The Role of c-Jun N-terminal Kinase in the Radiation-Induced Lung Fibrosis

Suh, Soo Taek; Hong, Ki Young; Lee, Young Mok; Kim, Kiup; Kim, Do Jin; Moon, Seung Hyuk; Kim, Yong Hoon; Park, Choon Sik; Kim, Eun Suk; Choi, Doo Ho

Abstract

BACKGROUND
The undrlying pathogenesis of radiation-induced lung fibrosis (RTLF) has not been very well defined. However, the role of TGF-Î² in the generation of RTLE has been a major focus because there is an increase in the expression of both the TGE-Î² stimulated lung fibrosis includes the activation of many mediators such as Smad and c-Jun N-terminal kinase (JNK) through TAK1. It is we hypothesized that JNK activation may play a pivotal role in RTLF pathogensis through increased transcription of the fibrogenic cytokines. The present study evaluates JNK activity in alveolar macrophages after irradiation and the relationship between JNK activity and the amount of collagen in the lung tissues.
METHODS
C57BL/6 mice(20-25 gr. males) received cholorotetracycline(2g/L) in their drinking water 1 week prior to irradiation and continuously there after. The mice were irradiated once with 1400 cGy of 60COÎ³-ray over the whole chest. The cellular composition of the whole lung bronchoalveolar lavage fluids(BALF), elastin expression in the lung tissues, the level of hydroxyproline in lung tissues, and an in vitro JNK assay was measured before irradiation and one, four, and eight weeks after irradiation (RT).
RESULTS
The volumes of BALF retrieved from instilled 4ml of saline with 2% heparin were 3.7-3.8ml for each group. The cell numbers were similar before(4.1Ã—10(4)±0.5±10(4)/ml) and 1 week(3.1Ã—10(4)±0.5±10(4)/ml) after RT. At four and eight weeks after RT, the cell number reached to 14.0Ã—10(4)±1.5±10(4)/ml and 10.0Ã—10(4)±1.3±10(4)/ml, respectively. There we no changes in the lymphocytes and neutrophils population obseved in the BALF after RT. The H-E stain of the lung tissues did not show any structural and fibrotic change in the lung tissues at 4 and 8 weeks after RT. In addition, the amount of elastin and collagen were not different on Verhoeff staining of the lung tissues before RT to eight weeks after RT. The hydroxyproine content was measured with the left lung dissected from the left main bronchus. The lung were homogenized and hydrolyzed with 6 N HCI for 12 hours at 110â„ƒ then measured as previously described. The content of hydroxyproline, standardized with a lung protein concentration, reached a peak 4 weeks after RT. and thereafter showed a plateau. An In vitro JNK assay using c-Jun(1-79)-GST sepharose beads were performed with the alveolar macrophages obtained from the BAL. JNK activity was not detected prior to RT, However, the JNk activity increased from one week after RT and reached a peak four weeks after RT.
CONCLUSION
JNK may be involved in the pathogensis because the JNK activity showed similar pattern observed with the hydroxyproine content. However, it is necessary to clarify that the JNK increases the transcription of fibrogenic cytokines through the transcription factor.