Department of Respiratory Medicine, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, Maastricht, The Netherlands.
Am J Physiol Lung Cell Mol Physiol. 2012 Jan 1;302(1):L103-10. doi: 10.1152/ajplung.00084.2011. Epub 2011 Oct 14.
Loss of diaphragm muscle strength in inflammatory lung disease contributes to mortality and is associated with diaphragm fiber atrophy. Ubiquitin (Ub) 26S-proteasome system (UPS)-dependent protein breakdown, which mediates muscle atrophy in a number of physiological and pathological conditions, is elevated in diaphragm muscle of patients with chronic obstructive pulmonary disease. Nuclear factor kappa B (NF-κB), an essential regulator of many inflammatory processes, has been implicated in the regulation of poly-Ub conjugation of muscle proteins targeted for proteolysis by the UPS. Here, we test if NF-κB activation in diaphragm muscle and subsequent protein degradation by the UPS are required for pulmonary inflammation-induced diaphragm atrophy. Acute pulmonary inflammation was induced in mice by intratracheal lipopolysaccharide instillation. Fiber cross-sectional area, ex vivo tyrosine release, protein poly-Ub conjugation, and inflammatory signaling were determined in diaphragm muscle. The contribution of NF-κB or the UPS to diaphragm atrophy was assessed in mice with intact or genetically repressed NF-κB signaling or attenuated poly-Ub conjugation, respectively. Acute pulmonary inflammation resulted in diaphragm atrophy measured by reduced muscle fiber cross-sectional area. This was accompanied by diaphragm NF-κB activation, and proteolysis, measured by tyrosine release from the diaphragm. Poly-Ub conjugation was increased in diaphragm, as was the expression of muscle-specific E3 Ub ligases. Genetic suppression of poly-Ub conjugation prevented inflammation-induced diaphragm muscle atrophy, as did muscle-specific inhibition of NF-κB signaling. In conclusion, the present study is the first to demonstrate that diaphragm muscle atrophy, resulting from acute pulmonary inflammation, requires NF-κB activation and UPS-mediated protein degradation.
在炎症性肺部疾病中，膈肌肌肉力量的丧失导致死亡率升高，并与膈肌纤维萎缩有关。泛素（Ub）26S-蛋白酶体系统（UPS）依赖性蛋白分解，在许多生理和病理条件下介导肌肉萎缩，在慢性阻塞性肺疾病患者的膈肌肌肉中升高。核因子 kappa B（NF-κB）是许多炎症过程的基本调节剂，已被牵连到 UPS 靶向肌肉蛋白多 Ub 连接的调节中。在这里，我们测试 NF-κB 在膈肌中的激活以及随后由 UPS 进行的蛋白降解是否是肺部炎症引起的膈肌萎缩所必需的。通过气管内注入脂多糖诱导小鼠急性肺部炎症。在膈肌肌肉中测定纤维横截面积、体外酪氨酸释放、蛋白多 Ub 连接和炎症信号传导。通过具有完整或遗传抑制 NF-κB 信号或减弱多 Ub 连接的小鼠，分别评估 NF-κB 或 UPS 对膈肌萎缩的贡献。急性肺部炎症导致膈肌纤维横截面积减少，从而导致膈肌萎缩。这伴随着膈肌 NF-κB 的激活和通过从膈肌释放酪氨酸来测量的蛋白水解。膈肌中多 Ub 连接增加，肌肉特异性 E3 Ub 连接酶的表达也增加。多 Ub 连接的遗传抑制可预防炎症引起的膈肌肌肉萎缩，肌肉特异性抑制 NF-κB 信号也是如此。总之，本研究首次证明了急性肺部炎症引起的膈肌肌肉萎缩需要 NF-κB 激活和 UPS 介导的蛋白降解。
