Misharin et al. elucidate the fate and function of monocyte-derived alveolar macrophages during the course of pulmonary fibrosis. These cells persisted throughout the life span, were enriched for the expression of profibrotic genes, and their genetic ablation ameliorated development of pulmonary fibrosis.
We use molecular dynamics simulations to characterize the influence of cholesterol (Chol) on the interaction between the anticancer drug doxorubicin (DOX) and a dipalmitoyl phosphatidylcholine/Chol lipid bilayer. We calculate the potential of mean force, which gives us an estimate of the free energy barrier for DOX translocation across the membrane. We find free energy barriers of 23.1 ± 3.1 k(B)T, 36.8 ± 5.1 k(B)T, and 54.5 ± 4.7 k(B)T for systems composed of 0%, 15%, and 30% Chol, respectively. Our predictions agree with Arrhenius activation energies from experiments using phospholipid membranes, including 20 k(B)T for 0% Chol and 37.2 k(B)T for 20% Chol. The location of the free energy barrier for translocation across the bilayer is dependent on composition. As Chol concentration increases, this barrier changes from the release of DOX into the water to flip-flop over the membrane center. The drug greatly affects local membrane structure by attracting dipalmitoyl phosphatidylcholine headgroups, curving the membrane, and allowing water penetration. Despite its hydrophobicity, DOX facilitates water transport via its polar groups.
Rationale: The identification of informative elements of the host response to infection may improve the diagnosis and management of bacterial pneumonia.Objectives: To determine whether the absence of alveolar neutrophilia can exclude bacterial pneumonia in critically ill patients with suspected infection and to test whether signatures of bacterial pneumonia can be identified in the alveolar macrophage transcriptome.Methods: We determined the test characteristics of alveolar neutrophilia for the diagnosis of bacterial pneumonia in three cohorts of mechanically ventilated patients. In one cohort, we also isolated macrophages from alveolar lavage fluid and used the transcriptome to identify signatures of bacterial pneumonia. Finally, we developed a humanized mouse model of Pseudomonas aeruginosa pneumonia to determine if pathogen-specific signatures can be identified in human alveolar macrophages.Measurements and Main Results: An alveolar neutrophil percentage less than 50% had a negative predictive value of greater than 90% for bacterial pneumonia in both the retrospective (n = 851) and validation cohorts (n = 76 and n = 79). A transcriptional signature of bacterial pneumonia was present in both resident and recruited macrophages. Gene signatures from both cell types identified patients with bacterial pneumonia with test characteristics similar to alveolar neutrophilia. Conclusions:The absence of alveolar neutrophilia has a high negative predictive value for bacterial pneumonia in critically ill patients with suspected infection. Macrophages can be isolated from alveolar lavage fluid obtained during routine care and used for RNA-Seq analysis. This novel approach may facilitate a longitudinal and multidimensional assessment of the host response to bacterial pneumonia.
RationaleFibrotic interstitial lung disease (ILD) is among the top indications for patients undergoing lung transplantation worldwide. While our group and others have demonstrated a role for monocyte‐derived alveolar macrophages in the development of lung fibrosis in murine models, it is unknown if human alveolar macrophages play a similar role in the development of fibrotic ILD. We hypothesized that transcriptional profiling of AMs isolated from lung transplant donors and recipients as well as from murine alveolar macrophages in a bleomycin‐induced lung fibrosis model would demonstrate homology of involved genes.MethodsFluorescence‐activated cell sorting (FACS) was used to isolate AMs (CD45+ CD169+ HLA‐DR+) from samples of 18 donor lungs and 22 explanted lungs from patients at the time of lung transplantation and to isolate separately tissue‐resident and monocyte‐derived AMs from mice at fourteen and nineteen days following the administration of intratracheal bleomycin. RNA extraction from sorted cells was performed with poly(A) enrichment, followed by single‐end RNA‐seq. Exploratory data analysis using principle component analysis (PCA) and K‐mean clustering were performed. Differentially expressed genes were estimated between donors and patients with interstitial lung disease, and between murine tissue‐resident and monocyte‐derived AMs during bleomycin‐induced fibrosis.ResultsThe median age of the 22 lung transplant recipients was 56 (IQR 13–64). Among recipients, there were eleven patients with the diagnosis of fibrotic ILD (five with scleroderma‐associated ILD, three with myositis‐ILD, two with idiopathic pulmonary fibrosis, and one with mixed connective tissue disease ILD). PCA of sorted populations showed grouping by diagnosis. 61 genes were identified that were differentially expressed (adjusted p < 0.05) in AMs between donors and patients with fibrotic ILD, and that were also homologs of genes highly expressed in murine monocyte‐derived AMs relative to tissue‐resident AMs during bleomycin‐induced lung fibrosis. Hierarchical clustering of samples according to expression of these homologous genes showed just one ILD sample clustering among donors, and of 61 total differentially expressed homologous genes, 51 were upregulated in AMs from patients with fibrotic ILD and only 10 were downregulated.ConclusionsTranscriptional profiling of AMs collected at the time of lung transplantation identifies homology between human fibrotic interstitial lung disease and a murine model of bleomycin‐induced lung fibrosis. By focusing on key lung cellular populations such as alveolar macrophages, future transcriptional studies of lung disease in humans may identify new pathways and new potential targets for therapy for patients with lung disease.Support or Funding Information5T32HL076139‐13, AG049665, HL071643, ES013995, The Veterans Administration, DOD W81XWH‐15‐1‐0215
The authors use molecular dynamics simulations to investigate viral peptide interactions as the cause of pH-dependent fusion in liposomal drug delivery. Viral peptides (LEFN) are composed of a linker peptide (LELELELE) connected to a synthetic viral peptide (DRGWGNGCGLFGKGSI). Rather than being anchored in a lipid bilayer, the viral peptides are anchored to a neutral surface by the amino termini of the linker peptide (anchor atoms are mobile in the xy-plane). Atomistic-level peptide pair arrangement on a surface depends on pH; however, the overall propensity to cluster is independent of pH, indicating that pH-sensitive liposome fusion is not due to peptide clustering. To further investigate a molecular cause of pH-sensitive fusion, the authors treat the linker peptides as ectodomains, with the assumption that the viral peptides are already inserted into a target membrane. In these simulations, the linker peptides are elongated to encourage them to bundle. At both high and low pH, the peptides readily bundle. At high pH, however, bundling was constrained by long-range order induced by sodium ions bridging negatively charged glutamic acid residues on neighboring peptides. The authors hypothesize that this constraint hinders the ability of the linker peptides to support viral peptide insertion, resulting in decreased levels of fusion observed experimentally.
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