Induction of a senescent like phenotype and loss of gap junctional intercellular communication by carbon nanoparticle exposure of lung epithelial cells

Inhalation of combustion-derived particles is associated with the development of age-related diseases like chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. In both diseases senescence of lung epithelial cells has been observed. Employing an in vitro system of repetitive exposure to pure carbon nanoparticles we asked whether this kind of particles are able to induce a senescent like phenotype, which might be accompanied by a loss of functionality at the level of gap junctional intercellular communication. Non-cytotoxic doses of carbon nanoparticles but not of bigger carbon particles led to an irreversible reduction of the proliferative capacity accompanied by the accumulation of the cell cycle blocking proteins p21 and p16 as well as a loss of both redox sensitive histone deacetylase SIRT1 and connexin-43. Gap junction intercellular communication detected by microinjection of fluorescent lucifer yellow was dramatically decreased after exposure. This loss of functionality was associated with a reduction of Connexin 43 at the plasma membrane. As the experimental system was chosen to study the effects of pure carbon nanoparticles in the absence of inflammatory cells, the data indicate that cumulative long-term exposure of the lung epithelium to low doses of combustion-derived nanoparticles might contribute to epithelial senescence and age-associated diseases of the airways.