Decoding the Molecular Mechanisms Underlying Electronic Cigarette Toxicity in Lung, Cancer and Stem Cells
- Author(s): Zahedi, Atena
- Advisor(s): Talbot, Prue
- et al.
Electronic cigarettes (ECs), popular nicotine-delivery devices, have emerged as potential health hazards. ECs contain nicotine, flavor chemicals, and solvents used to generate aerosols. The purpose of my dissertation was to develop bioassays and video bioinformatics tools to characterize effects of disposable-style ECs on cultured lung cells, stem cells, and cancer cells. A screening method was developed to identify toxic EC products and evaluate their modes of action (MOAs). StemCellQC software can assess the health of pluripotent embryonic stem cell (ESC) colonies and extract data on dynamic processes such as cell proliferation, spreading, migration, and cell death. MitoMo software was developed to assess mitochondrial (important and sensitive organelles) health parameters such as mitophagy, morphology, dynamics, membrane potential, oxidative stress, calcium levels, and mtDNA nucleoids.
A two-tiered screen was performed to identify harmful EC products. Based on tier 1 assays, two brands were identified for further investigation. In tier 2 assays, Greensmoke exposure led to a decrease in growth rate, cytoskeletal depolymerization, adhesion defects, oxidation of mitochondrial proteins, and eventual apoptosis. Vuse exposure produced an epithelial-to-mesenchymal transition (EMT) and increased α-smooth muscle actin, a fibrosis biomarker. It also caused loss of cell-to-cell junctions, migratory behavior, internalization of junctional stabilizers E-cadherin and P120-catenin, and nuclear translocation of β-catenin (dual role as a transcription factor for EMT). EMT is the initial step enabling metastasis of cancer cells, which is a concern for former smokers with a pre-existing lung tumor. Fibrosis, epithelial cell disruption, and oxidative damage can lead to chronic lung diseases.
The effects of ECs were studied on neural stem cells (NSCs) as an in vitro model for early development, since ECs are often targeted to youth and pregnant mothers, raising developmental risks. The high nicotine content in Vuse caused oxidative stress, autophagy defects, and a stress-induced mitochondrial hyperfusion (SIMH). Exposure to Vuse aerosols also led to upregulation and desensitization of nicotinic acetylcholine receptors (nAChRs). These findings are critical considering that nicotine is now widely available in EC products. Mitochondrial damage, oxidative stress and autophagy dysfunction can cause faulty stem cell populations, which may accelerate aging and lead to cancer, diabetes, neurodegenerative disorders.