Neonatal hyperbilirubinemia in a humanized UGT1 animal model

描述（由申请人提供）：人UDP-葡萄糖醛酸转移酶1A 1是由UGT 1基因座编码的9-UGT 1A蛋白的一部分，在正常病理生理学的许多方面发挥关键作用。认为UGT 1A 1进行的葡萄糖醛酸化是胆红素消除的限速步骤。超过50%的新生儿不能充分消除胆红素，主要是由于UGT 1A 1的发育表达滞后。临床上和在选择性遗传缺陷中，严重的高胆红素血症导致胆红素毒性，其被分类为核黄疸或胆红素沉积到脑中。核黄疸最常导致早期新生儿死亡。迄今为止，关于新生儿中导致人UGT 1A 1发育表达的机制和核黄疸发病的潜在机制的数据很少。为了更好地理解这些过程，我们的实验室创建了人源化小鼠模型，表达由人UGT 1基因座编码的所有9-UGT 1A基因。我们已经确定，在人源化成年小鼠中通过RNA定量测定的UGT 1A基因的表达水平与在人体组织中测定的这些基因的表达模式一致。这些观察结果表明，正常组织特异性和体液控制的UGT 1基因座在小鼠中的调节方式类似于在人类中发生的。有趣的是，人源化UGT 1小鼠发生新生儿高胆红素血症，这种情况在小鼠成年后恢复正常。这种与人源化UGT 1小鼠相关的独特表型将使我们能够研究与UGT 1A 1基因发育控制相关的调控机制及其对血清胆红素的影响。我们的初步研究结果表明，人源化UGT 1小鼠血清胆红素的发育控制与肝外UGT 1A 1活性密切相关，这是一项新的观察结果，将用于研究导致高胆红素血症控制的机制。此外，出生后14天血清胆红素极端水平的积累触发了脑组织中胆红素的积累，导致约10%的发育中小鼠癫痫发作和死亡。高胆红素血症与胆红素诱导的癫痫发作和脑毒性之间的一致性为我们提供了 用动物模型研究UGT 1A 1的发育调节与胆红素诱导脑毒性的细胞和分子机制之间的关联。总的来说，这些方法将使我们能够更详细地探索病理生理学，生物学和 控制UGT 1A 1发育表达的分子机制及其对正常胆红素稳态和疾病的影响。这些知识和信息将作为研究新疗法和潜在治疗方法的基础，以降低胆红素诱导的人类毒性的发生率。

DESCRIPTION (provided by applicant): Human UDP-glucuronosyltransferase 1A1, which is part of 9-UGT1A proteins encoded by the UGT1 locus, plays a key role in many aspects of normal pathophysiology. Glucuronidation carried out by UGT1A1 is considered the rate limiting step in bilirubin elimination. Over 50% of newborn babies do not process the elimination of bilirubin adequately, due mostly to a lag in developmental expression of UGT1A1. Clinically and in selective genetic deficiencies, severe hyperbilirubinemia leads to bilurubin toxicity, which is classified as kernicterus or the depositing of bilirubin into the brain. Kernicterus most often leas to early neonatal death. To date, there is a paucity of data regarding the mechanisms leading to developmental expression of human UGT1A1 in neonatal children and the mechanisms underlying the onset of kernicterus. To better understand these processes, our laboratory has created humanized mouse models that express all 9-UGT1A genes encoded by the human UGT1 locus. We have determined that expression levels of the UGT1A genes as determined by RNA quantitation in humanized adult mice are concordant with the expression patterns of these genes as determined in human tissues. These observations indicate that normal tissue specific and humoral control of the UGT1 locus in mice is regulated in a fashion similar to what occurs in humans. Interestingly, humanized UGT1 mice develop neonatal hyperbilirubinemia, a condition that returns to normal when the mice are adults. This unique phenotype associated with humanized UGT1 mice will allow us to investigate the regulatory mechanisms associated with developmental control of the UGT1A1 gene and its impact on serum bilirubin. Our preliminary findings indicate that developmental control of serum bilirubin in humanized UGT1 mice is tightly linked to extrahepatic UGT1A1 activity, a new observation that will be exploited in examining the mechanisms leading to control of hyperbilirubinemia. In addition, the accumulation of extreme levels of serum bilirubin by 14 days after birth triggers the accumulation of bilirubin in brain tissue resulting in seizures and death in approximately 10% of the developing mice. The consistency linking hyperbilirubinemia to bilirubin induced seizures and brain toxicity provides us with an animal model to examine the association between developmental regulation of UGT1A1 with the cellular and molecular mechanisms leading to bilirubin induced brain toxicity. Overall, these approaches will allow us to explore in greater detail the pathophysiological, biological, and molecular mechanisms that control the developmental expression of UGT1A1 and its impact on normal bilirubin homeostasis and disease. This knowledge and information will serve as the foundation for examining new therapies and potential treatments to reduce the incidence of bilirubin induced toxicities in humans.