Fibro-adipogenic remodeling of the diaphragm in obesity-associated respiratory dysfunction

摘要： 肥胖相关的呼吸道并发症包括从单纯性劳累呼吸困难到危及生命的肥胖。 换气不足综合征(OHS)。后者，由PaCO2&>45 Torr定义为体重指数的个体 (BMI)30 kg/m2且无其他原因引起高碳酸血症，与严重的心脏并发症和 死亡率上升。而肺对腹部和胸部脂肪组织的扩张能力是 被认为是导致这种呼吸系统损害的原因，临床研究也发现呼吸肌无力。 肥胖的病人。此外，OHS受试者的横隔膜中可见大的脂肪细胞包涵体，而OHS患者中未见。 肥胖/正常血糖或偏瘦的个体。这些发现表明，横隔膜本身可能受到 肥胖；然而，过度营养对这块肌肉的结构和功能的影响还没有很好的定义。在小鼠身上 根据长期饮食诱导肥胖(DIO)的时间进程，我们在6个月后观察到高碳酸血症 脂肪饮食(HFD)喂养。这在时间上与隔肌功能受损相对应--评估于 体内通过超声检查，体外通过测量收缩力。脂肪组织扩张与胶原蛋白 隔膜内的沉积在时间上对应于高碳酸血症，并与EX 活体收缩缺陷。谱系追踪显示所有的隔膜内脂肪细胞和许多产生胶原的细胞 细胞来源于纤维造脂前体细胞(FAPs)，这是一种骨骼肌间充质干细胞群体。 FAP数量、增殖和胶原沉积随肥胖增加而增加。 我们假设FAP介导的、纤维-成脂的隔膜重塑损害了呼吸。 在肥胖中的作用。在目标1中，我们将测试肥胖本身是否会通过以下方式损害呼吸和横隔膜功能 分析体重匹配的遗传肥胖和DIO小鼠。在体外，我们将测量收缩功能和 大肌分离和单个肌纤维的被动僵硬来确定生物力学缺陷 发生在组织或细胞水平。最后，我们将确定隔膜内的定量相关性 脂肪细胞数和聚合胶原与这些生理参数的关系。在目标2中，我们专门测试 FAP介导肥胖症患者横隔膜纤维成脂重塑和功能障碍的假说。我们会 用全球基因表达谱和体外增殖、脂肪生成分析FAP对肥胖的反应 胶原沉积定量。然后我们将确定(白喉毒素介导的)FAP消融术 预防DIO模型中的横隔膜纤维成脂改变和功能障碍。在目标3中，我们将分析组织 从人体尸检样本中分离的样本和FAP，以确定肥胖者是否发生类似的变化 人类，并与临床OHS诊断有关。这项工作将定义OHS的细胞机制；以及 该项目的完成将提供肌肉生物力学、RNA-Seq和人体样本分析方面的培训。

Abstract: Obesity-associated respiratory complications range from simple dyspnea on exertion to life-threatening obesity hypoventilation syndrome (OHS). The latter, defined by PaCO2 >45 torr in individuals with body mass index (BMI) >30kg/m2 and no alternative cause of hypercapnia, is associated with severe cardiac complications and increased mortality. While inability of the lungs to expand against abdominal and thoracic adipose tissue is thought to drive this ventilatory compromise, clinical studies have also identified respiratory muscle weakness in obese patients. Moreover, large adipocyte inclusions are seen in diaphragms of subjects with OHS but not in obese/normocapnic or lean individuals. These findings suggest the diaphragm itself may be compromised with obesity; however, impacts of over-nutrition on structure and function of this muscle are not well defined. In mice subjected to a long-term diet-induced obesity (DIO) time course, we observed hypercapnia after 6 months high fat diet (HFD) feeding. This temporally corresponded with impaired diaphragm muscle function—assessed in vivo by ultrasonography and ex vivo by measurement of contractile force. Adipose tissue expansion and collagen deposition within the diaphragm temporally corresponded with hypercapnia and quantitatively correlated with ex vivo contractile deficits. Lineage tracing showed all intra-diaphragmatic adipocytes and many collagen-producing cells to arise from fibro-adipogenic progenitors (FAPs), a skeletal muscle mesenchymal stem cell population. FAP number, proliferation, and collagen deposition increased with obesity. We hypothesize that FAP-mediated, fibro-adipogenic remodeling of the diaphragm impairs ventilatory function in obesity. In Aim 1, we will test whether obesity per se impairs ventilation and diaphragm function by analyzing weight-matched genetically obese and DIO mice. Ex vivo, we will measure contractile function and passive stiffness of large muscle isolates and individual myofibers to determine whether biomechanical defects occur at the tissue or cellular level. Finally, we will determine quantitative correlations of intra-diaphragmatic adipocyte number and polymerized collagen with these physiologic parameters. In Aim 2, we specifically test the hypothesis that FAPs mediate diaphragm fibro-adipogenic remodeling and dysfunction in obesity. We will analyze FAP response to obesity with global gene expression profiling and ex vivo proliferation, adipogenesis and collagen deposition quantification. We will then determine whether (diphtheria toxin-mediated) FAP ablation prevents diaphragm fibro-adipogenic changes and dysfunction in a DIO model. In Aim 3, we will analyze tissue samples and FAPs isolated from human autopsy samples to determine whether similar changes occur in obese humans and associate with clinical OHS diagnosis. The work will define a cellular mechanism of OHS; and completion of the project will provide training in muscle biomechanics, RNA-Seq and human sample analysis.