Mechanisms of Endothelial Cell Maturation and Vascular Quiescence in Infantile Hemangioma

血管异常包括一系列孤儿疾病，这些疾病本质上是先天性的，与血管发育障碍有关。根据组织病理学标准，定义了两个实体。血管肿瘤表现为病理性细胞增殖，出生后生长迅速，儿童后期消退缓慢。然而，它们可能会导致危及生命的并发症，如溃疡和出血。血管畸形不会经历异常的细胞周转，并与个体成比例地生长。大多数血管畸形是由血管内皮细胞的体细胞激活突变引起的，但对血管肿瘤的遗传原因知之甚少。婴儿血管瘤是最常见的血管肿瘤，目前使用非选择性肾上腺素能阻滞剂心得安治疗。普萘洛尔一般耐受性良好，但其作用机制尚不清楚，涉及的副作用有低血糖、心动过缓和低血压。比肖夫教授预定的宿主实验室发现了一种血管瘤干细胞(HemSC)，可以在小鼠身上重塑婴儿血管瘤。最近，Bischoff教授证明了心得安抑制SOX18依赖的HSC向血管内皮细胞(HEMEC)分化。我们推测，普奈洛尔阻断了所有从血细胞到血周细胞的分化，以及从血细胞到血周细胞的分化。为了研究心得安在婴幼儿血管瘤血管内皮细胞成熟和血管静止中的作用机制，我们有两个目的：i)通过在分化过程中给予不同的底物(心得安、SM4、雷帕霉素和皮质类固醇)来鉴定心得安在血液干细胞向血管内皮细胞/周细胞分化过程中的mRNA和蛋白靶点：我们通过RNA测序分析每种药物是如何改变转录组的，以确定关键途径。我们将选择2-3个由RNA测序数据确定的最佳候选者来进行功能获得和功能丧失的研究。Ii)通过下调内源性SOX18的表达，验证SOX18是HMSC向HEMEC分化所必需的前提：我们将在体内检测SOX18基因敲除的HEMSC和SOX18基因突变(SOX18杂乱的负鼠)的HMSC对血管形成的影响。普奈洛尔是治疗婴幼儿血管瘤的一线药物，因此寻找调节HMSC向HEC/周细胞分化的分子途径至关重要。心得安蛋白质靶点的确定将为那些遭受副作用或对心得安治疗无效的患者开辟新的治疗选择。这份申请的目的是获得奖学金，使我能够成为哈佛医学院波士顿儿童医院血管生物学项目比肖夫教授S小组的成员，在为期8个月的研究期间，以便在这一前景广阔的研究课题上进行合作。

Vascular anomalies comprise a broad spectrum of orphan diseases, which are congenital in nature and associated with dysfunctional vessel development. Due to histopathological criteria two entities are defined. Vascular tumors show pathologic cell proliferation, exhibit rapid postnatal growth and slow regression during late childhood. Nevertheless, they can cause life-threatening complications, like ulceration and bleeding. Vascular malformations do not undergo abnormal cellular turnover and grow proportionally with the individual. Most vascular malformations are caused by somatic activating mutations in endothelial cells, but much less is known about the genetic causes of vascular tumors. Infantile hemangiomas, the most common vascular tumor, currently are treated with propranolol, a nonselective adrenergic blocker. Propranolol is generally well tolerated, however, its mechanism is not yet revealed and concerning side effects are hypoglycemia, bradycardia and hypotension. The intended host laboratory of Professor Bischoff has discovered a hemangioma stem cell (HemSC) that recapitulates infantile hemangiomas in mice. Recently Professor Bischoff was able to demonstrate that propranolol inhibits SOX18 dependent HemSC to hemangioma endothelial cell (HemEC) differentiation. We hypothesize that all of the HemSC-to-HemEC differentiation, as well as the HemSC-to-HemPericyte differentiation is blocked by propranolol. To investigate the mechanism of action of propranolol in regard to endothelial cell maturation and vascular quiescence in infantile hemangioma we have 2 aims:I) Identification of mRNA and protein targets of propranolol in HemSC-to-HemEC/Pericyte differentiation by administration of different substrates (propranolol, Sm4, rapamycin and corticosteroids) during differentiation: we analyze how each drug changes the transcriptome by RNA-sequencing to identify critical pathways. We will select 2-3 top candidates identified by RNA-sequencing data to perform gain of function and loss of function studies. II) Testing the premise that SOX18 is required for HemSC to HemEC differentiation by knocking down endogenous SOX18 in HemSC: we will test HemSC with SOX18 knockdown and HemSC with a dominant-negative mutation in the SOX18 gene (SOX18 Ragged Opossum) in vivo to see effects on hemangioma vessel formation.As propranolol is the first line therapy for infantile hemangioma treatment, it is crucial to identify molecular pathways that regulate HemSC-to-HemEC/Pericyte differentiation. The identification of protein targets of propranolol will open up new treatment options for those patients who suffer from side effects or do not respond to propranolol treatment. The aim of this application is to receive a fellowship that allows me to be a member of Professor Bischoff´s group at the Vascular Biology Program at Boston Children's Hospital, Harvard Medical School, during an 8-month research period in order to collaborate on this promising research topic.