Tissue fibrosis is a major cause of mortality that results from the deposition of matrix proteins by an activated mesenchyme. Macrophages accumulate in fibrosis, but the role of specific subgroups in supporting fibrogenesis has not been investigated in vivo. Here we used single-cell RNA sequencing (scRNA-seq) to characterize the heterogeneity of macrophages in bleomycin-induced lung fibrosis in mice. A novel computational framework for the annotation of scRNA-seq by reference to bulk transcriptomes (SingleR) enabled the subclustering of macrophages and revealed a disease-associated subgroup with a transitional gene expression profile intermediate between monocyte-derived and alveolar macrophages. These CX3CR1 + SiglecF + transitional macrophages localized to the fibrotic niche and had a profibrotic effect in vivo . Human orthologues of genes expressed by the transitional macrophages were upregulated in samples from patients with idiopathic pulmonary fibrosis. Thus, we have identified a pathological subgroup of transitional macrophages that are required for the fibrotic response to injury.

No abstract

Rationale: Sepsis and acute lung injury (ALI) have devastatingly high mortality rates. Both are associated with increased vascular leak, a process regulated by complex molecular mechanisms. Objectives: We hypothesized that integrin avb3 could be an important determinant of vascular leak and endothelial permeability in sepsis and ALI. Methods: b3 subunit knockout mice were tested for lung vascular leak after endotracheal LPS, and systemic vascular leak and mortality after intraperitoneal LPS and cecal ligation and puncture. Possible contributory effects of b3 deficiency in platelets and other hematopoietic cells were excluded by bone marrow reconstitution experiments. Endothelial cells treated with avb3 antibodies were evaluated for sphingosine-1 phosphate (S1P)-mediated alterations in barrier function, cytoskeletal arrangement, and integrin localization. Measurements and Main Results: b3 knockout mice had increased vascular leak and pulmonary edema formation after endotracheal LPS, and increased vascular leak and mortality after intraperitoneal LPS and cecal ligation and puncture. In endothelial cells, avb3 antibodies inhibited barrier-enhancing and cortical actin responses to S1P. Furthermore, S1P induced translocation of avb3 from discrete focal adhesions to cortically distributed sites through Gi-and Rac1-mediated pathways. Cortical avb3 localization after S1P was decreased by avb3 antibodies, suggesting that ligation of the avb3 with its extracellular matrix ligands is required to stabilize cortical avb3 focal adhesions. Conclusions: Our studies identify a novel mechanism by which avb3 mitigates increased vascular leak, a pathophysiologic function central to sepsis and ALI. These studies suggest that drugs designed to block avb3 may have the unexpected side effect of intensifying sepsis-and ALI-associated vascular endothelial leak.Keywords: vascular endothelium; sepsis; acute lung injury; integrin Sepsis and acute lung injury (ALI) are associated with high mortality rates and worldwide healthcare burden (1-4). Development of these syndromes requires complex host responses involving multiple cell types, inflammatory mediators, and coagulation factors. One pathophysiologic hallmark common to both sepsis and ALI is increased vascular leak. Increased vascular leak in sepsis leads to redistribution of intravascular fluid to extravascular compartments, hypovolemia, hemoconcentration, and stasis of blood flow. In ALI, alveolar spaces become flooded with pulmonary edema, resulting in impaired gas exchange, arterial hypoxemia, and respiratory failure (4-6).It is generally believed that increased paracellular passage of solutes through the vascular endothelium occurs during acute inflammatory states (7,8). Frequently cited models suggest that paracellular gaps form because of disrupted homeostasis between cytoskeletal, adhesive cell-cell, and cell-matrix forces (8-10). Integrins, a large family of heterodimeric glycoprotein receptors, are important mediators of these cellular functions and have been shown to participa...

In epidermal wounds, precursor laminin 5 (α3β3γ2) is deposited in the provisional basement membrane (PBM) before other BM components. Precursor laminin 5 contains G4/5 globular domains at the carboxyl terminus of the α3 chain. Here, the function of G4/5 was evaluated in deposition of laminin 5. Soluble laminin 5, secreted by keratinocytes in culture, is cleaved by an endogenous protease releasing G4/5. Thrombin, a serum protease, cleaves G4/5 indistinguishably from endogenous protease. Soluble human precursor laminin 5, but not cleaved laminin 5, was bound and deposited by mouse keratinocytes null for mouse α3 chain (α3–/– MKs). The deposition rescued adhesion and spreading and survival. In a model for PBM assembly, precursor laminin 5 was deposited along fibronectin fibrils at the junction between co-cultures of keratinocytes and fibroblasts. In both models, the deposition of precursor laminin 5 was inhibited by removal of G4/5 with thrombin. To confirm that G4/5 participates in deposition, the human LAMA3A gene was modified to produce α3 chains either without or with G4/5 that cannot be cleaved. Both precleaved and noncleavable α3 isoforms were expressed in α3–/– MKs, where they deposited sufficiently to rescue adhesion via integrins α3β1 and α6β4. Despite this similarity, noncleavable laminin 5 was at least threefold more efficiently deposited than precleaved isoform. We conclude that the G4/5 domain in the α3 chain facilitates deposition of precursor laminin 5 into the PBM in epidermal wounds.

FDG PET contributes significantly to defining the extent of disease and deciding on treatment of patients with advanced breast cancer.