At 72 hours, however, bm-MPCs and HDMECs showed significant reductions in cell number at all concentrations of propranolol when compared to control (figure 2b). marrow-mesenchymal progenitor cells (bm-MPCs) as normal stem/progenitor counterparts to determine selectivity. == Results == Our results show that propranolol significantly reduced IH stem cell growth but failed to induce caspase-3 activation. Normal bm-MPCs and mature ECs showed maintained or increased caspase-3 activation and significantly reduced cyclin-D1 levels. We further show that IH stem cells may escape apoptosis by inducing anti-apoptotic pathways. == Conclusions == This study reveals that propranolol does not induce apoptosis in IH stem cells, which is in contrast to ECs. Escape from apoptosis in IH stem cells may involve induction of anti-apoptotic pathways. == Introduction == Infantile hemangioma (IH) is a benign vascular tumor affecting 1 out of 100 newborns (1,2). IH undergoes three developmental phases: a proliferative phase, where the tumour grows rapidly and comprises undifferentiated cells during the first year of life; an involuting phase, where tumor growth slows and vessels become prominent; and an involuted phase, where fibrofatty tissue replaces much of the tumor mass (3). A unique feature only seen in IH is that the tumor follows this natural course and spontaneously regresses. Hence, most IH pose no Yohimbine hydrochloride (Antagonil) serious threat or complications to the infant; however, in problematic cases that interfere with health and normal function due to the size or location of the tumor, patients may require immediate treatment (4). For example, obstructive IH in organs, such as eyes or airway, require immediate attention because the tumor may inhibit normal development and function of the organ to impair the infant permanently (3,5). Current treatments for IH include surgery when necessary and use of corticosteroids, despite the severe side effects when taken for extended periods at high doses. Recently, propranolol was Yohimbine hydrochloride (Antagonil) discovered to be an effective treatment for IH (6), with higher efficacy and minimal side effects when compared to corticosteroid use (7). Propranolol is a non-selective -adrenergic receptor antagonist that has been widely used for complications such as angina pectoris, myocardial infarction, and hypertension. Although the mechanism of therapeutic effect of propranolol is unknown, theories suggest vasoconstriction, endothelial cell apoptosis, and inhibition of angiogenesis by modulating vascular endothelial growth factors (811). In fact, a number of recent studies have shown that propranolol treatment of normal endothelial cells as well as endothelial cells derived from IH specimens causes activation of caspase-3 (12,13). Caspase-3 is an important regulator of cellular apoptosis and is recognized as an indispensable death protease for apoptotic chromatin condensation Yohimbine hydrochloride (Antagonil) and DNA fragmentation in all cell types examined (examined in (14)). In addition to inducing apoptosis, propranolol also decreases the manifestation of various cyclins in endothelial cell, therefore disrupting cell cycle progression and growth (12). A puzzling getting from a few propranolol treatment studies in patients is definitely that some IHs regrow upon cessation of propranolol treatment (1517). This has been attributed to early treatment withdrawal and/or a long proliferating phase of IH. Previously, we have demonstrated that IH arises from multipotential stem cells (termed hemSCs) (18). HemSCs, isolated based on manifestation of stem cell antigen CD133, form glucose transporter-1 (Glut1) positive microvessels in immunodeficient mice. These Glut1-positive vessels are later on replaced by human being adipocytes that mimic the natural phases of human being IH. Interestingly IH-derived endothelial cells are unable to create microvessels (18). This suggests that hemSCs may be responsible for the recurrence of IH upon cessation of propranolol treatment probably owing to the non-responsiveness of Mouse monoclonal to MAPK p44/42 hemSCs to propranolol. In this study, we have explored this probability by treating main hemSCs with propranolol to determine whether propranolol induces caspase-3 activation and apoptosis as offers been shown for vascular endothelial cells. We have also studied bone marrow-derived mesenchymal progenitor cells (bm-MPCs) as normal counterparts of hemSCs to determine whether changes (if any) observed in hemSCs are specific or whether the response depends on the stem/progenitor phenotype. In addition, we investigated possible signaling pathways involved upon propranolol treatment. == Results == == Atypical phenotype of IH endothelium == A number of studies have investigated the effect of propranolol on IH-derived endothelial cells to offer insight into the mechanisms of therapeutic effect of propranolol (12,13,19). These studies show that propranolol causes apoptosis in IH endothelial cells by activating caspase-3 and also blocks other cellular activities including migration.