The pathophysiology of SBP2 abnormalities

描述（由申请人提供）：项目概述人类硒蛋白质组包含至少25种硒蛋白。大多数是硒酶，其需要硒半胱氨酸（Se）形式的硒（Se）以获得适当的酶活性。有些作为抗氧化剂或氧化还原酶[谷胱甘肽过氧化物酶（GPx）和硫氧还蛋白还原酶]，在甲状腺激素代谢（脱碘酶），硒运输，储存和交付到大脑（SePP）和精子活力（PHGPx）。用于Sec掺入的机制重新编码UGA密码子，并且需要存在于所有硒蛋白的mRNA中的顺式作用序列、框内UGA和Sec插入序列（SECIS），而Sec特异性tRNASec和SECIS结合蛋白（SECISBP 2或SBP 2）是一些所需的反式作用因子。SBP 2被认为是Sec掺入的主要决定因素，因为其免疫耗竭消除了Sec掺入。一个不太清楚，但不同的层次结构存在于硒蛋白的合成，因为它们的表达是不同的硒缺乏症的影响，和优先SECIS识别SBP 2被证明。随着SBP 2基因突变的报道，硒蛋白合成受损的后果的重要医学线索变得明显，导致几个家庭的儿童部分SBP 2缺乏症。受影响的受试者表现出一过性生长延迟和甲状腺功能检查异常，这是由于脱碘酶缺乏导致甲状腺激素代谢改变所致。SBP 2基因突变的新报告描述了额外的特征，一种复杂的表型，在一种情况下具有先天性肌病和发育迟缓，另一种情况下具有无精子症和感音神经性听力损失，从而反映了多种硒蛋白缺乏症。这种新的遗传缺陷的动物模型需要回答人类表型所提出的许多问题。为了满足这一需求，我设计了一个研究计划，使用重组工程技术生成Sbp 2缺陷的小鼠模型。由于在体外未发现SBP 2功能的冗余，并且缺乏SBP 2是致命的，因此我将针对在具有严重表型的患者中报告的C-末端突变工程化Sbp 2KI小鼠和诱导型Sbp 2KO小鼠。对组织的无限接近将有助于区分体内不同的调节层和硒蛋白层次。对这些小鼠的初步研究将揭示甲状腺表型、不育、生长延迟的潜在机制、体内推定的C末端功能结构域的重要性以及肌病的具体原因。对老龄动物的研究将允许密切监测其在生命后期的表现，以及其他假定的表型，包括癌症，神经退行性疾病和免疫功能障碍。这些研究与多种生理功能和途径有关，将有助于阐明硒蛋白介导的病理学机制。最终，这些动物模型将使具有适用于人类的潜在治疗特性的各种化合物的体内测试成为可能，从而使该模型成为必要的工具。 公共卫生相关性：最近发现的人类SBP 2基因突变为硒蛋白生物学提供了独特的见解。通过研究Sbp 2基因敲入小鼠模型的表型和时间控制和组织特异性Sbp 2基因敲除小鼠的表型，将定义硒蛋白调节和层次的不同层。这些研究涉及多种生理功能和途径，有助于阐明硒蛋白介导的病理学机制

DESCRIPTION (provided by applicant): Project Summary The human selenoproteome comprises at least 25 selenoproteins. The majority are selenoenzymes that require selenium (Se) in the form of Selenocystein (Sec) for proper enzymatic activity. Some serve as antioxidants or oxido-reductases [glutathione peroxidases (GPx) and thioredoxin reductases], in thyroid hormone metabolism (deiodinases), in Se transport, storage, and delivery to the brain (SePP) and in sperm viability (PHGPx). The machinery for Sec incorporation recodes the UGA codon and requires cis-acting sequences present in the mRNA of all selenoproteins, the in frame UGA and the Sec insertion sequence (SECIS), while Sec-specific tRNASec, and SECIS-binding protein (SECISBP2 or SBP2) are some of the required trans-acting factors. SBP2 is believed to be the major determinant of Sec incorporation as its immunodepletion eliminates Sec incorporation. A not well understood but distinct hierarchy exists in the synthesis of selenoproteins as their expression is differentially affected by Se deficiency, and preferential SECIS recognition by SBP2 was demonstrated. Important medical clues to the consequences of impaired selenoprotein synthesis became apparent with the report of mutations in the SBP2 gene, causing partial SBP2 deficiency in children of several families. Affected subjects presented with transient growth delay and abnormal thyroid function tests resulting from altered thyroid hormone metabolism due to deficiency in the deiodinases. New reports of SBP2 gene mutations describe additional features, a complex phenotype with congenital myopathy and developmental delay in one case, and azoospermia, sensorineural hearing loss in another, thus reflecting multiple selenoprotein deficiencies. Animal models for this new genetic defect are required to answer the many questions raised by the human phenotype. To address this need, I designed a research plan to generate mouse models with Sbp2 deficiency, using recombineering techniques. As redundancy in SBP2 function was not found in-vitro and lack of SBP2 is putatively lethal, I will engineer a Sbp2KI mouse for a C- terminus mutation reported in a patient with a severe phenotype, and an inducible Sbp2KO mouse. The unlimited access to tissues will help distinguish in-vivo the different layers of regulation and selenoprotein hierarchy. Initial investigations of these mice will uncover the underlying mechanisms for the thyroid phenotype, infertility, growth delay, the importance of the putative C-terminal functional domain in-vivo, and the specific cause for the myopathy. The study of the ageing animals will allow close monitoring for manifestations later in life, and other presumed phenotypes, including cancer, neurodegenerative disorders and immune dysfunction. These investigations are relevant to multiple physiological functions and pathways, and will help elucidate the mechanisms underlying selenoprotein-mediated pathology. Ultimately, these animal models will make possible in-vivo testing of various compounds with potential therapeutic properties applicable to humans, thus making this model a necessary tool. PUBLIC HEALTH RELEVANCE: A unique insight into selenoprotein biology was provided by the recent identification of SBP2 gene mutations in humans. The different layers of selenoprotein regulation and hierarchy will be defined by studying the phenotype of an Sbp2 gene knock-in mouse model and that of temporally controlled and tissue specific Sbp2 gene knock-out mouse. These investigations are relevant to multiple physiological functions and pathways, and will help elucidate the mechanisms underlying selenoprotein-mediated pathology