Dual role of TGF-β1 on Fas-induced apoptosis in lung epithelial cells

Recent evidence suggests that TGF-β1 has a dual role in regulating cell response to Fas/Fas ligand (FasL)-induced apoptosis. TGF-β1 may play a positive or negative role on cell sensitivity to apoptosis via Fas/FasL system, depending on cell types and their specific environment. TGF-β1 and the Fas/FasL system are also involved in pathological processes of acute lung injury (ALI) and interstitial lung diseases including early lung injury and subsequent tissue repair. However, it is not well understood how TGF-β1 regulates Fas/FasL mediated apoptotic signaling in lung epithelium. In this study, we found that TGF-β1 could affect the sensitivity of lung epithelial A549 cells to Fas/FasL mediated apoptosis in a time-dependent manner. Apoptosis of A549 cells could be enhanced significantly by co-treatment with TGF-β1 and FasL, or pretreatment with TGF-β1 followed by FasL exposure, as evidenced by markedly increased caspase-8 and JNK activities. However, prolonged exposure to TGF-β1 could result in an obvious inhibition of the Fas/FasL-induced apoptosis, accompanied by down-regulation of Fas and up-regulation of c-Flip. Our results also showed that the effect of TGF-β1 on cell sensitivity to Fas-mediated apoptosis was independent of Akt pathway activation. These findings suggest that timely interplay of TGF-β1 and the Fas/FasL system could determine the final outcomes of cell survival/death signaling, for example, switching cell death signaling to survival signaling during early injury and later repair process of lung epithelium.     

Enhanced expression of Fas and FasL modulates apoptosis in the lungs of severe P. falciparum malaria patients with pulmonary edema

Apoptosis mediated by Fas/FasL has been implicated in pulmonary disorders. However, little is known about the relationship between Fas and FasL in the process of lung injury during malaria infection. Paraffin-embedded lung tissues from malaria patients were divided into two groups: those with pulmonary edema (PE) and those without pulmonary edema (non-PE). Normal lung tissues were used as the control group. Cellular expression of Fas, FasL, and the markers of apoptotic caspases, including cleaved caspase-3 and cleaved caspase-8 in the lung tissues were investigated by the immunohistochemistry (IHC) method. Semi-quantitative analysis of IHC staining revealed that cellular expression of Fas, FasL, cleaved caspase-8, and cleaved caspase-3 were significantly increased in the lungs of patients with PE compared with the lungs of patients with non-PE and control groups (all P < 0.05). In addition, significant positive correlations were obtained between Fas and apoptosis (r_s = 0.937, P < 0.001) and FasL and apoptosis (r_s = 0.808, P < 0.001). Significant positive correlations were found between Fas and FasL expression (r_s = 0.827, P < 0.001) and between cleaved caspase-8 and cleaved caspase-3 expression (r_s = 0.823, P < 0.001), which suggests that Fas-dependent initiator and effector caspases, including cleaved caspase-8 and caspase-3, are necessary for inducing apoptosis in the lungs of patients with severe P. falciparum malaria. The Fas/FasL system and downstream activation of caspases are important mediators of apoptosis and may be involved in the pathogenesis of pulmonary edema in severe P. falciparum malaria patients. The proper regulation of the Fas/FasL pathway can be a potential treatment for pulmonary complications in falciparum malaria patients.     

三七总皂甙降低兔肺缺血再灌注损伤和抑制细胞凋亡

 目的: 探讨细胞凋亡与肺缺血再灌注损伤的关系以及三七总皂甙的作用及机制。方法: 健康日本大耳白兔84只,随机分为对照组、肺缺血再灌注1、3、5h组和相应三七总皂甙干预组。复制肺缺血再灌注损伤模型。用原位缺口末端标记(TUNEL)法、聚丙烯酰胺凝胶电泳观测肺组织细胞凋亡,原位杂交技术检测肺组织细胞Fas/FasL系统和Caspase-3基因表达。结果: 肺缺血再灌注组肺组织细胞凋亡指数(肺缺血再灌注5h组:22.08±1.93;对照组:2.04±0.67)、Fas/FasL和Caspase-3基因表达(肺缺血再灌注5h组:0.241±0.029;对照组:0.121±0.015)均显著高于对照组(P<0.01),并出现电泳梯形条带结构;三七总皂甙干预组Fas/FasL mRNA及其Caspase-3的表达(三七总皂甙干预5h组:0.199±0.020;肺缺血再灌注5h组:0.241±0.029)显著低于缺血再灌注组(P<0.01),肺组织细胞凋亡指数(三七总皂甙干预5h组:12.58±1.82;肺缺血再灌注5h组:22.08±1.93)也显著低于缺血再灌注组(P<0.01),梯形条带结构基本消失。肺组织细胞凋亡指数分别与Caspase-3 mRNA及Fas/FasL mRNA之间均呈显著正相关(P<0.01)。结论:三七总皂甙可能通过抑制Fas/FasL系统的激活,阻遏肺组织细胞凋亡,从而减轻肺缺血再灌注损伤。     

Ghrelin 通过AKT/ ERK 信号通路对LPS 诱导的肺泡上皮细胞凋亡的影响

目的:研究Ghrelin 对内毒素(Lipopolysaccharide,LPS)所致的肺泡域型上皮细胞(A549)凋亡的影响及其机制。方法:CCK-8(Cell Counting Kit-8)法检测LPS 刺激对A549 的细胞毒性;原位末端标记法(TUNEL)检测细胞凋亡率;流式细胞术检测细胞内一氧化氮(NO)的产生;Western blot 检测诱导型一氧化氮合成酶(iNOS)、AKT、ERK、p-AKT、p鄄ERK 信号通路蛋白以及cleaved caspase-3、Bax、Bcl-2 凋亡相关蛋白的表达。结果:CCK-8 检测结果显示LPS 可显著抑制A549 细胞的增殖,降低细胞活力;TUNEL 检测发现Ghrelin 可显著抑制LPS 导致的A549 细胞的凋亡(P<0.05);LPS 可以促进iNOS 的表达,增加细胞内NO 的产生,并同时抑制AKT、ERK 通路的活性,上调下游促凋亡蛋白Bax 以及终末凋亡蛋白cleaved caspase-3 的表达,下调抗凋亡蛋白Bcl-2 的表达,而应用Ghrelin 预处理后可以逆转LPS 对AKT、ERK 通路活性的抑制,继而下调Bax 以及cleaved caspase-3 的表达,上调Bcl-2 的表达,差异均具有统计学意义(P<0.05),但Ghrelin 对细胞内NO 的产生无明显影响。结论:Ghrelin 可以通过上调AKT 及ERK 通路的活性抑制LPS 诱导的肺泡上皮细胞凋亡,但不能降低iNOS 诱导产生NO 的水平。     

牛磺酸对大鼠肢体缺血再灌注后肺损伤时细胞凋亡的影响

目的:从细胞凋亡的角度探讨肢体缺血再灌注(LIR)后急性肺损伤(ALI)的发病机制及牛磺酸的影响。方法:复制大鼠肢体缺血再灌注(LIR)损伤动物模型,采用TUNEL法、电泳法、半定量逆转录聚合酶链反应(SqRT-PCR)及免疫组织化学等技术观察LIR后肺损伤发生过程中,肺泡上皮及血管内皮细胞凋亡变化以及Fas/FasL系统蛋白质和mRNA表达的改变。结果:大鼠LIR后,肺泡上皮细胞和肺血管内皮细胞凋亡明显增加;肺组织Fas/FasLmRNA和蛋白质表达明显上调,DNA断链率、组织钙含量和活性氧(ROS)升高,且与肺泡上皮及血管内皮细胞凋亡的增加相一致。结论:肺泡上皮及血管内皮细胞凋亡以及Fas/FasL系统表达明显上调可能参与LIR后ALI的发生;牛磺酸可减少肺组织细胞凋亡,但并非通过影响Fas/FasL基因表达而实现其保护效应。     

Opposing effect by cytokines on Fas-mediated apoptosis in A549 lung epithelial cells.

Tissue repair is determined by many signals provided in the local environment. Central to this process is the commitment of the parenchymal cell to undergo apoptosis, survive, or proliferate following inflammation. We hypothesize that lung epithelial cell apoptosis is influenced by exposure to cytokines released into the alveolar microenvironment during the inflammatory process. In this investigation we demonstrate that interferon (IFN)-gamma and interleukin (IL)-1beta have opposing effects on Fas-mediated apoptosis in A549 cells, a human lung epithelial cell line. Exposure to IFN-gamma before Fas activation significantly increased caspase activity, caspase processing of CK-18, a key cytoskeletal protein in epithelial cells, and increased the appearance of apoptotic nuclei. Induction of Fas-mediated death by IFN-gamma was 3-fold higher than with Fas activation alone. In contrast, pretreatment with IL-1beta before Fas activation completely inhibited apoptosis. Furthermore, our results demonstrate that IFN-gamma and IL-1beta induce opposite effects at multiple checkpoints during Fas-mediated apoptosis. Most striking, IL-1beta prevented the activation of caspases involved in Fas-mediated death by inducing an anti-apoptotic effect proximal to or at the point of caspase-8 activation. Finally, our investigation demonstrates that the differential impact of IL-1beta and IFN-gamma on Fas-mediated apoptosis are in part dependent on modulation of the PI 3-K/Akt survival pathway.     

The role of apoptosis in the pathophysiology of Acute Respiratory Distress Syndrome (ARDS): An up-to-date cell-specific review

ARDS pathophysiology is characterized by complex mechanisms that involve cells of inflammation, lung tissue cells, cytokines, chemokines, as well as apoptosis activators and inhibitors. There are two important theories that link apoptosis with ARDS and suggest that epithelial cell apoptosis, as well as the accumulation of neutrophils in the lung, may contribute to a cascade of events and, finally, ARDS. The activation of the Fas/FasL pathway is an important mechanism of alveolar epithelial injury in the lungs of patients with ALI. In addition, neutrophilic inflammation in the alveolar spaces is characteristic of ALI in humans and in most animal models of ALI. The enhanced phagocytosis of apoptotic neutrophils could lead to resolution of inflammation and repair during ARDS. In this review, we will focus on elucidating the role of apoptosis in the pathophysiology of ARDS and the contribution of Fas-mediated inflammation in ARDS. Furthermore, we will give evidence that TNF-alpha, IL-1beta and IL-13 attenuate the pro-cell death effects of Fas/CD95 on A549 epithelial cells, at least partially, by the NF-kB and PI3-K pathways, suggesting that induction of the expression of antiapoptotic genes protects the epithelial cells from cell death.     

Fas/FasL途径介导的人肺癌细胞免疫逃逸

目的：观察在3种人肺癌细胞（A549、EBC-1、LCSC）和人T细胞(Jurkat) Fas/FasL表达情况，探讨人肺癌细胞免疫逃逸及反杀伤作用与Fas/FasL途径的关系。 方法： 用FACScan、RT-PCR方法检测Fas/FasL蛋白及mRNA表达；以荧光染色法观察细胞调亡；用台盼蓝拒染法检测细胞存活。 结果： 3种人肺癌细胞及T-细胞系(Jurkat)均表达 Fas及 FasL；肺癌细胞与Jurkat细胞共培养时，肺癌细胞可导致Jurkat细胞生长抑制(P<0.05)及凋亡；在共培养体系中加入FasL中和性抗体NOK1，可封闭肺癌细胞对Jurkat细胞的生长抑制作用(P>0.05)。 结论： Fas/FasL途径可介导上述3种人肺癌细胞对Jurkat细胞的生长抑制及致凋亡作用；中和性抗体可有效阻断Fas信号转导途径，抑制肿瘤细胞的反杀伤作用，有效保护免疫系统。     

Caspase-3基因沉默对肺炎链球菌感染的肺泡上皮细胞凋亡的影响

目的:通过siRNA抑制caspase-3基因的表达探讨肺炎链球菌对肺泡上皮细胞凋亡的影响及凋亡基因caspase-3对凋亡的调节作用,寻找治疗肺炎链球菌肺炎的新方法。方法:体外培养肺泡上皮细胞A549,用肺炎链球菌R6作用于A549细胞,使用siRNA技术抑制caspase-3表达,RT-PCT法检测caspase-3转录强度,化学荧光测定法检测caspase-3蛋白含量,ELISA法检测细胞上清中IL-6和IL-10浓度,TUNEL法检测细胞凋亡。结果:肺炎链球菌能诱导A549细胞凋亡、导致caspase-3的表达和IL-6的浓度升高、IL-10的浓度降低;使用siRNA抑制caspase-3表达后,caspase-3的表达降低,A549细胞的凋亡率降低,而IL-6和IL-10的浓度并无明显变化。结论:Caspase-3在肺炎链球菌引起的肺泡上皮细胞的凋亡中占据了重要的地位;运用RNA干扰技术抑制caspase-3的表达能降低肺泡上皮细胞的凋亡率,这可能对肺炎链球菌肺炎的治疗有积极意义。     

Induction of interleukin-8 secretion and apoptosis in bronchiolar epithelial cells by Fas ligation.

Epithelial cell injury is the common manifestation of lung injury. Contributing to such injury of epithelial cells is apoptosis. Although apoptosis is part of the normal process of epithelial renewal, in excess it is pathologic. We previously demonstrated the excessive apoptosis of lung epithelial cells and the upregulation of Fas and Fas ligand (FasL) in fibrosing lung diseases. We also showed that inhalation of anti-Fas antibody induced lung injury and fibrosis in mice. Interleukin (IL)-8 is one of the most important cytokines in the pathophysiology of acute lung injury and pulmonary fibrosis. In this study we investigated whether Fas ligation induces IL-8 secretion in addition to apoptosis in bronchiolar epithelial cells in vitro. Bronchiolar epithelial cells underwent apoptosis and also secreted IL-8 in response to tumor necrosis factor (TNF)-alpha or Fas ligation. New gene expression and protein synthesis were not necessary for Fas ligation- and TNF-alpha- mediated apoptosis, but were necessary for IL-8 secretion. We further found that Fas ligation induced activation of nuclear factor-kappa B. We conclude that the Fas/FasL pathway not only mediates apoptosis but also plays a proinflammatory role, and that stimulation of the Fas/FasL pathway in bronchiolar epithelial cells leads to IL-8 production, which may amplify the inflammatory cascade in lung injury and pulmonary fibrosis.     

Fas and fas ligand are up-regulated in pulmonary edema fluid and lung tissue of patients with acute lung injury and the acute respiratory distress syndrome

Apoptosis mediated by Fas/Fas ligand (FasL) interaction has been implicated in human disease processes, including pulmonary disorders. However, the role of the Fas/FasL system in acute lung injury (ALI) and in the acute respiratory distress syndrome (ARDS) is poorly defined. Accordingly, we investigated both the soluble and cellular expression of the Fas/FasL system in patients with ALI or ARDS. The major findings are summarized as follows. First, the soluble expression of the Fas/FasL system was assessed in undiluted pulmonary edema fluid and simultaneous plasma. Pulmonary edema fluid obtained from patients with ALI or ARDS (n = 51) had significantly higher concentrations of both soluble Fas (27 ng/ml; median; P < 0.05) and soluble FasL (0.125 ng/ml; P < 0.05) compared to control patients with hydrostatic pulmonary edema (n = 40; soluble Fas, 12 ng/ml; soluble FasL, 0.080 ng/ml). In addition, the concentrations of both soluble Fas and soluble FasL were significantly higher in the pulmonary edema fluid of the patients with ALI or ARDS compared to simultaneous plasma samples (soluble Fas, 16 ng/ml; soluble FasL, 0.058 ng/ml; P < 0.05), indicating local release in the lung. Higher soluble Fas concentrations were associated with worse clinical outcomes. Second, cellular expression of the Fas/FasL system was assessed by semiquantitative immunofluorescence microscopy in lung tissue obtained at autopsy from a different set of patients. Both Fas and FasL were immunolocalized to a greater extent in the patients who died with ALI or ARDS (n = 10) than in the patients who died without pulmonary disease (n = 10). Both proteins were co-expressed by epithelial cells that lined the alveolar walls, as well as by inflammatory cells and sloughed epithelial cells that were located in the air spaces. Semiquantitative immunohistochemistry showed that markers of apoptosis (terminal dUTP nick-end labeling, caspase-3, Bax, and p53) were more prevalent in alveolar wall cells from the patients who died with ALI or ARDS compared to the patients who died without pulmonary disease. These findings indicate that alveolar epithelial injury in humans with ALI or ARDS is in part associated with local up-regulation of the Fas/FasL system and activation of the apoptotic cascade in the epithelial cells that line the alveolar air spaces.     

Fas,FasL, and cleaved caspases 8 and 3 in glioblastomas: A tissue microarray-based study

This investigation analyzed the immunoexpression of FasL, Fas, cleaved caspase-8, and cleaved caspase-3 in glioblastomas. Formalin-fixed and paraffin-embedded glioblastoma tissues and control brain tissues from 97 patients were analyzed by tissue microarrays and immunohistochemistry. Patients with glioblastomas that were negative or weakly stained (<50% of cells positive) for cleaved caspase-8 had worse cancer-specific overall survival (median = 8.5 months) than did patients with tumors that highly expressed cleaved caspase-8 (median = 11.7 months; P = 0.0325), independent of clinical variables. There was no association of other markers with survival, treatment, sex, age, tumor size, and primary site. Among the tumors, there were reasonable to good positive correlations between the expression of FasL and Fas (r = 0.47) and between Fas and cleaved caspase-8 (r = 0.41), and there were poor positive correlations between Fas and cleaved caspase-3 (r = 0.26), FasL and cleaved caspase-8 (r = 0.22), and cleaved caspase-8 and -3 (r = 0.31). Our results suggest that Fas-Fas-ligand signal transduction could be inhibited, especially at the stage of caspase-8 activation, thereby establishing a major mechanism for evasion of apoptosis by these tumors. The absence or low expression of cleaved caspase-8 in the tumors was a negative prognostic indicator for patient survival.     

Evidence for a Novel, Caspase-8-Independent, Fas Death Domain-Mediated Apoptotic Pathway

Certain caspase-8 null cell lines demonstrate resistance toFas-induced apoptosis, indicating that the Fas/FasL apoptoticpathway may be caspase-8-dependent. Some reports, however, haveshown that Fas induces cell death independent of caspase-8. Herewe provide evidence for an alternative, caspase-8-independent,Fas death domain-mediated apoptotic pathway. Murine 12B1-D1 cellsexpress procaspase-3, -8, and -9, which were activated upon thedimerization of Fas death domain. Bid was cleaved andmitochondrial transmembrane potential was disrupted in thisapoptotic process. All apoptotic events were completely blockedby the broad-spectrum caspase inhibitor Z-VAD-FMK, but not byother peptide caspase inhibitors. Cyclosporin A (CsA), whichinhibits mitochondrial transition pore permeability, blockedneither pore permeability disruption nor caspase activation.However, CsA plus caspase-8 inhibitor blocked all apoptoticevents of 12B1-D1 induced by Fas death domain dimerization. Ourdata therefore suggest that there is a novel,caspase-8-independent, Z-VAD-FMK-inhibitable, apoptotic pathway in12B1-D1 cells that targets mitochondria directly.     

miR-29b通过调控Bax基因抑制LPS诱导的肺泡上皮细胞系A549凋亡

目的探讨miR-29b对脂多糖(LPS)诱导的肺泡上皮细胞系A549凋亡的影响及其机制。方法将体外培养的A549细胞分为对照组、LPS组(给予10 mg/L的LPS处理)、LPS+miR-NC组(转染miR-29b mimics阴性对照后给予LPS处理)、LPS+miR-29b组(转染miR-29b mimics后给予LPS处理);用RT-qPCR检测细胞中miR-29b的表达水平;MTT法检测细胞存活率;流式细胞仪检测细胞凋亡率;Western blot检测Bcl-2、Bax和cleaved caspase-3蛋白的表达;双荧光素酶报告基因实验检测Bax和miR-29b的靶向关系。结果与对照组相比,LPS组、LPS+miR-NC组和LPS+miR-29b组细胞中miR-29b、Bcl-2蛋白的表达水平和细胞存活率均明显降低,而细胞凋亡率和Bax、cleaved caspase-3蛋白的表达水平均明显升高(P<0.05);与LPS组相比,LPS+miR-29b组细胞中miR-29b、Bcl-2蛋白的表达水平和细胞存活率均明显升高,而细胞凋亡率和Bax、cleaved caspase-3蛋白的表达水平均明显降低(P<0.05)。双荧光素酶报告基因实验证实Bax是miR-29b的潜在靶基因。结论miR-29b可抑制LPS诱导的A549细胞凋亡,其作用机制可能与靶向调控Bax表达有关。     

Mitochondria-mediated apoptosis of lung epithelial cells in idiopathic interstitial pneumonias

We previously demonstrated that the up-regulation of p53, Fas, and DNA damage are present in lung epithelial cells from patients with idiopathic interstitial pneumonias (IIP). Fas ligation induces apoptosis of lung epithelial cells predominantly through the direct activation of the caspase cascade via caspase-8 activation, whereas the up-regulation of p53 and other cellular stresses can induce mitochondria-mediated apoptosis. In this study, we investigated the incidence of mitochondria-mediated apoptosis of epithelial cells in IIP. We performed TUNEL staining to detect apoptotic cells and western blot analysis and immunohistochemistry to assess the expression and activation of caspases and the cytochrome c release from mitochondria in lung tissues from eight patients with usual interstitial pneumonia, five patients with nonspecific interstitial pneumonia, and eight patients with normal lung parenchyma. The expressions of pro- and cleaved caspase-8, 9, 3, and cytochrome c release from the mitochondria were all significantly increased in the lung tissues of IIP compared with normal lung parenchyma. The positive signals for caspases in epithelial cells were increased in IIP compared with normal lung parenchyma by immunohistochemistry. The results of TUNEL and electron microscopy suggested that apoptotic cells were predominantly epithelial cells. TUNEL-positive cells in % of epithelial cells were significantly increased in IIP compared with normal lung parenchyma, and significantly correlated with cytochrome c release from the mitochondria and with the expression of cleaved caspase-3 in epithelial cells. We conclude that mitochondria-mediated apoptosis may be involved in the pathophysiology of IIP.     

TPX2对人肺癌细胞增殖、凋亡及cleavedcaspase-3表达的影响

目的 探讨Xklp2靶蛋白(TPX2)对人肺癌细胞增殖、凋亡及活化的半胱氨酸天冬氨酸蛋白酶3(cleaved caspase-3)表达影响。方法 培养人肺癌细胞A549,分为Control组(不进行细胞转染)、siRNA-NC组(细胞转染TPX2 siRNA control)、TPX2 siRNA组(细胞转染TPX2 siRNA),采用实时荧光定量PCR (qPCR)和Western blot检测TPX2 siRNA的转染效果。取转染后各组细胞,采用噻唑蓝检测细胞增殖情况,流式细胞术检测细胞凋亡情况,Western blot检测cleaved caspase-3蛋白表达情况。结果 TPX2 siRNA组中,TPX2 mRNA、蛋白水平和细胞光密度(OD)值均明显低于Control组和siRNA-NC组,细胞凋亡率、细胞中cleaved caspase-3蛋白表达水平均明显高于Control组和siRNA-NC组,差异均有统计学意义(P值均<0.05);而siRNA-NC组中,TPX2 mRNA、蛋白水平及细胞OD值、细胞凋亡率、细胞中cleaved caspase-3与Control组比较,差异均无统计学意义(P值均＞0.05)。结论TPX2 siRNA能够干扰人肺癌细胞A549中TPX2的表达。下调TPX2的表达能够抑制人肺癌细胞A549增殖,促进caspase-3活化,促进人肺癌细胞A549的凋亡。     

Relationship of acute lung inflammatory injury to Fas/FasL system

There is mounting evidence that apoptosis plays a significant role in tissue damage during acute lung injury. To evaluate the role of the apoptosis mediators Fas and FasL in acute lung injury, Fas (lpr)- or FasL (gld)-deficient and wild-type mice were challenged with intrapulmonary deposition of IgG immune complexes. Lung injury parameters ((125)I-albumin leak, accumulation of myeloperoxidase, and wet lung weights) were measured and found to be consistently reduced in both lpr and gld mice. In wild-type mice, lung injury was associated with a marked increase in Fas protein in lung. Inflamed lungs of wild-type mice showed striking evidence of activated caspase-3, which was much diminished in inflamed lungs from lpr mice. Intratracheal administration of a monoclonal Fas-activating antibody (Jo2) in wild-type mice induced MIP-2 and KC production in bronchoalveolar lavage fluids, and a murine alveolar macrophage cell line (MH-S) showed significantly increased MIP-2 production after incubation with this antibody. Bronchoalveolar lavage fluid content of MIP-2 and KC was substantially reduced in lpr mice after lung injury when compared to levels in wild-type mice. These data suggest that the Fas/FasL system regulates the acute lung inflammatory response by positively affecting CXC-chemokine production, ultimately leading to enhanced neutrophil influx and tissue damage.     

Epithelial cell apoptosis by fas ligand-positive myofibroblasts in lung fibrosis

The Fas/Fas ligand (FasL) apoptotic pathway has been shown to be involved in bleomycin-induced lung fibrosis. We examined the hypothesis that myofibroblasts from fibrotic lungs possess a cytotoxic phenotype that causes apoptosis of epithelial cells via the Fas/FasL pathway. We show in vivo epithelial cell apoptosis and associated upregulation of Fas and apoptotic Fas pathway genes in epithelial cells of lungs with bleomycin-induced fibrosis. In addition, we show that FasL surface molecules are overexpressed on alpha-SMA-positive cells in mice with bleomycin-induced fibrosis, and in humans with idiopathic pulmonary fibrosis. This enables the molecules to kill Fas-positive epithelial cells. In contrast, FasL-deficient myofibroblasts lose this myofibroblast cytotoxic phenotype, both in vivo and in vitro. In vivo, there was no bleomycin-induced epithelial cell apoptosis, as assessed by specific M30 staining in chimeric FasL-deficient mice that lacked FasL-positive myofibroblasts. In vitro, FasL-positive, but not FasL-negative myofibroblasts, induce mouse lung epithelial cell apoptosis. Thus myofibroblast cytotoxicity may underlie the absence of re-epithelialization, resulting in persistent lung fibrosis.