for fibrotic disease

Fibrosis affects multiple organs and is associated with hyperproliferation, cell transdifferentiation, matrix modification and contraction. It is therefore essential to discover the key drivers of fibrotic events, which in turn will facilitate the development of appropriate therapeutic strategies. The lens is an elegant experimental model to study the processes that give rise to fibrosis. The molecular and cellular organization of the lens is well defined and consequently modifications associated with fibrosis can be clearly assessed. Moreover, the avascular and non-innervated properties of the lens allow effective in vitro studies to be employed that complement in vivo systems and relate to clinical data. Using the lens as a model for fibrosis has direct relevance to millions affected by lens disorders, but also serves as a valuable experimental tool to understand fibrosis per se.

Early differential expression of oncostatin M in obstructive nephropathy

Interstitial fibrosis plays a major role in progression of renal diseases. Oncostatin M (OSM) is a cytokine that regulates cell survival, differentiation, and proliferation. Renal tissue from patients with chronic obstructive nephropathy was examined for OSM expression. The elevated levels in diseased human kidneys suggested possible correlation between OSM level and kidney tissue fibrosis. Indeed, unilateral ureteral obstruction (UUO), a model of renal fibrosis, increased OSM and OSM receptor (OSM-R) expression in a time-dependent manner within hours following UUO. In vitro, OSM overexpression in tubular epithelial cells (TECs) resulted in epithelial-myofibroblast transdifferentiation. cDNA microarray technology identified up-regulated expression of immune modulators in obstructed compared with sham-operated kidneys. In vitro, OSM treatment up-regulated CC chemokine ligand CCL7, and CXC chemokine ligand (CXCL)-14 mRNA in kidney fibroblasts. In vivo, treatment of UUO mice with neutralizing anti-OSM antibody decreased renal chemokines expression. In conclusion, OSM is up-regulated in kidney tissue early after urinary obstruction. Therefore, OSM might play an important role in initiation of renal fibrogenesis, possibly by inducing myofibroblast transdifferentiation of TECs as well as leukocyte infiltration. This process may, in turn, contribute in part to progression of obstructive nephropathy and makes OSM a promising therapeutic target in renal fibrosis.

Uhrf1 and Dnmt1 are required for development and maintenance of the zebrafish lens

DNA methylation is one of the key mechanisms underlying the epigenetic regulation of gene expression. During DNA replication, the methylation pattern of the parent strand is maintained on the replicated strand through the action of Dnmt1 (DNA Methyltransferase 1). In mammals, Dnmt1 is recruited to hemimethylated replication foci by Uhrf1 (Ubiquitin-like, Containing PHD and RING Finger Domains 1). Here we show that Uhrf1 is required for DNA methylation in vivo during zebrafish embryogenesis. Due in part to the early embryonic lethality of Dnmt1 and Uhrf1 knockout mice, roles for these proteins during lens development have yet to be reported. We show that zebrafish mutants in uhrf1 and dnmt1 have defects in lens development and maintenance. uhrf1 and dnmt1 are expressed in the lens epithelium, and in the absence of Uhrf1 or of catalytically active Dnmt1, lens epithelial cells have altered gene expression and reduced proliferation in both mutant backgrounds. This is correlated with a wave of apoptosis in the epithelial layer, which is followed by apoptosis and unraveling of secondary lens fibers. Despite these disruptions in the lens fiber region, lens fibers express appropriate differentiation markers. The results of lens transplant experiments demonstrate that Uhrf1 and Dnmt1 functions are required lens-autonomously, but perhaps not cell-autonomously, during lens development in zebrafish. These data provide the first evidence that Uhrf1 and Dnmt1 function is required for vertebrate lens development and maintenance.

Oxidative damage and TGF-β differentially induce lung epithelial cell sonic hedgehog and tenascin-C expression: implications for the regulation of lung remodelling in idiopathic interstitial lung disease

Idiopathic interstitial lung diseases (iILDs) are characterized by inflammation, hyperplasia of Type-II alveolar epithelial cells (AECs) and lung remodelling often with progressive fibrosis. It remains unclear which signals initiate iILD and/or maintain the disease processes. Using real-time RT-PCR and immunohistochemistry on archival biopsies of three patterns of iILD (usual interstitial pneumonitis/UIP, non-specific interstitial pneumonitis/NSIP and cryptogenic organizing pneumonia/COP) we investigated whether hedgehog signalling (previously associated with lung damage and repair) was functional and whether the damage associated extracellular matrix protein tenascin-C was present in activated Type-II AECs in all three iILDs. Using tissue culture, protein and mRNA detection we also determined how two signals (oxidative damage and TGF-β) associated with iILD pathogenesis affected Sonic hedgehog (SHH) and tenascin-C production by a Type-II AEC cell line. We report that SHH pathway and tenascin-C mRNA and proteins were found in UIP, NSIP and COP. SHH signalling was most active at sites of immature organizing fibrous tissue (fibroblastic foci) in UIP. In vitro Type-II AECs constitutively secrete SHH but not tenascin-C. Oxidative injury stimulated SHH release whereas TGF-β inhibited it. TGF-β and oxidative damage both upregulated tenascin-C mRNA but only TGF-β induced synthesis and release of a distinct protein isoform. SHH signalling is active in Type-II AECs from three types of ILD and all three express tenascin-C.

In vivo effects of adjunctive tetracycline treatment on refractory corneal ulcers in dogs

OBJECTIVE

To evaluate effect of adjunctive treatment with tetracycline analogues on time to complete corneal reepithelialization in dogs with nonhealing (ie, refractory) corneal ulcers.

DESIGN

Randomized controlled clinical trial.

ANIMALS

89 dogs with refractory corneal ulcers.

PROCEDURES

Corneal ulcers were treated via debridement and grid keratotomy. Dogs were assigned to receive 1 of 3 treatment regimens for up to 6 weeks: doxycycline (5 mg/kg [2.27 mg/lb], PO, q 12 h) with topically applied ophthalmic ointment containing neomycin, polymyxin B, and bacitracin (ie, triple antibiotic ointment; q 8 h); cephalexin (22 mg/kg [10 mg/lb], PO, q 12 h) with topically applied oxytetracycline ophthalmic ointment (q 8 h); or a control treatment of cephalexin (22 mg/kg, PO, q 12 h) with topically applied triple antibiotic ointment (q 8 h). Healing was monitored via measurements of the wound with calipers and evaluation of photographs obtained every 2 weeks. Treatment effectiveness was evaluated by wound healing and decreased signs of pain.

RESULTS

The Boxer breed was overrepresented in all groups. At the 2-week time point, wound healing was significantly more common in small-breed dogs, compared with large-breed dogs. Dogs treated with oxytetracycline ophthalmic ointment had a significantly shorter healing time than did dogs receiving the control treatment. Corneal ulcers in dogs that received doxycycline PO healed more rapidly than did ulcers in dogs in the control treatment group; however, this difference was not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Topical tetracycline ophthalmic ointment was a safe, inexpensive, and effective adjunctive treatment for refractory corneal ulcers in dogs.

Effect of delivery of MMP inhibitors from PDMS as a model IOL material on PCO markers

Posterior capsule opacification (PCO) or secondary cataract formation, following intraocular lens implantation, is a significant complication affecting an estimated 28% of cataract patients. Matrix metalloproteinases (MMPs) have been demonstrated to play a role in the formation of anterior subcapsular cataracts and it has been shown that the presence of MMP inhibitors (MMPI) decreases subcapsular cataract formation ex vivo. Since the mechanisms responsible for anterior subcapsular cataract formation and posterior capsule opacification are similar, it is reasonable to suggest that MMP inhibitors may also mitigate PCO. One of the most effective ways of delivering the inhibitors may be from the implanted intraocular lens (IOL) material itself. In the current work, delivery of three different MMP inhibitors from silicone rubber as a model IOL material was examined. Loading methods were developed which allowed continuous release of active MMPI for periods of over 5 months in some cases. Reduced migration rates were observed in human lens epithelial cells in vitro, suggesting that an effect on PCO may be possible. While further studies are necessary to tune the systems to achieve the desired rates of release, this work demonstrates that delivery of MMPI from silicone IOL materials has the potential to decrease the incidence of PCO.

Hepatocytes do not undergo epithelial-mesenchymal transition in liver fibrosis in mice

The origin of fibrogenic cells in liver fibrosis remains controversial. We assessed the emerging concept that hepatocytes contribute to production of extracellular matrix (ECM) in liver fibrosis through epithelial-mesenchymal transition (EMT). We bred triple transgenic mice expressing ROSA26 stop beta-galactosidase (beta-gal), albumin Cre, and collagen alpha1(I) green fluorescent protein (GFP), in which hepatocyte-derived cells are permanently labeled by beta-gal and type I collagen-expressing cells are labeled by GFP. We induced liver fibrosis by repetitive carbon tetrachloride (CCl(4)) injections. Liver sections and isolated cells were evaluated for GFP and beta-gal as well as expression of alpha-smooth muscle actin (alpha-SMA) and fibroblast-specific protein 1 (FSP-1). Upon stimulation with transforming growth factor beta-1, cultured hepatocytes isolated from untreated liver expressed both GFP and beta-gal with a fibroblast-like morphological change but lacked expression of other mesenchymal markers. Cells from CCl(4)-treated livers never showed double-positivity for GFP and beta-gal. All beta-gal-positive cells exhibited abundant cytoplasm, a typical morphology of hepatocytes, and expressed none of the mesenchymal markers including alpha-SMA, FSP-1, desmin, and vimentin. In liver sections of CCl(4)-treated mice, GFP-positive areas were coincident with fibrotic septa and never overlapped X-gal-positive areas.

CONCLUSION

Type I collagen-producing cells do not originate from hepatocytes. Hepatocytes in vivo neither acquire mesenchymal marker expression nor exhibit a morphological change clearly distinguishable from normal hepatocytes. Our results strongly challenge the concept that hepatocytes in vivo acquire a mesenchymal phenotype through EMT to produce the ECM in liver fibrosis.

CD44 expression is developmentally regulated in the mouse lens and increases in the lens epithelium after injury

Hyaluronan is an oligosaccharide found in the pericellular matrix of numerous cell types and hyaluronan-induced signaling is known to facilitate fibrosis and cancer progression in some tissues. Hyaluronan is also commonly instilled into the eye during cataract surgery to protect the corneal endothelium from damage. Despite this, little is known about the distribution of hyaluronan or its receptors in the normal ocular lens. In this study, hyaluronan was found throughout the mouse lens, with apparently higher concentrations in the lens epithelium. CD44, a major cellular receptor for hyaluronan, is expressed predominately in mouse secondary lens fiber cells born from late embryogenesis into adulthood. Surgical removal of lens fiber cells from adult mice resulted in a robust upregulation of CD44 protein, which preceded the upregulation of alpha-smooth muscle actin expression typically used as a marker of epithelial-mesenchyma transition in this model of lens epithelial cell fibrosis. Mice lacking the CD44 gene had morphologically normal lenses with a response to lens fiber cell removal similar to wildtype, although they exhibited an increase in cell-associated hyaluronan. Overall, these data suggest that lens cells have a hyaluronan-containing pericellular matrix whose structure is partially regulated by CD44. Further, these data indicate that CD44 upregulation in the lens epithelium may be an earlier marker of lens injury responses in the mouse lens than the upregulation of alpha-smooth muscle actin.

Induction of corneal myofibroblasts by lens-derived transforming growth factor beta1 (TGFbeta1): a transgenic mouse model

PURPOSE

Transforming growth factor beta (TGFbeta) is an important cytokine in corneal development and wound healing. Transgenic mice that express an active form of human TGFbeta1 driven by a lens-specific promoter were used in the current study to determine the biological effects of lens-derived TGFbeta1 on postnatal corneal development and homeostasis.

METHODS

The postnatal corneal changes in the TGFbeta1 transgenic mice were examined by fluorescein labeling and histology. Epithelial/endothelial-to-mesenchymal transition (E/EnMT) in the transgenic mouse cornea was demonstrated by immunostaining for alpha-smooth muscle actin (alpha-SMA) and cadherin-11. Expression of E- and N-cadherin in the corneal epithelial and endothelial cells, respectively, was analyzed by in situ hybridization.

RESULTS

Among the established TGFbeta1 transgenic lines, mice from line OVE853 and OVE917 had normal-sized eyeballs but developed a corneal haze after eyelid opening. Histological examination showed that prenatal corneal development appeared to be normal. However, after postnatal day 7 (P7), the corneal endothelial cells in transgenic line OVE853 began to lose normal cell-cell contact and basement membrane structure. The endothelial layer was eventually absent in the inner surface of the transgenic mouse cornea. The morphological changes in the cornea correlated with abnormal expression of alpha-SMA, a molecular marker of EMT, and stress fiber formation in myofibroblast-like cells, which initially appeared in the corneal endothelial layer and subsequently in the corneal epithelial and stromal layers. The E/EnMT in the transgenic mouse cornea was further demonstrated by loss of E- and N-cadherin expression in the corneal epithelial and endothelial cells, respectively, and meanwhile increasing expression of cadherin-11 in both corneal epithelium and stroma.

CONCLUSIONS

Elevated levels of active TGFbeta1 in the anterior chamber can lead to myofibroblast formation in the corneal endothelial layer and subsequently in the corneal epithelial and stromal layers. Our data suggest that the levels of biologically active TGFbeta in the aqueous humor must be under tight control to maintain corneal homeostasis. TGFbeta1 is the major cytokine during wound healing. Therefore, our findings also suggest a potential mechanism to explain the loss of corneal endothelial barrier and corneal opacification after intraocular surgery or trauma.

A cell polarity protein aPKClambda is required for eye lens formation and growth

The organisation of individual cells into a functional three-dimensional tissue is still a major question in developmental biology. Modulation of epithelial cell shape is a critical driving force in forming tissues. This is well illustrated in the eye lens where epithelial cells elongate extensively during their differentiation into fibre cells. It is at the lens equator that epithelial cells elongate along their apical–basal axis. During this process the elongating epithelial cells and their earliest fibre cell derivatives remain anchored at their apical tips, forming a discrete region or modiolus, which we term the lens fulcrum. How this is achieved has received scant attention and is little understood. Here, we show that conditional depletion of aPKCλ, a central effector of the PAR polarity complex, disrupts the apical junctions in elongating epithelial cells so that the lens fulcrum fails to form. This results in disorganised fibre cell alignment that then causes cataract. Interestingly, aPKCλ depletion also promotes epithelial–mesenchymal transition of the lens epithelial cells, reducing their proliferation, leading ultimately to a small lens and microphthalmia. These observations indicate that aPKCλ, a regulator of polarity and apical junctions, is required for development of a lens that is the correct size and shape.

Ex vivo quantification of the time course of contractile loading of the porcine lens capsule after cataract-like surgery

Cataract surgery is an invasive procedure that replaces the quasi-spherical native lens fibers with a flat prosthetic device, which initially reduces mechanical stress within the remnant lens capsule and, ultimately, leads to contraction of the capsule about the implant. Although resultant changes in geometry have been quantified previously, little is known about the loads associated with this contraction. We present a novel experimental culture device to quantify ex vivo the time course of increases in tension within the contracting lens capsule after cataract-like surgery. Results demonstrate that contraction reaches steady state within approximately one month with a mean tension of 1.45 mN/mm and Cauchy (true) stress of 13.4 kPa. A significant increase in alpha-smooth muscle actin (alpha-SMA) was also found in post-cultured compared to fresh lens capsules, thus suggesting that transdifferentiated lens epithelial cells (LECs) modulated the contraction. Quantification of loads imparted by the contracting lens capsule is important for assessing implant/capsule interactions and implant stability in vivo. Because contraction of the capsule may be modulated in part by LECs attempting to restore their native mechanical environment, our results further suggest a possible mechanism for the long-term errant changes in capsular structure commonly observed after surgery.

Tight junctions and the regulation of gene expression

Cell adhesion is a key regulator of cell differentiation. Cell interactions with neighboring cells and the extracellular matrix regulate gene expression, cell proliferation, polarity and apoptosis. Apical cell-cell junctions participate in these processes using different types of proteins, some of them exhibit nuclear and junctional localization and are called NACos for Nuclear Adhesion Complexes. Tight junctions are one type of such cell-cell junctions and several signaling complexes have been identified to associate with them. In general, expression of tight junction components suppresses proliferation to allow differentiation in a coordinated manner with adherens junctions and extracellular matrix adhesion. These tight junction components have been shown to affect several signaling and transcriptional pathways, and changes in the expression of tight junction proteins are associated with several disease conditions, such as cancer. Here, we will review how tight junction proteins participate in the regulation of gene expression and cell proliferation, as well as how they are regulated themselves by different mechanisms involved in gene expression and cell differentiation.

Prevention of posterior capsular opacification through aldose reductase inhibition

PURPOSE

The purpose of this study was to evaluate the effect of aldose reductase (AR) inhibition on posterior capsular opacification (PCO) with the use of a pig eye capsular bag model.

METHODS

Pig eye capsular bags were prepared by capsulorhexis and cultured in medium without or with AR inhibitors for 7 days. Immunostaining was performed in paraformaldehyde-fixed capsular bags to determine the expression of proliferating cell nuclear antigen (PCNA), alpha-smooth muscle actin (SMA), beta-crystallin, and intercellular adhesion molecule (ICAM)-1. The effect of AR inhibition on basic fibroblast growth factor (BFGF)-induced mitogenic signaling in cultured human lens epithelial cells (HLECs) was examined. Cell growth was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and cell counting, the expression of alpha-SMA, beta-crystallin, and ICAM-1 by Western blot and immunocytochemical analysis, protein kinases by Western blot analysis, and NF-kappaB activation by gel shift and reporter assays.

RESULTS

During culture of pig eye capsular bags, residual cells on both the anterior and the posterior capsule showed vigorous growth. Treatment with AR inhibitors significantly prevented the lens epithelial cell growth in capsular bags and expression of alpha-SMA, beta-crystallin, and ICAM-1. HLECs showed a dose-dependent response to BFGF, proliferation at lower concentrations (<20 ng/mL) and differentiation/transdifferentiation at higher concentrations (>50 ng/mL). Inhibition of AR also prevented the BFGF-induced activation of ERK1/2, JNK, and NF-kappaB in HLECs.

CONCLUSIONS

Results suggest that AR is required for lens epithelial cell growth and differentiation/transdifferentiation in the capsular bags, indicating that inhibition of AR could be a potential therapeutic target in the prevention of PCO.

The lens capsule

The lens capsule is a modified basement membrane that completely surrounds the ocular lens. It is known that this extracellular matrix is important for both the structure and biomechanics of the lens in addition to providing informational cues to maintain lens cell phenotype. This review covers the development and structure of the lens capsule, lens diseases associated with mutations in extracellular matrix genes and the role of the capsule in lens function including those proposed for visual accommodation, selective permeability to infectious agents, and cell signaling.

Lens intermediate filaments

The ocular lens assembles two separate intermediate filament systems sequentially with differentiation. Canonical 8-11 nm IFs composed of Vimentin are assembled in lens epithelial cells and younger fiber cells, while the fiber cell-specific beaded filaments are switched on as fiber cell elongation initiates. Some of the key features of both filament systems are reviewed.

Posterior capsule opacification

Posterior Capsule Opacification (PCO) is the most common complication of cataract surgery. At present the only means of treating cataract is by surgical intervention, and this initially restores high visual quality. Unfortunately, PCO develops in a significant proportion of patients to such an extent that a secondary loss of vision occurs. A modern cataract operation generates a capsular bag, which comprises a proportion of the anterior and the entire posterior capsule. The bag remains in situ, partitions the aqueous and vitreous humours, and in the majority of cases, houses an intraocular lens. The production of a capsular bag following surgery permits a free passage of light along the visual axis through the transparent intraocular lens and thin acellular posterior capsule. However, on the remaining anterior capsule, lens epithelial cells stubbornly reside despite enduring the rigours of surgical trauma. This resilient group of cells then begin to re-colonise the denuded regions of the anterior capsule, encroach onto the intraocular lens surface, occupy regions of the outer anterior capsule and most importantly of all begin to colonise the previously cell-free posterior capsule. Cells continue to divide, begin to cover the posterior capsule and can ultimately encroach on the visual axis resulting in changes to the matrix and cell organization that can give rise to light scatter. This review will describe the biological mechanisms driving PCO progression and discuss the influence of IOL design, surgical techniques and putative drug therapies in regulating the rate and severity of PCO.

Cell autonomous roles for AP-2alpha in lens vesicle separation and maintenance of the lens epithelial cell phenotype

In this study, we have created a conditional deletion of AP-2alpha in the developing mouse lens (Le-AP-2alpha mutants) to determine the cell-autonomous requirement(s) for AP-2alpha in lens development. Embryonic and adult Le-AP-2alpha mutants exhibited defects confined to lens placode derivatives, including a persistent adhesion of the lens to the overlying corneal epithelium (or lens stalk). Expression of known regulators of lens vesicle separation, including Pax6, Pitx3, and Foxe3 was observed in the Le-AP-2alpha mutant lens demonstrating that these genes do not lie directly downstream of AP-2alpha. Unlike germ-line mutants, Le-AP-2alpha mutants did not exhibit defects in the optic cup, further defining the tissue specific role(s) for AP-2alpha in eye development. Finally, comparative microarray analysis of lenses from the Le-AP-2alpha mutants vs. wild-type littermates revealed differential expression of 415 mRNAs, including reduced expression of genes important for maintaining the lens epithelial cell phenotype, such as E-cadherin.

Involvement of PI3K/Akt pathway in TGF-beta2-mediated epithelial mesenchymal transition in human lens epithelial cells

BACKGROUND

Epithelial mesenchymal transition (EMT) of postoperative remnants of lens epithelial cells (LECs) can lead to posterior capsule opacification. This study was designed to determine the effect of signaling pathways that contribute to TGF-beta2-mediated EMT in human lens epithelial B-3 cells (HLEB-3 cells).

METHODS

The HLEB-3 cells were cultured and stimulated with TGF-beta2 at different concentrations for an indicated time. The effect of TGF-beta2 on cell cycle distribution was measured by flow cytometry. Western blot and immunofluorescence were used to analyze changes in connexin 43, fibronectin, desmin and integrin beta(1) protein expression associated with EMT in HLEB-3 cells. Activation of phosphatidylinositol-3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways was also detected by Western blot.

RESULTS

The cell cycle progression of HLEB-3 cells was limited, and the cells underwent morphological alteration after treatment with TGF-beta2. Stimulation of HLEB-3 cells with TGF-beta(2) suppressed connexin 43 protein expression, increased fibronectin, desmin and integrin beta1 protein expression. TGF-beta2 activated PI3K/Akt in a time-dependent manner, but not extracellular signal-regulated kinase and p38 MAPK. The activation of PI3K/Akt was necessary for the TGF-beta(2)-stimulated downregulation of connexin 43, which in turn was necessary for TGF-beta2-induced EMT in HLEB-3 cells.

CONCLUSIONS

TGF-beta(2) is a potent growth factor for LEC EMT. TGF-beta(2)-induced EMT in LECs is mediated by the downregulation of connexin 43, which is regulated through the PI3K/Akt pathway.

Epithelial--mesenchymal and mesenchymal--epithelial transitions in carcinoma progression

Like a set of bookends, cellular, molecular, and genetic changes of the beginnings of life mirror those of one of the most common cause of death--metastatic cancer. Epithelial to mesenchymal transition (EMT) is an important change in cell phenotype which allows the escape of epithelial cells from the structural constraints imposed by tissue architecture, and was first recognized by Elizabeth Hay in the early to mid 1980's to be a central process in early embryonic morphogenesis. Reversals of these changes, termed mesenchymal to epithelial transitions (METs), also occur and are important in tissue construction in normal development. Over the last decade, evidence has mounted for EMT as the means through which solid tissue epithelial cancers invade and metastasize. However, demonstrating this potentially rapid and transient process in vivo has proven difficult and data connecting the relevance of this process to tumor progression is still somewhat limited and controversial. Evidence for an important role of MET in the development of clinically overt metastases is starting to accumulate, and model systems have been developed. This review details recent advances in the knowledge of EMT as it occurs in breast development and carcinoma and prostate cancer progression, and highlights the role that MET plays in cancer metastasis. Finally, perspectives from a clinical and translational viewpoint are discussed.