Friedreich ataxia (FA) is a rare neurodegenerative disease caused by decreased levels of the mitochondrial protein frataxin. Frataxin has been related in iron homeostasis, energy metabolism, and oxidative stress. Ferroptosis has recently been shown to be involved in FA cellular degeneration; however, its role in dorsal root ganglion (DRG) sensory neurons, the cells that are affected the most and the earliest, is mostly unknown. In this study, we used primary cultures of frataxin-deficient DRG neurons as well as DRG from the FXNI151F mouse model to study ferroptosis and its regulatory pathways. A lack of frataxin induced upregulation of transferrin receptor 1 and decreased ferritin and mitochondrial iron accumulation, a source of oxidative stress. However, there was impaired activation of NRF2, a key transcription factor involved in the antioxidant response pathway. Decreased total and nuclear NRF2 explains the downregulation of both SLC7A11 (a member of the system Xc, which transports cystine required for glutathione synthesis) and glutathione peroxidase 4, responsible for increased lipid peroxidation, the main markers of ferroptosis. Such dysregulation could be due to the increase in KEAP1 and the activation of GSK3β, which promote cytosolic localization and degradation of NRF2. Moreover, there was a deficiency in the LKB1/AMPK pathway, which would also impair NRF2 activity. AMPK acts as a positive regulator of NRF2 and it is activated by the upstream kinase LKB1. The levels of LKB1 were reduced when frataxin decreased, in agreement with reduced pAMPK (Thr172), the active form of AMPK. SIRT1, a known activator of LKB1, was also reduced when frataxin decreased. MT-6378, an AMPK activator, restored NRF2 levels, increased GPX4 levels and reduced lipid peroxidation. In conclusion, this study demonstrated that frataxin deficiency in DRG neurons disrupts iron homeostasis and the intricate regulation of molecular pathways affecting NRF2 activation and the cellular response to oxidative stress, leading to ferroptosis.

中文翻译：

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破译弗里德赖希共济失调模型背根神经节的铁死亡途径。 LKB1/AMPK、KEAP1 和 GSK3β 在 NRF2 反应损伤中的作用


弗里德赖希共济失调 (FA) 是一种罕见的神经退行性疾病，由线粒体蛋白 frataxin 水平下降引起。 Frataxin 与铁稳态、能量代谢和氧化应激有关。最近已证明铁死亡与 FA 细胞变性有关。然而，它在背根神经节 (DRG) 感觉神经元（受影响最大且最早的细胞）中的作用大多未知。在本研究中，我们使用 frataxin 缺陷的 DRG 神经元以及 FXNI151F 小鼠模型的 DRG 的原代培养物来研究铁死亡及其调节途径。 frataxin 的缺乏会诱导转铁蛋白受体 1 上调，并减少铁蛋白和线粒体铁积累，而铁积累是氧化应激的一个来源。然而，NRF2 的激活受损，NRF2 是参与抗氧化反应途径的关键转录因子。总 NRF2 和核 NRF2 的减少解释了 SLC7A11（Xc 系统的成员，转运谷胱甘肽合成所需的胱氨酸）和谷胱甘肽过氧化物酶 4 的下调，后者导致脂质过氧化增加，脂质过氧化是铁死亡的主要标志。这种失调可能是由于 KEAP1 的增加和 GSK3β 的激活所致，从而促进 NRF2 的胞质定位和降解。此外，LKB1/AMPK 通路存在缺陷，也会损害 NRF2 活性。 AMPK 作为 NRF2 的正调节因子，由上游激酶 LKB1 激活。当 frataxin 减少时，LKB1 的水平降低，这与 AMPK 的活性形式 pAMPK (Thr172) 的减少一致。 SIRT1 是一种已知的 LKB1 激活剂，当 frataxin 减少时，SIRT1 也会减少。 MT-6378 是一种 AMPK 激活剂，可恢复 NRF2 水平、增加 GPX4 水平并减少脂质过氧化。 总之，这项研究表明，DRG 神经元中 frataxin 缺乏会破坏铁稳态以及影响 NRF2 激活和细胞对氧化应激的细胞反应的分子途径的复杂调节，从而导致铁死亡。