Nicotine-induced mitophagy in bronchial epithelial cells and MYST1 downregulation in cigarette smoke-exposed lungs: potential mechanisms of COPD progression.

OBJECTIVE

To determine how nicotine exposure in vitro and cigarette smoke (CS) exposure in vivo, together with MYST1 silencing, regulate mitophagy-associated changes and contribute to bronchial epithelial dysfunction and COPD-like pathology. METHODS AND

RESULTS

Human 16HBE bronchial epithelial cells were treated with nicotine (0.1 or 1 µM) and/or transfected with siRNA targeting MYST1. Mitophagy-associated markers (LC3, PINK1, BNIP3) were assessed by Western blot and immunofluorescence. Mitochondrial ultrastructure and membrane potential were evaluated by transmission electron microscopy and JC-1 staining, respectively. Apoptosis was measured by flow cytometry, and cytokines (IL-2, IL-6, TNF-α, IL-10) were quantified by ELISA. MYST1 silencing increased mitophagy-associated markers and reduced mitochondrial membrane potential. Nicotine induced a dose-dependent increase in mitophagy-associated markers and mitochondrial fragmentation. Nicotine exposure and MYST1 silencing decreased proliferation, increased apoptosis, and shifted cytokine profiles toward a pro-inflammatory pattern. RT-qPCR and ChIP-qPCR showed that MYST1 silencing upregulated PINK1 transcription and was associated with increased H4K16ac enrichment at the PINK1 promoter despite reduced global H4K16ac. In vivo, a CS-induced mouse model was established, and MYST1 was silenced by intratracheal AAV9-shRNA delivery. CS exposure induced emphysema-like injury with increased mean linear intercept (MLI), enhanced α-SMA staining, and reduced MYST1 expression, which were further aggravated by MYST1 silencing.

CONCLUSIONS

Nicotine and MYST1 loss promote mitophagy-associated alterations, epithelial injury, and inflammation, and a MYST1/H4K16ac-related pathway may contribute to smoke-associated COPD-like pathology.