Probing into receptor-mediated trafficking and internalization functions of biologically active peptides

背景：血脑屏障(BBB)是一种强大的外源性物质守门人，在复杂神经元活动的脑内稳态中发挥着重要作用。因此，为了使大多数生物活性蛋白和多肽通过血脑屏障，需要大分子受体绕过血脑屏障的限制性通透性。因此，无论是用于脑成像对比剂配方还是开发脑穿透剂，都必须实现两个分子目标：更高的靶向选择性和更好的给药效果。实现这些目标的一个合理方法是了解生物活性配体如何选择性地与血脑屏障上的特定受体结合并通过其运输。然而，特定的大分子(Co)受体介导的转运之间的特性和相互依赖的功能关系，使细胞内吞作用到特定的细胞内间隔，仍然缺乏文献记载。增加生物活性分子在脑内递送的一个有吸引力的策略也是在细胞内靶向细胞器内专门递送它。因此，受体介导的配体细胞内转运/区隔过程在血脑屏障也仍有待更好的定义和理解。 我们研究计划的原创性：尽管多肽进入脑组织的过程部分是通过血脑屏障界面的低密度脂蛋白受体相关蛋白1(LRP1)发生的，但我们在LRP1/脑内皮细胞中发现了新的未被报道的代偿适应机制，这使我们能够假设通过来自硫酸肝素蛋白多糖和Vps10p结构域受体的新的大分子受体，交替的细胞转运过程具有重要意义。我们的研究计划带来技术进步的影响：通过检查脑内皮细胞和非内皮细胞类型的细胞外配体是否存在不同的内化和运输机制，我们将在分子水平上描绘细胞表面大分子受体的功能相互依赖。因此，识别新的大分子实体以调节跨血脑屏障的跨细胞作用的价值是双重的：作为帮助了解基本的体外分子和细胞运输过程的研究工具，以及作为解决有效靶向血脑屏障的重大机制需求的药理学工具。我们相信，我们的研究计划是原创的，因为它最终将为更好地选择血脑屏障表型提供理论依据，并有助于设计更好的脑内给药策略。因此，我们的研究计划产生的直接影响应该会激励未来一代生物偶联物选择性地与我们建议研究的受体结合。

Background: The blood-brain barrier (BBB) is a formidable gatekeeper toward exogenous substances, playing an important role in brain homeostasis for complex neuronal activities. Accordingly, in order for the majority of bioactive proteins and peptides to cross the BBB, macromolecular receptors are required to circumvent the BBB restrictive permeability. Whether it is for brain imaging contrast formulations or in the development of brain penetrating agents, two molecular goals must therefore be achieved : Greater targeting selectivity and better delivery efficacy. A rational approach to attain these goals is to understand how biologically active ligands can selectively bind to and be transported through specific receptors at the BBB. The identity and interdependent functional relationship between specific macromolecular (co)receptors-mediated transport, that enable endocytosis to specific intracellular compartments, remain however poorly documented. An attractive strategy to increase the intracerebral delivery of a bioactive molecule is also to specifically deliver it within an intracellular targeted organelle. Thus, receptor-mediated ligand intracellular trafficking/compartmentation processes also remain to be better defined and understood at the BBB. Originality of our research program: Although peptide transcytosis into brain tissue occurs, in part, via the low-density lipoprotein receptor-related protein 1 (LRP1) at the BBB interface, we have discovered novel undocumented compensatory adaptive mechanisms, in LRP1/brain endothelial cells, which allowed us to postulate for the significant involvement of alternate transcytosis processes through new macromolecular receptors from heparin sulfate proteoglycans and Vps10p-domain receptors. Impact of our research program leading to technology advancements: By examining whether different, yet undocumented, mechanisms exist for differential internalization and trafficking of extracellular ligands in both cerebral endothelial and non-endothelial cell types, we will delineate at the molecular level the functional interdependence of cell surface macromolecular receptors. The value of identifying new macromolecular entities that mediate transcytosis across the BBB is then two-fold: as research tools to help understand fundamental in vitro molecular and cellular transport processes, and as pharmacological tools to address the significant mechanistic needs to efficiently target the BBB. We are confident that our research program is original as it will ultimately provide rationale for greater targeting selectivity towards the BBB phenotype and help in the design of better intracerebral delivery strategies. As such, an immediate impact derived from our research program should inspire the future generation of bioconjugates to selectively bind to those receptors we propose to investigate.