De Filippis Bianca, Valenti Daniela, de Bari Lidia, De Rasmo Domenico, Musto Mattia, Fabbri Alessia, Ricceri Laura, Fiorentini Carla, Laviola Giovanni, Vacca Rosa Anna
Department of Cell Biology and Neuroscience, Istituto Superiore di Sanità, 00161 Roma, Italy.
Institute of Biomembranes and Bioenergetics, National Council of Research, Bari, Italy.
Free Radic Biol Med. 2015 Jun;83:167-77. doi: 10.1016/j.freeradbiomed.2015.02.014. Epub 2015 Feb 20.
Rett syndrome (RTT) is a pervasive neurodevelopmental disorder mainly caused by mutations in the X-linked MECP2 gene associated with severe intellectual disability, movement disorders, and autistic-like behaviors. Its pathogenesis remains mostly not understood and no effective therapy is available. High circulating levels of oxidative stress markers in patients and the occurrence of oxidative brain damage in MeCP2-deficient mouse models suggest the involvement of oxidative stress in RTT pathogenesis. However, the molecular mechanism and the origin of the oxidative stress have not been elucidated. Here we demonstrate that a redox imbalance arises from aberrant mitochondrial functionality in the brain of MeCP2-308 heterozygous female mice, a condition that more closely recapitulates that of RTT patients. The marked increase in the rate of hydrogen peroxide generation in the brain of RTT mice seems mainly produced by the dysfunctional complex II of the mitochondrial respiratory chain. In addition, both membrane potential generation and mitochondrial ATP synthesis are decreased in RTT mouse brains when succinate, the complex II respiratory substrate, is used as an energy source. Respiratory chain impairment is brain area specific, owing to a decrease in either cAMP-dependent phosphorylation or protein levels of specific complex subunits. Further, we investigated whether the treatment of RTT mice with the bacterial protein CNF1, previously reported to ameliorate the neurobehavioral phenotype and brain bioenergetic markers in an RTT mouse model, exerts specific effects on brain mitochondrial function and consequently on hydrogen peroxide production. In RTT brains treated with CNF1, we observed the reactivation of respiratory chain complexes, the rescue of mitochondrial functionality, and the prevention of brain hydrogen peroxide overproduction. These results provide definitive evidence of mitochondrial reactive oxygen species overproduction in RTT mouse brain and highlight CNF1 efficacy in counteracting RTT-related mitochondrial defects.
瑞特综合征（RTT）是一种广泛性神经发育障碍，主要由X连锁的MECP2基因突变引起，与严重智力残疾、运动障碍和自闭症样行为相关。其发病机制大多仍不清楚，且尚无有效的治疗方法。患者体内氧化应激标志物的循环水平升高，以及MeCP2基因缺陷小鼠模型中出现的氧化性脑损伤，提示氧化应激参与了RTT的发病机制。然而，氧化应激的分子机制和起源尚未阐明。在此，我们证明氧化还原失衡源于MeCP2 - 308杂合雌性小鼠大脑中异常的线粒体功能，这种情况更接近RTT患者的状况。RTT小鼠大脑中过氧化氢生成速率的显著增加似乎主要是由线粒体呼吸链功能失调的复合物II产生的。此外，当使用复合物II的呼吸底物琥珀酸作为能量来源时，RTT小鼠大脑中的膜电位产生和线粒体ATP合成均降低。呼吸链损伤具有脑区特异性，这是由于特定复合物亚基的cAMP依赖性磷酸化或蛋白质水平降低所致。此外，我们研究了用细菌蛋白CNF1治疗RTT小鼠是否对脑线粒体功能以及过氧化氢生成产生特定影响，此前有报道称CNF1可改善RTT小鼠模型中的神经行为表型和脑生物能量标志物。在用CNF1治疗的RTT大脑中，我们观察到呼吸链复合物的重新激活、线粒体功能的恢复以及脑过氧化氢过量生成的预防。这些结果为RTT小鼠大脑中线粒体活性氧过量产生提供了确凿证据，并突出了CNF1在对抗RTT相关线粒体缺陷方面的功效。
