Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Canada.
Fluids Barriers CNS. 2023 Nov 20;20(1):84. doi: 10.1186/s12987-023-00488-3.
Folates (Vitamin B9) are critical for normal neurodevelopment and function, with transport mediated by three major pathways: folate receptor alpha (FRα), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). Cerebral folate uptake primarily occurs at the blood-cerebrospinal fluid barrier (BCSFB) through concerted actions of FRα and PCFT, with impaired folate transport resulting in the neurological disorder cerebral folate deficiency (CFD). Increasing evidence suggests that disorders associated with CFD also present with neuroinflammation, oxidative stress, and mitochondrial dysfunction, however the role of brain folate deficiency in inducing these abnormalities is not well-understood. Our laboratory has identified the upregulation of RFC by nuclear respiratory factor 1 (NRF-1) at the blood-brain barrier (BBB) once indirectly activated by the natural compound pyrroloquinoline quinone (PQQ). PQQ is also of interest due to its anti-inflammatory, antioxidant, and mitochondrial biogenesis effects. In this study, we examined the effects of folate deficiency and PQQ treatment on inflammatory and oxidative stress responses, and changes in mitochondrial function.
Primary cultures of mouse mixed glial cells exposed to folate-deficient (FD) conditions and treated with PQQ were analyzed for changes in gene expression of the folate transporters, inflammatory markers, oxidative stress markers, and mitochondrial DNA (mtDNA) content through qPCR analysis. Changes in cellular reactive oxygen species (ROS) levels were analyzed in vitro through a DCFDA assay. Wildtype (C57BL6/N) mice exposed to FD (0 mg/kg folate), or control (2 mg/kg folate) diets underwent a 10-day (20 mg/kg/day) PQQ treatment regimen and brain tissues were collected and analyzed.
Folate deficiency resulted in increased expression of inflammatory and oxidative stress markers in vitro and in vivo, with increased cellular ROS levels observed in mixed glial cells as well as a reduction of mitochondrial DNA (mtDNA) content observed in FD mixed glial cells. PQQ treatment was able to reverse these changes, while increasing RFC expression through activation of the PGC-1α/NRF-1 signaling pathway.
These results demonstrate the effects of brain folate deficiency, which may contribute to the neurological deficits commonly seen in disorders of CFD. PQQ may represent a novel treatment strategy for disorders associated with CFD, as it can increase folate uptake, while in parallel reversing many abnormalities that arise with brain folate deficiency.
叶酸（维生素 B9）对正常的神经发育和功能至关重要，其转运主要通过三种主要途径：叶酸受体 alpha（FRα）、质子偶联叶酸转运蛋白（PCFT）和还原叶酸载体（RFC）。脑叶酸摄取主要通过 FRα 和 PCFT 的协同作用在血脑脊液屏障（BCSFB）中发生，叶酸转运受损导致神经疾病脑叶酸缺乏症（CFD）。越来越多的证据表明，与 CFD 相关的疾病也伴有神经炎症、氧化应激和线粒体功能障碍，然而，脑叶酸缺乏症在诱导这些异常中的作用尚不清楚。我们的实验室已经确定，核呼吸因子 1（NRF-1）在血脑屏障（BBB）中的上调可通过天然化合物吡咯喹啉醌（PQQ）间接激活，从而上调 RFC。PQQ 也因其抗炎、抗氧化和线粒体生物发生作用而受到关注。在这项研究中，我们研究了叶酸缺乏和 PQQ 治疗对炎症和氧化应激反应以及线粒体功能变化的影响。
将暴露于叶酸缺乏（FD）条件下并接受 PQQ 治疗的小鼠混合神经胶质细胞的原代培养物通过 qPCR 分析来分析叶酸转运体、炎症标志物、氧化应激标志物和线粒体 DNA（mtDNA）含量的基因表达变化。通过 DCFDA 测定法在体外分析细胞内活性氧（ROS）水平的变化。暴露于 FD（0 mg/kg 叶酸）或对照（2 mg/kg 叶酸）饮食的野生型（C57BL6/N）小鼠接受为期 10 天（20 mg/kg/天）的 PQQ 治疗方案，并收集和分析脑组织。
叶酸缺乏导致体外和体内炎症和氧化应激标志物表达增加，混合神经胶质细胞中观察到细胞内 ROS 水平升高，FD 混合神经胶质细胞中观察到线粒体 DNA（mtDNA）含量减少。PQQ 治疗能够逆转这些变化，同时通过激活 PGC-1α/NRF-1 信号通路增加 RFC 表达。
这些结果表明脑叶酸缺乏症的影响，这可能导致 CFD 相关疾病中常见的神经功能缺陷。PQQ 可能代表一种治疗 CFD 相关疾病的新策略，因为它可以增加叶酸摄取，同时平行逆转脑叶酸缺乏症出现的许多异常。
