Propranolol treatment of infantile hemangioma endothelial cells: A molecular analysis

Abstract

Infantile hemangiomas (IHs) are non-malignant, largely cutaneous vascular tumors affecting approximately 5–10% of children to varying degrees. During the first year of life, these tumors are strongly proliferative, reaching an average size ranging from 2 to 20 cm. These lesions subsequently stabilize, undergo a spontaneous slow involution and are fully regressed by 5 to 10 years of age. Systemic treatment of infants with the non-selective β-adrenergic receptor blocker, propranolol, has demonstrated remarkable efficacy in reducing the size and appearance of IHs. However, the mechanism by which this occurs is largely unknown. In this study, we sought to understand the molecular mechanisms underlying the effectiveness of β blocker treatment in IHs. Our data reveal that propranolol treatment of IH endothelial cells, as well as a panel of normal primary endothelial cells, blocks endothelial cell proliferation, migration, and formation of the actin cytoskeleton coincident with alterations in vascular endothelial growth factor receptor-2 (VEGFR-2), p38 and cofilin signaling. Moreover, propranolol induces major alterations in the protein levels of key cyclins and cyclin-dependent kinase inhibitors, and modulates global gene expression patterns with a particular affect on genes involved in lipid/sterol metabolism, cell cycle regulation, angiogenesis and ubiquitination. Interestingly, the effects of propranolol were endothelial cell-type independent, affecting the properties of IH endothelial cells at similar levels to that observed in neonatal dermal microvascular and coronary artery endothelial cells. This data suggests that while propranolol markedly inhibits hemangioma and normal endothelial cell function, its lack of endothelial cell specificity hints that the efficacy of this drug in the treatment of IHs may be more complex than simply blockage of endothelial function as previously believed.

Mechanisms of propranolol action in infantile hemangioma

“…HemECs show a greater proportion of cells in the G1 phase than the S/G2 phase when treated with propranolol. 29,52 This was further confirmed with decreased expression of cyclin proteins such as cyclins A1, A2, B2, D1, D2, D3, 29,50,52 while cell cycle inhibitor proteins p15, p21, p27, 52 were upregulated.…”

“…54 In addition to caspase-mediated apoptosis, propranolol may block phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR-2). 52 It was found that when hemECs were challenged with higher concentrations of propranolol (50 and 100 mmol/L), the expression of VEGF at the protein level was reduced in a dose-dependent manner. 49,55 This reduction in the level of activated VEGFR-2 receptors and VEGF protein upon propranolol exposure was a critical element that affected the survivability of these hemECs.…”

“…49,55 This reduction in the level of activated VEGFR-2 receptors and VEGF protein upon propranolol exposure was a critical element that affected the survivability of these hemECs. 52,56 In addition, decrease in key cyclin levels and an increase in cell cycle inhibitor levels were observed. 52 This suggested that cell cycle regulation is also another mechanism involved in mediating propranolol's therapeutic effect.…”

“…52,56 In addition, decrease in key cyclin levels and an increase in cell cycle inhibitor levels were observed. 52 This suggested that cell cycle regulation is also another mechanism involved in mediating propranolol's therapeutic effect. HemECs show a greater proportion of cells in the G1 phase than the S/G2 phase when treated with propranolol.…”

“…It has been shown that hemECs and other EC types express both b1-and b2-ADRs at very similar levels, but not b3. 52,53 We have shown that normal ECs express all 3 b-ADRs, with b1-ADR expression being significantly higher when compared to the other subtypes. 50 Despite the various b-ADRs expressed, it is believed that the main mechanism of action of propranolol in hemECs may involve b1 and/or 2-ADR pathway.…”