Uncovering mechanisms of phagocytosis by class A scavenger receptors

吞噬作用是一个进化上保守的过程，可能起源于单细胞生物促进营养吸收，随后成为多细胞生物宿主防御和体内平衡的必要条件。巨噬细胞A类清道夫受体是非声速吞噬受体，可识别多种天然（如细菌、修饰脂蛋白）和合成配体。与其他非声速吞噬受体一样，它们的细胞质区域没有传统的信号基序，但在配体识别和摄取时却传递了大量的信息。我们假设清扫剂受体含有以前未表征的基序，有助于吞噬和促炎信号，可通过这些目标进行测试；1)利用古代和现代遗传学发现清道夫受体的功能域。2)发现脂质组成和瞬时脂质相在清道夫受体摄取中的作用。3)了解细胞定位如何影响清道夫受体信号传导。尝试使用传统的生化技术来发现新的信号基序，已经为摄取所需的残基提供了见解，但并不像在听觉受体中的类似研究那样富有成果。我们已经证明（PMID:23181696），发现这些受体中进化保守和分化区域的系统发育方法为将功能归因于特定序列提供了丰富而强大的方法，并将在（Obj 1）中扩展和完善这种方法，包括对古代（前哺乳动物）和现代（灵长类动物）的研究。我们最近发现，清道夫受体可能更多地依赖于与膜脂的相互作用来启动吞噬作用听觉受体（如Fc受体）。我们将使用高分辨率显微镜来阐明这些脂质相互作用，以跟踪清道夫受体在膜中的迁移（实验2）。我们还确定清道夫受体与其他先天免疫受体（即toll样受体）协同作用，但它们对信号传导的贡献是基于它们是定位于质膜还是内体膜的根本不同。我们已经开发了许多分子生物学和细胞生物学分析来剖析这种相互作用（Obj 3），并相信这可能是迄今为止未描述的“微调”细菌生理反应的机制。我的研究计划的长期目标是了解非听觉吞噬受体的信号传导过程。由于吞噬受体对于低等生物的营养获取、宿主防御和多细胞性以及高等生物的稳态和宿主防御至关重要，因此了解这些受体的信号传导能力将有助于解决许多生物学问题。

Phagocytosis is an evolutionarily conserved process that likely originated to facilitate nutrient uptake in single-celled organisms and subsequently became essential to host-defence and homeostasis in multi-cellular organisms. The macrophage class A scavenger receptors are non-opsonic phagocytic receptors that recognize a number of natural (e.g. bacteria, modified lipoproteins) and synthetic ligands. Like other non-opsonic phagocytic receptors, they have no conventional signalling motifs in their cytoplasmic domains and yet transmit a phenomenal amount of information upon ligand recognition and uptake. We hypothesize that that the scavenger receptors contain previously uncharacterized motifs that contribute to phagocytosis and pro-inflammatory signalling, testable by these objectives;1) Discover functional domains in the scavenger receptors using ancient and modern genetics.2) Discover the role of lipid composition and transient lipid phases in scavenger receptor uptake. 3) Understand how cellular localization affects scavenger receptor signalling. Attempts to use traditional biochemical techniques to discover novel signalling motifs have provided insights into residues required for uptake, but have not been as fruitful as similar studies in opsonic receptors. We have shown (PMID:23181696) that a phylogenetic approach to discover evolutionarily conserved and divergent areas within these receptors provides a rich and robust method of attributing function to specific sequences and will expand and refine this approach in (Obj 1) by including studies of ancient (pre-mammalian) and modern (primates "> We have recently discovered that the scavenger receptors may depend more heavily on interactions with membrane lipids to initiate phagocytosis than the opsonic receptors (e.g. Fc receptors). We will elucidate these lipid interactions using high resolution microscopy to track scavenger receptor mobility in membranes (Obj 2). We have also determined that scavenger receptors collaborate with other innate immune receptors (i.e. the toll like receptors) but that their contribution to signalling is fundamentally different based on whether they are localized to the plasma membrane or the endosomal membrane. We have developed a number of molecular biology and cellular biology assays to dissect this interaction (Obj 3) and believe that this may be a heretofore undescribed mechanism of "fine-tuning" physiological responses to bacteria. The long-term goal of my research program is to understand the signalling processes of the non-opsonic phagocytic receptors. Since phagocytic receptors are essential for nutrient acquisition, host defence and multi-cellularity in lower organisms, and homeostasis and host defence in higher organisms, understanding the signalling capacity of these receptors will contribute to many biological questions.