Signaling Mechanisms in Stem Cell Plasticity

描述（由申请人提供）：造血干细胞（hsc）长期以来被认为仅限于形成淋巴和髓系的血细胞。居住在骨髓微环境中的造血干细胞可以在动物的一生中重新填充受照射移植受体的造血系统，使造血干细胞成为基因治疗应用的重要靶点。然而，最近的研究表明，造血干细胞的一个亚部分可能有能力促进不同的细胞类型，如神经元、肝细胞和肌细胞。这些令人惊讶的发现与长期存在的教条相矛盾，并为鉴定和表征这些潜在的多能干细胞开辟了一个重要的新领域。最近的研究显示骨髓细胞群对诱发性心肌梗死的治疗效果。虽然这些研究表明造血干细胞在直接注射、骨髓移植或细胞因子诱导动员后具有成为功能性心肌细胞的潜力，但这些研究具有高度侵入性，需要精细的小鼠手术。我们建议建立一种更简单的方法，即通过注射阿霉素诱导小鼠心肌病，从而为蒽环类药物的癌症化疗提供一种具有临床意义的损伤模型。该方法将用于测试造血干细胞心脏分化潜力，并将确定gp130/STAT3信号通路的激活是否促进HSC对心肌细胞再生的贡献。gp130/STAT3通路激活胚胎基因表达程序，导致心脏中心肌营养因子和血管内皮生长因子的肥大和水平升高。目的1将确定在心肌细胞中过度表达STAT3的转基因小鼠是否会提供一个最佳微环境，以刺激骨髓来源的前体细胞最大程度地分化心脏。目的2将确定供体骨髓细胞中STAT3的过表达是否会为心脏分化提供细胞内在的选择性优势。对具有这种潜力的细胞进行前瞻性鉴定可以规避使用人类胚胎干细胞的担忧。由于这种发育可塑性可能被用于创造新的干细胞疗法，因此需要产生有效的转分化潜力测定系统。干细胞介导的组织再生信号机制的表征是一个新的研究领域，对于理解干细胞对各种环境刺激反应背后的调节机制至关重要。

DESCRIPTION (provided by applicant): Hematopoietic stem cells (HSCs) have long been regarded as restricted to formation of blood cells of both the lymphoid and myeloid lineages. HSCs residing in the bone marrow microenvironment can repopulate the hematopoietic system of irradiated transplant recipients for the lifetime of the animal making HSCs important targets for gene therapy applications. However, recent studies have suggested that a subfraction of HSCs may have the ability to contribute to diverse cell types such as neurons, hepatocytes, and myocytes. These surprising findings contradict the long-standing dogma and have opened an important new field of investigation into identification and characterization of these potential pluripotent stem cells. Recent studies have shown the therapeutic efficacy of bone marrow cell populations following induced myocardial infarction. While these studies have suggested that HSCs have potential to become functional cardiomyocytes following direct injection, bone marrow transplant, or cytokine-induced mobilization, these studies are highly invasive and require delicate mouse surgery. We propose to establish a simpler method by inducing cardiomyopathy following injection of mice with doxorubicin, thus providing an injury model that is also clinically relevant for cancer chemotherapy with anthracycline drugs. This approach will be used to test for hematopoietic stem cell cardiac differentiation potential and will determine whether activation of the gp130/STAT3 signaling pathway promotes HSC contribution to cardiomyocyte regeneration. The gp130/STAT3 pathway activates an embryonic gene expression program resulting in hypertrophy and increased levels of cardiotrophin and vascular endothelial growth factor in the heart. Aim #1 will determine whether transgenic mice overexpressing STAT3 in cardiac cells will provide an optimal microenvironment to stimulate maximal cardiac differentiation from bone marrow derived precursor cells. Aim #2 will determine whether overexpression of STAT3 in donor bone marrow cells will provide a cell intrinsic selective advantage for cardiac differentiation. Prospective identification of cells with this potential could circumvent concerns about using human embryonic stem cells. Generation of systems for efficient assay of transdifferentiation potential are needed since this developmental plasticity might be exploited to create new stem cell therapies. Characterization of signaling mechanisms involved in stem cell-mediated tissue regeneration represents a new area of research that will be critical for understanding the regulatory mechanisms behind the response of stem cells to diverse environmental stimuli.