Using a 'Designer Receptor Exclusively Activated by Designer Drug' to define the role of short chain fatty acids in metabolic disease and inflammation

食物通常被认为是身体的燃料来源。然而，最近已经清楚的是，我们所吃的成分也直接起作用来调节细胞和组织功能，或者被转化为这样做的分子。“健康饮食”的概念以及肠道中大量细菌如何协调和定义这一概念并不新鲜，但近年来，人们对饮食、健康和人类疾病之间关系的认识和兴趣大幅增长。例如，人们普遍认为“纤维”是健康饮食的重要组成部分。肠道中的微生物将“纤维”转化为短链脂肪酸（SCFAs），并且高水平的这些存在于肠道中并被运输到体内。在这两个位置中，这些SCFA被认为通过结合并激活称为游离脂肪酸受体（FFAR）2和FFAR 3的跨膜受体来产生它们的许多重要作用。FFAR 2和FFAR 3都是G蛋白偶联受体（GPCR）家族的成员，开发激活或阻断其他GPCR的药物已被证明是应对多种人类疾病的非常有效的方法。由于这些受体存在于许多组织上，包括控制炎症和免疫力的各种白色血细胞、储存脂肪的脂肪细胞和释放激素的下肠的各种细胞，这些激素反过来改变胰岛素从胰腺的释放并对进食欲望产生影响，因此它们被认为是从炎症性肠病到糖尿病的疾病中可能的靶向受体。然而，在做出针对任何受体可能是一种有效方法的长期决定之前，制药公司寻求“验证”，以尽可能地对这个想法产生信心。FFAR 2或FFAR 3的验证存在许多问题。首先，这两种受体被相同的SCFA激活。这意味着在两者都存在的细胞和组织中，很难确定哪一个是最重要的。以前克服这一问题的努力包括制造缺乏FFAR 2或FFAR 3的小鼠。虽然有用，但两者中的一个的缺失导致另一个的量的变化。其次，一些关键效应可能需要两者都存在。为了克服这一点，我们制造了一种FFAR 2，它不是被SCFA激活，而是被一种叫做山梨酸的分子激活。提出的一个关键计划是产生小鼠，其中FFAR 2的正常拷贝被这种工程变体取代。在这些动物中，FFAR 2和FFAR 3都将存在，但现在它们可以被不同的分子激活，这将使我们能够梳理出它们对功能的单独贡献。这将提供FFAR 2或FFAR 3在不同治疗适应症中的验证。当然，这是达到目的的一种手段，长期计划是开发针对FFAR 2和FFAR 3的选择性药物。申请人已经开始开发这样做的测定和方法，并且已经产生了许多药理学“工具”化合物以帮助进一步定义FFAR 2和FFAR 3的功能。然而，制药公司能够更好地将这些“工具”化合物转化为具有“药物样”特性的分子所需的技能，因此，可以用于测试在简单细胞系统和小鼠中开发的想法。因此，申请人已同意与制药公司阿斯利康的科学家在该项目中合作。在这些研究中，我们将为FFAR 2和FFAR 3提供一系列新的“工具”化合物，以提供进一步的见解，其结果将有助于公司做出关键决策，确定FFAR 2和/或FFAR 3是否被“验证”为开发有效药物的现实目标。

Food is often considered simply as a source of fuel for the body. However, in recent times it has become clear that components of what we eat either also act directly to regulate cellular and tissue functions or are converted into molecules that do so. The concept of a 'healthy diet' and how this might be orchestrated and defined by the vast number of bacteria that populate the intestine is not new but, in recent times, knowledge about and public interest in the relationship between diet, well-being and human disease has grown substantially. For example, it is widely recognised that 'fibre' is an important component of a healthy diet. Microbes in the gut convert 'fibre' into short chain fatty acids (SCFAs) and high levels of these are present in the gut and are transported into the body. In both of those locations such SCFAs are believed to produce many of their important roles by binding to and activating transmembrane receptors called free fatty acid receptor (FFAR)2 and FFAR3. Both FFAR2 and FFAR3 are members of the G protein-coupled receptor (GPCR) family and developing drugs that either activate or block other GPCRs has proved to be a very effective approach to tackling a wide range of human diseases. As these receptors are present on a number of tissues including various white blood cells that control inflammation and immunity, adipocytes that store fat, and various cells of the lower gut that release hormones that in turn modify release of insulin from the pancreas and have effects on the desire to eat, they are being considered as possible receptors to target in diseases that range from inflammatory bowel disease to diabetes. However, prior to making long term decisions that targeting any receptor is likely to be a productive approach, pharmaceutical companies seek 'validation', to generate as much confidence in the idea as possible. There are a number of issues in relation to validation of either FFAR2 or FFAR3. Firstly these two receptors are activated by the same SCFAs. This means that in cells and tissues in which both are present it is difficult to be certain which is most important. Previous efforts to overcome this have involved making mice that lack either FFAR2 or FFAR3. Although useful, the absence of one of the two results in change in amount of the other. Secondly, a number of key effects may require both to be present. To overcome this we have made a version of FFAR2 that instead of being activated by SCFAs is instead activated by a molecule called sorbic acid. A key plan proposed is to generate mice in which the normal copy of FFAR2 is replaced with this engineered variant. In these animals both FFAR2 and FFAR3 will be present but now they can be activated by different molecules and this will allow us to tease out their individual contributions to function. This will provide validation of either FFAR2 or FFAR3 in different therapeutic indications. Of course this is a means to an end and the long term plan is to develop selective medicines that target FFAR2 and FFAR3. The applicants have begun to develop assays and approaches to do this and have generated a number of pharmacological 'tool' compounds to help further define the function of FFAR2 and FFAR3. However, pharmaceutical companies are better able to bring the skills required to convert such 'tool' compounds into molecules that have 'drug-like' properties and, therefore, might be used to test ideas developed in either simple cell systems and in mice into humans. As such, the applicants have agreed to collaborate in this project with scientists from the pharmaceutical company AstraZeneca. In these studies we will be provided with a range of novel 'tool' compounds for FFAR2 and FFAR3 to provide further insight and the outcomes will assist the company in making key decisions on whether FFAR2 and/or FFAR3 become 'validated' as realistic targets to develop effective medicines against.