Cell adhesion-dependent mechanisms of beta cell growth and homeostasis

本实验室最近发现，α E-连环蛋白是一种细胞粘附过程的调节剂，通过其作为Sonic Hedgehog（SHH）通路的抑制剂的功能，在胰岛细胞谱系的发育中起着关键作用。我们发现Pdx 1+多能胰腺祖细胞中α E-连环蛋白的缺失导致未成熟的双能Sox 9+祖细胞的积累。由于SHH通路的组成性激活，这些α E-cateninnull/Sox 9+祖细胞不能采用内分泌细胞表型。有趣的是，药物阻断这些α E-连环蛋白缺失/Sox 9+祖细胞中的SHH通路恢复了它们分化为表达激素的胰岛细胞的能力。最近，我们发现在人成年胰岛中通过siRNA暂时下调αE-catenin可以引起显著的β细胞复制。因此，基于这些结果，以及α E-连环蛋白也可以阻断Wnt信号传导的观点，我们假设在分化的胰岛细胞中，α E-连环蛋白可能代表另一种细胞周期进入的“制动器”，这是由于其对信号传导SHH和Wnt途径的相反功能，而这通常会促进细胞增殖。 为了验证这一假设，我们将集中研究以下具体目标：目标1：确定α E-连环蛋白在胚胎发育和出生后生活中，在生理条件下和损伤环境中作为β细胞生长调节剂的作用。在这些实验中，还将测试胚胎和出生后β细胞中α E-连环蛋白的条件性缺失是否会解除SHH和Wnt的抑制，进而预期引起细胞周期进入。在平行研究中，我们还将测试出生后α E-连环蛋白的条件性消融是否会增强β细胞损伤的链脲佐菌素模型中的β细胞再生，和/或对代谢应激源（如暴露于高脂饮食）的反应。 目标二：靶向α E-连环蛋白依赖性信号传导轴，用于体外和体内细胞移植模型中人胰岛细胞的体外扩增和导管细胞群的重编程。基于人胰岛细胞对促生长刺激表现出适度的反应倾向，这些研究将测试敲低人成人β细胞中的α E-连环蛋白是否会解除SHH和Wnt的抑制，并促进细胞增殖。将在通常从胰岛分离程序中丢弃的成人导管组织上测试类似的策略，以测试它们是否可以在体外和体内细胞移植模型中重新获得胚胎样分化为内分泌细胞的能力。 总的来说，我们暂时下调α E-连环蛋白表达、允许SHH途径去抑制的策略可能被证明是促进β细胞离体扩增和/或重新引导成人导管细胞分化能力的有力策略β细胞表型。因此，我们预计这些研究对糖尿病的细胞替代疗法具有重要的转化价值。

Our laboratory has recently discovered that αE-catenin, a regulator of cell adhesion processes, plays a critical role in the development of the islet cell lineage by virtue of its function as a repressor of the Sonic Hedgehog (SHH) pathway. We found that deletion of αE-catenin in Pdx1+ multipotent pancreatic progenitors results in the accumulation of immature bipotent Sox9+ progenitors. These αE-cateninnull/Sox9+ progenitors are unable to adopt an endocrine cell phenotype due to a constitutive activation of the SHH pathway. Interestingly, pharmacological blockade of the SHH pathway in these αE-cateninnull/Sox9+ progenitors restored their ability to differentiate into hormone expressing islet cells. More recently, we found that the temporal downregulation of αE-catenin by siRNA in human adult islets can elicit significant β-cell replication. Hence, based on these results, and on the notion that αE-catenin can also block Wnt signaling, we hypothesize that in differentiated islet cells αE-catenin may represent yet another “brake” on cell cycle entry by virtue of its opposing functions on signaling SHH and Wnt pathways that would normally promote cell proliferation. To test this hypothesis, we will focus our studies on the following Specific Aims: Aim 1: Determine the role of αE-catenin as a modulator of β-cell growth during embryonic development and in postnatal life, under physiologic conditions and in injury settings. In these experiments will also test if the conditional deletion of αE-catenin in embryonic and in postnatal β-cells will de-repress SHH and Wnt, which in turn are expected to elicit cell cycle entry. In parallel studies we will also test if the conditional ablation of αE-catenin in postnatal life will enhance β-cell regeneration in the streptozotocin model of β-cell injury, and/or in response to metabolic stressors such as exposure to high fat diet. Aim 2: Targeting αE-catenin-dependent signaling axis for the ex vivo expansion of human islet cells and for the reprogramming of ductal cell populations, both in vitro and in vivo in cell transplantation models. Based on the notion that human islet cells exhibit a modest propensity to respond to pro-growth stimuli, these studies will test if knocking down αE-catenin in human adult β-cells will de-repress SHH and Wnt, and foster cell proliferation. A similar strategy will be tested on human adult ductal tissue, usually discarded from islet isolation procedures, to test if they can regain an embryonic-like competency to differentiate into endocrine cells, both in vitro and in vivo in cell transplantation models. Collectively, our strategy to transiently down-regulate αE-catenin expression, allowing for the de-repression of the SHH pathway may prove as a powerful strategy to promote the ex vivo expansion of β-cells, and/or re-direct the differentiation competency of adult ductal cells toward a β-cell phenotype. Hence, we anticipate that these studies harbor significant translational value for cell replacement therapies in diabetes.