FGF-2 Induced by Interleukin-1β through the Action of Phosphatidylinositol 3-Kinase Mediates Endothelial Mesenchymal Transformation in Corneal Endothelial Cells

Effects of Angiogenic Factors on the Epithelial-to-Mesenchymal Transition and Their Impact on the Onset and Progression of Oral Squamous Cell Carcinoma: An Overview

High levels of vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF)-2 and angiopoietin (ANG)-2 are found in tissues from oral squamous cell carcinoma (OSCC) and oral potentially malignant disorders (OPMDs). As might be expected, VEGF, FGF-2, and ANG-2 overexpression parallels the development of new blood and lymphatic vessels that nourish the growing OPMDs or OSCCs and provide the latter with metastatic routes. Notably, VEGF, FGF-2, and ANG-2 are also linked to the epithelial-to-mesenchymal transition (EMT), a trans-differentiation process that respectively promotes or exasperates the invasiveness of normal and neoplastic oral epithelial cells. Here, we have summarized published work regarding the impact that the interplay among VEGF, FGF-2, ANG-2, vessel generation, and EMT has on oral carcinogenesis. Results from the reviewed studies indicate that VEGF, FGF-2, and ANG-2 spark either protein kinase B (AKT) or mitogen-activated protein kinases (MAPK), two signaling pathways that can promote both EMT and new vessels' formation in OPMDs and OSCCs. Since EMT and vessel generation are key to the onset and progression of OSCC, as well as to its radio- and chemo-resistance, these data encourage including AKT or MAPK inhibitors and/or antiangiogenic drugs in the treatment of this malignancy.

CHIR99021 balance TGFβ1 induced human corneal endothelial-to-mesenchymal transition to favor corneal endothelial cell proliferation

Corneal endothelial cells (CECs) play a major role in the maintenance of stromal hydration via the barrier and pump function for clear vision. Adult CEC cannot regenerate after injury. CECs cultured in vitro can undergo mitosis but may undergo corneal endothelial-to-mesenchymal transition (EnMT) and lose their endothelial characteristics. In this study, we examined the effects of CHIR99201 on transforming growth factor beta-1(TGFβ1)-induced EnMT in human CEC (hCECs) lines. CHIR99021 kept hCECs in the hexagonal shape and could downregulate the EnMT markers alpha-smooth muscle actin (α-SMA) and fibronectin (FN1), meanwhile maintained the hCECs function markers Na⁺/K⁺-ATPase and zonula occludens-1 (ZO-1) at levels comparable to those in the normal control. Interestingly, we found that the combination of CHIR99021 and TGFβ1 at appropriate concentrations would significantly promote the proliferation and migration of hCECs. These effects may be related to the inhibition of RhoA or Rac1, as well as the activation of Wnt and Erk pathway, with a calcium homeostasis. Our findings indicate that CHIR99021 inhibit EnMT and that the combination of CHIR99021 and TGFβ1 may provide new ideas for corneal endothelial regeneration and wound healing.

New developments in corneal endothelial cell replacement

Corneal transplantation is currently the most effective treatment to restore corneal clarity in patients with endothelial disorders. Endothelial transplantation, either by Descemet membrane endothelial keratoplasty (DMEK) or by Descemet stripping (automated) endothelial keratoplasty (DS(A)EK), is a surgical approach that replaces diseased Descemet membrane and endothelium with tissue from a healthy donor eye. Its application, however, is limited by the availability of healthy donor tissue. To increase the pool of endothelial grafts, research has focused on developing new treatment options as alternatives to conventional corneal transplantation. These treatment options can be considered as either 'surgery-based', that is tissue-efficient modifications of the current techniques (e.g. Descemet stripping only (DSO)/Descemetorhexis without endothelial keratoplasty (DWEK) and Quarter-DMEK), or 'cell-based' approaches, which rely on in vitro expansion of human corneal endothelial cells (hCEC) (i.e. cultured corneal endothelial cell sheet transplantation and cell injection). In this review, we will focus on the most recent developments in the field of the 'cell-based' approaches. Starting with the description of aspects involved in the isolation of hCEC from donor tissue, we then describe the different natural and bioengineered carriers currently used in endothelial cell sheet transplantation, and finally, we discuss the current 'state of the art' in novel therapeutic approaches such as endothelial cell injection.

Expression Analysis of FGF/FGFR and FOX Family Proteins in Mucosal Tissue Obtained from Orofacial Cleft-Affected Children

Orofacial clefts affect hundreds of thousands of children worldwide annually and are usually corrected by a series of surgeries extending to childhood. The underlying mechanisms that lead to clefts are still unknown, mainly because of the multifactorial etiology and the myriad of interactions between genes and environmental factors. In the present study, we investigated the role and expression of candidate genes belonging to the FGF/FGFR signaling pathway and FOX family in tissue material obtained from 12 pediatric patients undergoing cleft correction surgery. The expression was investigated using immunohistochemistry (IHC) and chromogenic in-situ hybridization (CISH) in three cell/tissue types-epithelial cells, connective tissue, and endothelial cells. We found elevated expression of FGFR1 in epithelial cells while no expression was observed in endothelial cells. Further, our results elucidate the potential pathogenetic role of FGFR1 in cellular proliferation, local site inflammation, and fibrosis in cleft patients. Along with bFGF (also called FGF2), FGFR1 could play a pro-inflammatory role in clefts. Over-amplification of FGFR2 in some patients, along with bFGF, could potentially suggest roles for these genes in angiogenesis. Additionally, increased expression of FOXE1 (also called TTF2) contributes to local site inflammation. Finally, zero to low amplification of FOXO1 could suggest its potential role in inducing oxidative stress in the endothelium along with reduced epithelial apoptosis.

Endothelium-derived stromal cells contribute to hematopoietic bone marrow niche formation

Bone marrow stromal cells (BMSCs) play pivotal roles in tissue maintenance and regeneration. Their origins, however, remain incompletely understood. Here we identify rare LNGFR⁺ cells in human fetal and regenerative bone marrow that co-express endothelial and stromal markers. This endothelial subpopulation displays transcriptional reprogramming consistent with endothelial-to-mesenchymal transition (EndoMT) and can generate multipotent stromal cells that reconstitute the bone marrow (BM) niche upon transplantation. Single-cell transcriptomics and lineage tracing in mice confirm robust and sustained contributions of EndoMT to bone precursor and hematopoietic niche pools. Interleukin-33 (IL-33) is overexpressed in subsets of EndoMT cells and drives this conversion process through ST2 receptor signaling. These data reveal generation of tissue-forming BMSCs from mouse and human endothelial cells and may be instructive for approaches to human tissue regeneration.

Effect of Stem Cell-Derived Extracellular Vesicles on Damaged Human Corneal Endothelial Cells

Purpose

Human corneal endothelial cells (HCECs) are essential to visual function; however, since they have limited proliferative capacity in vivo, they are prone to corneal endothelial dysfunction. At present, the only treatment is a corneal transplantation from donor cadavers. Also, due to a global shortage of donor corneas, it is important to find alternative strategies. Recent studies highlight that stem cell–derived extracellular vesicles (EVs) play a relevant role in stem cell-induced regeneration by reprogramming injured cells and inducing proregenerative pathways. The aim of this work is to evaluate whether EVs derived from mesenchymal stem cells (MSC-EVs) are able to promote regeneration of damaged HCECs.

Methods

We isolated HCECs from discarded corneas in patients undergoing corneal transplantation or enucleation (N = 23 patients). Bone marrow mesenchymal stem cells (MSCs) were obtained from Lonza, cultured, and characterized. MSC-EVs were obtained from supernatants of MSCs. In order to establish a valid in vitro damage model to test the regenerative potential of EVs on HCECs, we evaluated the proliferation rate and the apoptosis after exposing the cells to serum-deprived medium at different concentrations for 24 hours. We then evaluated the HCEC migration through a wound healing assay.

Results

In the selected serum deprivation damage conditions, the treatment with different doses of MSC-EVs resulted in a significantly higher proliferation rate of HCECs at all the tested concentrations of EVs (5‐20 × 10³ MSC-EV/cell). MSC-EVs/cell induced a significant decrease in number of total apoptotic cells after 24 hours of serum deprivation. Finally, the wound healing assay showed a significantly faster repair of the wound after HCEC treatment with MSC-EVs.

Conclusions

Results highlight the already well-known proregenerative potential of MSC-EVs in a totally new biological model, the endothelium of the cornea. MSC-EVs, indeed, induced proliferation and survival of HCECs, promoting the migration of HCECs in vitro.

Angiogenesis and nerve regeneration induced by local administration of plasmid pBud-coVEGF165-coFGF2 into the intact rat sciatic nerve

Vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) are well-known growth factors involved in the regeneration of various tissues and organs, including peripheral nerve system. In the present study, we elucidated the local and systemic effects of plasmid construct рBud-coVEGF165-coFGF2 injected into the epineurium of intact rat sciatic nerve. Results of histological examination of sciatic nerve and multiplex immunoassays of serum showed the absence of immunogenicity and biosafety of plasmid рBud-coVEGF165-coFGF2. Moreover, local administration of plasmid DNA construct resulted in significantly decreased levels of pro-inflammatory cytokines in the peripheral blood, including tumor necrosis factor α (TNFα) and interleukin-12, and significantly increased levels of cytokines and chemokines including Regulated upon Activation, Normal T Cell Expressed and Presumably Secrete (RANTES), epidermal growth factor, interleukin-2, and monocyte chemoattractant protein 1. These changes in the peripheral blood on day 7 after injection of plasmid construct рBud-coVEGF165-coFGF2 show that the plasmid construct has systemic effects and may modulate immune response. At the same time, reverse transcription-polymerase chain reaction revealed transient expression of coFGF2, coVEGF165, ratFGF2 and ratVEGFA with direct transport of transcripts from distal part to proximal part of the sciatic nerve. Immunohistochemical staining revealed prolonged presence of VEGFA in sciatic nerve till 14 days post-injection. These findings suggest that local administration of plasmid construct рBud-coVEGF165-coFGF2 at a concentration of 30 ng/µL results in the formation of pro-angiogenic stimuli and, and the plasmid construct, used as a drug for gene therapy, might potentially facilitate regeneration of the sciatic nerve. The study was approved by the Animal Ethics Committee of Kazan Federal University, procedures were approved by the Local Ethics Committee (approval No. 5) on May 27, 2014.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

Exploring a peptidomimetic approach of N-cadherin in modulating fibroblast growth factor receptor signaling for corneal endothelial regeneration

Endothelial rejection and a critical shortage of corneal transplants present an unmet medical need in corneal regeneration research area. Although basic fibroblast growth factor (bFGF) is a potent mitogenic factor for corneal ex vivo expansion, it is also a morphogen eliciting unfavorable endothelial-mesenchymal transition (EnMT) of corneal endothelial cells. A pharmacological reagent that retains the beneficial proliferative effect while lacking the EnMT effect of bFGF would be of great potential in corneal regeneration. In present study, we demonstrated that bFGF not only activated the canonical fibroblast growth factor receptor 1 (FGFR1) tyrosine kinase pathway, but also further upregulated matrix metalloproteinase activity to cleave N-cadherin into N-terminus and C-terminus fragments, which activated the classical FGFR1 tyrosine kinase pathway and a cryptic β-catenin pathway to affect corneal proliferation and EnMT, respectively. We generated the synthetic peptides resembling a critical motif in the ectodomain of N-cadherin and found these peptides enhanced downstream proliferative signaling of FGFR1 but without seemingly EnMT effect. The potential of these peptides can be demonstrated on both ex vivo cell culture and in vivo rat cryo-injury model. Our study indicated this peptidomimetic approach of N-cadherin can stimulate corneal regeneration and offer a promising therapeutic option to treat corneal endothelial dysfunction.

ZEB1 Mediates Fibrosis in Corneal Endothelial Mesenchymal Transition Through SP1 and SP3

Purpose

ZEB1 is induced during endothelial-mesenchymal transition (EnMT) in the cornea. Induction of SP1 and SP3 by ZEB1 along with identification of putative SP1 and SP3 binding sites in promoters of EnMT-associated gene lead us to investigate their roles in retrocorneal membrane formation in the corneal endothelium.

Methods

Expressions of SP1, SP3, and EnMT associated genes were analyzed by immunoblotting and semiquantitative reverse transcription polymerase chain reaction. Accell SMARTpool siRNAs targeting ZEB1, SP1, and SP3 were used for gene knockdown. SP1 and SP3 binding to promoters of EnMT associated genes was investigated by chromatin immunoprecipitation assay. Corneal endothelium in mice was surgically injured in vivo under direct visualization.

Results

Transient Fibroblast Growth Factor 2 stimulation increased the expression of both SP1 and SP3 in the human corneal endothelium ex vivo. ZEB1 siRNA knockdown inhibited FGF2-induced SP1 mRNA and protein but not the expression of SP3. FGF2-induced expression of EnMT-related genes, such as fibronectin, vimentin, and type I collagen, was reduced by both SP1 and SP3 siRNA knockdown, with inhibition of SP1 having a greater inhibitory effect than SP3. Additionally, although SP1 and SP3 proteins were found to bind together, SP1 and SP3 could bind to the same promoter binding sites of EnMT-related genes in the absence of the other. Moreover, siRNA knockdown of Zeb1 inhibited injury-dependent RCM formation in mouse corneal endothelium in vivo.

Conclusions

Zeb1, through SP1 and SP3, plays a central role in mesenchymal transition induced fibrosis in the corneal endothelium and suggests that Zeb1 could be targeted to inhibit anterior segment fibrosis.

Interleukin-18 and fibroblast growth factor 2 in combination is a useful diagnostic biomarker to distinguish adult-onset Still's disease from sepsis

OBJECTIVE

To identify potential biomarkers to distinguish adult-onset Still's disease (AOSD) from sepsis.

METHOD

We recruited 70 patients diagnosed with AOSD according to the Yamaguchi criteria, 22 patients with sepsis, and 118 age-matched controls. Serum levels of 40 cytokines were analyzed using multi-suspension cytokine array. We performed a cluster analysis of each cytokine in the AOSD and sepsis groups in order to identify specific molecular networks. Further, multivariate classification (random forest analysis) and logistic regression analysis were used to rank the cytokines by their importance and determine specific biomarkers for distinguishing AOSD from sepsis.

RESULTS

Seventeen of the 40 cytokines were found to be suitable for further analyses. The serum levels of eleven were significantly higher in patients with AOSD than healthy controls. Levels of serum fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), granulocyte colony-stimulating factor (G-CSF), and interleukin (IL)-18 were significantly elevated in patients with AOSD compared with those with sepsis, and cytokine clustering patterns differed between these two groups. Multivariate classification followed by logistic regression analysis revealed that measurement of both FGF-2 and IL-18 could distinguish AOSD from sepsis with high accuracy (cutoff value for FGF-2 = 36 pg/mL; IL-18 = 543 pg/mL, sensitivity 100%, specificity 72.2%, accuracy 93.8%).

CONCLUSION

Determination of FGF-2 and IL-18 levels in combination may represent a biomarker for the differential diagnosis of AOSD from sepsis, based on the measurement of multiple cytokines.

FGF2, an Immunomodulatory Factor in Asthma and Chronic Obstructive Pulmonary Disease (COPD)

The fibroblast growth factor 2 (FGF2) is a potent mitogenic factor belonging to the FGF family. It plays a role in airway remodeling associated with chronic inflammatory airway diseases, including asthma and chronic obstructive pulmonary disease (COPD). Recently, research interest has been raised in the immunomodulatory function of FGF2 in asthma and COPD, through its involvement in not only the regulation of inflammatory cells but also its participation as a mediator between immune cells and airway structural cells. Herein, this review provides the current knowledge on the biology of FGF2, its expression pattern in asthma and COPD patients, and its role as an immunomodulatory factor. The potential that FGF2 is involved in regulating inflammation indicates that FGF2 could be a therapeutic target for chronic inflammatory diseases.

Regeneration of the Corneal Endothelium

Penetrating keratoplasty was the only therapeutic choice for the treatment of corneal endothelial decompensation until the introduction of evolutional endothelial keratoplasties, namely Descemet's stripping automated endothelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK). Although now in widespread use, DSAEK and DMEK still have associated problems, such as difficulty of the surgical technique, acute and chronic cell loss, and shortage of donor corneas. Therefore, regeneration of the corneal endothelium by tissue engineering techniques is being researched to overcome these problems. The concept of transplantation of cultured corneal endothelial cells (CECs) was proposed in the 1970s. However, cultivation of human CECs (HCECs) in sufficient quantity and with acceptable quality for clinical use has proven surprisingly difficult, and the development of methods for transplanting cultured HCECs has been necessary. Numerous research groups have developed culture protocols and techniques that are now bringing corneal endothelial regeneration closer to real-world therapy. For instance, we started a clinical trial in 2013 involving the injection of cultured HCECs into the anterior chamber of patients with corneal endothelial decompensation. This review outlines the rapid progression of this research field, including clinical trial results, and is also intended to identify topics that still require further research or discussion.

Advances in culture, expansion and mechanistic studies of corneal endothelial cells: a systematic review

Human corneal endothelial cells are notorious for their restricted proliferative ability in vivo and in vitro. Hence, injury or dysfunction of these cells may easily result in blindness. Currently, the only treatment is to transplant a donor cornea that contains a healthy corneal endothelium. However there is a severe global shortage of donor corneas and there remains an unmet clinical need to engineer human corneal grafts with healthy corneal endothelium. In this review, we present current advances in the culture, expansion, and molecular understandings of corneal endothelial cells in vitro in order to help establish methods of engineering human corneal endothelial grafts.

A Rabbit Corneal Endothelial Dysfunction Model Using Endothelial-Mesenchymal Transformed Cells

Unlike humans, rabbit corneal endothelial wounds are known to spontaneously heal. The current study was aimed to develop a new rabbit bullous keratopathy model using corneal endothelial cells that were induced to undergo endothelial-mesenchymal transformation (EMT). EMT was induced in rabbit corneal endothelial cells (RCECs) by culturing with TGFβ and basic FGF Supplemented Medium. The corneal endothelia in recipient rabbits were mechanically scraped from the corneal endothelial surface inside an 8 mm mark. Then, a suspension of EMT-induced RCECs (EMT-RCECs) was injected into the anterior chamber. Eyes injected with freshly isolated RCECs (Fresh RCECs group) and eyes that were scraped without injection of cells (Scrape group) were used as controls. Immediately following operation, subepithelial and stromal edema was observed with increased central corneal thickness and corneal opacity in all groups. In the EMT-RCECs group, bullous keratopathy persisted for 42 days up to the end of the study. In the Fresh-RCECs and Scrape groups, corneal transparency and thickness recovered by 7 days after treatment and was maintained up to 42 days. The activated fibroblast marker, α-SMA, was observed spanning from corneal endothelium to corneal stroma in the EMT-RCECs group. Interestingly, α-SMA was upregulated in the Scrape-group as well. In all groups, there was no damage to other intraocular structures, and intraocular pressure was normal throughout the observation period. Transplanting a fresh donor cornea effectively treated corneal edema due to bullous keratopathy. This model is a promising tool for pre-clinical trials in the development of new therapies against corneal endothelial dysfunction.

Long Pentraxin-3 Modulates the Angiogenic Activity of Fibroblast Growth Factor-2

Angiogenesis, the process of new blood vessel formation from pre-existing ones, plays a key role in various physiological and pathological conditions. Alteration of the angiogenic balance, consequent to the deranged production of angiogenic growth factors and/or natural angiogenic inhibitors, is responsible for angiogenesis-dependent diseases, including cancer. Fibroblast growth factor-2 (FGF2) represents the prototypic member of the FGF family, able to induce a complex “angiogenic phenotype” in endothelial cells in vitro and a potent neovascular response in vivo as the consequence of a tight cross talk between pro-inflammatory and angiogenic signals. The soluble pattern recognition receptor long pentraxin-3 (PTX3) is a member of the pentraxin family produced locally in response to inflammatory stimuli. Besides binding features related to its role in innate immunity, PTX3 interacts with FGF2 and other members of the FGF family via its N-terminal extension, thus inhibiting FGF-mediated angiogenic responses in vitro and in vivo. Accordingly, PTX3 inhibits the growth and vascularization of FGF-dependent tumors and FGF2-mediated smooth muscle cell proliferation and artery restenosis. Recently, the characterization of the molecular bases of FGF2/PTX3 interaction has allowed the identification of NSC12, the first low molecular weight pan-FGF trap able to inhibit FGF-dependent tumor growth and neovascularization. The aim of this review is to provide an overview of the impact of PTX3 and PTX3-derived molecules on the angiogenic, inflammatory, and tumorigenic activity of FGF2 and their potential implications for the development of more efficacious anti-FGF therapeutic agents to be used in those clinical settings in which FGFs play a pathogenic role.

Fibroblast growth factor 2 decreases bleomycin-induced pulmonary fibrosis and inhibits fibroblast collagen production and myofibroblast differentiation

Fibroblast growth factor (FGF) signaling has been implicated in the pathogenesis of pulmonary fibrosis. Mice lacking FGF2 have increased mortality and impaired epithelial recovery after bleomycin exposure, supporting a protective or reparative function following lung injury. To determine whether FGF2 overexpression reduces bleomycin-induced injury, we developed an inducible genetic system to express FGF2 in type II pneumocytes. Double-transgenic (DTG) mice with doxycycline-inducible overexpression of human FGF2 (SPC-rtTA;TRE-hFGF2) or single-transgenic controls were administered intratracheal bleomycin and fed doxycycline chow, starting at either day 0 or day 7. In addition, wild-type mice received intratracheal or intravenous recombinant FGF2, starting at the time of bleomycin treatment. Compared to controls, doxycycline-induced DTG mice had decreased pulmonary fibrosis 21 days after bleomycin, as assessed by gene expression and histology. This beneficial effect was seen when FGF2 overexpression was induced at day 0 or day 7 after bleomycin. FGF2 overexpression did not alter epithelial gene expression, bronchoalveolar lavage cellularity or total protein. In vitro studies using primary mouse and human lung fibroblasts showed that FGF2 strongly inhibited baseline and TGFβ1-induced expression of alpha smooth muscle actin (αSMA), collagen, and connective tissue growth factor. While FGF2 did not suppress phosphorylation of Smad2 or Smad-dependent gene expression, FGF2 inhibited TGFβ1-induced stress fiber formation and serum response factor-dependent gene expression. FGF2 inhibition of stress fiber formation and αSMA requires FGF receptor 1 (FGFR1) and downstream MEK/ERK, but not AKT signaling. In summary, overexpression of FGF2 protects against bleomycin-induced pulmonary fibrosis in vivo and reverses TGFβ1-induced collagen and αSMA expression and stress fiber formation in lung fibroblasts in vitro, without affecting either inflammation or epithelial gene expression. Our results suggest that in the lung, FGF2 is antifibrotic in part through decreased collagen expression and fibroblast to myofibroblast differentiation. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A Cell Culture Approach to Optimized Human Corneal Endothelial Cell Function

Purpose

Cell-based therapies to replace corneal endothelium depend on culture methods to optimize human corneal endothelial cell (HCEC) function and minimize endothelial-mesenchymal transition (EnMT). Here we explore contribution of low-mitogenic media on stabilization of phenotypes in vitro that mimic those of HCECs in vivo.

Methods

HCECs were isolated from cadaveric donor corneas and expanded in vitro, comparing continuous presence of exogenous growth factors (“proliferative media”) to media without those factors (“stabilizing media”). Identity based on canonical morphology and expression of surface marker CD56, and function based on formation of tight junction barriers measured by trans-endothelial electrical resistance assays (TEER) were assessed.

Results

Primary HCECs cultured in proliferative media underwent EnMT after three to four passages, becoming increasingly fibroblastic. Stabilizing the cells before each passage by switching them to a media low in mitogenic growth factors and serum preserved canonical morphology and yielded a higher number of cells. HCECs cultured in stabilizing media increased both expression of the identity marker CD56 and also tight junction monolayer integrity compared to cells cultured without stabilization.

Conclusions

HCECs isolated from donor corneas and expanded in vitro with a low-mitogenic media stabilizing step before each passage demonstrate more canonical structural and functional features and defer EnMT, increasing the number of passages and total canonical cell yield. This approach may facilitate development of HCEC-based cell therapies.

MicroRNAs as critical regulators of the endothelial to mesenchymal transition in vascular biology

The endothelial to mesenchymal transition (EndMT) is a newly recognized, fundamental biological process involved in development and tissue regeneration, as well as pathological processes such as the complications of diabetes, fibrosis and pulmonary arterial hypertension. The EndMT process is tightly controlled by diverse signaling networks, similar to the epithelial to mesenchymal transition. Accumulating evidence suggests that microRNAs (miRNAs) are key regulators of this network, with the capacity to target multiple messenger RNAs involved in the EndMT process as well as in the regulation of disease progression. Thus, it is highly important to understand the molecular basis of miRNA control of EndMT. This review highlights the current fund of knowledge regarding the known links between miRNAs and the EndMT process, with a focus on the mechanism that regulates associated signaling pathways and discusses the potential for the EndMT as a therapeutic target to treat many diseases.

Endothelial to Mesenchymal Transition Represents a Key Link in the Interaction between Inflammation and Endothelial Dysfunction

Endothelial cells that line the inner walls of blood vessels are in direct contact with blood and display remarkable heterogeneity in their response to exogenous stimuli. These ECs have unique location-dependent properties determined by the corresponding vascular beds and play an important role in regulating the homeostasis of the vascular system. Evidence suggests that vascular endothelial cells exposed to various environments undergo dynamic phenotypic switching, a key biological program in the context of endothelial heterogeneity, but that might result in EC dysfunction and, in turn, cause a variety of human diseases. Emerging studies show the importance of endothelial to mesenchymal transition (EndMT) in endothelial dysfunction during inflammation. EndMT is a complex biological process in which ECs lose their endothelial characteristics, acquire mesenchymal phenotypes, and express mesenchymal cell markers, such as alpha smooth muscle actin and fibroblast-specific protein 1. EndMT is induced by inflammatory responses, leading to pathological states, including tissue fibrosis, pulmonary arterial hypertension, and atherosclerosis, via dysfunction of the vascular system. Although the mechanisms associated with inflammation-induced EndMT have been identified, unraveling the specific role of this phenotypic switching in vascular dysfunction remains a challenge. Here, we review the current understanding on the interactions between inflammatory processes, EndMT, and endothelial dysfunction, with a focus on the mechanisms that regulate essential signaling pathways. Identification of such mechanisms will guide future research and could provide novel therapeutic targets for the treatment of vascular diseases.

Fibroblast growth factor 2 induces proliferation and fibrosis via SNAI1-mediated activation of CDK2 and ZEB1 in corneal endothelium

Investigating stimulation of endogenous wound healing in corneal endothelial cells (CECs) may help address the global shortage of donor corneas by decreasing the number of transplants performed for blindness because of endothelial dysfunction. We previously reported that IL-1β stimulation leads to fibroblast growth factor (FGF2) expression, enhancing migration and proliferation of mammalian CECs. However, FGF2 also promotes the endothelial-mesenchymal transition, which can lead to retrocorneal membrane formation and blindness. This prompted us to investigate downstream FGF2 signaling targets that could be manipulated to prevent retrocorneal membrane formation. FGF2 stimulation altered cell morphology and induced expression of mesenchymal transition marker genes such as snail family transcriptional repressor 1 (SNAI1), SNAI2, zinc finger E-box-binding homeobox 1 (ZEB1), and ZEB2 This, in turn, induced expression of fibronectin, vimentin, and type I collagen, and suppressed E-cadherin in CECs in vitro and ex vivo siRNA-mediated SNAI1 knockdown revealed that SNAI1 induces ZEB1 expression, in turn inducing expression of type I collagen, the major component of retrocorneal membranes, and of cyclin-dependent kinase 2 (CDK2) and cyclin E1, promoting cell proliferation. siRNA-mediated knockdown of SNAI1 or ZEB1, but not of CDK2, inhibited FGF2-dependent expression of fibronectin, vimentin, and type I collagen and of suppression of E-cadherin expression. We conclude that SNAI1 is a key regulator of FGF2-dependent mesenchymal transition in human ex vivo corneal endothelium, with ZEB1 regulating type I collagen expression and CDK2 regulating cell proliferation. These results suggest that SNAI1 promotes fibrosis and cell proliferation in human corneal endothelium through ZEB1 and CDK2.

Bilateral Alterations in Corneal Nerves, Dendritic Cells, and Tear Cytokine Levels in Ocular Surface Disease

This review summarizes the recent literature regarding corneal imaging in human subjects using in vivo confocal microscopy. It also covers the recent literature on corneal immune cells, nerves, and tear cytokine levels in ocular surface diseases as well as corneal immune privilege. The significance of interactions between corneal immune cells and nerves in health, neurotrophic keratopathy, and infectious keratitis is discussed. Furthermore, bilateral alterations of immune cells and nerves in clinically unilateral corneal diseases and the link to changes of tear cytokines or neuropeptide levels in contralateral eyes are described. Recent studies reported increased density and morphologic changes of corneal dendritic cells in ocular surface disease that correlated with a decrease in subbasal nerve and corneal nerve density, suggesting potential interactions between the immune and nervous systems in the cornea. Although the relevance of tear cytokines is poorly understood, tear cytokines might have an important role in the pathogenesis of ocular surface diseases. In humans and experimental animal models, alterations in immune cells, cytokines, and immunomodulatory neuropeptide levels in contralateral eyes might mediate the incidence of bilateral infectious keratitis and loss of immune privilege of the cornea in bilateral corneal transplantation or neurotrophic keratopathy cases. The discovery of bilateral alterations of immune cells and nerves in ocular surface diseases is considered the missing link between the immune and nervous systems in the cornea, and demonstrates how studies of animal models and humans aid our understanding of human corneal disease phenomena.

Endothelial-to-mesenchymal transition: Cytokine-mediated pathways that determine endothelial fibrosis under inflammatory conditions

During the last decade, the endothelial-to-mesenchymal transition (EndMT) process has attracted considerable attention due to associations with the onset of certain diseases, such as organ fibrosis and cancer. Several studies have assessed the mechanisms and signaling pathways that regulate endothelial fibrosis in the context of human pathologies. A number of inflammatory mediators, including pro-inflammatory cytokines, growth factors, oxidative stress, and toxins, induce the conversion of endothelial cells into mesenchymal fibroblast-like cells that promote disease progression. This review is separated into five chapters that critically present current knowledge on EndMT in the context of pathology. First, the main characteristics of EndMT are summarized, with a focus on the endothelial protein pattern changes that modulate the expressions of endothelial/fibrotic markers and extracellular matrix proteins. These expressions could serve as mechanisms for explaining potential EndMT contributions to human pathologies in adults. Second, the main findings supporting a connection between EndMT-mediated endothelial fibrosis and inflammatory conditions are presented. These connections could be linked to the onset and progression of pathological conditions. Third, EndMT inducers are described in detail. This includes considerations on the actions of the first and most well-known EndMT inducer, TGF-β; of the most prominent pro-inflammatory cytokines released during inflammation, such as IL 1-β and TNF-α; and of the NF-κB transcription factor, a common player during inflammation-induced EndMT. Furthermore, thorough attention is given to EndMT induction by endotoxins in the context of bacterial infectious diseases. Additionally, the participation of the inflammatory oxidative stress environment in the EndMT induction was also reviewed. Fourth, the pathophysiological findings of inflammation-induced EndMT are presented, and, fifth, special focus is placed on associations with cancer onset and development. Altogether, this review highlights the important role of EndMT-mediated endothelial fibrosis during inflammation in human pathologies.

WNT10B enhances proliferation through β-catenin and RAC1 GTPase in human corneal endothelial cells

The cornea is the anterior, transparent tissue of the human eye that serves as its main refractive element. Corneal endothelial cells are arranged as a monolayer on the posterior surface of the cornea and function as a pump to counteract the leakiness of its basement membrane. Maintaining the cornea in a slightly dehydrated state is critical for the maintenance of corneal transparency. Adult human corneal endothelial cells are G1-arrested, even in response to injury, leading to an age-dependent decline in endothelial cell density. Corneal edema and subsequent vision loss ensues when endothelial cell density decreases below a critical threshold. Vision loss secondary to corneal endothelial dysfunction is a common indication for transplantation in developed nations. An impending increase in demand for and a current global shortage of donor corneas will necessitate the development of treatments for vision loss because of endothelial dysfunction that do not rely on donor corneas. Wnt ligands regulate many critical cellular functions, such as proliferation, making them attractive candidates for modulation in corneal endothelial dysfunction. We show that WNT10B causes nuclear transport and binding of RAC1 and β-catenin in human corneal endothelial cells, leading to the activation of Cyclin D1 expression and proliferation. Our findings indicate that WNT10B promotes proliferation in human corneal endothelial cells by simultaneously utilizing both β-catenin-dependent and -independent pathways and suggest that its modulation could be used to treat vision loss secondary to corneal endothelial dysfunction.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Promotion of mesenchymal-to-epithelial transition by Rac1 inhibition with small molecules accelerates hepatic differentiation of mesenchymal stromal cells

In vitro differentiation of stem cells into specific cell lineages provides a stable cell supply for cell therapy and tissue engineering. Therefore, understanding the mechanisms underlying such differentiation processes is critical for generating committed lineage-specific cell progenies effectively. We previously developed a two-step protocol to differentiate mesenchymal stromal cells (MSCs) into hepatocyte-like cells. Since hepatic differentiation involves mesenchymal-epithelial transition (MET), we hypothesize that promoting MET could further accelerate the differentiation process. Ras-related C3 botulinum toxin substrate 1 (Rac1) is involved in actin polymerization and its role in MET was investigated in the study. Our results showed that inhibition of Rac1 activation by Rac1-specific inhibitor, NSC23766, led to cells favoring epithelial morphology and being more packed during hepatic differentiation. In addition, Rac1 inhibition accelerated the upregulation of hepatic marker genes accompanied by more mature hepatic functions. Taken together, promotion of MET by inhibiting Rac1 accelerates the hepatic differentiation of MSCs. Our findings open a new prospect of directing the commitment of MSCs by manipulating cell morphology and cytoskeleton arrangement through small molecules. The results provide further insight into scaffold design for rapid production of MSC-differentiated hepatocytes.

FGF-2 inhibits Endothelial-Mesenchymal Transition through microRNA-20a-mediated repression of canonical TGF-β Signaling

Endothelial-to-Mesenchymal transition (EndMT) is characterized by the loss of endothelial cell markers and functions, and coincides with de novo expression of mesenchymal markers. EndMT is induced by TGFβ1 and changes endothelial microRNA expression. We found that miR-20a is decreased during EndMT and ectopic expression of miR-20a inhibits EndMT induction.

TGFβ1 induces cellular hypertrophy in human umbilical vein endothelial cells and abrogates VE-Cadherin expression, reduces endothelial sprouting capacity and induces the expression of the mesenchymal marker SM22α. We identified ALK5, TGFBR2 and SARA as direct miR-20a targets. Expression of miR-20a mimics abrogates the endothelial responsiveness to TGFβ1 by decreasing ALK5, TGFBR2, and SARA and inhibits EndMT, indicated by the maintenance of VE-Cadherin expression and sprouting ability and absence of SM22α expression. FGF2 increases miR-20a expression and inhibits EndMT in TGFβ1-stimulated endothelial cells.

In summary, FGF2 controls endothelial TGFβ1 signaling by regulating ALK5, TGFBR2 and SARA expression, through miR-20a. Loss of FGF2 signaling combined with a TGFβ1 challenge reduces miR-20a levels and increases endothelial responsiveness to TGFβ1 through elevated receptor complex levels and activation of Smad2/3, which culminates in EndMT.

Correlation between human tear cytokine levels and cellular corneal changes in patients with bacterial keratitis by in vivo confocal microscopy

PURPOSE

We investigated bilateral tear cytokine levels in patients with unilateral bacterial keratitis (BK) as associated with in vivo confocal microscopic (IVCM) alterations in corneal nerves and dendritiform immune cells (DCs).

METHODS

A total of 54 (13 BK, 13 contralateral, 28 healthy controls) tear samples was collected prospectively and analyzed by multiplex microbeads assay. The IVCM of the central cornea was performed on the same day, and assessed for corneal nerve and DC alterations.

RESULTS

Interleukin-1β, IL-6, and IL-8 were significantly elevated only in affected eyes (66.6 ± 26.8, 7174 ± 2430, and 810 ± 315 ρg/mL, respectively; P = 0.04, P < 0.001, and P < 0.001, respectively), compared to healthy controls (13.0 ± 4.0, 171.8 ± 32.1, and 56.5 ± 33.8 ρg/mL). Levels of chemokine ligand 2 (CCL-2), IL-10, and IL-17a were elevated only in contralateral eyes (813 ± 478, 86.7 ± 38.3, and 3350 ± 881 ρg/mL, respectively; P = 0.02, P = 0.01, and P = 0.04, respectively), compared to controls (73.7 ± 25.3, 17.5 ± 4.9, and 1350 ± 337 ρg/mL). Triggering receptor expressed on myeloid cells (TREM)-1 was significantly elevated in affected (551 ± 231 ρg/mL, P = 0.02) and contralateral unaffected (545 ± 298 ρg/mL, P = 0.03) eyes compared to controls (31.3 ± 12.4 ρg/mL). The density of DCs was significantly increased in affected (226.9 ± 37.3 cells/mm(2), P < 0.001) and unaffected (122.3 ± 23.7 cells/mm(2), P < 0.001) eyes compared to controls (22.7 ± 5.9 cells/mm(2)). Sub-basal nerve density significantly decreased in affected (3337 ± 1615 μm/mm(2), P < 0.001) and contralateral (13,230 ± 1635 μm/mm(2), P < 0.001) eyes compared to controls (21,200 ± 545 μm/mm(2)). Levels of IL-1β, IL-6, and IL-8 were significantly correlated with DC density (R = 0.40, R = 0.55, and R = 0.31, all P < 0.02) and nerve density (R = -0.30, R = -0.53, and R = -0.39, all P < 0.01).

CONCLUSIONS

Proinflammatory tear cytokines are elevated bilaterally in patients with unilateral BK, and are correlated strongly with alterations in DCs and nerve density as detected by IVCM.

Activation of RhoA-ROCK-BMP signaling reprograms adult human corneal endothelial cells

Activation of RhoA-ROCK-BMP signaling reprograms adult human corneal endothelial cells into neural crest–like progenitors, which effectively form corneal endothelial monolayers that may eliminate the need for corneal transplantation.

Currently there are limited treatment options for corneal blindness caused by dysfunctional corneal endothelial cells. The primary treatment involves transplantation of healthy donor human corneal endothelial cells, but a global shortage of donor corneas necessitates other options. Conventional tissue approaches for corneal endothelial cells are based on EDTA-trypsin treatment and run the risk of irreversible endothelial mesenchymal transition by activating canonical Wingless-related integration site (Wnt) and TGF-β signaling. Herein, we demonstrate an alternative strategy that avoids disruption of cell–cell junctions and instead activates Ras homologue gene family A (RhoA)–Rho-associated protein kinase (ROCK)–canonical bone morphogenic protein signaling to reprogram adult human corneal endothelial cells to neural crest–like progenitors via activation of the miR302b-Oct4-Sox2-Nanog network. This approach allowed us to engineer eight human corneal endothelial monolayers of transplantable size, with a normal density and phenotype from one corneoscleral rim. Given that a similar signal network also exists in the retinal pigment epithelium, this partial reprogramming approach may have widespread relevance and potential for treating degenerative diseases.

Regenerative Cell Therapy for Corneal Endothelium

Endothelial cell dysfunction as in Fuchs dystrophy or pseudophakic bullous keratopathy, and the limited regenerative capacity of human corneal endothelial cells (HCECs), drive the need for corneal transplant. In response to limited donor corneal availability, significant effort has been directed towards cell therapy as an alternative to surgery. Stimulation of endogenous progenitors, or transplant of stem cell-derived HCECs or in vitro-expanded, donor-derived HCECs could replace traditional surgery with regenerative therapy. Ex vivo expansion of HCECs is technically challenging, and the basis for molecular identification of functional HCECs is not established. Delivery of cells to the inner layer of the human cornea is another challenge: different techniques, from simple injection to artificial corneal scaffolds, are being investigated. Despite remaining questions, corneal endothelial cell therapies, translated to the clinic, represent the future for the treatment of corneal endotheliopathies.

Interleukin-1β-induced Wnt5a enhances human corneal endothelial cell migration through regulation of Cdc42 and RhoA

Wnt5a can activate β-catenin-independent pathways for regulation of various cellular functions, such as migration, that play critical roles in wound repair. Investigation of Wnt5a signaling may help identify therapeutic targets for enhancing corneal endothelial wound healing that could provide an alternative to corneal transplantation in patients with blindness from endothelial dysfunction. However, Wnt5a signaling in corneal endothelial cells (CECs) has not been well characterized. In this study, we show transient induction of Wnt5a by interleukin-1β (IL-1β) stimulation proceeds through NF-κB in human CECs. This leads to binding of Fzd5 to Ror2, resulting in activation of disheveled protein (Dvl) and subsequently disheveled-associated activator of morphogenesis 1 (DAAM1). This leads to activation of Cdc42 and subsequent inhibition of RhoA. Inhibition of RhoA leads to parallel dephosphorylation and inactivation of LIM domain kinase 2 along with dephosphorylation and activation of slingshot 1, resulting in dephosphorylation and activation of cofilin and leading to enhanced cell migration. These findings suggest that Wnt5a enhances cell migration through activation of Cdc42 and inactivation of RhoA in human CECs.

Deficient repair response of IPF fibroblasts in a co-culture model of epithelial injury and repair

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive disorder marked by relentless fibrosis and damage of the lung architecture. A growing body of evidence now suggests that IPF progresses as a result of aberrant epithelial-fibroblast crosstalk. Injured epithelia are a major source of growth factors such as PDGF which guide resident fibroblasts to injury sites.

RESULTS

In this study, we utilized a novel co-culture system to investigate the effect of fibroblast phenotype on their response to epithelial injury. Fibroblasts from normal lungs (NHLF) responded to epithelial injury and populated the wound site forming a fibroblast plug/mechanical barrier which prevented epithelial wound closure. IPF fibroblasts were impaired in their response to epithelial injury. They also expressed reduced PDGFRα compared to NHLFs and were defective towards PDGF-AA mediated directional movement. Neutralization of PDGF-AA and pan-PDGF but not PDGF-BB reduced the injury response of NHLFs thereby preventing the formation of the mechanical barrier and promoting epithelial wound closure. Co-culture of epithelial cells with IPF fibroblasts led to marked increase in the levels of pro-fibrotic growth factors - bFGF and PDGF and significant depletion of anti-fibrotic HGF in the culture medium. Furthermore, IPF fibroblasts but not NHLFs induced a transient increase in mesenchymal marker expression in the wound lining epithelial cells. This was accompanied by increased migration and faster wound closure in co-cultures with IPF fibroblasts.

CONCLUSIONS

Our data demonstrate that the IPF fibroblasts have an aberrant repair response to epithelial injury.

Notch signal regulates corneal endothelial-to-mesenchymal transition

Endothelial-to-mesenchymal transition (EnMT) is a cell transformation process involved in both morphogenesis and pathogenesis. EnMT of corneal endothelial cells happens after endothelial injury and during ex vivo culture. Previous studies have shown that the transforming growth factor-β signaling pathway is involved in this transition. In this study, we found that rat corneal endothelial cells could spontaneously undergo EnMT during ex vivo culture. This change in rat corneal endothelial cells was associated with Notch signaling pathway activation after the first passage, which was blocked by the Notch inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT). This inhibitor also prevented transforming growth factor β1-, β2-, and β3-induced EnMT and reversed transformed rat corneal endothelial cells to a normal phenotype. Furthermore, DAPT treatment blocked retrocorneal membrane formation in a rat corneal endothelium damage model. Our study indicates that the Notch signaling pathway is involved in the corneal EnMT process, which may be a novel therapeutic target for treating corneal endothelial fibrogenic disorders.

ROCK inhibitor converts corneal endothelial cells into a phenotype capable of regenerating in vivo endothelial tissue

Corneal endothelial dysfunction accompanied by visual disturbance is a primary indication for corneal transplantation. We previously reported that the adhesion of corneal endothelial cells (CECs) to a substrate was enhanced by the selective ROCK inhibitor Y-27632. It is hypothesized that the inhibition of ROCK signaling may manipulate cell adhesion properties, thus enabling the transplantation of cultivated CECs as a form of regenerative medicine. In the present study, using a rabbit corneal endothelial dysfunction model, the transplantation of CECs in combination with Y-27632 successfully achieved the recovery of corneal transparency. Complications related to cell injection therapy, such as the abnormal deposition of the injected cells as well as the elevation of intraocular pressure, were not observed. Reconstructed corneal endothelium with Y-27632 exhibited a monolayer hexagonal cell shape with a normal expression of function-related markers, such as ZO-1, and Na(+)/K(+)-ATPase, whereas reconstruction without Y-27632 exhibited a stratified fibroblastic phenotype without the expression of markers. Moreover, transplantation of CECs in primates in the presence of the ROCK inhibitor also achieved the recovery of long-term corneal transparency with a monolayer hexagonal cell phenotype at a high cell density. Taken together, these results suggest that the selective ROCK inhibitor Y-27632 enables cultivated CEC-based therapy and that the modulation of Rho-ROCK signaling activity serves to enhance cell engraftment for cell-based regenerative medicine.

NF-κB is the transcription factor for FGF-2 that causes endothelial mesenchymal transformation in cornea

PURPOSE

To determine the role of nuclear factor-κB (NF-κB) during FGF-2-mediated endothelial mesenchymal transformation (EMT) in response to interleukin (IL)-1β stimulation in corneal endothelial cells (CECs).

METHODS

Expression and/or activation of IL-1 receptor-associated protein kinase (IRAK), TNF receptor-associated factor 6 (TRAF6), phosphatidylinositol 3-kinase (PI 3-kinase), IκB kinase (IKK), IκB, NF-κB, and FGF-2 were analyzed by immunoblot analysis. Cell proliferation was measured by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. NF-κB activity was measured by NF-κB ELISA kit, while binding of NF-κB to the promoter region of FGF-2 gene was determined by chromatin immunoprecipitation.

RESULTS

Brief stimulation of CECs with IL-1β upregulated expression of IRAK and TRAF6 and activated PI 3-kinase; expression of IRAK and TRAF6 reached maximum within 60 minutes, after which the expression disappeared, while PI 3-kinase activity was observed up to 4 hours after IL-1β stimulation. Use of specific inhibitor to PI 3-kinase or IRAK demonstrated that IRAK activates PI 3-kinase, the signaling of which phosphorylates IKKα/β and degrades IκB, subsequently leading to activation of NF-κB. The induction of FGF-2 by IL-1β was completely blocked by inhibitors to NF-κB activation (sulfasalazine) or PI 3-kinase (LY294002), and both inhibitors greatly blocked cell proliferation of CECs. Chromatin immunoprecipitation further demonstrated that NF-κB is the transcription factor of FGF-2 as NF-κB binds the putative NF-κB binding site of the FGF-2 promoter.

CONCLUSIONS

These data suggest that IL-1β signaling combines the canonical pathway and the PI 3-kinase signaling to upregulate FGF-2 production through NF-κB, which plays a key role as a transcription factor of FGF-2 gene.

Increased invasiveness of MMP-9-deficient tumors in two mouse models of neuroendocrine tumorigenesis

Despite their apparent success in pre-clinical trials, metalloproteinase (MMP) inhibitors proved to be inefficacious in clinical settings. In an effort to understand the underlying causes of this unanticipated outcome, we modeled the consequences of long-term MMP inhibition by removing one of the major players in tumorigenesis, MMP9, in two complimentary mouse models of pancreatic neuroendocrine carcinogenesis: Myc;BclXl and RIP1-Tag2. By employing gel zymography and a fluoregenic solution assay, we first established that MMP9 is expressed and activated in Myc;BclXl tumors in an interleukin-1β-dependent manner. The genetic deletion of MMP9 in Myc;BclXl mice impairs tumor angiogenesis and growth analogous to its absence in the RIP1-Tag2 model. Notably, tumors that developed in the context of MMP9-deficient backgrounds in both models were markedly more invasive than their typical wild-type counterparts, and expressed elevated levels of pro-invasive cysteine cathepsin B. The increased invasion of MMP9-deficient tumors was associated with a switch in the spectrum of inflammatory cells at the tumor margins, involving homing of previously undetected, cathepsin-B expressing CD11b;Gr1-positive cells to the invasive fronts. Thus, plasticity in the tumor inflammatory compartment is partially responsible for changes in the expression pattern of tumor-associated proteases, and may contribute to the compensatory effects observed on MMP inhibition, hence accounting for the heightened tumor progression described in late stage clinical trials.

Human corneal endothelial cells employ phosphorylation of p27(Kip1) at both Ser10 and Thr187 sites for FGF-2-mediated cell proliferation via PI 3-kinase

PURPOSE

FGF-2 stimulates cell proliferation of rabbit corneal endothelial cells (rCECs) by degrading the cyclin-dependent kinase inhibitor p27(Kip1) (p27) through its phosphorylation mechanism. The authors investigated whether the cell proliferation of human CECs (hCECs) is also induced by FGF-2 stimulation through the p27 phosphorylation pathway.

METHODS

Expression and activation of protein were analyzed by immunoblotting. Cell proliferation was measured by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. Transfection of hCECs with small interference RNA (siRNA) was performed using a transfection reagent.

RESULTS

FGF-2 stimulated cell proliferation in hCECs; the FGF-2 action was completely blocked by pathway-specific inhibitors for PI 3-kinase (LY294002) and MEK1/2 (U0126), respectively. Using immunoblotting, the authors showed that FGF-2 induced phosphorylation of p27 at both serine 10 (Ser10) and threonine 187 (Thr187) sites. These effects were also completely blocked by LY294002 or U0126. The authors then determined cross-talk between PI 3-kinase and extracellular signal-regulated kinase (ERK)1/2; blocking of ERK1/2 activation by LY294002 indicated that in hCECs ERK1/2 works as a downstream effector to PI 3-kinase for cell proliferation induced by FGF-2, whereas the ERK1/2 pathway in rCECs is parallel to the PI 3-kinase pathway. However, the downstream mechanism involved in cell cycle progression in hCECs is identical to that of rCECs: phosphorylation of p27 at Ser10 was mediated by kinase-interacting stathmin (KIS), confirmed with siRNA to KIS, and phosphorylation of p27 at Thr187 was mediated by cell division cycle 25A (Cdc25A), confirmed using Cdc25A inhibitor. CONCLUSIONS; FGF-2 stimulates proliferation of hCECs through PI 3-kinase and its downstream target ERK1/2 pathways. This linear signal transduction significantly downregulates p27 through its phosphorylation at both Ser10 and Thr187 sites mediated by KIS and Cdc25A, respectively.

Endothelial mesenchymal transformation mediated by IL-1β-induced FGF-2 in corneal endothelial cells

This review describes the molecular mechanism of endothelial mesenchymal transformation (EMT) mediated by fibroblast growth factor-2 (FGF-2) in corneal endothelial cells (CECs). Corneal fibrosis is not frequently observed in corneal endothelium/Descemet's membrane complex; but when this pathologic tissue is produced, it causes a loss of vision by physically blocking light transmittance. Herein, we will address the cellular activities of FGF-2 and its signaling pathways during the EMT process. Furthermore, we will discuss the role of inflammation on FGF-2-mediated EMT. Interleukin-1β (IL-1β) greatly upregulates FGF-2 production in CECs, thus leading to FGF-2-mediated EMT; the whole spectrum of the injury-mediated inflammation (IL-1β pathway) and the subsequent EMT process (FGF-2 pathway) will be briefly discussed. Intervention in the two pathways will provide the means to block EMT before inflammation causes an irreversible change, such as the production of retrocorneal fibrous membrane observed in human eyes.

PI 3-kinase/Rac1 and ERK1/2 regulate FGF-2-mediated cell proliferation through phosphorylation of p27 at Ser10 by KIS and at Thr187 by Cdc25A/Cdk2

PURPOSE

To determine the mechanism of p27 phosphorylation through common and differential pathways triggered by FGF-2 in corneal endothelial cells (CECs).

METHODS

A GTP pull-down assay was performed to identify Rac1-GTP. Expression and activation of protein were analyzed by immunoblotting. Cell proliferation was measured by an MTT assay. Transfection of CECs with kinase-interacting stathmin (KIS) siRNA was performed.

RESULTS

FGF-2 activated Rac1 through Akt, and Rac1 inhibitor greatly inhibited the FGF-2-stimulated cell proliferation. Rac1 inhibitor reduced p27 phosphorylation at both serine 10 (Ser10) and threonine 187 (Thr187). ERK1/2 was also involved in FGF-2-stimulated CEC proliferation and phosphorylation of p27 at Ser10 and Thr187 in parallel to phosphatidylinositol (PI) 3-kinase. In both PI 3-kinase/Rac1 and ERK1/2 pathways, Ser10 of p27 is phosphorylated by KIS, confirmed by siRNA to KIS, which subsequently hampered the FGF-2-stimulated cell proliferation, while Thr187 of p27 was phosphorylated through Cdk2 activated by Cdc25A. Cdc25A inhibitor blocked activation of Cdk2, phosphorylation of p27 at Thr187, and cell proliferation. FGF-2 induced both KIS and Cdc25A during the G1 phase; the maximum KIS expression was observed 4 hours after FGF-2 stimulation, while the maximum Cdc25A expression was observed at 12 hours. Blockade of ERK1/2 and Rac1 greatly reduced KIS and Cdc25A expression.

CONCLUSIONS

Results suggest that FGF-2 uses both PI 3-kinase/Rac1 and ERK pathways for cell proliferation; two signals employ common pathways for phosphorylating p27 according to the sites (KIS for Ser10 and Cdc25A/Cdk2 for Thr187) with their characteristic kinetics (early G1 for Ser10 and late G1 for Thr187).

The detrimental effects of IFN-α on vasculogenesis in lupus are mediated by repression of IL-1 pathways: potential role in atherogenesis and renal vascular rarefaction

Systemic lupus erythematosus (SLE) is characterized by increased vascular risk due to premature atherosclerosis independent of traditional risk factors. We previously proposed that IFN-α plays a crucial role in premature vascular damage in SLE. IFN-α alters the balance between endothelial cell apoptosis and vascular repair mediated by endothelial progenitor cells (EPCs) and myeloid circulating angiogenic cells (CACs). In this study, we demonstrate that IFN-α promotes an antiangiogenic signature in SLE and control EPCs/CACs, characterized by transcriptional repression of IL-1α and β, IL-1R1, and vascular endothelial growth factor A, and upregulation of IL-1R antagonist and the decoy receptor IL-1R2. IL-1β promotes significant improvement in the functional capacity of lupus EPCs/CACs, therefore abrogating the deleterious effects of IFN-α. The beneficial effects from IL-1 are mediated, at least in part, by increases in EPC/CAC proliferation, by decreases in EPC/CAC apoptosis, and by preventing the skewing of CACs toward nonangiogenic pathways. IFN-α induces STAT2 and 6 phosphorylation in EPCs/CACs, and JAK inhibition abrogates the transcriptional antiangiogenic changes induced by IFN-α in these cells. Immunohistochemistry of renal biopsies from patients with lupus nephritis, but not anti-neutrophil cytoplasmic Ab-positive vasculitis, showed this pathway to be operational in vivo, with increased IL-1R antagonist, downregulation of vascular endothelial growth factor A, and glomerular and blood vessel decreased capillary density, compared with controls. Our study introduces a novel putative pathway by which type I IFNs may interfere with vascular repair in SLE through repression of IL-1-dependent pathways. This could promote atherosclerosis and loss of renal function in this disease.

Tissue factor expression in newt iris coincides with thrombin activation and lens regeneration

Lens regeneration in adult salamanders occurs at the pupillary margin of the mid-dorsal iris where pigmented epithelial cells (PEC) re-enter the cell cycle and transdifferentiate into lens. It is not understood how the injury caused by removal of the lens (lentectomy) in one location is linked to initiating the response in a different spatial location (dorsal iris) and to this particular sector. We propose that the blood provides a link between the localised coagulation and signal transduction pathways that lead to regeneration. A transmembrane protein (tissue factor) is expressed in a striking patch-like domain in the dorsal iris of the newt that localises coagulation specifically to this location, but is not expressed in the axolotl, a related species that does not show thrombin activation after lentectomy and cannot regenerate its lens. Our hypothesis is that tissue factor expression localises the initiation of regeneration through the activation of thrombin and the recruitment of blood cells, leading to local growth factor release. This is the first example of gene expression in a patch of cells that prefigures the location of a regenerative response, and links the immune system with the initiation of a regenerative program.

Induction of FGF-2 synthesis by IL-1beta in aqueous humor through P13-kinase and p38 in rabbit corneal endothelium

PURPOSE

To determine whether the elevated level of interleukin (IL)-1beta in aqueous humor after transcorneal freezing upregulates FGF-2 synthesis in rabbit corneal endothelium through PI3-kinase and p38 pathways.

METHODS

Transcorneal freezing was performed in New Zealand White rabbits to induce an injury-mediated inflammation. The concentration of IL-1beta was measured, and the expression of FGF-2, p38, and Akt underwent Western blot analysis. Intracellular location of FGF-2 and actin cytoskeleton was determined by immunofluorescence staining.

RESULTS

Massive infiltration of polymorphonuclear leukocytes (PMNs) to the corneal endothelium was observed after freezing, and IL-1beta concentration in the aqueous humor was elevated in a time-dependent manner after freezing. Similarly, FGF-2 expression was increased in a time-dependent manner. When corneal endothelium was stained with anti-FGF-2 antibody, the nuclear location of FGF-2 was observed primarily in the cornea after cryotreatment, whereas FGF-2 in normal corneal endothelium was localized at the plasma membrane. Treatment of the ex vivo corneal tissue with IL-1beta upregulated FGF-2 and facilitated its nuclear location in corneal endothelium. Transcorneal freezing disrupted the actin cytoskeleton at the cortex, and cell shapes were altered from cobblestone morphology to irregular shape. Topical treatment with LY294002 and SB203580 on the cornea after cryotreatment blocked the phosphorylation of Akt and p38, respectively, in the corneal endothelium. These inhibitors also reduced FGF-2 levels and partially blocked morphologic changes after freezing.

CONCLUSIONS

These data suggest that after transcorneal freezing, IL-1beta released by PMNs into the aqueous humor stimulates FGF-2 synthesis in corneal endothelium via PI3-kinase and p38.

Common and distinct pathways for cellular activities in FGF-2 signaling induced by IL-1beta in corneal endothelial cells

PURPOSE

To determine the mechanism by which IL-1beta induces FGF-2 and to elucidate the signaling pathways of IL-1beta-induced FGF-2 in corneal endothelial cells (CECs).

METHODS

Expression and/or activation of FGF-2, p38, ERK1/2, and Akt was analyzed by immunoblot analysis. Cell proliferation was measured by MTT assay. Pharmacologic inhibitors were used to block PI 3-kinase, p38, or ERK1/2.

RESULTS

Brief stimulation of CECs with IL-1beta activated PI 3-kinase and p38 in a biphasic fashion. The first wave of activation, triggered by IL-1beta, involves the inductive activity of IL-1beta on FGF-2 production; the second wave of activation, triggered by the induced FGF-2, involves the promotion of cellular activities. In both pathways, p38 acts downstream to PI 3-kinase. The inductive activity of IL-1beta on FGF-2 is further evidenced by the conditioned medium, which contains a large amount of FGF-2. Stimulation of CECs with IL-1beta also activated ERK1/2 in a delayed fashion. The IL-1beta-induced FGF-2 exerted cellular activities using distinct pathways: the second wave of activation of PI 3-kinase and p38 was involved in cell migration, whereas cell proliferation was simultaneously stimulated by ERK1/2 and the second wave of PI 3-kinase. Likewise, the conditioned medium demonstrated cellular activities and pathways identical with those observed in cells treated with IL-1beta.

CONCLUSIONS

These data suggest that CECs produce FGF-2 by IL-1beta stimulation through PI 3-kinase and p38. The IL-1beta-induced FGF-2 facilitates cell migration via PI 3-kinase and p38, whereas it stimulates cell proliferation using PI 3-kinase and ERK1/2 in parallel pathways.

IL-1beta differently involved in IL-8 and FGF-2 release in crystalline silica-treated lung cell co-cultures

Background

Inhalation of crystalline silica particles is in humans associated with inflammation and development of fibrosis. The aim of the present study was to investigate the effect of crystalline silica on the release of the fibrosis- and angiogenesis-related mediator FGF-2 and the pro-inflammatory mediator IL-8, and how IL-1β and TNF-α were involved in this release from various mono- and co-cultures of monocytes, pneumocytes and endothelial cells.

Results

Silica exposure induced an increase of IL-8 release from monocytes and from pneumocytes alone, and the FGF-2 level in the medium increased upon silica exposure of pneumocytes. Both the responses were enhanced in non-contact co-cultures with endothelial cells. The FGF-2 release seemed to increase with the silica-induced decrease in the number of pneumocytes. The release of IL-8 and FGF-2 was partially suppressed in cultures with pneumocytes in contact with monocytes compared to non-contact cultures. Treatment with anti-TNF-α and the IL-1 receptor antagonist revealed that release of IL-1β, and not TNF-α, from monocytes dominated the regulation of IL-8 release in co-cultures. For release of FGF-2, IL-1ra was without effect. However, exogenous IL-1β reduced the FGF-2 levels, strongly elevated the FGF-2-binding protein PTX3, and prevented the reduction in the number of pneumocytes induced by silica.

Conclusion

IL-1β seems to be differently involved in the silica-induced release of IL-8 and FGF-2 in different lung cell cultures. Whereas the silica-induced IL-8 release is regulated via an IL-1-receptor-mediated mechanism, IL-1β is suggested only indirectly to affect the silica-induced FGF-2 release by counteracting pneumocyte loss. Furthermore, the enhanced IL-8 and FGF-2 responses in co-cultures involving endothelial cells show the importance of the interaction between different cell types and may suggest that both these mediators are important in angiogenic or fibrogenic processes.