MITOCHONDRIAL SHORT CHAIN 3-OH-ACYL-COA DEHYDROGENASES

线粒体脂肪酸β-氧化是高度氧化的哺乳动物组织的主要能量来源，对于肝脏中的中间代谢和酮体的产生至关重要。人类脂肪酸氧化基因缺陷会导致急性肝功能衰竭，这是一种类似雷氏综合征的低酮症、低血糖表型；心肌病;骨骼肌病;或突然、意外的童年死亡。 该途径由四个酶步骤组成，由 12 种不同的核编码酶催化，这些酶受发育调节且组织特异性表达。 该提案重点关注催化第三步的两种酶，即短链 3-羟基-酰基-CoA 脱氢酶 (SCHAD)。 目标 1 和 2 将检验以下假设：SCHAD-1 和 -2 基因的组织特异性和发育表达与其他脂肪酸氧化酶基因协调，并涉及对能量需求和营养线索做出反应的核激素受体转录因子。目标 2 将使用人类 SCHAD-1 基因以及体外转染和转基因小鼠来定位关键的调控序列。基于 SCHAD-1 晶体结构和蛋白质同源性，Aim 3 将确定正常和突变 SCHAD 在细菌中表达后 SCHAD-1 的结构-功能关系，以探索 SCHAD-1 和长链 3-羟酰基-CoA 脱氢酶共享共同结构域的假设。 利用我们已确定的人类基因序列，Aim 4 将描绘儿童中的 SCHAD-1 或​​ -2 突变，以检验 SCHAD 缺陷和环境压力导致急性肝衰竭的雷氏综合征样表型的提议。 目标 5 将检查我们发现的三种人类 SCHAD-1 突变对结构和功能的影响以及 SCHAD 缺陷的发病机制，以探索 SCHAD 错义突变导致继发错误折叠后线粒体内快速降解的假设。 目标 6 是定义我们在小鼠中创建的 SCHAD-1 基因消融表型作为人类疾病模型，检查环境和药物（阿司匹林和对乙酰氨基酚）应激源对结果的影响，并类似地研究 SCHAD-2 敲除。 这些研究将增进对导致儿童急性肝衰竭、心肌病和猝死的脂肪酸氧化紊乱发病机制的了解。

Mitochondrial fatty acid beta-oxidation is the major source of energy in highly oxidative mammalian tissues and is essential for intermediary metabolism and production of ketone bodies in liver. Human genetic defects in fatty acid oxidation genes cause acute liver failure, a Reye's syndrome-like phenotype of hypoketotic, hypoglycemia; cardiomyopathy; skeletal myopathy; or sudden, unexpected childhood death. This pathway consists of four enzymatic steps catalyzed by 12 different nuclearly-encoded enzymes that are developmentally-regulated and tissue- specifically expressed. This proposal focuses on two enzymes catalyzing the third step, the short chain 3-hydroxy-acyl-CoA dehydrogenases (SCHAD). Aims 1 and 2 will examine the hypothesis that tissue-specific and developmental expression of the SCHAD-1 and -2 genes is coordinated with other fatty acid oxidation enzyme genes and involves nuclear hormone receptor transcription factors responsive to energy requirements and nutritional cues. Aim 2 will use the human SCHAD-1 gene and in vitro transfection and transgenic mice to locate critical regulatory sequences. Based upon the SCHAD-1 crystal structure and protein homologies, Aim 3 will determine structure-function relationships of SCHAD-1 of normal and mutant SCHADs after expression in bacteria to explore the hypothesis that SCHAD-1 and long chain 3-hydroxy- acyl-CoA dehydrogenase share common structural domains. Using the human gene sequences we have determined, Aim 4 will delineate SCHAD-1 or -2 mutations in children to examine the proposal that SCHAD deficiency and environmental stresses cause a Reye's syndrome-like phenotype of acute hepatic failure. Aim 5 will examine the effects of the three human SCHAD-1 mutations we have discovered on structure and function, the pathogenetics of SCHAD deficiency, to explore the hypothesis that SCHAD missense mutations result in rapid intramitochondrial degradation secondary to misfolding. Aim 6 is to define the phenotype of SCHAD-1 gene ablation we created in mice as a model of human disease, to examine the effects of environmental and drug (aspirin and acetaminophen) stressors on outcome and to similarly study an SCHAD-2 knockout. These studies will augment understanding of the pathogenesis of fatty acid oxidation disorders causing acute liver failure, cardiomyopathy, and sudden death in children.