Kimura Tomohiro, Kimura Atsuko K, Ren Mindong, Berno Bob, Xu Yang, Schlame Michael, Epand Richard M
Biochemistry. 2018 Apr 10;57(14):2162-2175. doi: 10.1021/acs.biochem.8b00042. Epub 2018 Mar 30.
Tafazzin is the mitochondrial enzyme that catalyzes transacylation between a phospholipid and a lysophospholipid in remodeling. Mutations in tafazzin cause Barth syndrome, a potentially life-threatening disease with the major symptom being cardiomyopathy. In the tafazzin-deficient heart, cardiolipin (CL) acyl chains become abnormally heterogeneous unlike those in the normal heart with a single dominant linoleoyl species, tetralinoleoyl CL. In addition, the amount of CL decreases and monolysocardiolipin (MLCL) accumulates. Here we determine using high-resolution P nuclear magnetic resonance with cryoprobe technology the fundamental phospholipid composition, including the major but oxidation-labile plasmalogens, in the tafazzin-knockdown (TAZ-KD) mouse heart as a model of Barth syndrome. In addition to confirming a lower level of CL (6.4 ± 0.1 → 2.0 ± 0.4 mol % of the total phospholipid) and accumulation of MLCL (not detected → 3.3 ± 0.5 mol %) in the TAZ-KD, we found a substantial reduction in the level of plasmenylcholine (30.8 ± 2.8 → 18.1 ± 3.1 mol %), the most abundant phospholipid in the control wild type. A quantitative Western blot revealed that while the level of peroxisomes, where early steps of plasmalogen synthesis take place, was normal in the TAZ-KD model, expression of Far1 as a rate-determining enzyme in plasmalogen synthesis was dramatically upregulated by 8.3 (±1.6)-fold to accelerate the synthesis in response to the reduced level of plasmalogen. We confirmed lyso-plasmenylcholine or plasmenylcholine is a substrate of purified tafazzin for transacylation with CL or MLCL, respectively. Our results suggest that plasmenylcholine, abundant in linoleoyl species, is important in remodeling CL in the heart. Tafazzin deficiency thus has a major impact on the cardiac plasmenylcholine level and thereby its functions.
塔法兹蛋白是一种线粒体酶，在重塑过程中催化磷脂与溶血磷脂之间的转酰基作用。塔法兹蛋白的突变会导致巴特综合征，这是一种可能危及生命的疾病，主要症状是心肌病。在缺乏塔法兹蛋白的心脏中，心磷脂（CL）的酰基链变得异常不均一，与正常心脏中单一占主导地位的亚油酰基种类——四亚油酰基CL不同。此外，CL的量减少，单溶血心磷脂（MLCL）积累。在这里，我们使用带有低温探头技术的高分辨率磷核磁共振来确定作为巴特综合征模型的塔法兹蛋白敲低（TAZ-KD）小鼠心脏中的基本磷脂组成，包括主要但易氧化的缩醛磷脂。除了证实在TAZ-KD中CL水平较低（占总磷脂的6.4±0.1→2.0±0.4摩尔%）和MLCL积累（未检测到→3.3±0.5摩尔%）外，我们还发现缩醛磷脂酰胆碱水平大幅降低（30.8±2.8→18.1±3.1摩尔%），而缩醛磷脂酰胆碱是对照野生型中最丰富的磷脂。定量蛋白质免疫印迹显示，虽然在TAZ-KD模型中进行缩醛磷脂合成早期步骤的过氧化物酶体水平正常，但作为缩醛磷脂合成中限速酶的Far1的表达显著上调了8.3（±1.6）倍，以响应缩醛磷脂水平的降低来加速合成。我们证实溶血缩醛磷脂酰胆碱或缩醛磷脂酰胆碱分别是纯化的塔法兹蛋白与CL或MLCL进行转酰基作用的底物。我们的结果表明，富含亚油酰基种类的缩醛磷脂酰胆碱在心脏中CL的重塑中很重要。因此，塔法兹蛋白缺乏对心脏缩醛磷脂酰胆碱水平及其功能有重大影响。
