Myeloid cells in infantile hemangioma

The placenta theory and the origin of infantile hemangioma

The pathogenesis of infantile hemangioma is unknown. In recent years, much of the focus has been placed at identifying the cell type(s) responsible for tumor initiation. New discoveries in infantile hemangioma suggest an involvement of progenitor cells in the pathogenesis of this vascular tumor. Both embryonic and extra-embryonic tissues have been postulated as potential sources for these progenitor cells. This review focuses on the placental theory, which proposes that a fetal placental progenitor is the cell type of origin for infantile hemangioma. Special emphasis will be placed on placental vasculogenesis and the presence and transit of placental progenitor cells during gestation.

Infantile hemangioma is originated from placental trophoblast, fact or fiction?

Infantile hemangiomas are common, benign tumors, distinctive for their perinatal presentation, rapid growth and subsequent involution. Hemangiomas can pose serious concerns to the cosmetic and psychosocial development of the afflicted child, but none of the current therapeutic modalities is ideal to date, partly because the origin of the pathogenic ECs in infantile hemangioma is unknown. Many clues and evidences suggest a link between infantile hemangiomas and the maternal placental trophoblasts. Shared expression of distinct endothelial markers in hemangioma and placental tissues raises a possibility that infantile hemangioma is originated from placental trophoblast. Moreover, the findings of a very high similarity between the transcriptomes of placenta and hemangioma provide strong support for this theory. Furthermore, epidemiologic and clinical evidences accumulated in recent years also suggest the placental trophoblast as the cell of origin for infantile hemangioma. These findings imply a unique relationship between hemangioma and the placental trophoblast and suggest a hypothesis that infantile hemangioma is originated from placental trophoblast. The hypothesis could provide new understanding of these vascular tumors of childhood and may become the most promising research fields for the etiology of infantile hemangiomas. Further study of the precise mechanisms for the placental trophoblast originated hemangiomas will produce new preventive strategies and therapeutic avenues, possibly immunologic treatment, to the very difficult problem.

Possibilities and potential roles of estrogen in the pathogenesis of proliferation hemangiomas formation

Hemangiomas, often categorized as angiogenic diseases, are the most common tumors of infancy, the life span of which is generally divided into proliferating phase, involuting phase, and involuted phase. Despite their high prevalence, the mechanism leading to proliferation hemangiomas formation is poorly understood and the best approach to their management remains controversial. None of the current therapeutic modalities is ideal, partly because the pathogenesis of hemangioma and the mechanism of its proliferation are far from clear. Many clues reveal that estrogen has an important role in developing the vascular system, experimental and clinical evidences accumulated in recent years also suggest the potential for estrogen to influence neovascularization. Based on those, we hypothesize that estrogen play a potential role in the development of hemangiomas, mainly by regulating some key angiogenic factors, including MMP-9, EPCs, VEGF, NO, etc. Accepting the hypothesis to be correct, a therapy that identify estrogen as a potential target for the design of new, more specific treatments can be used to prevent the proliferation hemangiomas formation. The hypothesis may lead a new direction in the study of mechanisms for proliferation hemangiomas formation, and further study of the precise mechanisms for estrogen-induced hemangiomas will produce effective antiestrogens and estrogen receptor antagonists as new medication for the very difficult problem.

Pathogenesis of infantile haemangioma: new molecular and cellular insights

Infantile haemangioma is the most common tumour of infancy, yet the origin of these lesions remains controversial and the predictable life cycle is poorly understood. Much new information on infantile haemangiomas has emerged over the past decade, but experts continue to debate fundamental features, including cell of origin, nonrandom distribution, and mechanisms regulating the sometimes explosive growth and slow involution. The development of useful laboratory models has been difficult, in turn restricting the development of treatment options available to the clinician. Despite this, new research and creative thinking has spawned several hypotheses on the origin of these tumours and their interesting clinical behaviour, including suggestions of an intrinsic defect in local endothelial cells, a contribution of circulating endothelial progenitors or haemangioblasts, embolisation of shed placental cells and developmental field defects. While no single hypothesis seems to describe all features of infantile haemangioma, continued research seeks to integrate these ideas, create a better understanding of these important tumours and bring new treatments to the clinic.

Hypoxia-induced mediators of stem/progenitor cell trafficking are increased in children with hemangioma

OBJECTIVE

The mechanism of neovascularization during the proliferative phase of infantile hemangioma is poorly understood. It is known that circulating bone marrow-derived endothelial progenitor cells (EPCs) form new blood vessels in ischemic tissues using mediators regulated by the transcription factor, HIF-1alpha. Mobilization of EPCs is enhanced by VEGF-A, matrix metalloproteinase (MMP)-9, and estrogen, whereas homing is secondary to localized expression of stromal cell-derived factor-1alpha (SDF-1alpha). We examined whether these mediators of EPC trafficking are upregulated during the proliferation of infantile hemangioma.

METHODS AND RESULTS

Surgical specimens and blood samples were obtained from children with proliferating hemangioma and age-matched controls (n=10, each group). VEGF-A and MMP-9 levels were measured in blood, and tissue sections were analyzed for SDF-1alpha, MMP-9, VEGF-A, and HIF-1alpha. The role of estrogen as a modulator of hemangioma endothelial cell growth was also investigated. We found that all these mediators of EPC trafficking are elevated in blood and specimens from children with proliferating infantile hemangioma. In vitro, the combination of hypoxia and estrogen demonstrated a synergistic effect on hemangioma endothelial cell proliferation.

CONCLUSIONS

These findings demonstrate that proliferating hemangiomas express known mediators of vasculogenesis and suggest that this process may play a role in the initiation or progression of this disease.

Overexpression of Notch1 ectodomain in myeloid cells induces vascular malformations through a paracrine pathway

We previously reported that truncation of Notch1 (N1) by provirus insertion leads to overexpression of both the intracellular (N1(IC)) and the extracellular (N1(EC)) domains. We produced transgenic (Tg) mice expressing N1(EC) in T cells and in cells of the myeloid lineage under the regulation of the CD4 gene. These CD4C/N1(EC) Tg mice developed vascular disease, predominantly in the liver: superficial distorted vessels, cavernae, lower branching of parenchymal vessels, capillarized sinusoids, and aberrant smooth muscle/endothelial cell topography. The disease developed in lethally irradiated normal mice transplanted with Tg bone marrow or fetal liver cells as well as in Rag-/- Tg mice. In nude mice transplanted with fetal liver cells from (ROSA26 x CD4C/N1(EC)) F1 Tg mice, abnormal vessels were of recipient origin. Transplantation of Tg peritoneal macrophages into normal recipients also induced abnormal vessels. These Tg macrophages showed impaired functions, and their conditioned medium inhibited the proliferation of liver sinusoid endothelial cells in vitro. The Egr-1 gene and some of its targets (Jag1, FIII, FXIII-A, MCP-1, and MCP-5), previously implicated in hemangioma or vascular malformations, were overexpressed in Tg macrophages. These results show that myeloid cells can be reprogrammed by N1(EC) to induce vascular malformations through a paracrine pathway.

Potential roles of allograft inflammatory factor-1 in the pathogenesis of hemangiomas

Hemangiomas are benign tumors of the vascular endothelium and are the most common tumors of infancy. These tumors are characterized by an initial phase of rapid proliferation in the first months of life, which is followed, in most cases, by spontaneous slow involution. Despite their high prevalence, their detailed pathogenesis remains unknown. Recent studies suggest that immunity responses, inflammatory cells and their precursors, myeloid cells, play important roles in the growth and involution of hemangiomas. The allograft inflammatory factor-1 is a powerful gene that is involved in several kinds of inflammatory response-related diseases. Studies also show that it is implicated in angiogenesis, proliferation and differentiation of stem cells, and development of tumors. Taken all these evidences into consideration, we hypothesize that allograft inflammatory factor-1 plays potential roles in pathogenesis, proliferation and involution of hemangioma. Investigating the role of allograft inflammatory factor-1 in the proliferation and involution of hemangioma will lead to a better understanding of pathogenesis of this lesion. Furthermore, the subtle regulation of allograft inflammatory factor-1 in the involution of hemangiomas will help design a new anti-angiogenic therapy for some tumors.

Immune response: A possible role in the pathophysiology of hemangioma

Hemangioma is a distinct category of benign vascular tumors characterized by presentation within the first weeks of life, rapid growth during the first year and variable degree of spontaneous involution over a period of several years. Recent research reported that CD8+ T cells in hemangiomas, and the endothelia of hemangioma uniquely expressed leukocyte marker FCgammaRII and myeloid cell marker. Presence of high levels of indoleamine 2,3-dioxygenase in proliferating hemangiomas and significantly decreasing during involution was also confirmed. Topical application of imiquimod cream, an immune regulator, to proliferating hemangiomas apparently accelerated regression of the lesions. These findings suggest immune response may be involved in the pathogenesis of hemangioma. The endothelia of hemangioma may express various markers to escape the immune surveillance. An immune response may be one of the mechanisms for hemangioma regression. Strategies with systemically or locally applying immune regulator into the tumor may be an applicable way in accelerating the involution of hemangioma.

Monocytes: a possible source of hemangioma endothelial cells

Hemangiomas have a distinctive proliferative phase characterized by rapid proliferation of capillaries within the first year of life, followed by an involuting phase characterized by spontaneous and steady regression of the tumor that may last up to 5-10 years. Angiogenesis has been proposed to be the predominant mechanism of vessel formation in hemangiomas. Emerging evidence shows that endothelial progenitor cells play an important role in the physiological and pathological angiogenesis. However, the numbers of endothelial progenitor cells in hemangioma are small. Recent studies show that large numbers of monocytes, the ancestor of endothelial progenitor cells, are present in hemangioma. In this paper, we hypothesize that monocyte is a possible source of hemangioma endothelial cells according to previous research evidence. This hypothesis suggests that monocytes contribute to early expansion of hemangioma. Further investigation is needed to determine which factors influence the homing and the differentiation of monocytes in hemangioma and potential therapeutic implications of these monocytes.

A postulated role for transcriptional regulator LMO2 in the proliferation and involution of hemangioma

Hemangiomas are common benign vascular tumors distinctive for their perinatal presentation, rapid growth during the first year of life and subsequent slowly involution. Many evidences suggest that hemangiomas are angiogenesis dependent entity. Research also indicated that the endothelium of hemangioma shared molecular phenotype with blood cells. LMO2 is a transcriptional regulator that play an important role in angiogenesis, hematopoiesis and oncogenesis of hematological tumor. It is logical to postulate that LMO2 may play a role in the pathogenesis, proliferating and involution of hemangioma. Therapies directed against LMO2 have potential importance for treatment of hemangioma because of hemangioma's limited localization and the fact that LMO2-associated protein complexes could regulate angiogenesis.