Treatment of CBS Deficiency with Proteostasis Modulators

描述(申请人提供)：先天性代谢障碍包括一大类遗传性疾病，涉及细胞代谢障碍。同型半胱氨酸是甲硫氨酸的中间代谢物。它既可以被循环回蛋氨酸，也可以在胱硫醚β-合成酶(CBS)的作用下沿着跨硫途径分流。CBS基因突变的个体具有临床CBS缺陷，其特征是血浆总同型半胱氨酸(THcy)极度升高，表型包括血栓形成、骨质疏松症、晶状体脱位和智力低下的发生率增加。目前的治疗策略包括饮食限制和维生素治疗，但这些只有部分有效，并不是对所有患者都有效。在CBS缺陷患者中所描述的突变中，超过85%是错义突变，其中单个错误的氨基酸被替换到CBS多肽中。这些突变被认为会影响酶的活性，因为突变的蛋白质无法组装成活性构象。蛋白质实现活性构象的能力受到多种细胞内蛋白质网络的影响，包括伴侣系统和泛素/蛋白酶体系统，统称为蛋白质平衡网络。蛋白平衡调节剂是扰乱这些网络的各个方面的药物。初步数据表明，通过蛋白调节药物可以刺激小鼠表达的不同突变的人CBS等位基因的适当折叠。这项建议的总体目标是在CBS缺乏的小鼠模型中探索蛋白平衡调节剂和CBS突变等位基因之间的相互作用。有三个具体的目标：(1)建立和表征新的CBS缺乏症小鼠模型；(2)测试四种已知的蛋白平衡调节剂在体内救援的有效性；(3)蛋白平衡调节剂如何影响细胞内伴侣环境的机制研究。如果成功，这里描述的实验可能会带来治疗CBS缺乏症和其他与错义突变相关的潜在遗传病的新方法。

DESCRIPTION (provided by applicant): Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of cellular metabolism. Homocysteine is an intermediary metabolite derived from methionine. It can either be recycled back to methionine, or shunted down the transsulfuration pathway by the action of cystathionine beta-synthase (CBS). Individuals with mutations in CBS have clinical CBS deficiency, characterized by extreme elevations in plasma total homocysteine (tHcy) and phenotypes including increased incidence of thrombosis, osteoporosis, dislocated lenses, and mental retardation. Current treatment strategies involve dietary restriction and vitamin therapy, but these are only partially effective and do not work in all patients. Over 85% of the described mutations in CBS deficient patients are missense mutations in which a single incorrect amino acid is substituted into the CBS polypeptide. These mutations are believed to effect enzymatic activity because the mutant protein fails to assemble into an active conformation. The ability of a protein to achieve an activ conformation is affected by a variety of intracellular protein networks including the chaperone system and the ubiquitin/proteasome system, collectively referred to as the proteostasis network. Proteostasis modulators are drugs that perturb various aspects of these networks. The preliminary data, shows that it is possible to stimulate proper folding of different mutant human CBS alleles expressed in mice by proteostasis modulating drugs. The overall goal of this proposal is to explore the interactions between proteostasis modulators and mutant alleles of CBS in a mouse model of CBS deficiency. There are three specific aims: (1) Generate and characterize new mouse models of CBS deficiency (2) Test four known proteostasis modulators for effectiveness of rescue in vivo and (3) Mechanistic studies of how proteostasis modulators effect the intracellular chaperone environment. If successful, the experiments described here could lead to novel treatments for CBS deficiency and potentially other genetic diseases associated with missense mutations.