Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, National Jewish Health, Denver, Colorado; and.
Pharmacology Graduate Program and.
Am J Respir Crit Care Med. 2019 Nov 1;200(9):1113-1125. doi: 10.1164/rccm.201812-2311OC.
The loss of pulmonary endothelial cells in emphysema is associated with increased lung ceramide. Ceramide perturbations may cause adaptive alterations in other bioactive sphingolipids, with pathogenic implications. We previously reported a negative correlation between emphysema and circulating glycosphingolipids (GSLs). Glucosylceramide (GlcCer), the initial GSL synthesized from ceramide by GCS (GlcCer synthase), is required for embryonic survival, but its role in the lung is unknown. To determine if cigarette smoke (CS) alters lung GlcCer and to elucidate the role of GCS in lung endothelial cell fate. GlcCer was measured by tandem mass spectrometry in BAL fluid of CS- or elastase-exposed mice, and GCS was detected by Western blotting in chronic obstructive pulmonary disease lungs and CS extract-exposed primary human lung microvascular endothelial cells (HLMVECs). The role of GlcCer and GCS on mTOR (mammalian target of rapamycin) signaling, autophagy, lysosomal function, and cell death were studied in HLMVECs with or without CS exposure. Mice exposed to chronic CS or to elastase, and patients with chronic obstructive pulmonary disease, exhibited significantly decreased lung GlcCer and GCS. In mice, lung GlcCer levels were negatively correlated with airspace size. GCS inhibition in HLMVEC increased lysosomal pH, suppressed mTOR signaling, and triggered autophagy with impaired lysosomal degradation and apoptosis, recapitulating CS effects. In turn, increasing GlcCer by GCS overexpression in HLMVEC improved autophagic flux and attenuated CS-induced apoptosis. Decreased GSL production in response to CS may be involved in emphysema pathogenesis, associated with autophagy with impaired lysosomal degradation and lung endothelial cell apoptosis.
肺气肿中肺内皮细胞的丧失与肺内神经酰胺增加有关。神经酰胺的改变可能导致其他生物活性神经鞘脂的适应性改变，具有发病意义。我们之前报道过肺气肿与循环糖脂（GSL）呈负相关。葡萄糖神经酰胺（GlcCer）是由神经酰胺通过 GCS（葡萄糖神经酰胺合酶）合成的初始 GSL，是胚胎存活所必需的，但它在肺部的作用尚不清楚。为了确定香烟烟雾（CS）是否改变肺中的 GlcCer，并阐明 GCS 在肺内皮细胞命运中的作用。通过串联质谱法在 CS 或弹性蛋白酶暴露的小鼠的 BAL 液中测量 GlcCer，并通过 Western blot 在慢性阻塞性肺疾病肺和 CS 提取物暴露的原代人肺微血管内皮细胞（HLMVEC）中检测 GCS。在有或没有 CS 暴露的情况下，在 HLMVEC 中研究了 GlcCer 和 GCS 对 mTOR（雷帕霉素的哺乳动物靶标）信号、自噬、溶酶体功能和细胞死亡的作用。暴露于慢性 CS 或弹性蛋白酶的小鼠以及慢性阻塞性肺疾病患者的肺 GlcCer 和 GCS 明显降低。在小鼠中，肺 GlcCer 水平与气腔大小呈负相关。HLMVEC 中的 GCS 抑制增加了溶酶体 pH，抑制了 mTOR 信号，并引发了自噬，同时伴有溶酶体降解和凋亡受损，再现了 CS 的作用。反过来，通过在 HLMVEC 中过表达 GCS 增加 GlcCer，可改善自噬流并减轻 CS 诱导的凋亡。CS 反应中 GSL 产量的降低可能与肺气肿发病机制有关，与自噬伴溶酶体降解受损和肺内皮细胞凋亡有关。
