Defining signal selection from the free fatty acid receptor FFA4; implications for physiological functions

G蛋白偶联受体(GPCRs)是一个蛋白质大家族，主要位于细胞表面，是细胞和身体组织外部环境变化的感受器。尽管GPCR家族的成员已经是最成功的药物靶标，但他们中相对较少的人还没有以这种方式成为靶标。我们认为这是由于缺乏对许多GPCR的基本生物学基础的了解，以及缺乏药理工具化合物和适当的动物模型来测试它们在正常生理和疾病背景下的体内功能。尽管传统上被认为是被设计来检测和指示细胞对各种激素和神经递质浓度的变化做出反应，但近年来已经变得明显的是，相当数量的GPCR被设计为直接对食物消化产生的代谢物的变化做出反应，并通过这样做，提醒身体器官协调对营养缺乏或过剩的反应。鉴于目前正在上升到流行比例的许多疾病，如糖尿病和肥胖症，都是由摄入明显过量的高热量食物和缺乏锻炼的“西方生活方式”发展而来的，那么模仿或阻止GPCR对这些代谢产物的影响可能会有有益的影响。事实上，对于我们计划详细研究的受体，被称为游离脂肪酸受体4(FFA4)，对其激活时调节血糖水平的能力的了解，以及提高激素胰岛素的有效性，导致制药业正在努力评估激活FFA4是否可能是治疗II型糖尿病的新方法。像许多其他GPCRs一样，FFA4由体内各种类型的细胞表达，这导致了激活或阻止这种受体在其他情况下也可能有好处。很明显，FFA4可以通过控制许多不同的信号通路来指示细胞做出反应，在拟议的研究中，我们计划揭开这种复杂性，并了解哪些信号在不同类型的细胞和组织中占主导地位，以及这如何决定激活FFA4的结果。我们将通过多种方式做到这一点。最令人兴奋和重要的是利用小鼠的细胞和组织，在我们目前对BBSRC资助的这种受体的研究中，我们已经通过基因工程表达了一种形式的FFA4，它只能与所谓的G蛋白相互作用，而不能与拦阻蛋白相互作用。阻滞素是一组关键的信号蛋白，与激活的FFA4强烈相互作用。比较FFA4在正常和arrestin相互作用缺陷小鼠细胞和组织中的功能的研究将提供这一信息，这将在从不同类型的脂肪细胞到免疫系统细胞的组织中进行检验。之所以选择这些药物，是因为FFA4被建议在从脂肪细胞发育和炎症到化疗中用于缩小癌症的药物如何产生耐药性等一系列领域发挥作用。除了这些宏大的总体目标，我们还计划开发和利用阻断FFA4作用的化学物质，这些化学物质在现有的基础上有了很大的改进，详细绘制了FFA4的表达模式，并利用我们从目前的BBSRC资金中开发的细胞，这些细胞已经进行了基因组编辑，以消除特定的信号通路子集，从而使我们能够评估激活FFA4的不同类型的分子是否可以选择性地控制FFA4的信号潜力。到拟议的研究结束时，FFA4将不再是一种研究较少的GPCR，我们将能够自信地指出，调节这种受体是否可能是治疗糖尿病以外的“西方生活方式”疾病的一种手段。

G protein-coupled receptors (GPCRs) are a large family of proteins, located predominantly at the surface of cells, that act as sensors of changes in the external environment of cells and tissues of the body. Although members of the GPCR family are already the most successful class of drug targets, relatively few of them have yet been targeted in this way. We believe this is due to a lack of understanding of the basic underpinning biology of many GPCRs, and a paucity of pharmacological tool compounds and appropriate animal models to test their in vivo function in both normal physiology and in the context of disease. Although traditionally viewed as being designed to detect and instruct cells to respond to alterations in the concentration of various hormones and neurotransmitters, in recent times it has become clear that a substantial number of GPCRs are designed to respond directly to alterations in metabolites that are produced by digestion of foodstuffs and, in so doing, they alert organs of the body to co-ordinate responses to either a dearth or a surplus of nutrients. Given that many diseases that are currently rising to epidemic proportions, e.g. diabetes and obesity, develop from a 'Western lifestyle' of intake of a marked excess of highly calorific foods and a lack of exercise, then mimicking or blocking the effects of the GPCRs for such metabolic products may have beneficial effects. Indeed, for the receptor we plan to study in detail, which is called free fatty acid receptor 4 (FFA4), understanding of its ability when activated to regulate blood glucose levels, and to increase the effectiveness of the hormone insulin, has resulted in ongoing efforts by the pharmaceutical industry to assess if activation of FFA4 might be a novel approach to treat type II diabetes.Like many other GPCRs, FFA4 is expressed by range of types of cells in the body, leading to suggestions that either activating or blocking this receptor might also have benefits in other conditions. It is clear that FFA4 can instruct cells to respond by controlling a number of different signalling pathways and in the proposed studies we plan to unravel this complexity and to understand which signals are predominant in different types of cells and tissues and how this determines the outcome of activating FFA4. We will do this in a number of ways. One of the most exciting and important will be to utilise cells and tissues from mice, that in our current studies on this receptor that BBSRC have funded, we have genetically engineered to express a form of FFA4 that can only interact with so called G proteins and not with arrestins. Arrestins are a key set of signalling proteins that interact strongly with activated FFA4. Studies that compare functions of FFA4 in cells and tissues from normal and arrestin-interaction deficient mice will provide this information, and this will be examined in tissues that range from different types of fat cells, to cells of the immune system. These have been selected because of the roles FFA4 has been suggested to play in areas that range from fat cell development and inflammation, to how resistance develops to drugs that are used to shrink cancers in chemotherapy. In parallel with these large, overarching objectives we also plan to develop and utilise chemicals that block the actions of FFA4 that are much improved on those currently available, map in detail the expression pattern of FFA4 and employ cells we have developed from current BBSRC funding that have been 'genome-edited' to eliminate specific subsets of signalling pathways to allow us to assess if different types of molecule that activate FFA4 can selectively control the signalling potential of FFA4. By the end of the proposed studies FFA4 will no longer be a poorly studied GPCR and we will be in position to state with some confidence if regulating this receptor might be a means to treat 'Western lifestyle' diseases beyond diabetes.