Regulation of Colon Epithelial Cell Survival by NRG4-ErbB4 Signaling

描述(申请人提供)：ErbB4受体酪氨酸激酶是由结肠上皮炎症诱导的，ErbB4过表达促进体外培养的结肠癌细胞存活，而不影响增殖或迁移。因此，ErbB4的诱导可能是一种旨在保护上皮的代偿反应。然而，为这一应用开发的初步数据显示，特定的ErbB4配体NeuRegin-4(NRG4)在人类IBD和小鼠结肠炎中都缺乏表达。此外，在小鼠结肠炎模型中，尽管ErbB4的表达增加，但它不被磷酸化/激活。这些结果表明，在炎症的背景下，NRG4下调导致信号不足，尽管ErbB4上调。进一步的初步研究表明，外源性NRG4在体外和体内都能保护结肠细胞免受细胞因子诱导的凋亡，并减轻急性小鼠DSS结肠炎的严重程度。因此，我们认为NRG4可用于在结肠炎过程中刺激ErbB4，从而抑制结肠细胞凋亡，改善病理。由于ErbB4(A)具有酪氨酸激酶所特有的配体结合特性和下游靶点，并且(B)可以直接与抗凋亡信号分子(例如PI3K、Src)和炎症介质(例如STAT1)结合，因此它具有作为新的选择性IBD治疗靶点的巨大潜力。然而，ErbB4在体内的结肠生物学中的作用以及对其选择性激活的结肠反应都还没有确定。因此，本项目旨在验证NRG4下调会加重结肠炎的假说，因此外源性NRG4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。计划中的实验将使用协调细胞培养、隐窝培养和体内模型来(1)确定NRG4-ErbB4功能丧失对结肠炎的影响并确定NRG4丢失的机制，(2)测试外源NRG4在结肠炎中的有效性，以及(3)确定NRG4诱导的结肠上皮细胞生存所需的信号通路。总之，这些研究将探索NRG4-ErbB4信号是治疗IBD的新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.