Myeloid cells in infantile hemangioma

Cell Fate Regulation During the Development of Infantile Hemangioma

As the most common benign vascular tumor in infants, infantile hemangioma (IH) is characterized by rapid growth and vasculogenesis early in infancy, followed by spontaneous involution into fibrofatty tissues over time. Extensive evidence suggests that IH originates from hemangioma stem cells (HemSCs), a group of stem cells with clonal expansion and multi-directional differentiation capacity. However, the intricate mechanisms governing the cell fate transition of HemSCs during IH development remain elusive. Here we comprehensively examine the cellular composition of IH, emphasizing the nuanced properties of various IH cell types and their correlation with the clinical features of the tumor. We also summarize the current understanding of the regulatory pathways directing HemSC differentiation into endothelial cells (ECs), pericytes, and adipocytes throughout the stages of IH progression and involution. Furthermore, we discuss recent advances in unraveling the transcriptional and epigenetic regulation of EC and adipocyte development under physiological conditions, which offer crucial perspectives for understanding IH pathogenesis.

Integrated WGCNA and PPI Network to Screen Hub Genes Signatures for Infantile Hemangioma

BACKGROUND

Infantile hemangioma (IH) is characterized by proliferation and regression.

METHODS

Based on the GSE127487 dataset, the differentially expressed genes (DEGs) between 6, 12, or 24 months and normal samples were screened, respectively. STEM software was used to screen the continued up-regulated or down-regulated in common genes. The modules were assessed by weighted gene co-expression network analysis (WGCNA). The enrichment analysis was performed to identified the biological function of important module genes. The area under curve (AUC) value and protein-protein interaction (PPI) network were used to identify hub genes. The differential expression of hub genes in IH and normal tissues was detected by qPCR.

RESULTS

There were 5,785, 4,712, and 2,149 DEGs between 6, 12, and 24 months and normal tissues. We found 1,218 DEGs were up-regulated or down-regulated expression simultaneously in common genes. They were identified as 10 co-expression modules. Module 3 and module 4 were positively or negatively correlated with the development of IH, respectively. These two module genes were significantly involved in immunity, cell cycle arrest and mTOR signaling pathway. The two module genes with AUC greater than 0.8 at different stages of IH were put into PPI network, and five genes with the highest degree were identified as hub genes. The differential expression of these genes was also verified by qRTPCR.

CONCLUSION

Five hub genes may distinguish for proliferative and regressive IH lesions. The WGCNA and PPI network analyses may help to clarify the molecular mechanism of IH at different stages.

Proliferating Infantile Hemangioma Tissues and Primary Cell Lines Express Markers Associated with Endothelial-to-Mesenchymal Transition

Supplemental Digital Content is available in the text.

Background:

We have previously shown that the endothelium of the microvessels of infantile hemangioma (IH) exhibits a hemogenic endothelium phenotype and proposed its potential to give rise to mesenchymal stem cells, similar to the development of hematopoietic cells. This endothelial-to-mesenchymal transition (Endo-MT) process involves the acquisition of a migratory phenotype by the endothelial cells, similar to epithelial-to-mesenchymal transition that occurs during neural crest development. We hypothesized that proliferating IH expresses Endo-MT–associated proteins and investigated their expression at the mRNA, protein, and functional levels.

Methods:

Immunohistochemical staining of paraffin-embedded sections of proliferating IH samples from 10 patients was undertaken to investigate the expression of the Endo-MT proteins Twist1, Twist2, Snail1, and Slug. Transcriptional analysis was performed for the same markers on proliferating IH tissues and CD34⁺ and CD34⁻ cells from proliferating IH-derived primary cell lines. Adipogenic and osteogenic differentiation plasticity was determined on the CD34-sorted fractions.

Results:

The endothelium of the microvessels and the cells within the interstitium of proliferating IH tissues expressed Twist1, Twist2, and Slug proteins. Twist1 was also expressed on the pericyte layer of the microvessels, whereas Snail1 was not expressed. Both CD34⁺ and CD34⁻ populations from the IH-derived primary cell lines underwent adipogenic and osteogenic differentiation.

Conclusions:

The expression of Endo-MT–associated proteins Twist1, Twist2, and Slug by both the endothelium of the microvessels and cells within the interstitium, and Twist1 on the pericyte layer of the microvessels of proliferating IH, suggest the presence of a process similar to Endo-MT. This may enable a tightly controlled primitive endothelium of proliferating IH to acquire a migratory mesenchymal phenotype with the ability to migrate away, providing a plausible explanation for the development of a fibrofatty residuum observed during involution of IH.

Expression of (pro)renin receptor and its effect on endothelial cell proliferation in infantile hemangioma

BACKGROUND

Propranolol is the preferred treatment for problematic proliferating infantile hemangioma (IH) by targeting the renin-angiotensin system (RAS) expressed by IH endothelium. (Pro)renin receptor (PRR) is a major component of the RAS associated with the canonical wnt signaling pathway. We proposed that activation of PRR by renin causes proliferation of IH.

METHODS

The expression of PRR in IH tissue samples was investigated using immunohistochemical (IHC) staining and NanoString analysis. NanoString analysis was also used to confirm transcriptional expression of PRR in CD34-sorted proliferating IH-derived primary cell lines. MTT assay was utilized to determine the effect of exogenous renin on the number of viable IH cells. RT-qPCR was used to determine the effect of renin on the stem cell gene expression.

RESULTS

NanoString analysis and IHC staining confirmed transcriptional and translational expression of PRR, which was localized to the non-endothelial and the endothelial IH cell populations. MTT assay demonstrated an increased number of viable IH cells by administration of renin and the effect was negated by the wnt receptor blocker dickkopf-1.

CONCLUSION

Our results present a model for renin-induced increased proliferation of IH cells through PRR acting via the wnt signaling pathway, which may account for accumulation of cells in IH during the proliferative phase of the tumor.

Mechanisms of Action of MicroRNAs in Infantile Hemangioma Tissue and Vascular Endothelial Cells in Different Periods

Background

The aim of this study was to investigate the developmental mechanisms of infantile hemangioma (IH) from the microRNA level.

Material/Methods

A total of 63 biological specimens of IH were obtained from the First Affiliated Hospital of Jinzhou Medical University and we assessed related miRNAs. Magnetic bead sorting, endocytosis test, canalization assay, and immunofluorescence detection were performed. The IH-derived cells were transfected with related factors and then we assessed the apoptosis and invasion.

Results

The contents of MiR-455, miR-206, and miR-29a in the proliferative period group (PP) were lower than in the complete regression period group (CR) (P<0.05), and the content of miR-29a in the regression period group (RP) was lower than in the group CR (P<0.05). The post-sorting proliferation capacity was faster than in human umbilical vein endothelial cells, and IH-derived vascular endothelial cells (VECs) exhibited faster canalization ability. The cells transfected with miR-29a exhibited obvious apoptosis 48 h later, the cells transfected with miR-206 exhibited significantly reduced proliferation capacity as well as apoptosis 48 h later, and the invasion capacity was decreased 24 h after transfection.

Conclusions

miR-29a, miR-206, and miR-455 are differently expressed in different periods of IH, and may participate in regulating multiple functions during the progression of IH.

M1 Macrophage-Induced Endothelial-to-Mesenchymal Transition Promotes Infantile Hemangioma Regression

Infantile hemangiomas are benign tumors of vascular endothelial cells (ECs), characterized by three distinct stages: proliferating phase, involuting phase, and involuted phase. The mechanisms that trigger involution of hemangioma into fibro-fatty tissue remain unknown. We report a novel mechanism by which M1-polarized macrophages induce endothelial-to-mesenchymal transition (EndMT) and promote hemangioma regression. M1- but not M2-polarized macrophages induced EndMT in ECs. Tumor necrosis factor-α and, to a lesser extent, IL-1β and interferon-γ were the most potent cytokines produced by the M1 macrophages that induce in vitro EndMT. Western blot analysis and gene expression profiling showed that ECs treated with M1 macrophages, tumor necrosis factor-α, or IL-1β decreased the expression of endothelial markers, whereas mesenchymal markers increased concomitantly. Immunohistochemical staining of patient samples revealed that a significant perivascular infiltration of M1, but not M2, macrophages coincides with endothelial expression of the critical EndMT transcription factors Snail/Slug in involuting hemangiomas. Most strikingly, M1 macrophage-treated ECs isolated from patient hemangiomas (HemECs) but not untreated HemECs readily differentiated into adipocytes on adipogenic induction. Thus, in vitro EndMT and adipogenesis of HemECs have, in part, recapitulated the natural history of hemangioma regression. In conclusion, our findings indicate that EndMT induced by M1 macrophages promotes infantile hemangioma regression and may lead to novel therapeutic treatments for this vascular tumor.

Estrogen-mediated hemangioma-derived stem cells through estrogen receptor-α for infantile hemangioma

Background

Infantile hemangiomas (IHs) are the most common benign vascular tumor of infancy. They occur more frequently in female infants. The cause of hemangioma is currently unknown; however, current studies suggested the importance of estrogen (E2) signaling in hemangioma proliferation.

Methods

Hemangioma-derived stem cells (HemSCs) were cultured with estrogen for 48–72 h; the cell viability and proliferation were evaluated with the messenger RNA (mRNA) and protein expression levels of fibroblast growth factor 2 (FGF2), vascular endothelial growth factor-A (VEGF-A) and estrogen receptor-α (ER-α), by application of several in vitro assays, such as methyl thiazolyl tetrazolium (MTT), reverse transcriptase–polymerase chain reaction (RT-PCR), real-time PCR, enzyme-linked immunosorbent assay (ELISA) and Western blotting. Also, the cell population’s response to external estrogen was investigated by in vivo experiments. HemSCs and human umbilical vein endothelial cells (HUVECs) were mixed and injected subcutaneously into 20 flank of BALB/c-nu mice, which were randomly divided into 5 groups based on different E2 treatment doses (0, 0.01, 0.1 and 1 mg, respectively), 0.1 mg dimethyl sulfoxide (DMSO) as control. Each group of mice were treated intramuscularly every week, then 2 and 4 weeks later, the subcutaneous implants were harvested and evaluated the tumor tissues with microvessel density (MVD) assay and immunohistochemistry.

Results

The study demonstrated that application of E2 increased the expression of FGF2, VEGF-A, and ER-α in HemSCs with the optimal concentration from 10⁻⁹ to 10⁻⁵ M. Two-week treatment of E2 promoted expression of VEGF-A and FGF2 in HemSCs culture. Morphological, histological and immunohistological improvements were observed in vivo using murine IH model in which HemSCs and HUVECs were implanted into BALB/c-nu mice that were post-injected with E2. In the grafts, mean MVD was markedly increased.

Conclusion

The results suggested that E2 promotes angiogenesis via combination with ER-α to up-regulate the expression of VEGF-A in HemSCs, promoting proliferation of IHs. These findings provide critical insight into the potential mechanisms of E2 action on IHs.

Monitoring Cell-surface N-Glycoproteome Dynamics by Quantitative Proteomics Reveals Mechanistic Insights into Macrophage Differentiation

The plasma membrane proteome plays a crucial role in inter- and intracellular signaling, cell survival, and cell identity. As such, it is a prominent target for pharmacological intervention. The relatively low abundance of this subproteome in conjunction with challenging extractability and solubility still hampers its comprehensive analysis. Here, we combined a chemical glycoprotein-tagging strategy with mass spectrometry to enable comprehensive analysis of the cell-surface glycoproteome. To benchmark this workflow and to provide guidance for cell line selection for functional experiments, we generated an inventory of the N-linked cell-surface glycoproteomes of 15 standard laboratory human cell lines and three primary lymphocytic cell types. On average, about 900 plasma membrane and secreted proteins were identified per experiment, including more than 300 transporters and ion channels. Primary cells displayed distinct expression of surface markers and transporters underpinning the importance of carefully validating model cell lines selected for the study of cell surface-mediated processes. To monitor dynamic changes of the cell-surface proteome in a highly multiplexed experiment, we employed an isobaric mass tag-based chemical labeling strategy. This enabled the time-resolved analysis of plasma membrane protein presentation during differentiation of the monocytic suspension cell line THP-1 into macrophage-like adherent cells. Time-dependent changes observed in membrane protein presentation reflect functional remodeling during the phenotypic transition in three distinct phases: rapid surface presentation and secretion of proteins from intracellular pools concurrent with rapid internalization of no longer needed proteins and finally delayed presentation of newly synthesized macrophage markers. Perturbation of this process using marketed receptor tyrosine kinase inhibitors revealed dasatinib to severely compromise macrophage differentiation due to an off-target activity. This finding suggests that dynamic processes can be highly vulnerable to drug treatment and should be monitored more rigorously to identify adverse drug effects.

Fell-Muir Lecture: Regulatory mechanisms of skeletal and connective tissue development and homeostasis - lessons from studies of human disorders

Studies of proliferative hemangiomas have led to the discovery that interactions of endothelial cells with extracellular matrix and/or Vascular Endothelial Growth Factor (VEGF)-A stimulate the expression of VEGFR1, the VEGF decoy receptor, and suppress VEGF-dependent VEGFR2 signalling by a mechanism that requires the matrix-binding receptor Anthrax Toxin Receptor (ANTXR)1, VEGFR2, β1 integrin and the Nuclear Factor of Activated T cells (NFAT). In hemangioma endothelial cells, all these components are present, but are functionally compromised, so that the levels of VEGFR1 are extremely low and VEGFR2 signalling is constitutively active. Consequently, the levels of Hypoxia Inducible Factor (HIF)-1α and its transcriptional targets, VEGF-A and C-X-C motif chemokine 12 (CxCl12), are elevated and a positive VEGF-A feedback loop is established. Overexpression of ANTXR1, carrying a heterozygous Ala-to-Thr mutation, induces hemangioma-like signalling in control endothelial cells; VEGF signalling is normalized when wild-type ANTXR1 is overexpressed in hemangioma cells. These findings suggest that ANTXR1 functions as a negative regulator of VEGF-A signalling. Studies of a mouse model of the Growth Retardation, Alopecia, Pseudo-anodontia and Optic Atrophy (GAPO) syndrome, caused by the loss-of-function mutations in ANTXR1, as well as knock-in mice carrying the Ala-to-Thr ANTXR1 mutation, confirm that ANTXR1 functions as a suppressor of VEGF-A signalling. Cutaneous endothelial cells isolated from ANTXR1-deficient mice exhibit low levels of VEGFR1, elevated levels of VEGF-A, HIF-1α and CxCl12 and activated VEGFR2 signalling as in hemangioma. Increased numbers of myeloid cells in the skin of ANTXR1-deficient mice are associated with reduced vascularity and increased skin fibrosis, suggesting a mechanism for hemangioma involution and replacement by fibrotic scars. Through controlling VEGF-A signalling and extracellular matrix synthesis, ANTXR1 is emerging as a key regulator of skeletal and connective tissue development and homeostasis.

Does hypoxia play a role in infantile hemangioma?

Infantile hemangioma (IH), the most common tumor of infancy, is characterized by rapid growth during infancy, followed by spontaneous involution over 5-10 years. Certain clinical observations have led to the suggestion that IH is triggered and maintained by hypoxia. We review the literature on the possible role of hypoxia in the etiology of IH, in particular, (1) the role of hypoxia inducible factor-1α (HIF-1α) and its downstream targets including GLUT-1 and VEGF; (2) the pathophysiological link between IH and retinopathy of prematurity; (3) hypoxic events in the early life including placental insufficiency, pre-eclampsia and low birthweight that have the potential to promote hypoxic stress; and (4) the evidence supporting the development of IH independent of HIF-1α. We also discuss these observations in the context of recent evidence of the crucial role of stem cells and the cytokines niche that governs their proliferation and inevitable differentiation, offering novel insights into the biology of IH. We propose that various triggers may simultaneously up-regulate HIF-1α, which is downstream of the renin-angiotensin system, specifically angiotensin II, which promotes production of HIF-1α. These developments shed light to the understanding of this enigmatic condition.

The embryo-placental CD15-positive "vasculogenic zones" as a source of propranolol-sensitive pediatric vascular tumors

OBJECTIVE

Propranolol-induced involution is a unique biological feature of some pediatric vascular tumors, for instance infantile hemangioma (IH), cerebral cavernoma or chorioangioma. Currently, the cellular origin of these distinct tumors is unclear. In this study, we tested the hypothesis that propranolol-responsive vascular tumors are derived from common vessel-forming CD15 + progenitor cells which occur in early gestation. The aim of this study was to identify the tumor-relevant CD15 + progenitors at the early stages of embryo-placental development.

MATERIALS AND METHODS

Human embryo-placental units of 4-8 weeks gestation and pediatric vascular tumors were tested for expression of the tumor-relevant markers CD15, CD31 and CD34.

RESULTS

Placental vessel-forming progenitors were characterized by immunostaining for CD15, CD31, and CD34. In embryonic tissue, a discontinuous CD15+/CD31+/CD34 + progenitors was detected in immature vessels of the skin, neural tube, spinal and cerebral meninges. Similarly, vessels in IH and chorioangioma exhibited a co-expression of CD15, CD31, and CD34. In contrast, the majority of embryonic vessels presented a CD31+/CD34+, but CD15-negative immunophenotypic pattern.

DISCUSSION

Our results suggest the existence of a CD15+ "vasculogenic zones" in the embryo-placental unit as well as in IH and chorioangioma. A site-specific correlation between normal embryo-placental and tumoral vessel-forming CD15 + progenitors was demonstrated.

CONCLUSION

Hence, site- and stage-specific CD15 + progenitors of vascular wall could be considered as propronalol-sensitive targets and source of pre- and postnatal vascular tumors. We propose, that the CD15+ "vasculogenic zones" are a site-specific reserve of multi-lineage progenitors that could be recruited in pre- and postnatal emergency situations.

Macrophages Contribute to the Progression of Infantile Hemangioma by Regulating the Proliferation and Differentiation of Hemangioma Stem Cells

Macrophage infiltration has been implicated in infantile hemangioma (IH), the most common tumor of infancy. However, the exact role of macrophages in IH remains unknown. This study aims to clarify the functional significance of macrophages in the progression of IH. The distribution of macrophages in human IH was analyzed, and our results revealed that polarized macrophages were more prevalent in proliferating IHs than in involuting IHs, which was consistent with the increased macrophage-related cytokines in proliferating IHs. In vitro results further demonstrated that polarized macrophages effectively promoted the proliferation of hemangioma stem cells (HemSCs) and suppressed their adipogenesis in an Akt- and extracellular signal-regulated kinase 1/2 (Erk1/2)-dependent manner. Moreover, M2- but not M1-polarized macrophages promoted the endothelial differentiation of HemSCs. Furthermore, mixing macrophages in a murine hemangioma model elevated microvessel density and postponed fat tissue formation, which was concomitant with the activation of Akt and Erk1/2 signals. Cluster analysis revealed a close correlation among the macrophage markers, Ki67, vascular endothelial growth factor (VEGF), p-Akt, and p-Erk1/2 in human IH tissues. Collectively, our results suggest that macrophages in IH contribute to tumor progression by promoting the proliferation and endothelial differentiation while suppressing the adipogenesis of HemSCs. These findings indicate that targeting the infiltrating macrophages in IH is a promising therapeutic approach to accelerate IH regression.

A hydrogel-endothelial cell implant mimics infantile hemangioma: modulation by survivin and the Hippo pathway

Microvascular endothelial cells cultured in three-dimensional hydrogel scaffolds form a network of microvessel structures when implanted subcutaneously in mice, inosculate with host vessels, and over time remodel into large ectatic vascular structures resembling hemangiomas. When compared with infantile hemangiomas, similarities were noted, including a temporal progression from a morphological appearance of a proliferative phase to the appearance of an involuted phase, mimicking the proliferative and involutional phases of infantile hemangioma. Consistent with the progression of a proliferative phase to an involuted phase, both the murine implants and human biopsy tissue exhibit reduced expression of Ajuba, YAP, and Survivin labeling as they progressed over time. Significant numbers of CD45+, CD11b+, Mac3+ mononuclear cells were found at the 2-week time point in our implant model that correlated with the presence of CD45+, CD68+ mononuclear cells observed in biopsies of human proliferative-phase hemangiomas. At the 4-week time point in our implant model, only small numbers of CD45+ cells were detected, which again correlated with our findings of significantly diminished CD45+, CD68+ mononuclear cells in human involutional-phase hemangiomas. The demonstration of mononuclear cell infiltration transiently in the proliferative phase of these lesions suggests that the vascular proliferation and/or regression may be driven in part by an immune response. Gross and microscopic morphological appearances of human proliferative and involutional hemangiomas and our implant model correlate well with each other as do the expression levels of Hippo pathway components (Ajuba and YAP) and Survivin and correlate with proliferation in these entities. Inhibitors of Survivin and Ajuba (which we have demonstrated to inhibit proliferation and increase apoptosis in murine hemangioendothelioma cell tissue culture) may have potential as other beneficial treatments for proliferating infantile hemangiomas. This implant model may have potential as a modest through-put screen for testing and development of therapeutics targeted at the proliferative phase of infantile hemangiomas, reducing the subsequent postinvolutional scarring or deformities sometimes associated with these lesions.

Expression of Cathepsins B, D, and G in Infantile Hemangioma

AIMS

The role of the renin-angiotensin system (RAS) in the biology of infantile hemangioma (IH) represents an emerging paradigm, particularly the involvement of renin, angiotensin converting enzyme, and angiotensin II. This study investigated the expression of cathepsins B, D, and G, enzymes that may modulate the RAS, in IH.

MATERIALS AND METHODS

The expression of cathepsins B, D, and G was examined using immunohistochemistry, enzyme activity assays, mass spectrometry, and NanoString gene expression assay in IH samples at different phases of development.

RESULTS

Immunohistochemical staining showed the expression of cathepsins B, D, and G in proliferating and involuted IH samples. This was confirmed at the transcriptional level using NanoString gene expression assays. Mass spectrometry confirmed the identification of cathepsins D and G in all three phases of IH development, whereas cathepsin B was detected in 2/2 proliferating and 1/2 involuting lesions. Enzyme activity assays demonstrated the activity of cathepsins B and D, but not G, in all phases of IH development.

CONCLUSION

Our data demonstrated the presence of cathepsins B, D, and G in IH. Their role in modulating the RAS and the biology of IH offers potential novel targets for the management of this tumor.

Characterisation of lymphocyte subpopulations in infantile haemangioma

Aims

Interstitial CD45+ cells and T lymphocytes have previously been demonstrated within infantile haemangioma (IH). This study investigated the expression of B and T lymphocyte markers by the CD45+ population, and the expression of Thy-1, a marker of thymocyte progenitors, which have the ability to give rise to both B and T cells.

Methods

Immunohistochemical (IHC) staining was performed on proliferating and involuted IHs for the expression of CD45, CD3, CD20, CD79a, Thy-1 and CD34. The presence of mRNA corresponding to CD45, CD3G, CD20 and Thy-1 was confirmed by reverse transcriptase-polymerase chain reaction in snap-frozen IH tissues. Cell counting of 3,3-diaminobenzidine IHC-stained slides was performed on CD45+ only cells and dually stained CD45+/CD3+ cells or CD45+/CD20+ cells and analysed statistically. In situ hybridisation and mass spectrometry were also performed to confirm the presence and abundance of Thy-1, respectively.

Results

IHC staining showed a subpopulation of CD45+ interstitial cells that expressed the T lymphocyte marker, CD3, and another subpopulation that expressed the B lymphocyte marker, CD20, in proliferating and diminished in involuted IHs. The abundant expression of Thy-1 on the endothelium of proliferating, but not involuted IH, was demonstrated by IHC staining and confirmed by in situ hybridisation and mass spectrometry.

Conclusions

Both B and T lymphocytes are present within the interstitium of proliferating and involuted IH. The expression of Thy-1 by the endothelium suggests that B and T cells in IH may have originated from within the lesion, rather than migrating from the peripheral circulation.

Giant chorioangioma treated in utero via laser of feeding vessels with subsequent development of multifocal infantile hemangiomas

We report a case of a giant placental chorioangioma (15.6 cm diameter) complicated by polyhydramnios and severe fetal heart failure. Fetoscopic laser occlusion of a dominant feeding vessel was performed at 29 weeks' gestation and partial devascularization was achieved. In the 33rd week of the pregnancy, the decision was made to preemptively deliver the fetus due to persistent signs of fetal cardiac failure. After birth, the infant developed multifocal infantile hemangiomas with extracutaneous involvement. We posit that the development of infantile hemangiomas may be linked to the presence of the large chorioangioma. Further study is required to ascertain if fetal treatment of the chorioangioma may have been an exacerbating factor.

Educational paper: Pathogenesis of infantile haemangioma, an update 2014 (part I)

Infantile haemangioma (IH) is the most frequent childhood tumour. Although it is benign and self-limiting, severe complications can arise due to localisation and fast tumour growth. Management and therapy of IH has changed greatly after 2008 with propranolol. However, the pathogenesis remains elusive. This update provides an overview of all possible mechanisms currently considered. We discuss the possibility that several mechanisms act together, although local hypoxia seems to be important. Clinically, in about half of the cases, an IH is preceded by an anaemic macula (local ischaemia) or a so-called precursor lesion. Laboratory findings indicate stabilisation and an increased transcription activity of hypoxia-inducible factor 1 alpha (HIF1α), leading to up-regulation of its downstream target genes (such as vascular endothelial growth factor (VEGF)), which normally occurs in cases of hypoxia.

CONCLUSION

Three main hypotheses have been proposed, namely (1) the theory of tissue hypoxia, (2) the theory of embolization of placental endothelial cells and (3) the theory of increased angiogenic and vasculogenic activity.

Support for the hypoxia theory in the pathogenesis of infantile haemangioma

BACKGROUND

The pathogenesis of infantile haemangioma (IH) is unknown. Several mechanisms have been proposed, including hypoxia, which triggers upregulation and stabilization of hypoxia-inducible factor (HIF)1α. HIF1α stimulates downstream transcription of target genes that enhance angiogenesis.

AIM

To identify possible involvement of hypoxia in the pathogenesis of IH, as hypoxia signalling constitutes a potential therapeutic target.

METHODS

IH tissue samples collected during the period 1991-2011 (preserved in paraffin wax) were immunohistochemically analysed for HIF1α and the known HIF1α targets: BCL2/adenovirus E1B kD-interacting protein family member 3 (BNIP3), carbon anhydrase (CA)-IX, glucose transporter (GLUT)-1, phosphorylated protein kinase B (pAKT), phosphorylated S6 protein (pS6) and vascular endothelial growth factor (VEGF). Four observers independently assessed the findings.

RESULTS

Of the 10 IH samples, 2 appeared to be in the growth phase. In all samples, GLUT-1, BNIP3, pAKT and VEGF were positive, CA-IX was weakly positive, and HIF1α was negative. pS6 was positive in 9/10 cases and negative in 1/10.

CONCLUSIONS

Several factors implicated in hypoxia-induced angiogenesis may be involved in IH development. However, the small sample size and retrospective approach of the study preclude definitive conclusions. Prospective studies are needed to conclusively determine which of the factors involved in the (hypoxia) cascade are required for an IH to grow, and could thus be a possible target of drugs for IH treatment.

CD15 - a new marker of pathological villous immaturity of the term placenta

INTRODUCTION

Idiopathic immaturity is one of the main reasons for latent placental insufficiency and antenatal hypoxia. Postnatal identification of the immature placental phenotype may help early stratification of a heterogeneous population of newborns and individually identify risk of disease in the immediate postnatal life. The aim of the study was to determine the relevant diagnostic markers associated with pathological placental immaturity.

METHODS

111 tissue samples from normal and pathological term placentas with persisting villous immaturity comprised the comparative immunohistochemical study (CD15, CD34). Positive immunohistochemical reactions were quantitatively assessed in the chorionic plate and vessels of the villi of different histological type.

RESULTS

We have shown that pathological villous immaturity is attended by significantly increased CD15-expression in the macro- and microvascular endothelium compared with the normal placenta. CD34-expression was not different from that in normal placentas.

DISCUSSION

This paper documents the correlation of CD15+ endothelium in the macrovascular fetoplacental vessels with a severe form of villous immaturity associated with fetal hypoxia/asphyxia and erythroblastosis. Increased CD15-expression only in the microvascular segment of the fetoplacental vessels correlated with moderate villous immaturity and was associated with GDM, idiopathic fetal macrosomia and nonspecific chronic villitis.

CONCLUSION

We propose that "immature" CD15+ endothelium is an important diagnostic marker of persisting villous immaturity and chronic placental dysfunction. The level of CD15 expression in the macro- and microvasculature reflects the degree of pathological placental villous immaturity.

Rapidly involuting congenital hemangioma with pustules: two cases

Rapidly involuting congenital hemangiomas (RICHs) are rare tumors that usually present as well-defined bluish or violaceous plaques or tumors with scattered telangiectasias and central or peripheral pallor. We report two previously unreported cases of RICH with associated pustules.

Beta-blockers as therapy for infantile hemangiomas

Infantile hemangiomas (IH) are common benign vascular tumors seen in children. Although the majority will improve spontaneously without treatment, a small subset will require therapy due to a variety of complications. Less than a decade ago, propranolol replaced corticosteroids as first-line treatment for most IH and it has proven to be a relatively safe, effective therapy. After initiation of propranolol, most hemangiomas show evidence of significant improvement relatively rapidly, often within days. Although propranolol is generally felt to have a more limited side-effect profile than systemic corticosteroids, its use has been infrequently associated with adverse events, including sleep disturbances, acrocyanosis, hypotension, bradycardia, respiratory events, and hypoglycemia. Rarely, hypoglycemic seizures have been reported, usually occurring in the setting of prolonged fasting.

Identification of three molecular and functional subtypes in canine hemangiosarcoma through gene expression profiling and progenitor cell characterization

Canine hemangiosarcomas have been ascribed to an endothelial origin based on histologic appearance; however, recent findings suggest that these tumors may arise instead from hematopoietic progenitor cells. To clarify this ontogenetic dilemma, we used genome-wide expression profiling of primary hemangiosarcomas and identified three distinct tumor subtypes associated with angiogenesis (group 1), inflammation (group 2), and adipogenesis (group 3). Based on these findings, we hypothesized that a common progenitor may differentiate into the three tumor subtypes observed in our gene profiling experiment. To investigate this possibility, we cultured hemangiosarcoma cell lines under normal and sphere-forming culture conditions to enrich for tumor cell progenitors. Cells from sphere-forming cultures displayed a robust self-renewal capacity and exhibited genotypic, phenotypic, and functional properties consistent with each of the three molecular subtypes seen in primary tumors, including expression of endothelial progenitor cell (CD133 and CD34) and endothelial cell (CD105, CD146, and αvβ3 integrin) markers, expression of early hematopoietic (CD133, CD117, and CD34) and myeloid (CD115 and CD14) differentiation markers in parallel with increased phagocytic capacity, and acquisition of adipogenic potential. Collectively, these results suggest that canine hemangiosarcomas arise from multipotent progenitors that differentiate into distinct subtypes. Improved understanding of the mechanisms that determine the molecular and phenotypic differentiation of tumor cells in vivo could change paradigms regarding the origin and progression of endothelial sarcomas.

Signaling pathways in the development of infantile hemangioma

Infantile hemangioma (IH), which is the most common tumor in infants, is a benign vascular neoplasm resulting from the abnormal proliferation of endothelial cells and pericytes. For nearly a century, researchers have noted that IH exhibits diverse and often dramatic clinical behaviors. On the one hand, most lesions pose no threat or potential for complication and resolve spontaneously without concern in most children with IH. On the other hand, approximately 10% of IHs are destructive, disfiguring and even vision- or life-threatening. Recent studies have provided some insight into the pathogenesis of these vascular tumors, leading to a better understanding of the biological features of IH and, in particular, indicating that during hemangioma neovascularization, two main pathogenic mechanisms prevail, angiogenesis and vasculogenesis. Both mechanisms have been linked to alterations in several important cellular signaling pathways. These pathways are of interest from a therapeutic perspective because targeting them may help to reverse, delay or prevent hemangioma neovascularization. In this review, we explore some of the major pathways implicated in IH, including the VEGF/VEGFR, Notch, β-adrenergic, Tie2/angiopoietins, PI3K/AKT/mTOR, HIF-α-mediated and PDGF/PDGF-R-β pathways. We focus on the role of these pathways in the pathogenesis of IH, how they are altered and the consequences of these abnormalities. In addition, we review the latest preclinical and clinical data on the rationally designed targeted agents that are now being directed against some of these pathways.

Approach to the patient with an infantile hemangioma

Infantile hemangioma is the most common soft tissue tumor of childhood. Despite its frequency, it has only been in the last decade that these lesions have been better characterized and become the subject of significant clinical and translational research. Although most infantile hemangiomas are uncomplicated and do not require intervention, they can be a significant source of parental distress, cosmetic disfigurement, and morbidity. The wide spectrum of disease in the morphology of these lesions and in their behavior has made it difficult to predict the need for treatment and has made it challenging to establish a standardized approach to management.

M2-polarised macrophages in infantile haemangiomas: correlation with promoted angiogenesis

AIMS

The pathogenesis of infantile haemangiomas (IHs) is still far from clear despite the fact that they are common vascular tumours distinctive for their perinatal presentation, rapid growth during the first year of life and subsequent slow involution.

AIMS

To determine the role of M2-polarised macrophages in IHs.

METHODS

M2-polarised macrophages were initially identified in 20 specimens of IHs by both immunochemistry and immunofluorescence for CD68 and CD163. The immunopositive M2-polarised macrophages in different phases of IHs were quantified, and further analysed for their correlations with the expression levels of Ki67, vascular endothelial growth factor (VEGF) and macrophage colony-stimulating factor (M-CSF).

RESULTS

The infiltrating macrophages in proliferative IHs were predominantly CD68/CD163, thus of the M2-polarised phenotype, whereas the density of these cells was significantly decreased in the involuting IHs. The high density of M2-polarised macrophages in proliferative IHs was closely correlated with overexpression of M-CSF, one of the cytokines considered to induce macrophages to polarise towards an M2 phenotype. The infiltrating M2-polarised macrophages probably contributed to the proliferation and angiogenesis of haemangioma endothelial cells, as evidenced by their close correlations with the immunoreactivities of Ki67 and VEGF.

CONCLUSIONS

Results indicate that the infiltrating M2-polarised macrophages may contribute to the progression of IHs by promoting the angiogenic process.

Mast cells in infantile haemangioma possess a primitive myeloid phenotype

AIMS

Recent reports on infantile haemangioma (IH) have demonstrated a primitive population of interstitial cells expressing the embryonic transcription factor, Nanog, with decreasing abundance during involution. In this report we investigated the expression of Nanog on mast cells in all three phases of IH progression.

METHODS

Paraffin-embedded sections of six proliferating, six involuting and six involuted IH lesions were used to investigate the expression of tryptase, Nanog, CD45, CD34 and GLUT-1 by immunostaining.

RESULTS

Mast cells, identified by their expression of tryptase, were located in the interstitium of IH lesions. 93%, 42% and 0% of these tryptase(+) cells also expressed Nanog, in proliferating, involuting and involuted IH, respectively.

CONCLUSIONS

The identification of an abundant population of tryptase(+)/Nanog(+) cells in IH is novel. The relative loss of Nanog expression as IH involutes may be a result of maturation and/or proliferation of these cells. This report supports the primitive nature of IH.

Evaluation of expression profiles of hematopoietic stem cell, endothelial cell, and myeloid cell antigens in spontaneous and chemically induced hemangiosarcomas and hemangiomas in mice

It is unclear whether the process of spontaneous and chemically induced hemangiosarcoma and hemangioma formation in mice involves the transformation of differentiated endothelial cells (ECs) or recruitment of multipotential bone marrow-derived hematopoietic stem cells or endothelial progenitor cells (EPCs), which show some degree of endothelial differentiation. In the present study, immunohistochemical staining for hematopoietic stem cell markers (CD45 and CD34), EC markers (vascular endothelial growth factor receptor 2 [VEGFR2], CD31, and factor VIII-related antigen), and a myeloid lineage marker (CD14) was employed to better define the origin of hemangiosarcomas and hemangiomas in mice. Staining was negative for CD45, factor VIII-related antigen, and CD14 and positive for CD34, VEGFR2, and CD31, indicating that mouse hemangiosarcomas and hemangiomas are composed of cells derived from EPCs expressing CD34, VEGFR2, and CD31 but not factor VIII-related antigen. The lack of CD45 expression suggests that mouse vascular tumors may arise from EPCs that are at a stage later than hematopoietic stem cells. Since factor VIII-related antigen expression is known to occur later than CD31 expression in EPCs, our observations may indicate that these tumor cells are arrested at a stage prior to complete differentiation.  In addition, myeloid lineage cells do not appear to contribute to hemangiosarcoma and hemangioma formation in mice.

E-selectin mediates stem cell adhesion and formation of blood vessels in a murine model of infantile hemangioma

Hemangioma stem cells (HemSCs) are multipotent cells isolated from infantile hemangioma (IH), which form hemangioma-like lesions when injected subcutaneously into immune-deficient mice. In this murine model, HemSCs are the primary target of corticosteroid, a mainstay therapy for problematic IH. The relationship between HemSCs and endothelial cells that reside in IH is not clearly understood. Adhesive interactions might be critical for the preferential accumulation of HemSCs and/or endothelial cells in the tumor. Therefore, we studied the interactions between HemSCs and endothelial cells (HemECs) isolated from IH surgical specimens. We found that HemECs isolated from proliferating phase IH, but not involuting phase, constitutively express E-selectin, a cell adhesion molecule not present in quiescent endothelial cells. E-selectin was further increased when HemECs were exposed to vascular endothelial growth factor-A or tumor necrosis factor-α. In vitro, HemSC migration and adhesion was enhanced by recombinant E-selectin but not P-selectin; both processes were neutralized by E-selectin-blocking antibodies. E-selectin-positive HemECs also stimulated migration and adhesion of HemSCs. In vivo, neutralizing antibodies to E-selectin strongly inhibited formation of blood vessels when HemSCs and HemECs were co-implanted in Matrigel. These data suggest that endothelial E-selectin could be a major ligand for HemSCs and thereby promote cellular interactions and vasculogenesis in IH. We propose that constitutively expressed E-selectin on endothelial cells in the proliferating phase is one mediator of the stem cell tropism in IH.

Evolution of hemangioma endothelium

Infantile hemangioma is a benign vascular tumor, characterized by a unique life cycle consisting of rapid growth and spontaneous regression. Three distinct phases (proliferating, involuting, and involuted) take place over the course of approximately 5-8 years, with specific cell types defining each separate phase. The origin of the cells comprising hemangiomas has been deliberated over since the late 1800s. We have recently provided experimental evidence that hemangiomas arise from multipotent stem cells. These hemangioma stem cells that give rise to the endothelial cells are also the essential source of adipocytes during hemangioma involution. The molecular mechanisms that regulate the differentiation of the hemangioma stem cells remain unclear. Although recent studies have elucidated a number of signaling pathways underlying hemangioma pathogenesis, many unanswered questions remain. Herein, we review the unique cellular composition of infantile hemangioma, as well as some of the signaling pathways active within hemangioma-genesis. Understanding the mechanisms behind changes in cellular fate throughout the hemangioma growth pattern will not only provide insight into the stem cell population that resides within the tumor, but will help to establish more effective eradicating therapies.

Nonselective β-blocker propranolol for orbital and periorbital hemangiomas in infants: a new first-line of treatment?

Purpose

To determine the effectiveness and possible side effects of using propranolol for the treatment of orbital and periorbital infantile hemangiomas.

Methods

Infants with periorbital or orbital hemangiomas who had not received either local or systemic corticosteroids were recruited. The changes in tumor size, color, and texture, and any side effects of the drug were recorded.

Results

Fifteen infants with a mean age of 8.13 ± 4.7 months were treated according to the set protocol. A change in the color and texture of the hemangioma occurred in the first week following treatment. Mean duration of treatment was 7.67 ± 3.96 months. The size of hemangiomas decreased from a mean of 2.4 ± 0.9 cm to a mean of 1.6 ± 1.0 cm 3 months after treatment (P = 0.001). One patient had to stop the drug because of peripheral vascular ischemia. Another case had the dose reduced to control a mild hyperglycemia. Serious side effects were not observed. A single case of tumor regrowth (8.3%) was recorded.

Conclusion

Treatment of 1–2 mg/kg/day propranolol proved to be effective and associated with minimal side effects. It is likely to replace steroids as the first-line of treatment of hemangiomas in infants.

Pharmacologic therapies for infantile hemangioma: is there a rational basis?

BACKGROUND

Infantile hemangioma is the most common tumor of infancy. The majority of cases are managed conservatively, but intervention is necessary in approximately 10 percent of cases because of the threat to life or function or because of tissue distortion or destruction. The mainstay treatment for these problematic proliferating infantile hemangiomas is pharmacologic therapy, mostly discovered serendipitously.

METHODS

This review examines the rational basis of the hitherto empirical pharmacologic therapies for the enigmatic infantile hemangioma, in light of new knowledge regarding its biology, including the critical roles of stem cells and the renin-angiotensin system.

RESULTS

Steroids have remained the first-line therapy for problematic infantile hemangioma for over 40 years despite their known side effects and failure rates. Vincristine has emerged as an alternative to interferon for steroid-resistant cases because of interferon's adverse effects, especially neurotoxicity. β-Blockers are now the preferred first-line therapy for problematic cases. There is increasing evidence that infantile hemangioma is a disorder of aberrant proliferation and differentiation of primitive mesoderm-derived neural crest phenotypic cells. This primitive phenotype that gives rise to a hemogenic endothelium intermediate has the ability to undergo primitive erythropoiesis and terminal mesenchymal differentiation.

CONCLUSIONS

The recent discovery of the crucial role of stem cells and the inferred role of the renin-angiotensin system in the biology of infantile hemangioma underscores the possibility of even more targeted therapies, by using modulators of the renin-angiotensin system, on infantile hemangioma. The observation of the potential role of these traditional antihypertensive agents in stem cell biology may lead to better understanding of developmental biology and tumor stem cell growth.

Mesenchymal stem cells in infantile haemangioma

Background

Fibro-fatty deposition commonly occurs during involution of infantile haemangioma (IH). Mesenchymal stem cells have been identified in this tumour and have been proposed to be recruited from the bone marrow and/or adjacent niches, and then give rise to the fibro-fatty tissue. The authors have recently demonstrated that the capillary endothelium of proliferating IH co-expresses primitive mesodermal, mesenchymal and neural crest markers and proposed that this same endothelium has the ability to give rise to cells of mesenchymal lineage that constitute the fibro-fatty deposition.

Methods

Immunohistochemistry and real-time RT-PCR were used to further characterise proliferating IHs and haemangioma explant-derived cells (HaemEDCs).

Results

The authors have further confirmed expression of the mesenchymal-associated proteins including preadipocyte factor-1, a mesenchymal differentiation inhibition-associated cytokine. The HaemEDCs could be differentiated into osteoblasts and adipocytes, indicating their functional potential for terminal differentiation.

Discussion

The collective expression of neural crest, mesenchymal and mesenchymal differentiation inhibition-associated proteins on the endothelium of proliferating IH suggests that the cells in the capillary endothelium within the lesion possess the ability to undergo terminal mesenchymal differentiation during the proliferating phase, but are inhibited from doing so.

Recent progress in studies of infantile hemangioma

A hallmark of infantile hemangioma, the most common tumor of infancy, is its dramatic growth after birth, by diffuse proliferation of immature endothelial cells, followed by spontaneous regression. The growth and involution of infantile hemangioma is quite different from other vascular anomalies, which do not regress and can occur at any time during life. Some hemangioma lesions can be extremely disfiguring and destructive to normal tissue and may even be life-threatening. Unfortunately, existing therapeutic approaches have limited success and significant adverse effects of some treatment modalities limit their use. Better understanding of the pathogenesis of hemangioma will enable the development of better therapeutic strategies. Here, we review recent studies and new hypotheses on the pathogenesis of the tumor. Detailed mechanisms of activated vascular endothelial growth factor signaling in tumor cells, identification of their origin and characterization of multipotent stem cells that can give rise to infantile hemangioma are shedding new light on this intriguing vascular tumor.

Hypothesis: the metastatic niche theory can elucidate infantile hemangioma development

Recent advances in the understanding of the metastatic phenomenon in cancer have led to the description of a metastatic niche. This concept describes a site prepared for the tumor cells in areas frequently associated with metastasis for the individual tumor studied. This niche is a "soil" that allows for the tumor cell or "seed" to lodge and grow. Certain aspects of the biology of infantile hemangioma cells suggest a relationship to the placenta as a possible site of origin for the hemangioma precursor cells. In this article, a relationship between the placenta, with or without a chorangioma and the hemangioma sites of localization, is hypothesized. The placenta is suggested as the site of humoral factors that prepare a niche similar to the function of malignant tumor cells. If the hypothesis proves to be valid, clues for possible treatment are outlined.

Overexpression of allograft inflammatory factor-1 promotes the proliferation and migration of human endothelial cells (HUV-EC-C) probably by up-regulation of basic fibroblast growth factor

Our previous study demonstrated that allograft inflammatory factor-1 (AIF-1) is present in the vessels of infantile hemangiomas but neither in the vessels of vascular malformations, pyogenic granulomas, normal skin, placental tissues nor in the neovessels of squamous cell carcinomas of the tongue. The purpose of this study was to explore the impact of AIF-1 alterations on endothelial cells (EC). Stable introduction of AIF-1 to the human umbilical vein EC line (HUV-EC-C) in vitro revealed that AIF-1 enhances the proliferation and migration of the EC and promotes G0/G1-to-S-phase transition, accompanied by up-regulation of basic fibroblast growth factor (p < 0.05). In contrast, AIF-1 did not affect the expression of granulocyte colony-stimulating factor, VEGF-a, monocyte chemoattractant protein-1, or tissue inhibitor of metalloproteinase-1. AIF-1 expression was not induced by hypoxia, VEGF-a, basic fibroblast growth factor, or insulin-like growth factor-2 in EC. Taken together, these findings suggest that the impact of AIF-1 on EC would stimulate angiogenesis and consequently affect the progression of infantile hemangiomas.

Signaling mechanisms in infantile hemangioma

PURPOSE OF REVIEW

Infantile hemangioma is a common vascular tumor with a unique lifecycle: rapid growth in infancy, followed by a period of involution, leading to complete regression. This review summarizes recent studies of molecular mechanisms of hemangioma formation and places new findings and hypotheses in the context of past accomplishments.

RECENT FINDINGS

The new work identifies a novel signaling pathway for vascular growth factor and extracellular matrix regulation in vascular endothelial cells and provides a basis for novel therapeutic strategies. In hemangioma-derived endothelial cells, defects in a vascular endothelial growth factor receptor/integrin complex reduce the expression of a vascular endothelial growth factor decoy receptor. As a consequence, hemangioma endothelial cells exhibit constitutive vascular endothelial growth factor signaling. Germline mutations in components of the growth factor receptor/integrin complex in some hemangioma patients, and somatic mutations in a phosphatase in sporadic hemangioma specimens, raise the possibility that hemangioma formation involves a combination of germline risk factor mutations and somatic mutations, similar to what recent studies have shown is the case for venous malformations.

SUMMARY

Alterations in pathways that negatively control vascular endothelial growth factor signaling in vascular endothelial cells are responsible for the formation and rapid growth of infantile hemangiomas.

Vasculogenesis in infantile hemangioma

Infantile hemangioma is a vascular tumor that occurs in 5-10% of infants of European descent. A defining feature of infantile hemangioma is the dramatic growth and development into a disorganized mass of blood vessels. Subsequently, a slow spontaneous involution begins around 1 year of age and continues for 4-6 years. The growth and involution of infantile hemangioma is very different from other vascular tumors and vascular malformations, which do not regress and can occur at any time during childhood or adult life. Much has been learned from careful study of the tissue morphology and gene expression patterns during the life-cycle of hemangioma. Tissue explants and tumor-derived cell populations have provided further insight to unravel the cellular and molecular basis of infantile hemangioma. A multipotent progenitor cell capable of de novo blood vessel formation has been isolated from infantile hemangioma, which suggests that this common tumor of infancy, long considered to be a model for pathologic angiogenesis, may also represent pathologic vasculogenesis. Whether viewed as angiogenesis or vasculogenesis, infantile hemangioma represents a vascular perturbation during a critical period of post-natal growth, and as such provides a unique opportunity to decipher mechanisms of human vascular development.

Suppressed NFAT-dependent VEGFR1 expression and constitutive VEGFR2 signaling in infantile hemangioma

Infantile hemangiomas are localized and rapidly growing regions of disorganized angiogenesis. We show that expression of vascular endothelial growth factor receptor-1 (VEGFR1) in hemangioma endothelial cells (hemECs) and hemangioma tissue is markedly reduced compared to controls. Low VEGFR1 expression in hemECs results in VEGF-dependent activation of VEGFR2 and downstream signaling pathways. In hemECs, transcription of the gene encoding VEGFR1 (FLT1) is dependent on nuclear factor of activated T cells (NFAT). Low VEGFR1 expression in hemECs is caused by reduced activity of a pathway involving beta1 integrin, the integrin-like receptor tumor endothelial marker-8 (TEM8), VEGFR2 and NFAT. In a subset of individuals with hemangioma, we found missense mutations in the genes encoding VEGFR2 (KDR) and TEM8 (ANTXR1). These mutations result in increased interactions among VEGFR2, TEM8 and beta1 integrin proteins and in inhibition of integrin activity. Normalization of the constitutive VEGFR2 signaling in hemECs with soluble VEGFR1 or antibodies that neutralize VEGF or stimulate beta1 integrin suggests that local administration of these or similar agents may be effective in hemangioma treatment.

Multipotential stem cells recapitulate human infantile hemangioma in immunodeficient mice

Infantile hemangioma is a benign endothelial tumor composed of disorganized blood vessels. It exhibits a unique life cycle of rapid postnatal growth followed by slow regression to a fibrofatty residuum. Here, we have reported the isolation of multipotential stem cells from hemangioma tissue that give rise to hemangioma-like lesions in immunodeficient mice. Cells were isolated based on expression of the stem cell marker CD133 and expanded from single cells as clonal populations. The CD133-selected cells generated human blood vessels 7 days after implantation in immunodeficient mice. Cell retrieval experiments showed the cells could again form vessels when transplanted into secondary recipients. The human vessels expressed GLUT-1 and merosin, immunodiagnostic markers for infantile hemangioma. Two months after implantation, the number of blood vessels diminished and human adipocytes became evident. Lentiviral expression of GFP was used to confirm that the hemangioma-derived cells formed the blood vessels and adipocytes in the immunodeficient mice. Thus, when transplanted into immunodeficient mice, hemangioma-derived cells recapitulated the unique evolution of infantile hemangioma--the formation of blood vessels followed by involution to fatty tissue. In summary, this study identifies a stem cell as the cellular origin of infantile hemangioma and describes for what we believe is the first time an animal model for this common tumor of infancy.