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Monocyte-derived macrophage and alveolar macrophage fibronectin production and cathepsin D activity
M D Rossman1, B T Maida, S D Douglas
1Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia.
Abstract:
Alveolar macrophages are thought to play an important role in ongoing tissue breakdown and repair processes in the normal lung. The secretion and regulation of cathepsin D (important for the final breakdown of collagen) and fibronectin (involved in the healing process) in human peripheral blood monocytes (PBM) and pulmonary alveolar macrophages (PAM) were investigated. Cathepsin D enzyme activity was measured by quantitating the TCA-soluble fragments of [3H]hemoglobin. Freshly isolated PBM contained less cell-associated cathepsin D activity than did freshly isolated PAM (314 +/- 35 micrograms/10(6) cells vs 381 +/- 35 micrograms/10(6) cells, respectively). After 7-10 days in culture, cell-associated enzyme levels in both PBM and PAM were significantly increased (P less than 0.001 for PBM; P less than 0.0001 for PAM). In addition, freshly isolated PAM secreted more cathepsin D than did freshly isolated PBM (5.8 +/- 3.2 micrograms/10(6) cells vs 0.83 +/- 0.83 micrograms/10(6) cells, P less than 0.02). In the presence of LPS (10 micrograms/ml), cell-associated cathepsin D was inhibited in both PBM and PAM. With the addition of gamma-IFN (500 U/ml), both cell-associated and secreted enzyme were increased in freshly isolated and 10-day-cultured PBM and PAM. In parallel studies, fibronectin secretion (by ELISA assay) in both PBM and PAM increased over time in culture. LPS had no effect on PBM or PAM secretion of human fibronectin while gamma-IFN increased PBM and PAM fibronectin levels. Thus, both macrophage cathepsin D activity and fibronectin secretion are increased by gamma-interferon while macrophage cathepsin D activity, but not fibronectin secretion, is decreased by LPS. These studies demonstrate that human macrophage cathepsin D activity is actively modulated by inflammatory mediators and that macrophage mediators of tissue breakdown and repair are not modulated synchronously.
Insights
Human alveolar macrophages and monocytes regulate tissue repair. Gamma-interferon boosts cathepsin D and fibronectin, while LPS inhibits cathepsin D, showing differential regulation of tissue breakdown and repair mediators.
Area of Science:
- Cell Biology
- Immunology
- Pulmonary Medicine
Background:
- Alveolar macrophages are crucial for lung tissue repair and breakdown.
- Cathepsin D and fibronectin are key mediators in these processes.
- Understanding their regulation in human peripheral blood monocytes (PBM) and pulmonary alveolar macrophages (PAM) is vital.
Purpose of the Study:
- To investigate the secretion and regulation of cathepsin D and fibronectin in human PBM and PAM.
- To determine the effects of inflammatory mediators like lipopolysaccharide (LPS) and gamma-interferon (gamma-IFN) on these functions.
Main Methods:
- Cathepsin D activity measured by [3H]hemoglobin breakdown.
- Fibronectin secretion quantified using ELISA assays.
- Cells cultured for 7-10 days with and without LPS or gamma-IFN.
Main Results:
- Freshly isolated PAM had higher cell-associated cathepsin D than PBM; both increased with culture.
- PAM secreted more cathepsin D than PBM; both increased with gamma-IFN but decreased with LPS.
- Fibronectin secretion increased with culture and gamma-IFN, but was unaffected by LPS.
Conclusions:
- Human macrophage cathepsin D activity and fibronectin secretion are differentially modulated by inflammatory mediators.
- Gamma-interferon enhances both cathepsin D and fibronectin.
- LPS inhibits cathepsin D but not fibronectin, indicating asynchronous regulation of tissue breakdown and repair.