Barth Syndrome: Identifying the missing enzyme function

描述（由申请人提供）：Barth综合征（BTHS）是一种罕见的X连锁遗传性疾病，发病率为1/300，000活产婴儿。临床表现包括扩张型心肌病、骨骼肌病、中性粒细胞减少症、3-甲基戊烯二酸尿症、严重生长迟缓和中度学习障碍。在BTHS中，肌病是由整体线粒体缺陷引起的。BTHS患者在tafazzin基因（TAZ）中具有突变，TAZ属于已建立和推定的甘油酯酰基转移酶家族。与这一发现一致的是，BTHS患者的组织含有减少的心磷脂（CL），这是一种对线粒体正常功能至关重要的膜脂质。到目前为止，已发表的证据表明TAZ在CL生物合成中的直接作用是强有力的，但是间接的。事实上，我们的研究表明，重组TAZ未能表现出单溶血心磷脂酰基转移酶活性，CL重塑的关键步骤。我们建议采取一种创新的方法，并确定TAZ介导的甘油脂质的变化。我们将使用改变脂质谱的信息作为有价值的线索，以确定TAZ的酶功能。我们的数据显示，TAZ诱导的脂肪酸掺入磷脂酰甘油（PG）的增加和减少到磷脂酸（PA）。在直接测定中，TAZ也干扰PA形成。最后，我们已经表明，缺乏TAZ减少双（单酰基甘油）磷酸（BMP），并导致酰基磷脂酰甘油（APG）的积累。我们假设tafazzin a）可能在PA形成或使用步骤的甘油脂质途径的早期起作用，并且B）可能在APG和BMP合成中起作用。我们将使用ESI/MS来确定过表达TAZ的细胞和BTHS淋巴母细胞的整个脂质谱的变化。我们将通过测定重组TAZ在甘油脂质途径中的活性来确定BTHS中的酶缺陷。我们提出这一建议的理由是，确定TAZ功能进一步加深了我们对BTHS缺陷的理解，并提供了有关异常脂质代谢破坏正常细胞功能的机制的关键知识。

DESCRIPTION (provided by applicant): Barth Syndrome (BTHS) is a rare X-linked genetic disorder with an incidence of 1/300,000 live births. Clinical manifestations include dilated cardiomyopathy, skeletal myopathy, neutropenia, 3-methylglutaconic aciduria, severe growth retardation, and moderate learning disabilities. In BTHS, the myopathy arises from a global mitochondrial defect. BTHS patients have mutations in the tafazzin gene (TAZ) which belongs to a family of established and putative glycerolipid acyltransferases. Consistent with this finding is that tissues from BTHS patients contain decreased cardiolipin (CL), a membrane lipid essential for proper mitochondrial function. To date, published evidence for a direct role of TAZ in CL biosynthesis is strong, but circumstantial. In fact, our studies show that recombinant TAZ fails to exhibit monolysocardiolipin acyltransferase activity, a critical step in CL remodeling. We propose to take an innovative approach and determine the TAZ-mediated changes in glycerolipids. We will use the information about altered lipid profiles as valuable clues to identify the enzymatic function of TAZ. Our data show TAZ-induced increases in fatty acid incorporation into phosphatidylglycerol (PG) and decreases into phosphatidic acid (PA). TAZ also interferes with PA formation in direct assays. Finally, we have shown that absence of TAZ decreases bis(monoacylglycerol)phosphate (BMP) and causes accumulation of acylphosphatidylglycerol (APG). We hypothesize that tafazzin a) may function early in the glycerolipid pathway at the step of PA formation or use, and b) may play a role in APG and BMP synthesis. We will use ESI/MS to determine changes in the entire lipid profile of cells overexpressing TAZ and in BTHS lymphoblasts. We will identify the enzymatic defect in BTHS by assaying recombinant TAZ for activities in the glycerolipid pathway. Our rationale for this proposal is that determining TAZ function furthers our understanding of the BTHS defect and provides critical knowledge about mechanisms by which abnormal lipid metabolism disrupt normal cellular functions.