Cholesterol-related genes in response to brain deafferentation in normal and transgenic mice

胆固醇相关基因对正常和转基因小鼠脑传入神经阻滞的反应

• 批准号: RGPIN-2020-04702
• 负责人: Poirier, Judes
• 金额: $ 2.4万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=740131
• 关键词: Cholesterol; related; genes; response; brain

Our team has documented over the years an elegant mechanism by which the injured adult brain uses the cholesterol and phospholipids released from dead/dying cells to feed surviving neurons with the lipids required for the proper rebuilding local synaptic networks. We call this process the cholesterol recycling cascade. Our team has already demonstrated that the intra- and extracellular transport of cholesterol by apolipoprotein E (apoE) and ABCA1, highly functional lipid transporters, is required and necessary for the replacement of synaptic networks in response to brain injury in rodents. In response, neuronal cell-surface receptors belonging to the LDL receptors family that recognize apoE-lipoprotein complexes mediate the internalization of the HDL-cholesterol used in the formation of new synapses. The complete absence of brain apoE or, of its main receptor, in knockout mice was shown to compromise i) synaptic integrity with aging, ii) lesion-induced synaptic recovery and iii) cognitive performance. We know very little about the triggering and regulating mechanisms controlling this cascade; i.e. the transport and packaging of cholesterol and phospholipids from the astroglial compartments toward the apoE-lipoprotein (HDL) assembly line, and the final LDL receptor (LDLR)-mediated internalisation. We know that certain ATP-Binding Cassette (ABC) proteins such as A1 are involved, facilitating the transfer of lipids to HDLs at the surface.  Hypothesis: In response to neuronal loss, brain cholesterol is mobilized by astrocytes where the coordinated expression of ABCA1, A7 or G1 facilitates its movement toward the cell surface where apolipoprotein E awaits to catalyze the transfer of the lipids to extracellular apoE-rich HDL complexes. These lipid-enriched lipoproteins are subsequently used to feed neighboring neurons via the LDL receptors family which are tightly regulated by the presence of the so-called of SREBF2 and PCSK9 proteins; one is a potent activator of LDL receptor production (SREBF2) while the other (PCSK9) facilitate the LDLR elimination and catabolism. Subsequently, large amounts of lipids are engulfed by surviving neurons and are used to rebuild new dentritic and synaptic networks. Objectives: We propose to dissect the molecular cascade regulating the cholesterol recycling process by examining i) the intracellular transport of the lipids by the ABC transport system in glial cells in vivo during deafferentation and reinnervation, ii) the assembly of apoE-lipoprotein complexes in presence/absence of ABCA7 and LDLR in lesioned mice,  iii) the interaction of apoE and ABCs with cell surface lipids and, iv) the binding and internalization of the apoE-HDL complex via the LDL receptors by neurons. Expected Outcome: We believe that these studies will provide crucial insights in regard to the molecular events leading to the activation of synaptic repair and the delivery of key lipid species during brain repair in the adult rodent brain.

我们的团队多年来记录了一种优雅的机制，通过这种机制，受伤的成人大脑利用死亡/垂死细胞释放的胆固醇和磷脂，为幸存的神经元提供正确重建局部突触网络所需的脂质。我们将此过程称为胆固醇回收级联。我们的团队已经证明，载脂蛋白 E (apoE) 和 ABCA1（高功能脂质转运蛋白）对胆固醇的细胞内和细胞外转运是啮齿类动物响应脑损伤而更换突触网络所必需的。作为响应，属于 LDL 受体家族的神经元细胞表面受体识别 apoE-脂蛋白复合物，介导用于形成新突触的 HDL-胆固醇的内化。基因敲除小鼠大脑中 apoE 或其主要受体的完全缺失被证明会损害 i) 衰老过程中突触的完整性，ii) 损伤引起的突触恢复，以及 iii) 认知能力。 我们对控制这一级联的触发和调节机制知之甚少。即胆固醇和磷脂从星形胶质细胞向apoE-脂蛋白（HDL）装配线的运输和包装，以及最终的LDL受体（LDLR）介导的内化。我们知道某些 ATP 结合盒 (ABC) 蛋白（例如 A1）参与其中，促进脂质向表面的 HDL 转移。  假设：为了响应神经元损失，星形胶质细胞动员脑胆固醇，其中 ABCA1、A7 或 G1 的协调表达促进其向细胞表面移动，载脂蛋白 E 等待催化脂质转移到细胞外富含 apoE 的 HDL 复合物。这些富含脂质的脂蛋白随后被用于通过 LDL 受体家族为邻近的神经元提供营养，而这些受体家族受到所谓的 SREBF2 和 PCSK9 蛋白的存在的严格调节；一种是 LDL 受体生成的有效激活剂 (SREBF2)，而另一种 (PCSK9) 则促进 LDLR 消除和分解代谢。随后，大量脂质被幸存的神经元吞噬，并用于重建新的树突和突触网络。目的：我们建议通过检查 i) 在传入神经阻滞和再神经支配期间体内神经胶质细胞中 ABC 转运系统对脂质的细胞内转运，ii) 在存在/不存在 ABCA7 和 LDLR 的病变小鼠中 apoE-脂蛋白复合物的组装，iii) 相互作用来剖析调节胆固醇循环过程的分子级联反应。 apoE 和 ABC 与细胞表面脂质，以及 iv) apoE-HDL 复合物通过神经元的 LDL 受体结合和内化。预期结果：我们相信，这些研究将为成年啮齿动物大脑修复过程中导致突触修复激活和关键脂质种类传递的分子事件提供重要见解。