Method for Depletion of Mitochondria DNA in Human Bronchial Epithelial Cells

Introduction: Mitochondria are increasingly recognized to play a role in the airway inflammation of asthma. Model systems to study the role of mitochondrial gene expression in bronchial epithelium are lacking. Here, we create custom bronchial epithelial cell lines derived from primary airway epithelium that are depleted of mitochondrial DNA. Methods: We treated BET-1A and BEAS-2B cells with ethidium bromide (EtBr) with or without 2',3'-dideoxycytidine (ddC) to create cells lacking mitochondrial DNA (mtDNA). Cells' mtDNA copy number were verified by quantitative polymerase chain reaction (qPCR) in comparison to nuclear DNA (nDNA). Cells were also assessed for oxidative phosphorylation by measures of oxygen consumption using the Seahorse analyzer. Results: One week of EtBr treatment led to ~95% reduction of mtDNA copy number (mtDNA-CN) in cells (mtDNA-CN, mean +/- SE, baseline vs. treatment: BEAS-2B, 820 +/- 62 vs. 56 +/- 9; BET-1A, 957 +/- 52 vs. 73 +/- 2), which was further reduced by addition of 25 uM ddC (mtDNA-CN: BEAS-2B, 2.8; BET-1A, 47.9). Treatment for up to three weeks with EtBr and ddC led to near complete loss of mtDNA (mtDNA-CN: BEAS-2B, 0.1; BET-1A, 0.3). The basal oxygen consumption rate (OCR) of mtDNA-depleted BET-1A and BEAS-2B cells dropped to near zero. Glycolysis measured by extracellular acidification rate (ECAR) increased ~two-fold in cells when mtDNA was eliminated [ECAR (mpH/min/103 cells), baseline vs. treatment: BEAS-2B, 0.50 +/- 0.03 vs. 0.94 +/- 0.10 P=0.005; BET-1A, 0.80 +/- 0.04 vs. 1.14 +/- 0.06 P=0.001]. Conclusion: Mitochondrial DNA-depleted BET-1A Rho 0 and BEAS-2B Rho 0 cell lines are viable, lack the capacity for aerobic respiration, and increase glycolysis. This cell model system can be used to further test mitochondrial mechanisms of inflammation in bronchial epithelial cells.