Regulation of Colon Epithelial Cell Survival by NRG4-ErbB4 Signaling

描述（由申请人提供）：ErbB 4受体酪氨酸激酶由结肠上皮炎症诱导，ErbB 4过表达促进体外结肠细胞存活，而不影响增殖或迁移。因此，ErbB 4诱导可能是一种旨在保护上皮的代偿反应。然而，为该应用开发的初步数据显示，特异性ErbB 4配体神经调节蛋白-4（NRG 4）的表达在人IBD和鼠结肠炎中都是缺乏的。此外，在鼠结肠炎模型中，尽管ErbB 4表达升高，但其未被磷酸化/活化。这些结果表明，在炎症的背景下，NRG 4下调导致信号传导不足，尽管ErbB 4上调。另外的初步研究表明，外源性NRG 4在体外和体内均保护结肠细胞免受苦参碱诱导的凋亡，并降低急性小鼠DSS结肠炎的严重程度。因此，我们建议NRG 4可以用来刺激ErbB 4在结肠炎，从而抑制结肠细胞凋亡和改善病理。由于ErbB 4（a）具有配体结合特性和在酪氨酸激酶中独特的下游靶点，并且（B）可以直接与两种抗凋亡信号分子（例如，PI 3 K，Src）和炎症介质（例如，STAT 1），其具有作为新型和选择性IBD治疗靶点的显著潜力。然而，ErbB 4在体内结肠生物学中的作用和结肠对其选择性激活的反应均未确定。因此，本项目旨在验证NRG 4下调导致结肠炎的假设，因此外源性NRG 4治疗可能通过激活结肠上皮细胞中的抗凋亡信号来改善结肠炎。计划的实验将使用协调的细胞培养、隐窝培养和体内模型来（1）确定NRG 4-ErbB 4功能丧失对结肠炎的影响并定义NRG 4丧失的机制，（2）测试外源性NRG 4在结肠炎中的有效性，以及（3）定义NRG 4诱导的结肠上皮细胞存活所需的信号传导途径。总之，这些研究将研究NRG 4-ErbB 4信号传导是IBD的新治疗途径的令人兴奋的可能性。

DESCRIPTION (provided by applicant): The ErbB4 receptor tyrosine kinase is induced by inflammation in the colon epithelium, and ErbB4 overexpression promotes colonocyte survival in vitro without affecting proliferation or migration. Thus, ErbB4 induction may be a compensatory response meant to protect the epithelium. However, preliminary data developed for this application show that expression of the specific ErbB4 ligand neuregulin-4 (NRG4) is deficient in both human IBD and murine colitis. Furthermore, in murine colitis models, although ErbB4 expression is elevated, it is not phosphorylated/activated. These results suggest that, in the context of inflammation, NRG4 downregulation leads to deficient signaling despite ErbB4 upregulation. Additional preliminary studies show that exogenous NRG4 protects colonocytes from cytokine-induced apoptosis both in vitro and in vivo, and reduces the severity of acute murine DSS colitis. We propose therefore that NRG4 could be used to stimulate ErbB4 during colitis, and thus to inhibit colonocyte apoptosis and improve pathology. As ErbB4 (a) has ligand binding properties and downstream targets that are unique among tyrosine kinases, and (b) can directly associate with both anti-apoptotic signaling molecules (e.g., PI3K, Src) and inflammatory mediators (e.g., STAT1), it has significant potential as a novel and selective IBD therapeutic target. However, neither the role of ErbB4 in colon biology in vivo nor the colonic response to its selective activation has been defined. Therefore, this project is designed to test the hypothesis that downregulation of NRG4 worsens colitis, and thus exogenous NRG4 treatment may improve colitis by activating anti-apoptotic signaling in colon epithelial cells. Planned experiments will use coordinated cell culture, crypt culture, and in vivo models to (1) determine the effects of loss of NRG4-ErbB4 function on colitis and define the mechanisms of NRG4 loss, (2) test the effectiveness of exogenous NRG4 in colitis, and (3) define signaling pathways which are required for NRG4-induced colon epithelial cell survival. Together, these studies will investigate the exciting possibility that NRG4-ErbB4 signaling is a novel therapeutic avenue for IBD.