Targeting the MEK1 cascade in lung epithelium inhibits proliferation and fibrogenesis by asbestos.
The extracellular signal-regulated kinases 1 and 2 (ERK1/2) are phosphorylated after inhalation of asbestos. The effect of blocking this signaling pathway in lung epithelium is unclear. Asbestos-exposed transgenic mice expressing a dominant-negative mitogen-activated protein kinase kinase-1 (dnMEK1) (i.e., the upstream kinase necessary for phosphorylation of ERK1/2) targeted to lung epithelium exhibited morphologic and molecular changes in lung. Transgene-positive (Tg+) (i.e., dnMEK1) and transgene-negative (Tg-) littermates were exposed to crocidolite asbestos for 2, 4, 9, and 32 days or maintained in clean air (sham controls). Distal bronchiolar epithelium was isolated using laser capture microdissection and mRNA analyzed for molecular markers of proliferation and Clara cell secretory protein (CCSP). Lungs and bronchoalveolar lavage fluids were analyzed for inflammatory and proliferative changes and molecular markers of fibrogenesis. Distal bronchiolar epithelium of asbestos-exposed wild-type mice showed increased expression of c-fos at 2 days. Elevated mRNA levels of histone H3 and numbers of Ki-67-labeled proliferating bronchiolar epithelial cells were decreased at 4 days in asbestos-exposed Tg+ mice. At 32 days, distal bronchioles normally composed of Clara cells in asbestos-exposed Tg+ mouse lungs exhibited nonreplicating ciliated and mucin-secreting cells as well as decreased mRNA levels of CCSP. Gene expression (procollagen 3-a-1, procollagen 1-a-1, and IL-6) linked to fibrogenesis was also increased in lung homogenates of asbestos-exposed Tg- mice, but reduced in asbestos-exposed Tg+ mice. These results suggest a critical role of MEK1 signaling in epithelial cell proliferation and lung remodeling after toxic injury.
Manning
Christopher B
CB
Environmental Pathology Program, University of Vermont College of Medicine, Department of Pathology, 89 Beaumont Avenue, Burlington, VT 05405, USA.
Sabo-Attwood
Tara
T
Robledo
Raymond F
RF
Macpherson
Maximilian B
MB
Rincón
Mercedes
M
Vacek
Pamela
P
Hemenway
David
D
Taatjes
Douglas J
DJ
Lee
Patty J
PJ
Mossman
Brooke T
BT
D000818:Animals; D017638:Asbestos, Crocidolite / Q000633:toxicity*; D001195:Asbestosis / Q000201:enzymology* / Q000473:pathology* / Q000517:prevention & control; D049109:Cell Proliferation / Q000187:drug effects*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D008168:Lung / Q000201:enzymology* / Q000473:pathology; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010766:Phosphorylation; D020545:Respiratory Mucosa / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology
D017638:Asbestos, Crocidolite; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse