Effect of cAMP on TGFbeta1-induced corneal keratocyte-myofibroblast transformation

Therapeutic effects of a novel venom abstract (ZK002) solution in an alkali-burned corneal wound-healing model

Purpose

Corneal alkali burns can progress to corneal epithelial defects, inflammation, scarring, and angiogenesis, potentially leading to blindness. Therefore, we examined the therapeutic effects of a novel ophthalmic solution (ZK002) on wound healing in alkali-burned rat corneas.

Methods

In this study, we attempted to treat alkali-exposed rat corneas using topical application of either an ophthalmic solution with ZK002 or an anti-vascular endothelial growth factor agent for 14 days. We evaluated corneal edema, corneal neovascularization area, and histological changes. We also assessed the inflammatory (MMP-9, MMP-2, and interleukin-1β) and angiogenic (vascular endothelial growth factor receptor 2, VEGFR2) markers. Levels of inflammatory (matrix metalloproteinase (MMP)-9, MMP-2, and interleukin-1β), profibrotic (α-smooth muscle actin, α-SMA; transforming growth factor-β2,TGF-β2), and angiogenic (vascular endothelial growth factor-receptor 2, VEGFR2) factors, as well as peroxisome proliferator-activated receptor γ (PPARγ) mRNA expression, were measured.

Results

The analyses showed that alkali exposure caused an increase in corneal edema and fibrosis with corneal neovascularization. The accumulation of α-smooth muscle actin-positive myofibroblasts and the deposition of transforming growth factor-β2 on the alkali-exposed corneas were noted on day 14. The mRNA expression levels of interleukin-1β, MMP-9, MMP-2, VEGFR2, and profibrotic factors were decreased in the ZK002 group compared with the control group during the early period of corneal alkali burns on day 14. However, the expression level of PPARγ mRNA was increased in the ZK002 group.

Conclusions

ZK002 decreased the fibrotic reaction and prevented neovascularization in the cornea after an alkali burn. Therefore, the novel ophthalmic solution ZK002 could be a potentially promising therapeutic clinical treatment for corneal wound healing.

Hyperosmolar Potassium Inhibits Corneal Myofibroblast Transformation and Prevent Corneal Scar

PURPOSE

Corneal myofibroblasts play a crucial role in the process of corneal scarring. Potassium has been documented to reduce skin scar tissue formation. Herein, we investigated the ability of potassium to prevent corneal fibrosis in cell culture and in vivo.

METHODS

Corneal fibroblasts (CFs) were isolated from the corneal limbus and treated with TGF-β1 to transform into corneal myofibroblasts. Corneal myofibroblast markers were detected by quantitative real-time PCR, Western blot, and immunofluorescence. The contractive functions of corneal myofibroblast were evaluated by the scratch assay and the collagen gel contraction assay. RNA sequencing in corneal fibroblasts was performed to explore the mechanisms underlying hyperosmolar potassium treatment. GO and KEGG analysis were performed to explore the underlying mechanism by hyperosmolar potassium treatment. The ATP detection assay assessed the level of cell metabolism. KCl eye drops four times per day were administered to mice models of corneal injury to evaluate the ability to prevent corneal scar formation. Corneal opacity area was evaluated by Image J software.

RESULTS

Treatment with hyperosmolar potassium could suppress corneal myofibroblast transformation and collagen I synthesis induced by TGF-β1 in cell culture. Hyperosmolar potassium could inhibit wound healing and gel contraction in CFs. RNA sequencing results suggested that genes involved in the metabolic pathway were downregulated after KCl treatment. ATP levels were significantly decreased in the KCl group compared with the control group. Hyperosmolar potassium could prevent corneal myofibroblast transformation after corneal injury and corneal scar formation in mice.

CONCLUSION

Potassium can suppress corneal myofibroblast transformation and collagen I protein synthesis. Moreover, given that KCl eye drops can prevent corneal scar formation, it has been suggested to have huge prospects as a novel treatment approach during clinical practice.

[Corneal wound healing-Pathophysiology and principles]

The cornea forms the anterior border of the eye and significantly contributes to a sharp optical image quality on the retina through its transparency, avascular nature and curvature. Because of its anatomical structure and as a barrier to the environment, the cornea is particularly exposed to various external factors, such as injuries and pathogens. A correct wound healing without the formation of light diverging scarring is therefore essential to preserve the integrity and function of the cornea. Misguided wound healing is of outstanding clinical relevance and can lead to corneal fibrogenesis. Corneal fibrosis results in scarring with a loss of optical transparency, which significantly reduces eyesight and can lead to blindness. Understanding the pathophysiological mechanisms of wound healing and fibrogenesis is of great importance for the diagnostics, treatment and evaluation of the subsequent healing process in order to prevent permanent damage as far as possible.

Cyclic Adenosine Monophosphate Promotes Odonto/Osteogenic Differentiation of Stem Cells from the Apical Papilla via Suppression of Transforming Growth Factor Beta 1 Signaling

INTRODUCTION

Stem cells from the apical papilla (SCAPs) possess strong odonto/osteogenic differentiation potential. This study investigated the effect of cyclic adenosine monophosphate (cAMP) on odonto/osteogenic differentiation of SCAPs and the underlining interplay between cAMP and transforming growth factor beta 1 (TGF-β1).

METHODS

SCAPs were stimulated with an activator of cAMP (forskolin) in the presence of either TGF-β1 or a TGF-β1 inhibitor. The amounts of calcium mineral deposition and alkaline phosphatase activity were determined. Quantitative real-time polymerase chain reaction was performed to elucidate cAMP on the TGF-β1-mediated odonto/osteogenic differentiation of SCAPs. The effect of cAMP on the phosphorylation of Smad2/Smad3 and extracellular-regulated kinase (ERK)/P38 induced by TGF-β1 was analyzed by Western blotting.

RESULTS

Cotreatment with forskolin and a TGF-β1 inhibitor enhanced alkaline phosphatase activity and deposition of calcium minerals in SCAPs. Moreover, the TGF-β1 inhibitor synergized the effect of forskolin on the expression of type I collagen and runt-related transcription factor 2. The results of Western blotting revealed that forskolin attenuated the unregulated expression of the phosphorylation of Smad3 and ERK induced by TGF-β1, and a cAMP inhibitor (H89) antagonized this effect.

CONCLUSIONS

This study showed that cAMP signaling exerts its up-regulating effects on the odonto/osteogenic differentiation of SCAPs by interfering with TGF-β1 signaling via inhibiting Smad3 and ERK phosphorylation.

Role of Bone Morphogenetic Protein 7 (BMP7) in the Modulation of Corneal Stromal and Epithelial Cell Functions

In the cornea, healing of the wounded avascular surface is an intricate process comprising the involvement of epithelial, stromal and neuronal cell interactions. These interactions result to the release of various growth factors that play prominent roles during corneal wound healing response. Bone morphogenetic proteins (BMPs) are unique multi-functional potent growth factors of the transforming growth factor-beta (TGF-β) superfamily. Treatment of corneal epithelial cells with substance P and nerve growth factor resulted to an increase in the expression of BMP7 mRNA. Since BMP7 is known to modulate the process of corneal wound healing, in this present study, we investigated the influence of exogenous rhBMP7 on human corneal epithelial cell and stromal cell (SFs) function. To obtain a high-fidelity expression profiling of activated biomarkers and pathways, transcriptome-wide gene-level expression profiling of epithelial cells in the presence of BMP7 was performed. Gene ontology analysis shows BMP7 stimulation activated TGF-β signaling and cell cycle pathways, whereas biological processes related to cell cycle, microtubule and intermediate filament cytoskeleton organization were significantly impacted in corneal epithelial cells. Scratch wound healing assay showed increased motility and migration of BMP7 treated epithelial cells. BMP7 stimulation studies show activation of MAPK cascade proteins in epithelial cells and SFs. Similarly, a difference in the expression of claudin, Zink finger E-box-binding homeobox 1 was observed along with phosphorylation levels of cofilin in epithelial cells. Stimulation of SFs with BMP7 activated them with increased expression of α-smooth muscle actin. In addition, an elevated phosphorylation of epidermal growth factor receptor following BMP7 stimulation was also observed both in corneal epithelial cells and SFs. Based on our transcriptome analysis data on epithelial cells and the results obtained in SFs, we conclude that BMP7 contributes to epithelial-to-mesenchymal transition-like responses and plays a role equivalent to TGF-β in the course of corneal wound healing.

Therapeutic effects of zerumbone in an alkali-burned corneal wound healing model

Cornea is an avascular transparent tissue. Ocular trauma caused by a corneal alkali burn induces corneal neovascularization (CNV), inflammation, and fibrosis, leading to vision loss. The purpose of this study was to examine the effects of Zerumbone (ZER) on corneal wound healing caused by alkali burns in mice. CNV was induced by alkali-burn injury in BALB/C female mice. Topical ZER (three times per day, 3μl each time, at concentrations of 5, 15, and 30μM) was applied to treat alkali-burned mouse corneas for 14 consecutive days. Histopathologically, ZER treatment suppressed alkali burn-induced CNV and decreased corneal epithelial defects induced by alkali burns. Corneal tissue treated with ZER showed reduced mRNA levels of pro-angiogenic genes, including vascular endothelial growth factor, matrix metalloproteinase-2 and 9, and pro-fibrotic factors such as alpha smooth muscle actin and transforming growth factor-1 and 2. Immunohistochemical analysis demonstrated that the infiltration of F4/80 and/or CCR2 positive cells was significantly decreased in ZER-treated corneas. ZER markedly inhibited the mRNA and protein levels of monocyte chemoattractant protein-1 (MCP-1) in human corneal fibroblasts and murine peritoneal macrophages. Immunoblot analysis revealed that ZER decreased the activation of signal transducer and activator of transcription 3 (STAT3), with consequent reduction of MCP-1 production by these cells. In conclusion, topical administration of ZER accelerated corneal wound healing by inhibition of STAT3 and MCP-1 production.

Post‑translational modification of CREB‑1 decreases collagen I expression by inhibiting the TGF‑β1 signaling pathway in rat hepatic stellate cells

Liver fibrosis is a reversible wound‑healing response to liver damage. Following liver injury, activated hepatic stellate cells (HSCs) cause excessive deposition of collagen and other components of the extracellular matrix, which may eventually impair liver function. Transforming growth factor‑β1 (TGF‑β1) is critical for the development of liver fibrosis, and acts by activating HSCs, stimulating matrix deposition and inducing other profibrotic responses. Certain studies have demonstrated that the transcription factor, cyclic adenosine monophosphate (cAMP)‑response element binding protein‑1 (CREB‑1) is important in the inhibition of fibrosis; however, the underlying mechanism remains to be elucidated. The present study hypothesized that CREB‑1 inhibits fibrosis via blocking the TGF‑β1 signaling pathway in HSCs. Treatment with the cAMP‑elevating agent, forskolin stimulated CREB‑1 phosphorylation and transcription activation in HSCs. In addition, treatment with the histone deacetylase inhibitor, trichostatin A extended CREB‑1 phosphorylation. The present study used a pRSV‑CREB‑1 expression vector to upregulate CREB‑1 gene expression. The results indicated that activated CREB‑1 reduced TGF‑β1‑stimulated expression of collagen I, activated Smad2/3 and upregulated expression of Smad7. In addition, activated CREB‑1 attenuated the activation of extracellular signal‑regulated kinase 1/2 induced by TGF‑β1, expression of Ras homolog gene family, member A (RhoA) and Rho‑associated coiled‑coil containing protein kinase 1. Thus, post‑translational modification of CREB‑1 inhibited the profibrotic effects of TGF‑β1 in HSCs via Smad‑dependent and ‑independent signaling pathways.

Small leucine-rich repeat proteoglycans in corneal inflammation and wound healing

The small leucine rich repeat proteoglycans are major components of the cornea. Lumican, keratocan, decorin, biglycan and osteoglycin are present throughout the adult corneal stroma, and fibromodulin in the peripheral limbal area. In the cornea literature these proteoglycan have been reviewed as structural, collagen fibril-regulating proteins of the cornea. However, these proteoglycans are members of the leucine-rich-repeat superfamily, and share structural similarities with pathogen recognition toll-like receptors. Emerging studies are showing that these have a range of interactions with cell surface receptors, chemokines, growth factors and pathogen associated molecular patterns and are able to regulate host immune response, inflammation and wound healing. This review discusses what is known about their innate immune-related role directly in the cornea, and studies outside the field that find interesting links with innate immune and wound healing responses that are likely to be relevant to the ocular surface. In addition, the review discusses phenotypes of mice with targeted deletion of proteoglycan genes and genetic variants associated with human pathologies.

Low-glucose enhances keratocyte-characteristic phenotype from corneal stromal cells in serum-free conditions

The avascular cornea is a uniquely-isolated organ, with its stroma constituting a nutrient-poor environment. Consequently, the availability of metabolites such as glucose to corneal stromal cells is considerably reduced compared with other tissues, or indeed with media commonly used to culture these cells in vitro. However, the role of glucose in the behaviour of human corneal keratocytes has been overlooked. As such, we sought to investigate the effects of low-glucose formulations on the phenotype of human corneal stromal cells. Cells cultured in low-glucose were able to survive for extended periods when compared to high-glucose, serum-free conditions. Furthermore, low-glucose enhanced their reversal to a keratocyte-characteristic phenotype. Specifically, cells within low-glucose medium assumed dendritic morphologies, with bean-shaped condensed nuclei, absence of alpha-smooth muscle actin or stress fibres, and a corresponding reduction in migratory and contractile activities when compared with high-glucose, serum-free conditions. Moreover, cells within low-glucose uniquely recovered the ability to express a robust keratocyte-characteristic marker, CD34, while still expressing elevated levels of other representative phenotypic markers such as keratocan, lumican, ALDH1A1, and ALDH3A1. These results indicate that low-glucose enhances keratocyte-characteristic phenotype above and beyond established media formulations and thus has important implications for corneal biology in health and disease.

Small GTPase Rap1 regulates cell migration through regulation of small GTPase RhoA activity in response to transforming growth factor-β1

Transforming growth factor (TGF)-β1 regulates diverse cellular functions. Particularly, TGF-β1 induces monocyte migration to sites of injury or inflammation in early period, whereas TGF-β1 inhibits cell migration in late phase. In this study, we attempted to understand how TGF-β1 suppresses cell migration in late phase. We found that TGF-β1 of short exposure induces the production of chemokines, such as macrophage inflammatory protein (MIP)-1α, by Raw 264.7 cells. However, knock-down of small GTPase RhoA by sh-RhoA inhibited the production of MIP-1α and macrophage migration, suggesting that RhoA is essential for expression of this chemokine. An activator of Epac (exchange proteins directly activated by cAMP; a guanine nucleotide exchange factor of Rap1), 8CPT-2Me-cAMP which leads to Rap1 activation abrogated MIP-1α expression and macrophage migration. Indeed, GTP-RhoA and GTP-Rap1 levels were reciprocally regulated in a time-dependent manner following TGF-β1 stimulation. 8CPT-2Me-cAMP suppressed GTP-RhoA levels, whereas si-Rap1 augmented GTP-RhoA levels and cell migration. TGF-β1 produced cAMP in late period and si-RNAs of Epac1 and Epac2 reduced GTP-Rap1 levels leading to promotion of GTP-RhoA levels. Furthermore, si-RNA of ARAP3 (Rap-dependent RhoGAP) increased GTP-RhoA level and cell migration. Therefore, we propose the mechanism that prolonged TGF-β1 treatment produce cAMP, which activates sequentially Epac, Rap1 and ARAP3, resulting in suppression of RhoA, chemokine expression, and macrophage migration. Contrary to the general concept that Rap1 stimulates cell migration, we demonstrated in this study that Rap1 inhibits cell migration by suppression of RhoA activity in response to TGF-β1.

Cyclic AMP enhances TGFβ responses of breast cancer cells by upregulating TGFβ receptor I expression

Cellular functions are regulated by complex networks of many different signaling pathways. The TGFβ and cAMP pathways are of particular importance in tumor progression. We analyzed the cross-talk between these pathways in breast cancer cells in 2D and 3D cultures. We found that cAMP potentiated TGFβ-dependent gene expression by enhancing Smad3 phosphorylation. Higher levels of total Smad3, as observed in 3D-cultured cells, blocked this effect. Two Smad3 regulating proteins, YAP (Yes-associated protein) and TβRI (TGFβ receptor 1), were responsive to cAMP. While YAP had little effect on TGFβ-dependent expression and Smad3 phosphorylation, a constitutively active form of TβRI mimicked the cAMP effect on TGFβ signaling. In 3D-cultured cells, which show much higher levels of TβRI and cAMP, TβRI was unresponsive to cAMP. Upregulation of TβRI expression by cAMP was dependent on transcription. A proximal TβRI promoter fragment was moderately, but significantly activated by cAMP suggesting that cAMP increases TβRI expression at least partially by activating TβRI transcription. Neither the cAMP-responsive element binding protein (CREB) nor the TβRI-regulating transcription factor Six1 was required for the cAMP effect. An inhibitor of histone deacetylases alone or together with cAMP increased TβRI expression by a similar extent as cAMP alone suggesting that cAMP may exert its effect by interfering with histone acetylation. Along with an additive stimulatory effect of cAMP and TGFβ on p21 expression an additive inhibitory effect of these agents on proliferation was observed. Finally, we show that mesenchymal stem cells that interact with breast cancer cells can simultaneously activate the cAMP and TGFβ pathways. In summary, these data suggest that combined effects of cAMP and TGFβ, as e.g. induced by mesenchymal stem cells, involve the upregulation of TβRI expression on the transcriptional level, likely due to changes in histone acetylation. As a consequence, cancer cell functions such as proliferation are affected.

cAMP and Epac in the regulation of tissue fibrosis

Fibrosis, the result of excess deposition of extracellular matrix (ECM), in particular collagen, leads to scarring and loss of function in tissues that include the heart, lung, kidney and liver. The second messenger cAMP can inhibit the formation and extent of ECM during this late phase of inflammation, but the mechanisms for these actions of cAMP and of agents that elevate tissue cAMP levels are not well understood. In this article, we review the fibrotic process and focus on two recently recognized aspects of actions of cAMP and its effector Epac (Exchange protein activated by cAMP): (a) blunting of epithelial-mesenchymal transformation (EMT) and (b) down-regulation of Epac expression by profibrotic agents (e.g. TGF-β, angiotensin II), which may promote tissue fibrosis by decreasing Epac-mediated antifibrotic actions. Pharmacological approaches that raise cAMP or blunt the decrease in Epac expression by profibrotic agents may thus be strategies to block or perhaps reverse tissue fibrosis. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

Effects of p-CREB-1 on transforming growth factor-β3 auto-regulation in hepatic stellate cells

Previous studies have demonstrated that transforming growth factor-β3 (TGF-β3) protected liver against fibrosis in vivo and vitro, but its regulation is poorly understood. In addition, the cAMP-responsive element (CRE) in TGF-β3 promoter is recognized as an important regulatory site for TGF-β3 auto-regulation. Thus, we hypothesize that transcription factor CRE-binding protein-1 (CREB-1) regulates the auto-induction of TGF-β3 in hepatic stellate cells (HSCs). We used exogenous TGF-β3 to activate the signal pathway of TGF-β3 auto-regulation in HSCs, results indicated that exogenous TGF-β3 could up-regulate the protein and mRNA expressions of TGF-β3, and provoke the phosphorylation of CREB-1 on Ser-133, besides, it could induce the DNA binding activity of p-CREB-1 and activate TGF-β3 promoter as well. Additionally, we used pGenesil-1.1-shRNA-CREB-1 and pRSV-CREB-1 expression vector to silence and up-regulate CREB-1 gene expression respectively, and the results indicated that inhibition of CREB-1 suppressed exogenous TGF-β3 stimulation of TGF-β3 mRNA and protein expressions in HSCs, whereas up-regulation of CREB-1 induced this stimulation. Our results indicate that exogenous TGF-β3 up-regulates the activity of TGF-β3 promoter by activating CREB-1, then induces the mRNA and protein expressions of TGF-β3. Especially, p-CREB-1 is a critical transcription factor in mediating TGF-β3 auto-induction.

Immune-regulatory transcriptional responses in multiple organs of Atlantic salmon after tributyltin exposure, alone or in combination with forskolin

Tributyltin (TBT) is a widespread marine pollutant that influences physiological conditions of fish and other aquatic organisms. In addition to effects on reproduction, the immune system has been proposed as a possible target for TBT effects. In the present study, the effects of TBT exposure were examined on the expression of genes involved in immune system compentence in liver and head kidney of Atlantic salmon, in the presence and absence of a second-messenger activator (forskolin). Juvenile salmon were force-fed a diet containing TBT (0-solvent control, 0.1, 1, or 10 mg/kg fish) for 72 h. Consequently, fish from the control group and 10-mg/kg TBT group were exposed to the adenylate cyclase (AC) activator forskolin (200 μg/L) for 2 or 4 h. Forskolin was selected for this study because it is known to exhibit potent immune system enhancement by activating macrophages and lymphocytes. After sacrifice, liver and head kidney were sampled and transcript changes for interleukin (IL)-1β, IL-10, transforming growth factor (TGF) β, interferon (INF) α, INFγ, tumor necrosis factor (TNF) α, Mx3, and insulin-like growth factor (IGF)-1 were determined in both tissues by quantitative polymerase chain reaction (qPCR) using gene-specific primers. TBT, when given alone and also in combination with forskolin, decreased IL-1β, TNFα, IFNγ, IFNα, Mx3, and IGF-1 gene expression. In contrast, IL-10 and TGFβ transcripts were increased after TBT exposure alone and also in combination with forskolin. Generally, these effects were largely dependent on TBT dose and time of exposure when given in combination with forskolin. Overall, our findings suggest a possible immunomodulatory effect of TBT, possibly involving cAMP activation.

New insights into the mechanism of fibroblast to myofibroblast transformation and associated pathologies

Myofibroblasts are a differentiated cell type essential for wound healing, participating in tissue remodeling following insult. Myofibroblasts are typically activated fibroblasts, although they can also be derived from other cell types, including epithelial cells, endothelial cells, and mononuclear cells. In most organ systems, cell signals initiated following tissue-specific insult or during the metastatic process lead to differentiation of fibroblasts or other precursor cells to the myofibroblast phenotype. In addition to their beneficial and necessary role in wound healing, myofibroblasts also contribute to a number of pathologies, primarily fibrotic processes and tumor invasiveness. This review explores both traditional and nontraditional concepts of myofibroblast differentiation in the cornea, skin, heart, and other tissues, as well as some of the pathologies associated with myofibroblast activities.

Growth factor regulation of corneal keratocyte differentiation and migration in compressed collagen matrices

PURPOSE

To evaluate a novel 3D culture model of the corneal stroma and apply it to investigate how key wound-healing growth factors regulate the mechanics of corneal keratocyte migration.

METHODS

Rabbit corneal keratocytes were seeded within collagen matrices that were compacted using external compression. Six-millimeter-diameter buttons were then incubated in media supplemented with 10% FBS, TGFbeta1, TGFbeta2, platelet-derived growth factor (PDGF), or no growth factor (control). After 1, 3, or 7 days, matrices were labeled with phalloidin and a nucleic acid dye, and were imaged using laser confocal microscopy. To study cell migration, buttons were nested within acellular uncompressed outer collagen matrices before growth factor stimulation.

RESULTS

Corneal keratocytes in basal media within compressed matrices had a broad, convoluted cell body and thin dendritic processes. In contrast, cells in 10% FBS developed a bipolar fibroblastic morphology. Treatment with TGFbeta induced the formation of stress fibers expressing alpha-smooth muscle actin, suggesting myofibroblast transformation. PDGF induced keratocyte elongation without inducing stress fiber formation. Both 10% FBS and PDGF stimulated significant keratocyte migration through the uncompressed outer matrix, but 10% FBS produced more cell-induced collagen matrix reorganization. TGFbeta induced the smallest increase in migration and the greatest matrix reorganization.

CONCLUSIONS

Corneal keratocytes are able to differentiate normally and respond to growth factors within compressed collagen matrices, which provide a high-stiffness, 3D environment, similar to native stromal tissue. In addition, nesting these matrices provides a unique platform for investigating the mechanics of keratocyte migration after exposure to specific wound-healing cytokines.