Dichotomous Effects of MT1-MMP on Adipose Tissue Remodeling

摘要 在快速膨胀的脂肪组织（AT）中，普遍性缺氧刺激大量诱导缺氧诱导的脂肪组织（AT）。 因子1 α（HIF 1 α），进而引发纤维化和局部炎症，最终导致胰岛素抵抗。 AT通过上调MMPs（一种切割胶原的内肽酶家族）来响应纤维化。MT1-MMP 基质金属蛋白酶14（MMP 14）是AT中的主要胶原酶，其在肥胖脂肪垫中上调。MT 1-MMP如何上调 以及MT 1-MMP激活的功能性后果在很大程度上仍是未知的。有趣的是， 我们最近发现了一种新的胶原蛋白6消化产物（我们称之为内营养素）， 以及不健康AT的局部炎症。然而，参与的MMPs和详细的消化事件仍然存在， 仍然在很大程度上未知。基于初步观察，假设MT 1-MMP负责 以产生内营养素。MT 1-MMP可能基于不同的 肥胖AT的代谢背景：一方面，在AT扩张的早期阶段，MT 1-MMP切割ECM， 蛋白质释放对脂肪细胞的高压，从而试图保持健康状况;另一方面， 另一方面，在肥胖AT重塑的晚期，它会抑制异常积累的胶原6α3，并产生 内营养因子进一步增强纤维化和炎症，最终导致微环境高度 不利于新陈代谢的灵活性。为了验证这一假设，本研究有三个具体目的：1）。到 探讨HIF 1 α在肥胖AT MT 1-MMP上调中的作用; 2）.为了确定MT 1-MMP是否 在肥胖发展的早期阶段发挥抗纤维化和促血管生成活性;和3）.为了确定 MT 1-MMP是否通过消化异常积聚的胶原6α3而产生内营养因子， 肥胖发展后期的脂肪垫。HIF 1 α模型的功能获得和功能丧失将 实现目标1。饮食诱导的肥胖和多西环素（Dox）诱导的AT特异性MT 1-MMP 转基因小鼠模型将用于目标2和3。具体地，MT 1-MMP的过表达将被抑制。 在肥胖发展的“早期阶段”和“晚期阶段”，在AT中诱导。内营养素生成，纤维化 将检测AT中的炎症并表征转基因小鼠中的代谢表型 在不同的代谢环境下。为了进一步研究内营养因子在形成不健康的 微环境，AT特异性内营养因子过表达和抗内营养因子中和抗体 将使用经处理的小鼠模型。内营养因子刺激局部神经元的分子机制 将在小鼠中进一步研究纤维化和炎症。 这项研究的结果将增强对AT生理学复杂性的总体理解， 强调了MT 1-MMP在肥胖发展过程中AT重塑动力学中的中心作用。因此，我们认为， 抑制MT 1-MMP和由MT 1-MMP产生内营养因子具有很大的治疗前景 肥胖和肥胖相关代谢紊乱的前景。

Abstract In rapidly expanding adipose tissue (AT), pervasive hypoxia stimulates massive induction of Hypoxia Induced Factor 1 α (HIF1α), which in turn initiates fibrosis and local inflammation ultimately leading to insulin resistance. AT responds to the fibrosis by up-regulating MMPs, a family of endopeptidases that cleave collagens. MT1-MMP (MMP14) is the major collagenase in AT that is up-regulated in obese fat pads. How MT1-MMP is up-regulated and what are the functional consequences of the activation of MT1-MMP remain largely unknown. Interestingly, we recently identified a novel collagen 6 digestion product (we refer to it as endotrophin) which stimulates fibrosis and inflammation locally in unhealthy AT. However, the participating MMPs and detailed digesting event still remain largely unknown. Based on the preliminary observations, it is hypothesized that MT1-MMP is responsible for the digestion event to produce endotrophin. MT1-MMP might have dichotomous effects based on different metabolic contexts in obese AT: On the one hand, at early-stage of AT expansion, MT1-MMP cleaves ECM proteins to release the high pressure on fat cells, thus attempting to maintain healthy conditions; On the other hand, at the late-stage of obese AT remodeling, it digests abnormally accumulated collagen 6α3 and produces endotrophin which further enhances fibrosis and inflammation, ultimately leading a microenvironment highly unfavorable for metabolic flexibility. To test the hypothesis, the current study has three specific Aims: 1). To investigate the role of HIF1α in upregulation of MT1-MMP in obese AT; 2). To determine whether MT1-MMP exerts anti-fibrotic and pro-angiogenic activity at early-stage of obesity development; and 3).To determine whether MT1-MMP produces endotrophin by digesting abnormal accumulating collagen 6α3 to shape unhealthy fat pads in late-stage of obesity development. Both gain-of-function and loss-of-function of HIF1α models will be applied to achieve Aim 1. Diet-induced obese and doxycycline (Dox)-inducible AT specific MT1-MMP transgenic mouse models will be used for Aim 2 and 3. Specifically, the overexpression of MT1-MMP will be induced in AT during both “early-stage” and “late-stage” of obesity development. Endotrophin production, fibrosis and inflammation in AT will be detected and metabolic phenotypes in the transgenic mice will be characterized under different metabolic contexts. To further study the role of endotrophin in shaping unhealthy microenvironment, both AT specific endotrophin overexpression and anti-endotrophin neutralizing antibody treated mouse models will be utilized. The molecular mechanism by which endotrophin stimulates the local fibrosis and inflammation will be further investigated in the mice. Findings from the study will enhance the general understanding of the complexity of AT physiology and highlight the central role of MT1-MMP in the dynamics of AT remodeling during obesity development. Therefore, inhibition of MT1-MMP and endotrophin produced by MT1-MMP bears great promise from a therapeutic perspective for obesity and obesity related metabolic disorders.