1 Department of Medicine, Division of Pulmonary, Allergy, Critical Care, and Occupational Medicine, Indiana University School of Medicine, Indianapolis, Indiana.
Am J Respir Cell Mol Biol. 2014 Mar;50(3):513-25. doi: 10.1165/rcmb.2013-0023OC.
Prolonged exposure to cigarette smoking is the main risk factor for emphysema, a component of chronic obstructive pulmonary diseases (COPDs) characterized by destruction of alveolar walls. Moreover, smoking is associated with pulmonary artery remodeling and pulmonary hypertension, even in the absence of COPD, through as yet unexplained mechanisms. In murine models, elevations of intra- and paracellular ceramides in response to smoking have been implicated in the induction of lung endothelial cell apoptosis, but the role of ceramides in human cell counterparts is yet unknown. We modeled paracrine increases (outside-in) of palmitoyl ceramide (Cer16) in primary human lung microvascular cells. In naive cells, isolated from nonsmokers, Cer16 significantly reduced cellular proliferation and induced caspase-independent apoptosis via mitochondrial membrane depolarization, apoptosis-inducing factor translocation, and poly(ADP-ribose) polymerase cleavage. In these cells, caspase-3 was inhibited by ceramide-induced Akt phosphorylation, and by the induction of autophagic microtubule-associated protein-1 light-chain 3 lipidation. In contrast, cells isolated from smokers exhibited increased baseline proliferative features associated with lack of p16(INK4a) expression and Akt hyperphosphorylation. These cells were resistant to Cer16-induced apoptosis, despite presence of both endoplasmic reticulum stress response and mitochondrial membrane depolarization. In cells from smokers, the prominent up-regulation of Akt pathways inhibited ceramide-triggered apoptosis, and was associated with elevated sphingosine and high-mobility group box 1, skewing the cell's response toward autophagy and survival. In conclusion, the cell responses to ceramide are modulated by an intricate cross-talk between Akt signaling and sphingolipid metabolites, and profoundly modified by previous cigarette smoke exposure, which selects for an apoptosis-resistant phenotype.
长期暴露于吸烟是肺气肿的主要危险因素，肺气肿是慢性阻塞性肺疾病（COPD）的一个组成部分，其特征是肺泡壁的破坏。此外，吸烟与肺动脉重塑和肺动脉高压有关，即使在没有 COPD 的情况下也是如此，其机制尚不清楚。在小鼠模型中，吸烟引起的细胞内和细胞旁神经酰胺的升高被认为与肺内皮细胞凋亡的诱导有关，但神经酰胺在人类细胞中的作用尚不清楚。我们模拟了原代人肺微血管细胞中旁分泌（外向型）的棕榈酰神经酰胺（Cer16）的增加。在从非吸烟者中分离的幼稚细胞中，Cer16 显著降低了细胞增殖，并通过线粒体膜去极化、凋亡诱导因子易位和多聚（ADP-核糖）聚合酶切割诱导 caspase 非依赖性凋亡。在这些细胞中，Cer16 通过诱导 Akt 磷酸化和自噬微管相关蛋白 1 轻链 3 脂质化来抑制 caspase-3。相比之下，从吸烟者中分离的细胞表现出与缺乏 p16(INK4a)表达和 Akt 过度磷酸化相关的基线增殖特征增加。这些细胞对 Cer16 诱导的凋亡具有抗性，尽管存在内质网应激反应和线粒体膜去极化。在吸烟者的细胞中，Akt 途径的显著上调抑制了 Cer16 触发的细胞凋亡，并与鞘氨醇和高迁移率族蛋白 1 的上调有关，使细胞的反应偏向自噬和存活。总之，Akt 信号和鞘脂代谢物之间的复杂相互作用调节了细胞对神经酰胺的反应，并且吸烟前暴露的强烈修饰选择了凋亡抗性表型。
