Dichotomous Effects of MT1-MMP on Adipose Tissue Remodeling

摘要 在快速扩张的脂肪组织(AT)中，普遍的低氧刺激大量诱导低氧诱导 因子1α(HIF1α)，继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来应对纤维化，MMPs是一种裂解胶原蛋白的内肽酶家族。MT1-基质金属蛋白酶 (MMP14)是AT中的主要胶原酶，在肥胖的脂肪垫中上调。基质金属蛋白酶-1是如何上调的 而MT1-MMPs激活的功能后果在很大程度上还不清楚。有趣的是， 我们最近发现了一种新的6型胶原蛋白消化产物(我们称之为内营养素)，它可以刺激纤维化。 不健康的AT有局部炎症反应。不过，参与的MMPs和详细的消化活动仍然 在很大程度上仍然不为人知。根据初步的观察结果，推测MT1-MMPs可能与此有关 以使消化事件产生内营养素。MT1-基质金属蛋白酶可能基于不同的不同而产生二分作用 肥胖AT的代谢环境：一方面，在AT扩张的早期，MT1-MMP裂解ECM 蛋白质释放脂肪细胞的高压，从而试图保持健康的状态；另一方面 另一方面，在肥胖的AT重塑的晚期，它消化异常堆积的胶原6α3，并产生 内营养素，进一步增强纤维化和炎症，最终导致微环境高度 不利于代谢的灵活性。为了验证这一假设，目前的研究有三个具体目的：1)。至 2)探讨HIF1α在肥胖性AT中表达上调中的作用。以确定MT1-MMPs是否 在肥胖发展的早期阶段发挥抗纤维化和促血管生成的活性；以及3)。确定 基质金属蛋白酶1-基质金属蛋白酶是否通过消化异常堆积的胶原6α3而产生内营养素来塑造不健康 肥胖症发展晚期的脂肪垫。HIF1α模型的功能增益和功能损失都将 应用于实现目标1.饮食诱导的肥胖和多西环素(Dox)诱导的特异性MT1-MMP 转基因小鼠模型将用于目标2和目标3。具体地说，MT1-MMPs的过表达 在肥胖发展的“早期”和“晚期”，AT均被诱导。内营养素的产生、纤维化 将检测AT的炎症，并将表征转基因小鼠的代谢表型 在不同的代谢环境下。进一步研究内营养素在塑造不健康中的作用 AT特异性内营养素过度表达和抗内营养素中和抗体的微环境 将使用经过处理的小鼠模型。内营养素刺激局部血管内皮细胞的分子机制 将在小鼠身上进一步研究纤维化和炎症。 这项研究的结果将加强对AT生理学和房颤复杂性的总体理解 突出MT1-MMPs在肥胖症发生过程中AT重塑动力学中的核心作用。因此， 抑制MT1-MMPs和由MT1-MMPs产生的内营养素具有很大的治疗前景 肥胖及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.