Rat alveolar macrophage-derived platelet-derived growth factor is chemotactic for rat lung fibroblasts

Our plain-English summary of Rat alveolar macrophage-derived platelet-derived growth factor is chemotactic for rat lung fibroblasts, by A.R. Osornio-Vargas, J.C. Bonner, A. Badgett, et al (American Journal of Respiratory Cell and Molecular Biology, 1990).

The study

• Authors: A.R. Osornio-Vargas, J.C. Bonner, A. Badgett, A.R. Brody
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 1990;3(6):595-602
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Alveolar macrophages and their products are thought to be important mediators of the inflammatory lesions and consequent interstitial fibrosis caused by inhalation of inorganic particles. Identification of a homolog of platelet-derived growth factor (PDGF) produced by rat alveolar macrophages that were stimulated with carbonyl iron particles and asbestos fibers motivated our studies on the biologic activity of this potent cytokine. Macrophage-derived PDGF (MD-PDGF) competes for specific membrane receptors on rat lung fibroblasts, initiating DNA synthesis and cell replication. The present report demonstrates that purified human PDGF and the MD-PDGF are chemotactic for early passage rat lung fibroblasts, but not for lung macrophages. Rat lung fibroblasts exhibit a typical bell-shaped, dose-related curve and respond optimally between 2 and 4 ng/ml PDGF. We found that alveolar macrophage-conditioned medium (AMCM), fractionated by gel filtration in 1 M acetic acid, induced a clear chemotactic response in the same fractions (20 to 22 ml) where PDGF was identified by enzyme immunoassay. In contrast, AMCM fractionated by gel filtration in phosphate-buffered saline did not induce any chemotactic activity unless the fractions were treated further with 1 M acetic acid. In this case, chemotactic activity was observed in those fractions with molecular weights of 150 and greater than 200 kD. All chemotactic activity observed with fractionated AMCM was blocked greater than 90% by an anti-PDGF antibody. These observations demonstrate that MD-PDGF is chemotactic for rat lung fibroblasts if it first is released from its binding protein, alpha-macroglobulin (alpha-M), which is secreted into the medium along with PDGF.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This laboratory study used lung cells from male rats. The authors' earlier work had found that rat alveolar macrophages (lung scavenger cells) stimulated with carbonyl iron particles or asbestos fibers released a substance resembling platelet-derived growth factor (PDGF). In this study the macrophages were stimulated only with carbonyl iron spheres. Asbestos was not tested. The authors tested whether purified human PDGF and macrophage-made PDGF attracted rat lung fibroblasts (cells that make scar-forming collagen). Fibroblasts moved toward human PDGF, most strongly between 2 and 4 ng/ml. Macrophages did not migrate toward human PDGF or the macrophage-fluid fractions, although they did respond to a control attractant. Fluid from iron-stimulated macrophages attracted fibroblasts only after acid treatment freed the PDGF-like substance from binding proteins. An anti-PDGF antibody blocked most of this activity. A plasma binding protein, alpha2-macroglobulin, blocked more than 90% of fibroblast movement toward human PDGF at one tested combination. The authors concluded that the macrophage-derived PDGF attracts lung fibroblasts once it is released from its binding proteins. They noted that activity in living animals remains to be established.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) experiments on rat lung cells: chemotaxis assays measuring whether cells migrate toward growth factors; six separate experiments, each run in triplicate
• Who was studied: Alveolar macrophages and lung fibroblasts taken from male CD rats aged 8 to 10 weeks (no human subjects); conducted at the National Institute of Environmental Health Sciences, North Carolina
• Exposure: Macrophages were stimulated for 24 hours with carbonyl iron spheres (0.4 to 3.0 micrometers in diameter; 0.5 mg/cm2). No asbestos was used in this study's experiments; asbestos appears only in the authors' description of their earlier work. Fibroblasts were also tested with purified human PDGF (0.25 to 256 ng/ml) and with bovine alpha2-macroglobulin (0.25 to 1.0 mg/ml).
• Main results:
  • Rat alveolar macrophages did not migrate toward human PDGF at any concentration from 0.25 to 256 ng/ml. They did respond to a positive control (zymosan-activated rat serum, 450 plus or minus 11 macrophages per 10 high-power fields).
  • Rat alveolar macrophages also did not migrate toward any of the tested fractions of macrophage fluid
  • Rat lung fibroblasts migrated toward human PDGF in a bell-shaped, dose-related pattern, peaking between 2 and 4 ng/ml, with a poor response above 16 ng/ml
  • In fibroblasts, an anti-PDGF antibody at 50 micrograms/ml reduced migration toward 4 ng/ml human PDGF from 104 plus or minus 9 to 2.4 plus or minus 1.0 cells per 10 high-power fields
  • In fluid from iron-stimulated macrophages, the PDGF-like substance measured 1.34 to 2.02 ng/ml across the six experiments. In fluid from untreated macrophages it was detected in only two of six experiments and never exceeded 1 ng/ml.
  • Fractions of macrophage fluid separated in neutral buffer (PBS) did not attract fibroblasts until they were acid-treated. After acid treatment, activity appeared in fractions around 150 kD and greater than 200 kD.
  • Anti-PDGF antibody inhibited fibroblast migration toward the macrophage-derived PDGF by more than 80% (Figure 4). For the acid-treated PBS fractions, the text reports inhibition greater than 90% (data not shown).
  • Pre-mixing bovine alpha2-macroglobulin (1 mg/ml) with human PDGF (0.5 ng/ml) inhibited fibroblast migration by more than 90%. Higher PDGF with lower alpha2-macroglobulin gave less inhibition.
• The authors' conclusion: The authors concluded that rat lung fibroblasts are attracted to human PDGF and to a PDGF-like substance made by rat alveolar macrophages after stimulation with inorganic particles. This attraction appears only after the substance is released from its binding proteins by acid treatment. They stated that the findings support, in vitro, the hypothesis that macrophage products could play a central role in fibrotic interstitial lung disease.
• Limitations the authors state:
  • The fibroblast preparation was not pure and could contain small numbers of endothelial, epithelial and smooth muscle cells
  • The amount of rat PDGF-like substance may be underestimated, because it was measured with an assay based on antibodies to human PDGF and because binding proteins alter it
  • The experiments were done only in cultured cells; whether the growth factor and its binding protein act in living animals was not established
  • The nature and role of the roughly 150-kD macrophage protein linked to the activity were not identified

Topics

Medical terms in this study, explained in our Lexicon: Alveolar Macrophage, Platelet-Derived Growth Factor (PDGF), Fibroblast, Interstitial Fibrosis, Cytokine, Macrophage.

Related studies

• Differential proliferation of rat lung fibroblasts induced by the platelet-derived growth factor-AA, -AB, and -BB isoforms secreted by rat alveolar macrophages — J.C. Bonner, A.R. Osornio-Vargas, et al. (1991)
• Chrysotile asbestos upregulates gene expression and production of alpha-receptors for platelet-derived growth factor (PDGF-AA) on rat lung fibroblasts — J.C. Bonner, A.L. Goodell, et al. (1993)
• Chrysotile asbestos stimulates platelet-derived growth factor-AA production by rat lung fibroblasts in vitro: evidence for an autocrine loop — J.A. Lasky, P.G. Coin, et al. (1995)
• Inorganic particles induce secretion of a macrophage homologue of platelet-derived growth factor in a density-and time-dependent manner in vitro — R.M. Schapira, A.R. Osornio-Vargas, et al. (1991)
• Alveolar macrophage stimulation of lung fibroblast growth in asbestos-induced pulmonary fibrosis — I. Lemaire, H. Beaudoin, et al. (1986)
• Early-passage rat lung fibroblasts do not migrate in vitro to transforming growth factor-beta — A.R. Osornio-Vargas, V.G. Kalter, et al. (1993)

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