p53-independent apoptotic responses in alveolar type II cells treated with air pollution-derived particulate matter

Abstract

Air pollution is a serious health problem, worsening respiratory, allergic and cardiovascular diseases, besides being associated to lung cancer. Despite the efforts of Brazilian environmental agencies in establishing regulations which decreased pollutant emissions by motor vehicles, the increasing number of vehicles in large cities is still responsible for high levels of air pollution. Among the air pollutants, particulate matter is of particular interest due to its major contribution to the health effects attributed to air pollution. The objective of this study was to evaluate the effects of particulate matter (PM) from different sources on apoptosis in immortalized human alveolar type II cells (A549). PM induced dose and time-dependent apoptosis, measured by quantification of sub-diploid nuclei using FACS. Apoptosis induced by PM derived from diesel exhausts was increased in cells pre-treated with the ATM/ATR kinases inhibitor caffeine. These kinases are known to phosphorylate and activate p53 in response to some types of stress. However, cells treated with die-sel-derived PM did not phosphorylate or activate p53, as evaluated by Western Blot. Despite the absence of p53 activation, increased expression of pro-apoptotic Bcl-2 family members Noxa and Puma was observed on cells treated with diesel-derived PM, as assessed by Real-Time PCR. We also found increased expression of Fas, determined by Real-Time PCR and western-blot. We are currently studying the specific role of these proteins on PM-induced apoptosis using RNAi. Results from these studies may help to understand the process of cell death in the lung of individuals exposed to air pollution.