Astrocytic regulation of energy balance on high-fat diet

星形胶质细胞对高脂饮食能量平衡的调节

• 批准号: 10734911
• 负责人: BAOJI XU
• 金额: $ 75.47万
• 依托单位: UNIVERSITY OF FLORIDA
• 依托单位国家: 美国
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-09 至 2027-04-30
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10734911
• 关键词: Ablation; Age; Astrocytes; Axon; Binding; Brain; Brain region; Brain-Derived Neurotrophic Factor; Ca(2+)-Transporting ATPase; Cell membrane; Cells; Development; Dimerization; Energy Intake; Energy Metabolism; Fat-Restricted Diet; Gene Deletion; Glutamates; Growth; High Fat Diet; Homeostasis; Human; Hyperactivity; Hyperphagia; Hypothalamic structure; ITPR1 gene; Impairment; Injections; Inositol; Knock-out; Knockout Mice; Lead; Length; Measures; Mediating; Minor; Morbid Obesity; Morphology; Mus; Mutation; NTRK2 gene; Nerve Degeneration; Neurons; Neurotransmitters; Neurotrophic Tyrosine Kinase Receptor Type 2; Nutritional; Nutritional Support; Obesity; Phosphotransferases; Play; Process; Protein Isoforms; RNA Splicing; Reducing diet; Regulation; Reporting; Research Project Grants; Resistance; Role; Signal Pathway; Signal Transduction; Site; Slice; Structure; Structure of nucleus infundibularis hypothalami; Synapses; Synaptic Cleft; Synaptic Transmission; Testing; Therapeutic Intervention; Tropomyosin; Tyrosine Kinase Domain; Variant; antagonist; astrogliosis; attenuation; conditional knockout; density; diet-induced obesity; energy balance; excitotoxicity; experimental study; feeding; knock-down; neuron development; neuronal survival; neurotoxic; neurotransmission; novel; obesity prevention; prevent; receptor; response; rho GTP-Binding Proteins; transmission process; tripolyphosphate; uptake

Summary Brain-derived neurotrophic factor (BDNF) binds to full-length tropomyosin receptor kinase (TrkB.FL), inducing its dimerization and activation. This activates many signaling cascades that cooperatively promote neuronal survival and regulate neuronal development and synaptic transmission in many brain regions. This signaling pathway is also critical for the control of energy balance, as mutations in the TrkB.FL kinase domain or BDNF lead to hyperphagia and severe obesity in mice and humans. In addition to TrkB.FL, the Ntrk2 gene produces two truncated receptors, a predominant TrkB.T1 and a minor TrkB.T2 (we use TrkB.T to refer both isoforms). TrkB.T has a short intracellular sequence and lacks the tyrosine kinase domain. Neurons mainly express TrkB.FL, whereas astrocytes only express TrkB.T. While binding of BDNF to TrkB.T1 induces Ca2+ signals and activates Rho GTPase in cultured astrocytes, it remains unclear if astrocytic TrkB.T plays a role in the control of energy balance. We generated astrocyte specific Ntrk2 conditional knockout (aNtrk2 cKO) mice where Ntrk2 deletion starts at 5 weeks of age and abolishes TrkB.T expression in astrocytes. We found that the Ntrk2 deletion in mature astrocytes blocked astrocytic reactivity in the arcuate nucleus of the hypothalamus (ARH) and gave mice total resistance to diet-induced obesity (DIO) by reducing energy intake and increasing energy expenditure. In addition to nutritional and trophic support to neurons, astrocytes contact synapses through their processes to regulate synaptic transmission by taking up neurotransmitters from the synaptic cleft and releasing gliotransmitters into the synaptic cleft. Thus, we hypothesize that TrkB.T-mediated Ca2+ signals promote astrocytic reactivity in response to high-fat diet (HFD) feeding, which in turn disrupts astrocytic support to neurons and astrocytic regulation of synapses and shifts energy homeostasis to energy surplus. Our studies will focus on astrocytes, AgRP/NPY neurons, and POMC neurons in the ARH. We propose to examine the impact of Ntrk2 gene deletion on astrocytes in the ARH (Aim 1), to determine the impact of astrocytic Ntrk2 deletion on neurons and synaptic transmission (Aim 2), to identify the site where astrocytic TrkB.T ablation blocks diet-induced obesity (Aim 3), and to determine if attenuating astrocytic Ca2+ signals can prevent obesity in HFD-fed mice (Aim 4). In conclusion, this research project will test several novel concepts, including a crucial role for TrkB.T- mediated Ca2+ signals in induction of astrocytic reactivity, an active role for TrkB.T in the regulation of energy balance, and altered astrocytic regulation of synaptic transmission in HFD-fed mice. Our studies will likely show that attenuating TrkB.T-mediated Ca2+ signals in astrocytes can be a novel and effective strategy for therapeutic interventions of DIO, the most common form of obesity in humans.

概括 脑源性神经营养因子 (BDNF) 与全长原肌球蛋白受体激酶 (TrkB.FL) 结合，诱导其 二聚化和活化。这激活了许多信号级联，协同促进神经元存活 并调节许多大脑区域的神经元发育和突触传递。该信号通路是 对于能量平衡的控制也至关重要，因为 TrkB.FL 激酶结构域或 BDNF 的突变会导致 小鼠和人类的食欲亢进和严重肥胖。除了 TrkB.FL 之外，Ntrk2 基因还产生两个 截短的受体，主要是 TrkB.T1 和次要 TrkB.T2（我们使用 TrkB.T 来指代两种亚型）。 TrkB.T 具有短的细胞内序列并且缺乏酪氨酸激酶结构域。神经元主要表达TrkB.FL， 而星形胶质细胞仅表达 TrkB.T。当 BDNF 与 TrkB.T1 结合时，会诱导 Ca2+ 信号并激活 培养的星形胶质细胞中的 Rho GTPase，目前尚不清楚星形胶质细胞 TrkB.T 是否在能量控制中发挥作用 平衡。我们生成了星形胶质细胞特异性 Ntrk2 条件敲除 (aNtrk2 cKO) 小鼠，其中 Ntrk2 缺失 从 5 周龄开始，消除星形胶质细胞中的 TrkB.T 表达。我们发现 Ntrk2 缺失 成熟的星形胶质细胞阻断下丘脑弓状核（ARH）的星形胶质细胞反应性，并给予小鼠 通过减少能量摄入和增加能量消耗来全面抵抗饮食引起的肥胖（DIO）。在 除了为神经元提供营养和营养支持外，星形胶质细胞还通过其过程接触突触 通过从突触间隙吸收神经递质并释放来调节突触传递 胶质递质进入突触间隙。因此，我们假设 TrkB.T 介导的 Ca2+ 信号促进 星形胶质细胞对高脂肪饮食 (HFD) 喂养的反应，进而破坏星形胶质细胞对神经元的支持 和星形细胞对突触的调节，并将能量稳态转变为能量盈余。我们的研究将集中 ARH 中的星形胶质细胞、AgRP/NPY 神经元和 POMC 神经元。我们建议检查 Ntrk2 的影响 ARH 中星形胶质细胞的基因缺失（目标 1），以确定星形胶质细胞 Ntrk2 缺失对神经元的影响 和突触传递（目标 2），以确定星形胶质细胞 TrkB.T 消融阻断饮食诱导的位点 肥胖（目标 3），并确定减弱星形细胞 Ca2+ 信号是否可以预防 HFD 喂养小鼠的肥胖（目标 4).总之，这个研究项目将测试几个新颖的概念，包括 TrkB.T- 的关键作用 介导的 Ca2+ 信号诱导星形胶质细胞反应性，这是 TrkB.T 在能量调节中的积极作用 平衡，并改变了 HFD 喂养小鼠突触传递的星形胶质细胞调节。我们的研究可能会表明 减弱星形胶质细胞中 TrkB.T 介导的 Ca2+ 信号可能是一种新颖且有效的治疗策略 DIO（人类最常见的肥胖形式）的干预措施。