Integrin alpha5beta1 mediates attachment, migration, and proliferation in human retinal pigment epithelium: relevance for proliferative retinal disease

Induction of apoptosis by cannabidiol and its main metabolites in human Leydig cells

Cannabidiol (CBD) is one of the most prevalent and abundant cannabinoids extracted from the plant Cannabis sativa. CBD has been reported to induce male reproductive toxicity in animal models. In this study, we examined the effects of CBD and its main metabolites, 7-carboxy-CBD and 7-hydroxy-CBD, on primary human Leydig cells, which play a crucial role in male reproductive health. Our results showed that CBD, at concentrations below the Bayesian benchmark dose (BMD)50, inhibited the growth of human Leydig cells by arresting the cell cycle at G1/S transition, disrupting cell cycle regulators, and decreasing DNA synthesis. Concentration-response transcriptomic profiling identified that apoptosis was one of the top biological processes significantly affected by treatment with CBD for 24 h. The occurrence of apoptosis was confirmed by increased activation of caspase-3/7 and an increased proportion of annexin V and propidium iodide (PI)-positive cells. Similar to CBD, both 7-carboxy-CBD and 7-hydroxy-CBD decreased cell viability and induced apoptosis after treatment for 24 h. 7-Hydroxy-CBD and 7-carboxy-CBD showed lower cytotoxicity than CBD, and 7-carboxy-CBD had the lowest cytotoxicity among the three compounds. Our findings revealed that CBD and its main metabolites can cause adverse effects on primary human Leydig cells.

Endogenous Galectin-1 Modulates Cell Biological Properties of Immortalized Retinal Pigment Epithelial Cells In Vitro

In the eye, an increase in galectin-1 is associated with various chorioretinal diseases, in which retinal pigment epithelium (RPE) cells play a crucial role in disease development and progression. Since little is known about the function of endogenous galectin-1 in these cells, we developed a galectin-1-deficient immortalized RPE cell line (ARPE-19-LGALS1-/-) using a sgRNA/Cas9 all-in-one expression vector and investigated its cell biological properties. Galectin-1 deficiency was confirmed by Western blot analysis and immunocytochemistry. Cell viability and proliferation were significantly decreased in ARPE-19-LGALS1-/- cells when compared to wild-type controls. Further on, an increased attachment of galectin-1-deficient RPE cells was observed by cell adhesion assay when compared to control cells. The diminished viability and proliferation, as well as the enhanced adhesion of galectin-1-deficient ARPE-19 cells, could be blocked, at least in part, by the additional treatment with human recombinant galectin-1. In addition, a significantly reduced migration was detected in ARPE-19-LGALS1-/- cells. In comparison to control cells, galectin-1-deficient RPE cells had enhanced expression of sm-α-actin and N-cadherin, whereas expression of E-cadherin showed no significant alteration. Finally, a compensatory expression of galectin-8 mRNA was observed in ARPE-19-LGALS1-/- cells. In conclusion, in RPE cells, endogenous galectin-1 has crucial functions for various cell biological processes, including viability, proliferation, migration, adherence, and retaining the epithelial phenotype.

Targeting integrin α5β1 in urological tumors: opportunities and challenges

Urological tumors, such as prostate cancer, renal cell carcinoma, and bladder cancer, have shown a significant rise in prevalence in recent years and account for a significant proportion of malignant tumors. It has been established that metastasis to distant organs caused by urological tumors is the main cause of death, although the mechanisms underlying metastasis have not been fully elucidated. The fibronectin receptor integrin α5β1 reportedly plays an important role in distant metastasis and is closely related to tumor development. It is widely thought to be an important cancer mediator by interacting with different ligands, mediating tumor adhesion, invasion, and migration, and leading to immune escape. In this paper, we expound on the relationship and regulatory mechanisms of integrin α5β1 in these three cancers. In addition, the clinical applications of integrin α5β1 in these cancers, especially against treatment resistance, are discussed. Last but not least, the possibility of integrin α5β1 as a potential target for treatment is examined, with new ideas for future research being proposed.

The Integrin Pathway Partially Mediates Stretch-Induced Deficits in Primary Rat Microglia

Stretch-injured microglia display significantly altered morphology, function and inflammatory-associated gene expression when cultured on a synthetic fibronectin substrate. However, the mechanism by which stretch induces these changes is unknown. Integrins, such as α5β1, mediate microglial attachment to fibronectin via the RGD binding peptide; following integrin ligation the integrin-associated signaling enzyme, focal adhesion kinase (FAK), autophosphorylates tyrosine residue 397 and mediates multiple downstream cellular processes. We therefore hypothesize that blocking the RGD binding/integrin pathway with a commercially available RGD peptide will mimic the stretch-induced morphological alterations and functional deficits in microglia. Further, we hypothesize that upregulation of stretch-inhibited downstream integrin signaling will reverse these effects. Using primary rat microglia, we tested the effects of RGD binding peptide and a FAK activator on cellular function and structure and response to stretch-injury. Similar to injured cells, RGD peptide administration significantly decreases media nitric oxide (NO) levels and iNOS expression and induced morphological alterations and migratory deficits. While stretch-injury and RGD peptide administration decreased phosphorylation of the tyrosine 397 residue on FAK, 20 nM of ZINC 40099027, an activator specific to the tyrosine 397 residue, rescued the stretch-induced decrease in FAK phosphorylation and ameliorated the injury-induced decrease in media NO levels, iNOS expression and inflammatory associated gene expression. Additionally, treatment alleviated morphological changes observed after stretch-injury and restored normal migratory behavior to control levels. Taken together, these data suggest that the integrin/FAK pathway partially mediates the stretch-injured phenotype in microglia, and may serve as a pathway to modulate microglial responses.

Above the Matrix: Functional Roles for Apically Localized Integrins

Integrins are transmembrane proteins that are most typically thought of as integrating adhesion to the extracellular matrix with intracellular signaling and cell regulation. Traditionally, integrins are found at basolateral and lateral cell surfaces where they facilitate binding to the ECM and intercellular adhesion through cytosolic binding partners that regulate organization of actin microfilaments. However, evidence is accumulating that integrins also are apically localized, either endogenously or due to an exogenous stimulus. Apically localized integrins have been shown to regulate several processes by interacting with proteins such as connexins, tight junction proteins, and polarity complex proteins. Integrins can also act as receptors to mediate endocytosis. Here we review these newly appreciated roles for integrins localized to the apical cell surface.

FHL-1 interacts with human RPE cells through the α5β1 integrin and confers protection against oxidative stress

Retinal pigment epithelial (RPE) cells that underlie the neurosensory retina are essential for the maintenance of photoreceptor cells and hence vision. Interactions between the RPE and their basement membrane, i.e. the inner layer of Bruch's membrane, are essential for RPE cell health and function, but the signals induced by Bruch's membrane engagement, and their contributions to RPE cell fate determination remain poorly defined. Here, we studied the functional role of the soluble complement regulator and component of Bruch's membrane, Factor H-like protein 1 (FHL-1). Human primary RPE cells adhered to FHL-1 in a manner that was eliminated by either mutagenesis of the integrin-binding RGD motif in FHL-1 or by using competing antibodies directed against the α5 and β1 integrin subunits. These short-term experiments reveal an immediate protein-integrin interaction that were obtained from primary RPE cells and replicated using the hTERT-RPE1 cell line. Separate, longer term experiments utilising RNAseq analysis of hTERT-RPE1 cells bound to FHL-1, showed an increased expression of the heat-shock protein genes HSPA6, CRYAB, HSPA1A and HSPA1B when compared to cells bound to fibronectin (FN) or laminin (LA). Pathway analysis implicated changes in EIF2 signalling, the unfolded protein response, and mineralocorticoid receptor signalling as putative pathways. Subsequent cell survival assays using H2O2 to induce oxidative stress-induced cell death suggest hTERT-RPE1 cells had significantly greater protection when bound to FHL-1 or LA compared to plastic or FN. These data show a non-canonical role of FHL-1 in protecting RPE cells against oxidative stress and identifies a novel interaction that has implications for ocular diseases such as age-related macular degeneration.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

Extracellular matrix and oxidative stress regulate human retinal pigment epithelium growth

Age-related macular degeneration (AMD), the most common cause of vision loss with ageing, is characterised by degeneration of the photoreceptors and retinal pigment epithelium (RPE) and changes in the extracellular matrix (ECM) underlying the RPE. The pathogenesis of AMD is still not fully understood. In this study we investigated the in vitro growth and function of primary human RPE cells in response to different ECM substrates, including nitrite-modified ECM. We initially confirmed the presence of disorganised retinal glial and photoreceptor cells, marked retinal cytoplasmic and Bruch's membrane expression of nitro-tyrosine (an oxidative stress marker) and increased numbers of Iba1⁺ macrophages/microglia in human donor eye sections (aged and AMD) using multi-marker immunohistochemistry (n = 3). Concurrently, we utilised two-photon microscopy to reveal topographical changes in flatmounts of RPE-associated ECM and in the underlying choroid of aged and AMD donor eyes (n = 3). To recapitulate these observations in vitro, we then used primary human RPE cells to investigate how different ECM proteins, including nitrite cross-linked RPE-secreted ECM, modified RPE cell growth and function. Collagen I or IV increased RPE attachment and spreading two-to three-fold, associated with significantly increased cell migration and proliferation, consistent with a preferential interaction with these matrix substrates. Primary human RPE cells grown on collagen I and IV also showed increased secretion of pro-inflammatory cytokines, MCP-1 and IL-8. Nitrite-modification of RPE-secreted ECM (simulating ageing of Bruch's membrane) significantly reduced in vitro RPE attachment to the ECM and this was mitigated with collagen IV coating of the modified ECM. Taken together, our observations confirm the importance of RPE-ECM interactions for normal RPE growth and function, and for inducing RPE secretion of pro-inflammatory cytokines. Furthermore, the findings are consistent with ageing and/or oxidative stress-induced disruption of RPE-ECM interactions contributing to the pathogenesis of AMD.

Retinal pigment epithelium polarity in health and blinding diseases

The polarized phenotype of the retinal pigment epithelium is crucial for the outer retina-blood barrier and support of photoreceptors and underlying choroid, and its disruption plays a central role in degenerative retinopathies. Although the mechanisms of polarization remain mostly unknown, they are fundamental for homeostasis of the outer retina. Recent research is revealing a growing picture of interconnected tissues in the outer retina, with the retinal pigment epithelium at the center. This review discusses how elements of epithelial polarity relate to emerging apical interactions with the neural retina, basolateral cross-talk with the underlying Bruch's membrane and choriocapillaris, and tight junction biology. An integrated view of outer retina physiology is likely to provide insights into the pathogenesis of blinding diseases.

ATN-161 as an Integrin α5β1 Antagonist Depresses Ocular Neovascularization by Promoting New Vascular Endothelial Cell Apoptosis

BACKGROUND ATN-161 (Ac-PHSCN-NH2), an antagonist of integrin α5β1, has shown an important influence in inhibiting tumor angiogenesis and metastasis of other tumor types. However, the mechanism of action of ATN-161 and whether it can inhibit ocular neovascularization (NV) are unclear. This study investigated the role of ATN-161 in regulating ocular angiogenesis in mouse models and explored the underlying signaling pathway. MATERIAL AND METHODS An oxygen-induced retinopathy (OIR) mouse model and a laser-induced choroidal neovascularization (CNV) mouse model were used to test integrin a5b1 expression and the effect of ATN-161 on ocular NV by immunofluorescence staining, Western blot analysis, and flat-mount analysis. The activation of nuclear factor-κB (NF-κB), matrix metalloproteinase-2/9 (MMP-2/9), and cell apoptosis were detected by immunofluorescence staining, Western blot, real-time RT-PCR, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). The cell proliferation was detected by BrdU labeling. RESULTS In OIR and CNV mice, the protein expression level of integrin α5β1 increased compared with that in age-matched controls. The mice given ATN-161 had significantly reduced retinal neovascularization (RNV) and CNV. Blocking integrin a5b1 by ATN-161 strongly inhibited nuclear factor-κB (NF-κB) activation and matrix metalloproteinase-2/9 (MMP-2/9) expression and promoted cell apoptosis, but the effect of ATN-161 on proliferation in CNV mice was indirect and required the inhibition of neovascularization. Inhibiting NF-κB activation by ammonium pyrrolidinedithiocarbamate (PDTC) reduced RNV and promoted cell apoptosis in ocular NV. CONCLUSIONS Blocking integrin α5β1 by ATN-161 reduced ocular NV by inhibiting MMP-2/MMP-9 expression and promoting the cell apoptosis of ocular NV.

Nitrite ion modifies tyrosine and lysine residues of extracellular matrix proteins

Age-related macular degeneration (AMD) is a disease characterized by degenerative changes in the retinal pigment epithelium and Bruch's membrane. Inflammation is considered a major risk factor for the development and progression of AMD. Nitrite is a potent byproduct of inflammation and has been detected at elevated concentrations in AMD donor tissue. We hypothesize that nitrite chemically modifies the extracellular matrix (ECM) of Bruch's membrane as an initial step to degenerative changes observed in AMD. Non-enzymatically nitrated synthetic ECM peptides, fibronectin and laminin, were used as model systems for inflammation. Using LC/MS, we identified that nitration preferentially occurred on tyrosine and deamination of lysine under the studied conditions. At tyrosine residues, 3-nitrotyrosine was produced and shifted the total mass by the addition of 45 amu. Deamination of lysine occurred and resulted in the formation of either an alkene or alcohol group. The alkene group was observed with a loss of 17 amu. An addition of 1 amu was observed with alcohol formation. We hypothesize that these initial chemical modifications to the structure of ECM proteins may be the responsible for altering the structure and consequent function of Bruch's membrane.

Distinct CD40L receptors mediate inflammasome activation and secretion of IL-1β and MCP-1 in cultured human retinal pigment epithelial cells

CD40L signaling occurs in several diseases with inflammatory components, including ocular and retinal diseases. However, it has never been evaluated as a pathogenic mechanism in age-related macular degeneration (AMD) or as an inducer of inflammasome formation in any cell type. mRNA and protein levels of CD40, IL-1β, NALP1, NALP3, caspase-1, and caspase-5 were determined by RT-PCR, qPCR, and Western blot. CD40L receptor (CD40, α5β1, and CD11b) expression was determined by Western and immunofluorescent staining. IL-1β, IL-18, and MCP-1 secretions were determined by ELISA. NALP1 and NALP3 inflammasome formation were determined by Co-IP. Experiments were conducted on primary human retinal pigment epithelial (hRPE) cells from four different donors. Human umbilical vein endothelial (HUVEC) and monocytic leukemia (THP-1) cells demonstrated the general applicability of our findings. In hRPE cells, CD40L-induced NALP1 and NALP3 inflammasome activation, cleavage of caspase-1 and caspase-5, and IL-1β and IL-18 secretion. Interestingly, neutralizing CD11b and α5β1 antibodies, but not CD40, reduced CD40L-induced IL-1β secretion in hRPE cells. Similarly, CD40L treatment also induced HUVEC and THP-1 cells to secret IL-1β through CD11b and α5β1. Additionally, the CD40L-induced IL-1β secretion acted in an autocrine/paracrine manner to feed back and induce hRPE cells to secrete MCP-1. This study is the first to show that CD40L induces inflammasome activation in any cell type, including hRPE cells, and that this induction is through CD11b and α5β1 cell-surface receptors. These mechanisms likely play an important role in many retinal and non-retinal diseases and provide compelling drug targets that may help reduce pro-inflammatory processes.

α5β1-Integrin inhibitor (CLT-28643) effective in rabbit trabeculectomy model

PURPOSE

Glaucoma filtration surgery (GFS) fails due to fibrosis. The α5β1-integrin plays a pivotal role in fibrosis, angiogenesis and inflammation. This is the first experiment evaluating the prevention of fibrosis after GFS by a specific small molecule α5β1-integrin inhibitor (CLT-28643).

METHODS

Twenty-four rabbits received trabeculectomy on their right eyes. The rabbits were randomized into three groups of eight eyes each. CLT-28643 was given as a single subconjunctival injection intraoperatively to two of the right eye groups followed by postoperative vehicle eye drops (CLT+ group) or CLT-28643 eye drops 4 times daily (CLT++ group). A third group received mitomycin-C (MMC) intraoperatively (sponge application, 0.04%, 2 min) followed by vehicle eye drops postoperatively. The control-surgery group consisted of 12 left eyes having trabeculectomy with no adjunctive therapy. The remaining 12 left eyes formed the untreated group. Clinical assessment included intraocular pressure (IOP) measurement, slit-lamp examination (including bleb survival and morphology) and bleb photography. The rabbits were killed after four weeks for histology.

RESULTS

Both CLT-28643-treated groups showed significantly prolonged bleb survival, and better bleb score compared to the control-surgery group. At end of the study, most functioning blebs were found in the MMC group (MMC group 75%; CLT+ group 12.5%, CLT++ group 25%; CLT+ group 12.5%, control-surgery group 0%). CLT-28643 was non-toxic and well tolerated.

CONCLUSIONS

This rabbit GFS study indicates that inhibition of α5β1-integrin by the novel α5β1-integrin antagonist CLT-28643 significantly improved the outcome. The effect of a single intro-operative application of CLT-28643 seems to be inferior to 0.04% MMC.

All-trans retinoic acid suppresses the adhering ability of ARPE-19 cells via mitogen-activated protein kinase and focal adhesion kinase

This study investigated the signaling mechanism underlying the anti-adhesive effect of all-trans retinoic acid (ATRA) on retinal pigment epithelial ARPE-19 cells. Adhesion kinetics with or without ATRA treatment were profiled by adhesion assay. Surface coating with type IV collagen, fibronectin, laminin, but not type I collagen, significantly enhanced adhesion and spreading of ARPE-19 cells, while ATRA at subtoxic doses (ranging from 10^-7 to 10^-6 M) profoundly suppressed the extracellular matrix-enhanced adhesion ability. Cell attachment on FN activated PI3K/Akt and MAPK cascades, whereas ATRA pretreatment blunted the early phosphorylation of Akt and MAPK signaling mediators including p38 MAPK, JNK1/2, and ERK1/2. Mechanistically, signaling blockade with selective kinase inhibitors demonstrated that all MAPK pathways were involved in the anti-adhesive effect of ATRA, whereas the PI3K inhibitor treatment significantly potentiated the ATRA-suppressed RPE cell adhesion. Moreover, ATRA treatment did not affect intracellular F-actin distribution, but remarkably reduced focal adhesion kinase (FAK) expression and its nuclear localization during ARPE-19 cell attachment. In conclusion, ATRA suppresses the adhering ability of ARPE-19 cells at least in part through MAPK and FAK pathways. Signaling blockade with PI3K inhibitor could be regarded as an alternative modality for treating proliferative vitreoretinopathy.

Fibronectin stimulates the osteogenic differentiation of murine embryonic stem cells

Conditioned medium from human hepatocarcinoma cells (HepG2-CM) has been shown to stimulate the osteogenic/chondrogenic differentiation of murine embryonic stem cells (mESCs). HepG2-CM is considered to contain visceral endoderm (VE)-like signals and attempts have recently been made to characterize it, using proteomic profiling, with fibronectin being identified as one promising candidate. Herein, we investigated whether fibronectin is able to mimic the activities of HepG2-CM during the osteogenic differentiation of mESCs. Specifically, the addition of RGD peptides and heparin in HepG2-CM significantly reduced the growth- and adhesion-promoting effects of HepG2-CM, in addition to suppressing its osteogenic-inductive activity. Furthermore, direct addition of fibronectin to basal medium was able to reproduce, at least partially, the function of HepG2-CM. In particular, fibronectin induced the early onset of osteogenic differentiation in mESCs, as confirmed by gene expression of osteogenic markers, and resulted in the three-fold higher calcium deposition at day 11 of osteogenic culture compared to the control group. These data clearly suggest that fibronectin contributes to the biological activities of HepG2-CM and plays a stimulatory role during the process of osteogenesis in mESCs. Copyright © 2015 John Wiley & Sons, Ltd.

Retinal pigment epithelial cell proliferation

The human retinal pigment epithelium forms early in development and subsequently remains dormant, undergoing minimal proliferation throughout normal life. Retinal pigment epithelium proliferation, however, can be activated in disease states or by removing retinal pigment epithelial cells into culture. We review the conditions that control retinal pigment epithelial proliferation in culture, in animal models and in human disease and interpret retinal pigment epithelium proliferation in context of the recently discovered retinal pigment epithelium stem cell that is responsible for most in vitro retinal pigment epithelial proliferation. Retinal pigment epithelial proliferation-mediated wound repair that occurs in selected macular diseases is contrasted with retinal pigment epithelial proliferation-mediated fibroblastic scar formation that underlies proliferative vitreoretinopathy. We discuss the role of retinal pigment epithelial proliferation in age-related macular degeneration which is reparative in some cases and destructive in others. Macular retinal pigment epithelium wound repair and regression of choroidal neovascularization are more pronounced in younger than older patients. We discuss the possibility that the limited retinal pigment epithelial proliferation and latent wound repair in older age-related macular degeneration patients can be stimulated to promote disease regression in age-related macular degeneration.

Human T-Cell Development and Thymic Egress: An Infectious Disease Perspective

Emigration of mature naïve CD4 SP T cells from the human thymus to the periphery is not fully understood, although elucidation of the mechanisms that govern egress of T cells is crucial to understanding both basic immunology and the immune response in diseases such as HIV infection. Recent work has brought to light the requirement for sphingosine-1-phosphate (S1P) and its receptors in a variety of fields including mature naïve T-cell egress from the thymus of mice. We are examining the expression and function of this novel requisite T-cell egress receptor within the human thymus, characterizing changes observed in the expression and function of this receptor in infectious diseases. To perform this work, we use a variety of humanized murine models reviewed in this article. Future work in the field of T-cell egress, especially as it pertains to S1P receptors, should advance the fields of basic T-cell immunology and immunopathology and open new avenues for exploration into novel therapeutics.

Using the neurofibromatosis tumor predisposition syndromes to understand normal nervous system development

Development is a tightly regulated process that involves stem cell self-renewal, differentiation, cell-to-cell communication, apoptosis, and blood vessel formation. These coordinated processes ensure that tissues maintain a size and architecture that is appropriate for normal tissue function. As such, tumors arise when cells acquire genetic mutations that allow them to escape the normal growth constraints. In this regard, the study of tumor predisposition syndromes affords a unique platform to better understand normal development and the process by which normal cells transform into cancers. Herein, we review the processes governing normal brain development, discuss how brain cancer represents a disruption of these normal processes, and highlight insights into both normal development and cancer made possible by the study of tumor predisposition syndromes.

P2Y2 nucleotide receptor activation enhances the aggregation and self-organization of dispersed salivary epithelial cells

Hyposalivation resulting from salivary gland dysfunction leads to poor oral health and greatly reduces the quality of life of patients. Current treatments for hyposalivation are limited. However, regenerative medicine to replace dysfunctional salivary glands represents a revolutionary approach. The ability of dispersed salivary epithelial cells or salivary gland-derived progenitor cells to self-organize into acinar-like spheres or branching structures that mimic the native tissue holds promise for cell-based reconstitution of a functional salivary gland. However, the mechanisms involved in salivary epithelial cell aggregation and tissue reconstitution are not fully understood. This study investigated the role of the P2Y2 nucleotide receptor (P2Y2R), a G protein-coupled receptor that is upregulated following salivary gland damage and disease, in salivary gland reconstitution. In vitro results with the rat parotid acinar Par-C10 cell line indicate that P2Y2R activation with the selective agonist UTP enhances the self-organization of dispersed salivary epithelial cells into acinar-like spheres. Other results indicate that the P2Y2R-mediated response is dependent on epidermal growth factor receptor activation via the metalloproteases ADAM10/ADAM17 or the α5β1 integrin/Cdc42 signaling pathway, which leads to activation of the MAPKs JNK and ERK1/2. Ex vivo data using primary submandibular gland cells from wild-type and P2Y2R(-/-) mice confirmed that UTP-induced migratory responses required for acinar cell self-organization are mediated by the P2Y2R. Overall, this study suggests that the P2Y2R is a promising target for salivary gland reconstitution and identifies the involvement of two novel components of the P2Y2R signaling cascade in salivary epithelial cells, the α5β1 integrin and the Rho GTPase Cdc42.

Pharmacological implications from the adhesion-induced signaling profiles in cultured human retinal pigment epithelial cells

Extracellular matrix (ECM) plays an active and complex role in regulating cellular behaviors, including proliferation and adhesion. This study aimed at delineating the adhesion-induced signaling profiles in cultured human retinal pigment epithelium (RPE) cells and investigating the antiadhesion effect of antiproliferative drugs in this context. RPE R-50 cells grown on various ECM molecules, such as type I and IV collagens, fibronectin, and laminin, were used for adhesion assay and for examining the phosphorylation profiles of signaling mediators including Akt, extracellular signal-regulated kinase (ERK) 1/2, and integrin-linked kinase (ILK) using Western blotting. The cells receiving antiproliferative drug treatment at subtoxic doses were used to evaluate their antiadhesive and suppressive effects on kinase activities. ECM coating enhanced adhesion and spreading of RPE cells significantly. The cellular attachment onto ECM-coated surfaces differentially induced Akt, ERK1/2, and ILK phosphorylation, and concomitantly increased p53 phosphorylation and cyclin D1 expression, but decreased Bcl-2/Bax ratios. Treatment with antiproliferative agents, including 5-fluorouracil, mitomycin C, and daunomycin, at subtoxic doses suppressed the ability of RPE cells to adhere to ECM substratum significantly. This suppression was in part mediated through reduction of integrin β1 and β3 expressions and interfering Akt-ILK signaling activity. Mechanistically, blockade of PI3K/Akt signaling resulted in the suppressed adhesion of RPE cells to ECM. These findings support the hypothesis that, in addition to their antimitogenic effect, antiproliferative agents also exhibit suppressive effect on the adhesiveness of cultured RPE cells. Moreover, inhibitors of the PI3K/Akt signaling mediator can potentially be used as therapeutic agents for proliferative vitreoretinopathy.

shRNA targeting β1-integrin suppressed proliferative aspects and migratory properties of airway smooth muscle cells

Dysfunction of airway smooth muscle (ASM) is an essential feature of airway remodeling in chronic asthma. However, the precise mechanisms of this pathological process have not been well studied. In previous study, we found that β1-integrin, which was dramatically upregulated in ASM cells in an asthmatic mouse model, was associated with the cell proliferation. In this study, we employed short hairpin RNA (shRNA) targeting β1-integrin to assess the effect of down-regulation of this receptor on the proliferative aspects and migratory properties of ASM cells in vitro. The cells were treated with shRNA expression vectors directed against β1-integrin, control vectors that included the blank control, empty vector without shRNA, and mismatched shRNA, respectively. The mRNA and protein expressions of β1-integrin were determined by real-time PCR and Western blotting. Cell proliferation was measured by BrdU ELISA and cell cycle by fluorescence-activated cell sorter. Cell apoptosis was detected by Annexin V-PE/7-AAD staining. Cell migration assays were evaluated by transwell assay and expression of IL-6 and IL-8 by ELISA. The results revealed that shRNA targeting β1-integrin significantly decreased the mRNA and protein expressions of β1-integrin, enhanced the proportion of cells in G0/G1 phase, decreased the proportion in S phase, promoted cell apoptosis, inhibited cell proliferation, migration, IL-6 and IL-8 secretion in vitro. In conclusion, the overexpression of β1-integrin in ASM cells is essential for airway dysfunction development because it promotes proliferative aspects and migratory properties of ASM cells. Importantly, shRNA targeting β1-integrin may provide a new approach to preventing airway remodeling in chronic asthma.

β1-integrin: a potential therapeutic target in the battle against cancer recurrence

Primary cancer treatment, involving both local and often systemic adjuvant therapy, is often successful, especially if the cancer is detected at an early stage of progression. However, for some patients, the cancer may recur either locally or as distant metastases, in some cases many years after apparently successful primary treatment. Significant tumor dormancy has been documented in several cancers, such as breast, melanoma, and renal cancer. Tumor dormancy has long been recognized as an important problem in management of cancer patients. Recent work has clarified biologic aspects of tumor dormancy and has shown that dormant tumor cells may be resistant to cytotoxic chemotherapy and radiation. This work has led to recognition of a key role for β1-integrin in regulating the switch from a dormant state to active proliferation and metastasis. Here we discuss the role of β1-integrin and its signaling partners in regulating the dormant phenotype. We also consider possible therapeutic approaches, such as small molecules or antibodies (ATN-161, volociximab, and JSM6427), directed against β1-integrin signaling to target dormant cancer cells and to prevent metastatic recurrence.

CNTF mediates neurotrophic factor secretion and fluid absorption in human retinal pigment epithelium

Ciliary neurotrophic factor (CNTF) protects photoreceptors and regulates their phototransduction machinery, but little is known about CNTF's effects on retinal pigment epithelial (RPE) physiology. Therefore, we determined the expression and localization of CNTF receptors and the physiological consequence of their activation in primary cultures of human fetal RPE (hfRPE). Cultured hfRPE express CNTF, CT1, and OsM and their receptors, including CNTFRα, LIFRβ, gp130, and OsMRβ, all localized mainly at the apical membrane. Exogenous CNTF, CT1, or OsM induces STAT3 phosphorylation, and OsM also induces the phosphorylation of ERK1/2 (p44/42 MAP kinase). CNTF increases RPE survivability, but not rates of phagocytosis. CNTF increases secretion of NT3 to the apical bath and decreases that of VEGF, IL8, and TGFβ2. It also significantly increases fluid absorption (J_V) across intact monolayers of hfRPE by activating CFTR chloride channels at the basolateral membrane. CNTF induces profound changes in RPE cell biology, biochemistry, and physiology, including the increase in cell survival, polarized secretion of cytokines/neurotrophic factors, and the increase in steady-state fluid absorption mediated by JAK/STAT3 signaling. In vivo, these changes, taken together, could serve to regulate the microenvironment around the distal retinal/RPE/Bruch's membrane complex and provide protection against neurodegenerative disease.

Retinoic acid receptor signaling regulates choroid fissure closure through independent mechanisms in the ventral optic cup and periocular mesenchyme

Retinoic acid receptor (RAR) signaling is required for morphogenesis of the ventral optic cup and closure of the choroid fissure, but the mechanisms by which this pathway regulates ventral eye development remain controversial and poorly understood. Although previous studies have implicated neural crest-derived periocular mesenchyme (POM) as the critical target of RA action in the eye, we show here that RAR signaling regulates choroid fissure closure in zebrafish by acting on both the ventral optic cup and the POM. We describe RAR-dependent regulation of eight genes in the neuroepithelial cells of the ventral retina and optic stalk and of six genes in the POM and show that these ventral retina/optic stalk and POM genes function independently of each other. Consequently, RAR signaling regulates ventral eye development through two independent, nonredundant mechanisms in different ocular tissues. Furthermore, the identification of two cohorts of genes implicated in ventral eye morphogenesis may help to elucidate the genetic basis of ocular coloboma in humans.

Experimental models for study of retinal pigment epithelial physiology and pathophysiology

We have developed a cell culture procedure that can produce large quantities of confluent monolayers of primary human fetal retinal pigment epithelium (hfRPE) cultures with morphological, physiological and genetic characteristics of native human RPE. These hfRPE cell cultures exhibit heavy pigmentation, and electron microscopy show extensive apical membrane microvilli. The junctional complexes were identified with immunofluorescence labeling of various tight junction proteins. Epithelial polarity and function of these easily reproducible primary cultures closely resemble previously studied mammalian models of native RPE, including human. These results were extended by the development of therapeutic interventions in several animal models of human eye disease. We have focused on strategies for the removal of abnormal fluid accumulation in the retina or subretinal space. The extracellular subretinal space separates the photoreceptor outer segments and the apical membrane of the RPE and is critical for maintenance of retinal attachments and a whole host of RPE/retina interactions.

MicroRNA-204/211 alters epithelial physiology

MicroRNA (miRNA) expression in fetal human retinal pigment epithelium (hfRPE), retina, and choroid were pairwise compared to determine those miRNAs that are enriched by 10-fold or more in each tissue compared with both of its neighbors. miRs-184, 187, 200a/200b, 204/211, and 221/222 are enriched in hfRPE by 10- to 754-fold compared with neuroretina or choroid (P<0.05). Five of these miRNAs are enriched in RPE compared with 20 tissues throughout the body and are 10- to 20,000-fold more highly expressed (P<0.005). miR-204 and 211 are the most highly expressed in the RPE. In addition, expression of miR-204/211 is significantly lower in the NCI60 tumor cell line panel compared with that in 13 normal tissues, suggesting the progressive disruption of epithelial barriers and increased proliferation. We demonstrated that TGF-beta receptor 2 (TGF-betaR2) and SNAIL2 are direct targets of miR-204 and that a reduction in miR-204 expression leads to reduced expression of claudins 10, 16, and 19 (message/protein) consistent with our observation that anti-miR-204/211 decreased transepithelial resistance by 80% and reduced cell membrane voltage and conductance. The anti-miR-204-induced decrease in Kir7.1 protein levels suggests a signaling pathway that connects TGF-betaR2 and maintenance of potassium homeostasis. Overall, these data indicate a critical role for miR-204/211 in maintaining epithelial barrier function and cell physiology.