Control of intestinal regeneration by an Msi-mTORC1 signaling axis

 描述(申请人提供)：肠上皮是一种高度再生的组织，在动态平衡期间经历快速周转。损伤后不能有效地再生上皮，例如与放射治疗相关的肠病或与一系列外科手术相关的缺血-再灌注，可能会导致肠道屏障的破坏和细菌移位到血液中，导致炎症循环和进一步的上皮细胞死亡。损伤后的肠道动态平衡和再生由分级干细胞系统控制。这个系统包括休眠储备肠道干细胞(ISCs)，它们能产生活跃的、快速循环的隐窝基柱状干细胞(CBCs)，为正常的肠道内环境稳定提供动力。现役CBCs定期耗尽，并从储备的ISC隔间中更换。在辐射暴露等急性损伤的情况下，活跃的CBCs被破坏，促使储备干细胞集体激活。这些储备的ISCs分裂以补充CBC群体，CBC群体随后再生上皮并恢复屏障功能。面对严重的急性损伤，低效的上皮再生最终会导致较高的发病率和死亡率。因此，这项建议的目的是阐明储备干细胞驱动的肠上皮再生的分子机制，以便操纵这些机制来促进急性肠道损伤后的再生，或预防性地提前减轻损伤的影响。直到最近，控制储备干细胞激活的分子机制仍然难以捉摸。我们提供了初步数据，确定了已知的第一个控制储备干细胞激活的分子机制：MSI-mTORC1轴。我们证明，刺激MSI-mTORC1轴足以将储备的ISCs从静止状态驱动到细胞周期，并且MSI RNA结合蛋白家族功能的丧失会取消上皮的再生能力。我们的中心假设是，MSI-mTORC1轴的激活既是必要的，也是充分的，以推动储备ISC的激活和损伤反应中的上皮再生。我们将在体内测试1)MSI损伤后功能丧失时储备ISCs的命运，2)MSI的功能贡献 RNA结合靶向mTORC1激活、储备ISC激活和上皮再生，以及3)饮食调节如何影响mTORC1活性(mTORC1是一个主要的营养传感复合体)，以及随后储备ISC对损伤的再生反应。这些研究将为储备ISC活性的治疗操作找到新的切入点，以促进损伤后有效的上皮再生，或在损伤前预防性保护上皮。

 DESCRIPTION (provided by applicant): The intestinal epithelium is a highly regenerative tissue that undergoes rapid turnover during homeostasis. Failure to effectively regenerate the epithelium after injury such as the enteropathy associated with radiation therapy or ischemia-reperfusion associated with an array of surgical procedures can result in breakdown of the intestinal barrier and bacterial translocation into the bloodstream, leading to cycles of inflammation and further epithelial cell death. Intestinal homeostasis and regeneration after injury are governed by a hierarchical stem cell system. This system includes dormant reserve intestinal stem cells (ISCs) that give rise to active, rapidly cycling crypt base columnar stem cells (CBCs) that fuel normal intestinal homeostasis. The active CBCs periodically undergo exhaustion and are replaced from the reserve ISC compartment. In the context of acute injury such as radiation exposure, active CBCs are destroyed, driving the reserve stem cells to become activated en masse. These reserve ISCs divide to replenish the CBC population, which subsequently regenerates the epithelium and restores barrier function. In the face of severe acute injury, inefficient epithelial regeneration can ultimately lead to high morbidity and mortaliy. Thus, the goal of this proposal is to elucidate the molecular mechanisms underlying reserve stem cell-driven regeneration of the intestinal epithelium in order to manipulate these mechanisms to either enhance regeneration after acute intestinal injury, or to prophylactically mitigate the effects of injury in advance. Until recently, the molecular mechanisms governing reserve stem cell activation have remained elusive. We present preliminary data identifying the first molecular mechanism known to govern reserve stem cell activation: the Msi-mTORC1 axis. We demonstrate that stimulation of the Msi-mTORC1 axis is sufficient to drive reserve ISCs out of quiescence and into the cell cycle, and that loss of function of the Msi family of RNA binding proteins abolishes the regenerative capacity of the epithelium. Our central hypothesis is that activation of the Msi-mTORC1 axis is both necessary and sufficient to drive reserve ISC activation and epithelial regeneration in response to injury. We will test 1) the fate of reserve ISCs upon Msi loss of function in response to injury in vivo, 2) the functional contribution of Msi RNA binding targets to mTORC1 activation, reserve ISC activation, and epithelial regeneration, and 3) how dietary modulation effects mTORC1 activity (mTORC1 is a major nutrient sensing-complex), and subsequently the regenerative response of reserve ISC to injury. These studies will identify novel points for therapeutic manipulation of reserve ISC activity to either promote efficient epithelial regeneration after injury, or to prophylactically protect the epithelium in advance of injury.