Muscle homeostasis: role of the microvascular niche

背景/理论依据：在正常肌肉稳态和修复过程中，炎症反应被启动以移除受损的肌纤维。这伴随着强健的血管生成，恢复受损肌肉的血流，以及激活通常静止的肌肉驻留卫星细胞（SCs）或其他肌肉祖细胞群（MPCs），这些细胞迁移到损伤部位形成新的肌纤维。然而，一个基本且未解决的问题是，激活的SCs/MPCs与微血管内皮细胞（ECs）和周细胞/壁细胞如何在诱导炎症反应后相互作用，以促进有效的组织修复。尽管越来越多的证据表明血管生成素/Tie2信号通路参与了这一过程，但由于传统的免疫组织学方法在高分辨率下检测这些参数的能力有限，微血管细胞群体的异质性及其与血流动力学和肌肉修复的关系仍然知之甚少。总体目标：实施和测试一种新的肌肉特异性干细胞/祖细胞跟踪系统，由我的团队在过去的NSERC DG资助下开发，结合先进的随荧光共聚焦/活体显微镜（IVM）技术来评估肌肉修复过程中复杂的细胞间关系。短期目标：1)利用我们的新型细胞跟踪系统和先进的外显荧光共聚焦显微镜/ IVM技术来评估SCs/MPCs， ECs和微血管周细胞/壁细胞之间的细胞间相互作用，以及由我们的报告基因转基因（Tg）小鼠模型建立的类器官培养中的炎症细胞。2)评估调节：(a) SC/MPC激活；(b)诱导或阻断炎症反应后，Tg小鼠类器官培养物中的微血管。3)如上所述，在体内Tg小鼠完整后肢肌肉损伤部位，评估类器官中SCs/MPCs、微血管和炎症细胞之间的细胞间相互作用。将进行常规生物力学测试。4)评估Tg小鼠完整后肢肌肉损伤部位的干细胞/祖细胞、微血管和炎症细胞的调节。再次进行生物力学测试。长期目标：通过结合PET成像，建立工具/动物模型开发，使我们能够无创地评估这些细胞群在活体动物中的归巢/迁移。影响：研究旨在缩小我们目前对正常肌肉稳态和修复过程中肌肉干/祖细胞归巢、血管生态位和炎症细胞之间关系的理解的明显差距，这对于在肌肉的自然稳态和修复能力耗尽或受损时恢复肌肉质量和功能至关重要。这需要开发前沿的、新颖的工具/动物模型。

Background/rationale: During normal muscle homeostasis and repair, an inflammatory response is initiated to remove damaged myofibers. This is accompanied by robust angiogenesis to restore blood flow to the damaged muscle as well as activation of normally quiescent muscle-resident satellite cells (SCs) or other muscle progenitor cell populations (MPCs) that migrate to the site of injury to form new myofibers. However, a fundamental and unanswered question is how activated SCs/MPCs and endothelial cells (ECs) and pericyte/mural cells of the microvasculature interact following induction of an inflammatory response to facilitate efficient tissue repair. While a growing body of evidence implicates the Angiopoietin/Tie2 signaling pathway in this process, heterogeneity in microvascular cell populations and their relationships to hemodynamics and muscle repair is still poorly understood due to the limited ability of traditional immunhistological methods to examine these parameters at high resolution. Overarching goal: To implement and test a novel musclespecific stem/progenitor cell tracking system, developed by my group with past NSERC DG funding, in conjunction with advanced epifluorecence confocal/intravital microscopy (IVM) technologies to assess complex intercellular relationships during muscle repair. Short-term Aims: 1) To utilize our novel cell tracking system and advanced epifluorecence confocal microscopy/ IVM technologies to assess intercellular interactions between SCs/MPCs, ECs and pericyte/mural cells of the microvasculature, and inflammatory cells in organoid cultures established from our reporter gene transgenic (Tg) mouse model. 2) To assess modulation of: (a) SC/MPC activation; (b) microvasculature in organoid cultures established from Tg mice following induction or blocking of an inflammatory response. 3) To assess, as above for organoids, intercellular interactions between SCs/MPCs, microvasculature, and inflammatory cells at a site of injury in the intact hind limb muscle of Tg mice in vivo. Routine biomechanical tests will be conducted. 4) To assess modulation of stem/progenitor cells, microvasculature and inflammatory cells at a site of injury in the intact hind limb muscle of Tg mice in vivo. Biomechanical tests again to be conducted. Longterm Objective(s): to build on tool/animal model development by incorporating PET imaging to allow us to noninvasively assess homing/migration of these cell populations in living animals. Impact: Studies aimed at closing the clear gap in our current understanding of the relationship between muscle stem/progenitor cell homing, the vascular niche and inflammatory cells during normal muscle homeostasis and repair are essential to restore muscle mass and function when the natural ability of muscle for homeostasis and repair is exhausted or impaired. This requires development of leading edge, novel tools/animal models.