Submitted on January 28, 2004
Accepted on January 14, 2005
Crystalline and amorphous silica differentially regulate the cyclooxygenase-prostaglandin pathway in pulmonary fibroblasts: implications for pulmonary fibrosis
Katherine M.A. O'Reilly1, Richard P. Phipps2, Thomas H. Thatcher1, Beth A. Graf3, John Van Kirk1, and Patricia J. Sime4*
1 Department of Medicine, University of Rochester School of Medicine, Rochester, NY, USA; Department of Lung Biology and Disease Program, University of Rochester School of Medicine, Rochester, NY, USA
2 Department of Environmental Medicine, University of Rochester School of Medicine, Rochester, NY, USA; Department of Lung Biology and Disease Program, University of Rochester School of Medicine, Rochester, NY, USA; The Cancer Center, University of Rochester School of Medicine, Rochester, NY, USA
3 Department of Environmental Medicine, University of Rochester School of Medicine, Rochester, NY, USA; Department of Lung Biology and Disease Program, University of Rochester School of Medicine, Rochester, NY, USA
4 Department of Medicine, University of Rochester School of Medicine, Rochester, NY, USA; Department of Environmental Medicine, University of Rochester School of Medicine, Rochester, NY, USA; Department of Lung Biology and Disease Program, University of Rochester School of Medicine, Rochester, NY, USA
* To whom correspondence should be addressed. E-mail: patricia_sime{at}urmc.rochester.edu.
Inhalation of crystalline (CS) and amorphous silica (AS) results in human pulmonary inflammation. However, silicosis only develops following CS exposure, and
the pathogenic mechanisms are poorly understood. This report describes the differential abilities of CS and AS to directly up-regulate the early inflammatory mediator COX-2, the recently identified prostaglandin E synthase and the downstream mediator PGE2 in primary human lung fibroblasts. Increased COX-2 gene transcription and protein production were demonstrated by ribonuclease protection assay, Western blot analysis, and immunocytochemistry. In each case the ability of AS to induce COX-2 exceeded that of CS. Similarly, downstream of COX-2, production of the anti-fibrotic prostaglandin PGE2, was induced in a dose-dependent fashion, but AS was significantly more potent, (maximal production: CS=4,710 pg/ml and AS=7,651 pg/ml). These increases in COX-2 and PGE2 were preceded by induction of the PGE2 synthase protein, demonstrating the
potential role of this novel molecule in silica-mediated inflammation. There was specificity of induction of prostaglandins, as PGF2
, but not PGD2 was induced. Using specific COX-2 inhibitors, increased PG production was shown to be dependent on the COX-2 enzyme. Furthermore stimulation of fibroblasts was particle specific, as silica but not carbon black resulted in fibroblast activation. These results demonstrate that silica can directly stimulate human lung fibroblasts to produce key inflammatory enzymes and prostaglandins. Furthermore they suggest a mechanism to explain the differing fibrogenic potential of CS and AS. The molecules COX-2, prostaglandin E synthase, and PGE2 are identified as effectors in silicosis.
