Regulatory Mechanisms of Folate Transporters by Transcription Factors in the Brain

大脑转录因子对叶酸转运蛋白的调节机制

• 批准号: RGPIN-2021-02809
• 负责人: Bendayan, Reina
• 金额: $ 2.4万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=762020
• 关键词: Regulatory; Mechanisms; Folate; Transporters; Transcription

Folates (Vit B9) are water soluble vitamins required for key biosynthetic processes in mammalian cells. Folate transport across biological membranes and tissues is mediated by three major pathways: folate receptor alpha (FRa), proton-coupled folate transporter (PCFT), and reduced folate carrier (RFC). The functional expression of these folate transport pathways can be regulated by several transcription factors such as the Vitamin D receptor (VDR). Folates are critical for brain development and function. Inactivation of FRa, the major folate transport pathway at the blood-cerebrospinal fluid barrier, through loss-of-function mutations or the presence of FRa autoantibodies, causes severe cerebral folate deficiency characterized by inflammation, oxidative stress, mitochondrial dysfunction and abnormal brain myelination. Recently, as part of the NSERC grant approved in April 2015, we demonstrated that modulating folate uptake at the blood-brain barrier (BBB) through induction of specific folate transporters (i.e., RFC) could present a novel strategy for enhancing brain folate delivery in the context of defective FRa. We provided evidence that activation of VDR through exposure to its activating ligand, 1,25-dihydroxyvitamin D3 (calcitriol), induced RFC function at the BBB and effectively restored folate levels in the brain of mice lacking FRa. Although these results are very exciting, we observed that the animals treated with calcitriol presented toxicities such as weight loss and high calcium blood levels. NRF-1 is a transcription factor primarily known for its role in promoting mitochondrial and respiratory function. We recently determined that it can also regulate the folate transporter, RFC at the BBB. We propose that, in the context of defective FRa in the brain, activation of NRF-1 by its specific ligand, pyrroloquinoline quinone (PQQ), a natural non-toxic compound, can enhance RFC function and increase folate delivery into the brain reversing inflammation, oxidative stress, as well as mitochondrial dysfunction. Our proposed work will uncover fundamental mechanisms involved in mitochondrial dysfunction, brain inflammation and oxidative stress related to cerebral folate deficiency, elucidate how these effects can be reversed when brain folate levels are restored, and provide novel treatment approaches for neurometabolic disorders caused by loss of FRa function. Further, the findings of this project present broader applications due to the growing body of evidence associating mitochondrial dysfunction to neurological disorders and may also be exploited as a novel delivery route for several pharmacological agents known to have very poor CNS permeability (i.e., anticancer drugs). With the undertaking of the proposed work, we plan to train and mentor highly qualified personnel to become future leaders in the natural sciences.

叶酸（维生素 B9）是哺乳动物细胞关键生物合成过程所需的水溶性维生素。叶酸跨生物膜和组织的转运由三个主要途径介导：叶酸受体α（FRa）、质子耦合叶酸转运蛋白（PCFT）和还原叶酸载体（RFC）。这些叶酸转运途径的功能表达可由维生素 D 受体 (VDR) 等多种转录因子调节。叶酸对于大脑发育和功能至关重要。由于功能缺失突变或 FRa 自身抗体的存在，血脑脊液屏障的主要叶酸转运途径 FRa 失活，导致严重的脑叶酸缺乏，其特征为炎症、氧化应激、线粒体功能障碍和脑髓鞘形成异常。 最近，作为 2015 年 4 月批准的 NSERC 拨款的一部分，我们证明，通过诱导特定叶酸转运蛋白（即 RFC）来调节血脑屏障 (BBB) 的叶酸摄取，可以提出一种在 FRa 有缺陷的情况下增强大脑叶酸输送的新策略。我们提供的证据表明，通过暴露于其激活配体 1,25-二羟基维生素 D3（骨化三醇）来激活 VDR，可诱导 BBB 处的 RFC 功能，并有效恢复缺乏 FRa 的小鼠大脑中的叶酸水平。尽管这些结果非常令人兴奋，但我们观察到用骨化三醇治疗的动物出现了体重减轻和血液钙水平升高等毒性。 NRF-1 是一种转录因子，主要因其在促进线粒体和呼吸功能中的作用而闻名。我们最近确定它还可以调节 BBB 处的叶酸转运蛋白 RFC。我们认为，在大脑中存在 FRa 缺陷的情况下，NRF-1 通过其特异性配体吡咯喹啉醌 (PQQ)（一种天然无毒化合物）激活，可以增强 RFC 功能并增加叶酸向大脑的输送，从而逆转炎症、氧化应激以及线粒体功能障碍。 我们提出的工作将揭示与脑叶酸缺乏相关的线粒体功能障碍、脑炎症和氧化应激的基本机制，阐明当脑叶酸水平恢复时如何逆转这些影响，并为因 FRa 功能丧失而引起的神经代谢紊乱提供新的治疗方法。此外，由于越来越多的证据表明线粒体功能障碍与神经系统疾病相关，该项目的研究结果呈现出更广泛的应用，并且还可以被用作几种已知中枢神经系统渗透性非常差的药物（即抗癌药物）的新递送途径。通过开展拟议的工作，我们计划培养和指导高素质人才，使其成为自然科学领域的未来领导者。