Blood monocytes attenuate lung fibroblast contraction of three-dimensional collagen gels in coculture

Investigating Fibroblast-Induced Collagen Gel Contraction Using a Dynamic Microscale Platform

Mechanical forces have long been recognized as fundamental drivers in biological processes, such as embryogenesis, tissue formation and disease regulation. The collagen gel contraction (CGC) assay has served as a classic tool in the field of mechanobiology to study cell-induced contraction of extracellular matrix (ECM), which plays an important role in inflammation and wound healing. In a conventional CGC assay, cell-laden collagen is loaded into a cell culture vessel (typically a well plate) and forms a disk-shaped gel adhering to the bottom of the vessel. The decrement in diameter or surface area of the gel is used as a parameter to quantify the degree of cell contractility. In this study, we developed a microscale CGC assay with an engineered well plate insert that uses surface tension forces to load and manipulate small volumes (14 μL) of cell-laden collagen. The system is easily operated with two pipetting steps and the microscale device moves dynamically as a result of cellular forces. We used a straightforward one-dimensional measurement as the gel contraction readout. We adapted a conventional lung fibroblast CGC assay to demonstrate the functionality of the device, observing significantly more gel contraction when human lung fibroblasts were cultured in serum-containing media vs. serum-free media (p ≤ 0.05). We further cocultured eosinophils and fibroblasts in the system, two important cellular components that lead to fibrosis in asthma, and observed that soluble factors from eosinophils significantly increase fibroblast-mediated gel contraction (p ≤ 0.01). Our microscale CGC device provides a new method for studying downstream ECM effects of intercellular cross talk using 7- to 35-fold less cell-laden gel than traditional CGC assays.

Reduced supply of monocyte-derived macrophages leads to a transition from nodular to diffuse lesions and tissue cell activation in silica-induced pulmonary fibrosis in mice

Pulmonary fibrosis (PF) is an intractable disorder with a poor prognosis. Lung macrophages have been reported to regulate both progression and remission of bleomycin-induced diffuse PF. However, it remains unclear how macrophages contribute to silica-induced progressive nodular PF and the associated tissue cell responses in vivo. We found that lack of monocyte-derived macrophages results in the formation of diffuse PF after silica instillation. We found that the proportion and the number of monocyte-derived macrophages were persistently higher in silica-induced progressive PF compared with bleomycin-induced PF. Surprisingly, in Ccr2(-/-) mice, in which monocyte-derived macrophage infiltration is impaired, silica administration induced diffuse PF with loose nodule formation and greater activation of tissue cells. In the diffuse lesions, the distribution of epithelial cells, distribution of myofibroblasts, and architecture of the basement membrane were disrupted. Consistent with the development of diffuse lesions, genes that were differentially expressed in CD45(-) tissue cells from the lung of wild-type and Ccr2(-/-) mice were highly enriched in human diffuse, progressive PF. In gene ontology network analyses, many of these genes were associated with tissue remodeling and included genes not previously associated with PF, such as Mmp14, Thbs2, and Fgfr4. Overall, these results indicate that monocyte-derived macrophages prevent transition from nodular to diffuse silica-induced PF, potentially by regulating tissue cell responses.

Amnion-derived cellular cytokine solution promotes macrophage activity

Activated macrophages play a significant role in wound healing and infected tissue repair. In this study, we investigate the recruitment of macrophages into the wound, and the effects on the bactericidal/phagocyte activity after exposure to amnion-derived cellular cytokine solution (ACCS). To evaluate the influence of ACCS on the migratory behavior of macrophages, cell migration was assayed quantitatively using a Boyden chamber. Chemotactic migration activity of macrophages through the membrane determined the influence of ACCS. In the presence of ACCS, macrophages demonstrated a statistically significant (P < 0.05) increase in migration as compared with controls. Subsequently, groups of macrophages were exposed to different concentrations of ACCS solution. The killing and phagocytic activity of each group was compared with the control after exposure to Escherichia coli. Macrophage activity following activation by higher concentrations of ACCS demonstrated significantly increased phagocytosis as well as a trend correlation between percentage ACCS concentration and bactericidal activity. These cell types, critical to normal wound healing, may be influenced by ACCS to accelerate migration and enhance bactericidal/phagocytic activity in wounds.

Reduced miR-146a increases prostaglandin E₂in chronic obstructive pulmonary disease fibroblasts

RATIONALE

Persistent inflammation plays a major role in chronic obstructive pulmonary disease (COPD) pathogenesis, but its mechanisms are incompletely defined. Overproduction of the inflammatory mediator prostaglandin (PG) E₂ by COPD fibroblasts contributes to reduced repair function.

OBJECTIVES

The present study determined if fibroblasts from subjects with COPD overproduce PGE₂ after stimulation with the inflammatory cytokines IL-1β and tumor necrosis factor-α, and further defined the mechanism for overproduction.

METHODS

Fibroblasts were isolated from parenchymal tissue obtained from smokers with and without COPD undergoing lung surgery. PGE₂, cyclooxygenases (COX), and miR-146a in these cells were evaluated by in vitro studies.

MEASUREMENTS AND MAIN RESULTS

After stimulation with inflammatory cytokines, COPD fibroblasts produced 2.7-fold more PGE₂ compared with controls with similar smoking history. The increase in PGE₂ depended on induction of COX-2, which increased to a greater degree in fibroblasts from subjects with COPD. Cytokines also induced microRNA miR-146a expression in both fibroblasts, but significantly less in COPD fibroblasts. miR-146a caused degradation of COX-2 mRNA; reduced expression prolonged COX-2 mRNA half-life in fibroblasts from subjects with COPD. Cytokine-stimulated PGE₂ production and miR-146a expression in cultured fibroblasts correlated with clinical severity assessed by expiratory airflow and diffusion capacity.

CONCLUSIONS

miR-146a seems to play a pathogenetic role in the abnormal inflammatory response in COPD. Increased half-life of inflammatory mRNAs is a mechanism of abnormal inflammation in this disease.

Fibroblasts and monocyte macrophages contract and degrade three-dimensional collagen gels in extended co-culture

BACKGROUND

Inflammatory cells are believed to play a prominent role during tissue repair and remodeling. Since repair processes develop and mature over extended time frames, the present study was designed to evaluate the effect of monocytes and fibroblasts in prolonged culture in three-dimensional collagen gels.

METHODS

Blood monocytes from healthy donors and human fetal lung fibroblasts were cast into type I collagen gels and maintained in floating cultures for three weeks.

RESULTS

Fibroblast-mediated gel contraction was initially inhibited by the presence of monocytes (P < 0.01). However, with extended co-culture, contraction of the collagen gels was greatly augmented (P < 0.01). In addition, with extended co-culture, degradation of collagen in the gels occurred. The addition of neutrophil elastase to the medium augmented both contraction and degradation (P < 0.01). Prostaglandin E2 production was significantly increased by co-culture and its presence attenuated collagen degradation.

CONCLUSION

The current study, therefore, demonstrates that interaction between monocytes and fibroblasts can contract and degrade extracellular matrix in extended culture.

Interactions between monocytes and smooth-muscle cells can lead to extracellular matrix degradation

BACKGROUND

Chronic infiltration of the airway wall with inflammatory cells characterizes both asthma and chronic bronchitis. Remodeling of the airway wall is also a feature of both diseases.

OBJECTIVE

We hypothesized that collagen degradation may take place during coculture of monocytes with smooth-muscle cells (SMCs) and that this degradation might be altered by agents that modify the inflammatory regimen.

METHODS

Monocytes (4.5 x 10(5)/mL) were cast into collagen gels containing human airway SMCs (4.5 x 10(5)/mL) and released into serum-free Dulbecco's modified Eagle's medium containing neutrophil elastase. Collagen content was quantified as total insoluble hydroxyproline on day 5. Zymography and immunoblotting were used to detect matrix metalloproteinases.

RESULTS

Monocytes cocultured with SMCs in 3-dimensional native type I collagen gels produced TNF-alpha and IL-1beta and resulted in collagen degradation (30.5 vs 17.9 mg per gel) through inducing matrix metalloproteinase 1, 2, and 9 by means of SMCs. PGE(2) was significantly increased in coculture (0.9 vs 10.5 ng/mL). Indomethacin (1 micromol/L) completely inhibited PGE(2) production but augmented collagen degradation (17.9 vs 2.3 microg per gel), and this was blocked by the addition of exogenous PGE(2). Dexamethasone also inhibited collagen degradation in coculture.

CONCLUSION

The current study supports the concept that interactions among cells present in the airway inflammatory milieu that characterize airway disease can lead to alterations in tissue structure and suggests mechanisms by which therapeutic strategies can be designed to modify tissue remodeling.

Collaborative interactions between neutrophil elastase and metalloproteinases in extracellular matrix degradation in three-dimensional collagen gels

BACKGROUND

Extended culture of monocytes and fibroblasts in three-dimensional collagen gels leads to degradation of the gels (see linked study in this issue, "Fibroblasts and monocytes contract and degrade three-dimensional collagen gels in extended co-culture"). The current study, therefore, was designed to evaluate production of matrix-degrading metalloproteinases by these cells in co-culture and to determine if neutrophil elastase could collaborate in the activation of these enzymes. Since co-cultures produce prostaglandin E2 (PGE2), the role of PGE2 in this process was also evaluated.

METHODS

Blood monocytes from healthy donors and human fetal lung fibroblasts were cast into type I collagen gels and maintained in floating cultures for three weeks. Matrix metalloproteinases (MMPs) were assessed by gelatin zymography (MMPs 2 and 9) and immunoblotting (MMPs 1 and 3). The role of PGE2 was explored by direct quantification, and by the addition of exogenous indomethacin and/or PGE2.

RESULTS

Gelatin zymography and immunoblots revealed that MMPs 1, 2, 3 and 9 were induced by co-cultures of fibroblasts and monocytes. Neutrophil elastase added to the medium resulted in marked conversion of latent MMPs to lower molecular weight forms consistent with active MMPs, and was associated with augmentation of both contraction and degradation (P < 0.01). PGE2 appeared to decrease both MMP production and activation.

CONCLUSION

The current study demonstrates that interactions between monocytes and fibroblasts can mediate tissue remodeling.