Role of pericytes in pancreatic islet fibrosis

摘要 纤维化是 2 型糖尿病患者 (T2D) 胰岛最常见的病变，并导致年龄依赖性的糖尿病 胰岛功能受损。胰岛脉管系统缺陷损害内分泌细胞之间的交换 和血液，破坏胰岛结构并最终导致内分泌细胞死亡。的重要组成部分 脉管系统是周细胞，一种包裹小血管的收缩性平滑肌样细胞。在不同的 在器官中，周细胞已被证明可以分化为肌成纤维细胞，导致纤维化和器官 功能障碍。胰岛周细胞是否也有助于导致胰岛的促纤维化肌成纤维细胞池 衰老和 T2D 期间观察到的纤维化尚未确定。该提案的长期目标是 了解血管功能障碍在衰老和糖尿病中的作用。该项目的目标是 确定胰岛周细胞表型在胰岛素抵抗状态（例如衰老和 T2D）期间如何变化 以及导致这些变化的原因，结合使用体外和体内方法。中心假设 是，在衰老或 T2D 过程中，过度接触胰岛素会加剧哺乳动物的信号传导 周细胞中雷帕霉素（mTOR）的靶标，使周细胞分化为肌成纤维细胞。在我们的模型中，如 高胰岛素血症的发生是为了补偿胰岛素抵抗，胰岛周细胞暴露于更高水平的胰岛素 胰岛素。胰岛素过度激活周细胞中的 mTOR 信号传导，有利于其分化为肌成纤维细胞 和这些促纤维化细胞的增殖。拟议研究的基本原理是，结果将使得 对我们对周细胞在胰岛生物学中的作用的理解产生了持久的影响。如果假设正确，则 将证明周细胞对胰岛纤维化和糖尿病发病机制的基本贡献。的 因此，拟议的研究与 NIH 的使命相关，该使命涉及追求基本原理 关于生命系统的性质和行为的知识。在强有力的初步数据的指导下，我们的中央 假设将通过追求两个具体目标来检验：1）确定年龄和糖尿病引起的变化 胰岛周细胞的表型； 2) 确定mTOR依赖性胰岛素信号传导在周细胞中的作用 转分化。第一个目标是，我们将检查老年人和 T2D 周细胞表型的变化 小鼠和人类胰岛，并直接可视化从周细胞到肌成纤维细胞的表型转变 体内。在第二个目标下，我们将确定是否可以直接在体外和体内刺激胰岛周细胞 胰岛素触发促纤维化的肌成纤维细胞样表型。我们将进一步操纵 mTOR 信号 体内周细胞并测量对血管功能和葡萄糖稳态的影响。拟议的 研究意义重大，因为可以靶向周细胞来限制肌成纤维细胞的产生和 伴随衰老和 T2D 的胰岛纤维化过程中间质胶原蛋白的积累。重要的是，这些 研究有可能影响糖尿病的治疗方式。

Abstract Fibrosis is the most frequent lesion in the islets of type 2 diabetics (T2D) and contributes to the age-dependent impairment of islet function. Defects in islet vasculature compromise exchanges between the endocrine cells and the blood, disrupt islet architecture and ultimately lead to endocrine cell death. An important component of the vasculature is the pericyte, a contractile smooth muscle-like cell that wraps small blood vessels. In different organs, pericytes have been shown to differentiate into myofibroblasts, leading to fibrosis and organ dysfunction. Whether islet pericytes also contribute to the profibrotic myofibroblast pool that causes islet fibrosis observed during aging and T2D has not been determined. The long-term goal of this proposal is to understand the role of vascular dysfunction in aging and diabetes. The objectives of this project are to determine how the islet pericyte phenotype changes during insulin resistant states (such as aging and T2D) and what causes the changes, using a combination of in vitro and in vivo approaches. The central hypothesis is that, during aging or T2D, the excessive exposure to insulin exacerbates signaling through the mammalian target of rapamycin (mTOR) in pericytes, which makes them differentiate into myofibroblasts. In our model, as hyperinsulinemia develops to compensate for insulin resistance, islet pericytes are exposed to higher levels of insulin. Insulin overactivates mTOR signaling in pericytes, which favors their differentiation into myofibroblasts and proliferation of these profibrotic cells. The rationale for the proposed research is that the results will make a lasting impact on our understanding of the role of the pericyte in islet biology. If the hypothesis is correct, it would demonstrate the fundamental contribution of pericytes to islet fibrosis and diabetes pathogenesis. The proposed research is therefore relevant to the mission of the NIH that pertains to the pursuit of fundamental knowledge about the nature and behavior of living systems. Guided by strong preliminary data, our central hypothesis will be tested by pursuing two specific aims: 1) Identify age- and diabetes-induced changes in the phenotype of the islet pericyte; 2) Determine the role of mTOR-dependent insulin signaling in pericyte transdifferentiation. Under the first aim, we will examine changes in the pericyte phenotype in aged and T2D mouse and human islets, and directly visualize the phenotypic transition from pericytes to myofibroblasts in vivo. Under the second aim, we will determine if direct in vitro and in vivo stimulation of islet pericytes with insulin triggers a pro-fibrotic myofibroblast-like phenotype. We will further manipulate mTOR signaling in pericytes in vivo and measure the effects on vascular function and glucose homeostasis. The proposed research is significant because pericytes can be targeted to limit the generation of myofibroblasts and interstitial collagen accumulation during islet fibrosis that accompanies aging and T2D. Importantly, these studies have the potential to impact the way diabetes is treated.