Molecular mechanisms and treatment of cardiomyopathy in Barth Syndrome

项目总结 他法津(TAZ，也被称为G4.5)的突变会导致巴特综合征(BTHS，MiM 302060)，一种威胁生命的 线粒体特异性磷脂(CL)代谢紊乱。心肌病是 BTHS的主要临床特征，突出了TAZ和CL代谢途径在BTHS中的重要性 心肌细胞(CMS)。TAZ编码一种线粒体磷脂-溶血磷脂转酰酶，它是 对CL重塑至关重要，以达到成熟CL特有的脂肪酸组成。Taz基因的突变 在BTHS患者中发现的结果是总CL浓度低，CL脂肪酰基组成异常，并升高 单体-CL(MLCL)与CL的比率。然而，人们对其具体的分子机制知之甚少。 TAZ缺乏和随之而来的CL异常导致心肌病的进展。到目前为止，有 BTHS没有根治疗法。虽然已经证实TAZ缺乏会导致BTHS，但缺乏 Taz基因敲除小鼠模型阻碍了分子病理学的研究和治疗方法的发展 BTHS的方法。目的：阐明BTHS心肌病的分子发病机制，并探讨其发病机制。 确定潜在的治疗干预靶点，我们已经产生了Taz CM特异性基因敲除(CKO)小鼠 并观察扩张型心肌病(DCM)的表型以及线粒体畸形和 TAZ CKO小鼠的功能障碍。我们的数据有力地表明了TAZ和CL在心脏和心脏中的关键作用 线粒体功能。我们的Taz CKO小鼠为我们提供了一个独特的模型来研究分子基础 BTHS的治疗和潜在的治疗方法。对培养细胞的研究表明，亚油酸(LA) 补充剂通过增加亚油酰基的掺入增加TAZ缺陷细胞的成熟CL水平 加入从头合成的CL，也改善MLCL的增加。对线粒体的抑制 溴烯醇内酯(BEL)诱导的磷脂酶A2(PLA2)也可改善Taz基因缺陷细胞MLCL的增加 通过阻止新生CL产生MLCL。然而，这些潜在的治疗方法并没有 已经在BTHS的活体哺乳动物模型中进行了研究。此外，还没有研究探索LA的组合 补充剂和BEL治疗可协同作用改善BTHS。因此，我们的假设是 Taz介导的CL重塑对于维持线粒体内稳态和CM功能是必不可少的，并且 亚油酸(LA)和/或溴烯醇内酯(BEL)治疗将为改善BTHS提供有益的效果 心肌病。我们的具体目标是：(1)研究Taz-1的作用和分子机制。 介导CL重塑是维持心肌线粒体稳态和正常心功能所必需的 通过对TAZ CKO小鼠的组织学、生理学、生化和分子分析；(2)评估 亚油酸(LA)和线粒体PLA2抑制剂溴烯醇内酯(BEL)单独用药的疗效 药物或组合，利用Taz CKO小鼠治疗BTHS心肌病。

PROJECT SUMMARY Mutations in tafazzin (Taz, also known as G4.5) cause Barth syndrome (BTHS, MIM 302060), a life-threatening disorder disrupting metabolism of the mitochondrial-specific phospholipid cardiolipin (CL). Cardiomyopathy is the major clinical feature in BTHS, highlighting the importance of Taz and the CL metabolism pathway in cardiomyocytes (CMs). Taz encodes a mitochondrial phospholipid-lysophospholipid transacylase, which is essential for CL remodeling to achieve the characteristic fatty acid composition of mature CL. Mutations in Taz found in BTHS patients result in low total CL concentrations, abnormal CL fatty acyl composition, and elevated monolyso-CL (MLCL) to CL ratios. However, little is known as to the detailed molecular mechanisms by which Taz deficiency and consequent CL abnormalities lead to the progression of cardiomyopathy. Thus far, there is no curative therapy for BTHS. Although it has been established that Taz deficiency causes BTHS, lack of a Taz knockout mouse model has hindered studies of molecular pathology and developments of therapeutic approaches for BTHS. To elucidate the molecular pathogenic mechanism of BTHS cardiomyopathy, and to identify potential targets for therapeutic intervention, we have generated Taz CM-specific knockout (cKO) mice and observed dilated cardiomyopathy (DCM) phenotypes, as well as mitochondrial malformations and dysfunction in Taz cKO mice. Our data strongly suggest a critical role of Taz and CL in cardiac and mitochondrial function. Our Taz cKO mouse provides us with a unique model to investigate the molecular basis for and potential therapeutic approaches to BTHS. Studies in cultured cells suggest that linoleic acid (LA) supplementation increases mature CL levels in Taz-deficient cells by increasing incorporation of linoleoyl groups into de novo synthesized CL and also ameliorating the increase in MLCL. Inhibition of the mitochondrial phospholipase A2 (PLA2) by bromoenol lactone (BEL) also ameliorates increased MLCL in Taz-deficient cells by blocking generation of MLCL from nascent CL. However, these potential therapeutic approaches have not been studied in an in vivo mammalian model of BTHS. Moreover, no study has explored if a combination of LA supplementation and BEL treatment can act synergistically to ameliorate BTHS. Accordingly, our hypothesis is that Taz-mediated CL remodeling is essential to maintain mitochondrial homeostasis and CM function, and that linoleic acid (LA) and/or bromoenol lactone (BEL) treatment will provide beneficial effects to ameliorate BTHS cardiomyopathy. Our specific aims are: (1) To investigate the role and molecular mechanisms by which Taz- mediated CL remodeling is required in maintaining CM mitochondrial homeostasis and normal cardiac function by histological, physiological, biochemical, and molecular analyses of Taz cKO mice; and (2) To assess therapeutic effects of linoleic acid (LA) and mitochondrial PLA2 inhibitor bromoenol lactone (BEL), as single agents or in combination, on BTHS cardiomyopathy by utilizing Taz cKO mice.