S118 Elk1 gene deletion leads to spontaneous early fibrotic changes in the ageing lung

Rationale Idiopathic pulmonary fibrosis is a chronic fibroproliferative disease with a median survival of approximately 3 years. αvβ6 integrins are upregulated in lung fibrosis and are associated with increased activation of the profibrotic cytokine TGF-β. The transcription factor Elk1 can repress gene expression of β6. We therefore hypothesise that animals lacking functional Elk1 (Elk1-/0) will develop age related pulmonary fibrosis. Methods Elk1 knock-out (Elk1-/0) and wild-type (Elk1+/0) mice were allowed to age for 365 days. At 365 days old mice were sacrificed and their lungs harvested for evaluation of collagen gene expression, lung hydroxyproline concentration and histological assessment. Results Lungs were extracted and lung wet weights were measured in Elk1-/0 mice and wild-type (Elk1+/0) controls and no significant difference between the two genotypes was shown (175.7 mg, 161.8 mg respectively n=6–8). However, assessment of total lung hydroxyproline established that there was significantly more hydroxyproline in Elk1-/0 mice compared with Elk1+/0 controls (852.3, 758.4 µg/lung set, respectively, n=5–8, p=0.0346). Assessment of Masson’s trichrome stained Elk1-/0 lung tissue sections found a small number of fibrotic lesions were present. Furthermore, there was a trend towards increased alveolar wall median thickness in Elk1-/0 mice compared with Elk1+/0 animals (5.94 vs 5.56 µm respectively). In a small number of 12 week old mice we identified a trend towards increased α-smooth muscle actin (αSMA) mRNA expression in the lungs of Elk1-/0 mice compared with Elk1+/0 controls (9.40, 2.24 median relative expression, respectively n=3). We therefore performed immunohistochemical staining for αSMA in the lungs of mice aged to 1 year and demonstrated visible increases in expression of αSMA in the alveolar epithelium of Elk1-/0 mice but not in Elk1+/0 controls. Conclusion These data suggest that Elk1 gene deletion result in age-related early fibrotic changes associated with the development of pulmonary fibrosis.