SGK1 is a regulator of islet beta cell mass and secretory function

在肥胖和胰岛素抵抗的早期阶段，胰岛β细胞大量扩张。相反，糖尿病患者的胰岛β细胞数量减少，功能减弱，这表明胰岛β细胞的扩张和丧失是受信号诱导调节的动态过程。利用发出胰岛素需求信号或产生胰岛素抵抗的外部信号，我们质疑啮齿动物和人类β细胞中基因表达的变化，以寻找与生长和增殖途径相关的可诱导基因。这种方法产生了血清和糖皮质激素诱导的激酶1(SGK1)，它在暴露于细胞因子、葡萄糖、糖皮质激素和脂类后迅速上调。因此，我们创造了在胰腺β细胞中缺乏SGK1的小鼠，以解决根本上重要的问题：抑制胰岛β细胞中的SGK1是否会阻止它们在卡路里超载和胰岛素抵抗状态下的扩张能力？我们的初步数据显示，在高脂肪喂养期间，β细胞中SGK1的缺失限制了胰岛质量的扩张。有趣的是，抑制β细胞中的SGK1可以增加体内和体外的胰岛素分泌，从而改善全身的葡萄糖耐量。基于这些初步数据，我们假设限制β细胞的增殖具有改善刺激-分泌耦合以促进胰岛素分泌的额外好处。为了检验这一总体假设，我们提出了以下目标。具体目标1将研究SGK1如何调节β细胞质量，以响应产生胰岛素需求的信号。使用我们的初步数据建立在体内的方法，使用SGK1β细胞缺失的小鼠，我们将使用两种已建立的实验范式来研究β细胞增殖的早期变化：高脂喂养和持续葡萄糖输注。具体目标2将研究促进增殖和胰岛素分泌改变的机制。在这一目标中，我们提出了几种体外综合分析，通过结合RNA测序技术和基于稳定同位素示踪剂的代谢组学分析来解决支持增殖和胰岛素分泌的关键途径。这些研究与其他机制方法相结合，旨在揭示热量过剩如何改变底物使用以驱动β细胞质量扩张，以及重要的是，SGK1抑制如何限制这种反应以改善代谢结果。完成这些目标将揭示关键的SGK1依赖的分子事件，这些分子事件负责调节热量超负荷、肥胖和胰岛素抵抗期间胰岛β细胞生长和分泌功能的变化。总的来说，这些研究的结果有望为未来针对细胞生长机制的治疗设计提供参考，这些机制对诊断和治疗代谢性疾病非常重要。

Pancreatic beta-cell mass expansion occurs in the early stages of obesity and insulin resistance. Conversely, humans with diabetes have reduced numbers and diminished function of pancreatic beta-cells, indicating that islet beta-cell expansion and loss are dynamic processes subject to signal-induced regulation. Using external cues that signal demand for insulin, or that produce insulin resistance, we queried changes in gene expression in rodent and human beta-cells for inducible genes linked with growth and proliferation pathways. This approach yielded the serum and glucocorticoid inducible kinase 1 (SGK1), which is rapidly upregulated after exposure to cytokines, glucose, glucocorticoids, and lipids. Thus, we created mice lacking SGK1 in pancreatic beta-cells to address the fundamentally important question: does inhibition of SGK1 in islet beta-cells block their ability to expand during states of caloric overload and insulin resistance? Our preliminary data shows that SGK1 deletion in beta-cells restricts islet mass expansion during high-fat feeding. Intriguingly, SGK1 inhibition in beta-cells augmented insulin secretion in vitro and in vivo, resulting in improved whole-body glucose tolerance. Based on these preliminary data, we hypothesize that restricting beta-cell proliferation has the added benefit of improving stimulus-secretion coupling to promote insulin secretion. To test this overarching hypothesis, the following aims are proposed. Specific Aim 1 will investigate how SGK1 regulates beta-cell mass in response to signals that create a demand for insulin. Using in vivo approaches that build on our preliminary data using mice with beta- cell deletion of SGK1, we will investigate the early changes in beta-cell proliferation using two established experimental paradigms: high-fat feeding and continuous glucose infusion. Specific Aim 2 will investigate the mechanisms underlying enhanced proliferation and alterations in insulin secretion. In this aim, we propose several ex vivo comprehensive analyses to address key pathways supporting proliferation versus insulin secretion by coupling RNA sequencing techniques with stable isotope tracer-based metabolomics analyses. These studies, in combination with additional mechanistic approaches, are designed to reveal how substrate usage is altered by caloric excess to drive beta-cell mass expansion and importantly, how SGK1 inhibition limits this response to improve metabolic outcomes. Completing these Aims will reveal the critical SGK1-dependent molecular events responsible for regulating islet beta-cell changes in growth and secretory function during caloric overload, obesity, and insulin resistance. Collectively, the results of these studies are expected to inform the future design of therapies targeting cellular growth mechanisms important for diagnosing and treating metabolic diseases.