Lysophospholipid Acyltransferase 9 Promotes Emphysema Formation via Platelet-activating Factor.

Cigarette smoking is known to be the leading cause of chronic obstructive pulmonary disease (COPD). However, the detailed mechanisms have not been elucidated. PAF (platelet-activating factor), a potent inflammatory mediator, is involved in the pathogenesis of various respiratory diseases such as bronchial asthma and COPD. We focused on LPLAT9 (lysophospholipid acyltransferase 9), a biosynthetic enzyme of PAF, in the pathogenesis of COPD. LPLAT9 gene expression was observed in excised COPD lungs and single-cell RNA sequencing data of alveolar macrophages (AMs). LPLAT9 was predominant and upregulated in AMs, particularly monocyte-derived AMs, in patients with COPD. To identify the function of LPLAT9/PAF in AMs in the pathogenesis of COPD, we exposed systemic LPLAT9-knockout (LPALT9-/-) mice to cigarette smoke (CS). CS increased the number of AMs, especially the monocyte-derived fraction, which secreted MMP12 (matrix metalloprotease 12). Also, CS augmented LPLAT9 phosphorylation/activation on macrophages and, subsequently, PAF synthesis in the lung. The LPLAT9-/- mouse lung showed reduced PAF production after CS exposure. Intratracheal PAF administration accumulated AMs by increasing MCP1 (monocyte chemoattractant protein-1). After CS exposure, AM accumulation and subsequent pulmonary emphysema, a primary pathologic change of COPD, were reduced in LPALT9-/- mice compared with LPLAT9+/+ mice. Notably, these phenotypes were again worsened by LPLAT9+/+ bone marrow transplantation in LPALT9-/- mice. Thus, CS-induced LPLAT9 activation in monocyte-derived AMs aggravated pulmonary emphysema via PAF-induced further accumulation of AMs. These results suggest that PAF synthesized by LPLAT9 has an important role in the pathogenesis of COPD.

Participant Selection from the General Japanese Population for Pulmonary Function Tests Using a Questionnaire on Symptoms and Smoking Habits during Annual Health Checkups: The Yamagata-Takahata Study.

Objective Pulmonary function tests are essential for diagnosing respiratory diseases, such as chronic obstructive pulmonary disease (COPD), but are typically not performed in Japan during annual health checkups, which hinders the early diagnosis of respiratory diseases. Methods Individuals who agreed to participate in the Yamagata-Takahata study during medical checkups in Takahata (Yamagata Prefecture, Japan) in 2011 were examined. We interviewed 669 participants (49.0% men; mean age, 67.7 years old) regarding their respiratory symptoms and smoking habits and performed pulmonary function tests during the study. Results Based on pulmonary function test results, 141 participants had pulmonary dysfunction, and 115 had obstructive pulmonary dysfunction. The risk of respiratory dysfunction, particularly obstructive respiratory dysfunction, was examined by referring to a questionnaire tool for an early COPD diagnosis. The associations between age, the smoking history, respiratory symptoms, and obstructive respiratory dysfunction were evaluated. Obstructive respiratory dysfunction was found in 17.6% of participants ≥50 years old and 19.5% ≥60 years old, 30.3% had a smoking history, and 32.8% had respiratory symptoms. Furthermore, the participants with multiple factors had a higher probability of obstructive respiratory dysfunction. Conclusion Subjects with obstructive pulmonary dysfunction are expected to be efficiently identified by extracting individuals by age and smoking habit and through a respiratory symptom questionnaire, although pulmonary function tests cannot be performed for all individuals during health checkups.

Effect of hyperhomocysteinemia on a murine model of smoke-induced pulmonary emphysema.

Hyperhomocysteinemia was reported to enhance endoplasmic reticulum (ER) stress and subsequent apoptosis in several cells. However, the precise mechanisms of smoking susceptibility associated with hyperhomocysteinemia has not been fully elucidated. This study included 7- to 9-week-old C57BL6 male mice induced with hyperhomocysteinemia and were exposed to cigarette smoke (CS). A549 cells (human alveolar epithelial cell line) were cultured with homocysteine and were exposed to cigarette smoke extract (CSE) to observe cell viability and expression of proteins related to the ER stress. After 6 months of CS exposure, pulmonary emphysema was more severely induced in the group under the condition of hyperhomocysteinemia compared to that in the control group. The apoptotic A549 cells increased as homocysteine concentration increased and that was enhanced by CSE. Protein expression levels of ER stress markers were significantly increased after simultaneous stimulation. Notably, vitamin B12 and folate supplementation improved ER stress after simultaneous stimulation of A549 cells. In this study, we showed that hyperhomocysteinemia exacerbates CS exposure-induced emphysema in mice, suggesting that hyperhomocysteinemia and CS stimulation enhance ER stress and subsequent induced apoptosis in alveolar epithelial cells. It was suggested that there is a synergistic effect between homocysteine and CS.

Effect of Iron Deficiency on a Murine Model of Smoke-induced Emphysema.

Smoking is a major risk factor for chronic obstructive pulmonary disease (COPD). Smoking susceptibility is important for the onset and development of COPD. We previously reported an association between serum iron concentrations and pulmonary function in male smokers. However, the mechanism governing smoking susceptibility in relation to iron deficiency is unclear; this study aimed to elucidate this mechanism. C57BL/6 male mice were fed an iron-deficient or normal diet and then exposed to cigarette smoke. BAL, histological analysis, and pulmonary function tests were performed after cigarette smoke exposure. Human alveolar type II epithelial A549 cells were treated with an iron chelator. Subsequently, A549 cells were exposed to cigarette smoke extract. In mice exposed to cigarette smoke for 2 weeks, the concentration of alveolar macrophages in the BAL fluid recovered from iron-deficient mice was significantly higher than that in normal diet mice. IL-6 and MCP-1 (monocyte chemotactic protein 1) concentrations in the BAL fluid increased significantly from baseline in iron-deficient mice, but not in normal diet mice. In mice exposed to cigarette smoke for 8 weeks, the pathological mean linear intercepts, physiological total lung capacity, and functional residual capacity in the lungs of iron-deficient mice were significantly greater than in normal diet mice. Phosphorylation of NF-κB was enhanced in the lungs of iron-deficient mice exposed to cigarette smoke and in the iron-chelating A549 cells exposed to cigarette smoke extract. Iron deficiency exaggerated cigarette smoke-induced pulmonary inflammation, suggesting that it may accelerate COPD development.

Impact of cigarette smoking on decline in forced expiratory volume in 1s relative to severity of airflow obstruction in a Japanese general population: The Yamagata-Takahata study.

BACKGROUND: Few studies are available regarding the annual decline of forced expiratory volume in 1s (FEV1) in chronic obstructive pulmonary disease patients with mild airflow obstruction. This study sought to clarify to what extent cigarette-smoking individuals with mild airflow obstruction lose pulmonary function annually. METHODS: From 2004 to 2006, pulmonary function tests were performed on people >40 years of age, during the annual health checkup held in Takahata, Yamagata, Japan (initial study population, n=3253). In 2011, pulmonary function tests were performed again on participants who agreed to undergo reexamination (follow-up study population, n=838). RESULTS: Smokers have decreased pulmonary function in terms of percent forced vital capacity (FVC), %FEV1, and FEV1/FVC; the stages of airflow obstruction were also more severe in smokers than never-smokers. The annual decline in FEV1 was significantly greater in smokers than in never-smokers. The median annual decline in FEV1 was most significant in individuals with mild airflow obstruction. The annual decline in FEV1 was greater in smokers with mild airflow obstruction than in smokers with moderate airflow obstruction. In analyzing the decline in %FEV1, the annual change in smokers with mild airflow obstruction was greater than that in smokers with normal spirometric values. CONCLUSION: The annual decline in FEV1 was most significant in smokers with mild airflow obstruction in a Japanese general population. This highlights the importance of early detection of chronic obstructive pulmonary disease patients among the general population in order to prevent disease progression in undiagnosed patients.

MafB enhances efferocytosis in RAW264.7 macrophages by regulating Axl expression.

The transcription factor MafB is involved in cellular differentiation and phagocytosis in macrophages. Macrophages phagocytose apoptotic cells in vivo; this process, which is known as efferocytosis, requires Axl receptor tyrosine kinase (Axl) activity. However, the association between MafB and efferocytosis, as well as that between MafB and Axl, in macrophages is unknown. We hypothesized that MafB modulates macrophage efferocytosis by regulating Axl expression. Fluorescent-labeled apoptotic thymocytes were added to RAW264.7-MafB-shRNA and control cells, and the proportion of phagocytosis-positivey fluorescence microscopy and flow cytometry. In addition, Axl mRNA and protein were quantified by real-time PCR and western blotting in each group. RAW264.7-MafB-shRNA cells were transfected with a plasmid expressing green fluorescent protein (GFP)-tagged Axl or a control empty plasmid expressing only GFP. The capacity for phagocytosis of apoptotic cells was assessed in GFP-positive cells gated based on fluorescence intensity. In RAW264.7-MafB-shRNA cells, capacity for phagocytosis of apoptotic thymocytes was significantly reduced compared with that of control cells, as determined by fluorescence microscope and flow cytometry. Axl mRNA and protein expression was significantly reduced in RAW264.7-MafB-shRNA cells relative to control cells. Furthermore, the capacity of RAW264.7-MafB-shRNA cells, transfected with an Axl-expressing plasmid, for phagocytosis of apoptotic thymocytes was significantly greater than that of cells transfected with the control plasmid. Collectively, the present findings indicate that MafB enhances efferocytosis by regulating Axl expression in RAW264.7 macrophages.

MafB silencing in macrophages does not influence the initiation and growth of lung cancer induced by urethane.

An increased number of tumor-associated macrophages (TAMs) that exhibit the M2 macrophage phenotype is related to poorer prognosis in cancer patients. MafB is a transcription factor regulating the differentiation of macrophages. However, involvement of MafB for the development of TAMs is unknown. This study was designed to investigate the role of MafB in a murine urethane-induced lung cancer model. Urethane was injected intraperitoneally into wild-type and dominant-negative MafB transgenic mice. Twenty-four weeks later, mice were sacrificed and their lungs removed for pathological analysis. The numbers and mean areas of lung cancer were evaluated. In addition, the numbers of Mac-3-positive macrophages were evaluated in each tumor. The numbers and mean areas of lung cancer induced by urethane administration were not significantly different between wild-type and dominant-negative MafB transgenic mice. The numbers of TAMs in lung cancer tissue were not significantly different between the two groups. MafB silencing using dominant-negative MafB did not influence the initiation and growth of lung cancer in mice exposed to urethane. These data suggest that MafB may not be related to the development of TAMs.