Sirtuin 1 reduction causes activation of Wnt/b catenin signalling

Background: The anti-ageing molecule Sirtuin-1 (SIRT1) has been reported to be decreased in COPD (Nakamaru Y et al, FASEB J, 2009). We have also reported an increase of osteoprotegerin (OPG) in COPD (To M et.al, CHEST 2011), which is b-catenin dependent. Our hypothesis is that the reduction of SIRT1 induced by oxidative stress may lead to increased b-catenin activation. Methods: U937 (human monocytic cell line), A549 (human alveolar epithelial cell line) and BEAS2B (human bronchial epithelial cell line) were grown until 70% confluent, starved for 24h and incubated with 2uM of sirtinol at 4 different time points (i.e. 1h, 4h, 8h, and 24h). The levels of b-catenin were measured in nuclear and cytoplasmic extracts by Western Blotting. Cells were also treated with H 2 O 2 for 24 hrs and sirt-1 protein level was also evaluated. Results: The level of b-catenin was higher in A549 and BEAS2B cells than U937 cells at baseline. In all three cell lines, nuclear b-catenin levels increased at 8h after treatment with 2uM of sirtinol by approximately 52% for the U937, 38% for the A549 and 25% for the BEAS2B cells. No difference was detected in cytoplasmic b-catenin levels in any cell line. Incubation with H 2 O 2 for 24h caused reduction in Sirt-1 levels in the A549 cells. Conclusions: This study shows that reduced SIRT1 protein leads to stabilization of β-catenin protein. This might give new insights in the understanding of COPD pathogenesis.