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

Unique Role of Vimentin in the Intermediate Filament Proteins Family

Intermediate filaments (IFs), being traditionally the least studied component of the cytoskeleton, have begun to receive more attention in recent years. IFs are found in different cell types and are specific to them. Accumulated data have shifted the paradigm about the role of IFs as structures that merely provide mechanical strength to the cell. In addition to this role, IFs have been shown to participate in maintaining cell shape and strengthening cell adhesion. The data have also been obtained that point out to the role of IFs in a number of other biological processes, including organization of microtubules and microfilaments, regulation of nuclear structure and activity, cell cycle control, and regulation of signal transduction pathways. They are also actively involved in the regulation of several aspects of intracellular transport. Among the intermediate filament proteins, vimentin is of particular interest for researchers. Vimentin has been shown to be associated with a range of diseases, including cancer, cataracts, Crohn's disease, rheumatoid arthritis, and HIV. In this review, we focus almost exclusively on vimentin and the currently known functions of vimentin intermediate filaments (VIFs). This is due to the structural features of vimentin, biological functions of its domains, and its involvement in the regulation of a wide range of basic cellular functions, and its role in the development of human diseases. Particular attention in the review will be paid to comparing the role of VIFs with the role of intermediate filaments consisting of other proteins in cell physiology.

A bibliometric and visualized analysis of the pathogenesis of cataracts from 1999 to 2023

Research on the pathogenesis of cataracts is ongoing and the number of publications on this topic is increasing annually. This study offers an overview of the research status, popular topics, and scholarly tendencies in the field of cataract pathogenesis over recent decades，which helps to guide future research directions, and optimize resource allocation. In the present study, we performed a bibliometric analysis of cataract pathogenesis. Publications from January 1, 1999, to December 20, 2023, were collected from the Web of Science Core Collection (WoSCC), and the extracted data were quantified and analyzed. We analyzed and presented the data using Microsoft Excel, VOSviewer, CiteSpace, and Python. In all, 4006 articles were evaluated based on various characteristics, including publication year, authors, countries, institutions, journals, citations, and keywords. This study utilized VOSviewer to conduct visualized analysis, including co-authorship, co-citation, co-occurrence, and network visualization. The CiteSpace software was used to identify keywords with significant bursts of activity. The number of annual global publications climbed from 76 to 277 between 1999 and 2023, a 264.47% rise. Experimental Eye Research published the most manuscripts (178 publications), whereas Investigative Ophthalmology & Visual Science received the most citations (6675 citations). The most influential and productive country, institution, and author were the United States (1244 publications, 54,456 citations), University of California system (136 publications, 5401 citations), and Yao Ke (49 publications, 838 citations), respectively. The top 100 ranked keywords are divided into four clusters through co-occurrence analysis: (1) secondary cataracts, (2) oxidative stress, (3) gene mutations and protein abnormalities, and (4) alteration of biological processes in lens epithelial cells. Further discussions on the four subtopics outline the research topics and trends. In conclusion, the specific mechanism of cataract formation remains a popular topic for future research and should be explored in greater depth.

The human lens is capable of trilineage differentiation towards osteo-, chondro-, and adipogenesis-a model for studying cataract pathogenesis

The potential for trilineage differentiation of cells in tissues represents a model for studying disease pathogenesis and regeneration pathways. Human lens trilineage differentiation has not yet been demonstrated, and so has calcification and osteogenic differentiation of human lens epithelial cells in the whole human lens. Such changes can pose a risk for complications during cataract surgery. Human lens capsules (n = 9) from cataract patients undergoing uneventful surgery were trilineage-differentiated toward osteogenesis, chondrogenesis, and adipogenesis. Furthermore, whole human healthy lenses (n = 3) collected from cadaveric eyes were differentiated into bone and characterized by immunohistochemistry. The cells in the human lens capsules were capable of undergoing trilineage differentiation, while the whole human healthy lenses could undergo osteogenesis differentiation, expressing osteocalcin, collagen I, and pigment epithelium-derived factor. We, hereby, show an ex vivo model for cataract formation through different stages of opacification, as well as provide in vivo evidence from patients undergoing calcified lens extraction with bone-like consistency.

The lens epithelium as a major determinant in the development, maintenance, and regeneration of the crystalline lens

The crystalline lens is a transparent and refractive biconvex structure formed by lens epithelial cells (LECs) and lens fibers. Lens opacity, also known as cataracts, is the leading cause of blindness in the world. LECs are the principal cells of lens throughout human life, exhibiting different physiological properties and functions. During the embryonic stage, LECs proliferate and differentiate into lens fibers, which form the crystalline lens. Genetics and environment are vital factors that influence normal lens development. During maturation, LECs help maintain lens homeostasis through material transport, synthesis and metabolism as well as mitosis and proliferation. If disturbed, this will result in loss of lens transparency. After cataract surgery, the repair potential of LECs is activated and the structure and transparency of the regenerative tissue depends on postoperative microenvironment. This review summarizes recent research advances on the role of LECs in lens development, homeostasis, and regeneration, with a particular focus on the role of cholesterol synthesis (eg., lanosterol synthase) in lens development and homeostasis maintenance, and how the regenerative potential of LECs can be harnessed to develop surgical strategies and improve the outcomes of cataract surgery (Fig. 1). These new insights suggest that LECs are a major determinant of the physiological and pathological state of the lens. Further studies on their molecular biology will offer possibility to explore new approaches for cataract prevention and treatment.

Human Vimentin Layers on Solid Substrates: Adsorption Kinetics and Corona Formation Investigations

Adsorption kinetics of human vimentin on negatively charged substrates (mica, silica, and polymer particles) was analyzed using atomic force microscopy (AFM), quartz microbalance (QCM), and the laser doppler velocimetry (LDV) method. AFM studies realized under diffusion conditions proved that the adsorbed protein layer mainly consisted of aggregates in the form of compact tetramers and hexamers of a size equal to 11–12 nm. These results were consistent with vimentin adsorption kinetics under flow conditions investigated by QCM. It was established that vimentin aggregates efficiently adsorbed on the negatively charged silica sensor at pH 3.5 and 7.4, forming compact layers with the coverage reaching 3.5 mg m^–2. Additionally, the formation of the vimentin corona at polymer particles was examined using the LDV method and interpreted in terms of the electrokinetic model. This allowed us to determine the zeta potential of the corona as a function of pH and the electrokinetic charge of aggregates, which was equal to −0.7 e nm^–2 at pH 7.4 in a 10 mM NaCl solution. The anomalous adsorption of aggregates exhibiting an average negative charge on the negatively charged substrates was interpreted as a result of a heterogeneous charge distribution. These investigations confirmed that it is feasible to deposit stable vimentin layers both at planar substrates and at carrier particles with well-controlled coverage and zeta potential. They can be used for investigations of vimentin interactions with various ligands including receptors of the innate immune system, immunoglobulins, bacterial virulence factors, and spike proteins of viruses.

Lens Epithelial Surface Disorders in Exfoliation Syndrome: A Scanning and Transmission Electron Microscopy Study

BACKGROUND

Hydrodissection was recently reported to occur more easily in patients with exfoliation syndrome (XFS). Transmission electron microscopy (TEM) studies have already revealed alterations of the lens epithelial cells (LECs) and their apical membrane towards the lens fibers.

OBJECTIVE

The aim of this work was to examine the three-dimensional appearance of the lens epithelium in patients with XFS.

METHODS

Fourteen patients with senile cataract, 7 of whom had XFS, were included. Anterior lens capsules (aLCs) were obtained with continuous curvilinear capsulorrhexis (CCC) during phacoemulsification and were examined with scanning electron microscopy (SEM) and TEM.

RESULTS

Exfoliation samples exhibited an overall more irregular apical surface of the lens epithelium compared to control aLCs. The height of LECs varied extensively. On the apical surface of LECs, amorphous, crystalline-like, or microgranular extracellular material and membranous, oval-shaped structures were documented with SEM. All findings were connected to corresponding observations with TEM and were not correlated to the type of cataract.

CONCLUSIONS

In XFS patients, the lens epithelial surface exhibited a highly irregular margin, with extracellular material covering the apical membrane of LECs. We suggest that XFS probably causes both epithelial and lens fiber degeneration which, during CCC and mechanical extraction of the aLC from the lens cortex, result in diverse alterations.

Ultrastructural Analysis of the Anterior Lens Epithelium in Cataracts Associated with Uveitis

PURPOSE

To investigate the transmission electron microscopic findings of lens epithelial cells (LECs) in patients with different subtypes of uveitis and to compare the findings with those in age-matched controls.

METHODS

In this prospective case-control study, the anterior lens capsules were taken from 47 eyes of 47 patients with uveitis of different subtypes (17 with Fuchs uveitis syndrome [FUS], 13 with -Behçet's uveitis, 10 with idiopathic uveitis, and 7 with herpetic keratouveitis) and from 15 eyes of 15 control patients.

RESULTS

In the FUS group, the LECs had homogeneous thickening and irregularity, with some small vacuoles and widespread, oval-shaped pigment clusters in some areas. In the Behçet uveitis group, there was evident thinning in the lens epithelium. The subepithelial tissue under the epithelium was thickened, and edematous areas were detected. In the idiopathic uveitis group, the LECs were thinner with small vacuoles, and the cubic structure of the LECs was transformed into a squamous one. Moreover, the LECs included some small vacuoles, similar to those in the FUS group. In the herpetic keratouveitis group, two prominent cell types were observed: (1) completely normal LECs and (2) degenerated-type LECs with pyknotic nuclei, condensation of chromatin, swelling in the cytoplasm, membrane ruptures, and intra-cytoplasmic inclusion bodies. In the control group, the LECs and all of their elements occurred in normal ultrastructural patterns, with the exception of a few small intraepithelial vacuoles, which were fewer in number and smaller than those in the FUS and idiopathic uveitis groups.

CONCLUSION

The electron microscopic analysis of LECs of patients with different subtypes of uveitis revealed significant ultrastructural alterations, which may be related to the summation of oxidative stress and intraocular inflammation.

The myofibroblast, biological activities and roles in eye repair and fibrosis. A focus on healing mechanisms in avascular cornea

Tissue healing is one of the mysteries of modern medicine. Healing involves complex processes and many cellular types, amongst which the myofibroblast plays a major role. In the eye, when needed, myofibroblasts can be found from the cornea to the retina, derived from a wide variety of different cells, and aimed at effectively repairing tissue damage. Myofibroblast differentiation requires transforming growth factor (TGF)-β1, the presence of specific extracellular matrix components such as the ED-A domain of fibronectin, and mechanical tension. Control of this process may, in some cases, be abnormal leading to development of fibrotic tissue, which alters and compromises the integrity of the original tissue. The eye is no exception to this rule with normal visual function, a highly demanding process, only possible in a fully integrated organ. The cornea, a transparent protective tissue and first dioptre of the eye, has the particularity of being entirely avascular and very richly innervated under normal physiological conditions. However, these anatomical features do not prevent it from developing myofibroblasts in the event of a deep corneal lesion. Activated by growth factors such as TGF-β1 and platelet-derived growth factor from the aqueous humour, tears or corneal epithelial cells, myofibroblasts can cause corneal scarring, sometimes with devastating consequences. Understanding the factors involved in healing and its signalling pathways, will potentially enable us to control corneal healing in the future, and thus avoid fibrotic ocular surface disease and the blindness that this may induce. Currently, this issue is the subject of very active research and development with the aim of discovering new antifibrotic therapies.

Severe Abnormalities of Lens Epithelial Cells in Exfoliation Syndrome: A Transmission Electron Microscopy Study of Patients with Age-Related Cataract

Background and objectives: The aim of this study was to examine via electron microscopy the lens epithelial cells in age-related cataracts and compare the findings between patients with and without exfoliation syndrome, in the Greek population. Materials and Methods: Twenty-one patients with age-related cataracts, older than 60 years, were included in the study. Eleven of them also suffered from exfoliation syndrome. Anterior lens capsules, obtained during phacoemulsification, were examined with a transmission electron microscope. Results: In all cases, ultrastructural features of diffuse intracellular and extracellular oedema were noticed to a varying degree and transparent vacuoles were detected. Often, there was more than one layer of cells, giving the impression that healthier cells tried to cover neighboring cells presenting extensive damage. Commonly, cells lost their regular shape and appeared with expanded nuclei carrying dense granules. Apoptotic cells were also detected. The epithelial cells frequently were completely destroyed or absent, exhibiting loose connections amongst them or with the basement membrane. In exfoliation syndrome (XFS) patients the alterations were more severe. Additionally, the lens epithelial cells (LECs) apical cell membrane appeared with varying distances from the basement membrane, due to different cell "heights", creating an irregular margin of the epithelium (p<0.05). Conclusion: Transmission electron microscope (TEM) examination revealed ultrastructural abnormalities in all patients' lens epithelia, more extended and more frequently observed in XFS group. In all cases, the lesions were comparable to those described in severe pathologies, all of which were excluded from the study. Environmental factors such as increased ultraviolet B (UVB) radiation exposure in Mediterranean countries, genetic factors, epigenetic factors, or all of them, could contribute to these alterations. Further epidemiological and molecular biology research is needed, so as to justify these results.

Diet-Related Metabolic Perturbations of Gut Microbial Shikimate Pathway-Tryptamine-tRNA Aminoacylation-Protein Synthesis in Human Health and Disease

Human gut bacterial Na(+)-transporting NADH:ubiquinone reductase (NQR) sequence is associated with Alzheimer disease (AD). Here, Alzheimer disease-associated sequence (ADAS) is further characterized in cultured spore-forming Clostridium sp. Tryptophan and NQR substrate ubiquinone have common precursor chorismate in microbial shikimate pathway. Tryptophan-derived tryptamine presents in human diet and gut microbiome. Tryptamine inhibits tryptophanyl-tRNA synthetase (TrpRS) with consequent neurodegeneration in cell and animal models. Tryptophanyl-tRNA synthetase inhibition causes protein biosynthesis impairment similar to that revealed in AD. Tryptamine-induced TrpRS gene-dose reduction is associated with TrpRS protein deficiency and cell death. In animals, tryptamine treatment results in toxicity, weight gain, and prediabetes-related hypoglycemia. Sequence analysis of gut microbiome database reveals 89% to 100% ADAS nucleotide identity in American Indian (Cheyenne and Arapaho [C&A]) Oklahomans, of which ~93% being overweight or obese and 50% self-reporting type 2 diabetes (T2D). Alzheimer disease-associated sequence occurs in 10.8% of C&A vs 1.3% of healthy American population. This observation is of considerable interest because T2D links to AD and obesity. Alzheimer disease-associated sequence prevails in gut microbiome of colorectal cancer, which linked to AD. Metabolomics revealed that tryptamine, chorismate precursor quinate, and chorismate product 4-hydroxybenzoate (ubiquinone precursor) are significantly higher, while tryptophan-containing dipeptides are lower due to tRNA aminoacylation deficiency in C&A compared with non-native Oklahoman who showed no ADAS. Thus, gut microbial tryptamine overproduction correlates with ADAS occurrence. Antibiotic and diet additives induce ADAS and tryptamine. Mitogenic/cytotoxic tryptamine cause microbial and human cell death, gut dysbiosis, and consequent disruption of host-microbe homeostasis. Present analysis of 1246 participants from 17 human gut metagenomics studies revealed ADAS in cell death diseases.

Vimentin Diversity in Health and Disease

Vimentin is a protein that has been linked to a large variety of pathophysiological conditions, including cataracts, Crohn's disease, rheumatoid arthritis, HIV and cancer. Vimentin has also been shown to regulate a wide spectrum of basic cellular functions. In cells, vimentin assembles into a network of filaments that spans the cytoplasm. It can also be found in smaller, non-filamentous forms that can localise both within cells and within the extracellular microenvironment. The vimentin structure can be altered by subunit exchange, cleavage into different sizes, re-annealing, post-translational modifications and interacting proteins. Together with the observation that different domains of vimentin might have evolved under different selection pressures that defined distinct biological functions for different parts of the protein, the many diverse variants of vimentin might be the cause of its functional diversity. A number of review articles have focussed on the biology and medical aspects of intermediate filament proteins without particular commitment to vimentin, and other reviews have focussed on intermediate filaments in an in vitro context. In contrast, the present review focusses almost exclusively on vimentin, and covers both ex vivo and in vivo data from tissue culture and from living organisms, including a summary of the many phenotypes of vimentin knockout animals. Our aim is to provide a comprehensive overview of the current understanding of the many diverse aspects of vimentin, from biochemical, mechanical, cellular, systems biology and medical perspectives.

Laminins in an in vitro anterior lens capsule model established using HLE B-3 cells

Cataracts are the most common eye disease to cause blindness in patients. The abnormal deposition of laminins (LMs) in the lens capsule and the disruption of capsular epithelium contribute to cataract development, although the mechanism by which this occurs is currently unclear. The present study aimed to reproduce HLE B-3 basement membranes (BMs) using HLE B-3 cells and to analyze the similarities of LM expression between HLE B-3 BMs and human anterior lens capsule (ALC). Immunohistochemistry (IHC), ELISA, western blot analysis and immunoprecipitation (IP)-western blot analysis were used to detect total LMs, LM trimers and 11 LM subunits in HLE B-3 cells, HLE B-3 BMs and human ALCs. In IHC staining, HLE B-3 cells and human ALCs were positive for LMs. In LM ELISA, all samples analyzed were positive for LMs. Western blot analysis detected all LM subunits except for LMγ3 in HLE B-3 cell lysate, 4 subunits (LMα4, LMα2, LMα1 and LMγ1) in HLE B-3 cell culture supernatant, 5 subunits (LMα4, LMα2, LMα1, LMβ3 and LMγ1) in HLE B-3 BMs, and 3 subunits (LMα4, LMγ2 and LMγ1) in human ALCs. The results of IP-western blot analysis revealed that the LM411 trimer was detected in HLE B-3 cell culture supernatant. These results indicated that HLE B-3 BMs were similar to human ALCs in terms of LM expression. Therefore, HLE B-3 BMs could be used as an in vitro ALC model to determine the role of LMs in ALC in the pathogenesis of cataracts and to select potential anti-cataract drugs.

Effects of Fuchs uveitis syndrome on the ultrastructure of the anterior lens epithelium: A transmission electron microscopic study

PURPOSE

The purpose of the study was to investigate the electron microscopic findings of the lens epithelial cells (LECs) in patients with Fuchs uveitis syndrome (FUS) who suffered from cataracts and to compare those with age-matched controls.

METHODS

This study was a prospective, comparative case series. The anterior lens capsules (ALC: basement membrane and associated LECs) were taken from 12 eyes of 12 cases of FUS and ten eyes of ten control patients. The ALCs were obtained from cataract surgery and prepared for transmission electron microscopy (TEM).

RESULTS

There were no statistically significant differences regarding the age or gender between the FUS group and the control group (P > 0.05). In the TEM examinations of the ALCs, all of the FUS cases revealed similar significant ultrastructural changes when compared to the control patients. In the FUS group, the LECs showed homogeneous thickening and irregularity which included some small vacuoles in different areas of the epithelial tissue. Moreover, in some areas of the LECs, widespread, oval-shaped, pigment clusters were detected. Conversely, in the control group, the LECs and all of their elements were in normal ultrastructural patterns, with the exception of some small intraepithelial vacuoles which were fewer and smaller than those in the FUS group.

CONCLUSION

Ultrastructural analysis of the ALC of the patients with FUS disclosed some significant alterations which may be related to the summation of oxidative stress, intraocular inflammation, and iris atrophy.

Electron microscopic evaluation of anterior lens epithelium in patients with idiopathic congenital cataract

PURPOSE

To investigate the ultrastructure of the lens epithelial cells (LECs) in patients with idiopathic congenital cataract.

METHODS

This is a prospective interventional study. The anterior lens capsules (aLC: basement membrane and associated LECs) were taken from 16 eyes of 12 consecutive patients who were diagnosed as having idiopathic congenital cataracts. The aLCs were obtained from cataract surgery and prepared for transmission electron microscopy (TEM).

RESULTS

Some significant ultrastructural changes were observed in all aLCs of the participants. The anterior LECs showed alterations in different areas which were partly cuboidal and partly squamous in shape. The LECs had euchromatic nucleus and included some vacuoles in the cytoplasms as a remarkable alteration. The sizes of these intraepithelial cell vacuoles were changeable.

CONCLUSIONS

We identified remarkable changes in LECs of the eyes with idiopathic congenital cataract by TEM. It can be assumed that oxidative damage may be associated with these ultrastructural changes in LECs of the eyes with idiopathic congenital cataracts.

Myofibroblast transdifferentiation: The dark force in ocular wound healing and fibrosis

Wound healing is one of the most complex biological processes to occur in life. Repair of tissue following injury involves dynamic interactions between multiple cell types, growth factors, inflammatory mediators and components of the extracellular matrix (ECM). Aberrant and uncontrolled wound healing leads to a non-functional mass of fibrotic tissue. In the eye, fibrotic disease disrupts the normally transparent ocular tissues resulting in irreversible loss of vision. A common feature in fibrotic eye disease is the transdifferentiation of cells into myofibroblasts that can occur through a process known as epithelial-mesenchymal transition (EMT). Myofibroblasts rapidly produce excessive amounts of ECM and exert tractional forces across the ECM, resulting in the distortion of tissue architecture. Transforming growth factor-beta (TGFβ) plays a major role in myofibroblast transdifferentiation and has been implicated in numerous fibrotic eye diseases including corneal opacification, pterygium, anterior subcapsular cataract, posterior capsular opacification, proliferative vitreoretinopathy, fibrovascular membrane formation associated with proliferative diabetic retinopathy, submacular fibrosis, glaucoma and orbital fibrosis. This review serves to introduce the pathological functions of the myofibroblast in fibrotic eye disease. We also highlight recent developments in elucidating the multiple signaling pathways involved in fibrogenesis that may be exploited in the development of novel anti-fibrotic therapies to reduce ocular morbidity due to scarring.

Cytomorphometric study of epithelial cells in normal and cataractous human lenses in relation with hyperglycemia

The aim of the study is to evaluate and correlate the morphology and cell density of epithelial cells adhering to lens capsule surgically removed from the anterior central region with lens clarity and type of cataract present in patients with or without type 2 diabetes. Capsulorhexis specimens were obtained from patients who had undergone phacoemulsification cataract surgery. All the samples were centrifuged and stained by the aid of Papanicolaou technique and were observed under light microscope. We determinated the mean cell density, the degree of epithelial damage, and morphological indicators of cells such as cell area and the nucleus-plasma ratio. Patients with cataract demonstrated a statistical significant decrease in cell density and an heterogeneous cell picture in which enlarged cells dominated. In addition, type 2 diabetics with cataract had a significantly even lower mean epithelial cell density by the presence of larger cell area with smaller nucleus-plasma ratio. More pronounced alterations in the lens epithelium were correlated not only with the presence of cortical cataract, increased fasting blood sugar, and increased HbA1c but also with the prolonged duration of diabetes and the co-existence of diabetic retinopathy. It seems that density and morphology of the anterior lens epithelial cells determine the lens epithelium damage which is more profound in hyperglycemia and in cortical cataracts. The changes in lens epithelium seem to play an important role in cataractogenesis.

Prevalence of and risk factors for age-related and anterior polar cataracts in a Korean population

Objective

To investigate the potential risk factors associated with nuclear, cortical, posterior subcapsular, and anterior polar cataracts (APC) in the Korean population.

Research Design and Methods

This was a population-based, cross-sectional study of 7992 adults (over 40 years of age) from the data of the fourth annual Korea National Health and Nutrition Examination Survey, performed from 2007 to 2009. The presence of lens opacity was examined by slit-lamp biomicroscopy and evaluated according to LOCS II standard photographs. The subtype of cataract present, including nuclear, cortical, posterior subcapsular, and anterior polar cataracts, was noted. Multivariable adjusted logistic regression analysis was conducted to examine the odds ratio (OR) and 95% confidence interval (CI) for association of each specific type of cataract with age, sex, health examination, and medical history.

Results

The prevalence of nuclear, cortical, and posterior subcapsular cataract increased gradually with increasing age. However, the prevalence of APC peaked in the 50- to 59-year-old subjects. All types of cataract except for APCs were more prevalent in women. Oral steroid use was associated with a lower risk of APC.

Conclusions

These findings showed the unique characteristics of APC in the Korean population.

Review on intermediate filaments of the nervous system and their pathological alterations

Intermediate filaments (IFs) of the nervous system, including neurofilaments, α-internexin, glial fibrillary acidic protein, synemin, nestin, peripherin and vimentin, are finely expressed following elaborated cell, tissue and developmental specific patterns. A common characteristic of several neurodegenerative diseases is the abnormal accumulation of neuronal IFs in cell bodies or along the axon, often associated with impairment of the axonal transport and degeneration of neurons. In this review, we also present several perturbations of IF metabolism and organization associated with neurodegenerative disorders. Such modifications could represent strong markers of neuronal damages. Moreover, recent data suggest that IFs represent potential biomarkers to determine the disease progression or the differential stages of a neuronal disorder. Finally, recent investigations on IF expression and function in cancer provide evidence that they may be useful as markers, or targets of brain tumours, especially high-grade glioma. A better knowledge of the molecular mechanisms of IF alterations, combined to neuroimaging, is essential to improve diagnosis and therapeutic strategies of such neurodegenerative diseases and glioma.

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.

The prevalence and demographic characteristics of anterior polar cataract in a hospital-based study in Korea

Purpose

Anterior Polar Cataract (APC) develops by a mechanism different from that of other age-related cataracts, and outside of Korea, it is an extremely rare condition. We investigated the prevalence and epidemiological characteristics of APC in Koreans.

Methods

The evaluation on the prevalence of APC in comparison to the other age-related cataracts was performed on the 2,108 cataract patients who were treated at 5 different areas in Korea from August 2003 to December 2003. The demographic characteristics of APC were studied on the, 656 cataract patients who were treated from January 2004 to January 2005 at one hospital. These patients were classified according to the type of lens opacity (nuclear, cortical, posterior subcapsular, mixed and APC).

Results

The prevalence of patients with APC among all the cataract patients was 6.02% during the 5 months in this hospital-based study. Eighty-seven per cent of patients with APC were male. In contrast, the proportion of female was greater than 50% in the other cataracts. The mean age of APC patients was 52.7 years. Among the APC patients, 38.9% were under 50 years of age, 42.6% in their 50s, 14.8% in their 60s, and 3.7% were in their 70s. However, 80% of patients were over the age of 60 years in nuclear, cortical, and mixed-type cataracts.

Conclusions

The prevalence of APC among all cataracts was high in comparision with another country. The proportion of APC was high in individuals younger than 60 years of age, and in males.

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).

Involvement of cytoskelatal proteins and growth factor receptors during development of the human eye

The spatial and temporal distribution of nestin, cytokeratins (CKs), vimentin, glial fibrillary acidic protein (GFAP), neurofilaments (NFs), beta-tubulin as well as fibroblast growth factor receptors (FGFRs) and platelet-derived growth factor receptor beta (PDGF-Rbeta) were investigated in the developing human eye in eight conceptuses of 5-9 postovulatory weeks using immunostaining. Nestin was found in the neuroglial precursors and the radial glial fibres of the optic nerve. In the pigmented retina, nestin was present only in the 5th week, while at later stages (6-9th week), co-expression of CKs and vimentin was seen. Nestin, CKs, vimentin, and GFAP were observed in the precursors to various cell types in the neural retina. Additionally, their expression was also apparent in the lens epithelium, showing its gradual fading following the lens fibre elongation. They appeared in the mesenchymal cells of the cornea, the choroid, the sclera, and the corpus vitreum, too. In the corneal epithelium, co-expression of nestin and CKs was detected. NFs and beta-tubulin were confined to the differentiating retinal neuroblasts. Growth factor receptors were seen in the retina, the lens epithelium while less intensely in the lens fibres, the corneal epithelium, and the mesenchymal cells. During the early eye development (5-9th week), IFs expressing normal pattern of distribution as well as acting in concert might contribute to the normal developmental processes occurring in certain parts of the human eye. Additionally, NFs and beta-tubulin seem to have an important role in the retinal ganglion cell differentiation, while FGFRs and PDGF-Rbeta may regulate the cell proliferation, differentiation, and survival in various parts of the developing eye.

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 TGF-β2 mRNA and PCNA, FN protein in lens epithelial cells in age-related nuclear and cortex cataract

By using RT-PCR and immunohistochemistry, the expressions of transforming growth factor beta2 (TGF-beta2) mRNA, proliferating cell nuclear antigen (PCNA) and fibronection (FN) protein in lens epithelial cells (LECs) of age-related nuclear and cortex cataract were detected and compared. The results of RT-PCR revealed that the expression of TGF-beta2 mRNA was higher in cortex cataract than in nuclear cataract. Immunohistochemistry demonstrated that the expression of PCNA protein was lower and the expression of FN protein was higher in cortex cataract than in nuclear cataract. It was suggested that TGF-beta2, PCNA and FN might take important parts in the process of age-related cataract. Cortex cataract was related to the transdifferentiation of LECs, and nuclear cataract to the proliferation of LECs.

Growth factor deposition in anterior subcapsular cataract

PURPOSE

To characterize immunohistochemically the distribution of growth factors and extracellular matrix (ECM) components in an anterior subcapsular cataract (ASC) and to determine the role of growth factors in the development of ASC.

SETTING

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

METHODS

During cataract surgery in 22 patients, anterior capsules with an ASC were obtained. Sections of each specimen were immunostained with a panel of antibodies against ECM components, growth factors, cytoskeletal components, and signal transduction-related molecules.

RESULTS

Collagen types I, V, and VI; fibronectin; fibrillin-1; and latent transforming growth factor beta binding protein-1 (LTBP-1) were localized to the ECM in ASC tissues. Collagen IV was localized to the ECM and the capsule. Lens epithelial cells (LECs) were positive for alpha-smooth muscle actin (alphaSMA). Lens epithelial cells and ECM stained for transforming growth factor beta2 (TGFbeta2) and TGFbeta3 in all samples, but TGFbeta1 latency-associated peptide (TGFbeta1-LAP) were detected in some samples. Fibroblast growth factor-2 (FGF-2) and hepatocyte growth factor-alpha (HGF-alpha) were localized to the ECM. Lens epithelial cells with nuclear staining for Erk-1, the mitogen-activated protein kinase (MAP kinase) cascade-related molecule, and Smad3, 1 of the Smad family members involving TGFbeta signaling, were detected.

CONCLUSIONS

Matrix components (ie, collagen types, fibronectin, fibrillin-1), as well as growth factors such as TGFbeta1-LAP, TGFbeta2, TGFbeta3, FGF-2, and HGF-alpha, were detected in ASC. Fibrillin-1 might serve as a repository for TGFbetas. These growth factors may modulate the phenotypic alteration and behavior of LECs. The MAP kinase cascade and TGFbeta signaling are both activated in LECs in ASC.

Epithelial transdifferentiation and cataract in the human lens

Anterior subcapsular cataracts cause a serious loss of vision and are normally associated with ocular trauma, inflammation or clinical skin conditions. They appear to be accompanied by epithelial cell growth and transdifferentiation where unscheduled production of a number of proteins, including alpha smooth muscle actin (alpha-sma), occurs. Clinical studies have also revealed an up-regulation of the TGFbeta signalling pathway in such cataracts. The present study, using phase contrast and immunofluorescent techniques, was undertaken to investigate the extent of alpha-sma expression in traumatic cataracts, in capsulorhexis specimens obtained during cataract surgery and in aged human lenses from donor eyes. The donor lenses were also exposed to trauma or TGFbeta in culture to observe their relative contribution to alpha-sma production. Dense anterior subcapsular cataracts were relatively rare (<1%), but all showed a pronounced up-regulation of alpha-sma, which was located both in anterior cells of normal appearance and in nucleated fibroblastic cells lying beneath the anterior epithelium. Surprisingly, more than 50% of capsulorhexis specimens from mature cataracts showed expression of alpha-sma, although to a limited extent. Alpha-sma was not expressed in any of the clear donor lenses and culture for 8 days in EMEM did not induce expression. Interestingly, unlike their young animal counterparts, human lenses failed to show the presence of alpha-sma when exposed to 10 ng ml(-1) TGFbeta. However, after culture, lenses with pre-existing cortical opacities did express alpha-sma, as did clear lenses subjected to injury or trauma. It appears that the greater the stress, the greater is the expression of alpha-sma. Cataract, and especially cortical cataract, should therefore be seen as associated with stress-induced signalling pathways in the lens that lead to the transdifferentiation of the anterior epithelial cells.

Downregulated expression of ADAM9 in anterior polar cataracts

PURPOSE

To determine whether ADAM (a disintegrin and metalloproteinase) is regulated in lens epithelial cells (LECs) of patients with anterior polar cataracts and by transforming growth factor (TGF)-beta 1 in cultured LECs.

SETTING

Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea, Seoul, Korea.

METHODS

Lens epithelial cells attached to the anterior capsules of human cataractous lenses with nuclear and anterior subcapsular cataracts and noncataractous lenses were analyzed by reverse transcribed-polymerase chain reaction for the expression of ADAMs. The effect of TGF-beta 1 on ADAM gene expression was also tested in mouse lens epithelial explants and cultured LEC lines (alpha TN-4 and HLE B-3).

RESULTS

Significantly reduced expression of mRNA for ADAM9 was observed in LECs from patients with anterior polar cataracts. The expression of mRNA for ADAM9 was downregulated by TGF-beta 1 in cultured human LECs. Treatment of cultured mouse LECs with TGF-beta 1 led to a reduction in ADAM1 mRNA.

CONCLUSIONS

ADAMs are expressed and regulated in LECs. The downregulated expression of ADAM9 may serve as a marker for anterior polar cataracts in addition to previously known proteins, fibronectin, alpha-SMA, and beta ig-h3. The functions of this protein in lens pathology require further investigation.

Downregulated Expression of Integrin α6 by Transforming Growth Factor-β1 on Lens Epithelial Cells in Vitro

Integrins represent the main cell surface receptors that mediate cell-matrix and cell-cell interactions. They play critical roles in adhesion, migration, morphogenesis, and the differentiation of several cell types. Previous studies have demonstrated that members of the fibroblast growth factor (FGF)-2, transforming growth factor (TGF)-beta(1), and insulin growth factor (IGF)-1 play important roles in lens biology. In particularly, TGF-beta(1) appears to play a key role in extracellular matrix production, cell proliferation, and cell differentiation of lens epithelial cells. In this study we investigated the effects of FGF-2, TGF-beta(1), and IGF-1 on the modulation of integrin receptors using lens epithelial cell lines (HLE B-3 and alphaTN-4) and lens explants. We found that the expression of integrin alpha6 is downregulated by TGF-beta(1), but is not responsive to FGF-2 or IGF-1. The promoter activity of the integrin alpha6 gene decreased upon TGF-beta(1) treatment in a transient transfection assay, and flow cytometric analysis demonstrated the reduced expression of integrin alpha6 by TGF-beta(1), whereas significant changes were not observed in the level of integrin alpha6 after the addition of FGF-2. These findings suggest that the reduced expression of integrin alpha6 caused by TGF-beta(1) might play a role in the activation of the cell cycle genes required during the fiber differentiation of the lens.

Effect of advanced glycation end products on lens epithelial cells in vitro

The extended exposure of proteins to reducing sugars leads to nonenzymatic glycation with the accumulation of advanced glycation end products (AGEs). Long-lived proteins, such as collagen and crystallins, are subjected to this modification, and are implicated as causal factors in several diseases including diabetic complications, cataracts, and arteriosclerosis. One means through which AGEs modulate cellular interactions is via binding to specific receptors. In the current study, the existence of AGEs in human anterior polar lens capsules of cataracts was confirmed using a combination of dot-immunoblot and fluorescent detection. Human lens epithelial cells (LECs) attached to anterior lens capsules expressed mRNA for the receptor for AGEs (RAGE). The interaction of LECs with AGEs using bovine lens epithelial explants demonstrated that AGEs induced mRNAs and proteins of fibronectin, collagen type I, aberrant extracellular matrix proteins, and alpha-SMA, a specific marker for myofibroblastic cells. These findings suggest that AGEs may alter cellular functions which induce mRNAs and proteins associated with fibrosis in LECs.