HOXA3 induces cell migration in endothelial and epithelial cells promoting angiogenesis and wound repair

Weak power frequency magnetic field acting similarly to EGF stimulation, induces acute activations of the EGFR sensitive actin cytoskeleton motility in human amniotic cells

In this article, we have examined the motility-related effects of weak power frequency magnetic fields (MFs) on the epidermal growth factor receptor (EGFR)-sensitive motility mechanism, including the F-actin cytoskeleton, growth of invasive protrusions and the levels of signal molecules in human amniotic epithelial (FL) cells. Without extracellular EGF stimulation, the field stimulated a large growth of new protrusions, especially filopodia and lamellipodia, an increased population of vinculin-associated focal adhesions. And, an obvious reduction of stress fiber content in cell centers was found, corresponding to larger cell surface areas and decreased efficiency of actin assembly of FL cells in vitro, which was associated with a decrease in overall F-actin content and special distributions. These effects were also associated with changes in protein content or distribution patterns of the EGFR downstream motility-related signaling molecules. All of these effects are similar to those following epidermal growth factor (EGF) stimulation of the cells and are time dependent. These results suggest that power frequency MF exposure acutely affects the migration/motility-related actin cytoskeleton reorganization that is regulated by the EGFR-cytoskeleton signaling pathway. Therefore, upon the MF exposure, cells are likely altered to be ready to transfer into a state of migration in response to the stimuli.

Review: placental homeobox genes and their role in regulating human fetal growth

The regulation of fetal growth is multifactorial and complex. Normal fetal growth is determined by the genetically predetermined growth potential and further modulated by maternal, fetal, placental, and environmental factors. The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by several growth factors, cytokines and transcription factors including homeobox genes. This review summarizes our current knowledge regarding homeobox genes in the human placenta and their differential expression and functions in human idiopathic fetal growth restriction (FGR). The review also describes the research strategies that were used for the identification of homeobox genes, their expression in FGR, functional role and target genes of homeobox genes in the trophoblasts and the hormonal regulators of homeobox gene expression in vitro. A better understanding of molecular pathways driven by placental homeobox genes and further elucidation of signaling pathways underlying the hormone-mediated homeobox gene developmental programs may offer novel strategies of targeted therapy for improving feto-placental growth in idiopathic FGR pregnancies.

Diabetes induces stable intrinsic changes to myeloid cells that contribute to chronic inflammation during wound healing in mice

Acute inflammation in response to injury is a tightly regulated process by which subsets of leukocytes are recruited to the injured tissue and undergo behavioural changes that are essential for effective tissue repair and regeneration. The diabetic wound environment is characterised by excessive and prolonged inflammation that is linked to poor progression of healing and, in humans, the development of diabetic foot ulcers. However, the underlying mechanisms contributing to excessive inflammation remain poorly understood. Here we show in a murine model that the diabetic environment induces stable intrinsic changes in haematopoietic cells. These changes lead to a hyper-responsive phenotype to both pro-inflammatory and anti-inflammatory stimuli, producing extreme M1 and M2 polarised cells. During early wound healing, myeloid cells in diabetic mice show hyperpolarisation towards both M1 and M2 phenotypes, whereas, at late stages of healing, when non-diabetic macrophages have transitioned to an M2 phenotype, diabetic wound macrophages continue to display an M1 phenotype. Intriguingly, we show that this population predominantly consists of Gr-1⁺ CD11b⁺ CD14⁺ cells that have been previously reported as ‘inflammatory macrophages’ recruited to injured tissue in the early stages of wound healing. Finally, we show that this phenomenon is directly relevant to human diabetic ulcers, for which M2 polarisation predicts healing outcome. Thus, treatments focused at targeting this inflammatory cell subset could prove beneficial for pathological tissue repair.

The dual roles of homeobox genes in vascularization and wound healing

Homeobox genes represent a family of highly conserved transcription factors originally discovered to regulate organ patterning during development. More recently, several homeobox genes were shown to affect processes in adult tissue, including angiogenesis and wound healing. Whereas a subset of members of the Hox-family of homeobox genes activate growth and migration to promote angiogenesis or wound healing, other Hox genes function to restore or maintain quiescent, differentiated tissue function. Pathological tissue remodeling is linked to differential expression of activating or stabilizing Hox genes and dysregulation of Hox expression can contribute to disease progression. Studies aimed at understanding the role and regulation of Hox genes have provided insight into how these potent morphoregulatory genes can be applied to enhance tissue engineering or limit cancer progression.

Hox transcription factor regulation of adult bone-marrow-derived cell behaviour during tissue repair and regeneration

INTRODUCTION

Bone marrow offers a valuable source of stem/progenitor cells that contribute to the repair of injured tissues. Failure in the function of these cells results in delayed or reduced tissue repair. Identification of factors that can correct these defects is critical to treating the underlying dysfunction. Notably, homeobox (Hox) transcription factors have been identified as having significant effects on BMDC behaviour, including differentiation, migration and adhesion in injured tissue, and may provide a basis for future therapies.

AREAS COVERED

Hox protein regulation of bone-marrow-derived cell (BMDC) differentiation, factors that influence BMDC behaviour in response to injury, the effects of the diabetic environment on BMDCs, methods that can be used to reprogramme BMDCs, and the use of Hox transcription factors to correct BMDC behaviour.

EXPERT OPINION

Hox gene therapy has been successfully employed to change cell behaviour using ex vivo 'reprogramming' strategies overexpressing selected Hox genes in BMDCs to direct the fate of these cells to the desired cell type, promoting tissue repair.

The role of placental homeobox genes in human fetal growth restriction

Fetal growth restriction (FGR) is an adverse pregnancy outcome associated with significant perinatal and paediatric morbidity and mortality, and an increased risk of chronic disease later in adult life. One of the key causes of adverse pregnancy outcome is fetal growth restriction (FGR). While a number of maternal, fetal, and environmental factors are known causes of FGR, the majority of FGR cases remain idiopathic. These idiopathic FGR pregnancies are frequently associated with placental insufficiency, possibly as a result of placental maldevelopment. Understanding the molecular mechanisms of abnormal placental development in idiopathic FGR is, therefore, of increasing importance. Here, we review our understanding of transcriptional control of normal placental development and abnormal placental development associated with human idiopathic FGR. We also assess the potential for understanding transcriptional control as a means for revealing new molecular targets for the detection, diagnosis, and clinical management of idiopathic FGR.

Temporal changes in Hox gene expression accompany endothelial cell differentiation of embryonic stem cells

In pluripotent embryonic stem cells (ESCs), expression of the Hox master regulatory transcription factors that play essential roles in organogenesis, angiogenesis, and maintenance of differentiated tissues, is globally suppressed. We investigated whether differentiation of endothelial cells (ECs) from mouse ESCs was accompanied by activation of distinct Hox gene expression profiles. Differentiation was observed within 3 days, as indicated by the appearance of cells expressing specific endothelial marker genes (Flk-1+ /VE-Cadherin+ ). Expression of HoxA3 and HoxD3, which drive adult endothelial cell invasion and angiogenesis, peaked at day 3 and declined thereafter, whereas expression of HoxA5 and HoxD10, which maintain a mature quiescent EC phenotype, was low at day 3, but increased over time. The temporal and reciprocal changes in HoxD3 and HoxA5 expression were accompanied by corresponding changes in expression of established downstream target genes including integrin β3 and Thrombospondin-2. Our results indicate that differentiation and maturation of ECs derived from cultured ESCs mimic changes in Hox gene expression that accompany maturation of immature angiogenic endothelium into differentiated quiescent endothelium in vivo.

Hoxa3 promotes the differentiation of hematopoietic progenitor cells into proangiogenic Gr-1+CD11b+ myeloid cells

Injury induces the recruitment of bone marrow-derived cells (BMDCs) that contribute to the repair and regeneration process. The behavior of BMDCs in injured tissue has a profound effect on repair, but the regulation of BMDC behavior is poorly understood. Aberrant recruitment/retention of these cells in wounds of diabetic patients and animal models is associated with chronic inflammation and impaired healing. BMD Gr-1(+)CD11b(+) cells function as immune suppressor cells and contribute significantly to tumor-induced neovascularization. Here we report that Gr-1(+)CD11b(+) cells also contribute to injury-induced neovascularization, but show altered recruitment/retention kinetics in the diabetic environment. Moreover, diabetic-derived Gr-1(+)CD11b(+) cells fail to stimulate neovascularization in vivo and have aberrant proliferative, chemotaxis, adhesion, and differentiation potential. Previously we demonstrated that gene transfer of HOXA3 to wounds of diabetic mice is taken up by and expressed by recruited BMDCs. This is associated with a suppressed inflammatory response, enhanced neovascularization, and accelerated wound healing. Here we show that sustained expression of Hoxa3 in diabetic-derived BMD Gr-1(+)CD11b(+) cells reverses their diabetic phenotype. These findings demonstrate that manipulation of adult stem/progenitor cells ex vivo could be used as a potential therapy in patients with impaired wound healing.

Microfluidic platforms for studies of angiogenesis, cell migration, and cell-cell interactions. Sixth International Bio-Fluid Mechanics Symposium and Workshop March 28-30, 2008 Pasadena, California

Recent advances in microfluidic technologies have opened the door for creating more realistic in vitro cell culture methods that replicate many aspects of the true in vivo microenvironment. These new designs (i) provide enormous flexibility in controlling the critical biochemical and biomechanical factors that influence cell behavior, (ii) allow for the introduction of multiple cell types in a single system, (iii) provide for the establishment of biochemical gradients in two- or three-dimensional geometries, and (iv) allow for high quality, time-lapse imaging. Here, some of the recent developments are reviewed, with a focus on studies from our own laboratory in three separate areas: angiogenesis, cell migration in the context of tumor cell-endothelial interactions, and liver tissue engineering.

Noninvasive stool-based detection of infant gastrointestinal development using gene expression profiles from exfoliated epithelial cells

We have developed a novel molecular methodology that utilizes stool samples containing intact sloughed epithelial cells to quantify intestinal gene expression profiles in the developing human neonate. Since nutrition exerts a major role in regulating neonatal intestinal development and function, our goal was to identify gene sets (combinations) that are differentially regulated in response to infant feeding. For this purpose, fecal mRNA was isolated from exclusively breast-fed (n = 12) and formula-fed (n = 10) infants at 3 mo of age. Linear discriminant analysis was successfully used to identify the single genes and the two- to three-gene combinations that best distinguish the feeding groups. In addition, putative "master" regulatory genes were identified using coefficient of determination analysis. These results support our premise that mRNA isolated from stool has value in terms of characterizing the epigenetic mechanisms underlying the developmentally regulated transcriptional activation/repression of genes known to modulate gastrointestinal function. As larger data sets become available, this methodology can be extended to validation and, ultimately, identification of the main nutritional components that modulate intestinal maturation and function.

MicroRNA-210: a unique and pleiotropic hypoxamir

Inadequate oxygen availability or hypoxia induces a complex and still incompletely understood set of adaptations that influence cellular survival and function. Many of these adaptations are directly controlled by a master transcription factor, hypoxia inducible factor-alpha (HIF-α). In response to hypoxia, HIF-α levels increase and directly induce the transcription of > 100 genes, influencing functions ranging from metabolism, survival, proliferation, migration, to angiogenesis, among others. Recently, it has been demonstrated that a specific set of microRNA molecules are upregulated by hypoxia, which we denote here as "hypoxamirs." In particular, the HIF-responsive hypoxamir microRNA-210 (miR-210) is a unique microRNA that is evolutionarily conserved and ubiquitously expressed in hypoxic cell and tissue types. A number of direct targets of miR-210 have been identified by in silico, transcriptional, and biochemical methods, a subset of which have been extensively validated. As a result, miR-210 has been mechanistically linked to the control of a wide range of cellular responses known to influence normal developmental physiology as well as a number of hypoxia-dependent disease states, including tissue ischemia, inflammation, and tumorigenesis. Thus, reflecting the pleiotropic actions of HIF-α, miR-210 appears to function as a "master microRNA" relevant for the control of diverse functions in the hypoxic state.

HOXA3 modulates injury-induced mobilization and recruitment of bone marrow-derived cells

The regulated recruitment and differentiation of multipotent bone marrow-derived cells (BMDCs) to sites of injury are critical for efficient wound healing. Previously we demonstrated that sustained expression of HOXA3 both accelerated wound healing and promoted angiogenesis in diabetic mice. In this study, we have used green fluorescent protein-positive bone marrow chimeras to investigate the effect of HOXA3 expression on recruitment of BMDCs to wounds. We hypothesized that the enhanced neovascularization induced by HOXA3 is due to enhanced mobilization, recruitment, and/or differentiation of BMDCs. Here we show that diabetic mice treated with HOXA3 displayed a significant increase in both mobilization and recruitment of endothelial progenitor cells compared with control mice. Importantly, we also found that HOXA3-treated mice had significantly fewer inflammatory cells recruited to the wound compared with control mice. Microarray analyses of HOXA3-treated wounds revealed that indeed HOXA3 locally increased expression of genes that selectively promote stem/progenitor cell mobilization and recruitment while also suppressing expression of numerous members of the proinflammatory nuclear factor κB pathway, including myeloid differentiation primary response gene 88 and toll-interacting protein. Thus HOXA3 accelerates wound repair by mobilizing endothelial progenitor cells and attenuating the excessive inflammatory response of chronic wounds.

Persistent inflammation and angiogenesis during wound healing in K14-directed Hoxb13 transgenic mice

Chronic, nonhealing wounds and inadequate tissue repair characterized by excessive fibrosis continue to have a considerable negative effect on health and quality of life. Understanding the molecular events required for adequate healing, including the transcriptional control of wound repair, will be important for the development of future therapies. We previously showed that loss of Hoxb13 from murine skin results in enhanced cutaneous wound healing, suggesting that Hoxb13 has a negative effect on wound repair. To test this, we generated skin-specific Hoxb13 transgenic (TG) mice that overexpress Hoxb13 in the basal layer of the epidermis by the human keratin 14 promoter. Using these mice, we evaluated the effects of Hoxb13 overexpression on cutaneous wound healing. Transgenic wounds were characterized by persistence of the fibrin clot and prolonged inflammation. Notably, neutrophils, which had cleared from wild-type wounds, were still pronounced in TG wounds. Marked epidermal hyperplasia was observed at TG wound edges, and dermal vessels were grossly abnormal compared with wild-type mice. Both vascular endothelial growth factor and tumor necrosis factor-alpha were upregulated in Hoxb13 TG skin. Together, our results identify Hoxb13 as a potential important clinical target in wound healing and other pathologies characterized by abnormal or excessive inflammation, angiogenesis, or epidermal proliferation.

Secretion of SDF-1alpha by bone marrow-derived stromal cells enhances skin wound healing of C57BL/6 mice exposed to ionizing radiation

Patients treated for cancer therapy using ionizing radiation (IR) have delayed tissue repair and regeneration. The mechanisms mediating these defects remain largely unknown at present, thus limiting the development of therapeutic approaches. Using a wound healing model, we here investigate the mechanisms by which IR exposure limits skin regeneration. Our data show that induction of the stromal cell-derived growth factor 1α (SDF-1α) is severely impaired in the wounded skin of irradiated, compared to non-irradiated, mice. Hence, we evaluated the potential of bone marrow-derived multipotent stromal cells (MSCs), which secrete high levels of SDF-1α, to improve skin regeneration in irradiated mice. Injection of MSCs into the wound margin led to remarkable enhancement of skin healing in mice exposed to IR. Injection of irradiated MSCs into the wound periphery of non-irradiated mice delayed wound closure, also suggesting an important role for the stromal microenvironment in skin repair. The beneficial actions of MSCs were mainly paracrine, as the cells did not differentiate into keratinocytes. Specific knockdown of SDF-1α expression led to drastically reduced efficiency of MSCs in improving wound closure, indicating that SDF-1α secretion by MSCs is largely responsible for their beneficial action. We also found that one mechanism by which SDF-1α enhances wound closure likely involves increased skin vascularization. Our findings collectively indicate that SDF-1α is an important deregulated cytokine in irradiated wounded skin, and that the decline in tissue regeneration potential following IR can be reversed, given adequate microenvironmental support

Triggering the regeneration and tissue repair programs

In early October 2008, researchers from diverse backgrounds gathered at an EMBO conference entitled 'The Molecular and Cellular Basis of Regeneration and Tissue Repair' to discuss the basic biology of regeneration. Topics included cell plasticity in regenerative and developmental contexts, and the link between wound healing and regeneration. The meeting also highlighted the progress made in identifying the molecular networks that underlie regeneration in a variety of model systems.

HoxB5 induces endothelial sprouting in vitro and modifies intussusceptive angiogenesis in vivo involving angiopoietin-2

AIMS

Homeobox (Hox) proteins are transcriptional regulators in embryonic patterning, cell differentiation, proliferation, and migration in vertebrates and invertebrates. A growing body of evidence suggests that Hox proteins are involved in endothelial cell regulation. We have shown earlier that HoxB5 upregulates vascular endothelial growth factor receptor-2 and thereby contributes to enhanced endothelial precursor cell differentiation. Here we aim to elucidate the role of HoxB5 in angiogenesis.

METHODS AND RESULTS

Endothelial cell sprouting was investigated in the human umbilical vein endothelial cell spheroid assay. We investigated in vivo angiogenesis in the chick (Gallus gallus) chorioallantoic membrane assay. Expression profiling of proangiogenic factors was done by quantitative PCR. The angiopoietin-2 (Ang2) promoter and deletion fragments thereof were cloned into the pGL3 reporter system for analysis of transcriptional activity. We observed that HoxB5 enhances endothelial cell sprouting and modulates the expression of adhesion molecules in vitro. Accordingly, we observed a modification of vascular growth by HoxB5 in vivo. The HoxB5 effect is reminiscent of the effects of angiopoietins. We demonstrate that Ang2 is upregulated upon HoxB5 overexpression and that the HoxB5 effect is abolished by the angiopoietin antagonist soluble Tie-2.

CONCLUSION

HoxB5 has an activating effect on Ang2 that is essential for endothelial cell sprouting and coordinated vascular growth.

Selective inhibition of matrix metalloproteinase-14 blocks tumor growth, invasion, and angiogenesis

Inhibition of specific matrix metalloproteinases (MMP) is an attractive noncytotoxic approach to cancer therapy. MMP-14, a membrane-bound zinc endopeptidase, has been proposed to play a central role in tumor growth, invasion, and neovascularization. Besides cleaving matrix proteins, MMP-14 activates proMMP-2 leading to an amplification of pericellular proteolytic activity. To examine the contribution of MMP-14 to tumor growth and angiogenesis, we used DX-2400, a highly selective fully human MMP-14 inhibitory antibody discovered using phage display technology. DX-2400 blocked proMMP-2 processing on tumor and endothelial cells, inhibited angiogenesis, and slowed tumor progression and formation of metastatic lesions. The combination of potency, selectivity, and robust in vivo activity shows the potential of a selective MMP-14 inhibitor for the treatment of solid tumors.

Cell migration into scaffolds under co-culture conditions in a microfluidic platform

Capillary morphogenesis is a complex cellular process that occurs in response to external stimuli. A number of assays have been used to study critical regulators of the process, but those assays are typically limited by the inability to control biochemical gradients and to obtain images on the single cell level. We have recently developed a new microfluidic platform that has the capability to control the biochemical and biomechanical forces within a three dimensional scaffold coupled with accessible image acquisition. Here, the developed platform is used to evaluate and quantify capillary growth and endothelial cell migration from an intact cell monolayer. We also evaluate the endothelial cell response when placed in co-culture with physiologically relevant cell types, including cancer cells and smooth muscle cells. This resulted in the following observations: cancer cells can either attract (MTLn3 cancer cell line) endothelial cells and induce capillary formation or have minimal effect (U87MG cancer cell line) while smooth muscle cells (10T 1/2) suppress endothelial activity. Results presented demonstrate the capabilities of this platform to study cellular morphogenesis both qualitatively and quantitatively while having the advantage of enhanced imaging and internal biological controls. Finally, the platform has numerous applications in the study of angiogenesis, or migration of other cell types including tumor cells, into a three-dimensional scaffold or across an endothelial layer under precisely controlled conditions of mechanical, biochemical and co-culture environments.

Regulation of angiogenesis: apoptotic cues from the ECM

The extracellular matrix (ECM) acts both as a physical scaffold for cells and as a repository for growth factors. Moreover, ECM structure and physical-chemical properties convey precise information to cells that profoundly influences their biology by interactions with cell surface receptors termed integrins. During angiogenesis, the perivascular ECM plays a critical role in determining the proliferative, invasive and survival responses of the local vascular cells to the angiogenic growth factors. Dynamic changes in both the ECM and the local vascular cells act in concert to regulate new blood vessel growth. The digestion of ECM components by proteolysis is critical for the invasive capacity of endothelial cells, but also creates ECM fragments, which antagonize the mechanosensory function of integrins, and can be apoptogenic. Here, we discuss the roles of integrins in modulating cellular responses to a changing ECM, in particular the regulation of survival and invasion among invasive endothelial cells.

Expression and function of HOXA genes in normal and neoplastic ovarian epithelial cells

We studied the roles of three HOXA genes in cultured normal ovarian surface epithelial (OSE) cells and ovarian cancer cells. They included HOXA4 and HOXA7 because, by cDNA microarray analysis, these were more highly expressed in invasive ovarian carcinomas than in benign or borderline (noninvasive) ovarian tumors, and HOXA9 because it characterizes normal oviductal epithelium, which resembles ovarian serous adenocarcinomas. The three HOXA genes were more highly expressed when OSE cells were dividing and motile than when they were confluent and stationary, and also when they dispersed in response to EGF treatment or to reduced calcium concentrations in culture media. The expression of the HOXA genes varied among ovarian cancer cell lines, but was highest in lines with compact epithelial morphologies. We focused on HOXA4 as the most highly expressed in the ovarian carcinoma array. HOXA4 expression did not parallel proliferative activities of either OSE or ovarian cancer lines. Moreover, modifying HOXA4 expression in ovarian cancer cell lines did not alter either E-cadherin expression or CA125 secretion. However, HOXA4 downregulation enhanced EGFR phosphorylation and migration in serum-starved OSE and ovarian cancer cells in response to EGF, and enhanced migration of all ovarian cancer lines in 5% serum even without EGF treatment. Thus, HOXA4 expression does not correlate with proliferation or with epithelial differentiation, but it increases in response to OSE cell dispersion and negatively regulates EGFR activation and the motility of OSE and of ovarian cancer cells. HOXA4 expression was highest in cancer lines with compact epithelial growth patterns, suggesting, again, an anti-dispersion function. In summary, increased HOXA4 expression in ovarian cancer appears to constitute a tumor-suppressive, homeostatic response to aberrant cell behavior, and, in particular, to cell dispersion and migration.

Evidence for Hox-specified positional identities in adult vasculature

BACKGROUND

The concept of specifying positional information in the adult cardiovascular system is largely unexplored. While the Hox transcriptional regulators have to be viewed as excellent candidates for assuming such a role, little is known about their presumptive cardiovascular control functions and in vivo expression patterns.

RESULTS

We demonstrate that conventional reporter gene analysis in transgenic mice is a useful approach for defining highly complex Hox expression patterns in the adult vascular network as exemplified by our lacZ reporter gene models for Hoxa3 and Hoxc11. These mice revealed expression in subsets of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) located in distinct regions of the vasculature that roughly correspond to the embryonic expression domains of the two genes. These reporter gene patterns were validated as authentic indicators of endogenous gene expression by immunolabeling and PCR analysis. Furthermore, we show that persistent reporter gene expression in cultured cells derived from vessel explants facilitates in vitro characterization of phenotypic properties as exemplified by the differential response of Hoxc11-lacZ-positive versus-negative cells in migration assays and to serum.

CONCLUSION

The data support a conceptual model of Hox-specified positional identities in adult blood vessels, which is of likely relevance for understanding the mechanisms underlying regional physiological diversities in the cardiovascular system. The data also demonstrate that conventional Hox reporter gene mice are useful tools for visualizing complex Hox expression patterns in the vascular network that might be unattainable otherwise. Finally, these mice are a resource for the isolation and phenotypic characterization of specific subpopulations of vascular cells marked by distinct Hox expression profiles.

JNK regulates cell migration through promotion of tyrosine phosphorylation of paxillin

The adaptor protein paxillin plays an important role in cell migration. Although the c-Jun amino-terminal kinase (JNK) phosphorylation of paxillin on Ser 178 has been found to be critical for cell migration, the precise mechanism by which JNK regulates cell migration is still not very clear. Here, the migration of human corneal epithelial (HCE) cells was used to determine which signaling pathways are involved in EGF-induced paxillin phosphorylation. Paxillin was phosphorylated on Tyr 31 and Tyr 118 after induction of migration by EGF in HCE cells. Specific inhibition of JNK activation by inhibitor SP600125 or overexpression of a dominant-negative JNK mutant not only blocked EGF-induced cell migration, but also eliminated tyrosine phosphorylation of paxillin on Tyr 31 and Tyr 118. HCE cells overexpressing paxillin-S178A mutant also exhibited lower mobility, and reduced phosphorylation of Tyr 31 and Tyr 118. However, paxillin-S178A-inhibited cell migration can be rescued by overexpression of paxillin-Y31E/Y118E mutant. Importantly, inhibition of JNK by SP600125 or overexpression of paxillin-S178A mutant prevented the association of FAK with paxillin. Taken together, these results suggest that phosphorylation of paxillin on Ser 178 by JNK is required for the association of paxillin with FAK, and subsequent tyrosine phosphorylation of paxillin.

Sustained expression of Hif-1alpha in the diabetic environment promotes angiogenesis and cutaneous wound repair

Impaired wound healing in diabetic patients is associated with deficiencies in the production of factors involved in cell proliferation and migration, such as vascular endothelial growth factor. However, it remains unclear how the transcriptional regulation of the genes encoding these factors is affected by the diabetic environment. Hypoxia-inducible factor-1alpha (Hif-1alpha), the regulatory subunit of the Hif-1 transcription factor, plays an important role in activating many of these genes. Therefore, we tested whether Hif-1alpha function is impaired in the diabetic wound environment and whether restoring Hif-1 function improves wound healing. Here, we show that Hif-1alpha protein levels are dramatically reduced in wounds of leptin receptor-deficient diabetic mice compared with nondiabetic littermates. Reduction in Hif-1alpha levels results in decreased DNA-binding activity and in decreased expression of several Hif-1 target genes, including vascular endothelial growth factor, heme oxygenase-1, and inducible nitric oxide synthase. Furthermore, we demonstrate that sustained expression of Hif-1alpha in leptin receptor-deficient diabetic wounds restores expression of these factors, enhances angiogenesis, and significantly accelerates wound healing. Taken together, these results suggest that Hif-1alpha function plays a significant role in wound healing and reduced levels of Hif-1alpha may contribute to impaired healing.

Transcriptional control of wound repair

Injury to the skin initiates a complex process of events involving inflammation as well as the formation and remodeling of new tissue. These processes result in at least partial reconstitution of the injured skin. However, wounds in adult mammals heal with a scar, which is accompanied by functional and aesthetic impairments. In addition to this problem, a large number of patients, in particular in the aged population, suffer from chronic, nonhealing ulcers. Therefore, there is a strong need to improve the wound healing process. This requires a thorough understanding of the underlying molecular and cellular mechanisms. During the past several years, important regulators of the wound healing process have been identified. In particular, the growth factors and matrix proteins, which orchestrate skin repair, have been characterized in detail. By contrast, much less is known about the transcription factors, which regulate gene expression at the wound site. This review summarizes recent data on the expression of transcription factors in skin wounds and their functions in the repair process.

miR-210 links hypoxia with cell cycle regulation and is deleted in human epithelial ovarian cancer

Tumor growth results in hypoxia. Understanding the mechanisms of gene expression reprogramming under hypoxia may provide important clues to cancer pathogenesis. We studied miRNA genes that are regulated by hypoxia in ovarian cancer cell lines by TaqMan miRNA assay containing 157 mature miRNAs. MiR-210 was the most prominent miRNA consistently stimulated under hypoxic conditions. We provide evidence for the involvement of the HIF signaling pathway in miR-210 regulation. Biocomputational analysis and in vitro assays demonstrated that e2f transcription factor 3 (e2f3), a key protein in cell cycle, is regulated by miR-210. E2F3 was further confirmed to be downregulated at the protein level upon induction of miR-210. Importantly, we found remarkably high frequency of miR-210 gene copy deletions in ovarian cancer patients (64%, n = 114) and that gene copy number correlates with miR-210 expression levels. Taken together, our results indicate that miR-210 plays a crucial role in tumor onset as a key regulator of the hypoxia response and provide evidence for a link between hypoxia and the regulation of cell cycle.

HOX gene analysis of endothelial cell differentiation in human bone marrow-derived mesenchymal stem cells

Human bone marrow-derived mesenchymal stem cells (hMSCs) have been shown to possess multilineage differentiation potential. HOX genes function in transcriptional regulators, and are involved in stem cell differentiation. The aim of the present study was to demonstrate HOX genes that are related to angiogenesis. To identify the expression patterns of 37 HOX genes in the endothelial cell differentiation of hMSCs, we analyzed HOX genes through profiling with multiplex RT-PCR. The results showed that the expression patterns of four HOX genes, HOXA7, HOXB3, HOXA3, and HOXB13, significantly changed during angiogenesis. The expression levels of HOXA7 and HOXB3 were dramatically increased, whereas those of HOXA3 and HOXB13 were decreased during endothelial cell differentiation. When further analysis of the expressions of these HOX genes was performed with real-time PCR and an immunoblot assay, the expression patterns were also found to be well-matched with the results of multiplex RT-PCR. Here, we report that HOXA7, HOXB3, HOXA3, and HOXB13 might be involved in the angiogenesis of hMSCs.

HoxA5 stabilizes adherens junctions via increased Akt1

Normal vascular development and angiogenesis is regulated by coordinated changes in cell-cell and cell-extracellular matrix (ECM) interactions. The Homeobox (Hox) family of transcription factors coordinately regulate expression of matrix degrading proteinases, integrins and ECM components and profoundly impact vascular remodeling. Whereas HoxA5 is down regulated in active angiogenic endothelial cells (EC), sustained expression of HoxA5 induces TSP-2 and blocks angiogenesis. Since HoxA5 is also lacking in EC in proliferating hemangiomas, we investigated whether restoring expression of HoxA5 could normalize hemangioma cell morphology and/or behavior. Sustained expression of HoxA5 in the murine hemangioma cell line (EOMA) reduced their growth in vivo and promoted branching morphogenesis in 3D BM cultures. Moreover, restoring HoxA5 expression increased the retention of beta-catenin in adherens junctions and reduced permeability. In addition we also show that the HoxA5 mediated increase in stability of adherens junctions requires Akt1 activity and introduction of constitutively active myr-Akt in EOMA cells also increased retention of beta-catenin in adherens junctions. Finally we show that HoxA5 increases Akt1 mRNA, protein expression and further enhances Akt activity via a coordinate down regulation of PTEN. Together these results demonstrate a central role for HoxA5 in coordinating a stable vascular phenotype.

Regulation and function of homeodomain proteins in the embryonic and adult vascular systems

During embryonic development, the cardiovascular system first forms and then gives rise to the lymphatic vascular system. Homeobox genes are essential for both the development of the blood and lymphatic vascular systems, as well as for their maintenance in the adult. These genes all encode proteins that are transcription factors that contain a well conserved DNA binding motif, the homeodomain. It is through the homeodomain that these transcription factors bind to the promoters of target genes and regulate their expression. Although many homeodomain proteins have been found to be expressed within the vascular systems, little is known about their downstream target genes. This review highlights recent advances made in the identification of novel genes downstream of the homeodomain proteins that are necessary for regulating vascular cellular processes such as proliferation, migration, and endothelial tube formation. Factors known to regulate the functions of vascular cells via modulating the expression of homeobox genes will be discussed. We will also review current methods used to identify and characterize downstream target genes of homeodomain proteins.

Gene therapy progress and prospects: therapeutic angiogenesis for ischemic cardiovascular disease

During the past decade, both in vitro and in vivo studies have provided new insights into the cellular and molecular mechanisms that govern angiogenesis and arteriogenesis. However, therapeutic angiogenesis clinical trials using recombinant protein or gene therapy formulations of single angiogenic growth factors have yielded at best only modest success to date. Among the second generation of angiogenic agents are therapeutic transgenes that enhance expression of two or more proangiogenic cytokines. These include synthetic constructs that mimic that activity of endogenous transcriptional regulators and other upstream, regulatory factors that have the potential to induce formation of morphologically and physiologically functional vessels. These agents are now beginning to be evaluated in clinical trials for patients with advanced ischemic cardiac and peripheral vascular disease.

Hemangiomas and homeobox gene expression

Hemangiomas are the most common benign tumor of childhood. Clinical management is limited primarily to observation. Non-surgical treatment modalities have had mixed results and with morbid side effects. Improved understanding of angiogenesis over the last two decades is helping to delineate differences between various vascular tumors. This molecular understanding will be central in helping to properly diagnose and potentially treat these childhood tumors. While a number of downstream effector cytokines have been shown to have altered expression in hemangiomas, a cause for the primary dysregulation within hemangiomas has not yet been clarified. Upstream modulators of angiogenesis are now being defined. Homeobox (Hox) genes are master transcription factors, which have a centrol role during organogenesis, and more recently have been documented to be involved in postnatal tissue remodeling and tumor angiogenesis. We document increased expression of Hox D3 in proliferating hemangiomas and propose a potential role for Hox A3, B3, A5 and D10.

The homeobox gene GAX activates p21WAF1/CIP1 expression in vascular endothelial cells through direct interaction with upstream AT-rich sequences

Tumors secrete pro-angiogenic factors to induce the ingrowth of blood vessels from the surrounding stroma, the end targets of which are vascular endothelial cells (ECs). The homeobox gene GAX inhibits angiogenesis and induces p21(WAF1/CIP1) expression in vascular ECs. To elucidate the mechanism through which GAX activates p21(WAF1/CIP1) expression, we constructed GAX cDNAs with deletions of the N-terminal domain, the homeodomain, or the C-terminal domain and then assessed these constructs for their ability to activate p21(WAF1/CIP1). There was an absolute requirement for the homeodomain, whereas deleting the C-terminal domain decreased but did not abolish transactivation of the p21(WAF1/CIP1) promoter by GAX. Deleting the N-terminal domain did abolish transactivation. Next, we performed chromatin immunoprecipitation and found, approximately 15 kb upstream of the p21(WAF1/CIP1) ATG codon, an ATTA-containing GAX-binding site (designated A6) with a sequence similar to that of other homeodomain-binding sites. GAX was able to bind to A6 in a homeodomain-dependent manner and thereby activate the expression of a reporter gene coupled to this sequence, and this activation was abolished by mutating specific residues in this sequence. On the basis of the sequence of A6, we were then able to locate other ATTA-containing sequences that also bound GAX and activated transcription in reporter constructs. Finally, we found that the ability of these GAX deletions to induce G(0)/G(1) arrest correlates with their ability to transactivate the p21(WAF1/CIP1) promoter. We conclude that GAX activates p21(WAF1/CIP1) through multiple upstream AT-rich sequences. Given the multiple biological activities of GAX in regulating EC function, identification of a putative GAX-binding site will allow the study of how GAX activates or represses other downstream targets to inhibit angiogenesis.

Gene therapy and wound healing

Wound repair involves the sequential interaction of various cell types, extracellular matrix molecules, and soluble mediators. During the past 10 years, much new information on signals controlling wound cell behavior has emerged. This knowledge has led to a number of novel therapeutic strategies. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trails indicates that a crucial aspect of the growth factor wound healing strategy is the effective delivery of these polypeptides to the wound site. A molecular approach in which genetically modified cells synthesize and deliver the desired growth factor in regulated fashion has been used to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. We have summarized the molecular and cellular basis of repair mechanisms and their failure, and we give an overview of techniques and studies applied to gene transfer in tissue repair.

Impact of the loss of Hoxa5 function on lung alveogenesis

The involvement of genes controlling embryonic processes in the etiology of diseases often escapes attention because of the focus given to their inherent developmental role. Hoxa5 belongs to the Hox gene family encoding transcription factors known for their role in skeletal patterning. Hoxa5 is required for embryonic respiratory tract morphogenesis. We now show that the loss of Hoxa5 function has severe repercussions on postnatal lung development. Hoxa5-/- lungs present an emphysema-like morphology because of impaired alveogenesis. Chronic inflammation characteristics, including goblet cell hyperplasia, mucus hypersecretion, and recruitment of inflammatory cells, were also observed. Altered cell specification during lung morphogenesis triggered goblet cell anomalies. In addition, the defective motility of alveolar myofibroblast precursors in the embryonic lung led to the mispositioning of the alveolar myofibroblasts and to abnormal elastin deposition postnatally. Both goblet cell hyperplasia and elastic fiber abnormalities contributed to the chronic physiopathological features of Hoxa5-/- lungs. They constituted an attractive stimulus to recruit activated macrophages that in turn generated a positive feedback loop that perpetuated macrophage accumulation in the lung. The present work corroborates the notion that altered Hox gene expression may predispose to lung pathologies.

Transcriptional regulators of angiogenesis

Angiogenesis, the process by which new blood vessels develop from a pre-existing vascular network, is essential for normal development and in certain physiological states. Inadequate or excessive angiogenesis has been incriminated in a number of pathologic states. For example, vaso-occlusive disease arising from atherosclerosis can lead to ischemia, a situation in which enhanced angiogenesis would be beneficial. Conversely, overzealous angiogenesis can contribute to tumor development and in this case inhibition of angiogenesis is desirable. Thus, strategies to induce or inhibit angiogenesis are of considerable therapeutic interest.

A role for Hox A5 in regulating angiogenesis and vascular patterning

BACKGROUND

Homeobox (Hox) genes are transcriptional regulators which modulate embryonic morphogenesis and pathological tissue remodeling in adults via regulation of genes associated with cell-cell or cell extracellular matrix (ECM) interactions. We previously showed that while Hox 3 genes promote angiogenesis, Hox D10 inhibits this process.

METHODS AND RESULTS

Here we show that another Hox family gene, Hox A5, also blocks angiogenesis but accomplishes this by targeting different downstream genes than Hox D10. Sustained expression of Hox A5 leads to down regulation of many pro-angiogenic genes including VEGFR2, ephrin A1, Hif1alpha and COX-2. In addition, Hox A5 also upregulates expression of anti-angiogenic genes including Thrombospondin-2. Furthermore, we show that while Hox A5 mRNA is expressed in quiescent endothelial cells (EC), its expression is diminished or absent in active angiogenic EC found in association with breast tumors or in proliferating infantile hemangiomas.

CONCLUSIONS

Together our results suggest that restoring Hox A5 expression may provide a novel means to limit breast tumor growth or expansion of hemangiomas.

Cellular and molecular events during early thymus development

The thymic stromal compartment consists of several cell types that collectively enable the attraction, survival, expansion, migration, and differentiation of T-cell precursors. The thymic epithelial cells constitute the most abundant cell type of the thymic microenvironment and can be differentiated into morphologically, phenotypically, and functionally separate subpopulations of the postnatal thymus. All thymic epithelial cells are derived from the endodermal lining of the third pharyngeal pouch. Very soon after the formation of a thymus primordium and prior to its vascularization, thymic epithelial cells orchestrate the first steps of intrathymic T-cell development, including the attraction of lymphoid precursor cells to the thymic microenvironment. The correct segmentation of pharyngeal epithelial cells and their subsequent crosstalk with cells in the pharyngeal arches are critical prerequisites for the formation of a thymus anlage. Mutations in several transcription factors and their target genes have been informative to detail some of the complex mechanisms that control the development of the thymus anlage. This review highlights recent findings related to the genetic control of early thymus organogenesis and provides insight into the molecular basis by which lymphocyte precursors are attracted to the thymus.

Pbx1 is required for Hox D3-mediated angiogenesis

Our previous studies showed that the homeobox (Hox) D3 transcription factor induces expression of alphavbeta3 integrin and promotes endothelial cell (EC) migration and angiogenesis. Since binding of Hox 3 factors to target DNA is enhanced by the co-factor Pbx, we investigated whether Pbx1 is also required for angiogenesis. We observed that EC predominantly express the Pbx1b isoform. Nuclear extracts from angiogenic EC express higher levels of active Pbx1 and more effectively form complexes on Pbx1/Hox consensus DNA oligonucleotides as compared to nuclear extracts from quiescent EC. Introduction of anti-sense against Pbx1 impaired the formation of Pbx1/Hox complexes on target DNA consensus in nuclear extracts from angiogenic EC. Anti-sense against Pbx1 also impaired EC migration and blocked angiogenesis induced by bFGF in vivo. Furthermore, although the levels of Hox D3 were unchanged, expression of its target gene, beta3 integrin was reduced, consistent with impaired transcriptional activation by Hox D3. Together, these studies suggest that Pbx1 is required for pro-angiogenic Hox DNA binding and transcriptional activity in endothelial cells.

Human skin cells support thymus-independent T cell development

Thymic tissue has previously been considered a requirement for the generation of a functional and diverse population of human T cells. We report that fibroblasts and keratinocytes from human skin arrayed on a synthetic 3-dimensional matrix support the development of functional human T cells from hematopoietic precursor cells in the absence of thymic tissue. Newly generated T cells contained T cell receptor excision circles, possessed a diverse T cell repertoire, and were functionally mature and tolerant to self MHC, indicating successful completion of positive and negative selection. Skin cell cultures expressed the AIRE, Foxn1, and Hoxa3 transcription factors and a panel of autoantigens. Skin and bone marrow biopsies can thus be used to generate de novo functional and diverse T cell populations for potential therapeutic use in immunosuppressed patients.