Abstract
We have recently demonstrated the expression of embryonic stem cell markers on the endothelium of infantile hemangioma, a functional hemogenic endothelium with the capacity for primitive erythropoiesis in vitro. Despite recent work characterizing stem cells within proliferating infantile hemangioma, the expression of STAT proteins, well documented for their roles in stem cell signaling, has not been investigated. 3,3-Diaminobenzidine and immunofluorescence immunohistochemical staining revealed expression of pSTAT1, pSTAT3 and pSTAT5 in proliferating infantile hemangioma samples with the strongest expression of pSTAT3. There was reduced expression of these pSTAT proteins in the involuted infantile hemangioma samples. Western blotting confirmed the identification of all these three proteins in proliferating infantile hemangioma. It is therefore not surprising that the phosphorylated/activated forms of these proteins are relatively abundantly expressed in proliferating, in comparison to involuted infantile hemangioma samples. We speculate that the reduced STAT activation, as infantile hemangioma involutes, is a reflection of the depletion of the abundant stem cells within proliferating infantile hemangioma, as the lesion involutes.
Highlights
Infantile hemangioma (IH), the most common tumor of infancy, affects up to 10% of infants with a predilection for female, Caucasian and premature infants [1,2,3]
We have recently demonstrated the expression of embryonic stem cell markers on the endothelium of infantile hemangioma, a functional hemogenic endothelium with the capacity for primitive erythropoiesis in vitro
We have previously shown the expression of the non-phosphorylated form of signal transducer and activator of transcription 3 (STAT3) on the endothelium and cells within the interstitium of proliferating IH, inferring its role in the stem cells within proliferating IH, the localization of the phosphorylated/activated form of this transcription factor remains to be determined [3]
Summary
Infantile hemangioma (IH), the most common tumor of infancy, affects up to 10% of infants with a predilection for female, Caucasian and premature infants [1,2,3] It typically undergoes rapid growth during infancy followed by a spontaneous gradual involution over 1–10 years, often leaving a fibro-fatty residuum [4]. The understanding of this enigmatic condition has been advanced by the appreciation of the role of stem cells within the endothelium and the interstitium of proliferating IH [5,6,7]. The endothelium of proliferating IH has been shown to be a functional hemogenic endothelium (HE) that expresses erythropoietin receptor (EPOR) and pSTAT1, pSTAT3 and pSTAT5 in Infantile Hemangioma hemoglobin ζ chain with a capacity for primitive erythropoiesis in vitro [9, 10]
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