Mitochondrial Complex III-generated Oxidants Activate ASK1 and JNK to
Induce Alveolar Epithelial Cell Death following Exposure to Particulate Matter
Air Pollution |
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Authors: | Saul Soberanes Daniela Urich Christina M Baker Zach Burgess Sergio E Chiarella Eric L Bell Andrew J Ghio Andrea De Vizcaya-Ruiz Jing Liu Karen M Ridge David W Kamp Navdeep S Chandel Paul T Schumacker G?khan M Mutlu G R Scott Budinger |
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Institution: | Divisions of ?Pulmonary and Critical Care Medicine and ∥Pediatrics, The Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, the §United States Environmental Protection Agency, Research Triangle Park, North Carolina 27709, and the ¶Sección Externa de Toxicología, Centro de Investigación y de Estudios Avanzados-IPN, México D.F., México 07360 |
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Abstract: | We have previously reported that airborne particulate matter air pollution
(PM) activates the intrinsic apoptotic pathway in alveolar epithelial cells
through a pathway that requires the mitochondrial generation of reactive
oxygen species (ROS) and the activation of p53. We sought to examine the
source of mitochondrial oxidant production and the molecular links between ROS
generation and the activation of p53 in response to PM exposure. Using a
mitochondrially targeted ratiometric sensor (Ro-GFP) in cells lacking
mitochondrial DNA (ρ0 cells) and cells stably expressing a
small hairpin RNA directed against the Rieske iron-sulfur protein, we show
that site III of the mitochondrial electron transport chain is primarily
responsible for fine PM (PM2.5)-induced oxidant production. In
alveolar epithelial cells, the overexpression of SOD1 prevented the
PM2.5-induced ROS generation from the mitochondria and prevented
cell death. Infection of mice with an adenovirus encoding SOD1 prevented the
PM2.5-induced death of alveolar epithelial cells and the associated
increase in alveolar-capillary permeability. Treatment with PM2.5
resulted in the ROS-mediated activation of the oxidant-sensitive kinase ASK1
and its downstream kinase JNK. Murine embryonic fibroblasts from ASK1
knock-out mice, alveolar epithelial cells transfected with dominant negative
constructs against ASK1, and pharmacologic inhibition of JNK with SP600125 (25
μm) prevented the PM2.5-induced phosphorylation of
p53 and cell death. We conclude that particulate matter air pollution induces
the generation of ROS primarily from site III of the mitochondrial electron
transport chain and that these ROS activate the intrinsic apoptotic pathway
through ASK1, JNK, and p53.Epidemiologic studies have consistently demonstrated a strong link between
the daily levels of particulate matter air pollution <2.5 μm in diameter
(PM2.5)3
and PM <10 μmin diameter (PM10) and cardiopulmonary morbidity
and mortality
(1–3).
In humans, exposure to PM10 has been associated with an increase in
mortality from ischemic cardiovascular events including stroke and myocardial
infarction, an acceleration in the age-related decline in lung function in
normal adults, impairment in normal lung development in children,
exacerbations of asthma in children and adults, accelerated atherosclerosis in
women, increased rates of lung cancer, and the development of myocardial
ischemia in men with stable coronary artery disease
(4–10).
The intracellular generation of reactive oxygen species (ROS) has emerged as a
common mechanism by which particulates might initiate signaling pathways that
end in these diverse pathologic conditions
(11). We have reported that
the PM-induced generation of ROS requires a functional electron transport
chain, suggesting that PM might induce the inadvertent transfer of electrons
from one or more sites in the electron transport chain to molecular oxygen
(12).One of the mechanisms by which exposure to PM can contribute to alveolar
epithelial dysfunction, lung injury and inflammation, and lung cancer is by
activating the intrinsic apoptotic pathway to induce cell death
(11,
12). We have reported that
this process requires the activation of p53; however, the molecular events
linking the generation of ROS by the mitochondrial electron transport chain
with the activation of p53 are not known
(12). In this paper, we show
that exposure of alveolar epithelial cells to PM2.5 induces the
generation of ROS from site III of the mitochondrial electron transport chain.
These mitochondrially derived oxidants activate the mitogen-activated
signaling kinase kinase kinase (MAPKKK) apoptosis signaling kinase 1 (ASK1),
which activates the c-Jun N-terminal kinase (JNK) signaling pathway. The
activation of JNK is required for the phosphorylation of p53 and the
subsequent cell death. Inhibition of mitochondrial oxidant production in mouse
lungs prevents PM2.5-induced cell death and the associated
PM2.5-induced increase in the permeability of the
alveolar-capillary barrier. |
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