Related Experiment Video
Updated: Aug 16, 2026
Oropharyngeal Administration of Bleomycin in the Murine Model of Pulmonary Fibrosis
Published on: May 9, 2025
Bleomycin induces alveolar epithelial cell death through JNK-dependent activation of the mitochondrial death pathway
Vivian Y Lee1, Clara Schroedl, Joslyn K Brunelle
1Div. of Pulmonary & Critical Care, Northwestern University, Chicago, IL 60611, USA.
Abstract:
Exposure to bleomycin in rodents induces lung injury and fibrosis. Alveolar epithelial cell death has been hypothesized as an initiating mechanism underlying bleomycin-induced lung injury and fibrosis. In the present study we evaluated the contribution of mitochondrial and receptor-meditated death pathways in bleomycin-induced death of mouse alveolar epithelial cells (MLE-12 cells) and primary rat alveolar type II cells. Control MLE-12 cells and primary rat alveolar type II cells died after 48 h of exposure to bleomycin. Both MLE-12 cells and rat alveolar type II cells overexpressing Bcl-X(L) did not undergo cell death in response to bleomycin. Dominant negative Fas-associating protein with a death domain failed to prevent bleomycin-induced cell death in MLE-12 cells. Caspase-8 inhibitor CrmA did not prevent bleomycin-induced cell death in primary rat alveolar type II cells. Furthermore, fibroblast cells deficient in Bax and Bak, but not Bid, were resistant to bleomycin-induced cell death. To determine whether the stress kinase JNK was an upstream regulator of Bax activation, MLE-12 cells were exposed to bleomycin in the presence of an adenovirus encoding a dominant negative JNK. Bleomycin-induced Bax activation was prevented by the expression of a dominant negative JNK in MLE-12 cells. Dominant negative JNK prevented cell death in MLE-12 cells and in primary rat alveolar type II cells exposed to bleomycin. These data indicate that bleomycin induces cell death through a JNK-dependent mitochondrial death pathway in alveolar epithelial cells.
Insights
Bleomycin exposure causes lung injury by triggering alveolar epithelial cell death. This study reveals that a JNK-dependent mitochondrial pathway, not receptor-mediated pathways, drives this cell death, offering insights into lung fibrosis mechanisms.
Area of Science:
- Cell Biology
- Pulmonary Medicine
- Toxicology
Background:
- Bleomycin (BLM) is a chemotherapeutic agent known to induce lung injury and fibrosis in animal models.
- Alveolar epithelial cell death is a proposed initiating event in BLM-induced lung pathology.
- Understanding the specific cell death pathways involved is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the roles of mitochondrial and receptor-mediated death pathways in BLM-induced alveolar epithelial cell death.
- To identify the key molecular regulators, such as stress kinases, involved in this process.
Main Methods:
- Utilized mouse alveolar epithelial cells (MLE-12) and primary rat alveolar type II cells.
- Examined the effects of BLM exposure on cell viability.
- Manipulated expression of key proteins like Bcl-X(L), Fas-associating protein with a death domain, Bax, Bak, and c-Jun N-terminal kinase (JNK).
- Employed dominant-negative constructs and inhibitors to probe specific signaling pathways.
Main Results:
- Bleomycin induced cell death in both MLE-12 and primary rat alveolar type II cells.
- Overexpression of Bcl-X(L) conferred resistance to BLM-induced cell death.
- Receptor-mediated pathways (Fas/caspase-8) were not involved.
- Mitochondrial pathway proteins Bax and Bak were critical, as cells deficient in them were resistant.
- Inhibition of JNK signaling prevented both Bax activation and cell death, indicating JNK is an upstream regulator.
Conclusions:
- Bleomycin-induced alveolar epithelial cell death is primarily mediated by a mitochondrial death pathway.
- This pathway is dependent on the activation of stress kinase JNK and downstream effectors Bax/Bak.
- Receptor-mediated death pathways do not play a significant role in this model of lung injury.
Related Concept Videos
01:31The Intrinsic Apoptotic Pathway
01:30Apoptosis
01:17The Extrinsic Apoptotic Pathway
01:30Overview of Cell Death
Cell death was observed in the early 19th century, but there was no experimental evidence to prove it. In 1842, Carl Vogt first discovered cell death in a metamorphic toad; however, it was not termed ‘cell death.’ Scientists discovered different cell death pathways only in the 20th century...
01:16Necrosis
Morphological Manifestations of Necrosis
Necrotic cells show different types of morphological appearance depending on the type of tissue and infection. In coagulative necrosis, cells become anucleated and die, but their...
01:23Chronic Obstructive Pulmonary Disease II: Emphysema