Fox01 in Beta-Cell Compensation

描述(申请人提供)：β细胞代偿是一种适应性机制，�细胞通过增加胰岛素分泌来克服胰岛素抵抗或氧化应激，以维持肥胖患者的正常血糖。β细胞代偿最终导致�细胞团的扩张和/或胰岛素合成/分泌的上调。�细胞不能补偿胰岛素抵抗或氧化应激导致胰岛素不足和显性糖尿病。多么 �细胞补偿胰岛素抵抗或氧化应激，而导致�细胞衰竭的原因却知之甚少。Foxo1是一种转录因子，它将胰岛素(或IGF-1)信号整合到细胞生存、增殖、分化、代谢和抗氧化的靶基因中。具有FOXO1基因变异的人类与�细胞功能障碍和2型糖尿病的风险增加有关。我们发现，在胰岛中使用RIP(大鼠胰岛素启动子)诱导产生FoxO1的转基因小鼠可以预防脂肪诱导的葡萄糖耐量异常和链脲佐菌素诱导的糖尿病。这一效应归因于葡萄糖刺激的胰岛素分泌增加和RIP-FoxO1转基因小鼠�细胞质量的增加。Foxo1活性在胰岛中上调，与饮食肥胖小鼠�细胞代偿的生理诱导相关。这些新的数据强调了FOXO1在�细胞功能中的重要性，刺激了FOXO1参与�细胞代偿的假说。为了解决这一假设，我们提出了三个具体目标：1)确定FOXO1功能增强对�细胞胰岛素抵抗补偿的影响；2)探讨FOXO1增强�细胞对氧化应激的补偿的机制；以及3)确定FOXO1功能丧失对肥胖和糖尿病�细胞补偿的影响。为了实现这些目标，我们将使用基因转移、转基因表达、基因敲除和siRNA介导的基因沉默方法来实现�细胞特异性FoxO1的产生，并在体内和体外的人胰岛中选择性地条件性地去除FoxO1，然后确定具有FoxO1得失功能的�细胞补偿胰岛素抵抗和氧化应激的能力。我们已经提供了原则性证明，并论证了该建议的可行性。该项目的完成将加深我们对糖尿病�细胞代偿和�细胞衰竭机制的理解。

DESCRIPTION (provided by applicant): Beta-cell compensation is an adaptive mechanism by which �-cells increase insulin secretion to overcome insulin resistance or oxidative stress for maintaining euglycemia in obesity. Beta-cell compensation culminates in the expansion of �-cell mass and/or upregulation of insulin synthesis/secretion. Failure of �- cells to compensate for insulin resistance or oxidative stress contributes to insulin insufficiency and overt diabetes. How �-cells compensate for insulin resistance or oxidative stress and what causes �-cell failure are poorly understood. FoxO1 is a transcription factor that integrates insulin (or IGF-1) signaling to target genes in cell survival, proliferation, differentiation, metabolism and anti-oxidation. Human with genetic FoxO1 variants are associated with an increased risk of �-cell dysfunction and type 2 diabetes. We show that transgenic mice with RIP (rat insulin promoter)-directed FoxO1 production in islets are protected against fat-induced glucose intolerance and streptozotocin-elicited diabetes. This effect is attributable to augmented glucose-stimulated insulin secretion and increased �-cell mass in RIP-FoxO1 transgenic mice. FoxO1 activity is upregulated in islets, correlating with the physiological induction of �-cell compensation in dietary obese mice. These new data underscore the importance of FoxO1 in �-cell function, spurring the hypothesis that FoxO1 contributes to �-cell compensation. To address this hypothesis, we propose three specific aims: 1) To determine the effect of FoxO1 gain-of-function on �-cell compensation for insulin resistance; 2) To address the mechanisms by which FoxO1 enhances �-cell compensation for oxidative stress; and 3) To determine the effect of FoxO1 loss-of-function on �-cell compensation in obesity and diabetes. To achieve these goals, we will employ gene transfer, transgenic expression, gene knockout and siRNA-mediated gene-silencing approaches to achieve �-cell specific FoxO1 production and alternatively conditional FoxO1 depletion in mature islets in vivo as well as in human islets ex vivo, followed by determining the ability of �-cells with FoxO1 gain- vs. loss-of-function to compensate for insulin resistance and oxidative stress. We have provided proof-of-principle and demonstrated the feasibility for the proposal. Accomplishing this project will deepen our understanding of the mechanisms of �-cell compensation and �- cell failure in diabetes.