The mitochondria-regulated death pathway mediates asbestos-induced alveolar epithelial cell apoptosis

Vijayalakshmi Panduri, Sigmund A. Weitzman, Navdeep Chandel, David W. Kamp*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

The mechanisms underlying asbestos-induced pulmonary toxicity are not fully understood. Alveolar epithelial cell (AEC) apoptosis by iron-derived reactive oxygen species (ROS) is one important mechanism implicated. The two major pathways regulating apoptosis include (i) the mitochondrial death (intrinsic) pathway caused by DNA damage, and (ii) the plasma-membrane death receptor (extrinsic) pathway. However, it is unknown whether asbestos activates either death pathway in AEC. We determined whether asbestos triggers AEC mitochondrial dysfunction by exposing cells (A549 and rat alveolar type II) to amosite asbestos and assessing mitochondrial membrane potential changes (ΔΨm) using a fluorometric technique involving tetremethylrhodamine ethyl ester (TMRE) and mitotracker green. Unlike inert particulates (titanium dioxide and glass beads), amosite asbestos caused dose- and time-dependent reductions in ΔΨm. Asbestos-induced ΔΨm was associated with the release of cytochrome c from the mitochondria to the cytoplasm as well as activation of caspase 9, a mitochondrial-activated caspase. In contrast, a lower level of caspase 8, the death receptor-activated caspase, was detected in asbestos-exposed AEC. An iron chelator (phytic acid or deferoxamine) or a hydroxyl radical scavenger (sodium benzoate) each blocked asbestos-induced reductions in ΔΨm and caspase 9 activation, suggesting a role for iron-derived ROS. Finally, Bcl-XL, a mitochondrial antiapoptotic protein that prevents cell death by preserving the outer mitochondrial membrane integrity, blocked asbestos-induced decreases in A549 cell ΔΨm and reduced apoptosis as assessed by DNA fragmentation. We conclude that asbestos-induced AEC apoptosis results from mitochondrial dysfunction, in part due to iron-derived ROS, which is followed by the release of cytochrome c and caspase 9 activation. Our findings suggest an important role for the mitochondria-regulated death pathway in the pathogenesis of asbestos-associated pulmonary toxicity.

Original languageEnglish (US)
Pages (from-to)241-248
Number of pages8
JournalAmerican journal of respiratory cell and molecular biology
Volume28
Issue number2
DOIs
StatePublished - Feb 1 2003

ASJC Scopus subject areas

  • Molecular Biology
  • Pulmonary and Respiratory Medicine
  • Clinical Biochemistry
  • Cell Biology

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