MICA: Deciphering the mechanism of action of miR-125b in beta cells and its therapeutic potential in Diabetes

世界上超过8.5%的成年人患有糖尿病。如果治疗不当，糖尿病会导致非常高的血糖水平，使疾病恶化，并导致肾衰竭和失明等并发症，在2型糖尿病(T2D)的情况下，预期寿命缩短10年。胰岛β细胞负责在血糖升高时分泌胰岛素。胰岛β细胞不能分泌足够的胰岛素导致糖尿病的发生。重要的是，高血糖的流行加速了β细胞的衰竭，并通过尚不清楚的机制促进了β细胞的丧失。更好地了解导致β细胞衰竭的过程对于开发能够阻止T2D发展的药物至关重要。MiRNAs是一种小的RNA分子，本身不产生蛋白质，但能够降低其他蛋白质(它们的“靶标”)的产生速度。MicroRNAs存在于β细胞中，它调节重要的功能，如产生和分泌胰岛素的能力。此外，β细胞中某些miRNAs水平的变化与T2 D的发展有关。我们最近有三个重要的发现。首先，当老鼠和人类的β细胞暴露在高水平的葡萄糖中时，它们的miRNA miR-125b(miR-125b-5p)的水平会上升。其次，在小鼠的β细胞中引入额外的miR-125b会导致它们产生和分泌更少的胰岛素并患上糖尿病。我们还观察到，减少培养中的人β细胞miR-125b的数量可以提高它们对葡萄糖的反应分泌胰岛素的能力。因此，我们假设，选择性抑制β细胞miR-125b有可能保护β细胞功能不受高血糖的影响。第三，我们已经看到，高水平的miR-125b会导致溶酶体增大，而低水平的miR-125b会导致线粒体形态和线粒体功能相关基因含量的变化。溶酶体和线粒体是亚细胞细胞器，分别对细胞成分和废物的循环利用和能量生产非常重要。因此，我们假设miR-125b通过调节溶酶体和/或线粒体功能来调节β细胞的功能。此外，我们还证明了miR-125b的靶标是阳离子依赖的溶酶体甘露糖-6-磷酸受体(M6PR)，该受体将溶酶体的酶运输到溶酶体以实现其正常的功能。然而，M6PR在β细胞中对溶酶体和分泌功能的作用还没有被研究。因此，本提案的具体目的是确定：1.选择性地消除/减少β细胞中的miR-125b是否以及如何阻止T2D进展。MiR-125b在溶酶体和线粒体功能中的作用M6PR在β细胞中的作用为了达到这些目的，我们将使用在β细胞中选择性地缺失/过表达miR-125b的小鼠的组合。使用小鼠是必要的，因为维持葡萄糖稳态需要所有代谢组织之间的相互作用，因此这些实验需要在整个身体的背景下进行。-捐赠的人类胰岛，经过改造以或多或少含有miR-125b。人类样本的使用对于确保我们的发现可转化到临床上是至关重要的。-小鼠和人类β细胞系，经过修改，含有或多或少的miR-125b或M6PR，允许详细研究生物过程，并减少对动物的不必要使用。miRNAs是药物靶向的新候选药物，我们的研究将提供关于抑制β细胞miR-125b治疗T2D的潜在临床前数据。它还将为β细胞如何在健康和疾病中发挥作用提供新的基本见解，从长远来看，这可能揭示治疗糖尿病的新方法。

Over 8.5% of the world's adult population suffer diabetes. If poorly treated, diabetes leads to very high blood sugar levels which worsen the disease and lead to complications such as kidney failure and blindness, shortening life expectancy by 10 years in the case of type 2 diabetes (T2D). Pancreatic beta cells are in charge of secreting insulin in response to rises in blood sugar. Failure of beta cells to secrete enough insulin contributes to the development of diabetes. Importantly, the prevalence of high-blood sugar accelerates beta cell failure and contributes to beta cell loss by mechanisms which are not yet clear. A better understanding of the process leading to beta cell failure is vital for the development of drugs capable of stopping the development of T2D. MiRNAs are small RNA molecules that do not produce proteins themselves but are capable to reduce the rate at which other proteins (their "targets") are produced. MicroRNAs exist in beta cells that regulate important functions such as their capacity to produce and secrete insulin. Also, changes in the levels of certain miRNAs in beta cells are associated with the development of T2D.We have recently made three important findings. Firstly, when mouse and human beta cells are exposed to high levels of glucose, their levels of the miRNA miR-125b (miR-125b-5p) go up. Secondly, the introduction of additional miR-125b in the beta cells of mice causes them to produce and secrete less insulin and develop diabetes. We have also observed that reducing the amount of miR-125b in human beta cells in culture improves their capacity to secrete insulin in response to glucose. Accordingly, we hypothesize that beta cell selective inhibition of miR-125b has the potential to protect beta cell function from hyperglycaemia. Thirdly, we have seen that high levels of miR-125b lead to the appearance of enlarged lysosomes while low levels of miR-125b lead to changes in mitochondria morphology and in the content of genes related to mitochondrial function. Lysosomes and mitochondria are subcellular organelles very important for the recycling of cellular components and waste and for energy production, respectively. Thus, we hypothesize that miR-125b regulates beta cell function by modulating lysosomal and/or mitochondrial function. Both processes are essential for adequate beta cell function and are altered in diabetes.Additionally, we have demonstrated that miR-125b targets the cation-dependent lysosomal mannose-6-phosphate receptor (M6PR) which transports lysosomal enzymes to lysosomes for their adequate functioning. Nevertheless, the role of M6PR for lysosomal and secretory function in beta cells hasn't been studied.Thus, the specific aims of this proposal are to determine:1. Whether and how selective elimination/reduction of miR-125b in beta cells prevents T2D progression2. The role of miR-125b in lysosomal and mitochondrial function3. The function of M6PR in beta cellsTo achieve these aims we will use a combination of- Mice deleted for/overexpressing miR-125b selectively in beta cells. The use of mice is necessary since maintenance of glucose homeostasis requires interplay between all metabolic tissues and therefore these experiments need to be done in the context of the whole body. - Donated human islets, modified to contain more or less miR-125b. The use of human samples is essential to ensure the translatability of our findings to the clinic.- Mouse and human beta cell lines, modified to contain more or less miR-125b or M6PR, which allow to study biological processes in detail and reduces an unnecessary use of animals.MiRNAs are novel candidates for drug targeting and our study will provide preclinical data on the potential of beta cell miR-125b inhibition for the treatment of T2D. It will also provide new fundamental insights into how beta cells work in health and disease, which, in the long term, could reveal new ways to treat diabetes.