Expression of HB-EGF by retinal pigment epithelial cells in vitreoretinal proliferative disease

Endothelial Notch Signaling Regulates the Function of the Retinal Pigment Epithelial Barrier via EC Angiocrine Signaling

The outer blood-retina barrier (oBRB), comprises tightly connected retinal pigment epithelium (RPE) cells, Bruch's membrane, and choroid blood vessels, and is essential for retinal health and normal visual function. Disruption of the RPE barrier and its dysfunction can lead to retinal disorders such as age-related macular degeneration (AMD). In the present study, we investigated the essential role of choroid endothelial cells (ECs) in the RPE barrier formation process and its dysfunction. We discovered that ECs promoted RPE barrier formation through angiocrine signaling. Through blocking or activating endothelial Notch signaling and conducting experiments in vitro and in vivo, we confirmed that endothelial Notch signaling regulated the expression of heparin-binding epidermal growth factor (HBEGF) and consequently impacted the expression and activity of matrix metalloproteinases (MMP)-9 in RPE cells. This modulation influenced the RPE extracellular matrix deposition, tight junctions and RPE barrier function. In in vivo experiments, the intravitreal administration of recombinant HBEGF (r-HBEGF) alleviated the RPE barrier disruption induced by subretinal injection (SI) or laser treatment and also rescued RPE barrier disruption in endothelial Notch-deficient mice. Our results showed that the endothelial Notch signaling drove HBEGF expression through angiocrine signaling and effectively improved RPE barrier function by regulating the MMP-9 expression in RPE cells. It suggests that the modulation of Notch signaling in the choroidal endothelium may offer a novel therapeutic strategy for retinal degenerative diseases.

p38 MAPK priming boosts VSMC proliferation and arteriogenesis by promoting PGC1α-dependent mitochondrial dynamics

Vascular smooth muscle cell (VSMC) proliferation is essential for arteriogenesis to restore blood flow after artery occlusion, but the mechanisms underlying this response remain unclear. Based on our previous findings showing increased VSMC proliferation in the neonatal aorta of mice lacking the protease MT4-MMP, we aimed at discovering new players in this process. We demonstrate that MT4-MMP absence boosted VSMC proliferation in vitro in response to PDGF-BB in a cell-autonomous manner through enhanced p38 MAPK activity. Increased phospho-p38 in basal MT4-MMP-null VSMCs augmented the rate of mitochondrial degradation by promoting mitochondrial morphological changes through the co-activator PGC1α as demonstrated in PGC1α^−/− VSMCs. We tested the in vivo implications of this pathway in a novel conditional mouse line for selective MT4-MMP deletion in VSMCs and in mice pre-treated with the p38 MAPK activator anisomycin. Priming of p38 MAPK activity in vivo by the absence of the protease MT4-MMP or by anisomycin treatment led to enhanced arteriogenesis and improved flow recovery after femoral artery occlusion. These findings may open new therapeutic opportunities for peripheral vascular diseases.

Geniposide alleviates choroidal neovascularization by downregulating HB-EGF release from RPE cells by downregulating the miR-145-5p/NF-κB axis

Age-related macular degeneration (AMD), mainly wet AMD, is the major reason for nonreversible vision loss worldwide. Choroidal neovascularization (CNV) is a characteristic pathological manifestation of wet AMD. Stress or injury to the retinal pigment epithelium (RPE) induces proangiogenic factors that drive CNV. An iridoid glycoside extracted from the fruit of gardenia, geniposide (GEN) plays an antiangiogenic role. In this study, GEN inhibited the transcription and expression of heparin-binding epidermal growth factor (HB-EGF), a proangiogenic factor, in hypoxic RPE cells and a mouse laser-induced CNV model. Inhibition of glucagon-like peptide-1 receptor (GLP-1R), a GEN receptor blocker, eliminated the protective effect of GEN. Additionally, GEN decreased the transcription and expression of HB-EGF in hypoxia-exposed RPE cells by downregulating the miR-145-5p/NF-κB axis. Therefore, our research provides a promising novel strategy for wet AMD therapy.

Compatibility of intravitreally applied epidermal growth factor and amphiregulin

Introduction

To examine the compatibility of intravitreally injected epidermal growth factor (EGF) and amphiregulin as EGF family member.

Methods

Four rabbits (age: 4 months; body weight: 2.5 kg) received three intravitreal injections of EGF (100 ng) uniocularly in monthly intervals and underwent ocular photography, tonometry, biometry, and optical coherence tomography. After sacrificing the rabbits, the globes were histomorphometrically examined. In a second study part, eyes of 22 guinea pigs (age: 2–3 weeks) received two intravitreal administrations of amphiregulin (10 ng) or phosphate buffered solution (PBS) in 10-day interval, or were left untouched. Ten days after the second injection, the guinea pigs were sacrificed, the enucleated eyes underwent histological and immune-histological examinations.

Results

The rabbit eyes with EGF injections versus the contralateral untouched eyes did not show significant differences in intraocular pressure (7.5 ± 2.4 mmHg vs. 6.8 ± 2.2 mmHg; P = 0.66), retinal thickness (158 ± 5 µm vs. 158 ± 3 µm; P = 1.0), cell counts in the retinal ganglion cell layer (3.3 ± 1.7 cells/150 µm vs. 3.0 ± 1.4 cells/150 µm; P = 0.83), inner nuclear layer (46.4 ± 23.2 cells/150 µm vs. 39.6 ± 6.4 cells/150 µm; P = 0.61), and outer nuclear layer (215 ± 108 cells/150 µm vs. 202 ± 47 cells/150 µm; P = 0.83), or any apoptotic retinal cells. The guinea pig eyes injected with amphiregulin versus eyes with PBS injections did not differ (P = 0.72) in the degree of microglial activation, and both groups did not differ from untouched eyes in number of apoptotic retinal cells and retinal gliosis.

Conclusions

Intravitreal applications of EGF (100 ng) in rabbits nor intravitreal applications of amphiregulin (10 ng) in guinea pigs led to intraocular specific inflammation or any observed intraocular destructive effect. The findings support the notion of a compatibility of intraocular applied EGF and amphiregulin.

Oleic Acid, Cholesterol, and Linoleic Acid as Angiogenesis Initiators

The current study determined the natural angiogenic molecules using an unbiased metabolomics approach. A chick chorioallantoic membrane (CAM) model was used to examine pro- and antiangiogenic molecules, followed by gas chromatography-mass spectrometry (GCMS) analysis. Vessel formation was analyzed quantitatively using the angiogenic index (p < 0.05). At embryonic day one, a white streak or circle area was observed when vessel formation begins. GCMS analysis and database search demonstrated that angiogenesis may initiate when oleic, cholesterol, and linoleic acids increased in the area of angiogenic reactions. The gain of function study was conducted by the injection of cholesterol and oleic acid into a chick embryo to determine the role of each lipid in angiogenesis. We propose that oleic acid, cholesterol, and linoleic acid are natural molecules that set the platform for the initiation stage of angiogenesis before other proteins including the vascular endothelial growth factor, angiopoietin, angiotensin, and erythropoietin join as the angiome in sprout extension and vessel maturation.

Heparin-Binding Epidermal Growth Factor-Like Growth Factor as a Critical Mediator of Tissue Repair and Regeneration

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family. It contains an EGF-like domain as well as a heparin-binding domain that allows for interactions with heparin and cell-surface heparan sulfate. Soluble mature HB-EGF, a ligand of human epidermal growth factor receptors 1 and 4, is cleaved from the membrane-associated pro-HB-EGF by matrix metalloproteinase or a disintegrin and metalloproteinase in a process called ectodomain shedding. Signaling through human epidermal growth factor receptors 1 and 4 results in a variety of effects, including cellular proliferation, migration, adhesion, and differentiation. HB-EGF levels increase in response to different forms of injuries as well as stimuli, such as lysophosphatidic acid, retinoic acid, and 17β-estradiol. Because it is widely expressed in many organs, HB-EGF plays a critical role in tissue repair and regeneration throughout the body. It promotes cutaneous wound healing, hepatocyte proliferation after partial hepatectomy, intestinal anastomosis strength, alveolar regeneration after pneumonectomy, neurogenesis after ischemic injury, bladder wall thickening in response to urinary tract obstruction, and protection against ischemia/reperfusion injury to many cell types. Additionally, innovative strategies to deliver HB-EGF to sites of organ injury or to increase the endogenous levels of shed HB-EGF have been attempted with promising results. Harnessing the reparatory properties of HB-EGF in the clinical setting, therefore, may produce therapies that augment the treatment of various organ injuries.

Controlled microenvironments to evaluate chemotactic properties of cultured Müller glia

Emerging therapies have begun to evaluate the abilities of Müller glial cells (MGCs) to protect and/or regenerate neurons following retina injury. The migration of donor cells is central to many reparative strategies, where cells must achieve appropriate positioning to facilitate localized repair. Although chemical cues have been implicated in the MGC migratory responses of numerous retinopathies, MGC-based therapies have yet to explore the extent to which external biochemical stimuli can direct MGC behavior. The current study uses a microfluidics-based assay to evaluate the migration of cultured rMC-1 cells (as model MGC) in response to quantitatively-controlled microenvironments of signaling factors implicated in retinal regeneration: basic Fibroblast Growth factor (bFGF or FGF2); Fibroblast Growth factor 8 (FGF8); Vascular Endothelial Growth Factor (VEGF); and Epidermal Growth Factor (EGF). Findings indicate that rMC-1 cells exhibited minimal motility in response to FGF2, FGF8 and VEGF, but highly-directional migration in response to EGF. Further, the responses were blocked by inhibitors of EGF-R and of the MAPK signaling pathway. Significantly, microfluidics data demonstrate that changes in the EGF gradient (i.e. change in EGF concentration over distance) resulted in the directional chemotactic migration of the cells. By contrast, small increases in EGF concentration, alone, resulted in non-directional cell motility, or chemokinesis. This microfluidics-enhanced approach, incorporating the ability both to modulate and asses the responses of motile donor cells to a range of potential chemotactic stimuli, can be applied to potential donor cell populations obtained directly from human specimens, and readily expanded to incorporate drug-eluting biomaterials and combinations of desired ligands.

Cigarette smoke-induced EGFR activation promotes epithelial mesenchymal migration of human retinal pigment epithelial cells through regulation of the FAK-mediated Syk/Src pathway

Epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells is inevitable change of age‑related macular degeneration (AMD). Smoking is a major risk factor for the development of EMT in several diseases, including lung cancer. Cigarette smoke‑induced stress promotes the production of epidermal growth factor (EGF) in RPE cells. However, the underlying signaling pathways induced by aberrant EGF receptor (EGFR) expression in cigarette smoke-exposed RPE cells remain largely unknown. In the present study, the morphological transformation and production of EMT-associated cytokines were investigated to analyze the effect of smoking on the retina. Furthermore, EGF‑treated or cigarette smoke‑exposed RPE cells, as well as the downstream targets of EGFR, were investigated to identify the key molecules involved in EMT of cigarette smoke‑stimulated RPE cells via immunoblotting. Exposure of RPE cells to cigarette smoke extract (CSE) induced secretion of VEGF and TGF‑β1, and increased the expression of EMT markers. CSE‑mediated focal adhesion kinase (FAK) activation resulted in the phosphorylation and activation of spleen associated tyrosine kinase (Syk)/Src proto‑oncogene, non‑receptor tyrosine kinase (Src), leading to migration and invasion of RPE cells. Knockdown of FAK or pharmacological inhibition of Syk/Src abrogated CSE‑mediated VEGF and TGF‑β1 production and blocked the phosphorylation of Smad2/3 in CSE‑stimulated RPE cells. Erlotinib (an EGFR inhibitor) suppressed EGF and CSE‑mediated switch from an epithelial to mesenchymal phenotype. Baicalein, an inhi-bitor of 12/15‑lipooxygenase, also efficiently suppressed CSE‑induced EMT processes by inhibiting EGFR‑associated downstream signaling transduction. The results identified a novel signaling pathway mediated by EGFR in CSE‑activated RPE cells, and suggest baicalein as a potential new therapeutic drug for CSE‑associated retinopathy.

Bevacizumab Injection in Patients with Neovascular Age-Related Macular Degeneration Increases Angiogenic Biomarkers

Purpose

To evaluate the expression of 19 angiogenic biomarkers in the aqueous humor before and after intravitreal bevacizumab injection (IVB) in eyes with neovascular age-related macular degeneration (AMD).

Design

Prospective, noncomparative, interventional case series.

Participants

Twenty-three eyes of 23 treatment-naïve patients with choroidal neovascularization (CNV) secondary to neovascular AMD.

Methods

Eyes were diagnosed with CNV secondary to neovascular AMD and were treated with 3 monthly IVBs. Aqueous humor samples were obtained by anterior chamber paracentesis at baseline and immediately before each intravitreal bevacizumab injection.

Main Outcome Measures

Aqueous humor levels of 19 angiogenic biomarkers (angiopoietin 2, bone morphogenetic protein 9 [BMP-9], epidermal growth factor [EGF], endoglin, endothelin 1, fibroblast growth factor [FGF]-1 and FGF-2, follistatin, granulocyte colony-stimulating factor [GCSF], heparin-binding EGF-like growth factor [HB-EGF], hepatocyte growth factor [HGF], interleukin 8, leptin, placental growth factor [PLGF], vascular endothelial growth factor [VEGF]-A, VEGF-C, VEGF-D, and tissue inhibitor of metalloproteinases [TIMP]-1 and TIMP-2) were measured. Best-corrected visual acuity (BCVA), spectral-domain OCT parameters, and intraocular pressure also were evaluated.

Results

Baseline aqueous VEGF-A expression was elevated in all study eyes before treatment initiation. A statistically significant decrease of VEGF-A was observed at the 1- and 2-month follow-ups. A statistically significant increased concentration was observed in 7 biomarkers: VEGF-C, angiopoietin 2, endothelin 1, follistatin, HB-EGF, HGF, and interleukin 8. The other 11 study biomarker levels (VEGF-D, BMP-9, EGF, endoglin, FGF-1, FGF-2, GCSF, leptin, PLGF, TIMP-1, and TIMP-2) did not show any significant difference during follow-up. The BCVA statistically improved significantly at 2 months. Spectral-domain OCT parameters improved significantly at all follow-ups. Mean intraocular pressure values were not statistically different during the study period.

Conclusions

Despite a decrease in VEGF-A, the aqueous levels of VEGF-C, angiopoietin 2, endothelin 1, follistatin, HB-EGF, HGF, and interleukin 8 increased significantly after intravitreal injection of bevacizumab. These upregulated angiogenic biomarkers may represent new therapeutic targets in exudative AMD.

Both Autocrine Signaling and Paracrine Signaling of HB-EGF Enhance Ocular Neovascularization

OBJECTIVE

The incidence of blindness is increasing because of the increase in abnormal ocular neovascularization. Anti-VEGF (vascular endothelial growth factor) therapies have led to good results, although they are not a cure for the blindness. The purpose of this study was to determine what role HB-EGF (heparin-binding epidermal growth factor-like growth factor) plays in ocular angiogenesis.

APPROACH AND RESULTS

We examined the role played by HB-EGF in ocular neovascularization in 2 animal models of neovascularization: laser-induced choroidal neovascularization (CNV) and oxygen-induced retinopathy. We also studied human retinal microvascular endothelial cells in culture. Our results showed that the neovascularization was decreased in both the CNV and oxygen-induced retinopathy models in HB-EGF conditional knockout mice compared with that in wild-type mice. Moreover, the expressions of HB-EGF and VEGF were increased after laser-induced CNV and oxygen-induced retinopathy, and their expression sites were located around the neovascular areas. Exposure of human retinal microvascular endothelial cells to HB-EGF and VEGF increased their proliferation and migration, and CRM-197 (cross-reactive material-197), an HB-EGF inhibitor, decreased the HB-EGF-induced and VEGF-induced cell proliferation and migration. VEGF increased the expression of HB-EGF mRNA. VEGF-dependent activation of EGFR (epidermal growth factor receptor)/ERK1/2 (extracellular signal-regulated kinase 1/2) signaling and cell proliferation of endothelial cells required stimulation of the ADAM17 (a disintegrin and metalloprotease) and ADAM12. CRM-197 decreased the grades of the fluorescein angiograms and size of the CNV areas in marmoset monkeys.

CONCLUSIONS

These findings suggest that HB-EGF plays an important role in the development of CNV. Therefore, further investigations of HB-EGF are needed as a potential therapeutic target in the treatment of exudative age-related macular degeneration.

Retinal and choroidal angiogenesis: a review of new targets

Retinal and choroidal neovascularization are a major cause of significant visual impairment, worldwide. Understanding the various factors involved in the accompanying physiopathology is vital for development of novel treatments, and most important, for preserving patient vision. The intraocular use of anti-vascular endothelial growth factor therapeutics has improved management of the retinal and choroidal neovascularization but some patients do not respond, suggesting other vascular mediators may also contribute to ocular angiogenesis. Several recent studies examined possible new targets for future anti-angiogenic therapies. Potential targets of retinal and choroidal neovascularization therapy include members of the platelet-derived growth factor family, vascular endothelial growth factor sub-family, epidermal growth factor family, fibroblast growth factor family, transforming growth factor-β superfamily (TGF-β1, activins, follistatin and bone morphogenetic proteins), angiopoietin-like family, galectins family, integrin superfamily, as well as pigment epithelium derived factor, hepatocyte growth factor, angiopoietins, endothelins, hypoxia-inducible factors, insulin-like growth factors, cytokines, matrix metalloproteinases and their inhibitors and glycosylation proteins. This review highlights current antiangiogenic therapies under development, and discusses future retinal and choroidal pro- and anti-angiogenic targets as wells as the importance of developing of new drugs.

Osmotic Induction of Angiogenic Growth Factor Expression in Human Retinal Pigment Epithelial Cells

BACKGROUND

Although systemic hypertension is a risk factor of age-related macular degeneration, antihypertensive medications do not affect the risk of the disease. One condition that induces hypertension is high intake of dietary salt resulting in increased blood osmolarity. In order to prove the assumption that, in addition to hypertension, high osmolarity may aggravate neovascular retinal diseases, we determined the effect of extracellular hyperosmolarity on the expression of angiogenic cytokines in cultured human retinal pigment epithelial (RPE) cells.

METHODOLOGY/PRINCIPAL FINDINGS

Hyperosmolarity was induced by the addition of 100 mM NaCl or sucrose to the culture medium. Hypoxia and oxidative stress were induced by the addition of the hypoxia mimetic CoCl2 and H2O2, respectively. Alterations in gene expression were determined with real-time RT-PCR. Secretion of bFGF was evaluated by ELISA. Cell viability was determined by trypan blue exclusion. Nuclear factor of activated T cell 5 (NFAT5) expression was knocked down with siRNA. Hyperosmolarity induced transcriptional activation of bFGF, HB-EGF, and VEGF genes, while the expression of other cytokines such as EGF, PDGF-A, TGF-β1, HGF, and PEDF was not or moderately altered. Hypoxia induced increased expression of the HB-EGF, EGF, PDGF-A, TGF-β1, and VEGF genes, but not of the bFGF gene. Oxidative stress induced gene expression of HB-EGF, but not of bFGF. The hyperosmotic expression of the bFGF gene was dependent on the activation of p38α/β MAPK, JNK, PI3K, and the transcriptional activity of NFAT5. The hyperosmotic expression of the HB-EGF gene was dependent on the activation of p38α/β MAPK, ERK1/2, and JNK. The hyperosmotic expression of bFGF, HB-EGF, and VEGF genes was reduced by inhibitors of TGF-β1 superfamily activin receptor-like kinase receptors and the FGF receptor kinase, respectively. Hyperosmolarity induced secretion of bFGF that was reduced by inhibition of autocrine/paracrine TGF-β1 signaling and by NFAT5 siRNA, respectively. Hyperosmolarity decreased the viability of the cells; this effect was not altered by exogenous bFGF and HB-EGF. Various vegetable polyphenols (luteolin, quercetin, apigenin) inhibited the hyperosmotic expression of bFGF, HB-EGF, and NFAT5 genes.

CONCLUSION

Hyperosmolarity induces transcription of bFGF and HB-EGF genes, and secretion of bFGF from RPE cells. This is in part mediated by autocrine/paracrine TGF-β1 and FGF signaling. It is suggested that high intake of dietary salt resulting in osmotic stress may aggravate neovascular retinal diseases via stimulation of the production of angiogenic factors in RPE cells, independent of hypertension.

Directional protein secretion by the retinal pigment epithelium: roles in retinal health and the development of age-related macular degeneration

The structural and functional integrity of the retinal pigment epithelium (RPE) is fundamental for maintaining the function of the neuroretina. These specialized cells form a polarized monolayer that acts as the retinal–blood barrier, separating two distinct environments with highly specialized functions: photoreceptors of the neuroretina at the apical side and Bruch's membrane/highly vascularized choriocapillaris at the basal side. The polarized nature of the RPE is essential for the health of these two regions, not only in nutrient and waste transport but also in the synthesis and directional secretion of proteins required in maintaining retinal homoeostasis and function. Although multiple malfunctions within the RPE cells have been associated with development of age-related macular degeneration (AMD), the leading cause of legal blindness, clear causative processes have not yet been conclusively characterized at the molecular and cellular level. This article focuses on the involvement of directionally secreted RPE proteins in normal functioning of the retina and on the potential association of incorrect RPE protein secretion with development of AMD. Understanding the importance of RPE polarity and the correct secretion of essential structural and regulatory components emerge as critical factors for the development of novel therapeutic strategies targeting AMD.

Differential expression of the ADAMs in developing chicken retina

The expression patterns of the seven members of the ADAM (a disintegrin and metalloprotease) family, ADAM9, ADAM10, ADAM12, ADAM13, ADAM17, ADAM22, and ADAM23 were analyzed in the developing chicken retina by in situ hybridization and immunohistochemistry. Results show that each individual ADAM is expressed and regulated spatiotemporally in the developing retinal layers. ADAM9, ADAM10 and ADAM17 are widely expressed in the differential layers of the retina throughout the whole embryonic period, while ADAM12 and ADAM13 are mainly expressed in the ganglion cell layer at a later stage. ADAM22 and ADAM23 are restricted to the inner nuclear layer and the ganglion cell layer at a later stage. Furthermore, ADAM10 protein is co-expressed with the four members of the classic cadherins, N-cadherin, R-cadherin, cadherin-6B and cadherin-7 in distinct retinal layers. Therefore, the differential expression of the investigated ADAMs in the developing retina suggests the contribution of them to the retina development.

Pathological neovascularization is reduced by inactivation of ADAM17 in endothelial cells but not in pericytes

RATIONALE

Pathological neovascularization is a critical component of diseases such as proliferative retinopathies, cancer and rheumatoid arthritis, yet much remains to be learned about the underlying causes. Previous studies showed that vascular endothelial growth factor (VEGF)-A activates the membrane-anchored metalloproteinase ADAM17 (a disintegrin and metalloproteinase 17) in endothelial cells, thereby stimulating crosstalk between VEGF receptor 2 and extracellular signal-regulated kinase. These findings raised interesting questions about the role of ADAM17 in angiogenesis and neovascularization in vivo.

OBJECTIVE

The objective of this study was to inactivate ADAM17 in endothelial cells or in pericytes to determine how this affects developmental angiogenesis, pathological retinal neovascularization and heterotopic tumor growth.

METHODS AND RESULTS

We generated animals in which floxed ADAM17 was removed by Tie2-Cre in endothelial cells, or by smooth muscle (sm) Cre in smooth muscle cells and pericytes. There were no evident developmental defects in either conditional knockout strain, but pathological retinal neovascularization and growth of heterotopically injected tumor cells was reduced in Adam17flox/flox/Tie2-Cre mice, although not in Adam17flox/flox/sm-Cre mice. Moreover, lack of ADAM17 in endothelial cells decreased ex vivo chord formation, and this could be largely restored by addition of the ADAM17 substrate HB-EGF (heparin-binding epidermal growth factor-like growth factor). Finally we found that ADAM17 is important for the VEGF receptor 2 stimulated processing of several receptors with known functions in endothelial cell biology.

CONCLUSIONS

These results provide the first evidence for a role for ADAM17 in pathological neovascularization in vivo. Because ADAM17 does not appear to be required for normal developmental angiogenesis or vascular homeostasis, it could emerge as a good target for treatment of pathological neovascularization.

Gene expression profiling of TGFbeta2- and/or BMP7-treated trabecular meshwork cells: Identification of Smad7 as a critical inhibitor of TGF-beta2 signaling

A distinct structural change in the trabecular meshwork (TM) of patients with primary open-angle glaucoma (POAG) is the increase in fibrillar extracellular matrix (ECM) in the juxtacanalicular region of the TM. Transforming growth factor (TGF)-beta2 signaling may be involved, as TGF-beta2 is significantly increased in the aqueous humor of patients with POAG. In cultured human TM cells, TGF-beta2 causes an increase in ECM deposition, an effect that is blunted or prevented, if BMP7 is added in combination with TGF-beta2. In order to know more about the signaling network that is induced in HTM cells treated with BMP7, TGF-beta2 or the combination of both factors, we identified differentially regulated genes by microarray analysis, and confirmed selected genes by quantitative RT-PCR, Western blotting, or immunohistochemistry. We observed multiple effects of both TGF-beta2 and BMP7 on the expression of a considerable number of genes involved in growth factor signaling, ECM structure and turnover, and modification of the cytoskeleton. Among the genes that were found to be regulated were CAPZA1, CDC42BPB, EFEMP1, FGF5, FSTL3, HBEGF, LTBP1, LTBP2, MATN2, NRP1, SERPINE1, SH3MD1, SMTN, SMAD7, TFPI2, TNFAIP6, and VEGF. Since SMAD7 encodes for Smad7, an inhibitory Smad that acts in a negative-feedback loop to inhibit TGF-beta activity, we silenced Smad7 mRNA in cultured human TM cells by a specific small interfering RNA. Silencing of its mRNA caused a substantial knock down of Smad7 in TM cells. Following combined BMP7/TGF-beta2 treatment, the antagonizing effect of BMP7 on TGF-beta2-induced CTGF expression was abolished. We conclude that Smad7 is the key molecular switch that inhibits TGF-beta2 signaling, and mediates the blunting effects of BMP7 on TGF-beta2 in TM cells. A therapeutic modulation of Smad7 might be a promising approach to influence ECM turnover in the TM and to treat POAG.

Cross talk between c-Met and epidermal growth factor receptor during retinal pigment epithelial wound healing

PURPOSE

The authors sought to determine how hepatocyte growth factor (HGF) receptor c-Met and epidermal growth factor receptor (EGFR) cross talk in response to injury in human ARPE-19 cells.

METHODS

A scratch wound was made on a cell monolayer of ARPE-19 cells using a sequence-comb or a pipet tip, and it was allowed to heal in the presence or absence of HGF and heparin-binding EGF-like growth factor (HB-EGF). The activation of EGFR was analyzed by immunoprecipitation with EGFR antibody, followed by Western blotting with phosphotyrosine-specific antibody. Phosphorylation of extracellular signal-regulated kinase (ERK) and AKT (a major substrate of phosphatidylinositol 3'-kinase (PI3K) was assessed by Western blotting. The release of c-Met ectodomain into the culture media was determined by Western blotting using an antibody against the extracellular region. Cell migration was assessed by Boyden chamber migration assay.

RESULTS

ARPE-19 cells underwent spontaneous wound healing in basal medium, and exogenously added HB-EGF and HGF significantly enhanced wound closure. Basal and growth factor-enhanced wound closures were attenuated but not slowed by hydroxyurea, a cell proliferation inhibitor. RPE cells expressed all four erbBs, and wounding induced EGFR transactivation and downstream ERK and PI3K phosphorylation in ARPE-19 cells. HGF also induced EGFR tyrosine phosphorylation. The EGFR kinase inhibitor AG1478 blocked wound- and HGF-stimulated EGFR transactivation and attenuated spontaneous and growth factor-induced wound closure. Wounding and EGFR ligands induced the release of c-Met into the culture media. Moreover, pretreatment of cells with HB-EGF impaired ARPE-19 migration toward HGF in a matrix metalloproteinase inhibitor-sensitive manner.

CONCLUSIONS

EGFR modulates HGF/c-Met activity by inducing c-Met ectodomain shedding, and HGF/c-Met transactivates EGFR, leading to an enhanced activation of downstream signaling pathways. Cross talk between EGFR and c-Met may play a key role in regulating RPE cell migration, proliferation, and wound healing.

Cross talk between c-Met and epidermal growth factor receptor during retinal pigment epithelial wound healing

PURPOSE

The authors sought to determine how hepatocyte growth factor (HGF) receptor c-Met and epidermal growth factor receptor (EGFR) cross talk in response to injury in human ARPE-19 cells.

METHODS

A scratch wound was made on a cell monolayer of ARPE-19 cells using a sequence-comb or a pipet tip, and it was allowed to heal in the presence or absence of HGF and heparin-binding EGF-like growth factor (HB-EGF). The activation of EGFR was analyzed by immunoprecipitation with EGFR antibody, followed by Western blotting with phosphotyrosine-specific antibody. Phosphorylation of extracellular signal-regulated kinase (ERK) and AKT (a major substrate of phosphatidylinositol 3'-kinase (PI3K) was assessed by Western blotting. The release of c-Met ectodomain into the culture media was determined by Western blotting using an antibody against the extracellular region. Cell migration was assessed by Boyden chamber migration assay.

RESULTS

ARPE-19 cells underwent spontaneous wound healing in basal medium, and exogenously added HB-EGF and HGF significantly enhanced wound closure. Basal and growth factor-enhanced wound closures were attenuated but not slowed by hydroxyurea, a cell proliferation inhibitor. RPE cells expressed all four erbBs, and wounding induced EGFR transactivation and downstream ERK and PI3K phosphorylation in ARPE-19 cells. HGF also induced EGFR tyrosine phosphorylation. The EGFR kinase inhibitor AG1478 blocked wound- and HGF-stimulated EGFR transactivation and attenuated spontaneous and growth factor-induced wound closure. Wounding and EGFR ligands induced the release of c-Met into the culture media. Moreover, pretreatment of cells with HB-EGF impaired ARPE-19 migration toward HGF in a matrix metalloproteinase inhibitor-sensitive manner.

CONCLUSIONS

EGFR modulates HGF/c-Met activity by inducing c-Met ectodomain shedding, and HGF/c-Met transactivates EGFR, leading to an enhanced activation of downstream signaling pathways. Cross talk between EGFR and c-Met may play a key role in regulating RPE cell migration, proliferation, and wound healing.