Cigarette Smoke Extract–Induced Necroptosis Causes Mitochondrial DNA Release and Inflammation of Bronchial Epithelial Cells

Chronic obstructive pulmonary disease (COPD) is characterized by airway inflammation and structural changes in the lungs, including emphysema. Cigarette smoke exposure induces mitochondrial damage, necroptosis-mediated pulmonary epithelial cell death, and emphysematous changes. However, the association between these events and airway inflammation remains unclear. Here, we focused on mitochondrial DNA (mtDNA) as a second messenger linking mitochondrial damage to airway inflammation, aiming to elucidate the mechanisms underlying extracellular mtDNA release and its role in airway inflammation. Human bronchial epithelial BEAS-2B cells were exposed to cigarette smoke extract and the release of mtDNA into the cytoplasm and extracellular space was examined. Real-time polymerase chain reaction was used to measure mtDNA levels. To examine the involvement of necroptosis, a necroptosis inhibitor (Nec-1) and mitochondria-targeted antioxidant (MitoQ) were used. To evaluate the inflammatory response induced by extracellular mtDNA, we quantified the levels of specific cytokines-interleukin (IL)-6 and IL-8-in the cell culture supernatants after mtDNA transfection, as these mediators are widely accepted as key markers of inflammation in bronchial epithelial cells. Cigarette smoke extract treatment induced the translocation of mtDNA from the mitochondria to the cytoplasm in BEAS-2B cells, followed by its extracellular release. Nec-1 and MitoQ inhibited the extracellular release of mtDNA without affecting its cytoplasmic translocation. Introducing mtDNA into BEAS-2B cells markedly elevated IL-6 and IL-8 levels, indicating that mtDNA may play a pro-inflammatory role. Necroptosis facilitated the release of extracellular mtDNA after cigarette smoke extract exposure, establishing a connection between mitochondrial damage and airway inflammation. mtDNA acted as a pro-inflammatory mediator by inducing cytokine production in pulmonary epithelial cells. These findings suggest that targeting necroptosis could offer a novel therapeutic strategy for COPD by addressing both airway inflammation and structural lung damage.