Differential proliferation of rat lung fibroblasts induced by the platelet-derived growth factor-AA, -AB, and -BB isoforms secreted by rat alveolar macrophages

Our plain-English summary of Differential proliferation of rat lung fibroblasts induced by the platelet-derived growth factor-AA, -AB, and -BB isoforms secreted by rat alveolar macrophages, by J.C. Bonner, A.R. Osornio-Vargas, A. Badgett, et al (American Journal of Respiratory Cell and Molecular Biology, 1991).

The study

• Authors: J.C. Bonner, A.R. Osornio-Vargas, A. Badgett, A.R. Brody
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 1991;5(6):539-47
• Cited by: 105 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Platelet-derived growth factor (PDGF)-like molecules secreted by alveolar macrophages have been postulated to be mediators of lung fibrogenesis since these cytokines stimulate the proliferation and chemotaxis of lung fibroblasts. We are studying the biology and biochemistry of rat macrophage-derived PDGF and have identified for the first time the specific isoforms of PDGF (-AA, -AB, and -BB) that these macrophages secreted in vitro following activation with either chrysotile asbestos or carbonyl iron spheres. Subsequently, the proliferative response of rat lung fibroblasts (RLF) to the different PDGF isoforms was established. Using several antibodies raised against the distinct isoforms, we established that two different PDGF-like factors with molecular masses of 30 to 34 kD and 16 to 18 kD were contained in alveolar macrophage-conditioned medium. Within each of these molecular mass regions was a mixture of all three PDGF isoforms. We estimated that the 30- to 34-kD PDGF was mainly PDGF-BB (approximately 50%), while the remaining consisted of PDGF-AA (approximately 13%) and PDGF-AB (approximately 37%). Purified recombinant PDGF isoforms were tested for their ability to stimulate the growth of early-passage RLF and Swiss 3T3 cells in a 3-day cell proliferation assay. PDGF-BB and PDGF-AB were the most potent inducers of RLF proliferation and stimulated growth half-maximally at approximately 1 ng/ml and approximately 7 ng/ml, respectively. While these two B-chain-containing dimers stimulated lung fibroblast growth by as much as 150% above control medium, the PDGF-AA homodimer stimulated lung fibroblast proliferation less than 25% above control medium at the highest concentrations tested (20 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

In this laboratory study of cells in dishes, the authors took alveolar macrophages (lung immune cells) from male CD rats, exposed them for 24 hours to chrysotile asbestos or carbonyl iron spheres, and measured the forms (AA, AB and BB) of platelet-derived growth factor (PDGF), a protein that makes fibroblasts multiply. Asbestos raised the PDGF-BB/AB released about 8-fold and iron about 4.5-fold. The authors estimated that the larger PDGF form was mainly PDGF-BB (about 50%), with AB about 37% and AA about 13%, though the estimates varied widely. In rat lung fibroblasts, purified BB and AB stimulated growth by as much as 150% above control medium. AA caused less than a 25% increase at the highest dose tested. An antibody against PDGF-BB/AB blocked 75% and 62% of the growth effect of two fractions of culture medium from asbestos-exposed macrophages. The authors concluded that macrophages produce all three forms and that the BB and AB forms appear to stimulate lung fibroblasts. They noted it remains to be shown whether this happens in living lungs.

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) cell-culture experiment
• Who was studied: Alveolar macrophages obtained by lung washing (bronchoalveolar lavage) from male CD rats; early-passage rat lung fibroblasts; Swiss 3T3 cells as a comparison cell line. The work was done at the National Institute of Environmental Health Sciences, North Carolina.
• Exposure: Macrophages in culture were exposed for 24 hours to chrysotile asbestos at 15 micrograms per square centimeter of culture surface, or to carbonyl iron spheres. Unstimulated macrophages served as controls. Fibroblasts were exposed to purified PDGF-AA, -AB and -BB.
• Main results:
  • Compared with unstimulated macrophages, asbestos treatment caused an 8-fold and iron treatment a 4.5-fold increase in PDGF-BB/AB secreted over 24 hours.
  • The 30- to 34-kD PDGF form from activated macrophages was estimated to be mainly PDGF-BB (about 50%), with PDGF-AA about 13% and PDGF-AB about 37%.
  • B-chain-containing forms (BB and AB) accounted for as much as 85% of the total PDGF from activated macrophages.
  • In rat lung fibroblasts, PDGF-BB and PDGF-AB were the most potent at causing growth, with half-maximal stimulation at about 1 ng/ml and about 7 ng/ml respectively. These two forms stimulated growth by as much as 150% above control medium.
  • In rat lung fibroblasts, the B-chain-containing forms stimulated growth by as much as 150% above control medium.
  • In rat lung fibroblasts, PDGF-AA caused less than a 25% increase in cell number at the highest concentration used (20 ng/ml).
  • Swiss 3T3 cells, unlike rat lung fibroblasts, grew in response to all three PDGF forms, with half-maximal stimulation between 1 and 3 ng/ml.
  • In medium from asbestos-exposed macrophages, an anti-PDGF-BB/AB antibody blocked the fibroblast growth-promoting activity of the 30- to 34-kD peak by 75% and of the 16- to 18-kD peak by 62%. These figures come from one experiment described as typical of three.
• The authors' conclusion: The authors concluded that their in vitro findings support the view that the BB and AB forms of PDGF stimulate rat lung fibroblasts during the development of interstitial lung disease. They also concluded that macrophages produce all three PDGF forms.
• Limitations the authors state:
  • The amount of PDGF-AB could not be measured directly and had to be estimated by calculation.
  • The calculated estimates of each form's share varied considerably, which the authors attributed to differing antibody affinities.
  • The work was done in vitro. Whether these PDGF forms drive scarring (fibrosis) in the living lung remains to be established.

Topics

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

Related studies

• Rat alveolar macrophage-derived platelet-derived growth factor is chemotactic for rat lung fibroblasts — A.R. Osornio-Vargas, J.C. Bonner, et al. (1990)
• 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)
• Chrysotile asbestos induces PDGF-A chain-dependent proliferation in human and rat lung fibroblasts in vitro — J.A. Lasky, J.C. Bonner, et al. (1996)
• Primary lung fibroblasts from the 129 mouse strain exhibit reduced growth factor responsiveness in vitro — D.M. Brass, S.Y. Tsai, et al. (2001)
• 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)

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