Biomechanical Regulation of Intra-Articular Adipose Tissue Inflammation

描述(申请人提供)：关节内脂肪组织是关节内一种重要的结构组织，越来越多地被认为是炎症的关键介质。调控关节内脂肪组织炎症的外在因素尚不清楚。确定这些因素及其影响关节炎症的分子机制将促进关节损伤和肌肉骨骼残疾的新治疗方法的发展。申请者的长期目标是开发治疗方法，通过识别促进关节炎症消退的生物力学和代谢因素来治疗和预防肥胖相关的骨关节炎。本应用侧重于关节内脂肪垫中炎症信号的机械生物学。本研究的目的是确定关节负荷对髌下脂肪垫(IFP)内炎性脂肪因子表达的影响，并确定脂肪组织巨噬细胞(ATM)是否介导了这一反应。中心假设是，运动引起的生理关节负荷诱导常驻ATM启动促纤维化反应，从而限制脂肪细胞肥大，从而减弱促炎症脂肪因子的表达。在IFP中，ATM作为机械敏感的促纤维化介质的假设和重点是基于全面的文献综述和申请者实验室产生的初步数据。这些发现表明，与皮下脂肪相比，IFP具有更高的促纤维化生长因子、纤维连接蛋白和细胞因子的表达。 初步的车轮跑步研究还表明，IFP是一种动态的结构组织，它会因运动而增加细胞外基质的沉积。在这些数据的指导下，该项目将使用两个特定的目标来检验这一假设：1)确定体内和体外生物力学刺激对巨噬细胞渗透、极化和IFP纤维化介质的时间过程；以及2)确定常驻ATM机对生物力学刺激的IFP纤维化和脂肪因子表达的要求。我们将使用一个公认的自主车轮运行的小鼠模型来评估增加IFP机械刺激对基因、蛋白质和细胞结果指标的影响。申请人的实验室还将利用体外组织压缩系统在大鼠IFP样本上进行压缩加载实验。在第二个目标下，在这些体内和体外模型中，使用脂质体氯屈膦酸盐来耗尽驻留的ATM，以确定ATM是否介导了生物力学刺激对IFP纤维化和脂肪因子表达的影响。这项研究意义重大，因为预计生物力学刺激将极大地促进关节内脂肪垫的旁分泌炎症信号功能。最终，这些知识有望导致开发新的治疗目标，用于预防或治疗涉及肌肉骨骼炎症和身体残疾的疾病的临床前测试。

DESCRIPTION (provided by applicant): Intra-articular adipose tissue is an important structural tissue within joints and is increasingly recognized as a critical mediator of inflammation. The extrinsic factors that regulate intra-articular adipose tissue inflammation are unknown. Identifying such factors and the molecular mechanisms by which they impact joint inflammation will advance the development of new treatments for joint injury and musculoskeletal disability. The applicant's long-term goal is to develop therapies to treat and prevent obesity-associated osteoarthritis by identifying biomechanical and metabolic factors that promote the resolution of joint inflammation. This application focuses on the mechanobiology of inflammatory signaling in intra-articular fat pads. The objective here is to identify the effect of joint loading on the expression of inflammatory adipokines within the infrapatellar fat pad (IFP) and to determine whether adipose tissue macrophages (ATMs) mediate this response. The central hypothesis is that physiologic joint loading due to exercise induces resident ATMs to initiate a pro-fibrotic response that restricts adipocyte hypertrophy and thereby attenuates pro-inflammatory adipokine expression. The hypothesis and focus on ATMs as mechano-sensitive pro-fibrotic mediators in the IFP is based on a comprehensive literature review and preliminary data generated in the applicant's laboratory. These findings indicate that compared to subcutaneous fat, the IFP has an elevated expression of pro-fibrotic growth factors, fibronectin, and cytokines. Preliminary wheel running studies also show that the IFP is a dynamic structural tissue that increases extracellular matrix deposition in response to exercise. Guided by these data, the project will test the hypothesis using two specific aims: 1) Determine the time-course of in vivo and ex vivo biomechanical stimulation on mediators of macrophage infiltration, polarization, and IFP fibrosis; and 2) Determine the requirement of resident ATMs on biomechanically-stimulated IFP fibrosis and adipokine expression. A well- established voluntary wheel running mouse model will be used to evaluate the effect of increased IFP mechanical stimulation on gene, protein, and cellular outcome measures. The applicant's lab will also utilize an ex vivo tissue compression system for conducting compressive loading experiments on rat IFP samples. Under the second aim, resident ATMs will be depleted in these in vivo and ex vivo models with liposomal clodronate to determine if ATMs mediate the effect of biomechanical stimulation on IFP fibrosis and adipokine expression. The proposed research is significant because it is expected that biomechanical stimulation will greatly contribute to the paracrine inflammatory signaling function of intra-articular fat pads. Ultimately, such knowledge is expected to lead to the development of novel therapeutic targets for pre-clinical testing in the prevention or treatment of diseases involving musculoskeletal inflammation and physical disability.