Imaging Brain Signal Transduction via Arachidonic and Docosahexaenoic Acids

通过花生四烯酸和二十二碳六烯酸对大脑信号转导进行成像

• 批准号: 8335770
• 负责人: Stanley I. Rapoport
• 金额: $ 51.73万
• 依托单位: NATIONAL INSTITUTE ON AGING
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8335770
• 关键词: Acute; Animals; Arachidonic Acids; Aspartate; Behavior; Biological Markers; Brain; Brain Injuries; Brain imaging; Brain region; Calcium; Cells; Cholinergic Receptors; Clinical Protocols; Cognition; Consumption; Data; Development; Diet; Disease; Docosahexaenoic Acids; Drug effect disorder; Dystonia; Enzymes; Glutamates; Goals; Hepatic; Human; Image; Imaging Techniques; In Vitro; Iron; Knock-out; Laboratories; Lesion; Measures; Mediating; Membrane; Messenger RNA; Metabolic; Metabolism; Methods; Modeling; Mus; Mutation; N-Methyl-D-Aspartate Receptors; N-Methylaspartate; Nerve Degeneration; Neurologic Dysfunctions; Organism; PLA2G6 gene; Parkinsonian Disorders; Patients; Phospholipase; Phospholipase A2; Phospholipids; Plasma; Polyunsaturated Fatty Acids; Positron-Emission Tomography; Postsynaptic Membrane; Proteins; Quantitative Autoradiography; Radioactivity; Radiolabeled; Rattus; Receptor Activation; Rest; Role; Second Messenger Systems; Signal Transduction; Structure; Synapses; Synaptic Membranes; alpha-Linolenic Acid; cholinergic; excitotoxicity; extracellular; healthy aging; human PLA2G6 protein; in vivo; intravenous injection; nervous system disorder; neuroinflammation; neuropathology; neurotransmission; radiotracer; second messenger; synaptic function; uptake

EXTRACELLULAR-DERIVED CALCIUM DOES NOT INITIATE NEUROTRANSMISSION VIA DOCOSAHEXAENOIC ACID. Docosahexaenoic acid (DHA, 22:6n-3), a nutritionally essential polyunsaturated fatty, is found in high concentrations in synaptic membrane phospholipids, but its role in neurotransmission in vivo is poorly understood. In vitro studies show that DHA is released from postsynaptic membrane phospholipid by calcium-independent phospholipase A2, iPLA2, but not by calcium-dependent cytosolic cPLA2, which selectively releases arachidonic acid (AA). Since glutamatergic N-methyl-D-aspartate (NMDA) receptor activation allows extracellular calcium into cells, we hypothesized that brain AA but not DHA signaling would be increased in rats injected with NMDA if iPLA2 also selectively modulated DHA signaling in vivo. We confirmed this hypothesis using quantitative autoradiography. Greater AA than DHA release during excess glutamate stimulation of NMDA receptors could contribute to excitotoxic brain damage (Ramadan et al., 2010). IMAGING DECREASED BRAIN DOCOSAHEXAENOIC ACID METABOLISM AND SIGNALING IN iPLA-DEFICIENT MICE. Calcium-independent phospholipase A2beta (iPLA2beta) selectively hydrolyzes docosahexaenoic acid (DHA, 22:6n-3) from membrane phospholipid. Mutations in the PLA2G6 gene encoding this enzyme occur in patients with neurological disorders including idiopathic neurodegeneration plus brain iron accumulation and dystonia-parkinsonism without iron accumulation. Mice lacking PLA2G6 show neurological dysfunction and neuropathology after 13 months, and we hypothesized that they would have disturbed DHA function. We confirmed this by showing with our quantitative imaging technique that brain DHA metabolism and cholinergic receptor mediated DHA-signaling were reduced in 4-month-old iPLA2beta-deficient mice, before overt neuropathology had developed. Thus, iPLA2beta is critical for maintaining normal brain DHA metabolism and signaling in the intact organism. Positron emission tomography (PET) would be expected to show disturbed brain DHA metabolism in patients with PLA2G6 mutations, and treatment with elevated dietary DHA may be helpful in such patients (Basselin et al., 2010). DOCOSAHEXAENOIC ACID (DHA) INCORPORATION INTO BRAIN FROM PLASMA IS AN IN VIVO BIOMARKER OF BRAIN DHA METABOLISM AND NEUROTRANSMISSION. Docosahexaenoic acid (DHA) is critical for maintaining normal brain structure and function, and is considered neuroprotective. Its brain concentration depends on dietary DHA content and hepatic conversion from its diet derived n-3 precursor, alpha-linolenic acid (alpha-LNA). Our in vivo method using quantitative autoradiography and intravenously injected radiolabeled DHA can be used to image net rate of incorporation into the brain of unesterified plasma DHA, which equals the rate of brain metabolic DHA consumption at rest and during activation. We also extended the method for use in humans with positron emission tomography (PET). Imaging in unanesthetized rats given acute N-methyl-d-aspartate (NMDA), regional DHA signaling is independent of extracellular calcium, and mediated by calcium-independent phospholipase A2 (iPLA2). Studies in mice in which iPLA2-VIA (beta) was knocked out confirmed that this enzyme is critical for baseline and cholinergic signaling involving DHA. Thus, quantitative imaging of DHA incorporation from plasma into brain, in animals or humans, can be used as an in vivo biomarker of brain DHA metabolism and neurotransmission (Rapoport et al., 2011).

细胞外钙不通过二十二碳六烯酸启动神经传递。 二十二碳六烯酸（DHA，22：6 n-3）是一种营养必需的多不饱和脂肪酸，存在于突触膜磷脂中，但其在体内神经传递中的作用尚不清楚。体外研究表明，DHA通过钙非依赖性磷脂酶A2（iPLA 2）从突触后膜磷脂中释放，但不通过钙依赖性细胞溶质cPLA 2释放，后者选择性释放花生四烯酸（AA）。由于谷氨酸能N-甲基-D-天冬氨酸（NMDA）受体激活允许细胞外钙进入细胞，我们假设，如果iPLA 2也选择性地调节体内DHA信号，则注射NMDA的大鼠脑AA而不是DHA信号将增加。我们用定量放射自显影证实了这一假设。在NMDA受体的过量谷氨酸刺激期间，比DHA释放更多的AA可能导致兴奋性毒性脑损伤（Ramadan等人，2010年）。 对iPLA缺乏小鼠中脑二十二碳六烯酸代谢和信号传导减少进行成像。 钙非依赖性磷脂酶A2 β（iPLA 2 β）选择性地从膜磷脂中水解二十二碳六烯酸（DHA，22：6 n-3）。编码这种酶的PLA 2G 6基因突变发生在患有神经系统疾病的患者中，包括特发性神经变性加上脑铁蓄积和无铁蓄积的肌张力障碍-帕金森综合征。缺乏PLA 2G 6的小鼠在13个月后表现出神经功能障碍和神经病理学，我们假设它们会扰乱DHA功能。我们通过定量成像技术证实了这一点，即在出现明显的神经病理学之前，4个月大的iPLA 2 β缺陷小鼠的大脑DHA代谢和胆碱能受体介导的DHA信号传导减少。因此，iPLA 2 β对于维持完整生物体中正常的大脑DHA代谢和信号传导至关重要。预期正电子发射断层扫描（PET）将显示具有PLA 2G 6突变的患者的脑DHA代谢紊乱，并且用升高的膳食DHA治疗可能对此类患者有帮助（Basselin等人，2010年）。 二十二碳六烯酸（DHA）从血浆进入脑是脑DHA代谢和神经传递的体内生物标志物。二十二碳六烯酸（DHA）对维持正常的大脑结构和功能至关重要，并被认为具有神经保护作用。其脑浓度取决于膳食DHA含量和来自其膳食衍生的n-3前体α-亚麻酸（α-LNA）的肝脏转化。我们使用定量放射自显影和静脉注射放射性标记的DHA的体内方法可用于成像未酯化血浆DHA掺入脑中的净速率，其等于休息时和激活期间脑代谢DHA消耗的速率。我们还扩展了该方法用于人类正电子发射断层扫描（PET）。在给予急性N-甲基-d-天冬氨酸（NMDA）的未麻醉大鼠中成像，局部DHA信号传导不依赖于细胞外钙，并由钙非依赖性磷脂酶A2（iPLA 2）介导。在敲除iPLA 2-VIA（β）的小鼠中进行的研究证实，这种酶对于基线和涉及DHA的胆碱能信号传导至关重要。因此，在动物或人类中，DHA从血浆掺入大脑的定量成像可用作大脑DHA代谢和神经传递的体内生物标志物（Rapoport等人，2011年）。