Stem cell niche and Wnt in liver injury and regeneration.

描述（申请人提供）：卵形细胞是成年肝祖细胞，在肝脏再生中起生理作用，具有吸引人的治疗潜力。它们被认为居住在门户周边区域的一个壁龛中。然而，损伤后激活卵圆细胞的信号尚不清楚。Wnt蛋白家族在多种哺乳动物组织的成体干细胞维持中发挥重要作用。Wnt信号也参与肝脏的发育和修复。有证据表明，Wnt信号是激活卵圆细胞的损伤反应的核心。在组织修复中，一个主要的未解之谜是损伤如何导致重建组织所必需的信号的激活。在一项新的研究中，Nusse实验室已经确定了一种转录控制元件（称为CAIRE，即Cis Acting Injury Responsive element），它控制Wnt在损伤反应中的表达。通过使用与该增强子相关的报告基因，已经在各种组织中检测了CAIRE功能。在初步工作中，实验室已经证明它位于肝脏的门静脉周围区域，并对损伤作出反应。假设是CAIRE在肝损伤激活卵形细胞区室时被激活。它通过驱动局部Wnt表达来诱导卵圆细胞增殖，这是再生反应所必需的。CAIRE上游存在一个特定的信号通路，控制CAIRE活性和Wnt表达。拟议的研究将解决这些假设。首先，CAIRE在三种表现出不同程度卵圆细胞激活的不同形式的肝损伤中的作用将被检查。CAIRE报告基因表达在激活卵圆细胞群的损伤中是预期的。接下来，将产生CAIRE有条件激活Wnt抑制剂Dkk的转基因小鼠，以确定由CAIRE驱动的局部Wnt信号是否需要用于卵圆细胞再生反应。Wnt抑制预计会导致损伤后卵圆细胞再生减少。最后，将确定结合和激活CAIRE的转录因子。生物信息学将用于识别与CAIRE结合的潜在转录因子。将检查这些因素是否与CAIRE直接结合。基于这些结果，将在CAIRE内的转录因子结合位点进行突变。转基因小鼠将用于评估功能丧失。预计这些小鼠的卵圆细胞再生反应会降低。这些研究将为Wnt表达的上游激活因子提供第一个证据。他们将进一步证明Wnt信号在肝损伤和随后涉及卵形细胞的再生反应中的关键作用。最后，结果将深入了解生态位在连接损伤反应和组织再生中的作用。

DESCRIPTION (provided by applicant): Oval cells are adult liver progenitor cells that play a physiologic role in liver regeneration and have attractive therapeutic potential. They are believed to reside in a niche within the periportal region. However, the signals that activate oval cells after injury are not known. The Wnt family of proteins plays important roles in adult stem cell maintenance in a variety of mammalian tissues. Wnt signaling is also involved in liver development and repair. Evidence suggests that Wnt signaling is central to the injury response that activates oval cells. A main unanswered question in tissue repair is how injury leads to activation of the signals necessary for rebuilding the tissue. Pursuing a novel line of research, the Nusse lab has identified a transcriptional control element (called CAIRE, for Cis Acting Injury Responsive Element) that governs the expression of Wnt in response to injury. Through the use of reporter genes linked to this enhancer, CAIRE function has been examined in various tissues. In preliminary work, the lab has shown that it is in the periportal region of the liver and responds to injury. The hypothesis is that CAIRE undergoes activation in response to liver injury that activates the oval cell compartment. It induces oval cell proliferation by driving local Wnt expression, which is required for the regenerative response. A specific signaling pathway exists upstream of CAIRE that controls CAIRE activity and Wnt expression. The proposed studies will address these hypotheses. First, the role of CAIRE in three distinct forms of liver injury that exhibit different degrees of oval cell activation will be examined. CAIRE reporter expression is expected in injury that activates the oval cell population. Next, transgenic mice in which CAIRE conditionally activates the Wnt inhibitor Dkk will be generated to determine if local Wnt signaling driven by CAIRE is required for the oval cell regenerative response. Wnt inhibition is expected to result in decreased oval cell regeneration after injury. Lastly, transcription factors that bind to and activate CAIRE will be identified. Bioinformatics will be used to identify potential transcription factors that bind to CAIRE. These factors will be examined for direct binding to CAIRE. Based on these results, mutations will be made in transcription factor binding sites within CAIRE. Transgenic mice will be made to assess for loss-of- function. These mice are expected to have decreased oval cell regenerative response. These studies will provide the first evidence of an upstream activator of Wnt expression. They will add to the evidence for a key role for Wnt signaling in liver injury and the subsequent regenerative response involving oval cells. Lastly, the results will give insight into the role of the niche in linking the injury response to tissue regeneration.