Role of Cited2 in lens development and hyaloid vascular regression

描述（由申请人提供）：Cited 2（CBP/p300相互作用反式激活因子，富含谷氨酸（E）和天冬氨酸（D）尾2）是一个新的转录调节因子家族的创始成员。本实验室克隆了Cited 2基因，发现Cited 2基因可被多种生物刺激物诱导表达，包括细胞因子、血清和LPS。它广泛表达，并且当过表达时是转化基因。为了解决Cited 2在体内的作用，我们产生了在Cited 2基因座处具有无效突变的小鼠，并发现Cited 2的缺失导致Cited 2-/-胚胎在妊娠中期至晚期死亡，并伴有几种发育缺陷。Cited 2表达在发育中的透镜中是可检测的。引用的2-/-胚胎的组织学检查显示持久的透镜柄、较小的透镜和玻璃体细胞过多，包括眼睛中的异常血管系统。后者类似于PHPV（持续性增生性原始玻璃体）的病理特征，PHPV是一种先天性眼部疾病，导致晶状体发育异常和视网膜和眼睛的继发性变化。组织特异性缺失透镜中的Cited 2也导致成人眼中透镜柄形成、较小的透镜和玻璃体血管系统（HVS）的失败退化。这些结果表明，它们是与透镜中Cited 2表达缺失相关的原发性缺陷，并且Cited 2参与发育过程中的透镜形态发生和玻璃体血管形成/退化。Cited 2是HIF-1功能的负调节剂，Cited 2的缺失可能导致HIF-1介导的缺氧反应上调。这种机制是部分负责在Cited 2 null胚胎中观察到的心脏缺陷。晶状体特异性HIF-1缺失消除了Cited 2缺陷胚胎中异常的玻璃体细胞过多，这表明HIF-1信号转导失调可能在Cited 2-/-眼中异常的HVS形成中起作用。虽然已知透镜是缺氧器官，并且HIF-1在透镜上皮细胞中高度表达，但是从未对发育中的小鼠透镜的缺氧水平及其失调的后果进行直接和详细的检查。这项初步研究是主要研究者的一个新的研究领域，试图产生Cited 2和HIF-1或VEGF缺失的复合小鼠，以探索Cited 2-HIF-1遗传相互作用对HVS形成和消退至关重要的假设。由于透镜特异性Cited 2敲除小鼠表现出失败的HVS消退，并且HIF-1的缺失挽救了Cited 2敲除眼中异常的玻璃体血管，因此透镜特异性Cited 2敲除小鼠不仅可以用作PHPV的新疾病模型，而且还可以用于测试潜在的HIF-1抑制剂。公共卫生相关性：本研究的完成不仅将促进我们对透镜发育和缺氧对玻璃体血管系统形成和退化的影响的认识，而且将为治疗眼部疾病和其他与HIF-1信号失调相关的系统性疾病提供潜在的治疗原则。

DESCRIPTION (provided by applicant): Cited2 (CBP/p300-interacting transactivators with glutamic acid (E) and aspartic acid (D)-rich tail 2) is a founding member of a new family of transcriptional modulators. My laboratory cloned Cited2 and showed that Cited2 is induced by many biological stimuli including cytokines, serum and LPS. It is widely expressed and is a transforming gene when overexpressed. In order to address the role of Cited2 in vivo, we generated mice with a null mutation at the Cited2 locus and found that deletion of Cited2 causes Cited2-/- embryos to die at mid- to late gestation with several developmental defects. Cited2 expression is detectable in the developing lens. Histological examination of Cited2-/- embryos revealed persistent lens stalk, a smaller lens and hyaloid hypercellularity consisting of aberrant vasculature in the eye. The latter is similar to the pathological features of PHPV (Persistent hyperplastic primary vitreous), a congenital eye disorder leading to abnormal lenticular development and secondary changes of the retina and the eye. Tissue specific deletion of Cited2 in the lens also resulted in lens stalk formation, a smaller lens and failed regression of hyaloid vascular system (HVS) in adult eyes. These results suggest that they are primary defects associated with loss of Cited2 expression in the lens and that Cited2 is involved in lens morphogenesis and hyaloid vascular formation/regression during development. Cited2 is a negative modulator for HIF-1 function and loss of Cited2 may result in upregulated HIF-1 mediated hypoxic responses. This mechanism is partially responsible for the heart defects observed in Cited2 null embryos. Lens-specific deletion of HIF-1 eliminates the aberrant hyaloid hypercellularity in Cited2 deficient embryos, suggesting that dysregulated HIF-1 signaling may play a role in aberrant HVS formation in Cited2-/- eyes. Although it is known that lens is a hypoxic organ and HIF-1 is highly expressed in the lens epithelial cells, a direct and detailed examination of the hypoxia level of a developing mouse lens and the consequences of its deregulation has never been performed. This pilot study, which is a new research area for the principal investigator, attempts generate compound mice with deletions of Cited2 and HIF-1 or VEGF to explore the hypothesis that a Cited2-HIF-1 genetic interaction is essential for HVS formation and regression. Since lens- specific Cited2 knockout mouse exhibits failed HVS regression and deletion of HIF-1 rescues the abnormal hyaloid vasculature in Cited2 knockout eyes, lens-specific Cited2 knockout mice could not only be used as a novel disease model for PHPV but also for testing potential HIF-1 inhibitors. PUBLIC HEALTH RELEVANCE: The accomplishment of the proposed study will not only advance our knowledge in the lens development and the influence of hypoxia on the formation and regression of hyaloid vascular system but also provide potential therapeutic principles in treating eye disorders and other systemic diseases with dysregulated HIF-1 signaling.