Growth factor receptor gene and protein expressions in the human lens

Hallmarks of lens aging and cataractogenesis

Lens homeostasis and transparency are dependent on the function and intercellular communication of its epithelia. While the lens epithelium is uniquely equipped with functional repair systems to withstand reactive oxygen species (ROS)-mediated oxidative insult, ROS are not necessarily detrimental to lens cells. Lens aging, and the onset of pathogenesis leading to cataract share an underlying theme; a progressive breakdown of oxidative stress repair systems driving a pro-oxidant shift in the intracellular environment, with cumulative ROS-induced damage to lens cell biomolecules leading to cellular dysfunction and pathology. Here we provide an overview of our current understanding of the sources and essential functions of lens ROS, antioxidative defenses, and changes in the major regulatory systems that serve to maintain the finely tuned balance of oxidative signaling vs. oxidative stress in lens cells. Age-related breakdown of these redox homeostasis systems in the lens leads to the onset of cataractogenesis. We propose eight candidate hallmarks that represent common denominators of aging and cataractogenesis in the mammalian lens: oxidative stress, altered cell signaling, loss of proteostasis, mitochondrial dysfunction, dysregulated ion homeostasis, cell senescence, genomic instability and intrinsic apoptotic cell death.

Association of IGF1R polymorphisms (rs1546713) with susceptibility to age-related cataract in a Han Chinese population

AIM

To explore the susceptible association between the insulin-like growth factor-1 receptor (IGF1R) single nucleotide polymorphism (SNP) and age-related cataract (ARC), and investigate the underlying mechanisms in human lens epithelium (HLE) cells.

METHODS

Totally 1190 unrelated participants, comprising 690 ARC patients and 500 healthy individuals in Han Chinese population were recruited and genotyped for target SNP. The χ ²-test was used to detect genotypic distribution between the patient and control groups and the logistic regression was performed to adjust the age and gender. Meanwhile, different biological experimental methods, such as cell counting kit 8 (CCK-8) assay, flow cytometry, quantitative real time polymerase chain reaction (Q-PCR) and Western blot, were used to detect cell viability, cell cycle progression and apoptosis in HLE cells or IGF1R knockdown HLE cells.

RESULTS

The rs1546713 in IGF1R gene was identified (P=0.046, OR: 1.606, 95%CI: 1.245-2.071), which shown a significant relevance with ARC risk under the dominant model. The results demonstrated that IGF1R knockdown inhibited cell proliferation by inducing cell cycle arrested at S phase and promoting apoptosis. Mechanistically, the cell cycle blocked at S phase was linked with the alterations of cyclin A, cyclin B, cyclin E and P21. The pro-apoptosis function of IGF1R may related with stimulating the activation of Caspase-3 and altering the expression levels of apoptotic proteins, including Bcl-2, Bax and Caspase-3.

CONCLUSION

This study first report that IGF1R polymorphisms may affect susceptibility to ARCs in Han Chinese population and provide new clues to understand the pathogenic mechanism of ARCs. Notably, IGF1R is likely a potential target for ARC prevention and treatment.

Development of a drug-eluting intraocular lens to deliver epidermal growth factor receptor inhibitor gefitinib for posterior capsule opacification prophylaxis

PURPOSE

Different molecular targets, such as the epidermal growth factor receptor, have been identified for the prophylaxis of posterior capsule opacification. This led to the proposal of several drugs, yet drug delivery into the capsular bag remains challenging. The intraocular lens as a drug delivery device would provide a convenient method to allow drug release in the location needed. This is to evaluate the effect of a drug-eluting intraocular lens using an epidermal growth factor receptor inhibitor.

METHODS

Hydrophobic and hydrophilic intraocular lenses were coated with gefitinib using the dip coating technique. The cellular response on the modified intraocular lenses was tested in a human lens epithelial cell line (FHL-124) in an anterior segment model. Furthermore, modified intraocular lenses were implanted into human capsular bags ex vivo. Drug release was determined as well as the biocompatibility on human corneal endothelial cells. Unmodified intraocular lenses served as controls. In addition, immunofluorescence staining with fibronectin as a marker for fibrotic response was conducted.

RESULTS

Both coated hydrophilic and hydrophobic intraocular lenses could attenuate the cell growth of FHL-124 cells in the human capsular bag in comparison to the unmodified controls. Furthermore, gefitinib-soaked intraocular lenses showed a constant drug release over the first 10 days. No reduction in cell viability of corneal endothelial cells occurred. A decrease in fibronectin expression under gefitinib treatment could be observed.

CONCLUSION

In vitro epidermal growth factor receptor seems to be a valuable target for the prevention of posterior capsule opacification. The gefitinib-eluting intraocular lens in this study could inhibit cell growth in non-toxic concentrations.

The intraocular lens as a drug delivery device for an epidermal growth factor-Receptor inhibitor for prophylaxis of posterior capsule opacification

PURPOSE

Posterior capsule opacification (PCO) occurs as a common complication after cataract surgery. Erlotinib is an inhibitor of the epidermal growth factor-Receptor and reduces critical cellular events leading to PCO. In this in vitro study, Erlotinib-modified intraocular lenses (IOLs) employed as a drug delivery device have been evaluated for PCO prevention.

METHODS

The IC₅₀ concentration of Erlotinib was determined by using FHL-124 cells. For the human capsular bag model, 40 cadaver eyes underwent sham cataract surgery. Sixteen capsular bags were exposed to the IC₅₀ of Erlotinib. Intraocular lens (IOL) of three different materials was pharmacologically modified and tested in the anterior segment model and implanted into 24 capsular bags. To test for corneal toxicity, pairs of human cornea were exposed to high concentrations of Erlotinib and corneal endothelial cells (CEC) were exposed to the modified IOL. Release kinetics of Erlotinib from the IOL was measured.

RESULTS

IC₅₀ of Erlotinib was determined to be 10 μm. Erlotinib alone (p = 0.002) and when soaked into IOLs (p < 0.001) significantly increased the number of days needed until total cell coverage of the capsular bags in comparison with the control. Modified IOLs mitigated cell growth in the anterior segment model (p < 0.001). No short-term corneal toxicity was observed up to a concentration of 100 μm, and IOLs did not show toxicity on CEC. Erlotinib was released constantly from IOL.

CONCLUSION

Erlotinib might be of clinical relevance in PCO prophylaxis, as its short-term application induces a long-term deceleration of cellular growth. Erlotinib can be introduced into the eye via soaked IOLs.

EGFR-blockade with erlotinib reduces EGF and TGF-β2 expression and the actin-cytoskeleton which influences different aspects of cellular migration in lens epithelial cells

INTRODUCTION

After cataract surgery, residual lens epithelial cells migrate and proliferate within the capsular bag resulting in posterior capsule opacification (PCO). The up-regulation of TGF-β2, EGF and FGF-2 has been identified as a key factor in PCO pathogenesis leading to actin fiber assembly and alterations in the migration pattern. In this in vitro study, the influence of Erlotinib as a selective EGFR inhibitor is investigated on the cellular features indicated, which might promote a future clinical application.

METHODS

Expression of EGF, FGF-2 and TGF-β2 was measured using RT-PCR and ELISA in human lens epithelial cells (HLEC). Computational data of an in vitro time lapse microscopy assay were used for statistical analysis of single cell migration with a particular focus on cell-cell interaction; cell velocity distribution; and displacement before, during and after mitosis. The effect of Erlotinib on the actin-cytoskeleton was evaluated using Alexa Fluor 488 Phalloidin and epifluorescence microscopy.

RESULTS

EGF and TGF-β2 mRNA expression and protein levels are reduced by Erlotinib, while FGF-2 expression remained stable. Overall fluidity of cell-cell interaction is less in the presence of Erlotinib compared to the control and the velocity distribution across all cells becomes less uniform within the cell cluster. After mitosis, HLEC move significantly faster without EGFR inhibition, which can be completely blocked by Erlotinib. Furthermore, Erlotinib diminishes the amount of actin stress fibers and the stress fiber diameter.

CONCLUSION

As a novel effect of Erlotinib on HLEC, we describe the down-regulation of EGF and TGF-β2 expression, both are crucial factors for PCO development. Cellular movement displays complex alterations under EGFR inhibition, which is partly explained by actin fiber depletion. These findings further underline the role of Erlotinib in pharmacologic PCO prophylaxis.

Prognostic associations of insulin-like growth factor-1 receptor in primary uveal melanoma

OBJECTIVE

To study the association between immunoreactivity for insulin-like growth factor-1 receptor (IGF-1R) in primary ciliary body and choroidal melanoma and metastatic death in a consecutive, population-based data set.

DESIGN

Retrospective, consecutive, population-based cohort study.

PARTICIPANTS

A total of 167 patients with choroidal and ciliary body melanoma, enucleated from 1972 to 1981, with long-term survival data.

METHODS

Specimens were immunostained by using the avidin-biotinylated peroxidase complex method and polyclonal antibodies to IGF-1R. The percentage of tumour area that was immunopositive was recorded. Survival was assessed by Cox multivariate regression analysis.

RESULTS

The tumour area could be reliably measured from 129 (78%) of the 167 choroidal or ciliary body melanomas. More heavy pigmentation (p = 0.001), larger number of macrophages (p = 0.003) and higher microvascular density (p = 0.060) were associated with a higher percentage of tumour area that was immunopositive for IGF-1R, the reverse being true of extrascleral extension (p = 0.049). No significant association was observed with ciliary body extension, largest basal tumour diameter, cell type, mean diameter of the 10 largest nucleoli, and presence of extravascular matrix loops and networks (p = 0.61-0.96). The percentage of tumour area that was immunopositive for IGF-1R was not associated with survival.

CONCLUSIONS

In our data set, immunoreactivity for IGF-IR did not independently predict metastasis from primary uveal melanoma. Partial loss of antigenicity can not be ruled out as a confounding factor because no frozen sections were available. Results of previous studies have likewise been variable, suggesting that immunohistochemical determination of IGF-1R from formalin-fixed, paraffin-embedded specimens is not practical as a routine test.

The Etiology of Steroid Cataract

Steroid-induced posterior subcapsular cataracts (PSCs) exhibit three main distinctive characteristics: (i) association only with steroids possessing glucocorticoid activity, (ii) involvement of aberrant migrating lens epithelial cells, and (iii) a central posterior location. The first characteristic suggests a key role for glucocorticoid receptor activation and subsequent changes to the transcription of specific genes. Glucocorticoid receptor activation is associated in many cell types with proliferation, suppressed differentiation, a reduced susceptibility to apoptosis, altered transmembrane transport, and enhancement of reactive oxygen species activity. Glucocorticoids may be capable of inducing changes to the transcription of genes in lens epithelial cells that are related to many of these cellular processes. This review examines the various mechanisms that have been proposed to account for the development of PSC in the context of recent DNA array studies. Additionally, given that the glucocorticoid receptor can also engender wide-ranging indirect activities, glucocorticoids could also indirectly affect the lens through the responses of other cells within the ocular compartment and/or through effects on cells at more remote locations. These indirect mechanisms, which, for example, could be mediated through alterations to the intraocular levels of growth factors that normally orchestrate lens development and maintain lens homeostasis, are also discussed. Although the mechanism of steroid cataract induction remains unknown, glucocorticoid-induced gene transcription events in lens epithelial cells, and also other intraocular or systemic cells, likely interact to generate steroid cataracts. Finally, although evidence for glucocorticoid-protein adduct formation in the lens is inconclusive, the generation of such adducts cannot yet be discounted as a contributing factor and must necessarily be retained in discussions of the etiology of steroid cataract.

Effect of growth factors on proliferation and expression of growth factor receptors in a human lens epithelial cell line

PURPOSE

To investigate the effect of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor 1 (IGF-1), and transforming growth factor beta 2 (TGFbeta2) on proliferation of a human lens epithelial cell line (HLEC-SRA 01/04); the effect of bFGF and TGFbeta2 on proliferation of human lens epithelial cells (HLECs); and the expression of bFGF, EGF, IGF-1, and TGFbeta2 receptors in an HLEC-SRA 01/04 cell line.

SETTING

Department of Ophthalmology, University of Ulm, Ulm, Germany.

METHODS

Both HLEC and HLEC-SRA 01/04 were treated with 1 to 50 ng/mL bFGF and TGFbeta2) Additionally, HLEC-SRA 01/04 were cultured with EGF and IGF-1 at a concentration of 1 to 50 ng/mL for 48 hours in the presence of [3H]-thymidine. In all experiments, untreated serum-free negative controls were used. (3H)-thymidine incorporation as a direct measure of lens epithelial cell proliferation was assessed by liquid scintillation counting. The expression of bFGF, EGF, IGF-1, and TGFbeta2 receptors in HLEC-SRA 01/04 were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). Statistical analysis was performed using the 2-sample t test for the means.

RESULTS

Proliferation of HLECs was dose dependently induced by bFGF and TGFbeta2, showing maximum effects at 10 ng/mL (P = .0003) and at 50 ng/mL (P < .0001), respectively. Proliferation of HLEC-SRA 01/04 was also induced by bFGF, showing slight but significant effects (P < .03). Additionally, HLEC-SRA 01/04 proliferation was dose-dependently induced by EGF with a maximum effect at 5 ng/mL (P < .01), IGF-1 with a maximum effect at 5 ng/mL (P < .0001), and TGFbeta2 with a maximum effect at 10 ng/mL (P < .0001) compared with the control. The RT-PCR analysis revealed bFGF, EGF, IGF-1, and TGFbeta2 receptor expression in the HLEC-SRA 01/04 cell line.

CONCLUSIONS

The data showed that bFGF and TGFbeta2 are strong mitogens for HLEC. The HLEC-SRA 01/04 cell line derived from HLEC reacted to growth factors, with cell proliferation only to a lesser extent. Such quiescence of these cells, when compared with cells in primary culture, cannot be explained by the lack of respective receptors for growth factors. Further investigation of growth factor-induced responses of both cell types will provide new insight into the proliferative processes involved in postoperative secondary cataract formation.

Age-associated oxidative damage leads to absence of gamma-cystathionase in over 50% of rat lenses: relevance in cataractogenesis

Oxidative damage to lens proteins and glutathione depletion play a major role in the development of senile cataract. We previously found that a deficiency in gamma-cystathionase activity may be responsible for glutathione depletion in old lenses. The aims of this study were: (1) to investigate the mechanism that causes the age-related deficiency in gamma-cystathionase activity in the eye lens, and (2) to determine the role of gamma-cystathionase deficiency in cataractogenesis. Two populations of old rats were found, one (56%) whose lenses lacked gamma-cystathionase activity and the rest that exhibited detectable enzyme activity. gamma-Cystathionase protein was absent in lenses from old rats without gamma-cystathionase activity. Oxidative stress targeted gamma-cystathionase in the eye lens upon aging, since the enzyme contained more carbonyl groups in old lenses than in young ones. gamma-Cystathionase mRNA was also markedly reduced in old lenses, thus contributing to the age-associated deficiency in gamma-cystathionase. Inhibition of gamma-cystathionase activity caused glutathione depletion in lenses and led to cataractogenesis in vitro. In conclusion, the lack of gamma-cystathionase activity in over 50% of old lenses is due to decreased gene expression and proteolytic degradation of the oxidized enzyme. This results in a high risk for the development of senile cataract.

Activation of epidermal growth factor receptor causes astrocytes to form cribriform structures

Epidermal growth factor receptor (EGFR) is expressed in reactive astrocytes following injury in the CNS. However, the effects of activation of the EGFR pathway in astrocytes are not well established. In the present study, we demonstrate that activation of EGFR causes optic nerve astrocytes, as well as brain astrocytes, to form cribriform structures with cavernous spaces. Formation of the cribriform structures is dependent on new protein synthesis and cell proliferation. Platelet-derived growth factor and basic fibroblast growth factor were not effective. Smooth muscle cells and epithelial cells do not form cribriform structures in response to EGFR activation. The formation of the cribriform structures appears to be related to a guided migration of astrocytes and the expression of integrin beta1 and extracellular fibronectin in response to activation of EGFR. The EGFR pathway may be a specific, signal transduction pathway that regulates reactive astrocytes to form cavernous spaces in the glial scars following CNS injury and in the compressed optic nerve in glaucomatous optic nerve neuropathy.

Studies of the mitogen-activated protein kinases and phosphatidylinositol-3 kinase in the lens. 1. The mitogenic and stress responses

The current understanding of the cellular signal transduction system is that cells initially respond to outside stimuli, such as growth factors or neurotransmitters, through ligand binding to the respective growth factor receptors or the G-protein-coupled receptors, to initiate transduction of the stimulus. This is followed by a series of association-dissociation and phosphorylation-dephosphorylation processes among the components of a well-defined and intricate infrastructure between the cell membrane and the cytosolic protein kinases to activate and initiate nuclear target genes for cell proliferation, differentiation and other cellular functions. Although some past reports have indicated this signaling machinery is present in the lens, certain pathways, namely the mitogen-response pathway (Raf-MEK-ERK cascade), the stress-response pathways (p38 and SAPK/JNK cascades) and the survival pathway (PI-3K-Akt), have not been thoroughly explored in an intact lens. These pathways were studied using porcine lenses cultured under mitogenic (10 ngml(-1) growth factor) or osmotic stress (30 mM galactose) conditions to examine the cellular response in the epithelial layer, using unstimulated lenses as controls. It was found that all the key members in the Raf-MEK-ERK cascade and PI-3K-Akt cascade were present and that growth factors had a differential stimulatory effect on them. Basic-FGF was the most potent stimulator for ERK followed by EGF and IGF-1, while PDGFab and VEGF were less active. The opposite was true for their stimulatory effect on PI-3K. Hyperglycemic-induced osmotic stress stimulated p38 but not SAPK/JNK, while bFGF could stimulate SAPK/JNK but not p38. Both stimuli activated the Raf-MEK-ERK and PI-3K-Akt pathways. Osmotic-induced activation could be normalized using an aldose reductase inhibitor.

p53 regulates cell survival by inhibiting PIK3CA in squamous cell carcinomas

Interactions between the p53 and PI3K/AKT pathways play a significant role in the determination of cell death/survival. In benign cells these pathways are interrelated through the transcriptional regulation of PTEN by p53, which is required for p53-mediated apoptosis. PTEN exerts its effects by decreasing the phosphorylated AKT fraction, thereby diminishing prosurvival activities. However, the link between these pathways in cancer is not known. In this study, PIK3CA, encoding the p110alpha catalytic subunit of PI3K, is identified as an oncogene involved in upper aerodigestive tract (UADT) carcinomas. Simultaneous abnormalities in both pathways are rare in primary tumors, suggesting that amplification of PIK3CA and mutation of p53 are mutually exclusive events and either event is able to promote a malignant phenotype. Moreover, the negative effect of p53 induction on cell survival involves the transcriptional inhibition of PIK3CA that is independent of PTEN activity, as PTEN is not expressed in the primary tumors. Conversely, constitutive activation of PIK3CA results in resistance to p53-related apoptosis in PTEN deficient cells. Thus, p53 regulates cell survival by inhibiting the PI3K/AKT prosurvival signal independent of PTEN in epithelial tumors. This inhibition is required for p53-mediated apoptosis in malignant cells.

Age-related changes in levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2 in the rat inferior colliculus: implications for neural senescence

Brain-derived neurotrophic factor and fibroblast growth factor 2, and their respective binding sites, tyrosine kinase B receptor and fibroblast growth factor receptor 2, are known to regulate neurite outgrowth and antioxidant enzyme activity. Several studies suggest that brain-derived neurotrophic factor and fibroblast growth factor are contained in the inferior colliculus. Previous work in our laboratories revealed dendritic and synaptic losses in the inferior colliculus of aged Fischer-344 rats, along with coincident increases in lipid peroxidation possibly linked to a decrease in activity of antioxidant enzymes. In an effort to identify potential causal mechanisms underlying age-related synaptic and dendritic losses that occur in the inferior colliculus, the present study attempted to determine if inferior colliculus levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2 expression are altered with age. Immunocytochemistry was performed in the inferior colliculus, hippocampus and cerebellum of 3-month-old F344 rats to study distributions of the full-length and truncated isoforms of tyrosine kinase B receptor, and fibroblast growth factor receptor 2. The latter two brain regions served as positive controls. For all three antigens, immunolabeling was localized primarily in somata and proximal dendrites in all subdivisions of the inferior colliculus, and in the dentate gyrus and Ammon's horn of the hippocampus. In the cerebellum, the somata and dendrites of the Purkinje cells were also immunolabeled.A significant reduction in levels of the full-length form of tyrosine kinase B receptor in 18- and 25-month-old rats (respectively, approximately 20% and 30% relative to 3-month-olds) was revealed using western blot analyses. Inferior colliculus and hippocampal levels of the truncated form were modestly decreased ( approximately 7%) as well in the two older age groups. In contrast, levels of fibroblast growth factor receptor 2 in the inferior colliculus and hippocampus were elevated by approximately 35% in the two older age groups when compared to 3-month-olds. Changes in cerebellar levels of tyrosine kinase B receptor and fibroblast growth factor receptor 2, while similar to those in the inferior colliculus and hippocampus among the age groups, did not achieve statistical significance in this study. These findings give rise to the possibility that age-related reductions in tyrosine kinase B receptor levels could be a causal factor in the degenerative changes observed in the inferior colliculus of aged animals, including mitochondrial damage and dendritic regression. The observed increases in fibroblast growth factor receptor 2 levels may be compensatory to the increased oxidative stress. The effectiveness of the fibroblast growth factor receptor 2 response is questionable given the damage that occurs in the inferior colliculus and hippocampus of aged animals. However, the deficits could worsen in the absence of an increase in fibroblast growth factor receptor 2.