Tsai Ellen A, Gilbert Melissa A, Grochowski Christopher M, Underkoffler Lara A, Meng He, Zhang Xiaojie, Wang Michael M, Shitaye Hailu, Hankenson Kurt D, Piccoli David, Lin Henry, Kamath Binita M, Devoto Marcella, Spinner Nancy B, Loomes Kathleen M
Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania; Genomics and Computational Biology Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania.
Cell Mol Gastroenterol Hepatol. 2016 May 26;2(5):663-675.e2. doi: 10.1016/j.jcmgh.2016.05.013. eCollection 2016 Sep.
BACKGROUND & AIMS: Alagille syndrome is an autosomal-dominant, multisystem disorder caused primarily by mutations in , resulting in bile duct paucity, cholestasis, cardiac disease, and other features. Liver disease severity in Alagille syndrome is highly variable, however, factors influencing the hepatic phenotype are unknown. We hypothesized that genetic modifiers may contribute to the variable expressivity of this disorder.
We performed a genome-wide association study in a cohort of Caucasian subjects with known pathogenic mutations, comparing patients with mild vs severe liver disease, followed by functional characterization of a candidate locus.
We identified a locus that reached suggestive genome-level significance upstream of the thrombospondin 2 () gene. codes for a secreted matricellular protein that regulates cell proliferation, apoptosis, and angiogenesis, and has been shown to affect Notch signaling. By using a reporter mouse line, we detected thrombospondin 2 expression in bile ducts and periportal regions of the mouse liver. Examination of -null mouse livers showed increased microvessels in the portal regions of adult mice. We also showed that thrombospondin 2 interacts with NOTCH1 and NOTCH2 and can inhibit JAG1-NOTCH2 interactions.
Based on the genome-wide association study results, thrombospondin 2 localization within bile ducts, and demonstration of interactions of thrombospondin 2 with JAG1 and NOTCH2, we propose that changes in thrombospondin 2 expression may further perturb JAG1-NOTCH2 signaling in patients harboring a mutation and lead to a more severe liver phenotype. These results implicate as a plausible candidate genetic modifier of liver disease severity in Alagille syndrome.
阿拉吉尔综合征是一种常染色体显性多系统疾病，主要由[基因名称]突变引起，导致胆管稀少、胆汁淤积、心脏疾病及其他特征。然而，阿拉吉尔综合征中肝脏疾病的严重程度差异很大，影响肝脏表型的因素尚不清楚。我们推测基因修饰因子可能导致了该疾病的可变表达。
我们在一组已知致病[基因名称]突变的白种人受试者中进行了全基因组关联研究，比较了轻度与重度肝病患者，随后对一个候选基因座进行了功能表征。
我们在血小板反应蛋白2（THBS2）基因上游发现了一个达到提示性基因组水平显著性的基因座。THBS2编码一种分泌性基质细胞蛋白，可调节细胞增殖、凋亡和血管生成，并已证明其会影响Notch信号通路。通过使用报告基因小鼠品系，我们在小鼠肝脏的胆管和门静脉周围区域检测到了血小板反应蛋白2的表达。对THBS2基因敲除小鼠肝脏的检查显示，成年小鼠门静脉区域的微血管增多。我们还表明，血小板反应蛋白2与NOTCH1和NOTCH2相互作用，并可抑制JAG1-NOTCH2相互作用。
基于全基因组关联研究结果、血小板反应蛋白2在胆管内的定位以及血小板反应蛋白2与JAG1和NOTCH2相互作用的证明，我们提出，在携带[基因名称]突变的患者中，血小板反应蛋白2表达的变化可能会进一步扰乱JAG1-NOTCH2信号通路，并导致更严重的肝脏表型。这些结果表明THBS2是阿拉吉尔综合征中肝脏疾病严重程度的一个合理候选基因修饰因子。
