Uncovering mechanisms of phagocytosis by class A scavenger receptors

吞噬作用是一种进化上保守的过程，其可能起源于促进单细胞生物中的营养吸收，随后成为多细胞生物中宿主防御和稳态的必要条件。巨噬细胞A类清道夫受体是识别许多天然（例如细菌、修饰的脂蛋白）和合成配体的非调理吞噬受体。与其他非调理素吞噬细胞受体一样，它们在其胞质结构域中没有常规的信号传导基序，但在配体识别和摄取时传递大量信息。我们假设，清道夫受体含有以前未表征的基序，有助于吞噬和促炎信号，这些目标可测试：1）发现功能域的清道夫受体使用古代和现代遗传学。2）发现脂质成分和瞬时脂质相的清道夫受体摄取的作用。3)了解细胞定位如何影响清道夫受体信号传导。尝试使用传统的生物化学技术来发现新的信号基序提供了对摄取所需的残基的见解，但并没有像调理素受体中的类似研究那样富有成效。我们已经表明（PMID：23181696），发现这些受体内进化上保守和不同区域的系统发育方法提供了将功能归因于特定序列的丰富和稳健的方法，并且将通过包括古代（前哺乳动物）和现代（灵长类）的研究来扩展和改进（目标1）中的这种方法。我们最近发现，清道夫受体可能比调理素受体（例如Fc受体）更严重地依赖于与膜脂质的相互作用来启动吞噬作用。我们将阐明这些脂质相互作用，使用高分辨率显微镜跟踪清道夫受体在膜（目标2）的流动性。我们还确定了清道夫受体与其他先天性免疫受体（即toll样受体）协作，但它们对信号传导的贡献基于它们是否定位于质膜或内体膜而根本不同。我们已经开发了许多分子生物学和细胞生物学测定来剖析这种相互作用（目标3），并认为这可能是迄今为止未描述的对细菌的“微调”生理反应的机制。 我的研究计划的长期目标是了解非调理吞噬受体的信号传导过程。由于吞噬细胞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体内平衡和宿主防御是必不可少的，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.