Involvement of B-cell CLL/lymphoma 2 promoter methylation in cigarette smoke extract-induced emphysema

Abnormal apoptotic events play an important role in the pathogenesis of emphysema. The B-cell CLL/lymphoma 2 (Bcl-2) family proteins are essential and critical regulators of apoptosis. We determined whether the anti-apoptotic Bcl-2 play a role in the cigarette smoke extract (CSE)-induced emphysema. Furthermore, given the involvement of epigenetics in chronic obstructive pulmonary disease, we hypothesized that the deregulation of Bcl-2 might be caused by gene methylation. The emphysema in BALB/C mice was established by intraperitoneally injection of CSE. 5-aza-2'-deoxycytidine (AZA; a demethylation reagent) and phosphate-buffered saline were also administered intraperitoneally as CSE. TUNEL assay was used to assess apoptotic index of pulmonary cells. The methylation status of CpG dinucleotides within the Bcl-2 promoter was observed in all groups by bisulfite sequencing PCR. Pulmonary expression of Bcl-2, Bax, and cytochrome C were measured after four weeks of treatment. The apoptotic index of pulmonary cells in CSE injection group was much higher than control ((25.88 +/- 7.55)% vs. (6.28 +/- 2.96)%). Compared to control mice, decreased expression of Bcl-2 and high methylation of Bcl-2 promoter was observed in CSE injected mice (0.88 +/- 0.08 vs. 0.49 +/- 0.11, (3.82 +/- 1.34)% vs. (35.68 +/- 5.99)%, P < 0.01).CSE treatment induced lung cell apoptosis and decreased lung function. AZA treatment increased Bcl-2 expression with Bcl-2 promoter demethylation. AZA also alleviated the lung cell apoptosis and function failure caused by CSE treatment. The decreased expression of anti-apoptotic Bcl-2 might account for the increased apoptosis in CSE induced-emphysema. Apparently, epigenetic alternation played a role in this deregulation of Bcl-2 expression, and it might support the involvement of epigenetic events in the pathogenesis of emphysema.