Serum response factor promotes re-epithelialization and muscular structure restoration during gastric ulcer healing

Therapeutic delivery of nucleic acids for skin wound healing

Though wound care has advanced, treating chronic wounds remains a challenge and there are many clinical issues that must be addressed. Gene therapy is a recent approach to treating chronic wounds that remains in its developmental stage. The limited reports available describe the therapeutic applications of various forms of nucleic acid delivery for treating chronic wounds, including DNA, mRNA, siRNA, miRNA and so on. Though these bioactive molecules represent great therapeutic potential, sustaining their bioactivity in the wound bed is a challenge. To overcome this hurdle, delivery systems are also being widely investigated. In this review, nucleic acid-based therapy and its delivery for treating chronic wounds is discussed in detail.

Gut homeostasis, injury, and healing: New therapeutic targets

The integrity of the gastrointestinal mucosa plays a crucial role in gut homeostasis, which depends upon the balance between mucosal injury by destructive factors and healing via protective factors. The persistence of noxious agents such as acid, pepsin, nonsteroidal anti-inflammatory drugs, or Helicobacter pylori breaks down the mucosal barrier and injury occurs. Depending upon the size and site of the wound, it is healed by complex and overlapping processes involving membrane resealing, cell spreading, purse-string contraction, restitution, differentiation, angiogenesis, and vasculogenesis, each modulated by extracellular regulators. Unfortunately, the gut does not always heal, leading to such pathology as peptic ulcers or inflammatory bowel disease. Currently available therapeutics such as proton pump inhibitors, histamine-2 receptor antagonists, sucralfate, 5-aminosalicylate, antibiotics, corticosteroids, and immunosuppressants all attempt to minimize or reduce injury to the gastrointestinal tract. More recent studies have focused on improving mucosal defense or directly promoting mucosal repair. Many investigations have sought to enhance mucosal defense by stimulating mucus secretion, mucosal blood flow, or tight junction function. Conversely, new attempts to directly promote mucosal repair target proteins that modulate cytoskeleton dynamics such as tubulin, talin, Ehm², filamin-a, gelsolin, and flightless I or that proteins regulate focal adhesions dynamics such as focal adhesion kinase. This article summarizes the pathobiology of gastrointestinal mucosal healing and reviews potential new therapeutic targets.

The Critical Role of Growth Factors in Gastric Ulcer Healing: The Cellular and Molecular Mechanisms and Potential Clinical Implications

In this article we review the cellular and molecular mechanisms of gastric ulcer healing. A gastric ulcer (GU) is a deep defect in the gastric wall penetrating through the entire mucosa and the muscularis mucosae. GU healing is a regeneration process that encompasses cell dedifferentiation, proliferation, migration, re-epithelialization, formation of granulation tissue, angiogenesis, vasculogenesis, interactions between various cells and the matrix, and tissue remodeling, all resulting in scar formation. All these events are controlled by cytokines and growth factors (e.g., EGF, TGFα, IGF-1, HGF, bFGF, TGFβ, NGF, VEGF, angiopoietins) and transcription factors activated by tissue injury. These growth factors bind to their receptors and trigger cell proliferation, migration, and survival pathways through Ras, MAPK, PI3K/Akt, PLC-γ, and Rho/Rac/actin signaling. The triggers for the activation of these growth factors are tissue injury and hypoxia. EGF, its receptor, IGF-1, HGF, and COX-2 are important for epithelial cell proliferation, migration, re-epithelialization, and gastric gland reconstruction. VEGF, angiopoietins, bFGF, and NGF are crucial for blood vessel regeneration in GU scars. The serum response factor (SRF) is essential for VEGF-induced angiogenesis, re-epithelialization, and blood vessel and muscle restoration. Local therapy with cDNA of human recombinant VEGF165 in combination with angiopoietin1, or with the NGF protein, dramatically accelerates GU healing and improves the quality of mucosal restoration within ulcer scars. The future directions for accelerating and improving healing include local gene and protein therapies with growth factors, their combinations, and the use of stem cells and tissue engineering.

Analysis of candidate biomarkers and related transcription factors involved in the development and restoration of stress-induced gastric ulcer by transcriptomics

Stress-induced gastric ulcer is one of the common complications affecting patients after trauma, mainly leading to gastrointestinal bleeding and perforation, and severe cases may be life-threatening. However, the molecular mechanism of stress-induced gastric ulcer remains unclear. In the present study, RNA-sequencing was performed on gastric tissues of normal rats (C), stress-induced gastric ulcer rats (T0), and rats recovered from gastric ulcer for 3 days (T3), and bioinformatics analysis was performed to determine changes in gene expression and biological pathways. The protein-protein interaction (PPI) networks of differentially expressed genes (DEGs) were constructed by STRING and visualized by the Cytoscape software. The associated transcriptional factor (TFs)-gene regulatory network of the hub DEGs was also constructed. Pairwise comparisons obtained 103 (T0_C), 127 (T3_T0), and 13 (T3_C) DEGs, respectively. Gene ontology (GO) enrichment analysis indicated DEGs in T0_C and T3_T0 were significantly enriched in response to oxygen-containing compound, response to organic substance, and response to external stimulus. Pathway analysis suggested that DEGs were enriched in TNF signaling pathway, PPAR signaling pathway, apoptosis, and IL-17 signaling pathway. Seven hub genes (Fos, Jun, Nfkbia, Dusp1, Pim3, Junb, and Fosb) were obtained from the PPI networks of T0_C and T3_T0. Key TFs with close interactions, such as Fos, Jun, Nfkbia, Junb, Egr1, and Fosb, were screened This study used RNA-sequencing and bioinformatics analysis to screen out genes associated with gastric ulcer, which can help reveal the molecular mechanism of gastric ulcer development and restoration, and provide reference for the treatment of human gastric ulcers.

SRF promotes gastric cancer metastasis through stromal fibroblasts in an SDF1-CXCR4-dependent manner

It has been suggested that the overexpression of serum response factor (SRF) in cancer cells may promote cancer metastasis. However, the exact pathway by which SRF promotes metastasis has not been clarified. Here we showed that SRF promotes gastric cancer (GC) metastasis through stromal fibroblasts in an SDF1-CXCR4-dependent manner. SRF expression was significantly increased in metastatic GCs compared with the non-metastatic GCs (n=50, p=0.013). Immuno-staining indicated that SRF was primarily expressed in a-smooth muscle actin (αSMA)-expressing periglandular fibroblasts in GCs. The conditioned medium (CM) from CCD18Co fibroblasts stably transfected with the SRF vector (CCD18Co-SRF) significantly enhanced migration of MKN45 gastric cancer cells. In contrast, the CM from CCD18Co fibroblasts, in which SRF was downregulated, inhibited mobility of MKN45 cells. Similar results were observed in cultured BGC823 cells even when they were treated with the NIH3T3-SRF CM. When MKN45 cells and SRF-upregulated or downregulated CCD18Co cells were simultaneously co-injected into the tail veins of NOD-SCID mice, a significant increase or decrease was, respectively, observed in the experimental pulmonary metastasis of cancer cells. Furthermore, SRF overexpression significantly upregulated `SMA and stromal cell derived factor1 (SDF1) expression in these fibroblasts, and an anti-SDF1 antibody or the SDF1 receptor CXCR4-specific inhibitor AMD3100 treatment completely reversed the SRF-enhanced migration of cancer cells. Quantitative RT-PCR demonstrated that the expression level of SRF was positively correlated with that of SDF1 in 92 GC samples (r=0.63, p<0.001). In conclusion, SRF promote GC metastasis by facilitating myofibroblast-cancer cell crosstalk in an SDF1-CXCR4 dependent manner, and maybe a therapeutic target.

Reduced NGF in Gastric Endothelial Cells Is One of the Main Causes of Impaired Angiogenesis in Aging Gastric Mucosa

BACKGROUND & AIMS

Aging gastric mucosa has increased susceptibility to injury and delayed healing owing to impaired angiogenesis, but the mechanisms are not fully known. We examined whether impairment of angiogenesis in aging gastric mucosa is caused by deficiency of nerve growth factor (NGF) in gastric endothelial cells (ECs), and whether NGF therapy could reverse this impairment.

METHODS

In gastric mucosal ECs (GECs) isolated from young and aging rats we examined the following: (1) in vitro angiogenesis, (2) NGF expression, and (3) the effect of NGF treatment on angiogenesis, GEC proliferation and migration, and dependence on serum response factor. In in vivo studies in young and aging rats, we examined NGF expression in gastric mucosa and the effect of NGF treatment on angiogenesis and gastric ulcer healing. To determine human relevance, we examined NGF expression in gastric mucosal biopsy specimens of aging (≥70 y) and young (≤40 y) individuals.

RESULTS

In cultured aging GECs, NGF expression and angiogenesis were reduced significantly by 3.0-fold and 4.1-fold vs young GECs. NGF therapy reversed impairment of angiogenesis in aging GECs, and serum response factor silencing completely abolished this response. In gastric mucosa of aging rats, NGF expression in GECs was reduced significantly vs young rats. In aging rats, local NGF treatment significantly increased angiogenesis and accelerated gastric ulcer healing. In aging human subjects, NGF expression in ECs of gastric mucosal vessels was 5.5-fold reduced vs young individuals.

CONCLUSIONS

NGF deficiency in ECs is a key mechanism underlying impaired angiogenesis and delayed ulcer healing in aging gastric mucosa. Local NGF therapy can reverse these impairments.

Neuroprotective effect of Ruminococcus albus on oxidatively stressed SH-SY5Y cells and animals

Recent evidence shows that the gut microbiota has an important role in gut-brain crosstalk and is linked to neuronal disorders. The aim of this study was to investigate the effects of intestinal Ruminococcus albus with probiotic potential on neuroprotection in oxidatively stressed SH-SY5Y neuroblastoma cells and animals. To investigate these effects, conditioned medium was prepared using Caco-2 cells cultured with heat-killed R. albus (CRA-CM). Caco-2 cells cultured with heat-killed R. albus showed increased BDNF expression and BDNF protein levels increased in CRA-CM. CRA-CM up-regulated the protein expression levels of SRF, C-fos and CDK2. In addition, CRA-CM protected SH-SY5Y cells from H₂O₂-induced cell death. CRA-CM significantly decreased the Bax/Bcl-2 ratio in oxidatively stressed SH-SY5Y cells. Animal experiments showed that oral administration of heat-killed R. albus for 15 days attenuated the oxidative stress induced by sodium arsenate. Treatment with heat-killed R. albus reduced the level of ROS, and the levels of SOD and GSH increased in oxidatively stressed brains. In conclusion, the secretome prepared from Caco-2 cells cultured with heat-killed R. albus might promote neuronal proliferation through the activation of cell proliferation-related proteins, and heat-killed R. albus protects neurons from oxidative damage by reducing ROS levels and increasing SOD and GSH levels.

Healing and Antisecretory Effects of Aqueous Extract of Eremomastax speciosa (Acanthaceae) on Unhealed Gastric Ulcers

OBJECTIVE

This work investigated the healing and antisecretory effects of the aqueous extract of Eremomastax speciosa on "unhealed gastric ulcers" associated with gastric acid hypersecretion.

MATERIALS AND METHODS

"Unhealed gastric ulcers" were induced using indomethacin following the establishment of acetic-acid-induced chronic gastric ulcers. The extract (200 and 400 mg/kg, per os) was administered concomitantly with indomethacin (1 mg/kg, subcutaneously). The effects of the extract on both basal and histamine-stimulated gastric acid secretion were determined. Mucus secretion and oxidative stress parameters were measured, and histological assessment of ulcer healing was carried out.

RESULTS

The extract significantly promoted the healing process in rats subjected to "unhealed gastric ulcers" (82.4-88.5% healing rates). Treatment with the extract significantly reduced the basal (25.95-49.51% reduction rates) and histamine-stimulated (24.25-47.41%) acid secretions. The healing effect of the extract was associated with a significant (p < 0.05) increase of mucus secretion and concentrations of antioxidant enzymes compared with the controls. The extract at the highest dose showed normalization of the mucosa, without glandular destruction and with the disappearance of fibrosis and lymphocyte infiltration.

CONCLUSION

The abilities of the extract to increase mucus secretion, to reinforce antioxidant status, and to inhibit acid secretion would be some of the mechanisms by which this extract would accelerate the healing process in "unhealed gastric ulcers."

HOPX functions as a tumour suppressor in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is generalized term that encompasses a diverse group of cancers that includes tumours of the oral cavity (OSCC), oropharynx (OPSCC) and nasopharynx (NPC). Genetic alterations that are common to all HNSCC types are likely to be important for squamous carcinogenesis. In this study, we have investigated the role of the homeodomain-only homeobox gene, HOPX, in the pathogenesis of HNSCC. We show that HOPX mRNA levels are reduced in OSCC and NPC cell lines and tissues and there is a general reduction of HOPX protein expression in these tumours and OPSCCs. HOPX promoter methylation was observed in a subset of HNSCCs and was associated with a worse overall survival in HPV negative tumours. RNAseq analysis of OSCC cells transfected with HOPX revealed a widespread deregulation of the transcription of genes related to epithelial homeostasis and ectopic over-expression of HOPX in OSCC and NPC cells inhibited cell proliferation, plating efficiency and migration, and enhanced sensitivity to UVA-induced apoptosis. Our results demonstrate that HOPX functions as a tumour suppressor in HNSCC and suggest a central role for HOPX in suppressing epithelial carcinogenesis.

Multi-phenotypic Role of Serum Response Factor in the Gastrointestinal System

Serum response factor (SRF) is a master transcription factor of the actin cytoskeleton that binds to highly conserved CArG boxes located within the majority of smooth muscle cell (SMC)-restricted promoters/enhancers. Although most studies of SRF focus on skeletal muscle, cardiac muscle, and vascular SMCs, SRF research has recently expanded into the gastrointestinal (GI) system. Genome scale analyses of GI SMC transcriptome and CArG boxes (CArGome) have identified new SRF target genes. In addition to circular and longitudinal smooth muscle layers, SRF is also expressed in GI mucosa and cancers. In the GI tract, SRF is the central regulator of genes involved in apoptosis, dedifferentiation, proliferation, and migration of cells. Since SRF is the cell phenotypic modulator, it may play an essential role in the development of myopathy, hypertrophy, ulcers, gastric and colon cancers within the GI tract. Given the multi-functional role displayed by SRF in the digestive system, SRF has received more attention emerging as a potential therapeutic target. This review summarizes the findings in SRF research pertaining to the GI tract and provides valuable insight into future directions.

Motile cilia harbor serum response factor as a mechanism of environment sensing and injury response in the airway

Nonmotile primary cilia are recognized as important sensory organelles during development and normal biological functioning. For example, recent work demonstrates that transcriptional regulators of the sonic hedgehog signaling pathway localize to primary cilia and participate in sensing and transducing signals regarding the cellular environment. In contrast, motile cilia are traditionally viewed as mechanical machinery, vital for the movement of solutes and clearance of bacteria and debris, but not participants in cellular sensing and signaling mechanisms. Recently, motile cilia were found to harbor receptors responsible for sensing and responding to environmental stimuli. However, no transcription factors are known to be regulated by cilia localization as a sensing mechanism in vertebrates. Using a mouse model of organic dust-induced airway inflammation, we found that the transcription factor serum response factor (SRF) localizes to motile cilia of airway epithelial cells and alters its localization in response to inflammatory stimuli. Furthermore, inhibition of SRF signaling using the small molecule CCG-1423 reduces organic dust-induced IL-8 release from bronchial epithelial cells and stimulates cilia beat frequency in ciliated mouse tracheal epithelial cells. Immunohistochemical analyses reveal that SRF localizes to the cilia of mouse brain ependymal and ovarian epithelial cells as well. These data reveal a novel mechanism by which a transcription factor localizes to motile cilia and modulates cell activities including cilia motility and inflammation response. These data challenge current dogma regarding motile cilia functioning and may lead to significant contributions in understanding motile ciliary signaling dynamics, as well as mechanisms involving SRF-mediated responses to inflammation and injury.

Key role of endothelial importin-α in VEGF expression and gastric angiogenesis: novel insight into aging gastropathy

Recent in vivo studies demonstrated that aging gastric mucosa has impaired angiogenesis and reduced expression of vascular endothelial growth factor (VEGF). Angiogenesis is triggered by hypoxia and VEGF gene activation, and the latter requires transport of transcription factor(s) into endothelial cell nuclei. We focused on gastric mucosal endothelial cells (GMEC), which are key targets and effectors of gastric angiogenesis, and determined whether and to what extent importin-α, a nuclear transport protein, regulates VEGF gene activation and gastric angiogenesis and the possible role of importin-α in aging gastropathy. GMEC were isolated from rats 3 and 24 mo of age, young (YGEC) and aging (AGEC), respectively. We examined in these cells 1) in vitro angiogenesis, 2) expression of VEGF and importin-α, 3) nuclear transport of hypoxia-inducible factor (HIF)-1α by importin-α, 4) binding of HIF-1α to the VEGF gene promoter, and 5) effects of importin-α silencing in YGEC and its upregulation in AGEC on angiogenesis and VEGF expression. AGEC exhibited significantly impaired in vitro angiogenesis by fourfold and decreased expression of VEGF, importin-α, and nuclear HIF-1α by 1.4-fold, 1.6-fold, and 2.9-fold, respectively, vs. YGEC. Upregulation of importin-α in AGEC significantly reversed all these abnormalities. In YGEC, knockdown of importins-α1 and -α3 significantly reduced in vitro angiogenesis by 93% and 73% and VEGF expression by 48% and 52%, respectively. The above findings demonstrate that importin-α is a novel and critical regulator of gastric angiogenesis. Its reduced expression in AGEC is the key mechanism for impaired angiogenesis and reduced VEGF.

Endoscopic application of EGF-chitosan hydrogel for precipitated healing of GI peptic ulcers and mucosectomy-induced ulcers

The gastrointestinal (GI) endoscopy has become a standard diagnostic tool for GI ulcers and cancer. In this study we studied endoscopic application of epidermal growth factor-containing chitosan hydrogel (EGF-CS gel) for treatment of GI ulcer. We hypothesized that directional ulcer-coating using EGF-CS gel via endoscope would precipitate ulcer-healing. EGF-CS gel was directly introduced to the ulcer-region after ulceration in acetic acid-induced gastric ulcer (AAU) and mucosal resection-induced gastric ulcer (MRU) rabbit and pig models. The ulcer dimensions and mucosal thicknesses were estimated and compared with those in the control group. Healing efficacy was more closely evaluated by microscopic observation of the ulcer after histological assays. In the AAU model, the normalized ulcer size of the gel-treated group was 2.3 times smaller than that in the non-treated control group on day 3 after ulceration (P < 0.01). In the MRU model, the normalized ulcer size of the gel-treated group was 5.4 times smaller compared to that in the non-treated control group on day 1 after ulceration (P < 0.05). Histological analysis supported the ability of EGF-CS gel to heal ulcers. The present study suggests that EGF-CS gel is a promising candidate for treating gastric bleeding and ulcers.

Pretreatment with epidermal growth factor enhances naked plasmid DNA transfer onto gastric serosal surface in mice

We have developed a simple administration method, which is gastric serosal surface instillation of naked plasmid DNA (pDNA) in experimental animals. The purpose of this study was to improve gastric gene transfer efficiency by pre-treatment with a macropinocytosis enhancer, such as fetuin or epidermal growth factor (EGF), in mice. A series of concentrations of fetuin were instilled onto gastric serosal surface prior to instillation of naked pDNA in mice; however, fetuin did not improve transgene expression in the stomach 6 h after administration of pDNA. EGF also did not affect transgene expression in the stomach when pDNA was instilled immediately after EGF instillation. On the other hand, when pDNA was instilled onto gastric serosal surface 24 h after EGF treatment, transgene expression in the stomach was significantly improved by 2.6-fold. In addition, transgene-positive cells were increased 5.3-fold by EGF pre-treatment. High transgene expression in the stomach lasted for 48 h in the EGF pre-treatment group in comparison with that in the no pre-treatment group. These findings are valuable to develop an effective method of in vivo gene transfer to the stomach.

Rubbing gastric serosal surface enhances naked plasmid DNA transfer in rats and mice

We have developed in vivo gene transfer to mesothelial cells on the peritoneal organs, including the stomach. Simple instillation of naked plasmid DNA onto the gastric serosal surface in mice resulted in effective but transient transgene expression. Here, we developed a simple method to improve not only the transfection efficiency but also the duration of transgene expression. Rubbing the gastric serosal surface using a medical spoon immediately after instillation of naked plasmid DNA onto the gastric serosal surface resulted in 59-fold higher transgene expression 24 h after administration in rats. Without rubbing, transgene expression decreased under the detection limit 7 d after administration. On the other hand, rubbing the gastric serosal surface with a medical spoon after instillation of plasmid DNA prolonged transgene expression for one month. Mechanistic study in mice revealed that improved transfection should not be due to stimulation of cell function such as macropinocytosis by rubbing because rubbing before instillation of plasmid DNA did not improve transfection. Plasmid DNA should enter effectively into cells during rubbing. These findings are valuable to develop an effective method of in vivo gene transfer into peritoneal organs.

Weak up-regulation of serum response factor in gastric ulcers in patients with co-morbidities is associated with increased risk of recurrent bleeding

Background

Serum response factor (SRF) is crucial for gastric ulcer healing process. The study determined if gastric ulcer tissues up-regulate SRF and if such up-regulation correlated with co-morbidities and the risk of recurrent bleeding.

Methods

Ulcer and non-ulcer tissues were obtained from 142 patients with active gastric ulcers for SRF expression assessed by immunohistochemistry. Based on the degree of SRF expression between these two tissue types, SRF up-regulation was classified as strong, intermediate, and weak patterns. The patients were followed-up to determine if SRF up-regulation correlated to recurrent bleeding.

Results

Gastric ulcer tissues had higher SRF expression than non-ulcer tissues (p < 0.05). Patients with strong SRF up-regulation had lower rates of stigmata of recent hemorrhage (SRH) on the ulcer base than the others (p < 0.05). Multivariate logistic regression confirmed that co-morbidities and weak SRF up-regulation were two independent factors of recurrent gastric ulcer bleeding (p < 0.05). Combining both factors, there was an 8.29-fold (95% CI, 1.31~52.62; p = 0.03) higher risk of recurrent gastric ulcer bleeding.

Conclusions

SRF expression is higher in gastric ulcer tissues than in non-ulcer tissues. Weak SRF up-regulation, combined with the presence of co-morbidities, increase the risk of the recurrent gastric ulcer bleeding.

Role of serum response factor in the pathogenesis of disease

Serum response factor (SRF) is a ubiquitously expressed transcription factor that binds to a DNA cis element known as the CArG box, which is found in the proximal regulatory regions of over 200 experimentally validated target genes. Genetic deletion of SRF is incompatible with life in a variety of animals from different phyla. In mice, loss of SRF throughout the early embryo results in gastrulation defects precluding analyses in individual organ systems. Genetic inactivation studies using conditional or inducible promoters directing the expression of the bacteriophage Cre recombinase have shown a vital role for SRF in such cellular processes as contractility, cell migration, synaptic activity, inflammation, and cell survival. A growing number of experimental and human diseases are associated with changes in SRF expression, suggesting that SRF has a role in the pathogenesis of disease. This review summarizes data from experimental model systems and human pathology where SRF expression is either deliberately or naturally altered.

CCN1 induces a reversible epithelial-mesenchymal transition in gastric epithelial cells

CCN1 is a matricellular protein that activates many genes related to wound healing and tissue remodeling in fibroblasts, but its effect on epithelial cells remains unclear. This study examined the role of CCN1 in epithelial wound healing using rat gastric epithelial cells and rat stomach ulcer as in vitro and in vivo models, respectively. We found that CCN1 expression is highly upregulated in the epithelial cells adjacent to a wound and remains high until the wound is healed. Upregulation of CCN1 activates a transient epithelial-mesenchymal transition in the epithelial cells at the migrating front and drives wound closure. Once the wound is healed, these epithelial cells and their progeny can resume their original epithelial phenotype. We also found that CCN1-induced E-cadherin loss is not due to transcriptional regulation but rather protein degradation due to the collapse of adherens junctions, which is contributed by beta-catenin translocation. CCN1-activated integrin-linked kinase mediates this process. Finally, our in vivo study showed that locally neutralizing CCN1 drastically impairs wound closure, whereas local injection of recombinant CCN1 protein induces expression of vimentin and smooth muscle alpha-actin in normal gastric mucosal epithelial cells and accelerates re-epithelialization during ulcer healing. In conclusion, our study indicates that CCN1 can induce reversible epithelial-mesenchymal transition, and this feature may have great value for clinical wound healing.

A pathogenic relationship between a regulator of the actin cytoskeleton and serum response factor

Cell hyperproliferation, inflammation, and angiogenesis are biological processes central to the pathogenesis of corneal disease, as well as other conditions including tumorigenesis and chronic inflammatory disorders. Due to the number of disease conditions that arise as a result of these abnormalities, identifying the molecular mechanisms underlying these processes is critical. The avascular and transparent cornea serves as a good in vivo model to study the pathogenesis of cell hyperproliferation, inflammation, and angiogenesis. Corneal disease 1 (Dstn(corn1)) mice are homozygous for a spontaneous null allele of the destrin (Dstn) gene, which is also known as actin depolymerizing factor (ADF). These mice exhibit abnormalities in the cornea including epithelial cell hyperproliferation, stromal inflammation, and neovascularization. We previously identified that the transcription factor, serum response factor (SRF) and a number of its target genes are upregulated in the cornea of these mice. In this study, we show that conditional ablation of Srf in the corneal epithelium of a diseased Dstn(corn1) cornea results in the rescue of the epithelial cell hyperproliferation, inflammation, and neovascularization phenotypes, delineating an epithelial cell-specific role for SRF in the development of all of these abnormalities. Our study also demonstrates that Dstn is genetically upstream of Srf and defines a new functional role for SRF as the master regulator of a hyperproliferative, inflammatory phenotype accompanied by neovascularization.

Serum response factor: Look into the gut

Serum response factor (SRF) is a transcription factor that regulates many genes involved in cellular activities such as proliferation, migration, differentiation, angiogenesis, and apoptosis. Although it has only been known for about two decades, SRF has been studied extensively. To date, over a thousand SRF studies have been published, but it still remains a hot topic. Due to its critical role in mesoderm-derived tissues, most of the SRF studies focused on muscle structure/function, cardiovascular development/maintenance, and smooth muscle generation/repair. Recently, SRF has received more attention in the digestive field and several important discoveries have been made. This review will summarize what we have learned about SRF in the gastrointestinal tract and provide insights into possible future directions in this area.

Proliferation of human primary vascular smooth muscle cells depends on serum response factor

Smooth muscle cells (SMCs) can switch between a differentiated/contractile and an alternative proliferative phenotype. The transcription factor serum response factor (SRF) has been implicated in the regulation of gene expression profiles determining both phenotypes. Whereas strong evidence exists for a role of SRF in SMC differentiation, the contribution of SRF to SMC proliferation is less well defined. For primary human vascular SMCs in particular, existing data are non-conclusive. To study SRF functions in primary human vascular SMCs, we used an siRNA approach. siRNA-mediated SRF suppression affected the expression of established SRF target genes such as smooth muscle alpha-actin (ACTA2) or SM22alpha (TAGLN) and decreased both F-actin formation and cell migration. Furthermore, SRF knockdown caused a cell-cycle arrest in G1 associated with reduced hyperphosphorylated pRB, cyclin A and SKP2 levels, and increased p27(kip1) (CDKN1B) protein levels. SRF-depleted cells expressed senescence-associated beta-galactosidase indicating an irreversible G1 arrest. siRNA-mediated suppression of SKP2 triggered senescence to a similar extent as SRF depletion, indicating that SRF knockdown-induced senescence may be dependent on a decrease in SKP2. Thus, SRF is an essential regulator of primary human vascular SMC proliferation and senescence. Interfering with SRF function may therefore be a promising strategy for the treatment of hyperproliferative SMC disorders such as atherosclerosis and in-stent restenosis.

Highly stomach-selective gene transfer following gastric serosal surface instillation of naked plasmid DNA in rats

BACKGROUND

The purpose of this study was to achieve stomach-selective gene transfer in rats by our simple and novel administration method, which is gastric serosal surface instillation of naked plasmid DNA (pDNA).

METHODS

Naked pDNA encoding firefly luciferase as a reporter gene was instilled onto the gastric serosal surface in male Wistar rats. As controls, we performed intraperitoneal, intragastric and intravenous administration of naked pDNA. At appropriate time intervals, we measured luciferase activities in the stomach and other tissues.

RESULTS

Gene expression in the stomach 6 h after gastric serosal surface instillation of naked pDNA (5 microg) was significantly higher than that after using other administration methods. The present study is the first report on stomach-selective gene transfer following instillation of naked pDNA onto the gastric serosal surface in rats. Also, the gene expression level in the stomach 6 h after gastric serosal surface instillation of naked pDNA was markedly higher than that in other tissues. In a dose-dependent study, the gene expression level was saturated over 5 microg. Gene expression in the stomach was detected 3 h after gastric serosal surface instillation of naked pDNA. The gene expression level peaked 12-24 h after instillation of naked pDNA, then decreased to a level similar to 3 h at 48 h.

CONCLUSIONS

Gastric serosal surface in stillation of naked pDNA can be a highly stomach-selective gene transfer method in rats.

Smad3 knockout mice exhibit impaired intestinal mucosal healing

Altered transforming growth factor-beta (TGFbeta) expression may contribute to inflammatory bowel disease and modulate epithelial cell restitution. Interference with TGFbeta-mediated signaling inhibits excisional skin wound healing, but accelerates healing of incisional cutaneous wounds and wounds in some other tissues. Therefore, we sought to clarify the potential role of Smad3-dependent TGFbeta signaling in intestinal mucosal healing in Smad3 null mice. Jejunal serosal application of filter disks saturated with 75% acetic acid yielded a circumscribed reproducible ischemic mucosal ulcer 1 day later. We compared ulcer area at 3 and 5 days to day 1 in Smad3 knockout mice and syngeneic wild-type mice, and evaluated mucosal immunoreactivity at the ulcer edge for TGFbeta, phosphorylated (activated) focal adhesion kinase (pFAK), phosphorylated extracellular signal-related kinase (pERK), proliferating cell nuclear antigen and apoptosis by TUNEL. Ulcer healing in Smad3 null mice was 17% less at day 3 (n=14, P=0.022) and 15% less at day 5 (n=14, P=0.004) than in wild-type littermates. In wild-type mice, pFAK, pERK and TGFbeta immunoreactivity were elevated in epithelium immediately adjacent to the ulcer compared with more distant mucosa. However, this pattern of immunoreactivity for pFAK, pERK and TGFbeta was not observed in Smad3 null mice. Smad3 null mice exhibited increased epithelial proliferation and no differences in apoptotic cell death compared with wild types, suggesting that ulcer healing may reflect differences in restitutive cell migration. Thus, Smad3-dependent disruption of the TGFbeta signaling pathway impairs the healing of murine intestinal mucosal ulcers and alters patterns of activated FAK and ERK immunoreactivity important for cell migration at the ulcer edge. These studies suggest a significant role for Smad3-dependent TGFbeta signaling in intestinal mucosal healing.

Glucagon-like peptide-2 improves both acute and late experimental radiation enteritis in the rat

PURPOSE

Acute and/or chronic radiation enteritis can develop after radiotherapy for pelvic cancers. Experimental and clinical observations have provided evidence of a role played by acute mucosal disruption in the appearance of late effects. The therapeutic potential of acute administration of glucagon-like peptide-2 (GLP-2) against acute and chronic intestinal injury was investigated in this study.

METHODS AND MATERIALS

Intestinal segments were surgically exteriorized and exposed to 16.7 or 19 Gy X-rays. The rats were treated once daily with vehicle or a protease-resistant GLP-2 derivative for 14 days before irradiation, with or without 7 days of GLP-2 after treatment. Macroscopic and microscopic observations were made 2 and 15 weeks after radiation exposure.

RESULTS

In the control animals, GLP-2 induced an increase in intestinal mucosal mass, along with an increase in villus height and crypt depth. GLP-2 administration before and after irradiation completely prevented the acute radiation-induced mucosal ulcerations observed after exposure to 16.7 Gy. GLP-2 treatment strikingly reduced the late radiation damage observed after 19 Gy irradiation. Microscopic observations revealed an improved organization of the intestinal wall and an efficient wound healing process, especially in the smooth muscle layers.

CONCLUSION

GLP-2 has a clear therapeutic potential against both acute and chronic radiation enteritis. This therapeutic effect is mediated through an increased mucosal mass before tissue injury and the stimulation of still unknown mechanisms of tissue response to radiation damage. Although these preliminary results still need to be confirmed, GLP-2 might be a way to limit patient discomfort during radiotherapy and reduce the risk of consequential late effects.

Severe intestinal obstruction on induced smooth muscle-specific ablation of the transcription factor SRF in adult mice

BACKGROUND & AIMS

SRF (Serum Response Factor), a widely expressed transcription factor, controls expression of mitogen-responsive and muscle-specific genes, thereby regulating the contractile actin microfilament. Genetic Srf deletion studies showed SRF to be indispensable for in vivo skeletal and cardiac muscle cell development. We now investigated for the first time in vivo SRF functions in smooth muscle cells of adult mice.

METHODS

We conditionally deleted a floxed Srf allele (Srf(flex1)) in adult mice by inducible activation of the CreER(T2) recombinase expressed specifically in smooth muscle cells. Tamoxifen-induced CreER(T2) activity stimulated deletion of exon 1 coding sequences of Srf(flex1), thereby abolishing full-length SRF protein expression in adult smooth muscle cells of the analyzed organs: colon, bladder, and stomach.

RESULTS

Smooth muscle cell-specific ablation of full-length SRF protein in adult mice showed impaired contraction of intestinal smooth muscle, resulting in defective peristalsis. Mutant mice died within 2 weeks of tamoxifen treatment, displaying clear symptoms of ileus paralyticus. Cultured primary SRF-deficient colon smooth muscle cells were viable, but displayed drastic structural alterations and elevated senescence, paralleled by degeneration of the actin microfilament and impaired expression of smooth muscle-specific genes.

CONCLUSIONS

SRF plays a vital role in the contractile activity and cytoskeletal architecture of adult smooth muscle cells and is therefore essential for physiologic functions of the gastrointestinal tract in vivo. Our mouse genetic model may resemble features of human chronic intestinal pseudo-obstruction.

Inducible mouse model of chronic intestinal pseudo-obstruction by smooth muscle-specific inactivation of the SRF gene

BACKGROUND & AIMS

Serum response factor (SRF) regulates the expression of muscle genes and immediate early genes. We investigated the consequences of inactivating this transcription factor SRF in adult gastrointestinal smooth muscle cells.

METHODS

SRF-floxed mice were crossed with SM-CreER(T2)(ki) mice expressing a tamoxifen-inducible recombinase in smooth muscle cells. Tamoxifen was injected into 12-week-old animals to activate the CreER(T2) and excise the SRF gene.

RESULTS

SRF was down-regulated in the smooth muscle cells of the gastrointestinal tract, urinary bladder, and aorta. The mutant mice developed severe dilation of the intestinal tract associated with food stasis and air-fluid levels in the lumen 13 days after tamoxifen treatment. Mutant mice displayed cachexia and died between days 13 and 22. The dilation was associated with a thinning of the muscularis propria and was also observed in the urinary bladder. Ex vivo colonic contraction induced by electric field stimulation and carbachol was impaired in the mutant mice before the occurrence of the dilation phenotype. The expression of several genes, including those encoding smooth muscle actin, the heavy chain of smooth muscle myosin, and smoothelin, was 60% to 70% lower in mutants than in controls, and mutants also had a lower F/G actin ratio.

CONCLUSIONS

SRF plays a central role in maintaining visceral smooth muscle contractile function in adults. Mice with a smooth muscle cell-specific SRF mutation develop a severe motility disorder resembling chronic intestinal pseudo-obstruction in humans and may be used as an inducible model of this disorder.

Novel roles of local insulin-like growth factor-1 activation in gastric ulcer healing: promotes actin polymerization, cell proliferation, re-epithelialization, and induces cyclooxygenase-2 in a phosphatidylinositol 3-kinase-dependent manner

The precise role of insulin-like growth factor (IGF)-1 in gastric ulcer healing is unknown. In experimental rat gastric ulcers, we examined expression of IGF-1 mRNA and protein by reverse transcriptase-polymerase chain reaction or enzyme-linked immunosorbent assay and immunostaining, respectively. In cultured rat gastric epithelial RGM1 cells, we examined effects of exogenous IGF-1 on cell migration, re-epithelialization, and proliferation-essential components of ulcer healing. We also examined whether IGF-1 induces cyclooxygenase (COX)-2 expression and determined the role of phosphatidylinositol 3-kinase and mitogen-activated protein kinase signaling pathways in mediating IGF-1 actions. Gastric ulceration triggered an approximately threefold increase in IGF-1 expression in epithelial cells of the ulcer margins (P < 0.001 versus control), especially in cells re-epithelizing granulation tissue and in mucosa in proximity to the ulcer margin. Treatment of RGM1 cells with IGF-1 caused a dramatic increase in actin polymerization, an eightfold increase in cell migration (P < 0.001), a 195% increase in cell proliferation (P < 0.05), and a sixfold increase in COX-2 expression (P < 0.01). Inhibitor of phosphatidylinositol 3-kinase abolished IGF-1-induced RGM1 cell migration and proliferation, actin polymerization, and COX-2 expression. The up-regulation of IGF-1 in gastric ulcer margin accelerates gastric ulcer healing by promoting cell re-epithelization, proliferation, and COX-2 expression via the phosphatidylinositol 3-kinase pathway.

TRPV6 mediates capsaicin-induced apoptosis in gastric cancer cells--Mechanisms behind a possible new "hot" cancer treatment

Capsaicin is an organic compound in chili peppers which are consumed by over one quarter of the world's population daily. Studies have shown that capsaicin can induce apoptosis in some cancer cells by unknown mechanisms. In this study, both gastric cancer and normal epithelial cells were treated with capsaicin and examined for apoptosis by Annexin V binding. Our results showed that capsaicin induces apoptosis in both cells, although cancer cells are more susceptible. This susceptibility is dependent on the availability of TRPV6, a calcium-selective channel protein, as overexpression of TRPV6 in normal cells increased capsaicin-induced apoptosis and knockdown of TRPV6 in cancer cells suppressed this action. Our results further demonstrated that capsaicin increases mitochondrial permeability through activation of Bax and p53 in a JNK-dependent manner.

CONCLUSIONS

(1) TRPV6, rather than TRPV1 (the well-known capsaicin receptor), mediates capsaicin-induced apoptosis in gastric cells; (2) abundance of TRPV6 in gastric cells determines their live or death under capsaicin treatment; and (3) capsaicin induces apoptosis by stabilization of p53 through JNK activation. Together, our data suggest that capsaicin may be a promising dietary candidate for cancer chemoprevention.

Serum response factor: master regulator of the actin cytoskeleton and contractile apparatus

Serum response factor (SRF) is a highly conserved and widely expressed, single copy transcription factor that theoretically binds up to 1,216 permutations of a 10-base pair cis element known as the CArG box. SRF-binding sites were defined initially in growth-related genes. Gene inactivation or knockdown studies in species ranging from unicellular eukaryotes to mice have consistently shown loss of SRF to be incompatible with life. However, rather than being critical for proliferation and growth, these genetic studies point to a crucial role for SRF in cellular migration and normal actin cytoskeleton and contractile biology. In fact, recent genomic studies reveal nearly half of the >200 SRF target genes encoding proteins with functions related to actin dynamics, lamellipodial/filopodial formation, integrin-cytoskeletal coupling, myofibrillogenesis, and muscle contraction. SRF has therefore emerged as a dispensable transcription factor for cellular growth but an absolutely essential orchestrator of actin cytoskeleton and contractile homeostasis. This review summarizes the recent genomic and genetic analyses of CArG-SRF that support its role as an ancient, master regulator of the actin cytoskeleton and contractile machinery.

Euroconference on tissue repair and ulcer/wound healing: molecular mechanisms, therapeutic targets and future directions

The meeting was part of the Euroconference series organised at the Pasteur Institute in Paris. Comprising delegates from both academia and industry, it drew on expertise from many aspects of tissue repair in a wide range of human disease. The principal component of this report concerns progress with the therapeutic application of biological agents in promoting tissue repair, as gene therapeutics, monoclonal antibodies and therapeutic proteins. In addition, the effect of pioglitazone on the rate and quality of wound healing in diabetic rats is also reported.

An overview of acetic acid ulcer models--the history and state of the art of peptic ulcer research

Four types of experimental chronic ulcer models, named acetic acid ulcer models, have been developed to examine the healing process of peptic ulcers, screen anti-ulcer drugs, and better evaluate the adverse effects of various anti-inflammatory drugs on the gastrointestinal mucosa. The model easily and reliably produces round, deep ulcers in the stomach and duodenum, allowing acetic acid ulcer production in mice, rats, Mongolian gerbils, guinea pigs, cats, dogs, miniature pigs, and monkeys. These ulcer models highly resemble human ulcers in terms of both pathological features and healing process. The models have been established over the past 35 years and are now used throughout the world by basic and clinical scientists. One of the characteristic features of acetic acid ulcers in rats is the spontaneous relapse of healed ulcers >100 d after ulceration, an endoscopically confirmed phenomenon. Indomethacin significantly delays the healing of acetic acid ulcers, probably by reducing endogenous prostaglandins and inhibiting angiogenesis in ulcerated tissue. Helicobacter pylori significantly delays healing of acetic acid ulcers and causes relapse of healed ulcers at a high incidence in Mongolian gerbils. Anti-secretory drugs (e.g. omeprazole), prostaglandin analogs, mucosal defense agents (e.g. sucralfate), and various growth factors all significantly enhance healing of acetic acid ulcers. Gene therapy with epidermal growth factor and vascular endothelial growth factor applied to the base of acetic acid ulcers in rats is effective in enhancing ulcer healing. Since an inhibitor of nitric oxide syntase prevents ulcer healing, nitric oxide might be involved in the mechanism underlying ulcer healing. We conclude that acetic acid ulcer models are quite useful for various studies related to peptic ulcers.

Cellular and molecular mechanisms of gastrointestinal ulcer healing

This paper reviews cellular and molecular mechanisms of gastrointestinal ulcer healing. Ulcer healing, a genetically programmed repair process, includes inflammation, cell proliferation, re-epithelialization, formation of granulation tissue, angiogenesis, interactions between various cells and the matrix and tissue remodeling, all resulting in scar formation. All these events are controlled by the cytokines and growth factors (EGF, PDGF, KGF, HGF, TGFbeta, VEGF, angiopoietins) and transcription factors activated by tissue injury in spatially and temporally coordinated manner. These growth factors trigger mitogenic, motogenic and survival pathways utilizing Ras, MAPK, PI-3K/Akt, PLC-gamma and Rho/Rac/actin signaling. Hypoxia activates pro-angiogenic genes (e.g., VEGF, angiopoietins) via HIF, while serum response factor (SRF) is critical for VEGF-induced angiogenesis, re-epithelialization and muscle restoration. EGF, its receptor, HGF and Cox2 are important for epithelial cell proliferation, migration re-epithelializaton and reconstruction of gastric glands. VEGF, angiopoietins, nitric oxide, endothelin and metalloproteinases are important for angiogenesis, vascular remodeling and mucosal regeneration within ulcer scar. Circulating progenitor cells are also important for ulcer healing. Local gene therapy with VEGF + Ang1 and/or SRF cDNAs dramatically accelerates esophageal and gastric ulcer healing and improves quality of mucosal restoration within ulcer scar. Future directions to accelerate and improve healing include the use of stem cells and tissue engineering.

Binding of serum response factor to cystic fibrosis transmembrane conductance regulator CArG-like elements, as a new potential CFTR transcriptional regulation pathway

CFTR expression is tightly controlled by a complex network of ubiquitous and tissue-specific cis-elements and trans-factors. To better understand mechanisms that regulate transcription of CFTR, we examined transcription factors that specifically bind a CFTR CArG-like motif we have previously shown to modulate CFTR expression. Gel mobility shift assays and chromatin immunoprecipitation analyses demonstrated the CFTR CArG-like motif binds serum response factor both in vitro and in vivo. Transient co-transfections with various SRF expression vector, including dominant-negative forms and small interfering RNA, demonstrated that SRF significantly increases CFTR transcriptional activity in bronchial epithelial cells. Mutagenesis studies suggested that in addition to SRF other co-factors, such as Yin Yang 1 (YY1) previously shown to bind the CFTR promoter, are potentially involved in the CFTR regulation. Here, we show that functional interplay between SRF and YY1 might provide interesting perspectives to further characterize the underlying molecular mechanism of the basal CFTR transcriptional activity. Furthermore, the identification of multiple CArG binding sites in highly conserved CFTR untranslated regions, which form specific SRF complexes, provides direct evidence for a considerable role of SRF in the CFTR transcriptional regulation into specialized epithelial lung cells.

Protective role of heat shock protein 27 in gastric mucosal injury

Heat shock protein 27 (HSP27) mediates cytoprotective effects through its function as a molecular chaperone and through the phosphorylation-dependent stabilization of actin filaments. The role of HSP27 in gastric ulcer formation and healing is, however, unknown. The expression of HSP27 was studied in human gastric tissue specimens obtained from patients with gastric ulcers and from healthy Helicobacter pylori-negative individuals, who received low-dose aspirin, rofecoxib, and the combination in a prospective study. The susceptibility of the gastric mucosa to indomethacin-induced lesions was further studied in transgenic mice overexpressing human HSP27 (Tg(huHSP27)) and compared with wild-type mice (Wt). The expression of HSP27, COX-1, and COX-2 was investigated in Tg(huHSP27) mice and Wt mice by immunohistochemistry and western blot analysis. While no specific changes in HSP27 expression were found following exposure of healthy human gastric mucosa to oral administration of aspirin or refocoxib, chronic gastric ulcers showed strong HSP27 expression at the ulcer base and margins. Here it was expressed by granulation tissue and regenerating surface epithelium. In Tg(huHSP27) mice, overexpression of HSP27 led to a significant decrease of indomethacin-induced erosions and ulcers compared with Wt mice. COX-1 and COX-2 levels did not change. HSP27 is involved in chronic gastric ulcer repair mechanisms in humans, while overexpression of human HSP27 in gastric epithelial cells in mice reduces the susceptibility to non-steroidal anti-inflammatory drug (NSAID)-induced gastric ulceration. This indicates that HSP27 expression is critical for mucosal protection in the stomach.