Restoration of mitochondrial function by small-molecule iron transporter in Friedreich’s ataxia

项目总结/摘要 弗里德赖希共济失调（FRDA）是一种遗传性常染色体神经退行性疾病引起的GAA重复 共济失调蛋白（FXN）基因的扩增，导致FXN（一种线粒体蛋白）的表达减少 对铁硫簇组装和线粒体功能至关重要。FRDA患者表现出神经系统 缺陷，包括进行性步态共济失调、构音障碍、反射消失和运动无力。其他功能还包括 心肌病和糖尿病。虽然已经评估了各种方法来改善临床症状 对于FRDA，迄今为止还没有有效的治疗方法。值得注意的是，脑线粒体中过量的铁是 在FRDA患者和FRDA动物模型中一致观察到。由于铁的增加会产生细胞毒性 氧化应激和细胞/亚细胞铁利用的破坏， 线粒体可以改善FRDA的神经症状。事实上，一种旨在减少 线粒体铁已被证明在减轻心脏中铁介导的毒性方面是成功的。但是这种方法 由于目前FDA批准的铁， 螯合剂既不穿过血脑屏障，也不进入线粒体铁库。此外，这些螯合剂 显示出显著的毒性，如骨髓抑制和中性粒细胞减少，这限制了它们的长期使用 神经系统疾病因此，对于一类新的可进入的BBB-1的主要未满足的需求。 交叉铁转运蛋白，解决脑线粒体铁积累和改善神经行为 FRDA的赤字。早期，我们证明了扁柏酚，一种具有高铁结合亲和力和细胞毒性的小分子， 渗透性，纠正线粒体膜上异常的铁积累（即，线粒体铁含量低， 高细胞溶质铁）由线粒体铁转运蛋白的遗传缺陷引起。与其他铁螯合剂不同 在与铁结合后变得亲水（例如，去铁酮），铁-扁柏酚复合物保持亲脂性， 从而可以沿着沿着浓度梯度穿过膜将过量的铁输出到线粒体外， 包括大脑。这些发现促使我们质疑扁柏酚是否可以逆转线粒体铁超载 在大脑里。受我们最近的进展和初步数据的启发，我们现在期待的治疗潜力， 扁柏酚纠正脑中线粒体铁超载，否则会影响神经系统 FRDA中的缺陷。因此，在这项拨款申请的基本假设是，扁柏酚动员， 将多余的铁从脑线粒体重新分配到细胞质，防止氧化损伤，从而恢复 FRDA中的神经缺陷。具体的目的是确定：i）扁柏酚在神经系统中的神经保护作用， 和ii）扁柏酚对线粒体功能的影响及其在FRDA小鼠中的安全性， 与其他相关FDA批准的铁螯合剂进行比较。我们的研究将提供一种新的治疗策略 逆转线粒体铁的异常积累和纠正FRDA的神经毒性，这是尚未解决的 迄今

PROJECT SUMMARY/ABSTRACT Friedreich’s ataxia (FRDA) is an inherited autosomal neurodegenerative disorder caused by the GAA repeat expansions of the frataxin (FXN) gene, which results in decreased expression of FXN, a mitochondrial protein critical for iron-sulfur cluster assembly and mitochondrial function. Patients with FRDA display neurological deficits, including progressive gait ataxia, dysarthria, areflexia, and motor weakness. Additional features include cardiomyopathy and diabetes. Although various approaches have been evaluated to improve clinical symptoms of FRDA, there is no effective treatment available to date. Notably, excess iron in brain mitochondria is consistently observed in FRDA patients and animal models of FRDA. Since increased iron generates cytotoxic oxidative stress and disruption of cellular/subcellular iron utilization, reversal of abnormal iron buildup in the mitochondria could ameliorate neurological symptoms of FRDA. Indeed, a therapy that aims to reduce mitochondrial iron has proven successful in mitigating iron-mediated toxicity in the heart. However, this approach does not provide therapeutic benefits for neurological problems in FRDA since current FDA-approved iron chelators neither cross the blood-brain barrier nor access the mitochondrial iron pool. Also, these chelators have demonstrated significant toxicities, such as myelosuppression and neutropenia, which limit their long-term use in neurological disorders. Thus, there is a major unmet need for a new class of mitochondria-accessible, BBB- crossing iron transporters that resolve brain mitochondrial iron accumulation and improve neurobehavioral deficits in FRDA. Earlier we demonstrated that hinokitiol, a small molecule with high iron binding affinity and cell permeability, corrects abnormal iron buildup across the mitochondrial membrane (i.e., low mitochondrial iron and high cytosolic iron) caused by genetic deficiency in mitochondrial iron transporters. Unlike other iron chelators that become hydrophilic after binding to iron (e.g., deferiprone), the iron-hinokitiol complex remains lipophilic and can thereby export excess iron out of the mitochondria along the concentration gradient across the membrane, including the brain. These findings prompted us to question if hinokitiol could reverse mitochondrial iron overload in the brain. Inspired by our recent progress and preliminary data, we now look to therapeutic potential of hinokitiol in correcting mitochondrial iron overload in the brain, which otherwise worsens neurological impairments in FRDA. Thus, the underlying hypothesis in this grant application is that hinokitiol mobilizes and redistributes excess iron from the brain mitochondria to cytosol and prevents oxidative damage, thereby restoring neurological deficits in FRDA. The specific aims are to determine: i) the neuroprotective effect of hinokitiol in a mouse model of FRDA and ii) the effect of hinokitiol on mitochondrial function and its safety in FRDA mice in comparison with other relevant FDA-approved iron chelators. Our studies will provide a new therapeutic strategy to reverse abnormal accumulation of mitochondrial iron and correct neurotoxicity of FRDA, which is unresolved to date.