Neural circuits of glucagon-like peptide-1 (GLP-1) action in health and disease

肥胖、糖尿病和高血压等合并症是患者的严重健康负担，也是公共资源的压力。可能对治疗这些疾病有益的有希望的药物是胰高血糖素样肽-1 （GLP-1）类似物。GLP-1是一种由肠道在饭后分泌的激素。它的主要作用是促进糖的消化，并产生饱腹感。除了它们的抗糖尿病作用外，GLP-1类似物已被证明可引起恶心、轻度高血压和心动过速，这可能表明它在大脑中起作用。事实上，在大脑中微量注射GLP-1可以减少食物摄入并降低血糖。我们项目的目的是提高我们对大脑和肠道GLP-1信号在控制血糖和食物摄入中的相对重要性的认识，并澄清已经在临床使用的GLP-1类似物是否激活了大脑GLP-1系统。为了了解GLP-1在脑中的作用，有必要了解GLP-1受体（GLP-1R）在脑中的详细表达模式。此外，通过控制GLP-1R表达细胞的活性来操纵大脑中的GLP-1R，将能够澄清这些受体在体内的作用。我们将使用一种新型转基因小鼠（GLP-1R -cre），它在表达GLP-1R的神经元中同时表达红色荧光标记（RFP）和cree -重组酶，从而可以在体外鉴定这些细胞以及在体内用“柔性开关”病毒构建物进行基因靶向。我们将使用一种基因治疗方法，通过病毒将新基因传递到大脑特定区域的GLP-1R细胞中。这些基因将产生蛋白质，允许细胞特异性抑制GLP-1R细胞的活性，具有前所未有的时间和空间分辨率。通过测量抑制特定glp - 1r表达细胞群的活性对血糖控制、食物摄入和行为的影响，我们将能够梳理出glp - 1r表达中枢神经元所发挥的确切生理功能。利用这一小鼠细胞系，我们拟确定和验证GLP-1R表达细胞在小鼠脑中的精确分布。然后，我们将确定这些细胞在不同脑区域的功能意义，并通过电生理和光学Ca2+记录在体外表征表达GLP-1R的神经元群体。最后，我们将评估GLP-1类似物在大脑中的作用，以及在高脂肪饮食下是否会发生变化。该项目将阐明大脑GLP-1Rs的生理重要性，并提供关于稳定的GLP-1类似物激活中枢GLP-1Rs的重要信息。这对于理解GLP-1治疗期间可能观察到的潜在不良影响尤其重要。这些数据将进一步揭示基于glp -1的治疗的临床益处，可能不仅适用于糖尿病患者，还适用于更广泛的代谢性疾病。此外，它将提供诸如恶心等不良副作用的原因的信息，并澄清神经元GLP-1Rs是否在心血管疾病和嗅觉信号处理中起作用。由于GLP-1类似物已经在市场上用于治疗2型糖尿病，我们期望从这个项目中获得的知识将用于药物开发和配方，从而在不久的将来有望对治疗产生影响。

Obesity, diabetes and co-morbidities, such as hypertension, are a serious health burden for the patient and a strain on public resources. Promising drugs that might be beneficial for the treatment of these conditions are glucagon-like peptide-1 (GLP-1) analogues. GLP-1 is a hormone that is secreted from the gut after a meal. Its principal role is to improve the digestion of sugars, and to generate the sensation of fullness, or satiety. Besides their anti-diabetic actions, GLP-1 analogues have been shown to cause nausea, mild hypertension and tachycardia, possibly indicating action in the brain. In fact, microinjection of GLP-1 into the brain reduces food intake and lowers blood glucose. The aim of our project is to improve our knowledge of the relative importance of the brain and gut GLP-1 signalling in the control of blood sugar and food intake, and to clarify whether GLP-1 analogues, which are already in clinical use, activate the brain GLP-1 system. To understand GLP-1 action in brain it is imperative to know the detailed expression pattern of the GLP-1 receptor (GLP-1R) in brain. In addition, manipulation of GLP-1R in the brain, by controlling the activity of GLP-1R expressing cells, would enable clarification of the role of these receptors in vivo. We will use a novel transgenic mouse (glp-1r-cre) that expresses both a red fluorescent label (RFP) and cre-recombinase in GLP-1R expressing neurons, and thus allows in vitro identification of these cells as well as their genetic targeting with 'flex-switch' virus constructs in vivo. We will use a gene therapy approach where new genes are delivered by a virus to GLP-1R cells in specific areas of the brain. These genes will produce proteins allowing cell-specific suppression of the activity of GLP-1R cells with unprecedented temporal and spatial resolution. By measuring the effects of inhibiting the activity of specific GLP-1R-expressing cells groups on blood glucose control, food intake and behaviour, we will be able to tease out the exact physiological function played by GLP-1R-expressing central neurons. Using this mouse line we propose to define and validate the precise distribution of GLP-1R expressing cells in mouse brain. We will then determine the functional significance of these cells in different brain regions and characterise the GLP-1R expressing neuron populations in vitro by electrophysiological and optical Ca2+ recordings. Finally, we will assess the action of GLP-1 analogues in brain and whether it changes under high fat diet. This project will clarify the physiological importance of brain GLP-1Rs and provide vital information regarding activation of central GLP-1Rs by stable GLP-1 analogues. This is especially important for understanding potential unwanted effects that may be observed during GLP-1 therapy. These data will provide further insight into the clinical benefit of GLP-1-based treatments, possibly not only for patients with diabetes, but more generally in metabolic disease. Furthermore, it will provide information on the cause of undesired side effects such as nausea, as well as clarifying whether there is a role for neuronal GLP-1Rs in cardiovascular disease and in olfactory signal processing. Since GLP-1 analogues are already on the market for the treatment of type 2 diabetes, we expect that the knowledge from this project will feed into drug development and formulation, and thus an influence on therapy could be hoped for in the near future.