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Regulation of Macrophage Foam Cell Formation during Nitrogen Mustard (NM)-Induced Pulmonary Fibrosis by Lung Lipids

ABSTRACT: Nitrogen mustard (NM) is a vesicant known to target the lung, causing acute injury which progresses to fibrosis. Evidence suggests that activated macrophages contribute to the pathologic response to NM. In these studies, we analyzed the role of lung lipids generated following NM exposure on macrophage activation and phenotype. Treatment of rats with NM (0.125 mg/kg, i.t.) resulted in a time-related increase in enlarged vacuolated macrophages in the lung. At 28 d post exposure, macrophages stained positively for Oil Red O, a marker of neutral lipids. This was correlated with an accumulation of oxidized phospholipids in lung macrophages and epithelial cells, and an increase in bronchoalveolar lavage fluid (BAL) phospholipids. RNA-sequencing analysis revealed that lipid handling pathways under control of the transcription factors LXR, FXR and PPAR-ɣ were significantly altered following NM exposure. Whereas at 1-3 d post NM, FXR and the downstream oxidized low density lipoprotein receptor, Cd36, were increased, Lxr and the lipid extrusion pump targets, Abca1 and Abcg1 were reduced. Treatment of naïve lung macrophages with lipid enriched fractions of BAL collected 3 d after NM resulted in upregulation of Nos2, Apoe and Ptgs2, markers of pro-inflammatory activation, while lipid-enriched BAL collected 28 d post NM upregulated expression of the anti-inflammatory markers, Il10, Cd163, and Cx3cr1, and induced the formation of lipid-laden foamy macrophages. These data suggest that NM-induced alterations in lipid handling and metabolism drive macrophage foam cell formation, potentially contributing to the development of pulmonary fibrosis.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE125619 | GEO | 2019/01/25

REPOSITORIES: GEO

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Project description:The objective of the study was to figure out the impact of LXR signaling on human macrophages. Primary human macrophages in an early differentiating and a mature differentiation state were treated with the LXR agonist T091317 for 4 and 24 h and transcriptome-wide expression analysis were performed. As LXRa is highly induced during macrophage differentiation and 68% of all LXRs targets change their expression during this process, we suggest that LXRs have essential functions in macrophage development. More than 238 genes are regulated in early as well as mature macrophages by activation of LXRs; most of them are up-regulated. LXRs administrate differentiation state specific as well as common macrophages functions related primarily to lipid homeostasis, immune response and cell fate. Interestingly, almost only genes related to lipid and cholesterol metabolism are overrepresented among early induced genes, whereas genes related to immune functions respond later, implying the existence of indirect mechanisms of control. Furthermore, in early differentiating macrophages cell proliferation and cell death associated genes are induced after 24 h of LXR activation, whereas in mature macrophages, showing high LXRa expression, the same functional cluster respond far earlier (4 h) after LXR ligand treatment. In conclusion, our data suggest that LXRs are modulators of macrophage differentiation, operating principally as positive transcriptional regulators of genes involved in lipid and cholesterol metabolism and by this indirectly influencing the immunophenotype of macrophages. CD14 positive cells of healthy donors were isolated by magnetic separation and differentiated in the presence of human serum to macrophages. At an early differentiating state (16 h after isolation) and at in mature differentiating state (day 11 after isolation) the cells were treated with the synthetical LXR agonist T091317 respective its solvent DMSO for 4 and 24 h. RNA was isolated and a whole genome microarray was performed.

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Regulation of Macrophage Foam Cell Formation during Nitrogen Mustard (NM)-Induced Pulmonary Fibrosis by Lung Lipids

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