Liver-islet and intra-islet cross talk in alpha cell hyperplasia and beta cell regeneration

摘要 在评估胰升糖素受体拮抗剂(GRAs)维持血糖稳态的可能性时 T1D啮齿动物，我们注意到GRAS促进β−细胞存活和再生。值得注意的是，GRA治疗的小鼠 维持正常血糖，即使在停止治疗后也是如此。我们最近公布的数据 提示：1)切除或拮抗胰高血糖素受体(GCGR)可钝化细胞凋亡并刺激 小鼠功能性β细胞团的再生；2)这种新的胰岛素+细胞团大部分来自于 将α−细胞前体转化为胰岛素产生细胞；3)GRAS恢复可持续的正常血糖和胰岛素 糖尿病NOD小鼠和移植了人胰岛的小鼠的生产。我们的初步结果表明， β-GRAS的细胞营养效应既通过胰岛自主效应，也通过众所周知的肝脏- α细胞轴4-7，通过AA依赖机制触发α细胞增殖(图1)。我们有 Foxn3是一种高血糖素反应转录抑制因子，也是血糖8-11的新介体，被鉴定为 先前未定义的整合因子，可通过它改变氨基酸代谢。与此同时，我们有 确定了GRA驱动的成纤维细胞生长因子2(FGF2)的上调，成纤维细胞生长因子2是增殖的靶点 转录共因子是相关蛋白1(YAP1)，在Sox9+导管细胞中表达，作为关键 GRA介导的胰岛内再生生态位复兴的贡献者。我们假设损害了 胰高血糖素通过改变氨基酸代谢促进Foxn3介导的α细胞增殖 以及在胰岛内由成纤维细胞生长因子2介导的再生生态位，以允许在T1D中将α细胞转化为β细胞。我们会 使用一组新颖的、经过验证的、唯一适合的小鼠模型来评估我们的假设，这些模型有助于 我们对胰高血糖素信号丢失与肝脏利用改变的机制的遗传剖析 氨基酸，α细胞增殖，以及通过两个目标恢复功能性β细胞群。1)使用恐慌- Attac糖尿病小鼠、培养的小鼠胰岛和培养的人胰岛，我们将检测胰岛自主 胰升糖素受体拮抗或消融对β细胞存活和β细胞再生的影响。2)我们会 肝移植后检测α细胞增殖、β细胞存活和功能性β−细胞团的再生 Foxn3基因的缺失或过表达。

ABSTRACT While evaluating the potential for glucagon receptor antagonists (GRAs) to maintain glucose homeostasis in T1D rodents, we noted that GRAs promote β−cell survival and regeneration. Remarkably, GRA-treated mice maintained normal blood glucose, even after the treatment was withdrawn. Our recently published data suggest that: 1) ablation or antagonism of the glucagon receptor (GcgR) blunts apoptosis and stimulates regeneration of functional β-cell mass in mice; 2) much of this new insulin+ mass derives from the conversion of α−cell precursors into insulin-producing cells; and 3) GRAs restore sustainable euglycemia and insulin production in diabetic NOD mice and in mice grafted with human islets. Our preliminary results suggest that the β-cytotrophic effects of GRAs occur through both islet autonomous effects and through a well described liver- α-cell axis4-7 which triggers α-cell hyperplasia through AA-dependent mechanisms (Figure 1). We have identified Foxn3, a glucagon-responsive transcriptional repressor and novel mediator of glycemia8-11, as the previously-undefined integrator by which glucagon alters amino acid metabolism. In parallel, we have identified the GRA-driven upregulation of fibroblast growth factor 2 (FGF2), a target of the proliferative transcriptional co-factor Yes-associated protein 1 (YAP1) that is expressed in Sox9+ ductal cells, as a key contributor to GRA-mediated revival of a regenerative niche within the islet. We hypothesize that impaired glucagon action promotes hepatic Foxn3-mediated α-cell hyperplasia via changes in amino acid metabolism and an FGF2-mediated regenerative niche within the islet to allow α-cell to β-cell conversion in T1D. We will evaluate our hypothesis using a cadre of novel, validated, and uniquely-suited mouse models which facilitate our genetic dissection of the mechanisms linking the loss of glucagon signaling to altered hepatic utilization of amino acids, α-cell hyperplasia, and the restoration of functional β-cell mass via two aims. 1) Using PANIC- ATTAC diabetic mice, cultured murine islets, and cultured human islets, we will examine the islet-autonomous effects of glucagon receptor antagonism or ablation on β-cell survival and β-cell regeneration. 2) We will examine α-cell hyperplasia, β-cell survival and the regeneration of functional β−cell mass after liver-specific deletion or overexpression of Foxn3.